Study on the Solidification Mechanism of Cr in Ettringite and Friedel’s Salt

The solidification of heavy metal Cr has always been a challenge in the treatment Cr-containing wastes, due to its high mobility alkaline environments. In addition, mechanism not fully investigated. this study, blast furnace slag (BFS)-based cementitious materials were used as binders for immobilization investigate different hydration products. From XRD, FTIR, XPS, and XANES analyses, it could be seen that SO42− ettringite was replaced by form CrO42−, making re-dissolve liquid phase. solution would compete with CrO42− ions, leading direct influence content on efficiency Cr. ettringite, mainly existed Cr6+, accounting more than 84% however, solidified Friedel’s salt under two coexisting valence states (Cr6+ Cr3+). This resulted only from slow excitation rate BFS system did contain sulfate, but also existence certain amount reducing substances BFS, such Fe2+ S2−, which reduce some Cr6+ Cr3+. salt, residual Cl− whereas Cr3+ Al3+. binding energies 2p3/1 2p3/2 decreased addition Cr, indicating coordination numbers increased, after entering structure salt.