Process and device for preparing borax from tail liquid obtained by extracting lithium from carbonate-containing brine

Abstract

The invention discloses a process and device for preparing borax from carbonate-containing brine lithium extraction raffinate, and the preparation process comprises the following steps: firstly, adjusting the pH value of the lithium extraction raffinate, so that H3BO3 can be promoted to be converted into a Na2B4O7 ionic solution, and the Na2B4O7 ionic solution is convenient to migrate and concentrate along with the action of an electric field in an electrodialysis process; besides, through a two-stage electrodialysis mode, the concentration is rapidly increased within a reasonable temperature range, lithium carbonate crystals can be prevented from being generated at a high temperature, and the purity of borax crystals is improved; the preparation process only needs to depend on an electrodialysis mode, is simple to operate and low in cost, does not need to depend on evaporation and concentration, avoids the use of a large amount of steam, and has remarkable significance in improving the comprehensive utilization efficiency of the salt lake brine.

Description

Technical Field

[0001] The invention relates to the technical field of borax preparation, in particular to a process and a device for preparing borax from lithium-extracting tail liquid from carbonate-containing brine. Background Art

[0002] Borax decahydrate is an important inorganic salt, which is widely used in metallurgy, medicine, glass, ceramics, fertilizer, textile, leather making, pigment, paint and other fields.

[0004] The traditional salt lake brine production process uses evaporation concentration plus cooling crystallization technology, but it is not suitable for the production of borax from the tail liquid of lithium extraction from carbonate brine. The main reason is that when the tail liquid of lithium extraction from carbonate brine is concentrated to 20 times and heated to above 90°C, a small amount of lithium carbonate crystals will appear. The formation of lithium carbonate crystals will have an adverse effect on the subsequent borax crystallization process and the quality of borax products. Chinese patent document CN116177557A discloses a method for preparing borax from the boron-containing wastewater discharged from the electrodialysis process section, using the boron-containing wastewater discharged from the lithium extraction process of the salt lake as raw material, after secondary reverse osmosis concentration, and then using MVR evaporation equipment for concentration. On the one hand, the reverse osmosis operation is difficult and costly, which restricts industrial application. On the other hand, the MVR evaporation process, such as the use of high temperature, leads to the generation of lithium carbonate crystals, which affects the crystallization of borax and the purity after crystallization.

[0005] Therefore, it is necessary to propose a process and device for preparing borax from lithium-extracting tail liquid containing carbonate brine, so as to solve the defects of the prior art preparation method, such as difficult operation and low crystal purity. Summary of the invention

[0006] The present invention aims to provide a process and a device for preparing borax from lithium-extracting tail liquid of carbonate brine, so as to solve the defects of the prior art preparation method, such as great difficulty in operation, high cost and low crystal quality.

[0007] In view of this, the scheme of the present invention is:

[0008] The process for preparing borax from lithium-extracting tail liquid of carbonate-containing brine comprises the following steps:

[0009] a) adjusting the pH value of the lithium extraction tail solution to 9.5-10;

[0010] b) subjecting the lithium extraction tail liquid after pH adjustment to a first electrodialysis to concentrate it to a sodium borate content of 35 to 38 g / L;

[0011] c) heating the concentrated solution obtained in step b) to 65-68° C., performing a second electrodialysis, and concentrating the concentrated solution to a sodium borate content of 200-210 g / L;

[0012] d) cooling and crystallizing the concentrated solution obtained in step c), and then separating and drying to obtain borax.

[0013] Furthermore, the boron trioxide content in the lithium extraction tail liquid is 5-10 g / L, the lithium ion content is less than 1 g / L, and the carbonate ion content is 1-4 g / L.

[0014] Furthermore, in step c), the desalinated water solution obtained by the second electrodialysis is subjected to a third electrodialysis, and the concentrated solution after the electrodialysis is combined with the solution in step a), and the third electrodialysis is performed to concentrate the solution to a sodium borate content of 12.5 to 14 g / L.

[0015] Furthermore, the mother liquor obtained in the separation process in step d) is combined with the mother liquor in step a).

[0016] Furthermore, the recovery rate of boron in the borax obtained in step d) is greater than 92%.

[0017] Furthermore, the purity of the borax obtained in step d) is greater than 99wt%, and the carbonate content is less than 0.08wt%.

[0018] Another object of the present invention is to propose an apparatus for use in the above-mentioned process, comprising a pH adjustment tank, a first electrodialysis unit, a heater, a second electrodialysis unit, and a crystallization and drying unit connected in sequence; the concentration output end of the first electrodialysis unit is connected to the heater, and the concentration output end of the second electrodialysis unit is connected to the crystallization and drying unit.

