EP1663860A2

EP1663860A2 - Method for the purification of sulphuric acids

Info

Publication number: EP1663860A2
Application number: EP04764379A
Authority: EP
Inventors: Olaf Halle; Wolfgang Podszun; Bruno Hees; Rheinhold Klipper; Jean-Marc Vesselle; Duilio Rossoni
Original assignee: Lanxess Deutschland GmbH; Bayer SpA; Bayer Italia SpA
Current assignee: Lanxess Deutschland GmbH; Bayer SpA
Priority date: 2003-09-04
Filing date: 2004-08-23
Publication date: 2006-06-07
Also published as: KR20060079206A; AU2004274134A1; US20080229882A1; WO2005028362A3; WO2005028362A2; CA2537709A1; ITRM20030416A0; CN1878726A; ITRM20030416A1; RU2006109814A; JP2007533578A; AU2004274134B2

Abstract

The invention relates to a method for the purification of sulphuric acids, in particular, metal-containing sulphuric acids, characterised in that monodisperse ion-exchangers with chelating functional groups are applied.

Description

Process for the purification of sulfuric acids

The present invention relates to a process for the purification of sulfuric acids, in particular of metal-containing sulfuric acids, with monodisperse ion exchangers which contain chelating, functional groups.

In recent times, the removal of impurities from sulfuric acids, particularly preferably from sulfuric acid copper electolytes, has become increasingly important. This process is used, for example, before the cathodic copper deposition in electrolytic processes which are carried out in copper extraction or refining processes. The task here is to remove metals that can occur in the + HI oxidation state.

In US-A 4,559,216 a method for the removal of antimony, bismuth or iron is described from sulfuric acid copper electrolyte, wherein ■ ^{ht, -} oi ^ pers ion exchangers come with special chelating aminomethylenephosphonic groups are generally used. For example, Unicellex® UR 3300 is mentioned there. In US-A 5 366 715, a method for removing antimony, AVismut or iron from sulfuric acid copper electrolytes by means of heterodisperse aminomethylenephosphonic acid-functionalized ion exchangers is preferred

Duolite TM C-467, described wherein first a reduction of iron (TU) to iron (H) is carried out. In US Pat. No. 6,153,081 the aforementioned reduction of iron (HJ) to iron (H) is carried out with copper and with sodium chloride in sulfuric acid and then the ion exchanger, after being loaded with the impurities, is subjected to a special elution in order to selectively add bismuth and then antimony isolate. Again, heterodisperse chelate exchangers are used, preferably polas® MX-2 from Miyoshi Oil Co., Duolite ^ M Q. 467 or Unicellex® UR 3300.

Common to all processes is low kinetics, selectivity and stability of the ion exchangers used. The object of the present invention was therefore to develop a new process for cleaning sulfuric acids, preferably for cleaning metal-containing ones

To provide sulfuric acids, which makes it possible to selectively remove impurities such as iron, antimony or bismuth in copper extraction or refining processes, without the ion exchanger used being exhausted too quickly. Surprisingly, it has now been found that the properties mentioned above can be improved if ion exchangers of a uniform particle size (hereinafter referred to as “monodisperse”) are used.

The particle size of the ion exchanger according to the invention is 5 to 500 μm, preferably 10 to 400 μm, particularly preferably 20 to 300 μm. As monodisperse in the present Application called ion exchangers, which have a small width of the particle size distribution. Conventional methods such as sieve analysis or image analysis are suitable for determining the average particle size and the particle size distribution. The ratio between the 90% value (0 (90) and the 10% value (0 (10) of the volume distribution) is formed as a measure of the width of the particle size distribution of the ion exchangers according to the invention

(0 (90) indicates the diameter which is below 90% of the particles. In a corresponding manner, 10% of the particles fall below the diameter of the 10% value (0 (10). Monodisperse particle sizes mean distributions in the sense of the invention (0 (9O) / 0 (10) <1.50, preferably (0 (9O) / 0 (10) <1.25, very particularly preferably (0 (9O) / 0 (10) <1.20.

