Effects of composition and canister centerline cooling on microstructure, phase distribution, and chemical durability of dehalogenated iron phosphate waste forms

This paper discusses the effects of composition and canister centerline cooling (CCC) on the microstructure, phase distribution, and chemical durability of dehalogenated iron phosphate waste forms starting from chloride-based salt simulants including KCl, NdCl ₃, SrCl ₂, LaCl ₃, LiCl, CsCl, as well as a complex seven-salt simulant called ERV2. The simulants represent salt constituents in salt wastes from electrorefiners used for electrochemical reprocessing. These salts are reacted with NH ₄H ₂PO ₄ resulting in a phosphate product containing dehalogenated salt cations and NH ₄Cl as a byproduct that is captured. This product is further stabilized using Fe ₂O ₃ through vitrification at higher temperatures. The results presented herein describe the properties of slow-cooled materials following dehalogenation and vitrification including phase identification and quantification, elemental distributions, and chemical durabilities. The phases formed upon CCC were very complex compositionally and microstructurally. The results show that the simple-salt experiments can be used to assess component effects on the waste forms.