Mechanistic breakthroughs in affordable adsorbents for heavy metal remediation: An in-depth exploration of next-generation sustainable water purification technologies
Muhammad Saad Khan, Muhammad Shafi, Junaid Raza, Inas A. Ahmed, Amir Zada, Katabathini Narasimharao, Xiaohui Sun
Abstract
The problem of water contamination with heavy metals is a global one with its continuous challenges, and new cost-effective and sustainable remediation procedures are required. The paper is a critical review of the recent advancement in the mechanism of adsorption of heavy metals with low-cost absorbents, with the emphasis on water purification technologies that are imminent towards commercial usage in the future. We explore the dominant adsorbing mechanisms, such as physical/chemical adsorption, ion exchange/complexation, and electrostatic and surface-precipitation. Particular emphasis is placed on the effect of surface treatments through various functional groups, acid and base treatment of adsorbent materials, temperature, and pH of the adsorption process. Furthermore, we have also investigated the quantitative modeling of the adsorption process in order to correlate the adsorption mechanism with sorption capacity. The efficiency of carbon-based materials, clay minerals, and magnetic adsorbents is examined, along with biological materials such as microorganisms and plant biomass. The adsorption potential of plant-derived materials (e.g., seeds, bark, peel, root, and leaf powder) for Pb, Hg, Cr, Cd, Zn, Cu, Mn, and As removal is discussed. Furthermore, the suitability of agricultural and municipal waste as adsorbents is assessed. Areas to be developed in the future involve predictive models, long-term stability, and real-world validation as a means of addressing the technological gap between lab-scale innovation and industrial application.