ES2360767T3 - CONTACT GRANULES AND ADSORBENTS. - Google Patents

Abstract

Agglomerates of finely divided iron oxyhydroxide of the α-FeOOH phase in the form of pieces with a grain size of 0.2 to 40 mm, the finely divided iron oxyhydroxide having a BET surface of 50 to 500 m 2 / g.

Description

The present invention relates to iron oxyhydroxide agglomerates of the α-FeOOH phase finely divided into pieces with a grain size of 0.2 to 40 mm, the iron oxyhydroxide finely divided having a BET surface of 50 to 500 m2 / g, to devices containing the aforementioned agglomerate, to a process to produce the agglomerate, as well as to the use of agglomerates and apparatus to purify gases and liquids, such as, in particular, to remove heavy metals such as phosphorus compounds , antimony, beryllium or selenium, tellurium, as well as cyano compounds and water arsenic compounds.

Contact granules and adsorbents, also those that are based on iron oxide and / or iron oxyhydroxide, have already been described. They are mainly used in continuous procedures, usually found in tower or column type apparatus through which the medium to be treated circulates, and chemical or physical reaction or adsorption processes take place on the inner and outer surface of the granules To this end, materials in powder form cannot be used, as they are compacted in the direction of flow of the medium and, thereby, increase the resistance to flow until the apparatus is locked. If a device is cleaned by backwashing (see below), large amounts of dust are discharged or lost, or cause an intolerable load of wastewater.

The circulating means also exert, however, forces on the granules, which can cause abrasion and / or movement until the agitation of the granules is intense. Therefore, the granules collide with each other and, as a consequence, unwanted abrasion wear is generated. This causes a loss of contact material or adsorbent and a contamination of the medium to be treated.

They are advantageously used, for example, in the field of water purification or gas purification, adsorption agents / reaction agents containing iron oxide and iron hydroxide. In the case of water purification, this agent is used in absorbent filters or columns with horizontal or vertical circulation or by adding to the water to be treated for the separation of compounds, organic or inorganic, dissolved, suspended or emulsified phosphorus , arsenic, antimony, sulfur, selenium, tellurium, beryllium, cyanocomposites and heavy metal compounds of drinking water, drinking water, industrial and domestic wastewater, mineral water, holy water and medicinal water, as well as garden pond water and water for agricultural use. It is also possible to use those known as reactive walls for the separation of contaminants from soils and infiltration water pipes from contaminated sites (landfills).

In the case of gas purification, the agent is used in adsorbers for binding to unwanted constituents such as sulfuric acid, mercaptans and cyanhydride acid, as well as phosphorus, arsenic, antimony, sulfur, selenium, tellurium compounds, as well as cyanocomposites and heavy metal compounds in exhaust gases. It is also possible to adsorb gases such as HF, HCl, H2S, SOx, NOx.

It is also possible to eliminate phosphorus, arsenic, antimony, selenium, tellurium compounds, as well as cyano compounds and heavy metal compounds from used oils and other contaminating organic solvents.

Contact granules and adsorbents based on iron oxides and / or iron oxyhydroxides are also used for catalysis of gas or liquid phase chemical reactions.

Methods of different types for removing trace elements and contaminants from aqueous systems using adsorption agents are also known.

Thus, in DE-A 3 120 891 a process is described in which, for the separation, particularly, of surface water phosphates, filtration is carried out through active alumina with a granulation of 1 to 3 mm.

DE-A 3 800 873 describes an adsorption agent based on porous materials such as, for example, hydrophobicized crete with a fine to medium granulation, for the removal of water contaminants.

In DE-A 3 703 169 a process for the manufacture of a granulated filter material for treating natural water is disclosed. The adsorbent is manufactured by granulating an aqueous kaolin suspension with the addition of dolomite in powder form in a fluidized bed. Next, the granules are calcined at 900 to 950 ° C.

From DE-A 40 34 417 a process is known for manufacturing and using reagents with high reactivity for the purification of exhaust gases and wastewater. This document describes mixtures of Ca (OH) 2 with clay additives, rocks in powder, volatile powder and volatile ash, which are manufactured with a porous shape and have an area of approximately 200 m2 / g.

The mentioned procedures or the contact agents used in said document have the general disadvantage that the corresponding components responsible for the selective adsorption of constituents of the media to be purified, that is, the true adsorbents, must be added with high amounts of aggregates, to allow a conformation to granules. This greatly reduces the ability to bond with aqueous contaminants that must be removed. In addition, subsequent processing or reuse of the material is problematic, since the foreign substance used as a binder must first be separated again.

In DE-A 4 214 487 a process and a reactor for removing contaminants from water are described. A funnel-shaped reactor, in which, as a sorbent for aqueous contaminants, iron hydroxide distributed in the form of flakes is used, has a horizontal circulation. The disadvantage in this process is the use of iron hydroxide in flakes, since due to the small difference in density between water and iron hydroxide, it results in a reactor of this type can only operate with flow rates very low and there is a risk that the sorbent, if already loaded with contaminant, is discharged from the reactor along with the water.

