Valorisation of heavy metals enriched tobacco biomass through slow pyrolysis and steam activation

BACKGROUND The disposal of metal-enriched plant biomass is an important and still unresolved issue associated with phytoextraction. Therefore, the aim of this study was to valorise these contaminated biomasses into valuable products, i.e. bio-chars and activated carbons (ACs), through slow pyrolysis followed by steam activation. The effects of pyrolysis/steam activation on metal availability in the chars/ACs were also evaluated. In addition, Cr(VI) adsorption by these ACs in aqueous solutions was studied. RESULTS Relevant chars/ACs yields were obtained due to applied thermochemical treatments. Leachability of heavy metals from those products was limited indicating that they may be safely applied as adsorption media. Prepared ACs demonstrated good Cr(VI) adsorption capacities occurring through a ‘coupled adsorption–reduction’ mechanism. It was found that Cr(VI) removal strongly depended on pH of Cr(VI) solutions and was higher for ACs activated at 800 °C. Among applied isotherm adsorption models, i.e. Langmuir and Freundlich, a better fit was obtained with the Langmuir model corresponding to monolayer coverage sorption of Cr(VI) on ACs surface. CONCLUSIONS Heavy metals enriched biomass can be successfully valorised through slow pyrolysis/steam activation into value added products, i.e. ACs that can be used as efficient and safe adsorbents for Cr(VI) removal