CN113735238A - Process for co-producing magnesium carbonate series products by seawater desalination device - Google Patents

Process for co-producing magnesium carbonate series products by seawater desalination device Download PDF

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CN113735238A
CN113735238A CN202111263839.0A CN202111263839A CN113735238A CN 113735238 A CN113735238 A CN 113735238A CN 202111263839 A CN202111263839 A CN 202111263839A CN 113735238 A CN113735238 A CN 113735238A
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magnesium
magnesium carbonate
series products
seawater desalination
carbonization
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宋丽英
胡晓波
胡庆福
李家栋
苏洪茹
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Noncommissioned Officer Academy of Army Medical University
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Noncommissioned Officer Academy of Army Medical University
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    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/52Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/46Removing components of defined structure
    • B01D53/62Carbon oxides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/77Liquid phase processes
    • B01D53/78Liquid phase processes with gas-liquid contact
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01FCOMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F5/00Compounds of magnesium
    • C01F5/14Magnesium hydroxide
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01FCOMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F5/00Compounds of magnesium
    • C01F5/24Magnesium carbonates
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/52Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/529Processes or devices for preparing lime water
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2251/00Reactants
    • B01D2251/40Alkaline earth metal or magnesium compounds
    • B01D2251/402Alkaline earth metal or magnesium compounds of magnesium
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2251/00Reactants
    • B01D2251/60Inorganic bases or salts
    • B01D2251/604Hydroxides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2258/00Sources of waste gases
    • B01D2258/02Other waste gases
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/08Seawater, e.g. for desalination

Abstract

The invention discloses a process for co-producing magnesium carbonate series products by a seawater desalination device, which belongs to the technical field of seawater energy utilization and comprises the following steps: calcining limestone to produce precipitated magnesium alkali agent lime, making lime milk with lime slaking device, reacting high-concentration magnesium concentrated brine discharged from seawater desalting device with lime milk in magnesium precipitating device to generate magnesium hydroxide precipitate, and reacting magnesium hydroxide with CO in calcining kiln gas2Carbonizing reaction in carbonizing device to obtain carbonized liquidAfter solid-liquid separation, the filter cake is dried, graded and packed to prepare light or heavy magnesium carbonate series products. The invention improves the utilization rate of seawater, utilizes chemical technology to recover magnesium, prepares magnesium carbonate series products, produces magnesium hydroxide as a byproduct, and has obvious economic and environmental benefits; the invention can improve the comprehensive efficiency of seawater desalination and achieve the aims of energy saving and environmental protection by comprehensive application of multiple technologies.

Description

Process for co-producing magnesium carbonate series products by seawater desalination device
Technical Field
The invention belongs to the technical field of seawater energy utilization, and particularly relates to a process for co-producing magnesium carbonate series products by a seawater desalination device.
Background
Along with the improvement of living standard of people and the development of national economy of all countries in the world, the demand of fresh water is larger and larger, the amount of fresh water provided by the nature is not enough, and seawater desalination devices are gradually built in countries and regions such as coastal regions, islands and the like to extract fresh water from seawater for people to need. The seawater contains rich inorganic salts, mainly sodium chloride, potassium chloride, magnesium sulfate, bromine and the like, is called sea as treasury of the inorganic salts, and has inorganic salts up to 35 per thousand. The inorganic salt is directly recovered from the seawater, and the low content of the inorganic salt needs to be recovered by a thermal method, so that the energy consumption is higher. At present, all countries in the world utilize solar energy to recover NaCl and MgCl by using a solar salt method on the coastal region2And a salt field is arranged on the coastal beach, the occupied area is large, and other inorganic salt is recycled through bittern.
Disclosure of Invention
The invention aims to provide a process for co-producing magnesium carbonate series products by a seawater desalination device, and aims to solve the technical problems that a beach salt field in the prior art occupies a large area and the batch recovery efficiency of various inorganic salts is low.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a process for co-producing magnesium carbonate series products by a seawater desalination device comprises the following steps:
(1) preparing raw materials: a byproduct of the seawater desalination treatment is magnesium-containing strong brine; calcining limestone or dolomite nonmetallic ore by a calcining device to prepare lime or dolomite as an alkaline magnesium precipitating agent, and purifying and collecting kiln gas as CO for carbonization2
(2) Magnesium deposition reaction: lime or dolomitic lime is subjected to digestion reaction to obtain lime milk, and the lime milk and strong brine react in a magnesium precipitation device to generate magnesium hydroxide precipitate;
(3) and (3) carbonization reaction: magnesium hydroxide suspension discharged by magnesium deposition device and CO in kiln gas2Carrying out carbonization reaction in a carbonization device to generate magnesium bicarbonate, and obtaining carbonization liquid containing magnesium bicarbonate;
(4) preparing magnesium carbonate: after the carbonization liquid is subjected to solid-liquid separation, the filtrate containing the magnesium bicarbonate is subjected to hydrothermal treatment, then the solid-liquid separation is carried out, and the filter cake is dried, graded and packaged to prepare the normal magnesium carbonate, light or heavy magnesium carbonate series products.
