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  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/0203—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04
  • B01J20/0225—Compounds of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt
  • B01J20/0229—Compounds of Fe
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  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
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  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
  • B01J20/08—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04 comprising aluminium oxide or hydroxide; comprising bauxite
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  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
  • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
  • B01J20/2803—Sorbents comprising a binder, e.g. for forming aggregated, agglomerated or granulated products
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
  • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J20/28057—Surface area, e.g. B.E.T specific surface area
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/3028—Granulating, agglomerating or aggregating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/0018—Mixed oxides or hydroxides
  • C01G49/0036—Mixed oxides or hydroxides containing one alkaline earth metal, magnesium or lead
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  • C01G49/0018—Mixed oxides or hydroxides
  • C01G49/0045—Mixed oxides or hydroxides containing aluminium
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  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
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  • C01G49/02—Oxides; Hydroxides
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  • C01G49/06—Ferric oxide [Fe2O3]
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  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
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  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/288—Treatment of water, waste water, or sewage by sorption using composite sorbents, e.g. coated, impregnated, multi-layered
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
  • B01D2253/10—Inorganic adsorbents
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
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  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01P2004/50—Agglomerated particles
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  • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
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  • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
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  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
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  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/002—Construction details of the apparatus
  • C02F2201/006—Cartridges

Definitions

• the present invention relates to particles, pellets or granules of fine-particle or nanoparticle iron oxides and/or iron oxyhydroxides having a large specific surface area (50 to 500 m 2 /g according to BET), and processes for their production.
• These pellets have high mechanical resistance and can be used as a contact, adsorbent, or catalyst for the catalysis of chemical reactions, for the treatment of fluid media like liquids and/or for gas, specifically the removal of impurities.
• Adsorbents/catalysts containing iron oxides and hydroxides can advantageously be used e.g. in the area of water purification or gas purification.
• this agent is used in horizontal- or vertical-flow filters or adsorber columns or added to the water to be treated in order to remove dissolved, suspended or emulsified organic or inorganic phosphorus, arsenic, antimony, sulfur, selenium, tellurium, beryllium, cyano and heavy metal compounds from, for example, drinking water, process water, industrial and municipal waste water, mineral, holy and medicinal water as well as garden pond and agricultural water. It can also be used in so-called reactive walls to separate the cited contaminants from ground water and seepage water aquifers from contaminated sites (waste disposal sites).
• the agent is used in adsorbers for binding undesirable components such as hydrogen sulfide, mercaptans and hydrogen cyanide, as well as other phosphorus, arsenic, antimony, sulfur, selenium, tellurium, cyano and heavy metal compounds in waste gases. Gases such as HF, HCl, H 2 S, SO x , NO x can also be adsorbed.
• DE-A 3 120 891 describes a process in which a filtration is performed using activated alumina with a grain size of 1 to 3 mm for the separation principally of phosphates from surface water.
• DE-A 3 800 873 describes an adsorbent based on porous materials such as e.g. hydrophobed chalk with a fine to medium grain size to remove contaminants from water.
• DE-A 3 703 169 discloses a process for the production of a granulated filter medium to treat natural water.
• the adsorbent is produced by granulating an aqueous suspension of kaolin with addition of powdered dolomite in a fluidised bed. The granules are then baked at 900 to 950° C.
• a process for the production and use of highly reactive reagents for waste gas and waste water purification is known from DE-A 40 34 417. Mixtures consisting of Ca(OH) 2 with additions of clays, stone dust, entrained dust and fly ashes, made porous and having a surface area of approx. 200 m 2 /g, are described here.
• the cited processes have the disadvantage that the component responsible in each case for the selective adsorption of constituents of the media to be cleaned, in other words the actual adsorbent, must be supplemented with large quantities of additives to enable it to be shaped into granules. This significantly reduces the binding capacity for the water contaminants to be removed. Moreover, subsequent reprocessing or reuse of the material is problematic since the binder substances first have to be separated out.
• DE-A 4 214 487 describes a process and a reactor for the removal of impurities from water.
• the medium flows horizontally through a funnel-shaped reactor, in which finely divided iron hydroxide in flocculent form is used as a sorption agent for water impurities.
• the disadvantage of this process lies in the use of the iron hydroxide in flocculent form, which means that because there is little difference in density between water and iron hydroxide, a reactor of this type can be operated at only very low flow rates and there is a risk of the sorption agent, which is possibly already loaded with contaminants, being discharged from the reactor along with the water.
