RECOVERY OF METAL VALUES

Abstract: Gold and silver, and their sulfides, selenides and tellurides are oxidized with water miscible dipolar aprotic solvents containing bromides and/or chlorides and as oxidant cupric and/or ferric ions. This oxidation reaction is used to recover gold and silver; to produce gold mirrors and to etch copper and gold.

Description: RECOVERY OF METAL VALUES THIS INVENTION relates to the reccvery of metal values an particularly gold and silver. Australian Patent Application No. 39230/78 is directed t a process for the recovery or refining of silver compris ing the steps of, if required, converting the silver t silver chloride, dissolving the silver chloride in dipolar aprotic solvent such as dimethylsulfoxide in th presence of additional chloride salts such that the silve chloride dissolves as the dichloroargenate salt, separat ing any insoluble solids, precipitating purified silve chloride from solution by the addition of water o methanol and separating the silver chloride precipitate. Throughout the following description and claims the ter halide refers only to chloride or bromide. It has no been established that copper (II) halides, or ferric halides dissolved in dimethylsulfoxide, dimethylfor amide or acetonitrile or other water miscible dipolar aprotic solvents or "' mixtures of such dipolar aprotic solvents containing halide salts of cations such as sodium, cop¬ per, potassium, lithium, tetraalkyla moniu , calcium and magnesium are very good oxidising agents for oxidising metals which form halo-complexes, such as copper, silver and gold, and that such an oxidising agent is very useful in the recovery of metal values from materials which can be oxidised to form halo-complexes. Other oxidants, such as chlorene or bromine in acetonitrile containing halide ions, can oxidise gold or silver. Thus in one form the invention resides in an oxidising agent comprising a water miscible dipolar aprotic solvent or mixtures of such solvents containing halide ions, copper (II) and/or ferric ions and cations (including cupric and ferric) which forms soluble salts with the halo complex anions in- the appropriate solvent. In another form the invention resides in a method o oxidising gold, silver and their sulfides selenides o tellurides and dissolving them as their gold or silve halo-complex salts leaving insoluble elemental sulfur, selenium or tellurium as appropriate, comprising leaching the material containing gold and/or silver with a wate miscible dipolar aprotic solvent containing halide salts and an oxidant which does not react extensively with the solvent but does oxidise gold, silver and their sulfides selenides and tellurides in solution in the solvent. The various aspects of the invention and the applicatio of the oxidising agent in the recovery of metal values will be readily apparent from the following descriptio in which dimethylsulfoxide (DMSO) is taken as a typical water miscible dipolar aprotic solvent and cupric chloride is the oxidant. Dimethylfor amide and acetonitrile are also preferred water miscible dipolar aprotic solvents, and cupric bromide or ferric halides are other preferred oxidants. The invention may be applied to a method of dissolving copper, silver, and gold such as are found in anode slimes and of recovering silver halide and gold from the result¬ ing solutions. It also may be applied to a method of refining silver and gold from oxidisable materials such as bullion or dental alloys containing those elements. Ref¬ ining is achieved by leaching said materials with copper (II) halide in a dipolar aprotic such as dimethylsulfoxide (DMSO) containing halide salts of inert cations such as sodium, potassium, lithium, calcium, tetraalkyl ammonium, magnesium, copper and iron, separating the resulting solu¬ tion, containing halo-complexes of silver, gold and copper, from insoluble material then adding a hydroxylic solvent, such as water or methanol. On addition of the MPI hydroxylic solvent, silver halide precipitates and i separated. If copper (I) halide and gold halo-complex a present, gold is reduced and precipitated and is separate also. Any remaining copper (I) halide may be oxidised t copper (II) halide for recycling, using for example oxyge and HCl or chlorine