Preferably, the calcining device in the step (1) calcines the limestone or the dolomite non-metallic ore at the temperature of 800-1200 ℃, and the limestone or the dolomite non-metallic ore contains CO2The kiln gas enters a boiler to recover waste heat, is cooled and then enters a dust removal device to remove dust and purify, and CO in the purified kiln gas2The content is 20-40%.
Preferably, the apparatus for calcining limestone or dolomite in step (1) is a double-hearth kiln, a sleeve kiln, a rotary kiln, a double-beam kiln or a shaft kiln.
Preferably, the dust removal device comprises a dry dust remover and a wet dust remover, the kiln gas firstly enters the dry dust remover to remove large-particle dust, then enters the wet dust remover to remove micro-dust, the temperature of the kiln gas is reduced to below 30 ℃, the purified kiln gas is pressurized to 2-3 MPa by a compressor, and then is conveyed to the carbonization device.
Preferably, the grey water ratio in the digestion reaction of the step (2) is 1: 4, after ash sealing for 1-3 hours, adding water to adjust the concentration to 5% -10% of the solid-to-liquid ratio, and stirring for 1-3 hours; and (3) metering the molar ratio of calcium to magnesium after deslagging to be 1: 0.9-1.0, feeding the magnesium hydroxide into a magnesium precipitation device for reaction to obtain magnesium hydroxide precipitate, and controlling the reaction time to be 20-24 hours; the supernatant of the magnesium deposition device is conveyed to a digestion machine for water for digestion reaction and water for purification in a dust removal device.
Preferably, a stirrer is arranged inside the magnesium precipitation device, a lime milk inlet and a strong brine inlet are formed in the top of the magnesium precipitation device, and a clear liquid outlet and a bottom suspension liquid outlet are formed in the upper portion of the magnesium precipitation device.
Preferably, the temperature and pressure are controlled during carbonization in the step (3), and the magnesium carbonate trihydrate precipitate MgCO is generated through carbonization3·3H2O, filtering and drying; the drying is divided into two steps: firstly removing free moisture, then raising the temperature to remove the combined moisture to obtain the magnesium carbonate MgCO3Grading and packaging.
Preferably, a carbonized liquid containing magnesium bicarbonate is obtained during carbonization in the step (3), and the filtrate enters a hydrothermal treatment device after solid-liquid separation of the carbonized liquid; adding Mg (HCO)3)2The molar ratio is 1:0.9 to 1.0 of MgO or Mg (OH)2Carrying out hydrothermal treatment; controlling the hydrothermal temperature and the hydrothermal treatment time according to the variety requirements of the final product to prepare the light or heavy magnesium carbonate series product xMgCO3·yMg(OH)2·zH2O, wherein x = 1-4; y = 0-1; z = 0-8;
drying the light or heavy magnesium carbonate filter cake obtained by solid-liquid separation after the hydrothermal treatment for two times: firstly, CO2Drying under atmosphere to remove free water, and adding Mg (OH)2Carbonization to MgCO3(ii) a Then the drying temperature is increased to 240 +/-20 ℃, and the combined moisture is removed to prepare magnesium carbonate MgCO3And (5) series products are classified and packaged.
Preferably, the carbonized liquid is subjected to solid-liquid separation to obtain a filtrate containing magnesium bicarbonate, namely heavy magnesium water, and the heavy magnesium water enters a hydrothermal treatment device to prepare different magnesium carbonate series products through the following hydrothermal treatment processes:
1) hydrolyzing heavy magnesium water at 80-100 ℃ for 30-60 min, filtering, drying and grading to prepare light magnesium carbonate series products;
2) hydrolyzing heavy magnesium water at 50-70 ℃ for 30-60 min, filtering, drying and grading to prepare heavy magnesium carbonate series products;
3) hydrolyzing heavy magnesium water at 30-45 deg.C for 30-60 min, filtering, drying, and adding CO2Drying at low temperature of 80-150 ℃ in the atmosphere, then drying at high temperature of 150-240 ℃ to remove the bound water, and preparing the normal magnesium carbonate series products in a grading manner.
