Synthesis Of Silica-based Inorganic Composite Adsorbent And Their Adsorption Behavior For Environmental Hazardous Ions

In this paper,the goal is to prepare new type of inorganic modified silica-based compound adsorption materials to remove the harmful ions in the environment,the research is mainly focused on the use of porous silica-based nano/micro particles or microspheres as the rigid carrier.For the first time,the Mg-Al hydrotalcite（Mg-Al-LDH）,hydrated cerium oxide（HCO）,layered inorganic material such as titanium zirconium phosphate（-Ti-O-P-Zr-O-）modified on silica-based carrier was prepared with different composite adsorbent and its specific application in different ion removal,the adsorption performance and mechanism of adsorption behavior is evaluated.In order to study the treatment of adsorption materials after adsorption of harmful ions,this paper focuses on the study of strontium solidification after adsorption by sodium titanate,and discusses the solidification effect and mechanism.Iodine ion（I^-）is a typical toxic anion pollutant,which leads to the increase of thyroid cancer,leukemia and metabolic disorder.It poses a huge threat to human health.Metal composite oxide（LDH）is the product of calcination of Mg-Al-LDH at 450℃.The composite material Mg-Al-LDO/Si O₂ is the main absorbent of iodide ions in this study.The internal morphology of the composite adsorbent was characterized by various analytical methods.The results of field emission scanning electron microscopy（FESEM）,infrared spectroscopy（FT-IR）and X-ray diffraction（XRD）showed that the hydrotalcite grew well in the channel of silica matrix.The influence of the amount of composite material,p H value of aqueous solution and initial I^-concentration on adsorption capacity was studied.The results of static experiments showed that Mg-Al-LDO/Si O₂ adsorbent had a good adsorption performance on I^-,and the removal efficiency was 99.81%from the I^-solution of 30 mg/L in 5 mins,and the dosage was 0.05 g/100 ml.The adsorption kinetics was fitted by pseudo-second-order model.The column experimental data show that Mg-Al-LDO/Si O₂ can continuously treat the iodine ion effluent in the column,and the best breakthrough curve can be obtained by adjusting the bed height.The breakthrough curve is related to Thomas,Adams Bohart and Yoon Nelson models.The excessive discharge of phosphorus in the water ecosystem leads to the deficiency of traditional treatment technology,which could not meet the increasingly strict environmental regulations on phosphorus discharge.Cerium oxide（Ce O₂）is one of the world’s most abundant rare earth metal oxides.Furthermore,it has the advantages of mesoporous structure,low elution,and high affinity for anions and it is one of the best adsorbents for dealing with harmful anions.In this paper,an effective method is proposed to immobilize the high price Ce element on the porous silica microspheres by impregnation,calcination and activation technology,so as to effectively remove the phosphate.Silica based composite adsorbent is synthesized by the following steps:（1）the Ce³⁺atoms adsorbed on the surface of silica spheres;（2）the cerium nitrate in hexahydrate is converted to cerium dioxide by thermal decomposition;（3）the anhydrous cerium oxide is converted to anhydrous cerium oxide（HCO-Si O₂）by acid activation.The results showed that the cerium oxide nanoparticles grew uniformly on the surface of the silica spheres at 90.5℃and 218.0℃,and the heating rate was 2℃/min.The results XRD and X-ray photoelectron spectroscopy（XPS）show that Ce³⁺atoms can be oxidized to Ce⁴⁺atoms and large number of reduction ion exchange sites can be generated.The static adsorption experiment shows that 15HCO-Si O₂has good phosphorus removal performance and the maximum adsorption capacity is 85.5 mg/g.Kinetic and isothermal studies showed that the experimental data were consistent with the model of second order kinetics and Langmuir,indicating that chemisorption and monolayer adsorption occurred simultaneously in the adsorption process.The adsorption mechanism analysis showed that phosphate ions were separated by reduction and ion exchange reaction（Ce O₂ and Ce PO₄occur reduction and ion exchange reactions）.Nickel is a kind of carcinogenic heavy metal,it will not only harm the environment and human health,but also cause waste of precious metal resources.For the removal of low concentration nickel ions,the silica-based laminated zirconium phosphate titanium composite（-Si-Ti-O-P-Zr-O-）was prepared by layer-by-layer grafting method,and its adsorption performance in nickel ion dilute solution was studied in detail by static experiments.The results of FESEM showed that the original adsorbent presented smooth and neat morphology,while the adsorbent after ion adsorption presented rough morphology.The results of elemental analysis（EDS）confirmed the existence of metal elements（Si,O,Ti,P,Zr）and adsorbed nickel elements.The formation of new bands of-Si-Ti-O-,-Si-Ti-O-,-Si-Ti-P-and-Si-Ti-P-Zr-O-was found by FT-IR.In the static experiment,the optimal p H value of nickel ion adsorption was 8,the equilibrium time at room temperature was 30 mins,and the maximum adsorption capacity was 50.1 mg/g.The adsorption kinetics of the adsorption process was consistent with the second order kinetics model,and the isothermal adsorption process was in good agreement with the Redlich-Peterson model.The results of thermodynamic simulation reveal the types of nickel ions in wastewater and provide a reasonable p H range for removing nickel from wastewater.Nuclear accidents and daily nuclear power plants are the main sources of strontium release.The secondary contamination can be avoided by curing the adsorbent properly.In this paper,sodium titanate powder(Na₂Tin O_2n+1)was prepared by improved sol-gel method.X-ray diffraction（XRD）results showed that Na₂Ti_nO_2n+1 was transformed into anatase structure after calcining at 400℃for 10 h,and the specific surface area（BET）of the synthesized adsorbent was65.01 m²/g.The results of static adsorption experiments show that Na₂Ti_nO_2n+1 is an effective adsorbent for removing Sr²⁺,and its maximum adsorption capacity can reach 49.6 mg/g.The adsorbent also showed high selectivity to Sr²⁺in the co-experiments of titanate ceramics in different media show that the adsorbed Sr²⁺has good solidification performance.