Abstract: Various metals including cobalt nickel and copper can be recovered from a roasted ground ore or waste and particularly from tailings of a pyritic gold ore by leaching with sulphuric acid, oxidizing the separated leach liquor, filtering and partially neutralizing the liquor. In an improved process, the oxidation is effected with peroxomonosulphuric acid and the neutralization with a 60:40 to 40:60 mixture of calcium and sodium hydroxide/oxide. By so doing, it is possible to minimize the number of process stages by elimination of either or both solid/liquid separations and to combine the leach and oxidation stage, or to improve the separation of metals from impurities.

Abstract: A process for the recovery of valuable metals from metallic alloys having iron as their principal constituent is disclosed in which the metal is leached by means of a sulfuric acid solution having such a concentration that a nearly saturated salt solution is obtained, and after the separation of a possible leach residue the solution is heated close to the boiling point, at which time an acid solution is added in an amount corresponding to the salt which has passed out of the solution, in order to crystallize the salt mixture, the crystallized material is separated from the solution and is decomposed under sulfating conditions, whereafter the metal salts are leached out from the iron oxide by means of water.

Abstract: The antimony in an antimony-containing copper electrolyte is removed by contacting the antimony-containing copper electrolyte with activated carbon at between room temperature and 60.degree. C.

Abstract: Arsenic is removed from a hydrocarbon containing arsenic as an impurity; e.g., shale oil, by contact with hydrogen in the presence of a contact material, such as coke, to deposit the arsenic on the contact material. The arsenic deposited on the contact material is subsequently reacted with an iron compound to produce an iron-arsenic compound suitable for disposal.

Abstract: Arsenic anhydride of high purity is inexpensively manufactured from an arsenic sulfide-containing substance by first contacting the arsenic sulfide-containing substance with a copper sulfate-containing aqueous solution so as to provide an extract solution containing arsenious acid, the extract solution is subjected to aeration in the presence of copper ions such that the arsenious acid therein is mostly oxidized to arsenic acid, the thus provided treated solution is subjected to a weak reducing agent to cause crystals of arsenious anhydride to form, and these crystals are then recovered.

Abstract: A process for the selective removal of arsenical materials, in the course of a continuous hot oxidizing attack process, comprising attacking a uraniferous ore containing arsenical materials as impurities in the presence of an oxidizing agent in the reaction medium by means of an aqueous liquor formed by a recycling solution containing alkali metal carbonate and bicarbonate, and uranium close to the limit of solubility thereof, under concentration, temperature and pressure conditions which causes solubilization of the uranium present in the ore, and re-precipitation thereof in the attack medium, then collecting a suspension of a solid phase in a liquid phase which, after cooling, is subjected to a separation operation, recycling the liquid phase to the attack operation, and treating the separated solid phase by means of an aqueous liquor to re-dissolve the precipitated uranium which is characterized in that the arsenic which is solubilized in the attack operation is extracted by means of a magnesium compound w

Abstract: A process for the removal of arsenic compounds from tungsten and/or molybdenum concentrates by selective extraction, characterized in that the concentrates are extracted with an aqueous solution of a ferric compound at a pH below 2.5 and a temperature of at least 60.degree. C.

Abstract: A process for growing crystals of an inorganic material by forming a solution of the material in a solvent for the compound, forming a film of the solution and etching the solvent from the film with an etching gas until crystals of the material form. The solution has a solidification temperature lower than the melting or sublimation temperature of the material and higher than the condensation temperatures of the etching gas and of reaction products formed by the etching. The etching temperature is between the solidification temperature of the solution and the melting or sublimation temperature of the material and is lower than the vaporization temperature of the solvent and solution and higher than the condensation temperatures of the etching gas and reaction products.

Abstract: A method for detoxification of spent catalyst from a fluorination process includes the step of hydrolyzing such spent catalyst in the presence of aqueous calcium chloride to produce insoluble compounds which are separable from the aqueous medium. The spent catalyst is one which includes at least one antimony halide, such as SbCl.sub.5, SbF.sub.5, SbCl.sub.3 and/or SbF.sub.3, usually with some halogenated hydrocarbons, such as partially chlorinated methane, partially chlorinated ethane and/or chlorofluorocarbons of 1 to 5 carbon atoms, often in the presence of arsenic compounds, such as AsCl.sub.3, hydrofluoric acid, and antimony chlorofluoride, such as SbCl.sub.4 F. The spent catalyst may be directly treated with the aqueous calcium chloride solution, very preferably with such solution containing small amounts of a transition metal ion, such as Fe.sup.++ or Fe.sup.+++, or aluminum ion, e.g., Al.sup.