Monodisperse ion exchangers can be obtained by functionalizing monodisperse bead polymers. One way of producing monodisperse bead polymers is to produce monodisperse monomer droplets by means of special atomization techniques and to harden them by polymerization. A uniform droplet size can be formed by vibration excitation, as described for example in EP-A 0 051 210. If the degree of monodispersity of the monomer droplets is to be maintained during the polymerization, the agglomeration and coalescence as well as the new formation of droplets must be prevented. Microencapsulation according to EP-A 0 046 535 is a particularly effective method for preventing agglomeration and coalescence as well as new droplet formation.

Various methods are known for producing monodisperse ion exchangers with chelating functional groups (hereinafter referred to as “monodisperse chelate resins”). US Pat. No. 4,444,961 describes a process for producing monodisperse, macroporous chelate resin. Haloalkylated polymers are aminated and the aminated polymer is amine An alternative method describes the functionalization via a phthalimide stage, which is described in EP-A 1 078 690 for a monodisperse chelate resin, both the content of US Pat. No. 4,444,961 and the content of the EP -A 1 078 690 are also included in the present description.

The present invention and thus the solution to the problem is a process for the purification of sulfuric acids, preferably sulfuric acidic metal-containing solutions, particularly preferably sulfuric acidic copper electrolytes, characterized in that metals, particularly preferably metals which may be present as anions or cations, particularly preferably metals , which may be in the oxidation state + HI, treated with monodisperse ion exchangers with chelating, functional groups, preferably of the aminomethylphosphonic acid type or their functionalization via the phthalimide stage. According to the invention, contaminated sulfuric acids such as those obtained in industrial production processes, preferably metal-containing sulfuric acids, particularly preferably sulfuric acid copper electrolytes which, in addition to copper, contain other metals such as iron, antimony or bismuth, can be worked up and returned to the industrial production processes.

In the case of copper extraction, there are various options for the production of a metal-containing sulfuric acid. On the one hand, copper-containing ground ore is extracted with sulfuric acid and then the pH is increased by adding alkalis. Copper and other metals are extracted from this ore-sulfuric acid mixture using one or more extractants. The extractant phase is separated off and the metals are re-extracted by adding sulfuric acid to the sulfuric acid phase. This sulfuric acid is then used as metal-containing sulfuric acid in the process according to the invention.

However, extractants or mixtures of sulfuric acid with several extractants can also be used in the production of sulfuric acid by this method for the cleaning process according to the invention. Suitable extractants are substances which form one or more further phases in the presence of sulfuric acid and preferably dissolve a metal, in the case of copper extraction, the copper, in ionic or complex-bound form. Preferred extraction agents are aliphatic or aromatic or mixed aliphatic and aromatic organic compounds with functional groups. Preferred functional groups are e.g. Phosphate (e.g. in trialkyl phosphate), aldoxime, ketoxime, alcohol, ketone, ß-diketone, ester and sulfonamide.

In a further alternative embodiment, elemental copper with impurities in metals, which can occur in the oxidation state + DI, is brought into solution in the presence of sulfuric acid by anodic oxidation in an electrical field. Even such

Sulfuric acid can be used as the intended metal-containing sulfuric acid in the process according to the invention.

The concentration of these sulfuric acids can vary within a wide range. The preferred sulfuric acid concentration for the process according to the invention is 50-500 g / 1, particularly preferably 75-400 g / 1, particularly preferably 125-275 g / 1.

The amounts of metal in the sulfuric acid to be used according to the invention, in particular the amount of copper and the amounts of other metals, can vary within wide ranges and are dependent on the quality of the ore and the extraction process. In case of The preferred copper concentration in sulfuric acid is 5-100 g / 1, particularly preferably 20-50 g / 1, particularly preferably 25-35 g / 1.

In the process according to the invention, metals which may be present in the + IT1 oxidation state are preferably removed from the sulfuric acids. Preferred metals are one or more metals of antimony, bismuth, arsenic, cobalt, nickel, molybdenum or iron. Particularly preferred metals are one or more metals from the group of antimony, bismuth or molybdenum, particularly preferably antimony or bismuth. The preferred antimony concentration is 0-5 g / 1, particularly preferably 0-2 g / 1, particularly preferably 0.1-1 g / 1. The preferred bismuth concentration is 0-5 g / 1, particularly preferably 0-2 g / 1, particularly preferably 0.1-1 g / 1.

