Effect of humic acid on the Cr(VI) adsorption onto Kaolin

The adsorption of chromate on kaolin/humic acid was studied at various conditions of initial solution pH, ionic strength, water hardness and temperatures. The increased adsorption of chromate in the presence of HA was attributed to the reducing action and complexation of HA. The addition of inorganic salts (Na+, Ca2+ and Mg2+) reduced the adsorption of chromate because of the high coagulation power of these ions. The Langmuir isotherm model fitted the equilibrium data well at low Cr(VI) concentrations. The saturation amounts for Cr(VI) adsorbed by kaolin were 0.14, 0.16 and 0.20 mmol Cr/g at 283 K, 293 K and 303 K, respectively. The adsorption process was endothermic.