Preparation of high purity silica from silica rock by leaching process: Optical application

Abstract

The objective of this work is to increase the quality of silica rock from grade C (SiO2 = 98.75%) to grade A (SiO2 = 99.8%) to fulfil the requirements for high-end products. The studied raw silica rock composed of 98.75% SiO2, 0.410% Fe2O3, 0.1750% Al2O3, and 0.067% TiO2. After leaching treatment, the Fe2O3 content was reduced to less than 0.008% for class A product specification and 0.015% for class B product specification, complying with the requirements of MS701:2017. In this study, three types of acid (sulfuric acid, citric acid, and oxalic acid) were considered to study the removal of impurities from silica rock via leaching process at constant temperature and speed of agitation of 60℃ and 150 rpm, respectively. The treated samples were characterized through X-ray fluorescence (XRF) analysis and wet method, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). The application of sulfuric acid (H2SO4) disclosed the highest silica recovery of 99.85% with significant reduction in the amounts of undesirable impurities present in the silica rock including Al, Cr, Ti, and Fe. Comparatively, C6H8O7 acid was also found considerably effecient in improving the purity of SiO2, where 99.53% purity was successfully achieved at 0.25 M acid concentration.