Method for preparing negative carbon cementitious material by dealkalization and carbon fixation of high calcium red mud

Abstract

The present invention provides a technology for preparing negative carbon cementitious materials by multiphase flow reaction distillation of high-calcium red mud and de-alkali carbonization. The red mud slurry is pumped to the top of a reaction distillation tower, and is countercurrently contacted with flue gas through multi-stage flow-through tower plates and fillers. The acidic gas in the flue gas and the alkali in the slurry are efficiently reacted and distilled, and the flue gas with dust removal, decarbonization and desulfurization flows out from the top of the reaction distillation tower, and the de-alkali carbonized red mud slurry flows out from the bottom of the reaction distillation tower and the concentrated brine is removed; the dehydrated red mud slurry is diluted again with part of the washing brine and then pumped to the top of a water washing and desalting tower for countercurrent water washing and desalting, and a part of the washing brine flowing out of the top of the water washing and desalting tower is used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section; the desalted red mud slurry flowing out of the bottom of the water washing and desalting tower can be used as a cementitious material in the presence of an acidic composite activator after being dehydrated.

Description

1. Technical Field

[0001] The invention provides a method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud, belonging to the field of environmental protection. 2. Background technology

[0002] Red mud is a polluting, high-alkali waste residue discharged when the electrolytic aluminum industry extracts alumina. Generally, for every ton of alumina produced, 1.0 to 2.0 tons of red mud are produced. Resource utilization is internationally recognized as an effective means of red mud utilization. Although five major utilization technologies have been developed at home and abroad, including powder materials, element extraction, cementitious materials, road materials and ceramic materials, they are currently in the technical growth stage and have not yet been commercialized.

[0003] The high-value utilization of high-calcium red mud containing more than 40% calcium oxide produced by the sintering method and the hybrid method has always been difficult to solve. The fundamental reason is that the sodium oxide content in the high-calcium red mud exceeds the standard. Red mud is a highly alkaline solid waste with a pH as high as 11-13. The alkaline substances in red mud are mainly soluble alkalis (free alkalis) and insoluble alkalis (bound alkalis). Free alkalis mainly include NaOH, Na2CO3, NaHCO3, NaAl(OH)4, Na2SiO3, etc. Insoluble alkalis include calcite, cancrinite, hydrated garnet, sodalite and tricalcium aluminate. Cancrinite is the main alkaline substance. Sodium oxide (Na2O) is the main alkaline oxide in its chemical composition, with a content of up to 12.91%, mainly in the form of caustic soda, sodium aluminate and sodium aluminosilicate. Soluble alkali can be removed by passing CO2 or washing with water at room temperature and pressure, but this part accounts for a small proportion, and most of it is insoluble alkali, especially sodium silicate slag, which accounts for a large proportion, about 35-45%. The removal of this part of alkali is one of the most difficult problems to solve in the world, and it is also a key issue affecting the further large-scale utilization of red mud. In addition, cementitious materials in building materials are widely used artificial materials. Among them, the production of cement and lime, which are more expensive, is a high-energy consumption, high-material consumption, and high-carbon emission industry. It is the second largest carbon emission source that my country urgently needs to decarbonize to achieve its carbon neutrality strategy. At present, the production process of red mud-based alkali-activated cheap cementitious materials is simple, does not require firing, and has low cost. It can effectively improve the 3-day and 28-day compressive strength of concrete. Replacing cement and lime is crucial for the low-carbon transformation of the building materials industry. It is currently a hot research direction for the high-value utilization of red mud. However, there are deficiencies and defects such as autogenous shrinkage far greater than that of ordinary Portland cement, alkali-aggregate reaction and surface alkali efflorescence that affect the durability of products, especially the interface bonding performance between blocks of alkali-activated cementitious materials. These deficiencies and defects have become a bottleneck for the promotion and application of red mud-based alkali-activated cheap cementitious materials. There is an urgent need to develop new red mud-based activated cementitious materials and their acidic activators.

