Recovery of lithium from Uyuni salar brine

A hydrometallurgical process was developed to recover lithium from a brine collected from Salar de Uyuni, Bolivia, which contains saturated levels of Na, Cl and sulphate, low Li (0.7–0.9 g/L Li) and high Mg (15–18 g/L Mg). Unlike other commercial salar brines currently being processed, the high levels of magnesium and sulphate in Uyuni brine would create difficulties during processing if conventional techniques were used. A two-stage precipitation was therefore first adopted in the process using lime to remove Mg and sulphate as Mg(OH)2 and gypsum (CaSO4.2H2O). Boron (at 0.8 g/L in the raw brine), a valuable metal yet deleterious impurity in lithium products, could also be mostly recovered from the brine by adsorption at a pH lower than pH11.3 in this first stage. The residual Mg and Ca (including that added from lime) which were subsequently precipitated as Ca–Mg oxalate could be roasted to make dolime (CaO ∙ MgO) for re-use in the first stage of precipitation. Evaporation of the treated brine up to 30 folds would produce 20 g/L Li liquors. The salt produced during evaporation was a mixture of NaCl and KCl, containing acceptable levels of sulphate, Mg, Ca, etc. The final precipitation of lithium at 80–90 °C produced a high purity (99.55%) and well crystalline lithium carbonate.