Iron in Soils and Clay Minerals

1. The Geobiochemical Cycle of Iron.- 1-1. Geochemical Characterization of Iron.- 1-2. Geochemical Behavior of Iron in the Weathering Environment.- 1-3. Iron in Organisms and Soil Organic Matter.- 1-3.1. Fe-Bearing Compounds in Organisms.- 1-3.2. Quantitative Relationships.- Literature Cited.- 2. An Introduction to Physical and Chemical Principles.- 2-1. Introduction.- 2-2. Nuclear Properties'and their Importance in Spectroscopy.- 2-3. Electronic Properties - Free Ions.- 2-4. Electronic Properties - Crystal Field Theory.- 2-5. Electronic Properties - Molecular Orbital Theory.- Literature Cited.- 3. Solubility and Redox Equilibria of Iron Compounds in Soils.- 3-1. Introduction.- 3-2. Equilibrium Reactions of Iron.- 3-3. Solubility of Iron(III) Oxides in Soils.- 3-4. Other Iron(III) Minerals.- 3-5. Hydrolysis of Iron(III).- 3-6. Other Iron(III) Complexes in Soils.- 3-7. Effect of Redox on Iron(II) Solubility.- 3-8. Effect of Redox on Total Iron Solubility.- 3-9. Electron Titration of Soils.- 3-10. Effect of Redox on Smectite Stability.- 3-11. Role of Chelation in Iron Solubility.- 3-11.1. Measuring Fe3+ Solubility in Soils.- 3-11.2. Role of Chelation in Iron Availability.- 3-12. Problems.- Literature Cited.- 4. Separation and Concentration of Iron-Containing Phases.- 4-1. Introduction.- 4-2. Physical Separation Procedures.- 4-2.1. Manual Separation of Iron-Rich Areas.- 4-2.2. Wet Sieving to Concentrate Iron-Rich Concretions.- 4-2.3. Particle Size Separation.- 4-2.4. Density Gradient Separation.- 4-2.5. Magnetic Separation.- Hand Magnet.- High Gradient Magnetic Separation.- 4-3. Chemical Separation Procedures.- 4-3.1. Dissolution of Aluminosilicates Using Strong Bases.- Acknowledgments.- Literature Cited.- 5. Phase Identification by Selective Dissolution Techniques.- 5-1. Introduction.- 5-1.1. Specificity and Selectivity.- 5-2. Dissolution Techniques.- 5-2.1. The Pyrophosphate Technique(s).- 5-2.2. The Oxalate Technique.- 5-2.3. The EDTA Technique.- 5-2.4. The Dithionite-Citrate-Bicarbonate Technique.- 5-3. Concluding Remarks.- Literature Cited.- 6. The Assay for Iron in Soils and Clay Minerals.- 6-1.Introduction.- 6-2. Preliminary Considerations.- 6-3. Sampling.- 6-4. Sample Preparation.- 6-5. Selective Dissolution.- 6-6. Total Dissolution.- 6-6.1.Hydrogen Peroxide.- 6-6.2. Acids.- 6-6.3. Ashing.- 6-6.4.Decomposition with Mineral Acids.- 6-6.5. Fusions.- 6-6.6.Resistant Minerals.- 6-6.7. Iron(II).- 6-7. The Determination of Iron.- 6-7.1. Titrimetry.- 6-7.2.Colorimetry.- 6-7.3.Electrical.- 6-7.4.Instrumental Analysis.- 6-8. Precision, Accuracy, and Reference Materials.- Acknowledgements.- Literature Cited.- 7. Introduction to Crystal Structures of Iron-Containing Minerals.- 7-1.Introduction.- 7-2. Chain Silicates.- 7-2.1. Olivine.- 7-2.2.Pyroxenes.- 7-2.3.Amphiboles.- 7-2.4.Garnet.- 7-3. Phyllosilicate Clay Minerals.- 7-4. Iron Oxides.- 7-3.1.Hematite.- 7-3.2.Umenite.- 7-3.3.Magnetite.