This chapter contains sections titled: Introduction Color (A. Scheinost) X-Ray Powder Diffraction Microscopy Surface Area, Porosity and Fractal Dimensions Acid Oxalate Extraction Infrared Spectroscopy Thermoanalysis Mössbauer Spectroscopy

This chapter contains sections titled: Quantity of Product Treatment after Synthesis Chemical Analysis Removal of Iron Oxides from Reaction Vessels Purity of Reagents

This chapter contains sections titled: The Major Iron Oxides Less Common or Rare Iron Oxides Iron Oxides in the Environment

Dissolution in HCl of hematite particles with different morphologies led to sigmoidal dissolution vs. time curves. The rate of dissolution was directly proportional to the sample surface area and independent of crystal morphology. Hematites produced by heating goethite at 600 or 800-degrees-C dissolved more rapidly per unit area than did hematites grown from solution. TEM showed that some platy crystals developed central holes after prolonged acid attack; the hole formation was attributed to enhanced dissolution at screw dislocations present on the (001) faces of the crystals. Except where particularly susceptible regions involving strained areas or dislocations were present, there appeared to be no preferential acid attack at any particular crystal face. The original morphology was usually maintained during the reaction.

The adsorption behavior of cesium on pure minerals is reviewed. Although this field has been investigated intensively, the data are extremely variable in scope and interpretation with detailed information being available for only a few minerals. In current investigations in this field, the emphasis is on the nature of the adsorption sites and identification of these sites using spectroscopic techniques. In the first section of this review, the general mechanism of cesium adsorption is discussed and this is followed by consideration of the effect of parameters such as cesium concentration, the properties of the mineral and the characteristics of the solution phase, on cesium adsorption. Finally, interaction of cesium with some different minerals is described in some detail.

The effects of a series of divalent. first row transition elements. i.e. Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ on the crystallization of ferrihydrite have been compared. With the exception of Mn2+, the metal ions considered, stabilized ferrihydrite and enhanced the amount of haematite in the reaction product. The stabilizing ability of these ions could be related to the increase in covalency of these metals along the series. With more than 15 mole% divalent metal ion present, ferrihydrite transformed to a spinel phase by a dissolution/reprecipitation mechanism.These metals can replace some Fe3+ in the structures of the crystallization products. Factors that influence the extent of isomorphous substitution are the match between the radii and charges of Fe3+ and the substituent ions and also, the congruency of dissolution of the M/ferrihydrite coprecipitate.

The effect of nickel (Ni) on the transformation of amorphous iron(III) hydroxide into more crystalline iron oxides has been followed using X-ray powder diffraction and chemical analysis. One aim of this study was to determine the fate of Ni that had been co-precipitated with amorphous iron(III) hydroxide as the amorphous phase recrystallised.Ni/amorphous iron(III) hydroxide co-precipitates transformed into Ni substituted alpha-FeOOH or alpha-Fe2O3, NiFe2O4 and alpha-3Ni(OH)2.2H2O in alkaline media. The type of reaction products formed depended on the concentration of Ni in the system and on the pH.Ni retarded the crystallisation of amorphous iron(III) hydroxide by stabilising the co-precipitate both against dissolution leading to alpha-FeOOH and against the internal rearrangement process which leads to alpha-Fe2O3.Chemical analysis showed that Ni was incorporated into the structure of alpha-FeOOH to a maximum level of 5.5 mol% and into the structure of alpha-Fe2O3 to up to 7 mol%. Excess Ni was adsorbed on the surface of the iron oxide or taken up by NiFe2O4 or the pure Ni phase. The b0 dimension of the unit cell increased from 0.9960 nm for alpha-FeOOH to 0.9965 nm for alpha-FeOOH with 5.5 mol% Ni substitution. The same maximum level of Ni could be incorporated in the alpha-FeOOH structure in the presence of either Mn (up to 8 mol%) or Co (up to 7 mol%).