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Long-term stability of organic carbon-stimulated chromatereduction in contaminated soils, and its relation to manganese redoxstatus

Description: In-situ reduction of toxic Cr(V1) to less hazardous Cr(II1)is becoming a popular strategy for remediating contaminated soils.However, the long term stability of reduced Cr remains to be understood,especially given the common presence of MnfIIIJV) oxides that reoxidizeCr(II1). This 4.6 year laboratory study tracked Cr and Mn redoxtransformations in soils contaminated with Cr(V1) which were then treatedwith different amounts of organic carbon (OC). Changes in Cr and Mnoxidation states within soils were directly and nondestructively measuredusing micro X-ray absorption near edge structure spectroscopy. Chromatereduction was roughly lst-order, and the extent of reduction was enhancedwith higher OC additions. However, significant Cr(||1) reoxidationoccurred in soils exposed to the highest Cr(V1) concentrations (2,560 mgkg"'). Transient Cr(II1) reoxidation up to 420 mg kg1 was measured at 1.1years after OC treatment, followed by further reduction. Chromateconcentrations increased by 220 mg kgm1a t the end of the study (4.6years) in one soil. The causal role that Mn oxidation state had inreoxidizing Cr was supported by trends in Mn K-edge energies. Theseresults provide strong evidence for longterm dependence of soil Croxidation states on balances between OC availability and Mn redoxstatus.
Date: March 13, 2007
Creator: Tokunaga, Tetsu K.; Wan, Jiamin; Lanzirotti, Antonio; Sutton,Steve R.; Newville, Matthew & Rao, William
Partner: UNT Libraries Government Documents Department


Description: Currently the effort to remove chromate from groundwater in the 100K and 100H Areas uses DOWEX 21K 16-20. This report addresses the procedure and results of a laboratory study for regeneration of the spent resin by sodium hydroxide, sulfuric acid, or sodium sulfate to determine if onsite regeneration by the Effluent Treatment Facility is a feasible option.
Date: January 24, 2007
Creator: DUNCAN, J.B.
Partner: UNT Libraries Government Documents Department

Ecological Interactions Between Metals and Microbes

Description: Analyses of chromium resistant microbes. Culturable xylene-degrading and chromate-resistant microbes were obtained from chronically cocontaminated soil using a microcosm enrichment technique, and shown to correlate to dominant soil populations using culture independent techniques. The soil microbial community proved able to mount a respiratory response to addition of xylene in the presence of chromate. The majority of isolates belonged to the ubiquitous but poorly studied high %G+C Gram positive genus Arthrobacter, and exhibited considerable genotypic and phenotypic variability. Phenotypic assays uncovered a wide variation in the levels of chromate resistance, even between very closely related strains. Primers designed against conserved motifs in the known chrA chromate efflux gene failed to detect similar sequences among the chromate resistant Arthrobacter isolates obtained through enrichment.
Date: June 1, 2004
Creator: Konopka, Allan E.
Partner: UNT Libraries Government Documents Department

Laboratory evaluation of the potential for in situ treatment of chromate-contaminated groundwater by chemical precipitation

Description: The objective of this paper is to present the results of a series of small-scale batch tests performed to assess the effectiveness of chemical precipitation in the remediation of chromate-contaminated groundwater. These tests involved treatment of chromate solutions with ferrous and sulfide ions. In addition, tests were conducted that involved treatment of mixtures of chromate-contaminated groundwater and uncontaminated soil with the ferrous ion. A combination of ferrous sulfate and sodium sulfide was also tested in the groundwater treatment tests, since this approach has been shown to be an efficient method for treating electroplating wastewaters.
Date: March 1, 1995
Creator: Thornton, E.C.; Beck, M.A. & Jurgensmeier, C.A.
Partner: UNT Libraries Government Documents Department

Engineering process instructions and development summary MC3642 thermal battery

Description: The MC3642 is a dual channel thermal battery used on the DE1010/W85 Command Disable Controller. It utilizes the CalCaCrO{sub 4} electrochemical system. The electrical requirements of this battery are as follows: RISE TIME PEAK VOLTAGE ACTIVE LIFE LOAD Channel 1 - 1.0 Sec. Max. 34 Volts 10 Sec. Min. 40.0 Ohms to 20 Volts above 20 Volts Channel 2 - .350 Sec. Max. 42 Volts 10 MSec. Min. 6.5 Ohms to 23 Volts above 23 Volts The battery consists of 14 cells connected in series (Channel 2) and 12 cells connected in series (Channel 1). Each cell is composed of an anode fabricated from a bimetallic sheet (0.005{double_prime} thick calcium on 0.005{double_prime} thick iron substrate), a depolarizer-electrolyte-binder (DEB) pellet and a heat pellet. Activation is achieved by mechanical primer. Optimum battery performance is achieved with a 35155/10 DEB pellet weighing .80g and a heat pellet, weighing 1.30 grams, of 88/12 heat powder.
Date: June 1, 1981
Creator: Jacobs, D.
Partner: UNT Libraries Government Documents Department