- 7-3.4.Maghemite.- 7-3.5. Goethite.- 7-3.6.Lepidocrocite.- 7-3.7.Akaganeite.- 7-3.8.Ferrihydrite and Feroxyhite.- Acknowledgements.- Literature Cited.- 8. The Application of Micro-Beam Methods to Iron Minerals in Soils.- 8-1.Introduction.- 8-2. Diffraction Theory.- 8-3. X-ray Diffraction.- 8-3.1.Mineral Identification.- 8-3.2. Crystal Size Estimation.- 8-3.3.Unit Cell Dimensions.- 8-3.4.Examples.- Goethite.- Lepidocrocite.- Hisingerite.- Nontronite.- 8-4. Transmission Electron Microscopy.- 8-4.1. Electron Diffraction.- Selected Area Diffraction (SAD).- Single-Crystal Diffraction.- 8-4.2. Electron Imaging.- Bright Field.- Dark Field.- n-Beam Images - High Resolution TEM.- 8-4.3. Specimen Preparation.- Grain Mounts.- Ion Thinning.- Microtomed Sections.- 8-4.4. Examples.- Goethite.- Hisingerite.- Ferrihydrite.- Iron Mineral Formation in Weathering.- 8-4.5. Analytical Electron Microscopy.- Literature Cited.- 9. Some Properties of Soil and Synthetic Iron Oxides.- 9-1.Introduction.- 9-2. Color.- 9-3. Crystal Morphology and Size.- 9-3.1. General Morphology.- 9-3.2.Crystal Size and Morphological Variations.- Electron Microscopy.- X-ray Diffraction.- 9-3.3.Mossbauer Spectroscopy.- 9-4. Surface Area.- 9-4.1.Gas and Dipole Adsorption.- 9-4.2.Phosphate Adsorption.- 9-4.3. X-ray Diffraction Line Broadening.- 9-5. Isomorphous Substitution.- 9-5.1. Aluminum.- 9-5.2. Other Metals.- 9-6. Thermal Behavior.- 9-7. Dissolution Kinetics.- 9-9. Interactions with Clay Silicates.- 9-10. Future Work.- Literature Cited.- 10. Introduction to the Surface Charge Properties of Iron oxides and Oxidic Soils.- 10-1. Introduction.- 10-2. Charging Phenomena at Iron Oxide Interfaces.- 10-2.1. Charge Development in the Presence of Indifferent Electrolytes.- 10-2.2. Charge Development in the Presence of Specifically Adsorbed Ions.- 10-2. Surface Charge Characteristics of Highly Weathered Soils Rich in Oxides.- Literature Cited.- 11. Occurrence and Formation of Iron Oxides in Various Pedoenvironments.- 11-1. Introduction.- 11-1.1. Role of Iron(III) Oxides in Pedogenesis.- 11-1.2. Basic Reactions.- 11-1.3. Ways to Study the Relationship Between Iron(III) Oxides and Pedoenvironments.- 11-2. Pedoenvironments and Iron(III) Oxide Minerals.- 11-2.1. The Goethite-Hematite Pair.- Soil Temperature and Soil Water Activity.- Organic Matter.- Soil Acidity.- Aluminum.- Mechanism of Hematite and Goethite Formation from Ferrihydrite.- Conclusions.- 11-2.2. Lepidocrocite.- Occurrence in Various Soils.- The Lepidocrocite-Goethite Pair.- Conclusions.- 11-2.3. Ferrihydrite.- General Remarks.- Formation in Various Pedoenvironments.- Conclusions.- 11-2.4. Maghemite and Magnetite.- Maghemite.- Magnetite.- 11-3. Pedoenvironments and Aluminum Substitutions.- 11-3.1. General Remarks.- 11-3.2. Goethite.- 11-3.3. Hematite and Other Iron(III) Oxides 301.- 11-4. Conclusions and Future Work.- Literature Cited.- 12. Properties and Behavior of Iron Oxides as Determined by Mossbauer Spectroscopy.