ED-XRD study of ferrihydrite transformation to goethite via the Fe~Ⅱ pathway

摘要

In this study, we apply ED-XRD to investigate the transformation of ferrihydrite to goethite in oxygen-free solutions at circumneutral pH with Fe_((aq))~Ⅱ/Fe_((s))~Ⅲ ratios (x) ranging from 0.04 to 0.18. Time resolved ED-XRD data show that poorly ordered ferrihydrite rapidly transforms into crystalline goethite in the presence of ferrous iron.Changes in diffraction peak area were used to investigate the reaction kinetics and reaction mechanism for experiments conducted at varying Fe~Ⅱ concentrations. The rate constants determined in this study provide insights into the formation of goethite at redox transition zones in low temperature water-rock systems.