Recovery of Manganese Ion in Industrial Wastewater of Trimanganese Oxide

Manganomanganic oxide is the main raw material in the production of soft magnetic ferrite, manganese zinc ferrite which is made widely used in electronic, electrical, power, and other industrial information. Since entering the industrial production in the mid-1990s, after more than ten years of development, China's production and scale of trimanganese tetraoxide have ranked first in the world. By the end of 2005, the national output has reached more than 70,000 tons. Preparation of manganese tetroxide mainly including manganese metal powder suspension processes, four water per ton trimanganese 5 ~ 20 t, manganese ions in waste water ^{(100 ~ 600) × 10 -6} , much greater than the national wastewater The 2×10 ^-6 specified in the emission standards will cause harm to the environment if it is directly discharged. In this study, the wastewater of trimanganese tetraoxide was treated. After treatment, the manganese ions in the wastewater reached the national sewage discharge standard GB8978-1996. The recovered manganese ions can be made into high-purity trimanganese tetraoxide after decontamination. Good economic and social benefits can be achieved.

First, reagents and instruments

(1) Reagents. Sodium hydroxide, ammonia, ammonia chloride, sodium (hydrogen)carbonate, flocculant, etc.

(2) Instruments. Reaction kettle, stirring tank, vacuum filter, air compressor, and the like.

Second, the test principle and process

The wastewater discharged from the production of trimanganese tetraoxide mainly contains manganese, calcium, magnesium , sodium, chlorine, silicon and the like, among which manganese ions are harmful to the environment, but have economic value after being recovered. Other ions affect the performance of the soft ferrite and require separation. The chemical suspension of manganese dioxide is used as a filter layer to remove traces of suspended solids and H ₂ SiO ₃ colloids, and ammonium fluoride is added to form calcium and magnesium precipitates to remove calcium and magnesium ions. There are two ways to recover manganese ions: one is manganese hydroxide conversion method (Fig. 1), that is, manganese ions are precipitated into manganese hydroxide with sodium hydroxide or ammonia water or a mixture thereof, ammonium chloride is added as a catalyst, and then oxidized by air. The formation of trimanganese tetraoxide; the second is manganese carbonate conversion method, that is, the manganese ion is precipitated by sodium carbonate or sodium hydrogencarbonate to form manganese carbonate, and then calcined at a high temperature to form trimanganese tetraoxide. Its reaction formula is:

Figure 1 Test procedure for manganese hydroxide conversion method

Third, the test steps

The wastewater discharged from the production is analyzed for water quality components, and the wastewater is passed through a filtration layer composed of chemical manganese dioxide at a constant rate. Add an appropriate amount of ammonium fluoride under stirring, let stand and age for a certain period of time, filter and remove calcium and magnesium precipitates by filter press, add sodium hydroxide, ammonia water, sodium carbonate, sodium hydrogencarbonate or The combination thereof is tested for the amount of addition, the order of addition, the stirring strength, the precipitation temperature, the type of flocculating agent, and the like. Precipitating the obtained manganese hydroxide or manganese carbonate for a certain period of time, filtering out most of the impurities, formulating the manganese hydroxide precipitate into a certain concentration, adding ammonium chloride as a catalyst, and oxidizing by air to form trimanganese tetraoxide, adding The complexing agent removes a small amount of impurities, and finally is dried and pulverized to obtain a product; or the manganese carbonate is precipitated and oxidized and fired at 1050 ° C to form trimanganese tetraoxide. The analysis results of wastewater water quality components are shown in Table 1.

Table 1 Results of water quality analysis of wastewater discharged from the workshop ×10 ^-6

Fourth, test results and analysis

(1) Manganese hydroxide conversion method

In the method of converting manganese ions into manganese hydroxide and then oxidizing to produce trimanganese tetraoxide, the key is how to completely precipitate the manganese ions in the wastewater to meet the national emission standards and how to prevent other impurities in the wastewater from being brought into the product. It was found through experiments that the type and amount of precipitant, precipitation temperature, flocculant and aging time were the main influencing factors. The results obtained by experiments under different precipitants and amounts are shown in Table 2. After orthogonal test, the amount of hydroxide required for precipitation of manganese ions was 1.02 times. At room temperature, sodium hydroxide and ammonia were respectively added at a constant rate of 30% and 70% of the theoretical amount for 0.5 h, and 1.5 滴 was added dropwise. Polyacrylamide flocculant, standing and aged for 1.5h, filtered and then washed 2~3 times with deionized water with pH=6~7, oxidized to obtain trimanganese tetraoxide, and then added with a small amount of complexing agent to remove Harmful impurities can reach the industrial standard of trimanganese tetraoxide HG/T2835-1997 (Table 3). The manganese ion in the wastewater is 1.5×10 ^-6 , which is lower than the national wastewater discharge standard of 2×10 ^-6 .

