Ammonium ion was introduced to enhance the sulfidization of heterogenite, the main cobalt oxide mineral. The flotation recovery was significantly improved from less than 20% to over 70%. Micro flotation and FT-IR analyses indicated that ammonium ions enhanced the adsorption intensity of xanthate and improved the flotation recovery of heterogenite. Zeta potential, ICP-OES, and XPS tests further illustrated that cobalt on the surface of heterogenite was transferred to the liquid phase by forming ammonia complexes, thereby increasing the sulfur adsorption sites on the mineral surface and promoting sulfidization. This study will contribute to a better understanding of the flotation behavior of heterogenite and provide a valuable reference for the efficient recovery of cobalt oxide ores.