Heavy metal adsorption on iron oxide and iron oxide-coated silica ...

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CHAPTER 3OBJECTIVES AND HYPOTHESESAs discussed in the review, sorption of trace elements onto reactive mineral surfaces is animportant process regulating contaminant mobility and bioavailability in natural systems.Iron oxide is an important phase (Fuller et al. 1996; Green-Pedersen et al. 1997) thatexists both discretely and as surface coatings. Although many studies have beenconducted on heavy <strong>metal</strong> <strong>adsorption</strong> to discrete iron oxides and/or iron oxide-coatedmedia, the coating process has not been systematically investigated. Furthermore, inmodeling <strong>adsorption</strong> mechanisms, physically realistic surface species based onspectroscopic analyses are needed (e.g., Hsi and Langmuir, 1985; Gunneriusson et al.1994; Robertson and Leckie, 1997, 1998; Sahai and Sverjensky, 1997).In an effort to model heavy <strong>metal</strong> distribution and transport in soils andsediments, the objectives of this proposed research are as follows:• Synthesize and characterize iron oxide-coated silica, which serves as a modelsystem for soils and sediments. A systematic investigation will be conducted toaddress the factors influencing goethite coating to silica. Also, a variety ofanalyses will be applied to characterize the goethite-coated silica.• Elucidate mechanistic interactions between heavy <strong>metal</strong> ions and the mineralsurfaces. XAS analysis will be performed on heavy <strong>metal</strong> <strong>adsorption</strong> to ironoxide samples under varying conditions relevant to the subsurface in an effort toelucidate sorption mechanisms.• Develop mechanistic models for heavy <strong>metal</strong> <strong>adsorption</strong> to mineral surfacesbased on macroscopic and spectroscopic information. Various types of<strong>adsorption</strong> data (including titration, <strong>adsorption</strong> isotherm, and <strong>adsorption</strong> edge)covering a wide range of experimental conditions will be used to calibrate thesurface complexation model.30
31• Understand the effect of competing ions on heavy <strong>metal</strong> <strong>adsorption</strong> to ironoxides. The ability of models developed in this research to predict heavy <strong>metal</strong>competition on iron oxide will be tested.Specific hypotheses for this research include:First, surface functional groups and reactions are similar between crystalline andamorphous iron oxides (Davis and Leckie, 1978; Charlet and Manceau, 1993; Bargar etal. 1997b; Villalobos et al. 2001; Dixit and Hering, 2003). Therefore, XAS results for<strong>metal</strong> ions sorbed on HFO may be applied to that on goethite. Bargar et al. (1997a, b)reported that iron oxides and aluminum oxides have fundamentally similar crystalchemistry — both form Fe06 or A106 octahedra with very similar average Al-O and Fe-Obond lengths, therefore, they may exhibit comparable surface structures and functionalgroups. Bargar et al. (1997a, b) found that Pb(II) ions sorbed as mononuclear bidentatecomplexes to edges of FeO6 or A1O6 octahedra on goethite, hematite, and aluminumoxide. Also, Pb <strong>adsorption</strong> to HFO (three hours contact time) and 2-line ferrihydrite(Manceau et al. 1992; Scheinost et al. 2001; Trivedi et al. 2003 [for pH > 4.5]) weredominated by similar surface complexes. The first hypothesis will be tested by analyzingPb/HFO sorption samples (4 hours contact time) with XAS and comparing to that ofPb/goethite.Secondly, coupled with XAS data, intrinsic surface complexation constants can beachieved by calibrating the SCM with a variety of <strong>adsorption</strong> data including titration,isotherm, and edge data covering a wide range of conditions. SCMs offer the advantageof representing surface chemical reactions with a set of quasi-thermodynamic constants,which are independent of changes in solution conditions (Hayes, 1987). However, fewstudies have addressed both isotherm and edge data over a large range of conditions withthe same model (e.g. Müller and Sigg, 1992; Waite et al. 1994; Heidmann et al. 2005);
Page 1 and 2: Copyright Warning & RestrictionsThe
Page 3 and 4: ABSTRACTHEAVY METAL ADSORPTION ON I
Page 5 and 6: HEAVY METAL ADSORPTION ON IRON OXID
Page 7 and 8: APPROVAL PAGEHEAVY METAL ADSORPTION
Page 9 and 10: Fan, M.; Boonfueng, T.; Xu, Y.; Axe
Page 11 and 12: ACKNOWLEDGMENTI would like to expre
Page 13 and 14: TABLE OF CONTENTS(Continued)Chapter
Page 15 and 16: TABLE OF CONTENTS(Continued)Chapter
Page 17 and 18: LIST OF TABLES(Continued)TablePageB
Page 19 and 20: LIST OF FIGURES(Continued)FigurePag
Page 21 and 22: LIST OF FIGURES(Continued)FigurePag
Page 23 and 24: CHAPTER 1INTRODUCTIONHeavy<
Page 25 and 26: 3and Sigg, 1992; Gunneriusson et al
Page 27 and 28: CHAPTER 2OXIDES AND THEIR EFFECT ON
Page 29 and 30: 7et al. 1996; Green-Pedersen et al.
