لایب سان

Authors
Dr. R. M. Cornell
Universitåt Bern
Department fçr Chemie und Biochemie
Freiestrasse 3
3000 Bern 9
Switzerland
Prof. em. Dr. Dr. h.c. U. Schwertmann
Technische Universitåt Mçnchen
Institut fçr Bodenkunde
85354 Freising
Germany
1st Edition 1996
1st Reprint 1997
2nd Reprint 1998
2nd Edition 2003
Cover Illustration
Prehistoric cave painting of a red horse from
Lascaux. The colours used in the painting
were obtained from the local deposits of red
and yellow ochres, i. e. iron oxides. Similar
ochre deposits in Southern France are still
mined for pigment production today. As
colouring agents, iron oxides have served
man more or less continuously for over
30,000 years. A major, modern technological
application of these compounds (mainly in
synthetic form) is as pigment.
(Courtesy of Muse National de Prhistorie
Les Eyzies).
This book was carefully produced. Never-
theless, authors and publisher do not war-
rant the information contained therein to be
free of errors. Readers are advised to keep in
mind that statements, data, illustrations,
procedural details or other items may
inadvertently be inaccurate.
Library of Congress Card No.: Applied for:
British Library Cataloguing-in-Publication
Data: A catalogue record for this book is
available from the British Library.
Bibliographicinformation published by
Die Deutsche Bibliothek
Die Deutsche Bibliothek lists this publication
in the Deutsche Nationalbibliografie;
detailed bibliographic data is available in the
Internet at <http://dnb.ddb.de>.
 2003 WILEY-VCH Verlag GmbH & Co.
KGaA, Weinheim
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Printed on acid-free paper
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Printing Druckhaus Darmstadt, Darmstadt
Bookbinding Litges & Dopf, Heppenheim
Printed in the Federal Republic of Germany
ISBN 3-527-30274-3
&

Contents
1 Introduction to the iron oxides 1
2 Crystal structure 9
2.1 General 9
2.2 Iron oxide structures 9
2.2.1 Close packing of anion layers 10
2.2.2 Linkages of octahedra or tetrahedra 13
2.3 Structures of the individual iron oxides 14
2.3.1 The oxide hydroxides 14
2.3.1.1 Goethite a-FeOOH 14
2.3.1.2 Lepidocrocite c-FeOOH 18
2.3.1.3 Akaganite b-FeOOH and schwertmannite
Fe16 O16 (OH) y(SO 4 )z 7 n H2 O 20
2.3.1.4 d-FeOOH and d'-FeOOH (feroxyhyte) 22
2.3.1.5 High pressure FeOOH 23
2.3.1.6 Ferrihydrite 23
2.3.2 The Hydroxides 27
2.3.2.1 Bernalite Fe(OH)3 7 n H 2 O 27
2.3.2.2 Fe(OH)2 27
2.3.2.3 Green rusts 28
2.3.3 The Oxides 29
2.3.3.1 Hematite a-Fe2 O3 29
2.3.3.2 e-Fe2 O3 31
2.3.3.3 Magnetite Fe3 O4 32
2.3.3.4 Maghemite c-Fe2O 3 32
2.3.3.5 Wçstite Fe1±xO 34
2.4 The Fe-Ti oxide system 37
Appendix 37
3 Cation substitution 39
3.1 General 39
3.2 Goethite and lepidocrocite 42
3.2.1 Al substitution 42
V
The Iron Oxides: Structure, Properties, Reactions, Occurences and Uses. R. M. Cornell, U. Schwertmann
Copyright # 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
ISBN: 3-527-30274-3

3.2.2 Other substituting cations 47 3.3 Hematite 51 3.3.1 Al substitution 51 3.3.2 Other cations 54 3.4 Magnetite and maghemite 55 3.5 Other iron oxides 57 4 Crystal morphology and size 59 4.1 General 59 4.1.1 Crystal growth 59 4.1.2 Crystal morphology 60 4.1.3 Crystal size 62 4.2 The iron oxides 63 4.2.1 Goethite 64 4.2.1.1 General 64 4.2.1.2 Domainic character 69 4.2.1.3 Twinning 71 4.2.1.4 Effect of additives 73 4.2.2 Lepidocrocite 74 4.2.3 Akaganite and schwertmannite 75 4.2.4 Ferrihydrite 78 4.2.5 Hematite 81 4.2.6 Magnetite 87 4.2.7 Maghemite 92 4.2.8 Other Iron