Adopt the aboveThe beneficial effect that technical scheme produced lies in: compared with the prior art, the method utilizes magnesium chloride in the strong brine of the seawater desalination device as a magnesium source, limestone or dolomite is calcined to obtain lime or dolomite as a magnesium precipitation alkaline agent, and kiln gas discharged by calcination is used as gas for carbonization; lime milk obtained by digesting the magnesium precipitation alkali agent reacts with strong brine in a magnesium precipitation device to obtain magnesium hydroxide suspension, and the magnesium hydroxide suspension and CO in kiln gas2Contacting to carry out carbonization reaction; finally, the carbonized liquid is subjected to solid-liquid separation, and filter cakes are dried, classified and packaged to prepare normal magnesium carbonate and light or heavy magnesium carbonate series products. The invention organically combines three new technologies, namely a new seawater desalination technology, a new non-metal ore processing technology, a new chemical material technology and the like, improves the utilization rate of seawater, produces magnesium hydroxide as a byproduct while preparing magnesium carbonate series products, and has obvious economic and environmental benefits. The invention can improve the comprehensive efficiency of seawater desalination and achieve the aims of energy saving and environmental protection by comprehensive application of multiple technologies.
Drawings
FIG. 1 is a process flow diagram of a process for co-producing magnesium carbonate series products by a seawater desalination plant according to an embodiment of the present invention;
FIG. 2 is a material balance diagram of a seawater desalination plant of example 1 for co-producing 10.8kt/a light magnesium carbonate and 10.8kt/a flame retardant magnesium hydroxide;
FIG. 3 is a material balance diagram of the seawater desalination plant of example 2 for co-producing 7.2kt/a magnesium orthocarbonate and 7.2kt/a industrial magnesium hydroxide.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly and completely understood, the technical solutions in the embodiments of the present invention are described below with reference to the accompanying drawings and specific embodiments, 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. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
With the development of the seawater desalination technology, fresh water is produced by seawater through a seawater desalination device such as a reverse osmosis method or electrodialysis, concentrated solution containing high-concentration magnesium is discharged at the same time, the salt content of the concentrated solution can be improved by 1-2 times, and therefore convenient conditions are provided for extracting Mg products by adopting a chemical technology.
As shown in figure 1, lime produced by calcining limestone by a calcining device is digested to prepare lime milk, the lime milk and strong brine react, thicken and clarify in a magnesium precipitation device, supernatant liquid is sent to a lime digesting device, and redundant clear liquid is discharged; the lower part of the magnesium hydroxide suspension is sent to a magnesium hydroxide preparation device, and a magnesium hydroxide slurry product with certain concentration is prepared by thickening, filter pressing or drying or is filter pressed into a paste magnesium hydroxide product with certain water content; or press filtering and drying to obtain powder magnesium hydroxide product; or the powder magnesium hydroxide is subjected to surface treatment by a wet method or a dry method to prepare products such as flame-retardant grade magnesium hydroxide and the like.
Directly sending the whole (when magnesium hydroxide is not produced) or part (magnesium hydroxide products are produced simultaneously) of the magnesium hydroxide suspension at the lower part to a carbonization device; after the kiln gas calcined by limestone recovers heat energy, and is subjected to dry-wet dust removal and purification, the carbon dioxide in the kiln gas and magnesium hydroxide suspension with a certain concentration are subjected to carbonization reaction in a carbonization tower to produce magnesium carbonate series products, the carbonization reaction is carried out under the control of different carbonization temperatures and pressures to produce light magnesium carbonate or heavy magnesium carbonate or normal magnesium carbonate series products, the light magnesium carbonate or heavy magnesium carbonate or normal magnesium carbonate series products are sent to a magnesium carbonate series preparation device, and the light magnesium carbonate or heavy magnesium carbonate or normal magnesium carbonate series products are subjected to filter pressing, drying, grading and packaging to prepare the magnesium carbonate series products.
