EFFECT OF PH ON EXCHANGE-ADSORPTION OR PRECIPITATION OF LEAD FROM LANDFILL LEACHATES BY CLAY-MINERALS

The capacity of kaolinite and montmorillonite clay minerals to remove Pb from municipal landfill leachates and the mechanisms by which removal is achieved were studied to evaluate the potential usefulness of clay minerals as liners for waste disposal sites under conditions of varying pH and ionic competition. Montmorillonite removed as much as 5 times more Pb from various solutions than kaolinite. Pb removal was reduced as much as 85% by leachate when compared to the amounts removed from pure Pb(NO3)2 solutions. Pb removal from solution is primarily a cation exchange-adsorption reaction that is affected by pH and ionic competition. At pH values > 6, a large increase in Pb removal from solution by clay can be expected, due to increased adsorption of Pb-hydroxyl complexes or formation of PbCO3 in landfill leachates. Formation of Pb-organic complexes is of secondary importance in landfill leachates due to competition from high concentrations of other cations. Pb migration through a montmorillonite liner was predicted to vary between < 2 cm/yr from pH 5 Pb(NO3)2 solutions and < 18 cm/yr from pH 3 DuPage leachate solutions of up to 1000 ppm Pb. Pb migration through a kaolinite liner varied between < 10 and < 79 cm/yr under the same conditions.