INTERACTIONS BETWEEN DIFFERENT ANIONS AND THE GEOTHITE SURFACE AS SEEN BY DIFFERENT METHODS

The present paper deals with the studies on adsorption of three anions (oxalate, benzoate and phosphate) on synthetic goethite. Adsorption isotherms, adsorption-desorption as a function of pH and electrophoretic mobility measurements were carried out to understand the nature of adsorption. Results indicate that the three anions exhibit different adsorption characteristics following different mechanisms. While benzoate seems to adsorb non-specifically, phosphate adsorbs (with strong interactions) specifically. Adsorption of oxalate is found to be less specific than that of phosphate. Adsorption of all the three anions is affected by pH. The different experiments carried out to understand the adsorption behaviour of the three anions complement each other. The results are discussed to arrive at the possible mechanism of adsorption of these anions on goethite.