• JP-A 55 132 633 describes granulated red mud, a by-product of aluminium production, as an adsorbent for arsenic. This consists of Fe 2 O 3 , Al 2 O 3 and SiO 2 . No mention is made of the stability of the granules or of the granulation process.
• a further disadvantage of this adsorbent is the lack of consistency in the composition of the product, its unreliable availability and the possible contamination of the drinking water with aluminium. Since aluminium is suspected of encouraging the development of Alzheimer's Disease, contamination with this substance in particular is to be avoided.
• DE-A 19 826 186 describes a process for the production of an adsorbent containing iron hydroxide.
• An aqueous polymer dispersion is incorporated into iron hydroxide in water-dispersible form. This mixture is then either dried until it reaches a solid state and the solid material then comminuted mechanically to the desired shape and/or size or the mixture is shaped, optionally after a preliminary drying stage, and a final drying stage then performed, during which a solid state is achieved.
• a material is obtained in which the iron hydroxide is firmly embedded in the polymer and which is said to display a high binding capacity for the contaminants conventionally contained in waste waters or waste gases.
• the disadvantage of this process lies in the use of organic binders, which further contaminate the water to be treated due to leaching and/or abrasion of organic substances. Furthermore, the stability of the adsorbent composite is not guaranteed in extended use. Bacteria and other microorganisms can also serve as a nutrient medium for an organic binder, presenting a risk that microorganisms may populate the contact and thereby contaminate the medium.
• DE-A 4 320 003 describes a process for the removal of dissolved arsenic from ground water with the aid of colloidal or granulated iron hydroxide. Where fine, suspended iron(III) hydroxide products are used, it is recommended here that the iron hydroxide suspension be placed in fixed-bed filters filled with granular material or other supports having a high external or internal porosity. This process likewise has the disadvantage that, relative to the adsorbent “substrate+iron hydroxide”, only low specific loading capacities are achievable. Furthermore, there is only a weak bond between substrate and iron hydroxide, which means that there is a risk of iron hydroxide or iron arsenate being discharged during subsequent treatment with arsenic-containing water.
• This publication also cites the use of granulated iron hydroxide as an adsorption material for a fixed-bed reactor.
• the granulated iron hydroxide is produced by freeze conditioning (freeze drying) of iron hydroxide obtained by neutralisation of acid iron(III) salt solutions at temperatures of below minus 5° C.
• This production process is extremely energy-intensive and leads to heavily salt-contaminated waste waters.
• this production process only very small granules with low mechanical resistance are obtained.
• this means that the size spectrum is significantly reduced by mechanical abrasion of the particles during operation, which in turn results in finely dispersed particles of contaminated or uncontaminated adsorption agent being discharged from the reactor.
• a further disadvantage of these granules lies in the fact that the adsorption capacity in respect of arsenic compounds is reduced considerably if the granules lose water, by being stored dry for extended periods for example.
• Adsorbent/binder systems obtained by removing a sufficiently large amount of water from a mixture of (a) a crosslinkable binder consisting of colloidal metal or non-metal oxides, (b) oxidic adsorbents such as metal oxides and (c) an acid such that components (a) and (b) crosslink to form an adsorbent/binder system, are known from U.S. Pat. No. 5,948,726. According to the disclosure, colloidal alumina or aluminium oxide is used as binder.
• compositions lie in the need to use acid in their production (column 9, line 4) and in the fact that they are not pure but heterogeneous substances, which is undesirable both for the production, regeneration, removal and permanent disposal of such adsorbents, e.g. on a waste disposal site.
• scope of disclosure of this publication is also intended to include adsorbents that are suitable for the adsorption of arsenic; specific examples are not provided, however. Aluminium oxide is known to be significantly inferior to iron oxides in regard to force of adsorption for arsenic.
• Continuous adsorbers which are commonly grouped together in parallel for operation, are preferably used for water treatment.
• such adsorbers are filled with activated carbon.
• the available adsorbers are then operated in parallel to prevent the flow rate from rising above the upper limit permitted by the particular arrangement.
• individual adsorbers are taken out of operation and can be serviced, for example, whereby the adsorption material is subjected to special loads, as described in greater detail below.
• the use of such materials in adsorbers, for example, particularly continuous models, for water purification is therefore of only limited interest.
