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 and Fe-C-CO), fabricated by co-pyrolysis of red mud and orange peel in N and CO, for As(V) and Ni(II). By the syngas production comparison test, it was confirmed that CO was more advantageous than N 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 for Fe-C-N and 5.6 and 15.1 mg g for Fe-C-CO, respectively. The adsorption ability of Fe-C-CO for both As(V) and Ni(II) was further enhanced in binary adsorption mode (As(V): 13.4 mg g, Ni(II):17.6 mg g) through additional removal of those ions by Ni(II)-As(V) complexation. The overall results demonstrated CO-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.