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This article in SSSAJ

  1. Vol. 46 No. 1, p. 56-61
    Received: June 23, 1980
    Accepted: Aug 17, 1981

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Concentration and pH Dependence of Calcium and Zinc Adsorption by Iron Hydrous Oxide Gel1

  1. D. G. Kinniburgh and
  2. M. L. Jackson2



The specific adsorption of calcium (Ca) (pH 8.0) and zinc (Zn) (pH 5.5 and 6.5) by iron (Fe) gel in 1M NaNO3 could be adequately described over three to five decades of concentration (c. 10-2M to 10-7M) by splitting the adsorption isotherm into one, two, or three regions and fitting the Freundlich isotherm to each region separately. Over the range of concentrations, 10-4M < c < 10-2M, Zn adsorption at pH 6.5 was about 10 times greater than at pH 5.5. Zinc adsorption at pH 5.5 was about the same as Ca adsorption at pH 8.0. No adsorption maxima were found. At trace concentrations (c < 10-7M) where the adsorption isotherm is linear, adsorption (x/m) may be described by the equation: log (x/m) = log k1 + n* pH + log c, where k1 and n* are empirical constants derived from percent adsorption against pH data. Estimates of log k1 and n* for trace adsorption of Ca, Sr, Ba, Co, Cu, Zn, Cd, Ag, Y, and Ce were derived from various sources. Naturally occurring iron oxides (and other hydrous oxides) could exert a significant control on Zn concentrations in soil solutions above about pH 6.0.

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