|Title of Invention||
FILTRATION UNITS SUITABLE FOR THE THROUGH-FLOW OF MEDIA
|Abstract||A filtration unit through which media can flow for removing pollutants from fluids consisting of cartridge housing (4) which consists of a container which has centered in the middle an inlet tube flat filter layers opposite one another at the ends (3), (10) a lid which ensures the influx (1) and efflux (12) of the fluid to be purified and a bottom part (9) characterized in that the filter cartridge housing (4) contains bed of agglomerates of finely divided iron oxide and/or iron oxyhydroxide having a bet surface area of 50 to iron oxide and/or iron having a bet surface area of 5 to 500 m preferably 8/0 top 200 with the agglomerates if appropriate being able to contain iron oxide pigments having bet surface areas below the above limits, the content of theses pigments having bet surface areas below the above the charge toward the forced of the charge by the flowing medium acting on it being high enough that the stressing of the charge by the flowing medium does not lead to an unwanted abrasion of the charge medium, such that the fluid to be purified as required leaves the inlet port the inlet tube (6) the lower frit plate (10) thereafter the absorber material (5) in the content chamber (4) the upper frit plate (3) and lid space with filter material (2) and then via the outlet port the outlet tube(12).|
|Full Text||FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
THE PATENTS RULES, 2003
[See Section 10; rule 13]
"FILTRATION UNITS SUITABLE FOR THE THROUGH-FLOW OF MEDIA"
BAYER AKTIENGESELLSCHAFT, a body corporate organized under the laws of Germany, D-51368 Leverkusen, Germany,
The following specification particularly describes the invention and the manner
in which it is to be performed:
The present invention relates to filtration units suitable for the through-flow media.
The invention relates to an adsorption container through which can flow a liquid to be treated, in particular a filter adsorption container which, filled with granulated or 5 pulverized, solid, water-insoluble adsorption media, in particular iron (oxy) hydroxide, is used for removing arsenic or heavy metals from drinking water. The apparatus can be attached, for example, in the home to the sanitary and drinking water supply.
10 The invention further relates to a process for synthesizing the.iron (oxy)hydroxide adsorber for charging into the inventive filtration units.
Studies of the National Academy of Sciences verified in 1999 that arsenic in drinking water causes bladder, lung and skin cancers.
Frequently one is faced with the problem, especially in regions where well water, mains water or drinking water in general is contaminated with arsenic or other heavy metals, of not having a suitable drinking water treatment plant in the vicinity, or not having a suitable system to hand which would continuously remove the pollutants.
Filter cartridges for purifying liquids, preferably contaminated water, which can also contain an adsorption medium, are known in various embodiments.
To remove solids from waters, membrane filter candles, for example, in suitable 25 housings are used.
The company Brita Wasser-Filter-Systeme GmbH has; disclosed cartridges and apparatuses for treating liquids (DE-A19 905 601; DE-A19 915 82.9; DE-A 19 814 008, DE-A 19 615 102, DE-A 4 304 536, US-A 6,099,728). These 30 apparatuses are highly suitable for the complete or partial desalination of drinking water in domestic jugs immediately before use of the drinking water.
US-A 4,064,876 discloses a filtration unit constructed as a filter cartridge which has a bed of activated carbon particles between a polyester urethane foam layer and a glass fiber layer.
DE-A 19 816 871 (Sartorius) describes a filtration unit for removing pollutants from fluids.
RU-A 2 027 676 describes a cartridge filter having a sorbent for drinking water purification having a connection to the water tap in the residence.
HU-A 00 209 500 describes a filter cartridge for removing radioactive material and heavy metals from water which is packed with a mixture of ion-exchange material, activated carbon, filter sand, zeolites, aluminum oxide and red mud.
Usually these adsorber cartridges are packed with activated carbon or ion-exchange resins. However, activated carbon has the disadvantage that-arsenic salts and. heavy metal salts, as they occur in aqueous systems, because of the low adsorption capacity of the activated carbon, are not removed to a sufficijn extent, which affects the service life of the cartridges.,.
Ion-exchange resins have the disadvantage that they bind ions from aqueous solution highly unselectively, and competing reactions frequently occur in the adsorption. A further disadvantage of ion-exchangers is the high dependency of the adsorption capacity of the ion exchanger on the pH of the water, so that large amounts of chemicals are required for pH adjustment of the water, which is not practicable when the adsorber cartridge is used in the home.
Contact granules and adsorber granules, including those based on iron oxides and/or iron oxyhydroxides, have already been described. They are used predominantly in continuous processes, where they are usually found in tower- or column-like apparatuses, through which the medium to be treated flows, and on the external and
internal surface of the granules of which the chemical or physical reaction or adsorption processes take place. For this purpose pulverulent materials cannot be used, because they compact in the direction of flow of the medium and as a result increase the resistance to flow until the apparatus plugs. If an apparatus is cleaned by backwashing (see below), large amounts of the powder are discharged, are lost or lead to an intolerable pollution of the wastewater.
However, the flowing media also exert forces on the granules which can lead to abrasion and/or to movement up to vigorous agitation of the granules. As a result the granules collide with one another and m consequence unwanted abrasion results. This leads to loss of contact or adsorber material and to contamination of the medium - to be treated.
In gas cleaning, the medium is used in adsorbers for binding unwanted constituents, such as hydrogen sulfide, mercaptans and prussic acid, and other phosphorus, arsenic, antimony, sulfur, selenium, tellurium compounds and also cyano compounds and heavy metal compounds in exhaust gases. It is also possible to adsorb gases such as HF, HC1, H2S, SOx NOx.
A filter cartridge for drying gases is described, for example, in US-A 5,110,330.
It is also possible to remove compounds.of phojphpxus. arsenic,_an.timony,.selenium and tellurium, and also cyano compounds and heaw metaJLcompounds from waste oils and other contaminated organic solvents.
Contact granules and adsorber granules based on iron oxides and/or iron oxyhydroxides are also used to catalyze chemical reactions in the gas phase or in the liquid phase.
Differing types of process are known to remove trace substances and pollutants from aqueous systems using adsorption media.
To remove pollutants from water, DE-A 3 800 873 describes an adsorption medium based on porous materials, for example hydrophobized chalk having fine to medium particle size.
DE-A 3 703 169 discloses a process for preparing a granulated filter substance for treating natural water. The adsorbent is prepared by granulating an aqueous suspension of kaolin with addition of pulverulent dolomite in a fluidized bed. The granules are then fired at 900 to 950°C.
DE-A 40 34 417 discloses a process for preparing and using highly reactive reagents for purifying exhaust gas and wastewater. Descriptions are given here of mixtures of Ca(OH)2 with additions of clays, stone flours, fly dust and fly ashes which can be prepared so as to be porous and have a surface area of approximately 200 m2/g.
Said processes and the contacts used for this purpose share the disadvantage that the respective component responsible for the selective adsorption of constituents of the media to be purified, that is to say the actual adsorbent, must have high levels of additives to permit shaping to form granules. As a result, the binding capacity for the water pollutants to be removed is decreased considerably. Furthermore, the later workup or further processing of the material is problematic, since the foreign materials used as binder must first be removed again.
