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Changes in the Physical Properties of Soil Clays due to Precipitated Aluminum and Iron Hydroxides: II. Colloidal Interactions in the Absence of Drying¹

ABSTRACT

Colloidal stability diagrams were constructed for suspensions of an illite, a kaolinite, and a mixture of the two into which Al(OH)₃ and Fe(OH)₃ were precipitated. These diagrams covered a pH range from 2.5 to 12.5 and electrolyte concentrations up to the flocculation value. It was revealed, in accordance with expected interactions of colloids with widely different isoelectric points, that the colloidal stability of each mixture was dependent on the charge balance between its individual constituents. Therefore, as long as a system has not encountered a drying cycle, hydroxides may provide favorable (flocculating) or nonfavorable (colloidally stable) effects on soil structure depending on hydroxide type, its surface reactivity, and the clay mineral with which it may be associated. Generally, the two hydroxides provided equal enhancement of clay colloidal stability above their isoelectric points. However, Al(OH)₃ was more active in inducing clay flocculation and charge reversal at low pH values.

¹ Contribution from the Dep. of Agronomy and Soil Science, Univ. of Hawaii, Honolulu, HI, 96822. Journal Series 1959 of the Hawaii Agric. Exp. Stn and Contribution no. 726 of the Hawaii Inst. of Geophysics. Work supported in part by Cooperative Agreement no. 12-14-5001-40 with the ARS-USDA and by the Office of International Programs, National Science Foundation.

² Professor of Soil Science.

Received for publication December 29, 1975. Accepted for publication April 5, 1976.