Abstract: Tungsten is recovered from alkaline brines by: (1) initial loading of metal values on an 8-hydroxyquinoline-resorcinol-formaldehyde resin, (2) selective desorption of boron, arsenic and sulfur from the resin by means of an NH.sub.4 Cl--NH.sub.4 OH solution having a pH of about 7.5 to 9.5, and (3) desorption of tungsten from the resin by means of water or an alkaline solution.

Abstract: A process for the recovery of uranium values from uranium-containing material which also contains iron, arsenic and siliceous matter, includes leaching the uranium-containing material in aqueous sulphuric acid solution under conditions to provide dissolved iron present in the resultant leach solution as predominantly ferrous iron rather than ferric iron and/or to provide a sulphuric acid concentration in the leach solution sufficiently high to substantially prevent the precipitation of arsenates. Uranium values are recovered from the leach solution by solvent extraction agent which has little affinity for arsenic.

Abstract: This invention relates to environmentally sound hydrometallurgical methods and processes for extraction of cobalt, nickel and silver from complex concentrates. The finely ground minerals are converted during an oxidative caustic leach at elevated pressures and temperatures to insoluble metal hydroxides and are separated from soluble sodium arsenate and sodium sulphate. Cobalt and nickel are extracted from the caustic cake during a two-stage sulphuric acid leach. Solution purification for cobalt and nickel recovery proceeds on the basis that only one waste residue and one liquid effluent are generated which meet strict environmental standards. A small amount of cyanidation residue is generated after silver extraction by cyanidation from the acid leach residue. Metal values extraction reaches +99.0%. Arsenic and sulphur can be recovered in an innovative recycle system as sodium, zinc or copper arsenate chemicals and as anhydrous sodium sulphate.

Abstract: There is disclosed an improved method of treating a spent electrolyte of copper from a cell for electrolytic refining of copper for the purpose of purification and reuse of the spent electrolyte. The process comprises the steps of: pretreating the spent electrolyte for removing copper therefrom until the copper content is greatly reduced but still remains at a level which is substantially higher than the total content of various metal ion impurities, preferably to a concentration of 10-13 g/l of Cu; blowing a hydrogen sulfide gas into the pretreated solution at a temperature of 40.degree. C. or higher until the redox potential of solution becomes a certain predetermined value to precipitate metal ions; filtering the treated solution to separate the residue available as a raw material for copper smelting from a filtrate which consists essentially of sulfuric acid; and returning the filtrate to the cell for electrolytic refining of copper.

Abstract: Arsenic is recovered from flue dusts by forming an aqueous slurry of the dust, treating the slurry with SO.sub.2 gas to solubilize arsenic, and precipitating the arsenic as As.sub.2 O.sub.3 by means of sulfuric acid.

Abstract: The present invention relates to a process for removing heavy metals, particularly cadmium, from differing qualities of wet-process phosphoric acids. The invention is based on the concept of removing the heavy metals in sulfide form.

Abstract: Novel sequestering agents useful for the extraction of metal values and in various organic syntheses comprise a cross-linked organic polymeric substrate, said substrate having covalently coupled thereto a plurality of functional groups, the free valence of which having the structural formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.6 and R.sub.7, which are identical or different, each represents a hydrogen atom or an alkyl radical having 1 to 4 carbon atoms, R.sub.5 and R.sub.8, which are also identical or different, each represents a hydrogen atom, an alkyl or cycloalkyl radical having 1 to 12 carbon atoms, a phenyl radical, a --C.sub.g H.sub.2q --.phi. or C.sub.q H.sub.2+1 --.phi.-- radical, and further wherein q ranges from 1 to about 12, and n, m and p, which are also identical or different, range from 1 to 10, and .phi. is phenyl.

Abstract: A process for leaching copper and arsenic from copper dross containing copper arsenide and separated from molten lead bullion comprises leaching the dross with an aqueous ammoniacal solution containing arsenate as the predominant anion under oxidizing conditions to obtain a leachate, removing copper from the leachate to obtain a raffinate and re-cycling raffinate to the leaching stage, and removing a bleed of raffinate from the circuit and precipitating a substantially insoluble arsenic compound from the raffinate bleed to remove arsenic from the circuit.

