Competing Interactions of Fe (III) – Al (III) – Hydr(oxide) CoPrecipitates with Quartz in Siliciclastics

Abstract

Quartz and hydr(oxides) of iron (hematite, goethite) and aluminium (gibbsite) are principal components of siliciclastics (sandstone and shale). Field observations and experimental studies have confirmed the nucleation and growth of these hydr(oxides) on quartz grains at surface temperatures. The structural stability of soils and sediments has been positively correlated with their iron and aluminium composition. However, both iron (Fe) and aluminium (Al) components have been treated distinctly. In this study, hydr(oxides) of Fe and Al were simultaneously synthesized on quartz grains, which were then characterized using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and Raman spectroscopy. The mixed synthesis shows agglomeration of goethite needles and gibbsite on the quartz. The goethite needles first precipitated, possibly because of its lower solubility, while the free flowing characteristic of gibbsite causes it to creep over the initially synthesized goethite needles. The Al ions hinder the growth of goethite, since it can replace as much as one third of Fe in goethite, with degree of substitution increasing with decreasing grain size.