Wet leaching test of manganese oxide ore

Manganese oxide ore containing large amounts of often primary sludge, so that the manganese beneficiation process losses. In this study, based on the principle that the redox reaction between the reducing agent and the manganese oxide ore in the acidic medium converts tetravalent manganese into divalent manganese and enters the liquid phase, the manganese oxide ore slurry is treated by the wet leaching process to separate the manganese and impurities, and utilize The leachate is used to prepare manganese sulfate and manganese carbonate products.

The reducing agent can be used for wet reduction of pyrite leaching manganese oxide has, ferrous sulfate, sodium thiosulfate, SO _2, coal, hydrogen peroxide, oxalic acid, aniline, phenol, straw, sawdust, bagasse, starch, sucrose And certain microorganisms, etc. In this study, the leaching test of manganese oxide ore sludge was carried out using pyrite and bagasse with low source and wide source of raw materials as reducing agents. The effect of process conditions on the leaching effect was investigated and the mechanism of the leaching process was discussed.

First, the sample and test

(a) sample

The manganese ore mud samples were taken from the CITIC Daxin manganese ore. The chemical multi-element analysis results are shown in Table 1. The manganese phase analysis results are shown in Table 2.

Table 1 Sample chemical multi-element analysis results %

Table 2 Analysis results of manganese phase of sample

The sample was grayish black under the naked eye. Identification of microscopic and X-ray diffraction analysis showed that a comprehensive study: sample metal minerals are hard manganese ore, manganese ore and times for limonite; gangue minerals are quartz and kaolinite, illite times. The main mineral content of the sample is shown in Table 3.

Table 3 Main mineral content of the sample

The negative cumulative particle size characteristic curve of the sample is shown in Fig. 1. It can be seen that the sample has a fine particle size and the content of -10 μm is 53.03%.

Figure 1 Sample negative cumulative particle size characteristic curve

(two) the main reagent

The main reagents used in the test are:

Pyrite, taken from a company in Nanning, S content 33.97%, Fe content 53.38%, As content, ≤0.07%, particle size -100 mesh ≥95%; bagasse, taken from Nanning Sugar Co., Ltd., The cellulose content is 47%, the total lignin content is 22.8%, the polypentose content is 22.9%, the ash content is 5.60%; the concentrated sulfuric acid is analytically pure, and the H ₂ SO ₄ content is 95%-98%.

Second, the leaching test method

The leaching test procedure is shown in Figure 2.

Figure 2 Test process

(1) Pyrite reduction leaching test

Weigh a certain amount of sulfuric acid and water, heat to a certain temperature, add 100g of manganese ore slurry sample and a certain amount of pyrite, keep the temperature and start stirring to leaching. After the leaching is completed, the filter is washed, dried, weighed, and tested for TMn to calculate the manganese leaching rate.

(2) Reduction and leaching test of sugarcane bagasse hydrolysis method

A certain amount of naturally dried bagasse is added to 500 g of a certain concentration of hot dilute sulfuric acid for hydrolysis for a certain period of time, and then the hydrolyzed slag is filtered and washed twice. The filtrate and the washing liquid are combined, a certain amount of concentrated sulfuric acid and water are added thereto, heated to a certain temperature, and a sample of 100 g of manganese ore mud is added, and the temperature is maintained and stirring is started to carry out leaching. After the leaching is completed, the filter is washed, dried, weighed, and tested for TMn to calculate the manganese leaching rate.

Third, the test results and discussion

(1) Reduction and leaching of pyrite method

1. Conditional test

(1) Effect of the amount of pyrite on the leaching rate of manganese The test conditions and results are shown in Fig. 3. It can be seen that the amount of pyrite has a significant effect on the leaching rate of manganese, and the appropriate amount should be 0.3 times of the amount of manganese ore.

