Method for recovering sodium thioglycolate from ethionine ester synthesis wastewater

Abstract

The invention provides a method for recovering sodium thioglycolate from ethionine ester synthesis wastewater. The method comprises the following steps: firstly adjusting the pH value, converting sodium thioglycollate in the wastewater into thioglycollic acid, then extracting the thioglycollic acid in the synthetic wastewater by adopting an organic phase with a neutral phosphorus extraction agent as a main component, then enriching the sodium thioglycollate in strip liquor through washing and reverse extraction, and adding low alcohol into the strip liquor to change the polarity of the solution, so that the sodium thioglycollate in the wastewater is obtained. The method has the characteristic of low energy consumption, and meanwhile, the purity of the sodium thioglycolate product is high.

Description

Technical Field

[0001] The invention belongs to the technical field of ethylthiocarbamide production wastewater treatment, and specifically relates to a method for recovering sodium thioglycolate from ethylthiocarbamide synthesis wastewater. Background Art

[0002] Ethiocarbamide is an excellent mineral processing agent with the advantages of high selectivity, low dosage and low pollution. Therefore, it is widely used in the flotation of primary minerals or secondary resources such as copper, cobalt, nickel and gold. The xanthate esterification-ammonolysis method is the mainstream method for the industrial production of ethiocarbamide. Every ton of ethiocarbamide produced will produce 5 to 6 tons of alkaline synthetic wastewater with sodium thioglycolate and sodium chloride as the main components. The content of sodium thioglycolate in the synthetic wastewater reaches 10 to 20%, resulting in a severe pungent odor in the wastewater, and it is easy to decompose into toxic gas hydrogen sulfide. If it is not properly treated, it will cause great harm to the environment.

[0003] At present, there are two main methods for treating ethylthiocarbamate synthesis wastewater: the first method is to directly sell the wastewater in the form of a crude sodium thioglycolate solution for copper and molybdenum flotation separation, or it can be simply enriched and concentrated before being sold. The second method requires adding an inorganic acid to adjust the pH value of the waste liquid to 0.5-2, thereby converting sodium thioglycolate into thioglycolic acid, and then extracting thioglycolic acid with an organic solvent such as ether, toluene, ethyl acetate, dichloromethane, etc., and using liquid alkali to strip to obtain a sodium thioglycolate solution, and finally obtaining a sodium thioglycolate solid product by evaporation and crystallization.

[0004] The prior art either directly sells the ethylthiocarbamate synthetic wastewater as a sodium thioglycolate aqueous solution for copper-molybdenum ore dressing, or obtains thioglycolate or sodium thioglycolate products after extraction-stripping with organic solvents such as ether and toluene. The shortcomings of these technologies are: 1) the content of sodium thioglycolate in the synthetic wastewater is less than 20%, and it contains a large amount of impurities, and the direct selling price is low. More importantly, direct selling does not solve the problem of the synthetic wastewater harming the environment, but only transfers the pollution to the copper-molybdenum mine; 2) the existing organic solvents such as ether, toluene, acetone, etc. used to extract thioglycolate have the disadvantages of being volatile and highly toxic, and the above-mentioned solvents have low extraction efficiency for thioglycolate, and often require multiple extractions to achieve a higher thioglycolate extraction rate; 3) Sodium thioglycolate can be enriched in the stripping solution by extraction and stripping, but the traditional method prepares sodium thioglycolate solid by evaporation and crystallization, which has the problems of high energy consumption and easy oxidation of sodium thioglycolate. Therefore, it is still necessary to develop a new method that can better recover sodium thioglycolate from ethylthiocarbamate synthetic wastewater. Summary of the invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a method for recovering sodium thioglycolate from ethylthiocarbamate synthetic wastewater, wherein the sodium thioglycolate in the wastewater is converted into thioglycolic acid by adjusting the pH value, and then the thioglycolic acid in the synthetic wastewater is extracted with an organic phase whose main component is a neutral phosphorus extractant, and then the sodium thioglycolate is enriched in the stripping solution by washing and stripping, and the polarity of the solution is changed by adding a lower alcohol to the stripping solution, so that the sodium thioglycolate is finally crystallized and precipitated.

[0006] A first aspect of the present invention provides a method for recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater, comprising the following steps:

[0007] S1: Adjust the pH of the wastewater so that all the sodium thioglycolate in the wastewater is converted into thioglycolic acid;

[0008] S2: extracting thioglycolic acid by extracting the organic phase, and separating the upper organic phase loaded with thioglycolic acid and the raffinate;

[0009] S3: washing the loaded organic phase produced in step S2 with water to remove impurities;

[0010] S4: stripping the washed loaded organic phase produced in step S3 with an alkaline solution to obtain a sodium thioglycolate-enriched solution;

[0011] S5: adding a precipitant to the sodium thioglycolate enriched solution obtained in step S4 to crystallize the sodium thioglycolate, filtering to obtain the sodium thioglycolate crystals, and drying them.

