Development of a sustainable magnetized bio-nano adsorbent from tomato residues for removal of Ni (II) ion from dairy effluents: Kinetics, thermodynamics, and practical applicability

This study investigates the feasibility of utilizing tomato processing by-products as a carbon-rich magnetic nano adsorbent for the removal of Ni(II), a major heavy metal pollutant in dairy industry effluents. The nano adsorbent was successfully synthesized and magnetized, enabling rapid and efficient separation from aqueous media. Its physicochemical properties were characterized using BET, SEM, and EDS analyses. The nanoscale material exhibited a high specific surface area and pronounced porosity, contributing to its strong adsorption performance. Key operational parameters—including pH (2.0–8.0), temperature (40–80 °C), contact time (10–115 min), adsorbent dosage (0.2–2.0 g/L), and initial metal concentration (20–100 mg/L)—were systematically optimized. Results revealed that adsorption capacity strongly depended on solution pH, with the highest Ni(II) removal observed at pH 5.0. Optimal conditions (60 °C, 25 min, 1.8 g/L adsorbent, and 60 mg/L initial concentration) yielded a maximum adsorption capacity of 83 mg/g. Kinetic analysis confirmed that the adsorption followed a pseudo-second-order model, while thermodynamic data supported a chemisorption-driven process. Additionally, equilibrium behavior was best described by the Freundlich isotherm. Overall, the magnetized tomato-derived nano adsorbent demonstrates strong potential as a sustainable and efficient material for removing Ni (II) ions from dairy wastewater. • Magnetized tomato by-product derived nanoadsorbent efficiently removes Ni(II) from dairy wastewater. • High porosity and large surface area confirmed via SEM, BET, and EDS characterization. • Optimal adsorption achieved at pH 5, 60 °C, 25 min, and 1.8 g/L adsorbent dose. • Adsorption follows pseudo-second-order kinetics and Freundlich isotherm, indicating chemical mechanism.