Recovery and preparation of high-grade silica from iron ore tailings by S-HGMS coupling with acid leaching technology: Description of separation mechanism and leaching kinetics

High-silicon iron ore tailings (IOTs) as mineral solid wastes derived from the processing and utilization of iron ore, which would threaten human health and the ecological environment if handled improperly. Coincidently, it consists of abundant quartz gangue. In this study, we proposed a superconducting high gradient magnetic sep-aration (S-HGMS) coupling with acid leaching technology to prepare high-grade silica from high-silicon IOTs. S-HGMS was applied to high-silicon IOTs to pre-concentrate silica into quartz concentrate. Under the optimized conditions, the SiO2 grade in quartz concentrate reached 92.06% with a SiO2 recovery of 43.54%. The results indicate that the S-HGMS effectively achieved a selective separation of silica from high-silicon IOTs, but entrainment occurred between silica and sub-micron impurities particles, reducing the SiO2 grade and recovery. Quartz concentrate was then subjected to a mixed acid leaching to remove metallic impurities. Under the con-ditions of the ratio of mixed acid of 5 mol/L HCl + 1 mol/L HF, leaching temperature of 353.15 K, and leaching time of 12 h, the SiO2 purity of high-grade silica reached 99.51%, and the removal efficiency of Fe, Al, Mg, and Ca from quartz concentrate was 95.20%, 85.60%, 97.99%, and 97.19%, respectively. During the leaching pro-cess, HF played a vital role and its' nucleophilic attack can provide the effective removal of metallic impurities. The dissolution behaviors of Fe, Al, Mg, and Ca were described as shrinking core models, but their controlled steps were significantly different. Thermodynamic results indicate that Fe, Al, Mg, and Ca leaching processes were dominated by dS0 rather than dH0, and their dG0 from lowest to highest were dG0Ca < dG0Mg < dG0Fe < dG0Al < 0, indicating that Ca ion may be leached more easily. Ultimately, a prospect was proposed for the high-value application of high-silicon IOTs resource. This study provides valuable insight to realize the recycling and utilization of tailings for its industrialization.