Title of Invention

AN IMPROVED METHOD FOR PROCESSING IRON ORE WITH HIGH ZINC CONTENT FOR PRODUCTION OF IRON AND STEEL

Abstract This invention relates to an improved method for processing high zinc iron ores for production of iron and steel comprising the steps of; producing agglomerate comprising a mixture of iron oxides, carbonaceous materials, and fluxes with mean-particle size respectively of 35 to 70, 25 to 60, and 45-85 microns, to form agglomerates of 8 to 15 mm size using combination of organic and inorganic binders and moisture to achieve the desired properties of the agglomerates; dezincificating and metallising the agglomerates in a furnace; smelting the reduced agglomerates, in hot / cold charging condition, to form hot metal (iron) in a furnace leading to production of crude steel; recovering zinc values from waste gas stream of the furnaces by carrying - out conventional zinc extraction process.
Full Text

FIELD OF INVENTION
This invention relates to a two stage method for removal of zinc, reduction of
iron ores and production of liquid metal using iron ores and process dust
containing high zinc. The invention further relates to a selection of binders in
agglomeration and thermal profile of the furnace through sequencial adjustment
of porosity which accelerates the removal of zinc vapors at high temperatures
during reduction reaction. In first stage, non-shaft furnaces are used for zinc
removal and direct reduction of iron ores and dust. In second stage, electric
furnace is used to produce liquid metal and remove the remaining zinc from
reduced metal by using innovative the slag chemistry.
BACKGROUND OF INVENTION
Blast Furnace process is used worldwide for production of hot iron metal using
variety of iron ores. The volatile impurities such as alkalis, zinc, lead, etc. creates
various operational problems in Blast furnace process. Therefore blast furnace
process is not convenient route for processing iron ores with high zinc content.
Alternative processes developed for iron and steel making, where shaft furnaces
are used, are also not suitable for treatment of these high zinc ores. The boiling
point of zinc metal is -910C and in oxidizing conditions it forms stable zinc oxide
(solid phase). In furnaces where various temperature zones and oxidizing
conditions exist, zinc recycles / accumulates inside the furnace. For example, in
the shaft furnace zinc vapor coming from high temperature zone (bottom part)
are condensed on the charge or furnace wall in the low temperature zone (T 900 C) at the top, which results in recirculation of zinc within the system. The

zinc recirculation increases the coke rate and creates many operations
difficulties. Therefore, high zinc iron ores are rarely used in iron and steel
industry.
OBJECTS OF THE INVENTION
It is therefore the object of invention to propose an improved method for h
processing iron ore with high zinc content for production of iron and steel by :
dezincificating and metallizing the iron ore during solid state reduction in non i|
shaft furnaces.
Another object of the invention is to propose an improved method for
processing iron ore with high zinc content for production of iron and steel by
suitable agglomeration and by using combination of binders which accelerates
the removal of zinc vapors during reduction reaction.
A further object of the invention is to propose an improved method for
processing iron ore with high zinc content for production of iron and steel by
selecting a suitable combination of processes by using product of first stage i.e.
direct reduced iron.
A still further object of the invention is to propose an improved method for
processing iron ore with high zinc content for production of iron and steel for
recovery of Zn values from waste gas stream for extraction of Zn metal.

SUMMARY OF INVENTION
Accordingly, there is provided an improved method for processing high zinc iron
ores for production of iron and steel comprising the steps of; producing of
agglomerate comprising a mixture of iron oxides, carbonaceous materials, and
fluxes with mean-particle size respectively of 35 to 70, 25 to 60, and 45-85
microns, to form agglomerates of 8 to 15 mm size using combination of organic
and inorganic binders and moisture to achieve the desired properties of the
agglomerates; dezincificating and metallising of agglomerates in a furnace;
smelting the reduced agglomerates, in hot / cold charging condition, to form hot
metal (iron) in a furnace leading to producing steel; recovering zinc values from
waste gas stream of the furnace by carrying - out conventional zinc extraction
process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention is explained in greater details with the accompanying drawing:
Figure 1, shows the plot of free energy change Vs temperature for reduction
reactions of Zn & Fe oxides, which is used for development of the present
invention.

