CN115415292B - Wet dealkalization method and treatment system for red mud - Google Patents

Abstract

The present invention discloses a red mud wet de-alkali method and a treatment system. A red mud wet de-alkali method comprises the following steps: (1) carbon dioxide gas is introduced into the red mud slurry to be treated for carbonization; (2) the red mud slurry after carbonization in step (1) is mixed and stirred with a composite gypsum slurry for calcification; (3) the red mud slurry after calcification in step (2) is subjected to solid-liquid separation, and the obtained solid is the de-alkali red mud. The red mud wet de-alkali method of the present invention utilizes carbon dioxide and gypsum to reduce and control alkali, which can significantly reduce the pH value, alkalinity, free alkali and bound alkali content of the red mud, reduce the alkalinity to an available range, and the alkali reduction effect is stable in the long term due to the reduction of the bound alkali content.

Description

A red mud wet de-alkali method and treatment system

Technical Field

The present invention relates to the technical field of solid waste treatment, and in particular to a red mud wet dealkalization method and a treatment system.

Background technique

Red mud is a solid waste generated during the production process of alumina industry. According to statistics, 0.8-1.5 tons of red mud will be produced for every ton of alumina produced. However, due to the strong alkalinity of red mud, its resource utilization is difficult, 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. Because red mud has multiple activities, red mud with reduced alkalinity can be used to make glass, cement, roadbed materials, etc., and has broad application prospects.

At present, the main methods for reducing the alkali content of red mud include water washing, acid leaching, carbonization, biological alkali adjustment, etc. However, the above methods generally have the disadvantages of long time and high cost, and are not suitable for large-scale industrial treatment of red mud. For example: the water washing method has high water consumption, poor de-alkali effect, and poor technical and economic performance; the acid leaching method, although it can effectively de-alkali, is too expensive and has problems such as difficult acid recovery, and is not suitable for industrial production processes; the carbonization method takes a long time, and the de-alkali rate can only reach about 40%-50%, which cannot meet the requirements for red mud reuse.

Summary of the invention

In order to overcome the problem that the existing red mud cannot be effectively dealkalized, one of the objects of the present invention is to provide a red mud wet dealkalization method; the second object of the present invention is to provide a red mud wet dealkalization treatment system.

The concept of the present invention is as follows:

The alkalinity of red mud mainly comes from free alkali and chemically combined alkali. The free alkali in red mud mainly includes NaOH, _{Na2CO3 , NaHCO3} , NaAl(OH) ₄ , etc. The chemically combined alkali of red mud mainly includes calcite _{( CaCO3 )} , sodalite ([ _Na6Al6Si6O24 ]·[ _2NaX or _Na2X ]), cancrinite ([ _Na6Al6Si6O24 ]·2[ _CaCO3 ] _{) ,} tricalcium aluminate (TCA _{, Ca3Al2} ( _OH ) ₁₂ ), hydrated garnet ( _Ca3Al2 ( _SiO4 ) _x (OH) _12-4x ). The existing water washing method, acid gas _{neutralization} method and other technologies can only play a good role in removing free alkali, but cannot effectively remove combined alkali. The present invention realizes effective removal of combined alkali by adding calcium ions to replace calcium and sodium with chemically combined alkali.

The first aspect of the present invention provides a red mud wet dealkalization method, comprising the following steps:

(1) introducing carbon dioxide gas into the red mud slurry to be treated for carbonization;

(2) mixing and stirring the red mud slurry carbonized in step (1) with the composite gypsum slurry to perform calcification;

(3) The calcified red mud slurry in step (2) is subjected to solid-liquid separation, and the obtained solid is dealkalized red mud.

Preferably, in the wet red mud dealkalization method, in step (1), the solid content of the red mud slurry to be treated is 20-30 wt%.

Preferably, in this red mud wet dealkalization method, in step (1), the mass volume ratio of red mud to carbon dioxide in the red mud slurry to be treated is (30-45) kg:1 L; further preferably, the mass volume ratio of red mud to carbon dioxide in the red mud slurry to be treated is (35-40) kg:1 L.

Preferably, in the wet dealkalization method for red mud, in step (1), the rate of introduction of carbon dioxide is 3-6 L/min; too fast or too slow an introduction rate cannot effectively carbonize the red mud slurry to be treated.

Preferably, in the red mud wet dealkalization method, in step (1), the carbon dioxide is introduced for 25-40 minutes.

