Iron Removal from Quartz Ore by Acid Leaching: From Lab- to Pilot-Scale

Quartz in high-purity form, i.e., with an iron content <100 mg/kg, has valuable properties such as superior UV transmission, thermal stability, and resistance to devitrification, which are highly useful for optical applications. In this study, acid leaching was tested to optimize the production of optical-grade quartz from mined quartz, transforming an environmentally polluting process into a sustainable one, aligning with several United Nations Sustainable Development Goals (SDGs). Initially, when iron removal was obtained with direct, cross-current, and counter-current leaching methods, the results were unsatisfactory. However, a variation consisting of incorporating sulfuric acid regenerated via membrane filtration into the typical counter-current scheme was proven effective, reducing acid consumption and enhancing water recycling in the process, mitigating the environmental impact. The best optimized combination was the three-step counter-current method, with acid regeneration and fresh make-up after each cycle. The conditions were temperature 90 °C, solid-to-liquid ratio 30% wt/vol, time 3 h, and H2SO4 concentration of 1 M. The iron extraction yield was close to 89%.