Flocculation and dispersion behaviour of two kaolinitic soil clays as affected by organic matter and iron oxides

Abstract

The effects of removal of organic matter, crystalline Fe oxides and amorphous Fe oxides on the flocculation and dispersion behaviour of two kaolinitic soil clays were measured. The critical coagulation concentrations (CCCs) of dilute suspension (0.01-0.26 moles m -3) of the kaolinitic soil clays in NaCl solution were determined for (i) untreated clays, (ii) clays treated with H2O2 for the removal of organic matter, (iii) clays treated with dithionite-citrate-bicarbonate (DCB) for the removal of crystalline Fe oxides, (iv) clays treated with ammonium oxalate for the removal of amorphous Fe oxides and (v) clays treated successively with H2O2/DCB/oxalate for the removal of organic matter, crystalline Fe oxides and amorphous Fe oxides. The treatment for the removal of organic matter decreased the CCC values, implying a decrease in clay dispersivity. This indicated that dissolved organic matter enhanced clay dispersion. The removal of crystalline Fe oxides increased the CCC values, indicating an increase in the clay dispersivity. This showed that crystalline Fe oxides were important in stabilizing the structure of the soils studied. The amorphous Fe oxides, however, did not play a stabilizing role. The clays whose crystalline Fe oxides, amorphous Fe oxides and organic matter were successively removed were the most flocculated and therefore had the lowest CCC values.

JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 2 (2000) pp. 107-113