Preparation Of Porous Polymeric Adsorbent And Its Separation Performance For Cesium

Elementary substance,salts and oxides of cesium play crucial role in the fields of national defense,aerospace and medical.However,the price of cesium rises as the mineral resources reverses.In the salt lake brine stores abundant cesium which can meet the needs of cesium with rational exploit.But the concentration of Cs+ is very low,while the concentration of accompanied K+and Na+is high,whose chemical properties are very similar to Cs+,which puts obstacle to the separation of Cs+from salt lake brine.Several methods have been explored,including precipitation,membrane filtration,solvent extraction and ion exchange.Precipitation is originally applied to extract Cs+from the leaching solution of mineral,which is not suitable for the salt lake system where the concentration of target ion is very low.Membrane filtration has been applied to the separation of radioactive 137Cs.Membrane materials are susceptible to contamination in the salt lake brine of high ion intensity and complicated components.The solution extraction method has been put into use,but some problems still unsolved,like requirement for high concentration of alkali and acid,producing of organic and acidic/alkaline wastes,and the leaking of extraction agent.Based on the absorbent,ion exchangers can be categorized into inorganic ion exchanger and organic ion exchanger.Inorganic ion exchanger includes zeolite,ferrocyanides,and heteropoly acid salts.These materials are usually poor in hydraulic property and reusability,which restrained their application in the field of separating radioactive 137Cs.Researches about organic ion exchangers are mainly focused on ion exchange resin,a kind of functional-groups-decorated polystyrene of low specific surface area and macropores,which shows low adsorption capacity and low selectivity to Cs+.To solve these problems,functional porous polymers with high adsorption capacity and selectivity were synthesized to investigate the influence of functional groups density and chemical structure of cross-linking agent on adsorption property.Firstly,a series of hyper-crosslinked polymers decorated with sulfonic groups of different areal density were synthesized by controlling sulfonation time,and applied the materials to adsorption of Cs+.It suggested that the qe value could reach 260.48 mg/g and was enhanced with the increase of sulfonic groups' surface density.Compared to traditional inorganic ion exchangers,adsorption rate was promoted as well.But SHCP materials show poor selectivity toward Cs+.In double element system of K+/Cs+,separation factor(S.F.)was 0.99-3.92.FT-IR and XPS result suggested that cation exchange was responsible for the materials' adsorption.Compared to commercial sulfonic ion exchange resin,SHCP polymers show better performance in adsorption capacity,but selectivity is not very ideal.In addition,two hydroxyl-rich porous polymers,PR-R and PR-P were synthesized through hydrothermal method with resorcinol and phloroglucinol as monomer.It showed that,in double element system of K+/Cs+,separation factor(S.F.)of PR-R and PR-P were 4.88-9.44 and 3.75-8.84,respectively.And the adsorption capacity to Cs+was promoted as well.Under the condition of NaOH concentration was approximately 10 mmol/L,saturated adsorption of PR-R and PR-P toward Cs+ were 344.21 mg/g and 413.31 mg/g,respectively.Elution and regeneration of the materials can be easily achieved with 0.05 mol/L hydrochloric acid.Saponification and reverse extraction process of traditional extractants typically achieved at pH=13 and 1,in comparison,operating condition of PR-R and PR-P is milder,and requires no organic solution,which is friendlier to environment.In the last part of the study,to investigate the influence of chemical structure on the materials' adsorption behavior,PR-BDA-R and PR-TDA-R was synthesized.It suggested that saturated adsorption capacity of the two materials reduced to 163.93 and 147.06 mg/g,and adsorption isotherm converted to Langmuir monolayer model from micropore-filling model.In the meanwhile,separation factor reduced to 2.39-9.02 and 1.51-5.25,respectively.Compared to PR-R,adsorption rate was promoted.