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China's battery industry originated in the 1920s. Today, the annual output of batteries has reached 14 billion, accounting for 1/3 of the world's total battery output. However, due to the dual management and technical reasons, the pollution control of waste batteries are seriously lagging behind, resulting in the vast majority of used batteries or throw anywhere together with landfill, where heavy metals and acid and other pollutants through a variety of Ways to enter the human food chain. There is also a part of the waste battery that was burned and landfilled with domestic garbage on the 1st day, causing serious pollution to the atmosphere.
The battery contains a lot of useful metals. According to statistics, annual national waste dry batteries has a considerable amount of recoverable valent metal, wherein the powder of manganese 109200t, zinc skin 38200t, 600T copper, iron skin 29600t, mercury 2.48t. The old zinc-manganese dry battery contains a large amount of MnO 2 which has not reacted, and Mn which exists in other forms. Manganese is not only one of the important positive electrode materials for power supplies, but also has a wide range of non-battery applications. In recent years, non-battery applications of manganese have also been gradually expanded. In addition to traditional metallurgy, fine chemicals, batteries and other fields, new uses have been made in environmental protection, advanced battery materials, manganese-zinc ferrite, and ceramic materials. . Because manganese has strong catalytic oxidation/reduction, ion exchange and adsorption capacity, it is a comprehensive and excellent water purification filter material after proper chemical treatment and molding. It is compatible with commonly used activated water, zeolite and other water purification media. It has stronger ability to decolorize and remove heavy metals. Therefore, recycling and utilization of various forms of manganese from the waste zinc-manganese dry battery has important environmental significance and good economic prospects.
At present, many developed countries have established complete waste battery recycling systems, mainly including pyrometallurgical recovery and hydrometallurgical recovery. On the basis of this, some domestic researchers have proposed some new technologies and technologies for the comprehensive utilization of waste batteries with development prospects through the improvement of traditional methods and the combination with actual production. From the perspective of environmental protection, the current fire method is likely to cause serious air pollution, the wet method uses a large amount of acid, and the cost is high, and the waste liquid residue after treatment is likely to cause environmental pollution. Aiming at the deficiencies of the existing methods, it is proposed to use the ion membrane slurry electrolysis method to reduce the cathode material of the waste dry battery in the cathode chamber to prepare a manganese sulfate solution, and convert the manganese sulfate into manganese dioxide or trimanganese tetraoxide in the anode chamber. In this paper, the technical conditions and leaching mechanism of the reduction and leaching of the cathode material of the waste dry battery in the cathode chamber are mainly introduced.
First, the experiment
(1) Reagents and instruments
The reagents required for the experiment were manganese sulfate (MnSO 4 ), silver nitrate (AgNO 3 ), mercury sulfate (HgSO 4 ), and nitric acid (HNO 3 ). Precision super constant temperature water tank DF-03, Nanjing Haoao Technology Co., Ltd.; digital current meter MB4206, Shaanxi Xieli Photoelectric Instrument Co., Ltd.: UV-visible spectrophotometer IU-1810, Beijing Pu Analysis General Instrument Co., Ltd. An ion exchange membrane electrolyzer made, both the anode and cathode chamber volume 800 mL, titanium ruthenium as the anode, graphite as a cathode, are cathanode area 0.008m 2. The used dry battery used in the experiment was Huatai brand No. 5 battery, and the manganese content was determined to be 35.0% by the method of 1.2.
(two) analytical methods
Weigh 0.5490g of manganese sulfate dissolved in about 200mL of deionized water, add 1.5mL of concentrated nitric acid, and then make up to 1000mL volumetric flask, then the manganese ion concentration in this solution is 0.2g / L. Take standard test solutions 0, 1.5, 2.5, 5, 7.5 mL, manganese sulfate in a 100 mL Erlenmeyer flask, add 1 mL of silver nitrate-mercuric sulfate solution to each of the 5 Erlenmeyer flasks, and add about 50 mL of deionized water. 1 g of ammonium persulfate was heated on an electric furnace until large bubbles appeared, and it was kept for 1 min, taken off, left for 1 min, and then cooled with cold water. Transfer to a 100mL volumetric flask, shake well, and dilute to the mark line, then the concentration of manganese ions in the five volumetric flasks is 0, 3.0, 5.0, 10.0, 15.0mgL. The absorbance of the standard series solution was measured at a wavelength of 530 nm using a 1 cm cuvette to obtain a standard curve as shown in FIG.
Figure 1 Manganese sulfate standard curve
(3) Experimental methods
Cut a number of used Huatai brand No. 5 batteries vertically, peel off the outer zinc skin, weigh a certain amount of the polished positive electrode part, add a certain liquid to solid ratio, add to the sulfuric acid solution, and carry out the electrolyte in the cathode chamber. Stirring at a constant speed, constant current electrolysis under various factors, electrolysis time 90 min, sampling 3 mL of filtration every 15 min, sampling 1 mL from it, diluting it to a 100 mL volumetric flask with deionized water, measuring the absorbance, and calculating the manganese ion concentration.
