Adsorption of As(V) and Ni(II) by Fe-Biochar composite fabricated by co-pyrolysis of orange peel and red mud

This study aimed to compare the adsorption performance of Fe-biochar composites (Fe-C-N-2 and Fe-C-CO2), fabricated by co-pyrolysis of red mud and orange peel in N-2 and CO2, for As(V) and Ni(II). By the syngas production comparison test, it was confirmed that CO2 was more advantageous than N-2 as a pyrolytic medium gas to produce more CO. The resulting Fe-biochar composite showed the aggregate morphology consisting of different Fe phases (magnetite or metal Fe) from the inherent hematite phase in red mud and carbonized carbon matrix, and there was no distinct difference between the structural shapes of two Fe-biochar composites. Adsorption experiments showed that the adsorption capacities for As(V) and Ni(II) in single mode were almost similar with 7.5 and 16.2 mg g(-1) for Fe-C-N-2 and 5.6 and 15.1 mg g(-1) for Fe-C-CO2, respectively. The adsorption ability of Fe-C-CO2 for both As(V) and Ni(II) was further enhanced in binary adsorption mode (As(V): 13.4 mg g(-1), Ni(II):17.6 mg g(-1)) through additional removal of those ions by Ni(II)-As(V) complexation. The overall results demonstrated CO2-assisted pyrolysis can provide a viable platform to convert waste materials into fuel gases and environmental media for co-adsorption of cationic and anionic heavy metals.