Simulation of the effect of impurities in recycled silicon used for the for the production of ferrosilicon

Abstract

Decarbonization of steel making and allied processes have been receiving immense attention of researchers. Similarly, recycling of waste resources and conversion or recovery of useful materials from waste destined for landfills to mitigate environmental impact, is also an important area of research. Ferrosilicon (FeSi) is currently produced using carbothermic reduction and an energy intensive process. However, silicon (Si) from electronic wastes could be combined with scrap steel to produce FeSi. The Si from electronic waste will, however, contain some impurities such as Aluminium (Al), copper (Cu) and Tin (Sn), which could be incorporated into the FeSi produced from such Si. Hence, in this work the impact of the impurities on the properties of FeSi was investigated theoretically and systematically with the help of FactSage simulations. The impact of three major impurities associated with recycled Si (Al, Cu and Sn) were analysed when present individually and then all together. The analysis was done with the help of phase diagrams for solidification process occurring under equilibrium conditions. It was found that the impurities impact the proportion of the final phases and the melting and phase-transition temperatures. Further, the presence of different intermetallic phases could impact the mechanical properties of the alloy as well. The presence of three impurities together with Fe and Si leads to a complex multicomponent system. While further experiments are needed to identify the actual phases formed during such process, this work provides as framework for carrying out such experiments in the future.