Keywords: strontium, strontium chloride, strontium carbonate
With magnesium, calcium, barium strontium Ⅱ for A family of elements, is A kind of soft silvery white metal, 2.6 g/cm3 density, melting point 769 ℃, boiling point 1384 ℃, + 2 valence. Strontium is a reactive chemical that burns red when heated to the melting point in air and is readily reacted with water and acids to give off hydrogen.
Strontium and its compounds have been widely used since 1808, when the British chemist David first extracted strontium from strontium carbonate. Whether in metallic materials or in organic and inorganic non-metallic materials, adding appropriate amount of metallic strontium or strontium compounds can change some of its properties and make it have special functions. Therefore, strontium has the reputation of “industrial monosodium glutamate” and is widely used and has a promising market prospect. At present, there are more than 50 kinds of strontium products in the world, mainly including strontium carbonate, strontium nitrate, strontium chromate, strontium ferrite, strontium chloride, strontium titanate and other strontium salts and strontium metal and its alloys. The largest amount is strontium carbonate and strontium metal and their alloys.
Strontium carbonate formula for SrCO3, density of 3.70 g/cm3, melting point is 1497 ℃, orthorhombic system, appearance is white powder, soluble in water, insoluble in alcohol. Strontium carbonate is mainly used in magnetic materials, optical glass, ceramics, coatings and other aspects, but also widely used in medicine, chemical reagents, pigments, coatings, fireworks, capacitors and signal bombs and other industries. In recent years, the demand for strontium carbonate, especially the high purity strontium carbonate, is increasing in the field of high performance magnetic materials.
Status of strontium mineral resources
Strontium in the earth’s crust is about 0.04%. Because strontium is highly reactive with air and water, there is no natural strontium in nature. The two major strontium-bearing minerals are celestine and strontium. Celestine is composed of strontium sulfate (molecular formula SrSO4), which is the most important strontium-containing mineral in nature. Strontiumite is composed of strontium carbonate (SrCO3), which is one of the main minerals for strontium extraction, second only to lapis lazuli.
2.1 distribution of strontium mineral resources
Global celestite resources distribution, has proven reserves lapis lazuli about 90 million t, the Mexican reserves of 20 million t, 10 million t in Spain, the country with the lapis lazuli resources and ancient, Turkey, Iran, tower, Pakistan, Russia, the United States, Britain, Germany, Canada, Morocco and Algeria, etc.
There are more than 100 mining areas with proved reserves of lapis lazuli in China, and the proved reserves are about 45 million t, mainly lapis lazuli. Although China’s strontium reserves are very large, their quality is not as good as those of Mexico, Spain, Turkey, Iran, Pakistan and other countries. The grade of lapis lazuli mineral products imported from Iran is generally above 85%, while the grade of domestic strontium mineral is generally between 60% and 80%.
2.2 domestic status of strontium ore
Domestic commercial strontium ore is mainly used as raw material for strontium salt industry. The annual consumption of strontium ore with a grade of over 60% is about 500,000 t, among which, enterprises in hebei and shandong import about 100,000 t of high-quality strontium ore from Iran and other countries every year.
China’s commercial strontium mineral deposits are mainly distributed in qinghai, chongqing, hubei, jiangsu, yunnan and other places. Tongliang and dazu strontium mines in chongqing are the largest and the best strontium mines in China. The strontium ore in qinghai is located in the remote gaofang mountain with difficult conditions and poor infrastructure. Although it has the largest strontium ore in China, the ore grade is low and the processing cost is high. Hubei strontium ore is the third largest strontium ore in China. The strontium ore in jiangsu is the fourth largest strontium ore in China.
Preparation of strontium and its compounds
Celestine is processed into strontium sulfide or strontium carbonate in industry, and then further processed into other strontium compounds. There are two processing methods of carbon reduction and double decomposition. Among them, carbon reduction process is short, low cost, but low utilization rate of lapis lazuli, product quality is not easy to guarantee, and waste gas pollution is serious. The double decomposition method can overcome the disadvantages of the carbon reduction method, but it consumes a large amount of acid and alkali.
