Abstract: A method for the removal and concentration of desired ions from a source solution which may contain larger concentrations of other ions including H.sup.+ comprises bringing the source solution into contact with a compound comprising a polytetraalkylammonium and/or polytrialkylamine-containing ligand covalently bonded through an organic spacer silicon grouping to a solid inorganic support. The polytetraalkylammonium and/or polytrialkylamine portion(s) of the compound has an affinity for the desired ions to form a complex thereby removing the desired ions from the source solution. The desired ions are removed from the compound by contacting the compound with a much smaller volume of a receiving solution having a greater affinity for the desired ions than does the polytetraalkylammonium and/or polytrialkylamine ligand portion of the compound. The concentrated ions thus removed may be recovered by known methods.

Abstract: A process for the removal of soluble selenium from aqueous media comprising contacting the aqueous media with a porous support material having exchanged thereon metal ions selected from transition metal ions, alkali earth metal ions and mixtures thereof.

Abstract: A process is described for regenerating and recycling a contaminated solution recovered from an aluminum or tin washer process wherein the contaminated solution contains contaminants comprising inorganic soils, organic soils, or both as a result of the use of the solution in the washer process, which comprises(A) regenerating said solution by(A-1) extracting said contaminants from the solution in a manner which does not substantially reduce the amount of any chemicals present in the solutions prior to use; and(A-2) selectively replenishing chemicals as required; and(B) recycling the regenerated solution to the washer process. The process of the present invention significantly reduces the amount of waste water containing chemicals which must be discarded or treated in waste treatment facilities. The process also reduces the amount of process chemicals and water necessary for maintaining the washer processes used for aluminum and tin coil and container washer processes.

Abstract: A method is disclosed for the quantitative removal and concentration of desired molecules or ions, such as gases, anions and amino acids, from a source solution which may contain larger concentrations of other molecules. The method comprises bringing the source solution into contact with a solid cation-ligand-matrix consisting of a cation complexed to a ligand molecule covalently bonded to a matrix consisting of an organic spacer bonded to a solid inorganic support through a silicon atom. The cation has an affinity for the desired molecules to form a complex between the desired molecules and the cation portion of the solid cation-ligand-matrix at binding sites initially held by H.sub.2 O or other weakly coordinated ligands or via ion pairing.

Abstract: The present invention relates to the removal of metal ion contaminants as their anionic complexes from a variety of solutions containing said metal ion contaminants on an anion exchange resin, and the separation and purification of the anionic metal complexes by chromatographic elution utilizing a specially designed apparatus that enhances and maximizes the effects caused by different metal complex dissociation constants.

Abstract: The present invention relates to an ion exchange device for purifying water by reducing the nitrite and/or nitrate content, consisting of at least one container with a basic anion exchanger in chloride and/or sulphate form arranged therein and at least one additional basic anion exchanger layer in hydroxyl form or a hydroxyl-group-containing layer, in which the anion exchanger layers are arranged one behind the other directly and/or with the interposition of an intermediate layer and the anion exchange layer(s) in chloride and/or sulphate form is/are arranged not as a mixture but in (a) separate layer(s). The chloride and/or sulphate containing layer is arranged near or beneath the inlet aperture, preferably beneath the filter layer and/or (in the direction of flow of the water) in front of the anion exchange layer in the form of hydroxyl or containing hydroxyl groups.

Abstract: Spherical, polymeric organosiloxane ammonium compounds are disclosed with a silica-like skeleton consisting of: ##STR1## units in which R.sup.1 and R.sup.2 stand for a group ##STR2## in which R.sup.5 is alkylene the oxygen atoms are saturated by silicon atoms of other groups (II) with the optional inclusion of cross-linking agents, R.sup.3 has the meaning of R.sup.1 and R.sup.2 or stands for hydrogen, alkyl, cycloalkyl or benzyl, R.sup.4 is hydrogen or alkyl, cycloalkyl, benzyl, allyl, propargyl, chloroethyl, hydroxyethyl or chloropropyl, X stands for a monovalent to trivalent anion of a protonic acid which forms stable salts with amine bases and x can be a number from 1 to 3.

Abstract: A method for the preparation of an ion exchange sorbent containing at least one anion exchange resin, a ferromagnetic substance, and a water permeable organic polymer binder, as well as a process for the use of said sorbent to separate removable anions from feedstreams containing said anion.

