Ultrasonic Aroma Humidifier,Aroma Diffuser Humidifier,Led Aroma Diffuser,Aroma Diffuser And Humidifier Guangzhou Chiyang Scent Technology Co., Ltd. , https://www.gzdiffuserscent.com
Discussion on the dissolution of metal and the formation of sludge in molten salt electrolysis
Neodymium metal is the main material of neodymium-iron-boron permanent magnet prepared, with the application demand neodymium boron permanent magnet materials widely developed Neodymium also increases year by year. At present, the electrolytic cell for producing metal ruthenium by molten salt electrolysis is a graphite material, and a graphite anode and a tungsten rod cathode are inserted in parallel above the tungsten cathode, and a tungsten or molybdenum crucible is placed under the tungsten cathode for electrolysis. Metal, the current electrolytic cell has the disadvantages of low current efficiency and easy formation of sludge at the bottom of the furnace. Few electrolytic cells can exceed 80% current efficiency. How to improve the current efficiency of the electrolytic cell is a problem worthy of discussion, among many factors. Finding the loss of metal in the molten salt and the cause of slagging is the key to the problem, such as which factors can affect the dissolution of the metal in the molten salt, and in what form the dissolved metal exists in the electrolyte, thereby finding a way to reduce metal loss. The method is very helpful in improving the current efficiency of electrolysis.
In this paper, with reference to the mass method for determining the solubility of aluminum in cryolite, the dissolution of metal ruthenium in the electrolyte at different temperatures was measured, and then the metal dissolution product was compared with the slag formed during the electrolysis process to analyze the electrolysis process. The formation of slag mud.
   I. Experimental methods and devices
There are usually two methods for determining the solubility of a metal: one is the difference in mass of the metal before and after the test (ie, the mass method); the other is the amount of metal dissolved in the salt phase (ie, the tolerance method). According to the latter, when the electrolyte sample is solidified, the dissolved metal is precipitated as a finely dispersed metal phase, and then reacted with hydrochloric acid to calibrate the amount of the metal according to the amount of gas generated. Compared to the two methods, the mass method is usually twice as large as the volume method, which is related to the method and conditions of the assay.
In this paper, under the conditions similar to the production conditions, the electrolyte ratio is consistent with the actual production, that is, the electrolyte composition is NdF 3 ; LiF = 10: 1.2, while the electrolyte contains a small amount of Nd 2 O 3 under the argon-protected sealing condition. The dissolution of the metal ruthenium in the electrolyte was determined by the mass method. The experimental device is shown in Figure 1. The total amount of electrolyte in the crucible is about 4000g. About 55g of bulk metal is added for each measurement. During the experiment, the prepared metal ingot is removed from the surface oxide scale and weighed. The electrolyte is heated to the predetermined temperature. The temperature is maintained and balanced, and the metal covered with the electrolyte is preheated to about 500 ° C and quickly placed in the electrolyte, and the cover is closed to pass the shielding gas. After a constant temperature of 3 h, the titanium crucible was taken out and placed in a new electrolyte powder to be rapidly cooled. After cooling, the outer layer of the metal was removed and weighed to obtain the metal mass after the experiment.
Figure 1 Experimental device for measuring the solubility of bismuth
The metal bismuth product is a hard shell that is cooled around the metal after the metal solubility test. The hard shell and the surrounding electrolyte are clearly different in color and hardness. The slag in the electrolysis process is formed by the bottom of the industrial electrolyzer. The paste was ground into a powder and analyzed by X-ray diffraction analysis.
   Second, the results and discussion
(1) The change of solubility of metal ruthenium with temperature
Mao Jianhui et al studied the effect of electrolyte composition on 10kA molten salt electrolysis of metal ruthenium. It is believed that with the electrolyte ratio NdF 3 : LiF increasing from 10:0.9 to 10:1.1, the current efficiency first increases and then decreases, when the electrolyte ratio is 10: At 1.0, the maximum value is reached, and the current electrolytic ratio of electrolytically produced metal ruthenium is generally 10:1.2. At this ratio, the electrolyte is more soluble. The current industrial production generally uses this ratio, and the operating temperature is controlled at about 1060 ° C, while pure metal The melting point of ruthenium is 1016 ° C. According to the selection of 980-1080 ° C, the difference of each phase is 20 ° C as an experimental point. The dissolution of metal ruthenium in the electrolyte is measured by the mass method in the above experimental method. Shown.
