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<p>Biochar colloids offer significant potential for soil heavy metal remediation, yet their interfacial interactions with metals and stability regulation mechanisms remain poorly understood. This study investigated the aggregation behavior of peanut shell biochar colloids in Zn²⁺ and Cu²⁺ systems by analyzing hydrodynamic diameter, zeta potential, and critical coagulation concentration (CCC). Results revealed distinct, ion-specific governing mechanisms: (1) In Zn²⁺ System, colloidal stability was governed primarily by electrostatic neutralization with a limited contribution from specific adsorption. At low Zn²⁺ concentrations (0.5–10 mmol/L), rapid aggregation (33&#xa0;nm/min) was induced via electrostatic neutralization compression of the electrical double layer, with a critical coagulation concentration (CCC) of 3.7 mmol/L. At higher concentrations (15–60 mmol/L), specific adsorption of Zn²⁺ led to charge reversal. (2) In Cu²⁺ System, a unique “aggregation–stability–reaggregation” transition was observed, driven by the synergistic effects of strong specific adsorption, stable complex formation, and electrical double-layer compression. At low Cu²⁺ levels (0.03–0.1 mmol/L), strong specific adsorption triggered rapid aggregation (32&#xa0;nm/min; CCC of 0.05 mmol/L). At intermediate concentrations (1–10 mmol/L), charge reversal occurred due to the formation of stable complexes, enhancing electrostatic repulsion and resulting in a temporarily stabilized state. At high concentrations (20–300 mmol/L), double-layer compression by NO₃⁻ ions led to re-aggregation (CCC of 9.5 mmol/L; rate: 30&#xa0;nm/min). This work elucidated how heavy metal ion type and adsorption characteristics differentially governed biochar colloid stability, providing critical theoretical insights for the precision design of biochar-based soil remediation strategies.</p> Graphical abstract <p></p>

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Influence of Zn2+and Cu2+on colloidal biochar aggregation kinetics and the underlying mechanisms

  • 期刊论文

  • 发表日期：

    2026年1月16日

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  • Ju Long,
  • Longhui Zhu,
  • Yanjun Qian,
  • Lei Wang,
  • Hua Qiao

摘要

Biochar colloids offer significant potential for soil heavy metal remediation, yet their interfacial interactions with metals and stability regulation mechanisms remain poorly understood. This study investigated the aggregation behavior of peanut shell biochar colloids in Zn²⁺ and Cu²⁺ systems by analyzing hydrodynamic diameter, zeta potential, and critical coagulation concentration (CCC). Results revealed distinct, ion-specific governing mechanisms: (1) In Zn²⁺ System, colloidal stability was governed primarily by electrostatic neutralization with a limited contribution from specific adsorption. At low Zn²⁺ concentrations (0.5–10 mmol/L), rapid aggregation (33 nm/min) was induced via electrostatic neutralization compression of the electrical double layer, with a critical coagulation concentration (CCC) of 3.7 mmol/L. At higher concentrations (15–60 mmol/L), specific adsorption of Zn²⁺ led to charge reversal. (2) In Cu²⁺ System, a unique “aggregation–stability–reaggregation” transition was observed, driven by the synergistic effects of strong specific adsorption, stable complex formation, and electrical double-layer compression. At low Cu²⁺ levels (0.03–0.1 mmol/L), strong specific adsorption triggered rapid aggregation (32 nm/min; CCC of 0.05 mmol/L). At intermediate concentrations (1–10 mmol/L), charge reversal occurred due to the formation of stable complexes, enhancing electrostatic repulsion and resulting in a temporarily stabilized state. At high concentrations (20–300 mmol/L), double-layer compression by NO₃⁻ ions led to re-aggregation (CCC of 9.5 mmol/L; rate: 30 nm/min). This work elucidated how heavy metal ion type and adsorption characteristics differentially governed biochar colloid stability, providing critical theoretical insights for the precision design of biochar-based soil remediation strategies.

Graphical abstract