Production Process and Application of High Molecular Ratio Cryolite

Jiaozuo City, Duo Duo Duo Chemical Co., Ltd. Hou Hongjun Zhang Fushan is still more than cryolite production technology and application In recent years, China's aluminum industry has developed rapidly, the design scale and equipment level continue to mention the Bureau, further mention current efficiency, reduce raw material consumption The technical problems such as prolonging the service life of the electrolytic cell are still the focus and problems of the technical progress of electrolytic aluminum technology. Cryolite is an auxiliary raw material for the electrolytic aluminum industry. The quality of its products is of great importance to the electrolytic aluminum process, especially the firing start-up technology and the service life of the bath. This article starts with the production process of high-molecular-weight cryolite and its start in electrolytic aluminum baking. A brief discussion of applications.

The molecular ratio of traditional cryolite production process is generally controlled between 1.8 and 2.2, and the impurity content is high, which is difficult to meet the needs of the development of electrolytic aluminum industry. With the advancement of aluminum electrolysis technology and the development of large-scale pre-baking technologies, cryogenic cryogenic process research and technological advancement of aluminum electrolysis have been actively developed. The cryolites for aluminum electrolysis with different molecular ratios and different performances continue to emerge. In particular, certain achievements have been made in controlling the molecular ratio of the cryolite, reducing the burn, and increasing the purity, which has promoted the technical progress of electrolytic aluminum. At present, the cryolite production process mainly includes fluorite method, fluorosilicic acid method, and aluminum electrolysis recovery method.

As the source of fluorine, first react with fluorite and sulfuric acid, absorb 30% hydrofluoric acid with water, add aluminum hydroxide to form aluminum hydrofluoride, and then add soda to synthesize cryolite. In addition, there is a clay salt halide method cryolite production process in which clay and industrial salt are used instead of aluminum hydroxide and soda ash.

The sodium process is representative, and other processes are currently not industrialized. Sodium fluorosilicate was used as a raw material, sodium fluorosilicate was decomposed using ammonia, and silica was removed by solid-liquid separation to obtain a fluorine-containing solution. Silica is washed with silica and dried. The fluorine-containing solution reacts with the sodium aluminate solution to obtain cryolite. The ammonia gas released during the synthesis is recovered and returned to aminolysis of sodium fluorosilicate. The process must first produce high-quality white carbon black seed crystals. This is the key to the production of high-quality silica: Preparation of ammonium fluoride with fluorosilicic acid and ammonia, separation of diosmium oxide, and addition of aluminum sulfate and sodium sulfate Produce cryolite and produce by-product ammonium sulfate: use fluoride acid to react with aluminum hydroxide to produce aluminum fluoride solution, remove silica by solid-liquid separation, get aluminum fluoride solution, use fluosilicic acid to react with soda, after solid-liquid separation Silica solution was removed while sodium fluoride solution was obtained. At a certain temperature, the aluminum fluoride solution reacts with the sodium fluoride solution to produce cryolite.

3. Aluminum electrolytic industry recycling method. The fluoride salt added in the process of aluminum electrolysis is partially decomposed to release hydrogen fluoride gas, and hydrofluoric acid is obtained by absorption. Then, sodium aluminate is used as a raw material to react with hydrofluoric acid to obtain cryolite.

Based on the above process analysis, the molecular ratio of fluorite to cryolite production is 2.7-3.0, which has certain difficulties in the process, serious equipment corrosion, and high production costs. The aluminum electrolysis recovery process is limited by raw materials, and the molecular ratio and product quality are difficult to meet the requirements of the aluminum electrolysis process. The use of sodium fluorosilicate instead of fluorite protects the fluorite resources that are of strategic importance to the country and complies with the national industrial policy. The cryolite produced by this process has a lower molecular weight than that of 2.7 to 3.0. The melting point is lower than that of ordinary cryolite. ~ 30 * C, product purity, production of mother liquor and ammonia can be recycled to achieve a true sense of clean production: high-quality white carbon black by-product is widely used in rubber, pesticides and fire extinguishing agents, etc., in reducing production costs Comparison of major production processes of cryolite Table Fluorspar method Silicic acid method Aluminum electrolytic recovery source from fluorspar Fluorine source From fluorosilicic acid Fluorine source From aluminum electrolysis Recovery production process Complex process equipment Simple production process Simple product Stability Good product stability Poor stability 51 , 6,5-wide high-content cryolite molecule ratio 2.02.5 cryolite molecular ratio 2.7-3.0 cryolite-molecule ratio 1.2~2.0 flammation decreased by high flaming and reduced burning higher than inconsistent with the national industrial policy in line with national industrial policy, easy to scale When production is not easily scaled, it also greatly enhances the competitiveness of the product.

