# Influence of Pb Bonding and Speciation on the Pyrolysis Products of Contaminated Biomass

## TL;DR

This paper studies how lead contamination affects the pyrolysis of poplar biomass, showing that lead's bonding and chemical form influence product yields and properties.

## Contribution

The study introduces a novel approach to investigate how Pb bonding and speciation specifically influence pyrolysis outcomes in contaminated biomass.

## Key findings

- Lead presence modifies pyrolysis pathways of lignocellulosic biomass.
- Pb bonding affects liquid product yields, while speciation alters product properties.
- Inherent inorganics like AAEMs moderate the effects of Pb during pyrolysis.

## Abstract

Phytoremediation
is receiving increasing attention as
an environmentally
friendly remediation technique for contaminated soils, as it can target
different contaminants, such as heavy metals. Phytoremediation processes
produce large volumes of contaminated biomass that must be disposed
of and possibly valorized. Among the possible treatments for heavy
metal-contaminated biomass, a promising approach is to pyrolyze these
biomasses. However, it must be considered that heavy metals can interact
with the biomass pyrolysis decomposition pathways, resulting in variations
in the yields and properties of pyrolysis products. In this work,
the effects of lead (Pb) contamination on poplar biomass during slow
pyrolysis were investigated. In particular, the focus of this paper
is on the effect of the type of bonding of Pb with the biomass tissue,
which is specific to the contamination type (authigenic or detrital),
and on the effect of the chemical speciation of Pb. To study these
aspects, poplar biomass was opportunely doped with lead acetate (Pb­(CH3COO)2) following different procedures aimed at
simulating different bonds between Pb and biomass tissues. Moreover,
to study the effect of Pb chemical speciation, poplar biomass was
also doped with lead nitrate (Pb­(NO3)2). All
the doped feedstocks, together with the parent biomass, were pyrolyzed
under slow pyrolysis conditions at two pyrolysis temperatures (465
and 600 °C), and the obtained products, namely, biochar, bio-oil,
and pyrolysis gases, were analyzed thoroughly. The obtained results
show that the presence of Pb can indeed modify the pyrolysis pathways
of lignocellulosic biomasses. The different bonding of Pb with biomass
causes modifications in the yield of the liquid products. On the other
hand, changing the Pb chemical speciation cause variations in the
properties of all pyrolysis products. However, the extent of many
Pb effects seems to be affected by the presence of inherent inorganics,
such as alkali and alkali-earth metals (AAEMs).