CN112520769A

CN112520769A - 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: CN112520769A
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: 2021-03-19
Anticipated expiration: 2040-12-08
Also published as: CN112520769B

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 treatment²⁺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, and the cement raw material is obtained at the same timeSodium salt, which recycles residual alumina and utilizes industrial waste 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:

the red mud is polluting waste residue discharged when aluminum oxide is extracted in the aluminum industry, and generally 1.0-2.0 tons of red mud are additionally generated when 1 ton of aluminum oxide is produced 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 much water, the concentration of alkali liquor is low, the recovery is difficult, and the time consumption is long; the heat consumption of the calcium ion replacement method is high; the wet carbonization method has high requirement on the compression resistance of equipment; the acid neutralization method in the leaching method consumes a large amount of acid and has the defects of red mud and the like, which limit the comprehensive utilization of the red mud and cannot fundamentally solve the problems of utilization of large 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 by directly utilizing the dealkalized red mud. 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 combining flue gas with alkaline materials, wherein the dealkalizing efficiency is above 80 percent by treating Bayer process red mud with acidic gas in flue gas and simulated flue gas, and alkali liquor in the dealkalizing 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 a portland cement plant. 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:

mixing red mud and water in an acid reaction tank according to the ratio of 2.5: 1-4: 1, adding sulfuric acid, adjusting the pH value to 2-4, stirring and reacting for 3-6 hours, wherein the reaction temperature is 70-85 ℃.

Secondly, 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 ℃.

Thirdly, mixing the slurry obtained in the second step with the carbide slag in a carbide slag reaction tank according to CaO_{Carbide slag}/Na₂O_{Red mud}3.5-4.0 percent; heating the slurry in the carbide slag reaction tank to 80-95 ℃, and stirring60-360 min, and the stirring speed is 100-; standing for 5-10 min.

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

Fifthly, feeding the primary filter residue into a washing tank for washing, wherein the weight ratio of the filter residue to water is 1: 1.5, stirring for 60-120 min at the stirring speed of 100-.

Sixthly, 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.

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

Eighthly, 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 flue gas₂Converting NaOH in alkali liquor into NaHCO₃And/or Na₂CO₃Separating 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 filtrate₃Or Na₂CO₃The 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 with calcium oxide in the carbide slag²⁺With SiO in red mud₃ ^2-，CO₃ ^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. The filtrate is cooled and then passes through BayerIn the method, the crystal is hydrolyzed to obtain aluminum hydroxide crystal, and the aluminum hydroxide crystal is washed and calcined to obtain aluminum oxide solid for recovery. Introducing the liquid into the kiln tail flue gas, and utilizing CO in the flue gas₂Reacting with sodium hydroxide to obtain Na₂CO₃And NaHCO₃. 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 when the carbon dioxide emission reaches the standard is dynamically predicted through the control system, and the input quantity of the alkali liquor is dynamically controlled through 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.

The dealkalized red mud filtered by the plate and frame filter press still has the water content of more than 30 percent, the water is not easy to be separated because of sticky blocks, the original drying is similar to sticky materials with larger water content, such as wet carbide slag (the water content is still more than 30 percent), a hammer type drying crusher is utilized, the materials are sticky and have large water content, so 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 flocculate and has larger viscosity than the carbide slag, so no proper low-temperature drying equipment exists so far, 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. Reducing the carbon dioxide emission of cement enterprises and improving the waste heat recovery utilization rate.

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%.

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; 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 flue gas is adopted to heat the jackets.

The low-temperature drying device 7 comprises a dryer 16, 3-6 groups of screw feeders 12 are uniformly arranged on the upper middle portion 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 of the high-temperature air cannon 15, a hammer crusher 14 is arranged on the lower portion of the shell of the dryer 12, a discharging groove 17 is located at the bottom of the dryer 16, and a flue gas inlet is further formed in the bottom of.

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 thin slice narrow passage, big end outside the inner is big, the directional wear-resisting perforated plate 13 of spout, blowout gas is fan-shaped sweeps and 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 screw feeder 12, and 3-6 groups of circular tube type screw feeders are uniformly arranged on a shell of a dryer 16 for feeding.

2. The wear-resistant porous plate 13 is arranged at the port of the circular tube type screw feeder 12, the aperture is 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 shape.

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 the particle mud, 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:

firstly, mixing red mud and water in an acid reaction tank 1 according to the ratio of 2.5:1, adding sulfuric acid, adjusting the pH value to 2.5, stirring and reacting for 6 hours, wherein the reaction temperature is 70 ℃.

Secondly, 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 ℃.

Thirdly, mixing the slurry obtained in the second step with the carbide slag in a carbide slag reaction tank 3 according to CaO_{Carbide slag}/Na₂O_{Red mud}3.5; heating the slurry in the carbide slag reaction tank 3 to 80 ℃, and stirring for 360min at the stirring speed of 200 r/min; standing for 5 min.

