CN112520769B

CN112520769B - Process and device for dealkalizing red mud and simultaneously recovering aluminum oxide by using waste flue gas and waste heat of cement plant

Info

Publication number: CN112520769B
Application number: CN202011423582.6A
Authority: CN
Inventors: 滕英跃; 未萌; 宋银敏; 韩丽萍; 梁志鹏
Original assignee: Inner Mongolia University of Technology
Current assignee: Inner Mongolia University of Technology
Priority date: 2020-12-08
Filing date: 2020-12-08
Publication date: 2023-02-03
Anticipated expiration: 2040-12-08
Also published as: CN112520769A

Abstract

The invention utilizes the waste flue gas of the cement plant and the waste heat thereof to carry out red mud dealkalization and simultaneously recover alumina, comprehensively utilizes the waste heat of the cement plant and the waste flue gas, and carries out acid-base treatment and Ca treatment ²⁺ Sodium salt and alumina in the red mud are extracted by an ion exchange method, so that the red mud treatment cost is reduced, the red mud becomes a low-cost cement raw material, the sodium salt is obtained, the residual alumina is recovered, and the industrial waste is utilized to the maximum extent; the invention also adopts a kiln tail waste gas low-temperature drying process to dry the dealkalized red mud, so that the moisture of the dealkalized red mud is reduced to 5 percent, and the red mud can be further applied to cement production; the invention also utilizes the alkali liquor removed from the red mud to absorb the carbon dioxide in the tail flue gas of the cement kiln, reduces the emission of the carbon dioxide, obtains sodium salt with low solubility, and simultaneously recycles the filtrate after recycling the sodium salt to the reaction tank to be reaction liquid, thereby reducing the environmental pollution and improving the recovery rate of Na element. The invention of the technology makes it possible to utilize the large amount of industrial waste residues of the red mud.

Description

Process and device for dealkalizing red mud and simultaneously recovering aluminum oxide by using waste flue gas and waste heat of cement plant

The technical field is as follows:

the invention relates to the field of red mud dealkalization, in particular to a process and a device for dealkalizing red mud and simultaneously recovering alumina by utilizing waste flue gas and waste heat of a cement plant.

Background art:

red mud is a polluting waste residue discharged when extracting alumina in the aluminum industry, and generally 1.0-2.0 tons of red mud are additionally generated when producing 1 ton of alumina on average. China, as the 4 th alumina producing country in the world, discharges up to millions of tons of red mud every year.

Chemical composition of Red mud (%)

The alkali content of the red mud is higher, generally higher than 4%, so that the red mud has great harm to soil and water sources, and the red mud particles are extremely fine and fly with wind to pollute air. In conclusion, the environmental problems caused by red mud treatment are not moderate. The dealkalization method of the red mud comprises a water washing dealkalization process, a calcium ion replacement method, a wet carbonization method, an acid neutralization method in a leaching method and the like. The water washing dealkalization process consumes a large amount of water, has low alkali liquor concentration and is difficult to recover, and consumes a long time; the heat consumption of the calcium ion replacement method is high; the wet carbonization method has high requirement on equipment compression resistance; the acid neutralization method in the leaching method consumes a large amount of acid and Na ⁺ The defects of red mud and the like still exist, which limit the comprehensive utilization of the red mud and can not fundamentally solve the problems of utilization of large amount of industrial waste residues of the red mud and environmental pollution.

In addition, the Bayer process red mud still contains 10-20% of alumina, and the alumina is greatly wasted when the alumina is directly utilized after dealkalization. The dealkalization method of the red mud in the prior art only considers the removal of sodium oxide, but does not consider the recovery of alumina in the red mud while removing the sodium oxide.

