Method for preparing high-concentration calcium chloride solution by using alkaline residues and ammonia distillation waste clear liquid

Abstract

The invention relates to a method for preparing a high-concentration calcium chloride solution by using alkaline residues and ammonia distillation waste clear liquid, which comprises the following steps of: reacting a byproduct hydrogen chloride with the alkaline residues and the ammonia distillation waste clear liquid to obtain a calcium chloride solution with a certain concentration, adding calcium oxide to remove magnesium ions in the calcium chloride solution, and evaporating and concentrating by using waste heat of the ammonia distillation waste clear liquid to obtain the high-concentration calcium chloride solution. And finally, acidifying by using a byproduct hydrogen chloride to obtain a raw material for producing calcium chloride dihydrate in a calcium chloride factory. The process is simple and effective, solves the problem that the alkaline residues are easy to block in the prior art, fully utilizes the alkaline residues and the ammonia distillation waste clear liquid generated in the process of preparing alkali by an ammonia-alkali method, recycles waste heat in the ammonia distillation waste clear liquid, and improves the concentration of the calcium chloride liquid, so that the process has good practicability and economic value.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium chloride preparation, and in particular relates to a method for preparing a high-concentration calcium chloride solution by utilizing alkali residue and ammonia evaporation waste clear liquid. Background Art

[0002] The ammonia-soda process is the largest process in the production of soda ash, accounting for about 45% of the global production scale. This process has the advantages of low cost, scalable production, and high product purity, but it also has disadvantages such as low raw material utilization and high discharge of waste liquid and waste residue. The treatment of waste liquid and waste residue has always been a problem that has troubled many large soda plants.

[0003] The waste materials produced by the ammonia-soda process mainly include alkali residue and ammonia evaporation waste liquid. The components of alkali residue are mainly calcium carbonate, calcium chloride, sodium chloride, magnesium salt and silicon dioxide, and the components of ammonia evaporation waste liquid are mainly calcium chloride, calcium hydroxide, sodium chloride and a small amount of aluminum and iron salt. The direct discharge of waste residue and waste liquid not only causes environmental pollution and waste of resources, but also restricts the further development of enterprises. In addition, the temperature of ammonia evaporation waste liquid is 80~90 degrees Celsius when it is discharged, and the waste heat of this part is not effectively utilized. At present, the utilization of alkali residue mainly includes the production of cement or bricks, but because the alkali residue contains a large amount of chloride ions and is difficult to remove, it will have a great impact on the strength of building materials, so it is difficult to use in large quantities. There is also a method to react alkali residue with acid to produce calcium chloride solution, but the concentration of the produced calcium chloride solution is generally low, and the alkali residue is prone to blockage during the utilization process. The ammonia evaporation waste liquid can be sent to calcium chloride to produce calcium chloride dihydrate after re-drying, but the concentration of calcium chloride in the production process is low, only about 20%, and a large amount of steam is required for evaporation, which is costly. Summary of the invention

[0004] The invention aims to provide a method for preparing a high-concentration calcium chloride solution by utilizing alkali residue and ammonia evaporation waste clear liquid, so as to solve the problems of low raw material liquid concentration and high steam consumption in traditional calcium chloride production.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing a high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid, comprising the following steps: (1) stirring and mixing the alkali residue and the ammonia evaporation waste clear liquid uniformly to obtain an alkaline mother liquor; (2) Passing the alkaline mother liquor into the first reactor with stirring, and stopping when the alkaline mother liquor level in the reactor reaches 1 / 2 to 2 / 3 of the reactor height, and then passing hydrogen chloride gas into the alkaline mother liquor and stirring to react to obtain an acidic slurry; when the pH of the acidic slurry drops to 0 to 1, stop passing hydrogen chloride gas, adjust the stirring rate, and then pass the acidic slurry into the pH adjustment tank; (3) Add calcium oxide to the pH adjustment tank and stir to react to obtain an alkaline suspension; (4) When the pH value of the alkaline suspension increases to 11.3-13, the alkaline suspension is clarified and settled to obtain an alkaline clear liquid, and the alkaline clear liquid is heat exchanged with the ammonia evaporation waste clear liquid to increase the temperature of the alkaline clear liquid and evaporate and concentrate it, and the ammonia evaporation waste clear liquid after heat exchange is recycled; (5) Then, hydrogen chloride gas is introduced into the alkaline clear liquid after the temperature is raised to adjust the pH value to between 4 and 6.5 to obtain a weakly acidic high-concentration calcium chloride solution. The tail gas generated during the reaction of step (2) and step (5) is absorbed by the ammonia evaporation waste clear liquid after heat exchange, and then the clear liquid is sent to step (1) to be mixed with alkaline slag to produce an alkaline mother liquor.

