Abstract: Aqueous iodine-iodide etching solutions are employed in the recovery of precious metals. Elemental iodine is precipitated from spent etching solutions and used to supply both the iodine and iodide of new etching solutions. Prior to extraction of the elemental iodine, used solutions, if not substantially contaminated, may be oxidized and recycled for further precious metal recovery. Aqueous etching solutions of hydriodic acid and iodine, or of ammonium iodide and iodine may be employed. Etching in such solutions, as well as in solutions of iodine and an alkali metal iodide, such as potassium iodide, may be accelerated by the use of small amounts of hydrogen peroxide (or equivalents) during etching.

Abstract: Gold is recovered from gold bearing materials by dissolving gold in an iodide-iodine solution, precipitating gold with a reducing solution, removing the precipitated gold and then regenerating the iodide-iodine solution with an oxidizing agent.