Preparation of Manganese Sulfate by Reduction of Low Content Pyrolusite by Cellulose

Manganese sulfate is an important chemical intermediate, and 80% of other manganese salts are made from manganese sulfate. Manganese sulfate is also an important feed additive and fertilizer additive. At present, the global consumption of manganese sulfate is about 600,000 t/a, of which more than 60% is produced in China. Developed countries such as the United States, the United Kingdom, Japan, Norway, etc., do not produce manganese sulfate due to the lack of manganese ore resources for the production of manganese sulfate, or the traditional process for producing manganese sulfate, which does not produce manganese sulfate, mainly from developing countries. It is imported from China. Pyrolusite is an important raw material for the production of manganese sulfate. About 80% of the world's manganese sulfate is produced from the processing of pyrolusite. Conventional processes generally require manganese mass fractions in pyrolusite ore to be greater than 28%. With the development and utilization of ore resources, the high content of manganese oxide ore is less and less, while the low content of manganese ore with a mass fraction of less than 25% is produced in large quantities. It is of strategic importance to develop and utilize low-content pyrolusite resources. The process for preparing manganese sulfate from pyrolusite can be divided into two categories, one is pre-reduction leaching method and the other is direct acid leaching method. The pre-reduction leaching method is to carry out reduction roasting of pyrolusite under the action of a reducing agent, and convert MnO 2 in the ore into MnO, and then leaching with dilute sulfuric acid. Traditional prereduction leaching process using coal as a reducing agent, high energy consumption, poor operating conditions, serious environmental pollution. Some studies have suggested that the co-firing process of pyrite and pyrolusite can be used to convert MnO 2 into MnSO 4 . The actual production proves that the two-mine roasting method also has some shortcomings. If it is required to be calcined for a long time at a high sulfur-manganese mass ratio, FeS 2 cannot be fully utilized, the amount of waste slag is large, difficult to handle, and there is also a problem of flue gas treatment. The direct acid leaching method has the disadvantages that it is difficult to fully utilize the soft manganese ore, the slag is difficult to handle, and the amount of sulfuric acid is large. This study uses a wide range of raw materials, non-toxic elements, low-cost renewable resources cellulose as a reducing agent, replacing the non-renewable resource coal used in the traditional process, and directly reacting with low-content pyrolusite under suitable conditions to make MnO 2 is converted to MnO, and then leached with sulfuric acid to prepare manganese sulfate. The experimental results show that the scheme does not require high temperature roasting, the reaction process does not require external heating, the raw materials are easy to obtain, the equipment is simple, the investment cost is low, the environmental pollution is small, and the obtained manganese sulfate product is excellent in quality and suitable for low-content pyrolusite. It is a feasible method to effectively utilize the low content of soft manganese ore.
I. Experimental (I) The low-content soft manganese ore powder used in the material experiment was taken from the Dongxiangqiao manganese mine in Yongzhou, Hunan Province. The chemical composition is shown in Table 1.

Table 1 Chemical composition of pyrolusite

Quality score /% Mn Fe Ca Cu P Mg
19.02 8.05 16.54 0.002 0.022 1.58
The cellulose reducing agent used in the experiment is an industrial processing by-product, rich in cellulose and hemicellulose, and has a granular appearance and a water content of ω (H 2 O) = 5% to 10%. The analysis results of the cellulose reducing agent components are shown in Table 2.

Table 2 Analysis of cellulose reducing agent components

Quality score /% H 2 O Volatile Ash Fixed carbon
5.93 71.91 7.90 14.26
(2) Method: The soft manganese ore powder (particle size less than 0.15mm, mass fraction is 90%) and cellulose reducing agent are uniformly mixed in a certain ratio, and directly reacted under the action of an appropriate amount of initiator. After the reaction is completed, the product is quickly isolated from air cooling. The cooled product is placed in a 1500 mL beaker, and ω (H 2 SO 4 )=30% sulfuric acid is added. The beaker is placed on a collecting heater with a stirrer, and the mixture is immersed, leached, filtered, and washed. The filtrate was made up to a 1000 mL volumetric flask and sampled for analysis. When examining the reduction effect of cellulose reducing agent on pyrolusite, the manganese leaching rate is the objective function.