[0012] The present invention relates to a technical solution in a method for recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater, which has at least the following beneficial effects:

[0013] In view of the problem of high toxicity of existing thioglycolic acid extractants, the present invention constructs a series of thioglycolic acid efficient extraction systems, avoiding the use of highly toxic organic solvents such as ether and toluene. In view of the high energy consumption and easy oxidation of the product in the evaporation and crystallization process of sodium thioglycolate, the present invention adds lower alcohols such as methanol, ethanol, isopropanol, etc. to the sodium thioglycolate enriched solution at room temperature to directly crystallize and precipitate sodium thioglycolate. Specifically, the present invention first converts sodium thioglycolate in the wastewater into thioglycolic acid by adjusting the pH value, and then uses an organic phase whose main component is a neutral phosphorus extractant (compared with the prior art, the extractant is different, and the extractant used in the disclosed method is ether) to extract the thioglycolic acid in the synthetic wastewater. Further, by washing and stripping, sodium thioglycolate is enriched in the stripping solution, and then the polarity of the solution is changed by adding lower alcohols to the stripping solution containing sodium thioglycolate, so that sodium thioglycolate is crystallized (compared with the prior art, the crystallization method is different, and the crystallization method of the disclosed method is evaporation crystallization).

[0014] Compared with the prior art, the present invention is different in that the extractant used in the present invention is a neutral phosphorus extractant, which is widely used in the extraction of metal ions, but has not been used for the extraction of sodium thioglycolate. More importantly, the present invention avoids the use of highly toxic traditional extractants such as ether and toluene by constructing a new extraction system, and has the advantages of high extraction rate, low toxicity and good circulation performance.

[0015] After the sodium thioglycolate enriched solution is obtained by extraction and stripping, the conventional method prepares the sodium thioglycolate solid by evaporation and crystallization, but there are problems of high energy consumption and easy oxidation of the sodium thioglycolate. However, the present invention directly crystallizes and precipitates the sodium thioglycolate by adding a lower alcohol to the sodium thioglycolate enriched solution, which has the characteristics of low energy consumption and high purity of the sodium thioglycolate product.

[0016] According to some embodiments of the present invention, in step S1, the content of sodium thioglycolate in the wastewater is 5 to 40 wt%.

[0017] According to some embodiments of the present invention, in step S1, the initial pH of the wastewater is 7.5-10.5.

[0018] According to some embodiments of the present invention, in step S1, the pH of the wastewater is adjusted to 0-2.

[0019] According to some embodiments of the present invention, in step S1, the pH of the wastewater may be adjusted using at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0020] According to some embodiments of the present invention, in step S1, when adjusting the pH of the wastewater, the concentration of hydrogen ions in the acid solution is maintained at 1 to 20 mol / L.

[0021] According to some embodiments of the present invention, in step S1, when adjusting the pH of the wastewater, the concentration of hydrogen ions in the acid solution is maintained at 10 to 20 mol / L.

[0022] According to some embodiments of the present invention, in step S2, the extracted organic phase includes a neutral phosphorus extractant with a volume fraction of 10 vol% to 80 vol% and a diluent with a volume fraction of 20 vol% to 90 vol%.

[0023] According to some embodiments of the present invention, the neutral phosphorus extractant includes at least one of tributyl phosphate (TBP), trioctyl phosphate (TOP), trialkyl phosphine oxide (TRPO or Cyanex923), trioctyl phosphine oxide (TOPO), methyl (1-methylheptyl) phosphonate (P350) and tributyl phosphine oxide (TBPO).

[0024] According to some embodiments of the present invention, the diluent includes at least one of sulfonated kerosene, No. 260 solvent oil, aviation kerosene, cyclohexane, n-heptane and ether.

[0025] According to some embodiments of the present invention, in step S2, the organic phase of the neutral phosphorus extractant includes a neutral phosphorus extractant with a volume fraction of 10 vol% to 80 vol% and a diluent of 20 vol% to 90 vol%, such as 20% TBP+40 TRPO%+40% sulfonated kerosene, or 40% TOP+60% No. 260 solvent oil.

[0026] According to some embodiments of the present invention, in step S2, the organic phase of the neutral phosphorus extractant includes 40 vol% to 70 vol% of the neutral phosphorus extractant and 30 vol% to 60 vol% of the diluent.

[0027] According to some embodiments of the present invention, in step S2, the temperature for extracting thioglycolic acid is 10-60°C.

[0028] According to some embodiments of the present invention, in step S2, the temperature for extracting thioglycolic acid is 20-40°C.

[0029] According to some embodiments of the present invention, in step S2, the extraction time for extracting thioglycolic acid is 2 to 30 minutes.

[0030] According to some embodiments of the present invention, in step S2, the extraction time for extracting thioglycolic acid is 5 to 15 minutes.

[0031] According to some embodiments of the present invention, in step S2, the number of extraction stages for extracting thioglycolic acid is 2 to 6.

[0032] According to some embodiments of the present invention, in step S2, the extraction flow ratio for extracting thioglycolic acid is 1:5 to 10:1.

[0033] According to some embodiments of the present invention, in step S2, the extraction flow ratio for extracting thioglycolic acid is 1:2 to 4:1.

[0034] According to some embodiments of the present invention, in step S2, when the number of extraction stages is greater than 2, the extraction method is countercurrent extraction.

[0035] According to some embodiments of the present invention, in step S2, the raffinate produced after extracting thioglycolic acid mainly contains sodium chloride, which can be discharged after being treated to meet the standards.

[0036] According to some embodiments of the present invention, in step S3, the washing temperature is 10-60°C.

[0037] According to some embodiments of the present invention, in step S3, the washing temperature is 20-40°C.

[0038] According to some embodiments of the present invention, in step S3, the washing time is 2 to 30 minutes.