[0006] Furthermore, in the step (1), the mass ratio of alkali residue to ammonia evaporation waste liquid is 0.2-0.5:1, the mechanical stirring rate is 200-350 r / min, and the stirring time is 30-60 min.

[0007] Furthermore, in the step (2), the alkaline mother liquor and hydrogen chloride gas are introduced into the stirred reactor, and the alkaline mother liquor is introduced into the first stirred reactor, and when the alkaline mother liquor is higher than the hydrogen chloride gas distribution pipe to a certain height, stirring is started first and then hydrogen chloride gas is introduced into the alkaline mother liquor.

[0008] Furthermore, in the step (2), the first reactor with stirring uses anchor stirring, and during the introduction of hydrogen chloride gas, the stirring rate is controlled to be 60-90 r / min, and after the introduction of hydrogen chloride gas is stopped, the stirring rate is controlled to be 200-300 r / min.

[0009] Furthermore, in the step (2), the 4-hydrogen chloride gas distribution pipe 1 in the first reactor 3 needs to be inserted below the liquid surface and the stirring paddle. The gas distribution pipe is a ring-shaped structure with holes. The holes are located on both sides of the bottom of the ring pipe and are spaced apart. Gas can be distributed to both sides at the same time, and the gas distribution pipe is located below the anchor stirring paddle.

[0010] Furthermore, in the step (3), the mechanical stirring rate is 150-300 r / min.

[0011] Furthermore, in the step (4), the temperature of the heat exchange evaporation alkaline clear liquid is 80-90°C and the time is 48-72h.

[0012] Furthermore, in the step (5), anchor stirring is adopted, and the stirring rate is 80 to 120 r / min.

[0013] Furthermore, the tail gas in step (2) and step (5) is then recycled by absorbing the tail gas in the ammonia evaporation mother liquor after heat exchange, and then sending it to step (1) to mix with the alkali residue to obtain the alkaline mother liquor. The specific method is as follows: when the pH of the liquid in the tail gas absorption tank 7 drops below 2.5, it is sent to the stirring barrel 1 through the discharge pipe to be mixed with the alkali residue raw material for slurry preparation.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses ammonia evaporation waste liquid and alkali residue to prepare alkali residue slurry, then introduces hydrogen chloride gas to react to obtain acidic slurry, then adds calcium oxide to obtain alkaline suspension, and then clarifies and settles the suspension, exchanges heat with ammonia evaporation waste liquid to increase temperature and evaporates and concentrates, and finally obtains a high-concentration calcium chloride solution. Compared with using ammonia evaporation waste liquid as a raw material liquid for producing calcium chloride, the above measures can increase the concentration of calcium chloride raw material liquid from 11% to 32.51-36.34%, so that the concentration of calcium chloride solution is increased by more than 10% compared with the concentration of calcium chloride solution obtained by conventional re-exposure. The steam consumption can be reduced by more than 400 kg per ton of calcium chloride dihydrate produced, saving 90-120 yuan in cost, and thus having good economic efficiency.

[0015] (2) The present invention controls the liquid level of the alkali residue slurry in the first reactor at 1 / 2 to 2 / 3, and introduces hydrogen chloride gas into the slurry through a gas distribution pipe located at the bottom of the first reactor. The lower part of the annular gas distribution pipe is symmetrically provided with gas outlet holes on both sides thereof. An anchor stirring is arranged above the annular gas distribution pipe. The rotating anchor stirring during gas distribution can further break up the hydrogen chloride bubbles. Compared with the existing spray feeding technology, the present invention can make the hydrogen chloride gas and the alkali residue slurry mix more evenly and have a longer contact time, thereby improving the reaction efficiency and further increasing the concentration of the calcium chloride solution.

