Title of Invention	A METHOD OF PRODUCING AN IRON ORE BRIQUETTE
Abstract	A method of producing an iron ore briquette is disclosed.The method is suitable for use is a blast furnace or other direct reduction furnace feedstock which involves the steps of: (a)mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux mixture and wherein there is no binder in the ore/flux mixture; (b)adjusting the water content of the ore prior to or during mixing step (a) so that the moisture content of the ore/flux mixture is 2-12% by weight of the total weight of the ore flux mixture; (c) pressing the ore flux mixture into a green briquette; and (d) indurating the green briquette to form a fired briquette.

Title of Invention

A METHOD OF PRODUCING AN IRON ORE BRIQUETTE

Abstract

A method of producing an iron ore briquette is disclosed.The method is suitable for use is a blast furnace or other direct reduction furnace feedstock which involves the steps of: (a)mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux mixture and wherein there is no binder in the ore/flux mixture; (b)adjusting the water content of the ore prior to or during mixing step (a) so that the moisture content of the ore/flux mixture is 2-12% by weight of the total weight of the ore flux mixture; (c) pressing the ore flux mixture into a green briquette; and (d) indurating the green briquette to form a fired briquette.

Full Text	The present invention is concerned with the production of iron ore briquettes suitable for transport and use in iron making processes. Methods of agglomerating iron orbs have been in development since the late 1800's. However, of all the available processes only the pelletising and sintering processes are now of significance, but these suffer from certain disadvantages. Pelletising consists of two distinct operations; forming pellets from moist ore fines and then firing them at a temperature in the region of 1300°C. It is critical in order to prepare suitable pellets that the ore be ground very fine, generally to a size where in the order of 60% of the ore passes 45 pm. It is then formed into pellets in either a horizontal drum or an inclined disc, generally with the addition of a suitable binder. The formed pellets are then fired in a process sometimes reffered to as induration in shaft kilns,horizontal travelling grates, or a combination of travelling grates and rotary kilns. Pelletising is a practicable and commercially attractive method of agglomerating fine concentrates, but requires substantial grinding in order to achieve the required particle sizing which is an energy intensive process. Pellets made from goethite-hematite ores require extended Induration times, affecting process economics. Solid fuel, in the form of coke, is often added to reduce induration time which results in the production of noxious emissions (including dioxins, NOX and SOx) . Sintering consists of granulating moist iron ore fines and other fine materials with solid fuel, normally coke breeze, and loading the granulated mixture onto a permeable travelling grate. Air is drawn downwards through the grate as the temperature is raised. After a short ignition period, external heating of the bed is discontinued and as the solid fuel in the bed burns a narrow combustion zone moves downwards through the bed, each layer in turn being heated to approximately 1300°C. Bonding takes place between the grains during combustion, and a strong agglomerate is formed. However, traditional sintering processes result in high levels of noxious emissions, particularly sulfur oxides and dioxins, and therefore the process is undesirable and unsustainable on environmental grounds. Briguetting is a process in which there was commercial interest in the late 1800's and early 1900's, but production of iron ore briquettes for use as a blast furnace feed material never reached any significant levels, decreased after 1950, and had ceased by about 1960. The process as practised involved the pressing of ore fines into a block of some suitable size and shape, and then indurating the block. A wide range of binders such as tar and pitch and/or other additives such as organic products, sodium silicate, ferrous sulfate, magnesium chloride, limestone and cement were tested. However, the earliest briquetting process, the Grondal process, simply involved mixing iron ore with water and pressing into oblong blocks the size of building bricks. These were then hardened by passing them through a tunnel kiln heated to 1350°C. While developments in briquetting processes have been generally directed towards the development of suitable binders, JP 60-243232 describes briquettes that have a flat shape in order to provide for stable distribution in a blast furnace. Specifically, the Japanese specification discloses that the flat-shaped briquettes are much more easily reduced at higher temperatures than conventional spherical pellets. The briquettes are made with a volume between 2 and 30cc in order to balance a relatively high compression strength against an inferior rotary or tumble strength and impact resistance with increasing size. The Japanese specification discloses that larger briquettes are less easily reduced in a blast furnace. However, aside from the size and shape of the briquettes there is no other factor described as critical, and, indeed, there is no detailed description of any other aspect of the production of the briquettes. The applicant has carried out extensive research work into the production of briquettes from iron ore and has invented a method that can produce briquettes that have suitable properties for use in blast furnaces and other direct reduction vessels. The applicant has found that there are a number of crucial factors in the success of this production method. These factors include characterising the raw material on the basis of mineralogy, porosity, size distribution and chemical composition, and then using this information to determine the required parameters, including the most suitable briquette forming parameters and induration parameters, to manufacture a suitable final product. According to the present invention there is provided a method of producing an iron ore briquette that is suitable for use as a blast furnace or other direct reduction furnace feedstock which includes the steps of: (a) mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux mixture; (b) adjusting the water content of the ore prior to or during mixing step (a) to optimise briquette quality and product yield; (c) pressing the ore/flux mixture into a green briquette; and (d) indurating the green briquette to form a fired briquette. One feature of the above-described method is that the predetermined particle size distribution of ore particles that is mixed with flux in step (a) can be produced without grinding ore. Preferably the method includes crushing and screening ore to form the predetermined particle size distribution that is mixed with flux in step (a) . Preferably the top size of the predetermined particle size distribution that is mixed with flux in step (a) is 3.5 mm. Preferably the top size is 3.0 mm. More preferably the top size is 2.5 mm. More preferably the top size is 1.5 mm. More preferably the top size is 1.0 mm. Preferably the predetermined particle size distribution that is mixed with flux in step (a) includes less than 50% passing a 45 µm screen. More preferably the particle size distribution includes less than 30% passing the 45µm screen. More preferably the particle size distribution includes less than 10% passing the 45µm screen. Preferably the ore is a hydrated iron ore. Preferably the hydrated ore is a goethite- containing ore. Preferably the flux has a particle size distribution that is predominantly less than 100 µm. Preferably the particle size distribution of the flux includes more than 95% passing a 250 µm screen. Preferably the flux is limestone. Preferably the ore/flux mixture produced in step (a) is selected so that the basicity of the fired briquette is greater than 0.2. More preferably the basicity is greater than 0.6. The term "basicity" is understood herein to mean (%CaO + %MgO)/(%SiO2 + %A12O3) of the fired briquette. Preferably there is no binder in the ore/flux mixture. Preferably step (b) includes adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 2-12% by weight of the total weight of the ore/flux mixture. The term "total weight of the ore/flux mixture" means the total of the (a) dry weight of the ore/flux mix, (b) the weight of the inherent moisture of the mixture, and (c) the weight of the moisture (if any) added to the mixture in the method. The term "moisture content" is the total of (b) and (c) above; Preferably step (b) includes adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 2-5% by weight of the total weight of the ore/flux mixture for ores that are dense hematite ores. Preferably step (b) includes adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 4-8% by weight of the total weight of the ore/flux mixture for ores containing up to 50% geothite. Preferably step (b) includes adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 6-12%by weight of the total weight of the ore/flux mixture for ores that are predominantly, ie contain more than 50%, goethite ores. Preferably pressing step (c) produces briquettes that are 10 cc or less in volume. More preferably pressing step (c) produces briquettes that are 8.5cc or less in volume. More preferably pressing step (c) produces briquettes that are 6.5 cc or less in volume. Preferably pressing step (c) includes pressing the ore/flux mixture using a low roll pressure. Preferably the low roll pressure is sufficient to produce briquettes having a green compressive strength of at least 2kgf. More preferably the green compressive strength is at least 4kgf. More preferably the green compressive strength is at least 5kgf. Preferably the low roll pressure is generated by a roll pressing force of 10-140 kN/cm on the mixture of ore/flux. More preferably the roll pressing force is 10-60 kN/cm. More preferably the roll pressing force is 10-40 kN/cm. Preferably indurating step (d) includes heating the briquette to a firing temperature with 40 minutes. Preferably indurating step (d) includes heating the briquette to a firing temperature within 35 minutes. More preferably indurating step (d) includes heating the briquette to the firing temperature within 30 minutes. More preferably step (d) includes heating the briquette to the firing temperature within 20 minutes. More preferably step (b) includes heating the briquette to the firing temperature within 15 minutes. Preferably the firing temperature is at least 1200°C. More preferably the firing temperature is at least 1260°C. More preferably the firing temperature is at least 1320°C. More preferably the firing temperature is at least 1350°C. More preferably the firing temperature is at least 1380°C. Preferably the fired briquette has a crush strength of at least 200kgf. More preferably the fired briquette has a crush strength of at least 200kgf. Iron ore fines are broadly characterised into four groups on the basis of petrological characteristics, such as mineralogy, mineral association and particle texture, porosity, size distribution and chemistry. The groups are: (a) HC - Dense hematite/magnetite ores; (b) GC - Ores containing up to 50% jgoethite; and; (c) G - Ores containing predominantly goethite, ie greater than 50% goethite, such as pisolites, detritals, and channel iron deposits. The following pages of the specification refer to two particular sub-groups of GC ores, namely: (i) HG - goethite-containing ores that are dominated by hematite; and (ii) GH - ores with approximately equal amounts of hematite and goethite. While not wishing to be bound by, theory, it is believed that the bonding mechanism in green briquettes involves a combination of bonds including the mechanical interlocking of particles, van der Waal's forces, and in the case of raw material types GC and G, hydrogen bonding to varying degrees is dependent on the percentage of hydrated iron species present, eg goethite. Several characteristics of the feed material have been identified as having a significant influence on the formation of such bonds that affect the quality and processing performance of the green and fired briquettes. These characteristics are the moisture level of the feed material and its flow characteristics, the chemical composition of the ore, its size distribution and petrological characteristics and porosity. Preferably the feed materials are of the widest size distribution possible in order to achieve a high packing density and increased bonding of the ore particles. As noted above, the bonding mechanism of green briquettes is believed to be through a combination of bonds arising from the mechanical interlocking of particles, van der Waal's forces, and hydrogen bonding in the cases of raw material types GC and G. Although a broad size distribution increases the packing density and improves the strength of the green briquette, it is possible to briquette closely sized iron ores. The top size of the particles is determined by the crushing process but is preferably less than 2.5 mm in order to produce briquettes of acceptable fired properties following the induration process. Generally, ore types HC and HG can be briquetted with coarser top j sizes due to the lower heat requirements of these raw materials to attain acceptable fired strength. The top size of the raw material can be reduced through either crushing or screening processes. The bottom size of the particles has no absolute limit, but it is not necessary or desirable, to grind the ore into very fine particles (as required for pelletising) as this is an additional economic burden rendered unnecessary by the present invention. Preferably less than 10% of the particles pass a 45 µm sieve. Advantageously the pocket dimensions of the briquetting apparatus should be selected on the basis of the maximum particle size to be briquetted, as well as for adequate induration performance, to ensure that satisfactory briquetting can be achieved. Typically the maximum particle size to achieve satisfactory briquetting is 25-30% of the minimum pocket dimension. If the maximum particle size exceeds this specification it may be necessary to select a larger pocket size. It is desirable to control feed moisture in order to optimise green briquette quality and product yield. Moisture addition should not exceed the level at which liquid bridging becomes a significant form of inter- particle bonding. This results in both decreased green strength and adversely affects thermal stability. Insufficient moisture can lead to overpressurisation in the briquette pressing step and adversely affect green briquette quality and yield. Depending on the feed characteristics of the ore to be processed, a moisture content of between 2 and 12 wt % for the feed material is used to optimise green briquette quality and product yield. Dense hematite concentrates (HC) have low optimum briquetting moistures. generally in the range of 2-5 wt %. These concentrates are often made up of closely sized particles with a smooth surface texture that generates low strength briquettes because of decreased interlocking of particles. More porous goethite-containing ores with up to 50% goethite (GC) briquette well in the range of 4-8 wt % moisture and more porous predominantly goethite ores (G) briquette well in the range of 6-12 wt% moisture. Such ores have a rough surface texture and shape enhancing their briquetting characteristics. Conventional briquetting apparatus may be used in the method of the invention. In essence, such apparatus includes two adjacent rolls with pockets which come together at a nip zone in order to compress the feed material into adjacent, aligned pockets to produce briquettes. In the case of the present invention, the rolls are preferably horizontally aligned to achieve the required throughput for economic feasibility. Although briquetting can be carried out over a wide range of roll pressures depending on the application, briquetting of iron ores is preferably conducted at roll pressing forces of 10-140 kN/cm and more preferably at the low end of this range, typically from 10-60 kN/cm. Such low pressure operation for iron ore briquetting is significant and makes it possible to achieve high production rates by the use of wide rolls on the briquetting machine up to 1.6m in length. Preferably the roll pressure is carefully controlled within the low pressure range in order to optimise the briquetting operation. If the roll pressure is too low, the rolls are forced apart producing a thick web and distorted briquettes impairing the product yield and the quality of the briquette, particularly after induration. If the roll pressure exceeds the optimum. poor closure of the briquettes occurs because of the "clamshell" effect on release of the briquettes from the pocket. The clamshell effect is more pronounced for small roll diameters and excess roll pressures, which also cause pocket binding/jamming. Although the density and crush strength of the green briquettes will be increased, the impact resistance of the fired briquettes will be severely impaired. Preferably the moisture level is selected to influence the flow characteristics of the material through the feed system, and moisture levels of 2-12 wt % for the feed material are generally suitable. If the moisture level is too high for the feed system, the feed pressure is adversely affected resulting in a decreased yield and some impairment of briquette quality, characterised by a lower green strength. It the