Causticizing device for sodium carbonate in sodium aluminate solution and application of causticizing device

Abstract

The invention provides a causticizing device for sodium carbonate in a sodium aluminate solution, and relates to the technical field of aluminum oxide production devices. The causticizing device comprises a pre-causticizing tank and a causticizing tank, wherein the pre-causticizing tank and the causticizing tank are respectively provided with an inlet I, an outlet I, an inlet II and an outlet II. The inlet I is communicated with a causticizing stock solution I pipeline and the lime milk tank, and the outlet I is communicated with the causticizing tank. The pre-causticizing filter is provided with a filtrate I outlet and a filter cake I outlet, the filtrate I outlet is communicated with an aluminum oxide production section, and the filter cake I outlet is combined with a causticizing stock solution II pipeline and then connected to the inlet II. The outlet II is connected with a causticizing filter, the causticizing filter is provided with a filtrate II outlet and a filter cake II outlet, the filtrate II outlet is communicated with an aluminum oxide production section, and the filter cake II outlet is used for discharging or comprehensively utilizing. According to the causticizing device, the lime efficiency is improved to 80% or above, the total causticizing efficiency reaches 80% or above, heating and cooling operation is not needed, and energy consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of alumina production devices, and in particular to a causticizing device for sodium carbonate in a sodium aluminate solution and application thereof. Background Art

[0002] Alumina (Al2O3) is an important inorganic compound with high hardness and high melting point. Alumina has a wide range of applications in industry and science, mainly including refractory materials, ceramics, catalysts and adsorbents, electronic and electrical insulation materials, and grinding and polishing materials. The various crystal forms of alumina (such as α-Al2O3, γ-Al2O3, etc.) make it exhibit different physical and chemical properties under different temperatures and conditions.

[0003] There are three main methods for preparing alumina in industry: Bayer process, soda lime sintering process and Bayer-sintering combined process. The Bayer process uses caustic soda solution to dissolve alumina in bauxite at high temperature to generate sodium aluminate solution. The aluminum hydroxide is reprecipitated by cooling and adding aluminum hydroxide seeds, and finally roasted to obtain alumina. The soda lime sintering method is suitable for processing high-silicon bauxite. Bauxite, sodium carbonate and lime are mixed and sintered to generate clinker such as sodium aluminate. Sodium aluminate is then dissolved with a dilute alkaline solution. After desiliconization and decomposition, aluminum hydroxide is finally obtained, which is then roasted into alumina. The Bayer-sintering combined process combines the advantages of the Bayer process and the sintering process, and improves the utilization rate and economic benefits of raw materials through series, parallel or mixed connection. Compared with the other two methods, the process flow of preparing alumina by the Bayer process is relatively simple, easy to operate and control. However, there is decausticization in the production of alumina by the Bayer process, that is, the process of converting caustic soda in sodium aluminate solution into sodium carbonate. Decausticization not only includes the process of various carbonates in ore and lime additives forming sodium carbonate with sodium aluminate solution, but also includes the decomposition of organic matter such as sodium humate and the conversion of caustic soda into sodium carbonate due to the introduction of CO2 during air stirring. In the actual production process, carbonates in various raw materials are the main cause of decausticization.

[0004] In the process of producing alumina by the Bayer process, the decausticization of carbonates will bring many hazards, including: converting part of the caustic soda in the solution into sodium carbonate, which is not conducive to the dissolution of alumina in the ore; the increase in the concentration of sodium carbonate in the solution will cause the solution viscosity to increase, making it difficult to separate the red mud from the sedimentation, and reduce the decomposition rate of the seed separation process. The precipitation of sodium carbonate during the evaporation of the mother liquor will also reduce the heat transfer efficiency of the evaporation heat exchanger and increase the energy consumption of evaporation. The most serious is that the carbonate will form scale on the surface and inside of the equipment during the dissolution and precipitation, affecting the overall operation and heat transfer of the system, resulting in increased system energy consumption, increased equipment maintenance and cleaning costs, and even causing production interruptions. Therefore, the production process of alumina produced by the Bayer process must be equipped with sodium carbonate removal and causticization processes to maintain the sodium carbonate balance in the production cycle.

[0005] The invention patent with the publication number CN 1868880 A discloses a side stream causticizing method for Bayer process alumina production to replace the evaporation and salt removal-causticizing process. The causticizing stock solution used in the side stream causticizing of this method is the secondary washing liquid from the red mud washing process. This method has the advantages of short process flow and low energy consumption compared with the evaporation and salt removal-causticizing process. However, this method can only be applied to low-concentration solutions such as secondary / tertiary washing liquids, and the amount of sodium carbonate in the causticizing stock solution is small, which cannot meet the production needs of alumina. Moreover, as the reaction proceeds, the surface of Ca(OH)2 particles will be covered with precipitated Na2CO3 particles, which will hinder the causticizing reaction. The content of the causticizing residue is high, the lime efficiency is low, and the causticizing rate of this method is low, about 25% to 35%.