[0016] (3) The present invention utilizes waste alkali residue, ammonia evaporation waste liquid and industrial by-product hydrogen chloride gas as production raw materials, and utilizes the waste heat of ammonia evaporation waste liquid as a heat exchange medium to evaporate and concentrate the alkaline liquid. This not only solves the problem of difficulty in utilizing waste residue and waste liquid from alkali plants and realizes the comprehensive utilization of waste resources, but also utilizes the waste heat in ammonia evaporation waste liquid to increase the concentration of calcium chloride raw material liquid and reduce steam consumption.

[0017] (4) The present invention uses the waste clear liquid of ammonia evaporation after heat exchange to recover the hydrogen chloride tail gas, and controls the pH value to be lowered to below 2.5 for waste liquid recycling and slurry adjustment, thereby solving the problem of hydrogen chloride loss during the reaction process and fully utilizing the hydrogen chloride gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the process flow of the present invention; Figure 2 This is a schematic diagram of the structure of the annular air distribution pipe of the present invention; DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention are clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] Refer to the attached Figure 1The device used in the method of the present invention includes a stirring barrel 1, a first reactor 2, a pH adjustment barrel 4, a sedimentation tank 5, a heat exchange evaporator 6, a second reactor 3, a tail gas absorption tank 7 and matching mud pumps, instruments, pipelines, valves, and control systems connected in sequence; a stirring structure is provided inside the first reactor 2, a hydrogen chloride inlet pipe and a tail gas outlet pipe are provided on the top, an alkaline mother liquor inlet pipe is provided on the upper part of the side wall, and an acid slurry outlet pipe is provided on the lower part of the side wall of the reactor 2. The hydrogen chloride inlet pipe extends vertically downward to the bottom of the reactor 2 and is fixedly connected to a horizontally arranged annular air distribution pipe. The lower part of the annular air distribution pipe is symmetrically provided with air outlet holes on both sides of the inner and outer sides. The stirring structure is an anchor stirring structure and is arranged above the annular air distribution pipe. Alkali residue and ammonia waste liquid are introduced into a stirring barrel 1 at a mass ratio of 0.2-0.5:1, stirred and mixed to obtain an alkaline mother liquor, and the alkaline mother liquor is sent to the first reactor 2 through a mud pump. When the alkaline mother liquor level in the first reactor 2 reaches 1 / 2-2 / 3 of the reactor height, the pump is stopped; hydrogen chloride gas is then introduced into the alkaline mother liquor through the hydrogen chloride inlet pipe and the annular air distribution pipe, and stirring is started at the same time. Hydrogen chloride reacts with calcium carbonate and calcium hydroxide in the alkaline mother liquor to produce calcium chloride and obtain an acidic slurry; when the pH of the acidic slurry drops to 0-1, the introduction of hydrogen chloride gas is stopped, and the acidic slurry is sent into a pH regulating barrel 4 through a mud pump. The carbon dioxide gas and excess hydrogen chloride tail gas generated during the reaction are recovered by entering the tail gas absorption tank 7 through the tail gas discharge pipe; solid calcium oxide is added to the pH regulating barrel 4, Stirring the reaction to obtain an alkaline suspension, adjusting the pH value of the alkaline suspension to 11.3-13; sending the alkaline suspension to a sedimentation tank 5 for clarification and sedimentation to obtain an upper clear liquid, i.e., an alkaline clear liquid, which is sent to a heat exchange evaporator 6 through a mud pump to exchange heat with ammonia waste clear liquid to increase the temperature, and the temperature of the alkaline clear liquid after heat exchange is increased to 80-85° C. After evaporation and concentration for 48-72 hours, the concentrated alkaline clear liquid is sent to a second reactor 3, and hydrogen chloride gas is introduced to adjust the pH value to 4-6.5 to obtain a weakly acidic high-concentration calcium chloride solution; the alkaline suspension is sent to a calcium chloride plant through a product discharge pipe to produce calcium chloride, and excess hydrogen chloride tail gas enters a tail gas absorption tank 7 through a tail gas discharge pipe. A part of the ammonia waste clear liquid after heat exchange is sent to a stirring tank 1, and the other part is sent to a tail gas absorption tank 7 to absorb hydrogen chloride tail gas and then sent to a stirring tank 1 to produce an alkaline mother liquor. Example 1

[0021]

[0022] The temperature of the ammonia evaporation waste liquid used for heat exchange is 80~90℃.

