Flash pyrolysis of heavy metal contaminated biomass from phytoremediation: Influence of temperature, entrained flow and wood/leaves blended pyrolysis on the behaviour of heavy metals

Phytoremediation crop disposal is a problem inhibiting the widespread use of the remediation technique. Flash pyrolysis as processing method for metal contaminated biomass is investigated: the rather low pyrolysis temperature prevents metal compounds from volatilisation while valuable pyrolysis oil is produced. Both plant stems and leaves are pyrolysed in a lab-scale semi-continuous reactor. Parameters under investigation are pyrolysis temperature (623, 723 and 823 K), the use of hot-gas filtration to prevent entrained flow and the blended pyrolysis of willow stems and leaves in their natural weight ratio. Biomass and pyrolysis products are analysed with the focus on the metal distribution; target elements include Zn, Cd, Pb and Cu. Knowledge of the metal distribution is of prime importance concerning the applications of the pyrolysis product streams. ICP-AES measurements confirm very low levels of metals in pyrolysis oil produced at 623 K (Cu and Zn <5 ppm; Cd and Pb <1 ppm) with almost all of the metals accumulated in the char/ash residue. Pyrolysis mass and energy balances are determined providing information in view of future valorisation purposes.Flash pyrolysis can likely offer a valuable processing method for heavy metal contaminated biomass, thus limiting the waste disposal problem associated with phytoremediation.