The present invention relates to a process method for preparing high purity magnesium oxide, and in particular relates to a method for preparing high purity magnesium oxide with low chlorine root content.
Magnesium oxide is an ionic compound, which is a white solid at room temperature, and high purity magnesium oxide has excellent alkali resistance and electrical insulation, coefficient of thermal expansion and high thermal conductivity at high temperature, and good light transmittance. It is widely used in high temperature refractory materials, and is widely used in optics, instrumentation, electronics, electrical appliances, metallurgy, aerospace and other fields.
In the existing technology, the preparation methods of high purity magnesium oxide are mainly: (1) using the rich magnesium mineral resources in northeast China, calcined into ordinary magnesium oxide, then hydrolyzed to produce magnesium hydroxide, and then filtered, washed, pyrolyzed to obtain high purity magnesium oxide. In this method, the magnesium hydroxide slurry is difficult to be separated and washed, resulting in high impurity content in the product. (2) Prepare magnesium oxide by first preparing magnesium chloride or magnesium sulfate and then pyrolyzing, the high temperature corrosive gas produced in this method, the equipment requirements are high. (3) Through the ammonium carbonate cycle method, the preparation of basic magnesium carbonate, further calcination to produce high-purity magnesium oxide, the method of higher purity but the cost is too high. (4) Brine-soda ash method, the reaction of magnesium chloride and soda ash, the precipitate by rinsing, centrifugal dehydration, calcination, crushing, wind selection, the production of light magnesium oxide, the method of chlorine root content is higher, the by-product of sodium chloride added value is low. (5) The use of high-purity magnesium metal and oxygen reaction to produce high-purity micro-powder magnesium oxide, the method of higher equipment requirements, high cost, and is not applicable to industrial mass production.
In the process of salt lake development, mainly stay in a single potassium chloride resource utilization, the development process of centralized discharge of magnesium-containing old halogen caused by the local enrichment of magnesium chloride, to a certain extent, has become a salt lake resource development and utilization of the process of “magnesium”, hindering the further development and utilization of the resources of the salt lake.
Content of the invention:
In view of this, the present invention provides a method of preparing magnesium hydroxide intermediate from magnesite as raw material, and then calcining it into high-purity low-chlorine magnesium oxide, which takes magnesium chloride precipitated from brine of a salt lake as raw material, produces high-purity magnesium hydroxide by ammonia method, and finally obtains high-purity low-chlorine magnesium oxide by calcining, and the purity of magnesium oxide reaches more than 99%, and the root of chlorine is 0.05% or less. Achieve the consumption of 6.7 tons of hydrochloromagnesite raw material per ton of magnesium oxide, to achieve the full use of raw materials.
In order to realize the above inventive purpose, the present invention adopts the following technical solution: a preparation process of high-purity low-chlorine magnesium oxide, characterized in that it includes the steps of:
(1) Dissolving magnesium chloride using condensate to produce magnesium chloride solution;
(2) Using ammonium chloride and calcium oxide to vaporize ammonia to make ammonia water;
(3) Pass the ammonia into the magnesium chloride solution reaction to produce magnesium hydroxide slurry;
(4) Use of non-saline water multi-stage washing of magnesium hydroxide slurry, and made of filter cake;
(5) Using flash dryer to dry the magnesium hydroxide filter cake into high purity magnesium hydroxide dry powder;
(6) The calcium chloride solution from the ammonia evaporation tower is filtered and heated and concentrated, and then granulated and dried into calcium chloride particles;
(7) Finally using roller kiln calcination equipment to produce high purity low chlorine magnesium oxide.
In step (1), according to the mass ratio, according to the quality of water magnesium chloride stone and condensate quality, adjust the solution concentration range of 28-32 ° Bé, at the same time to ensure that the solution temperature range of 18-22 ℃.
In step (2), a high-concentration calcium oxide emulsion is prepared, with a concentration range of 120-170 tt reacting with ammonium chloride, and ammonia is evaporated in an ammonia evaporation tower, and ammonia water is obtained after cooling and passed into a reaction tank.
In step (3), the continuous reaction tank is continuously passed into magnesium chloride solution and ammonia water to maintain the stability of the reaction, and the stability of the reaction tank is controlled at 72-80°C, and the particle size of the magnesium hydroxide is controlled to be 50-70 μm, and the particle size span is 1.2-1.6.
In step (4), a belt filter is used, and multi-stage countercurrent water washing is used to reduce the chlorine root in the filter cake to 0.3-0.37%.
In step (5), the drying of magnesium hydroxide adopts a flash dryer, using hot air to dry the material with moisture ≤ 0.5%, and then collected and packaged.
In step (6), the calcium liquid is concentrated in three stages, the concentration of which reaches 41-43%, and then sent to the fluidized bed slurry granulation, dried with hot air, and then collected and packaged, to produce by-products of calcium chloride.
In step (7), the calcination equipment is a new type of roller kiln equipment, the magnesium hydroxide calcined in the kiln temperature control at 900-1100 ℃, the calcination time is 8-12 hours, to ensure that the product chlorine root is reduced to less than 0.05%.
Any one of the said preparation process of high purity low chlorine magnesium oxide, characterized in that the said hydrochloromagnesite is the magnesium-rich old brine containing magnesium discharged after potassium extraction from the resource development of Qinghai Salt Lake.
A kind of calcination equipment for the preparation of high-purity low-chlorine magnesium oxide, characterized in that the said calcination equipment is roller kiln is equipped with induced draft fan, bag dust collector, cyclone dust collector, rotary vibration sieve, and raw material inlet, finished product; using natural gas as the fuel, in the firing mode in order to avoid fume pollution of the product, the magnesium hydroxide is placed in the sagger, the use of roller bar will be sent to the kiln, kiln is divided into the preheating section, the heating section, the high-temperature section Cooling section, the sagger in the kiln running about 10h, to ensure that the reaction is complete; heating section for the main reaction section and heat absorption section, high-temperature section to ensure that the temperature is controlled at about 1100 ℃, to further reduce the root of chlorine in the product, the product out of the kiln through the 100 mesh sieve through the air cooling and packaging, rollers are used in the roller bar of recrystallization of silicon carbide, rollers, transportation, and kiln outside the process connected together, automated control; in the combustion and Temperature control using PID intelligent instrumentation, can be easily adjusted and stabilized firing curve; equipment using lightweight insulation materials.
The advantages and effects of the present invention are.
Compared with the prior art, the present invention provides a method in which ammonium chloride is used as an intermediate instead of hazardous chemical liquid ammonia, ammonia produced by reaction between ammonium chloride and lime, and ammonia reacts with aqueous magnesia chloride to produce high-purity magnesium oxide, and ammonia is reused. Adopt industrialized continuous reaction tank to improve the stability of the product. Adopting new type of calcination equipment makes the purity of magnesium oxide products up to more than 99% and chlorine root 0.05% or less, the method is simple and low cost, and effectively utilizes the resources of the salt lake.