Emissions of Some Organochlorine Compounds in Experimental Aluminum Degassing with Hexachloroethane

Abstract

Degassing agents based on hexachloroethane (HCE) are used to remove hydrogen gas from molten aluminum, particularly in foundries and remelting plants. Previously considered fairly innocuous, recent studies of the emissions from this process have shown high yields of some toxic organochlorine compounds. To determine a wider spectrum of such compounds, a series of experimental degassings was carried out in a small foundry. Aluminum was melted at 740°C in an electric furnace equipped with a ventilated exhaust hood, and degassing was carried out with 0.12 percent (w/w) HCE. Particulate, condensed liquid, and gas phase samples of the emissions were collected in the exhaust suction duct and analyzed with gas chromatography and mass spectrometry. Chlorobenzenes, chlorophenols, chlorinated dibenzodioxins and dibenzofurans, and polyaromatic hydrocarbons, as well as hydrogen chloride, carbon monoxide, and total hydrocarbons were determined. In relation to HCE, the major organochlorine compounds in the fume were hexachlorobenzene (4300 μg/g), octachlorostyrene (780 μg/g), and unreacted HCE (550 μg/g). The emissions of these substances were substantially higher than for chlorinated dibenzodioxins (0.034 μg/g) and dibenzofurans (0.36 μg/g). The emission of inorganic compounds was dominated by hydrogen chloride (330,000 μg/g). These results indicate that HCE-based degassing is a source of a complex mixture of inorganic and organochlorine compounds and suggest that alternative degassing techniques should be used. Alternatively, environmental emissions should be substantially reduced by using proper ventilation and filter techniques, and workplace exposure should be closely monitored, tentatively by measurements of hexachlorobenzene and hydrogen chloride.