REMOVAL OF FREE IRON OXIDE FROM CLAYS

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Abstract
The sodium hydrosulfite (Na2 S2O4) method of bleaching clays has been developed to give a completely inorganic micro procedure for the removal of free iron oxide from soil clays. The method recommended involves alternate treatments with fresh 4% NaoS204 of pH 5.8 at 40-45[degree]C for 15 min. and with 0.05 [image] HC1 at 40[degree]C for 3 min., followed by 2 washings with neutral [image] NaCl. A centrifuge procedure is used throughout, and Fe2O3 in the extracts detd. colorimetrically. Expts. leading to the selection of the conditions of extraction are descr. and the effect of the treatment on soil clays and pure clay minerals assessed from cation-exchange capacity measurements. The method is compared with others as regards efficiency and clay mineral decomposition and various aspects of the technique are discussed.