An Experimental Lecture for Students on the Formation of Iron Oxides

Eight different iron oxides have been identified in the weathering environment to date. They are goethite and hematite (common), lepidocro-cite, maghemite, ferrihydrite and magnetite (moderately widespread) and akaganeite and feroxyhyte (rare). These minerals often occur in close association. Since they have similar or even identical composition, a logical question is - under what conditions do the different oxides form  

The pathways by which the different Fe oxides form are complex and not yet fully understood. Hence, the teaching of how Fe oxides form can be a challenge. The use of visual aids can help illustrate and clarify the topic and fortimately, the Fe oxides lend themselves well to this approach. In the first place, the different forms can be recognized and identified by their striking colors (yellow, brown, red and black) and secondly, as shown in previous chapters, they are easily and rapidly synthesized in the laboratory. 

By varying the conditions of synthesis much can be learned about the experimental parameters which govern iron oxide formation during weathering and soil formation (pedogenesis) (Schwertmann, 1985 1988a Fitzpatrick, 1988 Schwertmann and Taylor, 1989). 

This chapter consists of a 45 minute lecture/demonstration of iron oxide formation in vitro and in situ. Several simple bench syntheses of iron oxides are carried out and explained. The lecture may be concluded with a short video which illustrates iron oxide occurrence in a real landscape. 

Throughout each experiment, the solution/suspension must be stirred constantly, preferably using an overhead stirrer. The experimental equipment must be installed beforehand and the solution for hematite synthesis already heated to close to 90 °C, The syntheses must be started immediately and while the oxides form, the pathways of formation are discussed. 

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An Experimental Lecture for Students on the Formation of Iron Oxides... 

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