Method for producing lithium carbonate by separating magnesium out of low-lithium bittern and enriching lithium

The invention discloses a method for producing lithium carbonate by separating magnesium out of low-lithium bittern and enriching lithium. The method includes the steps of converting salt lake bittern serving as raw materials into halide salt through evaporation dehydration and crystallization separation, directly extracting halide salt through trixylyl phosphate alkane ester or a mixture of trixylyl phosphate alkane ester and monohydric alcohol, obtaining an organic extraction phase and the rest of halide salt after solid-liquid separation, conducting back extraction on the organic extraction phase through water to obtain a low-magnesium-lithium-ratio lithium-rich solution, and obtaining lithium carbonate through condensation and alkalization magnesium removal. The method has the advantages that processes related to the solid-liquid extraction method are simple, co-extraction agents are not needed, the solute distribution drive force is large, and the method is not influenced by bittern extractant two-phase balance; multiple stages of extraction processes are conducted on halide salt, the extraction rate of Li+ is larger than 90%, and the mass ratio of magnesium to lithium in the extraction phase is remarkably decreased; phase splitting is easy due to liquid-liquid back extraction, and the back extraction rates of Li+ and Mg2+ are both larger than 90%; the extraction process is operated under the neutral or weak-acid condition, the production cost is low, and the method is particularly suitable for producing lithium carbonate after separating magnesium out of bittern with the magnesium-lithium mass ratio of 120 or lower.