Preparation Of Novel Adsorbents And Study On The Removal Of Uranium From Aqueous Solusion

Uranium is a radioactive and toxic element. The water pollution resulting from uranium can cause serious threat to the health and safety of human and other bio-organisms. Adsorption technology played an important role in the removal of uranium ions from radioactive liquid waste. Because of their high surface areas, large pore size, uniform pore structures, excellent thermal and mechanical stability, mesoporous silica have attracted much attention with aims of removal of uranium ions from radioactive liquid waste. In order to improve the performance of mesoporous silica, the adsorption technologies of removing uranium ions from aqueous solution were investigated through improving adsorption procedure, functionalization of mesoporous silica and improving the structure of mesochannels.The performance of the removal of uranium ions from aqueous solution by mesoporous silica(SBA-15) was investigated. The maximum adsorption capacity of SBA-15 was 179 mg/g, and a contact time of 30 min was sufficient to achieve sorption equilibrium. The most favourable initial solution pH for the sorption of U(VI) by SBA-15 was 6.0, and the sorption process was exothermic. The influence of K+ and Na+ concentrations and the solid-to-liquid ratio on the sorption was very weak. A countercurrent two-stage adsorption-microfiltration process was developed by combining the advantages of countercurrent adsorption and complete mixing adsorption, and the SBA-15 was used as the adsorbent. The calculation method of the concentrations of U(VI) in effluents was derived while the countercurrent two-stage adsorption-microfiltration process was used to remove uranium ions from aqueous solution, and the calcaluted values of concentrations of U(VI) in effluents were very close to the experimental ones. When the dilution factor was 0.2, the removal efficiency of U(VI) by countercurrent two-stage adsorption-microfiltration process was 90.23%, and the efficiency by conventional adsorption-microfiltration process was 76.9% under the same condition. So the removal efficiency of U(VI) in aqueous solution was improved significantly by countercurrent two-stage adsorption-microfiltration process.A novel mesoporous material(DMS), synthesized by grafting dopamine onto SBA-15 that was synthesized by hydrothermal method, was developed as a sorbent to extract U(VI) from aqueous solution. The method used to modify SBA-15 has the advantages of simple, facile and cost-effective. The characterization results of DMS confirmed that the dopamine-functionalized SBA-15 was successfully prepared. The DMS had highly ordered 2D hexagonal mesochannels, and the BJH adsorption cumulative volume, specific surface area and pore size of DMS were calculated to be 0.74 cm3/g, 484 m2/g and 7.07 nm, respectively. The results of sorption experiment demonstrated that the adsorption capacity and rate of U(VI) in DMS were improved significantly compared with the unfunctionalized SBA-15. The maximum adsorption capacity of DMS was 196 mg/g at pH 6.0, and a contact time of 20 min was sufficient to achieve sorption equilibrium. The sorption process for U(VI) by DMS was exothermic, and the sorption was dependent on the pH of the solution, but the influence of K+ and Na+ concentrations and the solid-to-liquid ratio was very weak.Onion-like mesoporous silica(MOS) was synthesized by hydrothermal method, and it had clear multilayer structure. The BJH adsorption cumulative volume, specific surface area and pore size of MOS were calculated to be 1.27 cm3/g, 481.5 m2/g and 14.75 nm, respectively. The large pore size and pore volume was beneficial to the diffusing of U(VI) into the inside channels of MOS, so the adsorption capacity could be improved, and the maximum value was 196 mg/g. Moreover, large pore size could improve the adsorption rate, and a contact time of 20 min was sufficient to achieve sorption equilibrium. In the countercurrent two-stage adsorption-microfiltration process, the MOS was used as the adsorbent, and when the dilution factor was 0.2, the removal efficiency of U(VI) was 99.30%, and the efficiency by conventional adsorption-microfiltration process was 84.34% under the same condition.