Abstract: With ammonia and sodium hydroxide as precipitators，the secondary magnesium precipitation separation from high-Mg-Li-content salt lake brine and the extraction of lithium by the concentration of mother solution were studied.Results showed that the magnesium removal rate could reach 88.6% with 10%（mass fraction） ammonia as the first precipitator at room temperature.Based on the preliminary separation of Mg-Li，magnesium ions remained in the solution was further removed thoroughly with sodium hydroxide as the second precipitator and the magnesium removal rate reached 99.8%，under the conditions of 8 mol/L NaOH，dropping speed 3 mL/min，reactive time 20 min，pH=12.5 at solution final point，mixing speed 120 r/min，and funnel filter mode.NH₄Cl and NaCl crystals were obtained while the solution was concentrated，so that lithium was enriched.

Key words: magnesium ion and lithium ion separation, ammonia water, sodium hydroxide