CN112320826A - Method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite - Google Patents
Method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite Download PDFInfo
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- C—CHEMISTRY; METALLURGY
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- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/02—Magnesia
- C01F5/06—Magnesia by thermal decomposition of magnesium compounds
- C01F5/08—Magnesia by thermal decomposition of magnesium compounds by calcining magnesium hydroxide
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- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C1/00—Ammonia; Compounds thereof
- C01C1/24—Sulfates of ammonium
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/14—Magnesium hydroxide
- C01F5/20—Magnesium hydroxide by precipitation from solutions of magnesium salts with ammonia
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2/00—Lime, magnesia or dolomite
- C04B2/10—Preheating, burning calcining or cooling
- C04B2/102—Preheating, burning calcining or cooling of magnesia, e.g. dead burning
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- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
Abstract
The invention belongs to the technical field of non-metallic mineral processing, and particularly relates to a method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite, which is characterized by comprising the following specific steps: 1) calcining low-grade magnesite to prepare light calcined powder; 2) impurity removal treatment is adopted; 3) mixing light calcined powder and industrial pure water, and adding concentrated sulfuric acid for reaction; 4) adding sodium hydroxide solution, settling and separating impurities such as solid phase substances and the like to obtain refined magnesium sulfate solution; 5) mixing ammonia water and a magnesium sulfate solution to generate magnesium hydroxide crystal precipitate and an ammonium sulfate solution; 6) washing, drying and calcining the magnesium hydroxide crystals to obtain a high-purity magnesium oxide finished product with the purity of 99.6-99.87%; 7) the ammonium sulfate solution is filtered, neutralized, evaporated, crystallized and dried to obtain the refined ammonium sulfate by-product. The method has the advantages of improving the resource utilization rate and the product purity, reducing the production cost, realizing environment-friendly and clean production and the like.
Description
Technical Field
The invention belongs to the technical field of non-metallic mineral processing, and particularly relates to a method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite.
Background
The low-grade magnesite generally refers to magnesite (MgCO 3) with the content of magnesium oxide (MgO) lower than 43% purity standard, and China is a country with large reserves of low-grade magnesite. Due to the production cost and the production technology, a large amount of low-grade magnesite cannot be effectively utilized, and great resource waste is caused. The high-purity magnesia generally refers to magnesia materials with the purity of magnesia (MgO) being more than or equal to 98.5 percent, and comprises crystalline high-purity electrofused magnesia, single-crystal magnesia, high-purity (sintered) magnesia magnesite, amorphous light-burned magnesia and the like. The application is mainly amorphous high-purity light-burned magnesium oxide. The traditional amorphous high-purity light-burned magnesia mainly adopts the following production process and method:
it is produced with sea water or old brine as material and through soda process or ammonia process. The process is relatively mature, but the production pollution is large, the production cost is high, and the product harmful substances have large damage to the application of downstream products, such as impurities of chloride ions, boron and the like. The purity of the magnesium oxide is generally about 99.0 percent.
The magnesite is lightly burned and directly digested, magnesium oxide is converted into magnesium hydroxide, then carbon dioxide is introduced to obtain basic magnesium carbonate, and then the basic magnesium carbonate is calcined at high temperature to obtain a high-purity magnesium oxide finished product. The production process can avoid the generation of harmful substances such as chloride ions, boron impurities and the like, but the production cost is still overhigh, and the purity of the magnesium oxide product is between 99.0 and 99.5 percent.
The method comprises the steps of directly reacting (low-grade) magnesite or light burning powder with sulfuric acid to prepare magnesium sulfate, filtering or purifying the magnesium sulfate in a series, precipitating magnesium hydroxide by using sodium hydroxide or ammonia water, and calcining the magnesium hydroxide at high temperature to obtain a high-purity magnesium oxide finished product. The method is effective for separating iron and aluminum, but has poor effect on separating silicon and calcium impurities, and the purity of magnesium oxide is generally not more than 99%.