II. RESULTS AND DISCUSSION (I) Effect of mass ratio of cellulose reducing agent and pyrolusite on reduction effect The amount of soft manganese ore powder is fixed at 100g, and the amount of reducing agent with particle size less than 200μm is 5, 10, 15, 20, 25 respectively. 30g, after the reaction is completed, dilute sulfuric acid is added dropwise to the leaching process to keep the pH of the solution at 2.5±0.1, and the effect of the mass ratio of the reducing agent to the pyrolusite powder on the leaching rate of Mn is obtained, as shown in Fig. 1.

Fig.1 Effect of mass ratio of reducing agent to pyrolusite on reduction effect

It can be seen from Fig. 1 that the mass ratio of the reducing agent to the pyrolusite powder directly affects the reduction effect. Under the experimental conditions, when the reducing agent ink is 20% of the mass of the soft manganese ore powder, the reduction has been carried out quite well, and the leaching rate of Mn in the reaction material is more than 90%. Continue to increase the amount of reducing agent, the reduction effect is slightly increased. Considering that the reducing agent is very cheap and the appropriate excess does not adversely affect the subsequent process, it is preferred to take m (reducing agent): m (soft manganese ore powder) = 1:4.
(2) The effect of fineness of cellulose reducing agent on the reduction effect Take 25g of reducing agent under the Shanghai standard sieve of 97, 130, 139, 200, 295, 452μm, mix well with 100g of soft manganese ore powder, react for 30min, react with The leaching rate of Mn in the material indicates the reduction effect, as shown in Fig. 2.

Figure 2 Effect of reducing agent particle size on Mn leaching rate

As can be seen from Fig. 2, the finer the particle size of the cellulose reducing agent, the more advantageous it is for reduction. Considering that the reducing agent needs to consume electric powder during the preparation process, the reducing agent particle size is preferably 130-97 μm. (3) Change of phase composition of the material before and after the reaction Take 50 g of reducing agent with particle size less than 130 μm, 200 g of soft manganese ore powder, react for 30 min, rapidly cool with distilled water, filter at room temperature, filter cake is dried at 35 ° C under constant temperature, and the reaction is determined. The phase composition of the material was compared with that before the reaction. The results are shown in Table 3.

Table 3 Comparison of phase composition of materials before and after reaction

MnO 2 Mn 2 O 3 Mn 3 O 4 MnO Fe 2 O 3 Fe 3 O 4
Before the reaction, the mass fraction /% 29.78 0.15 0.23 0.00 11.00 0.65
After the reaction, the mass fraction /% 0.45 0.33 0.68 23.24 2.30 8.88
The phase measurement showed that Mn was mainly present in the form of MnO after the reaction, and also a small amount of Mn 2 O 3 and Mn 3 O 4 . Formed, Fe mainly exists in the form of Fe 3 O 4 . This is consistent with the reduction process of MnO 2 and Fe 2 O 3 in a reducing atmosphere and the general rule of the product to be obtained. The results show that the cellulose reducing agent can reduce MnO 2 well , which creates conditions for the subsequent sulfuric acid leaching process. (IV) Expanding the experiment and expanding the experiment in Hunan Kecheng Manganese Industry Co., Ltd. The scale of the experiment was expanded to 2t/d of manganese ore powder. The reduction reaction of the expanded experiment is carried out in a simple reactor made of red brick refractory mud, without external heating, the reaction process does not need to be turned over, the reaction is stable, and no toxic gas is generated. After the reduction reaction is completed, it is sprayed and cooled with water to prevent secondary oxidation of the product MnO. The results of the expanded experiment are shown in Table 4.

Table 4 Comparison of expanded experimental results with national standards

Expanding the experimental product of manganese sulfate into light rose red powder, the product quality index is compared with the national standard GB/T1622-86 and the national standard GB8253-87. The quality of the products obtained in this study exceeds the industrial grade manganese sulfate and feed grade manganese sulfate. Current national standards. After the completion of the expansion experiment, Yongda Manganese Industry Co., Ltd. invested 5 million yuan to build a 10000 t/a manganese sulfate production line, and Kecheng Manganese Industry Co., Ltd. invested 1 million yuan to build a 2000 t/ a manganese sulfate production line. At present, the production and operation of the two companies are stable, the product quality indicators are good, the energy consumption is low, and the three wastes are discharged.
III. Conclusion The processing of by-product cellulose as a reducing agent, direct reaction with low-content pyrolusite under suitable conditions, conversion of MnO 2 to MnO, and leaching of manganese sulfate with sulfuric acid, with simple equipment and manganese utilization The high rate, low energy consumption, and the three waste discharge standards, and the full utilization of low-content pyrolusite resources have a general promotion significance; this process also opens up a new way for the application of cellulose.


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