Silver Recovery from Silver Fluoride Solution Using Electrowinning

Abstract

As solar technology becomes more popular, more modules with limited lifetimes will be manufactured. By 2050 there are expected to be 78 million tons of waste modules, which are rarely recycled today. Each module contains approximately 6 grams of silver, which is the most precious metal found in silicon modules. Hydrofluoric acid is proposed as the leaching agent to remove silver and other metals from the surface of the silicon, while electrowinning is used to recover the silver from the leachate and plate it onto a cathode. The electrowinning setup uses a three-electrode configuration with a pseudo reference electrode to control the half-cell potential. A silver pseudo-reference electrode was found to be sufficient for achieving a high mass recovery rate. Variable voltage trials were conducted and 0.7 V with reference to silver achieved a high mass recovery rate of 96.4% with a high purity of silver. Current efficiency is below 7% for all the voltages tested, which suggests parasitic reactions in the reaction vessel such as O2(g) + 4H+ + 4e− ⇌ 2H2O. The trials at 0.7 V vs silver in a nitrogen purge environment eliminated corrosion at the vapor-liquid interface on the cathode but did not improve the current efficiency. It is possible that the nitrogen purge environment still contains residual oxygen.