[0039] According to some embodiments of the present invention, in step S3, the washing time is 5 to 15 minutes.

[0040] According to some embodiments of the present invention, in step S3, the number of washing stages is 2 to 6.

[0041] According to some embodiments of the present invention, in step S3, the flow ratio of washing is 10:1 to 1:5.

[0042] According to some embodiments of the present invention, in step S3, the flow ratio of washing is 10:1 to 4:1.

[0043] According to some embodiments of the present invention, in step S4, the alkaline solution includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0044] According to some embodiments of the present invention, in step S4, the concentration of sodium ions in the alkaline solution is 0.5 mol / L to 5 mol / L.

[0045] According to some embodiments of the present invention, in step S4, the concentration of sodium ions in the alkaline solution is 2 mol / L to 5 mol / L.

[0046] According to some embodiments of the present invention, in step S4, the stripping temperature is 10-60°C.

[0047] According to some embodiments of the present invention, in step S4, the stripping temperature is 20-40°C.

[0048] According to some embodiments of the present invention, in step S4, the stripping time is 2 to 30 minutes.

[0049] According to some embodiments of the present invention, in step S4, the stripping time is 5 to 15 minutes.

[0050] According to some embodiments of the present invention, in step S4, the number of stripping stages is 2 to 6.

[0051] According to some embodiments of the present invention, in step S4, the flow ratio of stripping is 1:5 to 10:1.

[0052] According to some embodiments of the present invention, in step S4, the flow ratio of stripping is 10:1 to 5:1.

[0053] According to some embodiments of the present invention, in step S4, when the number of stripping stages is greater than 2, the extraction method is countercurrent stripping.

[0054] According to some embodiments of the present invention, in step S4, the content of sodium thioglycolate in the sodium thioglycolate enriched solution is 1 mol / L to 10 mol / L.

[0055] According to some embodiments of the present invention, the organic phase after stripping produced in step S4 can be returned to step S3 after being washed with water to realize the recycling of the extractant.

[0056] According to some embodiments of the present invention, in step S5, the precipitant includes acetone or a lower alcohol.

[0057] According to some embodiments of the present invention, in step S5, the lower alcohol includes at least one of methanol, ethanol and isopropanol.

[0058] According to some embodiments of the present invention, in step S5, the lower alcohol is a mixed alcohol.

[0059] According to some embodiments of the present invention, in step S5, in the mixed alcohol, by volume, the content of methanol is 30-90%, the content of ethanol is 30-90%, and the content of isopropanol is 10-70%.

[0060] According to some embodiments of the present invention, in step S5, the lower alcohol is a single methanol followed by ethanol.

[0061] According to some embodiments of the present invention, in step S5, the amount of the precipitant added is 0.3 to 3 times the volume of the sodium thioglycolate enriched solution.

[0062] According to some embodiments of the present invention, in step S5, the amount of the precipitant added is 0.8 to 1.2 times the volume of the sodium thioglycolate enriched solution.

[0063] According to some embodiments of the present invention, in step S5, the temperature of the crystallization is 5 to 50°C.

[0064] According to some embodiments of the present invention, in step S5, the crystallization time is 2 to 6 hours.

[0065] According to some embodiments of the present invention, after the precipitant is filtered to obtain sodium thioglycolate crystals, it can be recovered by vacuum distillation at a distillation temperature of 60 to 90° C. and a pressure of -0.09 MPa.

[0066] According to some embodiments of the present invention, in step S5, the drying method is vacuum drying, the drying time is 1 to 4 hours, and the temperature is 40 to 60°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The present invention discloses a process flow chart for extracting and recovering sodium thioglycolate from synthetic wastewater.

[0068] Figure 2 This is the species distribution diagram of thioglycolic acid and its sodium salt at different pH values.

[0069] Figure 3 This is the XRD pattern of the sodium thioglycolate product recovered and prepared in Example 5. DETAILED DESCRIPTION

[0070] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0071] In a first aspect, in some embodiments of the present invention, there is provided a method for recovering sodium thioglycolate from ethionylthiocarbamate synthesis wastewater, comprising the following steps:

[0072] S1: Adjust the pH of the wastewater so that all the sodium thioglycolate in the wastewater is converted into thioglycolic acid;

[0073] S2: extracting thioglycolic acid by extracting the organic phase, and separating the upper organic phase loaded with thioglycolic acid and the raffinate;

[0074] S3: washing the loaded organic phase produced in step S2 with water to remove impurities;

[0075] S4: stripping the washed loaded organic phase produced in step S3 with an alkaline solution to obtain a sodium thioglycolate-enriched solution;

[0076] S5: adding a precipitant to the sodium thioglycolate enriched solution obtained in step S4 to crystallize the sodium thioglycolate, filtering to obtain the sodium thioglycolate crystals, and drying them.

[0077] It should be noted that, in view of the high toxicity of the existing thioglycolic acid, the present invention constructs a series of thioglycolic acid efficient extraction systems, avoiding the use of highly toxic organic solvents such as ether and toluene. In view of the high energy consumption and easy oxidation of the product in the evaporation and crystallization process of sodium thioglycolate, the present invention adds lower alcohols such as methanol, ethanol, isopropanol, etc. to the sodium thioglycolate enriched solution at room temperature to directly crystallize and precipitate sodium thioglycolate. Specifically, the present invention first converts the sodium thioglycolate in the wastewater into thioglycolic acid by adjusting the pH value, and then uses an organic phase whose main component is a neutral phosphorus extractant (compared with the prior art, the extractant is different, and the extractant used in the disclosed method is ether) to extract the thioglycolic acid in the synthetic wastewater.

