| As a kind of rare metals, rubidium is often used to prepare organic catalysts, photomultiplier tubes, special glass and antidepressants. Rubidium is found often coexisting with other alkali metals in lepidolite, pollucite, lithium pollux, natural carnallite, and underground brine. More than 90% of rubidium resources exists in salt lake brine and underground brine. The large reserves of underground brine in Hubei, Sichuan and Salt Lake brine in Tibet, Qinghai, have high levels of rubidium, so effectively extracting rubidium from these brine is one of the key technology research at the present. Although brine is rich in rubidium resources, it contains large amount of potassium with similar physical and chemical properties, so the isolation and purification of rubidium from brine is extremely difficult. At the same time, a lot of rubidium resources in brine have not been rational used, therefore, to carry out the separation and enrichment of rubidium in the high potassium brine, and extraction of rubidium chloride products have important economic and strategic significance. In this paper, the system with high ratio of potassium and rubidium of the deep brine in the flat sedimentary strata is researched. The extraction mechanism of rubidium and related thermodynamic parameters, kinetics parameters with the efficient extraction agent of rubidium 4-tert-butyl-2 (?-methyl benzyl) phenol (referred to as t-BAMBP) were studied to provide a theoretical basis for the process of extraction and separation of rubidium. Then multistage continuous countercurrent extraction experiments were tested on this basis to find the best extraction system and promote the development of this system solvent extraction technology.The extraction chemical behavior and mechanism of t-BAMBP with rubidium and potassium were studied. The composition of extraction compound is MOR·2ROH (M+is suitable for K+and Rb+) determined by slope method and saturation capacity method. The equilibrium equation of extraction reaction is: M(a)++3ROH(o)+OH(a)-= (MOR·2ROH)(o)+H2O(a the extraction apparent equilibrium constants were KRb=3.015?KK=1.741. Meanwhile, the thermodynamic constants of Rb and K are:?rHm(?)(Rb)=-22.28 kJ/mol, ?rSm(?) (Rb)=-66.83 J/(K·mol), ?rGm(?)(Rb)=-2.69 kJ/mol; ?rHm(?)(K)=-6.38 kJ/mol, ?rSm(?) (K)=-17.16 J/(K-mol), ?rGm(?)(K)=-1.351 kJ/mol. The relationship between distribution ratio and pH indicates that reaction mechanism is cation-exchange. The experimental results show that the extraction ability of Rb+ by t-BAMBP is greater than K+, and the extraction selectivity to Rb+ was higher than K+, Meanwhile it explained that Rb+ and K+ are easy to be separated, Rb+ is easy to be enriched under the extraction conditions. The extraction is exothermic reaction and low temperature is beneficial to the extraction.In this study, the kinetics and mechanism of extraction of rubidium in brine abundant with potassium by t-BAMBP/xylene has been studied at 25?, using a constant interfacial area cell with laminar flow by examining the effects of stirring rate, phase boundary area, temperature and initial concentration of reactants on the extraction rate. According to the results of this research, the reaction for the extraction of rubidium with t-BAMBP is found as a first order one. The extraction process is controlled by the diffusion of Rb+ in the aqueous phase and chemical reaction that takes place in the interface of the both phases jointly. The mechanism of the Rb+ extraction with t-BAMBP is revealed as follows:the rubidium ion in the aqueous phase and the t-BAMBP molecular in the organic phase diffuses from bulk to boundary layer firstly. Then, the Rb+ and the t-BAMBP molecular react chemically to form the extracted complex. Finally, the extract compound molecular passes through the organic phase boundary layer and diffuses into the bulk of it to finish the extraction process. The kinetic model was established, meanwhile, the mass transfer coefficient of Rb+ in the aqueous phase and the extraction reaction rate coefficient at two phase interface were obtained.On the basis of the research of thermodynamics, kinetics and after calculating theoretical stages, the rubidium purification amplification experiments for the high potassium and low rubidium feed liquid were conducted by extraction, washing and re-extraction process with t-BAMBP/D80 on a multistage continuous countercurrent extraction tank equipment. After four-stage countercurrent extraction, four-stage washing and two-stage stripping section, the enrichment liquid containing Rb+in which CRb+=5.767 g/L, Ck+=0.0103 g/L were got ultimately from the initial high potassium and low rubidium material liquid in which CRb+=2.634 g/L, Ck+=23.06 g/L The total recovery of rubidium is 81.3% in the first stage, and the second is 69.4%. After this countercurrent extraction process, Rb+accounted for 99.8% of metal ion ratio in the liquid enriched rubidium chloride, the purity of product rubidium chloride is 99.5% after evaporation, condensation and crystallization. |
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