The study on the purification of waste graphite thermal field material of FZ-Si crystal

Abstract

Abstract The rapid development of the photovoltaic industry has led to increased demand for monocrystalline silicon. Numerous waste graphite devices are generated in the process of crystal pulling, and the waste graphite thermal field contains the largest proportion of graphite. Reports on graphite purification from the waste graphite thermal for photovoltaic crystal pulling are relatively rare. In this study, we purified waste graphite using a combined process of ferric induction roasting and acid-leaching. Overall, HPG with a fixed carbon content of more than 99.9% was obtained after the sample was subjected to HCl and HF leaching at a temperature of 1300℃, an iron ratio of 30%, and roasting time of 90 min through induction hardening roasting with ball milling mixture as raw material.The removal rates of Si, Fe, Al, Mg, Zn, Ni, Ti Ca, and Na were 99.58, 99.56, 99.89, 98.32, 99.26, 99.47, 99.62, 98.48, and 98.98%, respectively. Meanwhile, the high-purity graphite carbon (HPG) products with a purity of 99.98% were obtained.