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

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106of pH, ionic strength, Pb loading, and reaction time. Pb <strong>adsorption</strong> on HFO is a two-stepprocess — a fast initial uptake followed by a slow surface diffusion step. The <strong>adsorption</strong>mechanism does not appear to change with reaction time (as long as 21 months)suggesting that internal sites on micropore walls are no different than the external ones.Intraparticle diffusion modeling based on this observation described the Pb/HFO longtermsorption data reasonably well. The surface diffusivity obtained from the modelingverifies a slow and rate-limiting diffusion process, which may occur for decadesaccounting for approximately 46% of total Pb uptake.XAS results suggest Pb(II) forms similar surface complexes on a series of ironoxides exhibiting comparable surface structures and functional groups — amorphous HFO(this study and Manceau et al. 1992 for difference contact time), 2-line ferrihydrite(Scheinost et al. 2001; Trivedi et al. 2003 [for pH > 4.5]), goethite, and hematite (Bargaret al. 1997b). It is possible that sorption mechanisms of other heavy <strong>metal</strong>s also arecontrolled by the sorbent surface structures and similar surface complexes will form onHFO and goethite. Therefore, in the next chapter, XAS analysis on Ni/HFO sorptionsamples is presented and is followed by Ni/goethite modeling.
CHAPTER 8NI(II) COMPLEXATION TO AMORPHOUS HYDROUS FERRIC OXIDE:AN X-RAY ABSORPTION SPECTROSCOPY STUDYIn this chapter, Ni/HFO sorption samples are analyzed with XAS at the Ni K-edge and FeK-edge. Macroscopic <strong>adsorption</strong> studies are performed first to prepare XAS samples.8.1 Ni/HFO Adsorption StudiesNi <strong>adsorption</strong> studies were conducted to investigate the effect of ionic strength, pH, andNi concentration. The characteristic sigmoid shape of the edges (Figure 8.1) shows 50%<strong>adsorption</strong> at pH 6. Consistent with others (Green-Pedersen et al. 1997; Hayes andLeckie, 1987; Dzombak and Morel, 1990), ionic strength did not affect <strong>adsorption</strong>potentially suggesting that Ni ions form inner-sphere complexes on the HFO surface.From isotherms (Figure 8.2), the sorbed concentration is linearly related to the bulkaqueous one over a large concentration range (10 -11 10 -3 M), potentially indicative of oneaverage type of <strong>adsorption</strong> site. This linear relationship was also observed in a studyconducted by Trivedi and Axe (2001b). The molecular level EXAFS analysis furtheraddresses <strong>adsorption</strong> mechanisms.8.2 EXAFS Analysis of NiThe measurement of EXAFS spectra at energies just greater than the Fe K-edge (i.e. Co,Ni, and Cu) is difficult because the fluorescence signal from trace elements is typicallytwo orders of magnitude less intense (1:100) than the Fe fluorescence from the matrix(Manceau et al. 2000). To overcome this difficulty, either a high flux X-ray beam or107
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Copyright Warning & RestrictionsThe
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ABSTRACTHEAVY METAL ADSORPTION ON I
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HEAVY METAL ADSORPTION ON IRON OXID
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APPROVAL PAGEHEAVY METAL ADSORPTION
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Fan, M.; Boonfueng, T.; Xu, Y.; Axe
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ACKNOWLEDGMENTI would like to expre
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TABLE OF CONTENTS(Continued)Chapter
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TABLE OF CONTENTS(Continued)Chapter
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LIST OF TABLES(Continued)TablePageB
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LIST OF FIGURES(Continued)FigurePag
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LIST OF FIGURES(Continued)FigurePag
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CHAPTER 1INTRODUCTIONHeavy<
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3and Sigg, 1992; Gunneriusson et al
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CHAPTER 2OXIDES AND THEIR EFFECT ON
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7et al. 1996; Green-Pedersen et al.