Application publication No. CN106745103A discloses a cyclic production process by ammonia distillation, which adopts light-burned magnesia powder to directly react with ammonium sulfate, ammonium chloride or ammonium nitrate to prepare magnesium sulfate, magnesium chloride or magnesium nitrate, then ammonia gas obtained by ammonia distillation is used to prepare ammonia water with a certain concentration, then the ammonia water is used to introduce the former magnesium sulfate, magnesium chloride or magnesium nitrate, after magnesium hydroxide is precipitated, and after filtration and washing, high-temperature calcination is adopted to obtain a high-purity magnesia finished product, the ammonium salt and the ammonia water can be recycled, no loss is caused theoretically, and the cost can be greatly reduced; however, the method is actually operated under the published conditions of reduced pressure and water bath temperature of 70-95 ℃, the ammonia distillation time is long, the energy consumption is high, and the method is difficult to be applied to practical application.
Application publication No. CN101372402A discloses a method for preparing magnesium oxide by calcining ammonium salt and magnesium-containing ore, which comprises calcining ammonium salt and pulverized magnesium-containing ore such as magnesite, brucite or talc to obtain solid magnesium salt, ammonia gas and carbon dioxide, absorbing gas with water to obtain ammonium bicarbonate solution or ammonia water, dissolving the solid magnesium salt, filtering, reacting with the ammonium bicarbonate solution or ammonia water to obtain magnesium carbonate or magnesium hydroxide and ammonium salt, filtering, and calcining magnesium carbonate to obtain high-purity magnesium oxide. Evaporating the ammonium salt solution to dryness to obtain solid ammonium salt for recycling. In each process cycle of the process, impurities can be separated only by dissolving solid magnesium salts obtained by roasting, then magnesium hydroxide is prepared in the solution, the ammonium salt solution is dried by distillation to be used for roasting, the water consumption and the energy consumption are high, and the final production cost is high.
Application publication No. CN103232047A discloses a preparation method of low-energy-consumption magnesium oxide, which is characterized in that ammonium salt is used for leaching a light-burned magnesium solution, and a large amount of steam generated in ammonia distillation pushes a steam turbine to generate electricity so as to save energy and reduce consumption. The relevant parameters of a steam turbine are not given in the process, but the introduction of the steam turbine inevitably increases fixed investment and operation cost, and the feasibility is not high.
Application publication No. CN102502722A discloses a production method of high-purity magnesium oxide, which comprises the steps of calcining low-grade magnesite, collecting carbon dioxide, leaching light calcined magnesium by using an ammonium salt solution, obtaining magnesium salt and ammonia water, filtering the magnesium salt solution, reacting the ammonia water with the collected carbon dioxide to obtain an ammonium bicarbonate solution, reacting the solution with the magnesium salt to obtain magnesium carbonate and an ammonium salt solution, filtering, drying and calcining the magnesium carbonate to obtain magnesium oxide, and reusing the ammonium salt solution. The key problems of the process are that the leaching time of the magnesium oxide leached by the ammonium salt solution is long at normal temperature, the leaching rate is very low in a short time, and when the magnesium salt solution is precipitated by ammonium bicarbonate, leached calcium ions are inevitably precipitated and impurities are introduced.
The principle of the method disclosed in application publication No. CN103241751A is basically the same as that of CN102502722A, which not only can not effectively improve the leaching rate, but also can cause calcium ions to precipitate into the magnesium oxide product.
Application publication No. CN103011630A discloses a method for producing high-purity magnesium hydroxide and magnesium oxide from low-grade magnesite, the method comprises the steps of calcining the low-grade magnesite, leaching ammonium salt to obtain ammonia gas and magnesium salt solution, filtering the magnesium salt solution, introducing part of the ammonia gas to react with carbon dioxide to generate calcium carbonate precipitate for calcium removal, filtering, and adding ammonia water to react to obtain the high-purity magnesium hydroxide. In order to improve the leaching rate of magnesium oxide, the leaching temperature is increased to 100-120 ℃, the leaching time is 2-4 hours, the leaching temperature exceeds the boiling point of water, the reaction time is long, the water consumption and the energy consumption are high, the cost is increased, and meanwhile, the finally unleached magnesite slag is used as a magnesium cement raw material, so that the added value is low.
