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<p>Hexagonal birnessite (Hex-birnessite) critically controls thallium (Tl) fate in the environment, but the role of nickel (Ni) incorporation during its formation remains unclear. We synthesized Ni-doped Hex-birnessite to assess Ni’s effect on Tl(I) retention. Characterization revealed that Ni(II) preferentially occupied octahedral vacancies and substituted Mn(III/IV). limiting Tl(I) oxidation sites. While 1%Ni-doping caused minimal structural changes, 10%Ni-doping reduced Tl(I) adsorption by 18% and oxidation capacity by 13% compared to pristine Hex-birnessite. Despite its larger surface area (41.9 m<sup>2</sup>/g vs. 21.6 m<sup>2</sup>/g), 10% Ni-doped birnessite showed compromised long-term Tl retention due to vacancy saturation and structural instability. Critically, these findings highlight a risk from ocean alkalinity enhancement (OAE), a geoengineering strategy to amplify oceanic CO<sub>2</sub> uptake. The required gigaton-scale deployment of olivine could release millions of tons of Ni into the ocean annually. As demonstrated in our study, this would promote the formation of Ni-rich, defective birnessite. Consequently, this mineralogical shift suppresses Tl(I) oxidation and enhances its mobility, with similar impacts on other heavy metals that rely on Mn oxide vacancies for immobilization, therefore, such Ni interference could amplify multi-metal toxicity. Our results necessitate reevaluating OAE’s environmental costs, as olivine-derived Ni may broadly destabilize natural metal sequestration pathways, thereby conflicting with carbon neutrality goals.</p>

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Nickel-modified birnessite’s environmental threats: compromised thallium sequestration in marine environment

  • 期刊论文

  • 发表日期：

    2026年2月1日

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  • Feng Li,
  • Tianqiang Zhu,
  • Wen Zhuang

摘要

Hexagonal birnessite (Hex-birnessite) critically controls thallium (Tl) fate in the environment, but the role of nickel (Ni) incorporation during its formation remains unclear. We synthesized Ni-doped Hex-birnessite to assess Ni’s effect on Tl(I) retention. Characterization revealed that Ni(II) preferentially occupied octahedral vacancies and substituted Mn(III/IV). limiting Tl(I) oxidation sites. While 1%Ni-doping caused minimal structural changes, 10%Ni-doping reduced Tl(I) adsorption by 18% and oxidation capacity by 13% compared to pristine Hex-birnessite. Despite its larger surface area (41.9 m2/g vs. 21.6 m2/g), 10% Ni-doped birnessite showed compromised long-term Tl retention due to vacancy saturation and structural instability. Critically, these findings highlight a risk from ocean alkalinity enhancement (OAE), a geoengineering strategy to amplify oceanic CO2 uptake. The required gigaton-scale deployment of olivine could release millions of tons of Ni into the ocean annually. As demonstrated in our study, this would promote the formation of Ni-rich, defective birnessite. Consequently, this mineralogical shift suppresses Tl(I) oxidation and enhances its mobility, with similar impacts on other heavy metals that rely on Mn oxide vacancies for immobilization, therefore, such Ni interference could amplify multi-metal toxicity. Our results necessitate reevaluating OAE’s environmental costs, as olivine-derived Ni may broadly destabilize natural metal sequestration pathways, thereby conflicting with carbon neutrality goals.