Robert A. Fjeld

Bio: Robert A. Fjeld is an academic researcher from Clemson University. The author has contributed to research in topics: Adsorption & Field strength. The author has an hindex of 20, co-authored 52 publications receiving 1183 citations. Previous affiliations of Robert A. Fjeld include Lawrence Livermore National Laboratory.

Pu(V)O2+ adsorption and reduction by synthetic magnetite (Fe3O4).

Abstract: Changes in aqueous- and solid-phase Pu oxidation state were monitored over time in magnetite (Fe3O4) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Oxidation state distribution was determined by leaching of Pu into an aqueous phase followed by an ultrafiltration/solvent extraction technique. The capability of the technique to measure Pu oxidation state distribution was verified using 230Th(IV), 237Np(V), and 233U(VI) as oxidation state analogues. Reduction of Pu(V) was observed at all pH values (pH 3 to 8) and magnetite concentrations (10 to 100 m2 L-1). In the pH range 5 to 8, adsorption was a rate-limiting step, and reduction was mediated by the solid phase; at pH 3 reduction occurred in the aqueous phase. The overall reaction (describing both adsorption and reduction of Pu(V)) was found to be approximately first order with respect to the magnetite concentration and of order −0.34 ± 0.02 with respect to the hydrogen ion concentration. Assuming first order dependence with respect to Pu, the overall...

Pu(V)O2+ adsorption and reduction by synthetic hematite and goethite.

Abstract: Changes in aqueous- and solid-phase plutonium oxidation state were monitored over time in hematite (alpha-Fe2O3) and goethite (alpha-FeOOH) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Solid-phase oxidation state distribution was quantified by leaching plutonium into the aqueous phase and applying an ultrafiltration/solvent extraction technique. The technique was verified using oxidation state analogues of plutonium and sediment-free controls of known Pu oxidation state. Batch kinetic experiments were conducted at hematite and goethite concentrations between 10 and 500 m2 L(-1) in the pH range of 3-8. Surface-mediated reduction of Pu(V) was observed for both minerals at pH values of 4.5 and greater. At pH 3 no adsorption of Pu(V) was observed on either goethite or hematite; consequently, no reduction was observed. For hematite, adsorption of Pu(V) was the rate-limiting step in the adsorption/reduction process. In the pH range of 5-8, the overall removal of Pu(V) from the system (solid and aqueous phases) was found to be approximately second order with respect to hematite concentration and of order -0.39 with respect to the hydrogen ion concentration. The overall reaction rate constant (k(rxn)), including both adsorption and reduction of Pu(V), was 1.75+/-2.05 x 10(-10) (m(-2) L)(-2.08) (mol(-1) L)(-0.39) (s(-1)). In contrast to hematite, Pu(V) adsorption to goethite occurred rapidly relative to reduction. At a given pH,the reduction rate was approximately independent of the goethite concentration, although the hydrogen ion concentration (pH) had only a slight effect on the overall reaction rate. For goethite, the overall reaction rates at pH 5 and pH 8 were 6.0 x 10(-5) and 1.5 x 10(-4) s(-1), respectively. For hematite, the reaction rate increased by 3 orders of magnitude across the same pH range.

Influence of Oxidation States on Plutonium Mobility during Long-Term Transport through an Unsaturated Subsurface Environment