Figure 2, presents the ZnFe204 - O2 phase diagram used for controlling the
gaseous atmosphere inside various zones in Furnace and for separation of zinc
from waste gas strem.
DETAILED DESCRIPTION OF THE INVENTION
Common zinc mineral is sphalerite, ZnS. However, zinc also found in the form of
Franklinite [(Zn, Fe, Mn) [Fe, MnJAJ.a oxide mineral. In magnetite lattice Zn2+ can
replace Fe2+ cations forming stable (Fe304 - Z11F2O4) solid solution phase. The Zn2+
cation is smaller in size than Fe2+ so replacement of Fe2+ by Zn2+ reduces the lattice
dilation and strain energy. Therefore dissolution of ZnO in magnetite increases
thermodynamic and structural stability. Although, the crystal structure of
hematite (HCP) does not favors dissolution of ZnO, structure can accommodate
partial replacement of Fe3+ by Zn2+ cations by vacancy formation and.lattice
dilation. Therefore, high zinc concentration is detected in hematite minerals (as
in case of oxidized ores of Thach Khe, Vietnam). It is not possible to remove this
lattice zinc in iron ores by conventional beneficiation techniques such as
magnetic separation, gravity separation, etc. Therefore present invention
provides a method capable of removing zinc locked in the iron mineral lattice and
also produces reduced iron, which can be integrated with conventional iron &
steel making process.
Important reduction reactions of ZnO, Fe304 and ZnFe204 with solid carbon and CO
gas are listed below and a plot of free energy change Vs temperature for these
reduction reactions is presented in Figure 1.


It is observed from the Figure 1 that Zinc oxide reduces to zinc metal by solid
carbon (reaction Rl) above 900C temperature, whereas reduction of pure
magnetite by carbon (reaction R3) starts above 710°C temperature. Zinc ferrite
reduction to metallic zinc and iron (reaction R5) is possible (AG temperature by solid carbon, as thermodynamic activity of zinc oxide changes
significantly when it is present in the form of zinc ferrite. The Figure 1 also
confirms that gaseous reduction of ZnO or ZnFe204 by carbon monoxide requires
high temperatures i.e. above 1200°C. The phase diagram of ZnFe204 - O2
computed using FACT-Sage program is shown in Figure 2, which shows the
boundary lines for thermodynamic stability of various phase (solid, liquid and
gas) Zn - Fe - 0 compounds. Therefore solid state reduction above 750C
temperature and below 10-16 oxygen partial pressure, are the critical
thermodynamic conditions for removal of zinc from magnetite lattice.

In magnetite lattice, Zn2+ and Fe3+ cations have zero octahedral site preferential
energy therefore the site occupancy of cations is mainly decided on basis of
cationic radii and charge. As a result, smaller Zn2+ and Fe3+ cations occupy both
tetrahedral & octahedral sites, whereas large Fe2+ cations preferentially occupy
octahedral sites in magnetite lattice. In reducing atmosphere, the imposed
oxygen chemical potential promotes the diffusion of Fe and Zn cations through
oxygen anions on CCP lattice in the magnetite, toward the reaction interface on
the surface of the grain. The vacancies generated during this process diffuse
inward and promote the cation diffusion toward a reaction interface. Because Fe3+
and Zn2+ cations have zero OSPE, these cations jump from one octahedral site to
another via a vacant neighboring tetrahedral site. The charge and ion balanced
diffusion path is energetically more favorable to direct jump between two
octahedral sites, which are separated by anions. At high temperatures, zinc is
homogeneously distributed in lattice (T > immiscibility dome), the rate of zinc removal
depends on the diffusion of Zn through anion lattice. The detail studies of th2
reaction kinetics and reduction mechanism also revealed that the rate limiting
process is diffusion of cations through oxygen anion lattice. Therefore reaction
temperatures are higher than thermodynamic conditions for dezincifaction.
In this innovative method, iron ores with high Zn content are mixed with
carbonaceous materials, as a reductant and other fluxes. The mixture is then
agglomerated in the form of pellets or briquettes. Desired properties of the
agglomerates comprises wet-drop number, dry-drop number, green crushing
strength and dry-crushing strength which respectively ranges 6 to 8, 10 to 15,
v- ■■-... .. ... - ».
1.5 kg pellet, and 15kg /pellet. The green agglomerates are dried to remove the

