Process for the extraction of precious metals from solutions thereof

A selective solvent extraction process for sequentially and selectively separating and removing gold and platinum group metal values from a chloride containing aqueous solution, the process comprising:

• (a) oxidizing ruthenium and osmium to their respective tetraoxides by adding an oxidizing agent to the solution,
• (b) adjusting the solution in step (a) above to about 0-2 pH units before the oxidizing agent is added and adding about 7-10 times the stoichiometric amount of the oxidizing agent required to oxidize all of ruthenium and osmium to their tetraoxides,
• (c) removing the tetraoxides from the solution,
• (d) selectively removing gold from the solution by solvent extraction to a residual content of less than two parts-per-million in order to avoid contamination of metals to be extracted subsequently,
• (e) removing the remaining solvent in the solution and reacidifying the solution to a hydrochloric acid concentration of from 3 to 6 M,
• (f) selectively removing palladium from the solution by solvent extraction with a dialkyl sulfide,
• (g) reducing iridium to the trivalent state until its redox potential is about +500 mV relative to a standard colomel electrode,
• (h) selectively removing platinum from the solution by solvent extraction with tributyl phosphate and then removing the solvent from the solution,
• (i) reoxidizing the iridium to the tetravalent state and extracting the trivalent state from the solution by solvent extraction with tributyl phosphate, and
• (j) extracting the rhodium with a reducing agent.