Pastor Vallés, Elisa; Ma, Yan; Pettersen, Johan Berg

As a Critical Raw Material of high economic importance in Europe, silicon is a relevant material for life cycle management. Conventionally, silicon is made by carbo-thermic reduction of quartz. In this paper we benchmark the life-cycle environmental performance of silicon produced by alumino-thermic reduction, evaluating, in particular, the effect of re-sourcing former waste streams for silicon and aluminium. We apply life cycle assessment to compare conventional and aluminothermic silicon production routes, with inventories constructed from thermodynamic process simulation to validate mass and energy balances. Different secondary input materials are explored in the aluminothermic route, for instance, the use of aluminium dross and post-consumer aluminium scrap, slags from conventional silicon production (silicon skulls), as well as possible scenarios for silicon products, aluminium-production from aluminium-containing waste flows, and energy sources. We find that aluminothermic reduction holds great potential to improve impacts when current waste flows such as dross is used for alumino-reduction agent, to reduce energy use and pollutants and improve the overall waste utilization rate. When aluminothermic reduction is based on post-consumer scrap fractions, the comparison of aluminothermic versus carbothermic is dependent on the expected alternative use of the specific aluminium scrap fraction. Scenarios for the future indicate possibilities for surplus volumes of aluminium scrap, and also an increase in demand for silicon products for electronics and solar energy applications in the coming years. In this lies an opportunity in the aluminothermic route as an example of industrial symbiosis for these two raw material industries.