Sorption and precipitation of iron on koalinitie. V. Comparison between kaolinite and ion exchange materials

Abstract

The uptake of low concentrations of iron(III) by ion exchange materials was measured in the presence of relatively concentrated supporting electrolyte solutions. The results were compared with those obtained under the same conditions in the preceding study of kaolinite suspensions. Distinctive differences between kaolinite and strongly acidic polystyrene resin systems at 0.15M ionic strength were found in (a) the nature of the sorption-pH relationships, (b) the reversibility of the reaction with respect to both concentration and temperature, (c) the effects of competing ions, and (d) the extraction of iron after sorption. Such observations confirmed that the iron-kaolinite bond formed under these conditions was stronger than that normally produced by electrostatic attraction at ion exchange sites. When the electrolyte concentration was lowered to 0.01M , some of the above characteristics of ion exchange uptake appeared in kaolinite systems. A comparison of the effects of time, temperature, and ionic strength between iron sorption by kaolinite and by cellulosic ion exchange materials suggested that both ion exchange and specific sorption mechanisms were operating at the lower ionic strength.