Preparation Process Optimization Of Active Manganese Oxides From Low-grade Rhodochrosite Ore

With the rapid development of industry, the demand of manganese resources wasgrowing. Therewas a trend toward full utilization of low-grade rhodochrosite ore(LGRO), owning to their abundant reserves and low price. Mn3O4and MnO2wereimportant metal oxides and widely used in the electronic industry, the chemical industry,environmental protection, and so on. In this study, MnSO4solution, which was obtainedby leaching and purifying of LGRO, was used as raw material of Mn3O4andMnO2preparation. The preparation procedures were studied and promoted. This researchwas of great significance to provide a possible high efficiency way for the utilization ofLGRO.Mn3O4was prepared by two-phase oxidation method, and the preparationprocedures were studied and promoted. The results showed that the Mn3O4with highpurity and high specific surface area could be obtained under the following processes.The MnSO4solution of1.0mol/L was added into beaker under a flow rate of30mL/h.The pH of the reaction solution was adjusted to10using NH3·H2O at80C. Thenthe solids were washed and dried at200C for2.5h. The total Mn content (TMC) ofMn3O4was72.0%, which was larger than that of the premium grade ofmangano-manganic oxide for preparing soft magnetic ferrites. The ionic distributionswas formulated as [Mn2+][Mn2+0.3024Mn3+0.2937Mn4+0.3786â–¡0.0254]2O4. The averagecrystallite size of Mn3O4with tetragonal hausmannite structure was about35nm byXRD analysis.BET specific surface area of the Mn3O4reached to31.8m2/g.High-purityMn3O4was prepared by decomposing MnCO3,and the effects ofdecomposition time and temperature on the TMC were studied. The Mn recoveryefficiency was more than97%with the blended precipitant of Na2CO3and NH4HCO3(1:1mol/mol). The TMC of product increased with increase of decomposition time andtemperature. The quantitative relationship between TMC and decomposition time aswell as decompositions temperature could be fitted by empirical formulas. WhenMnCO3decomposed at1323K for120min, the TMC of Mn3O4could reach to72.0%.The product was investigated by XRD, FTIR and SEM. SEM images revealed that theproduct consisted of small and uniform particles with smooth surface and gooddispersion. Through XRD, FTIR and determination of TMC, the as-prepared productwas confirmed to be high-purity γ-Mn3O4. The ionic distributions was formulated as [Mn2+][Mn2+0.3024Mn3+0.2937Mn4+0.3786â–¡0.0254]2O4.MnO2was prepared by chemical bath deposition (CBD) method in alkalinesolution using K2S2O8asoxidant. The synthesized sample was characterized by XRD,SEM and BET. The results showed that the optimum conditions were as following,OH-/Mn2+mole ratio was5.0:1.0, K2S2O8amount was110%, reaction temperature andtime were50C and20min, respectively. Under the above conditions, the Mn recoveryefficiency was over98.5%and content of MnO2could reach91.5%, which reached tothe premium grade of manganese dioxide for preparing battery. The XRD indicated thatthe structure of the product contained α-MnO2and β-MnO2.SEM image revealed thatthe particles were irregular and random in shape. BET specific surface area and mostprobable pore size of the MnO2were97.8m2/g and15.0nm, respectively. The obtainedmanganese dioxide showed catalytic activity on the oxidation and decoloration ofRhodamine B (RhB) dye with the assistance of H2O2. The decoloration degree was98.5%.MnO2was prepared by CBD method using KMnO4asoxidant. The synthesizedsamples were characterized by XRD, XPS, FTIR, SEM and BET. The XRD indicatedthat the n (MnO4-:Mn2+) had an influence on the structures of products, and the rule ofcrystalline state of manganese dioxides was δâ†'αâ†'α+γ with the decrease of theproportion of KMnO4. XPS and FTIR showed that the chemical composition of productwas MnO2. SEM images revealed that the particles were irregular and random in shape.The surfaces of MnO2-1(n(MnO4-:Mn2+)=1:1.1) were covered in a mass of nanowires.The BET specific surface area of MnO2-1reached to141.9m2·g-1. The degradationdegree of Methylene blue (MB) bye and chemical oxygen demand (COD) of landfillleachate achieved up to97.2%and44.5%, respectively.