Method for purifying sodium chloride and sodium fluoborate from synthetic waste liquid of sodium fluoborate

Abstract

The invention discloses a method for purifying sodium chloride and sodium fluoborate from synthetic waste liquid of sodium fluoborate, which comprises the following steps: heating and concentrating the synthetic waste liquid of sodium fluoborate to obtain concentrated liquid; cooling, crystallizing and filtering the concentrated solution to obtain filtrate I and filter residue I; leaching the filter residue I to obtain a filter residue II and a filtrate II, and drying the filter residue II to obtain a sodium chloride extract; mixing the filtrate I and the filtrate II, heating, concentrating, crystallizing and filtering to obtain filtrate III and filter residues III; and evaporating, crystallizing and drying the filtrate III to obtain the sodium fluoborate extract. The concentrated solution is cooled, crystallized and filtered to obtain a filtrate I and a filter residue I, sodium fluoride is dissolved in a filtrate II in the presence of a trace amount of sodium fluoborate, sodium chloride mainly remains in the filter residue II, the filtrate I and the filtrate II are combined, evaporated and crystallized, a filtrate III mainly contains sodium fluoborate, and a filter residue III is a mixed salt composed of sodium chloride and sodium fluoborate; and the waste liquid can be mixed with the next batch of waste liquid, so that sodium chloride and sodium fluoride in the waste liquid are recovered.

Description

Technical Field

[0001] The present application relates to the technical field of separation and purification, and in particular to a method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid. Background Art

[0002] Sodium fluoroborate's primary function in batteries is to transport ions, providing a conductive path for ions and boron ions, thereby enhancing the battery's ionic conductivity and improving the electrochemical performance of zinc-ion batteries, such as increasing their voltage and capacity.

[0003] The main synthesis method of sodium fluoborate is to produce sodium fluoborate using borax, sodium fluoride and hydrochloric acid. However, this synthesis method produces a large amount of synthetic waste liquid, which contains a large amount of sodium chloride, a small amount of sodium fluoborate and a trace amount of sodium fluoride. This affects the purity of the sodium fluoborate and the utilization rate of the sodium chloride. In addition, the sewage discharge cost is high and it is not environmentally friendly. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a method for purifying sodium chloride and sodium fluoborate from the synthetic waste liquid of sodium fluoborate, and recovering the sodium chloride and sodium fluoborate in the waste liquid.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate.

[0006] In a first aspect, the present invention provides a method for purifying sodium chloride and sodium fluoroborate from a synthetic waste liquid of sodium fluoroborate, comprising the following steps:

[0007] The synthetic waste liquid of sodium fluoroborate is heated and concentrated to obtain a concentrated liquid;

[0008] The concentrated solution is cooled and crystallized, and filtered to obtain filtrate 1 and filter residue 1;

[0009] The filter residue 1 is washed to obtain the filter residue 2 and the filtrate 2, and the filter residue 2 is dried to obtain the sodium chloride extract;

[0010] The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3;

[0011] The filtrate was triple evaporated, crystallized, and dried to obtain a sodium fluoroborate extract.

[0012] Therefore, in the technical solution of the embodiment of the present application, since the salt in the synthetic waste liquid of sodium fluoborate is mostly sodium chloride, a small part is sodium fluoborate, and a trace amount is sodium fluoride, the solubility of sodium chloride and sodium fluoborate in water is relatively large. The solubility of sodium chloride in water at 25°C is 36.2g, and the solubility of sodium chloride in water at 100°C is 39.8g. The solubility of sodium fluoborate in water at 25°C is 107g, and the solubility of sodium fluoborate in water at 100°C is 210g. The solubility of sodium fluoride in water at 25°C is 4.14g, and the solubility of sodium fluoride in water at 100°C is 5.08g. Therefore, because the content of sodium-chlor is the highest, the mode of separating out sodium-chlor can adopt evaporation solvent, in the solution of saturated sodium-chlor, along with the minimizing of aqueous solvent, and then first separate out sodium chloride crystal also i.e. the first filter residue, mainly sodium fluoborate and trace sodium chloride in the first filtrate, in the sodium chloride crystal of separating out, also can take a small portion of sodium fluoride and sodium fluoborate out, thus the first filter residue is carried out to drip washing, the second filter residue obtained is the higher crystal of sodium chloride purity, can be used as sodium chloride raw material and use.And in the remaining second filtrate, there is the sodium fluoborate that drip washing dissolves again, with the sodium fluoride that sodium fluoborate is dissolved in water, and the sodium chloride that a small portion is dissolved in water again, the second filtrate and the first filtrate are merged, for purifying sodium fluoborate.Because the solubility of sodium fluoborate varies greatly with temperature, therefore adopt the mode of heating concentration, the sodium-chlor in the merged filtrate can be separated, remaining most of sodium fluoborate is positioned at the 3rd filtrate, by evaporative crystallization, obtain sodium fluoborate crystal, and then sodium fluoborate is separated. The remaining third filter residue still contains some sodium chloride, sodium fluoroborate and sodium fluoride, which can be combined with the next batch of sodium fluoroborate synthetic waste liquid and purified again.

