Extraction of lithium and phosphorus from amblygonite using calcium sulfate roasting and water leaching

This work proposes the roasting of amblygonite with calcium sulfate followed by water leaching to extract lithium and phosphorus. Various roasting parameters including roasting temperature, the mass ratio CaSO₄/ore, roasting time as well as leaching parameters, such as the liquid/solid ratio, temperature and time, have been carefully investigated. The lithium extraction efficiency can be as high as 99.8% with a mass ratio of CaSO₄/ore of 0.85 after roasting at 775 °C for 1 h and water leaching at a liquid/solid ratio of 3 mL/g at 100 °C for 2 h. The XRD analysis demonstrates that the fluoride in the amblygonite can be converted into Ca₅(PO₄)₃F and CaF₂. Lithium in the leach liquor can be recovered as Li₂CO₃. Meanwhile, the phosphorus in the water leach residue can be recovered as FePO₄ with a high recovery of 96.6% after acid dissolution and precipitation, which can be further treated to produce LiFePO₄.