Application of ionic liquids for extraction of lithium from salt lake brine

Lithium is known as the energy metal and it's a key raw material for preparing lithium isotopes which have important applications in nuclear energy source. The amount of lithium resources in salt lakes occupies over 69% of its industrial reserves in the world, so the hot point in lithium industry is to exploit lithium resources in salt lakes. It is well known that many salt lakes exhibit characteristically high Mg to Li ratios, which render the efficient extraction of lithium very difficult. In this paper, the ionic liquids(ILs), [C4mim] [PF6], [C6mim] [PF6] and [C8mim] [PF6], are used as a kind of green solvent to study liquid/liquid extraction of lithium ion from salt lake brine. A new extraction system had been established in this paper. In this new system, the tributyl phosphate (TBP) was used as the extractant and the ionic liquids were used as extraction medium. It was found that the TBP in conjunction with the present ionic liquids provided extraordinary extraction of lithium ion. The close relationship between the extraction efficiency and the length of the alkyl chain is obvious. With decreasing number of carbon atom of alkyl group in the ionic liquids, the extraction efficiency of lithium increased. The effects of phase ratio, RTILs volume in TBP and solution pH on extraction efficiencies of metal ions had been investigated in detail and the optimal extraction conditions of these systems were obtained. The extraction efficiencies of these ionic liquids systems were all higher than 80%, and the highest the separation factor was over 100 when the experiments were conducted under the optimal conditions. Study on the mechanism revealed that the use of ionic liquids increased the extraction yield of lithium through cation exchange in these systems. The plots of [lgDLi+lg [Cnmim]aq+-lg [Cnmim]org+] versus lg [TBP] produce a straight line with a slope near to 2. According to the slope analysis, the lithium ion was extracted into the organic phase by forming a complex of [Li·2TBP]+. ©, 2015, Chemical Industry Press. All right reserved.