[0013] In any embodiment of the present application, the synthetic waste liquid of sodium fluoborate is heated and concentrated to obtain a concentrated liquid: when the heating temperature is 70-90° C., the water in the system is rapidly evaporated under vacuum, and sodium chloride gradually crystallizes out of the system. Due to the appropriate crystallization rate, the inclusion of sodium fluoborate and sodium fluoride is not serious, and the purity of the obtained sodium chloride crystals is better; optionally, the heating temperature is 75-85° C., the crystallization rate is more stable, the purity of the obtained sodium chloride is higher and more stable, and the purity of the sodium chloride can be further improved.

[0014] In any embodiment of the present application, the synthetic waste liquid of sodium fluoborate is heated and concentrated to obtain a concentrated liquid: the solid content of the concentrated liquid is 50% to 70%. At this solid content, most of the sodium chloride is fully crystallized during the evaporation and cooling process. At this time, since the sodium fluoborate is close to saturation, and the solubility of sodium fluoride in the system increases due to the affinity of sodium fluoborate, neither sodium fluoborate nor sodium fluoride will crystallize in large quantities. At this time, only a small amount of sodium fluoborate and sodium fluoride are mixed in the crystals, which can improve the purity of the sodium chloride. Optionally, the solid content of the concentrated liquid is 58% to 62%, which can further improve the purity of the sodium chloride.

[0015] In any embodiment of the present application, the concentrated liquid is cooled and crystallized, and filtered to obtain a filtrate and a filter residue: the crystallization temperature is 20 to 40° C. At this crystallization temperature, part of the sodium chloride that failed to crystallize during the evaporation process is fully crystallized, while reducing the effect of sodium fluoroborate and sodium fluoride on the purity of sodium chloride; optionally, the crystallization temperature is 23 to 27° C., which can reduce the effect of sodium fluoroborate and sodium fluoride on the purity of sodium chloride.

[0016] In any embodiment of the present application, the concentrated solution is cooled and crystallized, and filtered to obtain a filtrate and a filter residue. The crystallization time is 0.5 to 3 hours. Under this crystallization time, the crystallization of sodium chloride is more complete. At the same time, due to the redissolution of the previously crystallized sodium borate and sodium fluoride by water, the purity and yield of the sodium chloride crystals are higher. Optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the crystallization efficiency and improve the production efficiency. And / or,

[0017] The crystallization process includes stirred crystallization. The stirred crystallization method can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization and the purity and yield of the substance to be crystallized.

[0018] In any embodiment of the present application, the filter residue 1 is washed to obtain filter residue 2 and filtrate 2, and the filter residue 2 is dried to obtain a sodium chloride extract: the mass ratio of the filter residue 1 to the washing liquid is (1 to 5): 1. At this mass ratio, the crystallized sodium fluoride and sodium fluoroborate can be dissolved, and the dissolution of sodium chloride can be reduced, thereby improving the purity of sodium chloride; optionally, the mass ratio of the filter residue 1 to the washing liquid is (1 to 3): 1, which can further dissolve the crystallized sodium fluoride and sodium fluoroborate, reduce the dissolution of sodium chloride, and improve the purity of sodium chloride.