feed material is too low in moisture for the feed system the resultant feed pressure will cause clamshelling which may result in decreased yields, increased wear rates of the roll pockets, and inferior fired properties. The briquetting apparatus may be operated with a pre-compactor feed system or with a gravity feed system. The latter system is advantageous where high tonnages are to be briquetted, as in the iron ore industry. With regard to briquetting presses, a roll diameter is selected in order to ensure that briquette quality is obtained at an economic production rate. Large diameter rolls increase production rates, however they also increase the area of the nip zone. Careful control of the nip zone facilitates formation of quality green briquettes and avoids formation of briquettes with an excessively thick web. Alterations in roll diameter may also alter the optimum moisture level for feed material where increased roll diameters represent increases in feed moisture. Roll diameters typically vary from 250 mm - 1200 mm. In order to maximise production, preferably the rolls are operated at the fastest speed possible whilst maintaining briquette quality. However, a very low roll speed may be used if productivity is of a secondary concern. I ■ . Typically, roll speeds in the range of 1 rpm to 20 rpm are employed. It is desirable in order to maintain quality, particularly at high roll speeds, that the feed material be presented to the rolls at a rate that matches the briquette production rate and with a nip zone area that produces the forces required to form quality briquettes. Any suitable roll width may be selected provided that it is within the pressure capabilities of the briquetting machine. As briquetting of iron ores is a low pressure operation, wide rolls are preferred, increasing the capacity of the machine. The rolls are preferably horizontally aligned to allow for use with a gravity feed system. The flow characteristics of iron ores, whether HC, GC (including H6 and 6H), or G, are suitable for gravity feeding at the moisture ranges specified above for each classification. The pocket shape should not generally be of a sharp angular nature, but be more smooth and rounded to improve handling characteristics. By way of example, a length/width and width/depth ratio of approximately 0.65 is suitable. Pocket shapes also have specific release angles, 110-120° that combat the tendency for sticking in the pockets. The pocket size can be optimised according to the requirements for the induration process and the raw material top size and the iron making blast furnace. Typically the briquettes have a volume of between 2 and 30 cc. Preferably the volume is 10 cc or less. More preferably the volume is 8.5 cc or less. More preferably the volume is less than 6.5 cc. A staggered pocket configuration is preferred as this makes the optimum use of the available space on the face of the rolls, and hence maximises throughput. Preferably the induration method and conditions are selected having regard to the complex relationship between raw material characteristics and tie influence of the briquette dimensions. Consideration of the relationship between briquette volume, shape and the petrological characteristics of the raw material is required. The chemical composition of the feed material will have a significant influence on the properties of the fired briquette. Apart from moisture, the feed material includes the iron ore made up of iron oxide and gangue minerals, with the required flux added to give the required basicity level in the fired briquette. Test results have shown that the flux should preferably be finely sized, typically >95% passing 250 µm, in order to achieve the required properties in the fired briquette. While not wishing to be bound by theory, it is believed that the bonding mechanism for fired briquettes involves diffusion bonding and re-crystallisation of the iron oxide particles as well as slag bonding at higher flux levels. Therefore, flux level and faring temperature and, to a certain extent, firing time have a strong influence on briquette properties. Elevated basicity levels may improve reduced strengths as well as indurated strengths as higher flux levels encourage the formation of bonding phases which resist demormation under reducing conditions. Induration may be carried out using a straight grate, grate-kiln or a continuous kiln type process. It has been found that green briquettes produced under an optimised firing profile are thermally very stable compared to pellets prepared from the same material. The feed ore for pelletising must be ground to a fine size, typically up to 60% passing 45 µm, and the pellets dried slowly at low temperatures, typically to avoid spalling. In contrast, as indicated above, the feed ore for the present invention that can be indurated successfully can be much coarser, with top sizes preferably up to 2.5 mm, and hence does not need grinding to the same extent as is required to produce pellets. This characteristic represents major capital cost reductions for briquetting operations over traditional pellet production plants. An important characteristic of the briquette of the present invention is the ability to withstand high temperatures on heating at fast rates, such as heating to a firing temperature within 30 minutes, more preferably within 20 minutes. This is in direct contrast with conventional understanding of how goethitic ores respond in induration situations, where is has been shown that they spall when heated too fast through the dehydroxylation and free water removal zones. As is indicated above, the thermal stability of the briquettes of the present invention has been found to be much greater than pellets and they may be heated at much faster rates than pellets without spelling. This allows a much shorter heating cycle. Consequently, briquette productivity can be significantly higher than for pellets using the same material. For instance, briquette productivities potentially in the order of 30t/m2.day in a straight grate kiln can be achieved, compared to pellet productivities of 16t/m2.day for H6 ores in the same kiln. It will be clearly understood that, although prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in Australia or in any other Country. Preferred embodiments of the present invention will now be described, by way of example only with reference to the accompanying drawings, in which: FIG. 1 is a schematic illustration of suitable apparatus with 250 mm diameter rolls and a precompacted feed system for conducting the process of the present invention; FIG. 2 is a schematic illustration of suitable apparatus with 450 mm diameter rolls and a gravity feed system for conducting the process of the present invention; FIG. 3 is a schematic illustration of suitable apparatus with 650 mm diameter rolls and a gravity feed system for conducting the process of the present invention; FIG. 4 is a plot of yield of whole briquettes versus feed moisture for HG material on 450 mm rolls with 6 cc almond forms and 4 cc elongate almond pockets; FIG. 5 is a plot showing the effect of feed moisture on green briquette strength for HG material on 450 mm rolls with varying pocket dimensions; FIG. 6 is a plot showing the effect of feed moisture on green briquette strength for ICG material using 650 mm rolls and 7.5 cc 'pillows'; FIG. 7 shows the effect of roll pressing force on briquette properties; thickness, green strength and green density on 450 mm rolls and 9 cc almond forms; FIG. 8 is a plot showing the effects of roll pressing on green strength for HG material using 650 mm rolls and 7.5 cc 'pillows'; FIG. 9 is a plot showing the effect of roll pressing force on green strength for GH material using 650 mm rolls and 7.5 cc ^pillows'; FIG. 10 shows the effect of roll speed on briquette properties; thickness, green strength and green density for a rolls pressure of 90kg/cm2 and a feed moisture of 6 wt % using 450 mm rolls and 9 cc almond forms; FIG. 11 is the operating window for a briquetting machine with a pre-compactor, 250 mm rolls, 4 cc almond forms and HG material; FIG. 12 shows temperature profiles for briquette induration in a 500 mm deep bed; FIG. 13 shows temperature profiles for briquette induration that produced briquettes at high productivities and a typical temperature profile for pellet induration that produced pellets at a lower productivity; FIG. 14 is a plot showing the effect of average bed temperature on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' at the end of a grate cycle in a batch grate kiln; FIG. 15 is a plot showing the effect of average bed temperature on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' at the end of a grate- kiln firing cycle in a batch grate kiln; FIG. 16 is a plot showing the effect of time at firing temperature (1380°C) on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' during a test cycle in the batch grate kiln; FIG. 17 is a plot showing the effect of time at firing temperature (1380°C) on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' during a test cycle in the batch grate kiln; FIG. 18 is a plot showing the effects of residence time on 7.5 cc GH briquettes in the kiln during a test cycle in the kiln only. FIG. 19 is a plot showing the effect of bed height and grate firing profile on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' during a test cycle in the batch grate kiln; FIG. 20 is a plot showing the effect of bed height and grate firing profile on briquettes made with GH material using 650 mm rolls and 7.5 cc 'pillows' during a test cycle in the batch grate kiln; FIG. 21 shows the effect of basicity and firing temperature on the fired crush strength of briquettes made with HG material, 250 mm rolls and 4 cc almond forms; FIG. 22 shows the effect of basicity on the briquette reduced properties; swell, crush strength after reduction (CSAR) and reducibility index of briquettes made with HG material, 250 mm rolls and 4 cc almond form; EXAMPLE 1 Briquetting was performed using three different roll presses with varying roll diameter, width and feed systems. Initial testing was conducted using a Taiyo K- 102A. double roll press, which has a nominal, capacity of 300 kg/hr. This machine has 250 mm diameter rolls of 36 mm width and features a screw-type precompactor. A schematic showing its main components can be seen in •Figure 1. The briquettes produced were pillow- shaped with nominal dimensions of 13x19x28 mm and a volume of 4 cc. There was a single row of 30 pockets around the circumference of each roll. Of the two rolls, one was fixed whilst the other "floating roll" was held against the fixed roll by an oil and gas filled ram. The oil in the ram was pressurised to provide the desired load force between the rolls. Briquetting was also performed using a Romarek BH400 double roll press, with a roll diameter of 450 mm and a roll width of 75 mm. Feed material was gravity fed into the nip zone from a feed hopper located above the rolls. A schematic of its main components can be seen in Figure 2. Briquettes of varying dimensions were produced with the following details: (1) Nominally 17.5x28x34.3 mm with a volume of 8.9 cc. There was a double row of 48 pockets arranged in staggered alignment around the circumference of each row (9 cc Almond forms). (2) Nominally 14.5x22.1x33.9 mm with a volume of 6.3 cc. There was a double row of 60 pockets arranged in a staggered alignment around the circumference of each roll(6 cc Almond forms). (3) Nominally 15.2x21.7x22.9 mm with a volume of 3.9 cc. There was a triple row of 58 pockets arranged in a staggered alignment around the circumference of each row (4 cc spherical). (4) Nominally 11.2x17.3x32.1 mm with a volume of 3.9 cc. There was a double row of 72 pockets arranged in a symmetrical alignment around the circumference of each roll (4 cc elongate). Of the two rolls, one was fixed whilst the other "floating roll0 was held against the fixed roll by an oil and gas filled ram. The oil in the ram was pressurised to provide the desired specific pressing force between the rolls. Briquetting was also conducted using a Koppern 52/6.5 double roll press with a diameter of 650 mm and a roll width of 130 mm. Feed material was gravity fed into a nip zone from a hopper located above. Nip zone area was controlled through use of a 'nip zone adjuster'. A schematic of its main components can be seen in Figure 3. The briquettes produced were 'pillow' shaped with nominal dimensions of 30x24x16 mm and forms a volume of 7.5 cc. There were four rows of 77 pockets arranged symmetrically across the face of the roll. Of the two rolls, one was fixed Whilst the other "floating roll" was held against the fixed roll by an oil and gas filled ram. The oil in the ram was pressurised to provide the desired specific pressing force between the rolls. EXAMPLE 2 The effect of feed moisture content was investigated. Figure 4 illustrates that feed moisture had a significant effect on the yield of 6 cc and 4cc briquettes produced by the briquetting press with 450 mm rolls as described in Example 1. The feed material was gravity fed to the rolls while the rolls operated at a fixed roll speed of 20 rpm and a roll pressure of 90kg/cm2. Feed moisture control is also important as variation in moisture content affects green properties such as green strength, abrasion resistance and shatter strengths. This is illustrated in Figures 5 and 6. Figure 5 shows the relationship between feed moisture level and strength for briquettes made with HG using the 450 mm rolls, a gravity feed system, and a variety of pocket sizes. Figure 6 shows the same relationship for briquettes made with the 650 mm rolls and 7.5 cc pockets for HG material. Green strength tended to increase to a maximum for the optimum moisture content of approximately 6%. At moisture levels exceeding 7.5% the green strength was unacceptably low. Feed moisture had less of an influence on shatter strength and the green abrasion resistance of the briquettes. EXAMPLE 3 As is indicated above, although briguetting operations can be carried out over a wide range of rolls pressures, it is preferred that briguetting be carried out at low pressures. Such low pressure operation for iron ore briguetting is significant and opens up the possibility of achieving high production rates with wide rolls on a briguetting machines. However, as is indicated above, roll pressure should be carefully controlled within this low pressure range if the briguetting operation is to be optimised. If roll pressure is too low and nip zone area is not carefully controlled, the rolls are forced apart producing a thick web and distorted briquettes impairing the product yield and the quality of the briquette, particularly after induration. If roll pressure exceeds the optimum, poor closure of the briquettes occurs because of the "clamshell" effect on release of the briquette from the pocket. Although the density and crush strength of the green briquette will be increased, the impact resistance of the fired briguette will be severely impaired. Figure 7 shows the effect of roll pressure on briguette thickness and quality (measured in terms of crush strength) for raw material H6 produced in a gravity fed machine with 450mm diameter rolls with nominal 9 cc pockets. The figure shows that acceptable green strength was obtained at roll pressures as low as 60 kg/cm2. Figures 8 and 9 show the effect of pressing force and resultant green strength that was obtained using the 650 mm diameter rolls. The work was carried out on HG and 6H raw material types and illustrates a similar relationship between roll pressure and green strength as with the 450 mm work. Specifically, the figures show that acceptable green strengths were obtained at pressing forces of 20 kN/cm. Pressing force was also found to exert a significant influence on the shatter strength and the green abrasion resistance of the briquettes, with both variables increasing in response to increased roll pressure. EXAMPLE 4 Roll speed was also investigated. Roll speed, measured in rpm, was found to exert an influence on the amount of pressure applied to feed materials. Increased roll speeds result in shorter residence time in the nip zone of the rolls and hence lower pressure is exerted for a longer period of time. Roll pressure can be used primarily to control the amount of pressure exerted on feed material and roll speed can be altered to maximise the production rate. However, it is important to consider the effects of roll speed on briquette thickness and green strength when optimising the green briquetting operation. The effect of roll speed on briquette thickness and quality (measured in terms of crush strength) for raw material HQ is shown in Figure 10 for a gravity fed machine with 450 mm diameter rolls. The Figure shows that thickness and green strength decreased as roll speed increased. EXAMPLE 5 The process variables of the briquetting machine as described in Example 1, ie, roll speed, precompactor speed and roll pressure, and the briquette density were used to determine an operating window for this particular system of briquetting. The diagram shown in Figure 11 is an example of an operating window for briquetting with 250 mm rolls to form nominally 4 cc briquettes out of HG material on the Taiyo press. To simplify the curves, roll pressure was fixed at 150 kg/cm2 and precompactor speed was fixed at 20 rpm. A series of curves are shown for feed moisture from 4 wt % to 12 wt %. Each represents conditions that resulted in the formation of whole briquettes. To the right of the curves there is a region of low feed pressure