Fundamental Research On Novel Process Of Manganese Oxide Ores By Sulfur-based Reduction Roasting-acid Leaching

In recent years, with the rapid development of domestic manganese industry, the output of manganese alloy and electrolytic manganese occupies the first place all over the world. The abundant manganese ore resourses are classified as manganese oxide ore, manganese carbonate and polymetallic manganese ore. Traditional processes of handling manganese carbonate ores are relatively simple and mature, the deposit of which is increasingly decreased. Manganese oxide ores and polymetallic manganese ores are becoming the main sources of manganese product in the long run.High valence state of manganese existing in manganese oxide ore is insoluble in dilute sulphuric acid. Reducing agents should be used in order to realize the transformation of high valence Mn oxides to low valence Mn compounds, which are acid soluble or water soluble. This dissertation focuses on low-grade manganese ores from Xiangxi of Hunan. The physicochemical properties and embedded form of main minerals are systematically studied firstly. Thermodynamic basis of manganese dioxide during the reduction roasting by sulphur are subsequently found out. The phase transformation procedure of manganese dioxide reduced by sulphur is revealed using pure materials. Based on the above researches, a novel process for utilizing low-grade manganese oxide ores by sulphur-based reduction roasting followed by acid-leaching is developed.Thermodynamics investigation indicates that, in anaerobic system, MnO2can be reduced by liquid sulfur(T<718K) directly to MnO and MnSO4, or in the order of MnO2�'Mn2O3�'Mn3O4. After that, Mn3O4is easier to be reduced to MnS and MnSO4by liquid sulfur. Reaction between Mn3O4and MnS will occur and MnO together with SO2are generated if the roasting temperature T is above752.80K. During reduction roasting between MnO2and gaseous sulfur(S2/S6、T>718K), MnO2can be reduced directly to MnO and MnSO4, or in order of MnO2�'Mn2O3�'Mn3O4. In this condition, Mn3O4being reduced to MnO is much easier than MnS. In addition, MnSO4is formed because SO2is reacted with manganese oxides, nevertheless, high temperature is adverse to the generation of MnSO4.Research on the phase transformation of MnO2in the reduction roasting process reveals that: (1) MnS, MnSO4as well as a small amount of Mn3O4and MnO are found as main Mn phases when roasting temperature is below500℃. The temperature range of500℃-550℃is considered as transitory stage in which MnS and Mn3O4begin reacting, leading to weakening of diffration peaks of MnS and Mn3O4. Main Mn phases are MnO, MnSO4and a small number of Mn3O4when temperature exceeds550℃.(2) MnO2is reduced to Mn2O3, Mn3O4as well as MnSO4when S/Mn ratio is below0.27. Mn3O4will convert to MnS with the increase of S/Mn ratio.(3) It can be observed that MnO2is reduced rapidly by sulfur. The diffraction peaks of MnS and Mn3O4can be found when roasted at350℃for5min and nearly remain constant after that. When roasting temperature is550℃, the diffraction peaks of MnO2and Mn2O3disappear compeletely after roasting2min, main Mn phases are MnS and Mn3O4, simultaneously, a small amount of MnO are found. MnS and Mn3O4still coexist within5min, nevertheless, the diffraction intensity of MnO enhances. The diffraction intensity of MnS and Mn3O4weakens while that of MnO further enhences with prolonging roasting time.According to research on the process of low-grade manganese oxide ores reduction roasting by sulfur, appropriate roasting parameters are acquired as the following:roasting temperature550℃, roasting time10min, S/Mn=0.50, the proportion of-0.074mm grain grade of raw ores is80%. Appropriate leaching parameters are:H2SO4concentration10%, liquid-solid ratio5:1, leaching time5min, leaching temperature25℃and stirring speed200rpm. It can be seen that Mn and Fe leaching ratios of95.56%and14.54%respectively are obtained under the optimal conditions. This novel process is effective to the other type of manganese oxide ores, and Mn leaching ratio above95%is obtained.This investigation provides a new approach for the comprehensive utilization of low-grade manganese oxide ores and credible technological parameters for the industrial production of the novel process.