Adsorption Of Fluoride Ion From Aqueous Solution By Pillared Coal-bearing Kaolin

For a continuous development of aluminum smelting,phosphate fertilizer and steel industries,fluorine pollution has become a global environmental problem.In this paper,coal-bearing kaolin was adopted as the basic materials to develop the pillared coal-bearing kaolin composite adsorption materials by modification methods such as calcination,acid modification,intercalation and columnarization.The analytical methods such as scanning electron microscope?SEM?,X-ray diffraction?XRD?and infrared spectroscopy?IR?were used to investigate the characteristics of the coal-bearing kaolin before and after pillared.In the meanwhile,the preparation conditions,physical and chemical characteristics,fluoride ion adsorption characteristics and adsorption mechanism were investigated.The coal-bearing kaolin was first calcined at 500°C for 4 h to remove volatile substances in the structure to achieve preliminary stripping with specific surface area increasing.Secondly,the coal-based kaolin was modified with 20%HCl for 4 hours at a solid-liquid ratio of 1:10 and a temperature of 90°C to dissolve iron and partially active aluminum in the kaolin for the new pores appear.Then,potassium acetate was added at 5 mL/g to insert into the interlayer to provide possibility for the polyzirconium ions to enter the interlayer.Finally,It achieved the best adsorption efficiency that the pillared coal-based kaolin was prepared by concentration at 0.1mol/L ZrOCl₂ without NaOH,columnization time of 8 h,Zr/soil ratio of 1 mmol/g,and temperature of 60 ^oC.In static adsorption experiments,the highest removal efficiency?98.2%?was obtained under optimal conditions of adsorbent dosage was 10 g/L,pH of 4,initial concentration of F^-was 50 mg/L after 3 h of operation at 25 ^oC.The adsorption isotherm of F^-for the zirconium pillared coal-bearing kaolin was more consistent with the Langmuir equation.The adsorption kinetics was fitted with Pseudo-second-order kinetics.After modification,the zirconium pillared kaolin composite with special functional groups is formed due to the hydroxyl group between the coal-bearing kaolin layer and the carboxyl group introduced by the intercalation reacting with the hydroxyl group on the Zr complex.This increases the spacing of the coal-based kaolin layer and the specific surface area,which is beneficial to the adsorption of fluoride ions.Its adsorption mechanism includes physical adsorption,electrostatic attraction and chemical adsorption.The above results indicate that the pillared coal-based kaolin composite adsorbent is feasible for the adsorption of fluoride ions.