[0006] The invention patent with publication number CN 1323278 A discloses an improved process for causticizing Bayer liquor in an alumina refinery, which includes reacting lime with aluminate ions in Bayer liquor under controlled low to medium temperature (70-80°C) and stirring conditions in a primary reactor; and reacting hydrocalumite with Bayer liquor to form calcium carbonate in a secondary reactor under controlled conditions of 100-180°C, thereby obtaining causticized Bayer liquor. This method greatly improves the efficiency of lime utilization and minimizes alumina loss. However, this method requires cooling (primary reaction) and heating (secondary reaction) the alumina process solution, resulting in increased energy consumption in alumina production.

[0007] It can be seen that the existing Bayer liquor causticizing methods in the prior art cannot simultaneously take into account a high causticizing rate and low energy consumption, resulting in these methods having great limitations and being difficult to apply in actual industrial production. Therefore, it is necessary to provide a Bayer liquor causticizing method with a high causticizing rate and low energy consumption to solve the above problems. Summary of the invention

[0008] In order to solve the above problems, the present invention provides a causticizing device for sodium carbonate in a sodium aluminate solution, the causticizing device comprising a precausticizing tank 3 and a causticizing tank 6, the top and bottom of the precausticizing tank 3 are respectively provided with an inlet I and an outlet I, the top and bottom of the causticizing tank 6 are respectively provided with an inlet II and an outlet II;

[0009] Among them, the inlet I is connected with the causticizing raw liquid I pipeline and the lime milk tank I respectively, and the outlet I is connected with the causticizing tank 6 through the pre-causticizing filter 5; the pre-causticizing filter 5 is provided with a filtrate I outlet and a filter cake I outlet, the filtrate I outlet is connected with the alumina production section, the filter cake I outlet is connected to the inlet II after being merged with the causticizing raw liquid II pipeline, the outlet II is connected with the causticizing filter 8, the causticizing filter 8 is provided with a filtrate II outlet and a filter cake II outlet, the filtrate II outlet is connected with the alumina production section, and the filter cake II outlet is discharged to the red mud dump or transferred to other places for comprehensive utilization.

[0010] Furthermore, the number of the pre-causticizing tanks 3 and the number of the causticizing tanks 6 are n, respectively, where n is an integer ≥1.

[0011] Furthermore, a lime milk pump 2 is provided between the lime milk tank 1 and the precausticizing tank 3, a precausticizing pump 4 is provided between the precausticizing tank 3 and the precausticizing filter 5, and a causticizing pump 7 is provided between the causticizing tank 6 and the causticizing filter 8.

[0012] Furthermore, the causticizing device for sodium carbonate in the sodium aluminate solution further comprises a causticizing auxiliary agent tank 9, and the inlet I and the inlet II are respectively connected to the causticizing auxiliary agent tank 9.

[0013] Furthermore, a causticizing agent pump 10 is provided between the inlet II and the causticizing agent tank 9 .

[0014] Furthermore, the causticizing device for sodium carbonate in the sodium aluminate solution also includes a hot water pipeline, and the filter cake I outlet and the filter cake II outlet are respectively connected to the hot water pipeline.

[0015] The method for using the causticizing device for sodium carbonate in the sodium aluminate solution is as follows:

[0016] S1, pre-causticizing: firstly, the sodium aluminate solution in the Bayer process alumina production process is added as the causticizing stock solution I into the pre-causticizing tank 3, and then lime milk is added, stirred for reaction, to obtain the slurry I, and filtered to obtain the filtrate I and the filter cake I, the filtrate I is returned to the alumina production process, and the filter cake I enters step S2;

[0017] S2, pre-causticizing: the filter cake I is mixed with the causticizing stock solution II and added to the causticizing tank 6, stirred for reaction, and slurry II is obtained, and then the process proceeds to step S3; the weight of the causticizing stock solution II is equal to that of the causticizing stock solution I;

[0018] S3, causticizing slag treatment: the slurry II is filtered to obtain the filtrate II and the filter cake II, the filtrate II is returned to the alumina production process, and the filter cake II is directly discharged to the red mud dump or comprehensively utilized after washing.

[0019] Furthermore, in step S1, the causticized stock solution I is a washing solution obtained by washing red mud n times, a washing solution obtained by washing decomposition crystal seeds, or a washing solution obtained by washing product aluminum hydroxide, wherein n is an integer ≥1, and the washing solution obtained by washing product aluminum hydroxide is a strong filtrate or a weak filtrate.

