Abstract:

Aiming at salt lake brine with a high ratio of magnesium/lithium, extracting lithium was researched via the extractant tributyl phosphate(TBP) as well as the co-extraction reagent NaClO₄, and the effects of temperature, solution pH value, phase ratio, ClO₄^- amount and other factors on Li⁺ extraction rate have been investigated in detail. The optimum operating conditions of a single extraction from brine are the following: the extraction time of 10 min, temperature of 25℃, V_o/V_w=2.0, n(ClO₄^-)/n(Li⁺)=2.0 and pH value in a range of 5-8. Under these conditions, the highest extraction rate for Li⁺ and Mg²⁺ was 65.41% and 13.31%, respectively, and the Li/Mg separation coefficient reached 12.32. Reversed phase extraction was carried out with water in V_w/V_o=1.0 and 50℃, the stripping rate of Li⁺ reached 81.52%, and the mass ratio of Mg/Li decreased from 45.61 to 8.45. The extraction process of Li⁺ and Mg²⁺ presented exothermic effect, metal ions extracted into the organic phase had no effect on the chemical shifts of H in TBP, but made the IR stretching vibration frequencies of PO double bond shift to 1264 cm^-1 from 1280 cm^-1. The composition of extracted complex of Li⁺ was close to 2LiClO₄·5TBP determined by the slope method at 25℃, and Li₂CO₃ was prepared by the strip liquor after demagnesium deeply.

Key words: ClO₄^-, Tributyl phosphate, Brine with high Mg content, Li/Mg separation, Solvent extraction