Rai Enviro Chemical LLC

Yachats, OR, United States

Rai Enviro Chemical LLC

Yachats, OR, United States
SEARCH FILTERS
Time filter
Source Type

Rai D.,Rai Enviro Chemical LLC | Kitamura A.,Japan Atomic Energy Agency
Journal of Chemical Thermodynamics | Year: 2017

Isosaccharinic acid is a cellulose degradation product that can form in low-level nuclear waste repositories and is known to form strong complexes with many elements, including actinides, disposed of in these repositories. We 1) reviewed the available data for deprotonation and lactonisation constants of isosaccharinic acid, and the isosaccharinate binding constants for Ca, Fe(III), Th, U(IV), U(VI), Np(IV), Pu(IV), and Am(III), 2) summarized complexation constant values for predicting actinide behavior in geologic repositories in the presence of isosaccharinate, and 3) outlined additional studies to acquire reliable thermodynamic data where the available data are inadequate. © 2017 Elsevier Ltd.


Rai D.,Rai Enviro Chemical LLC | Felmy A.R.,Pacific Northwest National Laboratory | Moore D.A.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency | And 3 more authors.
Radiochimica Acta | Year: 2014

The solubility of Ba(SeO4, SO4 ) precipitateswas determined as a function of the BaSeO4 mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/ steady state conditions in this system are reached in ≤ 65 days. Pitzer's ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with log 10 [Ba] ranging from -3.6 to -5.9 mol kg -1, log10 [SeO4] rangingfrom -3.6 to -5.2 mol kg-1, andlog 10[SO4] ranging from -4.0 to -5.3 mol kg-1 can be explained with the formation of an ideal BaSeO 4 solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO4 (s) (log10 K°sp = -9.5instead of-10.05 for barite) that controls the sulfate concentrations. In these experiments the BaSO4 component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO4 solid solution phase and less-crystalline BaSO 4 (s) phase are in equilibrium with each other in the entire range of BaSeO4 mole fractions investigated in this study.


Rai D.,Rai Enviro Chemical LLC | Kitamura A.,Japan Atomic Energy Agency | Rosso K.M.,Pacific Northwest National Laboratory | Sasaki T.,Kyoto University | Kobayashi T.,Kyoto University
Radiochimica Acta | Year: 2016

Solubility studies were conducted with HfO2(cr) solid as a function HCl and ionic strength ranging from 2.0 to 0.004 mol kg-1. These studies involved 1) using two different amounts of the solid phase, 2) acid washing the bulk solid phase, 3) preheating the solid phase to 1400 °C, and 4) heating amorphous HfO2(am) suspensions to 90 °C to ascertain whether the HfO2(am) converts to HfO2(cr) and to determine the solubility from the oversaturation direction. Based on the results of these treatments it is concluded that the HfO2(cr) contains a small fraction of less crystalline, but not amorphous, material [HfO2(lcr)] and this, rather than the HfO2(cr), is the solubility-controlling phase in the range of experimental variables investigated in this study. The solubility data are interpreted using both the Pitzer and SIT models and they provide log10 K0 values of -(59.75±0.35)and -(59.48±0.41), respectively, for the solubility product of HfO2(lcr)[HfO2(lcr) + 2H2O ⇌ Hf4+ + 4OH-]. The log10 of the solubility product of HfO2(cr)is estimated to be < -63. The observation of a small fraction of less crystalline higher solubility material is consistent with the general picture that mineral surfaces are often structurally and/or compositionally imperfect leading to a higher solubility than the bulk crystalline solid. This study stresses the urgent need, during interpretation of solubility data, of taking precautions to make certain that the observed solubility behavior for sparingly-soluble solids is assigned to the proper solid phase. © 2016 Walter de Gruyter GmbH, Berlin/Boston.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Kitamura A.,Japan Atomic Energy Agency | Yoshikawa H.,Japan Atomic Energy Agency | Felmy A.R.,Pacific Northwest National Laboratory
Journal of Solution Chemistry | Year: 2013

The major objective of this study, based on critical review and experimental studies, was to develop a reliable thermodynamic model for the Nd-F system at 25 C. The SIT model was used to convert concentration constants reported in the literature to constants at zero ionic strengths for cross comparison and selection of reliable values. The critically evaluated thermodynamic constants for the formation of NdF2+ and NdF 2 + were then used to interpret the extensive NdF 3(cr) solubility data in NaF and NH4F solutions, ranging in concentrations from extremely low values to as high as 1.0 mol·kg -1, equilibrated for different periods ranging up to as long as 72 days. These efforts have resulted in 10 βn 0 for the reaction [Nd3+ + nF- ⇌ NdF n 3-n ] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n values of 1-3, respectively. The 10 K sp 0 for the solubility of NdF3(cr) (NdF3(cr) ⇌ Nd3+ + 3F-) was determined to be (-20.49 ± 0.37). Because (1) Nd is an excellent analog for trivalent actinides - An(III) (i.e.; Pu(III), Am(III), and Cm(III)), and (2) the available data for the An(III)-F system, especially the solubility products of AnF3(cr), are of extremely poor quality, the critical literature review in combination with the experimental Nd-F system data have been used to assign thermodynamic constants for the An(III)-F reactions until good quality specific data for them becomes available. © 2013 Springer Science+Business Media New York.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Schaef H.T.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency
Journal of Solution Chemistry | Year: 2011