moisture. A non shaft furnaces such as rotary hearth furnace is used for solid
state reduction and dezincification, However present invention does not exclude
operation in the other type of furnaces. In the rotary hearth furnace thj
agglomerated feed is charged continuously in layers to maintained appropriate
height of the burden on the hearth. The agglomerates are heated in different
zones of furnace. The heat required for endothermic reduction reactions is
supplied by the combustion products and radiation energy from the furnace
heaters / burners. The air : fuel ratio of the furnace burners is kept at
appropriate levels in different zones to maintain at desired reducing conditions in
various zones of furnace. The carbonaceous material in the agglomerate acts as
reductant and also maintain reducing atmosphere close to reaction interface. The
ratio of ore to carbonaceous materials is adjusted to provide to C required for
reduction and for maintaining reducing atmosphere at reaction interface.
Temperature profile of the furnace is maintained as desired to form a molten
slag at appropriate time and also allow coalesce of reduced metal. In cooling
zone, the reduced pellets are cooled to 800°C to 1000°C required for subsequent
processes. If required, the DRI are agglomerated by hot briquetting process. The
atmosphere of cooling zone and subsequent hot process is controlled to minimize
the reoxidation of newly formed metallic iron. In this innovative process, 70-95 %
degree of metallization with 80 - 95 % dezincification can be achieved in the
temperature range from 1100 to 1400 C and 10 - 60 minutes heating cycle. The
process also generates DRI with very low silicon (0.1 - 0.9%) and carbon (0.3 -
1.5%) content.

In the present invention, it is preferred to maintain furnace conditions in such a
way that the product gas flushes / carries the zinc vapors out of furnace as
shown in Figure 2. In the preferred case the gas flow follows the charge / heart
movement so that hot gas will not come in contact with low temperature charge,
on which Zn vapors can deposit and recirculate / accumulate inside the furnace.
Other option used in this innovative process is to collect the gas from high
temperature zone and cool to temperatures below 900C to separate the Zn
vapors and then recycle in the furnace to maintain the reducing atmosphere.
However, other applications of hot furnace gas (such as air and fuel preheating)
are not excluded in this invention.
According to a further advantageous embodiment of this invention, it is preferred
to adjust the porosity of dry carbon composite pellets to enhance the
vaporization of zinc near reaction interface and rapid transport of Zn vapor to
outlet gas stream. This is achieved by using combination of the hybrid binders
and moisture in the agglomeration. The inorganic binders doses ranges between
0.5 to 2%, and wherein the organic binders are used in the doses between 1 to
5%. The volume ratios of iron ore, coal, binder and moisture are adjusted in
innovative way to generate porosity within agglomerate as reduction and
dezincification reaction proceeds. The binder vaporization and coal utilization is
sequenced in such a way to compensate the shrinkage of the agglomerate
during reduction reaction and also to achieve the required strength in reduced
pellets. The composite pellets are dried in the temperature range from 110 to
300°C to remove the moisture and thereby generate the porosity (primary
pores). In this invention, the combination of organic and inorganic binders is

used so that the organic binder enhances the strength of dry pellets / briquettes
whereas inorganic binder provides strength at high temperature inside the
furnace during reduction reactions. The organic binder vaporizes in the early
stages of reduction reaction which increases 5 - 10 % porosity (secondary pores)
of the pellets / briquettes. These porous channels (primary and secondary pores)
generated at lower temperature enhance the rapid transport of Zn vapors
formed during solid state reduction of magnetite and zinc ferrite solid solution
phase above 800°C temperature. As the reduction reaction progresses, carbon /
reductant gets consumed which also maintains pore channels i.e. the high
porosity for rapid gas phase transport from reaction interface to furnace
atmosphere.
According to a further advantageous embodiment of this invention, particle size
and size distribution of feed (iron ore, reductant, flux and binders) used for
agglomeration process are adjusted to achieve the required green and dry pellet
strength, to generate the pore channels for rapid transport of gaseous products
and to enhance the rate of reduction reaction (topochemical). Iron oxides,
carbonaceous materials, and fluxes are prepared to achieve mean-particle size
respectively of 35 to 70, 25 to 60, and 45-85 microns, to form agglomerates of 8
to 15 mm size. As a result, high productivity (tones / hour / m2) is achieved in
this short time reduction process (heating and cooling cycle).
In present invention, a combination of fluxes is used to form slag with desired
liquidus. The rate of reduction reaction is also adjusted in innovative way to
produce desired amount of FeO oxide in the charge during reduction reaction

