Stabilization of Cr³⁺ using Iron Rich Slag-derived Phosphate Cement: An Integrated Solution for Heavy Metals and Hazardous Solid Wastes

Author

Ting Huang
Hongyan Ma, Missouri University of Science and TechnologyFollow
Zhongqiu Luo
Xintao Zhou
Zhengqing He
Peiwen Lv
Xiunan Cai
Pingyan Wang

Abstract

A novel iron-based phosphate cement (IPC), derived from iron-rich smelting slag (ISS), was developed as a sustainable and efficient binder for the stabilization/solidification of trivalent chromium (Cr³⁺). The mechanical properties, hydration behavior, microstructure, leaching toxicity, chromium chemical forms, and environmental safety of chromium-stabilized iron phosphate cement (CIPC) were thoroughly evaluated. The results showed that, with a mass ratio of ISS to ammonium dihydrogen phosphate (ADP) of 2.0, and even with the addition of 20 % chromium nitrate nonahydrate (CN), the compressive strength of CIPC reached 4.2 MPa after curing for 28 d. Furthermore, chromium leaching was well below 1 mg/L, significantly lower than the GB 5085.3–2007 standard limit of 15 mg/L, demonstrating the effective encapsulation of Cr³⁺ due to IPC's high early strength. In the IPC system, Cr³⁺ was primarily stabilized by forming CrPO₄ and Cr_xFe_1-x(OH)₃ co-precipitates, which were further solidified through the physical encapsulation of IPC hydration products, such as (NH₄)₂Fe(PO₃OH)₂·4H₂O, (NH₄)(Mg,Ca)PO₄·H₂O, and FePO₄. This process resulted in a solidification efficiency of up to 99 %. BCR analysis confirmed that more than 98 % of the chromium in the CIPC remained in a stable residual form. Finally, the ecological risk index (PERI) was found to be 23.52, far below the safety threshold of 150, indicating the solidified material's long-term environmental safety. This study provides an innovative approach for the reutilization of ISS while effectively stabilizing/solidifying chromium.

Recommended Citation

T. Huang et al., "Stabilization of Cr³⁺ using Iron Rich Slag-derived Phosphate Cement: An Integrated Solution for Heavy Metals and Hazardous Solid Wastes," Cement and Concrete Composites, vol. 161, article no. 106089, Elsevier, Aug 2025.

The definitive version is available at https://doi.org/10.1016/j.cemconcomp.2025.106089

Department(s)

Civil, Architectural and Environmental Engineering

Publication Status

Full Text Access

Comments

Yunan Ten Thousand Talents Plan Young and Elite Talents Project, Grant YNWR-QNBJ-2020-063

Keywords and Phrases

Iron-based phosphate cement (IPC); Leaching behavior; Smelting slag; Stabilization/solidification; Trivalent chromium (Cr ) 3+

International Standard Serial Number (ISSN)

0958-9465

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Elsevier, All rights reserved.

Publication Date

01 Aug 2025