Hebei Messi Biology Co., Ltd. stated that magnesium products mainly include magnesium carbonate, magnesium oxide, magnesium hydroxide, magnesium chloride and magnesium sulfate, etc., which are important inorganic products. They play a pivotal role and position in the national economic construction, and are widely used in material processing (such as flame retardant, fine ceramics), electronic materials, coatings, environmental protection, food processing, medical and health care, etc. The production of magnesium products using seawater and salt lake brine as raw materials has been widely adopted by countries around the world.
As an industrial magnesium-containing by-product, its impurity content and pre-treatment process have greater advantages than the preparation of magnesium products using liquid ore as raw materials. Therefore, the use of magnesium-containing by-products to prepare high-purity magnesium products has become one of the important and effective ways to improve the taste of magnesium products in the world. Xinjiang has the famous Lop Nur Salt Lake and many other salt lake resources, and the magnesium resources mainly composed of hydrated magnesium chloride have reached billions of tons. The production of magnesium products from salt lake waste is a very weak link in my country’s salt lake chemical industry. Due to various reasons, the development and utilization of salt lake resources still only stays on the single utilization of potassium chloride resources.
1. Production method of magnesium oxide
① The pyrolysis method is that the magnesium chloride solution is directly thermally decomposed in a high-temperature furnace to generate magnesium oxide and hydrogen chloride gas, and the generated hydrogen chloride gas can also be recovered. Therefore, the carbon ammonium method and pyrolysis method may be the most suitable process methods for the development of Xinjiang salt lake hydrochlorite at present.
② High-temperature solid phase method, gas phase method, sol-gel method, solvent thermal method, etc. High-temperature solid phase method and gas phase method are good methods for preparing high-purity and various morphological magnesium products. In recent years, there have been a lot of literature reports. In addition to the decomposition of solid ores, high-temperature oxidation of elemental magnesium, high-temperature decomposition of magnesium salts and chlorides, hydrolysis of magnesium salts, magnesium-aluminum alloy reduction method, etc., but due to the relatively expensive equipment and high energy consumption, it is not economical to implement. Sol-gel method and solvent thermal method are new inorganic chemical synthesis methods.
2. Purpose and significance of the topic
Based on the purpose of resource recycling, energy saving and consumption reduction, environmental friendliness and cost reduction, magnesium chloride, a magnesium byproduct of fireworks waste, is used as raw material. After purification, a high-purity magnesium oxide product with a purity of more than 98% and uniform morphology is prepared. Liquid minerals such as seawater and salt lake brine have less impurities, simpler production processes than solid minerals, and products are easier to meet high purity requirements. In addition, it is a renewable resource, so the production of magnesium products using hydrated magnesium chloride, a waste after potassium extraction from seawater and salt lakes, as raw materials has been widely adopted by countries around the world. At present, the United States is the largest producer of magnesia using brine in the world, with an annual production capacity of about 1.5 million tons of magnesia, of which about 90% is produced with liquid minerals such as seawater and salt lake brine as raw materials; followed by 13 countries, with an annual production capacity of about 1 million tons, most of which are produced with seawater as raw materials. Xinjiang has the famous Lop Nur Salt Lake and many other salt lake resources, and the content of magnesium resources, mainly hydrated magnesium chloride, reaches billions of tons. The production of magnesium products from salt lake waste is a very weak link in my country’s salt lake chemical industry.
3. Domestic and foreign research on high-purity magnesium oxide
3.1 Foreign research The production of magnesia using seawater as raw material is a mature technology in the world. In addition to the United States, Japan, and the United Kingdom, Italy, Ireland, Mexico, Norway, Greece and other countries have successively built factories and have developed rapidly. However, magnesium oxide is greater than 99% of the product, and only Japanese companies can use seawater as a raw material for rehydration to mass produce high-purity and high-quality magnesia.
3.2 Domestic research In recent years, a pear-shaped vortex furnace has been developed based on the principle of instantaneous pyrolysis of saturated magnesium chloride liquid. The saturated magnesium chloride liquid (mgcl2 content 400-440g/l) at 32-36°C is sprayed into a pear-shaped vortex furnace by a liquid lifter and an airflow nozzle into a diameter of less than 80 microns, thereby achieving a high-efficiency result of a pyrolysis rate greater than 98%, and the magnesium oxide content of the magnesia sample is 99.63%-99.7%, and the volume density is 3.24-3.38g/cm3. Because it is a small test device, the heat consumption is large, and the oil consumption reaches 1.7-2.okg/kg product. This defect will be completely reduced to less than 300kg/t product through the complete design of semi-industrial and industrial kilns. The seawater lime method has been improved, and high-purity low-boron magnesium sand containing 99.5% magnesium oxide and about 0.01% b203 has been developed. The research and development of high-purity magnesium oxide produced by serpentine rock chemical wet method was successfully tested in June 2000, and formal production began in 2001. Their research and production of 99.2%-99.68% high-purity industrial magnesium oxide has exceeded the level of many countries such as Israel (99.4%), former Yugoslavia (99.3%), and Mexico (99.01%). Compared with them, it has the advantages of low cao, c1-, and b203, which shows that China’s development and production of high-purity magnesium oxide has reached the world’s leading level and will occupy a place in the world’s magnesium salt production.
4. Existing problems and development direction
In the process of preparing high-purity magnesium oxide from basic magnesium carbonate, the number of washing and filtration will be directly related to the output of magnesium oxide; and in the process of basic magnesium carbonate entering the muffle furnace, if the basic magnesium carbonate is too wet, it will have a bad effect on the furnace and reduce its life, so it must be dried before that, and the degree of drying affects the later preparation; and during calcination, the calcination temperature is not easy to control, because if the calcination temperature is too high, it is easy to burn the product to death, and the calcination temperature is too low. In addition to the long calcination time, the content of light magnesium oxide cannot be guaranteed, so the temperature is not easy to control; in the final purity analysis, it cannot completely guarantee the removal of impurity ions, so it is necessary to verify step by step in the process, and try to do the best. High-purity magnesium oxide has excellent acid and alkali resistance and electrical insulation at high temperature, good light transmittance, high thermal conductivity, and large thermal expansion coefficient. It is widely used as a high-temperature heat-resistant material, and is used as a raw material for ceramic crucibles, substrates, etc. in the ceramic industry. It is used as a filler, insulating material and various carriers for magnetic devices in the electronics and electrical industries.
In addition, using high-purity magnesium oxide as raw material, special magnesium oxide series products such as fused magnesium oxide single crystal, high-purity fused magnesium oxide, and nano magnesium oxide can also be produced. These products are widely used in electronics, electrical appliances, optics, instruments, metallurgy, national defense, aerospace and other fields. With the rapid development of China’s economy, the scale of China’s adhesive and sealing material industry has expanded rapidly, and it has become a major adhesive and sealant production and consumption country in the world. It can make full use of existing resources, with low cost, solve environmental pollution, lay the foundation for the effective utilization of magnesium resources, and generate huge economic benefits.