[0078] Furthermore, the present invention enriches sodium thioglycolate in a stripping solution by washing and stripping, and then changes the polarity of the solution by adding a lower alcohol to the stripping solution containing sodium thioglycolate, thereby causing the sodium thioglycolate to crystallize and precipitate (compared with the prior art, the crystallization method is different, and the crystallization method of the disclosed method is evaporation crystallization).

[0079] It should also be noted that, compared with the prior art, the difference of the present invention is that the extractant used in the present invention is a neutral phosphorus extractant, which is widely used in the extraction of metal ions, but has not been used for the extraction of sodium thioglycolate.

[0080] More importantly, the present invention avoids the use of highly toxic traditional extractants such as ether and toluene by constructing a new extraction system, and has the advantages of high extraction rate, low toxicity and good recycling performance.

[0081] After the sodium thioglycolate enriched solution is obtained by extraction and stripping, the conventional method prepares the sodium thioglycolate solid by evaporation and crystallization, but there are problems of high energy consumption and easy oxidation of the sodium thioglycolate. However, the present invention directly crystallizes and precipitates the sodium thioglycolate by adding a lower alcohol to the sodium thioglycolate enriched solution, which has the characteristics of low energy consumption and high purity of the sodium thioglycolate product.

[0082] In combination with the first aspect, in some embodiments of the present invention, in step S1, the content of sodium thioglycolate in the wastewater is 5-40wt%.

[0083] In combination with the first aspect, in some embodiments of the present invention, in step S1, the initial pH of the wastewater is 7.5-10.5.

[0084] In combination with the first aspect, in some embodiments of the present invention, in step S1, the pH of the wastewater is adjusted to 0-2.

[0085] In combination with the first aspect, in some embodiments of the present invention, in step S1, the pH of the wastewater can be adjusted by using at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0086] In combination with the first aspect, in some embodiments of the present invention, in step S1, when adjusting the pH of the wastewater, the concentration of hydrogen ions in the acid solution is maintained at 1 to 20 mol / L.

[0087] In combination with the first aspect, in some embodiments of the present invention, in step S1, when adjusting the pH of the wastewater, the concentration of hydrogen ions in the acid solution is maintained at 10 to 20 mol / L.

[0088] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extracted organic phase includes a neutral phosphorus extractant with a volume fraction of 10 vol% to 80 vol% and a diluent with a volume fraction of 20 vol% to 90 vol%.

[0089] In combination with the first aspect, in some embodiments of the present invention, the neutral phosphorus extractant includes at least one of tributyl phosphate (TBP), trioctyl phosphate (TOP), trialkyl phosphine oxide (TRPO or Cyanex923), trioctyl phosphine oxide (TOPO), methyl phosphonic acid (1-methylheptyl) ester (P350) and tributyl phosphine oxide (TBPO).

[0090] It should be noted that in the present invention, neutral phosphorus extractants are organic compounds used in the extraction process of metal ions or other compounds, including but not limited to phosphate and phosphonate compounds. These compounds can form complexes or ion pairs with the target substance thioglycolic acid during the extraction process, thereby achieving effective separation. Therefore, in addition to the above-mentioned reagents, other reagents that can achieve the same or similar effects also belong to the "neutral phosphorus extractants" of the present invention.

[0091] In combination with the first aspect, in some embodiments of the present invention, the diluent includes at least one of sulfonated kerosene, No. 260 solvent oil, aviation kerosene, cyclohexane, n-heptane and ether.

[0092] In combination with the first aspect, in some embodiments of the present invention, in step S2, the organic phase of the neutral phosphorus extractant includes a neutral phosphorus extractant with a volume fraction of 10 vol% to 80 vol% and a diluent of 20 vol% to 90 vol%, such as 20% TBP+40 TRPO%+40% sulfonated kerosene, or 40% TOP+60% No. 260 solvent oil.

[0093] In combination with the first aspect, in some embodiments of the present invention, in step S2, the organic phase of the neutral phosphorus extractant includes a volume fraction of 40 vol% to 70 vol% of the neutral phosphorus extractant and 30 vol% to 60 vol% of the diluent.

[0094] In combination with the first aspect, in some embodiments of the present invention, in step S2, the temperature for extracting thioglycolic acid is 10-60°C.

[0095] In combination with the first aspect, in some embodiments of the present invention, in step S2, the temperature for extracting thioglycolic acid is 20-40°C.

[0096] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extraction time for extracting thioglycolic acid is 2 to 30 minutes.

[0097] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extraction time for extracting thioglycolic acid is 5 to 15 minutes.

[0098] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extraction stage of extracting thioglycolic acid is 2 to 6 stages.

[0099] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extraction flow ratio of extracting thioglycolic acid is 1:5 to 10:1.

[0100] In combination with the first aspect, in some embodiments of the present invention, in step S2, the extraction flow ratio of extracting thioglycolic acid is 1:2 to 4:1.

[0101] In combination with the first aspect, in some embodiments of the present invention, in step S2, when the number of extraction stages is greater than 2, the extraction method is countercurrent extraction.

