Raw materials:
(I) Magnesite ore is one of the main sources of magnesium oxide, with a (MgO) content of about 47%. MgCO3 is lightly calcined (400-600°C) and then ground into solid powder (MgO). The ore sources are widely distributed in Liaoning, Xinjiang, Sichuan, Shandong, Tibet and other provinces and autonomous regions, with a reserve of 2.8 billion tons, accounting for 30% of the world’s ore sources.
(II) Dolomite ore [CaMg(CO3)2] is also the main source of magnesium oxide, and its reserves are larger and more widely distributed, with a MgO content of about 22%. The CaO content accounts for about 30%, and the rest is 48%. The theoretical structure of MgCO3 and CaO is one to one. The demarcation line of dolomite is based on the MgCO3 content of more than 25%, otherwise it cannot be used as an ore for producing magnesium oxide, nor can it be called dolomite.
(III) Serpentine [Mg6(Si4O10)(OH)2] is also a raw material for the production of magnesium oxide, mainly hydrosilicate (3MgO•2SiO2•2H2O).
(IV) The slag from the smelting of lightweight magnesium alloys is also a raw material for the production of magnesium oxide.
Preparation process:
1. Brine-lime method: The brine that has been purified and refined in advance and the lime milk made from the lime that has been digested and deslagging are subjected to precipitation reaction in a sedimentation tank, and a flocculant is added to the obtained slurry. After sufficient mixing, it enters the sedimentation tank for separation, and then filtered, washed, dried, and crushed to obtain the finished magnesium oxide.
2. Brine-ammonia method: The brine that has been purified to remove sulfate, carbon dioxide, a small amount of boron and other impurities is used as the raw material, and ammonia water is used as the precipitant to carry out precipitation reaction in the reactor. A certain amount of seed crystals are added before the reaction and fully stirred. The ratio of brine to ammonia water is 1: (0.9~0.93), and the temperature is controlled at 40℃. After the reaction is finished, a flocculant is added, and the precipitate is filtered, washed, dried, and crushed to obtain the finished magnesium oxide. This test method needs to improve the yield, shorten the washing cycle, and improve and perfect the production process.
3. Magnesium-hydrochloric acid-ammonia method: Magnesium ore and anthracite or coke are calcined in a vertical kiln to produce magnesium oxide and carbon dioxide. Magnesium powder is mixed with water to form a slurry and reacted with hydrochloric acid of a specified concentration to prepare a magnesium chloride solution. The magnesium chloride solution reacts with a certain concentration of ammonia water in a reactor, and the product is washed, settled, filtered, separated, dried, and crushed to obtain a magnesium oxide product. Surface treatment agents can be added for surface treatment as needed.
4. Microcrystalline magnesium oxide is prepared into a saturated MgCl2·6H2O solution at room temperature, and an excess of concentrated ammonia water is passed through at 70°C under stirring, and magnesium oxide slowly precipitates. Note 1: The distilled water and ammonia water used must not contain CO2. The distilled water must be fully boiled, and the CO2 in NH3 must be removed by KOH. Device for preparing magnesium oxide Note 2: The reaction container should be made of hard glass to avoid the reaction of Mg(OH)2 with silicic acid. The obtained precipitate is left to stand in the mother liquor for two days, during which it can be heated several times, each time to 70°C, and then the precipitate is decanted and washed. Then it is placed in a nickel beaker coated with paraffin and centrifuged and washed with distilled water without CO2. The precipitation and decantation operations can be carried out in the device, and the obtained magnesium oxide is first vacuum dried on potassium oxide and then vacuum dried on phosphorus pentoxide.
5. Large-grained magnesium oxide. Add 243mL of water to a wide-mouthed platinum container, then add 1375g of KOH and 485g of MgCl2·6H2O, heat to 210°C on an electric furnace, and clarify after about half an hour. Then slowly cool it to room temperature within 18h, that is, crystals with a diameter of about 0.2mL are precipitated, and dried at 100°C for 2h to obtain large-grained magnesium oxide.