CN104445844A discloses a method for dealkalizing red mud by flue gas and alkaline material, which uses acid gas in flue gas and simulated flue gas to treat Bayer process red mud, the dealkalization efficiency is above 80%, and the alkali liquor in the dealkalization process can be recycled and used for salt extraction or recycling treatment of Bayer process red mud. In addition, according to the fluctuation problem of the composition of the acid gas in the flue gas, the invention provides that on the basis of flue gas dealkalization, an alkaline substance (carbide slag or lime) is used as an auxiliary substance, and the characteristics that the alkaline substance can be subjected to neutralization reaction with the acid substance and exchange reaction with alkali in the red mud are utilized to perform resource utilization on the red mud, the flue gas and the carbide slag, thereby realizing comprehensive treatment and changing waste into valuable. In the embodiment of the invention, the alkali content in the dealkalized red mud still reaches 1.72-2.0 percent, which does not meet the requirements of portland cement plants. The recovery of alumina from red mud is also not considered in this invention.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a process for dealkalizing red mud and recovering alumina by using waste flue gas and waste heat of a cement plant, and simultaneously, the process can also absorb carbon dioxide in the tail flue gas of a cement kiln by using alkali liquor obtained by the dealkalization of the red mud, thereby reducing the emission of the carbon dioxide. The technology utilizes the resources of cement plants to dealkalize the red mud at low cost, and recovers the alkali and the alumina, so that alumina production enterprises realize zero emission of solid waste residues.

The method of the invention comprises the following steps:

1. mixing the red mud and water in an acid reaction tank according to a ratio of 2.5.

2. And (3) feeding the reaction slurry into an alkali reaction tank, adding a sodium hydroxide solution, adjusting the pH value to 9-11, stirring and reacting for 2 hours, wherein the reaction temperature is 70-85 ℃.

3. Mixing the slurry obtained in the step two with the carbide slag in a carbide slag reaction tank according to CaO _{Carbide slag} /Na ₂ O _{Red mud} = 3.5-4.0; heating the slurry in the carbide slag reaction tank to 80-95 ℃, stirring for 60-360 min at the stirring speed of 100-500r/min; standing for 5-10min.

4. And after the reaction is finished, separating by using a solid-liquid separator to generate primary filter residue and primary filtrate.

5. And (3) feeding the primary filter residue into a washing tank for washing, wherein the weight ratio of the filter residue to water, solid and liquid is =1:1.5, stirring for 60-120 min at a stirring speed of 100-500r/min, separating by using a solid-liquid separator after washing, drying filter residues by using low-temperature drying equipment, taking the dried solid as a cement raw material, and sending filtrate into an absorption chamber.

6. And (3) sending the primary filtrate of the solid-liquid separator into a crystallization chamber, cooling to room temperature, and adding aluminum hydroxide seed crystals to crystallize and precipitate aluminum hydroxide in the filtrate.

7. And (4) sending the suspension in the crystallization chamber into a solid-liquid separator for separation, and washing and calcining the separated solid to obtain an alumina solid.

8. Sending the liquid obtained by the solid-liquid separator into an absorption chamber, introducing desulfurized low-temperature kiln tail flue gas into the absorption chamber, and utilizing CO in the desulfurized low-temperature kiln tail flue gas ₂ NaOH in alkali liquor is converted into NaHCO ₃ And/or Na ₂ CO ₃ Separating out sodium salt from the solution by utilizing the characteristic of low solubility of the 2 sodium salts, separating the separated sodium salt by a solid-liquid separator to obtain high-purity sodium salt, returning the filtrate to an alkali reaction tank, and adding NaHCO in the filtrate ₃ Or Na ₂ CO ₃ The enrichment will be recycled.

Wherein, the smoke at the kiln head of the cement rotary kiln is used for direct heating, or the smoke at the kiln tail or the waste heat of the smoke of a cylinder in the kiln is used for indirectly heating the materials in the acid reaction tank, the alkali reaction tank and the carbide slag reaction tank.