Preferably, in this red mud wet dealkalization method, in step (2), the composite gypsum slurry is a mixture of gypsum and ammonium chloride; the inventors found that adding ammonium chloride to the composite gypsum slurry makes the gypsum dissolve more fully, and the alkalinity reduction effect is more obvious when it is added to the red mud system and stirred together, thereby achieving further optimization.

Further preferably, the mass ratio of gypsum to ammonium chloride in the composite gypsum slurry is (40-55):1; further preferably, the mass ratio of gypsum to ammonium chloride is (45-50):1; when the amount of ammonium chloride added is too little, the alkali reduction effect is not obvious, and when the amount of ammonium chloride added is too much, the alkali reduction effect cannot be further improved, and the cost of alkali reduction is increased, thereby reducing the economic benefits of the process.

Preferably, in the wet dealkalization method for red mud, in step (2), the gypsum content in the composite gypsum slurry is 1.6-5wt%; and the mass ratio of the composite gypsum slurry to the red mud in the carbonized red mud slurry is 1:(8-12).

Preferably, in this red mud wet dealkalization method, in step (2), a surfactant is added while mixing and stirring, and the surfactant can be selected from at least one of sodium dodecyl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecylbenzene sulfonate, alkyl alcohol amide, sodium olefin sulfonate, sodium linear alkylbenzene sulfonate, and sodium stearate; the red mud particles in the system are easy to aggregate together, thereby wrapping the bound alkali, and the surfactant can divide the solid particle aggregates into fine particles, so that they are dispersed and suspended in the solution, and further play a role in releasing the bound alkali; further preferably, the mass ratio of the surfactant to the red mud in the carbonized red mud slurry is (0.1-0.2):100.

Preferably, in the red mud wet dealkalization method, in step (2), the stirring time is 8-15 min.

Preferably, in this red mud wet dealkalization method, in step (3), a coagulant and/or a flocculant is added when the calcified red mud slurry is subjected to solid-liquid separation; further preferably, a flocculant is added when the calcified red mud slurry is subjected to solid-liquid separation, and the addition of a coagulant and/or a flocculant can accelerate the solid-liquid separation rate of the red mud slurry; further preferably, the mass ratio of red mud to flocculant in the calcified red mud slurry is (42-45):1.

The second aspect of the present invention provides a treatment system for implementing the above-mentioned red mud wet dealkalization method, the treatment system includes a tubular carbonizer, a red mud stirring tank, a mixing stirring tank, and a solid-liquid separation device connected in sequence; the mixing stirring tank is also connected to a gypsum stirring tank.

Preferably, in this treatment system, the tubular carbonizer is in a vertical cylindrical shape, with a spiral shaft disposed inside and two openings disposed at the bottom, one of which is used for the entry of red mud slurry and the other is used for the entry of carbon dioxide gas.

Further preferably, the speed of the spiral shaft of the tubular carbonizer is 50-70r/min; further preferably, the speed of the spiral shaft of the tubular carbonizer is 55-65r/min; the tubular carbonizer is used for premixing carbon dioxide and red mud slurry, carbon dioxide gas enters the tubular carbonizer, the red mud slurry in the red mud stirring tank is pumped to the tubular carbonizer, the red mud slurry and carbon dioxide are premixed in the tubular carbonizer, and then transported to the red mud stirring tank for further carbonization. The speed of the spiral shaft of the tubular carbonizer has an important influence on the premixing and alkali reduction effect of the tubular carbonizer, and a speed that is too small or too large cannot achieve a good treatment effect.

Preferably, in this treatment system, a stirring paddle is provided in the red mud stirring tank, and the rotation speed of the stirring paddle is 50-70r/min.

Preferably, in this treatment system, a stirring paddle is provided in the gypsum mixing tank, and the rotation speed of the stirring paddle is 50-70r/min; the composite gypsum slurry is prepared in the gypsum mixing tank, and water, gypsum, and ammonium chloride are added and stirred for mixing, and the stirring time is ≥8min to ensure that the gypsum is fully dissolved.

Preferably, in this treatment system, a stirring paddle is provided in the mixing and stirring tank, the rotation speed of the stirring paddle is 50-70 r/min, and the stirring time is 15-30 min.

Preferably, in this treatment system, the solid-liquid separation device includes a thickening tank and a filter press, and a coagulant and/or flocculant is added to the thickening tank. The purpose of adding the coagulant and/or flocculant is to accelerate the solid-liquid separation of the red mud slurry in the thickening tank.

Further preferably, a stirring paddle is provided in the thickening tank.