or bromine as oxidants. The invention is also applicable as a method of recoverin gold from solutions containing halo-complexes of gold i dipolar aprotic solvents, whereby water or methanol ar added to such solutions to destabilize the gold halo complex. In the presence of copper (I) halide or othe reductant, gold is reduced and precipitates. AuCl " + CuCl " • CuCl 2 Au + 2C1~ -(1 The gold is believed to be in solution as Au(Eal 2 ) - Othe reductants besides Cu(I) salts include ferrous salts oxalic acid, SO-, hydrazine as are familiar to those skil *" I led in the art of reducing gold (I) and gold (III). Th invention is also applicable as a method of leachin copper, silver or gold from suitably masked materials t produce circuit boards for electronic devices. The reac tions in dipolar aprotic solvents containing chloride ion are believed to be as follows:- Cu + CuCl 2 + 2C1~ -> 2CuCl 2 -(2) Ag + CuCl 2 + 2C1 " • ¥ Agci " + CuCl- -(3) Au + CuCl 2 + 2C1 "" AuCl " + C CI2 -(4) The method of leaching halo-complexes of precious metal from materials containing the metals, their sulfides, their selenides their tellurides and their halides is especially well suited tc processing anode slimes fro copper refineries. The precious metals are recovered as metal, or halide by adding hydroxylic solvents, such a water or methanol, to the dipolar aprotic leach solutio containing the metal halo-ccmplexes and ferrous or cuprou halides and collecting the precipitated solids. The halo complexes are destabilized by adding hydroxylic solvent to the dipolar aprotic. Impurities such as silicates an sulfur selenium and tellurium remain in the leach residue The concept of oxidation and dissolution with cupric o ferric halides of oxidisable materials which form stabl halo-complexes, in dipolar aprotics, separation fro insolubles, precipitation of precious metal values eithe as halide or metal by adding a hydroxylic solvent to th dipolar aprotic solution, in the presence of a reductan if gold complexes are present and separation of the preci pitated precious metal values, provides a new method o recovering and refining materials containing silver an gold, such as gold bullion, coins, anode slimes, gol plate, dental alloys, cemented silver, computer scrap photographic residues and catalysts in inert supports. The methods are based en the following chemistry. In dr dipolar aprotics such as DMSO, containing a source o halide ions, either as a suspension or- in solution iro (III) or copper (II) halides are powerful oxidising agent of E° greater than 0.6V nhe. In dry acetonitrile cupri halides are even more powerful, even in the absence o other sources of halide ions, because of strong solvatio of copper (I) by acetonitrile. Thus many species which form halo-complexes can be gener ated in dipolar aprotic solvents containing halide ions b oxidising the appropriate compounds. The oxidant i useful for oxidising sulfides, selenides and tellurides o many metals, leaving a residue of sulfur, selenium o tellurium. Typical reactions are shown in equations 2 t 10 inclusive. Ag-S 2CuCl + 4C1~ -» 2AgCl~ + 2CuCl 2 + S -(5 Ag 2 Se + 2CuCl 2 + 4C1~ 2AgCl. 2CuCl~ + Se -(6 Pb + 2CuCl 2 + 3C1 -» PbCl 3 + 2CuCl. -(7 Cu 2 S + 2CuCl 2 + 4C1~ -? 4CuCl 2 + -(8 ZnS + 2CuCl 2 + 4C1 " ■ * ZnCl^ " + 2CuCl 2 + S -(9 CuFeS 2 + 4CuCl 2 + -4C1 " -» FeCl 2 + 5CuCl~ + 2S-(10 2— Of course, other halo-complexes, .e.g. AgCl- j than w have written may be present. In some cases (eg. wit chlorine as oxidant) , the gold may be oxidised to the + oxidation state. •It is possible to use other dry dipolar aprotic solvent than DMSO e.g. dimethylformamide, which are good catio sol ators or to mix them with DMSO. It is of cours essential that the halide salt be chosen so that it cations form soluble salts with halo-complexes of th metals being treated, even if the halide salt {eg. NaCl itself is not appreciably soluble in the dipolar aproti solvent (eg. DMF) . Acetonitrile is a somewhat specia case, since it solvates Cu + so selectively, such tha + — + — + salts like Cu AgCl-, Cu AuCl- are soluble, whereas Na an Li salts are not. Thus CuCl_ or CuBr_ without othe halide ions are especially good oxidants in acetonitrile. The following examples illustrate • some aspects of th invention