Extract lithium from clay-type lithium ore by mixed acid and its mechanism

A roasting-leaching test was carried out for the efficient utilization of clay-type lithium ore in the central region of Yunnan province. The test used the mixed acid of sulfuric acid and phosphoric acid as the leaching agent. Under the conditions of roasting temperature of 600 °C, roasting time of 1 h, liquid-solid ratio of 5:1, volume ratio of H2SO4 solution to H3PO4 solution of 45:5, leaching time of 2 h and leaching temperature of 80 °C, the leaching rate of lithium was as high as 97.83%. The leaching mechanism was studied by SEM, pore property analysis, XRD and XPS. It was found that the morphology of the ore changed obviously after roasting and leaching, and a certain degree of collapse and fragmentation occurred, which provided favorable spatial conditions for the leaching of lithium. The porosity, total intrusion volume and total pore area also increased after roasting and leaching, thus promoting the leaching of Li+. The results showed that chemical reaction taken placed during the roasting and leaching. The phase of the sample changed from chlorite, kaolinite and diaspore (boehmite) mainly to corundum, hematite, periclase and quartz after roasting. However, after leaching, no new phase was produced in the ore sample, and no S and P elements were found on the surface of the ore sample, indicating that the leaching mechanism of lithium might be the ion exchange between H+ and Li+.