A red mud alkali reduction auxiliary agent and its preparation method and application

Abstract

The invention discloses a mud alkali reduction agent and a preparation method and application thereof. A red mud alkali reduction agent, the preparation raw materials of which include gypsum, ammonium chloride, poly(meta-phenylenediamine) and water. The red mud alkali reduction agent of the invention, under the dual action of ammonium chloride and poly(meta-phenylenediamine), enables the gypsum to be basically completely ionized. When it is used for reducing the alkali of red mud treated by carbonization, the alkali reduction effect on the red mud treated by carbonization reaches the maximum value (calcium ions and carbonate ions are combined), and at the same time, the poly(meta-phenylenediamine) therein can break the colloid steady state and release the bound alkali by adsorbing the metal hydroxide colloid particles in the red mud system; the poly(meta-phenylenediamine) can also capture the hydrogen ions in the system, further promote the dissociation of bicarbonate, so that it is converted into carbonate to further generate precipitation, thereby ensuring that the alkalinity is further reduced while also ensuring the stability of the pH value of the system.

Description

Technical Field

[0001] The invention relates to the technical field of red mud resource utilization, and in particular to a red mud alkali reduction auxiliary agent and a preparation method and application thereof. Background Art

[0002] Red mud is a solid waste generated during the production of alumina. Due to its strong alkalinity, red mud is difficult to be used as a resource, resulting in a large amount of red mud accumulation. A large amount of red mud cannot be fully and effectively utilized and can only be piled up in large areas of yards, which not only causes serious pollution to the environment, but also hinders the development of the alumina industry. Red mud with reduced alkalinity can be used to make glass, cement, roadbed materials, etc., and has broad application prospects.

[0003] At present, the main methods for reducing the alkali content of red mud include water washing, acid leaching, carbonization, biological alkali adjustment, etc. The most commonly used method in industry is carbonization. The carbonization method is to use CO2 to dissolve in the solution to form carbonic acid, which continuously dissolves and releases H + , reacting with the hydroxide ions in the red mud, thereby achieving the regulation of the alkalinity of the red mud. As the hydrogen ions produced by the dissolution of carbonic acid continue to participate in the neutralization reaction, the red mud liquid phase system will eventually contain CO3 2- / HCO3 - Balance, the liquid phase pH can be reduced to about 10.0: However, after the carbonate and bicarbonate ions in the system are hydrolyzed, the entire system will still be alkaline, which cannot well meet the actual requirement of red mud pH of about 7. At present, the commonly used method for the situation of incomplete degradation by carbonization is to directly add gypsum (CaSO4) to the red mud treated by carbonization and stir them together. The calcium ions in the calcium sulfate in the gypsum react with the carbonate ions to form calcium carbonate precipitation, thereby achieving the purpose of further reducing the alkali. However, since calcium sulfate itself has a very small solubility (Ksp=9.1×10 -6 ), and the solubility of calcium sulfate decreases with the increase of pH value. The principle is: CaSO4+2OH - =Ca(OH)2+SO4 2-(Calcium hydroxide has a lower solubility). Due to the above reasons, even if the stirring speed is increased, calcium sulfate cannot be fully ionized, resulting in the inability to fully react with the carbonate ions in the carbonized red mud system to form a precipitate. This will not only prolong the stirring time and reduce the stirring efficiency, but also increase the overall pH value after stirring (the pH is generally around 9). In addition, if only gypsum is added, its effect on the red mud itself is too simple (it only combines with carbonate ions to form a precipitate), and it cannot effectively form a precipitate for the bicarbonate ions in the system. In addition, it has no substantial effect on the large amount of metal hydroxide colloids contained in the red mud slurry. In summary, if only gypsum is added, the overall alkali reduction effect and other effects will have a certain threshold. Summary of the invention

[0004] In order to overcome the defects of the existing red mud alkali reduction treatment methods, one of the objects of the present invention is to provide a red mud alkali reduction auxiliary agent, the second object of the present invention is to provide a preparation method of the red mud alkali reduction auxiliary agent, the third object of the present invention is to provide an application of the red mud alkali reduction auxiliary agent, and the fourth object of the present invention is to provide a red mud alkali reduction method.