[0102] In combination with the first aspect, in some embodiments of the present invention, in step S2, the raffinate produced after extracting thioglycolic acid is mainly composed of sodium chloride, which can be discharged after being treated to meet the standards.

[0103] In combination with the first aspect, in some embodiments of the present invention, in step S3, the washing temperature is 10-60°C.

[0104] In combination with the first aspect, in some embodiments of the present invention, in step S3, the washing temperature is 20-40°C.

[0105] In combination with the first aspect, in some embodiments of the present invention, in step S3, the washing time is 2 to 30 minutes.

[0106] In combination with the first aspect, in some embodiments of the present invention, in step S3, the washing time is 5 to 15 minutes.

[0107] In combination with the first aspect, in some embodiments of the present invention, in step S3, the number of washing stages is 2 to 6.

[0108] In combination with the first aspect, in some embodiments of the present invention, in step S3, the flow ratio of washing is 10:1 to 1:5.

[0109] In combination with the first aspect, in some embodiments of the present invention, in step S3, the flow ratio of washing is 10:1 to 4:1.

[0110] In combination with the first aspect, in some embodiments of the present invention, in step S4, the alkaline solution includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0111] In combination with the first aspect, in some embodiments of the present invention, in step S4, the concentration of sodium ions in the alkaline solution is 0.5 mol / L to 5 mol / L.

[0112] In combination with the first aspect, in some embodiments of the present invention, in step S4, the concentration of sodium ions in the alkaline solution is 2 mol / L to 5 mol / L.

[0113] In combination with the first aspect, in some embodiments of the present invention, in step S4, the stripping temperature is 10-60°C.

[0114] In combination with the first aspect, in some embodiments of the present invention, in step S4, the stripping temperature is 20-40°C.

[0115] In combination with the first aspect, in some embodiments of the present invention, in step S4, the stripping time is 2 to 30 minutes.

[0116] In combination with the first aspect, in some embodiments of the present invention, in step S4, the stripping time is 5 to 15 minutes.

[0117] In combination with the first aspect, in some embodiments of the present invention, in step S4, the number of stripping stages is 2 to 6.

[0118] In combination with the first aspect, in some embodiments of the present invention, in step S4, the flow ratio of stripping is 1:5 to 10:1.

[0119] In combination with the first aspect, in some embodiments of the present invention, in step S4, the flow ratio of stripping is 10:1 to 5:1.

[0120] In combination with the first aspect, in some embodiments of the present invention, in step S4, when the number of stripping stages is greater than 2, the extraction method is countercurrent stripping.

[0121] In combination with the first aspect, in some embodiments of the present invention, in step S4, the content of sodium thioglycolate in the sodium thioglycolate enriched solution is 1 mol / L to 10 mol / L.

[0122] In combination with the first aspect, in some embodiments of the present invention, the organic phase after stripping produced in step S4 can be returned to step S3 after being washed with water to achieve recycling of the extractant.

[0123] In combination with the first aspect, in some embodiments of the present invention, in step S5, the precipitant includes acetone or a lower alcohol.

[0124] In combination with the first aspect, in some embodiments of the present invention, in step S5, the lower alcohol includes at least one of methanol, ethanol and isopropanol.

[0125] In combination with the first aspect, in some embodiments of the present invention, in step S5, the lower alcohol is a mixed alcohol.

[0126] In combination with the first aspect, in some embodiments of the present invention, in step S5, in the mixed alcohol, by volume, the content of methanol is 30-90%, the content of ethanol is 30-90%, and the content of isopropanol is 10-70%.

[0127] In combination with the first aspect, in some embodiments of the present invention, in step S5, the lower alcohol is a single methanol followed by ethanol.

[0128] In combination with the first aspect, in some embodiments of the present invention, in step S5, the amount of precipitant added is 0.3 to 3 times the volume of the sodium thioglycolate enriched solution.

[0129] In combination with the first aspect, in some embodiments of the present invention, in step S5, the amount of precipitant added is 0.8 to 1.2 times the volume of the sodium thioglycolate enriched solution.

[0130] In combination with the first aspect, in some embodiments of the present invention, in step S5, the temperature of crystallization is 5-50°C.

[0131] In combination with the first aspect, in some embodiments of the present invention, in step S5, the crystallization time is 2 to 6 hours.

[0132] In combination with the first aspect, in some embodiments of the present invention, after the precipitant is filtered to obtain sodium thioglycolate crystals, it can be recovered by vacuum distillation, with a distillation temperature of 60 to 90° C. and a pressure of -0.09 MPa.

[0133] In combination with the first aspect, in some embodiments of the present invention, in step S5, the drying method is vacuum drying, the drying time is 1 to 4 hours, and the temperature is 40 to 60°C.

[0134] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0135] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0136] Unless otherwise specified, "room temperature" in the present invention means 25°C±5°C.

[0137] Unless otherwise specified, "about" in the present invention means that the allowable error is within ±2%.

[0138] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0139] It should be noted that ethionamide is a mineral processing agent with a molecular formula of C6H 13 NOS, ethylthiocarbamate is synthesized industrially by the xanthate esterification-ammonolysis method, and sodium chloride and sodium thioglycolate will be produced as by-products during the synthesis process.

[0140] Sodium thioglycolate is a by-product produced during the synthesis of ethiocarbamide.

[0141] Thioglycolic acid is an organic acid that can be obtained by acidifying sodium thioglycolate.

