Formation and Morphology Evolution from Ferrihydrite to Hematite in the Presence of Tartaric Acid

Abstract

Hematite, with ferrihydrite as the common precursor, is the most stable iron oxide in soils and sediments and has many applications in environmental systems. As a common reducing agent in soils, tartaric acid (L-TA) can reduce Fe3+ to Fe2+ and template the formation of hematite from ferrihydrite. Here, the formation of hematite in the presence of L-TA was investigated under different L-TA concentrations, initial suspension pH, and aging time. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high- resolution transmission electron microscopy (HRTEM). Both the transformation process and the particle morphology of hematite were affected by the initial suspension pHi at which the L-TA was added to the suspension. Optimal pHi values at a L-TA/Fe(III) molar ratio of 1.0% and an aging time of 10 h at 100 °C were pHi 7 and pHi 11. At pHi 7, the optimal L-TA/Fe(III) molar ratio for the transformation was 1.0% and aging at 100 °C was completed after about 20 h. The ...