as discussed above. Example I 0.65g of particulate gold was stirred for one hour wit 5ml of lMCaCl 2 in dry DMSO at 80°C, containing lg CuCl 2 - Some of the gold dissolved, leaving 0.23g undissolved and a solution containing 84g/l gold. On addition of 10ml of water gold metal (0.42g) slowly precipitated. OMPI Example II δ.5g of finely divided silver selenide was stirred wit 20g of CaCl 2 .2H 2 0 in 100ml of dry DMSO containing 17g of CuCl-.2H 2 0 at 80°C for one hour. The silver dissolved to give 41g/l of silver in solution. The residue contained selenium and a little unreaσted Ag 2 Se. On addition of 100ml of water to the DMSO solution, silver chloride precipitated quantitatively. A similar result was obtaine with silver sulfide, except that sulfur was found in the residue after leaching, rather than selenium. Example III 5g of particulate silver was stirred with 20g of CaCl_- 2H 2 0 in 100ml of dry DMSO containing 17g of C Cl 2 .2H 2 0 at 80°C. the silver dissolved to give 45g/l silver in solution. On addition of 150ml of water, silver chloride precipitated quantitatively. A similar result was obtained when a suspension of 15g NaCl or KCl replaced the CaCl 2 .2H 2 0 and when 17g FeCl 3 .6E 2 0 replaced the CuCl 2 - Oxygen was bubbled through the filtrate for 5 hours and the PH was maintained below 2 by the addition of HC1. The resulting CuCl 2 , CaCl 2 , DMSO, H 2 0 solution was distilled under reduced pressure to remove the water and the dry oxidant in DMSO dissolved a further 5g of particulate silver. On addition of 150ml of methanol, silver chloride precipitated. Caution: At temperatures aiove 130°C, CuCl 2 reacts vigorously with DMSO, so such temperatures should be avoided, or DMF used in place of DMSO. Example IV Experiment III was repeated with a solution containing 90ml of DMSO and 10ml of DMF in place of the 100ml of DMSO. All the silver dissolved and precipitated ' as AgC on addition of water. Example V 1.5g of dry anode slimes from Copper Refineries Pty. Ltd of Townsville, Australia, containing about 20% silver a well as copper lead, sulfur, selenium and other component including DMSO soluble organic material, was stirred fo one hour with 4.0g of CaCl 2 .2H 2 0 in 30 ml DMSO containin 4.2g CuCl 2 .2H 2 0 from which water had been distilled. Th slurry was centrifuged and the insoluble fraction weighe 1.13g. It contained no gold or silver. Water (15ml) wa added to the DMSO filtrate to precipitate O.lg of a whit solid containing silver and a barely detectable trace o gold. The remainder of the silver (60%) and most of th gold (74%) remained in the filtrate possibly as colloida gold because the leach solutions were less concentrated i gold and silver (-C3g/1) than desirable (>10g/l). Example VI The following materials dissolved in 50ml of dry DMS containing 5g CuCl 2 .2H 2 0, and 5g CaCl 2 .2H 9 0 from whic water had been distilled under reduced pressure. Solution o were stirred and heated at 80 C for one hour, filtere then 50ml of water was added and the precipitate was weighed. Material Weight Leach Residue Water Precipitated gm gm gm Silver 0.99 0.00 1.19 Gold a 0.50 0.00 0.49 Copper 1.07 0.00 0 . 03 Ag 2 S 1.05 0.03 1. 18 Ag 2 Se a 0.73 0.16 0 . 63 Cu 2 S 1.07 0.17 0. 01 Pb 1.00 0.00 0. 00 PbS 1.00 0.00 0. 00 Pt 0.55 0.-50 0. 00 CuFeS 2 1.00 0.50 0. 00 AgCl 1.00 0.03 0 . 90 Ag/Au b 1.00 . 0.17 0. 60 a) 25ml of solvent b) equal weights c) as gold Example VII Some scrap material (1.07g) frcm a computer consisting of mild steel, copper and silver in layers, such as is used for preparing printed circuits, was first treated with o CuSO4. in water at 80 C to dissolve the mild steel and cement out copper. The solid was dried and dissolved over 10 hours at 80 C in 50ml of dry DMSO containing 5g CaCl 2 . 