[0142] Figure 1 The present invention discloses a process flow chart for extracting and recovering sodium thioglycolate from synthetic wastewater.

[0143] The process consists of five parts: adjusting pH value, solvent extraction, washing of loaded organic phase, back extraction and crystallization of sodium thioglycolate.

[0144] The innovation and advancement of this process are mainly reflected in two aspects:

[0145] 1) Existing public materials all use organic solvents such as ether, toluene, and dichloromethane to extract thioglycolic acid, while the present invention uses low-toxic neutral phosphorus extractants TBP, TOP, TRPO, TOPO, and Cyanex923 to extract thioglycolic acid, solving the problems of high toxicity and low extraction efficiency of traditional methods;

[0146] 2) After obtaining the sodium thioglycolate enriched solution, the existing process generally adopts the method of evaporation and crystallization to prepare the sodium thioglycolate product, but the sodium thioglycolate is easily oxidized and deteriorated during the evaporation process. The present invention can crystallize the sodium thioglycolate at room temperature by adding lower alcohols such as methanol, ethanol, isopropanol, etc. to the enriched solution, which has the advantages of low energy consumption and high product purity.

[0147] Example 1

[0148] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0149] The ethylthiocarbamide synthesis wastewater contains 20wt% sodium thioglycolate and the initial pH value is 8.5.

[0150] First, the pH was adjusted to 1.0 with 1:1 hydrochloric acid to convert the sodium thioglycolate in the wastewater into thioglycolic acid.

[0151] Then, the following five extraction organic phases consisting of a single extraction solvent and a diluent were used to extract thioglycolic acid:

[0152] 1#: 50% TBP + 50% sulfonated kerosene;

[0153] 2#: 50% TOP + 50% sulfonated kerosene;

[0154] 3#: 50% TRPO + 50% sulfonated kerosene;

[0155] 4#: 50%TOPO+50%cyclohexane;

[0156] 5#: 50% Cyanex923 + 50% sulfonated kerosene.

[0157] When the above extraction organic phase is used to extract thioglycolic acid, the operating conditions are kept consistent, that is, the extraction flow ratio is 1:1, the extraction time is 10 minutes, the extraction temperature is 25°C, and the extraction level is 1.

[0158] The extraction test results are shown in Table 1.

[0159] Example 1 shows that neutral extractants such as TBP, TOP, TRPO, TOPO, and Cyanex923 have good extraction effects on thioglycolic acid. The extraction effects of TRPO, TOPO, and Cyanex923 are comparable, but significantly stronger than those of TBP and TOP.

[0160] Table 1 Extraction effect of different organic phases on thioglycolic acid

[0161]

[0162]

[0163] Example 2

[0164] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0165] The ethylthiocarbamate synthesis wastewater contains 40wt% sodium thioglycolate and the initial pH value is 10.5.

[0166] First, the pH was adjusted to 1.0 with 1:1 sulfuric acid to convert the sodium thioglycolate in the wastewater into thioglycolic acid.

[0167] Then, the following five composite extraction organic phases were used to extract thioglycolic acid:

[0168] 1#: 10% TBP + 30% TRPO + 60% sulfonated kerosene;

[0169] 2#: 40% TOP + 10% TRPO + 50% sulfonated kerosene;

[0170] 3#: 20% Cyanex923 + 20% TBP + 20% TOPO + 40% cyclohexane;

[0171] 4#: 50% Cyanex923+20% TBP+30% sulfonated kerosene;

[0172] 5#: 30% Cyanex923+10% TBP+40% TRPO+20% sulfonated kerosene.

[0173] When the above composite extraction organic phase is used to extract thioglycolic acid, the operating conditions are kept consistent.

[0174] That is, the extraction flow ratio is 2:1, the extraction time is 10 min, the extraction temperature is 25°C, and the extraction level is 1. The extraction experimental results are shown in Table 2.

[0175] Example 2 shows that the use of two or more neutral extractants as a composite extractant also has a good extraction effect. The higher the volume concentration of the extractant, the higher the extraction rate of thioglycolic acid.

[0176] Table 2 Effect of compound extraction organic phase on thioglycolic acid extraction

[0177]

[0178] Example 3

[0179] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0180] The ethylthiocarbamate synthesis wastewater contains 20wt% sodium thioglycolate and the initial pH value is 7.5.

[0181] First, the pH was adjusted to 0-2 with 1:1 nitric acid, and then thioglycolic acid was extracted with an organic extracting phase consisting of 30% TBP+20% TRPO+50% sulfonated kerosene.

[0182] The extraction flow ratio is 1:1, the extraction time is 10 min, the extraction temperature is 25 °C, and the extraction level is 3.

[0183] The extraction test results are shown in Table 3.

[0184] Example 3 shows that the initial pH value has a great influence on the extraction effect of thioglycolic acid. In order to obtain a higher extraction rate, it is best to control the pH value to about 1.

[0185] Figure 2is the distribution diagram of species of thioglycolic acid and its sodium salt at different pH values, Figure 2 It can be seen that when the pH is less than 2, the thioglycolic acid molecule is the main species.

[0186] Therefore, after adjusting the pH value of the synthetic wastewater to 0-2, thioacetic acid can be extracted using a neutral phosphorus extractant such as TBP (tributyl phosphate), TOP (trioctyl phosphate), TRPO (trialkyl phosphine oxide), TOPO (trioctyl phosphine oxide), and Cyanex923 (trialkyl phosphine oxide).