Figure 2 Solubility of ruthenium in NdF 3 -LiF molten salt
It can be seen from Fig. 2 that when the electrolyte temperature is lower than the melting point of the metal, a small portion of the metal can still be dissolved. When the temperature is raised, the solubility of the metal in the electrolyte is rapidly increased, and it can be seen that the temperature in the industrial electrolysis operation is increased. The solubility of the metal at 1060 ° C is close to 0.36%. Of course, in the mass spectrometry method, metal oxidation loss, evaporation loss, and compound loss are inevitable, so the measurement result is high. Usually, the solubility of aluminum in cryolite is measured, and the value measured by mass method is volumetric method. If the value obtained is 2 to 4 times, then even if the solubility value measured by the mass method is considered to be 4 times the actual solubility value, the solubility of the metal is about 0.09% when the electrolysis operation temperature is 1060 ° C, and the electrolysis operation temperature is 1040 ° C. When the solubility of the metal is close to 0.06%, from this point of view, minimizing the electrolysis operating temperature reduces the dissolution loss of the metal, thereby increasing the current efficiency, but too low a temperature causes the electrolyte to become viscous, affecting the mass transfer process of the electrolyte. At the same time, the melting point of the metal ruthenium should be considered. From the curve, after the temperature is lowered to 1020 ° C, the solubility of the metal ruthenium tends to decrease with the decrease of temperature, so the electrolysis temperature can be controlled within the range of 1040 ± 10 ° C.
(II) Comparative analysis of metal dissolved products and slag
In the metal solubility measurement experiment, we found that the dissolution loss of the metal is very large. In order to understand the dissolution loss of the metal in the electrolyte, what is the step, that is, the dissolution loss mechanism of the metal ruthenium, The coating of the layer was subjected to X-ray diffraction analysis, and the phase of the coating was measured, and the measurement results are shown in Fig. 3.
Figure 3 X-ray diffraction pattern of metal dissolution products
We can see from the XRD pattern, epigenetic metal is dissolved and became two new phases NdOF NdF 2, therefore description, dissolved Neodymium reacts with neodymium fluoride generate NdF divalent, while in the presence of oxygen ions The dissolved metal ruthenium also reacts to form oxyfluoride. Since the peak of the metal ruthenium in the XRD pattern is weak, it is impossible to determine from the XRD pattern of Fig. 3 whether or not there is a metal ruthenium phase.
In order to study whether there is a relationship between the dissolved product of the metal ruthenium and the sludge in the ruthenium electrolysis tank, the slag in the sputum electrolysis tank was taken and analyzed by X-ray diffraction, and the analysis results are shown in Fig. 4. As can be seen from Fig. 4, the slag phase in the ruthenium electrolysis cell is substantially identical to the metal ruthenium dissolution product, in addition to the presence of the Nd 2 O 3 phase. It can be seen that the formation of sludge in the electrolysis tank is related to the dissolution of the metal crucible. It is also related to the feed rate. When the feed rate is too fast, the Nd 2 O 3 that is too late to be electrolyzed will sink to the bottom of the furnace to participate in the production of sludge. . Therefore, the prevention of sludge formation should control the tank temperature and reduce the dissolution loss of the metal crucible; in addition, the feed rate should be controlled so that the addition and the addition are less, but the slower feed rate will lead to the anode effect, according to the production. In practice, the general feeding speed is 95 g·min -1 , which is more suitable; in addition, the dissolution loss of the metal crucible is unavoidable, so the bottom of the furnace should be stirred with a stir bar at regular intervals to consume the sludge.
Figure 4 X-ray diffraction pattern of slag mud in é’• electrolytic cell
   Third, the conclusion
(1) The dissolution loss of the metal ruthenium in the electrolyte is very large. Minimizing the electrolysis operation temperature to reduce the dissolution loss of the metal is an effective measure for improving the current efficiency, and the optimum temperature range is 1040±10 °C.
(2) The formation of sludge in the electrolysis tank is related to the dissolution of the metal crucible, and it is also related to the feed rate. When the feed rate is too fast, the Nd 2 O 3 which is too late to be electrolyzed will sink to the bottom of the furnace to participate in the production of sludge. .
(3) Preventing the formation of sludge. It is also necessary to control the feeding rate. It is more appropriate to add cerium oxide at a rate of 95 g·min -1 , and stir the bottom of the furnace with a stir bar at regular intervals to consume sludge.