From quartzose sandstone to metallurgical grade silicon feedstock for photovoltaics: an integrated sieving, magnetic separation and acid leaching protocol

Résumé

Finding new sources of high purity silica is becoming increasingly important for solar panel manufacturing. Behind quartz, sandstone can be one of the most important sources of silica for advanced technological applications. Despite its abundance in the Earth’s crust, the widespread use of sandstone is limited by the presence of undesirable oxide. This is the case for the studied sandstone rocks, where impurities, particularly iron and aluminum oxide, restrict the suitability of this silica for producing advanced materials. This work presents an optimized multistage purification protocol specifically engineered for quartzose sandstone. We systematically characterize quartzose sandstone from northern Algeria, an abundant yet underexploited sedimentary resource, demonstrating an initial rich silica content but with problematic levels of Fe 2 O 3 and Al 2 O 3 impurities. The core scientific contribution is the establishment of a tailored sequence: granulometric sieving to isolate the optimal 250–400 µm fraction (89.15% SiO 2 ), dry high intensity magnetic separation, and optimized acid leaching using 4 M HCl at 90 °C for 2 h that show leaching efficiency plateaus. Mechanical analysis reveals the 250–400 µm fractions as a liberation sweet spot where quartz grains are maximally freed from the detrital matrix. The results are encouraging, demonstrating that the applied process successfully increased the silica content from an average of 89.15%–99.28%. Furthermore, it significantly reduced the impurity levels, lowering the iron oxide content from 0.27% to 0.02% and the alumina content from 2.46% to 0.02%. By demonstrating the viability of sandstone as a photovoltaic grade feedstock precursor for metallurgical grade silicon (MG-Si) production, which is the essential first step in manufacturing solar grade silicon (SoG-Si) for photovoltaics., this work provides a scalable pathway for diversifying the solar industry’s silica supply chain.

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