Coating of quartz silica with iron oxides: Characterization and surface reactivity of iron coating phases

Although the coating of silica sand with reactive phases such as iron oxides was widely investigated in the literature, the impact of dissolved species (Si) leached from silica sand on the surface reactivity of the produced material has received scant attention. In this work, two different procedures were used for the synthesis of Goethite-Coated Sand (GCS) and Hematite-Coated Sand (HCS). The synthesized coated quartz samples were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffractometry, Raman and infrared spectroscopies, gas adsorption volumetry and chemical analysis. The surface and structural properties of iron oxide-coated sands were compared with the pure individual phases and the powder mechanical mixtures. For both GCS and HCS, the IR and Raman observations showed that the surface hydroxyls of quartz were involved in the coating process, providing a strong bonding between the coating iron oxides and the silica surface. The presence of dissolved silica has an impact on the formation of goethite crystallites, which have a smaller size and higher surface area than those formed in the absence of silica quartz. According to the sorption data and spectroscopic investigations, iron oxide particles of GCS sample may contain much more Si than those of HCS. Silicates can be covalently bonded to the goethite surface by replacement of OH group as shown by infrared spectroscopy. Due to the presence of sorbed silicates, the change of surface reactivity and PZC value of iron oxide coating phases may modify surface retention capacity of coated subsurface materials.