Process and system for treating Bayer solution by ozone micro-nano bubbles

Abstract

The invention belongs to the technical field of alumina production from bauxite, and particularly relates to a process and system for treating a Bayer solution by ozone micro-nano bubbles, and the process comprises the following steps: preparing ozone into ozone micro-nano bubbles; mixing the ozone micro-nano bubbles with a Bayer solution to prepare a mixed solution; unreacted ozone in the mixed solution is collected and then treated in a centralized manner. According to the method, the Bayer solution is efficiently subjected to carbon reduction, decoloration and bubble reduction treatment, the technological process is simple, and the production efficiency of aluminum oxide is effectively improved. The method has important practical significance and economic benefits for improving the quality and efficiency of alumina produced by the bauxite Bayer process.

Description

Technical Field

[0001] The invention belongs to the technical field of producing alumina from bauxite, and in particular relates to a process and system for treating Bayer solution with ozone micro-nano bubbles. Background Art

[0002] In the process of producing alumina from bauxite by the Bayer process, the sodium aluminate solution is reddish brown due to the large amount of humic acid organic matter it contains. In addition, corresponding organic flotation agents, organic flocculants and organic additives are also added in the process of bauxite desiliconization, red mud sedimentation and seed decomposition, resulting in the organic content in the Bayer solution being as high as tens of grams per liter. Organic matter will participate in red mud sedimentation, seed decomposition, scabbing and causticization in the Bayer process and be removed from the Bayer cycle. In order to reduce the impact of residual organic matter on alumina production, operations such as roasting mother liquor, sodium oxalate salt removal and activated carbon adsorption are often carried out. Studies have shown that organic matter in Bayer solution is mainly divided into humic acid, accounting for about 25% of the total organic carbon, intermediate products generated by the degradation and transformation of humic acid, mainly phenolic and phthalic acid organic matter, accounting for about 21% of the total organic carbon, and low molecular weight fatty acid organic matter, mainly formic acid, acetic acid and oxalic acid, accounting for about 44% of the total organic carbon.

[0003] The presence of high concentrations of organic matter in Bayer solution will affect the physicochemical properties of sodium aluminate solution, such as viscosity and boiling point. These changes in physicochemical properties will have certain negative effects on the production system, mainly: (1) Reduce the seed decomposition rate. When the concentration of organic matter increases to a certain level, some organic matter will precipitate along with aluminum hydroxide, thereby reducing the activity of the seed crystal, resulting in a decrease in its decomposition rate. (2) Affect the quality of alumina. Sodium oxalate in organic matter has low solubility under strong alkaline conditions and is easy to crystallize and precipitate, which will promote the formation of fine-grained aluminum hydroxide and increase the degree of grain refinement during the roasting process. In addition, some colored organic matter will cause the whiteness of aluminum hydroxide when it precipitates together with aluminum hydroxide. (3) Cause equipment scarring. Under high temperature conditions, some organic matter such as toluene and aromatic polymers will carbonize, making the scars asphalt and tar-like, which will cause great trouble in equipment cleaning. (4) Generate a large number of bubbles. High molecular weight organic matter such as humates will reduce the interfacial tension of the solution and produce a large amount of foam, which will reduce the effective use volume of the equipment. (5) Increase production costs. Organic matter exists in the Bayer solution in the form of organic sodium salts, which reduces the effective concentration of caustic soda, and eventually the organic sodium salts will be converted into sodium carbonate and precipitated, affecting the normal operation of production.

[0004] In recent years, the removal of organic matter in Bayer solution has received more and more attention. The Chinese patent application with publication number CN113896280A involves an ultrasound / ozone / H 2 O 2A system and method for combined removal of organic matter from sodium aluminate solution, the system comprising a closed ultrasound / ozone / H 2 O 2 Mixed contact reaction chamber, ultrasonic device and constant temperature device. Sodium aluminate solution and H 2 O 2 The mixed solution flows into the ultrasonic / ozone / H 2 O 2 Mixing contact chamber, then passing ozone, under ultrasonic and stirring action, the organic matter in the sodium aluminate solution can be removed by hydraulic retention for 3-6 hours. However, this method has a long process, high cost, and is difficult to operate in practice. The Chinese patent with publication number CN114408956 A reports that the seed mother liquor is evaporated, and then the evaporated mother liquor is forced to circulate and evaporate at 95-120°C, and 50-300g / L of crystal seeds are added during the forced circulation process, and then the circulating mother liquor is filtered to obtain an organic filter cake, thereby removing organic matter. However, this method has problems such as long process flow and high energy consumption. In addition, this method mainly discharges carbonates and oxalates, and the highest TOC precipitation rate is only 13.27%. The Chinese patent with publication number CN114832411A uses wet oxidation to degrade organic matter in sodium aluminate solution. The system adds a bypass at the discharge port of the multi-effect evaporator to add a pressure pump and oxidation equipment, and oxidizes organic matter at high temperature (80-300°C), but this method has the disadvantages of high energy consumption and large amount of chemical reagents. The Chinese patent with publication number CN116588960A uses a humic acid remover to Bayer crude liquor, and then adds a sodium oxalate adsorbent to Bayer fine liquor to remove non-sodium oxalate organic matter and sodium oxalate organic matter, but this method takes a long time and requires a large amount of seed crystals. The Chinese patent with publication number 114772622A uses a strategy of evaporation cooling and then adding seed crystals to remove organic matter. However, this method also has a long induction crystallization time of seed crystals, and fails to effectively remove amorphous organic matter.

