Reconstruction kinetics and structural evolutions of chromate and...

Understanding the early-stage reconstruction of Mg/Al layered double hydroxide (LDH) is critical for enhancing anion immobilization in low-carbon cementitious systems. Here, we combined in-situ and ex-situ synchrotron X-ray diffraction analyses to reveal the time-dependent and reversible layered structure transformation of Mg/Al-LDH from calcined Mg/Al-LDH (CLDH) in cementitious environments enriched with Cr(VI) and Cl⁻. Our observations revealed that the initial interlayer space of Mg/Al-LDHs ranged from 7.64 to 7.74 Å, typical for OH⁻ intercalated LDHs, while Cr(VI) hindered the LDH reconstruction. Intercalation of Cl⁻ and Cr(VI) anions expanded the interlayer space of Mg/Al-LDHs up to 8.35 Å, yet had a negligible impact on the lamellar skeleton. Density functional theory calculations indicated that Cr(VI) had a stronger affinity for Mg/Al-LDH layers than Cl⁻, evidenced by higher charge transfer (+2.04 e vs. +0.79 e) and lower interlayer adsorption energy (−1.92 eV vs. −0.29 eV). By selecting Cr(VI) and Cl–, two coexisting anions in hazardous wastes with different charges and geometry, we gained a mechanistic understanding of how a broader group of oxyanions (e.g., SO₄²⁻, AsO₄³⁻) behave in LDH-containing low-carbon cements. Real-time observation and theoretical calculations unveiled the anion-driven reconstruction of Mg/Al-LDH in low-carbon cement, guiding the development of LDH-modified low-carbon cement for immobilizing harmful anions in aggressive environments. These findings facilitated the broader adoption of sustainable cementitious materials across various aggressive environments.

Read more: https://doi.org/10.1016/j.cemconcomp.2025.106250