The solubility of SnO2(cassiterite) was studied at 23 ± 2 °C as a function of time (7 to 49 days) and pH (0 to 14.5). Steady state concentrations were reached in <7 days. The data were interpreted using the SIT model. The data show that SnO2(cassiterite) is the stable phase at pH values of <∼11.7. These extensive data provided a log 10K0 value of -64.39 ± 0.30 for the reaction (SnO2(cassiterite) +2H2O ⇄ Sn4+ + 4OH-) and values of 1.86 ± 0.30, ≤-0.62, -9.20 ± 0.34, and -20.28 ± 0.34 for the reaction (Sn4+ + nH2O ⇄ Sn(OH)4-n n + nH+) with values of "n" equal to 1, 4, 5, and 6 respectively. These thermodynamic hydrolysis constants were used to reinterpret the extensive literature data for SnO2(am) solubility, which provided a log10K0 value of -61.80 ± 0.29 for the reaction (SnO2(am) + 2H2O ⇄ Sn4+ + 4OH-). SnO2(cassiterite) is unstable under highly alkaline conditions (NaOH concentrations >0.003 mol·dm-3) and transforms to a double salt of SnO2 and NaOH. Although additional well-focused studies will be required for confirmation, the experimental data in the highly alkaline region (0.003 to 3.5 mol · dm-3 NaOH) can be well described with log10K0 of -5.29 ± 0.35 for the reaction Na2Sn(OH)6(s) ⇄Na2Sn(OH)6(aq). © Springer Science+Business Media, LLC 2011.


Felmy A.R.,Pacific Northwest National Laboratory | Moore D.A.,Pacific Northwest National Laboratory | Rosso K.M.,Pacific Northwest National Laboratory | Qafoku O.,Pacific Northwest National Laboratory | And 3 more authors.
Environmental Science and Technology | Year: 2011

Heterogeneous reduction of actinides in higher, more soluble oxidation states to lower, more insoluble oxidation states by reductants such as Fe(II) has been the subject of intensive study for more than two decades. However, Fe(II)-induced reduction of sparingly soluble Pu(IV) to the more soluble lower oxidation state Pu(III) has been much less studied, even though such reactions can potentially increase the mobility of Pu in the subsurface. Thermodynamic calculations are presented that show how differences in the free energy of various possible solid-phase Fe(III) reaction products can greatly influence aqueous Pu(III) concentrations resulting from reduction of PuO2(am) by Fe(II). We present the first experimental evidence that reduction of PuO 2(am) to Pu(III) by Fe(II) was enhanced when the Fe(III) mineral goethite was spiked into the reaction. The effect of goethite on reduction of Pu(IV) was demonstrated by measuring the time dependence of total aqueous Pu concentration, its oxidation state, and system pe/pH. We also re-evaluated established protocols for determining Pu(III) {[Pu(III) + Pu(IV)] - Pu(IV)} by using thenoyltrifluoroacetone (TTA) in toluene extractions; the study showed that it is important to eliminate dissolved oxygen from the TTA solutions for accurate determinations. More broadly, this study highlights the importance of the Fe(III) reaction product in actinide reduction rate and extent by Fe(II). © 2011 American Chemical Society.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Schaef H.T.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency
Journal of Solution Chemistry | Year: 2010

Prior to this study no data for the solubility product of BiPO 4(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO4(cr) was studied at 23 ± 2 °C from both the over- and under-saturation directions as functions of a wide range in time (6-309 days), pH values (0-15), and phosphate concentrations (reaching as high as 1.0 mol.kg-1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO4(cr) and an upper limit value for the formation of BiPO4(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi-Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi-Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol.kg-1. The study showed that BiPO4(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)3(am) is the solubility controlling phase. Reliable values for the Bi(OH)3(am) solubility reactions involving Bi(OH) 3(aq) and Bi(OH)- 4 and the formation constants of these aqueous species are also reported. © Springer Science+Business Media, LLC 2010.