Application publication No. CN102745724A discloses a method for producing high-purity magnesium oxide by using light-burned magnesium powder, in the process, ammonium acetate solution is used as a leaching agent, magnesium acetate solution and ammonia gas are obtained by leaching, the leaching time is not more than 1h, the ammonia gas reacts with the magnesium acetate to obtain magnesium hydroxide, and the magnesium hydroxide is filtered and calcined to obtain magnesium oxide. The process solves the problems of long ammonia steaming time, low magnesium ion leaching rate and high energy consumption of the existing ammonia steaming method under normal pressure, aims to reduce leaching time, save energy and improve productivity, but ammonium acetate is used for leaching light-burned magnesium powder, the principle is the same as that of ammonium sulfate, ammonium chloride or ammonium nitrate, the leaching rate cannot be fundamentally improved, the ammonium acetate has high viscosity and is easy to adhere to a magnesium hydroxide product, when trace organic matters of ammonium acetate or magnesium acetate in the magnesium hydroxide are not washed completely, the ammonium acetate or magnesium acetate can be carbonized after calcination, magnesium oxide can be discolored, the whiteness is reduced, and the appearance is influenced.
Application publication No. CN1212271C discloses a process for the co-production of magnesium sulfate, magnesium carbonate and magnesium hydroxide from magnesite. The method is characterized in that magnesite is ground to below 120 meshes after being calcined (the taste needs to be more than 90%), ammonium sulfate and sulfuric acid are added, ammonia is evaporated by adopting the heat of the reaction of the sulfuric acid and light calcined powder, ammonia gas is recycled, and impurities are removed by controlling the temperature and the acidity. Can be used for preparing pharmaceutical-grade magnesium sulfate, magnesium carbonate and magnesium hydroxide products. The method has certain production feasibility, and has the defect that over 90 percent of lightly calcined magnesia with taste is required to be used as a basic raw material, and the direct calcination of low-grade magnesite cannot be realized.
Application publication No. CN111017967A discloses a green environment-friendly clean production process of ultra-pure magnesium oxide. The production process adopts light-burned magnesia, sulfuric acid, water and CO2 as production raw materials, and adopts the production processes of distillation (ammonia distillation) → pulping → precipitant preparation → synthesis → pyrolysis → drying, calcination and the like to prepare 99.9% of ultrapure magnesia. The former stage of the process is similar to the invention published under No. CN106745103A, and adopts the procedure of ammonia distillation, for example, under the condition of normal pressure, the reaction temperature is controlled to be 85-100 ℃, the reaction time is 4-7h, and the method also has the disadvantages of long ammonia distillation time and high reaction temperature. In addition, the method comprises the steps of firstly preparing a basic magnesium carbonate intermediate product, and then calcining at 850-950 ℃ for 6-8h to obtain a high-purity magnesium oxide finished product. The calcination process further causes problems such as excessive production cost due to higher calcination temperature and longer calcination time. The production process is adopted to prepare 99.9 percent of ultrapure magnesium oxide, the production or preparation process does not provide key measures such as water purification requirement, impurity filtration and the like, and the doubt on whether 99.9 percent of ultrapure magnesium oxide products can be successfully prepared is large.
Application publication No. CN 108285160A discloses a method for preparing high-purity magnesium oxide. The method adopts heavy magnesium water (magnesium bicarbonate solution) as a production raw material, and prepares high-purity magnesium oxide after iron removal by a strong oxidant, pyrolysis and high-temperature calcination. The method has the defects that high-temperature pyrolysis and high-temperature calcination are needed for preparing high-purity magnesium oxide from the heavy magnesium water, the production cost is high, in addition, the method has no obvious effect on removing impurities such as silicon, calcium, aluminum and the like, and the purity of the obtained magnesium oxide finished product is only about 99 percent.
In conclusion, the recycling of ammonium salt to extract magnesium oxide from magnesite saves raw materials, cannot effectively reduce production cost, and cannot produce high-purity magnesium oxide with purity of more than 99.5%. In addition, the existing method has the defects of high leaching temperature, long time and high energy consumption, and part of the processes have the defects that calcium carbonate enters impurities, so the existing method is not widely applied. The magnesium oxide (MgO) produced by the above conventional production processes is generally less than 99.5% pure, and is very limited in application fields. Meanwhile, the production cost of the traditional production process is higher, such as the production process of seawater or brine plus a soda ash method or an ammonia method. Most of the methods have the problem of environmental pollution, such as a soda/ammonia method, an ammonia distillation method and the like. The production process has great limitation on large-scale production, and a ten-thousand-ton-grade production line is difficult to form.
