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.