[0005] In summary, developing an efficient and energy-saving method for removing organic matter from Bayer solution has important practical significance and economic benefits for improving the quality and efficiency of alumina production by the Bayer process of bauxite. Summary of the invention

[0006] In view of the above problems, the present invention provides a process and system for treating Bayer solution with ozone micro-nano bubbles, which can efficiently reduce carbon, decolorize and reduce foaming of Bayer solution. The process flow is simple and the production efficiency of alumina can be effectively improved.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] In a first aspect, the present invention provides a process for treating Bayer solution with ozone micro-nano bubbles, comprising the following steps: preparing ozone into ozone micro-nano bubbles; mixing the ozone micro-nano bubbles with the Bayer solution to obtain a mixed solution; and collecting unreacted ozone in the mixed solution for centralized treatment.

[0009] In some other embodiments, the mixed solution is mixed with ozone after refluxing to produce ozone micro-nano bubbles and the ozone micro-nano bubbles are mixed with the Bayer solution again;

[0010] Preferably, the reflux rate is 0.2-3 L / min.

[0011] In some other embodiments, the method for preparing the ozone micro-nano bubbles is: mixing ozone with water, the pressure of the mixture of ozone and water is 0.25-45 MPa, the amount of ozone is 40-60 g / h, and the gas flow rate of ozone is 0.3-5 L / min.

[0012] In some other embodiments, the ozone micro-nano bubbles have a particle size of less than 52 μm and a gas content of 1.0-2.5%.

[0013] In some other embodiments, the Bayer solution has an alkalinity of 120-250 g / L, a total organic carbon content of 5-50 g / L, and a temperature of 40-55°C.

[0014] In some other embodiments, the conditions for mixing the ozone micro-nano bubbles with the Bayer solution are: the mixing pressure is 0.1-0.25 MPa, the mixing time is 0.5-2 h, and the total number of micro-nano bubbles is greater than 1.3×10 8 Pieces / mL.

[0015] In some other embodiments, the conditions for mixing the mixed liquid with ozone after refluxing are: pressure of 0.25-0.45 MPa, ozone amount of 40-60 g / h, and ozone gas flow rate of 0.3-5 L / min.

[0016] In some other embodiments, the centralized treatment is solution absorption or thermal treatment.

[0017] In a second aspect, the present invention provides a system for treating Bayer solution with ozone micro-nano bubbles, which is used to implement the process of treating Bayer solution with ozone micro-nano bubbles in the first aspect, comprising an ozone generator, a micro-nano bubble generator, a mixer, an ozone collector and an ozone processor connected in sequence;

[0018] Ozone generator, used to convert oxygen into ozone;

[0019] A micro-nano bubble generator, used to convert ozone into ozone micro-nano bubbles;

[0020] A mixer, used for mixing ozone micro-nano bubbles with Bayer solution to form a mixed liquid;

[0021] An ozone collector, used to collect unreacted ozone in the mixer;

[0022] Ozone processor, used to centrally treat ozone in ozone collector.

[0023] In some other embodiments, a circulation device is further included, wherein the inlet of the circulation device is connected to the mixer, and the outlet of the circulation device is connected to the micro-nano bubble generator; a reflux pump is provided on the outlet pipeline of the circulation device;

[0024] The circulation device is used to return the mixed liquid in the mixer to the micro-nano bubble generator.

[0025] The beneficial effects of the present invention are:

[0026] (1) The process of the present invention is suitable for removing organic matter from the sodium aluminate solution produced by the Bayer process for producing alumina from bauxite. It does not require the addition of a remover, an adsorbent or a seed crystal, nor does it require a high temperature or a long period of forced evaporation cycle. It can effectively reduce the concentration of organic matter in the Bayer solution, significantly reduce the chromaticity of the oily yellow Bayer solution, and effectively reduce the foam of the treated Bayer solution. The Bayer solution can be treated conveniently and efficiently. The process flow is simple and can effectively improve the production efficiency of alumina.

