Processing of quartz lumps rejected by silicon industry to obtain a raw material for silica glass

This work aimed at analyzing quartz lumps rejected from a major metallurgical grade silicon producer and at studying the effect of several processing techniques over its purification. The final objective was to enable the use of these lumps as a raw material for silica glass production. Chemical analyses using ICP-MS technique were conducted to understand the nature of the chemical impurities in the rejected lumps, aiming to identify rather if the impurity was inside or outside the quartz lattice. The processing procedures were divided in two steps, the first consisting of only a physical treatment and the second one consisting of a chemical treatment. The physical treatment consisted of washing, milling (and separating the material by its particle size) and magnetic separation. This treatment reduced most of the impurities present in quartz, purifying over 90% of the Fe contamination and over 60% of the Al contaminations, but it was incapable of producing a powder with similar chemistry to commercial raw materials. The chemical treatment was conducted using two different acid mixtures (dilute HCl and dilute HCl + HF). Interesting results were obtained using the HF containing mixtures. These mixtures were able to produce a powder with commercial purity (with Al impurities lower than 50 ppm). This treatment was also able to reduce lattice impurities.