Rai D.,Rai Enviro Chemical LLC | Moore D.A.,Pacific Northwest National Laboratory | Felmy A.R.,Pacific Northwest National Laboratory | Rosso K.M.,Pacific Northwest National Laboratory | Bolton Jr. H.,Pacific Northwest National Laboratory
Journal of Solution Chemistry | Year: 2010

To determine the solubility product of PuPO4(cr, hyd.) and the complexation constants of Pu(III) with phosphate and EDTA, the solubility of PuPO4(cr, hyd.) was investigated as a function of: (1) time and pH (varied from 1.0 to 12.0), and at a fixed 0.00032 mol·L-1 phosphate concentration; (2) NaH2PO4 concentrations varying from 0.0001 mol·L-1 to 1.0 mol·L-1 and at a fixed pH of 2.5; (3) time and pH (varied from 1.3 to 13.0) at fixed concentrations of 0.00032 mol·L-1 phosphate and 0.0004 mol·L-1 or 0.002 mol·L-1 Na 2H2EDTA; and (4) Na2H2EDTA concentrations varying from 0.00005 mol·L-1 to 0.0256 mol·L-1 at a fixed 0.00032 mol·L-1 phosphate concentration and at pH values of approximately 3.5, 10.6, and 12.6. A combination of solvent extraction and spectrophotometric techniques confirmed that the use of hydroquinone and Na2S2O4 helped maintain the Pu as Pu(III). The solubility data were interpreted using the Pitzer and SIT models, and both provided similar values for the solubility product of PuPO4(cr, hyd.) and for the formation constant of PuEDTA-. The log10 of the solubility product of PuPO 4(cr, hyd.) [PuPO4(cr, hyd.) ⇆ Pu3+ + PO3- 4] was determined to be -(24.42 ± 0.38). Pitzer modeling showed that phosphate interactions with Pu3+ were extremely weak and did not require any phosphate complexes [e.g., PuPO4(aq), PuH2PO2+ 4, Pu(H2PO4) + 2, Pu(H2PO4)3(aq), and Pu(H2PO4)- 4] as proposed in existing literature, to explain the experimental solubility data. SIT modeling, however, required the inclusion of PuH2PO2+ 4 to explain the data in high NaH2PO4 concentrations; this illustrates the differences one can expect when using these two different chemical models to interpret the data. Of the Pu(III)-EDTA species, only PuEDTA- was needed to interpret the experimental data over a large range of pH values (1.3-12.9) and EDTA concentrations (0.00005-0.256 mol·L-1). Calculations based on density functional theory support the existence of PuEDTA- (with prospective stoichiometry as Pu(OH2) 3EDTA-) as the chemically and structurally stable species. The log10 value of the complexation constant for the formation of PuEDTA- [Pu3+ + EDTA4- ⇆ PuEDTA -] determined in this study is -20.15± 0.59. The data also showed that PuHEDTA(aq), Pu(EDTA)5- 4, Pu(EDTA)(HEDTA) 4-, Pu(EDTA)(H2EDTA)3-, and Pu(EDTA)(H 3EDTA)2-, although reported in the literature, have no region of dominance in the experimental range of variables investigated in this study. © Springer Science+Business Media, LLC 2010.


Rai D.,Rai Enviro Chemical LLC | Kitamura A.,Japan Atomic Energy Agency
Journal of Nuclear Science and Technology | Year: 2015

A great deal of disagreement exists in the literature regarding the intrinsic deprotonation and lactonisation constants of α-D-isosaccharinic acid (ISA). Based on a combination of nuclear magnetic resonance and interpretations using the specific ion interaction theory (SIT) of extensive experimental Ca(ISA)2(cr) solubility data involving α-D-isosaccharinic acid, the reliable value of log10 K° for [HISA(aq) (Figure presented.) ISA− + H+] is −3.27 ± 0.01 and for [HISA(aq) (Figure presented.) ISL(α-D-isosaccharinate-1,4-lactone)(aq) + H2O] is 0.49 ± 0.09. These data also provide log10 K° of −3.76 ± 0.09 for the reaction [ISL(aq) + H2O (Figure presented.) ISA− + H+] and −3.88 ± 0.09 for the composite reaction [HISA(aq) + ISL(aq) (Figure presented.) ISA− + H+]. Reinterpretation of extensive Ca(ISA)2(cr) solubility data using the SIT activity coefficient model provides log10 K° of −6.40 ± 0.09 for [Ca(ISA)2(cr) (Figure presented.) Ca2+ + 2(ISA)−] and of 1.70 ± 0.09 for [Ca2+ + ISA− (Figure presented.) CaISA+] which are consistent with all of the available values. © 2015 Atomic Energy Society of Japan. All rights reserved.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Kitamura A.,Japan Atomic Energy Agency
Journal of Solution Chemistry | Year: 2012

Only a limited number of experimental investigations have been conducted to determine hydrolysis constants of Pd(II) or the solubility product of Pd(II) hydroxide, and the reported values differ considerably from each other. No comprehensive reliable thermodynamic model is available for the Pd-OH and Pd-Cl systems. To obtain such a model, thermodynamic data for palladium compounds and complexes with chloride and hydroxide were critically evaluated using the SIT model. These evaluations, in most cases, involved reinterpretation of the original data reported in various publications to produce values of equilibrium constants for various reactions that are consistent with all of available reliable literature data. Final recommended values for solubility products and complexes of Pd(II) with hydroxide and chloride, along with the values for SIT ion interaction parameters, are tabulated. © 2012 Springer Science+Business Media New York.

Loading Rai Enviro Chemical LLC collaborators
Loading Rai Enviro Chemical LLC collaborators