Occurrence characteristics of free iron oxides in soil microstructure: evidence from XRD, SEM and EDS

Free iron oxides in soils usually have distinct electrochemical properties, relatively high surface energy, a strong ability to adsorb, and provide structural cementation in the soil. Thus, soil properties are influenced by the content, characteristics and occurrence of free iron oxides. This paper reports a study on Zhanjiang clay and Longmen laterite, both of which are rich in free iron oxides, to investigate the occurrence characteristics of free iron oxides in soils. Dithionite-citrate-bicarbonate solution was adopted to remove free iron oxides from the soils, and qualitative filter paper was used to extract particles with size d