precious metal refining Platinum refining process details

I. Introduction to the platinum refining process.
Refining technology for platinum in platinum group metals is relatively mature, refining process and precious metal separation process, refining raw materials can be grade > 90% of crude platinum, solutions containing platinum or extractive separation obtained from the reverse extract solution. Two methods, repeated ammonium chloride precipitation and oxidative hydrolysis, take advantage of the properties of platinum compounds.
1, acidic media to generate insoluble (NH4) 2PtCl6 precipitation, with the non-precipitated base metals and other platinum group metals of low-valent soluble chloride with ammonium salt separation.
2, alkaline media to generate soluble NaPt (OH) 6 and other precious and base metals of hydrolysis precipitation separation. Then calcine (NH4)2PtCl6 to metal, can output 99.9-99.999% of different purity of platinum products.

II, ammonium chloride precipitation method: adjust the solution containing Pt50-80g/L, stirring to the hot solution by adding NH4Cl, generating yellow (NH4)2PtCl6 precipitate: H2PtCl6 + 2NH4Cl = (NH4)2PtCl↓ + 2HCI add an excess of NHC so that the concentration of free NH4Cl in the solution is 5-10%. After cooling and filtering out the ammonium chloride, soluble base metal chlorides and gold, palladium, iridium, low-valent chloride with ammonium salt residues in the solution. Wash the ammonium platinum salt with 5% ammonium chloride solution (add HCl acidification to Ph = 1), take a small sample of calcination for sponge platinum sent to the spectroscopic analysis, the purity can be all calcined as crude platinum after repeated king not dissolved, but also available in the following simple method to re-solvate and precipitate again. After filtering off a small amount of insoluble matter, reduce the platinum black in the solution with hydrazine hydrate, dissolve it with HCl+H2O2, and add ammonium chloride to precipitate into pure platinum ammonium salt. To obtain pure (NH4)2PtCl6 ammonium chloride, it is necessary to precipitate crude platinum with a sub-dissolution grade of 90%, and calcinate at 800°C to obtain sponge platinum with a purity of 99.99%.