[0019] In any embodiment of the present application, the filtrate one and the filtrate two are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate three and a filter residue three: the heating and concentration temperature is 70 to 100° C. At this heating and concentration temperature, the water in the system evaporates rapidly, and most of the sodium chloride, a small amount of sodium fluoroborate, and a small amount of sodium fluoride gradually crystallize out of the system. Since the crystallization rate at this temperature is appropriate, sodium chloride crystallizes before sodium fluoroborate. The resulting crystallization mother liquor, i.e., the filtrate three, has less residual sodium chloride, so that the sodium fluoroborate content in the filtrate three is higher, which can improve the purity of the sodium fluoroborate in the subsequent steps; optionally, the heating and concentration temperature is 80 to 90° C., which can further improve the purity of the sodium fluoroborate in the subsequent steps.

[0020] In any embodiment of the present application, the filtrate one and the filtrate two are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate three and a filter residue three: the solid content of the heated and concentrated concentrated solution is 60-80%. Within this solid content range, since sodium chloride reaches supersaturation before sodium fluoborate during the concentration process, most of the sodium chloride in the system is fully crystallized before sodium fluoborate, and then a small amount of sodium fluoborate gradually crystallizes due to gradually reaching a supersaturated state. During the crystallization process, a small amount of sodium fluoride will also be mixed in the sodium fluoborate crystals, and the sodium chloride finally remaining in the crystallization mother liquor, i.e., the filtrate three, is very small. Therefore, the sodium fluoborate content in the filtrate three is relatively high, thereby improving the purity of the sodium fluoborate; optionally, the solid content of the heated and concentrated concentrated solution is 68-72%, which can further improve the purity of the sodium fluoborate.

[0021] In any embodiment of the present application, the filtrate one and the filtrate two are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate three and a filter residue three: the crystallization temperature is 65 to 75° C. At this crystallization temperature, part of the sodium chloride that failed to crystallize during the heating and concentration process is fully crystallized, while reducing the crystallization of sodium fluoroborate, increasing the content of sodium fluoroborate in the filtrate three, and thereby improving the purity of the sodium fluoroborate; optionally, the crystallization temperature is 68 to 72° C., which can further improve the purity of the sodium fluoroborate.

[0022] In any embodiment of the present application, the filtrate one and the filtrate two are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate three and a filter residue three: the crystallization time is 0.5 to 3 hours. Under this crystallization time, the crystallization of sodium chloride is more complete. At the same time, due to the redissolution of the previously crystallized sodium fluoroborate by water, some of the originally crystallized sodium fluoroborate returns to the crystallization mother liquor, thereby improving the purity of the sodium fluoroborate in the filtrate three; optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the crystallization separation efficiency and improve the purity of the sodium fluoroborate in the filtrate three; and / or,

[0023] The crystallization process includes stirring crystallization. Stirring crystallization can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization.

[0024] In any embodiment of the present application, the filtrate is triple evaporated, crystallized, and dried to obtain a sodium fluoborate extract: the evaporation and drying temperature is 70 to 120°C. At this drying temperature, the water in the system is rapidly evaporated, so that the sodium fluoborate crystals are precipitated, and the obtained crystals have a relatively uniform particle size and good fluidity, which is convenient for discharging; optionally, the evaporation and drying temperature is 90 to 100°C, which can further improve the uniformity of the sodium fluoborate crystal particles.

[0025] In any embodiment of the present application, the filtrate is triple evaporated, crystallized, and dried to obtain the sodium borofluoride extract: the evaporation and drying pressure is -0.1 to 0 MPa, which can improve the efficiency of the reaction. DETAILED DESCRIPTION

[0026] Below, the embodiment of the method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate of the present application is specifically disclosed. However, there may be cases where unnecessary detailed description is omitted. For example, there may be cases where the detailed description of well-known matters and the repeated description of actual identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the embodiments and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0027] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0029] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0030] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0031] Sodium fluoroborate's main function in batteries is to transport ions, providing a conductive path for ions and boron ions, enhancing the battery's ionic conductivity and improving the electrochemical performance of zinc-ion batteries, such as increasing the battery's voltage and capacity.