2H 2 0 and 5g CuCl 2 .2H 2 0. The residue weighed 0.02g. On addition of water (50ml) white silver chloride precipi¬ tated. Example VIII In another experiment with the material of Example VII, the mild steel face was masked as were portions of the silver face. After submersion in the DMSO oxidising solution for one hour, the unmasked silver faces were etched. Thus composition has application for etching copper and silver. OMPI In another form the invention resides in a method o recovering gold and silver from materials containing sam which comprises leaching the material containing the gol and silver with a water miscible dipolar aprotic solven containing halide salts and an oxidant which does no react extensively with the solvent but does oxidise gol and silver and their sulfides and selenides in th solvent, separating the leach solution from the material adding water to the leach solution to precipitate silve halide and, in the presence of a reducing agent such a CuClI or FeCl 2 or S0 2 to precipitate gold, said reducin agent being sufficiently reactive to reduce chlorine, bromine and gold salts in aqueous dipolar aprotic solvent but insufficiently reactive to reduce copper halides t copper metal. In acetonitrile and other nitriles the Cu ion is ver strongly solvated (other cations are not). Thus in dr CH_ CN the following useful reaction can occur without excess halide ions being present and cupric halides (but not ferric halides) are especially good oxidants. Cu 2+ + 2 Cl " + Au -» Cu + + Au ClJ or (Ag, g 2 S, g 2 Se) or Cu + + 2 Br~ + Au -^ Cu + + AuBrϋ Thus in dry acetonitrile additional chloride or bromide salts are not necessary to form the desired complex. The source of chloride and bromide ions may be excess Cu Cl 2 or Cu Br 2 when using dipolar aprotic solvents other than acetonitrile. OMPI C in the presence of bromide ions in DMF and DMSO is a more powerful oxidant for gold and silver than Cu + in the presence of chloride ions. Materials containing silver are oxidised faster and at lower potentials than are materials containing gold. In another form the invention resides in a method of recovering gold and silver separately from materials containing same which comprises leaching the material containing the gold and silver with a water miscible dipolar aprotic solvent containing halide salts and an oxidant which does not react extensively with the solvent but does oxidise gold and silver in solution in the solvent, separating the leach solution from the material, if necessary oxidising the leach solution to remove any reducing agents present in the leach solution, adding water to the leach solution to precipitate silver halide, separating the precipitated silver halide, and adding a reducing agent to the separated solution to- precipitate the gold, said reducing agent being sufficiently reactive to reduce chlorine, bromine and gold salts in aqueous dipolar aprotic solvents but insufficiently reactive to reduce copper halides to copper metal. Some further aspects of the invention will be better understood by reference to the following specific examples. Example IX A 0.69g lump of a dental allow containing 90% gold was leached with 15ml 1M CuCl.,, 1M CaCl 2 in DMF at room temp¬ erature for 7 days. 35% of the alloy dissolved and 0.23g of gold entered the solution. After 1 further day, only 2% more gold dissolved. On addition of water, 95% of the leached gold precipitated. The remaining lump (0.442g) was leached with 0.2M CuCl 2 , 0.5M LiBr in 15ml of DMSO. After 6 hours the weight had reduced to 0.420g. Example X 0.5g of an anode slime supplied by the Electrolytic Refin¬ ing and Smelting Co. of Pt. Kembla, was leached with 10ml of DMSO containing 0.15M C Cl 2 and 0.05M CuCl 2 in DMSO containing 0.2M CaCl 2 . After 22.5 hours at 25° with stirring, 70% of the silver and 15% of the gold had dis¬ solved. When 0.2M LiBr was added, a further 60% of the gold and the remainder of the silver dissolved in 2 hours. Example XI 0.2475g of -200 mesh chalcopyrite was oxidised with 5ml of 0.7M CuCl 2 , 0.7M CaCl 2 in DMSO at 80° for 1 hour. The residue weighed 0.115g and contained O.OSg sulfur. Thus CuFeS, is oxidised by this oxidant. Example XII 60ml of DMSO containing 124 CaCl- and 1M CuCl 2 was dehyd¬ rated by distilling off the water and mixed with 40ml of acetone. It was stirred for one hour with 2.5g of -40 micron silver powder and 2.5g copper powder. The residue weighed 1.077g and was mainly silver. On addition of water, easily filterable AgCl was obtained. Example XIII A solution of anhydrous CuCl 2 (1.5g), LiCl (5.8g) in 50ml acetone was stirred with 0.51g of gold powder for 2 hours. The solution had the odour of mesityl oxide. After 2 hours, 0.21g gold had dissolved and was precipitated by adding