Highly Efficient Adsorption of Co2+ from Wastewater on Alginate Immobilized Kaolin-Plantain Pseudo Stem-Snail shell Hydrochar: Isotherm modeling, Kinetics, Thermodynamic, and Mechanistic insight

A major challenge in environmental remediation is the development ofcost-effective processes that minimize the cost ofenergy andmaterial while enabling the reuse of adsorbents for pollutant removal. Hydrochar (HC) is a promising substitute for biochar in environmental remediation, offering cost-effective, energy-efficient methods and enhanced regeneration through alginate immobilization. The adsorptive bahaviour ofcobalt ions (Co2+) from wastewater on HC and hydrochar encapsulated in alginate (AHC) under different conditions and the physiochemical properties ofthe adsorbents were examined in this study. AHC had the highest Co2+ adsorption efficiency (100%), followedby AL (94.56%) and HC (91.31%). The adsorption ofCo2+ on HC andAHC was best fittedby the pseudo second order model, whereas the rate-determining steps were the Boyddiffusion andintraparticle diffusion models. The pseudo secondorder model providedthe best fit for the adsorption ofCo2+ on HC and AHC, while the intraparticle diffusion and the Boyd diffusion models were the rate determining steps. At all temperatures considered (25, 30 and 36 oC), the Freundlich isotherm model providedthe best fit for the experimental data andthe maximum adsorption capacities at these temperatures rangedbetween 81.66 to 98.04 mg/g. AHC demonstrated superior adsorption performance due to improved active site accessibility and surface interactions. Given its high adsorption efficiency, reusability, and environmental compatibility, alginate-based hydrochar composites (AHC) are recommended as a viable material for practical heavy metal remediation in wastewater treatment.