| With the continuous development of nuclear power and the application,more and more radioactive waste water is also generated.Due to great radiation hazard of radioactive waste water on environment and biological,the radioactive waste water treatment has received more attention and research by many experts and scholars in recent years.The processing of radioactive waste water treatment are mainly containing chemical precipitation method,evaporation concentration method,membrane separation,ion exchange method,adsorption method and so on.With simple operation,low cost,high efficiency adsorption and the advantages of easy to solidification of municipal solid waste,adsorption method become a research hotspot.Adsorption materials currently used are mainly zeolite mineral material.activated carbon material.chemical synthesis of phosphomolybdic acid salts,ferrocyanide material and chitosan polymer material.But most of these materials have many defects such as poor stability,complicated preparation process and difficult solid waste solidification,and most of these materials is easy to conglobation,difficult to dehydration and cannot be used for continuous radioactive wastewater treatment by the adsorption bed for the powder form.Based on this.using magnesium phosphate cement as matrix,magnesium phosphate matrix porous adsorption materials were prepared by different foaming process with hole connected,uniform pore diameter and high strength,the effect of types of foaming agent,foam dosage,air-entraining agent content and water solid ratio on the pore structure,pore size distribution and mechanical properties of MPCPM were systematacially study in this paper.Regard the simulate radioactive waste water containing Cs+ and Sr2+ as the research object,discussing the adsorption performance of MPCPM for Cs+ and Sr2+,and through the fitting of dynamic model and thermodynamic model to analysis the adsorption mechanism.In order to further improve the adsorption performance,zeolite was used to modify MPCPM and the adsorption performance of modified porous materials(MPCPM-Z)for Cs+ and Sr2+ was also discussed in this paper.The results shows that MPCPM prepared by physical foaming process with average air pore diameter of 200?400?m,the porosity of 55%?75%the dry density is 1000?600kg/m3 and compressive strength is 10?1MPa.Among them,the MPCPM prepared by animal protein foaming agent(FA)with the highest intensity,the morphology of most pores are spherical shape but all pores are closed structure.The samples prepared by homemade foaming agent(FB,FC)all with connected pores structure and has waterproof performance.The MPCPM prepared through chemical foaming process adopted zinc powder as air-entraining agent with porosity of 55%?65%,dry density of 1000?780kg/m3,the samples got the highest compressive strength of 14?6MPaand the greatest average pore diameter of 500?900?m compared to the process mentioned above,but all the samples are closed air pore structure.The MPCPM prepared by physical and chemical joint foaming process with homemade foaming agent of FC and air-entraining agent of zinc powder has porosity of 55%?74%,dry density of 80?600kg/m3,average pore diameter of 150?280?m and compressive strength of 4.5?2MPa,all samples have connected pore structure and can regulate the air pore size by changing the related parameters.Through the study of adsorption experiments,MPCPM with average pore diameter of 160?m,porosity of 69%,dry density of 700kg/m3 and compressive strength of 3MPa has best performance for absorption of Cs+ and Sr2+,which was prepared by physical and chemical joint foaming process with M/P of 1,dosage of foaming agent,air-entraining agent,respectively,1.5%,1.0%,water cement ratio of 0.16.With MPCPM dosage is 0.1g/100ml,96h was needed for adsorption balance of Cs+ and Sr2+,the biggest saturated adsorption capacity are 18.5 mg/g and 402 mg/g,the biggest removal rate are 32%and 96%,respectively.The adsorption process followed the pseudo second order model,thermodynamic model fitting can be described by the Freundlich model and the Langmuir model,respectively.The results indicate that the adsorption isotherm of MPCPM to Cs+ is uneven surface of multilayer adsorption and preferential adsorption.And the adsorption isotherm of MPCPM to Sr2+ is uniform surface single-layer chemical adsorption.In addition,the acid environment and the existence of K+ and Na+ will seriously affect the adsorption effect of Cs+ and Sr2+.Due to less Cs+ adsorption quantity,modified porous MPCPM-Z was prepared by adding zeolite powders,this material has a significant boost for Cs+ adsorption performance.Under the same conditions,the saturated adsorption capacity of MPCPM-Z to Cs+ is 28 mg/g and removal rate reached 75%the adsorption kinetics and adsorption thermodynamic model is same as preivous materials.However,the adsorption efficiency has little reduce,the removal rate is only 92%in the same conditions and the adsorption thermodynamics model followed the Freundlich model.That is the adsorption process of MPCPM-Z to Sr2+ changed into heterogeneous multi-layer chemical adsorption.MPCPM-Z is still very sensitive to the acidic environment and K+,Na+,Ca2+ and Mg2+,the adsorption efficiency will be severely reduced under these circumstances.In conclusion,the magnesium phosphate cement based porous materials prepared through physical and chemical foaming process has strongly adsorption performance to Cs+ and Sr2+.Especially for the Sr ions,removal rate can reach more than 96%,at the same time,Cs ions removal rate can reach 75%above through modification method.As a result,the technology in the field of radioactive waste water treatment has broad application prospects. |
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