100-D Area In Situ Redox Treatability Test for Chromate-Contaminated Groundwater: FY 1998 Year-End Report

Description: A treatability test was conducted for the In Situ Redox Manipulation (ISRM) technology at the US Department of Energy's Hanford, Washington 100D Area. The target contaminant was dissolved chromate [Cr(VI)] in groundwater. The ISRM technology involves creating a permeable subsurface treatment zone to reduce mobile chromate in groundwater to an insoluble form. The ISRM permeable treatment zone is created by reducing ferric iron [Fe(III)] to ferrous iron [Fe(II)] within the aquifer sediments. This is accomplished by injecting aqueous sodium dithionite into the aquifer and withdrawing the reaction products. The goal of the treatability test was to create a linear ISRM barrier by injecting sodium dithionite into five wells. Well installation and site characterization activities began in the spring of 1997. The first dithionite injection took place in September 1997. The results of this first injection were monitored through the spring of 1998; the remaining four dithionite injections were carried out in May through July of 1998. These five injections created a reduced zone in the Hanford unconfined aquifer 150 feet in length (perpendicular to groundwater flow) by 50 feet wide. The reduced zone extended over the thickness of the unconfined zone, which is approximately 15 feet. Analysis of recent groundwater sampling events shows that the concentrations of chromate [Cr(VI)] in groundwater in the reduced zone have been decreased from starting concentrations of approximately 900 ppb to below analytical detection limits (<7 ppb). Chromate concentrations are also declining in some downgradient monitoring wells. Laboratory analysis of iron in the soil indicates that the barrier should remain in place for approximately 20 to 25 years. These measurements will be confirmed by analysis of sediment cores in FY 1999.
Date: April 15, 1999
Creator: Williams, M. D.; Vermeul, V. R.; Szecsody, J. E.; Fruchter, J. S. & Cole, C. R.
Partner: UNT Libraries Government Documents Department

The effect of chromate concentration on the repassivation of corroding aluminum

Description: Current density maps of anodically polarized pure aluminum in chloride solutions were measured and the effect of chromate/dichromate buffer additions monitored. The higher the polarized potential the more chromate was required to repassivate the corroding surface. Small pits repassivated easily, crevice corrosion events were the last to repassivate. Open circuit potential measurements showed the presence of meta-stable pitting at chloride concentrations of 0.3M. The lifetime and magnitude of these metastable pits was reduced on the addition of 0.05M chromate buffer.
Date: February 9, 1999
Creator: Jeffcoate, C.S.; Isaacs, H.S.; Hawkins, J. & Thompson, G.E.
Partner: UNT Libraries Government Documents Department


Description: We used in situ X-ray adsorption near-edge structure (XANES) to investigate the formation of chromate conversion coatings on pure Al, commercial Al alloys (AA 1100, AA2024, and AA7075), and a series of binary Al-Cu alloys. The method employed a new electrochemical cell that can determine the ratio of hexavalent chromium (Cr(VI)) to total chromium (Cr(total)) speciation in conversion coatings as a function of exposure time to a chromate solution. The spectra showed that the initial Cr(VI)/Cr(total) ratios are greater than later ones for pure Al and AA1100, but not for AA2024 and AA7075. Measurements with Al-Cu alloys demonstrated that the difference observed in AA2024 and AA7075 may not be due to Cu alloying. The proportion of Cr(VI) in the coatings becomes approximately constant after 180 s of exposure for all the specimens examined even though the coatings continue to grow.
Date: September 2, 2001
Partner: UNT Libraries Government Documents Department

