REMOVAL OF METALLIC IMPURITIES FROM SILICON KERF WASTE

Abstract

Silicon (Si) serves as the primary semiconductor material in the solar industry; however, its production results in significant waste. During the sawing process of solar-grade Si ingots into wafers, approximately 30 – 50 % of Si is lost as kerf waste. To enhance sustainability, recent research has focused on optimizing the removal of impurities from this kerf waste to obtain high-quality Si. The study presented in this report utilized leaching with hydrochloric acid (HCl) to remove metallic impurities from diamond wire sawing (DWS) kerf waste. The starting material consisted of an average 0.514 wt% Al and 158 ppm Fe. The objective of this study was to assess the effects of solid-to-liquid (S:L) ratio, HCl concentration and leaching period. The findings revealed that increasing the HCl concentration from 5 to 18 wt% and leaching time from 5 to 180 minutes significantly improved impurity removal. For Al, the maximum removal of 83.6 % was achieved with 18 wt% HCl and 180 minutes of leaching. Conversely, a maximum of 93.3 % removal for Fe was realized using 14 wt% HCl and 60 minutes of leaching. The study also included kinetic analyses to identify potential rate control mechanisms for Al removal. Plotting Al dissolution rate versus time revealed the presence of two mechanisms. Shrinking core model (SCM) – chemical reaction control with first-order reaction rate concerning Al, best described the first 30 minutes of fast-paced leaching. The SCM-product layer diffusion appeared to be the best model to describe the remaining slow-paced dissolutions.