Adsorption of nitrate and Cr(VI) by cationic polymer-modified granular activated carbon

Modified granular activated carbon was prepared by coating quaternary ammonium-containing polymer [3-(methacryloylamino)propyl]-trimethylammonium chloride, onto granular activated carbon (GAC) to remove nitrate and Cr(VI) from aqueous solution. The removal efficiencies for nitrate and Cr(VI) increased as the concentration of the cationic polymer used for modification increased to 0.25%, but those decreased slightly when the polymer concentration further increased to 2.5%. Kinetics experiments indicated the adsorption was a fast process, reaching equilibrium in 90 and 120 min for nitrate and Cr(VI) adsorption, and the maximum equilibrium uptake of nitrate and Cr(VI) were about 26 and 81 mg g−1, respectively. The adsorption of both anions was well described by pseudo-second-order kinetics model and Langmuir isotherm model. There was a linear relationship between the amounts of desorbed chloride and adsorbed nitrate and Cr(VI), suggesting the main effect of modification was enhancement of ion exchange capacity of GAC. The thermodynamic data showed that adsorption process would be thermodynamically favorable, spontaneous, and exothermic nature. The adsorption capacity for Cr(VI) decreased continuously with an increase in initial solution pH from 3 to 8 but such an effect was less significant for nitrate. The nitrate and Cr(VI) adsorption decreased the most in the presence of sulfate, followed by chloride and phosphate. The overall results demonstrated the potential utility of a cationic polymer for enhancement of performances of GAC-based materials for anions removal from aqueous solutions.

► Activated carbons as a versatile and economic adsorbent for aqueous pollutants.
► Surface modification by cationic polymer to enhance absorption capacity for anions.
► Maximum absorption of nitrate and Cr(VI) observed when coated with 0.25 wt.% polymer.
► Adsorption capacity for nitrate and Cr(VI) increased about twice by the modification.