Industrial production of manganese metal electrolysis

Domestic electrolytic manganese metal plate made of stainless steel or titanium plate as the cathode, selection of lead antimony quaternary alloy tin-silver, tin-lead-silver or silver alloy is a ternary alloy sheet as an anode.
The total reaction formula of electrolysis is

That is, Mn is precipitated on the cathode, O 2 is precipitated on the anode, and a waste electrolyte containing H 2 SO 4 is produced. The waste electrolyte is returned to the leaching.
Electrolysis was carried out in an electrolytic cell lined with a wooden false bottom reinforced concrete PVC.
I. Electrolyte composition and electrolysis technical conditions
High liquid (new liquid) Mn 36~40g/L
Catholyte Mn 15~16g/L
(NH 4 ) 2 SO 4 100~120g/L
pH 6.8~7.2
Temperature 38~44°C
SeO 2 (calculated as Se) 0.03~0.04g/L
Cathode current density 350~400A/m 2
Anode current density 600~700A/m 2
Slot voltage 4.2~4.6V
The same name pole distance 70~80mm±
Electrolysis cycle 24h
Second, electrolysis operation
Electrolytic manganese production can not produce high quality and high yield. In addition to the liquid electrolyte process, it is necessary to provide qualified electrolyte. It is also necessary to strengthen the management of the tank surface, strictly control the electrolysis conditions, and ensure the normal operation of electrolysis.
1. Adjusting the tank 1 hour before the trough, sample and analyze the concentration of manganese sulfate in the bath. According to the results of the bath analysis, the flow rate of the additional liquid in each electrolytic cell is adjusted to gradually increase the concentration of manganese sulfate to the requirement when the tank is discharged.
The pH value of the catholyte in each electrolytic cell was measured 20 to 30 minutes before the trough, and ammonia water was slowly added to the tank to raise the pH value so that the pH value met the requirements of the trough.
When both the pH and the concentration of manganese sulfate are required, the aqueous solution of selenium dioxide is added in the amount required to be discharged from the tank, and then the trough is started.
2. Slot surface management The trough should check the newly installed electrolyzers immediately after the assembler: first, adjust the position of the anode and the anode so that the cathode plate is at the center position between the two diaphragm frames; Secondly, observe the conduction of the anode and cathode plates, and find and treat the poorly-conducting anode and anode plates in time. Third, measure the pH of the catholyte with pH test paper, and adjust the ammonia flow rate according to the pH value to keep the pH value. Within the process requirements; fourth, adjust the replenishment flow. After all the cells have been inspected once, check again and observe the upper manganese. At this time, if you find that there is a "dead" or "shell" phenomenon, you must take it out and replace it with a qualified new plate or "starting plate".
During the entire electrolysis process, the tanker should always check the current indicated by the ammeter on the rectifier cabinet and adjust the current to meet the process requirements. Always carry out inspections by the electrolysis tank, always keep the cathode and anode plates in a good conductive state, and keep the process parameters such as Mn 2+ ion concentration and pH value within the normal range to ensure the smooth progress of the electrolysis process. [next]
3. Treatment of the disease tank 1) Acidity in the bath liquid Under normal conditions, the pH of the cathode bath liquid should be between 7 and 7.2, generally not lower than 7. A decrease in pH (less than 6.5) is the acidity of the bath. Acidity in the bath may cause reverse dissolution of the cathode electrowinning manganese. The main causes of acidity are:
1 The new diaphragm bag has a large pore, and hydrogen ions in the anolyte easily permeate into the cathode region, so the pH value decreases rapidly and causes acidity. The acidity of the bath can be solved by simply adding ammonia water.
2 The diaphragm bag has been broken or the false bottom frame is loose, and the anolyte directly penetrates into the catholyte to cause acid. To deal with this situation, it is necessary to stop the groove, replace the diaphragm bag or fix the diaphragm frame, and seal the false bottom.
3 Sometimes the pH value may decrease due to the slow flow rate of the make-up solution or the low manganese content. At this time, the adjustment of the added ammonia water, and appropriately increase the flow rate of the supplemental liquid, can be solved.
