CN115108646B - Method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate - Google Patents
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Abstract
The application provides a method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate, which comprises the following steps: filtering the high-salt wastewater to be treated, decolorizing the wastewater by using activated carbon and filtering the wastewater by using cation exchange resin in sequence; carrying out first-stage electrodialysis treatment on the pretreated high-salt wastewater to obtain first-stage electrodialysis concentrated water and first-stage electrodialysis fresh water; and carrying out second-stage electrodialysis treatment on the first-stage electrodialysis concentrated water to obtain sodium chloride crystals and a second-stage electrodialysis mother solution. The method disclosed by the application has the advantages of simple process conditions and high flow stability, no wastewater is discharged in the whole treatment process, zero discharge treatment of high-salt wastewater is realized, the wastewater treatment cost is reduced, the enterprise pressure is relieved, the environment-friendly requirement is met, and good economic and social benefits are realized.
Description
Technical Field
The application belongs to the technical field of reverse osmosis, and particularly relates to a method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate.
Background
The high-salt wastewater has wide sources and is mainly concentrated in industries such as coal, electric power, oil refining, chemical industry, metallurgy, papermaking, pesticides and the like. With the development of modern industrial technology, the high-salt wastewater volume is rapidly increased, and great challenges are brought to the current wastewater treatment and recycling technology. The high-salt wastewater contains various substances including organic matters, inorganic salts, oil, organic heavy metals, radioactive substances and the like, and is difficult to treat by a biochemical method because of the difficulty in survival of strains due to high salt content, so that the high-salt wastewater is one of internationally recognized wastewater which is difficult to treat and has larger pollution to the environment compared with common wastewater.
The organic matters in the high-salt wastewater have larger difference of substance types and chemical properties according to different production processes, but the inorganic salt matters are mostly Cl - 、SO 4 2- 、Na + 、Ca 2+ Etc. At present, the evaporation desalination method is the most commonly used method for treating high-salt wastewater, and the basic flow is that the high-salt wastewater is evaporated and concentrated and then is sent into an evaporation pond for evaporation or an evaporation crystallizer for evaporation, and the generated solid is buried. The method has mature technology, wide wastewater treatment range and high treatment speed. However, the method does not carry out classification treatment on sodium sulfate and sodium chloride, the obtained mixed salt has excessive content of organic matters and heavy metals, and the method is not accepted by industries such as downstream chlor-alkali and the like. Therefore, the method can only treat dangerous wastes generally, has quite high treatment cost, brings heavy environmental protection pressure to enterprises such as coal chemical industry and the like, and restricts the development of the industries such as coal chemical industry and the like to a great extent.
In recent years, in order to fully utilize available resources in high-salt wastewater, a great deal of work has been done by researchers to extract high-purity sodium chloride. The patent CN104973726A is characterized in that sulfate ions are removed by primary evaporation crystallization, material is added to generate precipitation, sodium sulfate and sodium chloride are recovered by secondary evaporation crystallization, the residual sodium sulfate is removed more thoroughly by a precipitation method, the sodium chloride obtained by the next stage of evaporation crystallization is purer, the operation is simple, the energy consumption is lower, and the production period is shorter. However, the addition of precipitants (e.g., calcium chloride, barium chloride, etc.) introduces new impurities, resulting in a reduced purity of the sodium chloride product.
Therefore, there is a need to develop a method for separating high-purity sodium chloride with good effect, high product purity and low cost.
Disclosure of Invention
The application aims to solve the technical problem of low purity of sodium chloride in the recovery of high-salt wastewater in the prior art, and provides a method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate by utilizing electrodialysis.
In order to achieve the aim of the application, the application provides a method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate, which comprises the following steps:
s101: sequentially filtering and decoloring the high-salt wastewater to be treated;
s102: carrying out first-stage electrodialysis treatment on the pretreated high-salt wastewater to obtain first-stage electrodialysis concentrated water and first-stage electrodialysis fresh water until the mass fraction of sodium chloride in the concentrated water is not less than 16%, preferably not less than 20%; wherein the mass fractions of the sodium chloride and the sodium sulfate are calculated by the mass of the high-salt wastewater to be treated;
s103: and carrying out second-stage electrodialysis treatment on the first-stage electrodialysis concentrated water to obtain sodium chloride crystals and a second-stage electrodialysis mother solution.
In the application, concentrated liquid is concentrated water after one-stage electrodialysis treatment; the desalted liquid is fresh water.
