Adsorption technology for potentially toxic metals on chemically activated carbons derived from different precursors: A review

Activated carbon is a highly effective approach for removing potentially toxic elements (PTEs) from contaminated waters. In this context, this review focused on chemically activated carbons (CACs), employing distinct precursor materials and production processes to elucidate relationships among the precursor, the activated-carbon manufacturing methodology, and the application conditions that affect the efficiency of removing different PTEs. The data sources were Scopus and ScienceDirect, covering 2020–2025 and totaling 25 articles. Proper selection of the precursor material, activating agent, and activation/experimental conditions proved essential for obtaining high-quality CACs. Various isotherm models were used to elucidate adsorption mechanisms, with the Langmuir model standing out by demonstrating uniform monolayer adsorption. In the kinetic analyses, the pseudo-second-order model predominated, indicating chemisorption. The physicochemical properties of CACs influenced adsorption kinetics, typically yielding a rapid initial uptake. Optimization of parameters such as pH, initial concentration, and adsorbent mass was critical for PTE adsorption. Thermodynamic analysis indicated endothermic processes (positive ΔH° and ΔS°), while frequently negative ΔG° denoted the spontaneity of adsorption. Thus, among the materials studied, residues from lentil processing and palm leaves emerged as promising precursors for surface modification strategies aimed at enhancing maximum adsorption capacity.