EFFECTS OF FULVIC ACID AND pH ON ZINC SORPTION ON MONTMORILLONITE1

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Abstract
The objective of this work was to study the interaction between fulvic acid (FA) and Zn sorption in montmorillonite suspensions at various pH levels in order to elucidate the role of FA in solubilizing soil Zn. Increases in FA solution concentration up to 1.2 mM resulted in an appreciable increase in Zn concentration in solution at pH levels lower than 7.5. Higher FA concentrations (about 3.2 mM) were needed to solubilize Zn at pH .gtoreq. 7.5. A competitive adsorption model describing Zn sorption as a function of Zn and FA concentrations and of pH is presented. According to the model, the main pH effect was due to the larger bonding energy of ZnOH+ to the clay surface. The affinity of the Zn-FA complex to the clay is appreciably lower than that of ZnOH+; hence an addition of FA to the solution reduces Zn adsorption.
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