High purity magnesium oxide generally refers to magnesium oxide products with purity greater than 99%. Since high-purity magnesium oxide has excellent physical properties such as ultra-high melting point, good magnetic conductivity and excellent insulating properties, and specific chemical properties, it is widely used in many fields such as ceramics, metallurgy, medicine, electronics and national defense.
The development and industrialization of high purity magnesium oxide will greatly promote the development of electronics, national defense, aerospace and advanced ceramics industries[. The production of common grade magnesium oxide products in China is large, a large number of exports, the market is weak; and some fine magnesium oxide such as high purity magnesium oxide, active magnesium oxide, silicon steel magnesium oxide and other fine magnesium oxide market demand is large, the products are imported in large quantities.
1 common magnesium oxide preparation method
The production of magnesium oxide raw material sources are mainly liquid ore and solid ore. The former is mainly seawater, underground brine, salt lake brine; solid ore is mainly magnesite, hydromagnesite, dolomite, serpentine and asbestos tailings, etc. By the brine or water chloromagnesite preparation of magnesium oxide method mainly has lime milk method, ammonium carbon method, ammonia method, soda ash method, water chloromagnesite direct pyrolysis method; by solid ore preparation of magnesium oxide method mainly has calcined magnesite method, carbonization method, acid solution method, ammonium sulfate method and ammonium sulfate compound salt method, etc.
2 high purity magnesium oxide preparation method
The production of high-purity magnesium oxide is generally used in the preparation of ordinary magnesium oxide method, and a certain purification process to achieve.
2.1 brine precipitation method
2.1.1 Brine spray thermal decomposition method
After concentrating the brine to a certain concentration, directly sprayed into the thermal decomposition reaction furnace, thermal decomposition at 800 ℃ ~ 1000 ℃ output crude MgO. crude MgO by water washing to remove soluble chloride, and make crude MgO completely transformed into Mg(OH)2, and then calcined at 1600 ℃ ~ 2000 ℃ to generate high-purity MgO. its process principle is.
This method uses a secondary calcination process with a higher calcination temperature, resulting in higher production costs. At the same time, the by-production of HCl gas in the primary calcination process has serious corrosion for the production equipment.
2.1.2 Dolomite/lime method
Dolomite / lime method is a mature technology, widely used high-purity magnesium oxide production technology. At present, in addition to a few manufacturers, the world nearly 20 major high-purity magnesium oxide production enterprises are using dolomite / lime method to produce high-purity magnesium oxide products.
Dolomite/lime method is also called lime milk precipitation method, which is to add lime milk to brine containing MgCl2 with certain concentration to react to generate Mg(OH)2, and get magnesium oxide by washing, drying and calcination. The method requires high activity for Ca(OH)2, the generated precipitate is Mg(OH)2, the particles are small and easy to adsorb impurities, so the product purity is low; at the same time, the Mg(OH)2 precipitate is colloidal, difficult to filter, high water content of the filter cake, high energy consumption in the drying process, and the generated CaCl2 added value is low, serious environmental pollution.
2.1.3 Ammonia precipitation method
Similar to dolomite/lime method, ammonia precipitation method is mainly used to produce magnesium oxide by adding alkaline precipitant to the brine to prepare magnesium hydroxide intermediate, the alkaline precipitant used in ammonia method is liquid ammonia or ammonia gas. Ammonia method to produce high-purity magnesium oxide process is roughly as follows: first of all, the old brine solution will be decolorized and de-hybridized refining treatment, the treatment technology chosen is similar to dolomite/lime method; then pass liquid ammonia or ammonia precipitant into the refined old brine solution, the reaction generates magnesium hydroxide intermediate; finally washing, filtering, calcining magnesium hydroxide intermediate, producing high-purity magnesium oxide products, the filtrate can be used for by-production of ammonium chloride.
2.1.4 Soda ash method
Soda ash method by adding soda ash solution precipitant to the brine firstly to generate heavy magnesium carbonate (MgCO3-3H2O) precipitation, heavy magnesium carbonate after washing, pyrolysis and other processing, to get alkaline magnesium carbonate, and finally calcination can get light high purity magnesium oxide products. The production of high-purity magnesium oxide by soda ash method is a traditional production method with simple process, low equipment requirement and high purity of magnesium oxide products, which has more than 60 years of production history in China. At present, most of China\’s medium and small high-purity magnesium oxide production enterprises still use the soda ash method for production.
2.1.5 Ammonium carbon method
NH4HCO3 is used as precipitant, and react with MgCl2 in brine to produce 4MgCO3-Mg(OH)2-4H2O, and MgO is obtained by washing, drying and calcination. using this method the utilization rate of CO2 in NH4HCO3 is low, the production consumption of NH4HCO3 is large and the cost is high.
2.2 Solid ore calcination carbonization method
2.2.1 Magnesite calcination carbonization method
The method for magnesite calcined to generate lightly burned magnesium oxide, lightly burned magnesium oxide by digestion, carbonization of magnesium bicarbonate solution, using activated carbon as adsorbent to remove the iron ions in magnesium bicarbonate solution, by adsorption of magnesium bicarbonate solution and then pyrolysis, pyrolysis of alkaline magnesium carbonate filtered and washed and dried, and then in the calcination of high-purity magnesium oxide products.
2.2.2 Dolomite calcination carbonization method
Dolomite calcination carbonization method to prepare high-purity magnesium oxide and magnesite calcination carbonization method steps are basically the same, mainly including calcination, digestion, carbonization, pyrolysis and calcination and other five steps.
2.3 Other preparation methods
In addition to some traditional preparation methods introduced above, some other preparation methods have emerged in recent years, such as microwave radiation method, metal alcohol salt hydrolysis method, direct precipitation method, homogeneous precipitation method, vapor phase method and sol-gel method.
Recently, the domestic independent research and development of the \”original cell method ultra-high purity magnesium oxide\” technology to achieve a breakthrough, to solve the technical and industrialization problems since the 1970s, breaking the field has been foreign technology \”neck\” situation. It is understood that in the production process of using magnesium as fuel cell by primary cell method, it is found that ultra-high purity magnesium oxide can be generated.
The primary cell method selects magnesium as the anode metal material of fuel cell, which increases the safety of each link of fuel cell production, transportation, storage and refilling, and converts magnesium into magnesium oxide in a short time. At the same time, the process of obtaining ultra-high purity magnesium oxide can achieve no industrial waste emission. Compared with magnesite calcination and seawater/brine precipitation, the use of primary cell process can obtain ultra-high purity magnesium oxide with 99.95% purity, and lower cost, shorter process route, higher product yield, and the production process is accompanied by the generation of a large amount of high-quality direct current.
With the development of industry, the application scale of high purity magnesium oxide in traditional fields is expanding day by day, and new application fields are being explored and developed, and the market capacity is expanding. From the development trend, the proportion of high purity magnesium oxide consumption is increasing year by year. However, China has been lagging behind foreign countries in this field, and the industrialized production technology is \”stuck\” by foreign countries, therefore, it is urgent to increase the research and development of high-purity magnesium oxide preparation technology and industrialization.