Comparison of reactivity based on intercalation and host lattice reconstruction. Two routes for the conversion of the lamellar solid hydrogen uranyl phosphate to a lamellar hydrate of uranyl phosphate

The solid-state structural change accompanying intercalation can be profound and have been used to analyze interactions of guest species with host lattices. The authors and others have studied hydrogen uranyl phosphate (HUP), HUO2PO4, and demonstrated that the lamellar solid readily undergoes intercalative ion-exchange reactions, eq 1. Typically, the protons residing between the (1/n)M/sup n/ + HUO2PO4 → M/sub 1/n/UO2PO4 + H+ (1) (UO2PO4)/sub n//sup n-/ sheets can be exchanged simply by slurrying the HUP powder in an aqueous solution containing the ion to be intercalated. It occurred to the authors that use of UO22+ as the intercalant in eq 1 would lead to formation of uranyl phosphate (UP), (UO2)3(PO4)2. Furthermore, the report that UP can be prepared from an aqueous HUP slurry by thermal decomposition, eq 2, provided us with a 3HUO2PO4 → H3PO4 + (UO2)3(PO4)2 (2) novel opportunity to compare two pathways to the same product. They report herein that can be quantitatively converted by intercalation (eq 1) or host lattice reconstruction (eq 2) to a common lamellar hydrate of UP; both reactions are reversible at room temperature. Moreover, an Arrhenius treatment of calculated rates for the forward reactions supports the notion that they proceed by quite different mechanisms