3.1 carbon reduction method
The celestite was crushed to about 120 mesh, and the impurities such as silicon, iron, aluminum and calcium were removed by mineral processing. The strontium concentrate contained more than 70% strontium sulfate. Strontium ore concentrate and mixed pulverized coal in the calciner for roasting, water insoluble strontium sulfate reduction into water soluble strontium sulfide, the master equation for: SrSO4 + 4 c – > SrS + 4 co, roasting in reducing atmosphere in 1000 ~ 1200 ℃. Then strontium sulfide was leached with water and separated from the insoluble residue. The methods of producing strontium carbonate from this solution are carbonization and double decomposition. Strontium sulfide carbonation method: strontium sulfide water solution into the carbonization tower, and then pass carbon dioxide to get strontium carbonate and hydrogen sulfide gas. Strontium carbonate is released from the bottom of the tower and filtered, washed and dried. The carbon exhaust from the top of the tower contains a large amount of hydrogen sulfide, which can be recycled to make sulfur or sulfur compounds. (2) strontium sulfide double decomposition method: in the refined strontium sulfide solution add sodium carbonate (or ammonium bicarbonate) precipitation of strontium carbonate, filtered, washed, dried products. Recovery of sodium sulfide (ammonium) from waste liquor.
3.2 compound decomposition method
The method does not require high content of strontium sulfate in ore. Smash lapis lazuli to 200 mesh, loaded with stirring reaction kettle, adding sodium carbonate solution (or ammonium bicarbonate), about 90 ℃, the reaction after 1 ~ 2 hours, strontium sulfate into strontium carbonate, the main reactive as: SrSO4 + Na2CO3 – SrCO3 + Na2SO4, conversion rate can reach 95%, after filtering, washing coarse strontium carbonate, sodium filtrate can be recycled. The methods of refining crude strontium carbonate include acid hydrolysis and thermal decomposition. (1) acid solution: with hydrochloric acid decomposition of strontium carbonate, strontium chloride solution, filtered, washed, will strontium chloride solution to remove impurities, add sodium carbonate (or ammonium bicarbonate) to get strontium carbonate precipitation, filtered, washed, dried products. The sodium chloride (or ammonium) filtrate can be recycled, and strontium chloride products can be obtained by direct evaporation and crystallization of strontium chloride solution. (2) thermal decomposition method: coarse strontium carbonate is heated to 1350 ℃ is decomposed into carbon dioxide and strontium oxide, water leaching strontium oxide. Strontium hydroxide was dissolved in water and changed into strontium hydroxide. Strontium carbonate can be obtained by carbonizing strontium hydroxide. Strontium salts such as strontium chloride and strontium nitrate can also be further processed from strontium hydroxide.
3.3 preparation of strontium metal
Vacuum aluminothermic reduction is the main method for the preparation of strontium, which is similar to the production of calcium. Is brought (SrO) SrO aluminum and fully mixed and compressed into the gap of the hollow cylinder, with derrick stacked into a string of hanging in the closed reduction pot, vacuum first, then heated to 1100 ℃, reduction of strontium steam condenser on the upper back cans by metal solidification on the strontium, finally the condenser on the metal strontium block removed and immediately filled argon sealing packing. The residue of aluminothermic reduction reaction (SrO or Al2O3 or SrO·Al2O3 or 3SrO·Al2O3) is discarded as slag mass.
The development direction of strontium industry
China has abundant strontium resources, but the research and development of high-quality strontium products in China started late, and the foundation is weak. Strontium products are lack of deep processing technology, high production cost, poor product quality, low export price (only 1/3 ~ 1/4 of the international market price), and poor market competitiveness. The development direction of strontium industry should be to develop high quality strontium products: using high purity strontium chloride as the main raw material to produce high purity strontium salts, strontium hydroxide, strontium metal and its alloys.
From national strontium industry according to the strategy of sustainable development, make full use of strontium ore resources in China, by means of vacuum thermal reduction process of metal aluminum calcium process and equipment, as early as possible to overcome with high purity strontium chloride as main raw materials of high purity strontium product industrialization, the key technologies of strontium industry to achieve sustainable development has profound practical significance and historical significance.