The adsorption mechanism of Zn²⁺ by triclinic birnessite and the mechanism

ABSTRACT

In this paper, the reaction mechanism for the adsorption of Zn²⁺ by synthetic triclinic Na-birnessite was studied by reacting synthetic triclinic Na-birnessite with Zn²⁺ in solution, thereby providing a theoretical basis for the purification of heavy metal ions in acid soil and water by triclinic birnessite. The adsorption effect of Zn²⁺ on Na-birnessite enhances with an increase in either reaction time or Na-birnessite dosage, as well as decrease of pH. Na-birnessite can effectively adsorb Zn²⁺ in acidic solutions without any secondary pollution, and the stronger the acidity, the better the treatment effect. In acidic conditions, H⁺ in solution exchanges with Na⁺ in the interlayer of triclinic Na-birnessite, then a small part of Zn²⁺ in solution exchanges with the Mn²⁺ produced during the triclinic-to-hexagonal phase transformation, and most of the Zn²⁺ forms a complex with OH⁻ on the octahedral layer, which loses protons due to the consumption of H⁺ ions. Finally, Zn²⁺ adsorbs above and below octahedral vacancies in hexagonal birnessite in either an octahedral or tetrahedral coordination.

GRAPHICAL ABSTRACT

KEYWORDS:

• Triclinic Na-birnessite
• Zn²⁺ in solution
• adsorption effect
• reaction mechanism
• Hexagonal Na-birnessite

Acknowledgements

We are thankful for the support from the State Key Lab for Geological Processes and Mineral Resources. We are grateful to Xiang Gao for supporting my experimental work and thank Prof. Xionghan Feng for the laboratory work on birnessite synthesis. Discussions with Huaiyan Zhao and Jiangyan Yuan improved our presentation of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.