Sustainable Heavy-Metal Remediation Using Modified Fly Ash: An RSM-Optimized and Kinetically Validated Approach

Abstract The research investigated the sustainable utilization of fly ash, which was chemically modified by the hydrothermal carbonization method and named Chemically Modified Fly Ash (CMFA). This modified fly ash was subjected to treating wastewater with high concentrations of copper and zinc impurities. The study employed batch experiments to explore optimal conditions such as initial metal concentrations (5-25 mg/L) and contact times. It was found that pH 5.5 was most effective for removing copper (Cu) and zinc (Zn). Analytical techniques like Energy Dispersive X-Ray Analysis (EDX) and Field Emission Scanning Electron Microscopy (FESEM) were utilized to analyze the composition and structure of the adsorbent. Furthermore, the surface response approach was used to optimize the impacts of the parameters (contact time, metal concentration, adsorbent dosage, and pH) established for the Cu and Zn adsorption process, resulting in conditions that achieved 82.49% removal efficiency for Cu and 79.49% for Zn. Adsorption isotherms (Freundlich and Langmuir models) indicated favorable adsorption characteristics, with Freundlich fitting well both for Cu (R2 = 0.9985) and Zn (R2 = 0.9962). FESEM images revealed the porous nature of fly ash particles, underscoring their potential for efficiently adsorbing ionic pollutants from industrial effluents. These findings contribute in developing eco-friendly CMFA as a potential adsorbent due to its surface morphology and strong adsorption capabilities in heavy metal removal from wastewater.