DE-A 4 214 487 describes a process and a reactor for removing impurities from water. Flow passes horizontally through a funnel-shaped reactor in which the sorbent used for water impurities is very finely divided iron hydroxide in flock form. A disadvantage of this process is the use of the flock-form iron hydroxide which, owing to the low differences in density between water and iron hydroxide leads to the fact that such a reactor can only be operated at very low flow velocities and there is the risk that the sorbent, possibly already loaded with pollutants, is discharged from the reactor together with the water.
JP-A 55 132 633 describes a granulated red mud as byproduct of aluminum production as adsorbent for arsenic. This is composed of Fe2O3, AI2O3 and SiO2. The stability of the granules and the granulation process are not reported herein. A further disadvantage of this adsorbent is the lack of constancy in the product composition, the uncertain availability and the possible aluminum pollution of the drinking water. Since aluminum is under suspicion of promoting the development of Alzheimer"s disease, contamination with this is in particular to be avoided.
DE-A 19 826 186 describes a process for preparing an iron hydroxide-containing adsorption medium. An aqueous polymer dispersion is mixed into iron hydroxide in water-dispersible form. This mixture is then either dried to achieve a solid state and the solid material then mechanically comminuted into the desired shape and/or size, or the mixture is, if appropriate after predrying, submitted to shaping and then end-dried to achieve a solid state. As a result a material is obtained in which the iron hydroxide is firmly embedded in the polymer and is said to have a high binding capacity for the pollutants usually present in the wastewaters or exhaust gases.
A disadvantage of this process is the use of organic binders which additionally pollute the water to be treated by leaching out and/or abrading organic materials. In addition, stability with relatively long use of the adsorber compound is not ensured. An organic binder can also serve as nutrient medium to bacteria and other micro¬organisms, so that there is a risk of colonization of the contacts with microorganisms and contamination of the medium by the same.
In principle the presence of different types of aids required for the production of the adsorbents is disadvantageous in the workup, recycling or further processing of used adsorbents, because the utilization of pure substances is less of a problem than is the case with mixtures of substances. Thus, for example, polymeric binders in the further processing of adsorber materials based on iron oxide as pigments for coloring concrete is disadvantageous, since these binders impede the dispersion of the pigment in liquid concrete.
DE-A 4 320 003 describes a processfor removing dissolved arsenic from ground water using colloidal " granulated iron nydroxidej for the use of fine, suspence
iron(in) hydroxide products, it is recommended here to introduce the iron hydroxide suspension into fixed-bed filters which are packed with granular material or other supports having a high external or internal porosity. This process is also accompanied by the disadvantage that, based on the adsorbent "substrate + iron hydroxide", only low specific loading capacities are achievable. Furthermore, there is only weak binding between substrate and iron hydroxide, so that in a subsequent treatment with arsenic-containing water, there is the risk of discharge of iron hydroxide or iron arsenate. In this publication, in addition, the use of granulated iron hydroxide as adsorber material for a fixed-bed reactor is mentioned. The granulated iron hydroxide is prepared via a freeze-conditioning (freeze-drying) of iron hydroxide obtained by neutralizing acidic iron(in) salt solutions at temperatures below minus 5°C. This production process is highly energy-consuming and leads to wastewaters with a high salt pollution. In addition, the result of this production
process produces only very small grains having low mechanical stability. This leads,
in the case oFuseln a fixed-bed reactor, to the fact that the grain size spectrum is partially decreased by mechanical abrasion of the particles in the course of operations, which in turn leads to the fact that finely dispersed particles of loaded or unloaded adsorption medium are discharged from the reactor. A further disadvantage
of these granules is that the adsorption capacity with respect to arsenic compounds is considerably decreased if the granules lose water, for example as a result of relatively long dry idle time.
US-A-5,948,726 has disclosed adsorber/binder systems which are produced by withdrawing a sufficiently large amount of water from a mixture of (a) a cross-linkable binder of colloidal metal oxides or metalloid oxides, (b) oxidic adsorbents such as metal oxides and (c) an acid, in such a manner that the components (a) and (b) crosslink, forming an adsorber/binder system. From the evidence of the illustrative embodiments, the binders used are colloidal clay earths or aluminum oxide.
A disadvantage of these compositions is the use of acid (column 9, line 4) required in their production, and the circumstance that these are not pure substances, but heterogeneous substances, which is undesirable not only for production and regeneration of such adsorbers, but also for their disposal or final deposit, for example in landfill. The scope of the disclosure of this publication is also said to encompass adsorbers which are suitable for adsorbing arsenic; however, specific examples are not presented. It is known that aluminum oxide is considerably inferior to iron oxides with respect to the adsorption capacity for arsenic.
frequently operated in groups arranged in parallel. In order to free, for example drinking water, from organic impurities, such adsorbers are charged with activated carbon. At peak consumption times, the adsorbers present are then operated in parallel in order to prevent the flow velocity from increasing above the design-limit maximum. During times of lower water consumption, individual adsorbers are taken out of operation and during this can be serviced, for example, the adsorber material being exposed to particular stresses, as are described in more detail below.
The use of granules which can be produced by compacting, for example, pulverulent iron oxide by using high linear forces, has already been mentioned. Such granules have already been described for homogeneously coloring liquid concrete. The use of high linear forces in compacting is greatly energy intensive and costly and the stability of the compacted material is unsatisfactory for relatively long use in adsorbers. Therefore, such materials are not considered for use in, for example, adsorbers, in particular continuously operated adsorbers, in the purification of water. In particular during servicing or cleaning the adsorber systems by backwashing (see below), such granules, as a result of the associated agitation of the same, lose large amounts of substance. The backwash water is made highly turbid due to the abrasion. This is unacceptable for several reasons: firstly, adsorber material is lost which, after a long service time, is highly loaded with impurities and is therefore a toxicological hazard. The wastewater stream is then polluted with the abrasion which can sediment
and thus lead to impairment of the piping systems, and finally the sewage treatment plant is undesirably physically and toxicologically polluted, just to name some reasons.
It is an object underlying the present invention to provide a filtration unit for removing arsenic and heavy metal from drinkmg_water, service water .mineral water, garden pond water, agricultural water, holy water and therapeutLcjvjtoLusiiig iron oxynyoroxide particles or iron oxide particles as contact medium _or adsorption/reaction medium, which, owing to the^adsQrber_perforjnaac,e__o0.he_ packing medium ensure high removal of the aissoiveu pouuiants.,, which at the same time withstands the mechanical and hydraulic stresses in the adsorber housings and
in addition, for safety as a result of the filtration performance of installed Jilters,. to prevent the discharge of suspended impurities or abraded adsorber parts, possibly, loaded wit pojmtants.
The inventive contacts or adsorption media/reaction media, their production, their use and apparatuses charged with these achieve this complex object.