JP-A 55 132 633 describes granulated red sludge as a byproduct of aluminum production as an arsenic adsorbent. This is composed of Fe2O3, Al2O3 and SiO2. The stability of the granules and the granulation procedure is not reported in said document. Another disadvantage of these adsorbents is the lack of constancy of the composition of the product, the lack of security of availability and the possible loading with aluminum of the drinking water. Since it is suspected that aluminum favors the onset of Alzheimer's disease, contamination with it should be especially avoided.

A process for manufacturing an adsorption agent containing iron hydroxide is described in DE-A 19 826 186. A polymer dispersion is mixed with iron hydroxide in water in a dispersible form. This mixture dries well, obtaining a solid state, and the solid material is then mechanically ground into the desired shape and / or size or the mixture, if necessary after drying, is subjected to a shaping and, then, it has just dried obtaining a solid state. This results in a material in which iron hydroxide is solidly embedded in the polymer and must have a high binding capacity for contaminants included in wastewater or exhaust gas.

The disadvantage of this procedure is the use of organic binders, which additionally charge the water to be treated by erosion by washing and / or abrasion wear of organic substances. In addition, stability is not guaranteed with the long-term use of the combination of adsorbents. In addition, bacteria and other microorganisms can use an organic binder as a feeding medium, so that there is a risk of colonization of contact with microorganisms and contamination of the medium by them.

Basically, the presence of other auxiliary substances necessary for the manufacture of adsorbents in the processing, recycling or reuse of used adsorbents presents a disadvantage, since the use of pure substances is less problematic than the use of substance mixtures As in this case. Thus, for example, polymeric binders, in the reuse of iron oxide based adsorbent materials such as concrete coloring pigments, have the disadvantage that these binders prevent the dispersion of the pigment in the liquid concrete.

In DE-A 4 320 003 a process for removing arsenic dissolved in groundwater by means of granulated or colloidal iron hydroxide is described. For the use of fine, suspended iron (II) hydroxide products, it is recommended in said document to introduce the iron hydroxide suspension in solid bed filters, which are filled with the granulated material or other vehicles with high external or internal porosity . This procedure also has the disadvantage that, due to the adsorbent "substrate + iron hydroxide", only reduced specific loading capacities can be achieved. In addition, there is only a weak bond between the substrate and iron hydroxide, so that in a subsequent treatment with arsenic-containing water there is a risk of discharging iron hydroxide

or iron arsenate. This publication also mentions the use of granulated iron hydroxide as an adsorbent material for a solid bed reactor. The manufacture of the granulated iron hydroxide is carried out by means of a freezing (lyophilization) conditioning of iron hydroxide obtained by neutralizing acidic solutions of iron (III) salts at temperatures below 5 ° C. This manufacturing process consumes a large amount of energy and generates a wastewater very charged with salts. In addition, as a result of this manufacturing process only very small particles with reduced mechanical stability are obtained. This causes, in the case of using a solid bed reactor, that the particle spectrum by mechanical abrasion of the particles is clearly reduced over the course of the operation, which again has the consequence that the finely dispersed particles are discharge from the reactor with the adsorption agent charged or not charged. Another disadvantage of this granulate is that the adsorption capacity against arsenic compounds is greatly reduced if the granulate, for example, due to a longer drying period, loses water.

From US-A-5,948,726, adsorbent / binder systems have been disclosed which are obtained by extracting from a mixture of (a) a binder capable of cross-linking from metal oxides or metalloids, (b) oxidizing adsorbents as metalloid oxides and (c) an acid a sufficiently large amount of water, so that components (a) and (b) are crosslinked forming an adsorbent / binder system. As shown in the embodiments, an alumina or colloidal aluminum oxide is used as a binder.

The disadvantage of this composition is that for its manufacture it is necessary to use acid (column 9, row 4) as well as the fact that it is not a pure substance, but heterogeneous, which is undesirable for manufacturing, regeneration , disposal or definitive storage of adsorbents of this type, for example, in a landfill. Adsorbents that are suitable for arsenic adsorption should also be included in the scope of the disclosure of this publication, but no concrete examples are presented. It is known that aluminum oxide is clearly inferior with respect to the adsorption strength for arsenic to iron oxides.

For water treatment, adsorbents that operate continuously, which frequently operate in parallel oriented groups, are preferably used. For example, to release water from organic pollutants, adsorbent of this type is fed with activated carbon. At the time of maximum use, the adsorbents present operate in parallel, to allow the flow rate not to exceed the maximum allowed. During periods of reduced water use, the adsorbents are removed separately from the operation and can be kept on hold, meanwhile, for example, by fixing the adsorbent material at special loads, as explained in detail below.

The use of granules has also been considered, which can be generated by compacting, for example, iron oxide in powder form by using high linear forces. Granules of this type have already been described to homogeneously color liquid concrete. The use of high linear forces in compaction consumes a great deal of energy and is expensive and the stability of the compacting is insufficient in case of long-term use of the adsorbent. Therefore, the use of adsorbents of this type is considered, in particular in continuous operation, for example, for water purification, only to a limited extent. In particular, for the maintenance or purification of adsorbent installations by backwashing (see below), granules of this type lose, due to the agitation thereof associated with it, large amounts of substance. The backwash wastewater becomes heavily clouded due to abrasion. This is unacceptable for several reasons: First, adsorbent material is lost, which is heavily loaded with contaminants after a long period of operation and, therefore, is toxicologically worrying. In addition, the wastewater stream is loaded with the material produced by abrasion wear, which can sediment and thus cause a detrimental effect on the conduction system, and finally, the purification facility is physically and undesirably charged. Toxicologically, to mention just a few reasons.

