An XPS investigation of the effects of heat treatment on the chlorine surface chemistry of some lignites

X-ray photoelectron spectroscopy (XPS) was used to study the conversion of inorganic chlorine (chloride salts) to CCl bonds and subsequently chloro-organics on the surface of lignite by heat treatment at 300 °C in humid air. It is shown that a naturally chloride-rich lignite can form chloro-organics by heat treatment without added catalysts. The XPS method was used to verify CCl bonds on the lignite surface as a necessary condition of chloro-organic formation according to the so-called de novo synthesis. The chloro-organics were formed in a layer on the lignite surface with a chlorine content significantly higher than on the original surface. This implies that under the influence of air, chloride ions moved to the lignite surface, with subsequent oxidation and formation of CCl bonds on the surface, allowing subsequent release of toxic PCDDs and PCDFs.