where pockets are not filled or the briquettes are weak and split readily. To the left of the curves there is a region where the pressure on the feed is too high. Briquettes shear and pocket blockage occurred. Across the strength range, below 6 kgf, the briquettes were too weak to withstand pocket release and either remain in the pockets or split on release, Above 30 kgf, further compaction could not be achieved. The briquettes were thick and began to 'clam shell'. The strength range of 6 to 30 kgf defined the outer limits within which whole briquettes could be formed with the sample material and the Taiyo briquetting machine. To determine the operating window certain product and quality parameters including yield, density, crush strength and drop/shatter strength need to be considered. Once these properties are taken into consideration, a smaller region can be defined which is the operating region of the briquetting process. In Figure 11, this region occurs at rolls speeds between 5 and 9 rpm and green strengths between 6 kgf and 18 kgf. EXAMPLE 6 Green briquettes produced under optimised conditions were found to be thermally very stable compared to pellets formed from the same material. This is shown in Figures 12 and 13. Figure 12 shows the temperature profiles for the inlet and outlet gas and three positions within the bed of briquettes during laboratory-scale induration trials simulating a straight grate process. The bed temperatures were measured by thermocouples placed at 100, 250 and 500 mm from the top of the bed. The briquettes were found to be be thermally stable when heated at fast rates shown in the figures. The excellent drying performance allowed the inlet gas temperature to be raised from ambient to 1340°C in ten ninutes without spalling the briquettes. Figure 13 shows the temperature profiles for ariquette induration that produced nominal 4 cc briquettes of HG ore at productives of 32 t/m2. d and 25 t/xn2 .d. The figure also shows, by way of comparison, a typical induration temperature profile for pellets. The pellet profile was an optimised profile so that pellet spalling was minimised and fired properties were maximised. The pellet profile produced pellets with a productivity of 16t/m2.d, which is considerably lower than the productivities of the briquettes. The briquettes and the pellets were made from the same ore type. The high productivities for the briquettes was due to the thermal stability of the green briquettes which enabled the briquettes to be heated at fast rates. The thermal stability of the briquettes was found to be not exclusive to one induration method and to one ore type. EXAMPLE 7 A pilot scale grate-kiln system was used to determine the properties of briquettes as they exited a grate prior to entry to a kiln. The equipment consisted of a pot grate and a batch kiln. To simulate the travelling grate a LGP gas burner was used to generate the flame temperature. The pot grate was capable of up and down draught gas flow. The temperature of the material was measured throughout the bed using thermocouples set into and through the wall of the pot. These measurements were assumed to be the briquette temperature during the firing cycle. Due to the size of the briquettes tested, it may be that the temperature measurement shows the external briquette temperatures and not the internal temperatures. The temperature measured is most likely a mixture of briquette outside temperature and gas temperature at that location in the bed. Figure 14 shows how the temperature of the briquettes made from GH material (d95 = 1mm) with a green nominal size of 7.5cc initially increased to a maximum at approximately 300-400°C average bed temperature, and then fell to a minimum temperature at -700°C. At higher temperatures the strength then increased again. The strength fell to a minimum value at -700°C, which is lower than the green strength. This is a critical factor for transport of the material from the grate-to the kiln. As the strength was lowest at this temperature range, the maximum amount of degradation could be expected if the firing profile included transfer from the grate to the kiln at this temperature. For a straight grate process, the bed height selected for the induration process was found to be not critical and not inhibited by gas permeability generally selected to avoid deformation of the briquettes at the lower parts of the bed while achieving a reasonable productivity. In addition, at briquette volumes exceeding 6 cc, permeability of the bed was not greatly compromised by bed height. Consequently, the induration process is not restricted by this variable as is the case with pelletising operations. Green briquette bed depth can be selected to optimise productivity without compromising quality. A grate-kiln process may offer certain advantages in terms of producing a better fired product compared to products obtained from other induration processes. It also heats the briquettes more uniformly through high temperature ranges in a way that reduces temperature gradients within the briquette and avoids differential shrinkage of the briquette that may lead to cracking. Also, as all the briquettes are subject to similar firing temperatures and time in the rotating kiln, briquette quality is more uniform compared to the straight grate process. Possibilities also exist for the production of briquettes suitable for direct reduction processes, providing a raw material of a suitable grade is used. EXAMPLE 8 Firing temperature was investigated. Briquettes of GH material (d95 = 1mm) 7.5cc were fired in the grate-kiln pilot rig, all using the same firing profiles for the grate section. After transfer to the kiln, the same profile was applied for firing, except that the firing temperature reached was altered as shown. The results are shown in Figure 15. There is a clear indication in Figure 15 that to achieve suitable fired strength in briquettes of this size the firing temperature in the kiln should be at least 1380°C. Figure 15 also shows that tumble strength (Tumble Index - TI) and abrasion resistance (Abrasion Index - AI), improved with firing temperature. EXAMPLE 9 Firing temperature and time at temperature were investigated. Briquettes made from 6H material (d95 = 1mm) with a nominal size of 7.5cc were fired in a series of grate- kiln tests. The grate firing profile was the same, with only the firing time in the kiln at the firing temperature being changed from 6 to 9 minutes. The total firing time in the kiln remained the same, the extra time for the firing was taken from the rate of heating in the kiln, so that the 9 minutes firing time had a quicker heating rate to 1380° compared to the 6 minutes firing time. Tests were also conducted with 6.3cc 6H briquettes using the same firing profile as that used for the 7.5cc case. For the nominally 7.5cc size GH briquettes, the fired strength increased significantly from the longer firing time in the kiln. This was due to greater heat penetration of the briquettes during the firing cycle. The fired properties for the 6.3 cc GH briquettes were superior to those produced for the 7.5cc case, inferring that the issue of heat penetration is a significant issue for fired property generation of the briquettes. This result also suggests that when heat penetration in the briquettes is insufficient adequate strength will not be generated in the fired product. EXAMPLE 10 The effect of residence time in a grate kiln was investigated. Briquettes made from GH material (d95 = 1mm) and nominally 7.5cc were fired in a pilot scale batch grate kiln. They were charged green into a kiln that had been preheated to either 500 or 1000°C. Firing profiles were imposed on the briquettes and the total residence time reported. The results are shown in Figure 18. Figure 18 shows that the fired properties improved with increasing residence time, suggesting the importance of heating the product thoroughly to achieve the final properties required. The effect of rapid heating was not reduced by a larger bed depth of the grate. This is shown in Figures 19 and 20. The green briquette bed was highly permeable and did not restrict airflow, as often occurs with pellets. The maximum bed depth useable has not been defined, but is likely to be greater than 300mm. This far exceeded that possible for even the best pellet beds in a grate-kiln system. EXAMPLE 11 The effect of the chemistry of briquettes was investigated. The effect of basicity and temperature on the fired briquette properties made from HG material was determined by firing the briquettes in the muffle furnace at specific temperatures and times. The results are shown in Figure 21. Results for the chemical analyses of the fired briquettes made at varying basicities produced fired briquettes which varied in grade from 63.81% Fe at a basicity of 1.2 up to 65.93% Fe for a basicity of 0.2, reflecting the level of flux addition. As can be seen in Figure 21, crush strength increased with both temperature and as basicity increased from 0.2 to 0.8. This effect becomes more significant as the temperature increased across the range studied and it was possible to achieve 300 kgf at 1295°C for 0.6 basicity and at 1280°C for 0.8 basicity. The explanation for increased basicity levels resulting in increased strengths is related to changes in the bonding mechanism. At low basicity levels, bonding of the particles occurs as a result of recrystallisation of iron oxide and the formation of iron oxide-iron oxide bonds. At increased basicity levels, melt formation occurs at lover temperatures enhancing melting of iron oxide crystals, and slag bonding becomes more significant giving higher strengths for the same temperature. EXAMPLE 12 Reduction testing, using whole briquettes and standard reduction test methods JIS 8713/IS07215 was carried out on HG briquettes that were fired at 1300°C for 10 min. The results of reducibility, swell and crush strength after reduction (CSAR) are shown in Figure 22. The reducibility index (RI) remained relatively stable across the range of basicity levels. The RI varied from 53.8% at a basicity of 0.20 to just over 62.2% at a basicity of 1.00. The swell index showed some response and varied from 11% at the lowest basicity to 14.8% in the mid- ranges, decreasing to zero at a basicity of 1.20. The crush strength after reduction (CSAR) showed a large response to changes in the basicity level, ranging from 22 kgf at 0.20 basicity to 121 kgf at 1.20 basicity. This change in reduced strength reflects the fired crush strength results and is again related to variation in the bonding phases of the fired briquettes. The low basicity briquettes were predominantly bonded by iron oxide-iron oxide bonds, which degrade during reduction. At increased basicity levels, slag bonding becomes more significant. These bonds are more stable during reduction, accounting for the higher reduced strengths and little or no swell at a basicity of 1.20. Slag bonding also becomes a more important form of bonding in briquettes made from GH and G where higher Si02 and Al2O3 levels result in increased flux additions. Such briquettes generally prove stronger after reduction as the reduction process does not result in the breakdown of non-ferrous bonding phases. High grade ores, such as HC, which require low flux addition rely almost solely on oxide-oxide bonding and hence have lower strength after reduction values. Many modifications may be made to the embodiments of the present invention described above without departing from the spirit and scope of the invention. WE CLAIM: 1. A method of producing an iron ore briquette that is suitable for use as a blast furnace or other direct reduction furnace feedstock which involves the steps of: (a) mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux mixture and wherein there is no binder in the ore/flux mixture; (b) adjusting the water content of the ore prior to or during mixing step (a) so that the moisture content of the ore/flux mixture is 2-12% by weight of the total weight of the ore flux mixture; (c) pressing the ore/flux mixture into a green briquette; and (d) indurating the green briquette to form a fired 2. The method as claimed in claim 1 involving crushing and screening ore to form the predetermined particle size distribution that is mixed with flux in step (a). 3. The method as claimed in claim 1 or claim 2 wherein the top size of the predetermined particle size distribution of ore that is mixed with flux in step (a) is 3.5 mm. 4. The method as claimed in claim 3 wherein the top size is 3/0 mm. 5. The method as claimed in claim 3 wherein the top size is 2.5 mm. 6. The method as claimed in claim 3 wherein the top size is 1.5 mm. 7. The method as claimed in claim 3 wherein the top size is- 1.0 mm. 8. The method as claimed in any one of the preceding claims wherein the predetermined particle size distribution of ore that is mixed with flux in step (a) includes less than 50% passing a 45µm screen. 9. The method as claimed in claim 8 wherein the predetermined ore particle size is less than 30% passing the 45pm screen. 10. The method as claimed in claim 8 wherein the predetermined ore particle size is less than 10% passing the 45pm screen. claims wherein the ore is a hydrated iron pre. 12. The method as claimed in claim 11 wherein the hydrated ore is a goethite-containing ore. 13. The method as claimed in any one of the preceding claims wherein the flux has a particle size distribution that is predominantly less than 100 µm. 14. The method as claimed in any one of the preceding claims wherein the particle size distribution of the flux is more than 95% passing a 250 µm screen. 15. The method as claimed in any one of the preceding claims wherein the ore/flux mixture produced in step (a) is selected so that the basicity of the fired briquette produced in step (d) is greater than 0.2. 16. The method as claimed in claim 15 wherein the basicity is greater than 0.6. 17. The method as claimed in claim 1 wherein step (b) involves adjusting the water content of the ore so that the moisture content of the ore/flux-mixture is 2-5% by weight of the total weight of the ore/flux mixture for ores that are dense hematite ores. 18. The method as claimed in claim 1 wherein step (b) involves adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 4-8% by weight of the total weight of the ore/flux mixture for ores containing up to 50% goethite. 19. The method as claimed in claim 1 wherein step (b) involves adjusting the water content of the ore so that the moisture content of the ore/flux mixture is 6-10% by weight of the total weight of the ore/flux mixture for ores that are predominantly, ie contains more than50%, goethite. 20. The method as claimed in any one of the preceding claims wherein pressing step (c) produces briquettes that are 6 cc or less in volume. 21. The method as claimed in claim 1 wherein the briquettes are 8.5 cc or les in volume. 22. The method as claimed in claim 1 wherein the briquettes are 6.5 cc or less in volume. 23. The method as claimed in any one of the preceding claims wherein pressing step (c) involves pressing the ore/flux mixture using a low roll pressure. 24. The method as claimed in claim 23 wherein the low roll pressure is sufficient to produce briquettes having a green compressive strength of at least 2kgf. 25. The method as claimed in claim 23 wherein the low roll pressure is generated by a roll pressing force of 10- 140 kN/cm on the mixture of ore/flux. 26. The method as claimed in claim 23 wherein the roll pressing force is 10-40kN/cm. 27. The method as claimed in any one of the preceding claims wherein indurating step (d) involves heating the briquette to a firing temperature within 40 minutes. 28. The method as claimed in claim 27 wherein step (d) involves heating the briquette to the firing temperature within 35 minutes. 29. The method as claimed in claim 27 wherein step (b) involves heatinc? the briquetts to the firing temperature within 30 minutes. 30. The method as claimed in claim 27 wherein step (d) involves heating the briquette to the firing temperature within 20 minutes. 31. The method as claimed in claim 27 wherein step (d) including heating the briquette to the firing temperature within 15 minutes. 32. The method as claimed in any one of claims 27 to 31 wherein the firing temperature is at least 1200°C. 33. The method as claimed in claim 32 wherein the firing temperature is at least 1260 C. 34. The method as claimed in claim 32 wherein the firing temperature is at least 1320oC. 35. The method as claimed in claim 32 wherein the firing temperature is at least 1350 C. 36. The method as claimed in claim 32 wherein the - firing temperature is at least 1380oC. 37. The method as claimed in any one of the preceding claims wherein the fired briquette has a crush strength of at least 200 kgf. 38. A fired briquette produced by the method according to any one of the preceding claims which has a crush strength of at least 200 kgf. ABSTRACT A METHOD OF PRODUCING AN IRON ORE BRIQUETTE A method of producing an iron ore briquette is disclosed.The method is suitable for use is a blast furnace or other direct reduction furnace feedstock which involves the steps of: (a)mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux mixture and wherein there is no binder in the ore/flux mixture; (b)adjusting the water content of the ore prior to or during mixing step (a) so that the moisture content of the ore/flux mixture is 2-12% by weight of the total weight of the ore flux mixture; (c) pressing the ore flux mixture into a green briquette; and (d) indurating the green briquette to form a fired briquette.

