Perchlorate removal by granular activated carbon coated with cetyltrimethyl ammonium chloride

In this study, granular activated carbon (GAC) coated with cetyltrimethyl ammonium chloride (GAC-CTAC) was synthesized to remove perchlorate from water. Bench scale kinetics and adsorption isotherm tests were performed to evaluate the effects of factors affecting the adsorption efficiency, including the CTAC content, solution pH and ionic strength (I). When the content of CTAC on GAC increased from 0.031 to 0.16mmol/g, the rate constant in the pseudo-second order reaction was decreased from 46.35 to 23.24h.g/mmol, and the K value in the Freundlich equation was increased from 0.087 to 0.20mmol/g correspondingly. Typically, GAC-CTAC exhibited a higher adsorption capacity than GAC, which highlighted the key role of CTAC. The optimum perchlorate removal by GAC or GAC-CTAC was observed at pH 2-3, equivalent to pH_pzc determined by zeta potential measurement. The adsorption capacity of perchlorate onto GAC-CTAC at pH 2.5 (0.36mmol/g) was 3.8 times as high as that onto GAC-CTAC at pH 5.6 (0.094mmol/g). Ionic strength appeared to significantly inhibit the perchlorate adsorption on GAC-CTAC. Finally, our results demonstrated that the primary mechanisms for the adsorption of perchlorate on GAC-CTAC were associated with electrostatic interaction, surface complexation and ion exchange.