Method for preparing high-purity lithium carbonate by using fractional crystallization technology

Abstract

The invention relates to a method for preparing high-purity lithium carbonate by using a fractional crystallization technology. The method comprises the following steps: carrying out process treatmenton salt lake brine by adopting one or more of means selected from a group consisting of, but not limited to, electrodialysis, adsorption, nanofiltration, extraction, precipitation, reverse osmosis, ion exchange and evaporation to obtain a refined lithium chloride solution 1; introducing a sodium carbonate solution into the refined lithium chloride solution 1, carrying out a primary lithium precipitation reaction to obtain a wet lithium carbonate crystal 1, and then washing, drying, crushing and packaging the wet lithium carbonate crystal 1 to obtain a high-purity lithium carbonate product; introducing mother liquor of the primary lithium precipitation reaction into crystallization evaporation equipment, separating out saturated sodium chloride in the evaporation process, and filtering outa sodium chloride crystal to obtain a high-concentration lithium chloride solution 2; introducing a sodium carbonate solution for a secondary lithium precipitation reaction to obtain a wet lithium carbonate crystal 2; and dissolving the wet lithium carbonate crystal 2 with hydrochloric acid to obtain a lithium chloride solution 3, and combining the lithium chloride solution 3 with the refined lithium chloride solution 1.

Description

technical field [0001] The invention relates to the technical field of preparing lithium carbonate, in particular to a method for preparing high-purity lithium carbonate by fractional crystallization technology. Background technique [0002] In the traditional lithium carbonate crystallization process, after the refined lithium chloride solution undergoes a lithium precipitation reaction, the mother liquor enters the salt pan to evaporate, and the lithium in the mother liquor is recovered. However, there are problems such as leakage and sodium chloride entrainment in salt fields, and the yield of salt fields is only 50%. At the same time, there are secondary pollution problems in salt fields, and impurities such as sediment and colloids brought by sandstorms will enter into the lithium sinking mother liquor, resulting in the recovery of salt fields. Lithium carbonate is of poor quality and can usually only be dealt with at low prices. [0003] Therefore, in order to increas...

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Problems solved by technology

Before the lithium sinking mother liquor enters the salt field, in order to prevent the simultaneous precipitation of lithium carbonate and sodium chloride during the evaporation and concentration process, it is necessary to add a large amount of hydrochloric acid to the lithium sinking mother liquor to drive off the carbonate ions in the lithium sinking mother liquor, and the lithium in the lithium sinking mother liquor After the ions are concentrated, sodium carbonate needs to be added for secondary lithium precipitation. Every ton of lithium carbonate needs to consume 2-2.5 tons of sodium carbonate and 1.5-1.8 tons of hydrochloric acid (31% industrial grade hydrochloric acid), resulting in a large amount of sodium carbonate and hydrochloric acid. waste, while the comprehensive yield is low, generally less than 90%, and 10% of the products can only be sold at low prices

[0004] In addition, a serious excess of sodium carbonate in the process of sinking lithium will cause sodium carbonate to be entrained in the lithium carbonate product, and even the possibility of hydrated sodium carbonate solids may exist, resulting in excessive sodium ion quality indicators in lithium carbonate and increasing subsequent product refining costs.

And in order to increase the yield of lithium precipitation, the reaction temperature of lithium precipitation is too high (the higher the temperature, the lower the solubility of lithium carbonate), and the dosage of sodium carbonate is too large, the flow rate of the dosage is too large and other factors all cause excessive lithium carbonate in the lithium precipitation process. Excessive saturation results in fine crystals, low crystal purity, and large entrainment of impurities during crystallization of lithium carbonate. This is also the reason why the quality of lithium carbonate extracted from salt lake brine is poor and cannot reach battery-grade lithium carbonate.