In the process, firstly, sodium oxide, aluminum oxide and silicon dioxide in red mud are converted into sodium sulfate, sodium aluminate and sodium silicate through high-temperature acid-base treatment, and further, ca in carbide slag is subjected to replacement reaction through calcium oxide in the carbide slag ²⁺ With SiO in red mud ₃ ^2- ，CO ₃ ^2- ，AlO ^2- The plasma reaction generates precipitate, na + in the red mud is replaced to generate NaOH, and the filtrate comprises sodium hydroxide and sodium aluminate. And cooling the filtrate, hydrolyzing the crystals in the Bayer process to obtain aluminum hydroxide crystals, washing and calcining to obtain aluminum oxide solids, and recovering. Introducing the liquid into the kiln tail flue gas, and utilizing CO in the flue gas ₂ Reacting with sodium hydroxide to obtain Na ₂ CO ₃ And NaHCO ₃ . The obtained filtrate is continuously returned to the alkali reaction tank 2 for circular enrichment, and is separated out from the filtrate after reaching the solubility, and the high-purity sodium salt is recovered through solid-liquid separation.

As a further preferable scheme, in the step eight, the content of carbon dioxide in the flue gas is detected in real time, the alkali liquor demand is dynamically predicted by the control system when the carbon dioxide emission reaches the standard, and the input quantity of the alkali liquor is dynamically controlled by wireless communication.

The device for implementing the process method comprises an acid-acid reaction tank, an alkali reaction tank, a carbide slag reaction tank, a solid-liquid separator, a washing tank, low-temperature drying equipment, a crystallization chamber and an absorption chamber, wherein the three reaction tanks are sequentially connected, an outlet of the carbide slag reaction tank is communicated with the solid-liquid separator, a filter residue outlet for solid-liquid separation is connected with the washing tank, a washing water inlet is formed in the washing tank, a slurry outlet of the washing tank is communicated with the solid-liquid separator, a solid outlet of the solid-liquid separator is communicated with the low-temperature drying equipment, and a filtrate outlet is communicated with the absorption chamber; a filtrate outlet of the solid-liquid separator is communicated with the crystallization chamber, the crystallization chamber is provided with a crystal inlet and a stirring device, an outlet of the crystallization chamber is communicated with the solid-liquid separator, a filtrate outlet of the solid-liquid separator is communicated with the absorption chamber, the absorption chamber is provided with a flue gas inlet and a flue gas outlet, a slurry outlet of the absorption chamber is communicated with the solid-liquid separator, and a filtrate outlet of the solid-liquid separator is connected with the reactor; the acid reaction tank, the alkali reaction tank and the carbide slag reaction tank are all provided with heating jackets, and the jackets are heated by adopting flue gas.

The solid-liquid separator used in the present invention can be implemented by using the same solid-liquid separation apparatus, which is preferably a plate and frame filter press.

Dealkalized red mud filtered by a plate and frame filter press still has a water content of more than 30 percent, and is sticky massive, so the water is not easy to separate, the original drying is similar to sticky materials with larger water content, for example, wet carbide slag (the water content is still more than 30 percent) utilizes a hammer type drying crusher, because the materials are sticky and have large water content, the energy consumption is higher, a large amount of high-temperature smoke is needed, the equipment is frequently blocked, the red mud also contains a large amount of organic flocculates and has larger viscosity than the carbide slag, so no proper low-temperature drying equipment exists up to now, the high-temperature smoke (700-800 ℃) is generally adopted as a drying medium, the energy consumption is higher, the drying cost is high, and the application of the red mud is limited. The low-temperature drying equipment adopts kiln tail flue gas (about 320 ℃) after dust removal as a drying medium, leads the flue gas into a high-pressure air nozzle through a high-temperature air cannon, leads the gas to be swept to a perforated plate at a high speed and at intervals, cuts mud strips into blocks and granules, partially dries cylindrical mud blocks at the same time of cutting, reversely exchanges heat with hot gas flowing upwards in a countercurrent manner in the falling process, and dries the surface. And the red mud falls to a hammer crusher, is further crushed, and is continuously subjected to heat exchange with hot air for drying to finally obtain the granular dealkalized red mud with the water content of less than 5 percent.