The correction formula for the concentration of divalent manganese ions is as follows:
Where C n '- is the corrected concentration;
Cn - is the measured concentration at time n;
V- is the sampling volume:
V 0 - the total volume of the receiving liquid in the receiving tank.
Then M=C n '×V
Second, the results and discussion
(1) Influence of current density
Electrolysis at 0.8, 1.0, 1.26, 1.5 A, respectively, manganese ion concentration with electrolysis time, manganese ion recovery and apparent current efficiency are shown in Figures 2 and 3. It can be seen from Figure 2 that the lower the current, the manganese in the leachate
The smaller the subconcentration. Under the current conditions of 1.26A and 1.5A, the two curves of manganese ion concentration with leaching time are basically coincident, indicating that the leaching of manganese ions has reached the maximum under the condition of 1.26A, and the continuous increase of current cannot accelerate the leaching rate, but the cathode is made. The overpotential rises, the hydrogen evolution increases, and the cell voltage rises, so the current is 1.26A in the subsequent experiments. At the same time, it can be found that the concentration of Mn 2+ increases rapidly during the first 15 minutes of electrolysis, indicating that leaching of Mn 2+ at this stage has chemical leaching in addition to electrochemical reduction, and chemical leaching plays a major role. Subsequently, the manganese ion concentration increases almost linearly with current density and electrolysis time. After leaching for 15 minutes, it can be considered that the chemical leaching is almost finished, and the electrochemical reaction begins to play a leading role.
Figure 2 Concentration changes over time at different currents
Figure 3 Apparent Efficacy and Recovery at Different Current Densities
From the relationship between apparent current efficiency and current density, it can be seen that the recovery rate increases with the increase of current density at 90 min, but the apparent current efficiency decreases with the increase of current density at 119, 150 A/m 2 . The apparent current efficiency is basically the same, as shown in Figure 3. When the current is 0.8A, the current efficiency is >100%. Due to the use of used batteries, a part of Mn exists in the form of MnOOH, Mn(OH) 2 or the like, and Mn 2+ is leached in the solution. Not all are produced by electrolytic reduction, a considerable part is caused by acid dissolution. Assuming chemical leaching is completed for 15 min, followed by electrochemical reduction, so the approximate treatment is performed, that is, when the current efficiency is calculated, the leaching of the first 15 min is subtracted. The amount of manganese. The apparent current efficiency at 0.8 A was 128.3%, indicating that a large portion was leached by acid rather than electrochemically. When the current reaches 1.5A, the apparent current efficiency begins to decrease due to a severe hydrogen evolution reaction at the cathode. At a current of 1.26 A, the apparent current efficiency and recovery were highest, so the current was carried out at 1.26 A in subsequent tests.
(2) Effect of sulfuric acid concentration
The concentration of sulfuric acid affects the rate of chemical leaching, increases the conductance of the electrolyte, reduces the cell voltage, and has an effect on current efficiency.
The fine electrode part was added to different concentrations of sulfuric acid solution according to the liquid-solid ratio of 10:1, and the electrolysis experiment was carried out under a constant current of 1.26A. The law of manganese sulfate concentration changing with electrolysis time is shown in Fig. 4.
Figure 4 Variation of manganese concentration with time under different acidity
Similar to Fig. 2, the manganese ion concentration rapidly increased at 15 min of electrolysis and increased with increasing acidity, and then increased substantially linearly. This shows that the acidity not only affects the chemical leaching rate, but also increases the electrochemical leaching rate. When the current density is the same, the acidity increases from 0.5mol/L to 1.0mol/L, and the manganese sulfate concentration gradually increases and reaches the maximum value. When the acidity continues to increase, the concentration begins to decrease. At the same time, it can be concluded that when the reaction is carried out for 15 minutes, the rate of concentration increase is basically the same at different sulfuric acid concentrations due to the same current, again indicating that the reaction of chemically leaching soluble manganese ions can be completed in 15 minutes. When the acidity is 1.0 mol/L, the reduction leaching effect is the best. The same conclusion can be drawn from the current efficiency and the recovery at 90 min, as shown in Fig. 5.
Figure 5 Apparent electric effect and recovery rate under different acidity
It can be seen from Fig. 5 that the current efficiency is maximum when the acidity is 1.0 mol/L. If the acidity is too high, a more serious hydrogen evolution reaction will occur, and the acidity is too low to leaching low-priced manganese oxide. Both of the above conditions can lead to a decrease in current efficiency. Therefore, a sulfuric acid concentration of 1.0 mol/L was selected as the catholyte.