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9identify components, distribution,
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11oxides. Because extraction method
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13Table 2.2 Some Coating Work and C
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15increasing the sorbate concentrat
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17mole Cu g-1 goethite (-1-7% of th
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19Overall, macroscopic adso
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21hematite (up to 9.9 limo' Pb ril-
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23concentration in their system was
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25Surface complexation modeling (SC
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27Overall, surface complexation mod
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29Spectroscopic techniques, especia
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31• Understand the effect of comp
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33existing in almost all soils and
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CHAPTER 4EXPERIMENTAL METHODSIn thi
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37included coating temperature (T),
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39generated at 45 kV and 40 mA, sca
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41PZC include electrophoretic mobil
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43Lin-edge, from 8,133 to 8,884 eV
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CHAPTER 5CHARACTERIZATION OF IRON O
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47measured by potentiometric titrat
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Table 5.2 XRD Data of Alfa Aesar (A
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51Table 5.3 XRF Results for Alfa Ae
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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
Page 104 and 105: Figure 6.11 Ni adsorption</
Page 106 and 107: 84that for pure silica, and the goe
Page 108 and 109: Table 7.1 Sample Preparation Condit
Page 110 and 111: Figure 7.2 EXAFS spectra of Pb/HFO
Page 112 and 113: Figure 7.3 Fourier transform and fi
Page 114 and 115: Figure 7.4 Fourier transform and fi
Page 116 and 117: Table 7.3 EXAFS Results of Pb/HFO S
Page 118 and 119: 967.2 Fe XAS of Iron Oxides and Pb/
Page 120 and 121: Figure 7.7 EXAFS spectra of iron ox
Page 122 and 123: 100and Venturelli, 1999). Overall t
Page 124 and 125: 102(hematite, goethite, akaganeite,
Page 126 and 127: 104adsorption proc
Page 130 and 131: Figure 8.1 Ni adsorption</s
Page 132 and 133: 110high metal load
Page 134 and 135: Figure 8.3 x(k)•k3 spectra and Fo
Page 136 and 137: Figure 8.4 (k)•k3 spectra of Ni-H
Page 138 and 139: Figure 8.5 Fourier transforms (magn
Page 140 and 141: 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 154 and 155: 132Table 9.2 Model Parameters for N
Page 158 and 159: 1369.3 Zn Adsorption on GoethiteReg
Page 160 and 161: Figure 9.6 Zn adsorption</s
Page 162 and 163: 140data over a broad range of condi
Page 164 and 165: 142Figure 9.8 Ni adsorption
Page 166 and 167: 144oxide-coated silica. Ni and Zn s
Page 170 and 171: Figure 10.2 Zn adsorption</
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Page 176 and 177: Figure 10.6 Zn adsorption</
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CHAPTER 11CONCLUSIONS AND FUTURE WO
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158surfaces are needed for successf
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Figure A.2 Ni speciation in 1x10 -5
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Figure A.4 Pb speciation in 5x10 -8
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Figure A.6 Zn speciation in 1x10 -5
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166Table B.2 Potentiometric Titrati
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168Table BA Potentiometric Titratio
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170Table C.3 Zn Adsorption Edges on
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APPENDIX DADSORPTION STUDIES ON SIL
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174Table D.5 Zn Adsorption Isotherm
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176Table E.3 Pb CBC Study on 0.3 g
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APPENDIX GINTRAPARTICLE DIFFUSION M
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180DofA = flier ^ 2fA = Exp(-fD * f
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REFERENCES1. Adamson A. W. (1982) P
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18426. Blake R. L., Hessevick R. E.
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18650. Combes J. M., Manceau A. and
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18876. Elzinga E. J. and Sparks D.
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190102. Gupta V. K. (1998) Equilibr
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192126. Joshi A. and Chaudhuri M. (
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194150. Liu C. and Huang P. M. (200
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196175. Muller B. and Sigg L. (1992
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200. Perry R. H. and Green D. W. (1
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200226. Scheinost A. C., Kretzschma
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202252. Swallow C. K., Hume D. N. a
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204278. Villalobos M., Trotz M. A.
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304. Zhong Z. Y., Prozorov T., Feln
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