In the filtration, insoluble impurities may be removed by a laminated filter, a bag filter, or the like, and the present application is not particularly limited thereto.
Step S102 calculates the mass fraction of sodium sulfate and sodium chloride by measuring the concentration of chloride ions and sulfate ions, so that the sodium chloride content is saturated and sodium sulfate is removed.
The application provides a method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate, which utilizes the difference of migration speeds of sulfate ions and chloride ions in the electrodialysis process to concentrate and separate salt from the high-salt wastewater containing sodium chloride and sodium sulfate, and can effectively recover sodium chloride in the high-salt wastewater in industries such as coal chemical industry and the like, the obtained sodium chloride product reaches the first-grade standard of refined industrial salt specified by industrial salt national standard (GB/T5462-2015), the purity of the sodium chloride is more than or equal to 99%, the recovery rate of the sodium chloride and the sodium sulfate is more than 80%, and the comprehensive utilization of wastewater resources is realized. The method disclosed by the application has the advantages of simple process conditions and high flow stability, no wastewater is discharged in the whole treatment process, zero discharge treatment of high-salt wastewater is realized, the wastewater treatment cost is reduced, the enterprise pressure is relieved, the environment-friendly requirement is met, and good economic and social benefits are realized.
As a specific embodiment of the application, the method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate further comprises the following steps: s104: and mixing the second-stage electrodialysis mother solution with the first-stage electrodialysis fresh water, mixing with the first-stage electrodialysis inflow water, and performing first-stage electrodialysis treatment to recycle the second-stage electrodialysis mother solution.
In the application, the second-stage electrodialysis mother solution refers to a mixed solution of concentrated water and fresh water after sodium chloride crystallization is discharged.
As a specific embodiment of the present application, in the step S104, the reflux amount of the first-stage electrodialysis fresh water is controlled such that the mass fraction ratio of sodium chloride to sodium sulfate after mixing with the first-stage electrodialysis feed water and the second-stage electrodialysis mother solution is 8 to 13. The application measures the mass fraction of sodium chloride and sodium sulfate by measuring the concentration of chloride ions and sulfate ions, and determines the fresh water reflux quantity of one-stage electrodialysis by the mass fraction ratio of sodium chloride to sodium sulfate, thereby realizing good salt separation effect.
The mass fractions of sodium chloride and sodium sulfate were determined by measuring the concentrations of chloride and sulfate ions. The fresh water reflux quantity of the first-stage electrodialysis is determined by the mass fraction ratio of sodium chloride to sodium sulfate.
As a specific embodiment of the present application, in the step S101, activated carbon is used in an amount ranging from 5g to 15g, for example, from 5g,7g,9g,11g,13g,15g, and any combination thereof, more preferably, for example, from 7g to 9g, per liter of salt wastewater, at the time of the decoloring treatment.
As a specific embodiment of the present application, in the step S101, the decoloring treatment is performed until the removal rate of COD reaches 75% -85%.
Preferably, in the step S101, a filtration treatment with an ion exchange resin is further included. For removing Ca 2+ 、Mg 2 + Soluble substances such as silicate groups.
In a specific embodiment of the present application, the ion exchange resin is a sodium ion exchange resin.
As a specific embodiment of the present application, in the step S102, the number of stages of the one-stage electrodialysis is determined according to the salt content of the high-salt wastewater.
The salt content in the application refers to the mass fraction of the total salt content, and the salt content is Cl - 、SO 4 2- 、Na + 、Ca 2+ And the like.
Preferably, when the salt content in the high-salt wastewater is 6% -10%, two-stage electrodialysis is adopted; when the salt content in the high-salt wastewater is 10% -15%, first-stage electrodialysis is adopted.
As a specific embodiment of the present application, in the step S102, the current density of the one-stage electrodialysis is 20mA/cm 2 -50mA/cm 2 Preferably 30mA/cm 2 -40mA/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The direct voltage applied to each electrodialysis membrane unit is 0.1V-1V, preferably 0.3V-0.7V.
As a specific embodiment of the present application, in the step S102, the total mass percentage of sodium chloride and sodium sulfate in the one-stage electrodialysis concentrate is in the range of 12% -24%, for example, 12%,15%,18%,22%,24%, and any combination thereof, based on the mass of the one-stage electrodialysis concentrate.
The ratio of the mass content of sodium chloride to sodium sulfate is in the range of 8-13, e.g., 8,9, 10, 11, 12, 13, and any combination thereof.