[0023] The method of the present invention comprises the following steps: 100 kg of alkali residue and 500 kg of ammonia evaporation waste clear liquid are introduced into a stirring barrel 1, and the alkali residue and the ammonia evaporation waste clear liquid are uniformly mixed by mechanical stirring to obtain an alkaline mother liquor, wherein the mechanical stirring rate is 200 r / min and the stirring time is 30 min; The alkaline mother liquor obtained in step (1) is introduced into the first reactor 2 through a mud pump. When the alkaline mother liquor level in the first reactor reaches 2 / 3 of the reactor height, the introduction of the alkaline mother liquor is stopped, the anchor-type mechanical stirring is started, and the by-product hydrogen chloride gas is introduced into the alkaline mother liquor. The hydrogen chloride reacts with the calcium carbonate, calcium hydroxide, etc. in the alkaline mother liquor to obtain an acidic slurry, and carbon dioxide gas is released at the same time. The mechanical stirring rate in this process is 60 r / min; The carbon dioxide gas and the unreacted hydrogen chloride tail gas generated in step (2) enter the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH of the acidic slurry drops to 0, stop introducing the hydrogen chloride gas, adjust the mechanical stirring rate to 200 r / min, and pass the acidic slurry in the first reactor 2 into the pH adjustment barrel 4 through a mud pump; Add solid calcium oxide to the pH adjustment barrel 4 through the calcium oxide feeding tube, perform mechanical stirring at a stirring rate of 150 r / min, adjust the pH to 13, and obtain an alkaline suspension; The alkaline suspension obtained in step (5) is passed into a sedimentation tank 5 via a mud pump to clarify and settle the solids in the suspension; The alkaline clear liquid obtained after sedimentation in step (6) is introduced into a heat exchange evaporator 6 through a centrifugal pump, and heat exchanged with the ammonia waste clear liquid to raise the temperature. The alkaline clear liquid is maintained at 80-85° C. by heat exchange, and evaporated and concentrated for 72 hours; the ammonia waste clear liquid after heat exchange is consumed in three parts, the first part enters the stirring barrel 1, and is mixed with the alkali slag raw material for slurry preparation, the second part enters the tail gas absorption tank 7 to absorb the hydrogen chloride tail gas and then is sent to the stirring barrel 1, and the third part is discharged through the ammonia waste clear liquid discharge pipe; The alkaline clear liquid obtained in step (7) is introduced into the second reactor 3, and then the by-product hydrogen chloride gas is introduced and stirred for reaction. The stirring rate is 80r / min, and the pH is adjusted to 6.5. The high-concentration weakly acidic calcium chloride solution obtained is sent to the calcium chloride plant as a production raw material; the tail gas generated during the process enters the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH of the ammonia waste liquid in the tail gas absorption tank 7 drops below 2.5, it is sent to the mixing barrel 1 through the discharge pipe to be mixed with the alkali residue raw material for slurry preparation. Example 2

[0024] The raw materials used in this embodiment are mainly alkali residue, ammonia evaporation waste liquid, and by-product hydrogen chloride gas. The main components of the alkali residue are shown in the following table:

[0025] The temperature of the ammonia evaporation waste liquid used for heat exchange is 80~90℃.