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

Fifthly, feeding the primary filter residue into a washing tank 5 for washing, wherein the weight ratio of the filter residue to water is 1: 1.5, stirring for 60min at the 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. The low-temperature drying equipment 7 utilizes kiln tail flue gas waste heat at the temperature of about 250-320 ℃ to dry the red mud, and the moisture content of the dried red mud is less than 5%. The kiln tail flue gas after being dried and utilized is introduced into the absorption chamber 10 after being subjected to a desulfurization process.

Sixthly, 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.

Seventhly, the suspension in the crystallization chamber 8 is sent to a solid-liquid separator 9 for separation, and the solid obtained by separation is washed and calcined to obtain alumina solid.

Eighthly, sending the liquid obtained by the solid-liquid separator 9 into an absorption chamber 10, introducing desulfurized low-temperature kiln tail flue gas into the absorption chamber 10, and utilizing CO in the flue gas₂Converting NaOH in alkali liquor into NaHCO₃Or Na₂CO₃Separating 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 filtrate₃Or Na₂CO₃The 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％The alkali extraction rate was 93.7%, and the alumina recovery rate was 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 of:

firstly, mixing red mud and water in an acid reaction tank 1 according to a ratio of 4:1, adding sulfuric acid, adjusting the pH value to 4, stirring and reacting for 3 hours, wherein the reaction temperature is 85 ℃.

Secondly, 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 ℃.

Thirdly, mixing the slurry obtained in the second step with the carbide slag in a carbide slag reaction tank 3 according to CaO_{Carbide slag}/Na₂O_{Red mud}4.0 percent; heating the slurry in the carbide slag reaction tank 3 to 95 ℃, and stirring for 60min at the stirring speed of 500 r/min; standing for 10 min.

Fifthly, feeding the primary filter residue into a washing tank 5 for washing, stirring at normal temperature for 120min at a solid-liquid weight ratio of the filter residue to water of 1.5 at a 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. The low-temperature drying equipment 7 utilizes kiln tail flue gas waste heat at the temperature of about 250-320 ℃ to dry the red mud, and the moisture content of the dried red mud is less than 5%. The kiln tail flue gas after being dried and utilized is introduced into the absorption chamber 10 after being subjected to a desulfurization process.

Eighthly, sending the liquid obtained by the solid-liquid separator 9 into an absorption chamber 10, introducing desulfurized low-temperature kiln tail flue gas into the absorption chamber 10, and utilizing CO in the flue gas₂Converting NaOH in alkali liquorIs NaHCO₃Or Na₂CO₃Separating 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 filtrate₃Or Na₂CO₃The enrichment will be recycled. 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:

composition (I)	SiO₂	AL₂O₃	Fe₂O₃	CaO	Na₂O	Others	Total up to
								Raw red mud	11.38	18.07	41.58	6.57	10.24	12.16	100
Dealkalized red mud	5.36	2.30	73.62	8.63	0.58	9.51	100

Dealkalized red mud Na⁺0.58%, the alkali extraction rate 94.3%, and the alumina recovery rate 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 alkali and clinker from reacting to generate alkali minerals and solid solution, and avoids the phenomena of local expansion, structural deformation and cracking and the like caused by the heat release of 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 materials 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:

from the results, the cement clinker prepared by the dealkalized red mud completely meets 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:

firstly, mixing red mud and water in an acid reaction tank (1) according to the ratio of 2.5: 1-4: 1, adding sulfuric acid, adjusting the pH value to 2-4, stirring and reacting for 3-6 hours, wherein the reaction temperature is 70-85 ℃.

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

Thirdly, mixing the slurry obtained in the second step with the carbide slag in a carbide slag reaction tank (3) according to CaO_{Carbide slag}/Na₂O_{Red mud}3.5-4.0 percent; heating the slurry in the carbide slag reaction tank (3), heating to 80-95 ℃, stirring for 60-360 min at a stirring speed of 100-; standing for 5-10 min.

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

Fifthly, feeding the primary filter residue into a washing tank (5) for washing, wherein the weight ratio of the filter residue to water is 1: 1.5, stirring for 60-120 min at a stirring speed of 100-.

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

Seventhly, the suspension in the crystallization chamber (8) is sent to a solid-liquid separator (9) for separation, and the solid obtained by separation is washed and calcined to obtain alumina solid.

Eighthly, sending the liquid obtained by the solid-liquid separator (9) into an absorption chamber (10), introducing desulfurized low-temperature kiln tail flue gas into the absorption chamber (10), and utilizing CO in the flue gas₂Converting NaOH in alkali liquor into NaHCO₃And/or Na₂CO₃Separating 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 the filtrate to the reaction tank (2), and adding NaHCO in the filtrate₃Or Na₂CO₃The 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).

2. The process method for dealkalizing red mud and simultaneously recovering alumina by utilizing waste flue gas and waste heat of a cement plant according to claim 1, which is characterized by comprising the following steps of: 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.

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

4. 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: the low-temperature drying equipment utilizes kiln tail flue gas waste heat at the temperature of about 250-320 ℃ to dry the red mud to ensure that the moisture content is less than 5%. The kiln tail flue gas after being dried and utilized is introduced into the absorption chamber 10 after being subjected to a desulfurization process.