Dissolution of Oxide Films on Aluminum in Near Neutral Solutions

Description: Simple linear potentiodynamic cycling measurements have been made on abraded pure Al in borate, chromate, phosphate, sulfate and nitrate solutions. In borate and chromate solutions the currents continued to decrease with each subsequent cycle. In phosphate dissolution of the oxide takes place producing repetitive repeat curves. The current variations in borate and chromate were simulated using a high field conduction oxide growth model. Including oxide dissolution in the model simulated the phosphate behavior. Results in sulfate and nitrate solutions were more complex. The behavior in the sulfate solution was attributed to effects of sulfate the oxide/solution interface.
Date: October 17, 1999
Creator: Isaacs, Hugh S.; Xu, Feng & Jeffcoate, Carrol S.
Partner: UNT Libraries Government Documents Department


Description: Applications of x-ray absorption near-edge spectroscopy (XANES) and the design of cells for in situ corrosion studies are reviewed. Passive films studies require very thin metal or alloy layers be used having a thickness of the order of the films formed because of penetration of the x-ray beam into the metal substrate. The depth of penetration in water also limits the thickness of solutions that can be used because of water reduces the x-ray intensity. Solution thickness must also be limited in studies of conversion layer formation studies because the masking of the Cr in solution. Illustrative examples are taken from the anodic behavior of Al-Cr alloys, the growth of passive films on Fe and stainless steels, and the formation of chromate conversion layers on Al.
Date: March 25, 2001
Partner: UNT Libraries Government Documents Department

Characterization Activities Conducted at the 183-DR Site in Support of an In Situ Gaseous Reduction Demonstration

Description: In Situ Gaseous Reduction (ISGR) is a technology developed by DOE for the remediation of soil waste sites contaminated with hexavalent chromium. This document presents information associated with characterization activities conducted at the 183-DR site at Hanford, which is associated with a significant groundwater contaminant plume and was formerly a water treatment facility that utilized chromate as a corrosion inhibitor. Geotechnical and chemical data were collected during the excavation of trenches and the drilling of two vadose zone boreholes to support a possible ISGR demonstration at 183-DR. Although elevated total chromium and trace levels of hexavalent chromium were identified from one of the trenches and one of the boreholes, it appears that the boreholes missed the vadose zone contaminant source responsible for the chromium groundwater plume located downgradient of the 183-DR site. Recommendations are provided, however, for future work at 183-DR that may serve to identify the source for the groundwater plume and possibly provide an opportunity for an ISGR demonstration.
Date: March 30, 2001
Creator: Thornton, Edward C; Gilmore, Tyler J; Olsen, Khris B; Schalla, Ronald & Cantrell, Kirk J
Partner: UNT Libraries Government Documents Department

Thermal Stability and Aging Characteristics of Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Description: XANES and electrochemical impedance spectroscopes were used in parallel to correlate the amount of Cr(VI) in chromate conversion coatings (CCC) on Al 2024 and their corrosion resistance in order to understand the degradation mechanisms upon aging or heating. Cr(VI) species appear to be immobilized for temperatures higher than 80 C due to dehydration. CCC are shown to be dynamic in the first month of aging with no significant dehydration. Another degradation mechanism involving chemical changes is to be considered.
Date: October 17, 1999
Creator: Laget, V.; Jeffcoate, C.; Isaacs, H. S. & Buchheit, R. G.
Partner: UNT Libraries Government Documents Department


Description: We investigated the inhibition by chromate ions of the localized corrosion of aluminum by electrochemical transient measurements. In agreement with other work, the measurements demonstrated that chromate is a cathodic inhibitor for aluminum in open circuit. The reduction of hexavalent chromium to trivalent chromium is assumed to take place on catalyzed sites of the surface. The resulting products inhibit oxygen reduction reactions at these sites, thereby retarding pitting corrosion.
Date: September 2, 2001
Creator: SASAKI,K. & ISAACS,H.S.
Partner: UNT Libraries Government Documents Department


Description: The growth and dissolution behavior of oxide film on abraded pure Al has been investigated using cyclic polarization and has been found to be highly dependent on solution chemistry and temperature. The nature of the anions, borate, chromate, phosphate, and sulfate, at pH 3 to 11, and temperatures 0 to 60 C were examined. In near neutral solutions the dissolution behavior was greatly affected by each anion. In borate and chromate solutions at near neutral pH and room temperature, the currents continued to decrease with each subsequent cycle due to oxide thickening. In contrast, a significant rate of oxide dissolution occurred to produce reproducible repetitive curves during subsequent cycles in a phosphate and sulfate. Sulfate also produced a distinctly different mode during high field oxide growth. In increasing acidic (pH < 4) or basic (pH >9) solutions the oxide dissolution rate increased rapidly. The oxide dissolution rate was always enhanced with increasing temperature. At high pH (>9) or elevated temperature (60 C), a current maximum was observed in chromate, due to a diffusion controlled monochromate ion enhanced dissolution reaction at the oxide/solution interface.
Date: September 2, 2001
Creator: LEE,H. & ISAACS,H.S.
Partner: UNT Libraries Government Documents Department

