Cabbage waste derived activated carbon for removing hexavalent chromium from synthetic and tannery wastewater

Industrial wastewater discharge without proper treatment causes severe ecological and public health problems. Heavy metals like chromium are pollutants found in untreated or partially treated industrial wastewater. This study investigates the removal of hexavalent chromium ion (Cr (VI)) from synthetic and tannery wastewater using activated carbon derived from cabbage waste. The cabbage waste was activated with H₃PO₄ and carbonized at 450 °C. Characterization was performed using proximate analysis, XRD, and FTIR spectroscopy. Batch adsorption studies were conducted under various conditions, including initial chromium concentrations (10–100 mg/L), adsorbent dose (1–20 g/L), contact time (30–300 min), pH (2–11), shaker speed (50–250 rpm), and temperature (20–70 °C). The optimum conditions for maximum chromium removal (99.87%) from synthetic wastewater were pH 3, initial chromium concentration 10 mg/L, shaking speed 150 rpm, contact time 150 min, adsorbent dose 2 g/L, and temperature 25 °C. For tannery wastewater, 83.81% chromium removal was achieved under the same conditions. The Freundlich isotherm model best described the adsorption process, with an adsorption capacity of 4.9 mg/g. The adsorption followed pseudo second order kinetics. The thermodynamics study indicates that the adsorption of Cr (VI) is spontaneous, exothermic and driven by an increase in entropy. A negative value of Gibbs Free Energy change (ΔG°) indicates that the adsorption process is thermodynamically spontaneous and feasible.