[0026] The method of the present invention comprises the following steps: 220 kg of alkali residue and 550 kg of ammonia evaporation waste clear liquid are introduced into the stirring barrel 1, and the alkali residue and the ammonia evaporation waste clear liquid are uniformly mixed by mechanical stirring to obtain an alkaline mother liquor, wherein the mechanical stirring rate is 300 r / min and the stirring time is 50 min; The alkaline mother liquor obtained in step (1) is introduced into the first reactor 2 through a mud pump. When the alkaline mother liquor level in the first reactor reaches 1 / 2 of the reactor height, the introduction of the alkaline mother liquor is stopped, the anchor-type mechanical stirring is started, and the by-product hydrogen chloride gas is introduced into the alkaline mother liquor. The hydrogen chloride reacts with the calcium carbonate, calcium hydroxide, etc. in the alkaline mother liquor to obtain an acidic slurry, and carbon dioxide gas is released at the same time. The mechanical stirring rate in this process is 75 r / min; The carbon dioxide gas and the unreacted hydrogen chloride tail gas generated in step (2) enter the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH value of the liquid in the first reactor 2 reaches 1, stop introducing the hydrogen chloride gas, adjust the mechanical stirring rate to 260 r / min, and introduce the acidic slurry in the first reactor 2 into the pH adjustment tank 4 through a mud pump; Solid calcium oxide is added to the pH adjustment barrel 4 through the calcium oxide feeding tube, and mechanical stirring is performed at a stirring rate of 260 r / min, and the pH value is adjusted to 12.6 to obtain an alkaline suspension; The alkaline suspension obtained in step (5) is passed into a sedimentation tank 5 via a mud pump to clarify and settle the solids in the suspension; The alkaline clear liquid obtained after sedimentation in step (6) is introduced into a heat exchange evaporator 6 through a centrifugal pump, and heat exchanged with the ammonia evaporation waste clear liquid to raise the temperature. The alkaline clear liquid is maintained at 80-85° C. by heat exchange, and evaporated and concentrated for 48 hours; the ammonia evaporation waste clear liquid after heat exchange is consumed in three parts, the first part enters the stirring barrel 1, and is mixed with the alkali slag raw material for slurry preparation, the second part enters the tail gas absorption tank 7 as a raw material for absorbing acidic gas, and the third part is discharged through the ammonia evaporation waste clear liquid discharge pipe; The alkaline clear liquid obtained in step (7) is introduced into the second reactor 3, and then the by-product hydrogen chloride gas is introduced for anchor stirring. The stirring rate is 110r / min, and the pH is adjusted to 5.7. The high-concentration weakly acidic calcium chloride solution obtained is sent to the calcium chloride plant as a production raw material; the tail gas generated during the process enters the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH of the ammonia waste liquid in the tail gas absorption tank 7 drops below 2.5, it is sent to the mixing barrel 1 through the discharge pipe to be mixed with the alkali residue raw material for slurry preparation.

[0027] The raw materials used in this embodiment are mainly alkali residue, ammonia evaporation waste liquid, and by-product hydrogen chloride gas. The main components of the alkali residue are shown in the following table:

[0028] The temperature of the ammonia evaporation waste liquid used for heat exchange is 80~90℃.