MSO spent salt clean-up recovery process

Description: An effective process has been developed to separate metals, mineral residues, and radionuclides from spent salt, a secondary waste generated by Molten Salt Oxidation (MSO). This process includes salt dissolution, pH adjustment, chemical reduction and/or sulfiding, filtration, ion exchange, and drying. The process uses dithionite to reduce soluble chromate and/or sulfiding agent to suppress solubilities of metal compounds in water. This process is capable of reducing the secondary waste to less than 5% of its original weight. It is a low temperature, aqueous process and has been demonstrated in the laboratory [1].
Date: February 1, 1997
Creator: Adamson, M G; Brummond, W A; Hipple, D L; Hsu, P C; Summers, L J; Von Holtz, E H et al.
Partner: UNT Libraries Government Documents Department

The Role of Biogenic Solids in Thereductive Stabilization of Metal Contaminats: Influences Onmicrobial Versus Chemical Pathways and Reaction Products

Description: In situ stabilization of toxic metals and radionuclides such as chromium and uranium is an attractive approach for remediating many contaminated DOE sites. To enhance in situ remediation, microbiological reductive stabilization of contaminant metals has been, and continues to be, actively explored. It is likely that surface and subsurface microbial activity can alter the redox state of toxic metals and radionuclides so they are rendered immobile. The reaction products and their stability will depend on the specific mechanism by which reduction takes place--the focus of this work. Uranium and Cr exist in more than one oxidation state in the surface- and near-surface environment; different oxidation states of these elements have markedly different properties. The fully oxidized species of Cr and U, both hexavalent forms, have a high solubility in soils and groundwaters, and consequently they tend to be mobile in the environment. Chromate is also subject to biological uptake, a factor that contributes to its toxicity. In contrast, the reduced form of chromium, Cr(III), has a limited hydroxide solubility and forms strong complexes with soil minerals, it is therefore less mobile and has a lower bioavailability than Cr(VI). Similarly, the oxidized forms of U have a greater solubility and hence exhibit greater mobility in soils and subsurface environments than either U(VI) or U(V). They may conclude that oxidized forms of these radionuclides and metals are subject to enhanced migration through surface and subsurface environments. Reductive stabilization is therefore a desirable pathway for these elements.
Date: August 31, 2002
Creator: Fendrof, Scott
Partner: UNT Libraries Government Documents Department

Treatability Study of In Situ Technologies for Remediation of Hexavalent Chromium in Groundwater at the Puchack Well Field Superfund Site, New Jersey

Description: This treatability study was conducted by Pacific Northwest National Laboratory (PNNL), at the request of the U. S. Environmental Protection Agency (EPA) Region 2, to evaluate the feasibility of using in situ treatment technologies for chromate reduction and immobilization at the Puchack Well Field Superfund Site in Pennsauken Township, New Jersey. In addition to in situ reductive treatments, which included the evaluation of both abiotic and biotic reduction of Puchack aquifer sediments, natural attenuation mechanisms were evaluated (i.e., chromate adsorption and reduction). Chromate exhibited typical anionic adsorption behavior, with greater adsorption at lower pH, at lower chromate concentration, and at lower concentrations of other competing anions. In particular, sulfate (at 50 mg/L) suppressed chromate adsorption by up to 50%. Chromate adsorption was not influenced by inorganic colloids.
Date: November 13, 2006
Creator: Vermeul, Vince R.; Szecsody, Jim E.; Truex, Michael J.; Burns, Carolyn A.; Girvin, Donald C.; Phillips, Jerry L. et al.
Partner: UNT Libraries Government Documents Department

An Experimental Study of Micron-Size Zero-Valent Iron Emplacement in Permeable Porous Media Using Polymer-Enhanced Fluids

