Effective Extraction Of Cesium And Rubidium From Salt Lake Brine

Rubidium and cesium are important rare resources.There are plenty of rubidium(Rb+)and cesium ion(Cs+)in the salt lake brine,but the concentrations of them are very low.However,the concentration of K+ is very high and the chemical properties of it are very similar to Rb+ and Cs+.That makes the separation of Rb+ and Cs+ from salt lake brine very difficult.There are three main methods including precipitation,ion exchange and solvent extraction.The disadvantages of precipitation are high cost,complicated processes and low stability of sediment.The disadvantages of ion exchange are hard to desorp and the poor hydrodynamic performance.The extraction method has the advantages of high separation efficiency,simple and easy to continuous operation,which make it widely studied.At present,the commonly used extractants are crown ether species and phenolic alcohol reagents.Crown ether species are generally used for the extraction of Cs+ from strong acidic nuclear waste but the neutral system is hardly investigated.Phenolic alcohol reagents are commonly used in strong alkaline solution and the traditional methods is to add high concentration of sodium hydroxide in neutral aqueous,which could cause serious pollution to the environment and high processing cost.In view of the above problems,a novel process study was carried out on the extraction of Rb+ and Cs+ from salt lake brine.The extraction mechanism of different extraction regents was studied,which laid a foundation for the efficient and comprehensive utilization of rubidium and cesium resources.Firstly,the study of neutral extraction system was carried out for the extraction of Rb+ and Cs+ when the calixarene crown ether was used as extractant.The BPC6-octanol system was studied when 1,3-diisopropyloxycalix[4]crown-6(BPC6)was used as extractant.When the aqueous solution is neutral,the extraction percentage of Rb+ and Cs+ were only 20%.As the concentration of NO3-increased,the extraction percentage increased first and then decreased.The extraction conformed to the neutral complexes extraction mechanism.When the BPC6-ILs(Ionic Liquids)system was employed,the extraction conformed to the cation exchange mechanism.In neutral aqueous solution,more than 99%Rb+ and Cs+ could be extracted into ILs phase when concentration of BPC6 was 12 mmol/L.However,the separation factors of Cs+/K+ and Rb+/K+ were moderate and the imidazole cations of ILs were easy to run away.In addition,the study of weakly alkaline system was carried out for the extraction of Rb+ and Cs+ when the 4-tert-butyl-2-(a-methylbenzyl)phenol(t-BAMBP)was used as extractant to overcome the disadvantage of strong alkaline condition(0.1-1.0 mol/L NaOH)being needed.At first,we found that the extraction percentage decreased with the decrease of alkalinity in aqueous solution.However,when the concentration of NaOH in aqueous solution is 0.03 mol/L,the extraction percentage of Cs+could reach 94.1%and the βcs/K could reach 310.3.Then,we proposed that t-BAMBP-dodecane was first treated by NaOH solution and then was directly used in neutral water system to extract Rb+ and Cs+ selectively.Compared with the traditional process,the novel process was more environmentally friendly,which could save 70%to 97%of NaOH and the alkalinity of raffinate was lower.The kinetics difference K+,Rb+,Cs+ was enlarged in the ion exchange process,so the separation factors of Cs+ over K+ and Rb+over K+ increased by 71.0 and 5.8 times through controlling the extraction time.Based on the results of t-BAMBP system,the simulated brine solution which contained 21.5 mg/L Cs+,206.7 mg/L Rb+ and 4632 mg/L K+ was also studied.99.1%Cs+ and 86.5%Rb+ could be recovered through three-stages cross-current extraction.0.5 mol/L HC1 was effective for the stripping of Cs+ and Rb+.There was no significant extraction reduction when the extractant were reused for five times.The novel process showed promising application on the extraction of Cs+ and Rb+ from salt lake brine.