• the abraded material renders the waste water from back-flushing extremely turbid. This is unacceptable for a number of reasons: firstly, adsorption material, which is heavily laden with impurities and therefore toxic after extended use, is lost.
• the stream of waste water is laden with abraded material, which can sediment, damaging piping systems and ultimately subjecting the waste treatment plant to undesirable physical and toxicological stresses, to name but a few reasons.
• the abrasion should be below 20% by weight, more preferably below 15% by weight, 10% by weight or most preferably below 5% by weight according to the method described in the examples of the present invention.
• An object of the present invention was therefore to provide a contact or an adsorbent/catalyst based on iron-oxygen compounds in pellet form, exhibiting high mechanical resistance in conjunction with a good binding capacity for contaminants contained in liquids and gases without the need to use organic binders or inorganic foreign binders to achieve adequate mechanical resistance, and plants operated with such media.
• This object is achieved by the contacts or adsorbents/catalysts according to the invention, their preparation, their use and the units filled therewith.
• the invention relates to a unit suitable for the through-flow of a fluid medium at least partially filled with particles agglomerated from fine-particle iron oxide and/or iron oxyhydroxide, wherein the fine-particle iron oxide and/or iron oxyhydroxide displays a particle size of up to 500 nm and a BET surface area of 50 to 500 m 2 /g.
• the invention also relates to a process for the production of particles from fine-particle iron oxide and/or iron oxyhydroxide comprising the steps of producing an aqueous suspension of fine-particle iron oxides and/or iron oxyhydroxides having a BET surface area of 50 to 500 m 2 /g, and removing the water and dissolved constituents by either I) a) first removing only the water from the suspension, b) introducing the residue thus obtained in water, c) filtering the material obtained, d) washing the residue, and e) either e1) completely dehydrating the filter cake obtained as residue and comminuting the material thus obtained to the desired shape and/or size or e2) partially dehydrating the filtercake to obtain a paste, shaping the paste and subsequently additionally drying the paste until a pellet is obtained, or II) a) filtering the suspension, b) washing the residue, c) either c1) completely dehydrating the filter cake obtained as residue in the form of a solid to semisolid paste and then
• an aqueous suspension of fine-particle iron oxyhydroxides and/or iron oxides is first produced according to the prior art.
• the water and constituents dissolved within it can be removed from this in two different ways:
• the suspension is filtered and the residue washed until it is substantially free from salts.
• the filter cake obtained as residue is a solid to semisolid paste. This can then be completely or partially dehydrated, and the material thus obtained can then be comminuted to the desired shape and/or size.
• the paste or filter cake optionally after predrying to achieve a sufficiently solid state, can undergo shaping followed by (additional) drying until a pellet state is achieved.
• the subsequent application of the granules determines the preferred procedure to be followed for their production, which can be determined by the person skilled in the art in the particular field of application by means of simple preliminary orienting experiments. Both the directly dried filter cake and the dried shaped bodies can then be used as contact or adsorbent.
• the products obtained according to method 1 are less mechanically resistant, filtration can be performed more easily and quickly.
• the fine-particle pigments isolated in this way can moreover be incorporated very easily into paints and polymers, for example, because considerably less shear force is required than is needed to incorporate the fine-particle pigments obtained according to method 2.
• the fine-particle iron oxide and/or iron oxyhydroxide 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 m 2 /g, preferably 80 to 200 m 2 /g.
• the primary particle size was determined by measurement from scanning electron micrographs, e.g. at a magnification of 60000:1 (instrument: XL30 ESEM FEG, Philips). If the primary particles are needle-shaped, as in the ⁇ -FeOOH phase for example, the needle width can be given as a measurement for the particle size. Needle widths of up to 100 nm, but mainly between 4 and 50 nm, are observed in the case of nanoparticle ⁇ -FeOOH particles. ⁇ -FeOOH primary particles conventionally have a length:width ratio of 5:1 to 50:1, typically of 5:1 to 20:1. The length:width ratio of the needle shapes can be varied, however, by doping or by special reaction processes. If the primary particles are isometric, as in the ⁇ -Fe 2 O 3 , ⁇ -Fe 2 O 3 , Fe 3 O 4 phases for example, the particle diameters can quite easily also be below 20 nm.
• Products obtainable by methods 1) and 2) can then be comminuted further, for example by rough grinding or grinding. However, since the products reduce in size on first coming into contact with water, for example when a freshly charged adsorber unit is first filled with water, this will generally be unnecessary.
