Enhancement of Cu (II), Zn (II), Ni (II) and Humic Acid Adsorption in Modified Bentonite

Abstract

Environmental pollutants are recognized as a main problem around the world. Their toxicity can cause serious problems to living beings. Therefore, the removal of toxic inorganic and organic materials has been the great challenges of several researchers worldwide over the last decade. This study sought to enhance the metal and organic substance adsorption capacity of bentonite by improving its surfaces. Surface modification by the cationic surfactant (Benzyl hexadecyl dimethyl ammonium chloride, BCDMACI) was successful in this respect. Natural and modified bentonite were characterized by FTIR spectroscopy, XRF, BET, and swelling test. A major characteristic of BCDMACI is forming micelles that can intercalate into interlayers of clay and prevent swelling. The adsorption of heavy metals [Cu(II), Zn (II) and Ni (II)] and humic acid from aqueous solutions was studied in batch experiments, varying several effects; pH solution, contact time, concentrations of substances, and ionic strength. Concentration of the metals and humic acid in solution was detected by Atomic Absorption Spectroscopy (AAS) and UV-Visible, respectively. Kinetic results showed that the pseudo-second-order rate equation provided the best fit to observed adsorption kinetics (R2 almost equaled to 1), indicated as chemical adsorption. The adsorption data were fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, of which the Langmuir isotherm provided the best fit with experimental data, R2 and APE ranged 0.960- 0.998 and 2.35-9.43%, respectively for all cases. Moreover, all the three-parameter models fits supported the two-parameter Langmuir model, regarding these fundamental assumptions underlying it. The modified bentonite had significantly improved adsorption capacities (450.76, 35.21 and 25.06; and 86.21 mg/g for heavy metals [Cu (II), Zn (II), Ni (II)] and humic acid, respectively); about 1.7-2.5 fold improvements over natural bentonite. Competitive adsorption result indicated that each metal competed together (antagonism), adsorption of all metals decreases totally which adsorption equilibrium reduction (AY) ranged 35.41-47.41 % for all cases.