Abstract: Lysimeter and laboratory studies were conducted to identify the controlling chemical processes influencing Pu(IV) mobility through the vadose zone. A 52-L lysimeter containing sediment from the Savannah River Site, South Carolina and solid PuIV(NO3)4 was left exposed to natural wetting and drying cycles for 11 years before the lysimeter sediment was sampled. Pu had traveled 10 cm, with >95% of the Pu remaining within 1.25 cm of the source. Laboratory studies showed that the sediment quickly reduced Pu(V) to Pu(IV) (the pseudo-first-order reduction rate constant, Kobs, was 0.11 h(-1)). Of particular interest was that this same sediment could be induced to release very low concentrations of sorbed Pu under oxidizing conditions, presumably by oxidation of sorbed Pu(IV) to the more mobile Pu(V) species. Transport modeling supported the postulation that Pu oxidation occurred in the lysimeter sediment; the inclusion of an oxidation term in the model produced simulations that capture the Pu depth profile data. By not including the oxidation process in the model, Pu mobility was grossly underestimated by a factor of 3.5. It is concluded that both oxidation and reduction mechanisms can play an important role in Pu transportthrough the vadose zone and should be considered when evaluating disposal of Pu-bearing wastes.

Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff

Abstract: Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

The Effect of Silica and Phosphate on the Transformation of Schoepite to Becquerelite and Other Uranyl Phases

Abstract: The influence of silica and phosphate on schoepite weathering in calcium bearing systems has been examined. The presence of Si (IO M) retarded the transformation of schoepite to becquerelite in 10\" and Ι Ο 3 M Ca systems as compared to silica free systems. The formation of uranyl silicates was not observed. The presence of phosphate (10~ M) in a 10\" M Ca system led to the transformation of schoepite into autunite via several intermediate products, including becquerelite and one or more uranyl phosphates. These results indicate the importance of silica and phosphate in the transformation of secondary uranyl phases in natural systems.

Biogeochemical Redox Processes and their Impact on Contaminant Dynamics

Abstract: Life and element cycling on Earth is directly related to electron transfer (or redox) reactions. An understanding of biogeochemical redox processes is crucial for predicting and protecting environmental health and can provide new opportunities for engineered remediation strategies. Energy can be released and stored by means of redox reactions via the oxidation of labile organic carbon or inorganic compounds (electron donors) by microorganisms coupled to the reduction of electron acceptors including humic substances, iron-bearing minerals, transition metals, metalloids, and actinides. Environmental redox processes play key roles in the formation and dissolution of mineral phases. Redox cycling of naturally occurring trace elements and their host minerals often controls the release or sequestration of inorganic contaminants. Redox processes control the chemical speciation, bioavailability, toxicity, and mobility of many major and trace elements including Fe, Mn, C, P, N, S, Cr, Cu, Co, As, Sb, Se, Hg, Tc, a...