Abstract: A process and apparatus is provided in which aqueous based wastes are processed to remove solids, decant phase separated product, optimize chemically for solvent specific extraction, remove toxic metals and organics via solvent extraction and remove residual metals and organics via flocculation/filtration and adsorption with activated carbon. The system employs chemical optimization of the aqueous waste stream by the addition of reagents to optimize subsequent treatment and the addition of chelating agents which inhibit the precipitation of heavy metals so that they are maintained in the waste stream as an organometallic complex which can be extracted via carbon dioxide extraction and concentrated for recovery, recycling or final disposal.

Abstract: Method and apparatus (10) includes the use of multiple containers (B-1-B-3) containing a weak base ion resin (R) through which plating rinse water (W) is pumped with precious metal such as potassium gold cyanide adsorbed by said resin and then with the cyanide sequentially eluted by potassium hydroxide, water, potassium thiocyanate, water, and the resulting effluent evaporated (at 40) and then chilled (at 44) to remove for reuse the gold and inorganic salt and base.

Abstract: A gold selective ion exchange resin and process for the recovery of gold from solutions thereof is described. The resin has a macroporous structure and functional groups selected from alkylamine groups wherein the alkyl chain has between 3 and 6 carbon atoms, preferably tributylamine groups. The functional group content of the resin is from 0,4 mmol/g to 1,8 mmol/g and the water retention capacity is at least 30%. The process for recovering gold involves adsorption thereof onto such resin, optionally directly from a slurry, and elution preferably using a thiourea solution.

Abstract: An improved process for removal of soluble contaminants from wastewater is disclosed which provides significantly enhanced contaminant removal and overall process efficiencies. The improved contaminant removal process is especially suitable for treatment of industrial effluents having high levels of dissolved cyanide and arsenic contaminants. Wastewater undergoes multiple stage sludge treatment, wherein sludge is mixed with wastewater sequentially in a plurality of discrete reaction stages for relatively short retention times. Reaction conditions which promote chemical and/or physical reaction of soluble contaminants with sludge are maintained, and liquid/solids separation is effected after each sludge treatment stage. Oxidizing agent is preferably mixed with the wastewater prior to multiple stage sludge treatment to change the oxidation state of inorganic contaminants and remove cyanide contaminants from solution.

Abstract: A process and apparatus is provided in which aqueous based wastes are processed to remove solids, decant phase separated product, optimize chemically for solvent specific extraction, remove toxic metals and organics via solvent extraction and remove residual metals and organics via flocculation/filtration and adsorption with activated carbon. The system employs chemical optimization of the aqueous waste stream by the addition of reagents to optimize subsequent treatment and the addition of chelating agents which inhibit the precipitation of heavy metals so that they are maintained in the waste stream as an organometallic complex which can be extracted via carbon dioxide extraction and concentrated for recovery, recycling or final disposal.

Abstract: In a process of removing complexly bound titanium and/or zirconium from acid aqueous solutions the solution which contains the complexly bound titanium and/or zirconium is conditioned in that its pH value is raised to at least 8, any precipitate thus formed is removed and the solution thus treated is passed through an ion exchange plant comprising a cation exchange material and an anion exchange material. The solution is preferably passed through an ion exchange plant which contains the cation exchange material in the H.sup.+ form and the anion exchange material in the OH.sup.- form. The process is particularly intended for the treatment of solutions obtained by the chemical treatment of surfaces preferably of metals, which solutions contain titanium and/or zirconium in the form of fluoro complexes.

Abstract: A method for reducing the amount of anionic metal-ligand complex in a solution comprises: (a) contacting the solution with a substance selected from: a compound having the formula: A.sub.w B.sub.x (OH).sub.y C.sub.z.nH.sub.2 O, wherein A represents a divalent metal cation, B represents a trivalent metal cation, C represents a mono- to tetravalent anion, and w, x, y, z and n satisfy the following: 0.ltoreq. z.ltoreq.x.ltoreq.4.ltoreq.w.ltoreq.1/2y and 12.gtoreq.n.gtoreq.1/2(w-x); a calcined product of said compound and mixtures thereof; and (b) separating the substance from the solution. A method for removing substantially all metal-cyanide, -thiocyanate, -thiosulfate, -citrate and/or -EDTA complex from a solution containing one or more of said complexes is also disclosed.