Full Text

The present invention is concerned with the
production of iron ore briquettes suitable for transport
and use in iron making processes.
Methods of agglomerating iron orbs have been in
development since the late 1800's. However, of all the
available processes only the pelletising and sintering
processes are now of significance, but these suffer from
certain disadvantages.
Pelletising consists of two distinct operations;
forming pellets from moist ore fines and then firing them
at a temperature in the region of 1300°C. It is critical
in order to prepare suitable pellets that the ore be
ground very fine, generally to a size where in the order
of 60% of the ore passes 45 pm. It is then formed into
pellets in either a horizontal drum or an inclined disc,
generally with the addition of a suitable binder. The
formed pellets are then fired in a process sometimes
reffered to as induration in shaft kilns,horizontal
travelling grates, or a combination of travelling grates
and rotary kilns. Pelletising is a practicable and
commercially attractive method of agglomerating fine
concentrates, but requires substantial grinding in order
to achieve the required particle sizing which is an energy
intensive process. Pellets made from goethite-hematite
ores require extended Induration times, affecting process
economics. Solid fuel, in the form of coke, is often added
to reduce induration time which results in the production
of noxious emissions (including dioxins, NOX and SOx) .
Sintering consists of granulating moist iron ore

fines and other fine materials with solid fuel, normally
coke breeze, and loading the granulated mixture onto a

permeable travelling grate. Air is drawn downwards
through the grate as the temperature is raised. After a
short ignition period, external heating of the bed is
discontinued and as the solid fuel in the bed burns a
narrow combustion zone moves downwards through the bed,
each layer in turn being heated to approximately 1300°C.
Bonding takes place between the grains during combustion,
and a strong agglomerate is formed. However, traditional
sintering processes result in high levels of noxious
emissions, particularly sulfur oxides and dioxins, and
therefore the process is undesirable and unsustainable on
environmental grounds.
Briguetting is a process in which there was
commercial interest in the late 1800's and early 1900's,
but production of iron ore briquettes for use as a blast
furnace feed material never reached any significant

levels, decreased after 1950, and had ceased by about

1960. The process as practised involved the pressing of
ore fines into a block of some suitable size and shape,
and then indurating the block. A wide range of binders
such as tar and pitch and/or other additives such as
organic products, sodium silicate, ferrous sulfate,
magnesium chloride, limestone and cement were tested.
However, the earliest briquetting process, the Grondal
process, simply involved mixing iron ore with water and
pressing into oblong blocks the size of building bricks.
These were then hardened by passing them through a tunnel
kiln heated to 1350°C.
While developments in briquetting processes have
been generally directed towards the development of
suitable binders, JP 60-243232 describes briquettes that
have a flat shape in order to provide for stable
distribution in a blast furnace. Specifically, the
Japanese specification discloses that the flat-shaped
briquettes are much more easily reduced at higher

temperatures than conventional spherical pellets. The
briquettes are made with a volume between 2 and 30cc in
order to balance a relatively high compression strength
against an inferior rotary or tumble strength and impact
resistance with increasing size. The Japanese
specification discloses that larger briquettes are less
easily reduced in a blast furnace. However, aside from
the size and shape of the briquettes there is no other
factor described as critical, and, indeed, there is no
detailed description of any other aspect of the production
of the briquettes.
The applicant has carried out extensive research
work into the production of briquettes from iron ore and
has invented a method that can produce briquettes that
have suitable properties for use in blast furnaces and
other direct reduction vessels.

