Extraction of lithium from brines with high Mg/Li ratio by the crystallization-precipitation method

Abstract

A new crystallization-precipitation method is proposed to extract lithium from salt-lake brine with high Mg Li mass ratio (Mg Li > 40). A closed loop path for carnallite crystallization is established and a high magnesium removal efficiency is achieved via MgHPO4(S) precipitation through thermodynamic analysis and experiments. In the first stage, KCl is added into the brine to remove about 50% of magnesium by forming carnallite. When the amount of KCl is 55.9% of stoichiometric requirement and further evaporation at 17.6%, the removal efficiency of total magnesium is 53.1% and the loss of lithium is 5.4%. In the second stage, residual magnesium in the brine is further removed by forming MgHPO4(s). With the amount of Na2HPO4 at stoichiometric requirement, reaction temperature 40 °C, reaction time 30 mins and aging time 3 h, the removal efficiency of residual magnesium is 99.2% and the recovery of residual lithium is 98.5%. To sum up, the total removal efficiency of magnesium is 99.6% and the recovery of lithium is 93.2%. In addition, KCl and Na2HPO4 used in this method can be recycled, which will significantly reduce the cost.