Use of activated bentonite-alginate composite beads for efficient removal of toxic Cu2+ and Pb2+ ions from aquatic environment

Abstract

The toxic heavy metals contamination in water bodies is one of the major concerns in many countries. Copper and lead are the two common toxic metals present in aquatic environments due to their extensive usage in various industries for diverse applications. The present study deals with the removal of these two toxic heavy metal ions using activated bentonite-alginate (ABn-AG) composite beads which are easily separated and recovered after adsorption reaction. Composite beads were prepared by adapting the ionic gelation method and the materials; i.e., raw bentonite (BnR), activated bentonite (ABn) and ABn-AG were characterized by XRD, BET surface area, TGA-DTA, FT-IR, SEM analyses. The nitrogen adsorption-desorption isotherm obtained for the materials were the type IV isotherm with characteristics H₃ hysteresis loops indicating the presence of mesopores with slit-shaped pores. Batch experiments showed that reasonably high percent removal was achieved even at highly acidic conditions, i.e., 58% of Cu²⁺and 77% of Pb²⁺were removed at pH 2.0. The removal was fast during the initial contact time and the adsorption data obtained at various contact time were fit well to the pseudo-second order kinetic model. The maximum sorption capacity for Cu²⁺ was found to be 17.30 mg/g whereas Pb²⁺ was found to be 107.52 mg/g. The presence of MgCl₂, NaCl and KCl did not cause significant influence on the removal of Cu²⁺ and Pb²⁺ using ABn-AG. Binary adsorption study suggested that Cu²⁺ and Pb²⁺ were removed through different binding sites present in ABn-AG. Reusability test showed that removal of Cu²⁺ and Pb²⁺ decreased by 10% only after the same material was reused for 5 times indicating that ABn-AG is a highly robust material and can be reuse for several times without losing its efficiency. Thus, this study suggested that ABn-AG composite beads can be employed as an efficient adsorbent for the removal of Cu²⁺ and Pb²⁺ from aqueous waste.

Keywords: Acid activation; Alginate beads; Bentonite clay; Biopolymer; Removal; Toxic ions.