Sustainable Management of Industrial Waste for Chromium Remediation: Kinetic Insights into Cr(VI) Adsorption by Petroleum and Metallurgical Coke

Sustainable industrial waste management plays a critical role in protecting earth and environmental systems by reducing disposal-related impacts and enabling affordable technologies for pollution mitigation and resource recovery. Within this context, the reuse of industrial by-products as functional materials offers a promising pathway toward circular resource use and reduced environmental burdens. Certain carbon-rich residues have physicochemical properties ideal for functioning as adsorbents in water treatment systems, particularly for the removal of toxic heavy metals such as hexavalent chromium [Cr(VI)] from industrial effluents. This study investigates the adsorption kinetics of selected industrial waste materials (petroleum and metallurgical cokes), highlighting their efficiency in Cr(VI) retention and their potential role in waste valorization within a circular economy framework. The structural and morphological characterization of coke samples has been made by X-ray diffraction (XRD), and electron microscopy (SEM and TEM). Adsorption experiments were conducted at varying temperatures (25 °C and 50 °C) and pH values (2.5 and 5.0) to determine optimal removal conditions and the process was evaluated through kinetic, isotherm, and thermodynamic analyses. The negative ΔG° values indicate that the adsorption process is spontaneous, while the positive ΔH° suggests an endothermic nature. Four simplified kinetic models including a pseudo-first-order equation, pseudo-second-order equation, Elovich and intraparticle diffusion equation were selected to follow the adsorption process. The adsorption followed the pseudo-second-order model with high correlation coefficients (R²>0.99), indicating chemisorption as the dominant mechanism. Maximum removal efficiency reached 89.4% at 50 °C and pH 2.5 highlighting the suitability of coke-based materials for efficient chromium remediation. Beyond their technical performance, the valorization of coke residues provides an eco-efficient and low-cost remediation pathway, that simultaneously reduces industrial solid waste disposal and mitigates hazardous metal contamination in aquatic environments. By converting industrial solid wastes into functional adsorbents, the approach supports circular economy principles, enhances resource efficiency, and contributes to sustainable industrial water management within interconnected earth and environmetal systems. Graphical Abstract This graphical abstract illustrates the sustainable valorization of industrial by-products for water remediation. Petroleum coke and metallurgical coke, low-cost, carbon rich materials, generated from petroleum refining and metallurgical processes, with turbostratic microcrystalline structures confirmed by SEM and XRD analyses, are used as effective adsorbents for removing Cr(VI) from aqueous solutions. The adsorption experiments conducted under different operational conditions (pH 2.5-5 and temperatures 25–50 °C), and the kinetic modeling results demonstrate that Cr(VI) removal follows pseudo-second-order kinetics, and chemisorption, the dominant mechanism governing the adsorption process. The results confirm that coke-based adsorbents provide an eco-efficient and scalable approach for heavy-metal removal from industrial wastewater. Finally, the graphical abstract links the adsorption process to broader sustainability implications. By converting industrial solid wastes into functional adsorbents, the approach supports circular economy strategies, including waste recovery, resource reuse, and energy valorization. This integration of waste management and water treatment contributes to sustainable industrial development and environmentally responsible engineering solutions.