Silicon sawing waste treatment by electrophoresis and gravitational settling

Abstract

In silicon wafer manufacturing for solar cells, a great amount of hazardous sawing waste with tiny Si particles is produced, resulting in serious environmental problems. Recycling Si and abrasives from the waste is regarded as an effective solution. Based on the view of recycling, Al 2O 3 might be good abrasives for cutting Si ingot due to its larger density and higher isoelectric point than SiC. This study reports the separation of Si/SiC and Si/Al 2O 3 mixtures by electrophoresis and gravitational settling. At pH 9, nearly uncharged Al 2O 3 settled quickly and the negatively charged Si moved toward the anode, leading to an obvious Si distribution on the cell bottom. The experimental results show the separation performance of Si and Al 2O 3 at pH 9 was better than at pH 2.5, and the performance was higher than that between Si and SiC. The minimum and maximum Al 2O 3 contents remaining in Si/Al 2O 3 mixture were 9 wt% and 90 wt% after applying 1 V/cm for 24 h at pH 9. The recovered material with high Si content can be considered as a new Si source for solar cell, and the abrasives can be reused in the sawing process.