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Soil Science Society of America Journal Abstract -

Relationships among Adsorbed Phosphate, Silica, and Hydroxyl during Drying and Rewetting of Kaolinite Suspension1


This article in SSSAJ

  1. Vol. 33 No. 5, p. 672-677
    Received: Dec 9, 1968
    Accepted: June 19, 1969

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  1. B. Bar-Yosef,
  2. U. Kafkafi and
  3. N. Lahav2



Kaolinite suspensions after 1 week of equilibration with tagged phosphate solution were dried isothermally (24C) from an initial water: clay weight ratio of 24:1 to 0.89:1. At eight points along the drying process triplicate subsamples were removed and kept sealed until the final point of the drying stage was reached. The concentrations of 31P, 32P, and silica were determined in the supernatant. The equilibrium concentration of phosphate in the solution remained unchanged along the drying process. The silica concentration increased while drying, but to a lesser extent than would have occurred in the absence of the clay. The pH changed irregularly within the limits of 6.1 ± 0.4. Kaolinite at a moisture content of 0.89 ml water per 1 g clay was rewetted to the initial water content and equilibrated for seven days. Part of the air-dried kaolinite was oven-dried (110C) for 48 hours and then rewetted to its original moisture content. The amount of adsorbed P released into the solution when the pH increased from 6.5 to 11.0 was smaller in the oven-dried clay than in the air-dried sample. This is attributed to an increase in the negative charge of the surface of the oven-dried kaolinite. Increasing the pH, the silica was readsorbed to a maximum at pH 9.2, as expected, and released at higher pH values in accordance with the negative surface charge.

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