Handbook of Water Analysis

Abstract: Sampling and Data Treatment Methods Sampling Methods in Surface Waters, Munro Mortimer, Jochen F. Muller, and Matthias Liess Methods of Treatment of Data, Riccardo Leardi Radioanalytical Analysis Radioanalytical Methodology for Water Analysis, Jorge S. Alvarado Organoleptical Analysis Organoleptical Methodology, Abdul Moheman, Md. Musawwer Khan, and K. S. Siddiqi Analysis of Biological Parameters Bacteriological Analysis of Water, Paulinus Chigbu and Salina Parveen Marine Toxins Analysis, Luis M. Botana, A. Alfonso, M. R. Vieytes, N. Vilarino, A. M. Botana, C. Louzao, and C. Vale Algal Analysis, Leonardo Rubi Rorig Halogens, N-Compounds, and Phosphates Halogens, Geza Nagy and Livia Nagy Analysis of Sulfur Compounds in Water, Leo M. L. Nollet Determination of Ammonia in Water Samples, Juliana Antunes Galvao, Alexandre Matthiensen, Marilia Oetterer, Y. Moliner-Martinez, R. A. Gonzalez-Fuenzalida, M. Munoz-Ortuno, R. Herraez-Hernandez, J. Verdu-Andres, C. Molins-Legua, and P. Campins Falco Nitrites and Nitrates, Adnan Aydin Phosphates in Aquatic Systems, Alexandre Matthiensen, Juliana Antunes Galvao, and Marilia Oetterer Cyanides, Asbestos, Metals, and Si-Compounds Cyanides, Leo M. L. Nollet Asbestos in Water, James S. Webber Heavy Metals, Major Metals, Trace Elements, Jorge E. Marcovecchio, Sandra E. Botte, Claudia E. Domini, and Ruben H. Freije Determination of Silicon and Silicates, Salah M. Sultan Organic Parameters Main Parameters and Assays Involved with the Organic Pollution of Water, Lorena Vidal, Claudia E. Domini, and Antonio Canals Determination of Organic Nitrogen in the Aquatic Environment, Juliana Antunes Galvao, Alexandre Matthiensen, and Marilia Oetterer Determination of Urea in Aquatic Samples, Juliana Antunes Galvao, Alexandre Matthiensen, and Marilia Oetterer Organic Acids, Mercedes Gallego Fernandez, Evaristo Ballesteros Tribaldo, and Beatriz Jurado Sanchez Determination of Volatile Organic Compounds in Water, Ivan P. Roman Falco and Marta Nogueroles Moya Phenolic and Humic Compounds Determination of Phenolic Compounds in Water, Leo M. L. Nollet Characterization of Humic Matter, Leo M. L. Nollet Residues of Pesticides Determination of Pesticides in Water, Evaristo Ballesteros Tribaldo Analysis of Herbicide and Fungicide Residues in Waters, N. Sridhara Chary, Maria Jose Gomez Ramos, and Amadeo R. Fernandez-Alba Residues of PCBs, PCDDs, PCDFS, and PAHs Analysis of PCBs in Waters, L. Bartolome, O. Zuloaga, and N. Etxebarria PCDDs and PCDFs, Luigi Turrio-Baldassarri, Paola Pettine, and Laura Achene Polynuclear Aromatic Hydrocarbons, Chimezie Anyakora Surfactants and Petroleum Hydrocarbon Analysis Surfactants, Eva Pocurull and Rosa Maria Marce Petroleum Hydrocarbon Analysis, Ivan P. Roman Falco EDCs and Residues of Plastics Endocrine-Disrupting Chemicals, Pharmaceuticals, and Personal Care Products, Dimitra A. Lambropoulou and Eleni Evgenidou Residues of Plastics, Dimitra A. Lambropoulou and Eleni Evgenidou Index

Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.

Abstract: The formation constants of ternary complexes (MUO2(CO3)32- and M2UO2(CO3)30) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (01−5 mmol/L) at pH 81 and a constant ionic strength (01 mol/L NaNO3) under equilibrium with atmospheric CO2 The results indicate that the complexes of MUO2(CO3)32- and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)32- complex under our experimental conditions The cumulative stability constants for the MUO2(CO3)32- complex obtained at I = 0 are as follows: logβ113 = 2611 ± 004, 2718 ± 006, 2686 ± 004, and 2668 ± 004 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively For M2UO2(CO3)30, the value of logβ213 at I = 0 was measured to be 3070 ± 005 and 2975 ± 007 for Ca2+ and Ba2+, respectively Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2

Environmental speciation of actinides.

Abstract: Although minor in abundance in Earth’s crust (U, 2–4 ppm; Th, 10–15 ppm) and in seawater (U, 0.003 ppm; Th, 0.0007 ppm), light actinides (Th, Pa, U, Np, Pu, Am, and Cm) are important environmental contaminants associated with anthropogenic activities such as the mining and milling of uranium ores, generation of nuclear energy, and storage of legacy waste resulting from the manufacturing and testing of nuclear weapons. In this review, we discuss the abundance, production, and environmental sources of naturally occurring and some man-made light actinides. As is the case with other environmental contaminants, the solubility, transport properties, bioavailability, and toxicity of actinides are dependent on their speciation (composition, oxidation state, molecular-level structure, and nature of the phase in which the contaminant element or molecule occurs). We review the aqueous speciation of U, Np, and Pu as a function of pH and Eh, their interaction with common inorganic and organic ligands in natural waters...