The process according to the invention can be carried out continuously or batchwise. Continuous processes are preferred. The resin is operated in a column with perforated bottoms. The speed of the sulfuric acid to be purified through the column must be selected in such a way that a high volume flow passes through the column, but no increased concentrations of the metals to be removed pass through. The preferred flow rate is 5-30 times the ion exchange bulk volume per hour (this size is referred to below as bed volume per hour (BV / h)), particularly preferably 10-20 BV h.

Through the operation of the ion exchange resin according to the invention, the metals to be removed accumulate in the ion exchange resin. This can be done by setting

Conditions in which the chemical affinity of the metals for the ion exchange resin is reduced are eluted. An effective method for eluting ion exchangers is treatment with mineral acids or organic acids, preferably in a concentration of 0.1-10 eq / 1. The elution is usually carried out with 1-10 bed volumes (BV), preferably with 2-5 BV. Preferred mineral acids are hydrochloric acid or sulfuric acid, preferred organic acids are

Acetic acid, formic acid or tartaric acid. Organic salts (e.g. tartrates) or inorganic salts (e.g. sodium chloride) can also be present during the elution.

The sulfuric acid purified by means of the monodisperse chelate exchanger can finally be used directly in galvanic processes for the production of elemental copper by reduction at the cathode.

All chelating functional groups are suitable as functional groups for the monodisperse chelate exchangers to be used according to the invention. Functional groups of the type are preferred - (CH ^ NF ^ R 2

wherein

Ri represents hydrogen or a radical CH ₂ -COOH or CH ₂ -P (0) (OH) ₂ and

R _{2 stands} for a radical CH ₂ -COOH or CH ₂ -P (0) (OH) ₂ and n stands for an integer between 1 and 4.

Functional groups of the type - (CH) _n -NR 1 R ₂ are particularly preferred

Ri represents hydrogen or the radical CH P (0) (OH) ₂ ,

R _{2 is} CH P (0) (OH) ₂ and n is 1, 2, 3 or 4.

Equally preferred are all anionic forms or salts of metals of the oxidation state +1 and + π, which are formed by abstracting or substituting the acidic hydrogen of the functional group.

Various base bodies are known as the polymer base of the monodisperse chelate exchangers to be used according to the invention. Ion exchangers based on crosslinked vinylaromatic polymers and on the basis of condensation products of hydroxyaromatics and formaldehyde are customary. However, they are also ion exchangers based on aliphatic polyamines, polyesters or natural products, such as Cellulose or wood; known. Monodisperse chelate exchangers based on crosslinked vinylaromatic polymers are preferred according to the invention.

The monodisperse, crosslinked, vinyl aromatic base polymer can be prepared by the processes known from the literature. For example, such processes are described in US Pat. No. 4,444,961, EP-A 0 046 535, US-A 4419 245, WO 93/12 167.

A copolymer with a monovinylaromatic compound and a polyvinylaromatic compound is suitable as a copolymer in the sense of the present invention.

Mono-vinyl aromatic compounds for the purposes of the present invention are preferably monoethylenically unsaturated compounds such as, for example, styrene, vinyl toluene, ethyl styrene, α-methyl styrene, chlorostyrene, chloromethyl styrene, alkyl acrylate and alkyl methacrylate.

Styrene or mixtures of styrene with the aforementioned monomers are particularly preferably used. Preferred polyvinylaromatic compounds for the purposes of the present invention are multifunctional ethylenically unsaturated compounds such as, for example, divinylbenzene, divinyltoluene, trivinylbenzene, divinylnaphtalin, trivinylnaphtalin, 1,7-octadiene, 1,5-hexadiene, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate or allyl methacrylate.

The polyvinyl aromatic compounds are generally used in amounts of 1-20% by weight, preferably 2-12% by weight, particularly preferably 4-10% by weight, based on the monomer or its mixture with further monomers. The type of polyvinyl aromatic compounds (crosslinkers) is selected with a view to the later use of the spherical polymer. Divinylbenzene is suitable in many cases. For most applications, commercial divinylbenzene grades, which are in addition to the isomers of

Divinylbenzene also contain ethylvinylbenzene, sufficient. In a preferred production variant for monodisperse chelate exchangers to be used according to the invention, microencapsulated monomer droplets are used as bead polymers. For the microencapsulation of the monomer droplets, the materials known for use as complex coacervates come into question, in particular polyesters, natural and synthetic polyamides, polyurethanes, polyureas.

