https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:32238 VI) with fresh, (anoxic) aged and corroded nZVI particles was investigated under aqueous conditions conducive to the formation of thermodynamically stable U(_VI)-Ca-CO₃ ternary aqueous complexes. The first stage of the reaction between U(_VI) and nZVI was assigned to sorption processes with the formation of surface U(_VI)-carbonate complexes. Aged nZVI removed U(_VI) faster than either fresh or corroded nZVI and it is hypothesized that U reduction initially occurs through the transfer of one electron from Fe(_II) in the nZVI surface oxide layer. Evidence for reduction to U(_V) was obtained through X-ray photoelectron spectroscopy and by determination of U-O bond distances of ~2.05 and 2.27 Å, using U L_III -edge X-ray absorption spectroscopy, which are similar to those observed for the U(_v) site in the mixed U(_v)/U(_VI) carbonate mineral wyartite. Scanning transmission electron microscopy also demonstrated that U was present as a nanoparticulate phase after one day of reaction, rather than a surface complex. Further reduction to U(_IV), as observed in previous studies, would appear to be rate-limiting and coincident with the transformation of this meta-stable U-carbonate phase to uraninite (UO).]]> Tue 15 May 2018 16:00:13 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:30787 Sat 24 Mar 2018 07:37:51 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:25215 Sat 24 Mar 2018 07:13:59 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:35132 Raphidiopsis raciborskii is of environmental and social concern in view of its toxicity, bloom‐forming characteristics and increasingly widespread occurrence. However, while availability of macronutrients and micronutrients such as N and Fe are critically important for the growth and metabolism of this organism, the physiological response of toxic and non‐toxic strains of R. raciborskii to varying Fe and N availabilities remains unclear. By determining physiological parameters as a function of Fe and N availability, we demonstrate that R. raciborskii growth and N₂‐fixing activity are facilitated at higher Fe availability under N₂‐limited conditions with faster growth of the CS‐506 (cylindrospermopsin‐producing) strain compared with that of CS‐509 (the non‐toxic) strain. Radiolabelled Fe uptake assays indicated that R. raciborskii acclimated under Fe‐limited conditions acquires Fe at significantly higher rates than under Fe replete conditions, principally via unchelated Fe(II) generated as a result of photoreduction of complexed Fe(III). While N₂‐fixation of both strains occurred during both day and night, the CS‐506 strain overall exhibited higher N₂‐fixing and Fe uptake rates than the CS‐509 strain under N‐deficient and Fe‐limited conditions. The findings of this study highlight that Fe availability is of significance for the ecological advantage of CS‐506 over CS‐509 in N‐deficient freshwaters.]]> Fri 03 Apr 2020 12:05:38 AEDT ]]>