1. Three processes of Changjin smelting
Magnesium, look at smelting and smelting can be done in three stages Previously, there were only lithium, beryllium, three or three kinds of metals, and they were few, and the production was high. At present, high-level laboratories will use this method to prepare magnesium metal. There are several stages of melting, electric melting, electric melting, electrolysis and electrolysis, but there are several methods, such as silicothermal method and so on, but the power consumption is large. The characteristics of heat do not need electricity. Electricity is used to do it. The main method of magnetism is changed from the electrolysis method to the heat reduction method.
2. The mainstream of current magnesium smelting technology – thermal reduction method
According to the different types of reducing agents, the thermal reduction method can be divided into three types: carbothermal method, carbide method and silicon thermal method. The carbothermal method will use a lot of hydrogen in the process, so if you are not careful, it will cause labor safety problems; one of the reducing agents used in the carbide method is calcium carbide, which has low activity, is easy to hydrolyze and uses a large amount, so The above two are rarely used in industry. At present, the mainstream of thermal reduction method is silicothermal method, which is to reduce magnesium oxide by metal or its alloy (reducing agent), obtain magnesium vapor, and then condense and concentrate to obtain magnesium metal. The reducing agent can be silicon, aluminum, calcium, manganese, lithium and other metals. In terms of economy, ferrosilicon alloy with a silicon content of 75% is most commonly used, and because iron does not participate in the reaction, it is called silicon thermal method. Silicon thermal method can be divided into external thermal method and internal thermal method. The current mainstream Pidgeon method/Bolzano method belongs to external thermal method, and Magnetherm method belongs to internal thermal method. The following sub-item description.
(1)Pidgeon Process/Bolzano Process
In 1941, Professor Lloyd Montgomery Pidgeon, a Canadian scientist, invented a ferrosilicon thermal reduction method for smelting magnesium, called the Pidgeon Process. The Pidgeon method uses dolomite, ferrosilicon and fluorspar as raw materials, and the calcined dolomite, silicon and fluorspar are made into powder, and then the powder is mixed to make pellets, and heated at 1,150~1,200°C Reduction in a heat-resistant reduction tank, condensation at the extension end at 500°C, to obtain crown crystalline magnesium. Canada was the first to establish a magnesium factory using the Pidgeon method in 1942, and currently more than 90% of the magnesium raw material manufacturers in mainland China use the Pidgeon method to extract magnesium raw materials. The Bolzano Process is an improved method of the Pidgeon process for smelting magnesium. The main difference from the Pidgeon method of smelting magnesium is that the Bolzano Process uses a vertical electric internal heat reduction furnace. This method is named after the successful test of the Bolzano magnesium plant in Italy. In the 1980s, the highest annual output of magnesium by this method was 12,000 tons.
(2) Magnetocaloric process
The main goal of MagnEtherm pechiney pechiney company in the company’s 1990s is to reduce the melting point of slag, It is convenient for liquid slag discharge. The mobility of silicon in ferrosilicon decreases with the decrease of silicon concentration. When the silicon concentration drops to 18-20%, the reduction reaction will stop, and excessive iron needs to be added to the material. The reaction temperature is 1600~1700°C, and the vacuum degree is 0.266~13.3kPa. The biggest feature of this method is that all the substances in the furnace are in liquid state. 675°C) condenses condensed magnesium, flows in, passes through, is refined, then passes through, and then casts ingots. Slag After the slag has accumulated to a certain level, it will be penetrated to a certain extent, and then disassembled (the deoxidizer for steelmaking can be used if the Si content is 20%), then quenched with water, and directly manufactured into cement. Although the product purity strategy of the Magnetherm Process is lower than that of the Pidgeon method, the production capacity of the booth and life equipment of the booth is also large (a 4,500KW furnace can produce 7-9 tons per day), and it does not produce pollution and pollute the environment. Advantages of air. Therefore, in addition to France, the United States and South Wales State University have adopted this technology since the 1970s.
3. The latest magnesium smelting method
Magnesium was discovered only 200 years ago, and the smelting method of magnesium has changed from chemical method and electrolysis method to thermal reduction method. Since the Magnetherm method was applied in the 1960s, it seems that there has been no major progress. Fortunately, in the 21st century, two new smelting methods have been revealed, which are described below.
(1)Mintek Thermal Magnesium Process(MTMP)
In 2004, South Africa’s MINTEk and Eskom jointly published the Mintek Thermal Magnesium Process (MTMP method for short), and because this method was jointly developed by two South African companies, it is also called the South African thermal method. This technology can be produced continuously at room temperature. MINTEK company makes full use of the advantages of its own DC electric arc furnace smelting technology, calcines dolomite to generate magnesium vapor, forms liquid magnesium in the condenser, and releases liquid magnesium under normal pressure to condense again to form crude magnesium, and removes slag from the furnace. The method has the advantages of high labor productivity and low production cost. The MTMP method is an improvement of the Magnetherm method. Although an electric arc furnace is used, the main reaction is thermal reduction, so it can be classified as a type of thermal reduction method. On the premise of using a 35MW electric arc furnace, the production capacity is about 100 metric tons per day.
(2)Zuliani Process
Zuliani Process is a new magnesium metal smelting technology successfully developed by Douglas Zuliani, a doctor of metallurgical engineering at the University of Toronto, Canada. This technology claims to be able to directly produce magnesium metal from dolomite raw materials. In March 2007, Canada’s Gossan Resource Limited announced the purchase of this new technology, and exclusively owned 100% of the intellectual property rights of this new technology in the world. The new process technology adopts the original magnesium metal production process technology (that is, the Magnetherm method) of the French Pechiney company and the American Alcoa company to be improved.
The Zuliani Process reduces the use of energy and key raw materials, and improves magnesium recovery and silicon reduction frequency without vacuum by enhancing traditional silicothermal technology. However, the new magnesium production technology needs to be validated before it can be put into industrial production, and a three-stage evaluation process will be implemented. The first stage is to avoid melting solid magnesium, which is a big problem for Pidgeon and other silicothermal methods; the second stage includes the final standard rate test. The third phase is an intermediate pilot plant to demonstrate the service life of the new process technology. Compared with the traditional Pidgeon method magnesium production process technology, the new process technology claims to reduce the production cost by 25%.
4. Summary
The smelting of magnesium metal has progressed from the earliest chemical method (metal reduction method) to the electrolytic method, and then to the thermal reduction method. In the 21st century, some scientists improved the original process into a new magnesium smelting technology. The new process still revolves around production efficiency, such as faster production methods and reducing the original harsh conditions. The enthusiasm of scientists for the preparation of metal magnesium shows that the market is highly concerned about magnesium metal. The increase in global production and the increasingly wide application level show that magnesium metal is a very potential industrial metal. Compared with other metals, Magnesium metal and there is no danger of scarcity. The continuous evolution of magnesium smelting technology has benefited the downstream application industry. If the killer application of magnesium metal appears in time, I believe it will be a different prosperity.