[0032] The main synthesis method of sodium fluoborate is to produce sodium fluoborate from borax, sodium fluoride and hydrochloric acid. However, this synthesis method produces a large amount of synthetic waste liquid, which contains a large amount of sodium chloride (about 66%), a small amount of sodium fluoborate (about 32%) and a trace amount of sodium fluoride (about 2%). This affects the purity of the sodium fluoborate and the utilization rate of the sodium chloride. In addition, the sewage discharge cost is high and it is not friendly to the environment.

[0033] Therefore, research for the recovery of sodium fluoroborate emerges in an endless stream, for example, with methyl carbonate, extracting the method for sodium fluoroborate from the reaction system of the organic soluble complex of sodium carbonate and boron trifluoride, owing to adopting expensive solvent and not economical.For example, by the method for extracting sodium fluoroborate in the product reacted in aqueous solution with lithium fluoroborate and sodium fluoride, because the lithium fluoride in the system is slightly soluble in water, it and the solubility difference of sodium fluoroborate in water are very large, and the two are easier to separate.For example, potassium fluoroborate and sodium chloride separation method, because potassium fluoroborate is slightly soluble in water, it and the solubility difference of sodium chloride in water are very large, and the two are easier to separate.And sodium fluoroborate and sodium chloride are all soluble in water in the application, separation difficulty in aqueous solution.

[0034] Based on this, the present application provides a method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid.

[0035] In a first aspect, the present invention provides a method for purifying sodium chloride and sodium fluoroborate from a synthetic waste liquid of sodium fluoroborate, comprising the following steps:

[0036] The synthetic waste liquid of sodium fluoroborate is heated and concentrated to obtain a concentrated liquid;

[0037] The concentrated solution is cooled and crystallized, and filtered to obtain filtrate 1 and filter residue 1;

[0038] The filter residue 1 is washed to obtain the filter residue 2 and the filtrate 2, and the filter residue 2 is dried to obtain the sodium chloride extract;

[0039] The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3;

[0040] The filtrate was evaporated, crystallized and dried to obtain sodium fluoroborate extract.

[0041] Therefore, in the technical solution of the embodiment of the present application, since the salt in the synthetic waste liquid of sodium fluoborate is mostly sodium chloride, a small part is sodium fluoborate, and a trace amount is sodium fluoride, the solubility of sodium chloride and sodium fluoborate in water is relatively large. The solubility of sodium chloride in water at 25°C is 36.2g, and the solubility of sodium chloride in water at 100°C is 39.8g. The solubility of sodium fluoborate in water at 25°C is 107g, and the solubility of sodium fluoborate in water at 100°C is 210g. The solubility of sodium fluoride in water at 25°C is 4.14g, and the solubility of sodium fluoride in water at 100°C is 5.08g. Therefore, because the content of sodium-chlor is the highest, the mode of separating out sodium-chlor can adopt evaporation solvent, in the solution of saturated sodium-chlor, along with the minimizing of aqueous solvent, and then first separate out sodium chloride crystal also i.e. the first filter residue, mainly sodium fluoborate and trace sodium chloride in the first filtrate, in the sodium chloride crystal of separating out, also can take a small portion of sodium fluoride and sodium fluoborate out, thus the first filter residue is carried out to drip washing, the second filter residue obtained is the higher crystal of sodium chloride purity, can be used as sodium chloride raw material and use.And in the remaining second filtrate, there is the sodium fluoborate that drip washing dissolves again, with the sodium fluoride that sodium fluoborate is dissolved in water, and the sodium chloride that a small portion is dissolved in water again, the second filtrate and the first filtrate are merged, for purifying sodium fluoborate.Because the solubility of sodium fluoborate varies greatly with temperature, therefore adopt the mode of heating concentration, the sodium-chlor in the merged filtrate can be separated, remaining most of sodium fluoborate is positioned at the 3rd filtrate, by evaporative crystallization, obtain sodium fluoborate crystal, and then sodium fluoborate is separated. The remaining third filter residue still contains some sodium chloride, sodium fluoroborate and sodium fluoride, which can be combined with the next batch of sodium fluoroborate synthetic waste liquid and purified again.