In WO 83/03595, US 4,515,756 and US 4,481,087, amorphous forms of iron oxyhydroxides for the adsorption of tungsten and molybdenum or chromate from aqueous solutions are described, as well as a process for manufacturing them , in which iron salts are precipitated, in particular iron (III) salts, according to the procedure of weak bases such as ammonia.

The present invention is based, therefore, on the objective of providing a contact or adsorption agent / reaction agent based on iron oxyhydroxides of the α-FeOOH phase in the form of pieces having a high mechanical stability together with a high binding capacity with the contaminants included in liquids and gases without the use of organic binders or binders of different inorganic types to obtain sufficient mechanical stability or facilities that work with such means.

The contact or adsorption agents / reaction agents according to the invention, their provision, their use, as well as the apparatus that is fed with them, solve this objective complex.

To manufacture the agglomerate according to the invention, an aqueous suspension of iron oxyhydroxides of the α-FeOOH phase is first prepared in which iron (II) hydroxides are precipitated from the corresponding solutions of iron (II) salts with an excess of Sodium hydroxide and then oxidize, and then remove water and substances dissolved in it in two different ways.

Procedure 1:

For applications where few requirements have been established on the mechanical stability of the granulate / contact agent, only water is removed first, for example by evaporation. A residue is obtained, which contains, in addition to the finely divided iron oxide and / or hydroxide, also the total salt charge. This residue is dispersed in water after drying, for which only relatively low shear force should be applied. This suspension is then filtered, and the residue is washed until it is essentially free of salts. The filter cake obtained as a residue is a solid to semi-solid paste that generally contains a water content of between 10 and 90% by weight.

The water can then be removed totally or partially and the material obtained in this way can then be crushed in the desired shape and size. Alternatively, the filter cake or cake, if necessary after a pre-drying process with which a sufficiently solid state is obtained for this, can be subjected to shaping and then drying (additional), obtaining a sticky state. The subsequent application of the granulate determines the preferred method of proceeding for its manufacture, which can be determined by the expert in the corresponding sector of application by means of simple pre-directed tests. Both the filter cake, directly, and dried molded bodies can be used as a contact agent or adsorbent.

Procedure 2:

For applications where high demands have been established on the mechanical stability of the granules / contact agents, the suspension is filtered and the residue is washed until it is essentially free of salts. The filter cake obtained as a residue is a solid to semi-solid paste. The water can then be removed totally or partially and the material obtained in this way can then be crushed in the desired shape and size. Alternatively, the filter cake or cake, if necessary after a pre-drying process with which a sufficiently solid state is obtained for this, can be subjected to shaping and then drying (additional), obtaining a sticky state. The subsequent application of the granulate determines the preferred method of proceeding for its manufacture, which can be determined by the expert in the corresponding sector of application by means of simple pre-directed tests. Both the filter cake, directly, and dried molded bodies can be used as a contact or adsorbent.

The products obtained according to procedure 1 are certainly less mechanically stable, however, filtration is easier and faster to perform. In addition, finely divided pigments isolated in this way can be easily incorporated into, for example, varnishes or polymers, because for them a significantly lower shear force is needed than is necessary for the incorporation of finely divided pigments according to procedure 2 .

The finely divided iron hydroxide 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 of 50 to 500 m2 / g, preferably 80 to 200 m2 / g.

The primary particle size was determined by measurements by scanning with the scanning electron microscope, for example, with an increase of 60000: 1 (apparatus: XL30 ESEM FEG, Philips company). If the primary particles are needle-shaped, such as, for example, in the α-FeOOH phase, the width of the needle can be indicated as a measure of particle size. A needle width of 100 nm is observed for α-FeOOH nanoparticles, however, mainly between 4 and 50 nm. The α-FeOOH primary particles usually have a length: width ratio of 5: 1 to 50: 1, typically 5: 1 to 20: 1. By endowment or a special embodiment of the reaction, however, the length: width ratio of the needle shapes can be varied.

The products that can be obtained according to procedures 1 and 2 can, for example, be further shredded by grinding or grinding. Because the product, however, crumbles autogenously on its first contact with water, for example when a freshly fed adsorption apparatus is filled with water for the first time, this is generally not necessary.

Like other procedures for manufacturing granules, granulation of a semi-wet paste has given a good result. In this regard, pellets or skeins are formed from a semi-solid paste, for example through a simple perforated sheet, a cylindrical press or an extruder and dried, either immediately or by forming this extrusion product in the form of balls or granules using an additional spheronizer. The granules or pellets still wet can be dried, subsequently, until any moisture content is achieved. So that the granulate does not agglutinate, a residual moisture content <50% is recommended. Such a spherical shape can be an advantage for use in solid bed adsorbents, due to the better distribution in the container compared to the granules or pellets crushed in the form of a skein.

