Removal of Iron from Solar Grade Silicon (SoG-Si) Cutting Slurry Waste by Ultrasound-Assisted Leaching with Dilute Sulfuric Acid

Recovering silicon from hazardous solar grade silicon (SoG-Si) cutting slurry waste generated in silicon wafer production is of great significance, but it is distinctly important to remove iron first. Dilute sulfuric acid with assistance of ultrasound was used to remove iron from SoG-Si cutting slurry waste in this study. The occurrence state of iron in the SoG-Si cutting slurry waste were analyzed. Effects of ultrasound power, ultrasound frequency, liquid-solid ratio, acid concentration and reaction temperature on the iron leaching ratio were studied. Conventional leaching (CL) and ultrasound-assisted leaching (UAL) were compared by the leaching ratio, XRD, particle sizes and morphologies. It showed that ultrasound could disintegrate aggregations and disperse aggregated particles more efficiently than CL, and accelerate leaching ratio about 7.84%, and shorten leaching time as much as 50% at 70 degrees. Kinetics analysis showed that CL reaction follows classical shrinking core model and rate-controlling step is chemical reaction. However, the UAL reaction follows shrinking unreacted core model and rate-controlling step is chemical reaction within 20 min and converts to internal diffusion after 20 min. After leaching leached residues can be considered as precious silicon source for solar cells, and filtered leaching solutions were fully recycled.