Comprehensive recovery of Ca, V, Zn, and Si from black shale using a novel hydrochloric acid selective leaching-decarburization process

By traditional sulfuric acid leaching, the comprehensive recovery of valuable elements from black shale is difficult to achieve , the leaching residue containing large amounts of silicon , calcium, is an environ-mentally harmful waste. A two-stage hydrochloric acid leaching procedure and a subsequent purification process of the leaching residue were designed to produce a silicon-rich residue. Hydrochloric acid selectively eliminates acid-consuming minerals like calcium carbonate and pyrite in the first leaching stage, while the metals vanadium and zinc were leached in amounts of only 0.15 % and 9.82 %, respectively. Mica was severely degraded in the second leaching stage due to the combined effects of sodium fluoride and hydrochloric acid, with leaching percentages of 90.3 % for vanadium and 63.2 % for zinc, while only 25.6 % of the hazardous element iron was leached. After roasting the leaching residue of the second stage for 2 h at 750 degrees C to remove carbon, silicon-rich residue with a silica purity of 95.5 % was obtained. The proposed method is expected to achieve waste-free utilization of black shale.

Automated summary

Traditional sulfuric acid leaching fails to achieve comprehensive recovery of valuable elements from black shale, resulting in a leaching residue containing high amounts of silicon and calcium, which is environmentally harmful. A two-stage hydrochloric acid leaching procedure is used to selectively eliminate acid-consuming minerals, achieving leaching percentages of only 0.15% for vanadium and 9.82% for zinc. Subsequent leaching with sodium fluoride and hydrochloric acid degrades mica while leaching vanadium and zinc at percentages of 90.3% and 63.2%, respectively, and leaching only 25.6% of hazardous element iron. Roasting the leaching residue at 750 degrees C for 2 hours yields a silicon-rich residue with a silica purity of 95.5%. This method enables waste-free utilization of black shale.