Enhanced purification of low-grade silica ore through a synergistic direct roasting and leaching

Abstract
This study aims to investigate an integrated direct-roasting and pressure-leaching process for upgrading low-grade silica ore and producing high-purity silica suitable for metallurgical and advanced industrial applications. A representative silica ore from Hamedan, Iran, containing 92.45 wt% SiO₂, was ground and characterized by XRF analysis. The effects of roasting temperature, roasting time, heating rate, acid type, acid concentration, leaching time, and solid-to-liquid ratio were systematically evaluated. Roasted samples were subsequently subjected to pressure leaching in a Teflon-lined autoclave using different mineral acids under elevated temperature and pressure conditions. The results demonstrated that roasting significantly enhanced impurity liberation, particularly for Fe- and Al-bearing phases, with optimum performance achieved at high roasting temperatures, extended roasting times, and a moderate heating rate of approximately 11 °C/min. Among the leaching reagents tested, HCl exhibited the highest impurity-removal efficiency. Under optimized conditions, the silica grade increased from 92.45 wt% in the raw ore to above 99.5 wt%, accompanied by substantial removal of iron and aluminum impurities. The novelty of this work lies in the systematic evaluation of the synergistic interaction between direct roasting and pressure leaching for the purification of low-grade silica ore. The study provides practical operating conditions and mechanistic insights into impurity activation and removal, contributing to the development of efficient and economically viable pretreatment routes for the production of high-purity silica from low-grade resources.