- 12-1. Principles of Mossbauer Spectroscopy.- 12-1.1 Introduction.- 12-1.2. Hyperfine Interactions.- 12-2. Effects of Magnetic Properties on Mossbauer Spectroscopy.- 12-2.1. The Neel Temperature and the Magnetic Hyperfine Field.- 12-2.2. The Quadrupole Interaction in Magnetically Ordered Materials.- 12-2.3. Nonideal Behavior: Superparamagnetic Relaxation and Related Phenomena.- 12-3. Variatons of the Magnetic Hyperfine Field in Crystalline Iron Oxides.- 12-3.1. Influence of A1 Substitution.- 12-3.2. Influence of Crystallinity.- 12-4. Magnetic Hyperfine Field Distributions.- 12-5. Selected Mineral Examples.- 12-5.1. Hematite.- Room-Temperature Spectra.- Low-Temperature Spectra.- 12-5.2. Goethite.- Room-Temperature Mossbauer Spectra.- Low-Temperature Spectra.- 12-5.3. Ferrihydrite.- Room-Temperature Mossbauer Spectra.- Low-Temperature Spectra.- 12-5.4. Magnetite and Maghemite.- 12-5.5. Transient Phases: The Green Rusts.- Acknowledgements.- Literature Cited.- 13. Iron Compounds as Indicators of Pedogenic Processes: Examples from the Southern Hemisphere.- 13-1. Introduction.- 13-2. Ferruginous Pedogenic Materials.- 13-2.1. Overall Occurrences: Some General Considerations.- Climatic Considerations.- Paleographic Considerations.- 13-2.2. Localized Occurrences: Some Specific Considerations.- Red and Yellow Ferruginous Soils With Varying Base Status.- Black Cracking Clays.- Ferruginous Duricrusts.- 13.3. Iron Compounds.- 13-3.1. Magnetic Iron Oxides.- Primary and Secondary Magnetic Iron Oxides.- Authigenic Magnetic Iron Oxides.- 13-3.2. Goethite.- 13-3.3. Hematite.- 13-3.4. Lepidocrocite.- 13-3.5. Ferrihydrite and Feroxyhite.- 13-3.6. Secondary Layer-Silicate Iron.- 13-3.7. Organically Complexed Iron.- 13-3.8. Other Iron Minerals.- 13-4. Pedogenic Linkages between the Ferruginous Pedogenic Materials and Iron Compounds.- 13-4.1. Continental Scale: Age, Parent Materials, and Climate.- Magnetic Fe-Oxides.- Ferrihydrite in Cryumbrepts (Afro-Alpine Soils) and Vertisols.- Goethite and Hematite in Oxisols, Ultisols, and Aridisols.- Al-Substituted Goethites and Hematites in Ferricretes and Red-Brown Hardpans.- Goethite-Hematite Ratio: Distribution of Red and Yellow Soils.- Al-Substituted Goethites and Hematites: An Indicator of Contemporary and Fossil Soil Formation.- Lepidocrocites: An Indicator of Certain Reductomorphic Pedogenic Environments in Humid Temperate Climates.- 13-4.2. Local Landscape Scale.- Effects of Altitude and Aspect on Goethite and Hematite Formation.- Effects of Slope and Hydrology on Goethite and Hematite Formation and Transformation.- Effects of Altitude, Aspect, Slope, and Hydrology on Maghemite Formation and Transformation.- Effects of Topography and Hydrology on the Forma tion and Transformation of Iron-Rich Smectites.- 13-4.3. Profile Scale.- Formation and Transformation of Goethite and Hematite at the Profile Scale.- Formation and Transformation of Magnetic Fe Oxides at the Profile Scale.