The invention simultaneously realizes the high-efficiency recovery of alumina and sodium salt in the red mud by utilizing industrial waste residues, flue gas and heat thereof, and simultaneously removes acidic substances in the flue gas, and the like, and has the following specific advantages and characteristics:

1. the cost of cement production raw materials is reduced: the red mud component is similar to the cement raw material component, and the iron content is higher than that of the common raw material, so the red mud can replace the iron raw material; the red mud belongs to industrial waste residues, and is used at the cost of 0; the fineness of the red mud meets the production requirement of cement clinker, and the grinding cost of the cement raw material is reduced.

2. The cost of cement production fuel is reduced: the red mud contains about 10 percent of organic matters, so that the heat value of the red mud is increased; the red mud contains dicalcium silicate in clinker, so that the quality of cement clinker is improved.

3. The carbon dioxide emission of cement enterprises is reduced and the waste heat recovery utilization rate is improved.

4. The leaching rate of alkali in the red mud is improved while the alumina in the red mud is recovered by adopting an acid treatment method, and the alkali removal rate in the red mud is greatly improved by further combining a calcium replacement method. Meanwhile, the alumina in the red mud is efficiently recovered, the industrial waste is recycled, the environmental pollution caused by the industrial waste is reduced, and the environment is protected.

5. By adopting the low-temperature drying device, the drying moisture cost of the red mud is reduced, and the water content of the red mud is less than 5 percent.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Fig. 2 is a schematic view of the low-temperature drying apparatus of the present invention.

Fig. 3 is a schematic view of a high temperature air cannon of the dryer of the present invention.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the described embodiments are merely a few embodiments of the present application and not all 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 application.

Referring to fig. 1, the device of the invention comprises an acid reaction tank 1, an alkali reaction tank 2, a carbide slag reaction tank 3, solid-liquid separators 4,6,9,11, a washing tank 5, a low-temperature drying device 7, a crystallization chamber 8 and an absorption chamber 10, wherein the three reaction tanks are connected in sequence, an outlet of the carbide slag reaction tank 3 is communicated with the solid-liquid separator 4, a filter residue outlet of the solid-liquid separator 4 is connected with the washing tank 5, the washing tank 5 is provided with a washing water inlet, a slurry outlet of the washing tank 5 is communicated with the solid-liquid separator 6, a solid outlet of the solid-liquid separator 6 is communicated with the low-temperature drying device 7, and a filtrate outlet is communicated with the absorption chamber 10; a filtrate outlet of the solid-liquid separator 4 is communicated with a crystallization chamber 8, the crystallization chamber 8 is provided with a crystal inlet and a stirring device, an outlet of the crystallization chamber 8 is communicated with a solid-liquid separator 9, a filtrate outlet of the solid-liquid separator 9 is communicated with an absorption chamber 10, the absorption chamber 10 is provided with a flue gas inlet and an outlet, a slurry outlet of the absorption chamber 10 is communicated with a solid-liquid separator 11, and a filtrate outlet of the solid-liquid separator 11 is connected with the reactor 2; the acid reaction tank 1, the alkali reaction tank 2 and the carbide slag reaction tank 3 are all provided with heating jackets, and the jackets are internally heated by adopting flue gas.

The low-temperature drying device 7 comprises a dryer 16, 3-6 groups of screw feeders 12 are uniformly arranged at the upper middle part of a shell of the dryer, wear-resistant porous plates 13 are arranged at ports of the screw feeders 12, a high-temperature air cannon 15 extends downwards from the center of the top of the shell of the dryer 16, the top of the high-temperature air cannon 15 is an industrial waste flue gas inlet, a spray head is arranged at the lower end part of the high-temperature air cannon 15, a hammer crusher 14 is arranged at the lower part of the shell of the dryer 16, a blanking groove 17 is positioned at the bottom of the dryer 16, and a flue gas inlet is further formed in the bottom of the shell of the dryer 16.

The top of the dryer 16 is connected with a cyclone separator 19 through a pipeline, the top of the cyclone separator 19 is connected with a bag type dust collector 20, and an induced draft fan 21 is arranged at the downstream of the bag type dust collector 20. The solid material is conveyed by a belt conveyor 18, and the gas is processed by a cyclone separator 19, a bag type dust collector 20 and a draught fan 21 and then enters the absorption chamber 10.

