Preparation Of Pellet Silica-based Titanate Adsorbents For The Removal And Solidification Of Strontium

The use of nuclear energy has aroused great attention since the environmental pollution and the increasingly serious energy crisis.But coins have two sides;the use of nuclear energy will produce a large number of radioactive pollutants.After the Fukushima disaster,the high efficient method to remove radionuclides from wastewater with high concentration of salt and low concentration of radionuclides has received substantial attention from an environmental perspective.Because of the excellent removal ability,regeneration ability and simple in use,ion exchanger has become an important means to remove wastewater.Titanate-powder adsorbents are widely used in the removal of strontium from radioactive wastewater because of the special interlayer structure and the exchange between Na+ and Sr2+ in solution.However,the powder structure limits its large-scale application.The purpose of this work is to efficiently treat Sr2+ in high concentration salt and low concentration radioactive wastewater produced by nuclear accident.A novel silica-based titanate(Na2TinO2n+1/SiO2)was synthesized with different ratio of raw material and at different calcination temperature by sol-gel method for decontamination of above wastewater.The adsorption capacity of each adsorbent was compared and then characterized the adsorbents by FT-IR,SEM,EDS,XRD,TG-DSC,XPS and BET.Characterization results suggested that sodium titanate was successfully loaded in the pore of SiO2 and combined with SiO2 in a physical way;the crystal of the titanate was greatly affected by temperature,leading to the difference in the adsorption properties;the silica-based material showed a significant increase in specific surface area.Based on these properties,the Na2TinO2n+1/SiO2 adsorbent at the ratio of 4:1 sodium to titanium and calcination temperature of 500? was selected to conduct the following batch experiments.Adsorption results suggested that the adsorption data of Sr2+ can be well fitted by the Langmuir model with adsorption amount approaching 33.31 mg/g;the adsorption equilibrium could reach within 5 minutes and kinetic data was well fitted by the pseudo-second kinetic model;the pH from 3 to 10 contributed to a better Sr2+ adsorption behavior;and the selectivity coefficient revealed that this material had higher selectivity towards Sr2+ contrast to other alkali and alkaline-earth metals.Based on above static experimental results,the dynamic treatment was designed and carried out in a glass column.This test demonstrated that Na2TinO2n+1/SiO2 could remove the strontium from the simulated seawater effectively,showing a fast adsorption kinetics,with a dynamic adsorption capacity of 4.37mg/g.Large amounts of spent adsorbent were accumulated after adsorbing Sr2+,of which the disposal shows troublesome and challenging.The spent sodium titanate was cold pressed and calcined to form titanate ceramics.From loading experiments,it was suggested that,the sintered pellets exhibited a strong solidification capability towards adsorbed Sr2+.The measured leaching efficiencies was investigated on different medium(i.e.deionized water,0.1 mol/L HC1 and 0.1 mol/L NaOH)and at different temperatures(i.e.25? and 90?)and the leaching rates of sintered pellets on the above different medium at 25? were 1.26%,3.89%and 0.54%,respectively.This proved the feasibility of the:integration of the adsorption and the in-situ solidification processes.In summary,the selective adsorption and in-situ solidification of strontium using titanate material is simple,environmentally friendly,and highly efficient,and posses a bright future in the treatment of radioactive waste.