As a specific embodiment of the present application, in the step S103, the salt content of the two-stage electrodialysis mother solution is in the range of 3% -8%, for example, 3%,5%,8%, and any combination thereof, based on the mass of the two-stage electrodialysis mother solution.
Preferably, the ratio of sodium chloride to sodium sulfate mass fraction in the two-stage electrodialysis mother liquor is in the range of from 0.5 to 1, e.g., 0.5,0.7,0.1, and any combination thereof.
As a specific embodiment of the present application, in the step S102, the salt content of the electrodialysis fresh water is 0.5% -3% based on the mass of the electrodialysis fresh water.
Preferably, the mass fraction ratio of sodium chloride to sodium sulfate in the first electrodialysis fresh water is 0.2-1.
According to the method, the high-salt wastewater containing sodium chloride and sodium sulfate is concentrated and separated by electrodialysis by utilizing the difference of migration speeds of sulfate ions and chloride ions in the electrodialysis process, and the method is different from the traditional salt separation process, and has the advantages of good salt separation effect, low cost, simple operation and high efficiency.
Drawings
FIG. 1 is a flow chart of the separation of high purity sodium chloride from high salt wastewater containing sodium sulfate according to example 1 of the present application.
Detailed Description
The application is further illustrated below in connection with specific examples, which are not to be construed as limiting the application in any way.
The mass flow rate of the high-salt wastewater fed by the coal chemical industry enterprises is 1000kg/h, and the high-salt wastewater is analyzed by ion chromatography, wherein the mass fraction of sodium chloride is 6.28%, the mass fraction of sodium sulfate is 2.02% and the COD value is 500mg/L by adopting a potassium dichromate method.
The test method in the embodiment of the application refers to a water and wastewater monitoring and analyzing method (fourth edition), and the specific test method and instrument are as follows:
ca in water 2+ 、Mg 2+ The method for testing the concentration of silicate radical plasma comprises the following steps: ion chromatography, instrument: an ion chromatograph;
sodium chloride and sodium sulfate concentration testing method: ion chromatography, instrument: an ion chromatograph;
the COD test method comprises the following steps: potassium dichromate method, instrument: a spectrophotometer.
Example 1
Example 1 proposes a method for separating high purity sodium chloride from high salt wastewater containing sodium sulfate, as shown in fig. 1, comprising the steps of:
1. pretreating high-salt wastewater, namely firstly, enabling the high-salt wastewater to enter a laminated filter system, removing insoluble impurities by using a laminated filter and a bag filter, then, performing decoloration pretreatment by using activated carbon, wherein the addition amount of the activated carbon is 7g/L wastewater, the COD removal rate is 75%, and finally, removing Ca by using ion exchange resin 2+ 、Mg 2+ Soluble substances such as silicate groups.
2. And (3) the pretreated high-salt wastewater enters a first-stage electrodialysis for concentration and salt separation to obtain a first-stage electrodialysis concentrated water and fresh water. The electrodialysis of one section is two-stage electrodialysis, the membrane pair number is 200 pairs/table by adopting a mode of connecting 5500 x 1100 equipment two pieces in series, and the current density is 38mA/cm 2 The dc voltage applied across each set of membrane pair cells was 0.50V. The mass flow rate of the electrodialysis concentrated water is as follows: 645.65kg/h, the mass fraction of sodium chloride after concentration is 20.32%, the sodium sulfate concentration is 3.41%, and the mass fraction ratio of sodium chloride to sodium sulfate concentration is 5.95.
3. The first-stage electrodialysis concentrated water is used as the concentrated water and fresh water inflow of the second-stage electrodialysis to be sent into the second-stage electrodialysis for crystallization, 5500 x 1100 electrodialysis crystallization equipment is adopted for the second-stage electrodialysis, 200 pairs of membrane pairs are adopted, and the current density is 38mA/cm 2 The direct current voltage applied to each group of membrane stack units is 0.50V, electrodialysis crystallization treatment is carried out in an intermittent operation mode, and sodium chloride solids are separated out from the concentrated water side after the system is operated for 30 min. 58.75kg/h of sodium chloride are separated off by centrifugation and dried.
4. And after salt extraction by the second-stage electrodialysis, the mother solution and partial fresh water by the first-stage electrodialysis are mixed and returned to the first-stage electrodialysis for mixed recycling with the feed wastewater, wherein the mass flow of the mother solution after salt extraction by the second-stage electrodialysis is 380kg/h, and the mass flow of the fresh water by the first-stage electrodialysis is 354.35kg/h.