[0029] The method of the present invention comprises the following steps: 250 kg of alkali residue and 500 kg of ammonia evaporation waste clear liquid are introduced into the stirring barrel 1, and the alkali residue and the ammonia evaporation waste clear liquid are uniformly mixed by mechanical stirring to obtain an alkaline mother liquor, wherein the mechanical stirring rate is 350 r / min and the stirring time is 60 min; The alkaline mother liquor obtained in step (1) is introduced into the first reactor 2 through a mud pump. When the alkaline mother liquor level in the first reactor 2 reaches 7 / 12 of the reactor height, the introduction of the alkaline mother liquor is stopped, the anchor-type mechanical stirring is started, and the by-product hydrogen chloride gas is introduced into the alkaline mother liquor. The hydrogen chloride reacts with the calcium carbonate, calcium hydroxide, etc. in the alkaline mother liquor to obtain an acidic slurry, and carbon dioxide gas is released at the same time. The mechanical stirring rate in this process is 90 r / min; The carbon dioxide gas and the unreacted hydrogen chloride tail gas generated in step (2) enter the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH value of the liquid in the first reactor 2 reaches 0.6, stop introducing the hydrogen chloride gas, adjust the mechanical stirring rate to 300 r / min, and introduce the acidic slurry in the first reactor 2 into the pH adjustment tank 4 through a mud pump; Solid calcium oxide is added to the pH adjustment barrel 4 through the calcium oxide feeding tube, and mechanical stirring is performed at a stirring rate of 300 r / min, and the pH value is adjusted to 11.3 to obtain an alkaline suspension; The alkaline suspension obtained in step (5) is passed into a sedimentation tank 5 via a slurry pump to clarify and settle the solids in the suspension; The alkaline clear liquid obtained after sedimentation in step (6) is introduced into a heat exchange evaporator 6 through a centrifugal pump, and the ammonia evaporation waste clear liquid is heated and heated, and the alkaline clear liquid is maintained at 80-85° C. by heat exchange, and evaporated and concentrated for 68 hours; the ammonia evaporation waste clear liquid after heat exchange is consumed in three parts, the first part enters the stirring barrel 1, and is mixed with the alkali slag raw material for slurry preparation, the second part enters the tail gas absorption tank 7 as a raw material for absorbing acidic gas, and the third part is discharged through the ammonia evaporation waste clear liquid discharge pipe; The alkaline calcium chloride solution obtained in step (7) is introduced into the second reactor 3, and then the by-product hydrogen chloride gas is introduced for anchor stirring. The stirring rate is 120r / min, and the pH is adjusted to 4. The high-concentration weakly acidic calcium chloride solution obtained is sent to the calcium chloride plant as a production raw material; the tail gas generated during the process enters the tail gas absorption tank 7 through the tail gas discharge pipe for absorption; When the pH of the ammonia waste liquid in the tail gas absorption tank 7 drops below 2.5, it is sent to the mixing barrel 1 through the discharge pipe to be mixed with the alkali residue raw material for slurry preparation. Comparative Example 1:

[0030] The difference between Comparative Example 1 and Example 1 is that in step (2), the alkaline mother liquor is sprayed into the first reactor filled with hydrogen chloride gas. Comparative Example 2:

[0031] The difference between Comparative Example 2 and Example 1 is that in step (2) and step (8), the hydrogen chloride gas distribution pipe is located above the mechanical stirring. Comparative Example 3:

[0032] The difference between Comparative Example 3 and Example 1 is that the mechanical stirring in step (2) and step (8) adopts paddle stirring. Comparative Example 4:

[0033] The difference between Comparative Example 4 and Example 1 is that the heat exchange evaporation time in step (7) is 30 hours. Comparative Example 5:

[0034] The difference between Comparative Example 5 and Example 1 is that the heat exchange evaporation time in step (7) is 100 h. Comparative Example 6:

[0035] The difference between Comparative Example 6 and Example 1 is that in step (4), when the pH of the liquid in the first reactor 2 reaches 1.8, the introduction of hydrogen chloride gas is stopped.

[0036] Comparative Analysis The concentration of calcium chloride is calculated according to the calcium ion concentration after ICP detection. The following is a product data table of each embodiment and comparative example:

[0037] Comparing the concentration of calcium chloride solution in Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, spray feeding is used, the contact time between the alkaline slurry and the hydrogen chloride gas is short, and the reaction is not sufficient. In Example 1, an annular gas distribution pipe with vent holes symmetrically spaced on both sides of the lower inner and outer parts is used, and the hydrogen chloride gas escapes and reacts in the alkaline slurry, and mechanical stirring is used to make the hydrogen chloride gas and the alkaline slag slurry more evenly mixed, the contact time is longer, the reaction efficiency is improved, the concentration of the calcium chloride solution is also higher, and the risk of clogging of the alkaline slurry is reduced.

[0038] Comparing the concentration of calcium chloride solution in Example 1 and Comparative Example 2, it can be seen that the hydrogen chloride gas distribution pipe is located above the mechanical stirring, and there is a lack of an anchor stirring paddle to break up the hydrogen chloride bubbles, thereby reducing the reaction efficiency.

[0039] Comparing the concentrations of calcium chloride solutions in Example 1 and Comparative Example 3, it can be seen that the bubble breaking quality of paddle stirring is not as good as that of anchor stirring, and anchor stirring can accelerate the reaction.

[0040] Comparing the concentrations of the calcium chloride solutions in Example 1 and Comparative Example 4, it can be seen that the heat exchange evaporation time has a great influence on the concentration of the final product, and too short an evaporation time leads to too low a concentration.

