CN115108646A - Method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate - Google Patents
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Abstract
The invention provides a method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate, which comprises the following steps: sequentially filtering the high-salinity wastewater to be treated, decoloring the wastewater by using activated carbon and filtering the wastewater by using cation exchange resin; 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 second-stage electrodialysis mother liquor. The method has the advantages of simple process conditions, high flow stability, no discharge of any wastewater in the whole treatment process, realization of zero discharge treatment of high-salinity wastewater, reduction of wastewater treatment cost, alleviation of enterprise pressure, satisfaction of environmental protection requirements, and good economic and social benefits.
Description
Technical Field
The invention belongs to the technical field of reverse osmosis, and particularly relates to a method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate.
Background
The high-salinity wastewater has wide sources and is mainly concentrated in the industries of coal, electric power, oil refining, chemical industry, metallurgy, paper making, pesticides and the like. With the development of modern industrial technology, the amount of high-salinity wastewater is rapidly increased, and great challenges are brought to the current wastewater treatment and recycling technology. The high-salinity wastewater contains various substances including organic substances, inorganic salts, oil, organic heavy metals, radioactive substances and the like, and because the bacteria are difficult to survive due to high salinity, the high-salinity wastewater is difficult to treat by a biochemical method, so that the high-salinity wastewater is one of the internationally recognized wastewater difficult to treat, and has greater environmental pollution compared with the common wastewater.
The organic substances in the high-salinity wastewater have large differences in substance types and chemical properties according to different production processes, but most of the inorganic salt substances are Cl - 、SO 4 2- 、Na + 、Ca 2+ And so on. At present, the evaporative desalination method is the most common method for treating high-salinity wastewater, and the basic flow of the method is that the high-salinity wastewater is evaporated and concentrated and then sent into an evaporation pond for evaporation or evaporated in an evaporative crystallizer, and the generated solid is buried. The method has mature technology, wide range of waste water treatment and high treatment speed. However, this method does not fractionate sodium sulfate and sodium chloride, and a mixed salt is obtained, and the mixed salt isThe content of the organic matters and the heavy metals in the product exceeds the standard, and the product cannot be accepted by downstream chlor-alkali industries and the like. Therefore, the treatment can be generally carried out only according to dangerous wastes, the treatment cost is quite high, heavy environmental protection pressure is brought to enterprises in the coal chemical industry and the like, and the development of the industries in the coal chemical industry and the like is restricted to a great extent.
In recent years, researchers have performed a lot of work to extract high-purity sodium chloride by making full use of available resources in high-salinity wastewater. Patent CN104973726A is through once evaporation crystallization, add the material and generate the sediment and get rid of sulfate ion, secondary evaporation crystallization recovery sodium sulfate and sodium chloride, and it is more thorough that the residual sodium sulfate is got rid of to the precipitation method, and the next grade evaporation crystallization gained sodium chloride is purer, easy operation, and the energy consumption is lower, and production cycle is shorter. However, the addition of a precipitant (e.g., calcium chloride, barium chloride, etc.) introduces new impurities, which results in a reduction in the purity of the sodium chloride product.
Therefore, the development of a method for separating high-purity sodium chloride with good effect, high product purity and low cost is urgently needed.
Disclosure of Invention
The invention 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 using electrodialysis.
In order to achieve the aim of the invention, the invention provides a method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate, which comprises the following steps:
s101: sequentially filtering and decoloring the high-salinity wastewater to be treated;
s102: performing 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 according to the mass of the high-salinity 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 second-stage electrodialysis mother liquor.
In the application, after the first-stage electrodialysis treatment, the concentrated liquid is concentrated water; the desalted liquid is fresh water.
In the filtration, insoluble impurities may be removed by using a stack filter or a bag filter, and the present invention 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, saturates the sodium chloride content and removes the sodium sulfate.
The invention 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 by electrodialysis, can effectively recover the sodium chloride in the high-salt wastewater in industries such as coal chemical industry and the like, and the obtained sodium chloride product reaches the primary standard of refined industrial salt specified by the national standard for industrial salt (GB/T5462-2015), the purity of the sodium chloride is more than or equal to 99 percent, the recovery rate of the sodium chloride and the sodium sulfate reaches more than 80 percent, thereby realizing the comprehensive utilization of wastewater resources. The method has the advantages of simple process conditions, high flow stability, no discharge of any wastewater in the whole treatment process, realization of zero discharge treatment of high-salinity wastewater, reduction of wastewater treatment cost, alleviation of enterprise pressure, satisfaction of environmental protection requirements, and good economic and social benefits.
