The Effects of Iron Oxidation State on Clay Swelling,
ILLINOIS UNIV AT URBANA DEPT OF AGRONOMY
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The effects of the state of iron oxidation in clay crystals on their swelling pressure and surface charge were investigated. The minerals studied were the 2 micron, Na- saturated fractions of API 25 Upton UPM, Czechoslovakia 650 CZM, and New Zealand NZM montmorillonites, and API H-33a Garfield nontronite GAN. Methods and apparatus were developed to prepare reduced suspensions in a pH-buffered medium, as is to remove the undesired solutes and to prepare dried, oriented clay films while minimizing reoxidation of the ferrous iron in the mineral structure. In the composition range 0 Fe2 0.4 mmolg clay, the surface charge increased linearly with ferrous iron composition according to the charge deficits created by the reduction of Fe3 to Fe2. The swelling pressure decreased by 22, 31, 39, and 56 for the respective clays, UPM, CZM, GAN, and NZM containing 1.5 g H2Og clay. Above this range, the surface charge deviated from the predicted relationship and the swelling pressure was largely unchanged. Upon reoxidation these effects were reversible.
- Inorganic Chemistry
- Geology, Geochemistry and Mineralogy