Ammonium sulfate (NH4)2SO4 is colorless crystals or white particles. The ammonium sulfate can be used in textile, leather, medicine, etc. Common ammonium sulfate is a good nitrogen fertilizer (commonly called fertilizer powder). Ammonium sulfate can produce ammonium chloride by double decomposition reaction with common salt, and ammonium alum by reaction with aluminum sulfate, and refractory material can be produced together with boric acid. The addition of the plating solution can increase the conductivity. Is used as an acid dye dyeing auxiliary agent and a leather deliming agent. Refined ammonium sulfate (food grade) is a catalyst for food dark brown, and a nitrogen source for culturing yeast in fresh yeast production, and can be used in the fields of protein purification, yeast production, food catalysis, and beer production. The traditional refined ammonium sulfate is prepared by adopting a complex purification process after dissolving industrial ammonium sulfate, and has higher production cost and larger investment.
Disclosure of Invention
The invention aims to provide a method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite, which overcomes the defects of the prior art, uses a large amount of low-grade magnesite resources (the content of MgO is 35-45%) as raw materials, and adopts a simple early-stage pretreatment and processing mode and then calcinates the raw materials without early-stage chemical purification. After calcination, further grinding processing is not needed, gradient impurity removal is carried out by a physical method, and an energy-saving and environment-friendly mode is adopted in the production process. The purity of the produced magnesium oxide (MgO) is 99.6-99.87%, the application field of the product is further expanded, the production cost is reduced, and large-scale mass production can be realized. While producing high-purity magnesium oxide main product, the method can also synchronously produce refined ammonium sulfate by-product, the product purity is more than or equal to 99.9 percent, and the method can be widely applied to the fields of food additives and fine chemical engineering.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite specifically comprises the following steps:
1) crushing, sand making, screening, cleaning and dehydrating low-grade magnesite, and calcining at the temperature of 950 plus materials and 1000 ℃ to prepare light calcined powder, wherein the content of MgO in the light calcined powder is increased to 70-94%;
2) cooling the light calcined powder in the step 1) to normal temperature, removing impurities, firstly removing solid impurities which are not completely thermally decomposed and contain iron by adopting a heavy-magnetic method, then cleaning the light calcined powder by adopting industrial pure water, further removing soluble impurities, and dehydrating for later use;
3) mixing the calcined light powder treated in the step 2) with industrial pure water in a weight ratio of 1:10-30, and adding concentrated sulfuric acid into the mixed slurry for reaction; controlling the temperature of the mixed slurry not to exceed 80 ℃ in the adding process of concentrated sulfuric acid, wherein the adding amount is controlled until the PH value of the mixed slurry is 6.5;
4) step 3) neutralizing the mixed slurry to obtain magnesium sulfate heptahydrate, adding a sodium hydroxide solution with the concentration of 0.2-1.5mol/L, determining the addition amount of the sodium hydroxide solution by controlling the pH value, taking the pH value of 7.2 as a reaction end point, and after the reaction is finished, separating solid phase waste containing colloid impurities by using settling and filtering equipment to obtain a refined magnesium sulfate heptahydrate solution with the concentration of not less than 2.5 mol/L;
5) preparing the magnesium sulfate heptahydrate solution to the concentration of 1.5-2.5mol/L by using industrial pure water in the step 4), then heating to 60-75 ℃, mixing 10-19% ammonia water with the heated magnesium sulfate solution in a volume ratio of 1:95-100, controlling the pH value to be 9-10, stirring at the speed of 30-45rpm/min for not less than 10 minutes, standing and aging after stirring is finished for 1-1.5 hours to generate magnesium hydroxide crystal precipitate and ammonium sulfate solution;
6) after separating the magnesium hydroxide crystal from the ammonium sulfate solution, repeatedly washing the magnesium hydroxide crystal for 3-5 times by using industrial pure water, drying for 2-3 hours at the temperature of 220 ℃ after dehydration, calcining at the temperature of 500 ℃ and 600 ℃, and finally pulverizing and grading the calcined magnesium oxide particles to obtain a high-purity magnesium oxide finished product with the purity of 99.6-99.87%;
7) carrying out precision filtration and neutralization treatment on the ammonium sulfate solution obtained in the step 6), then carrying out multi-effect evaporation and crystallization, and finally drying to obtain a refined ammonium sulfate byproduct;
8) the solid phase waste separated in the step 4) can be reused after further cleaning, dehydration and drying.