[0020] Furthermore, in step S1, the content of effective CaO in the lime milk is 14wt.% to 16wt.%.

[0021] Further, in step S1, the stirring reaction temperature is 90°C to 110°C, and the reaction time is 5 to 60 minutes. Preferably, the stirring reaction time is 10 to 50 minutes. More preferably, the stirring reaction time is 10 to 30 minutes.

[0022] Furthermore, in step S1, the stirring speed is >30 r / min, preferably, the stirring speed is >80 r / min, and more preferably, the stirring speed is >200 r / min.

[0023] The temperature control of the stirring reaction of the present invention is mainly determined by the causticizing stock solution I, and no special regulation is required, so no additional heating or cooling is required. At the same time, the present invention accelerates the causticizing reaction speed through stirring and reaction temperature, improves the causticizing efficiency, and reduces energy consumption.

[0024] Further, in step S1, the amount of lime milk added is 0.5 to 1 times the total molar amount of sodium carbonate in the causticizing stock solution I and the causticizing stock solution II. Preferably, the amount of lime milk added is 0.7 to 0.9 times the total molar amount of sodium carbonate in the causticizing stock solution I and the causticizing stock solution II. More preferably, the amount of lime milk added is 0.8 times the total molar amount of sodium carbonate in the causticizing stock solution I and the causticizing stock solution II.

[0025] Furthermore, in step S1, a causticizing agent is added while adding the lime milk, and the causticizing agent is a borate pH buffer.

[0026] Furthermore, the borate is sodium metaborate or sodium tetraborate.

[0027] Furthermore, the amount of the causticizing agent added is 100 to 1000 ppm. Preferably, the amount of the causticizing agent added is 200 to 700 ppm. More preferably, the amount of the causticizing agent added is 300 to 500 ppm.

[0028] Furthermore, in step S1, the filter cake I is first washed with 95°C hot water before entering step S2, and the washing water is used for red mud washing.

[0029] Furthermore, in step S2, the causticized stock solution II is the red mud washing solution obtained by n times or the sodium carbonate solution obtained by the evaporation and salt removal process, where n is an integer ≥1.

[0030] Furthermore, in step S2, the stirring reaction temperature is 90-110°C, and the stirring reaction time is 30-120 min. Preferably, the stirring reaction time is 40-90 min, and more preferably, the stirring reaction time is 50-70 min.

[0031] The temperature of the stirring reaction of the present invention is mainly determined by the causticizing stock solution II, and no special regulation is required, so there is no need to increase or decrease the temperature additionally. At the same time, the present invention controls the reaction time so that the Ca(OH)2 reacts completely and the lime efficiency is high.

[0032] Further, in step S2, the stirring speed is >30 r / min. Preferably, the stirring speed is >80 r / min, and more preferably, the stirring speed is >200 r / min.

[0033] Furthermore, in step S2, a causticizing agent is added to the causticizing reaction tank before the stirring reaction, and the amount of the causticizing agent added is 100 to 1000 ppm. Preferably, the amount of the causticizing agent added is 200 to 700 ppm. More preferably, the amount of the causticizing agent added is 300 to 500 ppm.

[0034] Furthermore, in step S3, the filter cake II is washed with hot water, and the filtrate III and the filter cake III are obtained by filtering. The former is sent to the red mud washing as washing water, and the latter is directly discharged to the red mud dump, or used as a desulfurizer for desulfurization in power plants to achieve comprehensive utilization, thereby avoiding the occurrence of decausticization when calcium carbonate is returned to the red mud washing.

[0035] Furthermore, two rotary drum filters are used as filtering and separation equipment during the treatment of causticized slag, which are used for filtering and separation or washing respectively.

[0036] Furthermore, a flat plate filter is used as a filtering and separating device during the treatment of the causticized slag, and the flat plate surface is divided into a separation zone and a washing zone to achieve filtering separation or washing respectively.

[0037] In a conventional causticizing reaction unit, lime reacts with an aqueous solution of sodium carbonate (Na2CO3) to produce sodium hydroxide. This reaction is unlikely to go to completion but rather to equilibrium, which can be described by the following equation:

[0038] K=[OH - ] 2 / [CO3 2- ]

[0039] K is the apparent equilibrium constant. The conversion of sodium carbonate into sodium hydroxide is controlled by chemical equilibrium and reaction kinetics. The reaction usually proceeds rapidly at the beginning, and then becomes very slow after 20 to 30 minutes. There are two main reasons for this: first, the causticizing reaction equilibrium shifts to the left due to the increase in [OH-] concentration; second, as the reaction proceeds, the surface of the Ca(OH)2 particles will be covered with the precipitated Na2CO3 particles, which hinders the CO3 2- Ions diffuse from the solution to the core of the Ca(OH)2 particles.

