Single and binary pollutant adsorption of strontium and barium on waste-derived activated carbons: Modelling, regeneration and mechanistic insights

The global issue of waste and wastewater management presents significant environmental and health challenges, particularly in regions like Qatar, where rapid industrial growth exacerbates these problems. This study tackles these challenges by evaluating the potential of waste-derived activated carbons, produced from Gas-to-liquids (GTL) derived biosolids, cardboard, and mixed waste, to remove toxic metals such as strontium and barium from water. The activated carbons demonstrated exceptional adsorption capacities, with mixed samples achieving 91 mg/g for strontium and 99 mg/g for barium in single adsorption systems. In binary systems, the adsorption capacities were slightly lower, reaching 80.5 mg/g for strontium and 90.0 mg/g for barium, reflecting the competitive adsorption dynamics between the two metals. Isotherm modeling revealed the Toth model as the best fit for single pollutant adsorption, while the Langmuir model captured the dynamics of binary systems. Kinetic studies identified pollutant-specific behaviors, with pseudo-second-order (PSO) kinetics describing strontium adsorption and chemisorption modeling barium adsorption. For binary systems, the Avrami model provided the best fit, highlighting complex multi-site adsorption mechanisms. Thermodynamic analysis confirmed the spontaneity and exothermic nature of the adsorption process. Regeneration studies showed the reusability of activated carbons, with nitric acid achieving the highest desorption efficiency and minimal performance loss over three cycles. Mechanistic analysis indicated adsorption was driven by electrostatic attraction, π-electron interactions, and ion exchange, with a preference for larger pollutants like barium. This study highlights the potential of mixed waste-derived activated carbons as a sustainable and efficient solution for wastewater treatment, addressing critical environmental challenges while advancing circular economy initiatives. • Waste-derived activated carbons showed high adsorption of Sr (91 mg/g) and Ba (99 mg/g). • In binary systems, adsorption reached 80.5 mg/g for Sr and 90.0 mg/g for Ba. • Regeneration with 0.1 M HNO₃ showed high desorption and stable performance over cycles. • Toth and extended Langmuir models best describe the adsorption behaviors. • Adsorption mechanism involves electrostatic attraction, ion exchange, and π-electron interactions.