- Formation and Transformation of Lepidocrocite at the Profile Scale.- 13-4.4. Micro-Pedological Scale.- Mottles and Ferricrete Fragments: Soil Matrix Comparisons.- Ferruginous Bauxite Nodules: Soil Matrix Comparisons.- Pipestems: Soil Matrix Comparisons.- Magnetic and Non-Magnetic Glaebules: Soil Matrix Comparisons.- influence of Heat From Forest Fires.- Placic Horizons: Soil Matrix Comparisons.- 13-5. Summary and Conclusions.- Acknowledgements.- Literature Cited.- 14. Magnetic Properties of Iron in Soil Iron Oxides and Clay Minerals.- 14-1. Introduction.- 14-2. Paramagnetism.- 14-2.1. Susceptibility and Magnetization of Iron(III).- 14-2.2. Susceptibility and Magnetization of Iron(II).- 14-3. Collective Magnetic Order.- 14-3.1. Ferromagnetic Interactions.- 14-3.2. Antiferromagnetic Interactions.- Antiferromagnetism.- Ferrimagnetism.- Speromagnetism.- 14-3.3. Ferromagnetic and Antiferromagnetic Interactions.- 14-3.4. Anisotropic and Antisymmetric Exchange.- 14-3.5. Chemical Disorder.- 14-3.6. Domain Effects.- 14-3.7. Fine Particle Effects.- Surface Spin Structures and Moments of Fine Particles.- Superparamagnetism.- 14-4. Experimental Techniques.- 14-4.1. Susceptibility.- 14-4.2. Magnetization.- 14-4.3. Natural Remanence.- 14-4.4. Hyper fine Interactions.- 14-4.5. Magnetic Structures.- 14-5. Iron Oxides.- 14-5.1. Hematite.- 14-5.2. Ilmenite.- 14-5.3. Magnetite.- 14-5.4. Maghemite.- Titanomaghemites.- Magnetic Soils.- 14-5.5. Goethite.- 14-5.6. Other Crystalline Ferric Hydroxides.- 14-5.7. Disordered and Amorphous Ferric Hydroxides.- 14-5.8. Other Minerals.- 14-6. Clay Minerals.- 14-6.1. Triocta'nedrai Iron(II) Minerals.- Mossbauer Spectra.- Magnetic Properties.- Neutron Diffraction.- Computer Experiments.- 14-6.2. Trioctahedral Iron(IIl) Minerals.- 14-6.3. Dioctahedral Minerals.- 14- 6.4. Summary.- Acknowledgements.- Appendix: Quantitites and Units.- Literature Cited.- 15. Structural Iron in Kaolinites and in Associated Ancillary Minerals.- 15-1. Introduction.- 15-2. Terminology and Crystal Structure.- 15-3. Deposits.- 15-4. General Properties.- 15-4.1. Shape and Size.- 15-4.2. Rheological Properties.- 15-5. Analysis and Mineralogy.- 15-5.1. Elemental Analysis.- 15-5.2. Mineralogical Analysis.- 15-5.3. Illustrative Analyses.- 15-5.4. Iron in the Kaolinite Structure.- 15-5.5. Iron Oxides and Oxyhydroxides.- 15-5.6. Iron in the Ancillary Minerals.- 15-5.7. Titanoferrous Impurities.- 15-6. Optical Properties.- 15-6.1. Introduction to Absorption and Scattering.- 15-6.2. Kubelka-Munk Equations.- 15-6.3. Significance of k and s.- 15-6.4. Measurement of k ands.- 15-6.5. Measurement of Reflectance and Brightness.- 15-6.6. Brightness Values.- 15-6.7. Experimental Values of k and s.- 15-6.8. The Scattering Coefficient 495 15-6.9. The Absorption Coefficient.- 15-6.10. Interpretation of Light Absorption.- 15-7. Ceramics.- 15-8. Commercial Production of Kaolin.- 15-8.1. Reactions with Sodium Dithionite.- 15-8.2. Magnetic Separation.- Principles.