The object is achieved by a filtration unit which consists of_a housine of clastic, wood, glass, ceramic, metal or a comnosite material which is nrovided with inlet and outlet orifices. Examples of simple,
an/lb.^ThisJiousmg is described extensively in DE-A 19 816 871. The inlet and
outlrTorifices are separated from the actual housing space, which comprises a bed of the iron oxyhydroxide adsorption medium by the covering flat filter systems. The fluid to be treated thus passes successively through the first flat filter layer, the adsorber particles, the second flat filter layer and the outlet orifice. The housing space can be completely or partially filled with the adsorber particles. The housing space is preferably conical or pyramidal, but can also be cylindrical, spherical, parallelepipedal or in spiral shape. By means of a tapering of the housing space (see drawing fig. lb), the filtration can be operated in any desired layer and no bypass can form between the bed of the adsorber particles, which can pass unhindered the fluid
to be filtered without adsorption. By packing the housing space with a bed of 1 adsorber particles which occupies between 91 and 99% of the total housin volume, high flow rate of the fluid to be purified is ensured, since, owing to the stability of _*rr."rt".,;"r:"*"""","~
the dsorber granules, low resistance is encountered by the influent liquid.
In preferred embodiments of the invention the housing space, in the tapering
sections, is constructed as a truncated cone or truncated pyramid.
Various materials are shown for the flat filter layers, depending on the field of use,
for example in DE-A 19 816 871.
Brief Description of Drawings:
An improved embodiment of an adsorber tank is shown in the diagram/ng. 2aSand
figf 2b/phey show the domestic filter module, in each case in longitudinal section.
The adsorber housing (4) containing the iron oxyhydroxide adsorber material (5) having filter plates disposed at the top (3) and bottom (10) ends and a centrally disposed inlet tube (6) can be isolated as a unit via a threaded joint with the lid (13) at the top end and a threaded joint with the bottom support (9) at the bottom end by unscrewing the connections. If the cartridge is loaded, a new one can be inserted and the bottom plate and lid plate can be cleaned. At the top end, the inlet tube (6) is fixed-securely via a suitable gasket to the inlet port (2) during use. The inlet tube can be removed from the cartridge housing and inserted into a new fresh cartridge housing. As a result the incoming liquid flows directly onto a sieve basket (7) which
prefilters suspended matter, algae and the like, and retains these on entry into the
actual adsorber cartridge, so that the adsorber material does not clump or stick
together. The screen (7) serves for uniform distribution of the incoming hquid stream
into the bottom space, is therefore preferably conical, that is to say truncated cone-
shaped and completely encloses the inlet tube and is fixed via loose sealing rings
both to this and also to the filter plate (10) enclosing it. The screen cloth can consist
of customary fine-meshed filter materials, for example plastic, natural material or
to be filtered without adsorption. By packing the housing space with a bed of adsorber particles which occupies between 97 and 99% of the total housing volume, high flow rate of the fluid to be purified is ensured, since, owing to the stability of the adsorber granules, low resistance is encountered by the influent liquid.
In preferred embodiments of the invention the housing space, in the tapering sections, is constructed as a truncated cone or truncated pyramid.
Various materials are shown for the flat filter layers, depending on the. field of use, for example in DE-A 19 816 871. Brief Description of Drawings:
An improved embodiment of an adsorber tank is shown in the diagram fig. 2a and fig. 2b. They show the domestic filter module, in each case in longitudinal section.
The adsorber housing (4) containing the iron oxyhydroxide adsorber material (5)
having filter plates disposedat the , topf (3))and bottom/(lO),ends and a centrally
disposed inlet tube (6) can be isolated as a unit via a threaded joint with the lid (13)
at the top end and a threaded joint with the bottom support (9) at the bottom end by
unscrewing the connections. If the cartridge is loaded, a new one can be inserted and
the bottom plate and lid plate can be cleaned. At the top end, the inlet tube (6) is
fixed securely via a suitable gasket to the inlet port (2) during use. The inlet tube can
be removed from the cartridge housing and inserted into a new fresh cartridge
housing. As a result the incoming liquid flows directly onto a sieve basket (7) which
prefilters suspended matter, algae and the like, and retains these on entry into the
actual adsorber cartridge, so that the adsorber material does not clump or stick
together. The screen (7) serves for uniform distribution of the incoming liquid stream
into the bottom space, is therefore preferably conical, that is to say truncated cone-
shaped and completely encloses the inlet tube and is fixed via loose sealing rings
both to this and also to the filter plate (10) enclosing it. The screen cloth can consist
of customary fine-meshed filter materials, for example plastic, natural material or
The screwed-on bottom part (9) can in addition contain a suitable filter material or nonwoven filter (8) which can be selected depending on the type and amount of expected suspended matter. In the presence of large amounts of solid foreign matter,
the screen (7) and the nonwoven filter (8) can readily be removed and cleaned by unscrewing the bottom part. The filter plate (10) which can consist of fine-porous ceramic, separates the bottom space (9) from the contact space containing the iron oxhydroxide granules (5) so that no adsorber material passes into the bottom space and no prefiltered material passes into the contact space. By passing the water to be purified through the contact space containing the iron oxhydroxide,..,adsorber ascending from bottom to top, the pollutants to be removed are removed by physi-sorption and/or chemisorption to the adsorber material. An additional filter plate at the top end of the cartridge housing ensures that no adsorber material passes into the outlet (12). As a result of elevated water pressure or long service life of the adsorber. tank, fine matter can abrade from the adsorber material, which fine matter passes through the filter plate (3). In order to avoid this fine matter (loaded with pollutants) passing into the outlet, filter material or nonwoven filter (11) is embedded in the
interior of the lid (13), which retains the fine matter.
The filter(3) and (10) also serve for uniformly distributing the fluid into the |
adsorber space (5) or uniformly recollecting this after exit. The clean water freed
The lid (13) can additionally have a valve in order to allow escape of gases co-
entrained during initial operation during operations (for example air present in the cartridge housing).
Depending on the application, it can be advantageous to operate the above-described adsorber tank in reverse sequence (fig. 2b). This means that the water to be purified now enters from the inlet port (1) directly onto the prefilter (11) which retains suspended matter and foreign bodies, then passes through the filter plate (3), enters into the contact space where the dissolved pollutants adsorb to the adsorber material,
enters, via the cartridge bottom plate (10) into the bottom space (9), where filter material (8) may be embedded, in order to retain abraded adsorber material, the sieve basket (7) additionally performing filtration services, so that the purified water leaves, via the outlet tube (6) and the outlet port, the adsorber tank via the orifice (1).
pws the use (cartridge, filter cartridge) alone.
A simpler embodiment which operates, however, according to the same principle as 1 described above, is shown in figure : H\shows the adsorber tank which contains the
inventive adsorber granules, and in which the adsorber cartridge forms a unit.
In principle, obviously, further embodiments and designs are possible which are similar to the structures described and which operate according to the manners described, that is to say contain an inlet and outlet orifice for waters and iron oxide and/or iron (oxy)hydroxide as adsorber media.
s a filter bag which, filled with adsorber granules, can be supplied to water to be purified in order to remove the pollutants present therein by
Filter bags and extraction envelopes are known, for example in many forms and embodiments for preparing hot infused beverages, in particular tea. DE-A 839 405 describes, for example, such a folded bag as used for preparing tea and the like. By means of a special folding technique which forms a double-chamber system, intensive mixing of the eluent with the substance to be extracted is ensured.
However, by the same token, iron oxides and iron (oxy)hydroxides in pulverized, fine-granulated or coarse-granulated form may also be embedded into semipermeable bags having a filtering action (for example the above-described folding bag) and these packages may be supplied to the waters to be purified in order, by this means, after a certain contact time, to remove from the waters the pollutants by adsorption to the adsorber material (see diagram fig. 5). Firstly, the iron oxides and/or iron
(oxy)hydroxides withstand the mechanical and hydraulic stresses in the filter bag and, secondly, owing to the filter action of the filter membrane, exit of any fine material of the adsorption medium produced by abrasion into the waters to be purified is prevented.