Figure 3 Effect of pyrite content on manganese leaching rate

(60 g sulfuric acid, liquid to solid mass ratio 5:1, leaching temperature 95 ° C, leaching time 3 h)

(2) Effect of sulfuric acid dosage on manganese leaching rate

The test conditions and results are shown in Figure 4. It can be seen that the amount of sulfuric acid has a certain influence on the leaching rate of manganese. With the increase of the amount of sulfuric acid, the leaching rate of manganese increased. However, when the amount of sulfuric acid exceeded 0.5 times of the amount of manganese ore, the leaching rate of manganese did not change much.

Figure 4 Effect of sulfuric acid dosage on manganese leaching rate

(30g of pyrite, liquid to solid mass ratio of 5:1, leaching temperature of 95 ° C, leaching time of 3 h)

(3) Effect of liquid-solid mass ratio on manganese leaching rate

The test fixation conditions and results are shown in Figure 5. It can be seen that the liquid-solid mass ratio has little effect on the manganese leaching rate. However, the liquid-solid mass ratio is too small, the slurry viscosity increases, and the liquid-solid separation is difficult; the liquid-solid mass ratio is too large, and the manganese concentration in the leachate is low. Therefore, a suitable liquid-solid mass ratio is from 3:1 to 5:1.

(4) Effect of leaching temperature on manganese leaching rate

The test conditions and results are shown in Figure 6. It can be seen that the leaching temperature has a great influence on the manganese leaching rate, and the temperature at the leaching time should not be lower than 95 °C.

Figure 5 liquid-solid intestinal, the impact of the ratio of rejection

(30g of pyrite, 50g of sulfuric acid, 95°C leaching temperature, 3h leaching time)

Figure 6 Effect of leaching temperature on manganese leaching rate

(30g of pyrite, 50g of sulfuric acid, 4:1 liquid-solid mass ratio, 3h leaching time)

(5) Effect of leaching time on the leaching rate of Ming

The test conditions and results are shown in Figure 6. It can be seen that the leaching time is preferably 3-4 h.

Figure 7 Effect of leaching time on manganese leaching rate

(30g of pyrite, 50g of sulfuric acid, 5:1 liquid-solid mass ratio, 95°C leaching temperature)

The above test results show that the suitable process conditions for reduction and leaching of pyrite method are: slime quality: pyrite quality: concentrated sulfuric acid mass = 1:0.3:0.5, liquid-solid mass ratio 3:1-5:1, leaching temperature Not less than 95 ° C, leaching time 3-4h. Under this condition, the manganese leaching rate can reach more than 95%.

2. Study on the kinetics of reduction and leaching process of pyrite method

(1) Change temperature method

The reduction and leaching of pyrite method were carried out at 75, 85 and 95 ° C respectively, and the manganese content in the solution was analyzed at a certain time to obtain the manganese leaching rate φ as a function of time t.

Fig. 8 Variation of φ in the leaching process of pyrite process at different temperatures

(Mn manganese mud 100g, pyrite 30g, sulfuric acid 50g; liquid-solid mass ratio 5:1)

●-75°C; ■-85°C; ▲-95°C

The data of Fig. 8 is processed to obtain a relationship between 1-(1-φ) ^1/3 and 1-2/3φ-(1-φ) ^2/3 and t. It is found that the two relationship curves are almost straight, but the difference is that the relationship between 1-(1-φ) ^1/3 and t is close to the origin (Fig. 9), and 1-2/3φ-(1-φ The relationship between ^2/3 and t is not the origin, indicating that the relationship between 1-(1-φ) ^1/3 and t obeys the characteristic equation of chemical reaction control.

Fig. 9 Relationship between 1-(1-φ) ^1/3 and t in the leaching of pyrite method at different temperatures

●-75°C; ■-85°C; ▲-95°C

Linear regression was performed on the relationship between 1-(1-φ) ^1/3 and t, and the reaction rate constant k at each temperature was obtained. The results are shown in Table 4.

Table 4 Reaction rate constants at various temperatures during leaching of pyrite

The plot of Ink versus 1/T is shown in Figure 10. It can be seen that 1nk has a good linear relationship with 1/T.

1nk=-5.153 2 × 10 ³ (1/T)+8.4944.