- Commercial Applications.- Research Applications.- 15- 8.3. Micromineral Separation.- Froth Flotation.- Selective Flocculation.- Selective Coagulation.- Acknowledgements.- Literature Cited.- 16. Role of Iron in Mica Weathering.- 16-1. Introduction.- 16-2. Status of Iron in Micas.- 16-2.1. Occurrence.- 16-2.2. Location.- 16-2.3. Determination.- 16-2.4. Variability.- 16-3. Naturally Weathered Micas.- 16-3.1. Theoretical Considerations.- 16-3.2. Changes Observed.- 16-4. Mica Dissolution.- 16-4.1. Principles.- 16-4.2. K Release.- 16-4.3. Hydrolysis and Precipitation.- 16-4.4. Complexation.- 16-4.5. General Aspects.- 16-5. Chemically Induced Redox Changes.- 16-5.1. Laboratory Conditions for Oxidation.- 16-5.2. Relevance of Mica Expansion.- 16-5.3. Br 2- and H2 O2 -Treated Mica.- 16-5.4. Structural Fe Reduction.- 16-6. Mica Alterations by Wet Redox Treatmemts.- 16-6.1. Visible Changes.- 16-6.2. Interlayer K.- 16-6.3. Chemical Composition.- 16-6.4. Structural Properties.- 16-7. Thermally Altered Micas.- 16-7.1. General Approach 59716-7.2. Macro Flakes.- 16-7.3. Structural Fe.- 16-7.4. Inter layer K.- Acknowledgements.- Literature Cited.- 17. Structural Iron in Smectites.- 17-1. Introduction.- 17-2. Composition and Origin of Iron-Bearing Smectites.- 17-2.1. Classification.- 17-2.2. Natural and Synthetic Formation.- 17-2.3. Site Occupancy of Iron.- 17-3. Methods of Characterization.- 17-3.1. Infrared Spectroscopy.- 17-3.2. Mossbauer Spectroscopy and Other Nuclear Techniques.- 17-3.3. UV-Visible Spectroscopy.- 17-4. Effects of Structural Iron on Smectite Properties.- 17-4.1. Surface Area.- 17-4.2. Layer Charge and Cation Exchange Capacity.- 17-4.3. Swelling in Water.- 17-4.4. Color.- 17-4.5. Crystallographic b-Dimension.- 17-4.6. Chemical Stability.- 17-5. Redox Processes and Mechanisms.- 17-5.1. Oxidation of Iron(II) Smectites.- 17-5.2. Reduction of Iron(III) Smectites.- Literature Cited.- 18. The Characterization of Iron Complexes with Soil Organic Matter.- 18-1. Introduction.- 18-2. The Bonding of Iron to Humic Substances.- 18-3. Bonding of Iron to Organic Matter in Soils.- Literature Cited.- 19. Chemistry of Iron in Calcareous Systems.- 19-1. Introduction.- 19-2. Iron Oxides in Calcareous Soils.- 19-3. Equilibrium Relations of CaC03.- 19-4. Equilibrium Relations of Iron in Calcareous Systems.- 19-5. Synthetic Systems for Studying the Reactions of Aqueous Iron with CaCO3.- 19-6. Reactions of Iron with CaC03.- 19-7. Iron Oxides Formed During the Reactions of Iron with CaC03.- 19-8. Iron Oxides and the Availability of Iron to Plants in Calcareous Systems.- 19-9. Influence of Soil Components on the Reactions of Iron in Calcareous Systems.- 19-10. Implications of Synthetic Studies to the Management of Iron in Calcareous Soils.- 19-11. Conclusions.- Acknowledgements.- Literature Cited.- 20. Microbiological Reactions of Iron in Soils.- 20-1. Introduction.- 20-2. Preliminary Note on the Iron(II)/Iron(III) Redox System.- 20-3. Oxidation of Iron(II).