[0042] In any embodiment of the present application, the synthetic waste liquid of sodium fluoborate is heated and concentrated to obtain a concentrated liquid: when the heating temperature is 70 to 90°C, the water in the system is rapidly evaporated under vacuum, and sodium chloride gradually crystallizes out of the system. Due to the appropriate crystallization rate, the inclusion of sodium fluoborate and sodium fluoride is not serious, and the purity of the sodium chloride crystals obtained is good; the heating temperature can be 70°C, 75°C, 80°C, 85°C or 90°C. Optionally, the heating temperature is 75 to 85°C, the crystallization rate is more stable, the sodium chloride content obtained is higher and more stable, and the purity of the sodium chloride can be further improved. Among them, the heating concentration of the synthetic waste liquid of sodium fluoborate can be carried out at normal pressure or at -0.01 to 0 MPa.

[0043] In any embodiment of the present application, the synthetic waste liquid of sodium fluoborate is heated and concentrated to obtain a concentrated solution: the solid content of the concentrated solution is 50-70%. At this solid content, most of the sodium chloride is fully crystallized during the evaporation and cooling process. At this time, since the sodium fluoborate is just close to saturation, and the solubility of sodium fluoride in the system increases due to the affinity of sodium fluoborate, neither sodium fluoborate nor sodium fluoride will crystallize in large quantities. At this time, only a small amount of sodium fluoborate and sodium fluoride are mixed in the crystals, which can improve the purity of the sodium chloride; the solid content of the concentrated solution can be 50%, 53%, 55%, 58%, 60%, 62%, 65%, 67% or 70%. Optionally, the solid content of the concentrated solution is 58%-62%, which can further improve the purity of the sodium chloride.

[0044] In any embodiment of the present application, the concentrated liquid is cooled and crystallized, and filtered to obtain a filtrate and a filter residue: the crystallization temperature is 20 to 40°C. At this crystallization temperature, part of the sodium chloride that failed to crystallize during the evaporation process is fully crystallized, while reducing the impact of sodium fluoroborate and sodium fluoride on the purity of the sodium chloride; the crystallization temperature can be 20°C, 23°C, 25°C, 27°C, 30°C, 35°C or 40°C. Optionally, the crystallization temperature is 23 to 27°C, which can further reduce the impact of sodium fluoroborate and sodium fluoride on the purity of the sodium chloride.

[0045] In any embodiment of the present application, the concentrated solution is cooled and crystallized, and filtered to obtain a filtrate and a filter residue. The crystallization time is 0.5 to 3 hours. Under this crystallization time, the crystallization of sodium chloride is more complete. At the same time, due to the redissolution of the previously crystallized sodium fluoroborate and sodium fluoride by water, the purity and yield of the sodium chloride crystals are higher. The crystallization time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours. Optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the crystallization efficiency and improve the production efficiency.

[0046] In any embodiment of the present application, the process of cooling the concentrated liquid to crystallize, filtering, and obtaining crystals in the filtrate and the filter residue includes stirred crystallization. The use of stirred crystallization can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization and the purity and yield of the substance to be crystallized.

[0047] In any embodiment of the present application, the filter residue 1 is washed to obtain the filter residue 2 and the filtrate 2, and the filter residue 2 is dried to obtain the sodium chloride extract: the mass ratio of the filter residue 1 to the eluent is (1-5):1. At this mass ratio, the crystallized sodium fluoride and sodium fluoroborate can be dissolved, and the purity of the sodium chloride can be reduced, thereby improving the purity of the sodium chloride; the mass ratio of the filter residue 1 to the eluent can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1. Optionally, the mass ratio of the filter residue 1 to the eluent is (1-3):1, which can further dissolve the crystallized sodium fluoride and sodium fluoroborate, reduce the dissolution of sodium chloride, and improve the purity of the sodium chloride.

[0048] In any embodiment of the present application, the filtrate 1 and the filtrate 2 are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate 3 and a filter residue 3: the heating and concentration temperature is 70-100°C. At this heating and concentration temperature, the water in the system evaporates rapidly while most of the sodium chloride, a small amount of sodium fluoroborate, and a small amount of sodium fluoride gradually crystallize out of the system. Since the crystallization rate at this temperature is appropriate, sodium chloride crystallizes before sodium fluoroborate. The resulting crystallization mother liquor, i.e., the filtrate 3, has less residual sodium chloride, so that the sodium fluoroborate content in the filtrate 3 is higher, which can improve the purity of the sodium fluoroborate in the subsequent steps; the heating and concentration temperature can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C. Optionally, the heating and concentration temperature is 80-90°C, which can further improve the purity of the sodium fluoroborate in the subsequent steps.

