Method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by freezing method

Abstract

The invention belongs to the technical field of fertilizer production, and particularly relates to a method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method, which comprises the following steps: step 1, preparing calcium nitrate tetrahydrate by using nitric acid and limestone as raw materials by the freezing method; 2, adding water into the residual solution for preparing calcium nitrate tetrahydrate, and adjusting the mass concentration of calcium nitrate in the residual solution to 30-40%; 3, adding potassium chloride into the calcium nitrate solution with the mass concentration of 30-40%, reacting to generate potassium nitrate and calcium chloride, and further separating out potassium nitrate crystals; and 4, centrifugally separating or filtering the calcium chloride solution in which the potassium nitrate crystals are separated out to obtain the potassium nitrate crystals, and washing and purifying the potassium nitrate crystals.

Description

Technical Field

[0001] This application belongs to the technical field of fertilizer production, and specifically relates to a method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method. Background Art

[0002] Calcium nitrate is widely used as a fertilizer in agricultural production and often used as a coagulant accelerator for cement in the industrial construction field to accelerate the hardening process of cement and improve the early strength of concrete. Currently, calcium nitrate is usually produced by reacting nitric acid with limestone, and then obtained through pressure filtration and evaporation. This method of producing calcium nitrate requires a large evaporation cost and has poor economy.

[0003] Potassium nitrate is a chlorine-free nitrogen-potassium compound fertilizer with high solubility. Its active ingredients nitrogen and potassium can be quickly absorbed by crops, leaving no chemical residues. It is widely used as a fertilizer in agricultural production, and is an important raw material for manufacturing black powder and often used as a glass fining agent. Currently, potassium nitrate is mainly produced by the magnesium oxide-nitric acid-potassium chloride method, and a large amount of magnesium chloride solution containing potassium oxide is produced as a by-product, which is difficult to treat subsequently.

[0004] In view of the problems existing in the production of calcium nitrate and potassium nitrate, this application is proposed. Summary of the Invention

[0005] To solve the problems of the prior art, this application provides a method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method to overcome at least one defect in the production of calcium nitrate and potassium nitrate.

[0006] The technical solution of this application is as follows:

[0007] A method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method, comprising:

[0008] Step 1: Using nitric acid and limestone as raw materials, preparing calcium nitrate tetrahydrate by a freezing method;

[0009] Step 2: Adding water to the remaining solution for preparing calcium nitrate tetrahydrate, and adjusting the mass concentration of calcium nitrate in the remaining solution to 30-40%;

[0010] Step 3: Adding potassium chloride to the calcium nitrate solution with a mass concentration of 30-40% to react to generate potassium nitrate and calcium chloride, and then precipitating potassium nitrate crystals;

[0011] Step 4: Centrifugally separating or filtering the calcium chloride solution from which potassium nitrate crystals have precipitated to obtain potassium nitrate crystals, and performing washing and purification.

[0012] Furthermore, Step 1 is specifically:

[0013] React with nitric acid and limestone as raw materials, filter press the reaction solution to obtain a calcium nitrate solution with a mass concentration of 50% - 60%.

[0014] Freeze the calcium nitrate solution with a mass concentration of 50% - 60% to -5°C to -10°C, so that calcium nitrate precipitates in the form of calcium nitrate tetrahydrate, and perform filtration or centrifugal separation to obtain calcium nitrate tetrahydrate crystals.

[0015] Furthermore, in step one, filter press the acidolysis solution generated during the reaction of nitric acid and limestone to obtain a calcium nitrate solution with a mass concentration of 55%.

[0016] Furthermore, in step one, freeze the calcium nitrate solution with a mass concentration of 50% - 60% to -7.5°C.

[0017] Furthermore, in step two, add water to the remaining solution for preparing calcium nitrate tetrahydrate to adjust the mass concentration of calcium nitrate in the remaining solution to 35%.

[0018] Furthermore, in step one, react with nitric acid and limestone as raw materials, the mass ratio of nitric acid to limestone is 1:0.83, the reaction temperature is normal temperature, and the mass concentration of nitric acid is 50%.

