Co-pyrolysis of alkali-fused fly ash and corn stover to synthesize biochar composites for remediating lead-contaminated soil

• Published in: Environmental research 2024-07, Vol.252, p.118938-118938, Article 118938
• Main Authors: Ma, Yan, Shang, Xiufang, Zhang, Yaru, Chen, Wei, Gao, Yan, Guo, Jianda, Zheng, Hao, Xing, Baoshan
• Format: Article
• Language: English
• Subjects: Agricultural waste; Co-pyrolysis; Fly ash; Functionalized biochar composite; Soil remediation
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1016/j.envres.2024.118938

Fly ash (FA) is mainly composed of silica, alumina, and other metal oxide components, and has a positive stabilizing effect on soil heavy metals. Biochar composites produced from FA and corn stover (CS) can improve its remediation performance. Therefore, a batch of biochar composites (alkali-fused FA-CS biochars, ABs), synthesized via co-pyrolysis of CS and alkali-fused FA (AFFA) at different temperatures of 300, 500, and 700 °C (AB300-1, AB500-1, and AB700-1) and CS to AFFA mass ratios of 10:1, 10:2, and 10:5 (AB500-1, AB500-2, and AB500-5), was used to remediate lead (Pb)-contaminated soil. Compared with pristine biochars (BCs), ABs were enriched with oxygen-containing functional groups (Si–O–Si and Si–O) and aromatic structures. The ABs prepared at lower pyrolytic temperature (≤500 °C) and lower ratio of CS to AFFA (10:1) showed higher yield and stability. The contents of Toxicity Characteristic Leaching Procedure (TCLP)-extractable Pb and DTPA-CaCl2-triethanolamine (DTPA)-extractable Pb were generally lower in the soils amended with ABs than BCs. Compared with other ABs such as AB300-1, AB500-2, AB500-5, and AB700-1, the soil amended with AB500-1 had lower contents of TCLP and DTPA-extractable Pb (24% reduction), exhibiting superior performance in stabilizing Pb in the soil. The gradual decrease of DTPA-extractable Pb content in the soil with increasing dosage of AB500-1 amendments suggests that AB500-1 facilitated the conversion of bioavailable Pb to the stable and less toxic residual fractions. Specifically, the highest percentage of residual fraction of Pb in soil amended with AB500-1 was 14%. Correlation analyses showed that the soil DTPA-extractable Pb content decreased with the increase of soil pH and cation-exchange capacity (CEC) value. ABs stabilize Pb in the soils mainly via electrostatic attraction, precipitation, cation-π interaction, cation exchange, and complexation. These findings provide insights for producing functionalized biochar composites from industrial waste like FA and biomass waste for remediating the soils polluted by heavy metals. [Display omitted] •Physicochemical properties of fly ash improved with NaOH modification.•Co-pyrolysis of alkali-fused fly ash and corn stover synthesized biochar composites.•Biochar composites stabilized Pb via precipitation, cation-π interaction, and complexation.•Biochar composite properties, soil pH, and CEC determined Pb stabilization.