CN113413762A

CN113413762A - Treatment method of reverse osmosis concentrated solution

Info

Publication number: CN113413762A
Application number: CN202110579516.6A
Authority: CN
Inventors: 关丰忠; 武海杰; 李成; 吴国祥; 刘义; 李玉林; 朱德汉; 周超; 贺飞; 肖杰; 莘振东
Original assignee: Guoneng Xinjiang Chemical Co ltd; China Shenhua Coal to Liquid Chemical Co Ltd
Current assignee: Guoneng Xinjiang Chemical Co ltd; China Shenhua Coal to Liquid Chemical Co Ltd
Priority date: 2021-05-26
Filing date: 2021-05-26
Publication date: 2021-09-21

Abstract

The invention relates to the technical field of coal chemical wastewater treatment, in particular to a treatment method of reverse osmosis concentrated solution, which comprises the following steps: pretreating the reverse osmosis concentrated solution, and crystallizing the pretreated solution to obtain sodium sulfate crystals, sodium chloride crystals and miscellaneous salts; the molar ratio of sulfate ions to chloride ions in the reverse osmosis concentrated solution is 1: 1-1.5, the COD of the pretreatment solution is 500-700mg/L, and the concentration of the silicon dioxide in the pretreatment solution is 300-500 mg/L. According to the invention, through pretreatment of the reverse osmosis concentrated solution and control of the COD value and the concentration of silicon dioxide in the pretreated solution, high-purity sodium sulfate and sodium chloride crystal salt can be produced in the existing evaporative crystallization device, zero discharge of salt-containing sewage is realized, the recycling of resources is realized, the operation stability of the system can be improved, and the cleaning frequency of the device is reduced.

Description

Treatment method of reverse osmosis concentrated solution

Technical Field

The invention relates to the technical field of coal chemical wastewater treatment, in particular to a treatment method of reverse osmosis concentrated solution.

Background

At present, the domestic coal chemical industry belongs to resource intensive industry, and has large water resource consumption and large discharge capacity. The high-salt wastewater in the coal chemical industry has complex components, contains other organic and inorganic components besides a large amount of chloride, sulfate and nitrate, and has high treatment difficulty. At present, biochemical treatment and membrane treatment are generally adopted to treat wastewater, so that reverse osmosis clear liquid can meet the discharge standard, and reverse osmosis concentrated solution is subjected to multiple concentration and evaporative crystallization, but in order to ensure the quality of crystallized salt, partial mother solution has to be discharged, the discharged mother solution has the characteristics of high salt content, high COD (chemical oxygen demand), high chloride ion and sulfate radical content, a certain amount of nitrate radical and the like, the characteristics ensure that the mother solution cannot achieve the purpose of effective treatment by adopting a single method, and environmental pollution can still be caused.

Disclosure of Invention

The invention aims to solve the problem that the treatment method of reverse osmosis concentrated solution in the prior art still generates discharged waste liquid to cause environmental pollution, and provides the treatment method of reverse osmosis concentrated solution.

The inventor of the invention finds that in the hot method salt separation process, the quality of the crystal salt is simultaneously influenced by various factors such as the supersaturation degree of a solution, the addition of seed crystals, the selection of equipment, other impurities, the quality of incoming water and the like, and the formation of crystal nuclei and the growth of crystals can be influenced by regulating and controlling the COD value, the content of silicon dioxide and the content of ions of a crystallization mother liquor, so that the high-quality crystal salt with low water content is obtained.

In order to achieve the above object, the present invention provides a method for treating a reverse osmosis concentrate, the method comprising:

pretreating the reverse osmosis concentrated solution to obtain a pretreated solution, and crystallizing to obtain a sodium sulfate crystal, a sodium chloride crystal and miscellaneous salts;

wherein the molar ratio of sulfate ions to chloride ions in the reverse osmosis concentrated solution is 1: 1-1.5,

the COD of the pretreatment solution is 500-700mg/L, and the concentration of the silicon dioxide in the pretreatment solution is 300-500 mg/L.

