Thermodynamics And The Smelting Process Of Non-Traditional Ni-Co Resources Based On The MnO-SiO₂ System

Both cobalt and nickel are significant strategic metals and are also the main raw materials for producing lithium-ion battery cathode materials.In recent years,China’s new energy electric vehicle industry has entered an explosive growth period.Meanwhile,the consumption of cobalt and nickel has increased rapidly.However,China is severely short on the cobalt and nickel resources,with world totals of these resources accounting for just1.1%and 3.9%,respectively,resulting in a serious imbalance in the sup-ply-demand relationship.Deep-sea manganese nodules are not only high in nickel and cobalt contents,but also rich in reserves,which are viewed as the most commercial mineral resources in the 21st century.In addition,with the continuous growth of consumption and possession of new energy（battery）vehicles,the amount of spent LIBs will also increase significantly.As a result,the cobalt and nickel resources contained in spent LIBs will also be very large.Thus,extracting nickel and cobalt from manganese nod-ules and spent lithium ion batteries is critical for ensuring the supply secu-rity of cobalt and nickel strategic metals.A combinatorial reduction smelting-alloy oxidation process based on a manganese-rich slag system has been developed in order to extract valu-able metals from non-traditional Co and Ni resources such as polymetallic nodules and spent lithium ion batteries.This process is much more com-petitive because of its high production capacity and high adaptability.However,little information on the thermodynamic properties of nickel and cobalt oxides in the manganese-rich slag and the phase diagram for the slag containing manganese can be obtained.Thus,this study focuses on the thermodynamic properties of nickel and cobalt oxides in the manganese-rich slags and the phase diagrams for the slags containing manganese.The following main conclusions are summarized as follows:（1）An oxidation-blowing desilication and water atomizing technique based on a manganese-rich slag system has been developed to recover val-uable metals from cobalt white alloy.The results showed that 83.17%of Si in the white alloy was removed effectively by oxidizing it preferentially into the“Mn O”-Si O₂-Mg O slag.97.99%of cobalt and 97.78%of copper were leached under optimal conditions according to:temperature of 368 K,liquid/solid ratio of 10/1,excess of sulfuric acid of 1.3 times the stoichio-metric demand,stirring rate of 1500 rpm,leaching time of 8.0 hours,and oxygen gas flow rate of 0.15 L/min.The overall recovery in this process attained 94.33%for copper and 93.41%for cobalt,separately.The new process can also be connected with the reduction smelting process of the polymetallic manganese nodules and spent lithium-ion batteries based on the manganese-rich slag system.（2）Under controlled oxygen partial pressure ranging from 10^-7.3 to10^-5.0 at temperatures of 1573 K and 1623 K,phase equilibrias between Cu-Co（Ni）alloy and Si O₂-saturated Mn O-Si O₂ or Al₂O₃-saturated Mn O-Si O₂-Al₂O₃ slags were experimentally conducted.Cobalt and nickel in the Mn O-Si O₂ slag and Mn O-Si O₂-Al₂O₃ slag existed as CoO and NiO,re-spectively.The distribution ratios of Co and Ni were in the range of10^-1.76～10^-0.17 and 10^-3.07～10^-1.95,respectively.Increasing temperature or adding Al₂O₃ to Mn O-Si O₂ slag could decrease the solubility of cobalt and nickel.（3）The activity coefficient of CoO,which is solid CoO,in the Si O₂saturated Mn O-Si O₂ slag and Al₂O₃ saturated Mn O-Si O₂-Al₂O₃ slag at1623 K can be respectively calculated asγ_CoO（s）=-0.28w（CoO）+2.32 andγ_CoO（s）=1.46w（CoO）+2.92,respectively,where w（CoO）is the CoO con-tent in the slag,wt%.The activity coefficient of CoO,which is solid CoO,in the Al₂O₃ saturated Mn O-Si O₂-Al₂O₃ slag at 1573 K can be calculated asγ_CoO（s）=6.55w（CoO）+8.40,where w（CoO）is the CoO content in the slag,wt%.（4）The activity coefficient of NiO,which is solid NiO,in the Si O₂saturated Mn O-Si O₂ slag and Al₂O₃ saturated Mn O-Si O₂-Al₂O₃ slag at1623 K can be respectively calculated asγ_NiO（s）=8.58w（NiO）+3.18 andγ_NiO（s）=11.06w（NiO）+4.07,respectively,where w（NiO）is the NiO con-tent in the slag,wt%.The activity coefficient of NiO,which is solid NiO,in the Al₂O₃ saturated Mn O-Si O₂-Al₂O₃ slag at 1573 K can be calculated asγ_NiO（s）=46.77w（NiO）+9.85,where w（NiO）is the NiO content in the slag,wt%.（5）Phase equilibrium relations for the“Mn O”-Si O₂-Al₂O₃ system were studied at 1573 K and 1673 K in air by an equilibration/quench-ing/SEM/EDS/XRD technique.At 1573 K,the location of the“liquid+Si O₂+mullite”region and the Si O₂ saturated liquidus were consistent with the results calculated by Factsage 8.0.However,the Si O₂ content for the cubic-spinel saturated liquidus and the Al₂O₃ content for the mullite satu-rated liquidus were higher than those results calculated by Factsage 8.0.The location of the“liquid+Al₂O₃+cubic-spinel”region has a significant discrepancy compared to the calculation result.At 1673 K,the Si O₂ satu-rated liquidus was consistent with the results calculated by Factsage 8.0.However,the Si O₂ content for the cubic-spinel saturated liquidus and the Al₂O₃ content for the mullite saturated liquidus were higher than those re-sults calculated by Factsage 8.0.（6）Phase equilibrium relations for the“Mn O”-Si O₂-Mg O system were studied at 1573 K and 1673 K in air by an equilibration/quench-ing/SEM/EDS/XRD technique.At 1573 K,the lines of“Mn Si O₃-Mg Si O₃”and“Mn₂SO₄-Mg₂Si O₄”were consistent with the results calculated by Factsage 8.0.However,the area of the liquid region was obviously less than those results calculated by Factsage 8.0.The positions of the regions“liquid+rhodonite+olivine”,“olivine+monoxide+cubic-spinel”,and“clinopyroxene+pyroxmangite+Si O₂”differed significantly from the calculation result.The results from present work will not only give important guidance for process optimization,but also provide significant basic data for updat-ing the relevant thermodynamic databases.