Sustainable recovery of high-purity amorphous silica from local sand deposits in Zimbabwe using citric acid leaching pre-treatment

Abstract

This study presents an alternate process for utilization of Zimbabwean silica sand to produce high-purity amorphous silica. The objective was to develop an optimum multi-stage purification that is environmentally friendly. The methodology starts with pre-treatment step with hydrochloric acid, followed by citric acid chelation stage to remove metallic oxide impurities. The pre-treated silica sand was then converted into sodium silicate intermediate through digestion with sodium hydroxide, from which high-purity silicic acid was precipitated using sulfuric acid. Studies on the chelation stage identified the optimal conditions for maximum impurity removal as a citric acid concentration of 4 M , a leaching duration of 4 hours, and a solid-to-liquid ratio of 1:4, all conducted at a temperature of 90 °C . Under these conditions, 70.3 g of high-purity amorphous silica was obtained from 100 g of silica sand. The results demonstrate that this approach, using organic acid leaching with a chemical conversion and precipitation route, represents a viable and effective pathway for upgrading lower-grade silica resources into a high-value precursor material suitable for semiconductor applications.