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

Abstract

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 minutes 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 microfluidic 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.

Structural evolution of water and hydroxyl groups during thermal, mechanical and chemical treatment of high purity natural quartz

“…A method to fracture such inclusion by microwaves has recently been developed. 72 For quartz sand from the deposit used here, however, such a treatment is typically not considered to be necessary.…”

The effect of using solvent medium in the ultrasonication of silica precipitates

“…Silica can be synthesized from several kinds of natural materials such as marine sponge and diatoms, rice husk [5], quartz sand [6], [7], fly ash [8], ferronickel slag, etc. The synthesis method used can be through a chemical reaction with a leaching process [6], [9], microwave [10], [11], hydrothermal [12], [13], sol-gel [14], and sonochemistry [4], [5], [15], [16]. From these synthesis processes, silica can be produced with various sizes and certain morphological shapes, for example cubic, spherical, and mesoporous [2], [4].…”

Implementation of sulfuric acid leaching for aluminum and iron removal for improvement of low-grade silica from quartz sand of Sukabumi, Indonesia

“…Silica with a high level of purity is applied as important raw materials for special purposes, which have very strict requirements for quality [2,3]. High-purity silica is widely used in the glass industry [1,[4][5][6] and semiconductor industry for electronic components, optical fiber for communication and internet networks, solar panels [7][8][9][10][11][12], as well as in the catalytic chemistry industry for the synthesis of catalysts and adsorbent materials [3,4,13]. The SiO 2 con-of the materials used is oxalic acid, which is able to bind iron to form an iron oxalate solution, Fe (III) oxalate [18].…”