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

Lithium carbonate (Li2CO3) 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 SO4 2– ion concentration. The excessive concentration of SO4 2– ions potentially leads to the formation of unacceptable impurities in the final Li2CO3 product, which eventually lowers the recovery and purity of the product. The present work studied the effect of SO4 2– and CO3 2– ions concentration as well as temperature on the Li2CO3 precipitation from the lithium-containing leaching solution. Experimental works were carried out with various variations within controlled simple (Li+-Na+-CO3 2–-OH–) and complex (Li+-Na+-CO3 2–-SO4 2–-OH–) systems. The resulting Li2CO3 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 SO4 2–/Li+ ratio of 1:2 (0.25 M SO4 2–/0.5 M Li+) and at a temperature of 90 °C with a recovery of 80.54%. At higher SO4 2–/Li+ ratios, a relatively pure product could be obtained at lower operating temperatures to avoid the formation of sodium sulfate (Na2SO4), but it caused a drop in recovery. The presence of CO3 2– ions in the solution within a range of a CO3 2–/Li+ ratio of 1–2 had no effect on Li2CO3 product purity. However, when the ratio increased to 2.5, the purity dropped to 92.17% due to the impurity of Na2CO3 formed along with the precipitation process. It was also observed that the presence of CO3 2– ions led to a higher product crystallinity and recovery. Nonetheless, a further increase in the CO3 2–/Li+ ratio had an insignificant effect on the product recovery.