Abstract: A method for sorbing metal values from a slurry containing the same is disclosed. The slurry is advanced through a plurality of vessels arranged in series while countercurrently directing a sorbent through the vessels. Metal values are sorbed from the slurry in each of the vessels by mixing the pulp to achieve homogeneity with the pulp being maintained at a predetermined level in the vessel. A portion of the homogeneous pulp is directed into an interstage screening system disposed within the vessel and at least partially submerged beneath the predetermined pulp level, whereby the sorbent is separated from the slurry. The separated sorbent is primarily returned to the vessel while a portion of the sorbent is removed from the interstage screening system.

Abstract: Selenium can be removed from wastewater by contacting the wastewater with an adsorbent which is fly ash, peat moss, or a mixture thereof. The treated wastewater can then be discharged to the ground, and the spent adsorbent can be used as landfill or to enrich soils which are depleted in selenium.

Abstract: A method for extracting metal ions by contacting an aqueous solution containing the metal ions with an acidic phosphoric acid ester, characterized in that as the acidic phosphoric acid ester, an acidic phosphoric acid ester of the formula: ##STR1## wherein R.sup.1 is an alkylphenyl group having from 7 to 18 carbon atoms and R.sup.2 is an alkyl group having from 1 to 18 carbon atoms, is used.

Abstract: A process for removal and recovery of chromium ions (chromate, dichromate, or combinations thereof) from aqueous waste water of surface treatment phosphatizing solutions and for recycling of the treated waste water following replenishment wherein the aqueous waste water is initially partially clarified in a settling tank, with the effluent then being passed through an ion exchange column for removal of substantially all of the chromium ions therefrom. Following treatment in the ion exchange resin column, the chromium-free material is recharged with a supply of fresh chromium ions until the chrome ion content is at the desired level for metal surface treatment. The spent ion exchange resin columns are removed and replaced, as necessary, with the recharge of the resin columns making additional chromium available as a resource.

Abstract: A method for regenerating a carbon slurry used to produce a black matrix-type phosphor screen of a cathode ray tube is disclosed, in which excess carbon slurry is collected after the completion of a carbon-coating process onto a cathode ray tube panel. This collected carbon slurry is regenerated by means of an ion-exchange resin.

Abstract: Process for recovering gold from a leachate containing AuBr.sub.4.sup.-- comprising contacting the leachate with a quantity of sphagnum peat moss under conditions effective to concentrate the gold on the moss, and thereafter recovering the gold from the sphagnum peat moss.

Abstract: A method is disclosed for reducing the amount of a first contaminant and second contaminant in a solution to environmentally safe levels, said solution having a substantially greater amount of the first contaminant than the second contaminant. The method comprises: contacting the solution with an activated or calcined product of a compound having the formula A.sub.6 B.sub.2 (OH).sub.16 C.4H.sub.2 O, wherein A is a divalent metal cation, B is a trivalent metal cation and C is a mono- to tetravalent anion. The method further comprises separating the solution from the contacted product. The method is particularly useful for removing both selenium and sulfate, arsenic and sulfate, or arsenic and phosphate from a waste water stream. An unpredicted preference for selenium and arsenic, in the presence of other contaminants including sulfate and phosphate, was also shown herein.

Abstract: A liquid/solid contacting column and method of operating same is provided. The column is of the type in which a vertical series of stages is defined by vertically spaced perforated plates or trays which allow for forward flow up the column during which solid adsorbent in a fluidized state is contacted by liquid flowing up the column, and flow of solid adsorbent and liquid down the column during a reverse flow part of the operating cycle. The column is provided with outlet means in the form of one or more ports or ducts for a stream of liquid and solid adsorbent from the space above the lowermost plate or tray and wherein such outlet means is located at a predetermined height above said lowermost plate or tray.

Abstract: Disclosed is a novel activated carbon/alumina composite and a method of preparing the same. The method includes providing a blend containing alumina powder, peptizing agent, water and activated carbon powder and mixing the blend to peptize the alumina and form an aqueous mixture. A green body is then formed from the mixture, dried and heated to form the activated carbon/alumina composite.

Abstract: A process for pretreatment of chromium-rich oxide surfaces of nuclear reactor cooling system components involves application of a dilute acidic reagent comprising potassium permanganate and chromic acid, at elevated temperatures.