It is generally possible, to improve the filtration behavior of the suspensions, to apply usual filtration improvement measures, such as those described, for example, in Solid-Liquid Filtration and Separation Technology, A. Rushton, AS, Ward RG , Holdich, 2nd edition, 2000, Wiley VCH, Weinheim, as well as in the Handbuch der Industiellen Fest / Flüssig-Filtration manual, H. Gasper, D. Öchsle, E. Pongratz, 2nd edition, 2000, Wiley VCH Weinheim. In this way, flocculating agents can be added to the suspensions, for example.

In addition to iron hydroxides, iron carbonates can also be used.

The products according to the invention can be subjected to air and / or vacuum drying and / or in a drying cabinet and / or in a continuous-pass dryer or in a spray dryer, preferably at temperatures in which the range from -25 to 250 ° C, particularly preferably from 60 to 120 ° C.

The products according to the invention preferably have a residual water content of less than 20% by weight.

It has been found that the fragments or granules obtained in this way have a binding capacity with contaminants present in water, liquids or gases and, in addition, have a sufficiently high stability against fluid media with respect to their mechanical or hydraulic load.

It is particularly surprising that finely divided iron oxyhydroxides with high specific surfaces are compacted into very hard drying agglomerates, which have high resistance to mechanical abrasion and high hydraulic stability against contact with circulating water without the addition of binders , and that have a high binding capacity with contaminants and trace elements present in the water.

For use according to the invention of finely divided iron oxyhydroxides, for example, transparent iron oxyhydroxide pigments with a particle size of less than 0.1 µm and specific surfaces greater than 80 m2 are suitable.

The manufacture of yellow finely divided iron oxyhydroxide pigments (eg ghoetite) in the acidic or basic pH range, the so-called acidic or basic crystallization germs, is in the state of the art. Also the manufacture of other iron oxide or iron oxyhydroxide pigments is in the state of the art.

The manufacture of transparent iron oxyhydroxides is known, for example, from DE-A2 603 050 of BIOS 1144, pages 29 to 33 or FIAT 814, pages 1 to 26.

Finely divided yellow iron oxyhydroxide pigments are generally synthesized by precipitation of iron (II) hydroxides or carbonates from the corresponding iron (II) salt solutions such as, for example, FeSO4, FeCI2, in pure form or as pickling solutions, in an acidic or basic pH range, and subsequent oxidation in iron (III) oxyhydroxides (see, among others, G. Buxbaum, Industrial Inorganic Pigments, VCH Weinheim, 2nd edition, 1998, page 231 And next). The oxidation of divalent or trivalent iron is preferably carried out with air; In this regard, intensive gasification is an advantage. Also oxidation with H2O2 results in iron oxyhydroxides. As the precipitation agent, preferably, NaOH is used. However, other precipitation agents, such as KOH, Na2CO3, K2CO3, CaO, Ca (OH) 2, CaCO3, NH3, NH4OH, MgO and / or MgCO3, can also be used.

By the appropriate choice of the precipitation and oxidation conditions, α phases and mixed phases of iron oxyhydroxide nanoparticles having a high specific surface can be obtained, such that the nanoparticles agglomerate in a dry state and have a crushed form high stability against mechanical abrasion and fluid mechanics.

It is of particular practical advantage to obtain finely divided iron oxyhydroxides by the simultaneous rapid treatment of iron (II) salt solutions with NaOH and air, since this process of obtaining results in (oxy) iron hydroxides particularly finely divided and, thus, high stability of the finished material in addition to a high adsorption force.

To control precipitated pigments in the sense of a necessary high fine distribution, precipitation, for example of yellow α-FeOOH, as described in US-A 2 558 303 and US-A 2 558 304, they perform in the basic pH range with alkali carbonates as precipitating agents and generally adding modifiers, such as, for example, SiO2, zinc, aluminum or magnesium salts, hydroxycarboxylic acids, phosphates, metaphosphates. Products obtained in this way are described in US-A 2 558 302. Crystalline germ modifiers do not prevent further processing, recycling or other use of different types of adsorbents according to the invention. In precipitation procedures in aqueous media, precipitation in basic media results in agglomerated powders less hard than those made in acidic media, according to current knowledge.

However, crystallization germ modifiers have the advantage, among others, that at high reaction temperatures they can achieve a sufficiently fine distribution on their own.

Document DE-A 4 235 945 reports on obtaining finely divided iron oxide according to a precipitation procedure in the acidic pH range and without modifiers.

Document DE-A 4 434 969 describes a process with which yellow, chemically pure, very transparent pigments of iron oxide can be manufactured by post-treating them with sodium hydroxide.

In DE-A 4 434 972, very transparent, yellow, iron oxide pigments of the α-FeOOH modification with a specific surface area greater than 100 m2 / g with a high temperature stability are reported.