Through the technical scheme, the reverse osmosis concentrated solution is pretreated, the COD value and the concentration of silicon dioxide in the pretreated solution are controlled, the yield of high-purity sodium sulfate and sodium chloride crystal salt can be increased in the conventional evaporative crystallization device, the ion concentration in the crystallization mother solution is reduced, zero discharge of salt-containing sewage is realized, the resource recycling is realized, the operation stability of a system can be improved, and the cleaning frequency of the device is reduced.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

As described above, the present invention provides a method for treating a reverse osmosis concentrate, the method comprising:

The inventor of the invention finds that the reverse osmosis concentrated solution contains various salts such as sulfate ions, chloride ions, silicon dioxide, nitrate ions, fluoride and the like, wherein when the reverse osmosis concentrated solution contains the sulfate ions and the chloride ions in a molar ratio of 1: 1-1.5, when the COD value of the reverse osmosis concentrated solution is more than 500-700mg/L and the concentration of the silicon dioxide is more than 300-500mg/L, serious influence is caused on the system, the precipitation of sodium sulfate crystal salt and sodium chloride crystal salt is not facilitated, the crystallization mother solution after evaporation crystallization still contains a large amount of chloride and sulfate, the stable operation of equipment is also not facilitated, the scaling of the equipment is serious, and the cleaning frequency is high. When the COD value of the reverse osmosis concentrated solution is less than 500-700mg/L and the concentration of the silicon dioxide is less than 300-500mg/L, not only can high-quality (high purity, low water content and white color) crystal salt be obtained, but also the crystallization efficiency of the sodium sulfate and the sodium chloride can be improved, the content of chloride and sulfate in the mother solution after evaporation and crystallization can be reduced, the scaling of the system can be relieved only by adjusting the pH value of the system, and the cleaning frequency of the equipment can be reduced.

The method is particularly suitable for treating the reverse osmosis concentrated solution with high salt concentration, high COD and high silica content, and under the preferable conditions, the COD of the reverse osmosis concentrated solution is 1000-2000mg/L, the concentration of the silica in the pretreatment solution is 400-1000mg/L, and the concentration of the salt is 40000-80000 mg/L.

In some preferred embodiments of the present invention, the pretreatment comprises the following steps of: oxidizing the reverse osmosis concentrated solution in the presence of an oxidant; and/or adding a silicon removal agent into the reverse osmosis concentrated solution to remove silicon. Preferably, the pretreatment comprises: oxidizing the reverse osmosis concentrated solution in the presence of an oxidant; and adding a silicon removal agent into the reverse osmosis concentrated solution to remove silicon, wherein the oxidation and the silicon removal are not in sequence, the oxidation can be carried out firstly and then the silicon removal is carried out, or the oxidation can be carried out firstly and then the silicon removal, or an oxidant and the silicon removal agent can be simultaneously added into the reverse osmosis concentrated solution to carry out the oxidation and the silicon removal simultaneously.

In some preferred embodiments of the invention, the selection of the oxidation process depends on the COD content of the brine concentrate and affects the COD removal efficiency, sodium sulfate crystalline salt purity, and sodium chloride crystalline salt purity. Under the preferable condition, the oxidant is ozone and/or hydrogen peroxide; preferably, the catalyst is ozone; further preferably, the oxidation conditions are: the temperature is 20-40 deg.C, pH is 9-11, and the reaction time is 20-60 min.

In some preferred embodiments of the present invention, since the concentration of silica in the reverse osmosis concentrate is greater than 600mg/L, adding a silica removing agent to the reverse osmosis concentrate for silica removal can reduce the concentration of silica in the reverse osmosis concentrate, wherein the silica removing agent is selected from sodium metaaluminate and/or magnesium oxide according to the characteristics of high salt and high COD of the reverse osmosis concentrate, and further preferably, the weight ratio of the silica removing agent to the silica contained in the reverse osmosis concentrate is 1-3: 1, preferably 1.5-2.5: 1, for example, when the concentration of silicon dioxide in the reverse osmosis liquid is 600-900mg/L, the concentration of the silicon removing agent in the reverse osmosis liquid should be 1200-1800 mg/L.

The present invention can directly crystallize the pretreatment solution by using an existing thermal crystallization apparatus, such as at least one of vapor compression evaporation (MVR), forced circulation crystallization, and freezing crystallization.

In a preferred embodiment of the present invention, the crystallization method of the pretreatment solution comprises: and concentrating the pretreatment solution and then crystallizing.