[0004] As a high-energy-consuming and high-pollution industry, electrolytic aluminum is equipped with large-scale thermal power generation. With the 3060 dual carbon target proposed, it is currently facing the pressure of carbon emission reduction and ultra-low emissions. Using acidic gases such as CO2, SOx and NOx in flue gas for red mud dealkalization can achieve acid-base neutralization and waste treatment, and at the same time efficiently and low-cost solve the two major problems of red mud dealkalization and flue gas decarbonization and ultra-low emissions. Alcoa in Western Australia has applied CO2 dealkalization on a large scale, adding gaseous and liquid CO2 to thickened red mud slurry, and CO2 reacts with the alkaline components in the slurry to achieve the purpose of dealkalization. However, the gas dispersion method of passing flue gas into the red mud slurry or the red mud slurry spraying method currently used has a dealkalization rate of less than 50%. In addition, since SOx is more acidic than CO2, it is easy to react with insoluble alkaline substances, which can greatly increase the dealkalization rate, but the existing flue gas dealkalization process has not yet achieved flue gas graded utilization, causing insoluble alkaline substances to become a stubborn problem in red mud dealkalization. Therefore, it is urgent to develop red mud flue gas multiphase flow reactive distillation dealkalization and carbon fixation technology and equipment, break through industrial bottlenecks such as efficient utilization of SOx / CO2 by reaction activity classification, slurry blockage, efficient dispersed mass transfer and reaction, and build new technologies for the high-value utilization of red mud resources industry chain to provide guarantees for the sustainable and high-quality development of the electrolytic aluminum industry. 3. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing red mud-based alkali-activated cementitious material technology and propose a method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud. The method not only solves the problem of cheap and efficient removal of insoluble alkaline substances from red mud, but also creates conditions for preparing negative carbon cementitious materials by acid activation of red mud; it also realizes efficient utilization of acidic gases in flue gas according to reaction activity classification, and solves the problem of decarbonization and ultra-low emission of combustion flue gas with high efficiency and low cost; at the same time, an acidic activator is used to solve the problems of autogenous shrinkage of cheap red mud-based alkali-activated cementitious materials being much greater than that of ordinary silicate cement, alkali-aggregate reaction and surface alkali-induced degradation, which affect the durability of products, especially the shortcomings and defects of affecting the interface bonding performance between blocks of alkali-activated cementitious materials; in addition, the acidity (H + ) is too high, resulting in corrosion and foaming problems, as well as the defect of slow salt activation reaction.

[0006] The technical solution of the present invention:

[0007] The method for preparing negative carbon cementitious material by dealkalization and carbon fixation of high-calcium red mud provided by the present invention is characterized in that a red mud slurry at 10-100°C is pumped to the top of a reaction distillation tower, and is countercurrently contacted with a 30-180°C combustion flue gas introduced from the bottom of the tower through a flow-through tower plate or filler with 1-30 theoretical plates, and the feed ratio of the flue gas to the red mud slurry is 500-3000:1 (volume ratio); in the reaction distillation tower, the CO2, SOx and NOx acidic gases in the flue gas are subjected to efficient reaction distillation with NaO, KO and alkaline salts thereof in the slurry, SOx and NOx mainly react with insoluble alkaline substances in the lower part of the tower, and CO2 mainly reacts with soluble The red mud slurry is reacted with alkaline substances to reduce the pH value of the red mud slurry from 11-14 to no more than 8, the flue gas with dust removal, decarbonization and desulfurization flows out from the top of the reaction distillation tower, and the red mud slurry with dealkali and carbon fixation flows out from the bottom of the reaction distillation tower and the concentrated brine is removed; the dehydrated red mud slurry is diluted with part of the washing brine again, and then pumped to the top of the water washing and desalting tower for countercurrent water washing and desalting, and part of the washing brine flowing out of the top of the water washing and desalting tower is used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section; after the desalted red mud slurry flowing out of the bottom of the water washing and desalting tower is dehydrated, it can replace cement and lime as a cementitious material under the action of 0.01%-1% (weight) of an acidic composite activator.

[0008] The reactive distillation tower is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plates is 250-900mm. A combustion flue gas distributor is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and a red mud slurry outlet is arranged at the bottom of the tower.

[0009] The CO2 content in the combustion flue gas is 12%-25%, the SOx content is 0-50000PPm, the NOx content is 0-3000PPm, and the flow rate in the flue gas tower is 0.5-3.0m / s.

