Development of a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe-Mn-Zr ternary metal composite for heavy metal adsorption

Heavy metal contamination has become one of the greatest global environmental problems. In this study, a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe-Mn-Zr ternary-metal composite (MCHETC) was prepared through a combined co-precipitation and extrusion approach and used for the adsorption of heavy metals in aqueous solutions. The active sites were dispersed in the MCHETC, which can be separated by the magnetic force for the ease in operation. Above 80% of ultimate adsorption was completed at a contact time of 5 h. The copper uptake history was well described by the intraparticle surface diffusion model, suggesting a multi-step process for the adsorption. The optimum pH for adsorption was 4; the maximum adsorption capacity was 103.1 mg-Cu/g. The adsorption capability well remained after the 5 adsorption-desorption cycles and the copper could be recovered. Furthermore, the adsorbent performed well in the nature water spiked with copper ions. The mechanism studies illustrated that the adsorption was mainly controlled by the ion-exchange reaction. This study demonstrated that the MCHETC adsorption technology may be used for heavy metal removal and recovery with higher efficacy.