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

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 degrees 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.