After a conducting preliminary chromite reduction tests in a 18 kW combined plasma induction furnace, a 100 kW DC plasma-arc furnace facility was utilized to conduct additional reduction tests on North American chromite concentrate fines. The fines were successfully fed through a hollow graphite electrode with low chromium losses in the offgas. Reduction tests conducted with a plasma-arc produced a slag with a low chromium oxide content. After tapping, the slag was found to contain on average 3.6 percent Cr_2O_3. This resulted in chromium recoveries above 93.5 percent. When the liquid metal and slag were retained in the furnace after burden feeding ceased, the concentration of chromium oxide in the slag was observed to decrease with time reaching levels below 0.5 percent. In several tests, high quantities of sulfur, in the form of nickel sulfides, were added to the charge. It was found that in most cases more than 60 percent of the sulfur charged to the furnace could not be accounted for based upon assay results of the metal and slag produced. It is believed that the sulfur that cannot be accounted for has been transferred to the gas phase and leaves the furnace as yet to be identified gaseous components of the offgas. The sulfur concentrations in the alloy were below 0.030 percent. Similar analytical test results were also found in the small scale 18 kW plasma-arc/induction unit.
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