[0010] The concentration of red mud slurry is 5%-60% and the spray density in the tower is 5-120m 3 / m 2 ·h.

[0011] The water washing desalination tower is a flow-through plate tower, a packed tower or an empty tower.

[0012] The acidic composite activator is an inorganic and organic composite activator, and its weight composition is 15%-30% sulfuric acid, 10%-20% furan resin, 10%-20% sodium hexametaphosphate, 5%-15% sodium dodecylbenzene sulfonate, 33%-5% Al2(SO4), and 0-5% FeSO4. When preparing, firstly dissolve sodium hexametaphosphate, Al2(SO4)3, FeSO4, sodium dodecylbenzene sulfonate and furan resin in a reaction kettle with water, stir evenly, then slowly add concentrated sulfuric acid, and use it as the acidic composite activator after cooling.

[0013] The present invention will be described in detail with reference to embodiments. 4. Description of the drawings

[0014] Attached Figure 1 It is a schematic diagram of the present invention. The drawings of the accompanying drawings are as follows:

[0015] 1. Mud pump 2. Flue gas distributor 3. Reaction distillation tower 4. Filter press 5. Mixed mud pump 6. Water washing and desalination tower 7. Soft water distributor 8. Dehydration filter press.

[0016] The process characteristics of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments. 5. Specific implementation methods

[0017] Embodiment: Red mud at 10-100° C. is delivered to the top of a reaction distillation tower (3) through a slurry pump (1), and is countercurrently contacted with combustion flue gas at 30-180° C. introduced from a flue gas distributor (2) at the bottom of the tower through a flow-through tower plate or filler with 1-30 theoretical plates, and the feed ratio of flue gas to red mud slurry is 500-3000:1 (volume ratio); in the reaction distillation tower (3), the acidic gases CO2, SOx and NOx in the flue gas react with NaO, KO and their alkaline salts in the slurry for efficient reaction distillation, SOx and NOx mainly react with insoluble alkaline substances in the lower part of the tower, and CO2 mainly reacts with soluble alkaline substances in the upper part of the tower, thereby reducing the pH value of the red mud slurry from 11-14 to no more than 8, and removing dust and removing pollutants. The carbon-desulfurized flue gas flows out from the top of the reaction distillation tower (3), and the alkali-free carbon-fixed red mud slurry flows out from the bottom of the reaction distillation tower, and the concentrated brine is removed by the filter press (4); the dehydrated red mud slurry is diluted again with part of the water-washing brine, and then pumped to the top of the water-washing desalination tower (6) by the mixed mud pump (5), and is counter-currently washed and desalted with the soft water introduced by the soft water distributor (7); a part of the water-washing brine flowing out of the top of the water-washing desalination tower (6) is used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section; the desalted red mud slurry flowing out of the bottom of the water-washing desalination tower (6) is dehydrated by the dehydration filter press (8), and can be used as a cementitious material instead of cement and lime under the action of 0.01%-1% (weight) of an acidic composite activator.

[0018] The reaction distillation tower (3) is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plate is 250-900 mm. A combustion flue gas distributor (2) is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and the bottom of the tower is provided with a red mud slurry outlet. The CO2 content in the combustion flue gas is 12%-25%, and the flow rate of the flue gas in the reaction distillation tower (3) is 0.5-3.0 m / s. The mass concentration of the red mud slurry is 5%-60%, and the spray density in the reaction distillation tower (3) is 5-120 m / s. 3 / m 2 ·h.

[0019] The water washing desalination tower (6) is a flow-through plate tower, a packed tower or an empty tower.

[0020] The acidic composite activator is an inorganic and organic composite activator, and its weight composition is 15%-30% sulfuric acid, 10%-20% furan resin, 10%-20% sodium hexametaphosphate, 5%-15% sodium dodecylbenzene sulfonate, 33%-5% Al2(SO4), and 0-5% FeSO4. When preparing, firstly dissolve 150 kg of sodium hexametaphosphate, 50 kg of Al2(SO4)3, 50 kg of sodium dodecylbenzene sulfonate and 100 kg of furan resin in a reaction kettle with 450 kg of water, stir evenly, and then slowly drop 200 kg of 98% concentrated sulfuric acid, and cool it to obtain the acidic composite activator product.