- 20-3.1. Thiobacillus Ferrooxidans.- 20-3.2. Mechanism of Oxidation.- 20-3.3. Biomass Yield of the Reaction.- 20-3.4. Other Acidophilic Fe Organisms.- 20-4. Neutral pH Iron Oxidizing Bacteria...- 20-5. Decomposition of Organic Iron(II) Complexes.- 20-6. Types of Iron(III) Oxides Formed by Bacteria.- 20-7. Reduction of Iron(III).- 20-7.1. Source of Electrons for Iron(III) Reduction.- 20-7.2. Mechanism of Iron(III) Reduction.- 20-8. Rate of Reduction.- 20-8.1. Methods for Determination of Reduction Rates.- 20-9. Factors Influencing the Rate of Reduction.- 20-9.1. Types of Microorganisms.- 20-9.2. Bacterial Activity.- 20-9.3. Types and Concentration of Iron(III) Oxides.- 20-9.4. Sinks for Iron(II).- 20-10. Alteration of Other Iron Minerals.- Literature Cited.- 21. The Fate of Iron During Soil Formation in Humid-Temperate Environments.- 21-1. Introduction.- 21-2. Weathering and Braunification.- 21-3. Lessivage.- 21-4. Podzolization.- 21-5. Processes of Reductomorphism.- 21-5.1. Surfacewater Soils.- 21-5.2. Groundwater Soils.- 21-5.3. Dry Reductomorphism.- 21-6. Lateral Translocation of Iron in Landscapes.- Acknowledgements.- Literature Cited.- 22. Laterites and Laterization Processes.- 22-1. Definition and Concepts.- 22-1.1. Laterites.- 22-1.2. Relative and Absolute Accumulation of Sesquioxides.- 22-2. A Sketch of a "Typical" Laterite Profile.- 22-3. Isovolumetric Chemical Balances.- 22-3.1. General Comments.- 22-3.2. Isovolumetric Chemical Balances in the Diouga Laterite.- 22-4. Absolute Accumulation of Iron - The Epigenetic Replacement of Kaolinite by Hematite.- 22-4.1. Petrographic Observations.- 22-4.2. Inferences.- 22-5. The Hardening of the Iron Crust: The Transformation of the Soft Yellow Plasma Into Purple-Red Nodules and the Individualization of Pisolites.- 22-6. Mineralogy Versus Morphology.- 22-6.1. The Diouga Laterite.- Kaolinites.- Hematites.- Goethites.- 22-6.2. Tentative Generalizations.- Kaolinites.- Iron Oxides.- Literature Cited.- 23. Effects of Seasonal Redox Processes Involving Iron on the Chemistry of Periodically Reduced Soils.- 23-1. Introduction.- 23-2. Redox Processes in Soils and the Role of Iron.- 23-3. Forms of Iron(II) in Reduced Soils.- 23-4. Changes in Electrochemistry and Solution Chemistry of Soils Due to Reduction of Iron(III).- Acknowledgements.- Literature Cited.- 24. Long-Term Chemical, Mineralogical, and Morphological Effects of Iron-Redox Processes in Periodically Flooded Soils.- 24-1. Introduction.- 24-2. Ferrolysis.- 24-3. Segregation of Iron Due to Redox Processes.- 24-4. Mineralogy of Iron(III) Oxides in Periodically Flooded Soils.- Acknowledgements.- Literature Cited.- 25. Redox Processes of Iron and Sulfur Involved in the Formation of Acid Sulfate Soils.- 25-1. Introduction.- 25-2. Formation of Pyrite.- 25-3. Oxidation of Pyrite.- 25-4. Oxidation Products of Pyrite.- 25-5. Nontronite Formation Associated With Pyrite Oxidation.- Acknowledgements.- Literature Cited.