Dissolution of gold in cupric chloride solution

Abstract

HydroCopper™ is the name of a hydrometallurgical chloride-based copper production process. This new method is a more environmentally safe way of producing copper. Leaching includes a three-stage counter current atmospheric leaching of copper concentrate followed by solution purification and precipitation of cuprous oxide. The aim of this work is to find the optimum circumstances in the solution purification stage of the HydroCopper™ process to get as much gold leached as possible. The examination was made with electrochemical methods.

Gold has a very limited reactivity and high nobility and in order to substantially, dissolve the gold, the gold-ions have to be bound as a complex. Gold forms compounds in two oxidations states +1 and +3. In the presence of a strong oxidant and chloride ions gold can be dissolved as chloroaurate.

In the experiments the behavior of the gold was measured in a [NaCI] = 10-300 g/l, [Cu2] = 0.372 -40 g/l, T = 80 - 90 °C, pH 1-3. In the measurements, a gold wire was used with the dimensions 2.53 cm long and 1.5 mm in diameter. The other electrode was fabricated by Outokumpu Oyj and was a 10 mm long section of gold rod sealed into a plastic PTFE rod.

The dissolution of gold increases with increasing CuCI2 concentration, increasing chloride concentration, increasing temperature and with adequately acidic (pH<3) so that cupric ion precipitation as CU2{OH)3CI does not occur. Gold dissolves as [AuC12] complex when the potential is 0.8 V vs. SCE or lower and as [AuC14] at higher potentials.