• Granulation of a semi-wet paste has proven effective as another method of producing granules.
• pellets or strands are formed from a semi-wet paste, e.g. using a simple perforated metal sheet, a roll press or an extruder, and either dried immediately or additionally shaped into a spherical or granular form by means of a spheroniser.
• the still wet spherules or granules can subsequently be dried to any moisture content whatsoever.
• a residual moisture content of ⁇ 50% is recommended to prevent the granules from agglomerating.
• a spherical shape of this type can be advantageous for use in fixed-bed adsorbers due to the improved packing in the adsorber vessel that is obtained in comparison with rough-ground granules or pellets in strand form.
• the filtration performance of the suspensions can generally be improved by the use of conventional filtration-improving measures, 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 in Handbuch der Industriellen Fest/Flüssig-Filtration, H. Gasper, D. ⁇ chsle, E. Pongratz, 2nd edition 2000, Wiley-VCH Weinheim. Coagulants can thus be added to the suspensions, for example.
• Iron carbonates can also be used in addition to or in place of the iron oxyhydroxides.
• the products according to the invention can undergo drying in air, and/or in vacuo, and/or in a drying oven and/or on belt dryers or by spray drying, preferably at temperatures from ⁇ 25 to 250° C., particularly preferably at 60 to 120° C.
• the products according to the invention preferably have a residual water content of less than 20 wt. %.
• pellets or granules obtained in this way have a high binding capacity for contaminants contained in water, liquids or gases and they additionally have an adequately high resistance to flowing media in terms of mechanical or hydraulic stressing.
• Transparent iron oxyhydroxide pigments for example, having an average particle size of less than 0.1 ⁇ m and specific surface areas of greater than 80 m 2 , are suitable for the use according to the invention of fine-particle iron oxyhydroxides.
• fine-particle iron oxide pigments preferably haematite, magnetite or maghemite, can also be used, however.
• the production of yellow fine-particle iron oxyhydroxide pigments (e.g. goethite) in the acid or alkaline pH range, known as acid or alkaline nuclei, is known.
• the production of other fine-particle iron oxide or iron oxyhydroxide pigments is also known.
• Such pigments can contain structures based on ⁇ , ⁇ , ⁇ , ⁇ , ⁇ ′, ⁇ phases and/or Fe(OH) 2 and mixed and intermediate phases thereof.
• Fine-particle yellow iron oxyhydroxides can be calcined to fine-particle red iron oxides.
• Fine-particle yellow iron oxyhydroxide pigments are generally synthesized by precipitating iron(II) hydroxides or carbonates from corresponding iron(II) salt solutions such as e.g. FeSO 4 , FeCl 2 in pure form or as pickling solutions in the acid or alkaline pH range, followed by oxidation to iron(III) oxyhydroxides (see inter alia G. Buxbaum, Industrial Inorganic Pigments, VCH Weinheim, 2nd edition, 1998, p. 231ff). Oxidation of the divalent to the trivalent iron is preferably performed with air, whereby intensive aeration is advantageous. Oxidation with H 2 O 2 also leads to fine-particle iron oxyhydroxides.
• iron(II) salt solutions such as e.g. FeSO 4 , FeCl 2 in pure form or as pickling solutions in the acid or alkaline pH range
• Oxidation of the divalent to the trivalent iron is preferably performed with air, whereby intensive aeration
• the temperature chosen for precipitation and oxidation should be as low as possible in order to obtain very fine-particle yellow pigments. It is preferably between 15° C. and 45° C.
• NaOH is preferably used as alkaline precipitant.
• Other precipitants such as KOH, Na 2 CO 3 , K 2 CO 3 , CaO, Ca(OH) 2 , CaCO 3 , NH 3 , NH 4 OH, MgO and/or MgCO 3 , can also be used, however.
• nanoparticle ⁇ , ⁇ , ⁇ , ⁇ phases and mixed phases of iron oxyhydroxides displaying a large specific surface area can be prepared, such that the nanoparticles agglomerate in the dry state and possess a high resistance to mechanical and fluid-mechanical abrasion in comminuted form.
