Stability behavior of soil colloidal suspensions in relation to sequential reduction of soils

Flocculation and dispersion of colloidal particles of nine inorganic paddy soils were studied mainly based on turbidity measurements of the suspensions of soils which were previously incubated at 28°C under in vitro waterlogged conditions. After 1-week of incubation, the turbidity of the soils except for 1) two soils containing larger amounts of sodium salts and 2) one soil containing larger amounts of Fe and Al oxides, significantly decreased, and colloidal particles flocculated with 1) a decrease in soil Eh and 2) an increase in electric conductivity (EC). During the 3- to 4-week period of waterlogging, the turbidity of the three soils significantly increased with the 1) decrease in EC and 2) increase in pH of the soils although the Eh remained low. Infrared (IR) absorption analysis showed that the suspended colloidal particles consisted of layer silicates from respective soil clays. Oxidation of suspensions of waterlogged soils by air-bubbling led to an increase in turbidity with the 1) increase in Eh, and 2) decrease in pH, EC, and water-soluble Fe₂₊ concentration. It was suggested that the stability of the soil colloidal suspensions was affected by soil reduction with alterations in ionic species and their concentrations at clay surfaces and in soil solutions.