Effect of Sulfate and Carbonate Ions on Lithium Carbonate Precipitation from a Low Concentration Lithium Containing Solution

Abstract

Lithium carbonate (Li 2 CO 3 ) is one of the main precursors for lithium-ion batteries (LIBs). This compound can be obtained through direct extraction from primary sources such as ores and brines or from secondary sources such as spent LIBs. The extraction of lithium from both ores and LIBs commonly involves the use of sulfuric acid as an inexpensive solvent, often with relatively high concentrations and low solid−liquid ratios. This process results in a solution with low lithium concentration but high SO 42− ion concentration. The excessive concentration of SO 42− ions potentially leads to the formation of unacceptable impurities in the final Li 2 CO 3 product, which eventually lowers the recovery and purity of the product. The present work studied the effect of SO 4 2− and CO 3 2− ions concentration as well as temperature on the Li 2 CO 3 precipitation from the lithium-containing leaching solution. Experimental works were carried out with various variations within controlled simple (Li + -Na + -CO 3 2− -OH − ) and complex (Li + -Na + -CO 3 2− -SO 4 2− -OH − ) systems. The resulting Li 2 CO 3 precipitates were characterized using Raman microscope spectrometry and elemental analysis with ICP-OES. The results showed that a relatively pure lithium carbonate product can be achieved from a precipitation condition with a maximum SO 4 2− /Li + ratio of 1:2 (0.25 M SO 4 2− /0.5 M Li + ) and at a temperature of 90 °C with a recovery of 80.54%. At higher SO 4 2− /Li + ratios, a relatively pure product could be obtained at lower operating temperatures to avoid the formation of sodium sulfate (Na 2 SO 4 ), but it caused a drop in recovery. The presence of CO 3 2− ions in the solution within a range of a CO 3 2− /Li + ratio of 1−2 had no effect on Li 2 CO 3 product purity. However, when the ratio increased to 2.5, the purity dropped to 92.17% due to the impurity of Na 2 CO 3 formed along with the precipitation process. It was also observed that the presence of CO 3 2− ions led to a higher product crystallinity and recovery. Nonetheless, a further increase in the CO 3 2− /Li + ratio had an insignificant effect on the product recovery.