Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions.

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD) layers as an intermediate particle phase.

Multinuclear PFGSTE NMR description of K, Na, Li, and H specific activation energies governing diffusion in alkali nitrite solutions.

While pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has found widespread use in the quantification of self-diffusivity for many NMR-active nuclei, extending this technique to uncommon nuclei with unfavorable NMR properties remains an active area of research. Potassium-39 (K) is an archetypical NMR nucleus exhibiting an unfavorable gyromagnetic ratio combined with a very low Larmor frequency. Despite these unfavorable properties, this work demonstrates that K PFGSTE NMR experiments are possible in aqueous solutions of concentrated potassium nitrite.

Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions.

Ultraviolet (UV) photolysis of nitrite ions (NO2-) in aqueous solutions produces a suite of radicals, viz., NO·, O-, ·OH, and ·NO2. The O- and NO· radicals are initially formed from the dissociation of photoexcited NO2-.

Correction: Solubilities in aqueous nitrate solutions that appear to reverse the law of mass action.

Correction for 'Solubilities in aqueous nitrate solutions that appear to reverse the law of mass action' by Jacob G. Reynolds , , 2021, , 21407-21418, DOI: 10.1039/D1CP03124D.

Solubilities in aqueous nitrate solutions that appear to reverse the law of mass action.

Non-ideal aqueous electrolyte solutions have been studied since the start of the application of thermodynamics to chemistry in the late 19th century. The present study examines some of the most extreme non-ideal behavior ever observed: solubilities of alkali and NH nitrate salts in water that appear to behave the opposite of how the Law of Mass Action would predict. A literature review discovered that the solubilities of NHNO and many alkali nitrate salts increases when another nitrate-bearing electrolyte is added to solution.

The controlling role of atmosphere in dawsonite gibbsite precipitation from tetrahedral aluminate species.

In highly alkaline solution, aluminum speciates as the tetrahedrally coordinated aluminate monomer, Al(OH) and/or dimer AlO(OH), yet precipitates as octahedrally coordinated gibbsite (Al(OH)). This tetrahedral to octahedral transformation governs Al precipitation, which is crucial to worldwide aluminum (Al) production, and to the retrieval and processing of Al-containing caustic high-level radioactive wastes. Despite its significance, the transformation pathway remains unknown.

Influence of soluble oligomeric aluminum on precipitation in the Al-KOH-HO system.

The role of oligomeric aluminate species in the precipitation of aluminum (Al) phases such as gibbsite (α-Al(OH)) from aqueous hydroxide solutions remains unclear and difficult to probe directly, despite its importance for developing accurate predictions of Al solubility in highly alkaline systems. Precipitation in this system entails a transition from predominantly tetrahedrally coordinated aluminate (Al(OH)) species in solution to octahedrally coordinated Al in gibbsite. Here we report a quantitative study of dissolved Al in the Al-KOH-HO system using a combination of molecular spectroscopies.

Ion-ion interactions enhance aluminum solubility in alkaline suspensions of nano-gibbsite (α-Al(OH)) with sodium nitrite/nitrate.

Despite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion-ion and ion-solvent interactions. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S.

Large cemented gibbsite agglomerates in alkaline nuclear waste at the Hanford site and the impacts to remediation.

Recent work with the remediation of legacy alkaline nuclear waste has focused on nanometer and micrometer particle sizes, emphasizing how these small particles can impact efforts to treat the waste. Building upon this work, we present here findings that show very large particles (several centimeters in size) also exist in these waste which likewise play an important role in the remediation process. While large cemented gibbsite nodules have been periodically reported in acid soils in the literature, this study found similar large gibbsite agglomerates (7 cm in diameter) in alkaline nuclear waste, the first time that such large agglomerates have been identified in an alkaline environment.

Salt Solubilities in Aqueous Solutions of NaNO, NaNO, NaCl, and NaOH: A Hofmeister-like Series for Understanding Alkaline Nuclear Waste.

Nonelectrolyte solubility in electrolyte solutions follow the Hofmeister series, but the applicability of the series to salt solubility has been less appreciated. This study, using solubility data for thirteen sodium-bearing salts, shows that salts are consistently salted out by electrolytes important to alkaline nuclear waste in the order NaOH > NaCl > NaNO > NaNO at 298.15 K, which is the same order as the Hofmeister series.

Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation.

The characterization of prenucleation species is essential to understand crystallization mechanisms across many chemical systems and often involves the use of vibrational spectroscopy. Nowhere is this more evident than in the development of "green" aluminum processing technologies, where detailed understanding of the speciation of aluminum and its polynuclear analogues in highly alkaline, low water solutions is elusive. The aluminate anion Al(OH) predominates in alkaline conditions, yet equilibrium with dimeric species, either μ-oxo AlO(OH) or di-μ-hydroxo Al(OH), can be assumed.

Development of a carbonate crust on alkaline nuclear waste sludge at the Hanford site.

Hard crusts on aging plutonium production waste have hindered the remediation of the Hanford Site in southeastern Washington, USA. In this study, samples were analyzed to determine the cause of a hard crust that developed on the highly radioactive sludge during 20 years of inactivity in one of the underground tanks (tank 241-C-105). Samples recently taken from the crust were compared with those acquired before the crust appeared.

Solid-phase zirconium and fluoride species in alkaline zircaloy cladding waste at Hanford.

The United States Department of Energy Hanford Site, near Richland, Washington, USA, processed plutonium between 1944 and 1987. Fifty-six million gallons of waste of various origins remain, including waste from removing zircaloy fuel cladding using the so-called Zirflex process. The speciation of zirconium and fluoride in this waste is important because of the corrosivity and reactivity of fluoride as well as the (potentially) high density of Zr-phases.

The apparent solubility of aluminum (III) in Hanford high-level waste.

The solubility of aluminum in Hanford nuclear waste impacts on the processability of the waste by a number of proposed treatment options. For many years, Hanford staff has anecdotally noted that aluminum appears to be considerably more soluble in Hanford waste than the simpler electrolyte solutions used as analogues. There has been minimal scientific study to confirm these anecdotal observations, however.

Evidence for dawsonite in Hanford high-level nuclear waste tanks.

Gibbsite [Al(OH)(3)] and boehmite (AlOOH) have long been assumed to be the most prevalent aluminum-bearing minerals in Hanford high-level nuclear waste sludge. The present study shows that dawsonite [NaAl(OH)(2)CO(3)] is also a common aluminum-bearing phase in tanks containing high total inorganic carbon (TIC) concentrations and (relatively) low dissolved free hydroxide concentrations. Tank samples were probed for dawsonite by X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS) and Polarized Light Optical Microscopy.