The solution chemistry of the fe- and co-nh3-h2o-co3 systems was analyzed in terms of aqueous stability diagrams. Electrochemical techniques such as open-circuit potential and anodic polarization measurements were used to investigate the dissolution behavior of bulk and sintered fe, CO, and fe-co alloys in ammoniacal ammonium carbonate solutions. The open-circuit and anodic polarization behaviors were studied in terms of alloy composition, heat treatment, solution composition, metal particle size, and sintering conditions. In addition, metallurgical characterization of the electrochemically treated solid surface was conducted by using various metallographic techniques, including x-ray diffraction and auger electron spectroscopy. The results indicate that the passivation behavior of fe controls the dissolution behavior of fe- CO alloys. Thus the electrochemical dissolution behavior of fe-co alloys may be, in part, responsible for the poor recovery of cobalt when the reductive-roast ammonia leach process is applied to ferruginous oxide ores.