[0021] The method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud provided by the present invention solves the problem of decarbonization and ultra-low emission of combustion flue gas with high efficiency and low cost by realizing graded utilization of acidic gas in flue gas according to reaction activity through a reaction distillation tower, solves the problem of cheap and efficient removal of insoluble alkaline substances from red mud, and improves the dealkalization rate from the usual 50% to 98%, and the carbon fixation amount from less than 40KgCO2 / ton of 30% red mud to more than 150KgCO2 / ton of 30% red mud; the acidic composite activator solves the problems of the autogenous shrinkage of red mud-based alkali-activated cheap cementitious materials, which is much greater than that of ordinary silicate cement, and the surface frosting affects the durability of the products, especially the shortcomings and defects that affect the interface bonding performance between blocks of alkali-activated cementitious materials, and the 3-day and 28-day compressive strengths are improved by more than 80%; compared with the production of cement, the production of 1 ton of red mud-based cementitious materials can effectively reduce carbon dioxide emissions and energy consumption by more than 80%, creating conditions for the high-value utilization of red mud resources.

Claims

1. A method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud. It is characterized in that The red mud slurry at 10-100°C is pumped to the top of the reaction distillation tower, and is countercurrently contacted with the 30-180°C combustion flue gas introduced from the bottom of the tower through a flow-through tower plate with 1-30 theoretical plates. The volume ratio of the flue gas to the red mud slurry feed is 500-3000:

1. The CO in the flue gas in the reaction distillation tower 2 、SO X and NO X Acidic gas and Na in slurry 2 O.K 2 O and its alkaline salts for efficient reactive distillation, SO X and NO X It mainly reacts with insoluble alkaline substances in the lower part of the tower, CO 2 It mainly reacts with soluble alkaline substances in the upper part of the tower to reduce the pH value of the red mud slurry from 11-14 to no more than 8, and the flue gas with dust removal, decarbonization and desulfurization flows out from the top of the reaction distillation tower, and the red mud slurry with dealkali and carbon fixation flows out from the bottom of the reaction distillation tower and the concentrated brine is removed; the dehydrated red mud slurry is diluted with part of the washing brine again, and then pumped to the top of the water washing and desalting tower for water washing and desalting. The washing brine flowing out of the top of the water washing and desalting tower is partially used to dilute the dehydrated red mud slurry, and the remaining part is mixed with the concentrated brine and sent back to the alumina extraction section; After dehydration, the desalted red mud slurry flowing out of the bottom of the water washing desalination tower can be used as a cementitious material instead of cement and lime under the action of 0.01wt%-1wt% acidic composite activator; The acid composite activator is an inorganic and organic composite activator, which is composed of sulfuric acid, furan resin, sodium hexametaphosphate, sodium dodecylbenzene sulfonate, Al 2 (SO 4 ) 3 During the preparation, first dissolve 150 kg of sodium hexametaphosphate and 50 kg of Al in a reactor with 450 kg of water. 2 (SO 4 ) 3 , 50 kg of sodium dodecylbenzene sulfonate and 100 kg of furan resin, stir evenly, then slowly add 200 kg of 98% concentrated sulfuric acid, and after cooling, use it as an acid composite activator; burn the CO in the flue gas 2 The content is 12%-25%, SO X Content is 0-50000ppm, NO X The content is 0-3000ppm, among which SO X and NO X The content is not taken as 0ppm, and the flow rate in the flue gas tower is 0.5-3.0m / s.

2. The method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud according to claim 1, It is characterized in that The reactive distillation tower is a flow-through structure without a downcomer. A red mud slurry distributor is arranged at the top of the tower. The plate spacing of the flow-through tower plates is 250-900mm. A combustion flue gas distributor is arranged at the bottom of the tower. The top of the tower is a flue gas outlet, and a red mud slurry outlet is arranged at the bottom of the tower.

3. The method for preparing negative carbon cementitious materials by dealkalization and carbon fixation of high-calcium red mud according to claim 1, It is characterized in that The concentration of red mud slurry is 5%-60% and the spray density in the tower is 5-120m 3 / m 2 ·h.

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