[0041] Comparing the concentrations of the calcium chloride solution in Example 1 and Comparative Example 5, it can be seen that the concentration of the calcium chloride solution can be increased by about 10% in the first 72 hours during the heat exchange evaporation process, and the concentration is only increased by about 2% after continuing to evaporating for 28 hours. Too long an evaporation time will reduce the concentration efficiency, so it is necessary to control the appropriate evaporation time.

[0042] By comparing the concentrations of the calcium chloride solutions in Example 1 and Comparative Example 6, it can be seen that when the pH of the liquid in the first reactor 3 is high, the alkali slag reaction is not complete and the low calcium chloride concentration causes a waste of resources. Therefore, it is necessary to control the pH of the liquid in step (4) to be between 0 and 1 to ensure that the reaction is complete.

[0043] The above description is only a preferred embodiment of the present invention and cannot limit the scope of the present invention. That is, equivalent changes and modifications described in the scope of the present invention and the description should all fall within the scope of the present invention.

Claims

1. A method for preparing a high-concentration calcium chloride solution using alkali residue and ammonia evaporation waste liquid, characterized in that: The steps include: (1) mixing the alkali residue and the ammonia evaporation waste liquid uniformly to obtain an alkaline mother liquor; (2) Passing the alkaline mother liquor into the first reactor with stirring, and stopping when the alkaline mother liquor level in the reactor reaches 1 / 2 to 2 / 3 of the reactor height, and then passing hydrogen chloride gas into the alkaline mother liquor and stirring to react to obtain an acidic slurry; when the pH of the acidic slurry drops to 0 to 1, stop passing hydrogen chloride gas, increase the stirring rate, and pass the acidic slurry into the pH adjustment tank; (3) Add calcium oxide to the pH adjustment tank and stir to react to obtain an alkaline suspension; (4) When the pH value of the alkaline suspension increases to 11.3-13, the alkaline suspension is clarified and settled to obtain an alkaline clear liquid, and the alkaline clear liquid is heat exchanged with the ammonia evaporation waste clear liquid to increase the temperature of the alkaline clear liquid and evaporate and concentrate it, and the ammonia evaporation waste clear liquid after heat exchange is recycled; (5) hydrogen chloride gas is introduced into the alkaline clear liquid after evaporation and concentration to adjust the pH value to 4-6.5, thereby obtaining a weakly acidic high-concentration calcium chloride solution; the tail gas generated during the reaction of step (2) and step (5) is absorbed by the ammonia evaporation waste clear liquid after heat exchange, and then the clear liquid is sent to step (1) to be mixed with alkaline slag to prepare an alkaline mother liquor.

2. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid according to claim 1, characterized in that: In the step (1), the mass ratio of alkali residue to ammonia evaporation waste liquid is 0.2-0.5:1, the stirring rate is 200-350 r / min, and the stirring time is 30-60 min.

3. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid according to claim 2, characterized in that: The first reactor with stirring uses anchor stirring. During the introduction of hydrogen chloride gas, the stirring rate is controlled at 60-90 r / min. After the introduction of hydrogen chloride gas is stopped, the stirring rate is controlled at 200-300 r / min.

4. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid according to claim 3, characterized in that: An air inlet pipe is provided on the top of the first reactor, which extends downward to the bottom of the reactor and is fixedly connected to a horizontally arranged annular air distribution pipe. Air outlet holes are symmetrically spaced on both inner and outer sides of the lower part of the annular air distribution pipe, and the anchor agitator is arranged above the annular air distribution pipe.

5. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid according to claim 1, characterized in that: The stirring rate in step (3) is 150-300 r / min.

6. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste liquid according to claim 1, characterized in that: In the step (4), the temperature of the alkaline clear liquid after heat exchange is 80-85°C, and the evaporation concentration time is 48-72h.

7. The method for preparing high-concentration calcium chloride solution by using alkali residue and ammonia evaporation waste clear liquid according to claim 1, characterized in that: In the step (5), the pH of the ammonia evaporation waste clear liquid after absorbing the tail gas is controlled below 2.5.

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