Adsorption of nickel (II) ions onto activated carbon from tamarind seeds for synthetic wastewater treatment: Isotherm, kinetic, and thermodynamic studies

The removal of nickel from synthetic wastewater through adsorption using activated carbon derived from tamarind seeds was investigated. The study also compared two carbonization methods: traditional and hydrothermal. The results indicated that activated carbon synthesized via the hydrothermal method produced a higher surface area than that obtained through traditional carbonization. The synthesized activated carbon exhibited mesoporous and microporous structures with impressive specific surface areas of 1172 m²/g and micropore areas of 837 m²/g, at an 8.11 % yield. Structural analysis revealed a highly porous material retaining only C=C, C=O, C-O, and -OH groups. The activated carbon demonstrated high efficiency in Ni²⁺ ion adsorption, achieving approximately 100 % removal from a 20 mg/L solution using 50 mg of adsorbent at 30 °C for 120 min. The results were fitted to the Langmuir isotherm with an R² of 0.994, yielding a maximum Ni²⁺ adsorption capacity (q_max) of 39.25 mg/g. The kinetics model was fitted to a pseudo-second-order (PSO) kinetics model with a rate constant of 0.0807 g/mg∙min. A thermodynamic analysis suggested that the adsorption of Ni²⁺ ions on activated carbon derived from tamarind seeds is spontaneous and endothermic. This synthesis method provides a sustainable approach to enhancing the value of tamarind seeds by converting them into high-performance activated carbon. This process produces a bio-based adsorbent with significant potential for removing nickel from wastewater.