Mechanochemistry enables transformations of highly insoluble materials such as uranium dioxide or the mineral studtite [(UO2)(O2)(H2O)2]·(H2O)2 into uranyl triperoxide compounds that can subsequently assemble into hydroxide-bridged uranyl peroxide dimers in the presence of lithium hydroxide. Dissolution of these solids in water yields uranyl peroxide nanoclusters including U24, Li24[(UO2)(O2)(OH)]24. Insoluble uranium solids can transform into highly soluble uranyl peroxide phases in the solid state with miniscule quantities of water. Such reactions are potentially applicable to uranium processing in the front and back end of the nuclear fuel cycle.