[0019] This application has at least the following beneficial technical effects:

[0020] 1) The method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by the freezing method provided by this application uses nitric acid and limestone as raw materials, and makes calcium nitrate tetrahydrate by the freezing method, instead of obtaining calcium nitrate products by evaporation and cooling crystallization, which can save a large amount of evaporation costs;

[0021] 2) Utilize the remaining solution for preparing calcium nitrate tetrahydrate, adjust the concentration of calcium nitrate by adding a small amount of water, add potassium chloride to react to generate potassium nitrate and calcium chloride, precipitate potassium nitrate crystals, and then perform filtration, washing, and purification to obtain potassium nitrate products. This can not only reasonably utilize resources, but also, compared with the existing methods for preparing potassium nitrate, no longer produce magnesium chloride solution that is difficult to handle subsequently, and can by-product calcium chloride with relatively high application value. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some preferred embodiments of this application, rather than all embodiments. For the preferred embodiments of this application, for those of ordinary skill in the art, without creative efforts, other embodiments and drawings can be obtained based on these embodiments and drawings, and all belong to the protection scope of this application.

[0023] Figure 1 This is the reaction flow chart of the embodiment of the present application. Detailed implementation manners

[0024] To make the objectives, technical solutions and advantages of the present application clearer, the following will further describe the embodiments of the present application in detail. It should be understood that the orientation or positional relationships indicated by terms such as "upper", "lower", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. The above definitions are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the structures referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present application.

[0025] Example 1

[0026] A method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method is as follows:

[0027] Step 1: React nitric acid with limestone as raw materials, filter press the reaction solution to obtain a calcium nitrate solution with a mass concentration of 50%, freeze the calcium nitrate solution with a mass concentration of 50% to -5°C, so that calcium nitrate precipitates in the form of calcium nitrate tetrahydrate, and perform filtration or centrifugal separation to obtain calcium nitrate tetrahydrate crystals;

[0028] Step 2: Add water to the remaining solution for preparing calcium nitrate tetrahydrate, and adjust the mass concentration of calcium nitrate in the remaining solution to 30%;

[0029] Step 3: Add potassium chloride to the calcium nitrate solution with a mass concentration of 30%, react to generate potassium nitrate and calcium chloride, and then precipitate potassium nitrate crystals;

[0030] Step 4: Perform centrifugal separation or filtration on the calcium chloride solution from which potassium nitrate crystals have precipitated to obtain potassium nitrate crystals, and perform washing and purification.

[0031] In the above implementation, the recovery rate of the obtained calcium nitrate is 30% and the purity is 98.2%, the recovery rate of potassium nitrate is 86% and the purity is 98.6%, and the calcium chloride liquid is 31°Bé.

[0032] Example 2

[0033] A method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method is as follows:

[0034] Step 1: React nitric acid with limestone as raw materials, filter press the reaction solution to obtain a calcium nitrate solution with a mass concentration of 55%, freeze the calcium nitrate solution with a mass concentration of 55% to -7.5°C, so that calcium nitrate precipitates in the form of calcium nitrate tetrahydrate, and perform filtration or centrifugal separation to obtain calcium nitrate tetrahydrate crystals;

[0035] Step 2: Add water to the remaining solution for preparing calcium nitrate tetrahydrate, and adjust the mass concentration of calcium nitrate in the remaining solution to 35%.

[0036] Step 3: Add potassium chloride to the calcium nitrate solution with a mass concentration of 35%, react to generate potassium nitrate and calcium chloride, and then precipitate potassium nitrate crystals.

[0037] Step 4: Centrifuge or filter the calcium chloride solution from which potassium nitrate crystals have precipitated to obtain potassium nitrate crystals, and perform washing and purification.

[0038] In the above implementation, the recovery rate of the obtained calcium nitrate is 34% and the purity is 98.3%, the recovery rate of potassium nitrate is 89% and the purity is 98.3%, and the concentration of the calcium chloride liquid is 34 °Bé.

[0039] Example 3

[0040] A method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by a freezing method is as follows:

[0041] Step 1: React nitric acid with limestone as raw materials, press-filter the reaction solution to obtain a calcium nitrate solution with a mass concentration of 60%, freeze the calcium nitrate solution with a mass concentration of 60% to -10 °C, precipitate calcium nitrate in the form of calcium nitrate tetrahydrate, and perform filtration or centrifugal separation to obtain calcium nitrate tetrahydrate crystals.

[0042] Step 2: Add water to the remaining solution for preparing calcium nitrate tetrahydrate, and adjust the mass concentration of calcium nitrate in the remaining solution to 40%.

