China Nonferrous Metallurgy

The main metal elements in deep-sea polymetallic nodules include manganese, iron, nickel, cobalt, and copper, mainly existing in the form of silicate-aluminum-manganese oxides. To achieve green and efficient extraction of the target metals (manganese, nickel, cobalt, copper) from this ore, this study employs a ammonium chloride roasting-leaching process. Ammonium chloride roasting can convert the target metal ores into soluble chlorides, which can then be separated from gangue and impurities through water leaching. Single-factor experiments were used to optimize the process parameters, and various characterization methods were applied to investigate the changes in the occurrence states of the target metals, leading to the following main conclusions. Thermodynamic analysis indicates that at 300°C, CoO, NiO, CuO, and MnO₂ in the nodules can undergo chlorination to form chlorides, while the chlorination reaction of Fe₂O₃ has a ΔG much greater than 0, so it cannot occur spontaneously. Under the conditions of a mass ratio of deep-sea polymetallic nodules to ammonium chloride of 1:1.6, roasting temperature of 300°C, roasting time of 90 minutes, liquid-solid ratio (mL/g) of 6:1, leaching temperature of 40°C, and leaching time of 60 minutes, the leaching rates of manganese, nickel, cobalt, and copper can reach over 99%, while the leaching rate of iron is about 20%, effectively separating manganese, nickel, cobalt, and copper from iron, facilitating subsequent purification of the target metals. Multiple characterization analyses show that the chlorine element is successfully incorporated into the lattice of the roasted products, Mn⁴⁺ and Mn³⁺ oxides in the raw ore convert to Mn²⁺, accompanied by the formation of Fe₂O₃. The main phases in the leach residue were SiO₂, with only weak characteristic peaks of Fe₂O₃, and the extraction of manganese was nearly complete. These results can provide theoretical and technological references for the industrial utilization of deep-sea polymetallic nodule resources.