[0040] In order to eliminate the adverse effects of the calcium carbonate film covering the surface of Ca(OH)2, a causticizing agent is added when necessary. The causticizing agent can suppress the concentration of hydroxyl ions on the surface or near the Ca(OH)2 particles, shift the equilibrium of the causticizing reaction to the right, and thus improve the causticizing efficiency.

[0041] It is generally believed that the decausticizing reaction in the alumina production system is mainly the result of the action of free NaOH and CaCO3. This reaction can only be significantly carried out under high temperature (>150°C) conditions; under low temperature (<100°C) conditions, the decausticizing reaction of CaCO3 is relatively weak and has been ignored. Therefore, in alumina production enterprises, the causticizing slag with CaCO3 as the main component is directly mixed into the red mud washing system and discharged with the red mud after sedimentation and separation. However, even in low-temperature sodium aluminate solution, the decausticizing of CaCO3 is very obvious, which causes carbonate to dissolve back into the process and is accompanied by the loss of alumina. Therefore, washing the causticizing slag and then discharging it directly is very beneficial to avoid carbonate decausticizing.

[0042] The present invention allows a portion of the causticizing stock solution I (sodium aluminate solution) to enter the pre-causticizing (first stage) reaction tank to react with lime milk under vigorous stirring conditions, adds a causticizing auxiliary agent if necessary, and then filters and separates the causticized liquid with increased [OH-] concentration, and the filter cake is sent to the causticizing stage (second stage) as a causticizing agent, and the causticized liquid is returned to the alumina production process. The causticizing efficiency of this stage of causticizing reaction is about 25-45%.

[0043] The filter cake separated after pre-causticization is mixed with fresh causticization stock solution II and then enters the causticization stage (second stage) reaction tank for stirring and reaction. 2- The concentration of ions is reduced, the concentration of [OH-] is reduced, and the causticization reaction is pushed to the right. At the same time, the surface of Ca(OH)2 particles is covered with the precipitated CaCO3 particles by vigorous stirring, eliminating CO3 2- The diffusion of ions from the solution to the core of the Ca(OH)2 particles is hindered. If necessary, a causticizing agent can be added. In this way, the unreacted Ca(OH)2 particles after pre-causticizing can be completely reacted to achieve the effect of fully utilizing the lime. The causticizing efficiency of this stage of causticizing reaction is about 40-65%.

[0044] After causticizing, the slurry is sent to the causticizing slag treatment section (the third section). After filtration and separation, the filtrate is returned to the alumina process. The filter cake is washed with hot water and then filtered and separated. The washing liquid is sent to red mud washing as washing water. The filter cake is desulfurized in the power plant as a desulfurizer for comprehensive utilization or directly discharged to the red mud yard to avoid anti-causticization when calcium carbonate is returned to the red mud washing.

[0045] After two-stage causticizing reaction, the lime milk is washed and treated with causticizing residue. Finally, the residual Ca(OH)2 in the causticizing residue is almost zero, the lime efficiency can be increased to more than 80%, and the total causticizing efficiency can reach 80% and above. At the same time, it can avoid the causticizing product CaCO3 from being reversed and causing CO3 2- The ions are returned to the alumina production process.

[0046] Compared with the prior art, the beneficial technical effects of the present invention are:

[0047] The lime efficiency of the causticizing device of the present invention can be increased to more than 80%, and the total causticizing efficiency can reach 80% and above. In addition, the present invention does not require heating or cooling operations, which greatly reduces the energy consumption of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be further described below in conjunction with the accompanying drawings.

[0049] Figure 1 It is a diagram of a causticizing device for sodium carbonate in a sodium aluminate solution of the present invention;

[0050] Among them, 1 is a lime milk tank, 2 is a lime milk pump, 3 is a pre-causticizing tank, 4 is a pre-causticizing pump, 5 is a pre-causticizing filter, 6 is a causticizing tank, 7 is a causticizing pump, 8 is a causticizing filter, 9 is a causticizing auxiliary agent tank, and 10 is a causticizing auxiliary agent pump. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the following description is only for explaining the present invention and does not limit its contents.

