Simultaneous sorption of heavy metals on Algerian Bentonite: mechanism study

Abstract

Industrialization has induced tremendous environmental problems, particularly surface and underground water pollution by harmful heavy metals. In this work, we attempt to eliminate simultaneously iron and cadmium from aqueous solutions by adsorption on Algerian Bentonite. This abundant material was used without any modification. The sorption mechanism was investigated, and effects of pH, initial adsorbate and adsorbent concentrations were studied. The kinetics study revealed that equilibrium was reached after 120 min for both metals, and maximal adsorbed quantities of cadmium (76 mg/g) and iron (55 mg/g ) were obtained at pH = 10 and 8 respectively. Different kinetic models were tested, such as pseudo first-order, pseudo second-order, film and intraparticle diffusion models. The pseudo second-order model fits well the experimental data. Biot number values (2–39) show that the simultaneous sorption process is controlled by film diffusion due to electrostatic interactions between negatively charged surface and cations, then by the internal diffusion and formation of bonds between cations and adsorbent constituents. Also, compared to iron, the high and rapid sorption of cadmium reflects the selective nature of the sorption process. These results show that raw bentonite could be used without further treatment as an efficient sorbent for heavy metal mixtures. HIGHLIGHTS Algerian Bentonite used as raw and low cost adsorbent.; The maximal adsorbed quantities of cadmium and iron are respectively 76 mg/g and 55 mg/g at high pH.; Rate limiting steps are film diffusion and internal diffusion.; Rapid sorption of cadmium reflects the selective nature of the sorption process.; Cd/Fe sorption on bentonite could be due to electrostatic interactions, ion exchange, and formation of bonds.;

Keywords

• bentonite
• heavy metals
• kinetic model
• simultaneous adsorption