Preparation And Performance Of The Active Manganese Dioxide By Electrdeposition From Low-grade Rhodochrosite

Due to the excellent chemical and electrochemcial properities, δ–MnO2has beenwidely developed for applications in the fields of batteries, catalysis and adsorption.China has a sizable portion manganese ores, but the high-grade manganese ores fordirectly applied are rare, and the lean deposits are dumped. Therefore the study abouthow to use the low-grade manganese deposits rationally and effectively has animportant practical significance to ease the contradiction between supply and demand ofmanganese resources, and to ensure the sustainable development of manganese productsindustry. In this paper, the Mn was recoverd from the low-grade rhodochrosite fromXiushan Chongqing by the acid leaching technology. δ–MnO2was prepared byelectrochemical way and its properties was characterized.The refined MnSO4solution was obtained by acid leaching and removingimpurities. The results indicated that the optimal amount of chemical MnO2oxidatingFe2+is2g. The optimum conditions for removing the Fe and Al were as follows: thereaction time was1h and the temperature was85℃.δ–MnO2was prepared by electrodeposition technology from the MnSO4solution.The samples were characterized by XRD, XPS, IR, N2-absorption and SEM. Theresults showed that δ–MnO2can be obtained when the Mn:K was1:20and the potentialwas2.0V. The δ–MnO2with high purity obtained a layer spacing of0.75nm and havedlots of active–OH, and it was distributed equally with a sheet-like morphology. Theδ–MnO2was a kind of mesoporous material with a large specific surface area of138.66m2/g, and its average pore size was7.4nm.It was found that the decolorization rate of methylene blue reached at95%within0.5h by reacted with δ–MnO2. The repeated test after four times indicated that thedecolorization rate decreased gradually, but it still reached about55%. Thecharacteristic absorption peak of the reaction solution was blue-shifted, and free Mnwas found in the solution, it indicated that δ–MnO2had transferred charges withmethylene blue. The decolorization efficiency of methylene blue increased with theamout of δ–MnO2, and on the contrary, it showed an oppsite trend.Under acidic conditons, the decolorization rate was more than90%within0.5h.but it became lower in the basic solution, and it only reached39%and17%respectivelywhen the pH was8and10. The rate about oxidation of methylene blue increased with the initial concentration.The reaction can be modeled by Langmuir-Hinshelwood equation, and the kineticconstant was1.98mg/L.min, the adsorption was0.79L/mg.In addition, the removal efficiency of COD for leachate was42%by δ–MnO2,which indicated that δ–MnO2had application value.