Effect of pH on adsorption of copper, zinc, and cadmium from landfill leachate by clay minerals

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Abstract
The removal (exchange‐adsorption plus precipitation) of Cu, Zn, and Cd from a municipal landfill leachate by kaolinite and montmorillonite was found to be dependent upon the pH and the ionic strength of the leachate. Sorption increased with increasing pH values and with increasing concentration of heavy metals. Montmorillonite sorbed approximately five times more heavy metal from solution than kaolinite. Precipitation contributed significantly to removal of Cu, Zn, and Cd from leachate above pH 6. The removal versus pH data (pH range 2 to 8) were used to construct adsorption isotherms at several pH values. Leachate isotherms were constructed at pH 5.0 and compared with pure aqueous solution isotherms for the same pH. The amount of adsorption at pH 5.0 from leachate was significantly lower than that from pure nitrate salt solutions because of competition from the other cations present in the leachate. Migration of heavy‐metal ions through clay materials is predicted to be much greater in landfill leachate than in comparable aqueous solutions of lower ionic strength.