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Exchange Adsorption or Precipitation of Lead in Soils Treated with Chlorides of Aluminum, Calcium, and Sodium¹

ABSTRACT

The exchange behavior of Pb²⁺ present in small concentrations in kaolinitic, montmorillonitic, and illitic soils pretreated with Al³⁺ or Ca²⁺, and kept at a number of salt (Cl) levels, was in agreement with mass-action law principles. The mean values of the Gapon exchange coefficient describing the distribution of ions between the adsorbed and solution phases in Cecil, Winsum, and Yolo soils were 0.31, 0.11, and 0.24 for Pb-Al systems, and 4.13, 4.97, and 11.1 for Pb-Ca systems. In Na⁺-treated, alkalized soils, Pb precipitated. The solubility of the precipitate increased with decreasing pH and concentration of salt (NaCl). The solubility in solutions used for suspending the soil was less in the presence than in the absence of soil. This may indicate that the Pb-soil complex is less soluble than the precipitate formed in solution, so that when soil is present the composition of the precipitate shifts toward a less soluble form. This would imply a multi-component nature of the precipitate.

¹ Contribution from the Agricultural Chemicals Management Lab., ARS, USDA, National Agr. Res. Center, Beltsville, Md. 20705.

² Soil Scientists (Chemistry).

Received for publication March 31, 1972. Accepted for publication September 5, 1972.