which forms molten slag. The fluxes used in the charge impart desired physico -
chemical properties in molten slag and also control loss of Fe in the slag phase.
The slag properties are adjusted to dissolve gangue phases and also maintain
desired viscosity so that molten slag will not block the pores and thereby hinder
the flow of Zn vapors and product gases. At high temperatures, when desired
level of dezincification is achieved the designed slag chemistry forms fluid slag
which accelerate coalesce of reduced metallic particles and better separation of
slag and metal. Thus in this invention, rapid dezincification and better slag-metal
separation is achieved by innovative flux chemistry and heating cycle / rate.
In present invention, the higher degree of metallization and dezincification was
also achieved by using appropriate grade of iron ore concentrate. The increase in
Fe content of iron ore enhances the degree of metallization and removal of
gangue components help to reduce the flux requirement. However, the higher %
metallization and lower slag content decrease the cold crushing strength of the
reduced pellets. Therefore heating cycle, porosity, feed size, and slag chemistry
are adjusted to achieve the desired properties of reduced pellets / briquettes.
The process described in this invention was used for processing Iron ore
containing ~ 0.07 % Zinc. The agglomerates were prepared using anthracite
coal, iron ore fines and flux, using combination of binders as discussed in the
invention. The agglomerates were reduced in a furnace using desired heating
profile in the temperature range from 1100 to 1400 C. The DRI with metallization
in the range of 70 - 95% and zinc less than 0.01 % were produced by the
process. The DRI was used to produce liquid metal in electric furnace.

In the second step of this inventive process, the hot DRI is directly melted in
electric furnace to form either a) hot metal, which can be used of BOF steel
making, by adjusting the C, Si, S, P levels, or b) directly steel by using double
slag practice. Production process options will be dictated by local economics.
One of the embodiments of the present invention is recovery of zinc. The zinc
vaporized during reduction in the furnace is carried away by the waste gas
stream. The zinc vapors are condensed by reducing the temperature below 900C
and by readjusting the oxygen partial pressure of the gas stream, if required.
The waste gas stream from arc furnace used for iron and steel making is also
treated in similar way to recover the zinc values. The zinc oxide condensed in the
condenser is collected. Since, coal is used as a reductant, the zinc oxides dust
also contents many impurities which needs to be removed. When the
concentration of the zinc in the dust is > 40 % then dust is used directly for zinc
extraction. In this invention carbo-thermic reduction of zinc oxide is carried out
to extract metallic zinc which is then purified by conventional electrolysis
technique. On the other hand dust with zinc concentration lower than 40% are
reduced in separate campaign to separate the iron and produce high zinc dusts.
The other method used for zinc enrichment of dust is smelting of furnace dust in
electric arc furnace which generate high zinc dust which can then be treated ty
conventional routes.

We claim:
1. An improved method for processing iron ore with high zinc content for
production of iron and steel comprising the steps;
- producing agglomerate comprising a mixture of iron oxides, carbonaceous
material and fluxes with mean particle size respectively of 35 to 70, 25-60
and 45-85 microns to form agglomerates of 8 to 15mm size using
combination of organic and inorganic binders and moisture to achieve the
desired properties of the agglomerates;
dezincificating and metallising the agglomerates in a furnace comprising:-
- sequentially adjusting the porosity (Primary pores) in agglomerates during
water evaporation at temperature 80°-150°C;
- evaporating the organic binders at temperature between 130° to 300°C to
create secondary pores;
- consuming the carbonaceous materials in reduction at a temperature
between 500° to 1200°C to create tertiary pores;

- providing a pore-channel for rapid transportation of gaseous products
through selection of mean-particle sizes of the ingredients forming the
agglomerate.
- smelting the reduced agglomerates, in hot / cold charging condition, to form
hot metal (iron) in a furnace leading to production of crude steel;
- recovering zinc values from waste gas stream of the furnaces by carrying-
out conventional zinc extraction process.