2) Tank liquid alkali When SeO 2 is used as the antioxidant, the pH of the bath is more than 8.0, which is considered to be the alkali of the bath. The caustic alkali may cause the manganese in the black to black. The main reasons for the alkalinity of the bath are:
1 The working time of the electrolytic cell is too long, and the diaphragm bag is blocked by calcium, magnesium and ammonium salts. As the electrolysis, hydrogen molecules continuously deposited, OH - ions corresponding increase in the OH - ions migrate towards the anode region and the anode region of the H + ion holes are blocked by the membrane and migrate to the cathode region is hindered. Therefore, the pH of the catholyte is continuously increased to cause alkali. In this case, it can be temporarily treated by adding waste electrolyte, and after the tank is removed, the diaphragm bag can be cleaned and replaced.
2 The electrolyte temperature is too low, and the pH value increases when the Mn 2+ ion concentration is high. At this time, the cooling water can be turned off, and an appropriate amount of waste electrolyte is evenly added in the tank, and the flow rate of the small addition liquid can be turned off, and then the normal state can be transferred.
The high concentration of 3Mn 2+ ions and high temperature may also cause alkalinity in the bath.
4 The anode plate can work continuously for more than two weeks without knocking or changing, which can cause alkalinity in the bath.
3) Electromade manganese blackening Electromagnetism blackening affects product quality and yield. The main reasons are:
1 The electrolyte contains heavy metal impurities exceeding its maximum allowable amount.
The concentration of Mn 2+ ions in the 2 bath is too high.
3 The bath temperature is too low.
The concentration of sulfuric acid in the 4 bath is too high or too low.
5 The anode and cathode plates are poorly conductive, causing the manganese in the electromagnetism to black.
6 The amount of selenium dioxide added is not enough.
7 The pH of the cathode bath is too high.
4) Shelling The tank is electrolyzed for about 1 hour, and a large bubble is generated around the plate to determine the phenomenon of shelling. Shelling seriously affects the quality and yield of the product. The main reasons for the shelling are:
1 Some electrolytic process parameters do not meet the process requirements when grooving. For example, the concentration of Mn 2+ ions in the bath is too low, the pH of the bath is too low, and the bath temperature is too high.
2 The cathode plate is not clean.
3 water glass solution is too concentrated.
4 The new polished plate is not placed in the waste liquid tank to be immersed.
5 The amount of selenium dioxide added is too little or too much.
If the concentration of Mn 2+ ions in the 6 bath is too high, a large shell will be formed.
Therefore, it is necessary to prevent the groove from being installed when the process conditions are not adjusted, and the occurrence of the shell is fundamentally eliminated. Of course, it is difficult to completely avoid the occurrence of shelling. When the phenomenon of shelling occurs, the cause should be ascertained as soon as possible, the tank should be re-adjusted, and the plate that has been shelled should be taken out and replaced with a qualified plate or "starting plate".
5) Electrolytic manganese reverse solution In the process of electrolysis, when the white plate is severe at both ends or both sides of the plate, it may be reversed by electrolytic manganese. The reason may be:
1 Cathode plate or anode plate is poorly conductive.
2 The pH of the bath is too low.
The content of heavy metals such as Co and Ni in the 3 bath exceeded the standard.
6) Electrodemanganese is difficult to peel off If the electrowinning manganese is difficult to peel off, some products cannot be knocked down, causing waste. At the same time, the labor intensity of the workers is increased, and the cathode plate is also damaged. Therefore, this should be avoided. The main reason why electrolytic manganese is difficult to peel off is:
1 The concentration of the water glass solution is too low or the water glass is not applied.
2 The bath temperature is too low, the current density is too small, the concentration of Mn 2+ ions in the bath is too low, and the pH is too low.
3 cathode plate is severely hair white (surface roughness) [next]
Third, the post-treatment of electrolytic manganese
Post-treatment of electrolytic manganese refers to a series of operations for treating electrolytic manganese metal after electrolysis, including passivation, water washing, drying, peeling, packaging, and plate processing. The post-treatment of electrolytic manganese has a great influence on the quality of the product, especially the sulfur content, and must be done carefully according to the process requirements.
1. Passivation reaches the electrolysis cycle, the cathode plate is deposited a metal manganese removed from an electrolytic cell, the electrolyte drained, placed into a passivation solution (3% by weight of chromium potassium silicate solution) tank, which It is a passivation process. The purpose of passivation is to prevent or slow the oxidation of metallic manganese in the air. The principle is that when the metal manganese is immersed in the passivation liquid, the surface of the metal manganese forms a passivation film layer, and the passivation film layer is dense, which can prevent further oxidation of the metal manganese. In order to ensure the quality of manganese metal, the concentration of the passivation solution should be appropriate. If the concentration is too low, the passivation effect will not be achieved; and if the concentration is too high, the surface of the metal manganese will be blackened. The suitable concentration of potassium dichromate passivation solution is about 3%, and should be orange when viewed from the outside.
