Study On The Process Of Separating Boron And Lithium From Salt Lake Brine By Extraction

Solvent extraction is one of the methods for extracting boron and lithium from salt lake brine.However,due to so many types of salt lakes in China,the universal applicability rate of various processes is low.Therefore,the selection of appropriate extraction system and process route still requires further study.Qinghai province is one of the main gathering places of salt lake in China.In this paper,the process of separating boron and lithium by solvent extraction was studied according to the characteristics of brine in xitai jinaier salt lake.Because the presence of boron in brine would affect the extraction of lithium,the experiment was carried out according to the idea of extracting boron from the brine firstly,and then extracting lithium.In the experiment,2-ethyl-1,3-hexanediol?EHD?combination with n-octanol?CA?was used as an extractant for extracting boron,which achieved high separation effect of boron.Ethyl acetate?EAC?was added to the conventional lithium extraction system.In the extraction process did not have three-phase generated and the problem that the extraction agent easy emulsification was strongly improved.In the experiment,the factors affecting the composition,extraction,washing and stripping operation of organic extraction system which were explored,and the process conditions were optimized to enhance the extraction performance of the organic extraction system.The extraction ratio of lithium extract was obtained by the slope method.The changes of the extraction agent and the functional groups before and after mixed organic phase extraction were characterized by infrared spectroscopy.The main conclusions as follows:1.Extraction of boron from salt lake brine:an extraction system using2-ethyl1,3-hexanediol as extractant,n-octanol as co-extractant and ExxsoL D80 as diluent was determined.The optimal experimental conditions of the extraction process were determined by single factor experiments:10% EHD,40% CA,50% ExxsoL D80,brine pH was 2,extraction time was 10 minutes,phase ratio?O/A?was 0.5,extraction temperature was room temperature.Under this condition,the boron extraction rate during secondary extraction was 99.57% .NaOH solution as a stripping agent,when the condition was C_NaOH=0.05 mol/L,stripping time was 12 minutes,stripping ratio?O/A?was 1,and the primary stripping rate of boron was 81.14% ,and the total stripping rate of boron after secondary stripping was up to 98.11% .2.Extraction of lithium from the boron-extracted brine:The extraction system TBP–EAC–FeCl₃–120 solvent oil was determined.The optimal extraction conditions for the extraction process were determined by single factor experiments:60% TBP,10% EAC,30% No.120 solvent oil,iron-lithium ratio (n ?Fe?³⁺/nLi⁺) was 2,brine pH was 2,phase ratio?O/A?was 1,extraction time was 12 minutes,standing time was20 minutes.The single-stage extraction rate of lithium was 90.99% ,and the extraction rate can reach 99% or more by the four-stage extraction operation under the same condition.According to orthogonal experimental analysis,the most important influence on the extraction rate of lithium was the iron-lithium ratio(n _Fe³⁺/n⁺_Li).During the washing process,when the HCl solution was used alone,the loss of Li⁺was large and the washing effect on Mg²⁺was not good.Washing the supported organic phase with a mixed detergent?HCl+LiCl?not only enhances the washing effect but also inhibits the loss of Li⁺.The HCl solution was selected as the stripping agent.HCl solution concentration was 4.0 mol/L,and the stripping time was 10minutes,phase ratio?O/A?was 2,the single-stage stripping rate of lithium was82.43% .The slope method and infrared spectrum analysis showed that the P=O bond on the TBP interacted with the complex in the brine,and the structure of the extract formed was LiFeCl₄·2TBP.