DE-A 4 434 973 describes very transparent yellow iron oxide pigments that are manufactured by a process of precipitation of crystallization germs in the acidic pH range, the oxidation of the germs, the maturation of the germs and pigment formation

Thus, the corresponding iron oxyhydroxides are manufactured in pure form or in discretionary mixing by known precipitation and oxidation reactions from iron (II) salt solutions; The oxyhydroxide generated, if necessary after post-treatment, is separated from the suspension by filtration of the salt solution and washed until it is largely free of salts, preferably up to a residual conductivity <5 mS / cm, and the solid or semi-solid filter cake, as it is, or if necessary after a mechanical conformation, is then subjected to drying, obtaining a solid state; a material of high mechanical strength is obtained that has a binding capacity with the contaminants present in wastewater or exhaust gases.

Drying is carried out properly at temperatures up to 250 ° C. Vacuum drying or lyophilization of the material is also possible. The grain size of the material is discretionary, preferably between 0.2 and 40 mm, particularly preferably between 0.2 and 20 mm. This can be achieved by mechanical shaping of the semi-solid paste cake, before drying by means of a granulation or pelletizing installation or in an extruder, giving molded bodies with a size in the range of 0.2 to 20 mm. and then air drying, on a continuous-pass dryer or in a drying cabinet, and / or by mechanical grinding to the desired grain size after drying.

Against the state of the art, in the case of the products described, the procedure for its preparation and its use have an improvement. The granules according to the invention based on finely divided oxyhydroxides can be loaded much more than coarsely divided iron oxides and oxyhydroxides and therefore have superior abrasion stability against mechanical and hydraulic stresses. They can be used directly as such. In the crushing or grinding of the pure dry substances obtained below, from filter cakes

or extruders, for example, in the use in adsorbent installations, water purification can be avoided, since the thick pieces disintegrate on their own in case of contact with water. In this case a statistical distribution of grain size appears; however, no particle of a size that is discharged in considerable quantities through the medium in circulation from the adsorber.

In a separate granulation, as would be necessary in the use of conventional oxyhydroxides in powder form (loose), either by using binders other than the substance or high linear forces in compaction, it can be totally avoided.

In accordance with the invention, conventional iron oxydroxides or finely divided iron oxides or iron oxide or iron oxide powder may also be added to the suspensions. The corresponding amounts are determined by the properties of these iron oxyhydroxides or iron oxide oxides and the requirements established on the product according to the invention with respect to its mechanical stability and abrasion resistance. The addition of pigments in powder form certainly reduces, generally, the mechanical stability of the products according to the invention, facilitating, however, if necessary, the filtration of the suspensions. The expert in the corresponding application sectors can determine the optimal mixing behavior for the application purposes by a few targeted tests.

The crystalline germs of nanometric measurements are manufactured according to the invention with an excess of sodium hydroxide.

Particularly preferably, the agglomerates according to the invention are used for the purification of liquids, in particular for the removal of heavy metals. A preferred application in this technical field is the decontamination of water, in particular drinking water. Some time ago, the removal of arsenic from drinking water gave special attention. The granules according to the invention are very suitable for this, because the limit values established by the United States EPA administration by using the granules according to the invention are not only respected, but can even be lowered.

For this purpose, the granules can be used in conventional adsorption apparatus, as currently used, for example, fed with activated carbon, for the removal of contaminants of another type. A batch operation is also certainly possible, for example in tanks or similar containers, which if necessary are equipped with stirrers. However, use in continuous operating facilities such as step adsorbers is preferred.

Because the water treated for drinking water usually also contains organic pollutants such as algae and similar organisms, the surface of the adsorbents is covered, in particular the outer surface of adsorbents in the form of granules, during use, with sediments in mostly viscous, which hinder or completely prevent the entry of water and, with it, the adsorption of the components to be removed. For this reason, the adsorber devices are washed countercurrently from time to time with water, which is preferably carried out during periods with reduced water consumption (see above), individually, in the appliances removed from service. In this regard, the adsorbent according to the invention swirls, and by the mechanical stress of the implicit surface, the unwanted coating is removed and discharged against the direction of the fluid in useful operation. Washing water is usually fed to a purification facility. In this regard, the agglomerates according to the invention are preserved in a particularly good way, since their high stability allows a purification in a short period, without significant losses of adsorbent material being recorded or the backwashing water fed to the Waste water is enriched with expelled adsorbent material, if necessary, already heavily loaded with heavy metals.

Because the agglomerates according to the invention are free of binders of a different type, the material is easily removed in a similar manner after use. Thus, the adsorbed arsenic can, for example, in special apparatus, be removed thermally or chemically, obtaining an iron oxide pigment as pure material, which is either recycled for similar application purposes or can be supplied for conventional pigment applications. Depending on the application and legal determinations, the content of the adsorber can also be used without prior removal of heavy metals, for example, as a pigment for coloring long-lasting building materials such as concrete, because the heavy metals extracted from it Drinking water mode are immobilized in the long term and extracted from the water cycle.

Therefore, also the water treatment facilities or the water supply plants, in which it is operated with apparatus coated with the granules according to the invention are also object of the present invention, as well as the procedures for decontamination of water using devices of this type and the devices themselves.

For many applications, in particular for which maximum mechanical stability of the agglomerates is not necessary, the addition of powder pigments in the manufacture of the agglomerates is a preferred embodiment.