Will the slope -5.1532 x 103 generation Arrhenius equation

1nk=(-E/RT)+B

Have

-E/R=-5.1532×10 ³ ,

Linear regression was performed on the results of Fig. 10 to obtain a linear equation, where R is the gas constant, 8.314 5 J/(mol·K). Therefore, the activation energy of the reaction was E = 42. 845 8 kJ/mol. It can be seen that the pyrite leaching process is controlled by the chemical reaction step without being controlled by internal diffusion.

Figure 10 Ink and 1/T relationship during pyrite leaching

(2) Change the stirring strength method

The pyrite reduction leaching was carried out at a stirring speed of 800 and 1300 r/min, respectively. A small amount of slurry was taken at a certain time to analyze the manganese content in the solution, and the curve of the manganese leaching rate φ with time t is shown in Fig. 11.

Fig. 11 Variation of φ in the leaching process of pyrite process at different stirring speeds

(Mn manganese mud 100 g, pyrite 30 g, sulfuric acid 50 g, liquid-solid mass ratio 5:1, leaching temperature 95 ° C)

â– -1300r/min; â–²-800 r/min

It can be seen from Fig. 11 that the influence of the stirring strength on the manganese leaching rate is small in the test range. According to the data of Fig. 11, the relationship between 1-(1-φ) ^1/3 and t under two kinds of stirring strengths was found to be parallel and almost coincident, indicating that the stirring strength has no influence on the reaction rate constant. Therefore, it can be inferred that the pyrite leaching process is not controlled by external diffusion.

The results of kinetic studies show that the reduction and leaching process of pyrite method is controlled by the chemical reaction of particle surface. According to the kinetic characteristics of chemical reaction control, increasing the temperature and concentration of leaching agent can increase the reaction rate, which is consistent with the results of the conditional test. of.

3. Discussion on the mechanism of reduction and leaching of pyrite method

The main principle of the reduction and leaching of pyrite method is that the pyrite and manganese oxide ore undergo redox reaction under acidic conditions, and the tetravalent manganese in the manganese oxide ore is reduced to divalent manganese into the liquid phase, and the leaching process is complicated.

From a thermodynamic point of view, it is feasible to reduce the leaching of manganese oxide by pyrite at both normal temperature and high temperature. The higher leaching temperature is mainly due to the kinetics, and the high temperature leaching is beneficial to FeS ₂ . Iron remains in the slag in the form of Fe ₂ 0 ₃ .

Use of FeS ₂ as a reducing agent reducing ₂ MnO, FeS trend ₂ is ^{_{FeS 2 → Fe 2 + + S}} ( including ^{_{H 2 S) → SO 4 2}} - + Fe 3 + → SO 4 2 - + Fe 2 O 3 · nH ₂ O. The amount of acid used is different from that of pyrite, and the reactions and products that occur are also different. In summary, the main reactions that will occur are as follows:

FeS ₂ +MnO ₂ +H ₂ SO ₄ =MnSO ₄ +FeSO ₄ +H ₂ O+2S (1)

2FeS ₂ +3MnO ₂ +6H ₂ SO ₄ =3MnSO ₄ +Fe ₂ (SO ₄ ) ₃ +6H ₂ O+4S (2)

FeS ₂ + 7MnO ₂ + 6H ₂ SO ₄ =7 MnSO ₄ +FeSO ₄ +6H ₂ O (3)

2FeS ₂ +9MnO ₂ +10H ₂ SO ₄ =9MnSO ₄ +Fe ₂ (SO ₄ ) ₃ +10H ₂ O+2S (4)

2FeS ₂ +15MnO ₂ +14 H ₂ SO ₄ =15MnSO ₄ +Fe ₂ (SO ₄ ) ₃ +14H ₂ O (5)

2FeS ₂ +15MnO ₂ +11H ₂ SO ₄ =15 MnSO ₄ +Fe ₂ O ₃ +11H ₂ O (6)

It can be seen that it is economical to prepare a manganese sulfate solution according to the reaction of (6), but the reaction in actual production cannot be completely carried out according to the formula (6). Assuming that the leaching process is carried out according to the reaction (1), that is, the sulfur in the pyrite is produced in the form of the element S, the theoretical material ratio can be determined as the mass of the manganese ore: pyrite mass: sulfuric acid mass = 1:0.387 3: 0.632 5. Through experiments, it is found that the actual material ratio is manganese ore quality: pyrite quality: sulfuric acid quality = 1:0.3:0.5, that is, the actual material ratio of pyrite and sulfuric acid is more than the theoretical value of reaction (1). Low, indicating that a considerable portion of the sulfur S0 ₄ ^{2 -} and HSO ₄ ^- forms are produced during the leaching process, thereby reducing the acid consumption to some extent.

