Improving Pb(II) Removal via Ascorbic Acid-Enhanced Red Mud Adsorption: Kinetics and Isotherm Analysis

Abstract

This study explored the efficacy of red mud, an aluminum production by-product, as an adsorbent for Pb(II) ion removal from contaminated water and assessed the adsorption isothermal model and kinetics. Red mud, characterized by its richness in oxide minerals with reactive surfaces, has potential for heavy metal adsorption, but its capacity for larger ions like Pb(II) is limited. This research aimed to enhance red mud’s adsorption properties through modification with ascorbic acid. The modification process involved heating a mixture of red mud and ascorbic acid to its boiling point, followed by the formation of adsorbent beads using red mud and Na-alginate mixture dropped into a 2 % CaCl2 solution at −2 °C. The beads were tested over varying durations ranging from 30 to 210 min. The results indicated that ascorbic acid modification led to the transformation of minerals in red mud, improving its pore diameter, pore volume, and specific surface area of the adsorbent. The modified and unmodified red mud adhered to both Langmuir and Freundlich isotherms, with R² values converging to one, and displayed pseudo-second-order kinetics. Notably, the introduction of ascorbic acid augments the adsorption efficacy of red mud for Pb(II) ions from 84.8 % to a compelling 99.3 %. This underscores the augmented capability of ascorbic acid-modified red mud, highlighting its prospective applicability as a potent adsorbent in the remediation of heavy metal-contaminated water. HIGHLIGHTS Innovative Use of Red Mud: Explored the potential of red mud, a by-product of aluminum production, as an adsorbent for removing Pb(II) ions from contaminated water Ascorbic Acid Modification: Developed a novel modification process using ascorbic acid, including heating the red mud and ascorbic acid, enhancing the adsorption properties of red mud as pore diameter, pore volume, and specific surface area of the adsorbent Adsorption Isotherms and Kinetics: Conducted a comprehensive assessment of adsorption isothermal models and kinetics, with modified and unmodified red mud adhering to Langmuir and Freundlich isotherms and displaying pseudo-second-order kinetics Enhanced Adsorption Efficacy: the adsorption effectiveness is enhanced from 84.8 to 99.3 %, emphasizing its potential applicability for Pb(II) GRAPHICAL ABSTRACT