Analysis And Nanofiltration Separation Of Lithium In Brine With High Ca²⁺/Li⁺ Ratio

China is rich in brine resources,especially in the western Qaidam Basin and the northeast Sichuan basin.The brine is of good quality,high content of useful components and abundant lithium resources,which is of value for great development and application.However,it is difficult to analyze and separate the lithium in brine.On the one hand,it is because of the extremely high Ca²⁺/Li⁺ratio and complex co-existing elements in the later stage of evaporation and concentration.On the other hand,the ions concentration varies greatly during the whole evaporation and concentration process.In the aspect of lithium analysis,the traditional flame atomic absorption spectrometry has some problems,such as the serious matrix interference and the complicated group matching method.In terms of lithium separation,few studies have been reported on the application of nanofiltration in brine systems with high Ca²⁺/Li⁺ratio.And the effects of operating conditions and co-existing elements are not clear.Based on the above problems,the traditional flame atomic absorption method was optimized through significance analysis of co-existing elements and interference elimination based on DOE.The feasibility of nanofiltration with high Ca²⁺/Li⁺ratio was investigated.The experimental results mainly include the following aspects.?1?For the analysis of lithium,Ca²⁺,Sr²⁺,Mg²⁺,Na⁺and Ca²⁺*B have significant interference,and the significant degree is ranked as Ca²⁺>Sr²⁺>Mg²⁺>Ca²⁺*B>Na⁺.The effects caused by divalent ions could be effectively eliminated by potassium oxalate.Meanwhile,the interference caused by sodium could be eliminated through establishing interference model.Compared with the traditional method,the optimized flame atomic absorption spectrometry is simpler with wider applications and higher accuracy.?2?In the nanofiltration separation experiment,DL membrane is more suitable for the separation of calcium and lithium in the brine with high Ca²⁺/Li⁺ratio than DK membrane.Taking nanofiltration process conditions as investigation factors and Y_Li,SF,J_v as investigation indicators,DOE was used for significance analysis.After weighing the indexes,the preferred condition of DL membrane is the sample salinity 10 g/L,sample temperature 30 ^oC,membrane pressure 1.5 MPa and pump frequency 20 Hz.?3?The nanofiltration experiments showed that the order of ions intercepyion rate was Sr²⁺>Mg²⁺>Ca²⁺>Cl^->B>K⁺>Li⁺>Na⁺>NH₄⁺.With the increase of nanofiltration cycle times,the recovery rate of lithium increased,while the permeation flux and water quality decreased.When the cycle time was 12.5 min,the multilevel separation of concentrated solution can be considered.Only if Y_Li was taken as the index,Y_Li was94.88%when the sample concentration multiple was 5.33.?4?The main co-existing elements had different influencial degree on the nanofiltration separation.The interference elements of Y_Li were NH₄⁺and K⁺,which were all negative effects.The interference elements of R_Ca were NH₄⁺,B,K⁺,Mg²⁺*B,Sr²⁺*B,and K⁺*B.Among the ions,NH₄⁺,B,and K⁺had positive effects,while Mg²⁺*B,Sr²⁺*B and K⁺*B had negative effects.For the influences of SF,B had more important influence than Mg²⁺*B.Results showed B had positive effect,and Mg²⁺*B had negative effect.