Abstract: A process for removing arsenic from an aqueous solution containing arsenic in the form of a soluble arsenate includes adjusting the pH of the solution if necessary to at least about 10, adding a soluble barium salt to precipitate arsenic as barium arsenate, and removing the precipitated barium arsenate from the solution.

Abstract: A process for improving the flame-retardant properties of cellulose containing fibrous materials in the absence of halogen compounds which comprises treating said fibrous materials with an effective amount of a colloidal aqueous dispersion of an alkali metal polyantimonate containing a mole ratio of alkali metal to antimony in the dispersion of at least about 0.3:1, and drying said materials is described.

Abstract: A method of preparing antimony pentoxide from solids containing antimony sulfides is described. The method comprises the steps of(a) leaching the antimony values from the solids with an aqueous potassium hydroxide solution to form an antimony-containing solution and a gangue,(b) oxidizing the antimony present in the leaching solution to a pentavalent antimony,(c) recovering the oxidized solution, and(d) adding an inorganic acid to the solution to reduce the pH of the solution to about 5-7 whereby antimony pentoxide is precipitated from the solution. The gangue may be separated from the leach solution either prior to or after the oxidizing step.In a preferred embodiment, the oxidation of the solution is conducted in the presence of a catalyst which comprises a water-soluble copper salt, a quinone, a hydroquinone or mixtures of one or more of these.

Abstract: A process for the recovery of silver values from silver-containing material which also contains iron and arsenic includes leaching the material under oxidizing conditions at elevated temperature and pressure in aqueous nitric acid solution to dissolve a substantial amount of silver together with substantial amounts of arsenic, iron and other metals if present. The resultant leach solution is separated from undissolved leach residue and treated with a solution containing chloride ions to selectively precipitate substantially all dissolved silver as silver chloride without significant co-precipitation of other dissolved metals. The silver chloride precipitate is then separated from the remaining solution.

Abstract: A method for the separation of bismuth from a complex chloride solution obtained by leaching with chloride reagents ores containing bismuth and high concentrations of other metals comprising adding to said complex chloride solution at least a stoichiometric amount of a precipitating agent selected from the group consisting of hexamminecobalt (III) salts and hexamminechromium (III) salts soluble in said solution to precipitate said bismuth as a hexamminecobalt (III) bismuth salt or a hexamminechromium (III) bismuth salt and separating said precipitate from said solution.

Abstract: The method for recovering metals of Groups V-VI of the periodic system from solutions and pulps according to the present invention is effected by means of a selective ion-exchange resin which is the reaction product between a polyhydric phenol with formaldehyde with a specific surface area of from 50 to 600 m.sup.2 /g, pore volume of from 0.2 to 2.3 cm.sup.3 /g, content of hydroxy groups of at least 11.3 mg-equiv/g.

Abstract: To a coal-fired furnace that uses electrostatic precipitation or a mechanical collector to collect fly ash, a mix of magnesia-alumina or magnesia-talc is added above the fireball (2600.degree.-3300.degree. F.). The additive increases the mean particle size of the fly ash and reduces its surface resistivity, thereby causing improved collection in the electrostatic precipitators or mechanical collector. Fine particulates containing heavy metals tend to be agglomerated; thus the invention permits recovery of substantial amounts of heavy metal contaminants that would otherwise be lost as stack emission.

Abstract: A process for treating sulfide ores to reduce the sulfur content or recover the metal content therefrom comprises the use of enzymatic action to solubilize the sulfur and metal content.A nutrient, such as a saccharide, is used along with yeast spores which feed on the sugar and produce enzymes which act on sulfur in the sulfide ore to cause the sulfur to go into solution and to dissolve those metals which are soluble in strongly acidic solution. Sulfuric acid can be formed from the sulfide ores or from free sulfur by reaction with water, with evolution of hydrogen sulfide gas. Oxidation of at least a portion of the hydrogen sulfide can be achieved to regenerate sulfuric acid.

