Separation Behavior And Mechanisms Of Strontium By Adsorption And Extraction

This paper mainly focused on the utilization of liquid resources of strontium and removal of 90 Sr in the radioactive wastewater. Adsorbent for strontium was designed and chosen; adsorption performance and mechanisms were studied. DCH18C6 was used as the extractant for strontium, the extraction behavior and mechanisms of DCH18C6 were discussed.A crown ether adsorbent for strontium was designed and prepared with D564 resin as the framework. Its adsorption properties for strontium were studied. Five organic resins, D001, D113(hydrogen form), DJH003, LSC-100, and LSC-500, were initially chosen as the adsorbents for strontium. The equilibrium adsorption amount was found to follow a sequence of LSC-500(2.20 mmol/g) > DJH003(2.18 mmol/g) > D001(2.15 mmol/g) > LSC-100(2.05 mmol/g) > synthesized crown ether-grafted adsorbent(0.27 mmol/g) > D113(0.16 mmol/g). LSC-500, LSC-100, D001, and DJH003 adsorb strontium ions quite rapidly with an equilibrium time of 2 h, while the synthesized crown ether-grafted adsorbent has a long equilibrium time. The adsorption results of D113 resin was not satisfactory because of its low adsorption amount. Four organic resins including two ion exchange resins and two chelating resins were selected as absorbents for strontium for further experiments due to their relatively high equilibrium adsorption amount and relatively short equilibrium time.Adsorption performance and mechanisms were studied systematically for the selected resins LSC-500, LSC-100, D001, and DJH003 in noncompetitive and competitive systems. In unitary system, adsorption rate and equilibrium adsorption amount grew with the increase in initial alkaline earth metal ion concentration. Elvated temperature was helpful to promoting adsorption process. The equilibrium adsorption amount of D001 and DJH003 resins was nearly the same when the initial solution p H was 2 and the initial solution p H was not adjusted. However, when the initial solution p H was 2, the equilibrium adsorption amount of LSC-100 and LSC-500 resins was below 1 mmol/g. Under this condition, for the LSC-100 and LSC-500 resins, although the adsorption amount was low, there were relatively large differences in the adsorption amounts due to the different affinities of Mg2+, Ca2+, and Sr2+ ions to the resins at low p H. The competitive adsorption of alkaline earth metal ions presents obvious differences from the noncompetitive adsorption for D001 and DJH003 resins. The adsorption capacity of D001 and DJH003 resins for strontium was obviously higher than that of magnesium and calcium. The competitive adsorption results were explained by considering hydration of the metal ions, electrostatic attractions and complexation between the metal ions and the resins. The results obtained would be helpful for the understanding of the competitive adsorption processes and the recovery or removal of one or more alkaline earth metal ions from aqueous solutions.Calcium alginate was prepared using the sol-gel method and its strontium adsorption behavior was investigated. The effect of several parameters such as p H, initial strontium concentration, contact time, ionic strength and temperature were investigated. The results indicate that p H and ionic strength had an obvious influence on the equilibrium adsorption amount. When all the adsorption sites were occupied by the metal ions, the adsorption quantity remained the same. Because of the difference in the affinity of the Sr2+ and Ca2+ ions to the adsorbent, the adsoption for Sr2+ still happens even a large number of Ca2+ co-exists. The adsorption process was considered to be an ion exchange chemical adsorption based on the analysis of the adsorption dynamics and thermodynamics. The experimental results indicate that the calcium alginate is a promising adsorbent for the adsorption of strontium from dilute solutions.The extraction of strontium using dicycolhexyl-18-crown-6(DCH18C6) as the extractant from nitric acid solution was investigated as a function of various parameters. The results showed that strontium can be efficiently extracted by DCH18C6 dissolved in 1, 1, 2, 2-tetrachloroethane from a nitric acid solution. D(Sr) was found to increase as the phase ratio(O/A) increases. The proper concentration of nitric acid was 1.0-1.5 mol/L. When the concentration of DCH18C6 was 0.1 mol/L, the extraction percentage of Sr2+ was found to be higher than 90%. The extracted Sr2+ can be easily stripped with deionized water. Nearly 99% recovery of Sr2+ was achieved by four times of such stripping. The extraction results of strontium and calcium coexistence system showed that the presence of Ca2+ has a great influence on the extraction of Sr2+ because of the Ca2+ competitive extraction. The extraction mechanism analysis showed that the extracted compound should be DCH18C6-Sr(NO3)2.