As a specific embodiment of the invention, the method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate further comprises the following steps: s104: and mixing the second-stage electrodialysis mother liquor with the first-stage electrodialysis fresh water, mixing the second-stage electrodialysis mother liquor with the first-stage electrodialysis inlet water, and then carrying out first-stage electrodialysis treatment to recycle the first-stage electrodialysis inlet water.
In the present application, the second-stage electrodialysis mother liquor is a mixed solution of concentrated water and fresh water after sodium chloride crystallization is discharged.
As a specific embodiment of the present invention, in the step S104, the reflux amount of the first-stage electrodialysis fresh water is controlled so 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 liquor is 8 to 13. The mass fraction of sodium chloride and sodium sulfate is determined by measuring the concentration of chloride ions and sulfate ions, and the fresh water reflux of one-section electrodialysis is determined by the mass fraction ratio of sodium chloride and sodium sulfate, so that a good salt separation effect is realized.
The mass fractions of sodium chloride and sodium sulfate were determined by measuring the concentrations of chloride and sulfate ions. The reflux quantity of the fresh water of the first-stage electrodialysis is determined by the mass fraction ratio of the sodium chloride to the sodium sulfate.
As a specific embodiment of the present invention, in the step S101, in performing the decoloring treatment, activated carbon is used, and the amount of activated carbon is in a range of adding 5g to 15g of activated carbon, for example, 5g, 7g, 9g, 11g, 13g, 15g, and any combination thereof, more preferably, for example, 7g to 9g, per liter of the high-salinity wastewater.
As a specific embodiment of the present invention, in the step S101, the decoloring is performed until the COD removal rate thereof reaches 75% to 85%.
Preferably, in step S101, a filtration treatment with an ion exchange resin is further included. For removing Ca 2+ 、Mg 2 + And soluble substances such as silicic acid groups.
In a particular embodiment of the invention, the ion exchange resin is a sodium ion exchange resin.
As a specific embodiment of the present invention, in step S102, the number of stages of the first-stage electrodialysis is determined according to the salt content of the high-salinity wastewater.
The salt content in the application refers to the mass fraction of total salt, and the salt substance 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; and when the salt content in the high-salt wastewater is 10-15%, primary electrodialysis is adopted.
As the inventionIn step S102, the current density of the electrodialysis is 20mA/cm 2 -50mA/cm 2 Preferably 30mA/cm 2 -40mA/cm 2 (ii) a 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 invention, in the step S102, the total mass percentage content of the sodium chloride and the sodium sulfate in the one-stage electrodialysis concentrated water is 12% to 24%, for example, 12%, 15%, 18%, 22%, 24% and any combination thereof, based on the mass of the one-stage electrodialysis concentrated water.
The ratio of the mass content of sodium chloride to sodium sulfate is in the range of 8-13, such as 8, 9, 10, 11, 12, 13 and any combination thereof.
As a specific embodiment of the present invention, in the step S103, the salt content of the second-stage electrodialysis mother liquor is in a range of 3% to 8%, for example, 3%, 5%, 8% and any combination thereof, based on the mass of the second-stage electrodialysis mother liquor.
Preferably, the ratio of the mass fraction of sodium chloride to sodium sulphate in the mother liquor of the two-stage electrodialysis is in the range of 0.5-1, such as 0.5, 0.7, 0.1 and any combination thereof.
As a specific embodiment of the present invention, in the step S102, the salt content of the first-stage electrodialysis fresh water is 0.5% -3% by mass of the first-stage electrodialysis fresh water.
Preferably, in the one-stage electrodialysis fresh water, the mass fraction ratio of sodium chloride to sodium sulfate is 0.2-1.
According to the invention, the high-salinity wastewater containing sodium chloride and sodium sulfate is concentrated and desalted 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 desalting process, has the advantages of good desalting effect, low cost, simple operation and high efficiency, and can be completed by utilizing the traditional electrodialysis.
Drawings
FIG. 1 is a flow chart of the process for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate according to example 1 of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention in any way.
The mass flow of the high-salinity wastewater from the feeding high-salinity wastewater of a certain coal chemical industry enterprise in the embodiments and the comparative examples of the invention is 1000kg/h, and the mass fraction of sodium chloride is 6.28% and the mass fraction of sodium sulfate is 2.02% based on the mass of the high-salinity wastewater, and the COD value is 500mg/L measured by a potassium dichromate method.