Description: At the Hanford Site, an extensive In Situ Redox Manipulation (ISRM) permeable reactive barrier was installed to prevent chromate from reaching the Columbia River. However, chromium has been detected in several wells, indicating a premature loss of the reductive capacity in the aquifer. One possible cause for premature chromate breakthrough is associated with the presence of high-permeability zones in the aquifer. In these zones, groundwater moves relatively fast and is able to oxidize iron more rapidly. There is also a possibility that the high-permeability flow paths are deficient in reducing equivalents (e.g. reactive iron), required for barrier performance. One way enhancement of the current barrier reductive capacity can be achieved is by the addition of micron-scale zero-valent iron to the high-permeability zones within the aquifer. The potential emplacement of zero-valent iron (Fe0) into high-permeability Hanford sediments (Ringold Unit E gravels) using shear-thinning fluids containing polymers was investigated in three-dimensional wedge-shaped aquifer models. Polymers were used to create a suspension viscous enough to keep the Fe0 in solution for extended time periods to improve colloid movement into the porous media without causing a permanent detrimental decrease in hydraulic conductivity. Porous media were packed in the wedge-shaped flow cell to create either a heterogeneous layered system with a high-permeability zone in between two low-permeability zones or a high-permeability channel surrounded by low-permeability materials. The injection flow rate, polymer type, polymer concentration, and injected pore volumes were determined based on preliminary short- and long-column experiments.
Date: December 22, 2005
Creator: Oostrom, Mart; Wietsma, Thomas W.; Covert, Matthew A. & Vermeul, Vince R.
Partner: UNT Libraries Government Documents Department

Review of Techniques to Characterize the Distribution of Chromate Contamination in the Vadose Zone of the 100 Areas at the Hanford Site

Description: The purpose of this report is to identify and evaluate the state-of-the-art techniques for characteriza¬tion of chromate contamination in the vadose zone of the 100 Areas at the Hanford Site. The techniques include direct techniques for analysis of chromium in the subsurface as well as indirect techniques to identify contamination through geophysical properties, soil moisture, or co-contaminants. Characteri¬zation for the distribution of chromium concentration in the vadose zone is needed to assess potential sources for chromate contamination plumes in groundwater at the 100-D, 100-K, and 100-B/C Areas.
Date: September 1, 2007
Creator: Dresel, P. Evan; Truex, Michael J. & Sweeney, Mark D.
Partner: UNT Libraries Government Documents Department

Microstructural analyses of Cr(VI) speciation in chromite ore processing Residue (COPR)

Description: The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30percent of its total Cr(VI) (6000 mg/kg) as large crystals(>20 ?m diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50percent of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmilleritewasalso likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment ofHBCOPRis challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ~;;50percent of Cr(VI) in GB COPR.
Date: March 1, 2010
Creator: CHRYSOCHOOU, MARIA; FAKRA, SIRINE C .; Marcus, Matthew A.; Moon, Deok Hyun & Dermatas, Dimitris
Partner: UNT Libraries Government Documents Department

Letter report: Minor component study for low-level radioactive waste glasses

Description: During the waste vitrification process, troublesome minor components in low-level radioactive waste streams could adversely affect either waste vitrification rate or melter life-time. Knowing the solubility limits for these minor components is important to determine pretreatment options for waste streams and glass formulation to prevent or to minimize these problems during the waste vitrification. A joint study between Pacific Northwest Laboratory and Rensselaer Polytechnic Institute has been conducted to determine minor component impacts in low-level nuclear waste glass.
Date: March 1, 1996
Creator: Li, H.
Partner: UNT Libraries Government Documents Department

Electrokinetic demonstration at Sandia National Laboratories: Use of transference numbers for site characterization and process evaluation

Description: Electrokinetic remediation is generally an in situ method using direct current electric potentials to move ionic contaminants and/or water to collection electrodes. The method has been extensively studied for application in saturated clayey soils. Over the past few years, an electrokinetic extraction method specific for sandy, unsaturated soils has been developed and patented by Sandia National Laboratories. A RCRA RD&D permitted demonstration of this technology for the in situ removal of chromate contamination from unsaturated soils in a former chromic acid disposal pit was operated during the summer and fall of 1996. This large scale field test represents the first use of electrokinetics for the removal of heavy metal contamination from unsaturated soils in the United States and is part of the US EPA Superfund Innovative Technology Evaluation (SITE) Program. Guidelines for characterizing a site for electrokinetic remediation are lacking, especially for applications in unsaturated soil. The transference number of an ion is the fraction of the current carried by that ion in an electric field and represents the best measure of contaminant removal efficiency in most electrokinetic remediation processes. In this paper we compare the transference number of chromate initially present in the contaminated unsaturated soil, with the transference number in the electrokinetic process effluent to demonstrate the utility of evaluating this parameter.
Date: March 1, 1997
Creator: Lindgren, E.R. & Mattson, E.D.
Partner: UNT Libraries Government Documents Department