Specific energy consumption modelling of silver electrorefining process

Silver electrorefining is a process to produce pure silver (> 99.95 % purity) from impure Doré bullion (Au-Ag alloy). This process is generally conducted using Moebius cell with applied current density ranging from 350 - 500 A/m² at 2.0 - 2.6 V of cell potential. Sources of Doré bullion are varied from primary source such as gold and silver mining to secondary sources such as lead or copper smelter and recycling process. One of the growing secondary source for Doré bullion comes from WEEE recycling. The global production of WEEE is accounted for 45 million tons in 2016 and is expected to be 52 million tons in the next 5 years. The main valuable metals in WEEE are Au and Ag with the combined value of both metals is app. 50 % of the metals value in WEEE. The Doré quality produced from WEEE recycling is expected to have Au content within the range of 13 - 47 % in which higher in comparison another secondary source of Doré from anode slime treatment which has Au content of 8 - 9 %. High content of gold in silver anode is proven to cause passivation and forces the process to operate at higher potentials which further results in higher energy consumption. With the limitation of 20 % Au content in the industrial practice, future silver electrorefining will face the challenge due to increase in Au content. Therefore, this study investigates the energy consumption of silver electrorefining as a function of electrolyte parameters, [Ag⁺], [HNO₃], [Cu²⁺], [Pb²⁺] and temperature, and also the anode composition (Au content). The model in this study shows good validity based on the performed statistical test and industrial validation.