The test method in the embodiment of the present invention refers to "water and wastewater monitoring and analysis method (fourth edition)", and the specific test method and apparatus are as follows:
ca in water 2+ 、Mg 2+ The method for testing the concentration of the silicate plasma comprises the following steps: ion chromatography, instrument: an ion chromatograph;
the method for testing the concentration of sodium chloride and sodium sulfate comprises the following steps: ion chromatography, instrument: an ion chromatograph;
the COD test method comprises the following steps: potassium dichromate method, apparatus: a spectrophotometer.
Example 1
Example 1 proposes a method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate, as shown in fig. 1, comprising the steps of:
1. pretreating high-salinity wastewater, namely firstly introducing the high-salinity wastewater into a laminated filter system, removing insoluble impurities by using a laminated filter and a bag filter, then adopting activated carbon for decolorization pretreatment, wherein the adding amount of the activated carbon is 7g/L of wastewater, the removal rate of COD is 75%, and finally removing Ca by using ion exchange resin 2+ 、Mg 2+ And soluble substances such as silicic acid groups.
2. And (4) the pretreated high-salinity wastewater enters a section of electrodialysis for concentration and salt separation to obtain section of electrodialysis concentrated water and fresh water. One-section electrodialysis is two-stage electrodialysis, and two 5500 × 1100 devices are connected in series, the membrane number is 200 pairs/stage, and the current density is 38mA/cm 2 The DC voltage applied to the cells was 0.50V for each set of film pairs. The mass flow of the first-stage electrodialysis concentrated water is as follows: 645.65kg/h, sodium chloride after concentrationThe weight fraction was 20.32%, the sodium sulfate concentration was 3.41%, and the ratio of the mass fractions of the sodium chloride and sodium sulfate concentrations was 5.95.
3. Feeding the first-stage electrodialysis concentrated water as concentrated water and fresh water of the second-stage electrodialysis into the second-stage electrodialysis for crystallization, wherein the second-stage electrodialysis adopts 5500 x 1100 electrodialysis crystallization equipment, the number of membrane pairs is 200, and the current density is 38mA/cm 2 And the direct current voltage applied to each group of membrane stack units is 0.50V, the electrodialysis crystallization treatment is carried out in an intermittent operation mode, and sodium chloride solid is separated out from the concentrated water side after the system operates for 30 min. 58.75kg/h of sodium chloride were separated off by centrifugal filtration and dried.
4. And mixing the mother liquor subjected to salt extraction by the second-stage electrodialysis and part of fresh water subjected to the first-stage electrodialysis, returning the mixed mother liquor to the first-stage electrodialysis, and mixing the mixed mother liquor with the feed wastewater for recycling, wherein the mass flow of the mother liquor subjected to salt extraction by the second-stage electrodialysis is 380kg/h, and the mass flow of the fresh water subjected to the first-stage electrodialysis is 354.35 kg/h.
The sodium chloride product of example 1 was tested for purity according to the test methods described in GB/T5462-2015 for industrial salt, and 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 first-stage electrodialysis is 25mA/cm 2 The remaining steps and parameters are the same. After the first-stage 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 the sodium chloride to the sodium sulfate is as follows: 5.87. and (4) separating out sodium chloride solid on the concentrated water side after the two-stage electrodialysis system operates for 40 min. 56.14kg/h of sodium chloride were separated off by centrifugal filtration and dried.
The sodium chloride product of example 2 was tested for purity according to the test methods 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 (4) separating out sodium chloride solid on the concentrated water side after the two-stage electrodialysis system operates for 45 min. 56.15kg/h of sodium chloride were separated off by centrifugal filtration and dried. Purity was measured according to the method described in GB/T5462-2015 for industrial salt, and the 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: in step 2 of comparative example 2, the one-stage electrodialysis was one-stage electrodialysis using 5500 x 1100 equipment, 200 pairs of membranes per stage, and a current density of 38mA/cm 2 The DC voltage applied to the cells was 0.50V for each set of film pairs. The mass flow of the first-stage electrodialysis concentrated water is as follows: 620.18kg/h, the mass fraction of sodium chloride after concentration is 14.32%, the concentration of sodium sulfate is 3.14%, and the mass fraction ratio of the sodium chloride to the sodium sulfate is as follows: 4.56. the remaining steps and parameters were the same. And (4) separating out sodium chloride solid on the concentrated water side after the two-stage electrodialysis system operates for 60 min. 32.14kg/h of sodium chloride were separated off by centrifugal filtration and dried. Purity was measured according to the method described in GB/T5462-2015 for industrial salts, and the results are shown in Table 4.
