Mechanisms of heavy metal immobilization and transformation during co-pyrolysis of pig manure with typical organic solid wastes.

Authors

Fengxiao Zhao, Danni Li, Hongyuan Chen, Xianhai Zeng, Rui Shan, Lu Lin, Haoran Yuan, Yong Chen

Published in

Journal of hazardous materials. Volume 514. Pages 142739. Jun 18, 2026. Epub Jun 18, 2026.

Abstract

The accumulation of heavy metals restricts the safe agricultural utilization of pig manure. Co-pyrolysis with organic additives offers a promising strategy to overcome the physicochemical defects of manure-derived biochar and enhance metal sequestration. This study investigated the co-pyrolysis of pig manure with distinct solid wastes including food residue, tea stems, and spent coffee grounds at 450-750 °C to elucidate heavy metal transformation mechanisms. Results demonstrated highly efficient immobilization for Cu, Cr, and Ni; specifically, in the tea stem co-pyrolysis biochar at 750 °C, the residual fractions of Cr and Ni reached 87.15% and 80.55%, respectively. Supported by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, this stabilization is driven by a dual pathway: direct precipitation into stable mineral phases such as Cu₅FeS₄ and MgCrO₄, and surface complexation via persistent Si-O and C-O functional groups within the aromatized carbon network. Principal Component Analysis (PCA) confirmed that carbon skeleton aromatization and matrix alkalinity dictate the conversion of bioavailable fractions into inert residual forms. Conversely, Zn stabilization exhibited high temperature sensitivity, requiring over 650 °C for extensive mineralization. Furthermore, feedstock composition critically regulated metal fate: chloride-abundant food residue hindered Zn and Mn solidification by forming soluble chloro-complexes, whereas lignin-rich matrices significantly promoted biochar aromatization and porosity, reinforcing metal sequestration via enhanced cation-π interactions. Finally, comprehensive environmental risk evaluations revealed an asymmetrical characteristic of high total accumulation versus low ecotoxicity. Lignin-assisted high-temperature treatments effectively suppressed the ecological risk indices of the target metals, validating co-pyrolysis as a robust thermochemical strategy for the safe remediation and resource recovery of hazardous livestock waste.

PMID:
42320099
Bibliographic data and abstract were imported from PubMed on 20 Jun 2026.

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