UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

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5.5 Lead Geochemistry and K d Values 5.5.1 Overview: Important Aqueous- and Solid-Phase Parameters Controlling Retardation Lead has 3 known oxidation states, 0, +2, and +4, and the most common redox state encountered in the environment is the divalent form. Total dissolved lead concentrations in natural waters are very low (~10-8 M). Dissolved lead in natural systems may exist in free ionic form and also as hydrolytic and complex species. Speciation calculations show that at pH values exceeding 7, aqueous lead exists mainly as carbonate complexes [PbCO 3 5.25 " (aq), and Pb(CO3) 2 2- ]. Important factors that control aqueous speciation of lead include pH, the types and concentrations of complexing ligands and major cationic constituents, and the magnitude of stability constants for lead-ligand aqueous complexes. A number of studies and calculations show that under oxidizing conditions depending on pH and ligand concentrations, pure-phase lead solids, such as PbCO 3, Pb 3(OH) 2(CO 3) 2, PbSO 4, Pb 5(PO 4) 3(Cl), and Pb 4SO 4(CO 3) 2(OH) 2, may control aqueous lead concentrations. Under reducing conditions, galena (PbS) may regulate the concentrations of dissolved lead. It is also possible that lead concentrations in some natural systems are being controlled by solid solution phases such as barite (Ba (1-x)Pb xSO 4), apatite [Ca (1-x)Pb x(PO 4) 3OH], calcite (Ca (1-x)Pb xCO 3), and iron sulfides (Fe (1-x)Pb xS). Lead is known to adsorb onto soil constituent surfaces such as clay, oxides, hydroxides, oxyhydroxides, and organic matter. In the absence of a distinct lead solid phase, natural lead concentrations would be controlled by adsorption/desorption reactions. Adsorption data show that lead has very strong adsorption affinity for soils as compared to a number of first transition metals. Lead adsorption studies on bulk soils indicate that the adsorption is strongly correlated with pH and the CEC values of soils. Properties that affect CEC of soils, such as organic matter content, clay content, and surface area, have greater affect on lead adsorption than soil pH. 5.5.2 General Geochemistry Lead is an ubiquitous heavy metal and its concentration in uncontaminated soil ranges from 2 to 200 mg/kg and averages 16 mg/kg (Bowen, 1979). Annual anthropogenic lead input into soils has been estimated to be from 0.04 to 4 µg/kg (Ter Haar et al., 1967). In contaminated soils, lead concentrations may be as high as 18 percent by weight (Mattigod and Page, 1983; Ruby et al., 1994). Lead in nature occurs in 4 stable isotopic forms ( 204 Pb, 206 Pb, 207 Pb, and 208 Pb). The isotopes, 206 Pb, 207 Pb, and 208 Pb are the stable end products of the 238 U, 235 U, and 232 Th thorium decay series, respectively (Robbins, 1980). Additionally, heavier isotopes of lead ( 210 Pb, 211 Pb, 212 Pb, and 214 Pb) are known to occur in nature as intermediate products of uranium and thorium decay (Robbins, 1978). The
most common valence state of lead encountered in the environment is the divalent form (Baes and Mesmer, 1976). Extensive studies of lead biogeochemistry have been conducted due to its known adverse effects on organisms (Hammond, 1977). Comprehensive descriptions of environmental chemistry of lead have been published by Boggess and Wixson (1977) and Nriagu (1978). 5.5.3 Aqueous Speciation Lead exhibits typical amphoteric1 metal ion behavior by forming hydrolytic species (Baes and Mesmer, 1976). Formation of monomeric hydrolytic species, such as PbOH + " , Pb(OH) 2(aq) and - Pb(OH) 3 , is well established. Although several polymeric hydrolytic species such as Pb2OH3+ , 3+ 4+ 4+ Pb3(OH) 3 , Pb4(OH) 4 , and Pb6(OH) 8 are known to form at high lead concentrations, calculations show that these types of species are unlikely to form at concentrations of dissolved lead (~10-9 M) typically encountered even in contaminated environments (Rickard and Nriagu, 1978). These investigators also showed that computation models of speciation of dissolved lead in fresh- or seawater predicted that at pH values exceeding about 6.5, the dominant species are leadcarbonate complexes. Lead is known to form aqueous complexes with inorganic ligands such as carbonate, chloride, fluoride, nitrate, and sulfate. To examine the distribution of dissolved lead species in natural waters, M<strong>IN</strong>TEQA2 model calculations were completed using the water composition described in Table 5.1. The total lead concentration was assumed to be 1 µg/l based on the data for natural waters tabulated by Duram et al. (1971) and Hem (1985). A total of 21 aqueous species (uncomplexed Pb 2+ , and 20 complex species, listed in Table 5.8) were used in the computation. Results of the computation are plotted as a species distribution diagram (Figure 5.2). The data show that, under low pH (
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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
Page 7 and 8: TO COMMENT ON THIS GUIDE OR PROVIDE
Page 9 and 10: CONTENTS NOTICE ...................
Page 11 and 12: Concentrations Extractable Iron Con
Page 13 and 14: Appendix A - Acronyms and Abbreviat
Page 15 and 16: Figure E.1. Variation of K d for Cr
Page 17 and 18: Table 5.16. Uranium(VI) aqueous spe
Page 19 and 20: Table H.3. Simple and multiple regr
Page 21 and 22: 1.0 Introduction The objective of t
Page 23 and 24: discussed. The geochemical modeling
Page 25 and 26: 2.0 The K d Model The simplest and
Page 27 and 28: track many more parameters and some
Page 29 and 30: of interest. The retardation factor
Page 31 and 32: (e.g., soil). An increasing body of
Page 33 and 34: complexation constants for the cont
Page 35 and 36: the soil column. Additionally, the
Page 37 and 38: Element Table 5.2. Concentrations o
Page 39 and 40: 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: Table 5.7. Estimated range of Kd va
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
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Page 87 and 88: organic complexes likely predominat
Page 89 and 90: Thorium undergoes hydrolysis in aqu
Page 91 and 92: The distribution of thorium aqueous
Page 93 and 94: from about 10 -8.5 mol/l (0.0007 mg
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 ,
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No attempt was made to statisticall
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Table 5.18. Selected chemical and t
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Another objective of this report is
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6.0 REFERENCES Adriano, D. C. 1992.
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Bensen, D. W. 1960. Review of Soil
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Metals by Geomedia. Variables, Mech
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EPA (U.S. Environmental Protection
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Griffin, R. A., A. K. Au, and R. R.
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+ Keeney-Kennicutt, W. L., and J. W
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Mattigod, S. V., A. L. Page, and I.
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Oscarson, D. W., and H. B. Hume. 19
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Relyea, J. F. and D. A. Brown. 1978
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Schultz, R. K., R. Overstreet, and
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Szalay, A. 1964. “Cation Exchange
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Yariv, S., and H. Cross. 1979. Geoc
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APPENDIX A Acronyms, Abbreviations,
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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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UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

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