The shower nozzle by wear-resisting, heat-resisting material preparation, cavity, rotatable, the top sets up 3 ~ 6 spouts, the spout sets up to lamellar narrow passageway, big-end-up, the directional wear-resisting perforated plate 13 of spout, spout gaseous being fan-shaped sweeps spouts wear-resisting perforated plate 13, a plurality of reflection arris faces are set to the shower nozzle top, but the material of rebounding increases material heat transfer time.

The method and the equipment for drying the red mud at low temperature shown in the figure 2 have the following processes:

1. the red mud is extruded, cut and fed by a circular tube type spiral feeder 12, and 3-6 groups of circular tube type spiral feeders are uniformly arranged on a shell of a dryer 16 for feeding.

2. The port of the circular tube type screw feeder 12 is provided with a wear-resistant porous plate 13 with the aperture of 1-5 cm, and the red mud is extruded by the screw feeder 12 to pass through the circular hole of the porous plate 13, so that the red mud is changed into a strip.

3. High-temperature gas is introduced from a high-pressure air nozzle of the high-temperature air cannon 15, the gas can be provided by kiln tail flue gas (about 320 ℃) after dust removal, the nozzle enables the gas to be swept to the porous plate 13 at high speed and intervals in a sector mode, the mud strips are cut into blocks and particles, and the columnar mud blocks are partially dried during cutting. The intermittent air cannon 15 purges the discharge port to cut the extrusion material into blocks and particles. And adjusting the purging time interval and controlling the particle size.

4. The blocky mud block is reversely heat-exchanged with the hot gas flowing upwards in a countercurrent manner in the falling process, the flow velocity is controlled, and the drying is continued. Blowing off the particle mud, descending, exchanging heat with air, and drying the surface.

5. The blocky mud blocks continuously fall down, are crushed by the hammer crusher 14 and continuously fall down, and continuously exchange heat with the countercurrent high-temperature gas and are dried. The grinding roller is broken and continuously descends to contact with hot air, and heat exchange is continuously carried out.

6. Part of small particles rise with the gas to enter a cyclone dust collector 19, and most of materials enter a blanking groove 17 due to gravity, enter a belt 18 through the blanking groove 17 to be conveyed, and are conveyed to material storage.

7. The small particles pass through a cyclone dust collector 19 and a bag type dust collector 20, dust is collected and enters 18 belts for conveying, and purified air enters and is emptied through a draught fan 21.

Example 1

A process method for dealkalizing red mud and simultaneously recovering alumina by using waste flue gas and waste heat of a cement plant comprises the following steps:

1. mixing the red mud and water in an acid reaction tank 1 according to a ratio of 2.5.

2. And (3) feeding the reaction slurry into an alkali reaction tank 2, adding a sodium hydroxide solution, adjusting the pH value to 9, stirring and reacting for 2 hours, wherein the reaction temperature is 70 ℃.

3. Mixing the slurry obtained in the step two with the carbide slag in a carbide slag reaction tank 3 according to CaO _{Carbide slag} /Na ₂ O _{Red mud} =3.5; heating the slurry in the carbide slag reaction tank 3 to 80 ℃, and stirring for 360min at a stirring speed of 200r/min; standing for 5min.

4. After the reaction is finished, the solid-liquid separator 4 is used for separation, and primary filter residue and primary filter liquor are generated.

5. And (3) feeding the primary filter residue into a washing tank 5 for washing, wherein the weight ratio of the filter residue to water, solid and liquid is =1 at normal temperature: 1.5, stirring for 60min at a stirring speed of 200r/min, separating by using a solid-liquid separator 6 after washing, drying filter residues by using low-temperature drying equipment 7, and sending filtrate into an absorption chamber 10. And drying to obtain solid serving as a cement raw material. Wherein the low-temperature drying device 7 utilizes the kiln tail flue gas waste heat at the temperature of about 250-320 ℃ to ensure that the moisture of the dried red mud is less than 5 percent. The kiln tail flue gas after being dried and utilized is introduced into the absorption chamber 10 after being subjected to a desulfurization process.