A third aspect of the present invention provides dealkalized red mud, which is obtained by the above-mentioned red mud wet dealkalization method.

The beneficial effects of the present invention are:

1. The present invention adopts a method of carbonization and calcification combined with alkali reduction, and the alkali reduction effect is obvious. The use of carbon dioxide and gypsum to reduce alkali and control alkali can significantly reduce the pH value, alkalinity, free alkali and bound alkali content of red mud, reduce the alkalinity to an available range, and reduce the bound alkali content so that the alkali reduction effect is stable in the long term.

2. The red mud dealkalization method of the present invention has a simple process and low cost. Compared with the existing red mud dealkali reduction process, such as the existing lime dealkalization method, which requires temperature and pressure increase, has high requirements for equipment and a complex process; for example, the existing flocculation plus inorganic acid neutralization method has high cost and is not easy to promote, the method of the present invention has a simple production process, can be used for large-scale treatment of red mud, and the drugs used are extremely cheap and easy to promote.

3. The red mud dealkalization method of the present invention has good alkali reduction effect and high alkali reduction efficiency. The method provided by the present invention can reduce the pH value of the red mud leachate to 8.5 in about 1 hour, while the existing carbon dioxide gypsum method alkali reduction process has a slow dissolution process due to the low solubility of gypsum, resulting in a long reaction time of more than 6 hours.

4. The present invention optimizes the carbonization, calcification methods and process formula to control the weight gain of red mud after treatment to 10%-15%. Compared with the prior art which uses a gypsum/red mud dry weight ratio of 1:6, the gypsum/red mud dry weight ratio is controlled at about 1:10, and the addition of a co-solvent (ammonium chloride) reduces the weight gain of red mud while maintaining a good alkali reduction effect. The weight gain of each ton of red mud after alkali reduction in the dealkalization method of the present invention is only 10%-15%, while the weight gain of the prior art exceeds 20%.

5. The red mud wet dealkalization treatment system of the present invention creatively uses a tubular carbonizer. A spiral shaft is arranged in the center of the tubular carbonizer. After the red mud enters the tubular carbonizer, multiple stirrings can be performed; at the same time, carbon dioxide is introduced from the air holes at the lower end, and the contact area with the red mud slurry is large. The carbon dioxide bubbles that reach the bottom will float up, which greatly increases the reaction area. The spiral shaft also cuts the carbon dioxide bubbles to form smaller bubbles. As the stirring proceeds, the resistance on the liquid film side of the gas-liquid interface is reduced, the mass transfer of gas to the liquid phase is increased, and the dealkalization reaction rate is also increased, which significantly improves the reaction efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram of a red mud wet dealkalization treatment system according to the present invention.

FIG2 is a schematic diagram of a red mud wet dealkalization treatment system according to an embodiment.

Detailed ways

The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but should not be understood as limiting the present invention.

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

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

As shown in Figure 1, the present invention provides a red mud wet dealkalization treatment system, which includes a tubular carbonizer, a red mud stirring tank, a gypsum stirring tank, a mixing stirring tank, and a solid-liquid separation device; the tubular carbonizer, the red mud stirring tank, the mixing stirring tank, and the solid-liquid separation device are connected in sequence, and the gypsum stirring tank is connected to the mixing stirring tank.

The tubular carbonizer of the present invention is in a vertical cylindrical shape, with a spiral axis arranged in the center thereof, and two openings arranged at the bottom thereof, one of which is used for the entry of red mud slurry, and the other is used for the entry of carbon dioxide gas.

As shown in Figure 2, in some specific embodiments of the present invention, the red mud wet dealkalization treatment system includes a carbon dioxide gas tank, a tubular carbonizer, a red mud stirring tank, a circulation pump, a first row of mud pumps, a gypsum stirring tank, a second row of mud pumps, a mixing stirring tank, a dosing pump, a chemical barrel, a third row of mud pumps, a thickening tank, a filter press, a return water tank, and a water pump.

