Insights into Kinetics and Isotherms studies of Cadmium (II) adsorption behavior onto wood biochar from aqueous solution

Abstract Objectives: This study aims to investigate the Cd(II) adsorption from aqueous solutions via wood biochar (BC) as an adsorbent, using different parameters, adsorption isotherms, and kinetic models. Methods: Experimental tests were conducted to study the Cd(II) adsorption on a batch mode system. The study evaluated parameters such as pH, contact time, and Cd(II) concentration. To analyze the adsorption mechanism, various isotherms were utilized including Freundlich, Langmuir, Temkin, Redlich-Peterson, Sips, Flory-Huggins, Fowler-Guggenheim, and Harkin-Jura were used. Additionally, Pseudo-first-order and Pseudo-second-order were used to study the kinetics of adsorption. Findings: The Langmuir isotherm suggests that the maximum adsorption capacity ( q max ) is 28.57 mg/g. According to this model, the metal ions are adsorbed by forming a monolayer and do not interact or compete with each other. Based on the Temkin isotherm, it can be concluded that the adsorption of Cd(II) onto BC is mainly physical in nature, as the value of heat of adsorption is less than 1.0 kcal/mol. The Redlich-Peterson and Sips isotherms indicate that the adsorption process follows the Langmuir form and further supports the predominance of monolayer adsorption pattern. The negative value of Gibbs free energy (ΔG o ) suggests that the adsorption process is thermodynamically spontaneous and feasible. The Flory-Huggins and Fowler-Guggenheim isotherms indicate that the active zone of the adsorbent is occupied by adsorbate and also suggest the presence of repulsion between the adsorbate. The kinetics of the adsorption system followed a pseudo-second-order reaction rather than a pseudo-first-order reaction with an R 2 of 0.999 and 0.979, respectively. Novelty and applications: The results of various analyses indicate that the process of wood biochar adsorption is efficient and can be scaled up for the heavy metals removal from contaminated water.