[0043] Step 3: Add potassium chloride to the calcium nitrate solution with a mass concentration of 40%, react to generate potassium nitrate and calcium chloride, and then precipitate potassium nitrate crystals.

[0044] Step 4: Centrifuge or filter the calcium chloride solution from which potassium nitrate crystals have precipitated to obtain potassium nitrate crystals, and perform washing and purification.

[0045] In the above implementation, the recovery rate of the obtained calcium nitrate is 37% and the purity is 98.3%, the recovery rate of potassium nitrate is 92% and the purity is 96.4%, and the concentration of the calcium chloride liquid is 39 °Bé.

[0046] In the method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by the freezing method disclosed in the above examples, in Step 1, nitric acid and limestone are used as raw materials for reaction, the mass ratio of nitric acid to limestone is 1:0.83, the reaction temperature is normal temperature, and the mass concentration of nitric acid is 50%.

[0047] The method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by the freezing method disclosed in the above embodiments uses nitric acid and limestone as raw materials, and produces calcium nitrate tetrahydrate by the freezing method. Further treatment can obtain the required calcium nitrate, instead of obtaining calcium nitrate by evaporation and cooling crystallization, which can save a large amount of evaporation costs. In addition, using the remaining solution for producing calcium nitrate tetrahydrate, adjusting the concentration of calcium nitrate by adding a small amount of water, adding potassium chloride to react to generate potassium nitrate and calcium chloride, precipitating potassium nitrate crystals, and then filtering, washing, and purifying to obtain potassium nitrate products, which can not only reasonably utilize resources, but also, compared with the existing methods for preparing potassium nitrate, no longer produce magnesium chloride solution that is difficult to treat subsequently, and can by-produce calcium chloride with relatively high application value.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not restrictive. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present application, and they should all be covered within the scope of the claims of the present application.

Claims

1. A method for producing calcium nitrate tetrahydrate and potassium nitrate by freezing, characterized in that: include: Step 1, using nitric acid and limestone as raw materials, and preparing calcium nitrate tetrahydrate by freezing method; Step 2, adding water to the remaining solution of calcium nitrate tetrahydrate to adjust the mass concentration of calcium nitrate in the remaining solution to 30-40%; Step 3, adding potassium chloride to a calcium nitrate solution having a mass concentration of 30-40%, reacting to generate potassium nitrate and calcium chloride, and then precipitating potassium nitrate crystals; Step 4: centrifuge or filter the calcium chloride solution from which potassium nitrate crystals are precipitated to obtain potassium nitrate crystals, and then wash and purify them.

2. The method for producing calcium nitrate tetrahydrate and potassium nitrate by freezing as claimed in claim 1, characterized in that: The step 1 is specifically as follows: Using nitric acid and limestone as raw materials to react, and filtering the reaction solution to obtain a calcium nitrate solution with a mass concentration of 50% to 60%; A calcium nitrate solution with a mass concentration of 50% to 60% is frozen to -5°C to -10°C to precipitate the calcium nitrate in the form of calcium nitrate tetrahydrate, and then filtered or centrifuged to obtain calcium nitrate tetrahydrate crystals.

3. The method for producing calcium nitrate tetrahydrate and co-producing potassium nitrate by freezing as claimed in claim 2, characterized in that: In the step 1, the acid solution produced during the reaction of nitric acid and limestone is filtered to obtain a calcium nitrate solution with a mass concentration of 55%.

4. A method for producing calcium nitrate tetrahydrate and potassium nitrate by freezing as claimed in claim 2, characterized in that: In the step 1, a calcium nitrate solution with a mass concentration of 50% to 60% is frozen to -7.5°C.

5. The method for producing calcium nitrate tetrahydrate and potassium nitrate by freezing as claimed in claim 1, characterized in that: In the step 2, water is added to the remaining solution for preparing calcium nitrate tetrahydrate to adjust the mass concentration of calcium nitrate in the remaining solution to 35%.

6. The method for producing calcium nitrate tetrahydrate and potassium nitrate by freezing as claimed in claim 1, characterized in that: In step 1, nitric acid and limestone are used as raw materials for reaction, the mass ratio of nitric acid to limestone is 1:0.83, the reaction temperature is room temperature, and the mass concentration of nitric acid is 50%.

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