[0052] Experimental solutions and agents in the specific embodiments of the present invention:

[0053] Primary washing solution (Na2O T 80.70g / L, Al2O361.99 g / L, Na2O k 68.09g / L,N c / NT 15.72%), the secondary washing liquid and the tertiary washing liquid are solutions from domestic Shanxi Factory A, the evaporated salt solution is the solution from domestic Guizhou Factory B, and the seed washing liquid comes from domestic Shandong Factory C; the lime milk is prepared with industrial lime from domestic Shanxi Factory A, with an effective CaO weight content of 15.33wt.%; the causticizing agent is W-7201 causticizing agent purchased from the market.

[0054] Reference Examples:

[0055] like Figure 1 As shown, a causticizing device for sodium carbonate in a sodium aluminate solution comprises a precausticizing tank 3 and a causticizing tank 6. The top and bottom of the precausticizing tank 3 are respectively provided with an inlet I and an outlet I, and the top and bottom of the causticizing tank 6 are respectively provided with an inlet II and an outlet II; the inlet I is communicated with the causticizing stock solution I pipeline and the lime milk tank 1 respectively, and the outlet I is communicated with the causticizing tank 6 through a precausticizing filter 5; the precausticizing filter 5 is provided with a filtrate I outlet and a filter cake I outlet, the filtrate I outlet is communicated with an alumina production section, the filter cake I outlet is combined with the causticizing stock solution II pipeline and connected to the inlet II, the outlet II is connected to the causticizing filter 8, the causticizing filter 8 is provided with a filtrate II outlet and a filter cake II outlet, the filtrate II outlet is communicated with the alumina production section, and the filter cake II outlet is discharged to a red mud dump or transferred to other places for comprehensive utilization.

[0056] A lime milk pump 2 is provided between the lime milk tank 1 and the precausticizing tank 3 , a precausticizing pump 4 is provided between the precausticizing tank 3 and the precausticizing filter 5 , and a causticizing pump 7 is provided between the causticizing tank 6 and the causticizing filter 8 .

[0057] The device also includes a causticizing agent tank 9, and the inlet I and the inlet II are respectively connected to the causticizing agent tank 9. A causticizing agent pump 10 is provided between the inlet II and the causticizing agent tank 9.

[0058] The device also includes a hot water pipeline, and the filter cake I outlet and the filter cake II outlet are respectively connected to the hot water pipeline.

[0059] Examples 1 to 8 all use the apparatus of the reference example.

[0060] Comparative Example 1 (Existing Causticization Technology Simulation)

[0061] In a 6-head rotating bottle oil bath device, simulate the existing side stream causticizing. Add 100 mL of primary washing liquid to each rotating bottle, and at the same time, adjust the sodium carbonate (in the form of Na2O cThe caustic solution was reacted at 90°C with a rotating bottle at a speed of 30 RPM. A rotating bottle was taken out every 5, 15, 30, 60, 90, and 120 minutes, and the solid-liquid separation was carried out quickly with a vacuum filtration device. The Na2O in the caustic solution was analyzed. T 、Na2O k 、N c / NT. The experimental results are shown in Table 1.

[0062] Table 1 Analysis of causticizing solution and causticizing efficiency of comparative example 1

[0063] serial number Causticizing time (min) <![CDATA[Na2O T (g / L)]]> <![CDATA[Na2O c (g / )]]> <![CDATA[N c / No(%)]]> Causticizing efficiency (%) 1 5 75.22 9.22 12.26 22.05 2 15 74.71 8.50 11.38 27.63 3 30 73.39 7.88 10.74 31.73 4 60 73.13 7.81 10.69 32.05 5 90 75.53 7.92 10.48 33.35 6 120 74.51 7.76 10.41 33.77

[0064] As shown in Table 1, the causticization speed of the existing causticization technology increases rapidly from 0 to 30 minutes. After 30 minutes, as the causticization progresses, the concentration of [OH-] in the solution increases, and CO3 2- The ions decreased and the causticizing efficiency increased slowly. After 120 minutes of reaction, the causticizing efficiency was 33.77%.

[0065] Na2O T Indicates the concentration of total alkali (Na2O) in the solution g / L, Na2O c Indicates the concentration of sodium carbonate (Na2O) g / L, N c / NT represents the percentage of sodium carbonate to total alkali.

[0066] Causticizing efficiency: Causticizing sodium carbonate (Na2O c ) divided by the amount of sodium carbonate (Na2O c ) amount.

[0067] Total causticizing efficiency = causticizing efficiency of pre-causticizing + causticizing efficiency of causticizing. The same applies below.

[0068] Example 1 (Improved Causticizing Technology)

[0069] In a 6×150mL rotating bottle oil bath apparatus, take 200mL of the primary washing solution for each group (a total of 6 groups) and divide it into 2 equal parts of 100mL each. First, add 100mL of the primary washing solution to each rotating bottle, and at the same time, add sodium carbonate (in the form of Na2O c The reaction was carried out at 90°C with a rotating bottle at a speed of 30 RPM. The solid-liquid separation was carried out quickly with a vacuum filtration device. The filter cake was used as the second causticizing agent (lime) and the Na2O in the causticizing solution was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 2.