Abstract: Iodine and organic iodine compounds which may be radioactive and which may be found in waste gases or vapors from nuclear reactors can be removed from such gases or vapors by passing the iodine or organic iodine compound-containing gases or vapors through a layer of binder-free silver-exchanged molecular sieve granulates of the faujasite type.

Abstract: A method for recovery of metal and cyanide from plating baths and rinse waters includes formation of hydrogen cyanide by acid treatment of such solutions, followed by HCN removal through diffusion across a microporous membrane. The method is applicable in a system wherein soluable metal cyanides and metal cyanide complexes are concentrated through use of a basic anion exchange system. Free hydrogen cyanide is released from the anion exchange system by means of an acid regenerant. In a preferred application of the invention, HCN, once having diffused through the microporous membrane, is neutralized with sodium hydroxide, to form a sodium cyanide solution that can be returned to a plating bath.

Abstract: Recovery of precious metals such as gold and silver from aqueous cyanide solutions thereof, by contact with a reagent containing a guanidine functionality. The guanidine reagent extracts the precious metal from the aqueous solution which is subsequently stripped from the guanidine reagent and recovered by conventional methods. Certain novel guanidine compounds suitable for extracting gold and silver are disclosed.

Abstract: Strong base ion exchange resins derived from crosslinked vinylbvenzyl chloride polymers are particularly suitable for purifying condensate waters for steam regenerating equipment. Preferred embodiments utilize gellular anion exchange resins to remove corrosion products from boiler condensate waters.

Abstract: A method for cleansing metal-containing solutions, particularly, but not exclusively, process water which contains such metals as mercury, cadmium and/or lead, where the metals concerned are present in water-soluble form, such as the form of a chloride complex. The method is characterized by passing the solution through an ion-exchange material (4) which consists essentially of sulfhydrated cellulose, the metals being adsorbed in the sulfhydrated cellulose; regenerating the ion-exchange material (4) subsequent to the adsorption of a predetermined quantity of metal, by rinsing the ion-exchange material with an aqueous solution that contains hydrochloric acid (HCl) at a concentration of at least about 1 molar HCl; and precipitating the metals concerned in sulphide form, in a known manner, from the liquid that is eluted from the ion-exchange material (4) in the aforementioned rinsing process.The invention also relates to apparatus for carrying out the method.

Abstract: A method for extracting metal ions by contacting an aqueous solution containing the metal ions with an acidic phosphoric acid ester, characterized in that as the acidic phosphoric acid ester, an acidic phosphoric acid ester of the formula: ##STR1## wherein R.sup.1 is an alkylphenyl group having from 7 to 18 carbon atoms and R.sup.2 is an alkyl group having from 1 to 18 carbon atoms, is used.

Abstract: A method for reducing the amount of anionic metal-ligand complex in a solution comprises: (a) contacting the solution with a substance selected from: a compound having the formula: A.sub.w B.sub.x (OH).sub.y C.sub.z .multidot.nH.sub.2 O, wherein A represents a divalent metal cation, B represents a trivalent metal cation, C represents a mono- to tetravalent anion, and w, x, y, z and n satisfy the following: 0.ltoreq.z.ltoreq.x.ltoreq.4.ltoreq.w.ltoreq.1/2y and 12.gtoreq.n.gtoreq.3/2x; a calcined product of said compound and mixtures thereof; and (b) separating the substance from the solution. A method for removing substantially all metal-cyanide, -thiocyanate, -thiosulfate, -citrate and/or -EDTA complex from a solution containing one or more of said complexes is also disclosed. The latter method comprises contacting the solution with a sufficient amount of substance consisting essentially of a compound selected from: hydrotalcite, calcined hydrotalcite and mixtures thereof.

Abstract: An improved process is disclosed for the purification of an impure aqueous solution containing heavy metal ions which comprises passing the impure solution through a bed of activated alumina adsorbent. The heavy metal ions are removed from the impure aqueous solution by adsorption onto the activated alumina adsorbent. The adsorbent may be regenerated for reuse and the adsorbed metals recovered by subsequently stripping the metal ions from the adsorbent and recycling the metal ions back to the process of origin. The pH of the effluent may be monitored to determine when the capacity of the adsorbent has been reached and regeneration of the adsorbent should be commenced. In a preferred embodiment, a portion of the activated alumina is pretreated with acid before passing the impure solution through the adsorbent to enhance the chromium ion adsorption of the acid-treated activated alumina and a portion of the regenerated activated alumina is again treated with acid after each regeneration cycle.

