Silver recovery from photovoltaic fines by pressure leaching

Abstract

Since increasing amounts of photovoltaic are expected to become wastes in the upcoming years, it has become critical to develop efficient and profitable recycling process in order to fulfil European directives regarding the recycling of WEEE. In this work, photovoltaic fines (0 -0.5 mm) products from crystalline silicon panels were processed in order to recover silver, most valuable material in this type of waste. To achieve this purpose, it was decided to experiment an alternative leaching route based on pressure leaching using sulfuric acid at temperature and pressures higher than in ambient conditions. This type of process was successfully conducted and different experimental parameters were tested with the aim to improve the kinetics and the performances. A separation step using froth flotation was also tested to investigate the possibility to decrease the quantity of material processed and therefore enhance the economics of the process. Finally the cementation method was chosen to achieve the precipitation of metallic silver using metallic copper (Figure 1). The economics of two scenarios including the froth flotation step or not were then investigated in order to estimate the economic possibilities. From these estimations it was highlighted that the experimental process up-scaled in industrial conditions was significantly uneconomical, the manufacturing costs being dramatically higher than cash flows obtained from the sale of silver. The capital costs were found to be dragged down by the important cost of the autoclave necessary to the pressure leaching while the manufacturing costs were found to be influenced by the important operating labour costs. Despite certain improvement prospects, the process was therefore considered as non-economical.