• the precipitations e.g. of yellow ⁇ -FeOOH as described in patents U.S. Pat. No. 2,558,303 and U.S. Pat. No. 2,558,304, are performed in the alkaline pH range with alkali carbonates as precipitants, and modifiers such as SiO 2 , zinc, aluminium or magnesium salts, hydroxycarbonic acids, phosphates and metaphosphates are generally added. Products produced in this way are described in U.S. Pat. No. 2,558,302. Such nucleus modifiers do not interfere with the subsequent reprocessing, recycling or any other use of the adsorbents according to the invention. In the case of precipitation processes in an aqueous medium, it is known that precipitations in an alkaline environment lead to less solidly agglomerated powders than those in an acid environment.
• nucleus modifiers One of the advantages of nucleus modifiers, however, is that an adequate fine-particle character can be obtained even at elevated reaction temperatures.
• DE-A 4 235 945 reports on the production of fine-particle iron oxides using a precipitation method in the acid 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 produced by secondary treatment thereof with sodium hydroxide solution.
• DE-A 4 434 972 reports on highly transparent, yellow iron oxide pigments in the ⁇ -FeOOH modification having a specific surface area of over 100 m 2 /g and high temperature resistance.
• DE-A 4 434 973 describes highly transparent yellow iron oxide pigments, which are produced by means of the process steps of nuclear precipitation in the acid pH range, nuclear oxidation, nuclear maturation and pigment formulation.
• Red, transparent iron oxide pigments obtained by calcining from yellow, transparent iron oxide pigments are known from DE-A 4 434 668 and DE-A 4 235 946.
• Drying is conveniently performed at temperatures of up to 250° C.
• the material can also be vacuum or freeze dried.
• the particle size of the material can be freely selected but is preferably between 0.2 and 40 mm, particularly preferably between 0.2 and 20 mm. This can be achieved by shaping the semisolid, pasty filter cake mechanically, before drying, in a granulation or pelletising plant or in an extruder to form shaped bodies whose size is in the range between 0.2 and 20 mm, with subsequent drying in the air, on a belt dryer or in a drying oven, and/or by mechanical comminution to the desired particle size after drying.
• the products described, the process for their production and their use represent an improvement over the prior art.
• the granules according to the invention based on fine-particle iron oxyhydroxides and/or oxides can be subjected to much higher stresses and therefore display a much greater abrasion resistance to mechanical and hydraulic stressing. They can be used directly as such.
• adsorber plants for water purification for example, there is no need even for comminution or rough grinding of the crude dry substance initially obtained from filter cakes or extruders, since the coarse pellets break down independently on contact with water. This results in a random particle-size distribution, but no particles of such a size that they are discharged from the adsorber to any significant extent by the flowing medium.
• the suspensions of fine-particle iron oxyhydroxides or iron oxides can also be supplemented with conventional powdered iron oxyhydroxides or iron oxides.
• the quantities in each case are determined by the properties of these powdered iron oxyhydroxides or iron oxides and by the requirements of the product according to the invention in terms of its mechanical stability and abrasion resistance.
• powdered pigments will generally reduce the mechanical strength of the products according to the invention, filtration of the fine-particle suspensions is made easier.
• the person skilled in the art and practising in the particular field of application will be able to determine the optimum mixing ratio for the intended application by means of a few orienting experiments.
• nanoparticle nuclei are conveniently produced in an excess of sodium hydroxide solution.
• a quantity of Fe 2 (SO 4 ) 3 corresponding to the NaOH excess can also be added to the suspensions of the alkaline fine-particle nuclei. This measure considerably improves the filterability of the suspension.
• the initially amorphous Fe(OH) 3 produced matures over time, to the ⁇ -FeOOH phase, for example. This ensures that the sodium hydroxide solution used in excess to produce the alkaline nucleus is completely used up.
• the material thus obtained also displays large specific surface areas. Just like the iron oxyhydroxides described above, the material is extremely suitable for use in adsorbers since it possesses a high resistance to mechanical loading in addition to a high adsorption capacity.
• the granules according to the invention are particularly preferably used in the cleaning of liquids, especially for the removal of heavy metals.
• a preferred application in this industrial field is the decontamination of water, particularly of drinking water. Particular attention has recently been paid to the removal of arsenic from drinking water.
• the granules according to the invention are extremely suitable for this purpose, since levels that not only meet but actually fall below even the lowest limiting values set by the US authority the EPA can be achieved using the granules according to the invention.
• the granules can be used in conventional adsorber units, such as are already used with a charge of activated carbon, for example, to remove other types of contaminants.
• Batchwise operation in cisterns or similar containers for example, optionally fitted with agitators, is also possible.
