Advanced beneficiation of quartz ore for high-purity silica production

A laboratory-scale integrated beneficiation process was systematically developed and evaluated for the production of advanced industrial-grade, high-purity, high-whiteness silica from quartz ore sourced from the Zarrin-Cheshmeh deposit (Semnan Province, Iran). Initial characterization of the raw material (SiO₂ = 97.46 wt%) using XRF, XRD, PLM, and SEM-EDS revealed a complex mineralogical composition, comprising both free and locked impurity phases. These included lattice-bound and surface-associated contaminants such as Al₂O₃, Fe₂O₃, TiO₂, as well as clay minerals and chert fragments. A multi-stage beneficiation strategy was implemented, integrating physical pre-treatment steps (color sorting, scrubbing, shaking table separation, ultrasonic treatment, microwave treatment, and calcination) with subsequent chemical leaching stages (aqua regia at ambient temperature and 95 °C, followed by HF-HCl treatment). Color sorting effectively removed visually identifiable chert and iron-stained particles at an early stage. Scrubbing combined with ultrasonic pre-treatment enhanced the liberation of surface-bound impurities and improved the efficiency of downstream separation. Calcination significantly reduced volatile species such as sulfates and chlorides, resulting in improved whiteness and enhanced mineral reactivity. Chemical leaching played a decisive role in final purification. Aqua regia treatment at 95 °C achieved approximately 96.8% removal of Fe₂O₃, leading to a substantial improvement in silica grade. Subsequent HF-HCl leaching enabled near-complete breakdown of refractory aluminosilicate phases, with Al₂O₃ removal exceeding 92%, thereby producing ultra-high-purity silica. Although the integrated physical-chemical flowsheet was highly effective in upgrading silica quality, it resulted in an overall reduction of approximately 20% in SiO₂ recovery relative to the original feed. This trade-off reflects the selective removal of impurity-bearing mineral phases, which is necessary to achieve ultra-high purity levels.