Study On Gas-solid Synergistic Reduction Mechanism Of Deep Sea Polymetallic Nodules

Deep sea polymetallic nodules,rich in Mn,Fe,Ni,Co,Cu and other valuable metal elements,are the most widely distributed and the largest reserves of metal mineral resources.At present,the pyrometallurgical process of polymetallic nodules requires high temperature and high carbon to oxygen ratio,which produces a lot of greenhouse gases in the process of production.Therefore,a process of producing Fe-Ni-Co-Cu alloy and manganese-rich slag by prereduction of polymetallic nodules the simultaneous action of gas reducing agent（H₂,CO）and solid reducing agent（C）was proposed in this thesis,aiming at providing a new reference for the low-carbon utilization of polymetallic nodules.In this thesis polymetallic nodules with Mn/Fe ratio of 3,Mn/Si ratio of 3.95 and total Ni,Co and Cu of more than 4 were taken as the research object.The effects of reduction temperature,reduction atmosphere and carbon-oxygen ratio on the reduction of polymetallic nodules were systematically studied.（1）Firstly,the thermodynamics of reduction of polymetallic nodules were calculated to verify the feasibility of gas-solid collaborative reduction.（1）At low temperature,the reduction of Ni O,Co O and Cu O by gas reducers can be spontaneous.The reaction degree of manganese and iron hyperoxide with gas reducers is higher than that with solid carbon.However,gas reducers can reduce Fe O to Fe,but cannot reduce Mn O to Mn.（2）The formation temperature of manganese carbide is lower than the reduction temperature of metal Mn,and manganese carbide can continue to react with manganese oxide to form metal Mn,so that Mn appears in the reduction products at a temperature lower than that of C reduction Mn O.（3）Manganese and iron oxides are easy to react with gangue components in nodules（Si O₂,Al₂O₃）to produce insoluble olivine phase and spinel phase.At the same time,manganese oxides have a strong binding ability with these gangue components,which can replace the iron oxides in the generated iron olivine and iron spinel,and promote the reduction of iron.（2）Secondly,through the orthogonal experiment results of three factors and four levels,it is found that the order of influence of each factor on the reduction results of polymetallic nodules containing carbon pellets is as follows:reduction temperature>reduction atmosphere>carbon-oxygen ratio.（3）The reduction experiments show that the pellet reduction effect of gas-solid synergistic reduction is obviously higher than that of single gas reduction.（1）With the increase of temperature,Si O₂in nodules reacts with part of Mn O and Fe O to form silicates,and the alloy is reduced out.The reduction effect is better at 1100℃,and the continuous temperature rise can only promote the soft melting of pellets and has little effect on the reduction of nodules.（2）When the ratio of carbon to oxygen is 0.6,most of Ni,Co and Cu have been reduced.At low temperature,the reduction reaction is mostly completed by gas reducing agent,while solid reducing agent does not participate in the reduction well,resulting in a large amount of carbon remaining in the pellet,but hindering the reduction reaction and the accumulation of metal droplets.When the temperature is higher than1000℃,the effect of carbon gasification is enhanced,and the effect of gas reducing agent is weakened.（3）The change of H₂/CO ratio at 1100℃has no effect on the weight loss rate of pellets,indicating that the reducing ability of gas reducers on polymetallic nodules reaches its limit under such conditions.In the atmosphere with high H₂content,the alloy particles contain more Ni,Co and Cu,while in the atmosphere with high CO content,the alloy particles contain more Cu and less Ni and Co.Therefore,polymetallic nodules have better reducibility in H₂atmosphere.