(2) Reduction and leaching of sugarcane bagasse hydrolysis

1. Conditional test

(1) Effect of sulfuric acid concentration of hydrolyzate on manganese leaching rate

The test fixing conditions and results are shown in Fig. 12. It can be seen that in the range of 1%-2% hydrolyzed sulfuric acid concentration, the manganese leaching rate increases with the increase of sulfuric acid concentration, while the sulfuric acid concentration greater than 2% has little effect on the manganese leaching rate, so the suitable hydrolyzate sulfuric acid concentration It is 2%.

Figure 12 Effect of sulfuric acid concentration on the leaching rate of manganese

(The amount of sugar cane is 50g, the hydrolysis temperature is 100 ° C. The hydrolysis time is 2 h, and the amount of sulfuric acid leached is 50 g.

Leachate solid 11% 7:1, leaching temperature 95 ° C, leaching time 2 h)

(2) Effect of hydrolysis time and leaching time on manganese leaching rate

The test fixing conditions and results are shown in Fig. 13. It can be seen that the hydrolysis time is preferably 3 h, and the leaching time is preferably 2 h.

Figure 13 Effect of hydrolysis time and leaching time on manganese leaching rate

(The amount of bagasse is 50g. The concentration of sulfuric acid in the hydrolyzate is 2%, and the hydrolysis temperature is 100 °C.

The amount of leaching sulfuric acid is 50g. The leaching solution has a solid mass ratio of 7:1 and a leaching temperature of 95 °C.

■-hydrolysis 4h; ●-hydrolysis 3h; ▲-hydrolysis 2h; ▼-hydrolysis 1h

(3) Effect of bagasse dosage on manganese leaching rate

The test fixing conditions and results are shown in Fig. 14. It can be seen that the amount of bagasse has a great influence on the leaching rate of manganese, and the suitable amount of bagasse is 60g.

Figure 14 Effect of bagasse dosage on manganese leaching rate

(The hydrolyzate has a sulfuric acid concentration of 2%, a hydrolysis temperature of 100 ° C, a hydrolysis time of 3 h, and a leaching amount of sulfuric acid of 50 g,

The solid solution ratio of the leachate is 7:1, the leaching temperature is 95 °C, and the leaching time is 2 h)

(4) Effect of leaching sulfuric acid dosage on manganese leaching rate

The test fixing conditions and results are shown in Fig. 15. It can be seen that the amount of sulfuric acid also has a great influence on the leaching rate of manganese. When the amount of sulfuric acid is increased from 30g to 50g, the manganese leaching rate is rapidly increased. That is to say, lowering the pH helps to increase the leaching rate and the leaching speed of manganese. The potential-pH diagram of the Mn-H20 system also shows that the pH-reduced Mn02 stable region becomes smaller and is more likely to react with the reducing agent. Therefore, a suitable amount of concentrated sulfuric acid at the time of leaching is 50 g.

Figure 15 Effect of leaching sulfuric acid on leaching rate

(The amount of bagasse is 60 g, the concentration of sulfuric acid in the hydrolyzate is 2%, the hydrolysis temperature is 100 ° C, and the hydrolysis time is 3 h.

The solid solution ratio of the leachate is 7:1, the leaching temperature is 95 °C, and the leaching time is 2 h)

(5) Effect of solid-solid ratio of leachate on manganese leaching rate

The test fixing conditions and results are shown in Fig. 16. It can be seen that the solid-solid ratio of the leachate has little effect on the manganese leaching rate. Considering that the bagasse after hydrolysis is washed, the solid solution ratio of the leachate is 7:1.

