Retention of Boron by Layer Silicates, Sesquioxides, and Soil Materials: III. Iron- and Aluminum-Coated Layer Silicates and Soil Materials
1968
Sims, J. R. | Bingham, F. T.
Boron retention as a function of pH was determined for Fe- and Al-coated layer silicates using a previously described procedure (15). Treating the Na⁺ and K⁺ forms of South Africa vermiculite material with Al³⁺ prior to B treatment resulted in equivalent B retention by the two forms. Coating kaolinite with hydroxy iron compounds initially decreased B retention in comparison to uncoated kaolinite. However, as the amount of coating was increased to 4.2% Fe₂O₃ the amount of B retained was slightly greater than that retained by uncoated kaolinite. Boron retention by the Al-coated kaolinite and by both Fe- and Al-coated montmorillonite was significantly greater than B retention by the uncoated clays. A single regression line represented B retention as a function of Fe₂O₃ content for both clays. Boron retention as a function of Al₂O₃ content for the two coated clays fell on two lines which led to the conclusion that hydroxy Fe and Al compounds in the layer silicates dominate over clay mineral species per se in determining B retention characteristics and that B retention characteristics may be conditioned by clay mineral species. Boron retention at pH 6 by nine soil materials was determined from the difference in the initial and final B concentrations of the saturating solutions. Relationships between B retention and various chemical properties of the soil materials were examined statistically. The highest correlations with B retention were found with free iron oxide content and 1.0N KCl (pH2) extractable Al₂O₃. It was concluded that B retention by these soil materials was in response mainly to their free iron oxide and Al₂O₃ contents.
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