ADSORPTION OF PICLORAM BY HUMIC ACIDS AND HUMIN

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Abstract
More picloram (4-amino-3,5,6,-trichloropicolinic acid) was adsorbed by humin than by the organic low-moor peat soil humus from which the humin was prepared. However, less picloram was adsorbed by the humic acids extracted from the organic material. The pH-dependent adsorption found for all 4 preparations agreed with the concept that the adsorption of picloram is largely that of uncharged (or dipolar) molecules. The effects of salt concentration on adsorption are largely those due to exchange of hydrogen into solution, shifting the equilibrium toward the molecular form. Anion exchange apparently did not occur with the organic matter preparations. Salting out occurred with 0.1 M salt solutions. A slight decrease in adsorption took place at pH values below 1 and this is explained by the fact that picloram becomes diprotonated in this pH region, forming cations, which cannot compete with H+ for adsorption sites.

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