Fe(II)-induced Transformation of Ferrihydrite in Sulfate-rich Environment

摘要

The transformation from ferrihydrite to various iron oxides and iron oxyhydroxides has been given much attention not only in environmental science and geochemistry but also in biology and material science. This laboratory study attempted to delineate Fe(II)-induced transformation processes of ferrihydrite in sulfate-rich environment. The results indicated that the transformation in sulfate-rich media is different from that in Cl- media. The differences were shown not only in the species, the amount and the morphology of product but also in the transformation rate of ferrihydrite. Lepidocrocite predominates in the product at Room temperature (RT) in Cl- media while goethite is almost the only product in SO4 2- media. Goethite particles obtained in Cl- media are star-like and rod-like in SO4 2- media. Moreover, the transformation rate in the latter system is obviously less than that that in the former system. The transformation mechanism also varies with reaction conditions. A high temperature (in the range from room temperature (RT) to 100℃) and a high pH (in the range from 5 to 9) and a fast heating rate are favorable to solid state transformation of ferrihydrite in solution as well as the formation of hematite, while a low temperature and a low pH and a low heating rate are favorable dissolution reprecipitation mechanism as well as the formation of goethite, which is helpful to control the synthesis of iron oxides.