Gelatin, for example, is particularly suitable as a natural polyamide. This is used in particular as a coacervate and complex coacervate. For the purposes of the invention, gelatin-containing complex coacervates are understood to mean, above all, combinations of gelatin with synthetic polyelectrolytes. Suitable synthetic polyelectrolytes are

Copolymers with built-in units of, for example, maleic acid, acrylic acid, methacrylic acid, acrylamide and methacrylamide. Acrylic acid and acrylamide are particularly preferably used. Capsules containing gelatin can be hardened with conventional hardening agents such as, for example, formaldehyde or glutardialdehyde. The encapsulation of monomer droplets with gelatin, gelatin-containing coacervates and gelatin-containing complex coacervates is described in detail in EP-A 0 046 535. The methods of encapsulation with synthetic polymers are known. Phase interface condensation, for example, is particularly suitable, in which a reactive component (for example an isocyanate or an acid chloride) dissolved in the monomer droplet is reacted with a second reactive component (for example an amine) dissolved in the aqueous phase.

The optionally microencapsulated monomer droplets optionally contain an initiator or mixtures of initiators to initiate the polymerization. For the preparation of the chelate exchanger to be used according to the invention, initiators, for example peroxy compounds such as dibenzoyl peroxide, are preferably used for the preparation of the bead polymers. Dilauryl peroxide, bis (p-chlorobenzoyl peroxide), dicyclohexyl peroxydicarbonate, tert-butyl peroctoate, tert-butyl peroxy-2-ethyl-hexanoate, 2,5-bis (2-ethylhexanoyl peroxy) -2,5-dimethylhexane or tert-amylperoxy-2- ethylhexane, and azo compounds such as 2 ₅ 2'-azo-bis (isobutyronitrile) or 2,2'-azobis (2-methylisobutyronitrile) are used.

The initiators are generally used in amounts of 0.05 to 2.5% by weight, preferably 0.1 to

1.5 wt .-%, based on the monomer mixture, applied.

Porogens can optionally be used as further additives in the optionally microencapsulated monomer droplets in order to produce spherical bead polymers (starting material for the production of the monodisperse chelate exchanger) with a macroporous structure. Organic solvents that dissolve or swell the resulting bead polymer are poorly suited for this. Examples include hexane, octane, isooctane, isododecane, methyl ethyl ketone, bufanol or octanol and their isomers.

The terms microporous or gel-like or macroporous have already been described in detail in the specialist literature.

The optionally microencapsulated monomer droplet can optionally be up to

Contain 30% by weight (based on the monomer) of crosslinked or uncrosslinked polymer. Preferred polymers are derived from the aforementioned monomers, particularly preferably from styrene.

The average particle size of the capsules necessary for the preparation of the bead polymer (starting material for the production of the monodisperse chelate exchangers), if appropriate, encapsulated

Monomer droplet is 10-1000 μm, preferably 100-1000 μm.

The bead polymers can be functionalized to the desired monodisperse chelate exchanger to be used according to the invention by haloalkylation of the crosslinked polymer and subsequent conversion into the desired functional group. The methods for haloalkylating the polymers are known from US Pat. No. 4,444,961. A favorite

Haloalkylating agent is chloromethyl methyl ether.

The chloromethyl methyl ether can be used in unpurified form, it may contain, for example, mefhylal or methanol as secondary components. The chloromethylation reaction is catalyzed by the addition of Lewis acids. Suitable catalysts are e.g. Iron (HI) chloride, zinc chloride, tin (rV) chloride or aluminum chloride.

The general production of heterodisperse ion exchange resins with chelating groups is described, for example, in US Pat. No. 2,888,441, but is based on monodisperse ion exchangers transferable. Here, the haloalkylated bead polymer is initiated and the aminated bead polymer is reacted with suitable carboxyl-containing compounds, for example chloroacetic acid. However, it is also possible to react the haloalkylated bead polymer directly with suitable amino acids such as, for example, aminodiacetic acid, glycine, 2-picolylamine or N-methyl-2-picolylamine.

In a preferred form, the bead polymer is functionalized to the desired monodisperse chelate exchanger via direct amination. The amidomethylation reagent is first prepared for this. For this purpose, for example, phthalimide or a phthahmid derivative is dissolved in a solvent and mixed with formaldehyde or paraformaldehyde. A bis (phthalimido) ether is then formed from this with elimination of water.