The invention produces fresh water by a seawater desalination device, and simultaneously, magnesium in the concentrated water is comprehensively utilized by the chemical technology, lime produced by calcining limestone and kiln gas are firstly used for precipitating magnesium, and then purified kiln gas is used for preparing magnesium carbonate series products by a carbonization process, and simultaneously magnesium hydroxide series products can be produced, thereby improving the utilization rate of seawater, improving the comprehensive efficiency of seawater desalination, and achieving the purposes of energy saving and environmental protection by multi-technology synthesis. The following are detailed examples:
the invention provides a process for co-producing magnesium carbonate series products by a seawater desalination device, which comprises the following steps:
(1) preparing raw materials: a byproduct of the seawater desalination treatment is magnesium-containing strong brine; lime calcination by means of a calcination apparatusPreparing lime or dolomite as alkaline magnesium precipitating agent from non-metallic ore of stone or dolomite, and purifying and collecting kiln gas as CO for carbonization2
1) Adopting reverse osmosis method, multistage flash evaporation, electrodialysis and other sea water desalination technologies, and establishing one or more sea water desalination devices to prepare fresh water for storage and use by people, wherein the fresh water accounts for more than 60%, and the high-concentration liquid accounts for less than 40%; the concentrated solution is used as magnesium-containing concentrated brine and put into a high-magnesium concentrated water storage pool to be used as a magnesium raw material for standby. Wherein, the content of magnesium chloride in the magnesium-containing concentrated brine is within the range of 15 kg/t-40 kg/t.
2) Selecting one of limestone or dolomite, using natural gas as fuel, feeding the non-metallic ore into a calcining device (a calcining furnace) to calcine to prepare lime (or dolomite), and digesting and storing the lime (or the dolomite) to prepare for depositing magnesium.
Calcining limestone or dolomite nonmetallic ore at 800-1200 ℃, wherein the calcining temperature is in the range of 800-1200 ℃; the content of calcium oxide in the lime is more than or equal to 90 percent; the raw and over-burnt rate is less than or equal to 5 percent; lime is digested to prepare lime milk, and the concentration of the lime milk is controlled to be 8-12%. The calcining device can adopt a double-chamber kiln, a sleeve kiln, a rotary kiln, a double-beam kiln or a vertical kiln, etc.
Containing CO2The kiln gas is used for subsequent carbonization after being treated by a kiln gas treatment device and subjected to dry and wet dust removal purification after heat recovery. The high-temperature kiln gas firstly enters a boiler to recover waste heat and cool, then enters a dust removal device to remove dust and purify, and CO in the purified kiln gas2The content is 20-40%. The dust removal device comprises a dry dust remover and a wet dust remover, kiln gas firstly enters the dry dust remover to remove large-particle dust, then enters the wet dust remover to remove micro-dust, the temperature of the kiln gas is reduced to be below 30 ℃, the purified kiln gas is increased in pressure to be 2-3 MPa through a compressor, and then the kiln gas is conveyed to the carbonization device.
Continuously discharging lime from the lime kiln, conveying the lime into a lime bin through a belt conveyor for storage and stay, metering and conveying the lime into a lime slaking device according to production requirements, wherein the ash-water ratio of slaking reaction is 1: 4, after ash sealing for 1-3 hours, adding water to adjust the concentration to 5% -10% of the solid-to-liquid ratio, and stirring for 1-3 hours; and (3) metering the molar ratio of calcium to magnesium after deslagging to be 1: 0.9-1.0, entering a magnesium precipitation device to react to obtain magnesium hydroxide precipitate, and conveying the supernatant of the magnesium precipitation device to a digestion device for water for digestion reaction and water for purification in a dust removal device. The reaction equation involved is as follows:
lime digestion reaction: CaO + H2O →Ca(OH)2
B, carrying out a dolomitic lime digestion reaction: CaO MgO + H2O →Ca(OH)2 + Mg(OH)2
Magnesium deposition reaction: MgCl2 + Ca(OH)2 →Mg(OH)2↓+ CaCl2
Selecting a limestone calcining device, ensuring the supply of lime and having low price; in the magnesium precipitation process, equimolar magnesium is obtained from equimolar calcium, the value is improved by more than 20 times, and the economic benefit is obvious. Simultaneously, the CO is increased for preparing magnesium carbonate2Two purposes are achieved by one stroke.
(2) Magnesium deposition reaction: lime or dolomitic lime is subjected to digestion reaction to obtain lime milk, and the lime milk and strong brine react in a magnesium precipitation device to generate magnesium hydroxide precipitate. The inside of the used magnesium-precipitating device is provided with a stirrer, the top of the magnesium-precipitating device is provided with a lime milk inlet and a strong brine inlet, and the upper part of the magnesium-precipitating device is provided with a clear liquid outlet and a bottom suspension outlet.
