Arc plasma treatments of Fe-Co-Ni alloy using Ar, Ar-Cl-2, Ar-N-2, Ar-O-2, Ai-Cl-2-N-2 and Ar-Cl-2-O-2 arc plasmas with varying O-2 flow rate were examined. Large amounts of fumes were formed when Ar-Cl-2-N-2 and Ar-Cl-2-O-2 plasmas were used. The Fe component was separated selectively from the alloy using Ar-Cl-2, Ar-Cl-2-N-2 and Ar-Cl-2-O-2 plasmas with a small concentration of O-2 while the Co component was separated using Ar-Cl-2-O-2, plasmas with a high concentration of O-2. The separation of Fe F-7 components was attributed to the selective chlorination of Fe. The separation of Co was attributed to both the chlorination of Co and the oxidation of Fe.