![]() ![]() Now you stated in your example that the refiner has chosen to precipitate gold first using sodium bisulfite, where here he has made a choice to precipitate gold before other PGM metals, this does not have much to do with the reduction potential of the metals, he could have chosen to precipitate or complex any on of the PGM'S before reducing gold, even if those metals have a slightly higher reduction potential as the gold has. With evaporation or a chemical reaction we can remove the oxidizer (nitric) from solution, thus removing the oxidizing agent in the solution that will allow us to precipitate gold later with a reducing agent, but the removal of nitric this has no effect on the oxidation or reduction potential of the gold ions in solution or other metals, the gold can stay in this state of oxidation without reduction or a-gain in electrons to be able to form gold atoms, and the gold or other metals will not precipitate, yes we have changed the oxidation potential of the solution but not that of the metals or the ions in solution. You should never boil off nitric acid, a slow evaporation process with heat. ![]() This is a standard operation that many here are familiar with. ![]() For example, we boil-off the Nitric Acid in order to reduce the Oxidation Potential of the solution in order to precipitate Gold with Sodium Bisulphite. ![]()
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