Figure 16 Effect of solid-solid ratio of leaching solution on manganese leaching rate

(The amount of bagasse is 60 g, the acid concentration of the hydrolyzate bowl is 2%, the hydrolysis temperature is 100 ° C, and the hydrolysis time is 3 h.

Leaching sulfuric acid 50g, leaching temperature 95 ° C, leaching time 2h)

(6) Effect of leaching temperature on manganese leaching rate

The test fixing conditions and results are shown in Fig. 17. It can be seen that the leaching temperature also has a great influence on the leaching rate of manganese. In the same time, the leaching rate of manganese increases with the increase of temperature. Therefore, the leaching temperature should not be lower than 95 °C.

According to the above test results, the reasonable conditions for the reduction and leaching of sugarcane bagasse hydrolysis method are: slime quality: bagasse quality: leaching concentrated sulfuric acid mass = 5:3:2.5, hydrolyzate sulfuric acid concentration 2%, hydrolysis temperature 100 °C, hydrolysis time 3 h, the solid-liquid ratio of the leachate is 7: 1, the leaching temperature is not lower than 95 ° C, and the leaching time is about 2 h. Under this condition, the manganese leaching rate can reach more than 95%.

Figure 17 Effect of leaching temperature on manganese leaching rate

(The amount of bagasse is 60g, the concentration of sulfuric acid in the hydrolyzate is 2%, and the hydrolysis temperature is 100 °C.

The hydrolysis time is 3h, the amount of leaching sulfuric acid is 50g, and the solid ratio of leaching solution is 7:1)

■-95°C:. ●-85 °C: ▲-75 °C

2. Kinetics of reduction and leaching process of sugarcane bagasse hydrolysis

It can be seen from Fig. 17 that at each temperature, the reaction speed about 20 minutes before the leaching process is significantly higher than that at the later stage. The test data in Fig. 17 was processed, and the reaction rate constant k after 20 min and 20 min before the leaching process at each leaching temperature was determined as shown in Table 5. According to the results of Table 5, by the Arrhenius formula

Lgk=lgA-(Ea/2.303RT)

with

Lg(k ₁ /k ₂ ) =(Ea/2.303RT)[(1/T ₂ )-(1/T ₁ )

The apparent activation energy Ea in the different temperature ranges 20 min and 20 min before the leaching reaction of the bagasse hydrolysis was calculated as shown in Table 6.

Table 5 Reaction rate constants at different temperatures for each temperature of the hydrolysis method

Table 6 Performance activation energy kj/mol in different temperature ranges of hydrolysis method

It can be seen from Table 6 that when the temperature is changed in the range of 75-85 ° C and 85-95 ° C, the apparent activation energy of 20 min before the leaching process is greater than 12 kJ / mol, and the apparent activation energy after 20 min is relatively small.

Combined with the characteristics of the kinetic control step, it can be judged that the sugarcane residue hydrolysis process is controlled by chemical reaction and diffusion mixing 20 minutes before the leaching process, and is controlled by diffusion after 20 minutes. Therefore, increasing the leaching agent concentration and leaching temperature and reducing the initial particle size in the early stage of leaching can effectively improve the leaching rate and leaching speed of manganese, and the leaching efficiency can be improved by reducing the grain size of the granules in the later stage of leaching.

3. Mechanism of reduction and leaching process of bagasse hydrolysis

Bagasse is a by-product of the sugar industry. It is rich in cellulose and hemicellulose. The cellulose macromolecules are broken at the appropriate hydrogen ion concentration and temperature, and the degree of polymerization is reduced and hydrolyzed into various reductive singles. sugar. Monosaccharides are reductive because they contain free aldehyde or ketone groups in their molecules. Fang Hong et al. used high performance liquid chromatography to determine the type and content of monosaccharides in bagasse dilute acid hydrolysate. The results showed that the monosaccharides in hydrolysate were mainly xylose, glucose, arabinose and fructose. These reducing sugars can undergo redox reaction with manganese oxide ore under acidic conditions under acidic conditions, and reduce tetravalent manganese to divalent manganese into the liquid phase. Taking glucose and xylose as examples, the main reaction occurred was

C ₆ H ₁₂ O ₆ +MnO ₂ +H ₂ SO ₄ →MnSO ₄ +CO ₂ +H ₂ O,

C ₅ H ₁₀ O ₅ +MnO ₂ +H ₂ SO ₄ →MnSO ₄ +CO ₂ +H ₂ O.

