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Synthesis method 1: Electrolytic manganese suspension oxidation method

At present, more than 90% of Mn3O4 production in China adopts electrolytic manganese suspension oxidation method. The principle is to make electrolysis manganese metal sheet powder, and then disperse in the ammonium salt solution into a suspension, using air or oxygen as an oxidant, oxidation and corrosion at a fixed temperature and additive concentration, so as to prepare Mn3O4. However, this method uses electrolytic manganese metal as raw material, and the cost is higher. In Changsha Institute of Mining and Metallurgy, manganese powder is added into electrolyte solution to oxidize and rust manganese to produce Mn3O4 and Mn (OH) 2 mixture. Under the condition of P[O2] of 5~40kPa and P[H2O] of 10~50kPa, the mixture is heated and dried to make the electrolyte undergo thermal decomposition, and Mn (OH) 2 is oxidized to form Mn3O4. The content of Mn is 70%~71%, the content of other impurities is less than 0.01% except for carbon <0.05%, and the specific surface area is about 10m2/g.

Synthesis method 2: high - price manganese oxide method

Mn3O4 is prepared by thermal decomposition or reduction of high-valent manganese oxides (such as MnO2, Mn2O3, etc.) with a higher valence state of Mn3O4 as raw materials. The key to the preparation lies in the control of Mn3O4 ratio, potential and temperature. High temperature solid phase roasting is usually used, and the temperature is generally higher than 950℃.

Synthesis method 3: manganese carbonate method

In this method, Mn3O4 was obtained by roasting and decomposition of high purity manganese carbonate under high temperature and aerobic atmosphere.

The specific technological process is as follows: 500kg of manganese carbonate (its water content is 5%) and 50kg of starch (carbon source) are evenly mixed, and then it is put into the continuous microwave steel belt kiln for microwave heating, the temperature is controlled at 10℃/min, and the temperature is controlled at 700℃ for sintering, the sintering holding time is controlled for about 60min, and then the manganese t4 is obtained after cooling. Then, the manganese tetroxide was ground to 1000 mesh by wet grinding. After detection, the manganese content of the product was 71.3%, the unit energy consumption was 4500 degrees/ton, and the specific surface area was 7.8m2/g. After XRD analysis, it was pure manganese tetroxide.

Synthesis method 4: manganese brine thermal oxidation method

In this method, pure manganese sulfate solution is prepared by using manganese carbonate ore or manganese oxide ore as raw materials. Under alkaline conditions, divalent manganese or manganese hydroxide in manganese sulfate solution is oxidized to Mn3O4 by air or oxygen by adding certain additives to control potential. The main raw materials used are manganese ore, sulfuric acid and ammonia, which come from a wide range of sources and are cheap, and are economical without electrolysis process. For example, primary manganese carbonate ore is leached by sulfuric acid, and then neutralized with lime to pH 6.0, filtrate is filtered and washed, barium sulfide and ammonium fluoride are added to remove impurities and purify, and high purity manganese sulfate solution is prepared. Then ammonia water is added to sink manganese. After filtration and washing, slurry is mixed and ammonium chloride is added to catalyst, and high purity Mn3O4 is directly oxidized with oxygen.