Preparation And Applied Basic Research Of Selective Adsorbents For Cesium And Rubidium In Saline Lake

The application of cesium,rubidium and their compounds in MHD power generation technology promotes the development of new energy,the mineral resources with cesium and rubidium are scarce.However,the cesium and rubidium in saline lake are abundant while their concentrations are very low and the extraction has great difficulty.Therefore,a simple and efficient extraction technology is the key to the development of cesium and rubidium resources.Adsorption is a preeminent separation method for low concentration target ions,and the key to extracting cesium and rubidium from saline lake is to develop adsorbents with excellent absorption performance.The abundant and low cost leather scrap and its hydrolysate gelatin were used as the supporter of inorganic ion exchanger in this study.Two kinds of adsorbents,alkali-hydrolyzed leather scrap modified with potassium cobalt hexacyanoferrate（AHLS/KCo FC）and gelatin/alginate-Na/Mo-dopedhex-WO₃（Gel/SA/hex-MW）,wereobtained,whoseadsorption characteristics,adsorption mechanism and regeneration characteristics for cesium and rubidium were systematically discussed.Meanwhile,the adsorbents were applied to adsorb the cesium and rubidium from saline lake brine to evaluate their potential value in use,and the results are shown as follows:（1）The AHLS/KCo FC was prepared by in-situ synthesis.The effects of the mass ratio of Co（NO₃）₂·6H₂O to K₄Fe（CN）₆·3H₂O(m _Co/m _Fe)on the loading and chemical formula of KCo FC and the adsorption capacity were investigated.The results showed that the loading and chemical formula of KCo FC are 128 mg/g and K_2.14Co_1.88Fe（CN）₆ when the ratio of m _Co/m _Fee is 3:4,and under the same conditions,the adsorption capacity of cesium and rubidium were 16.793 mg/g and 13.912 mg/g,respectively.The results of batch experiments indicated that the maximum adsorption capacity of cesium and rubidium were achieved at p H6 and 7,respectively,and the AHLS/KCo FC was applied in a wide range of p H.The adsorption rate for cesium was 99.21%at p H 6.0,initial concentration 140mg/L and 0.09 g of AHLS/KCo FC,while that for rubidium was 93.55%at p H 7,initial concentration 20 mg/L and 0.09 g of AHLS/KCo FC.An increase in temperature is propitious to adsorption.With regard to cesium and rubidium,the equilibrium data were fitted well with Langmuir model and the maximum adsorption capacities were 37.258 mg/g and 38.476 mg/g,respectively.For cesium,adsorption equilibrium was achieved at 3 h,while that for rubidium was6 h.Thermodynamic and kinetic studies showed that the adsorption process was spontaneous and endothermic,and the pseudo-second-order kinetic model fitted accurately the data.In the process of adsorption,Cs⁺and Rb⁺were exchanged with K⁺located in the body center of KCo FC on AHLS.（2）Molybdenum-doped hexagonal tungsten（hex-MW）was synthetised by hydrothermal method,and the effects of temperature,time and doping amount of molybdenum on hex-MW structure were investigated.The results showed that hex-MW obtained could maintain the tungsten bronze structure and exhibits excellent adsorption efficiency for cesium and rubidium at 170℃for 24 h when the value of Mo/W is 0.07.Subsequently,the Gel/SA/hex-MW gel microsphere adsorbent was prepared by electrostatic injection.The effect of some factors on the compressive strength of the gel microspheres was discussed,such as the mass fraction of soliquid composed of gelatin and sodium alginate,the mass ratio of gelatin and sodium alginate,the mass fraction of calcium chloride and glutaraldehyde and the additive amount of hex-MW.According to exploration,the conditions for the synthesis of Gel/SA/hex-MW with good compressive strength and higher adsorption capacity are 3%soliquid composed of gelatin and sodium alginate with mass ratio of 2:3 as binder,1%glutaraldehyde and 5%calcium chloride as crosslinker,and 3%hex-MW as the active component.Through the static adsorption experiment,it was found that Gel/SA/hex-MW showed high adsorption capacity for cesium and rubidium at p H 4 and 6,respectively,and lowering the temperature greatly promoted the adsorption.The adsorption of cesium and rubidium by Gel/SA/hex-MW reached equilibrium at2.5 h and 3 h,respectively.The study on adsorption isothermal and adsorption kinetics concluded that the adsorption behavior of cesium and rubidium on Gel/SA/hex-MW can be described by Freundlich and the pseudo-second-order kinetic model.According to the analysis,the adsorption mechanism is the ion exchange between Cs⁺,Rb⁺and NH₄⁺located in the hexangular tunnel of hex-MW.（3）The co-existence of cesium and rubidium with sodium and lithium,the selective adsorption of these ions by AHLS/KCo FC and Gel/SA/hex-MW are Cs⁺>Rb⁺>K⁺>Mg²⁺>Ca²⁺>Na⁺>Li⁺andCs⁺>Rb⁺>K⁺>Na⁺>Ca²⁺>Mg²⁺>Li⁺,respectively,which indicated that AHLS/KCo FC and Gel/SA/hex-MW exhibit high selectivity for Cs⁺and Rb⁺,and conforming to the requirement of high selectivity for extracting Cs⁺and Rb⁺in saline lake.（4）Taking the actual saline lake brine as the experimental object,AHLS/KCo FC and Gel/SA/hex-MW can efficiently adsorbed cesium and rubidium from saline lake.The adsorption rates of AHLS/KCo FC for cesium and rubidiumare97.33%and51.19%,respectively,while thatfor Gel/SA/hex-MW are 90.46%and 71.23%,respectively,illustrating the AHLS/KCo FC and Gel/SA/hex-MW have great value on practice.（5）p H=2 and neutral KCl solution have good desorption effect on cesium and rubidium adsorbed on AHLS/KCo FC,respectively.With 2.5 mol/L KCl solution of p H=2 and 1.5 mol/L KCl as the desorption agent,the desorption rate of Cs⁺and Rb⁺were 87.48%and 98.63%,respectively,and the desorption equilibriums were reached at 18 h and 3 h,respectively.The results of regeneration and recycle of AHLS/KCo FC showed that the adsorption rate decreased from 92.55%to 81.31%after 5cycle for cesium,while that for rubidium decreased from 93.37%to 88.11%,which showed that AHLS/KCo FC has good recycling performance.In summary,the abundant leather scrap and its hydrolysate gelatin as the supporter of inorganic ion exchanger,the obtained AHLS/KCo FC and Gel/SA/hex-MW adsorbents have the advantages of low cost,high adsorption capacity,recyclable utilization and high selectivity adsorption,and they are of great application value in the extraction of cesium and rubidium from the brine of saline lake.