Functional forms of carbon and chlorine in dust samples formed in the sintering process of iron ores

The chemical forms of the carbon and chlorine present in dust samples obtained from windboxes of the iron ore sintering machine have been studied with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The chlorine in the dust samples is present as KCl with the average crystalline size of 40-50 nm and covalent C-Cl bonds in condensed aromatic structures of unburned carbon surface. The proportion of chlorinated aromatic structures increases almost linearly with increasing that of surface oxygen complexes on unburned carbon, strongly suggesting that active surface sites of the carbon formed in the sintering process work as reaction sites with HCl and Cl ₂. Model experiments using a coke show that HCl reacts with it at 500°C to form several types of Cl-functional forms, from which the HCl desorption takes place at the wide range of 500-900°C upon reheating. Such a profile for HCl formation is almost unchanged after washing of the HCl-treated coke by water. These observations indicate the formation of organic chlorides. It is therefore likely that HCl and Cl₂ evolved in the combustion process react with active sites of unburned carbon surface to form organic chlorine compounds.