UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

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Percent Distribution 100 80 60 40 20 0 + ThF3 2+ ThF2 o ThF4 (aq) ThF 3+ 2- Th(HPO4) 3 o ThHPO4 (aq) 3 4 5 6 7 8 9 10 5.59 pH - Th(OH) 3CO3 Figure 5.5. Calculated distribution of thorium aqueous species as a function of pH for the water composition in Table 5.1. [The species distribution is based on a concentration of 1 µg/l total dissolved thorium and thermodynamic data from Langmuir and Herman (1980) and Östhols et al. (1994, for - 6- Th(OH) 3CO3 and Th(CO3) 5 ). The thermodynamic database used for these speciation calculations did not include the constants for thorium humic acid complexes.] The maximum concentration of dissolved thorium that may occur in a low-temperature aqueous system can be predicted with the solubility of hydrous thorium oxide. This solid is known to precipitate in laboratory experiments conducted at low temperature, oversaturated conditions over several weeks. If this solid precipitates in a natural environment, it will likely alter with time to a more crystalline solid that has a lower solubility. The solubility of hydrous thorium oxide has been studied experimentally by Rai and coworkers (Felmy et al., 1991; Rai et al., 1995; Ryan and Rai, 1987). In 0.1 M NaClO 4 solutions, the measured solubility of hydrous thorium oxide ranges
from about 10 -8.5 mol/l (0.0007 mg/l) to less than 10 -9 mol/l (0.0002 mg/l) in the pH range from 5 to 10 (Ryan and Rai, 1987). The concentration of dissolved thorium increases to approximately 10 -2.6 mol/l (600 mg/l) as pH decreases from 5.0 to 3.2. Felmy et al. (1991) determined that the solubility of hydrous thorium oxide increases with increasing ionic strength. At pH values above 7 in 3.0 M NaCl solutions, the solubility of hydrous thorium oxide increased by approximately 2 to 3 orders of magnitude compared to that determined in 0.1 M NaClO 4 solutions. Moreover, the pH at which hydrous thorium oxide exhibits rapid increases in solubility with decreasing pH changes from pH 5 in 0.1 M NaClO 4 to approximately pH 7 in 3.0 M NaCl. In studies conducted at high hydroxide and carbonate concentrations, Rai et al. (1995) determined that the solubility of hydrous thorium oxide increases dramatically in high carbonate solutions and decreases with increases in hydroxide concentration at fixed carbonate concentrations. This supports the assertion that soluble thorium-carbonate complexes likely dominate the aqueous speciation of thorium dissolved in natural waters having basic pH values. 5.9.5 Adsorption/Desorption Thorium concentrations in surface- and groundwaters may also be controlled to very low levels (# few µg/l) by adsorption processes. Humic substances are considered particularly important in the adsorption of thorium (Gascoyne, 1982). Thibault et al. (1990) conducted a critical compilation and review of published K d data by soil type needed to model radionuclide migration from a nuclear waste geological disposal vault to the biosphere. Thibault et al. list K d values for thorium that range from 207 to 13,000,000 ml/g. The range of thorium K d values listed for organic soil was 1,579 to 1.3 x 10 7 ml/g. Based on our experience, the very high K d values reported for thorium should be viewed with caution. The studies resulting in these values should be examined to determine if the initial concentrations of thorium used for these K d measurements were too great and precipitation of a thorium solid (e.g., hydrous thorium oxide) occurred during the equilibration of the thorium-spiked soil/water mixtures. As noted in the letter report for Subtask 1B, precipitation of solids containing the contaminant of interest results in K d values that are erroneously too high. The adsorption of thorium on pure metal-oxide phases has also been studied experimentally in conjunction with surface complexation models. 1 Östhols (1995) studied the adsorption of thorium on amorphous colloidal particles of silica (SiO 2). Their results indicate that the adsorption of thorium on silica will only be important in the pH range from 3 to 6. In neutral and alkaline pH values, silica surface sites are not expected to be efficient adsorbents for thorium. Iron and manganese oxides are expected to be more important adsorbents of thorium than silica. Hunter et al. (1988) studied the adsorption of thorium on goethite ("-FeOOH) and nsutite ((-MnO 2) in marine electrolyte solutions. Their experiments indicate that adsorption of thorium 1 Surface complexation models are discussed in Volume I of this report. 5.60
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United States Office of Air and Rad
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NOTICE The following two-volume rep
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This publication is the result of a
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TO COMMENT ON THIS GUIDE OR PROVIDE
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CONTENTS NOTICE ...................
