Multi-scale investigation of uranium attenuation by arsenic at an abandoned uranium mine, South Terras

Detailed mineralogical analysis of soils from the UK’s historical key uranium mine, South Terras, was performed to elucidate the mechanisms of uranium degradation and migration in the 86 years since abandonment. Soils were sampled from the surface (0 – 2 cm) and near-surface (25 cm) in two distinct areas of ore processing activities. Bulk soil analysis revealed the presence of high concentrations of uranium (<1690 ppm), arsenic (1830 ppm) and beryllium (~250 ppm), suggesting pedogenic weathering of the country rock and ore extraction processes to be the mechanisms of uranium ore degradation. Micro-focus XRF analysis indicated the association of uranium with arsenic, phosphate and copper; µ-XRD data confirmed the presence of the uranyl-arsenate minerals metazeunerite (Cu(UO2)2(AsO4)2·8H2O) and metatorbernite (Cu(UO2)2(PO4)2·8H2O) to be ubiquitous. Our data are consistent with the solid solution of these two uranyl-mica minerals, not previously observed at uranium-contaminated sites. Crystallites of uranyl-mica minerals were observed to coat particles of jarosite and muscovite, suggesting that the mobility of uranium from degraded ores is attenuated by co-precipitation with arsenic and phosphate, which was not previously considered at this site

Enhancements of nucleate boiling under microgravity conditions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76852/1/AIAA-2000-853-986.pd

Recalcitrant bubbles

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles)

Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal

The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10-13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2-252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5-1.8 nm nanoparticles with a proportion forming 20-60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium-uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste

Study of the heat of reversible adsorption at the air-solution interface. II. Experimental determination of the heat of reversible adsorption of some alcohols

The surface tension of aqueous solutions of higher alcohols is measured as function of temperature at constant pressure and mole fraction. For all the studied alcohols a minimum in the σ (T) curves is obtained for sufficiently high concentrations, which minimum seems not to be explained by a solubility increase. The heat of reversible adsorption (or extension) is calculated for different temperatures following the procedure outlined in part I. The heat of reversible extension of the surface area vanishes at this minimum. © 1973.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Study of the heat of reversible adsorption at the liquid-liquid interface. Experimental determination of the heat of reversible adsorption of some arylcyclopropanecarboxamides and higher alcohols

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Study of the heat of reversible adsorption at the air-solution interface. I. Thermodynamical calculation of the heat of reversible adsorption of nonionic surfactants

From variation of surface tension with temperature of aqueous solutions of surfactants, the heat of reversible adsorption at constant temperature and surfactant mole fraction in the bulk can be calculated on a thermodynamic basis. Therefore, the Gibbs adsorption equation is rearranged in a suitable form, where the coefficient of dT does not depend on the choice of the standard entropy. © 1973.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Simple device for mounting crystals for single-crystal diffractometry

This work describes a micrometric manipulating device for easy mounting of small crystals on a needle along a preferred orientation