CO₂ mineralization of steel slag into vaterite for high-efficiency Zn²⁺ removal and upcycling into hydrozincite

Abstract

We developed an integrated strategy that simultaneously valorizes three major by-products of the steel industry, including CO₂, steelmaking slag, and Zn²⁺-containing wastewater. CO₂ mineralization was achieved by bubbling CO₂ into steel-slag leachate in the presence of amino acid crystallization modifiers, which selectively yielded the metastable CaCO₃ polymorph vaterite with L-arginine and the thermodynamically stable polymorph calcite with L-lysine. The resulting CaCO₃ was used for Zn²⁺ removal from aqueous media, where vaterite exhibited a high removal capacity of 633 mg/g, significantly higher than that of calcite (444 mg/g). Notably, Zn²⁺ removal by vaterite is governed not by simple surface adsorption but by a dissolution-reprecipitation mechanism, leading to an in situ transformation into Zn-rich hydrozincite. This study provides a potential pathway for CO₂ mineralization and Zn²⁺ removal while enabling the stabilization and recovery of Zn in a solid mineral form, offering a new strategy for waste to resource conversion in steel-related industries.

Graphical abstract

Keywords

Steel industry / Vaterite / calcite / Zn²⁺ removal / Hydrozincite

Highlight

	● Vaterite and calcite were synthesized via CO2 mineralization of steel slag.
	● Zn2+ removal efficiency was higher with vaterite than with calcite.
	● Vaterite was converted into hydrozincite during Zn2+ adsorption.
	● Time-dependent evolution confirmed hydrozincite via dissolution-reprecipitation.

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