[0005] A first aspect of the present invention provides a red mud alkali reduction auxiliary agent, wherein raw materials for preparing the red mud alkali reduction auxiliary agent include gypsum, ammonium chloride, poly-meta-phenylenediamine and water.

[0006] Preferably, in this red mud alkali reduction auxiliary agent, the mass ratio of gypsum to ammonium chloride is (20-30):1; further preferably, the mass ratio of gypsum to ammonium chloride is (24-29):1; further preferably, the mass ratio of gypsum to ammonium chloride is (25-28):1.

[0007] Preferably, in the red mud alkali reduction agent, the mass ratio of gypsum to poly(meta-phenylenediamine) is (2-4):1; further preferably, the mass ratio of gypsum to poly(meta-phenylenediamine) is (2.5-4):1.

[0008] Preferably, in the red mud alkali reduction agent, the mass concentration of ammonium chloride in the red mud alkali reduction agent is 0.2-1%; further preferably, the mass concentration of ammonium chloride in the red mud alkali reduction agent is 0.2-0.8%.

[0009] The second aspect of the present invention provides a method for preparing the above-mentioned red mud alkali reduction agent, comprising the following steps: dissolving gypsum in water, then adding ammonium chloride and mixing, and then adding poly-m-phenylenediamine and mixing to obtain the red mud alkali reduction agent.

[0010] In the original gypsum system, when a certain amount of ammonium chloride is added, the possibility of the dissociated anions and cations of the weak electrolytes combining into molecules is further reduced due to the increase in the ion concentration of the entire system, thereby reducing the concentration of weak electrolyte molecules and further increasing the concentration of ions in the system. Rapid stirring after adding ammonium chloride also further increases the degree of dissociation of calcium sulfate.

[0011] After adding poly(m-phenylenediamine), due to the weak acidity brought by ammonium chloride, the lone pair of electrons in the nitrogen atom of poly(m-phenylenediamine) will combine with the hydrogen ions in the system to form positive ions, and the sulfate ions in the system will combine with the positive ions, thereby achieving the adsorption of sulfate ions in the system. The reason for not adsorbing other anions is that sulfate has a large volume and is easily captured and adsorbed by positive ions. Such a reaction will cause the calcium sulfate precipitation to move in the positive direction, further increasing the degree of ionization of calcium sulfate. In addition, the added poly(m-phenylenediamine) may also have an adsorption effect on a large number of metal ions present in red mud, thereby further improving the excellent properties of red mud.

[0012] After the above two steps, a completely ionized composite calcium sulfate slurry can be basically prepared.

[0013] Preferably, in the preparation method of this red mud alkali reduction auxiliary agent, ammonium chloride is added in the form of ammonium chloride solution, and the pH of the ammonium chloride solution is adjusted to 5-6 using hydrochloric acid; under acidic conditions, it is more conducive to the ionization of calcium sulfate and poly(m-phenylenediamine) has certain requirements on the solution pH when it works (this is because its mechanism of action is to form positive ions by combining the lone pair of electrons of the nitrogen atom on the poly(m-phenylenediamine) with hydrogen ions, and then the sulfate ions are combined with the positive ions, thereby promoting the ionization of calcium sulfate). Therefore, an ammonium chloride solution acidified with hydrochloric acid is added in advance, and the hydrogen ions brought by the hydrochloric acid acidification and the hydrogen ions formed by the hydrolysis of ammonium chloride work together to reduce the pH of the red mud system, and the addition of ammonium chloride further promotes the ionization of calcium sulfate by reducing the concentration of weak electrolyte molecules and increasing the concentration of ions in the system.

[0014] Preferably, in the preparation method of the red mud alkali-reducing auxiliary agent, the time for adding ammonium chloride and mixing and stirring is 5-20 minutes; further preferably, the time for adding ammonium chloride and mixing and stirring is 10-15 minutes.

[0015] Preferably, in the preparation method of the red mud alkali-reducing auxiliary agent, the time for adding poly(meta-phenylenediamine) and mixing and stirring is 10-30 minutes; further preferably, the time for adding poly(meta-phenylenediamine) and mixing and stirring is 15-25 minutes.

[0016] The third aspect of the present invention provides the use of the above-mentioned red mud alkali reduction auxiliary agent in red mud alkali reduction.

[0017] Preferably, the above-mentioned red mud alkali reduction aid is used in the alkali reduction of red mud after carbonization treatment.