The monosaccharide is not a very stable compound, and the monoterpene formed by the hydrolysis of cellulose in the bagasse enters the aqueous solution and continues to be decomposed at a high temperature and in the presence of hydrogen ions to form an organic acid, a alditol or the like. Thus, the monosaccharide is not the final product of hydrolysis, and the content of the monosaccharide in the hydrolyzate depends on the difference between the rate at which the cellulose and hemicellulose are hydrolyzed into a monosaccharide and the rate at which the monosaccharide decomposes. Therefore, it is necessary to control the hydrolysis conditions in order to achieve the maximum manganese leaching rate at the lowest cost.

4. Purification and product preparation of leachate

Add a small amount of hydrogen peroxide to the leachate, oxidize all Fe ^{2 +} to Fe ^{3 +} , then add a neutralizing agent to adjust the pH to about 5.2, add appropriate amount of ammonium sulfide, control the temperature to 90 ° C for 1 h, Fe ^{3 +} , A1 ^{3 + is} removed together with heavy metal ions.

The removal methods of Ca ²⁺ and Mg ²⁺ in the two leachates are slightly different. The pyrite method leaching solution removes Ca ^{2 +} by preconcentration; the bagasse method has a slightly turbid leaching solution, and the solution is clear after adding an appropriate amount of ammonium fluoride, and at the same time, Ca ^{2 +} and Mg ^{2 +} can be removed.

The manganese sulfate solution obtained by leaching the pyrite with the pyrite as a reducing agent can prepare manganese sulfate by concentration and crystallization, and the product contains Mn 32.04%, which meets industrial requirements. The manganese sulfate solution obtained by leaching the bagasse hydrolyzate as a reducing agent is not easy to produce industrial manganese sulfate because of mixing with certain organic components, but manganese carbonate can be prepared, and the product contains Mn44.76%, which also meets industrial requirements.

V. Conclusion

(1) The suitable conditions for reducing and leaching Daxin manganese ore manganese ore by pyrite method are: slime quality: pyrite quality: concentrated sulfuric acid mass = 1:0.3:0.5, liquid-solid mass ratio 3:1-5:1 , the leaching temperature is not lower than 95 ° C. The leaching time is 3-4h. The suitable conditions for reducing and leaching Daxin manganese ore manganese ore by bagasse hydrolysis method are: slime quality: bagasse quality: leaching concentrated sulfuric acid mass = 5:3:2.5, hydrolyzate sulfuric acid concentration 2%, hydrolysis temperature 100 °C, hydrolysis time 3h The leaching solution has a solid mass ratio of 7:1, a leaching temperature of not less than 95 ° C, and a leaching time of about 2 h. Under the above conditions, the manganese leaching rate of both methods can reach more than 95%.

(2) Manganese sulfate product can be prepared by the pyrite method leaching solution, and the manganese carbonate product can be prepared by the bagasse hydrolysis method leaching solution. The manganese sulfate product contains 32.04% Mn, and the manganese carbonate product contains 44.76% Mn, which meets the requirements of industrial qualified products.

(3) The kinetic study shows that the leaching process of pyrite process is controlled by the chemical reaction of the surface of the particles, so the leaching efficiency can be improved by increasing the leaching temperature and the concentration of the leaching agent and reducing the original particle size of the ore particles; while the leaching process of the bagasse hydrolysis process is chemically affected. The reaction and diffusion are jointly controlled, and later controlled by diffusion. Therefore, the leaching efficiency can be improved by increasing the leaching agent concentration and leaching temperature in the early stage of leaching, reducing the original particle size of the ore particles, and reducing the grain size at the later stage of leaching.