Application of DGT to high pH environments: uptake efficiency of radionuclides of different oxidation states onto Chelex binding gel.

The DGT Chelex binding phase has not been tested for binding efficiency over the extreme high pH range (i.e., 10 to 13).

The effect of humic acid on uranyl sorption onto bentonite at trace uranium levels.

The effect of humic acid (HA) on U(VI) sorption on bentonite was studied in batch experiments at room temperature and ambient atmosphere at a (237)U(VI) concentration of 8.4 × 10(-11) M and HA concentration of 100 mg L(-1). The distribution of U(VI) between the liquid and solid phases was studied as a function of pH and ionic strength both in the absence and presence of HA.

The effect of EDTA on the groundwater transport of thorium through sand.

The effect of the anthropogenic complexing agent EDTA on thorium transport in groundwater has been studied using sand-packed columns and flow rates in the range of 20-100 m y⁻¹. The concentrations injected into the columns were in the range of 0.4-4 mM for Th and 4-40 mM for EDTA, and with EDTA:Th ratios in the range 1:1 to 10:1.

Estimation of Model VII humic binding constants for Pd2+, Sn2+, U4+, NpO2(2+), Pu4+ and PuO2(2+).

Using previously established procedures that utilise linear free energy relationships, we estimated binding constants for the Windermere Humic Aqueous Model VII (WHAM/Model VII) for several radionuclide cations (Pd(2+), Sn(2+), U(4+), NpO(2)(2+), Pu(4+) and PuO(2)(2+)). This extends the number of cations that can be calculated with the model above the 40 included in the original Model VII work. When combined with equilibrium constants for inorganic species this allows the calculation of equilibrium distributions of chemical species under a wide range of conditions.

Corrosion and transport of depleted uranium in sand-rich environments.

The firing of depleted uranium (DU) weapons during conflicts and military testing has resulted in the deposition of DU in a variety of sand-rich environments. In this study, DU-amended dune sand microcosm and column experiments were carried out to investigate the corrosion of DU and the transport of corrosion products. Under field-moist conditions, DU corroded to metaschoepite ((UO(2))(8)O(2)(OH)(12).

Humic acid sorption onto a quartz sand surface: A kinetic study and insight into fractionation.

A kinetic study of Aldrich humic acid sorption onto a quartz sand surface has revealed an initial rapid uptake of humic acid molecules followed by a much slower sorption. The humic acid molecular weight and chemical fractionation resulting from adsorption onto the simple quartz sand surface were investigated for the two kinetic steps by coupled asymmetric flow-field flow fractionation-UV/visible absorption spectrophotometry. The molecular weight distribution of residual humic acid in solution after adsorption deviated from the original molecular weight distribution, showing preferential adsorption of certain molecular weight components.

Magnesium hydroxide bulk and colloid-associated 152Eu in an alkaline environment: colloid characterisation and sorption properties in the presence and absence of carbonate.

The distribution of 152Eu between magnesium hydroxide bulk, colloids and solution has been assessed under alkaline conditions, such as those in nuclear fuel storage ponds. The colloidal phase has been characterised by two complementary methods: coupled ultrafiltration-ICP-AES and scanning electron microscopy. The quantity and the size distribution of the colloidal phase is strongly ionic strength-dependent.

The role of humic non-exchangeable binding in the promotion of metal ion transport in groundwaters in the environment.

Metal ions form strong complexes with humic substances. When the metal ion is first complexed by humic material, it is bound in an 'exchangeable' mode. The metal ion in this fraction is strongly bound, however, if the metal-humic complex encounters a stronger binding site on a surface, then the metal ion may dissociate from the humic substance and be immobilised.

The simultaneous modelling of metal ion and humic substance transport in column experiments.

Pulsed column experiments using Co, fulvic acid and porous sediment packing, along with up/down-flooding experiments using Eu, humic acid and intact sandstone blocks have been performed. The elution of metal and humic and their distribution along the sandstone columns have been measured. A mixed equilibrium and kinetic coupled chemical transport model has been used to simulate the results.