| Mn3O4 could be used as the raw material in the preparation of soft magnetic materials such as manganese zinc ferrite. The tons of Electrolytic Manganese Residue (EMR) have become a serious problem and the comprehensive utilization of EMR has great benefit to environment and economy. The research applied leaching EMR in sulfuric acid medium (H2SO4), MnSO4 solution containing various ions was obtained. Purifying the produced solution and then adding aqueous alkali to the purified MnSO4 solution to obtain Mn(OH)2. Aqueous solution oxidation method under atmosphere pressure and roasting method (500℃to 700℃) were employed to obtain Mn3O4 using the obtained Mn(OH)2. The produced samples were investigated by using several analysis techniques including total Mn content (TMC), X-ray powder diffraction (XRD), Fourier Transformation Infra-Red (FTIR) spectra, Brunauer-Emmett-Teller (BET) specific surface area, particle distribution (laser particle size analyzer), magnetic measurements [Vibrating Sample Magnetometer (VSM)]. The main conclusions could be obtained as follow.Adding ethanol during oxidation in the mixed medium has a marked increase for the final TMC (TMC could reach 72.04%); TMC of all samples produced by using roasting method are relatively low and it is hard to obtain a single phase Mn3O4. High temperature roasting could lead to better crystal growth, bigger grain size compared with drying at 100℃in aqueous solution oxidation method. Roasting at high temperature was not beneficial to obtain products with fine and good particle.Through XRD, FTIR and determination of TMC, the products prepared by adding ethanol during oxidation (sample A.pee) or by adding NH4OH-NH4Cl buffer solutions (sample A.B40) were confirmed to be a single phase Mn3O4; sample produced by roasting at 550℃contained a small amount of manganese oxide (Mn2O3).BET test results showed that BET Surface area of product synthesized by aqueous solution oxidation method were larger than that of roasting method. Sample prepared by adding NH4OH-NH4Cl buffer solutions during oxidation process had largest BET Surface Area, which could reach 32m2 g-1.Particle size distribution analysis reveals that the second particle size of the products by preparing in aqueous medium was smaller than that of roasting method. The size tested by particle size analyzer was about 1μm, which was greatly larger than the size (60nm) evaluated by using Scherrer formula; the reason was that Mn3O4 particle became agglomeration through hydration during the analyzer test process in aqueous medium.The products prepared by these two methods exhibited paramagnetic character, and Ms was 0.71 emu g-1.
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