Removal of hexavalent chromium (Cr(VI)) from aqueous solution using acid-modified poultry litter-derived hydrochar: adsorption, regeneration and reuse

BACKGROUND: Chromium (Cr) is widely used in industrial processes and is considered a major source of pollution when released to the environment. Of particular concern, hexavalent chromium (Cr(VI)) is amongst the most toxic heavy metals affecting human health and living organisms when fugitive emissions contaminate aqueous environments. Consequently, its removal and recovery are priorities for environmental remediation in the context of the circular economy. In this study, modified hydrochar (MHC) was generated by hydrothermal carbonisation of acid-treated (H2SO4) poultry litter (PL) and investigated for its ability to adsorb Cr(VI) from aqueous solution in batch studies. Recovery of Cr(VI) and the regeneration potential of MHC were also evaluated. RESULTS: Results indicated that Cr(VI) adsorption was strongly pH dependent, demonstrating an inverse relationship between solution pH and Cr(VI) uptake. A maximum adsorption capacity of 26.2 mg g−1 was achieved in 90 min at pH 2. Under optimal conditions, adsorption kinetics followed a pseudo-second-order kinetic model and the adsorption isotherm fitted most closely with the Langmuir model. Thermodynamic studies indicated that the adsorption process of Cr(VI) onto the MHC was exothermic and spontaneous. Regeneration studies demonstrated that the MHC can be re-used up to four times without significant loss of capacity to adsorb Cr(VI). CONCLUSIONS: Modified PL hydrochar offers potential as a low-cost, environmentally friendly solution for Cr(VI) adsorption in wastewater treatment applications. The ability of Cr(VI) to desorb from MHC demonstrates strong potential for Cr(VI) recovery and regeneration of the adsorbent.