Pumping concentrated liquid of the seawater desalination device into a magnesium precipitation device through a delivery pump, simultaneously continuously pumping lime milk into the magnesium precipitation device through a lime milk inlet according to a proportion, stirring, mixing and reacting to generate magnesium hydroxide crystals, growing, homogenizing and precipitating, wherein the total reaction and precipitation time of the precipitation device is controlled to be 24-48 h. Discharging the magnesium hydroxide suspension with a certain concentration from a lower outlet, and partially or completely sending the magnesium hydroxide suspension to a magnesium hydroxide preparation device to produce magnesium hydroxide series products; the carbonization device may also be conveyed partially or completely.
Preparation of magnesium hydroxide series products: the magnesium deposition device conveys magnesium hydroxide suspension to be filtered by a filter press, and the water content of the magnesium hydroxide is adjusted to prepare two products of slurry or filter cake, which are mainly used for environmental protection, such as magnesium-method smoke discharge and desulfurization. Wherein, when preparing slurry or filter cake products, the magnesium hydroxide is controlled at 28.0-35% and 40.0-50% through filtering and concentration. This part of the manufacturing process belongs to the prior art and is not described herein again.
Granular industrial magnesium hydroxide can be prepared, and a powder product with the content of the magnesium hydroxide controlled between 90.0 percent and 99.0 percent is prepared by filtering, drying and grading; or dry or wet modification treatment to prepare fire retardant magnesium hydroxide (the content of magnesium hydroxide is controlled at 91-98%), etc. This part of the manufacturing process belongs to the prior art and is not described herein again.
(3) And (3) carbonization reaction: magnesium hydroxide suspension discharged by magnesium deposition device and CO in kiln gas2The carbonization reaction is carried out in a carbonization device. The carbonization device is required to ensure that the magnesium hydroxide suspension and the kiln gas are in full contact, and the total carbonization time is controlled within 1-3 h. The carbonization device can adopt a carbonization tower, and the magnesium hydroxide suspension is pumped into the carbonization tower from the inlet at the upper part of the carbonization tower to flow from top to bottom after being mixed according to the carbonization requirement; the purified kiln gas enters the carbonization tower from a gas inlet at the lower part of the carbonization tower and is in gas-liquid contact from bottom to top for carbonization reaction:
Mg(OH)2 + 2CO2 →Mg(HCO3)2
the carbonized liquid containing magnesium bicarbonate enters a hydrothermal treatment device. Adding Mg (HCO) first3)2The molar ratio is 1:0.9 to 1.0 of MgO or Mg (OH)2Carrying out hydrothermal treatment; controlling the hydrothermal temperature and the hydrothermal treatment time according to the variety requirements of the final product to prepare the light magnesium carbonate xMgCO3·yMg(OH)2·zH2O, wherein x = 1-4; y = 0-1; z =0 ~ 8. The most typical light magnesium carbonate has the molecular formula of 4MgCO3·Mg(OH)2·4H2O, the bulk density is less than or equal to 1.4 g/mL; the bulk density of the heavy magnesium carbonate is more than or equal to 1.5 g/mL. The hydrothermal chemical reaction formula is as follows:
(x+y)Mg(HCO3)2 → xMgCO3·yMg(OH)2·zH2O + (x+2y)CO2
adding MgO and Mg (OH)2The chemical reaction formula is as follows:
MgO + H2O →Mg(OH)2
Mg(OH)2 + CO2 →MgCO3 + H2O
(x+y)MgCO3 +zH2O → xMgCO3·yMg(OH)2·zH2O + 2yCO2
because of different hydrothermal treatment temperatures and different treatment times, light magnesium carbonate or heavy magnesium carbonate with different gravities can be generated, the purposes are different, and magnesium carbonate with different densities can be prepared according to the needs of users.
(4) Preparing magnesium carbonate: by controlling the carbonization temperature and pressure, the filtrate containing magnesium bicarbonate is heavy magnesium water after solid-liquid separation of the carbonized liquid, the heavy magnesium water is subjected to hydrothermal treatment and solid-liquid separation, and filter cakes are dried, classified and packaged to prepare normal magnesium carbonate, light or heavy magnesium carbonate series products.
A. Preparation of magnesium carbonate MgCO3Two routes can be taken:
1) during carbonization, the temperature and the pressure are controlled to ensure that magnesium carbonate trihydrate precipitates MgCO generated by carbonization3·3H2O, filtering and drying; the drying is divided into two steps: firstly removing free moisture, then raising the temperature to remove the combined moisture to obtain the magnesium carbonate MgCO3Grading and packaging.
2) Adopting a route for preparing light magnesium carbonate to obtain light magnesium carbonate filter cake, drying the light magnesium carbonate filter cake into two sections, firstly, adding CO2Drying under atmosphere to remove free water, and adding Mg (OH)2Carbonization to MgCO3Then raising drying temperature to about 240 deg.C to remove combined water and prepare magnesium carbonate MgCO3Grading and packaging.
