| Ferrite is one kind of soft magnetic material, which is widely used in communication, the audio and video equipment, and magnetic head industry, etc. trimanganese tetraoxide is the main material to produce ferrite.Now trimanganese tetraoxide is prepared by electrolyzing manganese metal in our country. This method has advantages of simple technology, easy operation and low pollution, but most of products are high selenium and small specific surface area.Moreover, the cost of this method is high because of the price of manganese and the poor of its profitability.In view of the prombles above, this text puts forward a new method of preparing Mn3O4 with microwave-assisted.In this method, the row material is manganous sulfate, which is preparing from leaching solution of pyrolusite.The impurity removal in leaching solution of pyrolusie was discussed in this study.Hydrolyzation-precipiation method was chosen to remove Fe3+ and Al3+.The pH value was adjiusted to 4~5. Fe3+ and Al3+ were converted to Fe(OH)3 and Al(OH)3 which could be removed as precipitant.The principle and method of removal to heavy metal ions in leaching solution was discussed.Sulphide precipitation method was adopted. The heavy metal ions was precipited using (NH4)2S as a suifidizing agent and polyacrylamide as flocculant during the pH value from 4 to 5 within the stirring time of 2 hours at 50℃. Mg2+ and Ca2+ were converted to deposition adding NH4F during the pH value from 3 to 5 at 50℃.Finally, the pure solution of manganous sulfate was prepared.Using manganous sulfate solution as precursor, Mn2+ was converted to Mn(OH)2 by the addition of ammoni, then Mn(OH)2 was oxidized to Mn3O4 with microwave irradiation.The rea-brown Mn3O4 powder was obtained.The effect of various factor on the manganese content of product was studied by experiment. The optimum preparation conditions with microwave heating were sure:the reaction temperature 70~90℃, the reaction time 30 min, the microwave power 800~1000 W, the rate of adding NH3·H2O(9.5%)3 mL·min-1 at 120℃. The total manganese content of product was 71.62%, and the sulfur content was 0.0625%.The crystals structure of product was characterized by X-ray diffraction analysis (XRD). The crystal form of Mn3O4 was defined as a spinel type.Ion distribution model of product was (Mn2+)A(Mn20+.6 119Mn30+.5 483Mn04+.7 829□0.0569)BO4.The morphology and particle size of sample was observated with the help of scanning electron microscope(SEM).The average particle size of the powder was 4μm.The specific surface area of product was 187 m2·g-1,and the pore volume was 0.311991 cm3·g-1 by means of BET.The molecular structure and chemical bond of Mn3O4 was analyzed by using FT-IR. The 627.6 cm-1,522.5 cm-1 and 411.5 cm-1 are the stretch vibration absorption peaks of Mn-O.The particle distribution of sample was measured with laser particle sizer.The diameter of sample was about0.4μm in average and its distribution was also in accordance with the normal distribution.Based on the data of the experiment and the theory analysis, the mechanism of microwave assisted heating was analyzed, which explains rigorously that microwave-assisted heating is better than traditaional heating. Trimanganese tetraoxide prepared by microwave-assisted has large specific area and high purity.
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