R.M.Cornell U. Schwertmann. The Iron Oxides. Structure, Properties, Reactions, Occurrence and Uses. Weinheim New York Basel Cambridge Tokyo VCH

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1 R.M.Cornell U. Schwertmann The Iron Oxides Structure, Properties, Reactions, Occurrence and Uses VCH Weinheim New York Basel Cambridge Tokyo

Contents 1 Introduction to the iron oxides 1 2 Crystal structure 7 2.1 General 7 2.2 Iron oxide structures 7 2.2.1 Close packing of anion layers 10 2.2.2 Linkages of octahedra or tetrahedra 12 2.

2 Contents 1 Introduction to the iron oxides 1 2 Crystal structure General Iron oxide structures Close packing of anion layers Linkages of octahedra or tetrahedra Structures of the individual iron oxides The oxide hydroxides Goethite a-feooh Lepidocrocite y-feo(oh) Akaganeite ß-FeO(OH) and schwertmannite Fe (OH) y (S0 4 ) z n H FeOOH and 8'-FeOOH (feroxyhyte) High pressure FeOOH Ferrihydrite The hydroxides Bernalite Fe(OH) 3 nh Fe(OH) Green rusts The oxides Haematite a-fe Magnetite Fe Maghemite y-fe Wüstite Fe^O The Fe-Ti oxide System 33 3 Cation Substitution General Goethite AI Substitution Synthetic goethites Natural goethites Other substituting cations Haematite Other Fe oxides 50

VIII Contents 4 Crystal morphology and size 53 4.1 General 53 4.1.1 Crystal growth 53 4.1.2 Crystal morphology 55 4.1.3 Crystal size 57 4.2 The iron oxides 58 4.2.1 Goethite 59 4.2.1.1 General 59 4.2.1.2 Domainic character 64 4.

3 VIII Contents 4 Crystal morphology and size General Crystal growth Crystal morphology Crystal size The iron oxides Goethite General Domainic character Twinning Effect of additives on goethite morphology Lepidocrocite Akaganeite and schwertmannite Ferrihydrite Haematite Magnetite Maghemite Other iron oxides 85 5 Surface area and porosity Surface area Porosity Surface roughness and fractality The iron oxides Goethite Lepidocrocite Akaganeite and schwertmannite FeOOH and feroxyhyte Ferrihydrite Haematite Magnetite Maghemite Electronic, electrical and magnetic properties Electronic properties Free Fe 3+ and Fe 2+ ions Bound Fe ions Molecular orbital description of bonding in iron oxides Electrical properties Semiconductor properties of iron oxides Magnetic properties Basic definitions Types of magnetism Magnetic behaviour of iron oxides The different iron oxides Goethite Lepidocrocite 119

Contents IX 6.3.4.3 Akaganeite 119 6.3.4.4 8-FeOOH and feroxyhyte 119 6.3.4.5 High pressure FeOOH 120 6.3.4.6 Ferrihydrite 120 6.3.4.7 Haematite 120 6.3.4.8 Magnetite 123 6.3.4.9 Maghemite 123 6.3.4.10 e-fe 2 0 3 124 6.

4 Contents IX Akaganeite FeOOH and feroxyhyte High pressure FeOOH Ferrihydrite Haematite Magnetite Maghemite e-fe Fe(OH) Wüstite Characterization Introduction Infrared spectroscopy Goethite Lepidocrocite Ferrihydrite Haematite Other iron oxides Raman spectroscopy Ultraviolet-visible spectroscopy UV-Vis spectra Colour and optical properties Colour Pigment properties Mössbauer spectroscopy and magnetometry Mössbauer spectra and parameters Goethite Lepidocrocite Ferrihydrite Haematite Magnetite and maghemite Other iron oxides Magnetometry General Initial magnetic susceptibility Magnetic anisotropy, coercivity and Saturation magnetization Domain type Curie temperature analysis Applications Other spectroscopic techniques Diffraction techniques X-ray diffraction Other diffraction techniques Microscopy Thermoanalysis Thermal gravimetric analysis (TGA) 171

X Contents 7.9.2 Differential thermal analysis (DTA) 171 7.10 Dissolution methods 173 8 Thermodynamics of the Fe-0 2 -H 2 0 system 175 8.1 General 175 8.

5 X Contents Differential thermal analysis (DTA) Dissolution methods Thermodynamics of the Fe-0 2 -H 2 0 system General Standard free energy of reaction and the equilibrium constant Redox reactions Effect of complexing agents on redox potential Stability "Bulk" crystals Effect of particle size and AI Substitution Solubility General The solubility product The effect of hydrolysis reactions and ph on solubility Other factors influencing solubility and the solubility product Complexation Redox reactions Ionic strength Properties of the solid Particle size Ageing and isomorphous Substitution Methods of determining or calculating the solubility products Solubility products Surface chemistry and colloidal stability Surface functional groups Surface acidity and acidity constants The electrical double layer Electrochemical properties Surface charge and point of zero charge Stability of colloidal suspensions General Stability of iron oxide suspensions Adsorption of ions and molecules General Treatment of adsorption data The Langmuir, Freundlich and Temkin isotherm equations Surface complexation modeis Anion adsorption Modes of coordination Selected inorganic anions Organic anions and other organic Compounds Cation adsorption Ternary adsorption 261

Contents XI 11.6 Adsorption of gases 263 11.7 Photochemical reactions 264 12 Dissolution 267 12.1 Introduction 267 12.2 Dissolution reactions and mechanisms 268 12.2.1 Principles 268 12.2.2 Protonation 270 12.