[0049] In any embodiment of the present application, the filtrate 1 and the filtrate 2 are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate 3 and a filter residue 3: the solid content of the heated and concentrated concentrated solution is 60-80%. Within this solid content range, since sodium chloride reaches supersaturation before sodium fluoroborate during the concentration process, most of the sodium chloride in the system is fully crystallized before sodium fluoroborate, and then a small amount of sodium fluoroborate gradually crystallizes due to gradually reaching supersaturation. During the crystallization process, a small amount of sodium fluoride will also be mixed with the sodium fluoroborate crystals, and the sodium chloride that ultimately remains in the crystallization mother liquor, i.e., the filtrate 3, is very small. Therefore, the sodium fluoroborate content in the filtrate 3 is relatively high, thereby improving the purity of the sodium fluoroborate; the solid content of the heated and concentrated concentrated solution can be 60%, 63%, 65%, 68%, 70%, 72%, 77% or 80%. Optionally, the solid content of the heated and concentrated concentrated solution is 68-72%, which can further improve the purity of the sodium fluoroborate.

[0050] In any embodiment of the present application, the filtrate 1 and the filtrate 2 are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate 3 and a filter residue 3: the crystallization temperature is 65 to 75°C. At this crystallization temperature, some sodium chloride that fails to crystallize during the heating and concentration process is fully crystallized, while reducing the crystallization of sodium fluoborate, increasing the content of sodium fluoborate in the filtrate 3, and thereby improving the purity of the sodium fluoborate; the crystallization temperature can be 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, or 75°C. Optionally, the crystallization temperature is 68 to 72°C, which can further improve the purity of the sodium fluoborate.

[0051] In any embodiment of the present application, the filtrate 1 and the filtrate 2 are mixed, heated and concentrated, crystallized, and filtered to obtain a filtrate 3 and a filter residue 3: the crystallization time is 0.5 to 3 hours. Under this crystallization time, the crystallization of sodium chloride is more complete. At the same time, due to the redissolution of the previously crystallized sodium fluoroborate by water, some of the originally crystallized sodium fluoroborate returns to the crystallization mother liquor, thereby improving the purity of the sodium fluoroborate in the filtrate 3; the crystallization time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours. Optionally, the crystallization time is 0.5 to 1.5 hours, which can further improve the crystallization separation efficiency, improve the purity of the sodium fluoroborate in the filtrate 3, and improve the efficiency of the reaction.

[0052] In any embodiment of the present application, the filtrate one and the filtrate two are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate three and the filter residue three: the crystallization process includes stirred crystallization. The use of stirred crystallization can make the crystallization system more uniform, which is beneficial to improving the stability of the crystallization.

[0053] In any embodiment of the present application, the filtrate is triple-evaporated, crystallized, and dried to obtain a sodium fluoborate extract: the evaporation and drying temperature is 70-120°C. At this drying temperature, the water in the system is rapidly evaporated, so that the sodium fluoborate crystals are precipitated, and the resulting crystals are relatively uniform in size, have good fluidity, and are easy to discharge; the evaporation and drying temperature can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C. Optionally, the evaporation and drying temperature is 90-100°C, which can further improve the uniformity of the sodium fluoborate crystal particles.

[0054] In any embodiment of the present application, the filtrate is triple-evaporated, crystallized, and dried to obtain a sodium borofluoride extract: the evaporation and drying pressure is -0.1 to 0 MPa, which can improve the efficiency of the reaction. The evaporation and drying pressure can be -0.1 MPa, -0.08 MPa, -0.05 MPa, -0.03 MPa or 0 MPa.

