Recycle of silicon slurry cutting waste to prepare high purity SiC by salt-assisted carbothermic reduction

A technological route for recycling silicon slurry cutting waste (SSCW) as silicon source to prepare high purity silicon carbide as well as reducing the industry cost and avoiding the environmental pollution aroused by the waste was explored. The effect of Fe2O3, NaCl addition and smelting temperature on production of high quality SiC were studied. The existence of Fe element acts like a catalyst and contributes to the synthesis of SiC at relatively low temperatures (1550 °C). The excess of Fe element in the SSCW, however, would inhibit further improvement of the purity of the SiC product since Fe element would remain in the final product as Si–Fe alloy. Slight addition of salt was also verified to be positive for the improvement of SiC yield and purity. SiC product with a purity of more than 93 wt% was obtained after acid leaching for the removal of Fe impurity and under the optimized conditions as NaCl addition of 7 wt% and smelting temperature of 1850 °C. The thermodynamic analysis shows that a series of intermediate gas products (CO, SiO, SiO2) have been generated and taken an important role in the synthesis of SiC and excess carbon source is necessary for promoting the utilization of the SSCW since it can efficiently contribute to the formation of SiC and the intermediate products namely SiO and CO. The nucleation mechanism analysis indicates that both the original size and morphology of the carbon source and SiC particles have great influence on the forming particle size and morphology of the generated SiC since both can act as a nucleation center for a certain amount of SiC which is verified by the SEM analysis.