Page 31 and 32: 9identify components, distribution,
Page 33 and 34: 11oxides. Because extraction method
Page 35 and 36: 13Table 2.2 Some Coating Work and C
Page 37 and 38: 15increasing the sorbate concentrat
Page 39 and 40: 17mole Cu g-1 goethite (-1-7% of th
Page 41 and 42: 19Overall, macroscopic adso
Page 43 and 44: 21hematite (up to 9.9 limo' Pb ril-
Page 45 and 46: 23concentration in their system was
Page 47 and 48: 25Surface complexation modeling (SC
Page 49 and 50: 27Overall, surface complexation mod
Page 51: 29Spectroscopic techniques, especia
Page 55 and 56: 33existing in almost all soils and
Page 57 and 58: CHAPTER 4EXPERIMENTAL METHODSIn thi
Page 59 and 60: 37included coating temperature (T),
Page 61 and 62: 39generated at 45 kV and 40 mA, sca
Page 63 and 64: 41PZC include electrophoretic mobil
Page 65 and 66: 43Lin-edge, from 8,133 to 8,884 eV
Page 67 and 68: CHAPTER 5CHARACTERIZATION OF IRON O
Page 69 and 70: 47measured by potentiometric titrat
Page 71 and 72: Table 5.2 XRD Data of Alfa Aesar (A
Page 73 and 74: 51Table 5.3 XRF Results for Alfa Ae
Page 75 and 76: Figure 5.4 Particle size distributi
Page 77: 55Figure 5.5 ESEM micrograph for Al
Page 80 and 81: 585.2.5 Surface Charge Distribution
Page 82 and 83: Figure 5.10 Potentiometric titratio
Page 84 and 85: CHAPTER 6SYNTHESIS AND CHARACTERIZA
Page 86 and 87: Figure 6.1 Comparison between Fecon
Page 88 and 89: Figure 6.2 XRD patterns for goethit
Page 90 and 91: 68iron oxide coatings at 60 °C, go
Page 92 and 93: 70substrate diameter of 0.2 mm, an
Page 94 and 95: 72goethite and silica results in on
Page 96 and 97: Figure 6.7 ESEM micrograph (9000x)
Page 98 and 99: 76Furthermore, because discrete goe
Page 100 and 101: 78Table 6.2 Surface Area and Porosi
Page 102 and 103:
Figure 6.10 Surface charge distribu
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Figure 6.11 Ni adsorption</
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84that for pure silica, and the goe
Page 108 and 109:
Table 7.1 Sample Preparation Condit
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Figure 7.2 EXAFS spectra of Pb/HFO
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Figure 7.3 Fourier transform and fi
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Figure 7.4 Fourier transform and fi
Page 116 and 117:
Table 7.3 EXAFS Results of Pb/HFO S
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967.2 Fe XAS of Iron Oxides and Pb/
Page 120 and 121:
Figure 7.7 EXAFS spectra of iron ox
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100and Venturelli, 1999). Overall t
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102(hematite, goethite, akaganeite,
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104adsorption proc
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106of pH, ionic strength, Pb loadin
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Figure 8.1 Ni adsorption</s
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110high metal load
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Figure 8.3 x(k)•k3 spectra and Fo
Page 136 and 137:
Figure 8.4 (k)•k3 spectra of Ni-H
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Figure 8.5 Fourier transforms (magn
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118be fit using either Fe or Ni ato
Page 142 and 143:
1208.3 EXAFS Analysis of FeThe x(k)
Page 144 and 145:
Table 8.4 EXAFS Results of HFO and
Page 146 and 147:
CHAPTER 9SURFACE COMPLEXATION MODEL
Page 148 and 149:
Figure 9.1 Potentiometric titration
Page 150 and 151:
128Table 9.1 Surface Reactions and
Page 152 and 153:
Page 154 and 155:
132Table 9.2 Model Parameters for N
Page 156 and 157:
Page 158 and 159:
1369.3 Zn Adsorption on GoethiteReg
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Figure 9.6 Zn adsorption</s
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140data over a broad range of condi
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142Figure 9.8 Ni adsorption
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144oxide-coated silica. Ni and Zn s
Page 168 and 169:
Page 170 and 171:
Figure 10.2 Zn adsorption</
Page 172 and 173:
Page 174 and 175:
152one for GACS (2.77x10 -6 mole si
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Figure 10.6 Zn adsorption</
Page 178 and 179:
CHAPTER 11CONCLUSIONS AND FUTURE WO
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158surfaces are needed for successf
Page 182 and 183:
Figure A.2 Ni speciation in 1x10 -5
Page 184 and 185:
Figure A.4 Pb speciation in 5x10 -8
Page 186 and 187:
Figure A.6 Zn speciation in 1x10 -5
Page 188 and 189:
166Table B.2 Potentiometric Titrati
Page 190 and 191:
168Table BA Potentiometric Titratio
Page 192 and 193:
170Table C.3 Zn Adsorption Edges on
Page 194 and 195:
APPENDIX DADSORPTION STUDIES ON SIL
Page 196 and 197:
174Table D.5 Zn Adsorption Isotherm
Page 198 and 199:
176Table E.3 Pb CBC Study on 0.3 g
Page 200 and 201:
APPENDIX GINTRAPARTICLE DIFFUSION M
Page 202 and 203:
180DofA = flier ^ 2fA = Exp(-fD * f
Page 204 and 205:
REFERENCES1. Adamson A. W. (1982) P
Page 206 and 207:
18426. Blake R. L., Hessevick R. E.
Page 208 and 209:
18650. Combes J. M., Manceau A. and
Page 210 and 211:
18876. Elzinga E. J. and Sparks D.
Page 212 and 213:
190102. Gupta V. K. (1998) Equilibr
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192126. Joshi A. and Chaudhuri M. (
Page 216 and 217:
194150. Liu C. and Huang P. M. (200
Page 218 and 219:
196175. Muller B. and Sigg L. (1992
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200. Perry R. H. and Green D. W. (1
Page 222 and 223:
200226. Scheinost A. C., Kretzschma
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202252. Swallow C. K., Hume D. N. a
Page 226 and 227:
204278. Villalobos M., Trotz M. A.
Page 228:
304. Zhong Z. Y., Prozorov T., Feln
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