Steam assisted slow pyrolysis of contaminated biomasses: Effect of plant parts and process temperature on heavy metals fate

The post-treatment of biomass from phytoremediation is not yet a well-established practice due to the risk induced by the presence of Potentially Toxic Elements (PTEs). Pyrolysis is a thermochemical treatment that reduces the volume and weight of contaminated matter producing a combustible vapor phase and a solid residue (char). A key factor enhancing the economic and the environmental sustainability of biomass valorization through pyrolysis is the production of a market value char. A proper choice of the pyrolysis operating conditions should take into account the effect of final temperature on PTEs release, on the char physicochemical properties as well as on the mobility of retained PTEs. In particular, in this work the influence of both the temperature and the plant parts is discussed (branches and leaves of Populus Nigra L and rhizomes and culms of Arundo donax L) on the release of Cd, Pb, Cu, and Zn in the temperature range 653-873 K under steam assisted slow pyrolysis conditions. The mobility of the heavy metals retained in the chars was also studied as well as the product yields, the gas composition and char porosity.