The various embodiments of the present invention share the fact that iron hydroxide or iron oxhydroxide in fine granulated, coarse granulated or pulverized form~is~ embedded in housings having a filtering action and the liquid to be_purified is allowed to flow through the filter housing the filter packing is supplied to the liquid to be purified and thus ensures adsorption of the pollutants.
To prepare the Inventive granules, firstly an aqueous suspension of finely divided iron oxhydroxides and/or iron oxides is prepared according to the prior art. From this the water and constituents dissolved therein can be removed in two different ways:
For applications in which fewer demands are made of the mechanical strength of the granules/contacts, first only the water is removed, for example by evaporation. A residue is obtained which, in addition to the finely divided iron oxide and/or iron oxhydroxide also contains the entire salt loading. This residue, after drying, is redispersed in water, for which only a relatively small shearing force must be used. This suspension is then filtered and the residue is essentially washed salt-free. The filter cake which is obtained as residue is a solid to semisolid paste which generally has a water content between 10 and 90% by weight.
This can then be completely or partially dewatered and the resultant material can then be comminuted into the desired form and/or size. Alternatively, the paste or filter cake, if appropriate after predrying to achieve a sufficiently solid state, can be subjected to shaping and subsequent (further) drying to achieve a particulate state. The later use of the granules determines the preferred procedure for their production and can be determined by those skilled in the art for the particular field of application
by simple guideline preliminary experiments. Not only the immediately dried filter cake but also the dried shaped bodies can then be used as contact or adsorber.
For applications for which greater demands are made of the mechanical strength of the granules/contacts, the suspension is filtered and the residue is washed essentially salt-free. The filter cake which is obtained as residue is a solid to semisolid paste. This can then be completely or partially dewatered and the resultant material can then be comminuted into the desired shape and/or size. Alternatively, the paste or the filter cake, if appropriate after predrying to achieve a sufficiently solid state, can be subjected to shaping arid subsequent (further) drying to achieve a particulate state. The later use of the granules determines the preferred procedure in their production and can be determined by those skilled in the art for the respective field of application by simple guideline preliminary experiments. Not only the immediately dried filter cake but also the dried shaped bodies can then be used as contact or adsorber.
The products obtained according to method 1, although they are less mechanically stable, filtration can be carried out more readily and more rapidly. In addition, the finely divided pigments thus isolated can very readily be incorporated into paints and polymers, for example, because considerably less shear force needs to be used for this than is required for incorporating the finely divided pigments obtained according to method 2.
The finely divided iron oxide and/or iron oxhydroxide used has a particle size of up to 500 nm, preferably up to 100 nm, particularly preferably 4 to~50 nm, and a*BET surface area of 50 to 500 m2/g,preferably 80 to 200 m2/g.
The primary particle size was determined by scanning electron microscopy, for example at an enlargement of 60 000:1 by measurement (instrument: XL30 ESEM FEG, Philips). If the primary particles are needle-shaped, as, for example, in the
phase of cc-FeOOH, the needle width may be reported as a measure of the particle size. In the case of nanoparticulate oc-FeOOH particles, needle widths of up to 100 nm are found, but chiefly between 4 and 50 nm. oc-FeOOH primary particles customarily have a length:width ratio of 5:1 to 50:1 typically from 5:1 to 20:1. By i doping or special reaction procedures, the needle shapes, however, may be varied in their length:width ratio. If the primary particles are isometric, as, for example, in the phases a-Fe2O3, Y-Fe203) Fe3O4, the particulate diameters can equally well be less than 20 nm.
By mixing nanoparticulate iron oxides or iron oxhydroxides with pigments and/or Fe(OH)3, on the scanning electron micrographs, the presence of the added pigment or seed particles is recognized in their known particle morphology, which are held together or stuck to one another by the nanoparticulate seed particles or the amorphous Fe(OH)3 polymer.
Products obtainable by the methods 1) or 2) can then be further comminuted, for example by shredding or grinding. Since the products, on their first contact with water, for example during the first filling of a freshly charged adsorber apparatus with water, autogenously decrease in size, however, this is not generally necessary.
Another method of producing granules which has proven itself in practice is pelletizing a semimoist paste. In this process pellets or rods are formed from a semi¬solid paste, for example, by means of a simple perforated plate, a roller press or an extruder, and this is either dried straight away or the extrudates are additionally brought into a spherical or granular form by means of a spheronizer. The still-moist beads or granules can subsequently be dried to a desired moisture content. In order that the granules do not clump together, a residual moisture content of
In general it is possible, for improving the filtration behavior of the suspensions, to employ customary measures enhancing filtration, such as are described, for example, in Solid-Liquid Filtration and Separation Technology, A. Rushton, A.S., Ward R.G., Holdich, 2nd edition 2000, Wiley-VCH, Weinheim, and Handbuch der Industriellen Fest/Fliissig-Filtration [Handbook of industrial solid/liquid filtration], H. Gasper, D. Ochsle, E.Pongratz, 2nd edition 2000, Wiley-VCH Weinheim. Thus, for example, flocculents can be added to the suspensions.
In addition to, or in place of, the iron oxhydroxides, iron carbonates can also be used.
The inventive products can be subjected to drying in air and/or in vacuo, and/or in a drying cabinet and/or on belt dryers or by spray-drying, preferably at temperatures of -25 to 250°C, particularly preferably at 60 to 120°C.
The inventive products preferably have a residual water content of less than 20% by weight.
It has been found that the resultant pieces or granules have a high binding capacity for pollutants present in waters, liquids or gases, and, in addition, they have a sufficiently high stability with respect to mechanical or hydraulic stress due to flowing media.
In particular, it is surprising that finely divided iron oxhydroxides or iron oxides having high specific surface areas solidify on drying into very hard agglomerates which have, without addition of binder, a very high mechanical abrasion strength and very high hydraulic stability with respect to contact with flowing water, and which have a high binding capacity for the pollutants and trace substances present in the water.
For the_inventave use of finely divided iron oxhydroxidies for example transparent iron oxhydroxide„pig-ments having specific surface areas of greater than 80 m2 are
suitable. However, correspondingly finely divided iron oxide pigments can also be used, preferably hematites, magnetites or maghemites.
The production of yellow finely divided iron oxhydroxide pigments (for example goethite) in the acidic or alkaline pH range, what are termed acidic or alkaline seeds, is prior art. The production of other finely divided iron oxide or iron oxhydroxide pigments is also prior art. Such pigments can contain structures based on a-, (3-, y-, S-, 5"-, e-phases and/or Fe(OH)2 and mixed and interphases of the same. Finely divided yellow iron oxhydroxides can be ignited to form finely divided red iron oxides.
The preparation of transparent iron oxides and iron oxhydroxides is disclosed, for example, according to DE-A 2 603 050 by BIOS 1144, pp. 29 to 33, or by FIAT 814, • pp. 1 to 26.