The sodium chloride product of example 1 was tested for purity according to the test method described in GB/T5462-2015 industrial salt, the test results are shown in Table 1.
TABLE 1 purity of sodium chloride product of example 1
Example 2
Example 2 differs from example 1 only in that: the current density of the electrodialysis section is 25mA/cm 2 The remaining steps and parameters are the same. After electrodialysis concentration, the mass fraction of sodium chloride is 17.32%, the concentration of sodium sulfate is 2.95%, and the mass fraction ratio of sodium chloride to sodium sulfate concentration is as follows: 5.87. and (3) separating out sodium chloride solids on the concentrated water side after the second-stage electrodialysis system is operated for 40 min. The sodium chloride was separated by centrifugal filtration at a concentration of 56.14kg/h and dried.
The sodium chloride product of example 2 was tested for purity according to the test method described in GB/T5462-2015 industrial salt and the test results are shown in Table 2.
TABLE 2 purity of sodium chloride product of example 2
Comparative example 1
Comparative example 1 differs from example 1 only in that: comparative example 1 does not include step 4, and the remaining steps and parameters are the same. And (3) separating out sodium chloride solids on the concentrated water side after the second-stage electrodialysis system is operated for 45 min. 56.15kg/h of sodium chloride are separated off by centrifugation and dried. Purity was measured according to the method described in GB/T5462-2015 industrial salt, and the measurement results are shown in Table 3.
TABLE 3 purity of sodium chloride product of comparative example 1
Comparative example 2
Comparative example 2 differs from example 1 only in that: the electrodialysis of step 2 of comparative example 2 was first electrodialysis, using 5500 x 1100 units, with a membrane pair number of 200 pairs/unit and a current density of 38mA/cm 2 The dc voltage applied across each set of membrane pair cells was 0.50V. The mass flow rate of the electrodialysis concentrated water is as follows: 620.18kg/h, the mass fraction of sodium chloride after concentration is 14.32%, the sodium sulfate concentration is 3.14%, and the mass fraction ratio of the sodium chloride to the sodium sulfate concentration is: 4.56. the rest steps and parameters are the same. And (3) separating out sodium chloride solids on the concentrated water side after the second-stage electrodialysis system is operated for 60 min. 32.14kg/h of sodium chloride are separated off by centrifugation and dried. Purity was measured according to the method described in GB/T5462-2015 industrial salt, and the measurement results are shown in Table 4.
TABLE 4 purity of sodium chloride product of comparative example 2
As can be seen from comparing the examples with the comparative examples, the concentration of sodium chloride in the examples of the present application can finally reach more than 99%, the contents of sulfate ions and water insoluble substances are also greatly reduced, and it is demonstrated that the method in the examples of the present application finally achieves separation of high purity sodium chloride from high salt wastewater containing sodium sulfate by utilizing electrodialysis, and has good salt separation effect, low cost and high efficiency.
Any numerical value recited in this disclosure includes all values incremented by one unit from the lowest value to the highest value if there is only a two unit interval between any lowest value and any highest value. For example, if the amount of one component, or the value of a process variable such as temperature, pressure, time, etc., is stated to be 50-90, it is meant in this specification that values such as 51-89, 52-88 … …, and 69-71, and 70-71 are specifically recited. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 units may be considered as appropriate. This is only a few examples of the specific designations. In a similar manner, all possible combinations of values between the lowest value and the highest value enumerated are to be considered to be disclosed.
It should be noted that the above-described embodiments are only for explaining the present application and do not constitute any limitation of the present application. The application has been described with reference to exemplary embodiments, but it is understood that the words which have been used are words of description and illustration, rather than words of limitation. Modifications may be made to the application as defined in the appended claims, and the application may be modified without departing from the scope and spirit of the application. Although the application is described herein with reference to particular means, materials and embodiments, the application is not intended to be limited to the particulars disclosed herein, as the application extends to all other means and applications which perform the same function.