The bead polymer is then condensed with phthalimide derivatives. Oleum, sulfuric acid or sulfur trioxide is used as the catalyst.

The phthalic acid ester is split off and the aminomethyl group is thus exposed by treating the phthalimidomethylated crosslinked bead polymer with aqueous or alcoholic solutions of an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide

Temperatures between 100 and 250 ° C, preferably 120-190 ° C. The concentration of the sodium hydroxide solution is in the range from 10 to 50% by weight _; preferably 20 to 40% by weight. This process enables the production of crosslinked bead polymers containing aminoall units, with a substitution of the aromatic nuclei greater than 1.

The ion exchangers to be used according to the invention are subsequently produced by

Implementation of the animated monodisperse, cross-linked, vinyl aromatic base polymer in suspension with compounds that eventually develop chelating properties as functional Ainin.

The preferred reagents used are chloroacetic acid and its derivatives, formaldehyde in combination with P-H acidic (after modified Marmich reaction) compounds such as phosphorous acid, monoalkylphosphoric acid ester or dialkylphosphoric acid ester.

Chloroacetic acid or formaldehyde are particularly preferably used in combination with P-H acidic compounds such as phosphorous acid.

The monodisperse chelate exchangers to be used according to the invention preferably have a macroporous structure. Examples

example 1

la) Preparation of the monodisperse, macroporous bead polymer based on styrene, divinylbenzene and ethylstyrene

3000 g of fully demineralized water are placed in a 10 1 glass reactor and a solution of 10 g

Gelatin, 16 g of di-sodium hydrogen phosphate dodecahydrate and 0.73 g of resorcinol in 320 g of deionized water are added and mixed. The mixture is heated to 25 ° C. A mixture of 3200 g of microencapsulated monomer droplets with a narrow particle size distribution of 3.6% by weight of divinylbenzene and 0.9% by weight of ethylstyrene (used as a commercially available mixture of isomers of divinylbenzene and

Ethylstyi-ol roit 80%. Divinylbenzene), 0.5 wt .-% of dibenzoyl peroxide, 56.2 wt .-% styrene and 38.8 wt .-% isododecane (technical isomeric mixture given with a high proportion of pentamethylheptane), the microcapsule of a formaldehyde-cured complex ^' consists of gelatin and a copolymer of acrylamide and acrylic acid, and 3200 g of aqueous phase with a pH of 12 are added. The average particle size of the monomer droplets is 460 μm.

The batch is polymerized with stirring by increasing the temperature according to a temperature program at 25 ° C. and ending at 95 ° C. The mixture is cooled, washed over a 32 μm sieve and then dried in vacuo at 80 ° C. 1893 g of a spherical polymer having an average particle size of 440 μm, narrower, are obtained

Particle size distribution and smooth surface.

The polymer is chalky white when viewed from above and has a bulk density of approx. 370 g / l.

lb) Preparation of the amidomethylated bead polymer

1149 g of dichloroethane, 341 g of phthalimide and 238 g of a 29.8% by weight formaldehyde solution are initially introduced at room temperature. The pH of the suspension is adjusted to 5.5 to 6 with sodium hydroxide solution. The water is then removed by distillation. Then 24.8 g of sulfuric acid are added. The resulting water is removed by distillation. The batch is cooled. 91 g of 65% by weight oleum and then 424.8 g of monodisperse bead polymer, prepared by process step la), are metered in at 30 ° C. The suspension is heated to 70 ° C. and stirred at this temperature for a further 6 hours. The liquid phase is drawn off, demineralized water is metered in and residual amounts of dichloroethane are removed by distillation. Yield of amidomethylated bead polymer: 1480 ml

Elemental analysis composition:

Carbon: 80.7% by weight;

Hydrogen: 5.6% by weight;

Nitrogen: 3.9% by weight;

Rest: oxygen.

lc) Preparation of the aminomethylated bead polymer

To 1460 ml of amidomethylated polymer beads, 492 ^~ g "5C% by weight sodium hydroxide solution and 1006 ml of fully demineralized water are metered in at room temperature. The suspension is heated to 180 ° C. and stirred at this temperature for 8 hours.

The bead polymer obtained is washed with deionized water.