[0027] (2) The system of the present invention has a simple composition, is energy-efficient and highly efficient, does not require the addition of a large amount of chemical reagents when in use, and is relatively simple to operate in practice. It has important practical significance and economic benefits for improving the quality and efficiency of alumina produced by the Bayer process of bauxite. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a technical principle diagram in an embodiment of the present invention;

[0029] Figure 2 1 is a diagram showing the carbon reduction and decolorization effects of Bayer solution treated by different treatment processes in the embodiments of the present invention, wherein a is a conventional ozone treatment, b is a single hydrogen peroxide oxidation treatment, and c is an ozone micro-nano bubble treatment;

[0030] Figure 3 The system for treating Bayer solution with ozone micro-nano bubbles in Example 3 of the present invention comprises an ozone generator (1), a valve (2), a micro-nano bubble generator (3), a mixer (4), a circulation device (5), a reflux pump (6), an ozone collector (7), and an ozone treatment device (8). DETAILED DESCRIPTION

[0031] The main technical principle diagram of the present invention is as follows Figure 1 As shown:

[0032] Traditional ozone bubbling reactors use titanium plates for aeration, and the size of the ozone bubbles produced is generally in the centimeter level. The utilization rate and mass transfer rate of ozone are both low, and the system is unstable, which limits the apparent reaction rate of ozone oxidation, thereby reducing its ability to oxidize and treat organic matter. Micro-nano bubbles refer to bubbles smaller than 1 micron, which are small in size, large in specific surface area, and slow in floating speed. The total mass transfer coefficient of ozone from gas phase to liquid phase is positively correlated with factors such as the degree of gas-liquid two-phase disorder, the number of bubbles, and the gas-liquid contact area, and is negatively correlated with the size of the bubbles. Therefore, micro-nano bubbles can greatly improve the ozone-liquid mass transfer rate. In addition, micro-nano bubbles have the characteristics of self-contraction and rupture under liquid, and hydroxyl radicals are generated in the process, thereby improving the ozone oxidation capacity (as shown in the figure below). The size effect of ozone nanobubbles is manifested in long life under liquid, surface charge, high internal density, and the unique interface properties of nanobubbles make ozone micro-nano bubbles more efficient in degrading pollutants.

[0033] Example 1

[0034] The generated ozone was passed through a micro-nano bubble generator and mixed with 100 mL of Bayer solution (Na 2 The ozone content is 180g / L) and the mixing time is 0.5h. The ozone mass concentration is 100mg / L. The gas flow rate is 0.8L / min.

[0035] At the same time, direct ozone aeration is used to treat the Bayer solution. The contact method between the direct ozone aeration and the Bayer solution is bubbling, the bubble size is about 1 mm, and the operating pressure is 0.1 MPa. Table 1 shows the treatment effect of ozone micro-nano bubbles and traditional ordinary ozone on the Bayer solution.

[0036] Table 1 Treatment effects of ozone micro-nano bubbles and ordinary ozone

[0037] Process Type Ozone utilization rate Decolorization effect Foam reduction effect Ozone Micro-Nano Bubbles 90.3％ 92.5％ After shaking, the bubbles disappear faster Ordinary ozone 57.6％ 35.2％ After shaking, the bubbles disappear at a normal rate.

[0038] It is not difficult to see from Table 1 that ozone micro-nano bubbles are more effective in reducing carbon, decolorization and foaming.

[0039] Example 2

[0040] Take 100mL of actual Bayer solution, Na 2 The O content is 180g / L, and it is treated with micro-nano bubbles for 1h.

[0041] At the same time, the same volume of Bayer solution was oxidized by hydrogen peroxide, the amount of hydrogen peroxide (concentration of 30%) added was 10%, and the oxidation time of hydrogen peroxide was controlled at 4 hours. Table 2 shows the treatment effect of ozone micro-nano bubbles and hydrogen peroxide on Bayer solution.

[0042] Table 2 Treatment effects of ozone micro-nano bubbles and hydrogen peroxide

[0043]

[0044] It is not difficult to see from Table 2 that compared with hydrogen peroxide treatment, ozone micro-nano bubbles are better in reducing carbon, decolorization and foaming.

[0045] Figure 2 The following are the carbon reduction and decolorization effects of Bayer solution treated by different treatment processes in the embodiments of the present invention, where a is traditional ozone treatment, b is hydrogen peroxide oxidation treatment alone, and c is ozone micro-nano bubble treatment. Figure 2 It can be seen that the color of the Bayer solution after carbon reduction and decolorization by the treatment process of the present invention is significantly lighter than the color after the traditional ozone treatment and the single hydrogen peroxide oxidation treatment, thus proving that the carbon reduction and decolorization effect of the present invention is better. This is consistent with the treatment effects in Table 1 and Table 2.