The applicant has found that there are a number
of crucial factors in the success of this production
method. These factors include characterising the raw
material on the basis of mineralogy, porosity, size
distribution and chemical composition, and then using this
information to determine the required parameters,
including the most suitable briquette forming parameters
and induration parameters, to manufacture a suitable final
product.

According to the present invention there is
provided a method of producing an iron ore briquette that
is suitable for use as a blast furnace or other direct
reduction furnace feedstock which includes the steps of:
(a) mixing: (i) ore having a predetermined particle
size distribution with a top size of 4.0 mm or
less; and (ii) a flux; to form an ore/flux
mixture;

(b) adjusting the water content of the ore prior to
or during mixing step (a) to optimise briquette
quality and product yield;
(c) pressing the ore/flux mixture into a green
briquette; and
(d) indurating the green briquette to form a fired
briquette.

One feature of the above-described method is that
the predetermined particle size distribution of ore
particles that is mixed with flux in step (a) can be
produced without grinding ore.
Preferably the method includes crushing and
screening ore to form the predetermined particle size
distribution that is mixed with flux in step (a) .
Preferably the top size of the predetermined
particle size distribution that is mixed with flux in step
(a) is 3.5 mm.
Preferably the top size is 3.0 mm.
More preferably the top size is 2.5 mm.
More preferably the top size is 1.5 mm.
More preferably the top size is 1.0 mm.
Preferably the predetermined particle size
distribution that is mixed with flux in step (a) includes
less than 50% passing a 45 µm screen.
More preferably the particle size distribution

includes less than 30% passing the 45µm screen.
More preferably the particle size distribution
includes less than 10% passing the 45µm screen.
Preferably the ore is a hydrated iron ore.
Preferably the hydrated ore is a goethite-
containing ore.
Preferably the flux has a particle size
distribution that is predominantly less than 100 µm.
Preferably the particle size distribution of the
flux includes more than 95% passing a 250 µm screen.
Preferably the flux is limestone.
Preferably the ore/flux mixture produced in step
(a) is selected so that the basicity of the fired
briquette is greater than 0.2.
More preferably the basicity is greater than 0.6.
The term "basicity" is understood herein to mean
(%CaO + %MgO)/(%SiO2 + %A12O3) of the fired briquette.
Preferably there is no binder in the ore/flux
mixture.
Preferably step (b) includes adjusting the water
content of the ore so that the moisture content of the
ore/flux mixture is 2-12% by weight of the total weight of
the ore/flux mixture.
The term "total weight of the ore/flux mixture"
means the total of the (a) dry weight of the ore/flux mix,

(b) the weight of the inherent moisture of the mixture,
and (c) the weight of the moisture (if any) added to the
mixture in the method.
The term "moisture content" is the total of (b)
and (c) above;
Preferably step (b) includes adjusting the water
content of the ore so that the moisture content of the
ore/flux mixture is 2-5% by weight of the total weight of
the ore/flux mixture for ores that are dense hematite
ores.
Preferably step (b) includes adjusting the water
content of the ore so that the moisture content of the
ore/flux mixture is 4-8% by weight of the total weight of
the ore/flux mixture for ores containing up to 50%
geothite.
Preferably step (b) includes adjusting the water
content of the ore so that the moisture content of the
ore/flux mixture is 6-12%by weight of the total weight of
the ore/flux mixture for ores that are predominantly, ie
contain more than 50%, goethite ores.
Preferably pressing step (c) produces briquettes
that are 10 cc or less in volume.
More preferably pressing step (c) produces
briquettes that are 8.5cc or less in volume.
More preferably pressing step (c) produces

briquettes that are 6.5 cc or less in volume.
Preferably pressing step (c) includes pressing
the ore/flux mixture using a low roll pressure.

Preferably the low roll pressure is sufficient to

produce briquettes having a green compressive strength of
at least 2kgf.
More preferably the green compressive strength is
at least 4kgf.
More preferably the green compressive strength is
at least 5kgf.
Preferably the low roll pressure is generated by
a roll pressing force of 10-140 kN/cm on the mixture of
ore/flux.

More preferably the roll pressing force is 10-60
kN/cm.
More preferably the roll pressing force is 10-40
kN/cm.
Preferably indurating step (d) includes heating
the briquette to a firing temperature with 40 minutes.
Preferably indurating step (d) includes heating
the briquette to a firing temperature within 35 minutes.
More preferably indurating step (d) includes
heating the briquette to the firing temperature within 30
minutes.
More preferably step (d) includes heating the
briquette to the firing temperature within 20 minutes.
More preferably step (b) includes heating the
briquette to the firing temperature within 15 minutes.
Preferably the firing temperature is at least

1200°C.
More preferably the firing temperature is at
least 1260°C.

More preferably the firing temperature is at
least 1320°C.
More preferably the firing temperature is at
least 1350°C.

More preferably the firing temperature is at
least 1380°C.
Preferably the fired briquette has a crush
strength of at least 200kgf.
More preferably the fired briquette has a crush
strength of at least 200kgf.
Iron ore fines are broadly characterised into
four groups on the basis of petrological characteristics,
such as mineralogy, mineral association and particle
texture, porosity, size distribution and chemistry. The
groups are:

(a) HC - Dense hematite/magnetite ores;
(b) GC - Ores containing up to 50% jgoethite; and;
(c) G - Ores containing predominantly goethite, ie
greater than 50% goethite, such as pisolites,
detritals, and channel iron deposits.
The following pages of the specification refer
to two particular sub-groups of GC ores, namely:

(i) HG - goethite-containing ores that are
dominated by hematite; and

(ii) GH - ores with approximately equal
amounts of hematite and goethite.
While not wishing to be bound by, theory, it is
believed that the bonding mechanism in green briquettes
involves a combination of bonds including the mechanical
interlocking of particles, van der Waal's forces, and in
the case of raw material types GC and G, hydrogen bonding
to varying degrees is dependent on the percentage of
hydrated iron species present, eg goethite. Several
characteristics of the feed material have been identified
as having a significant influence on the formation of such
bonds that affect the quality and processing performance
of the green and fired briquettes. These characteristics
are the moisture level of the feed material and its flow
characteristics, the chemical composition of the ore, its size distribution and petrological characteristics and
porosity.

Preferably the feed materials are of the widest

size distribution possible in order to achieve a high
packing density and increased bonding of the ore
particles. As noted above, the bonding mechanism of green
briquettes is believed to be through a combination of
bonds arising from the mechanical interlocking of

particles, van der Waal's forces, and hydrogen bonding in
the cases of raw material types GC and G. Although a
broad size distribution increases the packing density and
improves the strength of the green briquette, it is
possible to briquette closely sized iron ores.
The top size of the particles is determined by
the crushing process but is preferably less than 2.5 mm in
order to produce briquettes of acceptable fired properties

following the induration process. Generally, ore types HC
and HG can be briquetted with coarser top j sizes due to the
lower heat requirements of these raw materials to attain
acceptable fired strength. The top size of the raw
material can be reduced through either crushing or
screening processes. The bottom size of the particles has
no absolute limit, but it is not necessary or desirable,
to grind the ore into very fine particles (as required for
pelletising) as this is an additional economic burden
rendered unnecessary by the present invention. Preferably
less than 10% of the particles pass a 45 µm sieve.

Advantageously the pocket dimensions of the
briquetting apparatus should be selected on the basis of
the maximum particle size to be briquetted, as well as for
adequate induration performance, to ensure that
satisfactory briquetting can be achieved. Typically the
maximum particle size to achieve satisfactory briquetting
is 25-30% of the minimum pocket dimension. If the maximum

particle size exceeds this specification it may be
necessary to select a larger pocket size.
It is desirable to control feed moisture in order
to optimise green briquette quality and product yield.
Moisture addition should not exceed the level at which
liquid bridging becomes a significant form of inter-
particle bonding. This results in both decreased green
strength and adversely affects thermal stability.
Insufficient moisture can lead to overpressurisation in
the briquette pressing step and adversely affect green
briquette quality and yield.
Depending on the feed characteristics of the ore
to be processed, a moisture content of between 2 and 12 wt
% for the feed material is used to optimise green
briquette quality and product yield. Dense hematite
concentrates (HC) have low optimum briquetting moistures.

generally in the range of 2-5 wt %. These concentrates
are often made up of closely sized particles with a smooth
surface texture that generates low strength briquettes
because of decreased interlocking of particles. More
porous goethite-containing ores with up to 50% goethite
(GC) briquette well in the range of 4-8 wt % moisture and
more porous predominantly goethite ores (G) briquette well
in the range of 6-12 wt% moisture. Such ores have a rough
surface texture and shape enhancing their briquetting
characteristics.
Conventional briquetting apparatus may be used in
the method of the invention. In essence, such apparatus
includes two adjacent rolls with pockets which come
together at a nip zone in order to compress the feed
material into adjacent, aligned pockets to produce
briquettes. In the case of the present invention, the
rolls are preferably horizontally aligned to achieve the
required throughput for economic feasibility.
Although briquetting can be carried out over a
wide range of roll pressures depending on the application,
briquetting of iron ores is preferably conducted at roll
pressing forces of 10-140 kN/cm and more preferably at the

low end of this range, typically from 10-60 kN/cm. Such
low pressure operation for iron ore briquetting is
significant and makes it possible to achieve high
production rates by the use of wide rolls on the
briquetting machine up to 1.6m in length.

Preferably the roll pressure is carefully
controlled within the low pressure range in order to
optimise the briquetting operation. If the roll pressure
is too low, the rolls are forced apart producing a thick
web and distorted briquettes impairing the product yield
and the quality of the briquette, particularly after
induration. If the roll pressure exceeds the optimum.

poor closure of the briquettes occurs because of the

"clamshell" effect on release of the briquettes from the

pocket. The clamshell effect is more pronounced for small
roll diameters and excess roll pressures, which also cause
pocket binding/jamming. Although the density and crush
strength of the green briquettes will be increased, the
impact resistance of the fired briquettes will be severely
impaired.
Preferably the moisture level is selected to
influence the flow characteristics of the material through
the feed system, and moisture levels of 2-12 wt % for the
feed material are generally suitable. If the moisture
level is too high for the feed system, the feed pressure
is adversely affected resulting in a decreased yield and
some impairment of briquette quality, characterised by a
lower green strength. It the feed material is too low in
moisture for the feed system the resultant feed pressure
will cause clamshelling which may result in decreased

yields, increased wear rates of the roll pockets, and

inferior fired properties.