[0187] Table 3 Effect of initial pH value of feed solution on the extraction effect of thioglycolic acid

[0188] Initial pH Extraction rate % 0 99.76 0.5 99.37 1 99.34 1.5 90.39 2.0 52.19

[0189] Example 4

[0190] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0191] The ethylthiocarbamate synthesis wastewater contains 25wt% sodium thioglycolate and the initial pH value is 8.5.

[0192] First, the pH was adjusted to 0.5 with 1:1 sulfuric acid, and then the organic phase composition of 30% TBP+20% TRPO+50% sulfonated kerosene was used for extraction with thioglycolic acid.

[0193] The extraction flow ratio is 1:5-10:1, the extraction time is 15 minutes, the extraction temperature is 15°C, and the extraction level is 1.

[0194] The extraction test results are shown in Table 4, which shows that the larger the extraction flow ratio, the higher the extraction rate.

[0195] Table 4 Effect of initial pH value of feed solution on thioglycolic acid extraction effect

[0196] Extraction flow ratio (O / A) Extraction rate % 1:5 20.14 1:3 39.71 1:1 88.17 2:1 90.19 5:1 98.78 7:1 99.52 10:1 99.91

[0197] Example 5

[0198] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0199] The ethylthiocarbamate synthesis wastewater contains 20wt% sodium thioglycolate, and the initial pH value is 8.5. The following steps are used to recover sodium thioglycolate:

[0200] 1) The pH value of the synthetic wastewater was adjusted to 0.5 using 1:1 hydrochloric acid;

[0201] 2) The organic phase composed of 40% TBP + 20% Cyanex923 + 40% 260 solvent oil was used to extract thioglycolic acid; the extraction flow ratio was 1:1, the extraction time was 10 minutes, the extraction temperature was 30°C, and the extraction level was 3. The extraction rate of thioglycolic acid reached 99.42%;

[0202] 3) washing the loaded organic phase produced in step 2) with pure water, with a washing flow ratio of 5:1, a washing time of 10 min, a temperature of 40° C., and a stage number of 1. After washing, the washing water and the loaded organic phase are separated, and the washed loaded organic phase is collected for the next step of the experiment;

[0203] 4) stripping the loaded organic phase produced in step 3) with a 5 mol / L sodium hydroxide solution, with a stripping flow ratio of 5:1, a stripping time of 10 min, a temperature of 25° C., and a level of 3. The stripping rate of thioglycolic acid reached 97.17%;

[0204] 5) adding an equal volume of methanol to the stripping solution produced in step 4), stirring at room temperature for 2 hours and filtering to obtain sodium thioglycolate crystals.

[0205] After testing, the crystallization rate of sodium thioglycolate was 90.17%.

[0206] The purity of sodium thioglycolate was tested in accordance with YS / T653-2018 "Sodium Thioglycolate for Nonferrous Metal Ore Dressing", and the purity reached 98%.

[0207] Figure 3 : is the XRD pattern of the sodium thioglycolate product recovered and prepared in this embodiment. Figure 3 Clear diffraction peaks can be observed, indicating that the sample has good crystallinity, and the high intensity of the peaks also indicates that the product has high purity.

[0208] Example 6

[0209] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0210] The sodium thioglycolate enriched solution containing 5 mol / L sodium thioglycolate is obtained after extraction-stripping of the ethylthiocarbamate synthetic wastewater.

[0211] Add equal volumes of precipitant to the enriched solution and react at 25°C for 6 hours:

[0212] 1#: methanol;

[0213] 2#: ethanol;

[0214] 3#: Isopropyl alcohol;

[0215] 4#: methanol / ethanol 1:1 mixed solution;

[0216] 5#: methanol / isopropanol 1:1 mixed solution;

[0217] 6#: 1:1 mixed solution of ethanol / isopropanol;

[0218] 7#: Methanol / ethanol / isopropanol 1:1:1 mixed solution.

[0219] The crystallization rate of sodium thioglycolate is shown in Table 5.

[0220] Table 5 Effect of precipitant on precipitation rate of sodium thioglycolate

[0221]

[0222] Comparative Example 1

[0223] The specific steps of recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater are as follows:

[0224] The synthetic wastewater of ethylthiocarbamate contains 20wt% sodium thioglycolate, and the initial pH value is 8.5. First, the pH value of the synthetic wastewater is adjusted to 1.0 using 1:1 hydrochloric acid, and then the thioglycolic acid in the acidified wastewater is extracted using 100% ether and an extraction organic phase composed of 50% TBP+50% sulfonated kerosene, respectively, with an extraction flow ratio of 1:1, an extraction time of 10min, an extraction temperature of 25°C, and an extraction level of 1.

[0225] The experimental results show that when 100% ether is used for extraction, the extraction rate of thioglycolic acid is 48.72%, while when the organic phase extraction is composed of 50% TBP + 50% sulfonated kerosene, the extraction rate of thioglycolic acid reaches 72.44%.

[0226] This comparative example shows that the neutral phosphorus extractant TBP has a significantly better extraction effect on thioglycolic acid than traditional ether, and TBP is not easily volatile and has low toxicity.

[0227] Therefore, compared with traditional organic solvents such as ether and toluene, neutral phosphorus extractants have the advantages of good extraction effect and low toxicity.

