A theoretical calculation method for impurity removal by cyclic evaporation crystallization

Abstract

The present invention discloses a theoretical calculation method for cyclic evaporation crystallization impurity removal, comprising the following steps: (1) evaporating a certain volume of stock solution to a predetermined volume at a certain temperature, performing solid-liquid separation on the obtained mother liquor and salt crystals after cooling, and the remaining mother liquor enters the next evaporation operation, and the cycle repeats; (2) performing impurity detection on the salt and mother liquor obtained by each evaporation, and statistically analyzing the distribution ratio of impurities in the salt and mother liquor obtained by each evaporation desalination; (3) establishing a relationship model between the impurity content in the salt crystals and the number of cycles according to the data obtained in step (2); (4) according to the impurity removal requirements, using the model obtained in step (3) to predict the maximum number of cyclic evaporation times that can be achieved when the impurity content in the salt crystals obtained by evaporation is not higher than the set maximum value. The method disclosed by the present invention is simple to operate, can effectively recover the salt in the waste liquid, and solves the problem of waste liquid pollution.

Description

Technical Field

[0001] The invention belongs to the field of chemistry, and in particular relates to a theoretical calculation method for cyclic evaporation crystallization impurity removal. Background Art

[0002] Extraction is one of the commonly used methods in the process of chemical purification. The extraction method uses the different solubility of solutes in immiscible solvents to extract the target solute from a solution composed of another solvent with one solvent. The organic phase is used as an extractant to extract the target solute from the aqueous phase, and finally an extract phase and a raffinate rich in the target solute are obtained. The extract phase enters the next production process for processing, while the raffinate phase is often directly discharged into the environment after simple treatment.

[0003] In the purification of metals such as cobalt and nickel, the obtained raffinate often contains a large amount of salt. If the raffinate rich in a large amount of salt is directly discharged, it will not only fail to meet environmental protection requirements, but also cause waste of resources. Therefore, it is necessary to provide a raffinate treatment method that can not only recover the salt in the raffinate, but also make the purity of the recovered salt meet the recycling standard. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a theoretical calculation method for impurity removal by cyclic evaporation crystallization, which specifically includes the following contents:

[0005] A theoretical calculation method for impurity removal by cyclic evaporation crystallization, characterized in that it comprises the following steps:

[0006] (1) Evaporation: A certain volume of stock solution is evaporated to a predetermined volume at a certain temperature. After cooling, the resulting mother liquor and salt crystals are separated into solid and liquid. The remaining mother liquor enters the next evaporation operation, and the cycle repeats;

[0007] (2) Calculating the impurity distribution ratio: performing impurity detection on the salt and mother liquor obtained by each evaporation, and calculating the distribution ratio of impurities in the salt and mother liquor obtained by each evaporation desalination;

[0008] (3) Establishing a relationship model between the impurity content in the salt crystals and the number of evaporation cycles: Based on the data obtained in step (2), establishing a relationship model between the impurity content in the salt crystals and the number of evaporation cycles;

[0009] (4) Prediction of the number of cycles: Based on the need for impurity removal, the model obtained in step (3) is used to predict the maximum number of cycles that can be used for evaporation when the impurity content in the salt crystals obtained by evaporation is not higher than the set maximum value.

[0010] Specifically, the method further comprises step (5) of calculating the minimum volume of the solution required for each evaporation: the minimum volume of the solution required for each evaporation is calculated based on the total volume of the stock solution to be decontaminated, the total decontamination time and the maximum number of cycles obtained in step (4).

[0011] Specifically, the method for establishing the relationship model between the impurity content in the salt crystal and the number of evaporation cycles in step (3) is: multiple cycles of evaporation are performed, and the distribution ratio of impurities in the mother liquor and the salt is statistically obtained as a fixed value m, assuming that the amount of impurities introduced by each evaporation is S, and the impurity content in the salt obtained by the nth evaporation is A n , the total amount of impurities in the salt obtained by the first n-1 evaporations is S n-1 ,but:

[0012] After the first evaporation,

[0013] After the second evaporation,

[0014] After the third evaporation, ...

[0016] After the nth evaporation,

[0017] The relationship between the impurity content An in the salt crystal and the number of cycles n is obtained as follows:

[0018] Specifically, the stock solution is the raffinate produced during the impurity removal and purification process of the cobalt-nickel solvent extraction method.

[0019] Specifically, the raw liquid is cobalt raffinate, and the impurities include Mg 2+ , Cl - , sulfate.

[0020] Beneficial effects of the invention: The invention provides a theoretical calculation method for cyclic evaporation crystallization impurity removal, which is suitable for recycling evaporation of raffinate to recover crystallized salt. Through a small amount of experiments, the relationship between impurities in the crystallized salt and the number of cyclic evaporations can be obtained, thereby calculating the maximum number of cyclic evaporations that the mother liquor can be cyclically evaporated to obtain salt crystals that meet the impurity content requirements. The method is simple to operate, can effectively recover salt in waste liquid, and solve the problem of waste liquid pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a graph showing the relationship between the impurity content and the number of cycles in an embodiment of the present invention;

[0022] Figure 2 Graph showing the relationship between the percentage of Cl in the salt obtained in the embodiment of the present invention and the number of evaporations;

[0023] Figure 3 Graph showing the relationship between the percentage of Mg in the salt obtained in the embodiment of the present invention and the number of evaporations. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments shown below do not limit the invention content described in the claims. In addition, the entire contents of the structures represented by the following embodiments are not limited to those necessary as solutions to the invention described in the claims.