Before the pretreatment solution is concentrated, the pretreatment solution is sent into a heat exchanger for heat exchange and then sent into a degasser for degassing to obtain the pretreatment solution with the temperature of 90-95 ℃. By degassing the heat-exchanged pretreatment solution, noncondensable gases such as oxygen and carbon dioxide in the pretreatment solution can be removed, and the corrosion of the gases to equipment can be reduced.

In some preferred embodiments of the present invention, the pre-treatment solution is concentrated using vapor compression evaporation (MVR) to obtain a concentrated mother liquor; the method for concentrating the pretreatment solution comprises the following steps: before the crystallization, heating the pretreatment solution to 101-103 ℃ in the presence of first steam, and concentrating for 2-4 times to obtain concentrated mother liquor; wherein the temperature of the first steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa.

According to the invention, in order to obtain high-quality sodium sulfate crystal salt and sodium chloride crystal salt, the TDS of the concentrated mother liquor needs to be controlled within a specific range, and preferably the TDS of the concentrated mother liquor is less than or equal to 200000 mg/L.

In some preferred embodiments of the present invention, the crystallizing comprises: carrying out first crystallization on the concentrated mother liquor to obtain sodium sulfate crystalline salt and first mother liquor; then, carrying out second crystallization on the first mother liquor to obtain sodium sulfate decahydrate crystal salt and second mother liquor; then, carrying out third crystallization on the second mother liquor to obtain sodium chloride crystal salt and third mother liquor; and drying the third mother liquor to obtain the mixed salt.

The invention adopts the prior MVR evaporation process combined with the freezing crystallization process to carry out evaporation crystallization on the concentrated mother liquor, and under the optimal condition, the first crystallization comprises the following steps: in the presence of second steam, heating the concentrated mother liquor to 105-107 ℃ to obtain first slurry containing crystal salt; and dehydrating the first slurry to obtain sodium sulfate crystalline salt and a first mother liquor. Preferably, the temperature of the second steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa.

According to the present invention, the first slurry may be dehydrated by a conventional method, for example, the first slurry is introduced into a hydrocyclone to be subjected to solid-liquid separation to obtain a solid substance and a first mother liquor, and the solid substance is introduced into a centrifugal dehydrator to be crystallized to obtain a sodium sulfate crystallized salt.

According to the invention, under preferred conditions, the second crystallization is a frozen crystallization, and specifically comprises: and cooling the first mother liquor to 3-8 ℃ to separate out mirabilite (sodium sulfate decahydrate crystal salt) to obtain sodium sulfate decahydrate crystal salt and a second mother liquor. The sodium sulfate in the freezing crystallization solution reaches the supersaturation state through lowering the temperature, and the improvement of supersaturation is favorable to increasing nucleation rate, and its technical advantage lies in: (1) the crystallization process is ensured to be carried out in a metastable zone, the generation of primary nucleation is avoided, and the generation of fine grains is avoided; (2) the influence of the continuous crystallizer on secondary crystallization is fully utilized, the occurrence of secondary nucleation is reduced, and the growth rate of the crystal is correspondingly improved.

According to the present invention, since a large amount of crystalline salts are precipitated from the first crystals and the second crystals, the salt content in the second mother liquor is greatly reduced, and therefore the second mother liquor is further concentrated before the third crystallization. Preferably, the second mother liquor is concentrated by vapor compression evaporation (MVR), and the concentration method comprises: and in the presence of third steam, heating the second mother liquor to 107-109 ℃ for concentration to obtain a re-concentrated solution. Preferably, the temperature of the third steam is 150-170 ℃, and the pressure is 1-1.1 MPa; further preferably, the TDS in the re-concentrated solution is 180000-220000 mg/L.

According to the invention, the existing MVR evaporation process is adopted to carry out evaporation crystallization on the re-concentrated mother liquor, and under the preferable conditions, the third crystallization comprises the following steps: in the presence of fourth steam, heating the re-concentrated solution to 111 ℃ at 108-.

According to the present invention, the second slurry may be dehydrated by a conventional method, for example, the second slurry is introduced into a centrifugal dehydrator and centrifuged to obtain sodium chloride crystal salt and a third mother liquor.

According to the invention, the third mother liquor still contains a certain amount of salt, and in order to ensure that no mother liquor is discharged from the whole system, the third mother liquor is further concentrated, dried and crystallized under the preferable conditions to obtain the miscellaneous salt, and further preferably, the water content of the miscellaneous salt is less than or equal to 30 wt%.

On the basis of the existing MVR evaporation process and forced circulation crystallization process, the pretreatment and freezing crystallization of the reverse osmosis concentrated solution are added, so that the running stability of a sodium sulfate crystallization system can be improved, sodium sulfate and sodium chloride in the reverse osmosis concentrated solution are crystallized as completely as possible, the concentrations of sulfate radicals and chloride ions in a crystallization mother solution (a third mother solution) are reduced, the generation amount of miscellaneous salts is reduced, the purity of sodium sulfate crystallized salt and other process indexes can be improved, and the product grade of sodium sulfate is ensured; because the COD value, the silicon dioxide content and the sulfate ion content of the second mother liquor are very low after pretreatment, the first crystallization and the second crystallization, the second mother liquor is discharged to a sodium chloride crystallization system, and the sodium chloride crystal salt with stable quality can be generated only by controlling the boiling point of the second mother liquor.

In the invention, the first steam, the second steam, the third steam and the fourth steam are all fresh steam.

According to a particularly preferred embodiment of the present invention, a method for treating a reverse osmosis concentrate comprises:

(1) oxidizing reverse osmosis concentrated solution at the temperature of 20-40 ℃ and the pH value of 9-11 for 20-60min in the presence of ozone, and then adding sodium metaaluminate to carry out chemical desiliconization to obtain a pretreatment solution, wherein the ratio of the desiliconization agent to the silicon dioxide concentration in the reverse osmosis concentrated solution is 1.5-2.5: 1;

(2) heating the pretreatment solution to 101-103 ℃ in the presence of first steam, and concentrating by 2-4 times to obtain concentrated mother liquor; the temperature of the first steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa;

(3) in the presence of second steam, heating the concentrated mother liquor to 105-107 ℃ to obtain first slurry containing crystal salt; dehydrating the first slurry to obtain sodium sulfate crystalline salt and first mother liquor; the temperature of the second steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa;

(4) cooling the first mother liquor to 3-8 ℃ to obtain sodium sulfate decahydrate crystal salt and second mother liquor;

(5) in the presence of third steam, heating the second mother solution to 107-109 ℃ for re-concentration to obtain a re-concentrated solution, wherein the temperature of the third steam is 150-170 ℃ and the pressure is 1.0-1.1 MPa;

in the presence of fourth steam, heating the re-concentrated solution to 108-111 ℃ to obtain second slurry containing crystal salt, and dehydrating the second slurry to obtain sodium chloride crystal salt and third mother liquor;

(6) evaporating and concentrating the third mother liquor to obtain mixed salt;

wherein the molar ratio of sulfate ions to chloride ions in the reverse osmosis concentrated solution is 1: 1-1.5, wherein the COD of the reverse osmosis concentrated solution is 1000-2000mg/L, the concentration of the silicon dioxide in the reverse osmosis concentrated solution is 400-1000mg/L, and the concentration of the salt is 40000-80000 mg/L;

The present invention will be described in detail below by way of examples.

In the following examples, the reverse osmosis concentrate was a reverse osmosis concentrate from a membrane concentration unit, the water quality index of the reverse osmosis concentrate is shown in table 1, and the feed flow rate of the reverse osmosis concentrate was 70m³/h。

The determination method of the content of sodium sulfate and the content of water in the sodium sulfate crystalline salt refers to GB/T6009-2014; the content of sodium chloride and the content of water in the sodium chloride crystal salt are determined by reference to GB/T5462-2015.

In the following examples, TDS refers to the total dissolved solids in the wastewater, TSS refers to the total suspended solids in the wastewater, and COD is the chemical oxygen demand of the wastewater.

TABLE 1

Detecting items	Unit of	Actual value
			pH value	-	10.39
TDS	mg/L	45408
			Alkalinity of	mg/L	726
Ammonia nitrogen	mg/L	0.9
			COD	mg/L	1380
Silicon dioxide	mg/L	870
			Sulfate radical	mg/L	15205
Chloride ion	mg/L	11000
			Nitrate radical	mg/L	1632
TSS	mg/L	180

Example 1

(1) Oxidizing the reverse osmosis concentrated solution for 30min at the temperature of 30 ℃ and the pH value of 10.39 in the presence of ozone, and then adding sodium metaaluminate (a silicon removal agent) to perform chemical silicon removal to obtain a pretreatment solution, wherein in the reverse osmosis concentrated solution, the weight ratio of the silicon removal agent to silicon dioxide contained in the reverse osmosis concentrated solution is 2: 1;

(2) introducing the pretreatment solution into a heat exchanger for heat exchange, and then introducing the pretreatment solution into a degasser for degassing to obtain a pretreatment solution with the temperature of 93 ℃;

introducing the pretreatment solution into an MVR evaporator to exchange heat with first steam (the temperature is 122 ℃ and the pressure is 0.46MPa), heating the pretreatment solution to 102.4 ℃, and concentrating by 2.8 times to obtain concentrated mother liquor;

(3) exchanging heat between the concentrated mother liquor and second steam (the temperature is 122 ℃ and the pressure is 0.46MPa) in a first crystallizer, heating the concentrated mother liquor to 106.2 ℃, and increasing the Boiling Point (BPE) to 6.2 ℃ to obtain first slurry containing crystalline salt; then introducing the first slurry into a hydraulic separator for solid-liquid separation to obtain solid substances and first mother liquor, and introducing the solid substances into a centrifugal dehydrator for crystallization to obtain sodium sulfate crystallized salt;

(4) cooling the first mother liquor to 5 ℃ to obtain sodium sulfate decahydrate crystal salt and second mother liquor;

(5) introducing the second mother liquor into an MVR evaporator, exchanging heat with third steam (the temperature is 165 ℃ and the pressure is 0.46MPa), heating the second mother liquor to 102.4 ℃ for re-concentration, wherein the BPE (boiling point rise) is 2.4 ℃, and concentrating by 2.5 times to obtain re-concentrated solution;

then, exchanging heat between the re-concentrated solution and fourth steam (the temperature is 165 ℃ and the pressure is 1.1MPa) in a second crystallizer, heating the re-concentrated solution to 109.5 ℃ to obtain second slurry containing crystalline salt, and then introducing the second slurry into a centrifugal dehydrator for dehydration to obtain sodium chloride crystalline salt and third mother liquor;

(6) and evaporating and concentrating the third mother liquor in a third crystallizer to obtain mixed salt, wherein the water content of the mixed salt is 20 wt%.

In the embodiment, no waste liquid is discharged; the cleaning frequency of each device was: the first crystallizer is not needed to be cleaned all the year round, the second crystallizer is cleaned once in 3 years, and the third crystallizer is cleaned once in 2 years; the water quality index of each liquid is shown in Table 2, and the indexes of the sodium sulfate crystal salt and the sodium chloride crystal salt are shown in Table 6.

TABLE 2

Detecting items	Unit of	Initial concentration	Concentrated mother liquor	First mother liquor	Second mother liquor	Reconcentrated solution	Third mother liquor
								pH value	-	10.39	10.37	10.56	10.89	10.67	10.89
TDS	mg/L	45408	12450	89345	47900	216700	320000
								Alkalinity of	mg/L	726	453	678	450	360	450
Ammonia nitrogen	mg/L	0.9	0.7	4.9	5.9	3.9	2.4
								COD	mg/L	1380	345	987	845	762	1500
Silicon dioxide	mg/L	870	320	707	1500	1340	2489
								Sulfate radical	mg/L	15205	25013	46790	180	340	230
Chloride ion	mg/L	11000	27900	78920	87650	98011	1890
								Nitrate radical	mg/L	1632	4568	1200	689	345	379
TSS	mg/L	180	324	350	243	340	130

Comparative example 1

The reverse osmosis concentrated solution is treated by adopting the existing method for treating high-salinity sewage, and the method comprises the following steps:

(1) introducing the reverse osmosis concentrated solution into a heat exchanger for heat exchange, and then introducing the reverse osmosis concentrated solution into a degasser for degassing to obtain a reverse osmosis concentrated solution with the temperature of 93 ℃;

introducing the reverse osmosis concentrated solution into an MVR evaporator to exchange heat with first steam (the temperature is 122 ℃ and the pressure is 0.46MPa), heating the pretreatment solution to 102.4 ℃, and concentrating by 2.8 times, wherein the BPE is 2.4 to obtain concentrated mother liquor;

(2) exchanging heat between the concentrated mother liquor and second steam (temperature is 122 ℃, pressure is 0.46MPa) in a crystallization system, heating the concentrated mother liquor to 108.2 ℃, and increasing the boiling point of BPE (boiling point increase) 8 to obtain first slurry (TDS is 300000mg/L) containing crystallized salt; then introducing the first slurry into a hydraulic separator, further increasing the TSS content of the system to 65% through the concentration effect of the hydraulic separator, carrying out solid-liquid separation to obtain a solid substance and a first mother liquor, introducing the solid substance into a centrifugal dehydrator for crystallization to obtain sodium sulfate crystalline salt, wherein the water quality index of the first mother liquor is shown in table 3, and the index of the sodium sulfate crystalline salt is shown in table 6;

(3) exchanging heat between the first mother liquor and third steam (temperature 165 ℃ and pressure 1.1MPa) in a second crystallization system, heating the first mother liquor to 109.8 ℃, and carrying out BPE (boiling point increase) 9.2 to obtain second slurry containing crystallized salt (TDS is 380000mg/L, and TSS is 16%); and then, concentrating the second slurry through a water conservancy separator to improve the TSS by 75 percent, and carrying out solid-liquid separation to obtain sodium chloride crystal salt and a second mother liquor, wherein the water quality of the second mother liquor is shown in Table 3, and the index of the sodium chloride crystal salt is shown in Table 6.

TABLE 3

In this comparative example, the discharge amount of discharged mother liquor was 1.4m³H; as can be seen from comparative example 1: the existing reverse osmosis concentrated solution passes throughA large amount of crystallization mother liquor is discharged after treatment, the TDS of the mother liquor is as high as 387900mg/L, and a large amount of sodium chloride and sodium sulfate are discharged to a wastewater buffer tank; the evaporation system and the crystallization system are frequently fouled, and the shutdown and the overhaul are carried out for 1 time every 3 months.

Comparative example 2

The process of example 1 was followed except that: the reverse osmosis concentrated solution is not pretreated and is directly subjected to evaporative crystallization, COD of the reverse osmosis concentrated solution without pretreatment is 1380mg/L, the concentration of silicon dioxide is 870mg/L, and the experimental results are shown in Table 4.

TABLE 4

Detecting items	Unit of	Initial concentration	Concentrated mother liquor	First mother liquor	Second mother liquor	Reconcentrated solution	Third mother liquor
								pH value	-	10.45	10.32	10.58	10.67	10.62	10.82
TDS	mg/L	42305	11089	789023	567000	208900	314560
								Alkalinity of	mg/L	765	442	651	430	377	410
Ammonia nitrogen	mg/L	1.7	2.9	5.0	7.9	8.2	7.6
								COD	mg/L	1380	3790	9802	6890	16900	27800
Silicon dioxide	mg/L	870	2400	5901	16002	32000	45670
								Sulfate radical	mg/L	14320	21023	52980	230	560	470
Chloride ion	mg/L	12020	30980	82101	86090	95342	1970
								Nitrate radical	mg/L	2900	5670	1089	765	564	469
Suspended matter	mg/L	390	340	289	240	359	167

Example 2

The procedure of example 1 was followed, except that the first mother liquor was not subjected to freeze crystallization, as follows:

(3) carrying out heat exchange on the concentrated mother liquor and second steam (the temperature is 122 ℃ and the pressure is 0.46MPa), heating the concentrated mother liquor to 106.2 ℃, and increasing the Boiling Point (BPE) to 6.2 ℃ to obtain first slurry containing crystal salt; then introducing the first slurry into a hydraulic separator for solid-liquid separation to obtain a solid substance and a first mother liquor, and introducing the solid substance into a centrifugal dehydrator for crystallization to obtain sodium sulfate crystallized salt;

(4) introducing the first mother liquor into an MVR evaporator, exchanging heat with third steam (the temperature is 165 ℃ and the pressure is 1.1MPa), heating the first mother liquor to 109.5 ℃ for re-concentration, and concentrating by 2.8 times the boiling point of BPE (boiling point elevation) 9.6 to obtain re-concentrated solution;

introducing the re-concentrated solution into a centrifugal dehydrator for dehydration to obtain sodium chloride crystal salt and second mother liquor;

(6) and (3) evaporating and concentrating the second mother liquor to obtain mixed salt, wherein the water content of the mixed salt is 50 wt%.

In this embodiment, the cleaning frequency of each apparatus is: the first crystallizer is not needed to be cleaned all the year round, the second crystallizer is cleaned once in 1 year, and the third crystallizer is cleaned once in 0.5 year; the water quality index of each liquid is shown in Table 5, and the indexes of the sodium sulfate crystal salt and the sodium chloride crystal salt are shown in Table 6.

TABLE 5

TABLE 6

As can be seen from the comparison of tables 2, 4 and 6, the reverse osmosis concentrate is not pretreated, the silica and COD content in the mother liquor is significantly high, and the sodium sulfate and sodium chloride obtained by crystallization have low purity, high water content and yellow color.

As can be seen from the comparison of table 2, table 5 and table 6, when the crystallization conditions were changed, the silica and COD contents and the sulfate and chloride contents in the mother liquor were significantly increased, and the sodium sulfate and sodium chloride obtained by crystallization were low in purity, high in water content and yellow in color.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A method of treating a reverse osmosis concentrate, the method comprising:

2. The treatment method as claimed in claim 1, wherein the COD of the reverse osmosis concentrated solution is 1000-2000mg/L, the concentration of the silica in the reverse osmosis concentrated solution is 400-1000mg/L, and the concentration of the salt is 40000-80000 mg/L.

3. The processing method according to claim 1 or 2, wherein the pre-processing comprises: and oxidizing and removing silicon from the reverse osmosis concentrated solution in the presence of an oxidizing agent and a silicon removing agent.

4. The treatment method according to claim 3, wherein the oxidizing agent is ozone and/or hydrogen peroxide.

5. The treatment process according to claim 3 or 4, wherein the silicon removal agent is sodium metaaluminate and/or magnesium oxide,

preferably, in the reverse osmosis concentrated solution, the weight ratio of the silicon removal agent to silicon dioxide contained in the reverse osmosis concentrated solution is 1-3: 1, preferably 1.5-2.5: 1.

6. the processing method according to any one of claims 1 to 5, wherein the processing method further comprises: before the crystallization, concentrating the pretreatment solution to obtain a concentrated mother liquor;

preferably, the concentrating comprises: heating the pretreatment solution to 101-103 ℃ in the presence of first steam, and concentrating by 2-4 times to obtain concentrated mother liquor;

preferably, the temperature of the first steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa;

preferably, TDS of the concentrated mother liquor is less than or equal to 200000 mg/L.

7. The process of claim 6, wherein the crystallizing comprises:

carrying out first crystallization on the concentrated mother liquor to obtain sodium sulfate crystalline salt and first mother liquor;

carrying out second crystallization on the first mother liquor to obtain sodium sulfate decahydrate crystal salt and second mother liquor;

carrying out third crystallization on the second mother liquor to obtain sodium chloride crystal salt and third mother liquor;

and drying the third mother liquor to obtain the mixed salt.

8. The processing method of claim 7, wherein the first crystallizing comprises: in the presence of second steam, heating the concentrated mother liquor to 105-107 ℃ to obtain first slurry containing crystal salt;

dehydrating the first slurry to obtain sodium sulfate crystalline salt and first mother liquor;

preferably, the temperature of the second steam is 120-130 ℃, and the pressure is 0.4-0.5 MPa.

9. The process according to claim 7 or 8, wherein the temperature of the second crystallization is between 3 and 8 ℃.

10. The process of any one of claims 7 to 9, wherein the third crystallization comprises: in the presence of third steam, heating the second mother solution to 107-109 ℃ for re-concentration to obtain a re-concentrated solution; then, in the presence of fourth steam, heating the re-concentrated solution to 108-111 ℃ to obtain second slurry containing crystal salt, and dehydrating the second slurry to obtain sodium chloride crystal salt and third mother liquor;

preferably, the temperature of the third steam is 150-170 ℃, and the pressure is 1-1.1 MPa;

preferably, the temperature of the fourth steam is 150-170 ℃, and the pressure is 1-1.1 MPa;

preferably, the TDS of the re-concentrated solution is 180000-220000 mg/L;

preferably, the TDS of the third mother liquor is 250000-350000mg/L, and the TSS of the third mother liquor is 100-500 mg/L.