B. Preparing magnesium carbonate series products: the carbonization liquid in the carbonization device is a magnesium bicarbonate solution, the filtrate containing magnesium bicarbonate is obtained after filtration and separation of precipitates, namely heavy magnesium water, and the heavy magnesium water enters a hydrothermal treatment device to be subjected to the following hydrothermal treatment to prepare different magnesium carbonate series products:
1) hydrolyzing heavy magnesium water at 80-100 ℃ for 30-60 min, filtering, drying and grading to prepare light magnesium carbonate series products;
2) hydrolyzing heavy magnesium water at 50-70 ℃ for 30-60 min, filtering, drying and grading to prepare heavy magnesium carbonate series products;
3) hydrolyzing heavy magnesium water at 30-45 ℃ for 30-60 min, filtering, drying at low temperature under the atmosphere of CO2 at 80-150 ℃, then drying at high temperature at 150-240 ℃, removing bound water, and preparing normal magnesium carbonate series products in a grading manner.
The process flow of the invention is as follows:
after being pretreated to remove silt and organic substances, the seawater enters a seawater desalination device, and produced fresh water is stored in a fresh water pool for users to use; the concentrated solution containing high magnesium is stored in a high magnesium concentrated water storage pool, and the concentrated solution of a common seawater desalination device contains 2.6kg/m magnesium3Reduced to 10.3kg/m magnesium chloride3And is used as a magnesium source for standby.
Lime stone is pretreated to remove soil, impurities are removed, the lime stone is crushed to a required block size conveying bin, the lime stone is metered and sent into a calcining device, the lime stone is calcined at the temperature of 800-1200 ℃, the lime stone is taken out of a kiln, is subjected to raw ash removal and burning, is sieved and then respectively stored in a block bin and a fly ash bin, the block ash is metered and sent into a slaking device to be digested to generate lime milk, is sieved to remove slag, is concentrated by 5-10% and then is stored to serve as a magnesium precipitation auxiliary agent, and the magnesium precipitation auxiliary agent is metered and sent into a magnesium precipitation device according to the requirement of magnesium precipitation.
The temperature of the outlet gas of the calcining device is 800-1200 ℃, and CO is2The content is 20-25%, the waste heat is recycled in a waste heat boiler, the temperature is reduced to below 200 ℃, fine dust particles are removed by a dry-wet dust removal device, the pressure is increased to 2-3 MPa by a compressor, and the fine dust particles are sent to a carbonization device to be used as CO for producing magnesium carbonate series products2And (4) source.
Recovering magnesium in the concentrated solution generated by the seawater desalination device, namely firstly dissolving MgCl2Conversion to sparingly soluble Mg (OH)2The precipitate is mixed with soluble inorganic salts such as NaCl, KCl, CaCl2After separation, Mg (OH) can be recovered2And magnesium carbonate series products.
Firstly, continuously feeding the concentrated solution of the recovered seawater desalination device into a magnesium precipitation device according to the magnesium-containing mole number and the liquid amount, starting a stirring device, continuously adding lime slaking solution of a calcining device into the magnesium precipitation device according to the magnesium-calcium mole ratio of 1: 0.9-1.00 for reaction, precipitating and thickening, mixing and contacting the magnesium and the calcium solution in the magnesium precipitation device for 20-24 hours, and feeding the supernatant into a clear solution tank for supplying digestion water, kiln gas wet-process dust removal water and the like; the concentrated solution is sent to be filtered to produce magnesium hydroxide series products; the production of products with different specifications is complex and simple due to different processes.
(1) Producing slurry-like magnesium hydroxide, filtering and preparing slurry, and pumping into a pool;
(2) producing filter cake-shaped magnesium hydroxide, adjusting the water content by filtering, packaging and waiting for sale;
(3) producing industrial magnesium hydroxide products, filtering, drying, grading, packaging and waiting for sale;
(4) producing fire retardant magnesium hydroxide, precipitating and thickening, carrying out hydrothermal treatment, carrying out surface treatment, filtering, drying, grading, packaging and waiting for sale.