[0070] The filter cakes were added to the corresponding primary washing liquid and rotated at 30 RPM in a rotating bottle. The reaction was carried out at a temperature of 95°C. One rotating bottle was taken out every 30, 50, 70, 90, 100 and 120 minutes. The solid-liquid separation was carried out quickly by vacuum filtration device. The Na2O in the causticized liquid was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 2.

[0071] Table 2 Analysis of causticizing solution and causticizing efficiency of Example 1

[0072]

[0073] As shown in Table 2, the three-stage causticizing technology has a significantly higher causticizing efficiency than the existing causticizing technology, from 33% to about 66%. When the causticizing time of the second stage (causticizing stage) is 0 to 70 minutes, the causticizing efficiency increases with time. After 90 minutes, the causticizing efficiency decreases.

[0074] Example 2 (Stirring and Strengthening Experiment)

[0075] In a 6×150mL rotating bottle oil bath apparatus, take 200mL of the primary washing solution for each group (a total of 6 groups) and divide it into 2 equal parts of 100mL each. First, add 100mL of the primary washing solution to each rotating bottle, and at the same time, add sodium carbonate (in the form of Na2O c The reaction was carried out at 90°C with a rotating bottle at a speed of 30 RPM. The solid-liquid separation was carried out quickly with a vacuum filtration device. The filter cake was used as the second causticizing agent (lime) and the Na2O in the causticizing solution was analyzed. T 、Na2O c 、N c / NT.

[0076] The filter cakes were added to the corresponding primary washing liquid and stirred in a 6-head water bath stirring device at 95°C for 60 minutes at stirring speeds of 50, 80, 120, 150, 170, and 200 RPM. After causticization, a vacuum filtration device was used to quickly separate the solid and liquid, and the Na2O in the causticized liquid was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 3.

[0077] Table 3 Analysis of causticizing solution and causticizing efficiency of Example 2

[0078]

[0079] It can be seen from Table 3 that with the increase of stirring speed, the causticizing efficiency of the causticizing stage (second stage) gradually increases, and the causticizing efficiency increases from 32.18% to about 38.12%.

[0080] Example 3 (Effect of causticizing aid)

[0081] In a 6×150mL rotating bottle oil bath apparatus, take 200mL of the primary washing solution for each group (a total of 6 groups) and divide it into 2 equal parts of 100mL each. First, add 100mL of the primary washing solution to each rotating bottle, and at the same time, add sodium carbonate (in the form of Na2O c CaO (lime milk) was added in a molar ratio of 1:1, and sodium metaborate causticizing agent was added to 6 groups of rotating bottles at 0, 50, 100, 250, 500, 750, and 1000 ppm respectively. The mixture was rotated at a speed of 100 RPM and reacted at a temperature of 90°C for 15 minutes. The solid-liquid separation was quickly performed using a vacuum filtration device, and the filter cake was retained as the second stage causticizing agent (lime). The Na2O in the causticized solution was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 4.

[0082] The filter cakes were added to the corresponding primary washing liquid and rotated in a rotating bottle at a speed of 100 RPM. The reaction was carried out at a temperature of 95°C. In each experiment, 0, 50, 100, 250, 500, 750, and 1000 ppm of causticizing agent were added. After reacting for 60 minutes, the solid-liquid separation was quickly carried out using a vacuum filtration device, and the Na2O in the causticizing liquid was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 4.

[0083] Table 4 Analysis of causticizing solution and causticizing efficiency of Example 3

[0084]

[0085]

[0086] As shown in Table 4, under the condition of enhanced external diffusion, the causticizing agent is added in the first stage, the second stage or both stages at the same time, and the causticizing efficiency is significantly improved. However, adding the causticizing agent in the second stage is better than that in the first stage, and adding it in the second stage at the same time has a better effect.

[0087] Example 4 (Effect of Decausticization)

[0088] In a 6×150mL rotating bottle oil bath device, 2 portions of the secondary washing liquid and the tertiary washing liquid were added to the rotating bottle, each portion was 100mL, and 3g of CaCO3 powder was added respectively. The reaction was carried out at a temperature of 95℃ for 360 minutes, and the solid-liquid separation was quickly carried out using a vacuum filtration device, and the Na2O in the causticized liquid was analyzed. T 、Na2O c 、N c / NT. The experimental results are shown in Table 5.