The total yield is 1399 ml

Elemental analytical composition: nitrogen 5.8% by weight

1 d) Preparation of the ion exchanger with aminomethylphosphonic acid groups

540 ml of the water-moist aminomethylated bead polymer from 1 c) are in one

Put the round bottom flask and mixed with 281 ml of completely deionized water. 209 g of 99% strength by weight dimethylphosphite are added dropwise with stirring over the course of 15 minutes and the mixture is then stirred for a further 30 minutes. Then 648 g of 98% sulfuric acid are metered in uniformly within four hours. After this time, the mixture is heated to 100 ° C., 291 g of a 29.8% strength by weight formaldehyde solution are metered in at this temperature and the mixture is stirred at the reflux temperature for a further six hours.

The reaction mixture is cooled, placed on a sieve and washed with deionized water until the process remains neutral. The resin is then transferred to a glass column with a glass frit base and, with 3 bed volumes, 4% by weight sodium hydroxide solution, which is introduced from above into the ion exchange bed, into the sodium form. The ion exchanger is then washed with 5 bed volumes of deionized water. 1060 ml of a water-moist ion exchanger are obtained

Elemental analysis composition: Nitrogen: 3.2% by weight

Phosphorus: 10.0% by weight

Before the intended use, the ion exchanger is transferred again into the glass column and converted into the hydrogen form with 2 bed volumes of 10% strength by weight sulfuric acid, which is introduced into the ion exchange bed from above. Then the

Ion exchanger washed with 5 bed volumes of demineralized water and discharged again from the glass column.

1 e) Preparation of an example sulfuric acid composition to be cleaned

3 l of fully demineralized water are placed in a 5-1 beaker, 1000 g of 98% sulfuric acid are added and 3.28 g of antimony (IH) chloride and 517.5 g of copper (II) sulfate pentifihydrate are dissolved with stirring. Then will. the batch was made up to 5000 g with deionized water and cooled to room temperature.

An intended sulfuric acid with 30 g / 1 copper and 0.4 g / 1 antimony is obtained.

1 f) cleaning of the sulfuric acid composition according to the invention from le)

100 ml of the monodisperse ion exchanger from 1 d) are placed in a glass column with a glass frit bottom

(Inner diameter = 22 mm) transferred. The sulfuric acid from 1 e) is introduced into this glass column at a volume flow of 500 ml / h in such a way that a small volume of constant amount of sulfuric acid always remains above the ion exchange bed.

The sulfuric acid emerging from the glass column is analyzed and with the incoming

Comparing sulfuric acid from 1 e).

Incoming sulfuric acid

Antimony concentration: 0.4 g / 1

Expiring sulfuric acid after 10 BV

Antimony concentration: 0.02 g / 1

The reduction of the antimony content in the sulfuric acid to be purified by means of a monodisperse chelate exchanger is surprisingly significantly better than when using the above-mentioned heterodisperse ion exchangers known from the prior art.

Claims

claims

1. A process for the purification of sulfuric acid, characterized in that monodisperse chelate exchangers are used.

2. The method according to claim 1, characterized in that the sulfuric acid to be purified are sulfuric acid metal-containing solutions.

3. The method according to claim 1 or 2, characterized in that the sulfuric acid solution is a copper electrolyte, from which the metals iron, antimony or bismuth are removed.

4. The method according to claims 2 or 3, characterized in that one or more metals from the group antimony, bismuth, arsenic, cobalt ^' I Rckelj ^", molybdenum or iron are removed from the sulfuric acids.

5. The method according to claim 1, characterized in that the monodisperse chelate exchanger carry functional groups of the type - (CH ₂ ) _n -NRι R, wherein

R 1 is hydrogen or a radical CH ₂ -COOH or CH ₂ P (0) (OH) ₂ and R _{2 is} a radical CH ₂ COOH or CH ₂ P (O) (OH) ₂ and n is an integer stands between 1 and 4.

6. The method according to claim 5, characterized in that the monodisperse chelate exchangers have a macroporous structure.

7. Use of monodisperse chelate exchangers for cleaning copper electrolytes.

8. A process for the production of elemental copper, characterized in that the copper is obtained directly from the sulfuric acids purified according to claim 1 by reduction at the cathode in galvanic processes.

9. Use according to claim 7, characterized in that the cleaning relates to the elements Sb and Bi.