| Index | i | frontpages.doc | ||
| Index to Plates and Figures | v | |||
| Abstracts | vi | |||
| Acknowledgements | x | |||
| Text | 1-225 | |||
| Bibliography | 226 | |||
| General Introduction | 1 | pages1-11.doc part1-plates1-8.doc | ||
| Part I: Crystal nucleation in Fe(III) solutions and hydroxide gels. | 5 | |||
| 1. | Fe(III) polymers and hydroxide gels. | 5 | ||
| 2. | Experimental methods | 8 | ||
| 2.1. | Preparation of goethites | 8 | ||
| 2.2. | Electron microscopy | 10 | ||
| 2.3. | X-ray diffractometry | 11 | ||
| 3. | Crystal morphology | 12 | pages12-18.doc | |
| 3.1. | Morphological types | 12 | ||
| 3.2. | Other morphological features | 14 | ||
| 3.3. | Crystal surfaces | 17 | ||
| 4. | The factors determining crystal morphology | 19 | pages19-32.doc part1-plates9-18-tab1.doc part1-plates19-32.doc pages33-45.doc | |
| 4.1. | The effect of OH/Fe mole ratio | 19 | ||
| 4.2. | The effect of ageing time | 20 | ||
| 4.3. | The effect of pH | 21 | ||
| 4.4. | Other observations | 23 | ||
| 5. | Mechanisms of crystal nucleation | 26 | ||
| 5.1. | Acicular crystal nucleation | 26 | ||
| 5.2. | Twinned crystal nucleation | 27 | ||
| 5.3. | Growth of crystal nuclei | 31 | ||
| 6. | Structure of Fe(III) hydroxide gel | 35 | pages33-45.doc part1-tab2-plates33-44.doc pages46-48-fig1-pages49-50.doc | |
| 7. | Crystal nucleation in Fe(III) chloride solutions | 38 | ||
| 8. | Growth of goethite in solutions and gels at low pH | 40 | ||
| 9. | Inhibition of crystal growth | 45 | ||
| 10. | Colours of goethite crystals | 47 | pages46-48-fig1-pages49-50.doc part1-tab3-plates45-50.doc | |
| 11. | Goethite preparations for surface chemistry experiments. | 49 | ||
| Part II: Surface chemistry of goethite. | 51 | pages51-62.doc pages63-74.doc | ||
| 1. | Structure of the goethite crystal surface | 51 | ||
| 2. | Coordination chemistry | 57 | ||
| 2.1. | Fe(III) aquo complexes and phosphato complexes | 58 | ||
| 2.2. | Solubility of iron oxides and Fe(III) phosphate solids | 61 | ||
| 2.3. | Surface charges on Fe(III) solids | 64 | pages63-74.doc pages75-83-tab1.doc | |
| 3. | Surface charges on goethite: Experimental methods | 69 | ||
| 3.1. | Preparations of goethite | 69 | ||
| 3.2. | Potentiometric titrations | 70 | ||
| 3.3. | Errors in potentiometric titrations | 72 | ||
| 3.4. | Contamination problems | 73 | ||
| 4. | Surface charges on goethite - Results | 78 | pages75-83-tab1.doc part2-figs1-11.doc | |
| 4.1. | Surface charge parameters | 78 | ||
| 4.2. | Surface charge parameters and crystal morphology | 80 | ||
| 4.3. | Surface charge parameters and contamination effects | 82 | ||
| 4.4. | Mechanism of charge development reactions | 84 | pages84-94.doc pages95-105.doc | |
| 4.5. | Physical significance of surface charge parameters | 92 | ||
| 5. | Phosphate adsorption by goethite: Experimental methods | 94 | ||
| 6. | Fe(III) phosphato complexes on goethite crystal surfaces | 97 | pages95-105.doc part2-figs12-15.doc pages106-114.doc | |
| 6.1. | Phosphate adsorption isotherms | 97 | ||
| 6.2. | Adsorption envelopes | 99 | ||
| 6.3. | Rates of complex formation and base hydrolysis reactions | 104 | ||
| 6.4. | Structure of Fe(III) phosphato complexes | 106 | pages106-114.doc pages115-123.doc | |
| 6.5. | The complex formation reaction | 111 | ||