Table 2 Results of manganese ion recovery test in manganese hydroxide conversion method

Table 3 Comparison of main indicators of trimanganese tetraoxide and industrial indicators in manganese hydroxide conversion method

1. Effect of precipitant and dosage

According to the calculation of the chemical reaction formula, the theoretical amount of sodium hydroxide or ammonia water is added. Under different temperatures and the amount of flocculant, the manganese ion precipitation result is difficult to reach the standard. The reason is that the precipitation of manganese ions requires a certain pH value, and a small amount of calcium, magnesium, iron and the like are present in the wastewater, so that a part of the hydroxide ions are consumed. Tests have shown that the addition of 1.05 times the theoretical amount of sodium hydroxide can completely precipitate manganese ions, and the manganese ions in the wastewater can reach 1.7×10 ^-6 . However, due to the presence of a large amount of sodium ions, inclusion, adsorption, and the like may occur during the reaction, and it is difficult to remove sodium ions or the like by washing. Tests show that 1.15 times the theoretical amount of ammonia can achieve the best results, the manganese ions in the wastewater can reach 3.8 × 10 ^-6 , and then continue to add and can not further precipitate manganese ions. Therefore, the use of ammonia or sodium hydroxide alone to precipitate manganese ions in the wastewater can not meet the standard discharge or can not get qualified products. It has been found through experiments that ammonia and sodium hydroxide can be added at a constant rate in a proper ratio at a constant rate. The manganese ion in the wastewater can be less than 2×10 ^-6 , and the sodium ion and sulfate in the final product can meet the requirements. The reason is that the amount of sodium ions in the reaction solution is reduced; the formed ammonium salt may contribute to the formation of coarse particles of manganese hydroxide crystals, reduce the encapsulation and adsorption of sodium ions; the rate of addition of precipitants affects the formation of precipitates. Speed, affecting the crystal size of the particles.

2, the impact of temperature

When the temperature is high, the manganese hydroxide crystal particles are coarser, the precipitation is relatively complete, and the fine particles in the suspended form are less in the solution. The coarse particles do not easily coat the adsorbed impurity ions, and are easy to wash and filter to remove impurities. However, the increase in temperature is not conducive to the removal of sulfate and calcium ions, and the precipitation at room temperature can also give ideal results when other conditions are appropriate.

3. Effect of flocculant

Since the produced manganese hydroxide is in a colloidal state, some of the fine particles of manganese carbonate are difficult to precipitate, and the flocculation agent does not require a long sedimentation time, and it is easy to pass through the filtration process, so it is necessary to add a flocculant to flocculate it. Large particles for sedimentation and filtration. In order to prevent the introduction of impurity ions, an organic polymer flocculant such as a polyacrylamide flocculant, a polyvinyl ether or a polyvinyl alcohol may be selected, and the amount thereof is related to the pH of the solution, the amount of suspended solids, and the colloidal substance. It was found that the timing of flocculant addition was related to the concentration of suspended solids in the solution. When the concentration of suspended solids was large, the precipitation of manganese ions was relatively complete, but the sodium ions contained in the inclusions were more and more difficult to remove. The concentration of suspended solids was too small to be added. It may be difficult to form manganese particles because the adsorption carrier is less likely to form large particles.

(2) Manganese carbonate conversion method

The manganese ion precipitate is converted into manganese carbonate, washed and filtered, and then calcined at high temperature to trimanganese tetraoxide. The advantage is that the manganese carbonate precipitates coarse particles and precipitates loosely, and can be washed and removed at room temperature to remove impurities such as calcium, magnesium, sodium sulfate and sulfate. . The disadvantage is that the manganese ion can be precipitated when the dosage is large, the high temperature roasting oxidation is required, the energy consumption is high, and the product produced by the roasting is less reactive. The precipitation effect of manganese ions is still related to the amount of precipitant, precipitation temperature, flocculant, aging time and so on. The indicators of trimanganese tetraoxide after calcination are shown in Table 4. The concentration of manganese ions in the treated wastewater is shown in Table 5.

Table 4 Main Indicators of Manganese Tetroxide Roasted and Oxidized by Manganese Sulfate and Industry Standards

Table 5 Manganese ion recovery test results of manganese carbonate conversion method

V. Conclusion

(1) Using a mixture of sodium hydroxide and ammonia or sodium carbonate (hydrogen) to precipitate the manganese-containing wastewater in the production of trimanganese tetraoxide, the manganese content of the wastewater can be lower than the national discharge standard 2 × l0 ^-6 High purity trimanganese tetraoxide can be produced by using recovered manganese ions.

(2) The manganese carbonate conversion method is easy to remove impurities, but has the disadvantages of high energy consumption, high cost, and poor product activity.

(3) The manganese hydroxide conversion process has simple operation and low cost, and can achieve better ecological and economic benefits.

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