2. The method as claimed in claim 1, wherein the desired properties of the
agglomerates comprise wet-drop number, dry-drop number, green crushing
strength and dry-crushing strength which respectively ranges 6 to 8, 10 to
15,1.5 kg pellets, and 15kg/pellets.
3. The method as claimed in claim 1, wherein the dezincificating and metallising
further comprises:
- controlling the viscosity of the formed slag through combination of the
fluxes so as to avoid blocking the pore channels which enables
smooth exit of the gaseous products.
4. The method as claimed in claim 1, wherein the furnace is selected from the
types of rotary hearth furnace, non-shaft furnace and multi-hearth furnace.

5. The method as claimed in claim 1, wherein said iron oxides are iron ores
containing high zinc concentration in the range of 0.01 to 1% from iron ores,
EAF dust, plant wastes and their combination.
6. The method as claimed in claim 1, wherein said carbonaceous materials
comprises of anthracite coal, bituminous coal, coking coal, pet coal, coke
breeze, other carbonaceous materials and their combinations.
7. The method as claimed in claim 1, wherein said binders comprises of
inorganic, organic binders and their combinations, wherein the inorganic
binders are used in the doses between 0.5 to 2%, and wherein the organic
binders are used in the doses between 1 to 5%.
8. The method as claimed in claim 1 or 7, wherein the organic binders comprise
of dextrins, celluoses, starches, flours and their combination, mono and
polyacrylics and acrylamides and their combinations, different gums like guar
gum.
9. The method as claimed in claim 1 or 7, wherein the inorganic binders,
comprise betonite, colloidal silica, expanding clays and their combinations,
cement, sodium, silicate.
10. The method as claimed in claim 1, wherein the step of producing
agglomeration comprises:

- preparing a feed (iron ores, coal, binders, and fluxes) to achieve
required particle size and size distribution including surface area;
- blending, mixing and prewetting of the feed fines to achieved required
mix for agglomeration;
- preparing the agglomerate in a disc / drum palletizer or briquetting
machines with desired moisture level and processing parameters to
achieve required properties / quality of agglomerates; and
- drying the agglomerates in a temperature range from 110 to 300°C to
remove the moisture and formation of primary pores

11. The method as claimed in claim 1 to 3, wherein the dezincification and
metallization is carried out in a furnace where different temperature is
maintained in different zones thereby removing the organic binder in early
stages to form interconnected pore channels and then reducing and
vaporizing zinc at higher temperatures.
12. The method as claimed in claim 1 to 3, wherein the fluxes minimize the Fe
loss in the slag.
13. The method as claimed in claim 1, 10 and 12, wherein the fluxes comprise
oxides of CaO, MgO and SiO2 and their compounds.

14.The method as claimed in claim 1, wherein the zinc values are separated
from waste gas stream of the furnace by reducing the temperature of the
waste gas below 900°C and by adjusting CO / CO2 ratio of the waste gas by
introducing air.
15. The method as claimed in claim 14, wherein the zinc values separated are
processed in a furnace to enrich the zinc concentration in the product
collected from waste gas stream, wherein the compounds collected from the
waste gas stream, having more than 40% zinc content, and being adapted
for extraction of zinc by conventional processes.



ABSTRACT


Title : An improved method for processing iron ore with
high zinc content for production of iron and steel
This invention relates to an improved method for processing high zinc iron ores
for production of iron and steel comprising the steps of; producing agglomerate
comprising a mixture of iron oxides, carbonaceous materials, and fluxes with
mean-particle size respectively of 35 to 70, 25 to 60, and 45-85 microns, to
form agglomerates of 8 to 15 mm size using combination of organic and
inorganic binders and moisture to achieve the desired properties of the
agglomerates; dezincificating and metallising the agglomerates in a furnace;
smelting the reduced agglomerates, in hot / cold charging condition, to form
hot metal (iron) in a furnace leading to production of crude steel; recovering
zinc values from waste gas stream of the furnaces by carrying - out
conventional zinc extraction process.

