METHOD FOR HYDROMETALLURGICAL PROCESSING OF A NOBLE METAL-TIN ALLOY

Abstract

A method for the hydrometallurgical processing of a noble metal-tin alloy consisting of (i) 0.45 to 25% by weight of at least one metal A selected from the group consisting of gold and platinum, (ii), 35 to 99.2% by weight of at least one metal B selected from the group consisting of palladium, silver, and copper, (iii) 0.3 to 30% by weight tin, and (iv) 0 to 50% by weight of at least one element other than gold, platinum, palladium, silver, copper, and tin, and has a weight ratio of metal A:tin of 0.7:1, comprising the steps of:

(a1) specifically selecting a noble metal-tin alloy
or
(a2) specifically producing a noble metal-tin alloy;
(b) dissolving nitric acid-soluble components of the noble metal-tin alloy with nitric acid while forming a nitric acid-containing solution comprising the at least one metal B in the form of the dissolved nitrate, and an undissolved residue;
(c) separating the undissolved residue from the nitric acid-containing solution; and
(d) dissolving the separated residue in a medium that comprises hydrochloric acid and at least one oxidation agent.

Claims

1. A process for hydrometallurgical processing of a precious metal-tin alloy consisting of (i) 0.45 to 25% by weight of at least one metal A selected from the group consisting of gold and platinum, (ii), 35 to 99.2% by weight of at least one metal B selected from the group consisting of palladium, silver, and copper, (iii) 0.3 to 30% by weight of tin, and (iv) 0 to 50% by weight of at least one element other than gold, platinum, palladium, silver, copper, and tin, and has a weight ratio of metal A:tin of greater than 0.7:1, comprising the steps of: (a1) specifically selecting a precious metal-tin alloy or (a2) specifically producing a precious metal-tin alloy; (b) dissolving nitric acid-soluble components of the precious metal-tin alloy with nitric acid while forming a nitric acid-containing solution comprising the at least one metal B in the form of a dissolved nitrate, and an undissolved residue; (c) separating the undissolved residue from the nitric acid-containing solution; and (d) dissolving the separated undissolved residue in a medium that comprises hydrochloric acid and at least one oxidation agent.

2. The process of claim 1, wherein the precious metal-tin alloy consists of (i) 3 to 20% by weight of the at least one metal A, (ii), 40 to 95% by weight of the at least one metal B, (iii) 2 to 17.5% by weight of tin, and (iv) 0 to 50% by weight of the at least one element other than gold, platinum, palladium, silver, copper, and tin, and the weight ratio of metal A:tin is in the range of 1:1 to 10:1.

3. The process of claim 1, wherein step (a2) is selected from one of procedures (a2-1)-(a2-5), wherein procedure (a2-1) comprises melting at least one recyclable material to be recycled while forming a multi-phase system comprising a lower phase made of the molten precious metal-tin alloy of the type, and an upper phase made of molten slag having a lower density, if applicable while adding collecting metal and/or slag forming agent and/or reducing agent, and separating the upper phase from the lower phase making use of the difference in density, followed by cooling the separated molten materials and allowing them to solidify, and obtaining the solidified precious metal-tin alloy; procedure (a2-2) comprises treating a molten alloy that is different from the precious metal-tin alloy with an oxidation agent while forming a multi-phase system comprising a lower phase made of the molten precious metal-tin alloy and an upper phase made of molten slag having a lower density, in which the oxidation products produced are present, if applicable while adding collecting metal and/or slag forming agent, and separating the upper phase from the lower phase making use of the difference in density, followed by cooling the separated molten materials and allowing them to solidify, and obtaining the solidified precious metal-tin alloy; procedure (a2-3) comprises alloying at least two alloys that are different from each other, possibly while adding into the alloy at least one element while forming the precious metal-tin alloy; procedure (a2-4) comprises alloying at least one element into an alloy while forming the precious metal-tin alloy; and procedure (a2-5) comprises removing tin by distillation from an alloy while forming the precious metal-tin alloy.

4. The process of claim 3, whereby the at least one recyclable material to be recycled contains, aside from precious metal and base metal, at least one substance that is not a precious metal and not a base metal.