Thus, for example, a suspension of crystalline germs according to example 2 of the present application can be added with up to 40% by weight of commercial ghoetite (Bayferrox® 920, Bayer AG, Leverkusen, Germany), without the granules obtained according to The invention should be used for the removal of arsenic from drinking water in adsorbents through which water circulates.

The determination of the specific surface of the products according to the invention according to BET is carried out by means of carrier gas processes (He: N2 = 90: 10) according to the one-point procedure, in accordance with DIN 66131 (1993). For measurement, the sample is heated 1 hour at 140 ° C in a stream of dry nitrogen

To measure the adsorption of arsenic (II) and arsenic (V), a 5-liter PE bottle is treated for a given period of 3 l of an aqueous solution of NaAsO2 or Na2HAsO4 with the corresponding initial indicated concentrations of 2-3 mg / 1 arsenic with 3 g of the sample to be analyzed and, in this regard, the bottle is added to a rotating roller. The adsorption rate of As ions on iron hydroxide during this given period, for example one hour, is indicated with mg (As3 + / 5 +) / g (FeOOH) · from the difference with As3 + / 5 + ions Remnants in solution.

The adsorption of Sb3 +, Sb5 +, Hg2 +, Pb2 +, Cr6 +, Cd2 + ions is measured according to the same sample and, specifically, the desired concentrations are prepared by dissolving the corresponding amounts of Sb2O3, KSb (OH) 6 , PbCI2, NaCrO4, CdCI2 in H2O and the pH value is adjusted to 7-9.

The contents in As, Sb, Cd, Cr, Hg or Pb of the charged iron hydroxide or solutions are determined by mass spectroscopy (ICP-EM) according to DIN 38406-29 (1999) or by optical emission spectroscopy (ICP-OES) according to EN-ISO 11885 (1998) with the corresponding inductive coupled plasma as an activation unit.

The mechanical and hydraulic abrasion resistance is evaluated according to the following procedure: 10 g of the granulate to be analyzed were introduced, with a grain size> 0.1 mm in a 500 ml Erlenmeyer flask with 150 ml of demineralized water in a LabShaker shaker (Modell Kühner, Braun company) for a period of 30 minutes with a rotation of 250 revolutions per minute. Next, the portion> 0.1 mm is isolated from the suspension by means of a sieve, dried and weighed. The weight ratio between the weighing out and the weighing determines the value of abrasion wear in%.

The invention will be explained in detail below by the following examples. The examples should serve as an illustration of the procedure and do not represent any limitations

Examples

Example 1

237 l of an aqueous solution of iron sulfate with a concentration of 150 g / l of FeSO4 at 24 ° C were placed. Then 113 l of an aqueous NaOH solution (227 g / l) were added rapidly and the light blue suspension was then oxidized with 40 l of air per hour and mol of iron for 1.5 h.

The yellow suspension obtained in this way was filtered off by a filter press and the solid was washed to a residual conductivity of the filtrate of 1 mS / cm. In this regard, a filter cake was produced in the form of an extensible and kneadable dough that was dried on sheets in an air-drying cabin at 75 ° C to a residual moisture content of 3% by weight. The dried material was then crushed to a particle size between 0.5 and 2 mm. The hard pieces obtained were used directly in an adsorbent tank.

The product consisted of 100% α-FeOOH with an extremely high proportion of short needles, the needles having condensed into solid macroscopic agglomerates. Scanning in the scanning electron microscope with an increase, for example, of 60000: 1 determined needle widths with measurements between 15 and 35 nm and needle lengths between 150 and 350 nm. The needles were very crowded.

The specific surface area according to BET amounted to 122 m2 / g. The adsorption rate with respect to NaAsO2 with an initial concentration of 2.3 mg / l (As3 +) was 2.14 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration of 2.7 mg / l (As5 +) gave 2.29 mg (As5 +) / g (FeOOH) · h.

Example 2 with crystallization germ modifier, not according to claim 7

800 l of an aqueous solution of iron sulfate with a concentration of 150 g / l of FeSO4 at 29 ° C were placed and 147 l of an aqueous solution of NaOH (227 g / l) was added with stirring in 20 minutes. Next, a germ modifier was added to the resulting light blue suspension to reduce the particle size of the germs in the form of a 57% aqueous solution of glycolic acid and was oxidized with 38 l of air per hour and mole of iron for 7 h.

The dark brown suspension thus obtained was filtered off by a filter press and the solid was washed to a residual conductivity of the filtrate of 1 mS / cm. The filter cake was dried in an air drying cabin at 70 ° C to a residual moisture content of 5% by weight and the very hard brown-black dry product was crushed with a particle size roller crusher up to 2 mm. The thin portion <0.2 mm was separated through a sieve.

The product was constituted, according to an X-ray diffractogram, by 100% α-FeOOH. Scanning in the scanning electron microscope with an increase, for example, of 60000: 1 determined needle widths with measurements between 15 and 20 nm and needle lengths between 50 and 80 nm. The particles were very agglomerated. The specific surface area according to BET gave 202 m2 / g. The granules obtained in this way were loaded directly into an adsorption tank without further treatment.

