Removal of Cr(VI) from low-temperature micro-polluted surface water by tannic acid immobilized powdered activated carbon

In this study, food-grade tannic acid-immobilized powdered activated carbon (TA-PAC) was prepared, and adsorption of Cr(VI) (0.500 mg/L) onto TA-PAC as a function of pH, contact time, adsorption capacities and adsorption isotherms at 280 K was investigated. The results indicated that the immobilization process introduced abundant acid functional groups. The adsorption capacity of TA-PAC was found to be pH-dependent, and the optimal pH value was found to be 4.0. The equilibrium time was 240 min for TA-PAC. Adsorption data for total chromium were modeled using both two-parameter and three-parameter isotherm models. Freundlich and linear forms of three-parameter models yielded the best results for all of the data. Desorption studies of immobilized material suggested that the immobilization of food-grade tannic acid is steady. The adsorption mechanism of Cr(VI) on TA-PAC was assumed to be a comprehensive process consisting of surface reduction of Cr(VI), esterification between catechol and chromate, and ion exchange.

► Food-grade tannic acid immobilized PAC (TA-PAC) was prepared and characterized. ► Immobilization of tannic acid was beneficial for removal of Cr(VI) from water. ► Freundlich and three-parameter models fitted data well. ► Food-grade tannic acid is permanently immobilized. ► Adsorption mechanism of Cr(VI) on TA-PAC was a comprehensive process.