Finely divided yellow iron oxhydroxide pigments are generally synthesized by precipitating iron(II) hydroxides or carbonates from corresponding iron(H) salt solutions, for example FeSO4, FeCk in pure form, or as pickling solutions in the acidic or alkaline pH range and subsequent oxidation to form iron(HI) oxide hydroxides (see, inter alia, G. Buxbaum, Industrial Inorganic Pigments, VCH Weinheim, 2nd edition, 1998, pp. 231 ff). Oxidation of divalent to trivalent iron is preferably performed with air, with intensive gas introduction being advantageous. Oxidation with H202 also leads to finely divided iron oxhydroxides. The temperature in the precipitation and in the oxidation should be selected to be as low as possible in order to achieve very finely divided yellow pigments. It is preferably between 15°C and 45°C. Preferably, NaOH is used as alkaline precipitant. However, other precipitants can be used, such as KOH, Na2C03, K2CO3, CaO, Ca(OH)2, CaCO3, NH3, NH4OH, MgO and/or MgC03.
In order to direct the precipitated pigments in the direction towards the necessary high finely divided character, the precipitations, for example of yellow cc-FeOOH,. as
described in US patents US-A 2 558 303 and US-A 2 558 304, are carried out in the alkaline pH range using alkali metal carbonates as precipitants and generally adding modifiers, for example SiO2, salts of zinc, aluminum or magnesium, hydroxy-carboxylic acids, phosphates, metaphosphates. Products thus produced are described in US-A 2 558 302. Such seed modifiers do not interfere [lacuna] prevent later workup, recycling or other type of use of the inventive adsorbents. In the case of the precipitation processes in the aqueous medium, according to previous knowledge, precipitation in the alkaline environment leads to less firmly agglomerated powders than those in the acidic environment.
DE-A 4 235 945 reports on the synthesis of finely divided iron oxides by a precipitation process in the acidic pH range and without modifiers.
DE-A 4 434 669 describes a process by which highly transparent yellow, chemically pure iron oxide pigments can be prepared by post-treatment of the same with sodium hydroxide solution.
DE-A 4 434 972 reports on highly transparent, yellow iron oxide pigments of the oc-FeOOH modification having a specific surface area of more than 100 m /g with high temperature stability.
DE-A 4 434 973 describes highly transparent yellow iron oxide pigments which are produced via the process steps seed precipitation in the acidic pH range, seed oxidation, seed ripening and pigment build up.
Red, transparent iron oxide pigments which are formed by ignition from yellow, transparent iron oxide pigments are disclosed by DE-A 4 434 668 and DE-A 4 235 946.
By means of the fact that iron oxhydroxides of the most varied phases each in pure form or in any mixture are prepared by the known precipitation and oxidation
reactions from iron(II) salt solutions, the resultant iron oxhydroxides, if appropriate after a post-treatment, are separated off from the suspension by filtration from the salt solution and washed substantially salt-free, preferably up to a residual conductivity of The drying is expediently performed at temperatures up to 250°C. Vacuum-drying or freeze-drying of the material is also possible. The particle size of the material is optional, it is preferably between 0.2 and 40 mm, particularly preferably between 0.2 to 20 mm. This can be achieved by mechanical shaping of the semisolid pasty filter cake before drying by a granulation or pelletizing system or in an extrusion press to give shaped bodies having a size in the range from 0.2 to 20 mm, and subsequent drying in air, on a belt dryer or in a drying cabinet, and/or by mechanical comminution to the desired particle size after drying.
Compared with the prior art, the products described, the process for their production and their use are an improvement. The inventive granules based on finely divided iron (oxy)hydroxides and/or iron oxides, in contrast to those made of coarse particulate iron oxhydroxides and/or iron oxides can bear considerably greater loads and thus have a much greater abrasion stability toward mechanical and hydraulic stress. They can be used directly as such. Even the comminution or shredding of the initially obtained crude dry substance from filter cake or extrusion presses can be dispensed with, for example when used in adsorber systems for water purification, since the coarse pieces reduce themselves in size on contact with water. In this case a random particle size distribution occurs, but no particles of a size which are discharged from the adsorber by the flowing medium to a significant extent.
A separate granulation, as would be necessary when conventional iron oxhydroxides are used in the form of (flowable) powder, either with the aid of foreign binders or very high linear forces in compacting, can be dispensed with completely.
According to the invention, the suspensions of the finely divided iron oxhydroxides or iron oxides can also be admixed with conventional pulverulent iron oxhydroxides or iron oxides. The respective amounts are determined by the properties of these pulverulent iron oxhydroxides or iron oxides and the requirements made of the inventive product with respect to its mechanical stability and abrasion strength. Although the addition of pulverulent pigments will generally decrease the mechanical strength of the inventive products, filtration of the finely divided suspensions if facilitated. Those skilled in the art active in the respective field of application will be able to determine by means of a few preliminary experiments the optimum mixing ratio for the respective use.
The suspensions of the alkaline finely divided seeds can also be additionally admixed with an amount corresponding to the NaOH excess of aqueous salts of Fe3+, Al3+, Mg2+, Ti4+ or mixtures thereof so that sufficiently slightly soluble precipitates of Fe(OH)3, Al(OH)3, Mg(OH)2, TiO(OH)2, or products of aging and secondary dehydrated products thereof precipitate onto the suspended iron oxide particles and/or iron(oxy)hydroxide particles. Vice versa, the slightly soluble precipitates Fe(OH)3, Al(OH)3, Mg(OH)2, TiO(OH)2 or their products of aging and secondary products can be precipitated onto the iron oxide or iron (oxy)hydroxide particles suspended in Fe3+, Al3+, Mg2+, Ti4+ by adding alkalis, for example NaOH, Ca(OH)2) KOH, CaC03, Na2C03, K2C03, NH4OH. The aluminum oxide or aluminum (oxy)hydroxide can also be precipitated from an aluminate suspension (for example NaA102) onto the iron oxide particles and/or iron (oxy)hydroxide particles.
The resultant initially amorphous Fe(OH)3 or Al(OH>3 age with time, for example to give the FeOOH or AlOOH phase. This ensures complete consumption of the sodium hydroxide solution which was used in excess for preparing the alkaline seed. The
resultant materials also have high specific surface areas. The material, just like the above-described nanoparticulate iron oxyhydroxides, is outstandingly suitable for use in adsorbers, since, in addition to a high adsorption capacity, it also has high stability toward mechanical stress.
Particularly preferably, the inventive granules are used in the purification of liquids, in particular for removing heavy metals A preferred use in this technical field is decontaminating water, in particular driking water very recently, particular attention has been paid to removing arsenic from drinking water. The inventive I granules are outstandingly suitable for this purpose, since using the inventive f granules achieves concentrations which not only comply with the low limiting valuesi specified by the US EPA, but can also be lower than these.
For this purpose the granules can be used in customary adsorber apparatuses as are currently used, for example charged with activated carbon, for removing other types of pollutants. A batchwise operation, for example in cisterns or similar containers, which may be equipped with stirrers, is also possible. However, use in continuous systems, such as continuous-flow adsorbers, is preferred.