The granules showed an outstanding adsorption behavior for the contaminants present in the circulating waters and showed a high resistance to abrasion, in particular during backwashing of the adsorbent tank in which, as a consequence thereof, the granulate formed eddies. violent. The abrasion wear value was after 30 minutes of 1%.

Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.4 mg (As3 +) / l amounted to 2.14 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration of 2.8 mg (As5 +) / l gave 2.07 mg (As5 +) / g (FeOOH) · h.

Example 3

To a suspension of α-FeOOH obtained according to example 2 were added with stirring, after a 2-hour maturation, at 30 ° C, 1.3 l of an aqueous solution of NaOH at 300 g / l and simultaneously oxidized with 190 l of air per hour. The product was processed as described in Example 2. Finely divided needles of pure α-FeOOH with a specific surface area according to BET of 130 m2 / g were generated. Scanning in the scanning electron microscope with an increase of 60000: 1 determined needle widths with measurements between 15 and 20 nm and needle lengths between 50 and 90 nm. The needles were very crowded. The granulate proved to be very mechanically and hydraulically stable, with the abrasion wear value being only 3.9%.

Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.3 mg (As3 +) / l was 1.1 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration of 2.8 mg (As5 +) / l gave 1.7 mg (As3 +) / g (FeOOH) · h.

Example 4

To 306 l of an aqueous solution of NaOH (45 g / l), 43 l of an aqueous solution of FeCl2 (344 g / l) were added rapidly with stirring and then oxidized with 60 l of air per hour and mol iron for 1.5

h. The dark yellow suspension obtained in this way was processed as described in example 1.

The product was constituted, according to an X-ray diffractogram, by 100% α-FeOOH. Scanning in the scanning electron microscope with an increase of 60000: 1 determined needle widths with measurements between 15 and 50 nm and needle lengths between 100 and 200 nm. The needles were very crowded. The specific surface area according to BET was 132 m2 / g.

The granules obtained in this way were loaded directly into an adsorption tank without further treatment. The granules showed an outstanding adsorption behavior for the contaminants present in the water and showed a high resistance to abrasion, in particular during the short-term washing of the adsorbent tank in which, as a consequence thereof, the granulate formed violent eddies. The abrasion wear value was after 30 minutes only 12%.

Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.4 mg (As3 +) / l amounted to 2.11 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration 2.7 mg (As5 +) / l gave 2.03 mg (As5 +) / g (FeOOH) · h.

Example 5

4096 kg of NaOH (as a solution with approximately 300 g / l) were placed and diluted with 40 m3 of water. 4950 kg of FeSO4 were dissolved with water to give a solution of 48.5 m3, cooled to 15 ° C and then pumped into the vessel with NaOH for 1 hour. The suspension was then oxidized with 1500 m3 / h of air for approximately 2 h. Approximately 2 m3 of the germ suspension was washed in a filter press to a residual conductivity of the filtrate of 1000 µS / cm, the filter cake was dried at 75 ° C in a drying booth and the dried material was crushed to a size of grain <1.5 mm. The thin portion <0.2 mm was separated through a sieve. The material obtained in this way had a specific surface area according to BET of 153 m2 / g and was made up of 100% α-FeOOH. Scanning in the scanning electron microscope with an increase of 60000: 1 determined needle widths with measurements between 15 and 35 nm and needle lengths between 50 and 100 nm. The needles were very crowded.

Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.7 mg (As3 +) / l amounted to 1.7 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration of 2.8 mg (As5 +) / l gave 1.4 mg (As5 +) / g (FeOOH) · h.

Example 6

To 1600 g of the germ suspension obtained according to example 5 (2.7% Feo) was added with stirring at room temperature an aqueous solution of FeSO4 (100 g / l) with simultaneous aeration with 130 l / h of air to a pH of 8. The germ suspension was filtered, washed and the cake of the filtrate was dried at 75 ° C and as in example 5 it was crushed to a grain size between 0.5 and 2 mm. The material obtained in this way had a specific surface area according to BET of 163 m2 / g and was constituted, according to the X-ray diffractogram, by 100% α-FeOOH. Scanning in the scanning electron microscope with an increase of 60000: 1 determined that the particles were very agglomerated. Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.7 mg (As3 +) / l amounted to 2.0mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration of 2.7 mg (As5 +) / l amounted to 1.9 mg (As5 +) / g (FeOOH) · h, for KSb (OH) 6 (initial concentration of 3.0 mg (Sb5 +) / l) amounted to adsorption 2.5 mg (Sb5 +) / g (FeOOH) · h, relative to Na2CrO4 (initial concentration 47 µg (Cr6 +) / l, 42 µg (Cr6 +) / g (FeOOH) · h were adsorbed, for PbCl2 (initial concentration 0.94 mg (Pb2 +) / l 0.46 mg (Pb2 +) / g (FeOOH) · h were adsorbed.

Example 7

6.4 l of an aqueous solution of NaOH (100 g / l) were placed at 29 ° C and simultaneously air was fed with 12.2 l of an aqueous solution of iron (II) sulfate (100 g / l) to a pH of 9. The suspension thus obtained was processed as in Example 1. The material had a specific surface area according to BET of 251 m2 / g and was constituted, according to X-ray diffractogram, by 100% α-FeOOH. In the scanning electron microscope with an increase, short, needle-shaped needles can be distinguished, which were very agglomerated. Abrasion wear behavior: 5%.