2. Washing After the passivated cathode plate and manganese metal are lifted, drain the passivation solution, soak it in a hot water tank, rinse it with tap water, and finally soak it in another hot water tank. The purpose of the water washing is to wash away the solution of the electrolyte, the passivation solution, etc. adhered to the surface of the metal manganese. If it is not cleaned, the sulfur content of the product must be high, so it must be washed repeatedly until it is rinsed clean.
3. Drying The metal manganese washed with water is placed on the shelf and pushed into the drying room for baking. The temperature of the drying room is preferably not more than 110 °C. The baking time is generally 20~30min. Drying operations should be careful to allow the product to completely dry out, otherwise the product is susceptible to oxidative deterioration. However, it must be noted that it cannot be over-baked. Otherwise, the product will be blue and black, which will also affect the appearance quality of the product.
4. Peeling Peeling is the separation of the dried manganese metal product from the cathode plate. When peeling off, it should be noted that: 1 first observe the appearance quality of the product, classify the product according to the appearance quality of the product, and the products with different appearance qualities should be peeled off in different peeling barrels; 2 When peeling off, the deformation and damage of the plates should be avoided as much as possible. Under no circumstances should the iron hammer be used for knocking; 3 metal manganese should be peeled off as much as possible.
5. Packaging After the product is peeled off, the on-site quality inspector samples the sample in the peeling bucket and sends it to the physical and chemical analysis room for analysis. Production workers are barreled and weighed according to the appearance quality of the products. Pay attention to the operation: 1 Whether the packaging drum and the inner bag are clean, and it is strictly forbidden to mix foreign impurities into the product to affect the quality of the product; 2 The weighing is accurate.
6. Treatment of Cathode Plate The cathode plate with residual manganese after stripping the product was placed in an anolyte tank to be immersed, and the sulfuric acid of the anolyte reacted with the residual manganese on the cathode plate to remove the residual manganese into manganese sulfate and remove it. The cathode plate from which residual manganese was removed and the cathode plate without residual manganese were placed in a washing solution (7% HNO 3 + 3% K 2 Cr 2 O 7 solution) for about 1 minute, and then taken out and rinsed with tap water. Observe the surface condition of the cleaned cathode plate, store the surface bright and flat at the designated position for use; pick out the severe hair white and send it to the polishing room for polishing.
Polishing is carried out in a polishing bath. In phosphoric acid and sulfuric acid (mass ratio of 3: 1) as electrolyte, glucose (in an amount of 2% of the mixture) of brightener to the cathode plate to be polished as the anode and cathode plates the same stainless steel Under the action of direct current, an anodic dissolution reaction occurs. When the anode is dissolved, the convex portion on the anode dissolves first, so that the uneven plate becomes a plate having a flat surface and a bright surface. Rinse the polished plate with water and reuse it. Polishing operations should be noted that the plates entering the polishing bath must be clean (no water, no residual manganese, etc.).
When the polishing bath is polished by direct current, the technical indicators to be controlled are:
Plate current density 700~1000A/m 2
Voltage 5~7V
Solution temperature 50~70°C
The same name pole distance 100~120mm
Polishing time 10~20min[next]
Fourth, the electrolyte cooling method
Due to the electrothermal effect of Mn 2+ during the precipitation of the cathode during electrolysis, Joule heat is continuously generated, and the manganese reversed heat release is added to increase the temperature of the catholyte in the electrolytic cell.
In order to eliminate the excess heat in the catholyte and control the normal operating temperature of the electrolyzer, the electrolytic manganese plants all over the world have used pipes (lead pipes, stainless steel pipes or plastic bellows) on both sides of the electrolyzer for decades. Cooling water is introduced into the tube to indirectly cool the catholyte in the cell. This cooling method has a small cooling contact area between the cooling pipe and the catholyte, and can only cool the catholyte near the cooling pipe, and the central portion of the electrolytic cell having the largest heat generation is not cooled, and the temperature of the entire electrolytic cell is not uniform, and the heat exchange efficiency is low. Low; the flow rate of the catholyte in the electrolytic cell is low, so that the cooling tube which is not originally high in thermal conductivity is more difficult to exert cooling effect, and a large amount of crystallization such as MgSO 4 , CaSO 4 , (NH 4 ) 2 SO 4 is required, so that the cathode working chamber needs Frequent cleaning, low equipment utilization, and high labor intensity; at the same time, due to the existence of cooling tubes in the electrolytic cell, the method has the defects of large power consumption, large material consumption, and large cooling water consumption.
