Study of heavy metals adsorption using a silicate-based material: Experiments and theoretical insights

Heavy metal toxicity in water is a serious problem with harmful effects on human health and the ecosystem. This research studied a silicate-based material as an adsorbent for removing four heavy metals from aqueous solutions. The target metal pollutants selected include manganese (Mn²⁺), copper (Cu²⁺), cobalt (Co²⁺), and zinc (Zn²⁺). First, theoretical tools including potential energy surface analysis, Natural Population Analysis, AIM, Wiberg Bond Index, QTAIM, and topological methods offer profound insights into the nature of interactions present in the Mg₂O₈Si₃M (M = Mn²⁺, Cu²⁺, Co²⁺, Zn²⁺) clusters. Second, the synthesis and characterization of eco-friendly hydrated amorphous magnesium silicate (MgOSiO₂nH₂O) was developed. Last, a simple kinetic adsorption test was applied to assess the material selectivity towards heavy metals and support theoretical results. The kinetic adsorption study was analyzed through the pseudo-first and second-order kinetics, Elovich, and the intraparticle diffusion models. The theoretical analysis of the adsorption energies indicates that the adsorption of four metal ions on the Mg₂O₈Si₃ surface is energetically favorable in all cases. The material displayed the following adsorption sequence: Cu²⁺ (59 mg g^-1) > Zn²⁺(25 mg g^-1) ≈ Co²⁺ (23 mg g^-1) > Mn²⁺ (15 mg g^-1). This knowledge can then be used to design and optimize low-cost silicate-based materials for effective heavy metal removal, contributing to efforts to address environmental pollution and protect public health.