Compared with the prior art, the invention has the following beneficial effects:
1) the method has the advantages that the resource utilization rate and the product purity are improved, a large amount of low-grade magnesite resources are used as raw materials, simple pretreatment is adopted without early-stage chemical purification, direct calcination is carried out, further grinding processing is not needed after calcination, and a high-purity magnesium oxide product with the (MgO) purity of 99.6-99.87% can be realized by adopting a normal-pressure reaction mode.
2) The production cost is reduced, energy-saving production modes such as reaction at a lower temperature (the reaction temperature is lower than 80 ℃) and calcination at a lower temperature (the calcination temperature of magnesium hydroxide is lower than 650 ℃) are adopted in the production process, the production cost can be greatly reduced under the same condition, the large-scale mass production can be favorably realized, and meanwhile, food-grade refined ammonium sulfate byproducts can be synchronously prepared.
3) Has great significance for environmental protection, clean and pollution-free production process, and trace harmful elements such as chloride ions, sulfate radicals, boron and other harmful heavy metals in main products and by-products. The produced by-product is a new product with high quality, and other solid wastes produced can be reused.
Drawings
FIG. 1 is a schematic process flow diagram of an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The method comprises the steps of crushing, sand making, screening, cleaning, dehydrating, removing argillaceous impurities in advance, calcining the dehydrated magnesite particles (ore sand) by a rotary kiln, and cooling after the calcining is finished. And (4) carrying out impurity treatment on the cooled light calcined powder by adopting a physical method. The impurity removal treatment method comprises the following specific steps: 1) removing solid impurities which are not pyrolyzed and contain iron by adopting heavy-magnetic separation equipment; 2) and cleaning with industrial pure water to further remove soluble impurities. And after physical impurity removal is finished, mixing the materials with industrial pure water according to a proportion, adding concentrated sulfuric acid, carrying out neutralization reaction, and controlling the pH value to be 6.5. After the reaction is finished, adding a sodium hydroxide solution with the concentration of 0.2-1.5mol/L for impurity adsorption and sedimentation, separating and filtering to obtain a refined magnesium sulfate solution and impurity solid waste, mixing an ammonia water solution with a prepared concentration with the refined magnesium sulfate solution with a prepared concentration to generate a magnesium hydroxide precipitate and an ammonium sulfate solution, separating, washing, dehydrating, drying and calcining a magnesium hydroxide crystal, pulverizing and grading to obtain a high-purity magnesium oxide main product, precipitating and separating magnesium hydroxide from refined magnesium sulfate to obtain a residual ammonium sulfate solution, further filtering to remove impurities and neutralize, evaporating, crystallizing and drying to obtain a refined ammonium sulfate byproduct.