The briquetting apparatus may be operated with a
pre-compactor feed system or with a gravity feed system.
The latter system is advantageous where high tonnages are
to be briquetted, as in the iron ore industry.
With regard to briquetting presses, a roll
diameter is selected in order to ensure that briquette

quality is obtained at an economic production rate. Large
diameter rolls increase production rates, however they
also increase the area of the nip zone. Careful control
of the nip zone facilitates formation of quality green
briquettes and avoids formation of briquettes with an
excessively thick web. Alterations in roll diameter may
also alter the optimum moisture level for feed material
where increased roll diameters represent increases in feed

moisture. Roll diameters typically vary from 250 mm - 1200
mm. In order to maximise production, preferably the rolls
are operated at the fastest speed possible whilst
maintaining briquette quality. However, a very low roll
speed may be used if productivity is of a secondary
concern.
I ■ .
Typically, roll speeds in the range of 1 rpm to
20 rpm are employed. It is desirable in order to maintain
quality, particularly at high roll speeds, that the feed
material be presented to the rolls at a rate that matches
the briquette production rate and with a nip zone area
that produces the forces required to form quality
briquettes.
Any suitable roll width may be selected provided
that it is within the pressure capabilities of the
briquetting machine. As briquetting of iron ores is a low
pressure operation, wide rolls are preferred, increasing
the capacity of the machine. The rolls are preferably
horizontally aligned to allow for use with a gravity feed
system. The flow characteristics of iron ores, whether
HC, GC (including H6 and 6H), or G, are suitable for
gravity feeding at the moisture ranges specified above for
each classification.
The pocket shape should not generally be of a
sharp angular nature, but be more smooth and rounded to
improve handling characteristics. By way of example, a
length/width and width/depth ratio of approximately 0.65
is suitable. Pocket shapes also have specific release
angles, 110-120° that combat the tendency for sticking in
the pockets.
The pocket size can be optimised according to the
requirements for the induration process and the raw
material top size and the iron making blast furnace.

Typically the briquettes have a volume of between 2 and 30
cc. Preferably the volume is 10 cc or less. More
preferably the volume is 8.5 cc or less. More preferably
the volume is less than 6.5 cc.
A staggered pocket configuration is preferred as
this makes the optimum use of the available space on the
face of the rolls, and hence maximises throughput.
Preferably the induration method and conditions
are selected having regard to the complex relationship
between raw material characteristics and tie influence of
the briquette dimensions.
Consideration of the relationship between
briquette volume, shape and the petrological
characteristics of the raw material is required. The
chemical composition of the feed material will have a
significant influence on the properties of the fired
briquette. Apart from moisture, the feed material
includes the iron ore made up of iron oxide and gangue
minerals, with the required flux added to give the
required basicity level in the fired briquette. Test
results have shown that the flux should preferably be
finely sized, typically >95% passing 250 µm, in order to
achieve the required properties in the fired briquette.
While not wishing to be bound by theory, it is

believed that the bonding mechanism for fired briquettes
involves diffusion bonding and re-crystallisation of the
iron oxide particles as well as slag bonding at higher
flux levels. Therefore, flux level and faring temperature
and, to a certain extent, firing time have a strong
influence on briquette properties. Elevated basicity
levels may improve reduced strengths as well as indurated
strengths as higher flux levels encourage the formation of
bonding phases which resist demormation under reducing

conditions.
Induration may be carried out using a straight
grate, grate-kiln or a continuous kiln type process.
It has been found that green briquettes produced
under an optimised firing profile are thermally very
stable compared to pellets prepared from the same
material. The feed ore for pelletising must be ground to
a fine size, typically up to 60% passing 45 µm, and the
pellets dried slowly at low temperatures, typically to avoid spalling. In contrast, as indicated above, the
feed ore for the present invention that can be indurated

successfully can be much coarser, with top sizes
preferably up to 2.5 mm, and hence does not need grinding
to the same extent as is required to produce pellets.
This characteristic represents major capital cost
reductions for briquetting operations over traditional
pellet production plants.
An important characteristic of the briquette of
the present invention is the ability to withstand high
temperatures on heating at fast rates, such as heating to
a firing temperature within 30 minutes, more preferably
within 20 minutes. This is in direct contrast with
conventional understanding of how goethitic ores respond
in induration situations, where is has been shown that
they spall when heated too fast through the
dehydroxylation and free water removal zones.
As is indicated above, the thermal stability of
the briquettes of the present invention has been found to
be much greater than pellets and they may be heated at
much faster rates than pellets without spelling. This
allows a much shorter heating cycle. Consequently,
briquette productivity can be significantly higher than
for pellets using the same material. For instance,

briquette productivities potentially in the order of
30t/m2.day in a straight grate kiln can be achieved,
compared to pellet productivities of 16t/m2.day for H6 ores
in the same kiln.
It will be clearly understood that, although
prior art publications are referred to herein, this
reference does not constitute an admission that any of
these documents form part of the common general knowledge
in the art, in Australia or in any other Country.
Preferred embodiments of the present invention
will now be described, by way of example only with
reference to the accompanying drawings, in which:
FIG. 1 is a schematic illustration of suitable
apparatus with 250 mm diameter rolls and a precompacted
feed system for conducting the process of the present
invention;
FIG. 2 is a schematic illustration of suitable
apparatus with 450 mm diameter rolls and a gravity feed
system for conducting the process of the present
invention;
FIG. 3 is a schematic illustration of suitable
apparatus with 650 mm diameter rolls and a gravity feed
system for conducting the process of the present
invention;
FIG. 4 is a plot of yield of whole briquettes
versus feed moisture for HG material on 450 mm rolls with
6 cc almond forms and 4 cc elongate almond pockets;
FIG. 5 is a plot showing the effect of feed
moisture on green briquette strength for HG material on
450 mm rolls with varying pocket dimensions;

FIG. 6 is a plot showing the effect of feed
moisture on green briquette strength for ICG material using
650 mm rolls and 7.5 cc 'pillows';
FIG. 7 shows the effect of roll pressing force on
briquette properties; thickness, green strength and green
density on 450 mm rolls and 9 cc almond forms;
FIG. 8 is a plot showing the effects of roll
pressing on green strength for HG material using 650 mm
rolls and 7.5 cc 'pillows';
FIG. 9 is a plot showing the effect of roll
pressing force on green strength for GH material using 650
mm rolls and 7.5 cc ^pillows';
FIG. 10 shows the effect of roll speed on
briquette properties; thickness, green strength and green
density for a rolls pressure of 90kg/cm2 and a feed
moisture of 6 wt % using 450 mm rolls and 9 cc almond
forms;
FIG. 11 is the operating window for a briquetting
machine with a pre-compactor, 250 mm rolls, 4 cc almond
forms and HG material;
FIG. 12 shows temperature profiles for briquette
induration in a 500 mm deep bed;
FIG. 13 shows temperature profiles for briquette
induration that produced briquettes at high productivities
and a typical temperature profile for pellet induration
that produced pellets at a lower productivity;
FIG. 14 is a plot showing the effect of average
bed temperature on briquettes made with GH material using

650 mm rolls and 7.5 cc 'pillows' at the end of a grate
cycle in a batch grate kiln;
FIG. 15 is a plot showing the effect of average
bed temperature on briquettes made with GH material using
650 mm rolls and 7.5 cc 'pillows' at the end of a grate-
kiln firing cycle in a batch grate kiln;
FIG. 16 is a plot showing the effect of time at
firing temperature (1380°C) on briquettes made with GH
material using 650 mm rolls and 7.5 cc 'pillows' during a
test cycle in the batch grate kiln;
FIG. 17 is a plot showing the effect of time at
firing temperature (1380°C) on briquettes made with GH
material using 650 mm rolls and 7.5 cc 'pillows' during a
test cycle in the batch grate kiln;
FIG. 18 is a plot showing the effects of
residence time on 7.5 cc GH briquettes in the kiln during
a test cycle in the kiln only.
FIG. 19 is a plot showing the effect of bed
height and grate firing profile on briquettes made with GH
material using 650 mm rolls and 7.5 cc 'pillows' during a
test cycle in the batch grate kiln;
FIG. 20 is a plot showing the effect of bed
height and grate firing profile on briquettes made with GH
material using 650 mm rolls and 7.5 cc 'pillows' during a
test cycle in the batch grate kiln;
FIG. 21 shows the effect of basicity and firing
temperature on the fired crush strength of briquettes made
with HG material, 250 mm rolls and 4 cc almond forms;
FIG. 22 shows the effect of basicity on the

briquette reduced properties; swell, crush strength after
reduction (CSAR) and reducibility index of briquettes made
with HG material, 250 mm rolls and 4 cc almond form;
EXAMPLE 1
Briquetting was performed using three different
roll presses with varying roll diameter, width and feed
systems.
Initial testing was conducted using a Taiyo K-
102A. double roll press, which has a nominal, capacity of
300 kg/hr. This machine has 250 mm diameter rolls of 36
mm width and features a screw-type precompactor. A
schematic showing its main components can be seen in
•Figure 1.
The briquettes produced were pillow- shaped with
nominal dimensions of 13x19x28 mm and a volume of 4 cc.
There was a single row of 30 pockets around the
circumference of each roll.
Of the two rolls, one was fixed whilst the other
"floating roll" was held against the fixed roll by an oil
and gas filled ram. The oil in the ram was pressurised to
provide the desired load force between the rolls.
Briquetting was also performed using a Romarek
BH400 double roll press, with a roll diameter of 450 mm
and a roll width of 75 mm. Feed material was gravity fed
into the nip zone from a feed hopper located above the
rolls. A schematic of its main components can be seen in
Figure 2.
Briquettes of varying dimensions were produced
with the following details:

(1) Nominally 17.5x28x34.3 mm with a volume of
8.9 cc. There was a double row of 48 pockets arranged in
staggered alignment around the circumference of each row
(9 cc Almond forms).
(2) Nominally 14.5x22.1x33.9 mm with a volume

of 6.3 cc. There was a double row of 60 pockets arranged
in a staggered alignment around the circumference of each
roll(6 cc Almond forms).
(3) Nominally 15.2x21.7x22.9 mm with a volume
of 3.9 cc. There was a triple row of 58 pockets arranged
in a staggered alignment around the circumference of each
row (4 cc spherical).
(4) Nominally 11.2x17.3x32.1 mm with a volume

of 3.9 cc. There was a double row of 72 pockets arranged
in a symmetrical alignment around the circumference of
each roll (4 cc elongate).
Of the two rolls, one was fixed whilst the other
"floating roll0 was held against the fixed roll by an oil
and gas filled ram. The oil in the ram was pressurised to
provide the desired specific pressing force between the
rolls.
Briquetting was also conducted using a Koppern
52/6.5 double roll press with a diameter of 650 mm and a
roll width of 130 mm. Feed material was gravity fed into
a nip zone from a hopper located above. Nip zone area was

controlled through use of a 'nip zone adjuster'. A

schematic of its main components can be seen in Figure 3.
The briquettes produced were 'pillow' shaped with
nominal dimensions of 30x24x16 mm and forms a volume of
7.5 cc. There were four rows of 77 pockets arranged
symmetrically across the face of the roll.

Of the two rolls, one was fixed Whilst the other
"floating roll" was held against the fixed roll by an oil
and gas filled ram. The oil in the ram was pressurised to
provide the desired specific pressing force between the
rolls.
EXAMPLE 2
The effect of feed moisture content was
investigated.
Figure 4 illustrates that feed moisture had a
significant effect on the yield of 6 cc and 4cc briquettes
produced by the briquetting press with 450 mm rolls as
described in Example 1. The feed material was gravity fed
to the rolls while the rolls operated at a fixed roll

speed of 20 rpm and a roll pressure of 90kg/cm2.
Feed moisture control is also important as
variation in moisture content affects green properties

such as green strength, abrasion resistance and shatter
strengths. This is illustrated in Figures 5 and 6.
Figure 5 shows the relationship between feed
moisture level and strength for briquettes made with HG
using the 450 mm rolls, a gravity feed system, and a
variety of pocket sizes.
Figure 6 shows the same relationship for
briquettes made with the 650 mm rolls and 7.5 cc pockets
for HG material.
Green strength tended to increase to a maximum
for the optimum moisture content of approximately 6%. At
moisture levels exceeding 7.5% the green strength was
unacceptably low.

