UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

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manufacturing (reviewed by Nriagu and Nieboer, 1988). Discussions of the production, uses, and toxicology of chromium have been presented by Nriagu and Nieboer (1988). Good review articles describing the geochemistry of chromium have been written by Rai et al. (1988), Palmer and Wittbrodt (1991), Richard and Bourg (1991), and Palmer and Puls (1994). A critical review of the thermodynamic properties for chromium metal and its aqueous ions, hydrolysis species, oxides, and hydroxides was published by Ball and Nordstrom (1998). 5.4.3 Aqueous Speciation Chromium exists in the +2, +3, and +6 oxidation states in water, of which only the +3 and +6 states are found in the environment. Chromium(III) exists over a wide range of pH and Eh conditions, whereas Cr(VI) exists only under strongly oxidizing conditions. According to Baes and Mesmer (1976), Cr(III) exists predominantly as Cr3+ below pH 3.5 in a Cr(III)-H2O system. With increasing pH, hydrolysis of Cr3+ yields CrOH2+ + " - , Cr(OH) 2, Cr(OH)3(aq), and Cr(OH)4, 4+ 5+ Cr2(OH) 2 , and Cr3(OH) 4 . At higher chromium concentrations, polynuclear species, such as 4+ 5+ " Cr2(OH) 2 and Cr3(OH) 4 , can form slowly at 25 C (Baes and Mesmer, 1976). Chromium(VI) hydrolyses extensively, forming primarily anionic species. These species are HCrO4 2- 2- CrO4 (chromate), and Cr2O7 (dichromate) (Baes and Mesmer, 1976; Palmer and Wittbrodt, 1991; Richard and Bourg, 1991). Palmer and Puls (1994) presented some Cr(VI) speciation 2- diagrams representative of groundwater conditions. They showed that above pH 6.5, CrO4 - generally dominates. Below pH 6.5, HCrO4 dominates when the total concentration of dissolved 2- Cr(VI) is low (
(tarapacaite) in chromium sludge from a plating facility. They also reported that BaCrO 4 formed a complete solid solution with BaSO 4. They concluded that these solid solutions can be a major impediment to the remediation of chromium-contaminated sites by pump-and-treat technologies. Chromium(VI) is a strong oxidant and is rapidly reduced in the presence of such common electron donors as aqueous Fe(II), ferrous iron minerals, reduced sulfur, microbes, and organic matter (Bartlett and Kimble, 1976; Nakayama et al., 1981). Studies indicate that Cr(VI) can be reduced to Cr(III) by ferrous iron derived from magnetite (Fe 3O 4) and ilmenite (FeTiO 3) (White and Hochella, 1989), hematite (Fe 2O 3) (Eary and Rai, 1989), 1 and pyrite (FeS 2) (Blowes and Ptacek, 1992). The reduction of Cr(VI) by Fe(II) is very rapid. The reaction can go to completion in a matter of minutes (Eary and Rai, 1989). The rate of reduction of Cr(VI) increases with decreasing pH and increasing initial Cr(VI) and reductant concentrations (Palmer and Puls, 1994). Interestingly, this reaction does not appear to be slowed by the presence of dissolved oxygen (Eary and Rai, 1989). When the pH is greater than 4, Cr(III) can precipitate with Fe(III) to form a solid solution with the general composition Cr xFe 1-x(OH) 3 (Sass and Rai, 1987). The solubility of chromium in this solid solution decreases as the mole fraction of Fe(III) increases. The oxidation reaction proceeds much more slowly than the reduction reaction; the former reaction requires months for completion (Eary and Rai, 1987; Palmer and Puls, 1994). Only 2 constituents in the environment are known to oxidize Cr(III): dissolved oxygen and manganese-dioxide minerals [e.g., pyrolusite ($-MnO 2)]. Eary and Rai (1987) reported that the rate of Cr(III) oxidation was much greater in the presence of manganese-dioxide minerals than dissolved oxygen. 5.4.5 Sorption/Desorption The extent to which Cr(III) sorbs to soils is appreciably greater than that of Cr(VI) because the former exists in groundwater as a cation, primarily as Cr 3+ (and its complexed species), whereas 2- - the latter exists as an anion, primarily as CrO4 or HCrO4. Most information on Cr(VI) adsorption comes from studies with pure mineral phases (Davis and Leckie, 1980; Griffin et al., 1977; Leckie et al., 1980). These studies suggest that Cr(VI) adsorbs strongly to gibbsite ("-Al2O3) and amorphous iron oxide [Fe2O3·H2O(am)] at low to medium pH values (pH 2 to 7) and adsorbs weakly to silica (SiO2) at all but very low pH values (Davis and Leckie, 1980; Griffin et al., 1977; Leckie et al., 1980). These results can be explained by considering the isoelectric points (IEP) 2 of these minerals. When the pH of the system is greater than the isoelectric point, the mineral has a net negative charge. When the pH is below the isoelectric point, the mineral has a net positive 1 Eary and Rai (1989) attributed the reduction of Cr(VI) to Cr(III) by hematite (Fe2O 3) as containing having trace quantities of Fe(II). 2 The isoelectric point (IEP) of a mineral is the pH at which it has a net surface charge of zero. More precisely, it is the pH at which the particle is electrokinetically uncharged. 5.20
