Sorption and precipitation of iron of kaolinite. I. Factors involved in sorption equilibria

Abstract

Sorption of low concentrations of ferric iron (10-5M or less) by kaolinite, under conditions excluding precipitation, was affected by iron originally present in the clay. The extent of interference (measured by isotopic dilution) was examined after extraction by several methods, including a new one in which ascorbic acid was used. Only after the most exhaustive extractions could the influence of native iron on sorption equilibria be neglected. Irregular effects of clay : solution ratio upon iron uptake were observed when clays were extracted with reducing agents. Although only partially rectified by oxidative pretreatment, these irregularities could be fully suppressed by the presence of oxidizers during the measurement of iron uptake. To a lesser degree, iron uptake by various sorbing materials not previously treated with reducing agents was influenced by the addition of oxidizers to the reaction medium. This additional effect was attributed to an increase in the oxidation potential of the otherwise weakly poised systems examined. To obtain valid sorption isotherms, all the above factors must be taken into account.