Oxides 94 5 Surface area and porosity 95 5.1 Surface area 95 5.2 Porosity 98 5.3 Surface roughness and fractal dimensions 100 5.4 The iron oxides 101 5.4.1 Goethite 102 5.4.2 Lepidocrocite 103 5.4.3 Akaganite and schwertmannite 104 5.4.4 d-FeOOH and feroxyhyte 105 5.4.5 Ferrihydrite 106 5.4.6 Hematite 108 5.4.7 Magnetite 109 5.4.8 Maghemite 109 6 Electronic, electrical and magnetic properties and colour 111 6.1 Electronic properties 111 6.1.1 Free Fe3+ and Fe2+ ions 111 6.1.2 Bound Fe ions 112 6.1.3 Molecular orbital description of bonding in iron oxides 113 VI Contents 6.2 Electrical properties 115 6.2.1 Semiconductor properties of iron oxides 116 6.3 Magnetic properties 118 6.3.1 Basic definitions 118 6.3.2 Types of magnetism 119 6.3.3 Magnetic behaviour of iron oxides 121 6.3.4 The different iron oxides 123 6.3.4.1 Goethite 123 6.3.4.2 Lepidocrocite 124 6.3.4.3 Akaganite 124 6.3.4.4 d-FeOOH, feroxyhyte and high pressure FeOOH 125 6.3.4.5 Ferrihydrite 125 6.3.4.6 Hematite 126 6.3.4.7 Magnetite and maghemite 128 6.3.4.8 Other Fe oxides 130 6.4 Colour 130 6.4.1 General 130 6.4.2 Colours 133 6.4.3 Pigment properties 136 7 Characterization 139 7.1 Introduction 139 7.2 Infrared spectroscopy 141 7.2.1 Goethite 141 7.2.2 Lepidocrocite 144 7.2.3 Ferrihydrite 144 7.2.4 Hematite 145 7.2.5 Other iron oxides 146 7.3 Raman spectroscopy 146 7.4 Ultraviolet-visible spectroscopy 147 7.4.1 General 147 7.4.2 Spectra of the different Fe oxides 148 7.5 Mæssbauer spectroscopy 152 7.5.1 General 152 7.5.2 Spectra of the various Fe oxides 157 7.5.2.1 Goethite and lepidocrocite 157 7.5.2.2 Ferrihydrite 157 7.5.2.3 Hematite 158 7.5.2.4 Magnetite and maghemite 158 7.5.2.5 Other iron oxides 160 7.6 Magnetic properties (Magnetometry) 161 7.6.1 General 161 7.6.2 Magnetic susceptibility v 162 7.6.3 Magnetic anisotropy, coercivity and saturation magnetization 163 7.6.4 Domain type 164 VIIContents 7.6.5 Curie temperature analysis 167 7.6.6 Applications 167 7.7 Other spectroscopic techniques 168 7.7.1 Photoelectron spectroscopy 169 7.7.2 X-ray absorption spectroscopy 171 7.8 Diffractometry 172 7.8.1 X-ray diffraction 172 7.8.2 Other diffraction techniques 177 7.9 Microscopy 179 7.10 Thermoanalysis 181 7.11 Dissolution methods 183 8 Thermodynamics of the Fe-O2 -H 2O system 185 8.1 General 185 8.2 Standard free energy of reaction and the equilibrium constant 186 8.3 Redox reactions 189 8.4 Effect of complexing agents on redox potential 192 8.5 Stabilities of iron oxides 193 8.5.1 ªBulkº crystals 193 8.5.2 Effect of particle size and Al substitution 197 9 Solubility 201 9.1 General 201 9.2 The solubility product 201 9.3 The effect of hydrolysis reactions and pH on solubility 203 9.4 Other factors influencing solubility and the solubility product 208 9.4.1 Complexation 208 9.4.2 Redox reactions 209 9.4.3 Ionic strength 211 9.4.4 Properties of the solid 211 9.4.4.1 Particle size 211 9.4.4.2 Ageing and isomorphous substitution 214 9.5 Methods of determining or calculating the solubility product 214 9.6 Solubility products of the various oxides 217 10 Surface Chemistry and Colloidal Stability 221 10.1 Surface functional groups 221 10.2 Surface acidity and acidity constants 227 10.3 The electrical double layer and electrochemical properties 232 10.4 Point of zero charge 236 10.5 Stability of colloidal suspensions 241 10.5.1 General 241 10.5.2 Stability of iron oxide suspensions 243 10.6 Tactoids, gels and schiller layers 250 10.7 Rheological properties 250 VIII Contents 11 Adsorption of Ions and Molecules 