Page 1 and 2: United States Office of Air and Rad
Page 3 and 4: NOTICE The following two-volume rep
Page 5 and 6: 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 51: 5.3.6.2.1 Limits of K d Values with
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 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 ,
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
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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
Page 145 and 146:
APPENDIX B Definitions
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Clay Content - particle size fracti
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Polynuclear Species - an aqueous sp
Page 151 and 152:
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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Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
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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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Page 191 and 192:
Page 193 and 194:
Cesium K d (ml/g) Clay (wt%) Mica (
Page 195 and 196:
Bruggenwert, M. G. M., and A. Kamph
Page 197 and 198:
Shiao, S. Y., P. Rafferty, R. E. Me
Page 199 and 200:
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.,
Page 222 and 223:
APPENDIX G Partition Coefficients F
Page 224 and 225:
A number of investigators have exam
Page 226 and 227:
pH value, which is typical of the m
Page 228 and 229:
These significant reductions in ads
Page 230 and 231:
This is typically accomplished by t
Page 232 and 233:
The scatterplots are typically disp
Page 234 and 235:
Table G.2. Regression models for pl
Page 236 and 237:
G.4.0 References Barney, G. S. 1984
Page 238 and 239:
Nelson, D. M., R. P. Larson, and W.
Page 240 and 241:
APPENDIX H Partition Coefficients F
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1.6 ml/g for a measurement made on
Page 244 and 245:
Figure H.1. Relation between stront
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Figure H.2. Relation between stront
Page 248 and 249:
H.2.4 Approach Figure H.4. Relation
Page 250 and 251:
A second look-up table (Table H.5)
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Sr K d (ml/g) Clay Content (%) pH C
Page 254 and 255:
Sr K d (ml/g) Clay Content (%) pH C
Page 256 and 257:
Sr K d (ml/g) Clay Conten t (%) pH
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Page 264 and 265:
Konishi, M., K. Yamamoto, T. Yanagi
Page 266 and 267:
APPENDIX I Partition Coefficients F
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descriptive statistics of the thori
Page 270 and 271:
Figure I.1. Linear regression betwe
Page 272 and 273:
The look-up table (Table I.5) for t
Page 274 and 275:
Thorium K d (ml/g) pH Clay (wt.%) C
Page 276 and 277:
Rai, D., A. R. Felmy, D. A. Moore,
Page 278 and 279:
J.1.0 Background Appendix J Partiti
Page 280 and 281:
J.2.2 Uranium K d Studies on Soils
Page 282 and 283:
Washington. The studies included an
Page 284 and 285:
and then decreases with increasing
Page 286 and 287:
Kd (ml/g) 100,000 10,000 1,000 100
Page 288 and 289:
papers. Warnecke et al. (1984) indi
Page 290 and 291:
Anderson et al. (1982) summarize an
Page 292 and 293:
McKinley and Scholtis (1993) compar
Page 294 and 295:
In a similar comparison of sorption
Page 296 and 297:
J.3.1 K d Values as a Function ff p
Page 298 and 299:
discussed, and one would have to ma
Page 300 and 301:
al., 1992; and others). These refer
Page 302 and 303:
· Manskaya et al. (1956) studied a
Page 304 and 305:
concentrations of humic acid, there
Page 306 and 307:
pH U Kd (ml/g) Clay Cont. (wt.%) CE
Page 308 and 309:
Page 310 and 311:
Page 312 and 313:
Page 314 and 315:
Page 316 and 317:
Page 318 and 319:
Page 320 and 321:
Page 322 and 323:
Page 324 and 325:
Page 326 and 327:
J.6.0 References Ames, L. L., J. E.
Page 328 and 329:
Erikson, R. L., C. J. Hostetler, R.
Page 330 and 331:
R. C. Ewing. Materials Research Soc
Page 332 and 333:
Sheppard, M. I., and D. H. Thibault
Page 334:
Yamamoto, T., E. Yunoki, M. Yamakaw
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