A review on zeolites as cost-effective adsorbents for removal of heavy metals from aqueous environment

This study provides a review of the adsorption of heavy metals using zeolite. This became necessary as the search for cost-effective remediation measures for polluted water towards the circular economy is increasing. For contextual and perspective purposes, the detrimental effect of heavy metals on water resources as well as the concomitant health impacts associated with the consumption of such contaminated water was discussed. The fate of toxic metals like mercury, cadmium, lead, chromium, nickel, zinc, copper, and arsenic in the aquatic environment was discussed. The application of natural and modified zeolite as an adsorbent for containment of heavy metals in aqueous ecosystems was also discussed. Furthermore, a detailed analysis of adsorption isotherms and kinetics was undertaken, revealing that most zeolite-based adsorption studies reported in the literature favored the pseudo-second-order kinetic model for both metals and nonmetals. Kinetic models highlighted include the Lagregren’s pseudo-first-order model (PFO), pseudo-second-order model (PSO), intra-particle diffusion model, Elovich model, and Bangham’s pore diffusion model. Only very few cases favored other kinetic models such as the pseudo-first-order kinetic model or the intra-particle diffusion model. The review shows that zeolite has gained global recognition as an effective and cost-effective adsorbent that can be adapted/modified to suit the problem at hand.