Soviet scholars Fedchev and Ilinski showed that the melting point of cryolite is 1000 *c, while the melting point of subcrystalline cryolite is only 725 * c. X-ray analysis of cryolite with different molecular ratios can be seen with the molecular With the increase of the ratio, the content of cryolite increases and the content of sub-freezing stones decreases. Therefore, the melting point of macromolecules is higher than that of cryolite when the melting point of cryolite is higher than that of ordinary cryolite 20~30*C. The volatilization loss is mainly due to the effect of the melt and water. The ignition loss of different molecular ratio cryolites was measured. As a result, the macromolecules than cryolite greatly decreased its loss of ignition due to its high cryolite content and low crystal water content.

The production of cryolite by the sodium fluorosilicate method has a good use performance due to its high polymer ratio, high purity, high melting point, and low loss of ignition, which in particular provides strong support for the starting of electrolytic aluminum firing. This process represents the current level of cryolite production technology in China.

Application. The use of sodium fluorosilicate to produce cryolite complies with national industrial policies. The production process is simple and the product quality is stable. In the past, microwave electron tubes were used for oxygen-free copper materials. Due to their low mechanical strength, especially after high-temperature hydrogen burning, they could not be used to process magnetron inner cavities. Tuning rings and other key parts. Researched by Luoyang Copper Processing Group Co., Ltd., this project adopts the method of internal oxidation of powder metallurgy, that is, the introduction of trace, fine, dispersed A1203 hard cryolite molecular ratio in the copper matrix: NaF/AlF3) At present, the only process that can reach 2.8 or above in China is very suitable for roasting the electrolytic cell to start, and its ignition is reduced (less than 1.5%). It is very beneficial to the aluminum electrolysis bath and the improvement of the field operation environment of the aluminum electrolysis process, and because of its low impurity content. Adapt to the development trend of the international aluminum electrolysis industry. From the use of macromolecule ratio cryolite in Jiaozuo City Polyfluoride Chemical Co., Ltd. in Guizhou Aluminium Plant, Baotou Aluminum Group Corporation and Jiaozuo Wanfang Aluminum Industry Co., Ltd., the quality shrinkage was relatively slow, and the ratio of electrolyte molecules was flattened. Mainly due to its high cryolite content and low volatilization (water content), it can reduce the hydrolysis reaction, which is conducive to the stable maintenance of the electrolyte composition.

Small and easy to control.

The use of macromolecules compared to cryolite baths solves the problem of local concentration of alkalis caused by the addition of a large amount of alkali using ordinary cryolite. The uneven absorption of sodium at the cathode affects the expansion stress concentration, causing the expansion and splitting of the cathode carbon block, and ultimately affecting the life of the electrolytic cell. The problem. At the same time, since the melting point of the polymer is higher than that of the cryolite, the temperature is higher than that of ordinary cryolite by 30°C. In the roasting start-up phase of the electrolytic cell (blend of the mixture), due to the incorporation of macromolecules than cryolite, it has a high melting point and does not contain high strength and high. The copper-conducting alloys studied the particle phase, and because their pinning effect prevented the movement of dislocations, they effectively reduced the recovery and recrystallization of the copper matrix, which greatly increased the strength and thermal stability of the matrix copper while conducting its conductivity. However, the thermal conductivity has been reduced by a small amount. In the process, a new process such as isostatic pressing, high-temperature sintering and rotary swaging has also been adopted, which fundamentally solves the problem of difficult processing of the material and has greatly improved the performance of the liquid. In the electrolyzed melt of aluminum, during the electrolytic temperature reduction after the start of the electrolyzer, an electrolyte having a higher primary crystal point is formed in the interstices of the liner, thereby effectively clogging the etched passage of the metallic aluminum from the tank liner, thereby prolonging Groove liner service life.

Taking the 190KA electrolyzer as an example, 2.5 to 3 tons of soda ash can be saved per start.

The small size of the product has effectively improved the poor on-site operation conditions caused by the volatilization of fluorine during electrolysis.

The sodium fluorosilicate method cryolite production process is in line with national industrial policies. Compared with other processes, it has a high molecular ratio, reduced seizures, lower Fe203, SO42- and other impurities, and has no 'three wastes' emissions. One of the potential processes represents the development direction of today's fluoride salts.

High molecular ratio cryolite can effectively reduce the production cost of aluminum electrolysis, improve the operating environment of aluminum electrolysis, and also help to control the technical parameters of the electrolysis cell and play a role in prolonging the service life of the electrolysis cell. More importantly, it is high. Compared with cryolite, its molecular properties provide an important technical support for China to seize the international electrolytic aluminum market. The â–¡ mark effectively controls the size change of the material after hydrogen burning. This material can be applied to spot welding electrodes in automobiles, air conditioners, kinescopes, and integrated circuit industries to replace imports and save foreign exchange. It not only has important social value, but also has good economic benefits. This project has filled the domestic gap and reached the leading domestic level.