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Concentrations Extractable Iron Con
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Appendix A - Acronyms and Abbreviat
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Figure E.1. Variation of K d for Cr
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Table 5.16. Uranium(VI) aqueous spe
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Table H.3. Simple and multiple regr
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1.0 Introduction The objective of t
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discussed. The geochemical modeling
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2.0 The K d Model The simplest and
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track many more parameters and some
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of interest. The retardation factor
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(e.g., soil). An increasing body of
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complexation constants for the cont
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the soil column. Additionally, the
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Element Table 5.2. Concentrations o
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5.2.3 Aqueous Speciation Cadmium fo
Page 41 and 42: 5.2.4 Dissolution/Precipitation/Cop
Page 43 and 44: cadmium, indicating that cadmium an
Page 45 and 46: 5.2.6.2.2 Limits of K d Values with
Page 49 and 50: organic chelates (e.g., EDTA). Init
Page 53 and 54: (tarapacaite) in chromium sludge fr
Page 55 and 56: K d). Soils containing Mn oxides ox
Page 57 and 58: Table 5.7. Estimated range of Kd va
Page 59 and 60: most common valence state of lead e
Page 61 and 62: Table 5.8. Lead aqueous species inc
Page 63 and 64: Under reducing conditions, galena (
Page 65 and 66: C Adsorption of lead increases with
Page 69 and 70: (Choppin, 1983). Plutonium hydrolyt
Page 71 and 72: Table 5.10. Plutonium aqueous speci
Page 73 and 74: 5.6.5 Sorption/Desorption Plutonium
Page 75 and 76: content in the system. Additionally
Page 81 and 82: much greater concentrations. Thus,
Page 83 and 84: exchanged which they attributed to
Page 85 and 86: up tables was based in part on thei
Page 87 and 88: organic complexes likely predominat
Page 89 and 90: Thorium undergoes hydrolysis in aqu
Page 91: The distribution of thorium aqueous
Page 95 and 96: Based on the assumptions and limita
Page 97 and 98: 5.10 Tritium Geochemistry And K d V
Page 99 and 100: uranium. Uranium(VI) species domina
Page 101 and 102: gives 0.1 to 10 µg/l as the range
Page 103 and 104: mineral in reducing ore zones (Fron
Page 105 and 106: Percent Distribution 100 80 60 40 2
Page 107 and 108: 5.11.6 Partition Coefficient, K d ,
Page 109 and 110: No attempt was made to statisticall
Page 111 and 112: Table 5.18. Selected chemical and t
Page 113 and 114: Another objective of this report is
Page 115 and 116: 6.0 REFERENCES Adriano, D. C. 1992.
Page 117 and 118: Bensen, D. W. 1960. Review of Soil
Page 119 and 120: Metals by Geomedia. Variables, Mech
Page 121 and 122: EPA (U.S. Environmental Protection
Page 123 and 124: Griffin, R. A., A. K. Au, and R. R.
Page 125 and 126: + Keeney-Kennicutt, W. L., and J. W
Page 127 and 128: Mattigod, S. V., A. L. Page, and I.
