Pedosphere 1(1): 29--39, 1991
ISSN 1002-0160/CN 32-1315/P
©1991 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Relationship between iron oxides and surface charge characteristics in soils |
| Shao, Z. C. and Wang, W. J. |
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| ABSTRACT |
| The relationship between iron oxides and surface charge characteristics in variable charge soils (latosol and red earth) was studied by (a) removing free iron oxides (Fed) and amorphous iron oxides (Feo) from the soils with sodium dithionite and acid ammonium oxalate solution respectively, (b) adding 2% glucose and incubating the soils under submerged conditions to activate iron oxides, followed by air-drying to age the iron oxides and ? precipitating various crystalline forms of iron oxides onto kaolinite. The results showed that free iron oxides (Fed) were the chief carriers of variable positive charge, of which crystalline iron oxides (Fed-Feo) present mainly as discrete particles in the soils played a minor role as carriers of positive charge, and had little influence on negative charge. Amorphous iron oxides (Feo), present mainly as coatings with a large specific surface area not only carried positive charges, but blocked the negative charge sites in soils. Submerged incubation activated the iron oxides in the soils, and increased the amount of amorphous iron oxides and the degree of activation of iron oxide, which resulted in increases in positive and negative charges. Dehydration and air-drying of the aged iron oxides decreased the amount of amorphous iron oxides and the degree of activation of iron oxide, and also led to the decreased positive and negative charges. Both submerged incubation and dehydration and air-drying had no significant influenced on the net charge. Precipitation of iron oxides onto kaolinite markedly increased positive charges and decreased negative charges. Amorphous iron oxide having a larger surface area contributed more positive charge sites and blocked more negative charge sites in kaolinite than crystalline goethite. |
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| Citation: Shao, C., Z., Wang and J., W. 1991. Relationship between iron oxides and surface charge characteristics in soils. Pedosphere. 1(1): 29-39. |
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