[0019] Furthermore, the device also includes a third electrodialysis unit; the fresh water output end of the second electrodialysis unit is connected to the feed end of the third electrodialysis unit, and the concentrated water output end of the third electrodialysis unit is connected to the pH adjustment tank.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The preparation process of the present invention first adjusts the pH value of the lithium extraction tail liquid, which can promote the conversion of H3BO3 into Na2B4O7 ion solution, so that it is easy to migrate and concentrate with the action of the electric field during the electrodialysis process; in addition, through the two-stage electrodialysis method, the concentration can be quickly increased within a reasonable temperature range, and the generation of lithium carbonate crystals at high temperature can be avoided, thereby improving the purity of borax crystals; the preparation process only relies on the electrodialysis method, which is simple to operate and low in cost, and does not need to rely on evaporation concentration to avoid the use of a large amount of steam, which is of significant significance for improving the comprehensive utilization efficiency of salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention provides an overall schematic diagram of a device for preparing borax from lithium-extracting tail liquid from carbonate-containing brine.

[0023] Among them: BC1, belt conveyor; C1, centrifuge; ED1, first electrodialysis unit; ED2, second electrodialysis unit; ED3, third electrodialysis unit; H1, heater; K1, pH adjustment tank; K2, crystallization kettle; S1, separator; T1, solution tank one; T2, solution tank two; 11, feed pipe; 12, alkali solution pipe; 13, concentrate pipe one; 14, fresh water pipe one; 15, concentrate pipe two; 16, fresh water pipe two; 17, crystallization feed pipe; 18, concentrate pipe three; 19, fresh water pipe three; 20, seed feeding pipe; 21, mother liquor circulation pipe. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be understood that the orientations or positional relationships indicated by terms such as “upper”, “lower”, “top”, “bottom”, “inside” and “outside” are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0026] It should also be noted that, unless otherwise clearly specified and limited, the terms such as "installation", "connection", "connection", "fixation", "setting" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be determined according to the specific circumstances.

[0027] In one embodiment, a process for preparing borax from lithium-extracting tail liquid from carbonate brine is provided, the steps comprising:

[0028] 1) adding 32 wt % sodium hydroxide solution to the lithium extraction tail solution to adjust the pH value to 9.5-10;

[0029] 2) subjecting the lithium extraction tail liquid after pH adjustment to a first electrodialysis to concentrate it to a sodium borate content of 35-38 g / L;

[0030] 3) heating the concentrated solution obtained in step 2) to 65-68° C., performing a second electrodialysis, and concentrating the concentrated solution to a sodium borate content of 200-210 g / L;

[0031] 4) The concentrated solution obtained in step 3) is cooled and crystallized, and then separated and dried to obtain borax.

[0032] In the above embodiment, the pH value is adjusted to 9.5-10, so that H3BO3 can be converted into sodium borate (Na2B4O7) ion solution, which is convenient for migration and concentration under the action of the electric field during the electrodialysis process; in addition, through the two-stage electrodialysis method, the concentration can be rapidly increased within a reasonable temperature range, and the formation of lithium carbonate crystals at high temperature can be avoided, thereby improving the purity of borax crystals.

[0033] In one working condition, the main components of the lithium extraction tail liquid are as follows: boron content is 5-10g / L (in terms of B2O3), lithium ions <1g / L, sodium ion content is 1.5g / L, carbonate ion content is 1-4g / L, and chloride ion content is 3g / L. Through the process described in the above embodiment, through ordinary cooling crystallization and conventional separation and drying steps, the purity of the obtained borax can be greater than 99wt%, and the carbonate content is less than 0.08wt%, which is better than the national quality requirements for superior products. In addition, the above embodiment process can maximize the concentration and improve the recovery efficiency by controlling the temperature combined with electrodialysis, and the recovery rate of boron is above 92%.

[0034] In a preferred embodiment, in step 3), the sodium borate content of the freshwater solution obtained by the second electrodialysis is 3.45-4 g / L. In order to improve the recovery rate of boron and improve the utilization rate. The freshwater solution obtained by the second electrodialysis is subjected to a third electrodialysis, and the concentrated solution after electrodialysis is combined with step 1), and the third electrodialysis is concentrated to a sodium borate content of 12.5-14 g / L; if the mother liquor obtained in the separation process in step 4) has a content greater than 0.8 g / L, it is combined with step 1). By dialyzing the freshwater solution at a low concentration and recovering the mother liquor, the boron recovery rate can be increased to more than 95%.