Page 129 and 130: Oscarson, D. W., and H. B. Hume. 19
Page 131 and 132: Relyea, J. F. and D. A. Brown. 1978
Page 133 and 134: Schultz, R. K., R. Overstreet, and
Page 135 and 136: Szalay, A. 1964. “Cation Exchange
Page 137 and 138: Yariv, S., and H. Cross. 1979. Geoc
Page 139 and 140: APPENDIX A Acronyms, Abbreviations,
Page 141 and 142: PC Personal computers operating und
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A.3.0 List of Symbols and Notation
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APPENDIX B Definitions
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Clay Content - particle size fracti
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Polynuclear Species - an aqueous sp
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C.1.0 Background Appendix C Partiti
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Cadmium K d Table C.2. Correlation
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C.3.0 Data Set for Soils Table C.4
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Cd K d (ml/g) Clay Cont. (wt%) pH C
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D.1.0 Background Appendix D Partiti
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A second data set (see Section D.4)
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Table D.3. Correlation coefficients
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By transposing the CEC and cesium K
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Table D.6. Cesium K d values measur
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eported in Table D.8 are described
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a 1 b 1 Range of Solution Cs Concen
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Figure D.4. Generalized cesium Freu
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Table D.10. Estimated range of K d
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D.3.0 K d Data Set for Soils and Pu
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Cesium Kd (ml/g) Clay (wt.% ) Mica
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Cesium K d (ml/g) Clay (wt%) Mica (
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Bruggenwert, M. G. M., and A. Kamph
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Shiao, S. Y., P. Rafferty, R. E. Me
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E.1.0 Background Appendix E Partiti
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chromium-reductive soils may stem f
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E.2.0 Approach The approach used to
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Table E.3. Estimated range of K d v
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Table E.4. Data from Rai et al. (19
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E.4.0 References Davis, J. A. and J
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APPENDIX F Partition Coefficients F
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(CEC) of the soils. Such an anomaly
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Table F.1. Summary of K d values fo
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Figure F.2. Variation of K d as a f
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F.4.0 References Abd-Elfattah, A.,
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APPENDIX G Partition Coefficients F
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A number of investigators have exam
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pH value, which is typical of the m
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These significant reductions in ads
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This is typically accomplished by t
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The scatterplots are typically disp
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Table G.2. Regression models for pl
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G.4.0 References Barney, G. S. 1984
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Nelson, D. M., R. P. Larson, and W.
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APPENDIX H Partition Coefficients F
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1.6 ml/g for a measurement made on
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Figure H.1. Relation between stront
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Figure H.2. Relation between stront
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H.2.4 Approach Figure H.4. Relation
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A second look-up table (Table H.5)
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Sr K d (ml/g) Clay Content (%) pH C
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Sr K d (ml/g) Clay Content (%) pH C
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Sr K d (ml/g) Clay Conten t (%) pH
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Konishi, M., K. Yamamoto, T. Yanagi
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APPENDIX I Partition Coefficients F
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descriptive statistics of the thori
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Figure I.1. Linear regression betwe
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The look-up table (Table I.5) for t
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Thorium K d (ml/g) pH Clay (wt.%) C
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Rai, D., A. R. Felmy, D. A. Moore,
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J.1.0 Background Appendix J Partiti
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J.2.2 Uranium K d Studies on Soils
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Washington. The studies included an
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and then decreases with increasing
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Kd (ml/g) 100,000 10,000 1,000 100
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papers. Warnecke et al. (1984) indi
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Anderson et al. (1982) summarize an
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McKinley and Scholtis (1993) compar
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In a similar comparison of sorption
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J.3.1 K d Values as a Function ff p
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discussed, and one would have to ma
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al., 1992; and others). These refer
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· Manskaya et al. (1956) studied a
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concentrations of humic acid, there
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pH U Kd (ml/g) Clay Cont. (wt.%) CE
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J.6.0 References Ames, L. L., J. E.
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Erikson, R. L., C. J. Hostetler, R.
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R. C. Ewing. Materials Research Soc
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Sheppard, M. I., and D. H. Thibault
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Yamamoto, T., E. Yunoki, M. Yamakaw
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