The following describes a method for red mud dealkalization by a red mud wet dealkalization treatment system according to an embodiment of the present invention according to FIG. 2, specifically including the following:

The red mud to be treated is added into the red mud stirring tank, and an appropriate amount of water is added into the red mud stirring tank for stirring; the gas in the carbon dioxide gas tank enters the tubular carbonizer, and the circulating pump simultaneously extracts the red mud slurry at the bottom of the red mud stirring tank and transports it to the tubular carbonizer. In the tubular carbonizer, the carbon dioxide gas and the red mud slurry are pre-mixed, and finally enter the red mud stirring tank for full mixing. The red mud slurry in the red mud stirring tank enters the mixing stirring tank through the first row of mud pumps;

The clean water in the return water tank is added to the gypsum mixing tank through the water adding pump. At the same time, gypsum and ammonium chloride are added to the gypsum mixing tank for mixing and mixing, and then enter the mixing mixing tank through the second row mud pump; surfactant and water are added to the reagent barrel to prepare the reagent, and then enter the mixing mixing tank through the reagent adding pump. The mixing mixing tank is fully stirred to achieve further dealkalization of the red mud;

The red mud after the reaction in the mixing and stirring tank enters the thickening tank through the third row of mud pumps for solid-liquid separation, and the red mud slurry at the bottom enters the filter press for filtration, and harmless red mud is obtained after filtration; the supernatant in the thickening tank enters the return water tank for the preparation of gypsum slurry in the gypsum mixing tank and the preparation of red mud slurry in the red mud mixing tank.

Example 1

This embodiment provides a red mud wet dealkalization method, which uses the red mud wet dealkalization treatment system shown in Figure 2 for treatment, and specifically includes the following steps:

(1) Carbonization of red mud and preparation of composite gypsum slurry: raw red mud and water are added to a red mud stirring tank, the carbon dioxide gas tank is opened, the carbon dioxide gas enters the tubular carbonizer, the red mud slurry in the red mud stirring tank is transported to the tubular carbonizer by a circulation pump, and the carbon dioxide gas and the red mud slurry are pre-mixed in the tubular carbonizer; then the red mud slurry enters the red mud stirring tank for comprehensive carbonization; at the same time, gypsum, ammonium chloride and water are added to the gypsum stirring tank and stirred together to prepare the composite gypsum slurry;

(2) discharging the red mud slurry and the composite gypsum slurry into a mixing tank through a mud discharge pump, adding a surfactant, and stirring again;

(3) Discharge the fully stirred red mud into a thickening tank and add flocculants to achieve rapid solid-liquid separation;

(4) The red mud that has settled at the bottom of the thickening tank is quickly drained through a filter press to obtain dealkalized red mud.

The process parameters in the whole process are:

In step (1), the original red mud: water = 1:5, the solid content in the red mud stirring tank is controlled to be 20-25%; before the introduction of carbon dioxide, the pH of the supernatant in the red mud stirring tank is 11.4-11.6; the red mud: carbon dioxide in the red mud slurry = 35kg: 1L, the carbon dioxide flow rate is 5L/min, the introduction time is 30min, and the pH after the introduction of carbon dioxide treatment is 9.12;

In step (1), the composite gypsum slurry contains 4 g of ammonium chloride and 189.4 g of desulfurized gypsum per 5 kg of water, and the stirring time during the preparation process is 10-15 min;

In step (2), the amount of composite gypsum slurry added is 10% of the total amount of red mud in the red mud slurry;

In step (2), the red mud slurry has a ratio of red mud: surfactant = 100: (0.1-0.2), and the stirring time is 10 min;

In step (3), the red mud slurry has a ratio of red mud: flocculant = (42-45): 1, and is allowed to stand in a thickening tank for 18-20 minutes;

In step (4), the filter press pressure value is the filter press thrust of 30 t/m ² .

In order to test whether the red mud after dealkalization in this example has alkali reversion phenomenon, the red mud mixed solution after adding flocculant in step (3) is placed in a bucket, and the initial pH is measured to be 8.07. Then, the mixture is allowed to stand and stirred, and the pH is measured. The specific operation process and pH change are shown in Table 1 below:

Table 1

It can be seen from the data in Table 1 that the red mud wet dealkalization method of this embodiment will not experience alkali reversion even after a long period of time.

Example 2

The difference between the wet red mud dealkalization method of this embodiment and that of Example 1 is that in step (1) of this embodiment, the ratio of red mud to carbon dioxide in the red mud slurry is 20 kg: 1 L, and the pH after the treatment with carbon dioxide is measured to be 10.12.

Example 3

The difference between the wet red mud dealkalization method of this embodiment and that of Example 1 is that in step (1) of this embodiment, the ratio of red mud to carbon dioxide in the red mud slurry is 25 kg: 1 L, and the pH after treatment with carbon dioxide is measured to be 9.87.