[0035] In another embodiment, a device for preparing borax from tail liquor of lithium extraction from carbonate brine is provided, the device comprising a pH adjusting tank K1, a first electrodialysis unit ED1, a heater H1, a second electrodialysis unit ED2, and a crystallization drying unit; the pH adjusting tank K1 is provided with a feed pipe 11 and an alkali solution pipe 12, which are respectively used for feeding tail liquor of lithium extraction from carbonate brine and adding sodium hydroxide; the pH adjusting tank K1 is connected to the feed end of the first electrodialysis unit ED1, and a concentration pipe 13 is provided at the concentrated output end of the first electrodialysis unit ED1, which is connected to the solution tank 1 T1 and the heater H1 in sequence, and is connected to the feed end of the second electrodialysis unit ED2. A concentration pipe 2 15 is provided at the concentrated output end of the second electrodialysis unit ED2, which is connected to the solution tank 2 T2, and is pumped into the crystallization drying unit by a crystallization feed pipe 17 for subsequent cooling crystallization, centrifugation and drying steps. The device can promote the conversion of H3BO3 into Na2B4O7 ion solution by adding 32wt% sodium hydroxide solution to the pH adjusting tank K1. Then, the first electrodialysis unit ED1 is used to concentrate the borax to a sodium borate content of 35 to 38 g / L. The concentrated solution is then heated to 65 to 68°C by a heater H1, and then the second electrodialysis is performed by a second electrodialysis unit ED2 to concentrate the borax to a sodium borate content of 200 to 210 g / L. Finally, the borax is processed by a crystallization drying unit to obtain a high-purity finished borax product.

[0036] In a preferred embodiment, the first electrodialysis unit ED1 is further provided with a fresh water pipe 14, and the second electrodialysis unit ED2 is further provided with a fresh water pipe 2 16, which are respectively used to discharge low-concentration fresh water. The device also includes a third electrodialysis unit ED3, which is similarly provided with a concentration pipe 3 18 and a fresh water pipe 3 19. The fresh water pipe 2 16 is connected to the feed end of the third electrodialysis unit ED3, and is used to further concentrate the discharged low-concentration solution. The concentration pipe 3 18 is connected to the pH adjustment tank K1, and is used to recycle the concentrated solution of the third electrodialysis unit ED3, so as to further improve the boron recovery rate.

[0037] In the above embodiment, the low-concentration solution discharged from the fresh water pipe 14 and the fresh water pipe 3 19 can be discharged back to the salt lake to dissolve solid minerals for resource utilization.

[0038] In a preferred embodiment, in order to increase the crystallization rate, the solution tank T2 is also connected to a seed crystal feeding pipe 20, and the crystallization efficiency is improved by introducing seed crystals.

[0039] In the above embodiment, the crystallization and drying unit includes a crystallization kettle K2, a separator S1, and a centrifuge C1 which are connected in sequence; a belt conveyor BC1 is arranged below the centrifuge C1, and the belt conveyor BC1 is used to convey the crystallized wet material to the dryer (not shown in the figure). If the concentration of the mother liquor separated by the separator S1 and the centrifuge C1 is relatively low, it can be used to dissolve solid ore. If the concentration is greater than 0.8 g / L, the mother liquor is collected and returned to the pH adjustment tank K1 through the mother liquor circulation pipe 21 for further extraction of boron to improve the recovery rate. 5°C chilled water is used in the crystallization kettle K2 for cooling crystallization to improve the crystallization efficiency and control the smaller particle size.

[0040] In the above embodiments, the device for preparing borax also includes a power pump, valves, instruments and meters commonly used in the art, and their settings and functions are conventional means and will not be repeated here.

[0041] It will be understood that the terms "concentrate" and "fresh water" are only used to distinguish the boron-containing solution effluent from electrodialysis, and refer to materials with different concentrations after electrodialysis treatment.

[0042] In the following preferred embodiments, the main components of the lithium extraction tail liquid are as follows: boron trioxide content is 10g / L, lithium ion content is 0.3g / L, sodium ion content is 1.5g / L, carbonate ion content is 4g / L, and chloride ion content is 3g / L.

[0043] Example 1

[0044] 1) adding 32 wt % sodium hydroxide solution to the lithium extraction tail solution to adjust the pH value to 10;

[0045] 2) The lithium extraction tail liquid after pH adjustment is subjected to a first electrodialysis to be concentrated to a sodium borate content of 38 g / L;

[0046] 3) heating the concentrated solution obtained in step 2) to 68° C. and performing a second electrodialysis to concentrate the concentrated solution to a sodium borate content of 210 g / L;

[0047] 4) The concentrated solution obtained in step 3) is cooled and crystallized, and then separated and dried to obtain borax.

[0048] Example 2

[0049] 1) adding 32 wt % sodium hydroxide solution to the lithium extraction tail solution to adjust the pH value to 9.5;

[0050] 2) subjecting the lithium extraction tail liquid after pH adjustment to a first electrodialysis to concentrate it to a sodium borate content of 35 g / L;

[0051] 3) heating the concentrated solution obtained in step 2) to 65° C. and performing a second electrodialysis to concentrate the concentrated solution to a sodium borate content of 200 g / L;

[0052] 4) The concentrated solution obtained in step 3) is cooled and crystallized, and then separated and dried to obtain borax.

