These methods are to process concentrates and are usually not worth processing small quantities. The details have been left out for the Ruthenium and Osmium as these are really dangerous metals and should only be handled in closed reactors.
Separation and Purification Au,Pt,Pd,Ag,Rh,Os,Ir,Ru
This is a general schematic for processing a concentrate of any combination of the above listed metals usually generated from anode slimes or slimes collected from cementation of waste acids holding values.
Roast the slimes to convert any PdO to metal to assure its place in the soluble fraction.
The concentrate is treated in aqua regia, this solubilizes the gold, platinum and palladium and leaves the other metals in insoluble form.
The solution basically contains HAuCl4, H2PtCl6, H2PdCl4. Drive off the NOx by classic boil down and successive 3X’s addition of HCl. Drop the gold with either Sulfur dioxide or Ferrous sulfate. It has been suggested that reducing the gold with Ferrous sulfate results in a more complete drop of the platinum in the following steps. Gold, with either precipitant, will have to be re-refined for high purity. Alternatively the gold can be extracted with Dibutyl carbitol and recovered with oxalic acid resulting in a high purity gold and leaving the Platinum and Palladium behind for recovery.
The Pt is dropped by treatment with Ammonium chloride to drop the insoluble (NH4)2PtCl6. These salts are washed with a solution of 15% ammonium chloride and dried. The salts are collected and further purified via bromate hydrolysis.
Pd is dropped with a solution of dimethylglyoxime dissolved in dimethyl sulfoxide. The yellow palladium glyoxime is filtered and washed with 60% alcohol and 10% HCl. The alcohol assists in the drying and the dry palladium glyoxime is dissolved in excess ammonium hydroxide until dissolved and generating a clear solution. The addition of HCl results in the precipitation of diaminopalladous chloride salt or “palladium yellow”
You have now completed the easy part, the following treatment is for the insolubles left behind in the aqua regia process.
The insolubles are smelted with lead carbonate, carbon, borax and soda ash. This forms a slag with silica, alumina and base metal impurities. The PM’s are dissolved in the lead. Separate the lead and the slag, remelt the lead and granulate it in nitric acid. Filter off the insolubles, Rh, Ru, Ir, and Os.
The silver and lead are in the Nitric acid, sulfuric acid is added to drop out the lead as insoluble lead sulfate. This is collected and converted to lead carbonate and recycled. Classically the silver is dropped as a chloride and smelted but cementation with copper yields an effective product for further electrolytic purification.
The insolubles filtered off are fused at 500 C with molten sodium bisulfate. This converts the Rhodium to water soluble Rh2(SO4)3 . The Ru, Os, and Ir are untouched. The sulfate cake is cooled and dissolved in water, the insolubles filtered off and the Rhodium is precipitated with NaOH and collected for further purification as quantities warrant.
The remaining insolubles are fused with sodium peroxide and sodium hydroxide at 500 C forming water soluble sodium hyperosmate and sodium ruthenate. The iridium is now Iridium dioxide.
The iridium dioxide is dissolved in aqua regia and precipitated as ammonium hexachloroiridiate with ammonium chloride. The salt is further purified by digestion in dilute ammonium sulfide which will precipitate impurities filtered and re-precipitated with ammonium chloride to reform the ammonium hexachloroiridiate. This can be reduced in hydrogen at 1000 C to pure metal.
Separation and Purification Au,Pt,Pd,Ag,Rh,Os,Ir,Ru
This is a general schematic for processing a concentrate of any combination of the above listed metals usually generated from anode slimes or slimes collected from cementation of waste acids holding values.
Roast the slimes to convert any PdO to metal to assure its place in the soluble fraction.
The concentrate is treated in aqua regia, this solubilizes the gold, platinum and palladium and leaves the other metals in insoluble form.
The solution basically contains HAuCl4, H2PtCl6, H2PdCl4. Drive off the NOx by classic boil down and successive 3X’s addition of HCl. Drop the gold with either Sulfur dioxide or Ferrous sulfate. It has been suggested that reducing the gold with Ferrous sulfate results in a more complete drop of the platinum in the following steps. Gold, with either precipitant, will have to be re-refined for high purity. Alternatively the gold can be extracted with Dibutyl carbitol and recovered with oxalic acid resulting in a high purity gold and leaving the Platinum and Palladium behind for recovery.
The Pt is dropped by treatment with Ammonium chloride to drop the insoluble (NH4)2PtCl6. These salts are washed with a solution of 15% ammonium chloride and dried. The salts are collected and further purified via bromate hydrolysis.
Pd is dropped with a solution of dimethylglyoxime dissolved in dimethyl sulfoxide. The yellow palladium glyoxime is filtered and washed with 60% alcohol and 10% HCl. The alcohol assists in the drying and the dry palladium glyoxime is dissolved in excess ammonium hydroxide until dissolved and generating a clear solution. The addition of HCl results in the precipitation of diaminopalladous chloride salt or “palladium yellow”
You have now completed the easy part, the following treatment is for the insolubles left behind in the aqua regia process.
The insolubles are smelted with lead carbonate, carbon, borax and soda ash. This forms a slag with silica, alumina and base metal impurities. The PM’s are dissolved in the lead. Separate the lead and the slag, remelt the lead and granulate it in nitric acid. Filter off the insolubles, Rh, Ru, Ir, and Os.
The silver and lead are in the Nitric acid, sulfuric acid is added to drop out the lead as insoluble lead sulfate. This is collected and converted to lead carbonate and recycled. Classically the silver is dropped as a chloride and smelted but cementation with copper yields an effective product for further electrolytic purification.
The insolubles filtered off are fused at 500 C with molten sodium bisulfate. This converts the Rhodium to water soluble Rh2(SO4)3 . The Ru, Os, and Ir are untouched. The sulfate cake is cooled and dissolved in water, the insolubles filtered off and the Rhodium is precipitated with NaOH and collected for further purification as quantities warrant.
The remaining insolubles are fused with sodium peroxide and sodium hydroxide at 500 C forming water soluble sodium hyperosmate and sodium ruthenate. The iridium is now Iridium dioxide.
The iridium dioxide is dissolved in aqua regia and precipitated as ammonium hexachloroiridiate with ammonium chloride. The salt is further purified by digestion in dilute ammonium sulfide which will precipitate impurities filtered and re-precipitated with ammonium chloride to reform the ammonium hexachloroiridiate. This can be reduced in hydrogen at 1000 C to pure metal.