| 6.6. | Thermodynamics of complex formation | 117 | ||
| Part III: Kinetics of heterogeneous isotopic exchange reactions. | 124 | pages124-134.doc pages135-145.doc | ||
| 1. | Effects of surface heterogeneity | 124 | ||
| 2. | General equation for rates of isotopic exchange reactions | 125 | ||
| 3. | Over-equilibration during heterogeneous isotopic exchange | 131 | ||
| 4. | Heterogeneous isotopic exchange described by approximations to McKay type equations | 132 | ||
| 4.1. | Approximations when n ≥ 2 | 132 | ||
| 4.2. | Approximations to obtain n = 1 | 139 | pages135-145.doc | |
| 5. | Diffusion models for heterogeneous isotopic exchange | 143 | ||
| 6. | Empirical relationships | 150 | pages146-156.doc pages157-168.doc | |
| 7. | An Elovich equation for heterogeneous isotopic exchange | 155 | ||
| 7.1. | The model and the derivation | 155 | ||
| 7.2. | Derivation of the Elovich equation when isotope is initial present in the solid phase | 163 | pages157-168.doc pages169-180.doc | |
| 7.3. | Dependence of the Elovich equation parameters on reaction mechanism, concentrations of the exchanging species, pH and temperature | 166 | ||
| 8. | Mechanisms of heterogeneous isotopic exchange reactions | 168 | ||
| 9. | Isotopic exchange between dilute orthophophate solutions and Fe(III) phosphato complexes on α-FeOOH crystal surfaces: Introduction | 170 | pages169-180.doc part3-tab1-figs1-8.doc part3-figs9-17-tab2.doc | |
| 10. | Materials and Methods | 171 | ||
| 10.1. | Goethite preparations | 171 | ||
| 10.2. | Preparation of the equilibrium systems | 172 | ||
| 10.3. | Isotopic exchange | 173 | ||
| 10.4. | Maintaining equilibrium conditions | 176 | ||
| 10.5. | Basic calculations | 177 | ||
| 11. | Results | 178 | ||
| 11.1. | The Elovich equation | 178 | ||
| 11.2. | Interpretation of parameters: Rate laws | 181 | pages181-194.doc | |
| 11.3. | Interpretation of parameters: Reference states | 186 | ||
| 11.4. | Limits of the Elovich equation: log(1-F) plots | 190 | ||
| 11.5. | Models for heterogeneous isotopic exchange | 192 | ||
| 11.6. | Mechanism of the exchange reaction | 195 | pages195-203.doc | |
| 11.7. | Mechanism: Structure and bonding in Fe(III) phosphato complexes | 199 | ||
| 11.8. | Mechanism: Transition states and acid-base catalysis | 204 | pages204-214.doc pages215-225.doc | |
| 11.9. | Origin of surface heterogeneity | 211 | ||
| 11.10. | Hydrolysis of Fe(III) phosphato complexes | 216 | pages215-225.doc | |
| Appendix | 222 | |||
| Bibliography | 226 | pages226-236.doc | ||
| Index to Plates, Tables and Figures | ||||
| Part I | ||||
| Plates 1-8 after p. 11 | part1-plates1-8.doc | |||
| Plates 9-12, Table 1 and Plates 13-32 after p.18 | part1-plates9-18-tab1.doc part1-plates19-32.doc | |||
| Table 2 and Plates 33-44 after p. 45 | part1-tab2-plates33-44.doc | |||
| Fig. 1 after p. 48 | pages46-48-fig1-pages49-50.doc | |||
| Table 3 and Plates 45-50 after p. 50 | part1-tab3-plates45-50.doc | |||
| Part II | ||||
| Table 1 and Figs. 1-11 after p. 83 | pages75-83-tab1.doc part2-figs1-11.doc | |||
| Figures 12-15 after p. 105 | part2-figs12-15.doc | |||
| Part III | ||||
| Table 1 and Figures 1-8 after p. 180 | part3-tab1-figs1-8.doc | |||
| Figures 9-17 and Table 2 after p. 194 | part3-figs9-17-tab2.doc | |||
| Figure 18 after p. 203 | part3-fig18.doc | |||