Extraction of Lithium from Salt Lake Brine using N523-TBP Mixture System

In this work, problems encountered by tri-butyl phosphate (TBP) in the industrialization of lithium extraction from salt lake brine were discussed in detail. The behavior of N, N-bi-(2-ethylhexyl) acetamide (N523) during lithium extraction was investigated, and its disadvantages were analyzed in the view of practical application. An N523-TBP mixture extraction system was proposed to alleviate or avoid the defects that N523 and TBP met when they were used separately. The optimal composition of this mixture extraction system was determined to be 20%N523-30%TBP-50% kerosene. The effects of brine acidity, Fe/Li molarity ratio, phase ratio and chloride ion concentration on lithium extraction efficiency were discussed. The operation conditions in single-stage extraction were optimized as brine acidity=0.05 mol/L, Fe/Li molarity ratio=1.3, and phase ratio=2. The high concentration of chloride ions in brine was beneficial for the extraction of lithium. The structure of the extracted complex was proposed as (LiFeCl 4 · n N523 · m TBP)·(2- n )N523 ·(2- m )TBP (m+n=2) by chemical analysis and slope-fitting methods. The extraction thermodynamic functions were calculated preliminarily, and the results suggested that the extraction process was an exothermic (ΔH <0) and spontaneous (ΔG <0) reaction, and the degree of disorder increased (ΔS >0) during the extraction process. This work will give some guidance to the lithium industry of Qinghai in both the fundamental theory and practical application.