A comparative study on decarburization of silicon kerf through high temperature oxidation and froth flotation techniques

The need for sustainability and equitable use of resources is ever increasing because of global climate challenges and consequently, there have been increased efforts in the use of renewable energy sources like solar energy. The recycling of silicon kerf (sawdust), a waste material from the manufacture of solar wafers, is an important step in sustainability and circularity within the photovoltaic (PV) industry. The presence of carbon impurities in kerf presents challenges in the performance of the refined product in PV applications and thus it is important that it is reduced to acceptable levels. In this study a thermal oxidative decarburization of silicon kerf was conducted between 400 °C and 700 °C. Reaction mechanisms for the decarburization and simultaneous partial oxidation of silicon kerf particles were proposed based on the obtained results and effective decarburization of more than 90 % was achieved. Froth flotation was also conducted as an alternative low temperature route and under the conditions used was found not to be effective for decarburization of silicon kerf from diamond wire sawing due to limited selectivity at the very fine particle sizes of silicon kerf. The moderate temperature oxidative decarburization was therefore found to be effective for removal of carbon impurities. • More than 93 % decarburization during thermal oxidative decarburization of Si-kerf. • Thermal oxidative decarburization increased the crystallinity of silicon kerf. • Silicon oxidation via the oxide surface layer is slow at temperatures below 500 °C.