• use in continuous plants such as continuous-flow adsorbers is preferred.
• adsorbents Since untreated water to be processed into drinking water conventionally also contains organic impurities such as algae and similar organisms, the surface of adsorbents, especially the outer surface of granular adsorbents, becomes coated during use with mostly slimy deposits, which impede or even prevent the inflow of water and hence the adsorption of constituents to be removed. For this reason adsorber units are periodically back-flushed with water, a process which is preferably performed at times of low water consumption (see above) on individual units that have been taken out of service. The adsorbent is whirled up and the associated mechanical stress to which the surface is subjected causes the undesirable coating to be removed and discharged against the direction of flow during active operation.
• the wash water is conventionally sent to a sewage treatment plant.
• the adsorbents according to the invention have proven to be particularly effective in this process, since their high strength enables them to be cleaned quickly without suffering any significant losses of adsorption material and without the back-flush water sent for waste treatment being rich in discharged adsorption material, which is possibly already highly contaminated with heavy metals.
• the material is comparatively easy to dispose of after use.
• the adsorbed arsenic can be removed by thermal or chemical means in special units, for example, resulting in an iron oxide pigment as a pure substance which can either be recycled for use in the same application or supplied for conventional pigment applications.
• the content of the adsorber can also be used without prior removal of the heavy metals, for example as a pigment for colouring durable construction materials such as concrete, since the heavy metals removed from the drinking water are permanently immobilised in this way and taken out of the hydrological cycle.
• the invention therefore also provides water treatment plants or waterworks in which units filled with the granules according to the invention are operated, and processes for the decontamination of water by means of such units, as well as such units themselves.
• the sample is baked for 1 h at 140° C. in a stream of dry nitrogen before measurement.
• the As, Sb, Cd, Cr, Hg or Pb contents of the contaminated iron oxyhydroxide or of the solutions are determined using mass spectrometry (ICP-MS) according to DIN 38406-29 (1999) or by optical emission spectroscopy (ICP-OES) according to EN-ISO 11885 (1998), with inductively coupled plasma as excitation agent in each case.
• ICP-MS mass spectrometry
• ICP-OES optical emission spectroscopy
• the mechanical and hydraulic abrasion resistance was assessed using the following method: 150 ml of demineralised water were added to 10 g of the granules to be tested, having particle sizes >0.1 mm, in a 500 ml Erlenmeyer flask, which was rotated on a LabShaker shaking machine (Kühner model from Braun) for a period of 30 minutes at 250 rpm. The >0.1 mm fraction was then isolated from the suspension using a screen, dried and weighed. The weight ratio between the amount weighed out and the amount weighed in determines the abrasion value in %.
• the yellow suspension thus obtained was filtered out through a filter press and the solid washed until the residual filtrate conductivity was 1 mS/cm.
• the filter cake was in the form of a spreadable and kneadable paste, which was dried on metal sheets in a circulating air drying oven at 75° C. until the residual moisture content was 3 wt. %.
• the dried material was then roughly ground to produce particle sizes of between 0.5 and 2 mm.
• the hard pellets thus obtained were then placed directly in an adsorber tank.
• the product consisted of 100% ⁇ -FeOOH with an extremely short-needled habit, whereby the needles were congregated to form solid macroscopic agglomerates.
• the needle widths were measured at between 15 and 35 nm, the needle lengths between 150 and 350 nm.
• the needles were extremely agglomerated.
• the BET specific surface area was 122 m 2 /g.
• the adsorption rate for NaAsO 2 with an original concentration of 2.3 mg (As 3+ )/l was 2.14 mg(As 3+ )/g(FeOOH).h
• Na 2 HAsO 4 with an original concentration of 2.7 mg (As 5+ )/l it was 2.29 mg(As 5+ )/g(FeOOH).h.
• the dark brown suspension was filtered out through a filter press and the solid washed until the residual filtrate conductivity was 1 mS/cm.
• the filter cake was dried at 70° C. in a circulating air drying oven to a residual moisture of 5%, and the very hard blackish brown dry product was roughly ground in a roller crusher to particle sizes of up to 2 mm. The fine fraction ⁇ 0.2 mm was separated out using a screen.
• An X-ray diffractogram showed that the product consisted of 100% ⁇ -FeOOH.
• the needle widths were measured at between 15 and 20 nm, the needle lengths between 50 and 80 nm.
• the particles were extremely agglomerated.
