Silicate and Phosphate Influence on Kaolin‐Iron Oxide Interactions

Abstract

AbstractInteractions between kaolin and iron oxide minerals are important in understanding the physical properties of highly weathered soils. This study shows that anions (silicate and phosphate) play a major role in determining the type and strength of particle associations, both during and after the formation of the iron oxide minerals in soils. The presence of silicate as an adsorbed anion on kaolinite inhibited iron oxide cyrstallization from ferric hydroxide gel and facilitated an intimate coulombic association between fine positively charged iron oxide particles and kaolin minerals whereas adsorbed phosphate did not affect the crystallization of iron oxide or the kaolinite iron oxide association. Mossbauer spectroscopy was used to demonstrate the existence of strong attractive forces between fine iron oxide particles and the kaolinite surface. The specific adsorption of silicate ions by associated kaolinite‐iron oxide systems, disrupted the attractive forces between kaolinite and iron oxides and effectively dispersed the system in most cases. This was taken as an evidence for the existence of coulombic type attractions. Attractions which could not be disrupted by silicate treatment were observed in cases where goethite was formed by the oxidation of Fe2+ ions in the presence of kaolinite and halloysite.