6. And (3) sending the primary filtrate of the solid-liquid separator 4 into a crystallization chamber 8, cooling to room temperature, and adding aluminum hydroxide seed crystals to precipitate aluminum hydroxide crystals in the filtrate.

7. The suspension in the crystallization chamber 8 is sent to a solid-liquid separator 9 for separation, and the separated solid is washed and calcined to obtain an alumina solid.

8. The liquid obtained by the solid-liquid separator 9 is sent into an absorption chamber 10, desulfurized low-temperature kiln tail flue gas is introduced into the absorption chamber 10, and CO in the flue gas is utilized ₂ NaOH in alkali liquor is converted into NaHCO ₃ Or Na ₂ CO ₃ Separating out sodium salt from the solution by utilizing the characteristic of low solubility of the 2 sodium salts, separating the separated sodium salt by a solid-liquid separator 11 to obtain high-purity sodium salt, returning filtrate to an alkali reaction tank 2,NaHCO in the filtrate ₃ Or Na ₂ CO ₃ The enrichment will be recycled.

Wherein, the smoke at the kiln head of the cement rotary kiln is used for direct heating, or the smoke at the kiln tail or the waste heat of a cylinder in the kiln is used for indirectly heating the materials in the acid reaction tank 1, the alkali reaction tank 2 and the carbide slag reaction tank 3.

And step eight, detecting the content of carbon dioxide in the flue gas in real time, dynamically predicting the alkali liquor demand when the carbon dioxide emission reaches the standard through a control system, and dynamically controlling the input quantity of the alkali liquor through wireless communication.

And the solid-liquid separators of the fourth, fifth, seventh and eighth steps are completed by using the same solid-liquid separation equipment, and the solid-liquid separation equipment is a plate and frame filter press.

The dealkalization effect of the red mud is shown in the following table:

dealkalized red mud Na ⁺ =0.62%, alkali extraction =93.7%, and alumina recovery =90.2%.

Example 2

A process method for dealkalizing red mud and simultaneously recovering alumina by using waste flue gas and waste heat of a cement plant is characterized by comprising the following steps:

1. mixing the red mud and water in an acid reaction tank 1 according to a ratio of 4.

2. And (3) feeding the reaction slurry into an alkali reaction tank 2, adding a sodium hydroxide solution, adjusting the pH value to 11, stirring and reacting for 2 hours, wherein the reaction temperature is 85 ℃.

3. Mixing the slurry obtained in the step two with the carbide slag in a carbide slag reaction tank 3 according to CaO _{Carbide slag} /Na ₂ O _{Red mud} =4.0; heating the slurry in the carbide slag reaction tank 3 toStirring for 60min at 95 ℃ and the stirring speed of 500r/min; standing for 10min.

5. And (3) feeding the primary filter residue into a washing tank 5 for washing at normal temperature, wherein the weight ratio of the filter residue to water is =1.5, stirring for 120min at the stirring speed of 500r/min, separating the filter residue by using a solid-liquid separator 6 after washing, drying the filter residue by using low-temperature drying equipment 7, and feeding the filtrate into an absorption chamber 10. And drying to obtain solid serving as a cement raw material. Wherein the low-temperature drying device 7 utilizes the kiln tail flue gas waste heat at the temperature of about 250-320 ℃ to ensure that the moisture content of the dried red mud is less than 5 percent. The kiln tail flue gas after being dried and utilized is introduced into the absorption chamber 10 after being subjected to a desulfurization process.

6. And (3) sending the primary filtrate of the solid-liquid separator 4 into a crystallization chamber 8, cooling to room temperature, and adding aluminum hydroxide seed crystals to crystallize and precipitate aluminum hydroxide in the filtrate.