Abstract: An improvement in the hydrometallurgical recovery of metals, such as, lead, silver, gold, antimony, and bismuth from materials such as flue dust in the presence of arsenic, comprising precipitating arsenic as an insoluble ferric-arsenic compound in the first processing step, carrying the insoluble arsenic compound through a chloride leach step, in which it is insoluble, to recover the metals, and disposing of the residue in which the arsenic has been fixed with ferric ions to render it non-polluting, or alternatively, recovering the arsenic by caustic leach and crystallization.

Abstract: An improvement in hydrometallurgical recovery of metals, i.e. copper, zinc, cadmium, germanium, indium, lead, silver, gold, antimony and bismuth from materials such as flue dust containing arsenic in which the metals are selectively separated in successive process steps for final recovery, the improvement comprising precipitating arsenic as an insoluble ferric-arsenic compound in the first processing step, carrying the insoluble arsenic compound through subsequent processing steps in which it is insoluble until the other metals have been recovered leaving the ferric-arsenic compound as the final residue which can be disposed of without violating pollution requirements or converted to soluble sodium arsenate and recovered from solution by crystallization.

Abstract: An arsenic-recovery process primarily for use in conjunction with the hydrometallurgical processing of arsenic-containing materials for metal recovery. Arsenic is recovered from ferric arsenate by reaction with sodium hydroxide in accordance with the following general reaction:3NaOH+FeAsO.sub.4 .fwdarw.Na.sub.3 AsO.sub.4 +Fe(OH).sub.3During the processing of high arsenic materials such as smelter flue dust, extremely insoluble ferric-arsenic compounds are generated to immobilize the arsenic during leaching of the metals. The arsenic may be recovered in saleable form from the arsenic-containing residues by leaching with sodium hydroxide and crystallizing the arsenic salts from the leach residue.

Abstract: A method of removal of arsenic from an acidic solution, in which ferrous ions contained in the solution are oxidized in the presence of high pressured oxygen and sulfuric acid to ferric ions, the solution with said ferric ions being mixed with the solution which has not subjected to oxidation, and the mixture of said solutions being controlled of its pH whereby ferric hydroxide is precipitated, which coprecipitates and adsorbs arsenic thereto.

Abstract: A multi-step process for recovering metal values from lead smelter matte. The matte is mixed with sulfuric acid and manganese oxide and leaching is effected at atmospheric pressure to form an aqueous solution including dissolved metal sulfates and a residue containing sulfur and lead sulfate. The sulfur is removable by conventional means and the lead sulfate may be returned to the smelter. The pH of the aqueous sulfate solution is adjusted to 3.5 to 4.5 to precipitate ferric iron and arsenic and pH is readjusted to about 3.0 to redissolve coprecipitated copper. After separation from the precipitate, the aqueous solution is mixed with a sulfiding agent, such as sodium sulfide at a pH of not more than 3 to selectively precipitate copper sulfide. After separating the copper sulfide, the aqueous solution is mixed with further sulfiding agent at a pH of 3 to 4.5 to form a cobalt-nickel sulfide precipitate in which the weight ratio of copper-nickel to sulfur is 1.8.

Abstract: Process and apparatus for the electrowinning of metals from sulphide ores wherein a sulphide ore is initially leached in a water soluble sulphide solution, alkali is then added, and the resulting solution is electrolyzed so as to deposit metal at the cathode and obtain water soluble sulphide as a by-product. The process is particularly suitable for obtaining antimony from stibnite.

Abstract: Molybdenum or other heavy metal anions and ferric sulfate are reclaimed from wastewater skimmings, that result from treatment of wastewaters through formation of insoluble heavy metal ferric salts and flotation, by treating the skimmings with aqueous caustic at 150.degree.-225.degree. F. to form a solution of the heavy metal anions and a residual solids fraction, separating the solids and contacting the residual solids with sulfuric acid to produce ferric sulfate.

Abstract: A process for the treatment of raw materials which contain arsenic and metal to produce a metal-free arsenic product and an arsenic-free metal sulfate is disclosed, in which the raw material is leached by using an aqueous solution of sulfuric acid and then the metals are crystallized as sulfates from the separated aqueous solution, which is separated from the metal sulfate crystals. The leach is performed at elevated temperature under oxidizing conditions, in order to bring the arsenic to a 5-valent form, the metal sulfates are crystallized out from the selectively separated, arsenate-bearing aqueous solution by cooling, and arsenic is removed from at least part of this aqueous solution before the aqueous solution is returned to the leach.