Adsorption behavior: The adsorption rate with respect to NaAsO2 with an initial concentration of 2.7 mg (As3 +) / l amounted to 1.1 mg (As3 + / g (FeOOH) · h, relative to Na2HAsO4 with an initial concentration 2.7 mg (As5 +) / l gave 1.0 mg (As5 +) / g (FeOOH) · h.

Example 8

3100 kg of NaOH (as a solution with 100 g / l) were placed in a shaker vessel, and diluted with 31 m3 of cold water. The temperature of this NaOH solution was 26 ° C.

They were dissolved with water to a solution of 38 m3 3800 kg of FeSO4, cooled to 13-14 ° C and then pumped with stirring in 40 minutes to the NaOH vessel. The resulting suspension was then oxidized with stirring with 2500 m3 / h of air in 75 minutes.

Next, 18.2 m3 of a FeSO4 solution (100 g / l) in 150 l / min was added with aeration with 1300 m3 / h of air with stirring.

The germ suspension was washed in a filter press to a conductivity of the filtrate <1 mS / cm, the filter paste was compressed by a perforated sheet and dried in a continuous-pass dryer to a residual humidity <20% by weight . The material dried in this way was crushed to a grain size <2 m. The thin portion <0.5 mm was separated by a sieve.

The product obtained was constituted, according to the X-ray diffractogram, by 100% of α-FeOOH. Scanning in the scanning electron microscope with an increase of 60000: 1 determined needle widths with measurements between 15 and 35 nm and needle lengths between 50 and 300 nm. The particles were very agglomerated. The specific surface area according to BET gave 145 m2 / g. The abrasion wear value was after 30 minutes of only 5.1%.

Claims (14)

one.

 Agglomerates of finely divided iron oxyhydroxide of the α-FeOOH phase in the form of pieces with a grain size of 0.2 to 40 mm, the finely divided iron oxyhydroxide having a BET surface of 50 to 500 m2 / g.

2.

 Agglomerates according to claim 1, characterized in that the α-FeOOH has a needle width of 4 nm to 50 nm.

3.

 Apparatus for circulating means, characterized in that they contain agglomerates according to claim 1 or 2.

Four.

 Apparatus according to claim 3, characterized in that in the case of apparatus through which media circulate, they are continuous adsorbents.

5.

 Water treatment facilities comprising apparatus according to claims 3 or 4.

6.

Water supply plants comprising water treatment facilities according to claim 5.

7.

 Process for the manufacture of agglomerates according to claims 1 or 2, characterized in that an aqueous suspension of finely divided iron oxyhydroxides of the α-FeOOH phase is first prepared in which iron (II) hydroxides are precipitated from the corresponding solutions of iron (II) salts with an excess of sodium hydroxide and then oxidized, and then the water and substances dissolved in it are removed, in which

or First, only water, preferably by evaporation, is removed from the suspension, and the residue obtained is dispersed again in water, the suspension obtained is filtered and the residue is preferably washed until it is free of salts, from the filter cake obtained as a residue, the water is partially or totally eliminated and the material obtained in this way is crushed in the desired shape and / or size or the water is partially removed to obtain a sufficiently solid state and the paste obtained in this way is subjected to a conformation and then to another drying obtaining a state in the form of pieces O well the suspension is filtered and the salt-poor residue is washed, to the filter cake in the form of a solid to semi-solid paste that has been obtained as a residue, the water is completely removed and the material thus obtained is crushed in the form and / or desired size or the water is partially removed to obtain a sufficiently solid state and the paste thus obtained is subjected to a conformation and then to another drying obtaining a state in the form of pieces and the material obtained in this way, if necessary, is subjected to intense fragmentation by grinding or grinding.

8.

 Method according to claim 7, characterized in that the oxidation is carried out with air.

9.

 Method according to claim 7 or 8, characterized in that the precipitation and oxidation temperature is between 15 ° C and 45 ° C.

10.

 Use of the agglomerates according to claims 1 or 2 and the apparatus according to claims 3 and 4 to purify gases.

eleven.

 Use of the agglomerates according to claims 1 or 2 and the apparatus according to claims 3 and 4 to purify liquids.

12.

Use of the agglomerates according to claims 1 or 2 and the apparatus according to claims 3 and 4 and of the water treatment facilities according to claim 5, as well as the water supply plants according to claim 6 for water treatment .

13.

Use of the agglomerates according to claims 1 or 2 and the apparatus according to claims 3 and 4 and of the water treatment facilities according to claim 5, as well as the water supply plants according to claim 6 for removing heavy metals, as well as phosphorus, antimony, beryllium, selenium, tellurium compounds, as well as cyanocomposites from phosphorus, antimony, beryllium, selenium, tellurium compounds, as well as water cyanocomposites.

14.

Use of the agglomerates according to claims 1 or 2 and the apparatus according to claims 3 and 4 and of the water treatment facilities according to claim 5, as well as the water supply plants according to claim 6 to remove arsenic compounds of the water.