| Adsorption of heavy metal ion from aqueous solution onto activated carbon prepared from tobacco stems (AC1) and coconut shell (AC2) by microwave heating were investigated in a batch system. Adsorption Kinetic, mechanism and isotherm were studied in this article.A systematic study was carried out to investigate influence of different conditions on the adsorption, such as dosage of activated carbon, initial concentration, shaking time, pH value, temperature etc. It determined the optimal adsorption conditions.The study find the optimal pH were 4.0, 6.0 and 5.0 for chromium, copper and lead.Thermodynamic parameters such as standard Gibbs free energy (△G~0), standard enthalpy (△H~0), and standard entropy (△S~0) were evaluated by applying the Van't Hoff equation. Langmuir and Freundlich isotherms were used to analyze the equilibrium data at different temperatures. The canculated Langmuir limit adsorption capacity were 11.64,7.57 and 10.66 mg/L for chromium, copper and lead respectively of AC1 and 11.11, 8.57 and 22.57 mg/L of AC2, from which we can find that AC2 adsorption capacity was better than AC1 except the adsorption of lead by AC2.The sorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the sorption kinetics was found to follow a pseudo-second-order kinetic model. The initial sorption rate, pseudo-first-order and pseudo-second-order rate constants for different initial concentrations were evaluated and discussed.Using mathematics method analysed adsorption mechanism and find out the rate controlling step.The regeneration of spent activated carbon is very important in applications. The regeneration by means of acid and alkali treatment was studied. The result showed that using alkali-acid treatment can regenerate the activated carbon adsorbed chromium and using acid-alkali treatment can regenerate the activated carbon adsorbed copper and lead. The percent of metal ion desorbed can reach 80 % by using pretty concentration of acid or alkali. |
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