Feed moisture had less of an influence on shatter
strength and the green abrasion resistance of the
briquettes.
EXAMPLE 3
As is indicated above, although briguetting
operations can be carried out over a wide range of rolls
pressures, it is preferred that briguetting be carried out
at low pressures. Such low pressure operation for iron
ore briguetting is significant and opens up the
possibility of achieving high production rates with wide
rolls on a briguetting machines.
However, as is indicated above, roll pressure
should be carefully controlled within this low pressure
range if the briguetting operation is to be optimised. If
roll pressure is too low and nip zone area is not
carefully controlled, the rolls are forced apart producing
a thick web and distorted briquettes impairing the product
yield and the quality of the briquette, particularly after
induration. If roll pressure exceeds the optimum, poor
closure of the briquettes occurs because of the
"clamshell" effect on release of the briquette from the
pocket. Although the density and crush strength of the
green briquette will be increased, the impact resistance
of the fired briguette will be severely impaired.
Figure 7 shows the effect of roll pressure on
briguette thickness and quality (measured in terms of
crush strength) for raw material H6 produced in a gravity
fed machine with 450mm diameter rolls with nominal 9 cc
pockets. The figure shows that acceptable green strength
was obtained at roll pressures as low as 60 kg/cm2.
Figures 8 and 9 show the effect of pressing force

and resultant green strength that was obtained using the
650 mm diameter rolls. The work was carried out on HG and
6H raw material types and illustrates a similar
relationship between roll pressure and green strength as
with the 450 mm work. Specifically, the figures show that
acceptable green strengths were obtained at pressing
forces of 20 kN/cm.
Pressing force was also found to exert a
significant influence on the shatter strength and the
green abrasion resistance of the briquettes, with both
variables increasing in response to increased roll
pressure.
EXAMPLE 4
Roll speed was also investigated.
Roll speed, measured in rpm, was found to exert
an influence on the amount of pressure applied to feed
materials.
Increased roll speeds result in shorter residence
time in the nip zone of the rolls and hence lower pressure

is exerted for a longer period of time. Roll pressure can
be used primarily to control the amount of pressure
exerted on feed material and roll speed can be altered to
maximise the production rate. However, it is important to
consider the effects of roll speed on briquette thickness
and green strength when optimising the green briquetting
operation.
The effect of roll speed on briquette thickness
and quality (measured in terms of crush strength) for raw
material HQ is shown in Figure 10 for a gravity fed
machine with 450 mm diameter rolls.

The Figure shows that thickness and green
strength decreased as roll speed increased.
EXAMPLE 5
The process variables of the briquetting machine
as described in Example 1, ie, roll speed, precompactor
speed and roll pressure, and the briquette density were
used to determine an operating window for this particular
system of briquetting.
The diagram shown in Figure 11 is an example of
an operating window for briquetting with 250 mm rolls to
form nominally 4 cc briquettes out of HG material on the
Taiyo press.
To simplify the curves, roll pressure was fixed
at 150 kg/cm2 and precompactor speed was fixed at 20 rpm.
A series of curves are shown for feed moisture from 4 wt %
to 12 wt %. Each represents conditions that resulted in
the formation of whole briquettes.
To the right of the curves there is a region of
low feed pressure where pockets are not filled or the
briquettes are weak and split readily. To the left of the
curves there is a region where the pressure on the feed is

too high. Briquettes shear and pocket blockage occurred.
Across the strength range, below 6 kgf, the briquettes
were too weak to withstand pocket release and either
remain in the pockets or split on release, Above 30 kgf,
further compaction could not be achieved. The briquettes
were thick and began to 'clam shell'. The strength range
of 6 to 30 kgf defined the outer limits within which whole
briquettes could be formed with the sample material and
the Taiyo briquetting machine.
To determine the operating window certain product

and quality parameters including yield, density, crush
strength and drop/shatter strength need to be considered.
Once these properties are taken into consideration, a
smaller region can be defined which is the operating
region of the briquetting process.
In Figure 11, this region occurs at rolls speeds
between 5 and 9 rpm and green strengths between 6 kgf and
18 kgf.
EXAMPLE 6
Green briquettes produced under optimised
conditions were found to be thermally very stable compared
to pellets formed from the same material. This is shown
in Figures 12 and 13.
Figure 12 shows the temperature profiles for the
inlet and outlet gas and three positions within the bed of

briquettes during laboratory-scale induration trials
simulating a straight grate process.
The bed temperatures were measured by

thermocouples placed at 100, 250 and 500 mm from the top
of the bed.
The briquettes were found to be be thermally

stable when heated at fast rates shown in the figures.
The excellent drying performance allowed the inlet gas
temperature to be raised from ambient to 1340°C in ten
ninutes without spalling the briquettes.
Figure 13 shows the temperature profiles for
ariquette induration that produced nominal 4 cc briquettes
of HG ore at productives of 32 t/m2. d and 25 t/xn2 .d. The
figure also shows, by way of comparison, a typical
induration temperature profile for pellets. The pellet

profile was an optimised profile so that pellet spalling
was minimised and fired properties were maximised. The
pellet profile produced pellets with a productivity of
16t/m2.d, which is considerably lower than the
productivities of the briquettes. The briquettes and the
pellets were made from the same ore type.
The high productivities for the briquettes was
due to the thermal stability of the green briquettes which
enabled the briquettes to be heated at fast rates.
The thermal stability of the briquettes was found
to be not exclusive to one induration method and to one
ore type.
EXAMPLE 7
A pilot scale grate-kiln system was used to
determine the properties of briquettes as they exited a
grate prior to entry to a kiln.
The equipment consisted of a pot grate and a
batch kiln. To simulate the travelling grate a LGP gas
burner was used to generate the flame temperature. The pot
grate was capable of up and down draught gas flow. The
temperature of the material was measured throughout the
bed using thermocouples set into and through the wall of
the pot. These measurements were assumed to be the
briquette temperature during the firing cycle. Due to the
size of the briquettes tested, it may be that the
temperature measurement shows the external briquette
temperatures and not the internal temperatures. The
temperature measured is most likely a mixture of briquette
outside temperature and gas temperature at that location
in the bed.
Figure 14 shows how the temperature of the

briquettes made from GH material (d95 = 1mm) with a green
nominal size of 7.5cc initially increased to a maximum at
approximately 300-400°C average bed temperature, and then
fell to a minimum temperature at -700°C. At higher
temperatures the strength then increased again. The
strength fell to a minimum value at -700°C, which is lower
than the green strength. This is a critical factor for
transport of the material from the grate-to the kiln. As
the strength was lowest at this temperature range, the
maximum amount of degradation could be expected if the
firing profile included transfer from the grate to the
kiln at this temperature.
For a straight grate process, the bed height
selected for the induration process was found to be not
critical and not inhibited by gas permeability generally
selected to avoid deformation of the briquettes at the
lower parts of the bed while achieving a reasonable
productivity. In addition, at briquette volumes exceeding
6 cc, permeability of the bed was not greatly compromised
by bed height. Consequently, the induration process is not
restricted by this variable as is the case with
pelletising operations. Green briquette bed depth can be
selected to optimise productivity without compromising
quality.
A grate-kiln process may offer certain advantages
in terms of producing a better fired product compared to
products obtained from other induration processes. It
also heats the briquettes more uniformly through high
temperature ranges in a way that reduces temperature
gradients within the briquette and avoids differential
shrinkage of the briquette that may lead to cracking.
Also, as all the briquettes are subject to similar firing
temperatures and time in the rotating kiln, briquette
quality is more uniform compared to the straight grate
process.

Possibilities also exist for the production of
briquettes suitable for direct reduction processes,
providing a raw material of a suitable grade is used.
EXAMPLE 8
Firing temperature was investigated.
Briquettes of GH material (d95 = 1mm) 7.5cc were
fired in the grate-kiln pilot rig, all using the same
firing profiles for the grate section. After transfer to
the kiln, the same profile was applied for firing, except
that the firing temperature reached was altered as shown.
The results are shown in Figure 15.
There is a clear indication in Figure 15 that to

achieve suitable fired strength in briquettes of this size
the firing temperature in the kiln should be at least
1380°C.
Figure 15 also shows that tumble strength (Tumble
Index - TI) and abrasion resistance (Abrasion Index - AI),
improved with firing temperature.
EXAMPLE 9

Firing temperature and time at temperature were
investigated.
Briquettes made from 6H material (d95 = 1mm) with
a nominal size of 7.5cc were fired in a series of grate-
kiln tests. The grate firing profile was the same, with
only the firing time in the kiln at the firing temperature
being changed from 6 to 9 minutes. The total firing time
in the kiln remained the same, the extra time for the
firing was taken from the rate of heating in the kiln, so

that the 9 minutes firing time had a quicker heating rate
to 1380° compared to the 6 minutes firing time.
Tests were also conducted with 6.3cc 6H
briquettes using the same firing profile as that used for
the 7.5cc case.
For the nominally 7.5cc size GH briquettes, the
fired strength increased significantly from the longer
firing time in the kiln. This was due to greater heat
penetration of the briquettes during the firing cycle.
The fired properties for the 6.3 cc GH briquettes
were superior to those produced for the 7.5cc case,
inferring that the issue of heat penetration is a
significant issue for fired property generation of the
briquettes. This result also suggests that when heat
penetration in the briquettes is insufficient adequate
strength will not be generated in the fired product.
EXAMPLE 10
The effect of residence time in a grate kiln was
investigated.
Briquettes made from GH material (d95 = 1mm) and
nominally 7.5cc were fired in a pilot scale batch grate
kiln. They were charged green into a kiln that had been
preheated to either 500 or 1000°C. Firing profiles were
imposed on the briquettes and the total residence time
reported. The results are shown in Figure 18.
Figure 18 shows that the fired properties
improved with increasing residence time, suggesting the
importance of heating the product thoroughly to achieve

the final properties required.
The effect of rapid heating was not reduced by a
larger bed depth of the grate. This is shown in Figures

19 and 20. The green briquette bed was highly permeable
and did not restrict airflow, as often occurs with
pellets. The maximum bed depth useable has not been
defined, but is likely to be greater than 300mm. This far
exceeded that possible for even the best pellet beds in a
grate-kiln system.
EXAMPLE 11
The effect of the chemistry of briquettes was
investigated.
The effect of basicity and temperature on the
fired briquette properties made from HG material was
determined by firing the briquettes in the muffle furnace
at specific temperatures and times. The results are shown
in Figure 21.
Results for the chemical analyses of the fired
briquettes made at varying basicities produced fired
briquettes which varied in grade from 63.81% Fe at a
basicity of 1.2 up to 65.93% Fe for a basicity of 0.2,
reflecting the level of flux addition.
As can be seen in Figure 21, crush strength
increased with both temperature and as basicity increased
from 0.2 to 0.8. This effect becomes more significant as
the temperature increased across the range studied and it
was possible to achieve 300 kgf at 1295°C for 0.6 basicity
and at 1280°C for 0.8 basicity.
The explanation for increased basicity levels
resulting in increased strengths is related to changes in

the bonding mechanism. At low basicity levels, bonding of
the particles occurs as a result of recrystallisation of
iron oxide and the formation of iron oxide-iron oxide

bonds. At increased basicity levels, melt formation

occurs at lover temperatures enhancing melting of iron
oxide crystals, and slag bonding becomes more significant
giving higher strengths for the same temperature.
EXAMPLE 12
Reduction testing, using whole briquettes and
standard reduction test methods JIS 8713/IS07215 was
carried out on HG briquettes that were fired at 1300°C for
10 min. The results of reducibility, swell and crush
strength after reduction (CSAR) are shown in Figure 22.
The reducibility index (RI) remained relatively
stable across the range of basicity levels. The RI varied
from 53.8% at a basicity of 0.20 to just over 62.2% at a
basicity of 1.00.