Since untreated water to be treated to produce drinking water customarily also contains organic impurities such as algae and similar organisms, the surface of adsorbers, in particular the outer surface of a granule-type adsorbent, becomes coated during use with generally slimy deposits which impede or even prevent the ingress of water and thus* the adsorption of the constituents to be removed. For this reason, the adsorber apparatuses are backwashed with water from time to time, which is preferably carried out during times of low water consumption (see above) on apparatuses which are individually taken out of operation. In this case the adsorbent is swirled up and, as a result of the associated mechanical stressing of the surface, the unwanted coating is removed and discharged in counterflow to the direction of flow during operation in service. The washing water is customarily fed to a sewage treatment plant. In this case the inventive adsorbents prove themselves particularly
well in service, since their high strength makes possible cleaning in a short time, without significant losses of adsorber material being encountered or the backwashing water fed to the wastewater being highly polluted with discharged adsorber material, or possibly even highly polluted with heavy metals.
A suitable prefilter and postfilter retain the impurities which can plug the adsorber cartridge.
As a result of the inventive stability of the granules and owing to suitable packing of the adsorber granules, material abrasion is minimized.
Sprayed granules of the iron oxyhydroxide adsorbers having a particle size Since the inventive granules are free from foreign binders, the material is relatively simple to dispose of after use. Thus the adsorbed arsenic can be removed thermally or chemically, for example in special apparatuses, and an iron oxide pigment is obtained as a pure substance, which can be either recycled for the same use, or can be fed to customary pigment applications. Depending on the application and legal provisions, the adsorber content can also be used without the prior removal of heavy metals, for example as pigment for pigmenting permanent construction materials such as concrete, since the heavy metals removed from the drinking water are permanently immobilized in this manner and are removed from the water cycle.
Therefore, water treatment plants or waterworks in which apparatuses charged with
the inventive granules are operated are also subject-matter of the present invention, as are processes for decontaminating water using such apparatuses, and apparatuses
of this type themselves.
For many applications, in particular those in which a maximum mechanical strength of the granules is not required, the addition of pulverulent pigments in the production of the inventive granules is a preferred embodiment.
Thus, for example, a seed suspension in accordance with example 2 of the present application can be admixed with up to 40% by weight of commercially customary goethite (for example Bayferrox® 920, Bayer AG, Leverkusen DE), if the resultant inventive granules are to be used for removing arsenic from drinking water in adsorbers through which water flows.
The specific surface area of the inventive products is determined in accordance with BET via the carrier gas method (He:N2 = 90:10) using the one point method as specified by DIN 66131 (1993). Before measurement, the sample is heated for 1 h at 140°C in a stream of dry nitrogen.
To measure the adsorption of arsenic(III) and arsenic(V), 3 1 of an aqueous solution of NaAs02 or Na2HAsC>4 having a concentration in each case of approximately 2-3 mg/1 of arsenic is treated with 3 g of the sample under test in a 5 1 PE flask over a defined period, and the flask is agitated in the course of this on rotating rollers. The adsorption rate of As ions on iron hydroxide over this defined period, for example one hour, is reported as mg(As3+/5+)/g(FeOOH)-h from the difference from the As3+/5+ ions remaining in solution.
To measure the adsorption of Sb3+, Sb5+, Pb2+, Hg2+, Cr6+, Cd2+ ions, the same pattern is followed, more precisely the desired concentrations are prepared by dissolving appropriate amounts of Sb203, KSb(OH)6, PbCl2, NaCr04, CdCl2 in H20 and the pH is set to 7-9.
The As, Sb, Cd, Cr, Hg and Pb contents of the loaded iron oxyhydroxide or of the solutions is determined using mass spectrometry (ICP-MS) as specified in DIN 38406-29 (1999) or via optical emission spectroscopy (ICP-OES) as specified by
EN-ISO 11885 (1998), in each case using inductively coupled plasma as the excitation unit.
Mechanical and hydraulic abrasion strength was evaluated according to the following method: 10 g of the granules under test having particle sizes > 0.1 mm were admixed with 150 ml of deionized water in a 500 ml conical flask and rotated at 250 rotations/minute for a period of 30 minutes in a LabShaker shaking machine (Kuhner model, from Braun). The fraction >0.1 mm was then isolated from the suspension using a screen, dried and weighed. The weight ratio between final weight and initial weight gives the abrasion value in %.
The invention will now be described in more detail below with reference to examples. The examples are intended to illustrate the process and do not represent a limitation.
2371 of an aqueous iron sulfate solution having a concentration of 150 g/1 of FeS04 were charged at 24°C. 113 1 of an aqueous NaOH solution (227 g/1) were then added rapidly and the light blue suspension was then oxidized for 1.5 hours with 401 of air per hour and mole of iron.
The resultant yellow suspension was filtered off via a filter press and the solids were washed to a residual filtrate conductivity of 1 mS/cm. The filter cake was produced as a spreadable and kneadable paste, which was dried on sheets in a circulated-air drying cabinet at 75°C to a residual moisture content of 3% by weight. The dried material was then brought to particle sizes between 0.5 and 2 mm by coarse grinding. The resultant hard pieces were used directly in an adsorber tank.
The product consisted 100% of a-FeOOH having an extreme short-needled habit, ttie
needles having aggregated to form solid macroscopic agglomerates. From the
scanning electron micrograph, for example at a magnification of 60 000:1, the needle
widths were determinedbyjriejsuremeM^ 35 nm, and the needle
lengths between 150 and 350 nm. The needles were highly agglomerated.
The specific BET surface area was 122 m2/g. The adsorption rate with respect to
NaAs02 at a starting concentration of 2.3 mg (As3+)/l was 2014 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAs04 at a starting concentration of
2Tmgof (As3+)/l was 2.29ingof (As5+)/g(FeOOH)-h,
8001 of an aqueous iron sulfate solution having a concentration of 150 g/1 of FeS04 were charged at 29°C and were admixed with stirring with 147 1 of an aqueous
NaOH solution (300 g/1) in 20 minutes. The resultant grayish-blue suspension was then admixed with 2.16 kg of a 57% strength aqueous glycolic acid solution and oxidized for 7 hours with 38 1 of air per hour and mole of iron.
The dark-brown suspension was filtered off via a filter press and the solids were washed to a residual filtrate conductivity of 1 mS/cm. The filter cake was dried to a residual moisture of 5% at 70°C in a circulating air drying cabinet and the very hard blackish-brown dried material was coarsely ground to particle sizes up to 2 mm via a roller crusher. The fines content
The product consisted, "according to an x-ray diffractogram("l00% of a-FeOOH. "
From the scanning electron micrograph, for example at a magnification of 60 000:1, the needle widths were determined by measurement between 15 and 20 nm, and the needle lengths were determined between 50 and 80 nm. The particles were highly agglomerated. The specific BET surface area was 202 m2/g. The resultant granules were packed into an adsorber tank directly without further treatment.
The granules exhibited an excellent adsorption behavior for the pollutants present in the water flowing through and exhibited a high adbrastion strength, in particular while the adsorber tank is being backwashed and as a result the granules are highly vortexed. The abrasion value, after 30 minutes, was only 1%.
Adsorption behavior: The adsorption rate with respect to NaAsC>2, at a starting concentration of 2.4 mg (As3+)/l was OW of (As3+)/g(FeOOH)-h, and with
respect to NaiHAsCXt at a starting concentration ofjp^fn^ of (As5+)/l was/2T07 njtg of (As3+)/g(FeOOH)-h.
