Development of iodide process of extraction of precious metals out of waste from electronics

摘要

A process of anodic dissolution of noble metals in alkaline solution of potassium iodine has been investigated. The kinetics of gold solution process was measured by coulometry. It was found that the process is limited by kinetic factors (E_a = 48 kJ/mol) at the concentration of potassium iodine C_(KI) < 0,0075 mol/l. When KI content increases, the process passes into the diffusion region (E_a = = 21,3 kJ/mol). A strong passivation of silver arises in solution with C_(KI) < 0,03 mol/l at increase of anodic polarization potential +0,4 V relative to silver-chloride electrode, the cause of which is deposition of a film of poorly-soluble common silver iodide on the electrode surface. The effect of electrode potential and concentration of I~- and OH ions on the gold dissolution rate has been studied. The reaction was found to be of the first order in I~-. The greatest gold dissolution rate in 0,03 M solution of KI is observed at OH~- concentration equal to 0,25 mol/l. An attempt is made to explain the effect of OH ions on the gold dissolution process kinetics.