Abstract: Recovery of precious metals such as gold and silver from aqueous cyanide solutions thereof, by contact with a reagent containing a guanidine functionality. The guanidine reagent extracts the precious metal from the aqueous solution which is subsequently stripped from the guanidine reagent and recovered by conventional methods. Certain novel guanidine compounds suitable for extracting gold and silver are disclosed.

Abstract: A process for treating a waste water containing uranium and fluorine comprises a neutralizing precipitation step wherein slaked lime is added to the waste water containing uranium and fluorine and precipitate thus formed in separated and removed, and an adsorption step wherein supernatant from the neutralizing precipitation step is contacted with a chelating resin which can selectively adsorb fluorine ions and another chelating resin which can selectively adsorb uranyl ions to thereby adsorb and remove the fluorine and uranyl ions remaining in the supernatant. Eluates of the ions adsorbed by the chelating resins and waste liquors for washing and regeneration of these resins are returned to the neutralizing precipitation step. Prior to the neutralizing precipitation step, a decarbonation step may be provided for decomposing carbonate ions, if they are contained in the waste water to be treated.

Abstract: A process for extracting metals from aqueous solutions containing such metals comprising contacting such an aqueous solution with an asphaltene to extract at least one metal from the aqueous solution to the asphaltene, and recovering the thus extracted at least one metal from the asphaltene. Also disclosed is a process for sulfonating a petroleum fraction containing asphaltenes, the thus sulfonated asphaltenes being advantageously employable in the process for extracting at least one metal from an aqueous solution containing such metal.

Abstract: Disclosed is a method of preparing an activated carbon/alumina composite. The method includes providing a blend containing activated alumina powder and activated carbon powder. Added to the blend is an aqueous solution to form a mixture. A green body is then formed from the mixture and heated to form the activated carbon/alumina composite.

Abstract: Amine extractants useful in extracting metallic anions are modified with Lewis bases, having substantial organic solubility, such as tributyl phosphate, to improve the extraction capability of such amines. Generally, addition of Lewis bases to weakly basic amines increases the basicity of such amines.

Abstract: This invention relates to a process for treating waste solutions and rinse waters, especially those from electroless plating processes to remove organometallic complexes and complexing agents, particularly copper and copper-EDTA complexes by eluting the waste solutions through anionic exchange resins.

Abstract: An improved process for the recovery of precious metal values is disclosed. By this process precious metals in the form of anionic complexes are contacted with a weak-base anion exchange resin capable of complexing with the anionic complex. Such weak-base anion exchange resins contain weak-base functionalities derived from linear or cyclic polyaminoalkylene amines which have more than 1 amine moiety and at least 3 carbon atoms in a 1,X-alkylene moiety or moieties separating at least 1 amine moiety from a second amine moiety (i.e., X is an integer greater than 2).

Abstract: An improved process is disclosed for the purification of an impure aqueous solution containing heavy metal ions which comprises passing the impure solution through a bed of activated adsorbent containing at least 20 wt. % activated hydrotalcite formed by reacting activated magnesia with an aqueous solution containing ions of aluminate, carbonate, and hydroxyl. The heavy metal ions are removed from the impure aqueous solution by adsorption onto the activated hydrotalcite-containing adsorbent. The adsorbent may be regenerated for reuse and the adsorbed metals recovered by subsequently stripping the metal ions from the adsorbent and recycling the metal ions back to the process of origin. The pH of the effluent may be monitored to determine when the capacity of the adsorbent has been reached and regeneration of the adsorbent should be commenced.

Abstract: In accordance with the invention, an improved process is provided for the efficient removal and recovery of silver from an impure solution containing silver ions which comprises contacting the silver-containing solution with an activated alumina adsorbent to selectively adsorb the silver ions from the solution and the lower the subsequent effluent discharge to less than 1 ppm silver, treating the activated alumina with a regeneration fluid to recover the silver ions from the adsorbent, and reducing the recovered silver ions to metallic silver.