5. The process of claim 4, whereby the at least one substance that is not a precious metal and not a base metal is selected from the group of inorganic refractory materials.

6. The process of claim 5, whereby the group of inorganic refractory materials consists of silicon dioxide, aluminium oxide, calcium oxide, iron oxide, calcium sulfate, calcium phosphate, and tin dioxide.

7. The process of claim 4, whereby the at least one substance that is not a precious metal and not a base metal is a component of ceramic filter materials, abrasives, polishing agents and/or inorganic carrier materials.

8. The process of claim 3, whereby the at least one recyclable material to be recycled is selected from the group consisting of mining concentrates, waste and mixed waste, whereby the waste is selected from the group consisting of waste from jewellery production, waste from dentistry, electronics scrap, precious metal scrap, precious metal-containing scrap from precious metal-processing operations, precious metal sweepings, spent precious metal catalysts, precious metal catalyst dusts, precious metal-containing slag, precious metal dross, precious metal-containing and possibly dried sludge, and overburden from precious metal mines.

9. The process of claim 1, whereby the concentration of the nitric acid used in step (b) is in the range of 10 wt % to 67 wt. %.

10. The process of claim 1, whereby the concentration of the hydrochloric acid used in step (d) is in the range of 3 mol/L to 12 mol/L.

11. The process of claim 1, whereby the at least one oxidation agent used in step (d) is selected from the group consisting of nitric acid, chlorates, nitrates, bromates, iodates, chlorites, bromites, iodites, hypochlorites, hypobromites, hypoiodites, perchlorates, ozone, ozonides, superoxides, oxygen, chlorine, bromine, iodine, peroxo compounds, permanganates, and chromates.

Description

EXAMPLES

Inventive Examples 1-6

[0031] A total of 4 mL nitric acid (53% by weight) per gram of alloy were added to each of the alloys of the compositions specified in the table below and the batch was heated carefully from room temperature to 100 C. while stirring. The alloys dissolved partially in this context while forming a residue with a black to metallic gloss and NOx gas. The cessation of the production of NOx signaled the end of the dissolution reaction (duration between 2 and 7 hours). After cooling, it was possible to filter the mixture obtained in each case within a period of 10 to 60 minutes and it was possible to wash the residue repeatedly with water.

[0032] Aqua regia (a mixture of 75 mL 10M hydrochloric acid and 25 mL nitric acid (53% by weight nitric)) or 6M hydrochloric acid was added to the washed residue and the total volume was adjusted to 100 mL. The mixture was heated to 80 C. while stirring and, unless this had already been done, nitric acid (53% by weight) was added until no change in the reaction mixture and no further formation of NOx was observed upon further addition (10 to 20 mL of the nitric acid (53% by weight)). The residue dissolved while forming a yellow to orange, clear solution. After cooling, it was possible to filter the mixture obtained in each case within a period of 10 to 60 minutes and it was possible to wash the residue with 6M hydrochloric acid.

TABLE-US-00001 Weight wt. % ratio Exam- Gram Metal A Other Au + ple alloy Metal B Au Pt Sn elements Pt:Sn 1 15.41 Ag 56.1 16.2 1.24 15.6 Zn 3.3 1.12:1 Cu 11.6 Fe 1.0 Pd 3.74 Ni 0.4 Co 0.6 2 12.36 Ag 32.1 6.7 0.45 9.85 Zn 0.5 0.73:1 Cu 9.0 Fe 4.9 Pd 1.3 3 15.33 Ag 44.3 17.2 1.36 14.5 Zn 3.0 1.28:1 Cu 9.8 Ni 0.6 Pd 3.9 Fe 0.2 4 23.00 Ag 55 14.5 1.25 7.9 Co 0.7 1.99:1 Cu 10.2 Fe 0.6 Pd 3.9 Ni 0.6 Zn 0.6 5 9.08 Ag 34.2 10.6 0.97 5.8 Zn 0.47 1.99:1 Cu 43.26 Ni 0.4 Pd 2.72 6 9.36 Ag 54.97 16.36 1.45 5.96 Zn 0.49 2.99:1 Cu 10.0 Ni 0.46 Pd 4.23 Fe 0.1 Co 0.1

Reference Examples 7 to 9

[0033] A total of 4 mL nitric acid (53% by weight) per gram of alloy were added to each of the alloys of the compositions specified in the table below and the batch was heated carefully from room temperature to 100 C. while stirring. The alloys dissolved partially in this context while forming a purple voluminous residue and NOx gas. The cessation of the production of NOx signaled the end of the dissolution reaction (duration between 2 and 7 hours). After cooling, it was possible to filter the mixture obtained in each case within a period of 10 to 60 minutes and it was possible to wash the residue repeatedly with water.

