Revealing the immobilization mechanism of Nd(III) through in‐situ C–S–H formation: Status and coordination of Nd

This study aims to reveal the immobilization mechanism of Nd(III) during the in situ formation of C–S–H. The experimental results indicate that during the formation of C–S–H, Nd was incorporated into its dreierketten silicate chain as Nd tetrahedra via substituting Si tetrahedra at the Q 2b site, which exhibited the lowest defect formation energy according to simulation, resulting in the formation of calcium neodymate silicate hydrates (C–Nd–S–H). These results are highly comparable to density functional theory calculations. The incorporation of Nd into C–Nd–S–H resulted in the elongation of silicate chains, an increase in the inter‐layer space and Q 2 proportion, and local enrichment of Nd without altering the tobermorite‐like structure. The immobilization efficiency of C–S–H for Nd reached 99.99% during synthesis.