Synergistic leaching of lithium from clay-type lithium ore using sulfuric acid and oxalic acid

With the escalating market demand for lithium, the development and efficient utilization of lithium resources have become crucial. This study introduced a method for leaching lithium from raw clay-type lithium ores using a composite sulfuric acid oxalic acid system. The experimental results revealed that the optimal conditions for the leaching process included roasting temperature of 600 °C, sulfuric acid concentration of 0.8 mol/L, liquid-solid ratio of 5 mL/g, leaching temperature of 90 °C, leaching duration of 90 min, and oxalic acid dosage of 2 g. Under these conditions, the leaching efficiency of lithium reached 93.45 %. The structural changes during the lithium leaching process and leaching mechanism were analyzed by XRD, SEM, TOF-SIMS. It was found that the minerals after mixed-acid leaching showed a loose morphology, a decrease in the average particle size, and a significant increase in the specific surface area as well as the pore volume, leading to improved lithium leaching efficiency. Furthermore, the mechanism underlying the mixed-acid leaching of lithium from clay-type lithium ores was explored. According to this mechanism, sulfuric acid first dissociated H⁺, which disrupted the mineral structure, allowing further destruction by oxalic acid. During this process, Li⁺ was continuously replaced by H⁺ and reacted with C₂O₄²⁻ dissociated from oxalic acid to form water-soluble Li₂C₂O₄.