Removal of copper from aqueous solutions by bentonites and the factors affecting it

In order to study the ability of bentonites to remove heavy metal ions from waste water and its factors affecting it, batch sorption experiments of Cu2+ were conducted on Ca-bentonite and Na-bentonite under various conditions. The results show that the adsorption process of bentonite accorded with the Freundlich isotherm model and that the sorption results of Na-bentonite are better than those of Ca-bentonite. Adsorption behavior of both bentonites was strongly depending on pH, initial concentration and additional amounts of bentonites. There are three kinds of adsorption mechanism at different ranges of pH values: the competition adsorption between Cu2+ and H+ (pH<3), ion-exchange adsorption (pH=3∼7) and precipitation adsorption of copper hydroxyl compounds (pH>8.3). The removal rate of bentonite decreases with an increase in the initial metal ion concentration. The maximum adsorption capacity of Na-bentonite was 26 mg/g and that of Ca-bentonite 12 mg/g. The removal rate of Cu2+ was practically 100% at the initial concentration of 40 mg/L, when 4 g/L of Na-bentonite and 14 g/L of Ca-bentonite were added to the solution.