Preparation Of Activated Carbon Modified By Manganese Oxide And Its Removal Of Thallium

In this study,activated carbon modified by manganese oxide was prepa red by redox precipitation-roasting method,and the optimal preparation parameters of modified activated carbon were determined by orthogonal experiment.The influence factors of removing thallium were studied by static adsorption experiments.The regeneration performance was investigated by regeneration experiments.The adsorption mechanism was studied by adsorption kinetics,thermodynamic model and characterization.Orthogonal experiments indicated that the optimum preparation conditions of modified activated carbon were as follows:the concentration of KMnO₄ was 0.175mol/L,roasting temperature was 450°C,roasting time was 3 h.Compared with the unmodified activated carbon,the modified activated carbon prepared under the optimal preparation conditions has a removal rate of 80.49%,and the adsorption performance is greatly improved.Static adsorption experiments indicated that the removal efficiency of modified activated carbon was about 96.7%when the pH was between 2 and 8.When the optimum dosage of adsorbent was 0.3 g/L,the removal rate was 95.35%.When the initial concentration of Tl???was 40 mg/L,the adsorption capacity of the activated carbon was 111.78 mg/g.The adsorption process of modified activated carbon for Tl???was divided into three types:rapid adsorption,slow adsorption and adsorption equilibrium.The effect of coexisting ions on the adsorption rate was as follows:Ca²⁺>Mg²⁺>Na⁺;the regeneration experiments indicated that HCl has the best desorption effect,the desorption reaction has a faster reaction rate,the desorption reaction was completed within 4 min,and when the concentration was 0.05 mol/L,the desorption rate reached 85.92%.After three regenerations,the desorption rate was at84.32%.The adsorption kinetics and thermodynamic experiments showed that the modified activated carbon is fitted with the pseudo-second-order equation and the Langmuir isotherm adsorption model as well.The kinetic and thermodynamic fitting parameters indicates that the adsorption reaction is chemical adsorption,spontaneous process and belongs to the endothermic reaction.Characterization experiments showed that the color of activated carbon changed from black to brown,indicating that manganese oxide was successfully loaded on activated carbon.After modified,the specific surface area of activated carbon decreased sharply,and there were granular and flake-like manganese oxide on the surface.X-ray diffraction analysis showed that manganese oxide was loaded on the surface of activated carbon in two types:?-MnO₂ and Mn₃O₄,and a large number of-OH bonds existed on the surface.A layer of flocculent material existed on the surface of the modified activated carbon after adsorption,indicating that Tl???was adsorbed to the surface;From the result of Fourier Transform infrared spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy,it can be seen that the removal mechanism of modified activated carbon includes surface complexation and oxidation.