[0018] The red mud alkali reduction agent of the present invention has calcium ions that are substantially completely ionized and fully react with carbonate ions in the red mud to generate calcium carbonate. In addition, since the nitrogen atoms in the poly-m-phenylenediamine have lone pairs of electrons, they have a very strong adsorption effect on hydrogen ions, through which the further ionization of bicarbonate can be promoted to convert it into carbonate, and the calcium ions in the red mud alkali reduction agent will quickly combine with the carbonate ions that are already in a free state to form precipitation, and the alkali reduction effect is maximized through the composite action of organic + inorganic.

[0019] In the red mud slurry system, there are a large number of colloidal particles of metal hydroxides or oxides, and their presence will further increase the alkalinity of the system. When the alkali-reducing agent is added, the stability of the colloidal particles decreases due to the increase in the ionic strength of the entire system and the adsorption of poly(m-phenylenediamine) to metals, thereby converting the bound alkali in the system into free alkali. After the red mud system is initially subjected to carbonization, a small amount of carbonic acid exists in the solution, which can capture the free alkali in the system and neutralize it, thereby achieving the purpose of reducing alkali again.

[0020] A fourth aspect of the present invention provides a method for reducing alkali in red mud, comprising the following steps: mixing the above-mentioned red mud reducing alkali aid with the red mud slurry after carbonization treatment, and stirring.

[0021] In this red mud de-alkali method, the carbonized red mud slurry refers to: fresh red mud slurry produced by aluminum smelting is treated with carbon dioxide for de-alkali treatment or red mud is added with water to prepare red mud slurry and then treated with carbon dioxide for de-alkali treatment.

[0022] Preferably, in this red mud dealkali treatment method, the pH of the red mud slurry after carbonization treatment is ≥9.

[0023] Preferably, in this red mud alkali reduction method, the liquid-to-solid ratio of the red mud slurry after carbonization treatment is (3-4):1; the mass ratio of the red mud alkali reduction auxiliary agent to the red mud slurry after carbonization treatment is 1:(14-20).

[0024] The beneficial effects of the present invention are:

[0025] The red mud alkali reduction auxiliary agent of the present invention enables gypsum to be basically completely ionized under the dual effects of ammonium chloride and poly(m-phenylenediamine). When it is used for red mud alkali reduction after carbonization, the alkali reduction effect on the red mud treated by carbonization reaches the maximum value (calcium ions and carbonate ions are combined), and the poly(m-phenylenediamine) therein can break the colloid steady state and release the bound alkali by adsorbing the metal hydroxide colloid particles in the red mud system; in addition, the poly(m-phenylenediamine) can also capture the hydrogen ions in the system, further promote the dissociation of bicarbonate, so that it is converted into carbonate to further generate precipitation, ensuring that the alkalinity is further reduced while also ensuring the stability of the pH value of the system. DETAILED DESCRIPTION

[0026] The following detailed description of the embodiments of the present invention is only used to explain the present invention and is not to be construed as limiting the present invention.

[0027] The present invention is further described in detail below through specific examples.

[0028] Unless otherwise specified, the raw materials, reagents or devices used in the examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0029] Example 1

[0030] This embodiment provides a method for preparing a red mud alkali reduction additive, which specifically comprises the following steps:

[0031] At 30°C, first take 6.5 kg of water and 1.7 kg of gypsum (qualified product) and mix and stir for 17.5 min (about 40 rpm), then add 7L of NH4Cl solution (63.6 g of ammonium chloride) with a pH of about 5-6 prepared with hydrochloric acid in advance, and stir for 12.5 min (about 60 rpm); finally, add 515 g of poly(m-phenylenediamine) and stir for 20 min (45-50 rpm) to obtain the red mud alkali reduction agent (ie, PCR reagent).

[0032] Example 2

[0033] This embodiment provides a red mud alkali reduction method, which specifically comprises the following steps:

[0034] (1) Prepare 5 kg of raw red mud slurry without any treatment, and measure its initial pH to be about 14.

[0035] (2) 30 L of CO2 was introduced into the red mud slurry at a rate of 2 L / min and stirred continuously for 15 min. After carbonization, its pH was measured.

