The crystallinity and surface characteristics of synthetic ferrihydrite and its relationship to kaolinite surfaces

Abstract

AbstractSynthetic ferrihydrites with Si added at mass ratios of Si/Fe = 0, 10, 20, 40, 80, and 160 × 10−3 have been studied to examine the effect of Si on the properties of ferrihydrite. The Si proportionally reduces the point of zero charge but influences surface area, loss of weight to 800°C and solubility in acid oxalate solution to varying degrees. At a critical concentration of Si (when Si/Fe = 20 × 10−3) these measured properties indicate a greater particle size and a more ordered structure. The relationship between synthetic ferrihydrite and the surface of kaolinite has been studied by a combination of surface area and charge determinations and TEM. An attraction predicted at pH 3 between ferrihydrite particles and the basal surface of kaolinite has been confirmed, and resulted in a stable coating. However, at pH 6 any attraction between the minerals appears to be too weak to produce a coating of the kaolinite surfaces.