The present invention relates to the following chemical reaction principles:
step 2 involves a chemical reaction
MgO+CaO+H2O=Mg(OH)2+Ca(OH)2+H2O
Step 3 involves a chemical reaction
Mg(OH)2+H2O+H2SO4=MgSO4+2H2O
Fe2O3+H2SO4+H2O=Fe2(SO4)3+3H2O
Step 4 involves a chemical reaction
NaOH + H2O = NaOH (solution)
MgSO4+ NaOH (solution) = Na2SO4+Mg(OH)2↓
Step 5 involves a chemical reaction
MgSO4+2NH3'H2O=(NH4)2SO4+Mg(OH)2↓。
Examples
1) Firstly, crushing, sand making, screening, cleaning and dehydrating low-grade magnesite (MgCO 3) with the average content of magnesium oxide (MgO) of 38.6% to obtain magnesite sand with the particle size range of 200 meshes to 15 mm, wherein the water content is 6.5%, a rotary kiln is used, the set temperature is 990 ℃, the light calcined powder is prepared after heat preservation is carried out for 1 hour, and the content of MgO in the light calcined powder is further increased to 88.2% after detection; the early stage of the step is to utilize the water solubility difference principle of magnesite sand and impurities, the average content of magnesium oxide (MgO) in magnesite can be improved from 38.6 percent to 43.8 percent, and the purity of the calcined light-burned magnesium oxide (MgO) is 88.2 percent;
2) naturally cooling the light calcined powder in the step 1) to normal temperature, and then performing impurity removal treatment, specifically including removing incompletely thermally decomposed and iron-containing solid impurities by a heavy-magnetic method, cleaning the light calcined powder by industrial pure water, further removing soluble impurities, and dehydrating for later use; the impurity removing principle is that the purity of the magnesium oxide after treatment is detected and further improved to 95.2 percent, and metal oxide impurities such as silicon, calcium, iron, aluminum and the like are further and effectively removed by utilizing the difference principle that the density of the magnesium oxide after pyrolysis is different from that of the impurities after pyrolysis, the iron-containing impurities after calcination are easily separated by magnetic separation, and the difference principle of the hydration rates of calcium oxide and magnesium oxide;
3) mixing the calcined light powder treated in the step 2) with industrial pure water according to a mixing ratio (by weight) of 1:25, adding concentrated sulfuric acid into the mixed slurry, wherein the concentration of the concentrated sulfuric acid is 95%, the optimal temperature of the mixed slurry is controlled to be 75 ℃ in the adding process, and the adding amount of the concentrated sulfuric acid is controlled until the pH value of the mixed slurry is 6.5;
4) step 3) neutralizing the mixed slurry to obtain a magnesium sulfate heptahydrate solution, preparing a sodium hydroxide solution with the concentration of 1.2mol/L from 99% sodium hydroxide granules and industrial pure water, slowly adding the sodium hydroxide solution with the concentration into the magnesium sulfate heptahydrate solution, stopping adding the sodium hydroxide solution when the pH value reaches 7.2, standing for reaction for 1 hour, separating solid-phase impurities out through settling and filtering equipment after the reaction is finished to obtain a refined magnesium sulfate heptahydrate solution with the concentration of 2.55mol/L, wherein the refined magnesium sulfate heptahydrate belongs to a first intermediate product;
5) preparing magnesium sulfate heptahydrate to the concentration of 2.3mol/L by using industrial pure water in the step 4), heating to 70 ℃, taking industrial ammonia water with the concentration of 28%, diluting to the concentration of 16% by using the industrial pure water, mixing with the magnesium sulfate heptahydrate solution at the mixing volume ratio of 1:100, controlling the pH value to be 9.5, the stirring speed to be 35rpm/min, the stirring time to be ten minutes, standing and aging after the stirring is finished, and generating magnesium hydroxide crystal precipitate and an ammonium sulfate solution after the aging time is 1 hour; magnesium hydroxide crystals belong to the second intermediate product;
6) separating magnesium hydroxide crystals, repeatedly washing the magnesium hydroxide crystals with industrial pure water for three times, dehydrating the magnesium hydroxide crystals, drying the magnesium hydroxide crystals for 4 hours at the temperature of 220 ℃, calcining the magnesium hydroxide crystals at the temperature of 550 ℃, and finally pulverizing and grading the magnesium hydroxide crystals to obtain a high-purity magnesium oxide finished product with the purity of 99.8683%;
7) filtering the ammonium sulfate solution obtained in the step 5) twice by a precision filter, and neutralizing by adopting a sulfuric acid solution with the concentration of 1mol/L until the pH value is 6.5. And then evaporating in vacuum by a triple-effect evaporator until white crystals are precipitated, sending the white crystals into a crystallizing tank for cooling and crystallizing, and circulating the residual mother liquor to the evaporator for repeated evaporation-crystallization procedures. Dehydrating the crystallized ammonium sulfate by a centrifugal machine, feeding the ammonium sulfate into a drying furnace, and drying the ammonium sulfate at the temperature of 150 ℃ for 2 hours to obtain a refined ammonium sulfate byproduct;
8) the main components of the solid phase impurities separated in the step 4) are SiO2, Ca (OH)2 and FeSO4, and the solid phase impurities can be used for preparing magnesium cement or other magnesium building material production raw materials after further cleaning, dehydration and drying.
