Dissolution-Desorption Dynamics of Strontium During Elution Following Evaporation: pH and Ionic Strength Effects

Radioactive strontium-90 (90Sr2+) is a fission byproduct of uranium and plutonium production, and therefore understanding its environmental fate is of particular importance for predicting the evolution of long-term risk from historical releases. The nonradioactive strontium cation, Sr2+, is a chemical analog for 90Sr2+ that is often used in studies designed to understand the environmental behaviors of 90Sr2+. The focus of this work was on understanding the dynamics of remobilization of strontium following evaporation to dryness in porous media. Evaporation is ubiquitous in the unsaturated zone, and has the potential to significantly impact the dynamics of transport by driving adsorption or precipitation on solid surfaces. For this work, a series of transport experiments were conducted examining the behavior of strontium over a range of pH values, ionic strengths, and concentrations. Saturated transport experiments were conducted, followed by experiments designed to examine the release and transport following evaporation to dryness. Results show increasing saturated retardation with increasing pH, decreasing ionic strength, and decreasing concentration, with the concentration exhibiting the strongest effect. Breakthrough curves at low concentrations were also found to be consistent with significant rate-limited desorption. Remobilization elution curves measured following evaporation to dryness exhibited the high initial effluent concentrations, exceeding the influent strontium concentration, most likely caused by the initial dissolution and accumulation of strontium by the advancing solution. Concentrations at later times were found to be largely consistent with the dynamics of saturated transport for the systems studied.

Characterization of Hydrothermal Processing Influence on Strontium Substituted Apatite by Investigating Stable Oxygen Isotope Ratio and Antibacterial Activity of Obtained Peroxyapatite

Synthetic hydroxyapatite (HAp) has weak antibacterial and mechanical properties. The antibacterial activity of HAp can be enhanced by strontium cation substitution and incorporation of peroxide ion via hydrothermal processing at 100 °C and 150 °C temperature using 50% H2O2 solution. The starting reagents and products of HAp processing were analyzed by thermal conversion elemental analyser – isotopic ratio mass spectrometer in order to determine the δ18O values. Using different host materials it could be possible to determine differences of δ18O values between untreated and hydrothermally treated HAp samples. The enhanced antibacterial properties of processed HAp samples were investigated using Pseudomonas aeruginosa and Staphylococcus aureus. Hydrothermal processing by H2O2 solutions provides additional antibacterial activity and peroxide content of hydrothermally treated samples affect δ18O values.

High-temperature dynamic octahedral tilting in the ionic conductor Sr11Mo4O23

This work presents the crystal structure evolution of a novel ionic conductor Sr11Mo4O23at high temperature. The formula of this phase can be rewritten as Sr1.75□0.25SrMoO5.75, highlighting the relationship with double perovskitesA2B′B′′O6. The crystal network contains oxygen-anion and strontium-cation vacancies. The structure is complex; Sr, Mo and O atoms are distributed in four, two and six distinct Wyckoff sites, respectively. It was refined from neutron powder diffraction data collected at 473, 673, 873 and 1073 K. The thermal evolution of crystallographic parameters supports the known reversible process of removal/uptake of O-atom content in the 673–873 K temperature range. Above 873 K, from difference Fourier maps, it was found that the structure exhibits an oxygen delocalization around one of the Mo sites. This delocalization was understood as a dynamical octahedral tilt of the MoO6octahedron, yielding an increase in the ionic conductivity at high temperature.