6 Contents XI 11.6 Adsorption of gases Photochemical reactions Dissolution Introduction Dissolution reactions and mechanisms Principles Protonation Complexation Reduction General Examples of reductants Photochemical reduction Biological and other reduction reactions in natural environments Comparison of the three different types of dissolution reactions Dissolution modeis Individual iron oxides Goethite Unsubstituted goethite Substituted goethite Natural goethite and haematite Lepidocrocite and akaganeite Ferrihydrite Haematite Magnetite and maghemite Comparison of different oxides Formation General Formation in Fe 111 Systems Hydrolysis reactions Polynuclear species Crystalline products formed in acid media Mechanisms of formation Transformation of ferrihydrite in neutral to alkaline media Factors affecting the goethite-to-haematite ratio Effect of foreign Compounds General Anions and neutral molecules in acid media Anions and neutral molecules in alkaline media Cations Formation in aqueous Fe 11 Systems General Effect of ph Effect of oxidation rate Effect of foreign Compounds Decomposition of Fe complexes 347

XII Contents 14 Transformations 349 14.1 Introduction 349 14.2 Thermal transformations 351 14.2.1 Dehydration and dehydroxylation 351 14.2.1.1 General 351 14.2.1.2 Goethite 352 14.2.1.3 Lepidocrocite 356 14.

7 XII Contents 14 Transformations Introduction Thermal transformations Dehydration and dehydroxylation General Goethite Lepidocrocite Akaganeite and schwertmannite FeOOH and feroxyhyte Ferrihydrite Isochemical transformations Maghemite to haematite Via-solution transformations Lepidocrocite to goethite/haematite Akaganeite to goethite/haematite Schwertmannite to goethite Maghemite and goethite to haematite Oxidative and reductive transformations Oxidation of magnetite to maghemite or haematite Reduction of Fe 111 oxides and oxyhydroxides to magnetite Reduction of iron ores to iron Interaction of iron oxides with other metal oxides and carbonates Rocks and ores Introduction Magmatic and metamorphic rocks and ores Sediments and sedimentary rocks Red beds Sedimentary iron ores Other Sediments Ferricretes and bauxites Recent geological environments Terrestrial surfaces Spring and ground water Deep sea Continental shelves Lakes and streams Hydrothermal marine environments Martian surface Soils Soils - a unique environment for iron oxide formation in terrestrial ecosystems Iron oxide formation in soils Iron oxide content and soil development Occurrence and formation Historical aspects 399

Contents 16.4.2 Morphology of appearance 400 16.4.3 The various oxides 401 16.4.3.1 Goethite 401 16.4.3.2 Haematite and its association with goethite 402 16.4.3.3 Lepidocrocite and feroxyhyte 406 16.

8 Contents Morphology of appearance The various oxides Goethite Haematite and its association with goethite Lepidocrocite and feroxyhyte Ferrihydrite Magnetite and maghemite Iron oxide mineralogy based on differential dissolution Properties Crystal morphology and size Aluminium Substitution Significance for soil properties Colour Charge and redox properties Anion and cation binding Aggregation Organisms General Goethite and lepidocrocite Ferrihydrite Magnetite Magnetite in Chirons' teeth Magnetite in bacteria and other organisms Biotically induced precipitation Products of iron metal corrosion General Electrochemical corrosion High temperature oxidation/corrosion in gases Other types of corrosion The products of corrosion Iron oxides formed by electrochemical corrosion Iron oxides in passive films Thermally grown oxide films Prevention of corrosion; protective oxide layers Applications Historical background Pigments Natural pigments Synthetic pigments Magnetic pigments Ferrites Catalysts Other uses of iron oxides Abrasives 477

XIV Contents 19.6.2 Thermite welding 477 19.6.3 Ferrofluids 477 19.6.4 Water purification and treatment of radioactive waste 478 19.6.5 Other applications 479 19.

9 XIV Contents Thermite welding Ferrofluids Water purification and treatment of radioactive waste Other applications Raw material for the iron and steel industries Undesirable iron oxides Synthesis of iron oxides Industrial synthesis General Solid State transformations The copperas process Other solid State processes Reduction of organic Compounds Precipitation from Fe 11 Solutions Other processes Magnetic pigments Laboratory synthesis methods Goethite Lepidocrocite Akaganeite Schwertmannite Feroxyhyte Ferrihydrite Haematite Magnetite Maghemite Fe(OH) Green rusts Other Compounds Production of iron oxides on subtrates and in confined spaces References 497 Index 559 Sources of figures and tables 571

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