[0055] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0056] The methods for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate in Examples 1 to 25 of the present application are according to the parameters of Table 1. It should be noted that heating temperature one and concentrated liquid solid content one refer to heating and concentrating the synthetic waste liquid of sodium fluoroborate to obtain the heating temperature and concentrated liquid solid content in the concentrated liquid. Crystallization temperature one refers to cooling the concentrated liquid for crystallization, filtering, and obtaining the crystallization temperature in filtrate one and filter residue one. Heating temperature two, crystallization temperature two and concentrated liquid solid content two refer to mixing filtrate one and filtrate two, heating and concentrating, crystallizing, filtering, and obtaining the heating temperature, crystallization temperature and concentrated liquid solid content in filtrate three and filter residue three. Among them, the method of cooling the concentrated liquid for crystallization, filtering, obtaining stirred crystallization in filtrate one and filter residue one for 2h, mixing filtrate one and filtrate two, heating and concentrating, crystallizing, filtering, obtaining stirred crystallization in filtrate three and filter residue three for 2h, evaporating filtrate three for crystallization, drying, and obtaining the evaporation and drying pressure of -0.09MPa in the sodium fluoroborate extract is used as an example for explanation.

[0057] Table 1 Parameters of the method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate in Examples 1 to 25

[0058]

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 18 is that, in the step of "rinsing the filter residue 1 to obtain the filter residue 2 and the filtrate 2, and drying the filter residue 2 to obtain the sodium chloride extract", no rinsing was performed.

[0061] In Comparative Example 1, since no elution was performed, the sodium fluoroborate and sodium fluoride contained in the filter residue were not removed, resulting in low purity of the final sodium chloride and low yield of sodium fluoroborate. In Comparative Example 1, the purity of sodium chloride was 70.1% and the yield was 78.9%; the purity of sodium fluoroborate was 43.6% and the yield was 3.1%.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Example 18 is that in the step of "mixing filtrate 1 and filtrate 2, concentrating by heating, crystallizing, filtering, and obtaining filtrate 3 and filter residue 3", heating, concentrating, crystallizing, and filtering are not performed.

[0064] In Comparative Example 2, since heating, concentration, crystallization, and filtration were not performed, the mixture of filtrate 1 and filtrate 2 was not further crystallized and separated, resulting in low purity of the final sodium fluoborate. In Comparative Example 2, the purity of sodium chloride was 74.9%, and the yield was 69.6%; the purity of sodium fluoborate was 33.2%, and the yield was 44.9%.

[0065] Comparative Example 3

[0066] The difference between Comparative Example 3 and Example 18 is that, in the step of "rinsing the filter residue 1 to obtain the filter residue 2 and the filtrate 2, and drying the filter residue 2 to obtain the sodium chloride extract", no rinsing was performed;

[0067] In the step of “mixing filtrate 1 and filtrate 2, concentrating by heating, crystallizing, and filtering to obtain filtrate 3 and filter residue 3”, heating, concentrating, crystallizing, and filtering are not performed.

[0068] Comparative Example 3 did not undergo elution, heating, concentration, crystallization, or filtration, which reduced the purity of sodium chloride and sodium fluoroborate. The purity of sodium chloride in Comparative Document 3 was 70.1%, with a yield of 78.8%; the purity of sodium fluoroborate was 30.4%, with a yield of 30.3%.

[0069] Performance Testing

[0070] Purity test: by testing the anion and cation concentration of the sample, and then calculating based on the anion and cation test data. The details are as follows:

[0071] 1) ICP detection of cations:

[0072] Instrument model: ICAP-7000;

[0073] Carrier gas: argon;

[0074] Concentration range: 0.1~8ppm;

[0075] Na + Absorption wavelength: 589.592nm;

[0076] 2) Anions are detected by ion chromatography:

[0077] Instrument model: 930 Compact IC Flex;

[0078] Chromatographic column model: Metrosep A Supp5-250 / 4.0;

[0079] Mobile phase: 3.2 mmol / L Na2CO3 aqueous solution;

[0080] Detection column temperature: 30℃;

[0081] 3) Calculation of purity of each component:

[0082] P i =w i ×M i / M i - ;

[0083] Among them, P i Represents the purity of salt, expressed as a percentage; w i Indicates the percentage of ions; M i Indicates the molar mass of the salt; M i - Indicates the molar mass of the ion.

[0084] The cation data can be used to check the reliability of the anion data.