[0034] The purple colour of the residue indicated the production of Au particles in tin dioxide matrix (purple of Cassius). A phase analysis on a sample of the residue done by x-ray diffractometry showed tin dioxide to be the main phase.

[0035] The washed residue was filled up with 6M hydrochloric acid to 200 mL, heated to 80 while stirring, and either 4.5 M sodium chlorate solution or nitric acid (53% by weight) were added in drops until the redox potential of the mixture was >900 mV vs. Ag/AgCl standard electrode. In the process, the mixture changed colour from purple to yellow, and a milky suspension was produced.

[0036] The mixture was allowed to cool down and was then filtered through a blue band paper filter. A clear filtrate was obtained in no case in this context, since fine white particles passed through the filter. The filtration proceeded slowly and could be done in no case within a period of time of less than 6 hours. In some cases, the mixture formed a stable suspension of a gel-like to slimy consistency that clogged the filter and made solid/liquid separation impossible.

TABLE-US-00002 Weight wt. % ratio Exam- Gram Metal A Other Au + ple alloy Metal B Au Pt Sn elements Pt: Sn 7 125.6 Ag 50 1.2 0.11 26 Pb 1.7 0.05:1 Cu 17 Bi 2.4 Pd 0.45 Ni 0.14 Fe 0.3 8 89.05 Ag 47.5 3.0 0.25 26 Pb 1.5 0.125:1 Cu 16 Bi 2.0 Pd 0.9 Zn 1.0 Co 0.3 Ni 0.2 Fe 0.5 9 67.98 Ag 64 4.4 0.3 7.7 Pb 0.66 0.61:1 Cu 18 Pd 1.2

Reference Example 10

[0037] A metal button with a composition of 18 wt. % Cu, 26 wt. % Sn, 49 wt. % Ag, 0.7 wt. % Au, 0.35 wt. % Pd, 1.7 wt. % Pb, 2.4 wt. % Bi, 1 wt. % Zn, 0.3 wt. % Fe, 0.13 wt. % Ni, 0.12 wt. % Co; weight ratio of Au:Sn=0.027:1 was used.

[0038] The metal button was divided and a fragment of approximately 10 g each was placed in a beaker and 4 mL nitric acid (53% by weight) per gram of alloy were poured over it, and this was diluted with water to obtain - and -concentrated nitric acid:

TABLE-US-00003 Metal 9.91 g 9.44 g 9.53 g Nitric acid 40 ml 40 ml 40 ml Water 0 ml 40 ml 13.3 ml Nitric acid concentrated -concentrated -concentrated concentration

[0039] A vigorous dissolution reaction commenced immediately. After 5 hours at room temperature, a green solution had formed. This was heated to 100 C. while stirring for 4 hours. The metal button fragment disintegrated in each case and a purple-red suspension was formed; in some cases, a white precipitate was visible.

[0040] The mixture was stirred overnight at room temperature, then for another 3 hours at 100 C. Initially, some reaction was observed to proceed after heating, but ceased later on. The sample was allowed to cool down while stirring it. The supernatant solution was filtered through a blue band filter.

[0041] The residues were placed in a beaker right away and the beaker was filled up to approximately 100 mL with 6M hydrochloric acid. Droplets of 4.5M sodium chlorate solution were added at 60 C. while stirring. Once 0.2 mL had been added, the mixture changed colour from purple to milky yellow in each case. A total of 1 mL sodium chlorate solution was added in each case. The sample was stirred for 1.5 hours, then the excess chlorate was boiled off and the solution was allowed to cool down. The mixtures were filtered, upon which a white precipitate was observed again in each case, with the precipitate being so fine that it penetrated through the filter.