Claims (14)
1. A method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate is characterized in that,
the method comprises the following steps:
s101: sequentially filtering and decoloring the high-salt wastewater to be treated;
s102: carrying out first-stage electrodialysis treatment on the pretreated high-salt wastewater to obtain first-stage electrodialysis concentrated water and first-stage electrodialysis fresh water until the mass fraction of sodium chloride in the first-stage electrodialysis concentrated water is not less than 16%;
s103: carrying out second-stage electrodialysis treatment on the first-stage electrodialysis concentrated water to obtain sodium chloride crystals and a second-stage electrodialysis mother solution;
s104: mixing the second-stage electrodialysis mother liquor with the first-stage electrodialysis fresh water, mixing with the first-stage electrodialysis inflow water, and performing first-stage electrodialysis treatment to recycle the second-stage electrodialysis mother liquor;
in the step S104, the reflux quantity of the first-stage electrodialysis fresh water is controlled so that the mass fraction ratio of sodium chloride to sodium sulfate after the reflux quantity is mixed with the first-stage electrodialysis water inlet and the second-stage electrodialysis mother solution is 8-13.
2. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 1, wherein S102: and carrying out first-stage electrodialysis treatment on the pretreated high-salt wastewater to obtain first-stage electrodialysis concentrated water and first-stage electrodialysis fresh water, wherein the mass fraction of sodium chloride in the first-stage electrodialysis concentrated water is not less than 20%.
3. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 2, wherein in said step S101, activated carbon is used in an amount of 5g to 15g per liter of salt wastewater in the decoloring treatment.
4. A method for separating high purity sodium chloride from high salt wastewater containing sodium sulfate according to claim 3, wherein in said step S101, activated carbon is used in an amount of 7g to 9g per liter of salt wastewater in the decoloring treatment.
5. The method for separating high purity sodium chloride from high salt wastewater containing sodium sulfate according to any of claims 1-4, wherein in said step S101, the decoloring treatment is performed until the removal rate of COD reaches 75% -85%.
6. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 5, further comprising a filtration treatment with an ion exchange resin in said step S101.
7. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 6, wherein in said step S102, the number of stages of said one-stage electrodialysis is determined according to the salt content of the high-salt wastewater.
8. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 7, wherein two-stage electrodialysis is employed when the salt content in the high-salt wastewater is 6% -10%; when the salt content in the high-salt wastewater is 10% -15%, first-stage electrodialysis is adopted.
9. The method of claim 8, wherein the sodium sulfate-containing high saltA method for separating high-purity sodium chloride from wastewater, characterized in that in the step S102, the current density of the one-stage electrodialysis is 20mA/cm 2 -50mA/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The direct current voltage applied to each electrodialysis membrane unit is 0.1V-1V.
10. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 9, wherein in said step S102, the current density of said one-stage electrodialysis is 30mA/cm 2 -40mA/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The direct current voltage applied to each electrodialysis membrane unit is 0.3V-0.7V.
11. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 10, wherein in said step S102, the mass content ratio of sodium chloride to sodium sulfate in said one-stage electrodialysis concentrate is 8 to 13 based on the mass of said one-stage electrodialysis concentrate.
12. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 11, wherein in said step S103, the ratio of sodium chloride to sodium sulfate in the two-stage electrodialysis mother solution is 0.5 to 1 in terms of mass fraction of the two-stage electrodialysis mother solution.
13. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 12, wherein in said step S102, the salt content of the electrodialysis fresh water is 0.5% -3% by mass of the electrodialysis fresh water.
14. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 13, wherein in said step S102, the ratio of sodium chloride to sodium sulfate in the one-stage electrodialysis fresh water is 0.2 to 1 in terms of mass of the one-stage electrodialysis fresh water.
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| CN105906111A (en) * | 2016-05-11 | 2016-08-31 | 合肥科佳高分子材料科技有限公司 | Method for separating salt from coal-chemical-industry wastewater through electroosmosis technique |
| CN106242133B (en) * | 2016-09-30 | 2017-06-16 | 厦门市科宁沃特水处理科技股份有限公司 | A kind of Desulphurization for Coal-fired Power Plant waste water homogeneous ion-exchange membrane electrodialysis minimizing handling process |
| CN107459200A (en) * | 2017-09-26 | 2017-12-12 | 江苏中圣高科技产业有限公司 | A kind of high slat-containing wastewater salinity recycling new recovering technology |
| CN107867707A (en) * | 2017-10-23 | 2018-04-03 | 天津大学 | The sodium sulfate in high purity and the sub-prime method for crystallising of sodium chloride that extraction resourcebility utilizes from high-salt wastewater |
| CN110272061A (en) * | 2018-03-14 | 2019-09-24 | 国家能源投资集团有限责任公司 | A kind of salt extraction process |
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