Example 4

The difference between the wet red mud dealkalization method of this embodiment and that of Example 1 is that in step (1) of this embodiment, the ratio of red mud to carbon dioxide in the red mud slurry is 30 kg: 1 L, and the pH value after the treatment with carbon dioxide is measured to be 9.53.

Example 5

The difference between the red mud wet dealkalization method of this embodiment and that of Example 1 is that in step (1) of this embodiment, the ratio of red mud to carbon dioxide in the red mud slurry is 40 kg: 1 L, and the pH after the treatment with carbon dioxide is measured to be 9.15.

Example 6

The difference between the wet red mud dealkalization method of this embodiment and that of Example 1 is that in step (1) of this embodiment, the ratio of red mud to carbon dioxide in the red mud slurry is 45 kg:1 L, and the pH value after the treatment with carbon dioxide is measured to be 9.18.

Example 7

The difference between the wet red mud dealkalization method of this embodiment and that of embodiment 1 is that in step (2) of this embodiment, the amount of composite gypsum slurry added is 5% of the total amount of red mud; and the pH of the red mud mixed solution after adding the flocculant in step (3) is measured to be 8.49.

Example 8

The difference between the wet red mud dealkalization method of this embodiment and that of embodiment 1 is that in step (2) of this embodiment, the amount of composite gypsum slurry added is 15% of the total amount of red mud; and the pH of the red mud mixed solution after adding the flocculant in step (3) is measured to be 8.39.

Example 9

The difference between the wet red mud dealkalization method of this embodiment and that of embodiment 1 is that in step (2) of this embodiment, the amount of composite gypsum slurry added is 20% of the total amount of red mud; and the pH of the red mud mixed solution after adding the flocculant in step (3) is measured to be 8.42.

Example 10

The difference between the wet red mud dealkalization method of this embodiment and that of embodiment 1 is that in step (2) of this embodiment, the amount of composite gypsum slurry added is 25% of the total amount of red mud; and the pH of the red mud mixed solution after adding the flocculant in step (3) is measured to be 8.47.

Comparative Example 1

The difference between the red mud wet dealkalization method of this comparative example and Example 1 is that in step (1) of this comparative example, ammonium chloride is not added to the composite gypsum slurry, and the pH of the red mud mixed solution after adding the flocculant in step (3) is measured to be 9.48, and the pH rebounds significantly within the subsequent 1-2 days.

Comparative Example 2

The difference between the red mud wet dealkalization method of this comparative example and Example 1 is that in step (1) of this comparative example, carbon dioxide is introduced through an ordinary gas pipe (D12*8) instead of a tubular carbonizer, and the carbon dioxide gas is mixed with the red mud slurry in a red mud stirring tank. The pH value after the treatment with carbon dioxide is measured to be 10.12.

Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, 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 (5)

1. A red mud wet dealkalization method, characterized in that it comprises the following steps: (1) Carbon dioxide gas is introduced into the red mud slurry to be treated for carbonization; (2) mixing the carbonized red mud slurry obtained in step (1) with the composite gypsum slurry to perform calcification; (3) The calcified red mud slurry in step (2) is subjected to solid-liquid separation, and the obtained solid is dealkalized red mud; In the step (1), the mass volume ratio of red mud to carbon dioxide in the red mud slurry to be treated is (30-45) kg:1 L; In the step (1), the carbon dioxide is introduced at a rate of 3-6 L/min; In the step (2), the composite gypsum slurry is a mixture of gypsum and ammonium chloride; In the step (2), the mass ratio of gypsum to ammonium chloride is (40-55):1; In the step (2), the gypsum content in the composite gypsum slurry is 1.6-5wt%; the mass ratio of the composite gypsum slurry to the red mud in the carbonized red mud slurry is 1:(8-12). 2. The red mud wet dealkalization method according to claim 1, characterized in that, in the step (2), a surfactant is added while the mixing and stirring. 3. A treatment system for implementing the red mud wet dealkalization method according to claim 1 or 2, characterized in that the treatment system comprises a tubular carbonizer, a red mud stirring tank, a mixing stirring tank, and a solid-liquid separation device connected in sequence; the mixing stirring tank is also connected to a gypsum stirring tank. 4. The treatment system according to claim 3 is characterized in that the tubular carbonizer is in a vertical cylindrical shape, with a spiral shaft inside and two openings at the bottom, one of which is for the entry of red mud slurry and the other is for the entry of carbon dioxide gas. 5. A dealkalized red mud, characterized in that the dealkalized red mud is obtained by the red mud wet dealkalization method according to claim 1 or 2.