water. Example XIV 1M NEt 4 Cl plus 0.5M anhydrous CuCl 2 in 15ml acetonitril was stirred at 35°C for 3 hours with 0.503g gold powder The residue weighed 0.222g. On dilution with 15ml o water, 0.247g of gold precipitated. Example XV 10ml of 0.124 AuCl_ in dry DMSO was stirred with 0.550 gold powder at 40°C for 2 days. 0.526g of the gold di solved. On addition of H_0 no gold precipitated but o addition of CuCl, gold precipitated. Thus AuCl 3 dipolar aprotics containing chloride ions is also an oxi dant for gold and a reducing agent like CuCl is needed gold is to be precipitated from solutions of AuCl " in su solvents by adding water. Example XVI 10 ml of solution containing 0.25 M CuCl 2 and 1 M LiC in dry acetonitrile was stirred with 0.2 g geld at 17° for 2.5 hours. The gold dissolved to give 0.1 M gol in solution. On addition of 10 ml of water all the gol precipitated. -When the experiment was repeated wi silver an insoluble salt, LiAgCl , was formed. This sal dissolved in DMSO containing 1 M LiCl. Example XVII 10 ml -of a solution containing 4% bromine and 1 M lithi chloride in dry acetonitrile rapidly dissolved 0.2 g finely divided gold at 17°C. When hydrazine was added a reductant, 99% of the gold precipitated. O Example XVIII 10 ml of a solution containing 0.25 M CuBr 2 in dry ac tonitrile was stirred with 0.2 g silver at 17°C for thre hours. The silver dissolved. On addition of 5 ml o water silver bromide precipitated. The experiment was repeated with 0.1 g gold. On additio of water, gold precipitated. The forms in which gold metal precipitates from solution of gold (I) or gold (III) salts include powders, flakes colloidal suspensions and mirrors. Gold flakes, powder and colloids have many practical applications which ar described in the literature. Gold mirrors are especiall desirable and so called electroless or chemical depositio of gold onto surfaces relies on in-situ reduction of soluble gold compound with chemical reductants, such a hydrazine / - and borohydrides or else via replacement or less noble metallic surface (e.g. copper or nickel). Suc methods - have the disadvantage that the reaction product of the reductant build up in the solution in a continuou process. The soluble gold compounds are often cyano comp lexes which are undesirable for environmental reasons Halo complexes of gold (I) are preferable as sources o soluble gold, for mirrors, colloids, flakes and powders. The discovery that solutions of gold halo-complexes con taining cuprous or ferrous halides and other halide salt in dimethylformamide, acetonitrile or dimethylsulfoxid give flakes, powders, colloidal suspensions and mirrors o surfaces such as glass, when water is added to the solu tions, suggests a new method of making gold films, gol flakes, colloidal gold and gold powders. As disclose herein solutions of a variety of concentrations up to 0.5M gold can be prepared by dissolving gold with cupric halide OMPI in dimethylformamide acetonitrile or di ethylsulfoxid containing salts of halide ions. On addition of water the copper (I) halide acts as a reductant and a gol mirror forms on surfaces, such as glass, which are clean The solution is colloidal but in time, gold powders an flakes form in addition to the gold mirror. It should be appreciated that the method involves reversible redox couple CuCl 2 /CuCl 2 or CuBr 2 /CuBr 2 o FeCl 3 /FeCl 2 or FeBr 3 /FeBr 2 so that the solutions can b recycled, after removing water, to dissolve more gold an precipitate new films without further addition of oxidan or reductant. Thus impurities do not build up in th solutions on cycling. The method involves dissolving gol as the AuCl~ or AuBr complex as described herein, the reducing it with cuprous or ferrous halide as a film ont surfaces prepared by methods familiar to those skilled i the art, by adding water to the dry DMF acetonitrile o DMSO solution. Thus in another form the invention resides in a method o producing gold mirrors which comprises applying a solu tion of gold as the AuCl " or AuBr " complex in a wate miscible dipolar aprotic solvent as described herein a a film to a suitably prepared glass surface, reducing i by the addition of water in the presence of cuprous o ferrous halides to deposit a film of gold on the surface.