The swell index showed some response and varied
from 11% at the lowest basicity to 14.8% in the mid-
ranges, decreasing to zero at a basicity of 1.20.
The crush strength after reduction (CSAR) showed a large
response to changes in the basicity level, ranging from 22
kgf at 0.20 basicity to 121 kgf at 1.20 basicity. This
change in reduced strength reflects the fired crush
strength results and is again related to variation in the
bonding phases of the fired briquettes. The low basicity
briquettes were predominantly bonded by iron oxide-iron
oxide bonds, which degrade during reduction. At increased
basicity levels, slag bonding becomes more significant.
These bonds are more stable during reduction, accounting
for the higher reduced strengths and little or no swell at
a basicity of 1.20. Slag bonding also becomes a more
important form of bonding in briquettes made from GH and G

where higher Si02 and Al2O3 levels result in increased flux
additions. Such briquettes generally prove stronger after
reduction as the reduction process does not result in the
breakdown of non-ferrous bonding phases. High grade ores,
such as HC, which require low flux addition rely almost
solely on oxide-oxide bonding and hence have lower
strength after reduction values.
Many modifications may be made to the embodiments
of the present invention described above without departing

from the spirit and scope of the invention.

WE CLAIM:
1. A method of producing an iron ore briquette that
is suitable for use as a blast furnace or other direct
reduction furnace feedstock which involves the steps of:
(a) mixing: (i) ore having a predetermined particle
size distribution with a top size of 4.0 mm or
less; and (ii) a flux; to form an ore/flux
mixture and wherein there is no binder in the
ore/flux mixture;
(b) adjusting the water content of the ore prior to
or during mixing step (a) so that the moisture
content of the ore/flux mixture is 2-12% by
weight of the total weight of the ore flux
mixture;
(c) pressing the ore/flux mixture into a green
briquette; and
(d) indurating the green briquette to form a fired
2. The method as claimed in claim 1 involving
crushing and screening ore to form the predetermined
particle size distribution that is mixed with flux in step
(a).
3. The method as claimed in claim 1 or claim 2
wherein the top size of the predetermined particle size
distribution of ore that is mixed with flux in step (a) is
3.5 mm.
4. The method as claimed in claim 3 wherein the top
size is 3/0 mm.

5. The method as claimed in claim 3 wherein the top
size is 2.5 mm.
6. The method as claimed in claim 3 wherein the top
size is 1.5 mm.
7. The method as claimed in claim 3 wherein the top
size is- 1.0 mm.
8. The method as claimed in any one of the preceding
claims wherein the predetermined particle size
distribution of ore that is mixed with flux in step (a)

includes less than 50% passing a 45µm screen.
9. The method as claimed in claim 8 wherein the
predetermined ore particle size is less than 30% passing
the 45pm screen.
10. The method as claimed in claim 8 wherein the
predetermined ore particle size is less than 10% passing
the 45pm screen.
claims wherein the ore is a hydrated iron pre.
12. The method as claimed in claim 11 wherein the
hydrated ore is a goethite-containing ore.
13. The method as claimed in any one of the preceding
claims wherein the flux has a particle size distribution
that is predominantly less than 100 µm.
14. The method as claimed in any one of the preceding
claims wherein the particle size distribution of the flux
is more than 95% passing a 250 µm screen.
15. The method as claimed in any one of the preceding

claims wherein the ore/flux mixture produced in step (a)

is selected so that the basicity of the fired briquette
produced in step (d) is greater than 0.2.
16. The method as claimed in claim 15 wherein the

basicity is greater than 0.6.
17. The method as claimed in claim 1 wherein step (b)
involves adjusting the water content of the ore so that
the moisture content of the ore/flux-mixture is 2-5% by
weight of the total weight of the ore/flux mixture for
ores that are dense hematite ores.
18. The method as claimed in claim 1 wherein step (b)
involves adjusting the water content of the ore so that
the moisture content of the ore/flux mixture is 4-8% by
weight of the total weight of the ore/flux mixture for
ores containing up to 50% goethite.
19. The method as claimed in claim 1 wherein step (b)
involves adjusting the water content of the ore so that

the moisture content of the ore/flux mixture is 6-10% by
weight of the total weight of the ore/flux mixture for

ores that are predominantly, ie contains more than50%,
goethite.
20. The method as claimed in any one of the preceding
claims wherein pressing step (c) produces briquettes that
are 6 cc or less in volume.
21. The method as claimed in claim 1 wherein the
briquettes are 8.5 cc or les in volume.
22. The method as claimed in claim 1 wherein the
briquettes are 6.5 cc or less in volume.
23. The method as claimed in any one of the preceding
claims wherein pressing step (c) involves pressing the

ore/flux mixture using a low roll pressure.
24. The method as claimed in claim 23 wherein the low
roll pressure is sufficient to produce briquettes having a
green compressive strength of at least 2kgf.
25. The method as claimed in claim 23 wherein the low

roll pressure is generated by a roll pressing force of 10-
140 kN/cm on the mixture of ore/flux.
26. The method as claimed in claim 23 wherein the
roll pressing force is 10-40kN/cm.
27. The method as claimed in any one of the preceding
claims wherein indurating step (d) involves heating the
briquette to a firing temperature within 40 minutes.
28. The method as claimed in claim 27 wherein step
(d) involves heating the briquette to the firing
temperature within 35 minutes.
29. The method as claimed in claim 27 wherein step
(b) involves heatinc? the briquetts to the firing
temperature within 30 minutes.
30. The method as claimed in claim 27 wherein step
(d) involves heating the briquette to the firing
temperature within 20 minutes.
31. The method as claimed in claim 27 wherein step
(d) including heating the briquette to the firing
temperature within 15 minutes.
32. The method as claimed in any one of claims 27 to
31 wherein the firing temperature is at least 1200°C.
33. The method as claimed in claim 32 wherein the

firing temperature is at least 1260 C.

34. The method as claimed in claim 32 wherein the
firing temperature is at least 1320oC.
35. The method as claimed in claim 32 wherein the
firing temperature is at least 1350 C.
36. The method as claimed in claim 32 wherein the
- firing temperature is at least 1380oC.
37. The method as claimed in any one of the preceding
claims wherein the fired briquette has a crush strength of
at least 200 kgf.
38. A fired briquette produced by the method

according to any one of the preceding claims which has a
crush strength of at least 200 kgf.

ABSTRACT

A METHOD OF PRODUCING AN IRON ORE BRIQUETTE
A method of producing an iron ore briquette is
disclosed.The method is suitable for use is a blast
furnace or other direct reduction furnace feedstock which
involves the steps of: (a)mixing: (i) ore having a
predetermined particle size distribution with a top size of
4.0 mm or less; and (ii) a flux; to form an ore/flux
mixture and wherein there is no binder in the ore/flux
mixture; (b)adjusting the water content of the ore prior to
or during mixing step (a) so that the moisture content of

the ore/flux mixture is 2-12% by weight of the total weight
of the ore flux mixture; (c) pressing the ore flux mixture

into a green briquette; and (d) indurating the green
briquette to form a fired briquette.

Documents:

168-KOLNP-2004-ABSTRACT-1.1.pdf

168-kolnp-2004-abstract.pdf

168-KOLNP-2004-AMANDED CLAIMS.pdf

168-KOLNP-2004-ASSIGNMENT.pdf

168-KOLNP-2004-CANCELLED PAGES 1.1.pdf

168-KOLNP-2004-CANCELLED PAGES.pdf

168-kolnp-2004-claims.pdf

168-KOLNP-2004-CORRESPONDENCE-1.1.pdf

168-kolnp-2004-correspondence.pdf

168-KOLNP-2004-DESCRIPTION (COMPLETE)-1.1.pdf

168-kolnp-2004-description (complete).pdf

168-KOLNP-2004-DRAWINGS-1.1.pdf

168-kolnp-2004-drawings.pdf

168-KOLNP-2004-EXAMINATION REPORT.pdf

168-KOLNP-2004-FORM 1-1.1.pdf

168-kolnp-2004-form 1.pdf

168-KOLNP-2004-FORM 18 1.1.pdf

168-kolnp-2004-form 18.pdf

168-KOLNP-2004-FORM 2-1.1.pdf

168-kolnp-2004-form 2.pdf

168-KOLNP-2004-FORM 3-1.1.pdf

168-KOLNP-2004-FORM 3-1.2.pdf

168-kolnp-2004-form 3.pdf

168-kolnp-2004-form 5.pdf

168-KOLNP-2004-GPA 1.1.pdf

168-kolnp-2004-gpa.pdf

168-KOLNP-2004-GRANTED-ABSTRACT.pdf

168-KOLNP-2004-GRANTED-CLAIMS.pdf

168-KOLNP-2004-GRANTED-DESCRIPTION (COMPLETE).pdf

168-KOLNP-2004-GRANTED-DRAWINGS.pdf

168-KOLNP-2004-GRANTED-FORM 1.pdf

168-KOLNP-2004-GRANTED-FORM 2.pdf

168-KOLNP-2004-GRANTED-FORM 3.pdf

168-KOLNP-2004-GRANTED-FORM 5.pdf

168-KOLNP-2004-GRANTED-SPECIFICATION-COMPLETE.pdf

168-KOLNP-2004-INTERNATIONAL PUBLICATION.pdf

168-KOLNP-2004-OTHERS-1.1.pdf

168-KOLNP-2004-PA 1.1.pdf

168-KOLNP-2004-PA.pdf

168-KOLNP-2004-PETITION UNDER RULE 137 1.1.pdf

168-KOLNP-2004-PETITION UNDER RULE 137.pdf

168-KOLNP-2004-REPLY TO EXAMINATION REPOR 1.2T.pdf

168-KOLNP-2004-REPLY TO EXAMINATION REPORT-1.1.pdf

168-KOLNP-2004-REPLY TO EXAMINATION REPORT.pdf

168-kolnp-2004-specification.pdf

« Previous Patent

Next Patent »

Patent Number

256482

Indian Patent Application Number

168/KOLNP/2004

PG Journal Number

26/2013

Publication Date

28-Jun-2013

Grant Date

24-Jun-2013

Date of Filing

09-Feb-2004

Name of Patentee

COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION

Applicant Address

LIMESTONE AVENUE, CAMPBELL, AUSTRALIAN CAPITAL TERRITORY

Inventors:

#	Inventor's Name	Inventor's Address
1	BEROS GEOFFREY STUART	13 ALBATROSS COURT, YANGEBUP, WESTERN AUSTRALIA 6164
2	GANNON JOHN FRANCIS	1 SKENES AVENUE, EASTWOOD, NEW SOUTH WALES 2122

PCT International Classification Number

C22B 001/14

PCT International Application Number

PCT/AU2002/01033

PCT International Filing date

2002-08-02

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	PR 6783	2001-08-02	Australia