Abstract: A process for removal of heavy metals in their anionic state, particularly tungsten and molybdenum, from industrial mining wastewater by chemical precipitation of the heavy metal values, followed by gas flotation.

Abstract: A process is disclosed for the selective extraction of arsenic from oxidic materials containing compounds such as arsenic trioxide, arsenic pentoxide, antimony trioxide, antimony pentoxide, antimony tetroxide and mixtures thereof in which arsenic is effectively separated from antimony. Said oxidic materials are subjected to a leach with a lixiviant containing arsenic acid or hydrogen peroxide at a temperature in the range of 40.degree. C. to the boiling point of the reaction mixture, preferably in the range of 80.degree. to 100.degree. C., for 5 to 90 minutes. The leach solution containing arsenic oxides is separated from leach residue. The leach solution is either cooled to a temperature in the range of 5.degree. to 25.degree. C. to crystallize and subsequently recover arsenic trioxide or the solution is oxidized and evaporated and arsenic pentoxide is recovered.

Abstract: The process of the invention is for the separate recovery of elemental sulfur and residual sulfides and metal salt solution from reaction slurries obtained from leaching of metal sulfides in ores and concentrates.

Abstract: A method for removing As, or As and Sb and/or Bi wherein acidic solution of sulfuric acid such as a copper electrolyte of having a free sulfuric acid concentration of less than 700g./l. and containing at least arsenic among arsenic, antimony and bismuth as impurities is warmed to be above 50.degree. C. or preferably above 60.degree. C. with the addition of H.sub.3 AsO.sub.4 in advance as required, one or a mixture of both of Sb.sub.2 O.sub.3 and Bi.sub.2 O.sub.3 preferably kneaded with water or the added solution is added to and mixed with the solution and the produced precipitate is separated to discharge the impurities out of the solution.

Abstract: Antimony and bismuth are selectively removed from an electrolyte solution, especially a solution used for the electrolytic refining of copper by adding to the electrolyte solution a carbonate of barium, strontium, or lead.

Abstract: Arsenic-containing waste materials comprising water-soluble arsenic salts are processed to a product which comprises water-insoluble arsenic salts by reacting the same in an aqueous system with sulfuric acid and calcium hydroxide in the presence of sulfate ions and ferrous and/or ferric ions, and thereafter curing the system to solid form.The process can be practiced with conventional waste materials without preliminary special processing, and provides a product which can be easily handled and is amenable to secure landfill disposal.

Abstract: A method is disclosed for removing arsenic by solvent extraction from a copper and/or nickel bearing aqueous solution containing about 100 to 600 gpl sulphuric acid. The method comprises contacting the solution with an organic solution consisting of about 5 to 80% by volume of tributylphosphate in an organic diluent, and subsequently stripping the arsenic from the loaded organic solution with a suitable stripping agent. Particularly, when the sulphuric acid concentration in the aqueous solution is lower than 300 gpl, the organic solution advantageously comprises up to about 15% of a quaternary ammonium reagent. Preferred quaternary ammonium reagents are tricaprylmethyl ammonium chloride and mixtures of tri-C.sub.8 -C.sub.10 methylammonium chlorides.

Abstract: Anion exchange resins containing borohydride counter ions display essentially the same chemical activity as solutions of sodium borohydride but have the added advantage that products treated therewith are not contaminated with sodium ions or borate ions. Thus, alcohols can now be freed of carbonyl components without thereby being contaminated with borate; metal ions, such as silver, can be reduced to the free element; metal ions of groups IV-A to VI-A can be converted to volatile metal hydrides; and transition metal ions can be converted to the boride. The anion exchange resin is prepared by treating a strong base anion exchanger with aqueous sodium borohydride or sodium cyanoborohydride. Regeneration of the borohydride form from the borate proceeds directly with aqueous sodium borohydride.

Abstract: In a process for treating a metal bearing material containing arsenic and antimony by leaching in an acid solution with an oxygen-containing gas under pressure at a temperature of between 20.degree. and 200.degree. C, the improvement which consists in adding at least one element chosen from the group consisting of arsenic and phosphorus in such an amount to the leach mixture that the molar ratio (As + 4P) : Sb therein shall be at least equal to 8, thus dissolving at least the major part of the arsenic and antimony contained in the starting material.