Table 4 purity of sodium chloride product of comparative example 2
Comparing the examples and the comparative examples, the concentration of sodium chloride in the examples of the invention can reach more than 99% finally, and the content of sulfate ions and water-insoluble substances is greatly reduced, which shows that the method in the examples of the invention finally realizes the separation of high-purity sodium chloride from high-salt wastewater containing sodium sulfate by electrodialysis, and has good salt separation effect, low cost and high efficiency.
Any numerical value mentioned in this specification, if there is only a two unit interval between any lowest value and any highest value, includes all values from the lowest value to the highest value incremented by one unit at a time. For example, if it is stated that the amount of a component, or a value of a process variable such as temperature, pressure, time, etc., is 50 to 90, it is meant in this specification that values of 51 to 89, 52 to 88 … …, and 69 to 71, and 70 to 71, etc., are specifically enumerated. For non-integer values, units of 0.1, 0.01, 0.001, or 0.0001 may be considered as appropriate. These are only some specifically indicated examples. In a similar manner, all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be disclosed in this application.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described in relation to an exemplary embodiment, and it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Modifications may be made to the invention as defined within the scope of the claims and modifications may be made without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (10)
1. A method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate is characterized in that,
the method comprises the following steps:
s101: sequentially filtering and decoloring the high-salinity wastewater to be treated;
s102: performing 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%, preferably not less than 20%; wherein the mass fractions of the sodium chloride and the sodium sulfate are calculated according to the mass of the high-salinity 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 second-stage electrodialysis mother liquor.
2. The method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate according to claim 1, characterized by further comprising the steps of: s104: and mixing the second-stage electrodialysis mother liquor with the first-stage electrodialysis fresh water, mixing the second-stage electrodialysis mother liquor with the first-stage electrodialysis inlet water, and then carrying out first-stage electrodialysis treatment to recycle the first-stage electrodialysis inlet water.
3. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to claim 2, wherein in the step S104, the reflux amount of the primary electrodialysis fresh water is controlled so that the mass fraction ratio of sodium chloride to sodium sulfate after mixing with the primary electrodialysis feed water and the secondary electrodialysis mother liquor is 8-13.
4. The method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate according to claim 1 or 2, characterized in that in the step S101, activated carbon is adopted when performing decolorization treatment, and the amount of activated carbon is 5g to 15g of activated carbon per liter of high-salinity wastewater; preferably, the dosage of the activated carbon is 7g to 9g of activated carbon added in each liter of high-salinity wastewater.
5. The method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate according to any one of claims 1 to 3, characterized in that in the step S101, the decolorization treatment is carried out until the COD removal rate reaches 75 to 85 percent; preferably, in step S101, a filtration treatment with an ion exchange resin is further included.
6. The method for separating high-purity sodium chloride from high-salt wastewater containing sodium sulfate according to any one of claims 1 to 4, wherein 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; preferably, when the salt content in the high-salt wastewater is 6-10%, two-stage electrodialysis is adopted; and when the salt content in the high-salt wastewater is 10-15%, primary electrodialysis is adopted.
7. The method for separating high-purity sodium chloride from sodium sulfate-containing high-salt wastewater as claimed in any one of claims 1 to 5, wherein 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 (ii) a The direct voltage applied to each electrodialysis membrane unit is 0.1V-1V, preferably 0.3V-0.7V.
8. The method for separating high-purity sodium chloride from high-salinity wastewater containing sodium sulfate according to any one of claims 1 to 6, characterized in that in the step S102, the total mass percentage content of sodium chloride and sodium sulfate in the one-stage electrodialysis concentrated water is 12 to 24 percent, and the mass percentage ratio of sodium chloride to sodium sulfate is 8 to 13 based on the mass of the one-stage electrodialysis concentrated water.
9. The method for separating high-purity sodium chloride from sodium sulfate-containing high-salt wastewater as claimed in any one of claims 1 to 7, wherein in the step S103, the salt content of the secondary electrodialysis mother liquor is 3 to 8 percent based on the mass of the secondary electrodialysis mother liquor; preferably, in the mother liquor of the two-stage electrodialysis, the mass fraction ratio of sodium chloride to sodium sulfate is 0.5-1.
10. The method for separating high-purity sodium chloride from sodium sulfate-containing high-salt wastewater as claimed in any one of claims 1 to 8, wherein in the step S102, the one-stage electrodialysis fresh water contains salt in an amount of 0.5 to 3% based on the mass of the one-stage electrodialysis fresh water; preferably, in the one-stage electrodialysis fresh water, the mass fraction ratio of sodium chloride to sodium sulfate is 0.2-1.
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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 |
| CN106242133A (en) * | 2016-09-30 | 2016-12-21 | 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 processes technique |
| 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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