The high purity magnesium oxide product obtained in the examples was analyzed by X-ray fluorescence Spectroscopy (XFS) to find that the weight percentage of MgO component was 99.8683% (the XFS test results are shown in the following Table 1). The content of chloride ion (CI-) is 0.0025 percent and the content of sulfate radical (SO 4) is 0.0251 percent by adopting a multi-parameter water quality analysis detector, and the product reaches the quality standard of second part-709 (medicinal magnesium oxide) of the Chinese pharmacopoeia 2000 edition.
Attached table 1: the high-purity magnesium oxide product adopts an X-ray fluorescence spectrum analyzer to analyze the result
By-products are detected by referring to GB29206-2012 ammonium sulfate quality standards and detection methods, and the detection results of the by-products ammonium sulfate are shown in an attached table 2.
Table 2 chemical composition table of by-product ammonium sulfate.
11) The detection result shows that the purity of the ammonium sulfate byproduct (NH4)2SO4 is 99.9568%, the purity of free acid is less than 0.03%, and the total harmful metal impurities (selenium, lead, arsenic and mercury) are less than 0.0003%, which all reach the quality standard of food-grade ammonium sulfate.
In the above examples, the content of magnesium oxide (MgO) in the low-grade magnesite (MgCO 3) is in the range of 35% to 45%, and the particle size is 300 mm or less; industrial grade sulfuric acid with the concentration of 90-98 percent; the 16% industrial-grade ammonia water is prepared by diluting and modulating 28% industrial-grade ammonia water and industrial pure water; the sodium hydroxide solution is prepared by diluting and modulating sodium hydroxide particles with the purity of more than or equal to 99 percent and industrial pure water; the conductivity of the industrial pure water is 0.05-1.5 uS/cm.
The index requirements of crushing, sand making, screening, cleaning and dewatering in the step 1) are as follows: the crushing particle size range is below 80 mm; the granularity range of the sand making is below 30 mm; sieving the particle size range below 15 mm; cleaning by adopting a spiral sand washer and common circulating water, desliming, taking away muddy impurities below 200 meshes through water flow, wherein the granularity range of the cleaned magnesite sand is 200 meshes-15 mm, and naturally stacking and dehydrating for 10-24 hours through a stock yard or a storage bin after cleaning is finished, so that the water content of the material is controlled to be 3% -10%. The operation sequence in the step 2) is as follows: removing incompletely thermally decomposed and iron-containing solid impurities from the light calcined powder by a heavy-magnetic method, wherein the heavy-magnetic method adopts a heavy-magnetic integrated machine or a single gravity separation device or a single magnetic separation device, after the solid impurities are separated from the light calcined powder, the light calcined powder is cleaned by industrial pure water in an intermittent or continuous cleaning mode, and the cleaning process is finished when the light calcined powder is clarified in water. And 4) settling by using a settling tank or a thickener, and filtering by using a plate and frame filter or a centrifuge.
The above embodiments are merely specific examples selected for illustrating the objects, technical solutions and advantages of the present invention in detail, and should not be construed as limiting the scope of the present invention, and various modifications, equivalent substitutions and improvements can be made without departing from the spirit and principle of the present invention.
