Pre-concentration and recovery of silver and indium from crystalline silicon and copper indium selenide photovoltaic panels

The circular use of critical raw materials is regarded as a topic of contemporary interest stimulating continuous research and development to reduce primary resource use and waste production. However, due to the low mass share of such materials in waste streams, the industrial sector mainly focuses on the recovery of bulk components (e.g. base metals). Even in laboratory-scale studies, the fate of critical raw materials through the recycling chain, and the important role of pre-concentration prior to selective recovery have not been sufficiently addressed. To this scope, this study evaluates the mass flow of Ag and In during the treatment of waste polycrystalline silicon and monocrystalline silicon, as well as copper indium selenide photovoltaic panels in order to produce valuable pre-concentrates of these metals. The treatment routes, used in various combinations, are (a) thermal treatment and gravimetric separation, (a) mechanical crushing, sieving and thermal treatment, as well as (c) chemical and thermal treatment of the panels. The pre-concentration yield was investigated assessing the content of Ag or In (mg/kg) in the treated mass share (%) as compared to the initial content and photovoltaic mass used. Then, the selective recovery of Ag or In from the produced treated fractions, which are enriched in Ag or In, was studied through acid leaching and precipitation. Thermal treatment and gravimetric separation resulted in intact target-components and optimal pre-concentration yield of Ag and In (91.42 and 94.25% for crystalline panels, and 96.10% for copper indium selenide panel). A maximum leaching capacity of Ag and In was obtained using HNO3 and H2SO4 solution, respectively. Pure silver chloride (AgCl) was recovered using HCl as precipitating agent and pure indium hydroxide (In2O3) using NH4OH. Overall, the study pointed out that waste photovoltaic panels are new and complex products that can be considered as secondary sources to recover Ag and In, when a suitable combination of treatment processes is applied. (C) 2019 Elsevier Ltd. All rights reserved.