[0046] Example 3

[0047] A system for treating Bayer solution with ozone micro-nano bubbles, the system comprising an ozone generator (1), a micro-nano bubble generator (3), a mixer (4), an ozone collector (7) and an ozone treatment device (8) which are connected in sequence; and a circulation device (5), wherein an inlet of the circulation device (5) is connected to the mixer (4), and an outlet of the circulation device (5) is connected to the micro-nano bubble generator (3); and a reflux pump (6) is provided on the outlet pipeline of the circulation device (5).

[0048] An ozone generator (1) for converting oxygen into ozone;

[0049] A micro-nano bubble generator (3) is used to convert ozone into ozone micro-nano bubbles;

[0050] A mixer (4) is used to mix the ozone micro-nano bubbles with the Bayer solution to form a mixed solution;

[0051] an ozone collector (7) for collecting unreacted ozone in the mixer (4);

[0052] The ozone processor (8) is used to centrally process the ozone in the ozone collector (7).

[0053] The circulation device (5) is used to reflux the mixed liquid in the mixer (4) to the micro-nano bubble generator (3).

[0054] Figure 3 The present invention is a system for treating Bayer solution with ozone micro-nano bubbles. Figure 3As shown, a valve (2) is provided on the pipeline connecting the ozone generator (1) and the micro-nano bubble generator (3); a valve (2) is provided on the pipeline connecting the micro-nano bubble generator (3) and the Bayer solution reactor (4); a valve (2) and a reflux pump (6) are provided on the pipeline between the circulation device (5) and the micro-nano bubble generator (3), and the reflux pump (6) is used to reflux the mixed liquid in the mixer (4) in the circulation device (5) to the micro-nano bubble generator (3). The upper end of the mixer (4) is connected to the ozone collector (7), and the ozone collector (7) is connected to the ozone processor (8), so as to achieve centralized adsorption treatment or heat treatment of unreacted ozone.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for treating Bayer solution with ozone micro-nano bubbles, characterized in that: The method comprises the following steps: preparing ozone into ozone micro-nano bubbles; mixing the ozone micro-nano bubbles with Bayer solution to prepare a mixed liquid; and collecting unreacted ozone in the mixed liquid for centralized treatment.

2. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1, characterized in that: The invention also includes mixing the mixed solution with ozone after refluxing to produce ozone micro-nano bubbles and mixing the ozone micro-nano bubbles with the Bayer solution again; Preferably, the reflux rate is 0.2-3 L / min.

3. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1, characterized in that: The preparation method of the ozone micro-nano bubbles is: mixing ozone with water, wherein the pressure of the mixture of ozone and water is 0.25-0.45 MPa, the amount of ozone is 40-60 g / h, and the gas flow rate of ozone is 0.3-5 L / min.

4. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1, characterized in that: The particle size of the ozone micro-nano bubbles is less than 52 μm, and the gas content is 1.0-2.5%.

5. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1, characterized in that: The Bayer solution has an alkalinity of 120-250 g / L, a total organic carbon content of 5-50 g / L, and a temperature of 40-55°C.

6. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1 or 2, characterized in that: The conditions for mixing the ozone micro-nano bubbles with the Bayer solution are: the mixing pressure is 0.1-0.25 MPa, the mixing time is 0.5-2 h, and the total number of micro-nano bubbles is greater than 1.3×10 8 Pieces / mL.

7. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 2, characterized in that: The conditions for mixing the mixed liquid with ozone after refluxing are: pressure of 0.25-0.45 MPa, ozone amount of 40-60 g / h, and ozone gas flow rate of 0.3-5 L / min.

8. The process for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 1, characterized in that: The concentrated treatment is solution absorption or thermal treatment.

9. A system for treating Bayer solution with ozone micro-nano bubbles, used to implement the process for treating Bayer solution with ozone micro-nano bubbles as described in any one of claims 1 to 8, characterized in that , including an ozone generator, a micro-nano bubble generator, a mixer, an ozone collector and an ozone processor connected in sequence; Ozone generator, used to convert oxygen into ozone; A micro-nano bubble generator, used to convert ozone into ozone micro-nano bubbles; A mixer, used for mixing ozone micro-nano bubbles with Bayer solution to form a mixed liquid; An ozone collector, used to collect unreacted ozone in the mixer; Ozone processor, used to centrally treat ozone in ozone collector.

10. The system for treating Bayer solution with ozone micro-nano bubbles as claimed in claim 9, characterized in that: It also includes a circulation device, the inlet of which is connected to the mixer, and the outlet of which is connected to the micro-nano bubble generator; a reflux pump is provided on the outlet pipeline of the circulation device; The circulation device is used to return the mixed liquid in the mixer to the micro-nano bubble generator.

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