[0089] Table 5 Analysis of causticizing solution and calcium carbonate decausticizing rate of Example 4

[0090]

[0091] As shown in Table 5, according to the prior art, the causticized slag is directly discharged into the red mud washing system, and the calcium carbonate in the causticized slag will be decausticized, which will cause the carbon and alkali content of the secondary washing liquid and the tertiary washing liquid to increase by about 20%. For this reason, the present invention proposes to directly discharge the causticized slag after washing to improve the actual effect of causticization.

[0092] The causticizing reaction is initially affected by the chemical reaction rate. As the reaction proceeds, the [OH-] concentration in the reaction system increases and inhibits the chemical reaction rate. These experiments are used to remove the feasibility of promoting the chemical reaction to the right.

[0093] For further explanation, Examples 5 to 8 are different process combinations.

[0094] Embodiment 5:

[0095] The first washing liquid from the red mud separation and washing is added to the precausticizing tank as the precausticizing stock solution, and lime milk and causticizing aid are added to the precausticizing tank for precausticizing. The stirring speed of the precausticizing tank is 100RPM, the reaction temperature is 90°C, the reaction time is 15min, the causticizing aid dosage is 150ppm, and the lime addition amount is 1 times the molar amount of sodium carbonate. After the reaction is completed, the precausticized slurry is quickly sent to the precausticizing filter for filtration and separation; the filtrate returns to the original alumina production process, and the filter cake and 150ppm causticizing aid are added to the causticizing tank at the same time to carry out causticizing reaction with another first washing liquid (causticizing stock solution) also from the red mud separation and washing. The stirring speed of the causticizing tank is 100RPM, the reaction temperature is 90℃, and the reaction time is 90min. After the reaction is completed, the causticized slurry is sent to the causticizing filter for solid-liquid separation; the filtrate returns to the original process, and the causticized slag is washed with 95℃ hot water at the same time, and the washing water is sent to the red mud washing as red mud washing water, and the causticized slag is directly discharged to the yard. The results are shown in Table 6.

[0096] Embodiment 6:

[0097] The secondary washing liquid separated from the red mud washing is added to the precausticizing tank as the precausticizing stock solution. At the same time, lime milk is added to the precausticizing tank at a molar amount of 0.9 times of sodium carbonate, and 250ppm of causticizing aid is added for precausticizing. The stirring speed of the precausticizing tank is 200RPM, the reaction temperature is 90℃, and the reaction time is 30min. After the reaction is completed, the precausticizing slurry is quickly sent to the precausticizing filter for filtration and separation; the filtrate returns to the original process of alumina production, the filter cake and 100ppm of causticizing aid are added to the causticizing tank, and react with the same amount of primary washing liquid (causticizing stock solution) for 120min, the stirring speed is 80RPM, after the reaction is completed, the causticized slurry is sent to the causticizing filter for solid-liquid separation, the filtrate returns to the original process, and the causticizing slag is washed with 95℃ hot water at the same time, the washing water is sent to the red mud washing as red mud washing water, and the causticizing slag is used as a desulfurizer for power plants. The results are shown in Table 6.

[0098] Embodiment 7:

[0099] The washing liquid separated from the red mud washing is added to the precausticizing tank as the precausticizing stock solution. At the same time, lime milk is added to the precausticizing tank at 1 times the total molar amount of sodium carbonate, and 300ppm of causticizing aid is added for precausticizing. The stirring speed is 30RPM, the reaction temperature is 95℃, and after 10 minutes of reaction, the precausticizing slurry is quickly sent to the precausticizing filter for filtration and separation. The filtrate returns to the original process of alumina production, the filter cake is added to the causticizing tank together with 200ppm of causticizing aid, and reacts with an equal amount of salt solution (causticizing stock solution) from evaporation and salt removal at a reaction temperature of 100℃ and a stirring speed of 30RPM for 60min. After the reaction is completed, the causticized slurry is sent to the causticizing filter for solid-liquid separation; the filtrate returns to the original process, and the causticizing slag is washed with 95℃ hot water at the same time, the washing water is sent to the red mud washing as red mud washing water, and the causticizing slag is used as a desulfurizer for power plants. The results are shown in Table 6.

[0100] Embodiment 8:

[0101] The washing liquid from the decomposition seed washing is added to the precausticizing tank as the precausticizing stock solution. At the same time, lime milk is added to the precausticizing tank at 0.7 times the total molar amount of sodium carbonate, and 100ppm of causticizing aid is added for precausticizing. The stirring speed is 120RPM, the reaction temperature is 92℃, and after 15 minutes of reaction, the precausticized slurry is quickly sent to the precausticizing filter for filtration and separation. The filtrate returns to the original process of alumina production, the filter cake is added to the causticizing tank together with 200ppm of causticizing aid, and reacts with an equal amount of the first washing liquid (causticizing stock solution) from the sedimentation separation washing at a reaction temperature of 100℃ and a stirring speed of 120RPM for 60min. After the reaction is completed, the causticized slurry is sent to the causticizing filter for solid-liquid separation; the filtrate returns to the original process, and the causticized slag is washed with 95℃ hot water at the same time, the washing water is sent to the red mud washing as red mud washing water, and the causticized slag is used as a desulfurizer for power plants. The results are shown in Table 6.