NaOH solution and simultaneously reoxidized for one hour with 1901 of air. The product was worked up as described in example 2. Finely divided needles of pure a-FeOOH resulted which had a specific BET surface area of 130 m2/g. From the scanning electron micrograph, for example at a magnification of 60 000:1, the needle
widths were detarmi
lengths between 50 and 90 nm. The needles were highly agglomerated. The granules
proved to be very mechanically and hydraulically stable, and the abrasion value was
Adsorption behavior: The adsorption rate with respect to NaAs02, at a starting concentration of 2.3 mg of (As3+)/l was 1.1 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAs04 at a starting concentration of 2.8 mg of (As5+)/l was 1.7 mg of (As3+)/g(FeOOH)-h.
306 1 of an aqueous NaOH solution (45 g/1) were charged at 31°C and, with stirring, were rapidly admixed with 43 1 of an aqueous FeCl2 solution (344 g/1) and then oxidized with 601 of air per hour and mole of Fe. The resultant dark-yellow suspension was worked up as described in example 1.
According to the x-ray diffractogram, the product consisted\100% of a-FeOOH. From the scanning electron microgram, for example at an enlargement of 60 000:1, the needle widths were determined by measurement between 15 and 50 nm, and the
needle lengths between 100 and 200 nm. The needles were highly agglomerated. The
specific BET surface area was 132 mVg.
The resultant granules were packed without further treatment into an adsorber tank. The granules displayed an excellent adsorption behavior for the pollutants present in the water and displayed a high abrasion strength, in particular while the adsorber
tank is being backwashed and as a result the granules are highly vortexed. The abrasion value after 30 minutes was only 12% by weight.
Adsorption behavior: The adsorption rate with respect to NaAs02 at a starting concentration of 2.4 mg of (As3+)/l was 2.11 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAs04 at a starting concentration of 2.7 mg of (As5+)/l was 2.03 mg of (As5+)/g(FeOOH)-h.
1241 of an aqueous NaOH solution (114 g/1) were charged at 24°C and, with stirring, were rapidly mixed with 1711 of an aqueous solution of FeS04 (100 g/l) and then oxidized with 10 1 of air per hour and mole of Fe. Immediately after oxidation was complete, 561 of an aqueous solution of Fe2(SC>4)3 (100 g/l) were added and the mixture was stirred for 30 minutes. The resultant yellowish-brown suspension was worked up as in example 1.
According to the x-ray diffractogram, the product consisted \100% of oc-FeOQ
From the scanning electron microgram, for example at an enlargement of 60 000:1, the needle widths were determined by measurement between 15 and 35 nm, and the needle lengths between 70 and 180 nm. The needles were highly agglomerated. The specific BET surface area was 131 m /g. The abrasion value after 30 minutes was only 7% by weight.
Adsorption behavior: The adsorption rate with respect to NaAs02 at a starting concentration of 2.3 mg of (As3+)/l was 1.7 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAsC>4 at a starting concentration of 2.7 mg of (As5+)/l was 1.2 mg of (As5+)/g(FeOOH)-h.
7905 kg of FeSO4 were charged, dissolved with water to a volume of 53.3 m3, the solution was cooled to 14°C and this solution admixed with 1000 kg of MgS04-7 H20. This charge was then diluted at 14°C with 5056 kg of NaOH as a solution of approximately 300 g/1; and then oxidized with 4000 m3/h of air up to a degree of precipitation > 99.5%. The batch was washed on a filter press to a residual filtrate conductivity of Adsorption behavior: The adsorption rate with respect to NaAsCh at a starting concentration of 2.5 mg of (As3+)/l was 1.8 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAs04 at a starting concentration of 2.9 mg of (As5+)/l was 1.5 mg of (As5+)/g(FeOOH)-h.
4096 kg of NaOH were charged (as a solution of approximately 300 g/1) and diluted with water to 40 m3. 4950 kg of FeS04 are diluted with water to give a solution of 48.5 m3, cooled to 15°C and then pumped in 1 h to the NaOH charge. The suspension was then oxidized with 1500 m3/h of air in approximately 2 h. Approximately 2 m3 of the seed suspension was washed on a filter press to a filtrate conductivity of
fraction Adsorption behavior: The adsorption rate with respect to NaAsC>2 at a starting concentration of 2.7 mg of (As3+)/l was 1.7 mg of (As3+)/g(FeOOH>h, and with respect to Na2HAs04 at a starting concentration of 2.8 mg of (As5+)/l was 1.4 mg of (As5+)/g(FeOOH)-h.
1600 g of the alkaline seed suspension synthesized as in example 7 (2.7% FeOOH) were admixed at room temperature with stirring with an aqueous solution of FeSC>4 (100 g/1) with simultaneous aeration with 1301/h of air to pH 8. The resultant seed suspension was filtered and washed, and the filter cake was dried at 75 °C and coarsely ground as in example 7 to particle sizes between 0.5 and 2 mm. The resultant material had a specific BET surface area of 163 m /g and, according to the x-ray diffractogram, consisted/100% of a-FeOOH. fjj±>m the scanning electron micrograph, for example at an enlargement of 60 000:1, it could be seen that the needles were highly agglomerated. Adsorption behavior: The adsorption rate with respect to NaAsC>2 at a starting concentration of 2.7 mg of (As3+)/l was 2.0 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAsC>4 at a starting concentration of " 2.7 mg of (As5+)/l was 1.9 mg of (As5+)/g(FeOOH)-bfTn the case of KSb(OH)6 (starting concentration 3.0 mg of (Sb5+)/l), the adsorption was 2.5 mg of (Sb5+)/g(FeOOH)-h, and with respect to Na2Cr04 (starting concentration 47 jLXg of | (Cr6*)/!), 42 ng of (Cr6+)/g(FeOOH)-h were adsorbed, and in the case of PbCl2 (starting concentration 0.94 mg of (Pb2+)/l, 0.46 mg of (Pb2+)/g(FeOOH)-h were
6.41 of an aqueous solution of NaOH (100 g/1) were charged at 29°C with stirring and were admixed with simultaneous feed of air with 12.21 of an aqueous iron(U) sulfate solution (100 g/1) to pH 9. The resultant suspension was worked up as in example 1. The material had a specific BET surface area of 251 m2/g and consisted, according to the x-ray diffractogram, 100%of a-FepJOHHbrthe scanning electron micrograph short stumpy needles may be observed which are highly agglomerated. Abrasion behavior: 5%.
Adsorption behavior: The adsorption rate with respect to NaAs02 at a starting concentration of 2.7 mg of (As3+)/J was 1.1 mg of (As3+)/g(FeOOH)-h, and with respect to Na2HAsO4 at a starting concentration of 2.7 mg of (As3+)/l was 1.0 mg of (As5+)/g(FeOOH)-h.
4096 kg of NaOH (as a solution containing approximately 300 g/1) were charged and diluted with water to 40 m3. 4950 kg of FeS04 are dissolved with water to give a solution of 48.5 m3, cooled to 15°C and then pumped in 1 h to the NaOH charge. The suspension was then oxidized in approximately 2 h with 1500 m3/h of air. Approximately 87 m3 of this suspension were admixed with stirring with 14.4 m3 of FeClS04 solution (113.4 g/1) and stirred for a further 30 min. The batch was washed on a filter press to a residual filtrate conductivity of
50 nm, and the needle lengths between 10 and 150 nm. The needles were highly agglomerated.
