A Sustainable Low-Temperature Roasting and Water Leaching Process for Simultaneously Extracting Mn, Cu, Co, and Ni from Ocean Manganese Nodules

Ocean manganese nodules are rich in Mn, and also contain the strategic metals Cu, Co, and Ni. In this study, a sustainable low-temperature roasting and water leaching process for simultaneously extracting Mn, Cu, Co, and Ni from ocean manganese nodules was proposed. The results show that the primary mineral phase of iron-manganese oxides in the ocean manganese nodules reacted with ammonium sulfate during the roasting process, converting it to (NH4)(2)Mn-2(SO4)(3) , MnSO4, and NH4Fe(SO4)(2) . As the primary mineral phase was destroyed, Cu, Co, and Ni dispersed in the other host minerals could be released to react with ammonium sulfate and form metal sulfates. The sulfation reaction was completed at the roasting temperature of 380 degrees C, the mass ratio of ammonium sulfate to ocean manganese nodules of 1.25:1, and the roasting time of 90 min. The roasted slag was then leached with pure water and the leaching efficiencies for Mn, Cu, Co, and Ni reached 95.87%, 83.53%, 75.02%, and 87.04% under the liquid-to-solid ratio of 5:1, the leaching temperature of 40 degrees C, and leaching time of 30 min. The ammonium sulfate roasting-water leaching technology is a promising process, and the roasting temperature of 380 degrees C is much lower than that of pyrometallurgical techniques proposed in other studies, resulting in significant energy savings for the process. [GRAPHICS]