Producing magnesium carbonate series products, and sending magnesium hydroxide precipitation liquid to a carbonization device. Magnesium hydroxide suspension and CO-containing gas supplied from calcining kiln2The kiln gas is in gas-liquid contact for carbonization reaction to generate magnesium bicarbonate solution, the solution is filtered and separated from precipitate, and the filtered heavy magnesium water is processed by hydrothermal treatment to prepare different magnesium carbonate series products:
the following are two specific examples:
example 1
Basic data
(1) 2.6kg/m magnesium in concentrated solution of seawater desalination device3Reduced to a magnesium chloride content of 10.3kg/m3(ii) a Reduced concentrated water flow rate 390m3/h。
(2) After lime slaking, the effective utilization rate of CaO is 90% (CaO in lime is burnt and over-burnt more than or equal to 5%, impurities such as silicon and the like are more than or equal to 3%, and CaO loss in the process of magnesium deposition is more than or equal to 1%). Reduced to CaO of 2.36t/h, Ca (OH)2Is 3.12 t/h; MgOH in the suspension discharged by the magnesium precipitation device is 2.44t/h, one part of the suspension is used for preparing magnesium hydroxide series products (MgOH is 1.5 t/h), and the other part of the suspension is carbonized to form magnesium bicarbonate carbonization liquid (converted into Mg (HCO)3)22.35 t/h) for preparing magnesium carbonate series products.
(3) CO after dedusting and cooling kiln gas2Up to 25%, carbonizing CO2% utilization 90%; 25% CO2The flow rate is 2920m3/h。
Production capacity: 10.8kt/a (1.5 t/h) light magnesium carbonate (4 MgCO)3·Mg(OH)2·4H2O)
10.8kt/a (1.5 t/h) flame retardant magnesium hydroxide (Mg (OH)2
The material balance data for example 1 is shown in detail in FIG. 2.
The production capacity requires the consumption of 10.3kg/m magnesium chloride3Concentrated solution 390m of seawater desalination device3Per hour, 2808km for the whole year3A; 2.41t/h of lime is consumed, and 17.4kt/a is needed all the year round; 2920m of consumed kiln gas3/h(CO2Percent: 25%), 21024km for the whole year3/a。
Example 2
The basic data are the same as example 1, and the concentrated solution of the seawater desalting plant contains 2.6kg/m of magnesium3Reduced to a magnesium chloride content of 10.3kg/m3
(1) High magnesium concentrated water flow 271.7m3/h。
(2) After lime slaking, the effective utilization rate of CaO is 90% (CaO in lime is burnt and over-burnt more than or equal to 5%, impurities such as silicon and the like are more than or equal to 3%, and CaO loss in the process of magnesium deposition is more than or equal to 1%). Reduced to CaO of 1.66t/h, Ca (OH)2Is 2.18 t/h; MgOH in suspension discharged by the magnesium precipitation device is 1.7t/h, one part of the suspension is used for preparing magnesium hydroxide series products (MgOH is 1.0 t/h), and the other part of the suspension is carbonized to form magnesium bicarbonate carbonization liquid (converted into Mg (HCO)3)21.74 t/h) for preparing magnesium carbonate series products.
(3) CO after dedusting and cooling kiln gas2Up to 25%, carbonizing CO2% utilization 90%; 25% CO2The flow rate is 2160m3/h。
Production capacity: 7.2kt/a (1 t/h) magnesium carbonate (MgCO)3
7.2kt/a (1 t/h) Industrial magnesium hydroxide (Mg (OH)2
The material balance data in the graph is shown in detail in fig. 3.
The production capacity requires the consumption of 10.3kg/m magnesium chloride3Concentrated liquid 271.7m of seawater desalination device3Per hour, 2000km for the whole year3/a;Lime is consumed at 1.66t/h, and 12.0kt/a is needed all the year round; the consumed kiln gas is 2160kg/m3(CO2Percent: 25%) need 15552km all year round3/a。
The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims (9)

1. A process for co-producing magnesium carbonate series products by a seawater desalination device is characterized by comprising the following steps:
(1) preparing raw materials: a byproduct of the seawater desalination treatment is magnesium-containing strong brine; calcining limestone or dolomite nonmetallic ore by a calcining device to prepare lime or dolomite as an alkaline magnesium precipitating agent, and purifying and collecting kiln gas as CO for carbonization2
(2) Magnesium deposition reaction: lime or dolomitic lime is subjected to digestion reaction to obtain lime milk, and the lime milk and strong brine react in a magnesium precipitation device to generate magnesium hydroxide precipitate;
(3) and (3) carbonization reaction: magnesium hydroxide suspension discharged by magnesium deposition device and CO in kiln gas2Carrying out carbonization reaction in a carbonization device to generate magnesium bicarbonate, and obtaining carbonization liquid containing magnesium bicarbonate;
(4) preparing magnesium carbonate: and (3) after solid-liquid separation of the carbonized liquid in the step (3), carrying out solid-liquid separation on the filtrate containing the magnesium bicarbonate after hydrothermal treatment, drying, grading and packaging filter cakes to prepare normal magnesium carbonate and light or heavy magnesium carbonate series products.
2. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 1, wherein the process comprises the following steps: in the step (1), the calcining device calcines the limestone or the dolomite non-metallic ore at the temperature of 800-1200 ℃, and the limestone or the dolomite non-metallic ore contains CO2Kiln gas enters a boiler to recover waste heat and reduceAfter the temperature is increased, the kiln gas enters a dust removal device for dust removal and purification, and CO in the purified kiln gas2The content is 20-40%.
3. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 1, wherein the process comprises the following steps: the equipment for calcining the limestone or dolomite in the step (1) is a double-hearth kiln, a sleeve kiln, a rotary kiln, a double-beam kiln or a vertical kiln.
4. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 2, wherein the process comprises the following steps: the dust removal device comprises a dry dust remover and a wet dust remover, kiln gas firstly enters the dry dust remover to remove large-particle dust, then enters the wet dust remover to remove micro-particle dust, the temperature of the kiln gas is reduced to be below 30 ℃, the purified kiln gas is increased to 2-3 MPa through a compressor, and then the kiln gas is conveyed to the carbonization device.
5. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 4, wherein the process comprises the following steps: the grey water ratio in the digestion reaction of the step (2) is 1: 4, after ash sealing for 1-3 hours, adding water to adjust the concentration to 5% -10% of the solid-to-liquid ratio, and stirring for 1-3 hours; and (3) metering the molar ratio of calcium to magnesium after deslagging to be 1: 0.9-1.0, feeding the magnesium hydroxide into a magnesium precipitation device for reaction to obtain magnesium hydroxide precipitate, and controlling the reaction time to be 20-24 hours; the supernatant of the magnesium precipitation device provides water for digestion reaction and purification of the dust removal device.
6. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 1, wherein the process comprises the following steps: the magnesium deposition device is characterized in that a stirrer is arranged inside the magnesium deposition device, a lime milk inlet and a strong brine inlet are formed in the top of the magnesium deposition device, and a clear liquid outlet and a bottom suspension outlet are formed in the upper portion of the magnesium deposition device.
7. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 1, wherein the process comprises the following steps: carbonizing in step (3) to generate magnesium carbonate trihydrate precipitate MgCO3·3H2And O, filtering and drying to obtain the normal magnesium carbonate.
8. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 1, wherein the process comprises the following steps: obtaining a carbonized liquid containing magnesium bicarbonate during carbonization in the step (3), and after solid-liquid separation of the carbonized liquid, feeding the filtrate into a hydrothermal treatment device; adding Mg (HCO)3)2The molar ratio is 1:0.9 to 1.0 of MgO or Mg (OH)2Hydrothermal treatment is carried out to prepare light or heavy magnesium carbonate series products xMgCO3·yMg(OH)2·zH2O, wherein x = 1-4; y = 0-1; z = 0-8;
drying the light or heavy magnesium carbonate filter cake obtained by solid-liquid separation after the hydrothermal treatment for two times: firstly, CO2Drying under atmosphere to remove free water, and adding Mg (OH)2Carbonization to MgCO3(ii) a Then raising the drying temperature to 240 +/-20 ℃, removing the combined moisture to prepare a normal magnesium carbonate series product, grading and packaging.
9. The process for the co-production of magnesium carbonate series products by a seawater desalination plant as claimed in claim 8, wherein: the carbonized liquid is subjected to solid-liquid separation to obtain a filtrate containing magnesium bicarbonate, namely heavy magnesium water, and the heavy magnesium water enters a hydrothermal treatment device to be subjected to the following hydrothermal treatment to prepare different magnesium carbonate series products:
1) hydrolyzing heavy magnesium water at 80-100 ℃ for 30-60 min, filtering, drying and grading to prepare light magnesium carbonate series products;
2) hydrolyzing heavy magnesium water at 50-70 ℃ for 30-60 min, filtering, drying and grading to prepare heavy magnesium carbonate series products;
3) hydrolyzing heavy magnesium water at 30-45 deg.C for 30-60 min, filtering, drying, and adding CO2Drying at low temperature of 80-150 ℃ in the atmosphere, then drying at high temperature of 150-240 ℃ to remove the bound water, and preparing the normal magnesium carbonate series products in a grading manner.
CN202111263839.0A 2021-10-28 2021-10-28 Process for co-producing magnesium carbonate series products by seawater desalination device Pending CN113735238A (en)

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