Synthesis Of Clay Mineral Adsorbents And Their Adsorption Performance For Cd(Ⅱ)and Tl(Ⅰ)

Toxic heavy metal pollution poses a serious threat to human health and environmental ecological security.Clay mineral materials are excellent adsorption materials for heavy metals removal due to their advantages of low cost,good adsorption performance,and non-toxicity.However,natural clay minerals are limited by their inherent structure,resulting in low reactivity,few exchangeable ions and small specific surface area,so it is difficult to achieve large-scale application.In this study,three kinds of clay mineral adsorption materials for Cd(Ⅱ)and Tl(Ⅰ)treatment were prepared by high temperature and hydrothermal activation.The adsorption mechanism was discussed by studying their adsorption properties,combining with model fitting and instrumental characterization.(1)An activated aluminosilicate adsorbent(CSRM)was prepared by two-stage modification(calcination with mixed salts and the hydrothermal activation)of Potash feldspar.The Cd(Ⅱ)removal in aqueous solution by CSRM was studied,and the adsorption mechanism was explored by SEM-EDX,XPS,XRD,XRF and SBET analysis.The results show that the isotherm adsorption data was more in line with the Langmuir model,and the adsorption kinetics could be described by a pseudo-second-order model.The adsorption isotherm study also indicated that there was a monolayer adsorption process on the CSRM surface,and the maximum adsorption capacity obtained by the Langmuir model was 273.20 mg/g at 328 K.The analysis showed that the interaction between CSRM and Cd(Ⅱ)was feasible,spontaneous and endothermic.Ion exchange is the most important mechanism in the adsorption process,followed by precipitation,surface complexation and adsorption.(2)Based on the above-mentioned characteristics of CSRM for heavy metal removal,a thallium-contaminated adsorbent(FSAM)was prepared by hydrothermally modifying CSRM with potassium ferrate.The effects of the amount of FSAM,initial pH and concentration of Tl(Ⅰ)solution,reaction time and temperature on the adsorption performance of Tl(Ⅰ)on FSAM were investigated.The FSAM was characterized by SEM-EDX,FT-IR and XRD before and after adsorption,and the specific surface area and pore size of the material were determined by SBET.The results indicated that the adsorption rate of Tl(I)on FSAM reached the maximum when the pH is 6.The adsorption process of Tl(Ⅰ)on FSAM conformed with the pseudo-second-order kinetic model,and the results of isothermal adsorption experiment accorded with Langmuir isothermal adsorption equation,indicating that the adsorption process was monolayer and chemical adsorption.Thermodynamic data demonstrated that the adsorption process was spontaneous and endothermic.The main mechanisms of Tl(Ⅰ)removal are oxidation,precipitation and surface hydroxyl complexation.(3)Mg-Fe composites were prepared by coprecipitation method to remove Tl(Ⅰ)from water.The effects of adsorption dosage,initial pH and concentration of solution and reaction time on the adsorption properties of the Mg-Fe composites were explored.The results indicated that when the initial concentration is 1 mg/L,the adsorption efficiency of Tl(Ⅰ)on the materials can achieve over 96.00%at a wide pH and high ionic strength.The reaction reached equilibrium within 80 min,and the adsorption process was in accordance with the pseudo-second-order kinetic model.ΔG0 is negative,implying that the adsorption process is spontaneous and feasible.Instrumental analysis suggests that the adsorption mechanism is mainly surface complexation accompanied by electrostatic attraction.