Claims: THE CLAIMS defining the invention are as follows :- 1. A method of oxidising gold, silver and their su fides selenides or tellurides and dissolving them as the gold or silver halide complex salts leaving element sulfur selenium or tellurium as appropriate, comprisi leaching the material containing gold and/or silver wi a water-miscible dipolar aprotic solvent containi halide salts and an oxidant which does not react exten ively with the solvent but does oxidise gold, silver a their sulfides, selenides and tellurides in the solvent. 2. A method of recovering gold from solutions of go halo-complexes in water miscible dipolar aprotic solven wherein the gold complex is reduced to gold by t addition of water in the presence of a reducing agent by the addition of water followed by the addition of reducing agent, said reducing agent being sufficient reactive to reduce chlorine, bromine and gold salts aqueous dipolar aprotic solvents but insufficient reactive to reduce copper halides to copper metal. 3. A method of recovering gold which comprises disso ving the gold as a gold halo complex in a water miscib dipolar aprotic solvent containing halide salts and oxidant which does not extensively react with the solve but does oxidise the gold in solution, adding water to t solution in the presence of a reducing agent, or addi water to the solution followed by the addition of reducing agent, said reducing ' agent being sufficientl reactive to reduce chlorine, bromine and gold salts i aqueous dipolar aprotic solvents but insufficientl reactive to reduce copper halides to copper metal. OMPI 4. A method of recovering gold and silver from materials containing same which comprises leaching the material con¬ taining the gold and silver with a water miscible dipolar aprotic solvent containing halide salts and an oxidant which does not react extensively with the solvent but does oxidise gold and silver in solution in the solvent, separating the leach solution from the material, adding water to the leach solution to precipitate silver halide and, in the presence of a reducing agent gold, said reduc¬ ing agent being sufficiently reactive to reduce chlorine bromine and gold salts in aqueous dipolar aprotic solvents but insufficiently reactive to reduce copper halides to copper metal. 5. A method as claimed in claim 4 wherein the reducing agent is present in the leach solution as a result of reactions occurring during the leaching step. 6. A method of recovering gold and silver separately from materials containing same which comprises leaching the material containing the gold and silver with a water miscible dipolar aprotic solvent containing halide salts and an oxidant which does not react extensively with the solvent but does oxidise gold and silver in solution in the solvent, separating the leach solution from the material, if necessary oxidising the leach solution to remove any reducing agents present in the leach solution, -adding water to the leach solution to precipitate silver halide, separating the precipitated silver halide, and adding a reducing agent to the separated solution to pre¬ cipitate the gold, said reducing agent being sufficiently reactive to reduce chlorine bromine and gold salts in aqueous dipolar aprotic solvents but insufficiently reac¬ tive to reduce copper halides to copper metal. OMPI 7. A method as claimed in any one of claims 1 to wherein the solvent is selected from the group comprisi dimethylsulfoxide, dimeth lformamide, dimethyl cetamid N-methylpyrrolidone, acetonitrile, acetone and mixture thereof. 8. A method as claimed in any one of claims 1 to wherein the halide salts are salts of cations selecte from the group comprising sodium, potassium, lithium calcium, magnesium, tetraalkyl ammonium, copper and iron. 9. A method as claimed in any one of claims I to wherein the oxidant is selected from the group comprisin cupric bromide, cupric chloride, ferric chloride, ferri bromide, chlorine and bromine. 10. A method as claimed in any one of claims 1 to wherein the solvent is dimethylsulfoxide or dimethylfor raamide, or mixtures of dimethylsulfoxide and dimethylfor mamide and the oxidant is selected from the group com prising cupric chloride, cupric bromide, ferric chlorid and ferric bromide. 11. A method as claimed in any one of claims 1 to wherein the solvent is acetonitrile and the oxidant i cupric chloride or cupric bromide. 12. A method as claimed in claims 2, 3, 4 or 6 or an claim appended thereto wherein ' the reducing agent i selected from the group comprising ferrous chloride, ferrous bromide, ferrous sulfate, oxalic acid, hyαroxyla ine, sulfur dioxide, hydrazine, cuprous chloride, cuprou bromide and copper sulfide. 13. An oxidising agent comprising a water miscible dip lar aprotic solvent or mixtures of such solvents co taining -halide ions, copper II, and/or ferric ions a cations (including cupric and ferric) which form solub salts with halo complex anions in the appropriate so vent. 14. An oxidising agent as claimed in claim 1 wherein t solvent is selected from the group comprising dimethylsu foxide, dimethylfor amide, dimethylacetamide, N-methy pyrrolidone, acetonitrile, acetonitrile mixtures, di thylsulfoxide-acetonitrile mixtures, mixtures of t foregoing and mixtures of the foregoing with acetone. 15. A method of producing gold mirrors which compris applying a solution of gold as AuCl " or AuBr " i a wat miscible dipolar aprotic solvent as a film to a suitab prepared glass surface and reducing it to deposit a fi of gold on the surface by the addition of water in t presence of CuCl " , CuBr 2 , Fe * Cl 2 or Fe3r 2 - 16. A method of oxidising gold and silver substantial as herein described. 17. A method of recovering gold and silver . substantial as herein described.

Inventors: PARKER A
Applicants: ANUMIN PTY LTD, PARKER A
Application year: 1981
Main classification: C23C3
IPC codes: C01G5, C01G7, C22B3, C22B11