[0085] 4) Yield test:

[0086] Y i =G i / (G×S)×100%;

[0087] Among them, Y i Represents the salt yield, expressed as a percentage; G i It represents the mass of salt in g; G represents the total mass of raw materials used in g; S represents the solid content of the raw materials, expressed as a percentage.

[0088] The sodium chloride and sodium fluoroborate extracted in Examples 1 to 23 were tested for purity and yield. The test results are shown in Table 1.

[0089] In the data in Table 1:

[0090] It can be seen from Examples 1 to 4 that the purity of sodium chloride can be improved within the range of 65 to 90°C.

[0091] It can be seen from Examples 4 to 7 that, within the range of 50-80%, the greater the solid content of the concentrate, the greater the impact on the purity of sodium chloride, but the purity of sodium chloride can be improved.

[0092] It can be seen from Examples 7 to 10 that the purity of sodium chloride can be improved within the range of 20 to 45°C.

[0093] It can be seen from Examples 10 to 13 that the purity of sodium chloride can be improved within the range of (5-30):1.

[0094] It can be seen from Examples 13 to 16 that the purity of sodium fluoroborate can be improved within the range of 60 to 100°C.

[0095] It can be seen from Examples 16 to 19 that the purity of sodium fluoroborate can be increased within the range of 55 to 80%.

[0096] It can be seen from Examples 19 to 22 that the purity of sodium fluoroborate can be improved within the range of 60 to 75°C.

[0097] It can be seen from Examples 22 to 25 that the purity of sodium fluoroborate can be improved within the range of 60 to 120°C.

[0098] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid, characterized in that: The following steps are involved: The synthetic waste liquid of sodium fluoroborate is heated and concentrated to obtain a concentrated liquid; The concentrated solution is cooled and crystallized, and filtered to obtain filtrate 1 and filter residue 1; The filter residue 1 is washed to obtain the filter residue 2 and the filtrate 2, and the filter residue 2 is dried to obtain the sodium chloride extract; The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3; The filtrate was evaporated, crystallized and dried to obtain sodium fluoroborate extract.

2. The method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate according to claim 1, wherein: The synthetic waste liquid of sodium fluoroborate is heated and concentrated to obtain the concentrated liquid: The heating temperature is 70-90°C.

3. The method for purifying sodium chloride and sodium fluoroborate from the synthetic waste liquid of sodium fluoroborate according to claim 1 or 2, characterized in that: The synthetic waste liquid of sodium fluoroborate is heated and concentrated to obtain the concentrated liquid: The solid content of the concentrated liquid is 50-70%.

4. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 3, characterized in that: The concentrated solution is cooled and crystallized, and filtered to obtain a filtrate and a filter residue: The crystallization temperature is 20-40°C.

5. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 4, characterized in that: The concentrated solution is cooled and crystallized, and filtered to obtain a filtrate and a filter residue: The crystallization time is 0.5 to 3 hours; and / or, The crystallization process includes stirred crystallization.

6. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 5, characterized in that: The filter residue 1 is washed to obtain the filter residue 2 and the filtrate 2, and the filter residue 2 is dried to obtain the sodium chloride extract: The mass ratio of the filter residue and the eluent is (1-5):

1.

7. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 6, characterized in that: The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3: The temperature for heating and concentrating is 70-100°C.

8. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 7, characterized in that: The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3: The solid content of the concentrated liquid after heating and concentration is 60-80%.

9. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 8, characterized in that: The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3: The crystallization temperature is 65-75°C.

10. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 9, characterized in that: The filtrate 1 and the filtrate 2 are mixed, concentrated by heating, crystallized, and filtered to obtain the filtrate 3 and the filter residue 3: The crystallization time is 0.5 to 3 hours; and / or, The crystallization process includes stirred crystallization.

11. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 10, characterized in that: The filtrate is evaporated and crystallized three times, and dried to obtain the sodium fluoroborate extract: The evaporation drying temperature is 70-120°C.

12. The method for purifying sodium chloride and sodium fluoroborate from sodium fluoroborate synthesis waste liquid according to any one of claims 1 to 11, characterized in that: The filtrate is evaporated and crystallized three times, and dried to obtain the sodium fluoroborate extract: The pressure of evaporation drying is -0.1~0MPa.

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