Zinc and Copper Sorption and Fixation by an Acid Soil Clay: Effect of Selective Dissolutions1
- N. Cavallaro and
- M. B. McBride2
Copper and zinc sorption-desorption studies were carried out over a range of pH values using clay fractions separated from two horizons of an acid soil from New York. In the pH range of high sorption, as much as 95% of the sorbed metal could not be desorbed by several washes with 0.05M CaCl2 and thus was considered fixed. Sorption and fixation of Cu and Zn increased rapidly above pH 4 and 5, respectively, for the whole soil clays. Following removal of the oxide fraction by oxalate and citrate-dithionite extractions, sorption and fixation were reduced considerably at pH values below the onset of hydrolysis of the metals in bulk solution, indicating a significant role of the oxides in metal retention. Citrate-dithionite extraction was more effective than oxalate in reducing Zn sorption and fixation, suggesting a significant influence of the more crystalline iron oxide fraction. These extraction procedures had less effect on the ability of the clays to sorb and fix Cu. Treatment of the clays by hypochlorite to remove organics tended to either enhance or have little effect on sorption and fixation of Cu and Zn. It is concluded that microcrystalline and noncrystalline oxides in the clay fraction of this soil, representing < 20% of the clay by weight, provide reactive surfaces for the chemisorption of Cu and Zn. At low pH, adsorption at these surfaces may be the dominant mechanism of heavy metal immobilization, especially in the subsoil horizons.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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