Electrical fragmentation as a novel route for the refinement of quartz raw materials for trace mineral impurities

Abstract

The availability of a selective liberation method to eliminate contaminating minerals in quartz is crucial to achieve high purity silicon feedstock for solar cell Si-production. In this study we evaluate and compare the effects of electrical fragmentation to conventional mechanical crushing; particularly to remove fine-grained trace-minerals that often jeopardize otherwise promising high purity quartz commodities. The possibility to combine both comminution techniques upstream in the solar silicon value chain is also discussed.A bulk hydrothermal vein quartz sample containing trace impurities of muscovite and orthoclase is fragmented. After fragmentation the particles are sieved in two fraction sizes [0.3–0.5mm] and [0.5–4mm] and are magnetically separated. The morphology of the particles, the crack distribution, and the degree of mineral liberation are studied by optical microscopy, electron probe micro-analyzer (EPMA), and X-ray diffraction (XRD).Electrical fragmentation generates particles with spherical geometries and deep cracks that selectively are pointing towards contaminant mineral inclusions, and produce a higher percentage of liberated minerals. Mechanical crushing, on the contrary, produces elongated fragments with fewer cracks that predominantly run parallel to the fragment surfaces.Muscovite fractures both along its cleavage planes and along its grain boundaries whereas orthoclase fractures along its grain boundaries, only. Muscovite containing 5.8wt.% Fe was easily removed by magnetic separation.