Study On Modification And Adsorption Properties Of Peanut Shell And Medical Stone

Along with the expansion of metal-producing and consuming industries,large amount of sewage containing quantities of heavy metal ions have been discharged into the water bodies.The presence of these toxic metal compounds causing harm not only severe environmental pollution but also human beings diseases globally.Activated carbon is widely used as an excellent absorbent for metal pollutants in wastewater treatment.However,further application of the activated carbon is restricted,due to its difficulties in regeneration,low recovery rate,and high cost.In this paper,our research work addressed the utilization of modified peanut shells and medical stone for preparing a new type of adsorbent with high efficiency and stability properties,which is expected to replace activated carbon in the future.NaOH,HNO₃,citric acid,KMn O₄,H₂O₂,and ethanol were used to modify peanut shells and medical stone under different conditions.The parameters of modified peanut shell were studied:the modified reagent is HNO₃,the concentration of nitric acid is 2 mol·L^-1,the modified temperature is 50℃,the contact time is 5 h,and the maximum iodine adsorption value is 798.73 mg·g^-1.As for modified medical stone,the parameters of it were studied:the modified reagent is citric acid,the concentration of citric acid is 0.6 mol·L^-1,the modified temperature is 30℃,the contact time is 4 h,and the maximum Cd²⁺adsorption value is 14.36 mg·g^-1.SEM investigations demonstrated that the adsorption capacity enhancement ascribed to pore widening,increased cation-exchange capacity by oxygen groups.From N₂ adsorption/desorption isotherm,the higher adsorption capacity of modified peanut shells and medical stone were justified by the relatively high surface area and total pore volume.Moreover,the thermogravimetric analysis illustrated that the chemical and thermal stability of modified peanut shells and medical stone were improved greatly.Meanwhile,the results of XRD test showed that the particle size of the adsorbent became smaller and the spacing of interplanar was increased after modification,resulting in the specific surface area increased and the adsorption performance enhanced.Several kinetic models were used to determine the biosorption mechanism.It was determined that the biosorption system obeyed the pseudo-second-order kinetic model by taking into account the correlation coefficient value.The linear forms of the Freundlich and Langmuir isotherms were applied to the biosorption data,and it was concluded that the Langmuir isotherm gave a better fit than the Freundlich model based on the physical biosorption mechanisms occurred.The results of adsorption and regeneration experiments showd that the modified peanut shell has a smaller decrease in the process of the Cd²⁺adsorption,indicating that it can adsorb metal ions repeatedly in aqueous solution.Through the above design and analysis,we successfully modified the materials with high-efficiency adsorption performance,which had a great superiority for the removal of pollutants and had a great potential application value in the field of adsorption.