8. The liquid obtained by the solid-liquid separator 9 is sent into an absorption chamber 10, desulfurized low-temperature kiln tail flue gas is introduced into the absorption chamber 10, and CO in the flue gas is utilized ₂ Converting NaOH in alkali liquor into NaHCO ₃ Or Na ₂ CO ₃ Separating out sodium salt from the solution by utilizing the characteristic of low solubility of the 2 sodium salts, separating the separated sodium salt by a solid-liquid separator 11 to obtain high-purity sodium salt, returning filtrate to an alkali reaction tank 2, and adding NaHCO in the filtrate ₃ Or Na ₂ CO ₃ Enrichment will be cycled. The content of carbon dioxide in the flue gas is detected in real time, alkali liquor demand is dynamically predicted by the control system when the carbon dioxide emission reaches the standard, and the input quantity of the alkali liquor is dynamically controlled through wireless communication.

The dealkalization effect of the red mud is shown in the following table:

dealkalized red mud Na ⁺ =0.58%, alkali extraction =94.3%, and alumina recovery =87.3%.

Example 3

The dealkalized red mud has low alkali content, can avoid the blockage phenomenon caused by the adhesion of alkali compounds to the cone part of the preheater caused in the clinker sintering process, can also avoid the alkali mineral and solid solution generated by the reaction of alkali and clinker, and avoids the phenomena of partial expansion, structural deformation, cracking and the like caused by the heat release of the alkali aggregate reaction. This example examines the properties of cement clinker prepared from the dealkalized red mud prepared in examples 1 and 2.

Preparing cement ingredients from red mud:

name of raw materials	Limestone	Sandstone powder	Sandstone waste	Iron ore sludge	Dry red mud	Raw material
							Ratio of ingredients	80.00	6.00	4.00	3.00	7.00	100

Setting the batching rate of red mud prepared cement:

KH＝0.87；SM＝2.07；IM＝1.58

the preparation process of the cement clinker comprises the following steps:

adding the prepared raw material into a rotary kiln preheater, preheating at the temperature lower than 950 ℃ in the preheater, calcining for 15 minutes at the temperature of 1300-1400 ℃ in a rotary kiln, and discharging and cooling clinker.

Performance of cement clinker:

the results show that the cement clinker prepared by the dealkalized red mud completely conforms to the regulations of the national standard GB/T21372-2008.

It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, various alterations, modifications and/or variations may be made to the present invention by those skilled in the art after reading the technical content of the present invention, and all such equivalents may fall within the scope of the present invention as defined by the appended claims.

Claims

1. A process method for dealkalizing red mud and simultaneously recovering alumina by using waste flue gas and waste heat of a cement plant is characterized by comprising the following steps of:

1. mixing the red mud and water in an acid reaction tank (1) according to a ratio of 2.5;

2. sending the reaction slurry into an alkali reaction tank (2), adding a sodium hydroxide solution, adjusting the pH value to 9-11, stirring and reacting for 2 hours, wherein the reaction temperature is 70-85 ℃;

3. mixing the slurry obtained in the step two with the carbide slag in a carbide slag reaction tank (3) according to CaO _{Carbide slag} /Na ₂ O _{Red mud} = 3.5-4.0; heating the slurry in the carbide slag reaction tank (3), heating to 80-95 ℃, and stirring for 60-360 min at a stirring speed of 100-500r/min; standing for 5-10min;

4. after the reaction is finished, a solid-liquid separator (4) is used for separation to generate primary filter residue and primary filtrate;

