Environmental Management Science Program Research Articles

Oxidative Leaching of Plutonium from Simulated Hanford Tank‐Waste Sludges

The behavior of surface‐sorbed plutonium during leaching of four Hanford tank waste sludge simulants with alkaline permanganate solutions has been investigated. The sludge simulants are representative of materials created as a result of the operation of the Bismuth Phosphate (sludges B and M), PUREX (sludge P), and REDOX (sludge R) processes at Hanford. Leaching with oxidants under alkaline conditions has been proposed as a means of reducing the chromium content of actual sludge samples prior to their vitrification. With identical amounts of plutonium deposited on each sludge sample, the percentage of radiotracer Pu leached from the sludges increased in the order P≥R>B. This order is the reverse of the chromium content of the sludges. The percentage of plutonium leached was independent of its initial oxidation state. The reverse trends of chromium content and plutonium leaching can be understood in terms of Pu re‐adsorption onto the MnO2 generated as Cr(III) (and other substrates) are oxidized by permanganate/manganate. The effect of chelating agents that are known to be present in tank wastes (EDTA, gluconate, glycolate, oxalate, and citrate) on KMnO4 reduction/MnO2 production and redeposition of plutonium was also studied and found to have varied effects on the process of oxidative dissolution/Pu redeposition. Overall, it appears that the MnO2 produced as a byproduct of oxidation helps to control Pu concentrations in the leachate phase. Oxidation of Pu to the hexavalent state without concomitant production of MnO2 leads to greater plutonium content in the leachate. The results are discussed, emphasizing the potential impact of oxidative leaching on plutonium mobilization from actual tank‐waste sludge. Work performed under the auspices of the Environmental Management Science Program (EMSP) of the U.S. Department of Energy at Argonne National Laboratory under contract number W‐31‐109‐ENG‐38

Cone-based geophysical imaging: A proposed solution to a challenging problem

There are many locations throughout the world where subsurface contamination impacts the natural environment, with potentially serious consequences for the quality of our water and for human heath. At U.S. Department of Energy (DOE) sites alone there are estimated to be “about 6.4 billion cubic meters of contaminated soil, groundwater and other environmental media” (DOE Environmental Management Science Program announcement 02–03). One of the initial steps in dealing with a contaminated site is that referred to as site characterization. During site characterization, measurements are made that allow for the development of an accurate model of the physical, chemical, biological, and hydrogeological properties of the subsurface. Such a model is required to design an appropriate plan for remediation of a contaminated site and can also be used, and continually updated, for short-term or long-term monitoring of the site. Site characterization can involve locating and identifying a known or suspected contaminant, and can also involve determining the properties of the subsurface controlling the fate and transport of the contaminant. The challenging problem we face, at many sites, is identifying an approach to site characterization that provides the required information about the subsurface while minimizing the risks associated with contacting the contaminated region. The most common approach to site characterization involves drilling and directly sampling the near surface (top ∼100 m) of the earth. Boreholes are used to extract samples for laboratory analyses, for borehole logging, and to conduct on-site testing. Examples of on-site testing include water sampling for the direct detection of contaminants and pump tests, slugs tests, and tracer tests to estimate hydraulic conductivity. While the borehole-based methods can provide direct and accurate measurement of subsurface properties of interest, they are limited in terms of the spatial density of the sampling (dictated by the number of boreholes) and the volume of …

A Survey of Department of Energy–Sponsored Geophysical Research for Shallow Waste Site Characterization

Subsurface contamination plagues many USDOE sites and threatens groundwater supplies. This survey discusses research sponsored by the DOE Environmental Management Science Program (EMSP) for geophysical characterization of the vadose zone at the Idaho National Engineering and Environmental Laboratory (INEEL) and other contaminated sites. Various types of geophysical imaging techniques are used to characterize the shallow subsurface, including electromagnetic (EM), ground‐penetrating radar (GPR), electrical, seismic, and nuclear magnetic resonance (NMR). Three common themes appear in the research surveyed in this article: (i) the development of high‐resolution imaging capabilities to capture important details of the heterogeneous nature of subsurface properties and processes, (ii) the coupling of nonintrusive survey geophysical measurements (e.g., electrical surveys) with detailed quantitative precise point‐sensor measurements (e.g., lysimeters and vapor‐port systems) or borehole (e.g., NMR, neutron‐based moisture, and geochemical tools) measurements to extend high‐precision knowledge away from the borehole, and finally (iii) the application of multiple geophysical methods to constrain the uncertainty in determining critical subsurface physical properties. Laboratory, field, theoretical, and computational studies are necessary to develop our understanding of the manner in which contaminants travel through the vadose zone. Applications of geophysical methods to various contaminated areas at the INEEL are given.