Claims (8)
1. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite specifically comprises the following steps:
1) crushing, sand making, screening, cleaning and dehydrating low-grade magnesite, and calcining at the temperature of 950 plus materials and 1000 ℃ to prepare light calcined powder, wherein the content of MgO in the light calcined powder is increased to 70-94%;
2) cooling the light calcined powder in the step 1) to normal temperature, removing impurities, firstly removing solid impurities which are not completely thermally decomposed and contain iron by adopting a heavy-magnetic method, then cleaning the light calcined powder by adopting industrial pure water, further removing soluble impurities, and dehydrating for later use;
3) mixing the calcined light powder treated in the step 2) with industrial pure water in a weight ratio of 1:10-30, and adding concentrated sulfuric acid into the mixed slurry for reaction; controlling the temperature of the mixed slurry not to exceed 80 ℃ in the adding process of concentrated sulfuric acid, wherein the adding amount is controlled until the PH value of the mixed slurry is 6.5;
4) step 3) neutralizing the mixed slurry to obtain magnesium sulfate heptahydrate, adding a sodium hydroxide solution with the concentration of 0.2-1.5mol/L, determining the addition amount of the sodium hydroxide solution by controlling the pH value, taking the pH value of 7.2 as a reaction end point, and after the reaction is finished, separating solid phase waste containing colloid impurities by using settling and filtering equipment to obtain a refined magnesium sulfate heptahydrate solution with the concentration of not less than 2.5 mol/L;
5) preparing the magnesium sulfate heptahydrate solution to the concentration of 1.5-2.5mol/L by using industrial pure water in the step 4), then heating to 60-75 ℃, mixing 10-19% ammonia water with the heated magnesium sulfate solution in a volume ratio of 1:95-100, controlling the pH value to be 9-10, stirring at the speed of 30-45rpm/min for not less than 10 minutes, standing and aging after stirring is finished for 1-1.5 hours to generate magnesium hydroxide crystal precipitate and ammonium sulfate solution;
6) after separating the magnesium hydroxide crystal from the ammonium sulfate solution, repeatedly washing the magnesium hydroxide crystal for 3-5 times by using industrial pure water, drying for 2-3 hours at the temperature of 220 ℃ after dehydration, calcining at the temperature of 500 ℃ and 600 ℃, and finally pulverizing and grading the calcined magnesium oxide particles to obtain a high-purity magnesium oxide finished product with the purity of 99.6-99.87%;
7) carrying out precision filtration and neutralization treatment on the ammonium sulfate solution obtained in the step 6), then carrying out multi-effect evaporation and crystallization, and finally drying to obtain a refined ammonium sulfate byproduct;
8) the solid phase waste separated in the step 4) can be reused after further cleaning, dehydration and drying.
2. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the content range of magnesium oxide in the low-grade magnesite is 35-45%, and the granularity is below 300 mm; the concentration of the concentrated sulfuric acid is 90-98%; the conductivity of the industrial pure water is 0.05-1.5 uS/cm.
3. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the index requirements of crushing, sand making, screening, cleaning and dewatering in the step 1) are as follows: the crushing particle size range is below 80 mm; the granularity range of the sand making is below 30 mm; sieving materials with the granularity range of below 15 mm and the granularity of 15 mm-30 mm, and returning the materials to the sand making machine; cleaning by adopting a spiral sand washer and common circulating water, desliming, taking away muddy impurities below 200 meshes through water flow, wherein the granularity range of the cleaned magnesite sand is 200 meshes-15 mm, and naturally stacking and dehydrating for 10-24 hours through a stock yard or a storage bin after cleaning is finished, so that the water content of the material is controlled to be 3% -10%.
4. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the gravity-magnetic method in the step 2) adopts a gravity-magnetic integrated machine or single reselection equipment or single magnetic separation equipment; the cleaning mode is intermittent or continuous, and the cleaning process is finished when the caustic soda powder is clear in water.
5. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: a settling tank or a thickener is adopted for settling in the step 4), and a plate and frame filter or a centrifuge is adopted for filtering; the sodium hydroxide solution with the concentration of 0.2-1.5mol/L is prepared by diluting and blending 95% -99% of sodium hydroxide solid and industrial pure water.
6. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the ammonia water with the concentration of 10% -19% in the step 5) is prepared by diluting and blending 28% of industrial ammonia water and industrial pure water.
7. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the purity of the ammonium sulfate byproduct in the step 7) is more than or equal to 99.9 percent, wherein the total content of harmful heavy metals of selenium, lead, arsenic and mercury is less than 0.0003 percent.
8. The method for jointly preparing high-purity magnesium oxide and refined ammonium sulfate by using low-grade magnesite according to claim 1, is characterized in that: the solid phase waste in the step 8) mainly comprises SiO2, Ca (OH)2 and FeSO4, and can be used for preparing magnesium cement or other magnesium building materials.
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