Al2O3 and CaO as sintering aids: A strategy to remove impurity boron and SiO2 surface-layer of diamond wire saw silicon waste

Abstract

Removing the SiO2 surface-layer and impurity boron in diamond wire saw silicon powder waste (DWSSP) are two difficulties in the field of photovoltaic waste recycling. Aiming at the two difficulties, this paper proposes a method of mixing sintering aids to digest the SiO2 layer and remove impurity boron. Firstly, sintering aids Al2O3 and CaO were mixed into DWSSP, and DWSSP-ceramics were prepared by pressure-less sintering. The mixed sintering aids reacted with the SiO2 surface-layer of DWSSP, and the formed liquid slag phase plays a role in promoting the densification of DWSSP-ceramics (the relative density reached 85.97% when sintered at 1300 °C). Secondly, to obtain low-boron silicon, the slag phase was separated from DWSSP-ceramics by smelting treatment. The results showed that an optimal boron removal effect of 45.32% was reached after only 10.11 wt% sintering aids were mixed into DWSSP. The mechanism that the liquid slag phase gathered impurity boron during the sintering process, and then promoted boron to remove from silicon was reasonably deduced. The method of mixing sintering aids to remove the SiO2 surface-layer and impurity boron provides a novel insight into purification and recovery of DWSSP.