[0025] This example takes cobalt raffinate as an example. The solution after heavy metal removal mainly includes Na + Mg 2+ 、SO4 2- , Cl - The salt to be recovered is sodium sulfate, and the impurities to be removed mainly include Mg 2+ 、SO4 2- , Cl - .

[0026] (1) Experimental equipment and raw materials

[0027] Distillation flask, condenser, electric heating equipment.

[0028] (2) Theoretical model

[0029] A single desalination experiment was conducted. For the first time, 1.2L of stock solution was added and heated to about 95°C for evaporation. When the volume was evaporated to about 200ml, the heating was stopped. After cooling, the mother liquor and salt were separated into solid and liquid. The remaining mother liquor was used for the next evaporation experiment, and the cycle was repeated.

[0030] The salt and mother liquor of each experiment were tested, and the detection range included Mg 2+ 、SO4 2- , Cl - After multiple cycles of evaporation, the distribution ratio of impurity ions in the mother liquor and the salt was calculated each time. The results for magnesium ions are shown in Table 1, and the results for chloride ions are shown in Table 2.

[0031] Table 1 Magnesium distribution ratio under different cycle times

[0032]

[0033] Table 2 Chlorine distribution ratio under different cycle times

[0034]

[0035] According to the table above, after evaporation, the distribution ratio of magnesium ions and chloride ions in the mother liquor and salt is about 9:1. Therefore, according to this fixed distribution ratio, the impurity content in the salt and the impurity content in the mother liquor after the nth evaporation are calculated.

[0036] Assuming that the amount of impurities introduced each time is S, after the nth cycle, the impurity content in the salt is A n , the total amount of impurities in the salt in the first n times is S n .

[0037] After the first evaporation, A1=0.1*S

[0038] After the second evaporation, A2 = (2-0.1)*0.1*S = 0.19*S

[0039] After the third evaporation, A3 = (3-0.1-0.19)*0.1*S = 0.271*S ...

[0041] After the nth evaporation, A n =(nS n-1 )*0.1*S

[0042] A n The relationship with n is: n =[1-0.9 n ]*S

[0043] According to A n =[1-0.9 n The relationship between the impurity content in the salt obtained by ]*S and the number of cycles is shown in the figure Figure 1 As shown. Figure 1 It can be seen that after 88 cycles, the impurity content in the salt is the same as the impurity content in the salt after a single full steaming (based on 0.9999% as the standard).

[0044] (3) Process calculation

[0045] According to the salt content of the original solution after single full steaming (Table 3) and the trend of impurity content in the salt after the experiment ( Figure 2 , Figure 3 ), the relationship between the impurities in the precipitated salt and the number of evaporations can be calculated.

[0046] Table 3 Impurity content and standard after single full steam desalination (%)

[0047] Mg content Mg Standard Cl content Cl standard 2.67 0.5 6.22 1.5

[0048] According to the content of Cl ions and Mg ions in the initial salt and the impurity standard in the salt, substitute into the cycle evaporation relationship Figure 1It can be seen that after 16 rounds of evaporation, the magnesium ion content in the salt reached the upper limit standard; after 58 rounds of evaporation, the chloride ion content in the salt reached the upper limit standard.

[0049] Table 4 Impurity standards in sodium sulfate salt (%)

[0050] Mg Cl 0.5 1.5

[0051] The daily raffinate is 1200m 3 Calculation shows that the minimum volume of magnesium ions required to open the circuit is 1200 / 16=75m 3 The minimum volume of chloride ions that need to be opened regularly is 1200 / 58=20.7m 3 .

[0052] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A theoretical calculation method for impurity removal by cyclic evaporation crystallization, characterized in that: The following steps are involved: (1) Evaporation: A certain volume of stock solution is evaporated to a predetermined volume at a certain temperature. After cooling, the resulting mother liquor and salt crystals are separated into solid and liquid. The remaining mother liquor enters the next evaporation operation, and the cycle repeats; (2) Calculating the impurity distribution ratio: performing impurity detection on the salt and mother liquor obtained by each evaporation, and calculating the distribution ratio of impurities in the salt and mother liquor obtained by each evaporation desalination; (3) Establishing a relationship model between the impurity content in the salt crystals and the number of evaporation cycles: Based on the distribution ratio data obtained in step (2), establishing a relationship model between the impurity content in the salt crystals and the number of evaporation cycles; the specific method is: After multiple cycles of evaporation, the distribution ratio of impurities in the mother liquor and the salt is statistically obtained to be a fixed value m. Assuming that the amount of impurities introduced by each evaporation is S, the impurity content in the salt obtained by the nth evaporation is A. n , the total amount of impurities in the salt obtained by the first n-1 evaporations is S n-1 ,but: After the first evaporation, After the second evaporation, After the third evaporation, ... After the nth evaporation, The relationship between the impurity content An in the salt crystal and the number of cycles n is obtained as follows: ; (4) Cycle number prediction: Based on the impurity removal requirements, the model obtained in step (3) is used to predict the maximum number of cycles that can be used for evaporation when the impurity content in the salt crystals obtained by evaporation is not higher than the set maximum value; (5) Calculating the minimum volume of solution required for each evaporation: Calculate the minimum volume of solution required for each evaporation based on the total volume of the stock solution to be decontaminated, the total decontamination time, and the maximum number of cycles obtained in step (4).

2. A theoretical calculation method for impurity removal by circulating evaporation crystallization according to claim 1, characterized in that: The stock solution is the raffinate produced during the impurity removal and purification process of the cobalt-nickel solvent extraction method.

3. A theoretical calculation method for impurity removal by circulating evaporation crystallization according to claim 1, characterized in that: The raw liquid is cobalt raffinate, and the impurities include Mg 2+ , Cl - , sulfate.

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