The evaluation of immobilization behavior and potential ecological risk of heavy metals in bio-char with different alkaline activation
2021
Zhao, Bing | Xu, Xinyang | Liu, Wenbao | Zhang, Ran | Cui, Miao | Liu, Jie | Zhang, Wenbo
The bio-char was prepared by co-pyrolysis of municipal sewage sludge and biomass with chemical activation. The alkaline activating agents of KOH and K₂CO₃ were used to develop multilevel pore structure without heavy metal. The proximate analysis, ultimate analysis, SEM, and surface area and porosity analyzer were applied to present the physico-chemical properties and multilevel pore structure of bio-char. After impregnation pretreatment, the KOH provided more functional ingredients and reacted with C to expand pore structure for bio-chars. It was confirmed the specific surface area reached 2122.43 m²/g, and micropore area was 1674.85 m²/g after co-pyrolysis at 800 °C. Through the pretreatment of alkaline activation, the novel evaluation of heavy metal immobilization behavior in bio-char matrix were investigated by BCR sequential extraction and leaching tests. The KOH activation showed prominent immobilization behavior relatively, and the K₂CO₃ activation had more noticeable effects on leaching behavior. For Cu, Ni, Cr, Cd, Pb, and Zn, after co-pyrolysis at 900 °C, the proportion of unstable fraction decreased significantly, and the residual fractions of heavy metals were above 89.44% according to BCR sequential extraction procedure. Under optimal pyrolysis temperature, the Eᵣ value of bio-char reduced to 41.93, and the potential ecological risks decreased from considerable risk to low risk to ensure the further eco-friendly application.
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