Fe and Mn Oxidation States by TEM-EELS in Fine-Particle Emissions from a Fe–Mn Alloy Making Plant

Abstract

Fine particles were sampled both inside the chimneys and in the near-field of an Fe-Mn-alloy manufacturing plant. The transfer from one point to another point in the environment, as well as the bioavailability and toxicity of these two metals, depend above all on their speciation. The oxidation states of iron and manganese in the collected particles were determined by using transmission electron microscopy coupled with electron energy-loss spectroscopy (TEM-EELS). The mineralogical identity of these metal-rich particles was determined by selected area electron diffraction (SAED) coupled with energy-dispersive X-ray spectroscopy (EDX). This study shows that both iron and manganese in metallic particles are prone to oxidation reactions via gas/particle conversion mechanisms, which take place in the flue gases within the smoke stacks. This phenomenon is more pronounced for the smallest Fe-rich particles. However, no further change of oxidation state of the two elements was observed in the near-field of the plant, after emission into the atmosphere (within <2000 m of the smoke stacks). The oxidation states of iron and manganese remain mainly between +II and +III, which is probably due to short residence time of these particles in the pollution plume.