Potential of BCDMACl modified bentonite in simultaneous adsorption of heavy metal Ni (II) and humic acid

Ni (II) and humic acid (HA) were used as representatives of a heavy metal and an organic substance in a study of adsorption potential onto a cationic surfactant (bencylhexadecyldimethyl ammonium chloride, BCDMACl) modified bentonite (MB) compared to natural bentonite (NB). Batch experiments were conducted to fit the adsorption kinetics with both pseudo-first and pseudo-second-order models, of which the pseudo-second order fit the experimental data better. Several factors were experimentally observed to affect adsorption, such as pH, contact time, initial concentration, and ionic strength. Acidic pH and low ionic strength proved to be desirable for the adsorption of Ni (II). In contrast, acidic pH and high ionic strength were good conditions for HA adsorption. The experimental equilibrium data were analyzed using both two-parameter isotherms (Langmuir, Freundlich, and Temkin models) and three-parameter isotherms (Redlich-Peterson, Sips, and Toth model). The Langmuir isotherm was deemed appropriate, as the three-parameter model fits also support its underlying assumptions, and the quality of fit was overall very good. MB had approximately 1.7-fold the adsorption capacity of NB, achieving up to 27.22-27.37 and 75.39-75.90 mg/g for Ni (II) and HA, respectively.