[0102] Table 6 Analysis of causticizing solution and calcium carbonate decausticizing rate of Examples 5 to 8

[0103]

[0104] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A causticizing device for sodium carbonate in sodium aluminate solution, characterized in that: The causticizing device comprises a precausticizing tank (3) and a causticizing tank (6). The top and bottom of the precausticizing tank (3) are respectively provided with an inlet I and an outlet I, and the top and bottom of the causticizing tank (6) are respectively provided with an inlet II and an outlet II; the inlet I is communicated with the causticizing raw liquid I pipeline and the lime milk tank I respectively, and the outlet I is communicated with the causticizing tank (6) through a precausticizing filter (5); the precausticizing filter (5) is provided with a filtrate I outlet and a filter cake I outlet, the filtrate I outlet is communicated with the alumina production section, the filter cake I outlet is combined with the causticizing raw liquid II pipeline and connected to the inlet II, the outlet II is connected to the causticizing filter (8), the causticizing filter (8) is provided with a filtrate II outlet and a filter cake II outlet, the filtrate II outlet is communicated with the alumina production section, and the filter cake II outlet is discharged to a red mud dump or transferred to other places for comprehensive utilization; the number of the precausticizing tank (3) and the causticizing tank (6) is n, and n is an integer ≥1.

2. The causticizing device for sodium carbonate in a sodium aluminate solution according to claim 1, characterized in that: The causticizing device for sodium carbonate in the sodium aluminate solution further comprises a causticizing auxiliary agent tank (9), and the inlet I and the inlet II are respectively connected to the causticizing auxiliary agent tank (9).

3. The causticizing device for sodium carbonate in a sodium aluminate solution according to claim 1, characterized in that: A causticizing agent pump (10) is provided between the inlet II and the causticizing agent tank (9).

4. The causticizing device for sodium carbonate in a sodium aluminate solution according to claim 1, characterized in that: The causticizing device for sodium carbonate in the sodium aluminate solution also includes a hot water pipeline, and the filter cake I outlet and the filter cake II outlet are respectively connected to the hot water pipeline.

5. The method for using the sodium carbonate causticizing device in the sodium aluminate solution according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, pre-causticizing: firstly, sodium aluminate solution in the Bayer process alumina production process is added as the causticizing stock solution I into the pre-causticizing tank (3), then lime milk is added, stirred for reaction, to obtain the slurry I, filtered to obtain the filtrate I and the filter cake I, the filtrate I is returned to the alumina production process, and the filter cake I enters step S2; S2, pre-causticizing: the filter cake I is mixed with the causticizing stock solution II and added to the causticizing tank (6), stirred for reaction, and slurry II is obtained, and then the process proceeds to step S3; the weight of the causticizing stock solution II is equal to that of the causticizing stock solution I; S3, causticizing slag treatment: the slurry II is filtered to obtain the filtrate II and the filter cake II, the filtrate II is returned to the alumina production process, and the filter cake II is directly discharged to the red mud dump or comprehensively utilized after washing.

6. The method of use according to claim 5, characterized in that: In step S1, the causticized stock solution I is the washing liquid of red mud washing n times, the washing liquid of decomposition seed washing, or the washing liquid of product aluminum hydroxide washing, wherein n is an integer ≥1, and the washing liquid of product aluminum hydroxide washing is a strong filtrate or a weak filtrate.

7. The method of use according to claim 5, characterized in that: In step S1, the stirring reaction temperature is 90°C to 110°C, the reaction time is 5 to 60 min, and the stirring speed is >30 r / min.

8. The method of use according to claim 5, characterized in that: In step S2, the stirring reaction temperature is 90-110°C, the stirring reaction time is 30-120 min, and the stirring speed is >30 r / min.

9. The method of use according to claim 5, characterized in that: During the treatment of the causticized slag, two rotary drum filters are used as filtering and separation equipment, which are used for filtering and separation or washing respectively.

10. The method of use according to claim 5, characterized in that: When treating the causticized slag, a flat plate filter is used as filtering and separating equipment, and the flat plate surface is divided into a separation area and a washing area, respectively realizing filtering and separating or washing.

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