Abstract: A process for recovering antimony and sodium compounds from antimony-containing spent ethylene glycol residues resulting from the manufacture of polyethylene-terephthalate polyester, which comprises combusting the spent glycol residues to produce an ash, and then contacting the ash with water to form an ash-water mixture having a liquid phase and a solid phase, the water-soluble sodium compounds being essentially contained in the liquid phase and the water-insoluble antimony compounds being essentially contained in the solid phase. The liquid phase and solid phase are then separated in order to recover therefrom sodium and antimony compounds, respectively.

Abstract: Disclosed is a method for the recovery and purification of arsenic/selenium alloys which are contaminated with organic and inorganic materials. The method comprises:A. dissolving the alloy in an aqueous solution of morpholine, piperidine or a lower aliphatic primary or secondary amine which is a solvent for the alloy but a non-solvent for the contaminants therein,B. physically separating the resulting alloy solution from the undissolved contaminants, andC. evaporating the alloy solution to dryness to recover the alloy.

Abstract: A method for extracting antimony from solids containing antimony sulfides is described. An improvement in the method of extracting antimony by oxidation of an aqueous mixture of the solids in an acid or by oxidation of a leaching liquor obtained by leaching the antimony from the solids with an aqueous basic solution comprises conducting the oxidation in the presence of a catalyst comprising a water-soluble copper salt, a quinone, a hydroquinone or mixtures of one or more of these. The catalyst significantly increases the rate of oxidation and the rate of the recovery of the antimony from antimony sulfide bearing solids, particularly natural ores. Where the oxidation is conducted in a basic solution, the antimony is recovered as pentavalent antimony in the form of metal antimonates. Facile reduction of the metal antimonate to antimony trioxide also is described.

Abstract: A catalytic process is provided for the selective production of para-xylene by contacting, under conversion conditions, a charge stock containing, as a major reactant, at least one hydrocarbon selected from the group consisting of toluene, a C.sub.3 -C.sub.10 olefin, a C.sub.5 -C.sub.10 naphthene, a C.sub.3 -C.sub.10 paraffin, and mixtures of the foregoing with a catalyst comprising a composite of a crystalline aluminosilicate zeolite and antimony oxide, said zeolite having a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12.

Abstract: Disclosed is a process for extracting antimony trioxide from antimony sulfide ore concentrate by solubility differential of the trioxide in lower alkanol solutions of sodium or potassium hydroxide and wherein the total amount of water contained in the concentrate, the alkanol and the hydroxide is not more than 26.52 volume percent of the antimony sulfide content; which process includes treating the ore in the absence of substantial amounts of air with an alkanol solution containing an excess of sodium or potassium hydroxide, basis Sb.sub.2 S.sub.

Abstract: Finely-divided metal oxides are prepared by the steps of (a) contacting a compound of a metal with a carbohydrate material to obtain an intimate mixture thereof, (b) igniting this mixture to oxidize the same and to insure conversion of substantially all of said metal compound to a fragile agglomerate of its metal oxide, and (c) pulverizing the product of step (b) to form a finely-divided metal oxide powder having a mean particle size below about 1.0 micron. Certain of the finely-divided metal oxide powders produced by this process have the useful property of sinterability at temperatures significantly lower than metal oxide powders heretofore readily available. The powders are useful in the preparation of high strength compacted shapes for use in high temperature and/or corrosive environment, in the preparation of refractory cements, catalysts, catalysts supports and the like.

Abstract: A process for treating an aqueous acid solution containing at least one element selected from the group of elements consisting of As, Sb and Bi, said process comprising contacting the aqueous solution with an organic phase comprising an organophosphoric compound having the general formula (RO).sub.3 P = O wherein R represents an unsubstituted or substituted alkyl, aryl or aralkyl group, while maintaining a temperature of between 10.degree. and 60.degree. C and an organic phase/aqueous phase ratio of between 0.1 and 5, whereby the elements of said group and acid are extracted from the aqueous phase to the organic phase, and separating the resultant pregnant organic phase from the aqueous phase.

Abstract: A process in which metal foil is introduced into a fluid containing one or more heavy metals, so that one part of the surface of the foil is in contact with the fluid and another part thereof is in contact with air and that an activator in the form of a solution of a complex compound, preferably based on the metal comprising the foil, preferably an NaAl complex, is brought into contact with the foil and the fluid whereby the metal or metals precipitate and after precipitation are separated from the fluid in a way known per se.