Summary
The sorption of Cu by different clay minerals from dilute CuSO4 solutions was studied as a function of pH. It was found that Cu sorption increased with increasing the equilibrium pH. The low sorption at low pH values was attributed to the competition effect of H+ ions and the release of octahedral Mg, Fe and Al from the 2: 1 minerals in acid solutions. The higher sorption of copper at higher pH values was related to the absence of H+ ions and to the increase in the pH-dependent negative charge in kaolinite and gibbsite.
The desorption of copper using solutions of 1 N NaCl at different pH values indicated that kaolinite and montmorillonite released large amounts of their adsorbed Cu even at high pH values. Vermiculite, on the other hand, exhibited a strong retention of Cu against extraction with NaCl. Oven-drying had no significant effect on the desorption characteristics of the Cu-saturated clays.
The Ca-Cu exchange isotherms on montmorillonite were studied at two different pH values. The isotherms indicated a preference of Ca at the lower pH (pH 3.5), with K = 0.931 and ΔG = +41.0 cal./mole. At the higher pH (5.2) the isotherms indicated a preference of Cu with K = 1.282 and ΔG = −141.0 cal./mole. The difference was attributed to the competition of H+ at low pH.
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Kishk, F.M., Hassan, M.N. Sorption and desorption of copper by and from clay minerals. Plant Soil 39, 497–505 (1973). https://doi.org/10.1007/BF00264168
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DOI: https://doi.org/10.1007/BF00264168