[0053] Example 3

[0054] 1) adding 32 wt % sodium hydroxide solution to the lithium extraction tail solution to adjust the pH value to 9.7;

[0055] 2) The lithium extraction tail liquid after pH adjustment is subjected to a first electrodialysis to be concentrated to a sodium borate content of 36 g / L;

[0056] 3) heating the concentrated solution obtained in step 2) to 66° C. and performing a second electrodialysis to concentrate the concentrated solution to a sodium borate content of 205 g / L;

[0057] 4) The concentrated solution obtained in step 3) is cooled and crystallized, and then separated and dried to obtain borax.

[0058] Example 4

[0059] When each step of Example 2 is running stably, the sodium borate content in the freshwater solution obtained by the second electrodialysis in step 3) is measured to be 3.6 g / L. The third electrodialysis is performed, and the concentration is controlled to be 14 g / L of sodium borate, and the concentrated solution obtained by the third electrodialysis is merged into step 1). In addition, the content of the mother liquor obtained by crystallization separation in step 4) is measured to be 1.0 g / L, and the obtained mother liquor is merged into step 1). The preparation process of Example 2 is repeated.

[0060] Comparative Example 1

[0061] Borax is prepared using patent document CN116177557A. The pressure of the last stage of the MVR evaporation process is 65-70 KPa, and the temperature reaches 88-90°C.

[0062] Comparative Example 2

[0063] The difference from Example 1 is that step 3) adopts MVR evaporation concentration, and the pressure of the last stage is controlled to be 65-70 KPa until the sodium borate content reaches 210 g / L. The other steps are the same as Example 1.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that the pH is adjusted to 9, and it is found that the first electrodialysis concentration is difficult to reach the target concentration.

[0066] The borax prepared in the above Examples 1-4 and Comparative Example 1 was analyzed, including the purity and the recovery rate of boron relative to the lithium extraction tail liquid. The results are shown in Table 1.

[0067]

[0068] It is not difficult to see from the data in Table 1 that the borax obtained by the boron preparation process described in Examples 1 to 3 has a high purity and a recovery rate of more than 92%. In Example 4, the three-stage electrodialysis concentration and crystallization mother liquor application of low-concentration fresh water further improve the recovery rate of boron. Comparative Examples 1-2 respectively use the MVR evaporation concentration method, and the purity decreases, which may be due to the inevitable formation of lithium carbonate crystals under normal pressure.

[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing borax from lithium-extracting tail liquid from carbonate brine, characterized in that the steps include: a) adjusting the pH value of the lithium extraction tail solution to 9.5-10; b) subjecting the lithium extraction tail liquid after pH adjustment to a first electrodialysis to concentrate it to a sodium borate content of 35 to 38 g / L; c) heating the concentrated solution obtained in step b) to 65-68° C., performing a second electrodialysis, and concentrating the concentrated solution to a sodium borate content of 200-210 g / L; d) cooling and crystallizing the concentrated solution obtained in step c), and then separating and drying to obtain borax.

2. The process according to claim 1, characterized in that In step c), the desalted water solution obtained from the second electrodialysis is subjected to a third electrodialysis, and the concentrated solution after the electrodialysis is combined with the solution in step a), and the third electrodialysis is performed to concentrate the solution to a sodium borate content of 12.5 to 14 g / L.

3. The process according to claim 1, characterized in that The lithium extraction tail liquid has a boron trioxide content of 5-10 g / L, a lithium ion content of less than 1 g / L, and a carbonate ion content of 1-4 g / L.

4. The process according to claim 1, characterized in that The mother liquor obtained from the separation process in step d) is combined with the mother liquor in step a).

5. The process according to claim 1, characterized in that The recovery rate of boron in the borax obtained in step d) is greater than 92%.

6. The process according to claim 1, characterized in that The purity of the borax obtained in step d) is greater than 99wt%, and the carbonate content is less than 0.08wt%.

7. The device used in the process for preparing borax according to claim 1, characterized in that: The invention comprises a pH regulating tank (K1), a first electrodialysis unit (ED1), a heater (H1), a second electrodialysis unit (ED2), and a crystallization drying unit which are connected in sequence; the concentration output end of the first electrodialysis unit (ED1) is connected to the heater (H1), and the concentration output end of the second electrodialysis unit (ED2) is connected to the crystallization drying unit.

8. The device according to claim 7, characterized in that It also includes a third electrodialysis unit (ED3); the fresh water output end of the second electrodialysis unit (ED2) is connected to the feed end of the third electrodialysis unit (ED3), and the concentrated output end of the third electrodialysis unit (ED3) is connected to the pH adjustment tank (K1).

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