engleski

Microstructural properties of goethite particles precipitated in highly alkaline media

Goethite (α-FeOOH) is a widespread iron oxide mineral found in soils, sediments and rocks. Due to its acid-base surface properties it plays an important role in the geochemistry of plant nutrients and it is found to be responsible for the adsorption and distribution of potentially toxic heavy metals in nature. The goethite colour may vary from lemon yellow to dark brown and this property has been utilized in practical application as a pigment. Goethite particles can be used as the starting compound in the production of magnetic materials. Besides magnetite (Fe₃O₄) and hematite (α-Fe₂O₃), goethite is the third most important ore in raw iron production. In the laboratory, goethite particles may be precipitated using different chemical procedures. In this study, the iron choline citrate was used as starting chemical for the precipitation of goethite in a highly alkaline media. Goethite particles, precipitated in highly alkaline media by adding the NaOH solution to the iron choline citrate solution, were in the form of long rods of micron size in length and nanosize in width. The microstructure and phase composition of these particles did not change with ageing of their suspension for up to 14 days at 90 ºC. Autoclaving at 160 ºC showed a goethite-to-hematite phase transformation where the hematite yield was increasing with a prolonged ageing time of the goethite suspension (dissolution/recrystallization mechanism). The heating of goethite particles in air for up to 4 h at 300 ºC yielded hematite particles, where the original morfology of goethite particles was preserved. The changes in the morfology of hematite particles produced at 800 ºC were assigned to the loss of residual OH groups during solid state structural rearrengement and sintering.

goethite; hematite; Mossbauer; XRD

nije evidentirano