EQUILIBRIUM THERMODYNAMICS OF THE VACUUM METALLOTHERMAL REDUCTION OF LITHIUM OXIDE AND SPODUMENE

The extraction of lithium metal from spodumene (Li 2 O.Al 2 O 3 .4SiO 2 ) is a complicated and expensive process. A possible novel extraction method is vacuum thermal reduction. Two promising reductants for such a process are aluminium and silicon. Thermodynamic equilibria calculated using the SOLGASMIX program show that with both reductants pure lithium vapour can be obtained at various combinations of temperature and pressure. Aluminium compares favourably with silicon both from the point of view of reduction temperature and of vapour purity. With silicon as a reductant, silicon monoxide is formed, which contaminates the lithium vapour. Its formation can however be suppressed through addition of CaO.