Terry F. Rees

Speciation patterns of actinides in natural waters: a laboratory investigation

The results of laboratory investigations of actinide speciation in ground waters of varying compositions are summarized, re-evaluated and further interpreted, with the inclusion of additional data. Actinide speciation (solubility, oxidation state distributions) in these water samples exhibits great variability at 10−10 to 10−8 M total actinide concentrations. Americium solubility appears to be controlled by the formation of radiocolloids. neptunium is predictably oxidized and soluble in these water samples, with only a few exceptions. Plutonium exhibits widely varying oxidation state distributions—and hence solubility— despite the presence of 6 mg liter−1 dissolved oxygen in all experiments. Plutonium solubility is enhanced by carbonate and fluoride but is diminished by sulfate in reducing waters. In general, these results are compatible with the limited information available for actinide speciation from previous in-situ investigations but they emphasize the paucity of accurate thermodynamic data to describe these systems.

Collection and analysis of colloidal particles transported in the Mississippi River, U.S.A.

Abstract Sediment transport has long been recognized as an important mechanism for the transport of contaminants in surface waters. Suspended sediment has traditionally been divided into three size classes: sand-sized (> 63 μ M), silt-sized ( μ M but settleable) and clay-sized (non-settleable). The first two classes are easily collected and characterized using screens (sand) and settling (silt). The clay-sized particles, more properly called colloids, are more difficult to collect and characterize, and until recently received little attention. From the hydrologic perspective, a colloid is a particle, droplet, or gas bubble with at least one dimension between 0.001 and 1 μm. Because of their small size, colloids have large specific surface areas and high surface free energies which may facilitate sorption of hydrophobic materials. Understanding what types of colloids are present in a system, how contaminants of interest interact with these colloids, and what parameters control the transport of colloids in natural systems is critical if the relative importance of colloid-mediated transport is to be understood. This paper describes the collection, concentration and characterization of colloidal materials in the Mississippi River. Colloid concentrations, particle-size distributions, mineral composition and electrophoretic mobilities were determined. Techniques used are illustrated with samples collected at St. Louis, Missouri, U.S.A.

Plutonium Speciation in Water from Mono Lake, California

The solubility of plutonium in Mono Lake water is enhanced by the presence of large concentrations of indigenous carbonate ions and moderate concentrations of fluoride ions. In spite of the complex chemical composition of this water, only a few ions govern the behavior of plutonium, as demonstrated by the fact that it was possible to duplicate plutonium speciation in a synthetic water containing only the principal components of Mono Lake water.

Investigation of solubilization of plutonium and americium in soil by natural humic compounds

An investigation was conducted under simulated natural conditions to determine the solubilization of plutonium and americium in contaminated soil by humic compounds. The results indicate that the solubilization of plutonium and americium by fulvic acid--the more soluble humic compound--is slight. In no instance did the plutonium and americium concentrations in solution approach the drinking water limits. What little solubilization that occurs is probably due to complex formation and/or colloid peptization. The resulting solutions are unstable, and over a period of a few days, most of the plutonium and americium precipitate, either as a result of colloid coagulation or hydrolysis. Two other factors appear to limit the solubilization of these elements: only a relatively small fraction of the plutonium and americium seems to be readily soluble, and there is apparently a low saturation value for these elements in both water and fulvic acid solution.

A review of light-scattering techniques for the study of colloids in natural waters

Abstract In order to understand the movement of colloidal materials in natural waters, we first need to have a means of quantifying their physical characteristics. This paper reviews three techniques which utilize light-scattering phenomena to measure the translational diffusion coefficient, the rotational diffusion coefficient, and the electrophoretic mobility of colloids suspended in water. Primary emphasis is to provide sufficient theoretical detail so that hydrologists can evaluate the utility of photon correlation spectrometry, electrophoretic light scattering, and electric birefringence analysis.

Neptunium and americium speciation in selected basalt, granite, shale, and tuff ground waters

Neptunium and americium are relatively insoluble in ground waters containing high sulfate concentrations, particularly at 90�C. The insoluble neptunium species is Np(IV); hence reducing waters should enhance its formation. Americium can exist only in the trivalent state under these conditions, and its solubility also should be representative of that of curium.

Plutonium Speciation in Selected Basalt, Granite, Shale, and Tuff Groundwaters

The speciation of added plutonium was determined in ground waters of widely varying composition from four rock types: basalt, granite, shale, and tuff. Plutonium was soluble in the basalt water, which contained a high fluoride ion concentration, probably as a result of its stabilization in solution as fluorocomplexes, primarily of plutonium (IV); it was insoluble, however, in the shale ground water, which contained the highest concentration of sulfate ion. Results were intermediate in the granite and tuff ground waters. In synthetic waters containing significant concentrations of both sulfate and fluoride, the effects were smaller and less predictable. Dissolved oxygen, ionic strength, carbonate ion concentration, and pH had little effect on plutonium speciation in the ranges encountered in this study. However, other ionic species not involved in this study may also influence plutonium speciation. The results have potential significance in establishing site-selection criteria for radioactive waste repositories. All other factors being equal, host rocks whose associated waters contain low concentrations of free fluoride ion should be preferable for the location of waste repositories.

Characterization of plutonium in ground water near the idaho chemical processing plant

Plutonium is present in very low concentrations in ground water near the disposal well at the Idaho Chemical processing plant but was not detected in waters at greater distances. Because of the absence of strong complexing agents, the plutonium is present as an uncomplexed (perhaps hydrolyzed) tetravalent species, which is readily precipitated or sorbed by basalt or sediments along the ground-water flow path.

ON THE INTERPRETATION OF SCHUBERT PLOT SLOPES FOR METAL-HUMATE SYSTEMS

In this paper we identify an error in the literature pertaining to the interpretation of nonintegral slopes in Schubert plots for metal-humate and metal-fulvate systems, and we derive equations that correctly describe the behavior of these systems.

Colloid particle sizes in the Mississippi River and some of its tributaries, from Minneapolis to below New Orleans

An on-board technique was developed that combined discharge-weighted pumping to a high-speed continuous-flow centrifuge for isolation of the particulate-sized material with ultrafiltration for isolation of colloid-sized material. In order to address whether these processes changed the particle sizes during isolation, samples of particles in suspension were collected at various steps in the isolation process to evaluate changes in particle size. Particle sizes were determined using laser light-scattering photon correlation spectroscopy and indicated no change in size during the colloid isolation process. Mississippi River colloid particle sizes from twelve sites from Minneapolis to below New Orleans were compared with sizes from four tributaries and three seasons, and from predominantly autochthonous sources upstream to more allochthonous sources downstream.