A Separation Process Of Lithium/Boron/Magnesium From The Brine By Precipitation Method And Three-Liquid-Phase Extraction

There are high concentration of magnesium and relatively low concentration of lithium and boron in our native salt lake brine. Lithium, boron and magnesium were separated from brine with steps, low efficiency and a long process. In this paper,magnesium was separated with ammonium sulfate by precipitation method to prepare magnesium salt products. Then, lithium, boron and magnesium in the mother liquor from magnesium precipitation process were separated by three liquid phases extraction method.The process of magnesium precipitation and three liquid phases extraction was explored and it was a shorter process with higher efficiency.To obtain magnesium salt products with high yield and less loss of lithium and boron,the effect factors on the residual mass fraction of lithium, boron and magnesium in the mother liquor wereinvestigated including reaction time, dilution water volume and ammonium sulfate quality. The optimal experimental conditions were determined with a ratio of salt lake brine, dilution water and ammonium sulfate, 1 : 2 : 1.3( mL/mL/g).Magnesium salt product rate is 95.7% with 18% of lithium and 8.5% of boron lost in the brine. Magnesium salt products were characterized by XRD, SEM and EDS. Experimental data showed that the main ingredients of magnesium salt products were hexahydrate magnesium sulfate ammonium, its structure was hexahedron with side length of 20 ~ 70 um,and the purity was more than 97.7%.Extraction agent and polymers were screened to separate lithium and boron in the middle and top phase in the three liquid phases. And PEG2000 and organic extraction,solution of BEPD in BA, were determined, with which mother liquor could be formed three liquid phases and lithium, boron and magnesium would be separated. In the separation of mother liquor, PEG2000 and BEPD in BA were added to the mother liquor.On the purpose of higher lithium extraction rate in the middle phase and boron extraction rate in the top phase, the mass of PEG2000, ratio of organic phase and liquid volume and the concentration of BEPD in BA were investigated. The optimum experimental conditions were determined with a ration of mother liquor, PEG2000 and BEPD in BA, 5:1.8:7.5(mL/g/mL), the concentration of BEPD in BA were 0.5 mmol/mL. The results showedextraction rate of boron was 87.2% in the top phase, extraction rate of lithium was 73.5% in the middle phase, and over 90%t of magnesium were in bottom phase. The separation of lithium boron and magnesium in mother liquor from magnesium precipitation process were realized.The process of three liquid phases extraction was optimized by an orthogonal test,which was also tested in a salt lake brine. The optimum experimental conditions were determined with a ration of mother liquor, PEG2000 and BEPD in BA, 5:1.8:7.5(mL/g/mL), the concentration of BEPD in BA were 0.6 mmol/mL. Extraction rate of boron was 87.2% in the top phase, and extraction rate of lithium was 73.5% in the middle phase.