In order to improve the existing cooling method for producing manganese metal, it can achieve the purpose of not only controlling the normal operating temperature of the electrolytic cell, improving the heat exchange efficiency, but also the quality of the product and greatly reducing the production cost. Through technology development, March 29, 2001 Riliang Teng, Zhou Yuanmin, Mei Guanggui, Liu Rongyi and others applied for the invention patent, the name is: a method of external cooling of manganese electrolysis cathode tank and recovery of magnesium. The patent application number is 01111078.3.
In order to achieve the above object, the technical scheme adopted by the present invention is to cancel the conventional cooling water pipe in the manganese electrolysis cell; and to maintain a partial cathode in a state where the liquid level difference of the anolyte in the manganese electrolysis cathode liquid and the diaphragm is relatively stable. The liquid is taken out of the electrolytic cell, and is cooled by a high-efficiency anti-exciting crystal nozzle by means of blast or natural wind; as the catholyte is cooled, the solubility of Mg 2+ and Ca 2+ in the solvent is lowered, in the chute or the sump The crystal is precipitated with supersaturated calcium and magnesium, and the crystal is periodically removed to remove some impurities such as MgSO 4 and CaSO 4 in the solution, and the magnesium, manganese and ammonium sulfate are effectively recovered; the cooled catholyte through the sump is self-flowing or used. The pump returns to the cathode compartment of the electrolysis cell.
The advantages and positive effects of the present invention over the prior art are:
1 The catholyte is introduced from the inside of the electrolytic cell to the outside of the electrolytic cell for cooling, thereby realizing the control of the flow amount and temperature of the catholyte. Appropriately increase the flow rate, the flow rate of the cathode chamber solution in the electrolytic cell is increased, the temperature in the cathode chamber is uniformly distributed with the concentration of Mn 2+ , and the heat exchange effect is good; the precipitation of MgSO 4 and CaSO 4 in the cathode chamber is greatly reduced, and the phenomenon is reduced. The cleaning of the cathode chamber improves the utilization rate of the equipment, reduces the labor intensity, and improves the production environment.
2 The catholyte is introduced from the electrolytic cell to the outside of the electrolytic cell for cooling, and the recovery of magnesium, manganese and ammonium sulfate is also realized.
3 Remove the cooling water pipe from the electrolytic cell, so that the effective utilization rate of the electrolytic cell can be increased by 12%, and the production capacity can be increased by 10% to 12%.
4 The implementation of the invention not only can control the normal operating temperature of the electrolytic cell, but also has high heat exchange efficiency and greatly reduces the production cost. Continuous operation in the production tank for 36h, no precipitation of crystals in the cathode chamber, the Mn 2+ concentration in the cathode chamber is uniform, not exceeding the range of 14~18g/L; the pH of the cathode chamber is measured at 7~7.5.
5 As the outer circulation of the tank is cooled, the crystalline MnSO 4 , CaSO 4 and the like are cooled, so that the uncharged impurities such as C, p, SiO 4 and S which are difficult to penetrate the separator in the catholyte are carried away along with the cooling crystals outside the catholyte tank, It will accumulate and enrich in the cathode chamber, and C, P, SiO 2 and S in the cathode chamber have only 10% to 40% of the cooling in the tank. As a result, these impurities entrained in the electrolytic manganese product are greatly reduced, and the product quality is remarkably improved. Under the same qualified liquid quality conditions, the impurity content of the external cooling of the tank and the cooling of the electrolytic manganese metal product in the tank is as follows (%):
Element Mn C S P Si Se Fe
Out-of-slot cooling 99.895 0.011 0.005 0.0010 0.0010 0.080 0.0064
Cooling in the tank 99.70 0.04 0.05 0.005 0.01 0.080 0.010
The impurities such as C, S, P, Si, Fe, etc. of the electrolytic manganese metal produced by the cooling outside the tank are lower than the DJMnB index of the electrolytic manganese industry standard (YB/T051-2003).

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