Development of Coal Magnetic Activated Carbon for Cd(II) Removal: Adsorption Isotherm and Kinetic Modelling

The metal coating process produces wastes containing heavy metals such as cadmium that are harmful to health. One method to remove cadmium is adsorption. This research developed an adsorber, specifically magnetic activated carbon derived from coal (CMAC). Activated carbon is modified with a Fe₃O₄ composite to make it magnetic and reusable. The objective of this investigation is to optimise the key parameters of activator concentration and thermal activation conditions for the fabrication of high-quality activated carbon. The investigation will evaluate the characteristics of the resulting carbon and its cadmium removal efficiency. The experimental adsorption data were fitted to both the Freundlich and Langmuir isotherm models and evaluated using kinetic equations. Chemical activators were used in a mixture of phosphoric and hydrochloric acid (1: 1) at concentrations of 0.5 M - 1.25 M. Physical activation was carried out at (873 - 1173) K. The optimal activation temperatures were identified as 1123 K and 1173 K. The CMAC removal percentage for Cd was 98.10 %. The Freundlich isothermal adsorption equation shows n = 0.4530 and K_F = 3.9823 mg/g with R² = 0.9691. The adsorption data were well-fitted by the Langmuir model, which yielded a maximum monolayer adsorption capacity qₘ of 238.10 mg/g and an affinity constant K_L of 0.0787 L/mg, supported by a high coefficient of determination (R² = 0.9082). Furthermore, the adsorption kinetics model yielded a pseudo-second-order equation. The regeneration test over five cycles showed decreases in Cd removal efficiency of 97.04 %, 81.89 %, 42.75 %, 13.83 %, and 9.71 %, respectively, indicating limited stability of the adsorbent after repeated use.