• the BET specific surface area was 202 m 2 /g.
• the granules thus obtained were placed directly in an adsorber tank with no further treatment.
• the granules displayed an excellent adsorption performance in respect of the contaminants contained in the flowing water and demonstrated a high abrasion resistance, particularly when the adsorber tank is being back-flushed causing the granules to be whirled up strongly.
• the abrasion value after 30 minutes was only 1%.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.4 mg (As 3+ )/l was 1.0 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.8 mg (As 5+ )/l it was 2.07 mg(As 3+ )/g(FeOOH).h.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.3 mg/l was 1.1 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.8 mg/l it was 1.7 mg(As 3+ )/g(FeOOH).h.
• An X-ray diffractogram showed that the product consisted of 100% ⁇ -FeOOH.
• the needle widths were measured at between 15 and 50 nm, the needle lengths between 100 and 200 nm.
• the needles were extremely agglomerated.
• the BET specific surface area was 132 m 2 l/g.
• the granules thus obtained were placed in an adsorber tank with no further treatment.
• the granules displayed an excellent adsorption performance in respect of the contaminants contained in the water and demonstrated a high abrasion resistance, particularly when the adsorber tank is being back-flushed causing the granules to be whirled up strongly.
• the abrasion value after 30 minutes was only 12 wt. %.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.4 mg (As 3+ )/l was 2.11 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.7 mg (As 5+ )/l it was 2.03 mg(As 5+ )/g(FeOOH).h.
• An X-ray diffractogram showed that the product consisted of 100% ⁇ -FeOOH.
• the needle widths were measured at between 15 and 35 nm, the needle lengths between 70 and 180 nm.
• the needles were extremely agglomerated.
• the BET specific surface area was 131 m 2 /g.
• the abrasion value after 30 minutes was only 7 wt. %.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.3 mg (As 3+ )/l was 1.7 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.7 mg (As 5+ )/l it was 1.2 mg(As 5+ )/g(FeOOH).h.
• the strands were dried on a belt dryer to a residual moisture of approx. 3%.
• An X-ray diffractogram showed that the product consisted of 100% ⁇ -FeOOH with very short needles.
• the needle widths were measured at between 30 and 50 nm.
• the needle lengths could not be clearly determined as the needles were too greatly agglomerated.
• the BET specific surface area was 145 m 2 /g.
• the abrasion value after 30 minutes was only 6%.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.5 mg (As 3+ )/l was 1.8 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.9 mg (As 5+ )/l it was 1.5 mg(As 5+ )/g(FeOOH).h.
• the material thus obtained had a BET specific surface area of 153 m 2 /g and consisted of 100% ⁇ -FeOOH.
• the needle widths were measured at between 15 and 35 nm, the needle lengths between 50 and 100 nm.
• the needles were extremely agglomerated.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.7 mg (As 3+ )/l was 1.7 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.8 mg (As 5+ )/l it was 1.4 mg(As 5+ )/g(FeOOH).h.
• the suspension was filtered on a filter press and washed until the residual filtrate conductivity was ⁇ 1000 ⁇ S/cm, the paste was pushed through a perforated metal plate and were dried on a belt dryer to a residual moisture of less than 20%.
• the dry pellets were roughly ground to obtain a particle size of less than 2 mm. The portion of the particles with less then 0.5 mm was removed.
• the material thus obtained had a BET specific surface area of 145 m 2 /g and consisted of 100% ⁇ -FeOOH.
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.7 mg (As 3+ )/l was 2.0 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.7 mg (As 5+ )/l it was 1.9 mg(As 5+ )/g(FeOOH).h, for KSb(OH) 6 (original concentration 3.0 mg (Sb 5+ )/l) the adsorption was 2.5 mg (Sb 5+ )/g (FeOOH).h, for Na 2 CrO 4 (original concentration 47 ⁇ g (Cr 6+ )/l) 42 ⁇ g (Cr 6+ )/g(FeOOH).h were adsorbed, for PbCl 2 (original concentration 0.94 mg (Pb 2+ )/l) 0.46 mg (Pb 2+ )/g
• Adsorption performance The adsorption rate for NaAsO 2 with an original concentration of 2.7 mg (As 3+ )/l was 1.1 mg(As 3+ )/g(FeOOH).h, for Na 2 HAsO 4 with an original concentration of 2.7 mg (As 5+ )/l it was 1.0 mg(As 5+ )/g(FeOOH).h.

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