Sustainable trivalent chromium remediation from tanning spent liquor using high surface area activated carbon derived from water hyacinth as a circular economy approach

This study addresses the ecological threat of invasive water hyacinth (Eichhornia crassipes) by transforming it into high-surface-area activated carbon (ACWH) for the remediation of Cr (III) from actual tanning spent liquor. Characterization revealed a high specific surface area of 712.8 m2/g and a fixed carbon content of 62.75%, while FTIR and XRD confirmed a well-carbonized structure with active N–H and C–N functional groups and a pHpzc of 6.0. Under optimized conditions, pH 5.0, temperature 40 °C, adsorbent dose 12.5 g/L, and a contact time of 150 min, the ACWH achieved a maximum Cr (III) removal efficiency of 99.65%. Equilibrium data were best described by the Langmuir isotherm model (R2 > 0.96) with an experimental capacity of 74.86 mg/g, while kinetics followed the pseudo-second-order model (R2 = 0.98), indicating a chemisorption mechanism. Regeneration studies using 1 M NaOH demonstrated that the adsorbent maintained a removal efficiency of 87.34% after three cycles and remained functional at 64.67% after five cycles. These results provide a robust, circular economy solution for removing trivalent chromium from complex industrial matrices using a sustainable, low-cost biomass.