LABORATORY-SCALE THERMAL PLASMA-ARC VITRIFICATION STUDIES OF HEAVY METAL-LADEN WASTE

Plasma processing has been identified as a useful tool for immobilizin g heavy metal-contaminated wastes into safe, leach-resistant slag. Alt hough much effort has gone into developing this technology on a pilot scale, not much information has been published on basic research topic s. A laboratory-scale plasma are furnace located at the University of Illinois was operated in cooperation with the U.S. Army Construction E ngineering Research Laboratories in an effort to establish an understa nding of the chemical and physical processes (such as metal volatiliza tion and resultant gas evolution) that occur during thermal plasma tre atment of metal-spiked samples. Experiments were conducted on nickel a nd chromium using a highly instrumented furnace equipped with a 75 kW transferred are plasma torch. The volatility of nickel and chromium wa s examined as a function of varying oxygen partial pressures. Oxidizin g conditions reduced the total dust gathered for both the nickel and c hromium samples, although each dust sample was found to be metal-enric hed. Plasma treating increased the leach-resistance of the slags by at least one order of magnitude when compared to unprocessed specimens. The leach resistance of the nickel-containing slags increased in the p resence of oxygen, whereas chromium samples remained relatively consta nt.