Extraction of lithium as lithium phosphate from bauxite mine tailings via mixed acid leaching and chemical precipitation

Abstract

Phosphate can be used to facilitate the concentration and precipitation of lithium from low-concentration solutions. In this study, a novel process has been developed to extract lithium as lithium phosphate from bauxite mine tailings, which includes: 1) leaching with mixed acid (H3PO4 + H2SO4), 2) leachate neutralization, and 3) Li3PO4 preparation. Mixed acid was used to effectively leach lithium (Li) without roasting pretreatment, the Li leaching rate can be up to 96.67%. Subsequently, NH3·H2O and H2O2 were used to separate Al and Fe from the leachate by chemical precipitation. After investigating the effects of the temperature, NH3·H2O concentration, and the dilution ratios of leachate and gel solution on the Li loss rate, we propose that the optimal conditions are: zero leachate dilution ratio, 45℃ temperature, 6 mol·L-1 NH3·H2O concentration, and a gel solution dilution ratio of one, which gives a 28.22% Li loss rate. In our experiment, lithium in the mother liquor was precipitated as Li3PO4 with Na2CO3. Our results provide a simple and effective route to extract lithium from low-Li resources.