Adsorption behavior: The adsorption rate with respect to NaAs02 at a starting concentration of 2.7 mg of (As3+)/l was 2.1 mg of (As3+)/g(FeOOH)-h, and with respect to NaaHAsO^ at a starting concentration of 2.8 mg of (As5+)/l was 2.0 mg of (As5+)/g(FeOOH)-h,Wth respect to CdCl2 (starting concentration 2.7 mg of (Cd2+)/l) the adsorption was 1.1 mg of (Cd2+)/g(FeOOH)-h, with respect to KSb(OH)6 (starting concentration 2.6 mg of (Sb5+)/l), it was 1.9 mg of (Sb5+)/g(FeOOH)-h, with respect to Sb2C>3 (starting concentration 2.3 mg of (Sb3+)/l) it was 2.0 mg of (Sb3+)/g(FeOOH)-h, with respect to Na2Cr04 (starting concentration 2.6 mg of (Cr6+)/l) it was 1.1 mg of (Cr6+), with respect to PbCb (starting concentration 1.6 mg \ of (Pb2+)/l it was 1.57 mg of (Pb2+)/g(FeOOH)-h. ~"~^
11 of a suspension of Bayferrox 920 having a solids content of 50 g/1 of FeOOH was admixed with 569 ml of an MgS04 solution (100 g/l), then admixed with stirring with 173 g of a 24% strength NaOH solution and stirred for a further 15 min.
The yellow suspension was washed on a vacuum filter to a residual filtrate conductivity of 1 mS/cm, and the filter cake was dried at 75 °C in a drying cabinet with a residual moisture of The product, according to the x-ray diffractogram, consists of a-FeOOH and Mg(OH)2. From the scanning electron micrograph, for example at a magnification of 60 000:1, it may be seen that the needles of the a-FeOOH type of amorphous layers
are stuck to one another or agglomerated. The specific BET surface area was 43 m /e
and has thus more than doubled, compared with Bayferrox 920 (BET approximately 15 m2/g). The abrasion value after 30 minutes was only 11%.
The adsorption rate with respect to an aqueous NaAs02 solution at a starting concentration of 2.6 mg of (As3+)/l was 1.2 mg of (As3+)/g(FeOOH)-h, and with respect to an Na2HAs04 solution at a starting concentration of 2.7 mg of (As5+)/l was 1.5 mg of (As5+)/g(FeOOH)-h.
950 g of a suspension of an alkaline nanoparticulate seed of oc-FeOOH (solids content: 5.26 g/1 of FeOOH, 1.14% NaOH) were admixed with stirring with 46 ml of an Al2(S04)3 solution (100 g/1 of AI2O3) and stirred for a further 15 minutes. The brown suspension was washed on a vacuum filter to a residual filtrate conductivity of
1 mS/cm, and the filter cake was dried at 75 °C in a drying cabinet to a residual moisture of 2 mm and the granules were used for adsorbing arsenic.
In the x-ray diffractogram of the product, only^a-FeOOH was detected/which, as may be seen from the scanning electron micrograph, is present as very short and highly agglomerated needles. The specific BET surface area was 102 m7g. The abrasion value after 30 minutes was only 5%.
The adsorption rate with respect to an aqueous NaAsOj solution at a starting concentration of 2.6 mg of (As3+)/l was 2.0 mg of (As3+)/g(FeOOH)-h, and with respect to an Na2HAs04 solution at a starting concentration of 2.1 mg of (As +)/l was 1.5 mg of (As5+)/g(FeOOH)-h.
3100 kg of NaOH (as a solution of 100 g/1) were charged into a stirred tank and \ diluted with cold water to 31 m3. The temperature of this NaOH solution was 26°C.
3800 kg of FeS&t are dissolved with water to give 38 m3 of solution, cooled to 13-14°C and then, with stirring, pumped in 40 min to the NaOH charge. The resultant suspension was then oxidized with stirring with 2500 m3/h of air in 75 min.
Then, 18.2 m3 of an FeS04 solution (100 g/l) are added at 1501/min with aeration with 1300 m3/h of air with stirring.
The seed suspension was washed on a filter press to a filtrate conductivity of The product, according to the x-ray diffractogram, consisted of 100% cc-FeOOH. From the scanning electron micrograph, for example at an enlargemenToT"6"01)00:l, the needle widths were determined by measurement between 15 and 35 nm, and the needle lengths were between 50 and 300 nm. The particles were highly agglomerated. The specific BET surface area was 145 m2/g. The abrasion value after 30 min was only 5.1 % by weight.
Illustrative embodiment 14
Adsorber granules synthesized according to examples 1-13, typically between 0.5 and 2 mm, or in comminuted form, are introduced into a contact chamber shown according to fig. 1 or 2. The filtration unit has a flow rate for air as fluid of 2000 ml per minute at a pressure difference of 0.1 bar.
1. Filtration units suitable for the through-flow of media for the removal of
contaminants from fluids, consisting of a cartridge housing (4), which
comprises a vessel having a centrally positioned inlet pipe (6), flat filter layers
(3), (10) facing one another on the front, a cover ensuring the inflow (1) and
outflow (12) of the fluid to be cleaned, together with a base part (9),
characterized in that the filter cartridge housing (4) contains a bed of
agglomerates of fine-particle iron oxide and/or iron oxyhydroxide in pellet form,
where said fine-particle iron oxide and/or iron oxyhydroxide in pellet form are
prepared with a strong base, whereby the fine-particle iron oxide and/or iron
oxyhydroxide displays a BET surface area of 50 to 500 m2/g, preferably 80 to
200 m2/g, and an abrasion value of from 1 to 12 %, the agglomerates can
optionally contain iron oxide pigments with BET surface areas below the above
limits, whereby the maximum content of these is such that the resistance of
the charge to the forces exerted upon it by the flowing medium is sufficiently
great that the stress exerted on the charge by the flowing medium does not
lead to an undesirable abrasion of the charge material, such that in accordance
with requirements the fluid to be cleaned leaves the feed nozzle (1), the inlet
pipe (6), the strainer basket (7), any filter material (8) in the base chamber (9),
the lower fritted plate (10), followed by the adsorbent material (5) in the contact
chamber (4), the upper fritted plate (3), the cover chamber with filter material
(2) and then the outlet pipe (12) via the discharge nozzle.
2. Filtration unit as claimed in claim 1, wherein the housing chamber (4) can be separated from the cover (13) and/or from the base part (9) by means of a plug-in or screw fitting.
3. Filtration unit as claimed in claims 1 to 2, wherein the inlet pipe can be removed from the cartridge housing.
|Indian Patent Application Number||295/MUMNP/2003|
|PG Journal Number||12/2008|
|Date of Filing||11-Mar-2003|
|Name of Patentee||BAYER AKTIENGESELLSCHAFT|
|Applicant Address||D-51368 LEVERKUSEN, GERMANY|
|PCT International Classification Number||C01G49/02|
|PCT International Application Number||PCT/EP01/10930|
|PCT International Filing date||2001-09-21|