Iron Removal during Recovery of Silicon from Sawing Waste by Applying Magnetic Field

Abstract

The removal of metal impurities is essential when recycling silicon sawing waste. In this study, Si, SiC, and metal fragments were separated by sedimentation in an applied electrical field. A magnetic field was incorporated into the system to promote the separation of iron-based fragments from the sawing waste. When a 1 V/cm electrical field and a 0.3 T magnetic field were applied for 24 h to the system in a pH7 solution, the residual amount of iron reduced to less than 0.0185% of the initial amount. The maximum SiC content in the recovered powder was 87.8 wt%, while the minimum was 12.3 wt%, i.e., roughly 87.7 wt% Si. Applying a magnetic field to the recycling system can effectively reduce the residual iron content; in addition, Si, SiC, and metal fragments can be separated in a single procedure.

Keywords:

• electrical field
• magnetic field
• recycling
• sedimentation
• silicon sawing waste

ACKNOWLEDGEMENTS

The author would like to thank the National Science Council of Taiwan for financially supporting this research under Contract No. NSC 99-2221-E-027-099-MY2, and thank Yung-Fu Wu of Electrochemical engineering lab II (Ming-Chi University of Technology) for assistance in separation tank design and system construction. The material support from Sino-American Silicon Products, Inc. is also greatly acknowledged.

Notes

^a Residual fraction: the residual amount of iron divided by the initial amount.

^b B: magnetic field.