Abstract: A process is described for the substantially complete recovery of cyanide reagent and metal forming water soluble metal-cyanide complexes contained in mill effluents and waste waters. The process is comprised of a loading cycle wherein the metal-cyanide complexes are adsorbed onto a basic ion exchange resin and the free cyanide containing column effluent is returned to the mill. The metal ions, which are usually mostly copper, nickel and zinc, and the complexing cyanide are eluted in the subsequent regenerant cycle by an acid solution having controlled pH and controlled redox potential, the latter being measured against the saturated calomel electrode. The preferred oxidant to control the redox potential of the regenerant solution is hydrogen peroxide. The generated hydrogen cyanide is sparged with air, or removed by subatmospheric pressure from the regenerant solution, and dissolved in an alkaline scrubber solution for reuse. The metal ions are recovered from a bleed solution.

Abstract: A solvent extraction process for the separation of one or more precious metal species from other precious metal species and possibly also base metal species contained in an aqueous acidic solution of the type produced during the recovery of precious metals from ore or scrap in which the solvent contains an extractant which is a mono-N-substituted amide. Also a mono-N-substituted amide extractant. The extractant permits better separation factors generally and also enables platinum to be extracted before palladium and permits improved extraction of iridium from rhodium.

Abstract: A gold recovery process is disclosed in which the gold content of ores, including carbonaceous ores or mixtures of carbonaceous and oxide ores, is extracted by a simultaneous chlorine leach and ion exchange resin adsorption procedure. The process eliminates or reduces the degree of oxygenation and cyanidation required to conduct a standard gold extraction process.

Abstract: A process for the extraction of metals selected from the group consisting of zinc (II), silver (I), cadmium (II), mercury (II), nickel (II), cobalt (II), and copper (II) from an aqueous solution containing, in addition to said metals, metals selected from the group consisting of calcium (II) and magnesium (II) is disclosed. The process comprises contacting the aqueous solution having an equilibrium pH within the range of about 0.2 to about 3 with an extractant. The extractant comprises an organic-soluble dithiophosphinic acid or ammonium, alkali or alkaline earth metal salt thereof represented by the formula: ##STR1## wherein R.sup.1 and R.sup.2 are the same or different and are selected from the group consisting of substituted or unsubstituted alkyl, cycloalkyl, alkoxyalkyl, alkylcycloalkyl, aryl, alkylaryl, aralkyl and cycloalkylaryl radicals having from about 2 to about 24 carbon atoms and X is either hydrogen or an ammonium, alkali or alkaline earth metal salt forming radical.

Abstract: A process is provided for removing cyanide from a dilute cyanide solution. The solution is passed through a weak base anion exchange resin to absorb cyanide complexes. The resin is eluted with a weakly basic Ca(OH).sub.2 solution, to produce a cyanide-rich eluate. Elution is accomplished by recycling the eluting fluid past a bed of solid Ca(OH).sub.2, to maintain the eluting fluid in Ca(OH).sub.2 saturation. Recycling in this manner produces an eluate with relatively high cyanide concentration using economical reagents. The eluate is subjected to an acidification/volatilization process including acidification, preferably with H.sub.2 SO.sub.4, heating by introduction of steam and removal of volatilized HCN by an air sparge. The HCN-rich off-gas and slats produced therefrom may be recycled in the process. The cyanide-depleted waste streams may be disposed of in, for example, tailings ponds.

Abstract: A method of decontaminating radionuclide-contaminated acid insoluble corrosion products from primary system surfaces in pressurized water reactors by oxidation and concurrent dissolution in an acidic decontamination solution of the corrosion products which have been made acid-soluble by the oxidation. The characterizing feature of the method is that the oxidation is carried out at relatively low temperatures with a water-based oxidation agent having a pH below 7 and containing cerium nitrate, chromic acid and ozone.

Abstract: Noble metals are recovered from their cyanide complexes in aqueous solution by reaction with red phosphorus. To this end, red phosphorus is used in quantities of 1 to 5 weight %, based on the aqueous solution of the noble metal cyanide complex, in combination with an additional strong oxidizing agent.

Abstract: Method of separating heavy metals from complex-forming substance of aminocarboxylic acid type, or salts thereof in aqueous solutions, as well as a method of removing heavy metals from the solutions containing said complex-forming substance. A solution containing heavy metals in complex form and complex-forming substances of aminocarboxylic acid type is contacted with a ion exchanger having polyethyleneimine active groups, whereupon free non-complexed heavy metal cations are displaced out of said ion exchanger by an acid solution of 0.5-30 percent concentration, and the ion exchanger is converted back into its active form by a solution of an alkali hydroxide, carbonate, or hydrogen carbonate of 0.5-30 percent concentration.