Biosorption of hexavalent chromium by a low-cost sorbent (potato peels): kinetics, equilibrium, and thermodynamics

The contamination of water by heavy metals, particularly hexavalent chromium (Cr(VI)), poses a serious threat to aquatic life and human health. Developing low-cost and eco-friendly adsorbents from agricultural waste offers a sustainable solution to this problem. In this context, potato peels, an abundant agro-waste, can serve as an efficient biosorbent for Cr(VI) removal. This study investigates the potential of potato peels (RPP) as a cost-effective and sustainable material for the removal of Cr(VI) from aqueous systems. The RPP was characterized using several techniques including FTIR, pH_pzc, TGA/DTG, and XRD. The effect of various adsorption parameters was examined, such as initial pH (2-5), contact time (0-360 min), initial concentration (10-200 mg L^-1), and solution temperature (30-50 °C). A maximum chromium (VI) adsorption capacity of 15.09 mg g^-1 was achieved under optimal conditions of pH 2, initial concentration 100 mg L^-1, adsorbent dosage of 4 g L^-1, and contact time of 360 min. Isotherm analysis showed that the Langmuir model fit the data (R² = 0.98), indicating monolayer adsorption behavior. Kinetic data followed a pseudo-second-order model indicating a chemisorption process. Furthermore, thermodynamic analysis revealed negative ΔG° < 0, while ΔH° = 44.13 kJ mol^-1 > 40 kJ mol^-1 and ΔS° = 145.80 kJ mol^-1 K^-1, suggesting that the process is spontaneous and endothermic. Desorption and reusability studies confirmed successful adsorbent reuse for three cycles. These findings indicate that potato peel waste is an environmentally friendly and effective biosorbent for the removal of chromium (VI) from aqueous media.