[0228] In view of the problem of high toxicity of existing thioglycolic acid, the present invention constructs a series of thioglycolic acid efficient extraction systems, avoiding the use of highly toxic organic solvents such as ether and toluene. In view of the problems of high energy consumption and easy oxidation of the product in the evaporation and crystallization process of sodium thioglycolate, the present invention adds lower alcohols such as methanol, ethanol, isopropanol, etc. to the sodium thioglycolate enriched solution at room temperature to directly crystallize and precipitate sodium thioglycolate. Specifically, the present invention first converts sodium thioglycolate in the wastewater into thioglycolic acid by adjusting the pH value, and then uses a neutral phosphorus extractant mixed with an organic phase (compared with the prior art, the extractant is different, and the extractant used in the disclosed method is ether) to extract the thioglycolic acid in the synthetic wastewater.

[0229] In addition, the present invention enriches sodium thioglycolate in a stripping solution by extraction and stripping, and then changes the polarity of the solution by adding a lower alcohol to the stripping solution containing sodium thioglycolate, thereby causing the sodium thioglycolate to crystallize and precipitate (compared with the prior art, the crystallization method is different, and the crystallization method of the disclosed method is evaporation crystallization).

[0230] Compared with the prior art, the present invention is different in that the extractant used in the present invention is a neutral phosphorus extractant, which is widely used in the extraction of metal ions, but has not been used for the extraction of sodium thioglycolate.

[0231] After the sodium thioglycolate enriched solution is obtained by extraction and stripping, the conventional method prepares the sodium thioglycolate solid by evaporation and crystallization, but there are problems of high energy consumption and easy oxidation of the sodium thioglycolate. However, the present invention directly crystallizes and precipitates the sodium thioglycolate by adding a lower alcohol to the sodium thioglycolate enriched solution, which has the characteristics of low energy consumption and high purity of the sodium thioglycolate product.

[0232] The present invention has been described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for recovering sodium thioglycolate from ethylthiocarbamate synthesis wastewater, characterized in that: The following steps are involved: S1: Adjust the pH of the wastewater so that all the sodium thioglycolate in the wastewater is converted into thioglycolic acid; S2: extracting thioglycolic acid by extracting the organic phase, and separating the upper organic phase loaded with thioglycolic acid and the raffinate; S3: washing the loaded organic phase produced in step S2 with water to remove impurities; S4: stripping the washed loaded organic phase produced in step S3 with an alkaline solution to obtain a sodium thioglycolate-enriched solution; S5: adding a precipitant to the sodium thioglycolate enriched solution obtained in step S4 to crystallize the sodium thioglycolate, filtering to obtain the sodium thioglycolate crystals, and drying them.

2. The method according to claim 1, characterized in that: In step S1, the content of sodium thioglycolate in the wastewater is 5-40wt%, the initial pH of the wastewater is 7.5-10.5, and the pH of the wastewater is adjusted to 0-2.

3. The method according to claim 1, characterized in that In step S2, the extraction organic phase includes a neutral phosphorus extractant with a volume fraction of 10 vol% to 80 vol% and a diluent with a volume fraction of 20 vol% to 90 vol%.

4. The method according to claim 3, characterized in that The neutral phosphorus extractant includes at least one of tributyl phosphate, trioctyl phosphate, trialkyl phosphine oxide, trioctyl phosphine oxide, methylphosphine (1-methylheptyl) phosphonate and tributyl phosphine oxide.

5. The method according to claim 3, characterized in that: The diluent includes at least one of sulfonated kerosene, No. 260 solvent oil, aviation kerosene, cyclohexane, n-heptane and ether.

6. The method according to claim 1, characterized in that In step S2, the temperature for extracting thioglycolic acid is 10 to 60° C.; and / or, the extraction time for extracting thioglycolic acid is 2 to 30 min; and / or, the number of extraction stages for extracting thioglycolic acid is 2 to 6; and / or, the extraction flow ratio for extracting thioglycolic acid is 1 / 5 to 10 / 1; and / or, when the number of extraction stages is greater than 2, the extraction method is countercurrent extraction.

7. The method according to claim 1, characterized in that In step S3, the washing temperature is 10-60°C; and / or the washing time is 2-30 min; and / or the number of washing stages is 2-6; and / or the flow ratio of washing is 10:1-1:

5.

8. The method according to claim 1, characterized in that: In step S4, the alkaline solution includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate; and / or, the concentration of sodium ions in the alkaline solution is 0.5 mol / L to 5 mol / L; and / or, in step S4, the stripping temperature is 10 to 60° C.; and / or, the stripping time is 2 to 30 min; and / or, the stripping stage is 2 to 6; and / or, the stripping flow ratio is 1:5 to 10:1; and / or, when the stripping stage is greater than 2, the extraction method is countercurrent stripping; and / or, in step S4, the content of sodium thioglycolate in the sodium thioglycolate enriched solution is 1 mol / L to 10 mol / L.

9. The method according to claim 1, characterized in that: In step S5, the precipitant includes acetone or a lower alcohol; and / or the lower alcohol includes at least one of methanol, ethanol and isopropanol; the amount of the precipitant added is 0.3 to 3 times the volume of the sodium thioglycolate enriched solution.

10. The method according to claim 1, characterized in that In step S5, the crystallization temperature is 5 to 50° C.; and / or the crystallization time is 2 to 6 hours.

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