[0036] (3) Take 300 g of the PCR reagent prepared in Example 1, add it to the red mud slurry and stir for 10 min. After standing for 30 min, monitor the pH of the supernatant. Then, stir until uniform and stand, monitor the pH of the supernatant, and repeat several times.

[0037] The pH results measured in each step of this embodiment are shown in Table 1 below:

[0038] Table 1

[0039]

[0040] The treatment method in Table 1 above is a continuous operation.

[0041] Comparative Example 1

[0042] The red mud alkali reduction method of this comparative example is different from that of Example 2 in that the PCR reagent in step (3) is replaced with gypsum slurry (6.5 kg of water and 1.7 kg of gypsum are mixed and stirred to prepare gypsum slurry), and the rest is the same as Example 2. The pH results measured in each step of this example are shown in Table 2 below:

[0043] Table 2

[0044]

[0045] The treatment method in Table 2 above is a continuous operation.

[0046] Comparative Example 2

[0047] The red mud alkali reduction method of this comparative example is different from that of Example 2 in that the PCR reagent in step (3) is replaced with gypsum + ammonium chloride slurry (6.5 kg of water and 1.7 kg of gypsum are mixed and stirred for 17.5 min, and then 7 L of NH4Cl solution with a pH of about 5-6 prepared by hydrochloric acid is added and stirred for 12.5 min), and the rest is the same as Example 2. The pH results measured in each step of this example are shown in Table 3 below:

[0048] Table 3

[0049]

[0050] The treatment method in Table 3 above is a continuous operation.

[0051] It can be seen from the data in Tables 1-3 that the example in which PCR reagent is added has the fastest alkali reduction speed, the best alkali reduction effect and no rebound. The pH is reduced to about 7 in just one operation, and even after continuous operation, the pH is still maintained at about 7. However, the comparative example 2 in which ammonium chloride and gypsum are added has a slower alkali reduction speed, and the alkali reduction effect is poor in the same time. It takes multiple continuous operations to reduce the alkali to about 8. The comparative example 1 in which only gypsum slurry is added has the slowest alkali reduction speed, the worst alkali reduction effect, and an obvious rebound phenomenon in the alkali reduction process. It is finally stabilized to about pH 9 after multiple continuous operations.

[0052] In summary, the PCR reagent developed by the present invention has obvious advantages in further reducing the alkali of carbonized red mud, achieving the technical effect of rapid alkali reduction in a short time and maintaining stability for a long time without rebound. It is a major innovation in the technology of further reducing the alkali of carbonized red mud.

[0053] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A red mud alkali reduction aid, characterized in that: The raw materials for preparing the red mud alkali reduction auxiliary agent include gypsum, ammonium chloride, poly-metaphenylenediamine and water.

2. The red mud alkali reduction agent according to claim 1, characterized in that The mass ratio of gypsum to ammonium chloride is (20-30):

1.

3. The red mud alkali reduction agent according to claim 1, characterized in that: The mass ratio of gypsum to poly(m-phenylenediamine) is (2-4):

1.

4. The red mud alkali reduction agent according to claim 1, characterized in that: The mass concentration of ammonium chloride in the red mud alkali reduction auxiliary agent is 0.2-1%.

5. A method for preparing the red mud alkali reduction auxiliary agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: Gypsum is dissolved in water, and then ammonium chloride is added and mixed and stirred, and then poly-m-phenylenediamine is added and mixed and stirred to obtain the red mud alkali reduction auxiliary agent.

6. The method for preparing the red mud alkali reduction auxiliary agent according to claim 5, characterized in that: The time for adding ammonium chloride and mixing is 5-20 minutes; the time for adding poly-m-phenylenediamine and mixing is 10-30 minutes.

7. Use of the red mud alkali reduction aid according to any one of claims 1 to 4 in red mud alkali reduction.

8. A method for reducing alkali in red mud, characterized in that: The method comprises the following steps: mixing the red mud alkali reduction aid described in any one of claims 1 to 4 with the red mud slurry after carbonization treatment, and stirring.

9. The red mud alkali reduction method according to claim 8, characterized in that: The pH of the red mud slurry after carbonization treatment is ≥9.

10. The red mud alkali reduction method according to claim 8, characterized in that: The liquid-to-solid ratio of the carbonized red mud slurry is (3-4):1; the mass ratio of the red mud alkali reduction additive to the carbonized red mud slurry is 1:(14-20).

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