Effect of H3PO4 coordination on vanadium extraction and iron separation in a H2SO4 leaching system

Abstract

The selectivity of the full wet leaching process for vanadium extraction using H₂SO₄ is low, resulting in a high impurity content in vanadium extracted from vanadium-bearing shale. This study focused on vanadium extraction and iron separation from vanadium-bearing shale, involving the coordination of H₃PO₄ in an H₂SO₄ leaching system. The effects of the ratio and quantity of H₂SO₄–H₃PO₄, leaching time, leaching temperature, and liquid-to-solid ratio on vanadium-bearing shale leaching were investigated. The dissolution processes of various minerals and the mechanism of iron coordination precipitation were analyzed. Results showed that vanadium leaching efficiency was 91.07% and iron leaching efficiency decreased from 84% to 23.86% under optimal leaching conditions—H₂SO₄-to-H₃PO₄ ratio of 2 : 1, H⁺ content of 8 mol kg⁻¹, liquid-to-solid ratio of 0.8 L kg⁻¹, and leaching time of 12 h at 95 °C. Leaching kinetics showed that the leaching process of vanadium shale was a mixed-control process in the H₃PO₄–H₂SO₄ leaching system; additionally, the leaching process was mainly controlled by a chemical reaction with an activation energy of 67 kJ mol⁻¹. The preferential dissolution order of minerals in the vanadium-bearing shale was calcite, apatite, magnetite, muscovite, and pyrite. Under the H₂SO₄–H₃PO₄ leaching system, the iron content was reduced by inhibiting the dissolution of pyrite and coordination precipitation of Fe³⁺ with PO₄³⁻, thus separating iron and vanadium from the source. This provides guidance for vanadium extraction and impurity separation from vanadium-bearing shale using an all-wet method.