Production of high purity silica by microfluidic-inclusion fracture using microwave pre-treatment

• Published in: Minerals engineering Vol. 131; pp. 407 - 419
• Main Authors: Buttress, A.J., Rodriguez, J.M., Ure, A., Ferrari, R.S., Dodds, C., Kingman, S.W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.01.2019
• Subjects: Micro-fracture; Microwave processing; Silica; Micro-fracture; Silica; Microwave processing
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2018.11.025

•Upgrading quartz powder enhanced with microwave pretreatment.•Microwave heating of fluidic inclusions causes their explosive decrepitation.•Total contaminants have been reduced from 158 ± 22 ppm to 30 ± 3 ppm. Demand for high purity silica used in component manufacture is set to outstrip current supply in the near future. As such, alternative processing routes to feed-stock materials suitable for use in lighting and solar cell fabrication are required, without having to rely on reject material from semi-conductor manufacture. In this work, we report a facile, environmentally friendly method of producing quartz powder with a total residual impurity level of 30 ± 3 ppm from whole pebbles having an initial impurity level of 158 ± 22 ppm. This has been achieved using a metallurgical upgrading process incorporating microwave pre-treatment, crushing and milling, High Intensity Wet Magnetic Separation (HIWMS) and acid leaching. This process yielded a quartz powder having an 80% reduction in residual impurities compared to the untreated quartz pebbles. Pre-treatment of whole quartz pebbles in a multimode microwave cavity for 10 min yielded a reduction of the residual elemental impurity content associated with micro-fluidic inclusion sites containing calcium, potassium and sodium of 84, 78, and 50% respectively. Statistically significant reduction in residual aluminium phases was also observed (83%) compared to the as received material to below the IOTA® specification for Ultra High Pure Quartz produced by Sibleco. Mechanistically, this has been achieved by selectively heating impurity containing micro-fluidic inclusion sites. Resulting in their explosive decrepitation and enabling removal of the impurities in subsequent processing steps. It has been concluded that natural quartz pebbles can be upgraded through a combination of microwave treatment, magnetic and chemical refinement to produce a viable feedstock for the subsequent production of solar grade silicon.