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This article in SSSAJ

  1. Vol. 41 No. 4, p. 814-817
    Received: Mar 8, 1976
    Accepted: Mar 9, 1977

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Solution Activities of Aluminum and Silicon in Highly Weathered Soils that contain Gibbsite and Kaolinite1

  1. R. M. Weaver and
  2. P. R. Bloom2



Solution activities of aluminum (Al3+) and monosilicic acid (Si(OH)4) in dilute acid suspensions of six Brazilian Oxisols were measured over a period of 145 days. The steady state activity function of pH-⅓pAl ranged from 1.86 to 2.69, while that of pSi(OH)4 ranged from 3.69 to 4.22. Although all of the soils contained kaolinite and gibbsite, the observed solute activity functions of pH-⅓pAl and pSi(OH)4 deviated considerably from those expected for a thermodynamic equilibrium between gibbsite and kaolinite. It was found that the solution activities of Al and Si(OH)4 in these soils appeared to result from the dissolution of a surface aluminosilicate component (R) of variable composition-{[Al(OH)3](1-x)[SiO2]x}R rather than gibbsite and kaolinite.

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