253 11.1 General 253 11.2 Treatment of adsorption data 254 11.2.1 The Langmuir, Freundlich and Temkin isotherm equations 254 11.2.2 Surface complexation models 255 11.3 Anion adsorption 258 11.3.1 Modes of coordination 265 11.3.2 Examples of inorganic ligands 267 11.3.2.1 Phosphate 267 11.3.2.2 Other anions 270 11.3.2.3 Organic anions and other organic compounds 273 11.4 Cation adsorption 279 11.4.1 General 279 11.4.2 Examples of cations 284 11.5 Adsorption from mixed systems 288 11.5.1 Competition between anions 289 11.5.2 Competition between cations 289 11.5.3 Interactions between cations and anions 290 11.5.4 Ternary adsorption 290 11.6 Adsorption of water 293 11.7 Adsorption of gases 293 11.8 Photochemical reactions 295 12 Dissolution 297 12.1 Introduction 297 12.2 Dissolution reactions and mechanisms 298 12.2.1 General 298 12.2.2 Protonation 299 12.2.3 Complexation 301 12.2.4 Reduction 306 12.2.4.1 General 306 12.2.4.2 Examples of reductants 312 12.2.4.3 Photochemical reduction 316 12.2.4.4 Biological and other reduction reactions 319 12.2.5 Comparison of the three different types of dissolution reactions 323 12.3 Dissolution equations 324 12.4 Individual iron oxides 326 12.4.1 Goethite 328 12.4.1.1 Unsubstituted goethite 328 12.4.1.2 Substituted goethite 330 12.4.1.3 Natural goethite and hematite 332 12.4.2 Lepidocrocite and akaganite 334 12.4.3 Ferrihydrite 335 12.4.4 Hematite 337 IXContents 12.4.5 Magnetite and maghemite 338 12.4.6 Comparison of different oxides 339 13 Formation 345 13.1 General 345 13.2 Formation in FeIII systems 347 13.2.1 Hydrolysis reactions 347 13.2.2 Formation of the different FeIII oxides 350 13.3 Formation in aqueous FeII systems 355 13.3.1 General 355 13.3.2 Effect of pH 356 13.3.3 Effect of oxidation rate 359 13.3.4 Effect of foreign compounds 360 13.4 Decomposition of Fe complexes 363 14 Transformations 365 14.1 Introduction 365 14.2 Thermal transformations 367 14.2.1 General 367 14.2.2 Goethite to hematite 369 14.2.3 Lepidocrocite to maghemite or hematite 373 14.2.4 Akaganite and schwertmannite to hematite 375 14.2.5 d-FeOOH and feroxyhyte to hematite 378 14.2.6 Ferrihydrite to hematite 378 14.2.7 Interconversions between maghemite and hematite 382 14.3 Via solution transformations 383 14.3.1 Lepidocrocite to goethite/hematite 383 14.3.2 Akaganite to goethite/hematite 384 14.3.3 Schwertmannite to goethite 385 14.3.4 Maghemite and goethite to hematite 386 14.3.5 Ferrihydrite to other Fe oxides 388 14.3.5.1 Rate of transformation 388 14.3.5.2 Hematite versus goethite formation 390 14.3.5.3 Mechanism of transformation 391 14.3.5.4 Effect of foreign compounds 393 14.3.5.4.1 General 393 14.3.5.4.2 Anions and neutral molecules 395 14.3.5.4.3 Cations 398 14.4 Oxidative and reductive transformations 402 14.4.1 Oxidation of magnetite to maghemite or hematite 402 14.4.2 Reduction of FeIII oxides to magnetite 405 14.4.3 Reduction of iron ores to iron 406 14.5 Interaction of iron oxides with other metal oxides and carbonates 407 X Contents 15 Rocks and ores 409 15.1 Introduction 409 15.2 Magmatic and metamorphic rocks and ores 409 15.3 Sediments and sedimentary rocks 412 15.3.1 Red beds 413 15.3.2 Sedimentary iron ores 416 15.3.3 Other sediments 420 15.3.4 Ferricretes and bauxites 421 15.4 Recent geological environments 422 15.4.1 Terrestrial surfaces 423 15.4.2 Spring and ground water 423 15.4.3 Deep sea 424 15.4.4 Continental shelves 424 15.4.5 Lakes and streams 425 15.4.6 Hydrothermal marine environments 427 15.4.7 Martian surface 