(3) Influence of liquid-solid ratio
Weigh 67, 80, 100, 133g of the uniformly mixed fine electrode part, add it to 1.0mol/L sulfuric acid solution, and carry out electrolysis under the constant current of 1.26A. The variation of Mn 2+ concentration with electrolysis time is shown in the figure. 6.
Figure 6 Concentration change with time at different liquid-solid ratios
It can be concluded from the figure that when the liquid-solid ratio is too small, the acidity in the electrolyte is decreased due to the increase in acid consumption in the chemical leaching, and the reduction rate of MnO 2 is decreased, so that the liquid-solid ratio is the lowest in the manganese ion concentration at 6:1. When the solid ratio is too large, it is not favorable for reduction leaching, and the suitable liquid-solid ratio is 8:1.
Figure 7 Apparent current efficiency with different liquid to solid ratio
Figure 7 shows the apparent current efficiency as a function of liquid-solid ratio under different liquid-solid ratio conditions. When the liquid-solid ratio is 6:1, the current efficiency is higher than 100%, mainly due to the increase of the amount of mineral sample, so that the chemical leaching amount is greatly improved, and the electrochemical leaching amount is relatively reduced. The current efficiencies of the liquid to solid ratios of 8:1 and 10:1 are substantially the same. When the liquid-solid ratio continues to increase to 12:1, the current efficiency drops rapidly, indicating that too large a liquid-solid ratio is detrimental to electrolytic reduction.
(four) the impact of temperature
According to the liquid-solid ratio of 8:1, the ground positive electrode portion was added to a sulfuric acid solution with a concentration of 1.0 mol/L, and the electrolyte temperature was maintained at 20, 35 ° C and 40 ° C with a constant temperature water tank at a constant current of 1.26 A. Electrolysis, the experimental results are shown in Figure 8. As can be seen from the figure, the temperature has little effect on the leaching rate over the temperature range of the test.
Figure 8 Variation of manganese concentration with time at different temperatures
(5) Leaching mechanism
According to the "unreacted nuclear reduction model" followed by general solid leaching, the leaching rate of different current and acidity is substituted into 1-(1-α) 1/3 to make 1-(1-α) 1/3 versus time curve. The results are shown in Figures 9 and 10.
Fig. 9 Relationship between leaching time and 1-(1-α) 1/3 at different currents
Figure 10 Relationship between leaching time and 1-(1-α) 1/3 at different acid concentrations
It can be seen from Figures 9 and 10 that the leaching reaction follows the "unreacted nuclear reduction model", the product manganese sulfate is dissolved in water, and the outer dimensions of the solid phase manganese dioxide are reduced as the reaction progresses until disappearing.
If the reaction rate is controlled by chemical reaction, it should be consistent with: k ' t=1-(1-α) 1/3 . If the reaction rate is controlled by interfacial diffusion, it should be consistent with: K 〃 t=1-2/3α-(1- α) 2/3 .
The leaching rate 1 h before leaching at 20 ° C and 40 ° C was substituted into the formula 1-(1-α) 1/3 and 1-2/3α-(1-α) 2/3 , respectively, and the leaching time was plotted separately. Indicates a non-linear relationship. This shows that neither the interface diffusion control nor the chemical reaction control is supposed to be mixed control.
Substituting the leaching rate after immersing for 1 hour at the above two temperatures into 1-(1-α) 1/3 has a good linear relationship with time, as shown in Fig. 11, indicating that the leaching rate should be controlled by chemical reaction. The calculated slope of the two lines is 0.0002, 5 E-05, which is the apparent velocity constant, which is substituted into the Arrhenius formula:
1nK=1nA-Ea/RT
K-apparent velocity constant in the formula:
Ea-leaching activation energy;
T-reaction absolute temperature:
R-universal constant, 8.314.
The activation energy of the reaction was found to be 52.5 kJ/mol, which further indicates that the leaching reaction rate is controlled by chemical reaction.
Figure 11 Relationship between leaching time and 1-(1-α) 1/3 at different leaching temperatures
Third, the conclusion
(1) The leaching reaction rate of the ion-exchange membrane slurry of the waste battery positive electrode material can be explained by the “unreacted nuclear reduction modelâ€. The leaching can be roughly divided into three stages: the first stage is basically completed within 15 minutes, mainly the soluble manganese compound. Sulfuric acid leaching; the second stage occurs between 15 min and 1 h of leaching, the control step of the leaching reaction is mixed control; the third stage occurs after 1 h of leaching reaction, the leaching rate is controlled by chemical reaction, and the apparent activation energy is 52.85 kJ/ Mol.
(B) The results of single factor experiments show that the preferred conditions are: current density 150 A/m 2 , ie current 1.26A, sulfuric acid concentration 1.0mol/L, liquid-solid ratio 8:1, temperature 20 °C. Under this condition, constant current was energized for 90 min, the recovery was 25.77%, and the apparent current efficiency was 101.1%.
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