Documents:

01142-kol-2008-abstract.pdf

01142-kol-2008-claims.pdf

01142-kol-2008-correspondence others.pdf

01142-kol-2008-description complete.pdf

01142-kol-2008-drawings.pdf

01142-kol-2008-form 1.pdf

01142-kol-2008-form 2.pdf

01142-kol-2008-form 3.pdf

01142-kol-2008-gpa.pdf

1142-KOL-2008-(09-11-2012)-CORRESPONDENCE.pdf

1142-KOL-2008-(23-05-2012)-ABSTRACT.pdf

1142-KOL-2008-(23-05-2012)-AMANDED CLAIMS.pdf

1142-KOL-2008-(23-05-2012)-AMANDED PAGES OF SPECIFICATION.pdf

1142-KOL-2008-(23-05-2012)-DESCRIPTION (COMPLETE).pdf

1142-KOL-2008-(23-05-2012)-DRAWINGS.pdf

1142-KOL-2008-(23-05-2012)-EXAMINATION REPORT REPLY RECIEVED.pdf

1142-KOL-2008-(23-05-2012)-FORM-1.pdf

1142-KOL-2008-(23-05-2012)-FORM-2.pdf

1142-KOL-2008-(23-05-2012)-FORM-3.pdf

1142-KOL-2008-(23-05-2012)-OTHERS PCT FORM.tif

1142-KOL-2008-(23-05-2012)-OTHERS.pdf

1142-KOL-2008-(23-05-2012)-PCT SEARCH REPORT.pdf

1142-KOL-2008-(23-05-2012)-PETITION UNDER RULE 137.pdf

1142-KOL-2008-(7-06-2013)-CLAIMS.pdf

1142-KOL-2008-(7-06-2013)-CORRESPONDENCE.pdf

1142-KOL-2008-CANCELLED PAGES.pdf

1142-KOL-2008-CORRESPONDENCE OTHERS 1.1.pdf

1142-KOL-2008-CORRESPONDENCE.pdf

1142-KOL-2008-DECISION.pdf

1142-KOL-2008-EXAMINATION REPORT.pdf

1142-KOL-2008-FORM 1.1.pdf

1142-KOL-2008-FORM 18.pdf

1142-KOL-2008-GPA.pdf

1142-KOL-2008-GRANTED-ABSTRACT.pdf

1142-KOL-2008-GRANTED-CLAIMS.pdf

1142-KOL-2008-GRANTED-DESCRIPTION.pdf

1142-KOL-2008-GRANTED-DRAWINGS.pdf

1142-KOL-2008-GRANTED-FORM 1.pdf

1142-KOL-2008-GRANTED-FORM 2.pdf

1142-KOL-2008-GRANTED-FORM 3.pdf

1142-KOL-2008-GRANTED-SPECIFICATION-COMPLETE.pdf

1142-KOL-2008-INTERNATIONAL SEARCH REPORT & OTHERS.pdf

1142-KOL-2008-PETITION UNDER RULE 137.pdf

1142-KOL-2008-REPLY TO EXAMINATION REPORT.pdf

1142-KOLNP-2008-ASSIGNMENT.pdf

1142-KOLNP-2008-CORRESPONDENCE 1.2.pdf

abstract-01142-kol-2008.jpg


Patent Number 257313
Indian Patent Application Number 1142/KOL/2008
PG Journal Number 39/2013
Publication Date 27-Sep-2013
Grant Date 23-Sep-2013
Date of Filing 30-Aug-2008
Name of Patentee TATA STEEL LIMITED
Applicant Address RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831001, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 VILAS D. TATHAVADKAR C/O. RESEARCH & DEVELOPMENT AND SCIENTIFIC SERVICES, TATA STEEL JAMSHEDPUR-831001, INDIA
2 AMITABH SHANKAR C/O. RESEARCH & DEVELOPMENT AND SCIENTIFIC SERVICES, TATA STEEL JAMSHEDPUR-831001, INDIA
3 GAJANAN U. KAPURE C/O. RESEARCH & DEVELOPMENT AND SCIENTIFIC SERVICES, TATA STEEL JAMSHEDPUR-831001, INDIA
4 SRINIVAS DWARAPUDI C/O. RESEARCH & DEVELOPMENT AND SCIENTIFIC SERVICES, TATA STEEL JAMSHEDPUR-831001, INDIA
PCT International Classification Number C01G9/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA