A method for preparing borax by discharging boron-containing wastewater from an electrodialysis process

Abstract

A method for preparing borax from boron-containing wastewater discharged from an electrodialysis process section relates to the technical field of borax preparation, and comprises the following steps: S1, using the boron-containing wastewater discharged from the electrodialysis process in the process of extracting lithium from a salt lake as a raw material, adjusting the pH of the wastewater and pumping it into a first-stage reverse osmosis device for concentration to obtain product water 1 and concentrated water 1; S2, continuing to pump concentrated water 1 into a second-stage reverse osmosis device for concentration to obtain product water 2 and concentrated water 2; S3, performing MVR evaporation and concentration on concentrated water 2 to obtain a concentrated solution, and recovering fresh water; S4, adjusting the pH of the concentrated solution, cooling, crystallizing, and drying to obtain borax. The boron resources in the boron-containing wastewater of the present invention can be developed and utilized, and the boron removal rate can reach more than 95%. The production of borax products using a boron-containing wastewater generated in the process of extracting lithium from a salt lake is an efficient and reliable brine boron resource development technology, which can realize the comprehensive development and utilization of boron-lithium symbiotic salt lake resources in my country.

Description

Technical Field

[0001] The invention relates to the technical field of borax preparation, and in particular to a method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section. Background Art

[0002] Although the technology of extracting sodium, potassium, magnesium, lithium and other substances from salt lake brine is becoming more and more perfect and mature, and with the continuous optimization of process technology, various production capacities have been further released, the direct extraction of boron from salt lake resources is still a global problem. After a large number of verification experiments, the present invention has found a shortcut to extract boron resources, namely "using boron-containing wastewater to produce borax". The process technology of each section of the process method route is now very mature, so the project has good promotion and effectiveness. It effectively solves the problem of difficult extraction of salt lake boron resources, and finds a practical technical route and process solution for the development of my country's salt lake boron resources, which is of milestone significance. Summary of the invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section. The production method uses the electrodialysis boron-containing wastewater generated in the process of extracting lithium from a salt lake as a raw material, and can realize a process method for producing borax from boron wastewater through a series of process combinations, which fully embodies the economic and environmental protection principles of waste recycling.

[0004] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0005] A method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section, characterized in that it comprises the steps of:

[0006] S1, using the boron-containing wastewater discharged from the electrodialysis process of lithium extraction from the salt lake as a raw material, adjusting the pH of the wastewater with sodium hydroxide and pumping it into a reverse osmosis device for concentration to obtain produced water 1 and concentrated water 1; wherein the boron-containing wastewater has a lithium content of 10.0-100.0 mg / L, a sodium content of 10.0-50.0 mg / L, a boron content of 1.0-2.5 g / L, and a pH of 2.5-4.0;

[0007] The lithium content in the produced water 1 is: 0.0~10.0 mg / L, the sodium content is: 10.0~30.0 mg / L, the boron content is: 0.5~1.2 g / L, and the pH is: 6.5~8.0;

[0008] The lithium content in concentrated water 1 is 200.0~300.0 mg / L, the sodium content is 1.8~3.0 g / L, the boron content is 3.5~6.0 g / L, and the pH is 7.5~10.0;

[0009] S2, continue to pump concentrated water 1 into the second-stage reverse osmosis device for concentration to obtain product water 2 and concentrated water 2;

[0010] The lithium content in produced water 2 is 5.0~15.0 mg / L, the sodium content is 20.0~50.0 mg / L, the boron content is 0.8~1.5 g / L, and the pH is 6.5~8.0;

[0011] The lithium content in concentrated water 2 is: 300.0~600.0 mg / L, the sodium content is: 3.0~6.0 g / L, the boron content is: 7.0~15.0 g / L, and the pH is: 7.5~10.0;

[0012] S3, concentrate the concentrated water 2 by MVR evaporation to obtain a concentrated solution, and recover fresh water; the concentrated solution has a lithium content of 500.0-1100.0 mg / L, a sodium content of 7.0-15.0 g / L, a boron content of 30.0-40.0 g / L, and a pH of 7.5-10.0;

[0013] S4. Adjust the pH value of the concentrated solution, cool, crystallize and dry to obtain borax (Na2B4O7·10H2O); wherein the borax (Na2B4O7·10H2O) meets the requirements of industrial disodium tetraborate decahydrate "GB / T 537-2009" with a main content of ≥99.5%, a carbonate content (in terms of CO2) ≤0.1%, a sulfate content (in terms of SO4) ≤0.1%, a chloride content (in terms of Cl) ≤0.03%, an iron content ≤0.002%, and a water-insoluble matter content ≤0.04%.

[0014] In the step S1, the pH of the boron-containing wastewater needs to be adjusted to 7.0-9.5 when entering a reverse osmosis device. Under this pH condition, the boron retention rate of the reverse osmosis device is as high as 92.0% or more.

[0015] In the step S1, the first-stage reverse osmosis device is a medium-pressure reverse osmosis membrane with a salt removal rate of 95%, and its operating water inlet and membrane pressure is appropriately controlled at 4.0-6.0 MPa.

[0016] In step S2, the second-stage reverse osmosis device is a high-pressure reverse osmosis membrane with a salt removal rate of 98%, and its operating water inlet and membrane pressure is appropriately controlled at 5.0-10.0 MPa.

[0017] In step S3, the MVR evaporation concentration is a falling film evaporation device, which can concentrate the boron element to more than 30.0 g / L.

[0018] In the step S4, the concentrated solution is adjusted to a pH of 10.5-12.5 using sodium hydroxide, and the crystallization temperature is 30.0-50.0° C. Under this pH condition, the borax crystallization rate can reach more than 90.0%.

[0019] In the steps S1 to S4, the electrodialysis process for producing borax from boron-containing wastewater is described, and the boron element in the produced boron-containing wastewater can be redeveloped and utilized as a raw material for producing boric acid, borax and other products, and the product indicators meet the requirements of the industrial disodium tetraborate decahydrate "GB / T 537-2009" standard.

[0020] Beneficial effects: The invention discloses a method for preparing borax by using boron-containing wastewater discharged from an electrodialysis process. The boron-containing wastewater discharged from an electrodialysis process in a lithium extraction process from a salt lake is used as a raw material. The wastewater is adjusted in pH value and then pumped into a first-stage reverse osmosis device for concentration to obtain product water 1 and concentrated water 1; the concentrated water 1 is further pumped into a second-stage reverse osmosis device for concentration to obtain product water 2 and concentrated water 2; the concentrated water 2 is concentrated by MVR evaporation to obtain a concentrated solution, and fresh water is recovered; the concentrated solution is adjusted in pH value and then cooled, crystallized and dried to obtain borax (Na2B4O7·10H2O).

[0021] According to the process route of the present invention, the boron resources in a large amount of boron-containing wastewater generated in the process of extracting lithium from salt lakes can be developed and utilized. It is difficult to completely separate the boron and lithium elements in the production and development, but the boron and lithium elements can be efficiently separated by using an electrodialysis device, and the boron removal rate can reach more than 95%. The present invention can produce borax products using a boron-containing wastewater generated in the process of extracting lithium from salt lakes. It is an emerging process route with a utilization rate of salt lake boron resources of more than 86.0%, and is an efficient and reliable brine boron resource development technology, which can realize the comprehensive development and utilization of boron-lithium symbiotic salt lake resources in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other aspects, features and advantages of the embodiments of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0023] Figure 1 A simplified diagram of the technical process flow of the present invention. Implementation

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention may be implemented in many different forms, and the present invention should not be construed as being limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided to explain the principles of the present invention and their practical applications, so that other persons skilled in the art can understand the various embodiments of the present invention and various modifications suitable for specific intended applications.

[0025] The invention provides a method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section.

[0026] Specific reference Figure 1 , the production method comprises the following steps:

[0027] S1. Medium-pressure reverse osmosis concentration: The boron-containing wastewater discharged from the electrodialysis process of lithium extraction from the salt lake is used as raw material. After adjusting the pH of the wastewater, it is pumped into the first-stage reverse osmosis device for concentration to obtain product water 1 and concentrated water 1. The pH of the boron-containing wastewater needs to be adjusted to 7.0~9.5 when entering the first-stage reverse osmosis device. Under this pH condition, the boron retention rate of the reverse osmosis device is as high as 92.0% or more. The first-stage reverse osmosis device is a medium-pressure reverse osmosis membrane with an efficient salt removal rate of 95%. Its operating water inlet and membrane pressure is appropriately controlled at 4.0~6.0MPa.

[0028] In the embodiment of the present invention, the raw material used is boron-containing wastewater, with a lithium content of 10.0-100.0 mg / L, a sodium content of 10.0-50.0 mg / L, a boron content of 1.0-2.5 g / L, and a pH of 2.5-4.0;

[0029] After the treatment in step S1, produced water 1 and concentrated water 1 are obtained. The produced water 1 has a lithium content of 0.0-10.0 mg / L, a sodium content of 10.0-30.0 mg / L, a boron content of 0.5-1.2 g / L, and a pH of 6.5-8.0. The concentrated water 1 has a lithium content of 200.0-300.0 mg / L, a sodium content of 1.8-3.0 g / L, a boron content of 3.5-6.0 g / L, and a pH of 7.5-10.0.

[0030] S2, high-pressure reverse osmosis concentration: The concentrated water 1 is continuously pumped into the second-stage reverse osmosis device for concentration to obtain product water 2 and concentrated water 2. The second-stage reverse osmosis device is a high-pressure reverse osmosis membrane with an efficient salt removal rate of 98%, and its operating water inlet membrane pressure is appropriately controlled at 5.0-10.0 MPa.

[0031] After the treatment in step S2, produced water 2 and concentrated water 2 are obtained, wherein the produced water 2 has a lithium content of 5.0-15.0 mg / L, a sodium content of 20.0-50.0 mg / L, a boron content of 0.8-1.5 g / L, and a pH of 6.5-8.0; the concentrated water 2 has a lithium content of 300.0-600.0 mg / L, a sodium content of 3.0-6.0 g / L, a boron content of 7.0-15.0 g / L, and a pH of 7.5-10.0.

[0032] S3, MVR evaporation concentration: The concentrated water 2 is subjected to MVR evaporation concentration to obtain a concentrated solution, and fresh water is recovered. MVR evaporation concentration is a falling film evaporation device that can concentrate the boron element to more than 30.0 g / L.

[0033] After the treatment in step S3, the concentrated solution has a lithium content of 500.0-1100.0 mg / L, a sodium content of 7.0-15.0 g / L, a boron content of 30.0-40.0 g / L, and a pH of 7.5-10.0.

[0034] S4. Cooling and crystallization: After adjusting the pH of the concentrated solution, cool, crystallize and dry to obtain borax (Na2B4O7·10H2O). The pH of the concentrated solution is adjusted to 10.5~12.5, and the crystallization temperature is 30.0~50.0 ℃. Under this pH condition, the crystallization rate of borax can reach more than 90.0%.

[0035] After being processed by steps S1 to S4, the obtained borax (Na2B4O7·10H2O) meets the requirements of industrial disodium tetraborate decahydrate "GB / T 537-2009" with a main content of ≥99.5%, a carbonate content (calculated as CO2) ≤0.1%, a sulfate content (calculated as SO4) ≤0.1%, a chloride content (calculated as Cl) ≤0.03%, an iron content ≤0.002%, and a water-insoluble matter content ≤0.04%.

[0036] It will be understood that although the terms "boron-containing wastewater", "concentrated liquid", "produced water 1 concentrated water 1", "produced water 2 concentrated water 2" and the like may be used here to describe the materials, these materials should not be limited by these terms. These terms are only used to distinguish the materials at different stages in the process technology method of preparing borax by discharging boron-containing wastewater from electrodialysis.

[0037] In this way, the technology of preparing borax by using boron-containing wastewater discharged from electrodialysis is realized through the above process route. The boron-containing wastewater discharged from electrodialysis in the process of extracting lithium from salt lake is used as raw material. The wastewater is adjusted in pH and pumped into a first-stage reverse osmosis device for concentration to obtain produced water 1 and concentrated water 1; concentrated water 1 is further pumped into a second-stage reverse osmosis device for concentration to obtain produced water 2 and concentrated water 2; concentrated water 2 is subjected to MVR evaporation and concentration to obtain a concentrated solution, and fresh water is recovered; the concentrated solution is adjusted in pH and then cooled, crystallized, and dried to obtain borax (Na2B4O7·10H2O). According to the process route of the present invention, the boron resources in a large amount of boron-containing wastewater generated in the process of extracting lithium from salt lake can be developed and utilized. It is difficult to achieve complete separation in the reproduction and development of boron and lithium elements, but after using an electrodialysis device, efficient separation of boron and lithium elements can be achieved, and the boron removal rate can reach more than 95%. The present invention can utilize boron-containing wastewater generated during the lithium extraction process in salt lakes to produce borax products. The borax crystallization rate can reach more than 90.0%. The present invention is an efficient and reliable brine boron resource development technology, which can realize the comprehensive development and utilization of boron-lithium symbiotic salt lake resources in my country, and fully embodies the principle of economic and environmentally friendly resource development.

[0038] The following is a specific example to illustrate the technology of preparing borax by using electrodialysis to discharge boron-containing wastewater. Example 1

[0039] Firstly, the boron-containing wastewater discharged from electrodialysis during lithium extraction from salt lakes was used as raw material. The boron wastewater had a lithium content of 53.0 mg / L, a sodium content of 20.0 mg / L, a boron content of 1.8 g / L, and a pH of 3.78. The wastewater was adjusted to a pH of 7.89 and then pumped into a reverse osmosis device for concentration. The membrane inlet pressure was controlled at 4.2 MPa to obtain product water 1 and concentrated water 1. The product water 1 had a lithium content of 7.8 mg / L, a sodium content of 11.2 mg / L, a boron content of 0.57 g / L, and a pH of 7.8. The concentrated water 1 had a lithium content of 202.0 mg / L, a sodium content of 2.6 g / L, a boron content of 4.99 g / L, and a pH of 8.5.

[0040] Then, the concentrated water 1 was continuously pumped into the second-stage reverse osmosis device for concentration, and the membrane inlet pressure was controlled at 5.5 MPa to obtain produced water 2 and concentrated water 2. The lithium content in produced water 2 was 13.0 mg / L, the sodium content was 25.0 mg / L, the boron content was 1.07 g / L, and the pH was 7.5. The lithium content in concentrated water 2 was 488 mg / L, the sodium content was 5.2 g / L, the boron content was 13.89 g / L, and the pH was 9.5.

[0041] Then, the concentrated water 2 is concentrated by MVR evaporation to obtain a concentrated solution, and fresh water is recovered. The concentrated solution has a lithium content of 860.0 mg / L, a sodium content of 8.8 g / L, a boron content of 32.5 g / L, and a pH of 7.8.

[0042] Finally, the concentrated solution was adjusted to pH 12.0, and then cooled, crystallized and dried to obtain borax (Na2B4O7·10H2O). The cooling crystallization temperature was 45.0 °C, the borax crystallization rate was 92.0%, the main content was 98.1%, the carbonate content (in terms of CO2) was 0.08%, the sulfate content (in terms of SO4) was 0.09%, the chloride content (in terms of Cl) was 0.02%, the iron content was 0.002%, and the water-insoluble matter content was 0.003%. Example 2

[0043] Firstly, the boron-containing wastewater discharged from electrodialysis during lithium extraction from salt lakes was used as raw material. The boron wastewater had a lithium content of 20.0 mg / L, a sodium content of 30.0 mg / L, a boron content of 1.5 g / L, and a pH of 3.0. The wastewater was adjusted to a pH of 8.5 and then pumped into a reverse osmosis device for concentration. The membrane inlet pressure was controlled at 4.8 MPa to obtain product water 1 and concentrated water 1. The product water 1 had a lithium content of 5 mg / L, a sodium content of 15.5 mg / L, a boron content of 0.85 g / L, and a pH of 7.5. The concentrated water 1 had a lithium content of 230.0 mg / L, a sodium content of 2.4 g / L, a boron content of 4.5 g / L, and a pH of 8.0.

[0044] Then, the concentrated water 1 was continuously pumped into the second-stage reverse osmosis device for concentration, and the membrane inlet pressure was controlled at 6.5 MPa to obtain product water 2 and concentrated water 2. The lithium content of product water 2 was 7.8 mg / L, the sodium content was 20.4 mg / L, the boron content was 0.95 g / L, and the pH was 6.5. The lithium content of concentrated water 2 was 421 mg / L, the sodium content was 4.4 g / L, the boron content was 10.7 g / L, and the pH was 7.5.

[0045] Then, the concentrated water 2 is concentrated by MVR evaporation to obtain a concentrated solution, and fresh water is recovered. The concentrated solution has a lithium content of 630.0 mg / L, a sodium content of 8.4 g / L, a boron content of 35.5 g / L, and a pH of 8.3.

[0046] Finally, the concentrated solution was adjusted to pH 12.5, and then cooled, crystallized and dried to obtain borax (Na2B4O7·10H2O). The cooling crystallization temperature was 48.0 °C, the borax crystallization rate was 93.0%, the main content was 99.6%, the carbonate content (in terms of CO2) was 0.07%, the sulfate content (in terms of SO4) was 0.09%, the chloride content (in terms of Cl) was 0.022%, the iron content was 0.0021%, and the water-insoluble matter content was 0.002%. Example 3

[0047] Firstly, the boron-containing wastewater discharged from electrodialysis during lithium extraction from salt lakes was used as raw material. The boron wastewater had a lithium content of 80.0 mg / L, a sodium content of 48.0 mg / L, a boron content of 2.5 g / L, and a pH of 3.8. The pH of the wastewater was adjusted to 9.5 and then pumped into a reverse osmosis device for concentration. The membrane inlet pressure was controlled at 5.5 MPa to obtain product water 1 and concentrated water 1. The product water 1 had a lithium content of 10 mg / L, a sodium content of 29 mg / L, a boron content of 1.15 g / L, and a pH of 8.0. The concentrated water 1 had a lithium content of 300.0 mg / L, a sodium content of 2.8 g / L, a boron content of 6.0 g / L, and a pH of 9.0.

[0048] Then, the concentrated water 1 was continuously pumped into the second-stage reverse osmosis device for concentration, and the membrane inlet pressure was controlled at 7.0 MPa to obtain produced water 2 and concentrated water 2. The lithium content in produced water 2 was 15 mg / L, the sodium content was 46.8 mg / L, the boron content was 1.5 g / L, and the pH was 7.5. The lithium content in concentrated water 2 was 550 mg / L, the sodium content was 6.0 g / L, the boron content was 14.5 g / L, and the pH was 8.5.

[0049] Then, the concentrated water 2 is concentrated by MVR evaporation to obtain a concentrated solution, and fresh water is recovered. The concentrated solution has a lithium content of 850.0 mg / L, a sodium content of 11.0 g / L, a boron content of 37.8 g / L, and a pH of 8.7.

[0050] Finally, the concentrated solution was adjusted to pH 10.0, and then cooled, crystallized and dried to obtain borax (Na2B4O7·10H2O). The cooling crystallization temperature was 40.0 °C, the borax crystallization rate was 90.0%, the main content was 95.0%, the carbonate content (in terms of CO2) was 0.09%, the sulfate content (in terms of SO4) was 0.10%, the chloride content (in terms of Cl) was 0.060%, the iron content was 0.003%, and the water-insoluble matter content was 0.005%.

[0051] The above examples show that when the pH of the borax concentrate is adjusted to 12.5, the cooling crystallization temperature is 48.0 ℃, and the borax crystallization rate reaches 93.0%, the obtained borax (Na2B4O7·10H2O) has a main content of 99.6%, a carbonate content (in terms of CO2) of 0.07%, a sulfate content (in terms of SO4) of 0.09%, a chloride content (in terms of Cl) of 0.022%, an iron content of 0.0021%, and a water-insoluble content of 0.002%. The product quality is the best.

[0052] While the invention has been shown and described with reference to the particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the claims and their equivalents.

Claims

1. A method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section, characterized in that: The following steps are involved: S1, using the boron-containing wastewater discharged from the electrodialysis process of lithium extraction from the salt lake as a raw material, adjusting the pH of the wastewater with sodium hydroxide and pumping it into a reverse osmosis device for concentration to obtain produced water 1 and concentrated water 1; wherein the boron-containing wastewater has a lithium content of 10.0-100.0 mg / L, a sodium content of 10.0-50.0 mg / L, a boron content of 1.0-2.5 g / L, and a pH of 2.5-4.0; The lithium content in the produced water 1 is: 0.0~10.0 mg / L, the sodium content is: 10.0~30.0 mg / L, the boron content is: 0.5~1.2 g / L, and the pH is: 6.5~8.0; The lithium content in concentrated water 1 is 200.0~300.0 mg / L, the sodium content is 1.8~3.0 g / L, the boron content is 3.5~6.0 g / L, and the pH is 7.5~10.0; S2, continue to pump concentrated water 1 into the second-stage reverse osmosis device for concentration to obtain product water 2 and concentrated water 2; The lithium content in produced water 2 is 5.0~15.0 mg / L, the sodium content is 20.0~50.0 mg / L, the boron content is 0.8~1.5 g / L, and the pH is 6.5~8.0; The lithium content in concentrated water 2 is: 300.0~600.0 mg / L, the sodium content is: 3.0~6.0 g / L, the boron content is: 7.0~15.0 g / L, and the pH is: 7.5~10.0; S3, concentrate the concentrated water 2 by MVR evaporation to obtain a concentrated solution, and recover fresh water; the concentrated solution has a lithium content of 500.0-1100.0 mg / L, a sodium content of 7.0-15.0 g / L, a boron content of 30.0-40.0 g / L, and a pH of 7.5-10.0; S4. After adjusting the pH value of the concentrated solution, the concentrated solution is cooled, crystallized and dried to obtain borax Na2B4O7·10H2O, wherein the borax Na2B4O7·10H2O content is ≥99.5%, the carbonate content is ≤0.1% in terms of CO2, the sulfate content is ≤0.1% in terms of SO4, the chloride content is ≤0.03% in terms of Cl, the iron content is ≤0.002%, and the water-insoluble matter content is ≤0.04%; In the step S4, the concentrated solution is adjusted to a pH of 10.5-12.5 using sodium hydroxide, and the crystallization temperature is 30.0-50.0° C. Under this pH condition, the borax crystallization rate can reach more than 90.0%; In the step S1, the pH of the boron-containing wastewater needs to be adjusted to 7.0-9.5 when entering a reverse osmosis device. Under this pH condition, the boron retention rate of the reverse osmosis device is as high as 92.0% or more.

2. The method for preparing borax by discharging boron-containing wastewater from an electrodialysis process section according to claim 1, characterized in that: In step S3, the MVR evaporation and concentration uses a falling film evaporation device, which can concentrate the boron element to more than 30.0 g / L.

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