429 15.5 Iron fractionation in sediments 430 Appendix 431 16 Soils 433 16.1 Soils ± a unique environment for iron oxide formation in terrestrial ecosystems 433 16.2 Iron oxide formation in soils 435 16.3 Iron oxide content and soil development 437 16.4 Occurrence and formation 439 16.4.1 Historical aspects 439 16.4.2 Distribution pattern 440 16.4.3 The various oxides 441 16.4.3.1 Goethite 441 16.4.3.2 Hematite and its association with goethite 442 16.4.3.3 Lepidocrocite, feroxyhyte and green rust 447 16.4.3.4 Ferrihydrite and its association with goethite 448 16.4.3.5 Magnetite and maghemite 450 16.5 Properties 452 16.5.1 Surface area, crystal morphology and size 452 16.5.2 Aluminium substitution 456 16.6 Significance for soil properties 459 16.6.1 Colour 459 16.6.2 Charge and redox properties 461 16.6.3 Anion and cation binding 463 16.6.4 Aggregation and cementation 468 17 Organisms 475 17.1 General 475 17.2 Biotically-mediated formation 476 XIContents 17.2.1 Goethite and lepidocrocite 476 17.2.2 Ferihydrite 477 17.2.3 Magnetite 480 17.2.3.1 Magnetite in chitons' teeth 481 17.2.3.2 Magnetite in bacteria and other organisms 481 17.3 Biotically induced formation 486 18 Products of iron metal corrosion 491 18.1 General 491 18.2 Electrochemical corrosion 491 18.3 High temperature oxidation/corrosion in gases 494 18.4 Other forms of corrosion 496 18.5 The products of corrosion 497 18.5.1 Iron oxides formed by electrochemical corrosion 499 18.5.2 Iron oxides in passive films 503 18.5.3 Thermally grown oxide films 504 18.6 Prevention of corrosion; protective oxide layers 506 19 Applications 509 19.1 Historical background 509 19.2 Pigments 511 19.2.1 Natural pigments 512 19.2.2 Synthetic pigments 514 19.3 Magnetic pigments 516 19.4 Ferrites 517 19.5 Catalysts 518 19.6 Other uses of iron oxides 522 19.7 Undesirable iron oxides 524 20 Synthesis 527 20.1 Industrial synthesis 527 20.1.1 General 527 20.1.2 Solid state transformations 528 20.1.2.1 The copperas process 528 20.1.2.2 Other solid state processes 528 20.1.3 Reduction of organic compounds 529 20.1.4 Precipitation from FeII solutions 530 20.1.5 Other processes 531 20.1.6 Magnetic pigments 532 20.2 Laboratory synthesis methods 533 20.2.1 Goethite 533 Other methods 533 20.2.2 Lepidocrocite 534 Other methods 534 20.2.3 Akaganite 534 XII Contents Other methods 534 20.2.4 Schwertmannite 535 20.2.5 Feroxyhyte 535 20.2.6 Ferrihydrite 535 2-line ferrihydrite 535 6-line ferrihydrite 535 Other methods 536 20.2.7 Hematite 536 Other methods 536 20.2.7.1 Coated hematite 537 20.2.8 e-Fe2 O3 538 20.2.9 Magnetite 538 Other methods 538 20.2.10 Maghemite 539 Other methods 539 20.2.11 Fe(OH)2 540 Other methods 540 20.2.12 Green rust 540 20.2.13 Other compounds 541 FeO (nonstoichiometric) 541 High pressure FeOOH 541 20.2.14 Production of iron oxides on substrates or in confined spaces 541 Goethite, hematite and ferrihydrite 541 Magnetite 541 Precipitation of goethite, ferrihydrite or magnetite in vesicles 542 21 Environmental significance 543 21.1 Introduction 543 21.2 Retention of pollutants by Fe oxides in water purification and in natural systems 544 21.2.1 Water treatment systems 544 21.2.2 Natural systems 546 21.3 Acid mine tailings 547 21.4 Detoxification reactions 549 21.5 Bacterial turnover of environmental pollutants 551 21.6 Anthropogenic dust and industrial sites 551 21.7 Iron-oxide rich waste products 552 References 555 Subject Index 651 Sources of Figures and Tables 659

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