Magnesium potassium phosphate cements (MKPCs), blended with 50wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25Mg, 27Al, 29Si, 31P and 39K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC

Fenton or Fenton-like oxidation for treatment of organic radioactive wastes is a promising technology with applications to a range of organic wastes. This review details this process; exploring potential challenges, pitfalls and opportunities for industrial usage with radioactive wastes. The application of this process to real radioactive wastes within pilot-plant settings has been documented, with key findings critically assessed in the context of future waste production. Although this oxidation process has not found mainstream success in treatment of radioactive wastes, a lower temperature oxidation system bring certain benefits, specifically for higher volume or problematic organic wastestreams.

Uranium (U) is a ubiquitous element in the Earth’s crust at ~2 ppm. In anoxic environments, soluble hexavalent uranium (U(VI)) is reduced and immobilized. The underlying reduction mechanism is unknown but likely of critical importance to explain the geochemical behavior of U. Here, we tackle the mechanism of reduction of U(VI) by the mixed-valence iron oxide, magnetite. Through high-end spectroscopic and microscopic tools, we demonstrate that the reduction proceeds first through surface-associated U(VI) to form pentavalent U, U(V). U(V) persists on the surface of magnetite and is further reduced to tetravalent UO₂ as nanocrystals (~1–2 nm) with random orientations inside nanowires. Through nanoparticle re-orientation and coalescence, the nanowires collapse into ordered UO₂ nanoclusters. This work provides evidence for a transient U nanowire structure that may have implications for uranium isotope fractionation as well as for the molecular-scale understanding of nuclear waste temporal evolution and the reductive remediation of uranium contamination.

Radioactive waste streams that include metallic uranium are incompatible with conventional ordinary Portland cement (OPC)-based encapsulation matrices. These encapsulation systems are essentially composite materials that incorporate high replacement levels of pulverised fly ash (PFA) or blast furnace slag (BFS). A potential alternative encapsulant for the treatment of problematic waste streams is magnesium phosphate cement. This paper discusses the fundamental characterisation results obtained from two magnesium phosphate cement formulations being developed in the UK for the encapsulation of metallic intermediate level waste (ILW). When compared to conventional OPC based systems, the two magnesium phosphate cement formulations investigated have lower pH, are able to chemically combine more mix water into the system and provide sufficient workability at water/solid ratios close to the theoretical confines needed for paste saturation. The results presented have confirmed compliance of this material against NDA RWMD guidelines for strength and expansion. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results obtained for both formulations up to 360 days cure time have indicated that the cement system shows evidence of chemical stability.