One rock and Patinum-Group Elements in Sulphide Minerals.
Step 1: Digest the material in aqua regia (one part nitric acid to three parts hydrochloric acid) and boil the solution down to a syrup-like consistency. This evaporation is repeated three times, with the addition of hydrochloric acid after each evaporation. Step 2: Dilute the last evaporation with three or four volumes of water and filter it. The residue on the filter is iridium, ruthenium, rhodium, osmium, and silver chloride. The original solution contains platinum, palladium, and gold in solution. Step 3: Bubble sulphur dioxide gas through the platinum, palladium, and gold solution. This precipitates the gold as a brown powder. Filter the solution; wash, dry, and set aside the precipitated gold for purification. All washings should be added to the pregnant original solution at each precipitation. Step 4: The solution, stripped of gold values, contains platinum and palladium. Add a saturated solution of ammonium chloride to the mother solution to bring down the platinum as ammonium chloroplatinate, an orange powder precipitate. Filter this from the solution, wash it, and set it aside for reduction to platinum sponge. Step 5: The solution should now contain only palladium values. Add sodium chlorate crystals to the solution to precipitate the palladium as palladium ammonium chloride, a red powder precipitate. Wash, dry, and set this aside for reduction to palladium sponge. The solution should be valueless: spot test and discard it. It will show traces of platinum regardless of how complete your precipitation was. Step 6: Fuse the residue of iridium, ruthenium, rhodium, osmium, and silver chloride from the aqua regia digestion with lead. Step 7: Granulate and digest the lead fusion in nitric acid; then dilute the solution and filter it. The residue on the filter is iridium, ruthenium, rhodium, and osmium. Strip the solution of its silver ions by adding hydrochloric acid or table salt, which precipitates the silver as silver chloride (AgCl). Filter the silver chloride from the solution, wash it, and dry it. It is stored in the dark until ready for reduction to metallic silver by cementation or by flame reduction followed by purification in a Thurn cell. The solution is spot tested and discarded. Step 8: Fuse the residue from Step 7 with sodium bisulphate. Grind up the fusion in a cast-iron mortar and dissolve it in water. The rhodium is now in the water extraction, and the iridium, ruthenium, and osmium form a residue in the water extraction. Filter off the residue, wash it on the filter, and set it aside. Place the solution and the wash water containing the rhodium in a clean flask. Step 9: To the water extraction, add 2% barium chloride (BaC12) solution and heat. This should cause a precipitation. Bring the solution and precipitate to a boil, and boil them for several minutes. Step 10: Allow the solution and the precipitate to cool, run the precipitate off onto a filter, and wash it, first with a solution of hot water and barium chloride and then with distilled water. Step 11: Transfer the precipitate (designated as the #1 precipitate) to a clean flask and add a solution of one volume of hydrochloric acid and three volumes of distilled water to it. Heat this until the precipitate is in solution. Step 12: When the precipitate is in solution, raise the temperature to boiling and bubble hydrogen sulphide through the solution slowly. This will precipitate the rhodium as rhodium sulphide. The precipitation should take 35-50 min to complete. Step 13: Filter off the rhodium sulphide at once onto a filter and wash it with dilute ammonium chloride. Step 14: Dry and reduce the rhodium sulphide to metallic rhodium, using low ignition; cool it under a stream of hydrogen. Step 15: Fuse the residue of iridium, ruthenium, and osmium from Step 8 with a flux composed of 50% potassium nitrate (saltpeter) and 50% potassium hydroxide. Crush the fusion and extract the water-soluble elements with water. Step 16: This extraction leaves the ruthenium and osmium in the aqueous solution and the iridium as iridium oxide. Filter off the iridium oxide and wash it with water. Step 17: Dissolve the iridium oxide in aqua regia and then add ammonium chloride to form iridium chloride (lrC14). Filter this precipitate, wash it with dilute ammonium chloride and then with water, and dry it. Step 18: Reduce the iridium chloride to metallic iridium by ignition under the hydrogen torch or in a hydrogen atmosphere. All your ignitions or reductions of metallic salts-such as platinum chloride and rhodium sulphide-are easily made with a standard hydrogen melting torch. The ignition is done in a crucible in exactly the same manner that you did the ignition for platinum chloride, except that, when the chlorine {the white fumes) is driven off completely, the metallics are allowed to cool under the cool hydrogen gas from the unlit hydrogen torch.