Ferrosilicon Production from Silicon Wafer Breakage and Red Mud

Luisa Blaesing, Alexander Walnsch, Sebastian Hippmann, Christian Modrzynski, Claudia Weidlich, Sandra Pavón, and Martin Bertau

ACS Sustainable Resour. Manage. 1 (2024) 3, 404–416, https://doi.org/10.1021/acssusresmgt.3c00035

The increasing importance of recycling end-of-life photovoltaic modules is demonstrated by the rising quantity of discarded crystalline silicon solar cells that contain valuable metals. Despite advanced recycling methods, the surplus of broken Si wafers poses challenges for reintegration into new module manufacturing. The present study introduces a novel recycling process that addresses this issue and promotes sustainable waste processing, focusing on the untapped resources of Si wafer breakage and environmentally harmful red mud. The proposed method uses these two critical waste materials to enable a silicothermal reduction, yielding ferrosilicon-based alloys. To comprehensively analyze the influence of the iron oxide source on alloy composition, a readily available iron oxide pigment (Bayferrox 110) is implemented as a reference material. Fe–Si-based alloys containing 15 to 65 wt % Si are produced by the silicothermal reduction with soda ash as a flux, at a temperature of 1600 °C. The use of Bayferrox as an iron oxide source facilitates the production of Fe–Si alloys that are free from additional impurities. Moreover, the use of red mud as the source of iron oxide leads to the production of Fe–Si–Ti alloys, containing up to 8.6 wt % of Ti. The inclusion of Ti in the ferrosilicon-based alloy elevates the market value of the resulting products, emphasizing the commercial viability of the suggested recycling process. By simultaneously utilizing two critical waste materials, namely, red mud and Si wafer breakage, this novel recycling strategy demonstrates significant potential, especially in view of a circular and holistic waste management.

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