V and Cr substitution in dicalcium silicate under oxidizing and reducing conditions – Synthesis, reactivity, and leaching behavior studies

• Published in: Journal of hazardous materials Vol. 442; p. 130032
• Main Authors: Ahmed, Muhammad Jawad, Cuijpers, Remco, Schollbach, Katrin, Van Der Laan, Sieger, Van Wijngaarden-Kroft, Mary, Verhoeven, Tiny, Brouwers, H.J.H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-01-2023
• Subjects: Cr and V doped C2S; Leaching; Oxidation state; Polymorphs; Reducing conditions; Sol-gel synthesis; Cr and V doped C2S; Reducing conditions; Polymorphs; Leaching; Oxidation state; Sol-gel synthesis
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2022.130032

Dicalcium silicate (C2S) is known to incorporate potentially hazardous metals (Cr and V) in a belite-rich cementitious system. The effect of the electrovalence nature of V and Cr on C2S polymorphs’ (α´, β, γ) stability under oxidizing and reducing conditions as well as their reactivity are systematically investigated via analyzing oxidation states, phase composition, bonding system, and microstructure as well as oxide composition quantitively. It is shown that C2S can incorporate Cr (VI) and V(V) consequently leading to stabilization of α´, β-C2S. Instead, Cr (II, III) and V < (V) tend not to substitute in C2S. Despite reactive polymorphs (α´, β-C2S) stability due to Cr (VI) and V(V) incorporation, the early age (48–72 h) C2S reactivity is drastically reduced due to Cr (VI) and V (V) incorporation. Moreover, one batch leaching test revealed that the V (V) leaching is inversely proportional to aqueous Ca2+ ion at pH > 12 while Cr leaching is sensitive to its oxidation state, and dissolution of C2S. Even though C2S can incorporate Cr (VI) and V (V) ions, the final leaching is governed by the immobilization potential of C-S-H gel, pH as well as types of calcium chromate and vanadate complexes.
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•Cr and V doped C2S was synthesized via the sol-gel method.•Reducing conditions restrict the incorporation of Cr and V in C2S.•Stabilization of α ´ -C2S can be attributed to matrix constraint.•Cr and V incorporation reduces reactivity compared to a reference.