5. and (3) feeding the primary filter residue into a washing pool (5) for washing, wherein the solid-liquid weight ratio of the filter residue to water is =1:1.5, stirring for 60-120 min at a stirring speed of 100-500r/min, separating by using a solid-liquid separator (6) after washing, drying filter residues by using low-temperature drying equipment (7), taking the dried solid as a cement raw material, and sending filtrate into an absorption chamber (10); the low-temperature drying equipment (7) comprises a dryer (16), 3-6 groups of screw feeders (12) are uniformly arranged at the middle upper part of a shell of the dryer, a wear-resistant porous plate (13) is arranged at the port of each screw feeder (12), a high-temperature air cannon (15) extends downwards from the center of the top of the shell of the dryer (16), the top of the high-temperature air cannon (15) is an industrial waste flue gas inlet, a spray head is arranged at the lower end part of the high-temperature air cannon (15), a hammer crusher (14) is arranged at the lower part of the shell of the dryer (16), a blanking groove (17) is positioned at the bottom of the dryer (16), and a flue gas inlet is also formed at the bottom of the shell of the dryer (16); the top of the dryer (16) is connected with a cyclone separator (19) through a pipeline, the top of the cyclone separator (19) is connected with a bag type dust collector (20), and an induced draft fan (21) is arranged at the downstream of the bag type dust collector (20); solid materials are conveyed by a belt conveyor (18), and gas is treated by a cyclone separator (19), a bag type dust collector (20) and an induced draft fan (21) and then enters an absorption chamber (10); the low-temperature drying equipment adopts the kiln tail flue gas after dust removal as a drying medium, and the flue gas is introduced into a high-pressure air nozzle through a high-temperature air cannon, so that the gas is swept to a perforated plate at a high speed and at intervals in a sector manner, mud strips are cut into blocks and particles, and the columnar mud blocks are partially dried, reversely exchange heat with hot gas flowing upwards in a countercurrent manner in the falling process, and are dried on the surface; dropping the red mud into a hammer crusher, further crushing the red mud, and continuously performing heat exchange and drying with hot air to finally obtain granular dealkalized red mud with the water content of less than 5 percent;

6. sending the primary filtrate of the solid-liquid separator (4) into a crystallization chamber (8), cooling to room temperature, and adding aluminum hydroxide seed crystals to crystallize and precipitate aluminum hydroxide in the filtrate;

7. sending the suspension in the crystallization chamber (8) into a solid-liquid separator (9) for separation, and washing and calcining the separated solid to obtain an alumina solid;

8. the liquid obtained by the solid-liquid separator (9) is sent into an absorption chamber (10), desulfurized low-temperature kiln tail flue gas is introduced into the absorption chamber (10), and CO in the flue gas is utilized ₂ Converting NaOH in alkali liquor into NaHCO ₃ And/or Na ₂ CO ₃ Precipitation of NaHCO sodium salt ₃ And/or Na ₂ CO ₃ Separating the separated sodium salt by a solid-liquid separator (11) to obtain high-purity sodium salt, returning the filtrate to an alkali reaction tank (2), and adding NaHCO in the filtrate ₃ Or Na ₂ CO ₃ Will be cyclically enriched;

wherein, the smoke at the kiln head of the cement rotary kiln is used for direct heating, or the smoke at the kiln tail or the waste heat of a cylinder in the kiln is used for indirectly heating the materials in the acid reaction tank (1), the alkali reaction tank (2) and the carbide slag reaction tank (3); and step eight, detecting the content of carbon dioxide in the flue gas in real time, dynamically predicting the alkali liquor demand when the carbon dioxide emission reaches the standard through a control system, and dynamically controlling the input quantity of the alkali liquor through wireless communication.

2. The process method for dealkalizing red mud and simultaneously recovering aluminum oxide by using the waste flue gas and the waste heat thereof in the cement plant according to claim 1, which is characterized by comprising the following steps: and the solid-liquid separators of the fourth, fifth, seventh and eighth steps are completed by using the same solid-liquid separation equipment, and the solid-liquid separation equipment is a plate and frame filter press.

3. The process method for dealkalizing red mud and simultaneously recovering aluminum oxide by using the waste flue gas and the waste heat of the cement plant according to claim 1, which is characterized by comprising the following steps: wherein the low-temperature drying equipment utilizes the kiln tail flue gas waste heat at 250-320 ℃ to dry the red mud to ensure that the moisture content is less than 5 percent; and the dried and utilized kiln tail flue gas is introduced into an absorption chamber (10) after being subjected to a desulfurization process.