Optimization of Gas-Solid Co-Reduction Conditions for Deep-Sea Polymetallic Nodules

The use of hydrogen during the reduction of deep-sea polymetallic nodules is an attractive method to reduce carbon consumption. The effect of hydrogen on the pre-reduction of deep-sea polymetallic nodule pellets was investigated. The results show that the presence of H2 effectively destroys the lattice of the manganese mineral phase and releases the NiO, CoO, and CuO in it, thus successfully generating a Fe-Ni-Co-Cu alloy. The H2 atmosphere has limited ability to reduce polymetallic nodules, so a gas-solid synergistic reduction process is proposed, which is significantly better than that of carbon-free pellets with the improved reduction effect. The average values of Ni, Co, and Cu contents in the alloy particles generated at 1100 degrees C can be significantly increased to 26.85%, 3.97%, and 13.69%, respectively. When the reduction temperature is higher than 1100 degrees C, the metal droplets migrate further and gather to form millimeter-sized alloy particles, while the reduction effect of H2 is weakened. In addition, the change of the carbon to oxygen ratio has less effect on the reduction effect because H2 completes the reduction of most of the oxides at a lower temperature. This study provides a new process and reference for the low carbon and efficient reduction of deep-sea polymetallic nodules.