Adsorption of Metal Ions from Single and Binary Aqueous Systems on Bio-Nanocomposite, Alginate-Clay

Abstract

The aim of this work is to characterize and evaluate the retention of Cu²⁺ and Ni²⁺ from single and binary systems by alginate-Moroccan clay bio-composite with the utilization of calcium chloride as a cross-linking agent, using the ionotropic gelation method. The bio-nanocomposite was characterized by using a variety of techniques (SEM, EDX, XRD, and pH_PZC). The efficiency of the adsorbent was investigated under different experimental conditions by varying parameters such as pH, initial concentration, and contact time. To demonstrate the adsorption kinetics, various kinetic models were tried and assessed, including pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. The research results show that the adsorption process of Cu²⁺ and Ni²⁺ metal ions follows a pseudo-second-order kinetic model, and the corresponding rate constants were identified. To evaluate the parameters related to the adsorption process in both single and binary systems, different mathematical models of isotherms, such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich, were investigated. The correlation coefficients obtained showed that the most suitable isotherm for describing this adsorption process is the Langmuir model. The process is considered to be physical and endothermic, as suggested by the positive values of Δ<i>H°</i> and Δ<i>S°</i>, indicating increased randomness at the solid/liquid interface during Cu²⁺ and Ni²⁺ adsorption. Furthermore, the spontaneity of the process is confirmed by the negative values of ∆<i>G</i>°. The bio-nanocomposite beads demonstrated a maximum adsorption capacity of 370.37 mg/g for Ni²⁺ and 454.54 mg/g for Cu²⁺ in the single system. In the binary system, the maximum adsorption capacities were observed to be 357.14 mg/g for Ni²⁺ and 370.37 mg/g for Cu²⁺. There is significant evidence for the use of alginate-Moroccan clay bio-nanocomposite as a cost-effective alternative adsorbent for the efficient removal of metal ions in single and binary systems.