Effect of electrode configurations on phase equilibria with applied electric fields1This research was supported by the Environmental Management Science Program, Office of Environmental Management, US Department of Energy, under contract DEAC05-96OR22464 with Lockheed Martin Energy Research Corporation.1

Applying an electric field to some boiling binary mixtures has been shown experimentally to increase the separation factor by as much as 10%. In this work, an electric field was applied across the interface of boiling mixtures of 2-propanol–water via electrodes located in the vapor and the liquid. The shape and separation of the electrodes and the strength and polarity of the electric field were altered to investigate their effect on the vapor mole fraction, the current, and the vapor temperature. The results show that greater voltage differences, in the absence of excessive electrical current, lead to higher concentrations of 2-propanol in the vapor. However, it was found that varying the electrode separation at a given potential difference, and thus the electric field strength, has little effect on the vapor composition. The effects of the applied potential difference are reduced with elevated current and under conditions where liquid dynamics such as dripping, splashing, or jetting provide an opportunity for charge to be transferred between the electrode in the vapor and the liquid. It is also shown that directing the electric field from the vapor to the liquid produces a lower current, and the effect on the composition is larger. These findings, in combination with calculations of the interface charge density, suggest that improvements in the separation efficiency achieved by an applied potential difference are not due to effects of the electric field in the bulk fluids, but rather are induced by charge accumulation at the vapor–liquid interface.

DISTILLATION UNDER ELECTRIC FIELDS*

ABSTRACT Distillation is the most common separation process used in the chemical and petroleum industry. Major limitations in the applicability and efficiency of distillation come from thermodynamic equilibria, that is, vapor-liquid equilibria (VLE), and heat and mass transfer rates. In this work, electric fields are used to manipulate the VLE of mixtures. VLE experiments are performed for various binary mixtures in the presence of electric fields on the order of a few kilovolts per centimeter. The results show that the VLE of some binary mixtures is changed by electric fields, with changes in the separation factor as high as 10% being observed. Batch distillation experiments are also carried out for binary mixtures of 2-propanol and water with and without an applied electric field. Results show enhanced distillation rates and separation efficiency in the presence of an electric field but decreased separation enhancement when the electric current is increased. The latter phenomenon is caused by the formation at the surface of the liquid mixture of microdroplets that are entrained by the vapor. These observations suggest that there should be an electric field strength for each system for which the separation enhancement is maximum. * This research was supported by the Environmental Management Science Program, Office of Environmental Management, U.S. Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

DOE Gives $47 Million for Core Research

The Department of Energy (DOE) last week took what it hopes will amount to a giant step toward solving its massive nuclear waste cleanup problem by funding the first round of 139 grants for basic research at universities and DOE labs. The $47 million Environmental Management Science Program, created last year by Congress, has been embraced by DOE as a fresh approach to a mind-boggling problem—3700 sites in 34 states that could take $230 billion and 75 years to clean up. The 3-year awards, from $200,000 to $2.9 million, cover projects ranging from the dynamics of plume flow and the cleansing characteristics of sound waves to the genetics of waste-eating microbes and metal-absorbing plants. DOE expects to give out $112 million over the 3 years.

Nuclear Cleanup: DOE Gives $47 Million for Core Research

The Department of Energy (DOE) last week took what it hopes will amount to a giant step toward solving its massive nuclear waste cleanup problem by funding the first round of 139 grants for basic research at universities and DOE labs. The $47 million Environmental Management Science Program, created last year by Congress, has been embraced by DOE as a fresh approach to a mind-boggling problem—3700 sites in 34 states that could take $230 billion and 75 years to clean up. The 3-year awards, from $200,000 to $2.9 million, cover projects ranging from the dynamics of plume flow and the cleansing characteristics of sound waves to the genetics of waste-eating microbes and metal-absorbing plants. DOE expects to give out $112 million over the 3 years.