Foreword Although many areas of soft manganese ore and high-grade manganese has been drying up, but a variety of low-grade manganese ore resource is still Keziliyong. However, the production of battery-grade manganese dioxide or other manganese chemical reagents requires low- iron and high-manganese raw materials, which requires the modification of existing manganese-manufacturing technology to meet the needs of developing low-grade manganese ore. If the physical method is not technically feasible and economically unsuitable, chemical methods are usually employed. The chemical methods for treating low-grade manganese ore are Nossen nitric acid cycle, hydrochloric acid treatment and sulfuric acid treatment. Many researchers manganese ferrous metals and other materials containing sulfated been fired, the better. The sulfated reagents tested were sulfuric acid, ammonium sulfate, sodium sulfate and sodium hydrogen sulfate. The battery grade manganese dioxide product can then be produced from the influent produced by the above process using conventional electrolysis techniques. In this paper, the addition of ammonium sulfate to the sulphation roasting of low-grade manganese ore was carried out, and the method of producing manganese dioxide from the leached manganese compound by calcination without electrolysis was discussed. 1. Treatment of low grade manganese ore Chemical analysis showed that the chemical composition of low-grade manganese ore samples from Sinai, Egypt was 23.43% Mn, 36.16% MnO 2 , 33.77% Fe (48.25% Fe 2 O 3 ), 3.97% SiO 2 and 2.4% Al 2 O 3 , and the rest was P 2 O 5 , CaO, MgO, CO 2 and H 2 O. X-ray diffraction analysis and phase detection indicated that the main minerals in the ore were pyrolusite, hematite and goethite. Thermogravimetric analysis and differential thermal analysis were performed using a Netzsch Gerateball, GmbHSTA409 instrument. The ore was calcined in a calibrated muffle furnace by controlling the time, temperature and ammonium sulfate/mineral weight ratio. The calcine is then leached with water. Table 1 lists the leaching rates of iron and manganese after the materials of different ammonium sulfate/mine (-200 mesh) weight ratio were calcined at 400 ° C for 3 h. Both iron oxide and manganese oxide are converted to soluble sulfate. The leaching rate of manganese increases with the increase of the proportion of ammonium sulfate, and the leaching rate of iron decreases with the increase of the proportion of ammonium sulfate. Table 1 Effect of iron and manganese leaching rate on ammonium sulfate/mineral weight ratio The effects of calcination time on the leaching rate of iron and manganese were studied under the conditions of temperature of 400 °C, ammonium sulfate/mineral weight ratio of 7, and calcination time of 1, 2 and 3 h, respectively. The results (see Table 2) indicate that the reaction time increases from 1 h to 3 h at 400 ° C, and the conversion of iron and manganese to soluble salts also increases accordingly. Table 2 Effect of roasting time on leaching rate of iron and manganese Table 3 shows the effect of the calcination temperature on the leaching rate of iron and manganese under the conditions of ammonium sulfate/mineral weight ratio of 7 and calcination for 3 h. The results show that when the calcination temperature is increased from 400 °C to 700 °C, the leaching rate of manganese is slightly decreased, while the iron is different. When the calcination temperature is increased to 500 °C, the leaching rate increases with the increase of temperature, but When calcined at 700 ° C for 3 h, the leaching rate decreased significantly. Table 3 Effect of Iron and Manganese Leaching Rate at Roasting Temperature Second, the mechanism of the roasting process In order to determine the decomposition products of the respective temperature regions, a sample of pure ammonium sulfate was heated from 20 ° C to 500 ° C for differential thermal and thermogravimetric analysis. The results are shown in Figures 1 and 2. Figure 1 Thermogravimetric analysis of pure ammonium sulfate Figure 2 Differential thermal analysis of pure ammonium sulfate The experimental results show that the weight loss of ammonium sulfate is completed in two steps. The first step is from 280 ° C to 340 ° C, and the weight loss corresponds to the weight loss of ammonium sulfate decomposed into ammonium hydrogen sulfate. Its chemical reaction is as follows: The second step is between 340 ° C and 420 ° C. Ammonium bisulfate is completely decomposed by the following formula: As indicated by the differential thermal analysis curve, the two-step decomposition reaction is an endothermic reaction (with the appearance of an endothermic peak). It is well known that when the temperature is ≥ 500 ° C, manganese dioxide is decomposed into Mn 2 O 3 . Therefore, at different experimental temperatures, the following reactions may occur: When the temperature is ≥400 °C, the following reactions may occur: When the temperature is lower than 400 ° C, the iron oxide may react as follows: All of the above iron and manganese compounds were confirmed by X-ray diffraction analysis. When the temperature is ≥ 500 ° C, the iron sulfate double salt is decomposed into ferrous sulfate and iron sulfate. Both compounds are more soluble than their double salts. Therefore, the experimental results of high iron leaching rate at this temperature can be explained. X-ray diffraction analysis confirmed that at this temperature, only these two compounds. The temperature is further increased and the ferrous sulfate is oxidized and decomposed as follows: X-ray diffraction analysis showed that the decomposition product of iron sulfate was mainly ferric oxide at 700 °C. It is worth noting that the conversion of manganese and iron from the ore to the corresponding sulfates (Equations 3 and 6) requires nearly three times the ammonium sulfate. This means that when the experimentally determined leaching rate is good, the ammonium sulfate/mineral weight ratio (Table 1) is twice the theoretical amount. The leaching rate of iron at a higher temperature is lowered (Table 3), and it can be considered that ferrous sulfate is oxidized and iron sulfate is decomposed into iron oxide. This has been confirmed by X-ray diffraction analysis, and it is well known that for manganese sulfate, it is still stable up to 700 °C. When the temperature reaches 700 °C, the leaching rate of manganese slightly decreases, which may be related to the decomposition rate of the sulfating reagent, because the reaction between the manganese dioxide and the decomposition products of the sulfating reagent does not have enough time. carry out. Based on these data, the manganese ore sample was calcined at 400 ° C with an optimum sulfation ratio of 7 and ammonium sulfate for 3 h, then heated to 700 ° C for 1 h, and then the mixture was leached. The leaching rates of manganese and iron are about 92% and 5%, respectively. Third, the production of manganese dioxide After the sulphated roasting manganese ore is leached at 70 ° C, a solution containing 15% to 20% of the soluble manganese salt can be obtained. A small amount of ferrous sulfate can be oxidized by adding an excess of manganese ore powder, and the pH is adjusted to 6.5 with ammonia water, and iron, phosphorus and other impurities are removed by filtration to obtain a pure manganese solution. Ammonium carbonate was added to the solution until the pH was 8.5, under which the manganese in the solution was converted to carbonate. The obtained manganese carbonate was dried at 300 ° C for 5 h, mixed with the theoretical amount of nitric acid, and melted at 200 ° C until all of the nitrogen oxides were removed. Thermogravimetric analysis of manganese nitrate was carried out in the range of 20 to 400 ° C (Fig. 3). Manganese nitrate began to lose weight at 304 ° C, and the weight loss ended at 340 ° C. The total weight loss rate was 51%. Figure 3 Thermogravimetric analysis of manganese nitrate This is in good agreement with the decomposition of manganese nitrate as shown in the following formula to the corresponding weight loss rate of manganese dioxide (51.40%): The manganese nitrate was calcined at 320 ° C for 3 h, and the calcined product was subjected to chemical analysis and X-ray diffraction analysis. The analysis results show that the product is r-MnO 2 and the chemical composition is qualified. The cathode behavior of the obtained manganese dioxide and its suitability for dry batteries will continue to be studied.
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