Chemical dissolution techniques in the study of soil clays: Part II

Abstract The removal of the alkali-soluble fraction from soil clays has been found to influence markedly the efficiency with which iron oxides can be removed from such clays. In clays pretreated with 5% Na 2 CO 3 , up to 40% more iron oxide was extracted by dithionite (Na 2 S 2 O 4 ) than from soil clays treated with this reagent alone. Chemical analysis, electron microscopy, X-ray and differential thermal examination, and specific surface area and cation-exchange capacity measurements indicated an improved dispersion brought about by the removal of aluminosilicate binding material by Na 2 CO 3 . The electron-optical studies also showed that the dithionite-soluble iron was principally in the form of small granules. These were amorphous to X-rays and electrons and chemical analysis of the dithionite-soluble fraction suggested that they were ferruginous complexes containing considerable quantities of silica and alumina.