Anhydrous magnesium chloride melting system
The main raw material used is magnesite or light-burned magnesite. Magnesite contains MgO> 45%, CaO <1.5%, and SiO2 <1.5%. Lightly burned magnesite is lightly burned from magnesite at a temperature of 973-1373K. The production of anhydrous magnesium chloride melt from magnesite mainly includes the two operations of furnace charge preparation and shaft furnace chlorination.
Charge preparation
The charge is mainly composed of magnesite (or lightly burned magnesia) and carbon reducing agent. The charge for the chlorination of the shaft furnace must be a block or a granular material, and the charge must have a high purity, a reasonable chemical composition, sufficient mechanical strength, a high porosity, and a uniform size or particle size. According to different preparation methods, the charge can be divided into three types: Solel cement charge, dry mass charge, and ore pellet charge
Shaft furnace chlorination
The chlorination of the charge is carried out in the shaft furnace, and the temperature required for the chlorination process is mainly maintained by the heat released from the reaction of the material. The shaft furnace chlorination has the characteristics of low energy consumption.
(1) Shaft furnace. Also called vertical electric furnace, the shell is turned into a cylindrical body by steel welding, and it is lined with shaped refractory bricks with an inner diameter of 3.1m and a height of about 7m. The top of the furnace is provided with a feeding device, an operation hole and an exhaust gas exhaust hole, and the lower part of the furnace is provided with two rows of electrodes. Each row is equipped with three electrodes at an angle of 120 ° to each other. The lower row is set on the horizontal surface of the furnace bottom. The upper row is 2m higher than the lower row. The upper and lower rows of electrodes form a 60 ° angle with each other. Carbon grids are filled between the upper and lower electrodes as resistors, and the two electrodes are powered by two adjustable transformers. Chlorine gas ports are formed on the furnace wall between the two rows of electrodes at an angle of 120 ° to each other, and the chlorine gas is sent into the furnace. There are 3 slag removal holes at the same height as the upper row electrode, which is used for slag removal when the furnace is stopped. The front side of the furnace bottom wall is provided with a drain port for periodically discharging the magnesium chloride melt from the furnace.
(2) Chlorination process. The charge is added into the furnace from the top, and it is divided into three layers: upper, middle and lower in the chlorination furnace. The upper layer uses the exhaust heat of the furnace to preheat the charge, which is called the preheating layer. The thickness of the preheating layer is 2-3m and the temperature is 1123 ~ 523K. The middle layer is a reaction layer, located between the lower layer of the upper charge and the slag layer, with a height of 0.5-1.0m and a temperature of 1123-1373K. The lower layer is a slag layer and a carbon grid layer. The chlorine gas (concentration 65% -70%) sent in this layer rises through the grid layer to be uniformly distributed, while the magnesium chloride melt flows down the surface of the carbon grid. The two are fully contacted in countercurrent, and a small amount of unchlorinated oxide is chlorinated in this part, and there is still unchlorinated residue. The lower layer also functions as a filter residue. The magnesium chloride melt is heated by a carbon grid, so that the temperature of the accumulation chamber in the lower part of the furnace reaches 1023-1073k. In order to release the magnesium chloride melt from the nozzle.
Anhydrous magnesium chloride molten salt electrolysis
The anhydrous magnesium chloride melt prepared from magnesite chlorination is used as an electrolytic raw material, and electrolysis is performed in an electrolytic cell having a separator with an anode inserted thereon.
The structure of the electrolytic cell with a separator inserted on the anode is simple. The anode can be replaced continuously when the anode is worn or the cathode is deformed. The repair time of the tank generally depends on the service life of the separator. The service life of the latter is generally about 1-1.5a. The current strength of this slot type has increased from 15-32kA in the 1930s to 105-110kA. Due to the large pole spacing, the slot voltage is high, and the DC power consumption is high.
Crude magnesium produced by electrolysis needs to be refined and recast into ingots. Chlorine gas is sent to the shaft furnace for chlorination of magnesite and other furnace materials. The insufficient part is supplemented with liquid chlorine. The minimum chlorine consumption is 1.5 per ton of refined magnesium.
Magnesium chloride melt produced by magnesite chlorination is also suitable as raw material for electrolytic cell without separator. This magnesium chloride melt is electrolyzed in a separatorless tank with a current intensity of 6.25 ~ 64kA, and the DC power consumption per kilogram of crude magnesium is 15.18-14.42kW · h. The application of baffle-free electrolytic cells in the molten salt electrolytic magnesium smelting industry has attracted people's attention