Method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic matters in naphthol wastewater

Abstract

According to the method, when the concentration of sodium sulfate decahydrate and sodium sulfite heptahydrate in wastewater is nearly saturated, pure sodium sulfate hydrate mixed salt can be separated out by water cooling at the temperature of 10-25 DEG C, so that pure sodium sulfate and sodium sulfite hydrate mixed salt crystals are obtained; organic matters adsorbed on the surface of the hydrate mixed salt are eluted and decolored in a manner of washing with dilute alkali liquor, and the sodium sulfate hydrate mixed salt subjected to alkali washing and decoloring completely meets the technical index requirements for preparing anhydrous sodium sulfite / sodium pyrosulfite; according to the method, naphthalene sulfonic acid organic matters are separated from alpha / beta naphthalene sulfonate, sulfone and other organic matters (TOC) contained in wastewater through heat preservation and filtration by utilizing the characteristic that the solubility of the organic matters in nearly saturated saline water is extremely low; therefore, after the organic wastewater containing sodium sulfate, sodium sulfite and other salts can be repeatedly evaporated and concentrated to be nearly saturated, pure and decolored sodium sulfate hydrate mixed salt and low-salt naphthalene sulfonic acid organic matters are separated from the wastewater by adopting the modes of insulating and filtering to remove organic matters, water-cooling to separate out salt and alkali washing; after the process scheme is industrially implemented, the naphthol wastewater treatment can avoid the traditional treatment method for removing organic matters by resin adsorption or extraction, and sodium sulfate mixed salts and naphthalene sulfonic acid organic matters in the wastewater are directly purified, so that the wastewater treatment cost and investment are greatly reduced; according to the process route, the bottleneck problem of high treatment cost of the naphthol wastewater is solved, and resource recycling of the wastewater and the waste salt is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection wastewater treatment, and particularly relates to a method for purifying sodium sulfate hydrate mixed salt from naphthol wastewater and recycling naphthalene sulfonic acid organic matter. BACKGROUND

[0002] Naphthol is an important fine chemical, and α-naphthol is also called mononaphthol, and β-naphthol is also called dinaphthol. At present, the production of naphthol still adopts the traditional sulfuric acid sulfonation production process, that is, refined naphthalene is used as raw material to produce naphthol through the processes of sulfonation, hydrolysis, neutralization, alkali fusion, acidification, and refining. Taking β-naphthol as an example, a large amount of organic wastewater with high salt and high TOC is generated in the production process, and about 6.5-8.0 cubic meters of production wastewater is generated per ton of β-naphthol. The naphthol wastewater is generally dark brown due to the high content of naphthalene sulfonic acid organic matter, and the salt content mainly includes inorganic salts such as sodium sulfate and sodium sulfite. The inorganic salt content is about 10.0-15.0%, and the naphthalene sulfonic acid organic matter content is 55,000.0-80,000.0 mg / L. The main components mainly include α-naphthalene sulfonic acid sodium, β-naphthalene sulfonic acid sodium, and a small amount of sulfone, pyrosulfonic acid, sulfonic acid anhydride, and naphthalene isomers. If such highly polluted wastewater is not treated, it will cause serious environmental pollution, and the most economical and effective treatment scheme is to separate and purify the large amount of inorganic salt and naphthalene sulfonic acid organic matter contained in the wastewater, so that they can be recycled and utilized.

[0003] At present, the main naphthol wastewater treatment processes include resin adsorption, extraction, high-temperature carbonization and incineration, membrane separation, chemical oxidation, and biochemical methods to separate organic matter in wastewater. The commonly used methods are mainly "resin adsorption method" and "solvent extraction method". The "resin adsorption method" has high operation conditions and requirements, short resin saturation time, frequent backwashing, large volume of regeneration liquid, and difficult resin regeneration. In addition, the resin is expensive and the device investment is large. The main disadvantage of the "solvent extraction method" is that the wastewater needs to be acidified, which consumes a large amount of sulfuric acid and alkali for back extraction, and the cost of alkali neutralization is also high. The membrane filtration method is prone to membrane clogging, and the membrane assembly needs to be frequently replaced, which has a higher operation cost. The direct chemical oxidation method consumes a large amount of oxidizing agent, which is costly. The biochemical method is not feasible for treating wastewater with high salt and high TOC. The main reason is that the naphthol wastewater is highly biotoxic and difficult to degrade, and the microorganisms required need to be specially domesticated and cultured. The resin adsorption method, solvent extraction method, and MVR or multi-effect evaporator combined method for treating naphthol wastewater can evaporate sodium sulfate mixed salt crystals in the form of solid from naphthol wastewater and concentrate naphthalene sulfonic acid organic matter through desorption or back extraction, but they cannot obtain relatively pure sodium sulfate and naphthalene sulfonic acid organic matter with low salt content and high utilization value. These colored and high-impurity-containing sodium sulfate and organic matter solid waste are difficult to be used as by-products for secondary utilization, and can only be disposed of by incineration or landfill. The obvious disadvantages are large investment, high energy consumption, and low recycling value.

[0004] The pure colorless sodium sulfate hydrate mixed salt (containing sodium sulfite) can be used as a raw material for producing sodium sulfite or sodium pyrosulfite. The naphthalene sulfonate organic matter contains 65-70% of sodium a-naphthalene sulfonate and 25-30% of sodium β-naphthalene sulfonate, which can be recycled as an intermediate for producing a-naphthol and returned to the workshop for reuse. In addition, the naphthalene sulfonate organic matter is an excellent surfactant, has strong dispersion and water reducing effects, and has high anti-coagulation, polymerization inhibition and stabilization effects on liquid fluid, and can be used as a dispersing, stabilizing and homogenizing additive for coal water slurry.

[0005] Currently, the naphthol wastewater treatment mainly uses the resin adsorption or solvent extraction method to separate the naphthalene sulfonate organic matter in the wastewater, and only removes most of the organic matter. The wastewater with colority is sent to the MVR or multi-effect evaporator for concentration and crystallization, the anhydrous sodium sulfate mixed salt with color and containing many organic impurities is separated, and the condensed water is returned to the workshop for reuse. The resin adsorption or solvent extraction needs to consume a large amount of liquid alkali (NaOH) to elute the organic matter adsorbed by the resin or the extraction agent, and a large amount of alkaline naphthalene sulfonate organic matter desorption liquid needs to be sent to the spray drying treatment, so the energy consumption is very high. Although it can meet the zero discharge disposal of naphthol wastewater, the resin adsorption capacity is small, the regeneration is difficult, the elution liquid volume is large (the concentration ratio of the original water volume is only 5-6 times), and a large amount of alkali is consumed. When the wastewater is treated by the extraction method, a series of problems such as a large amount of acid consumption in the acidification process, easy emulsification and loss of the extraction agent, flammability of the diluent, and high cost of the back-extraction alkali are difficult to overcome. In view of the process defects and technical problems in the naphthol wastewater treatment process, the present application provides a method for directly separating and purifying sodium sulfate hydrate mixed salt and naphthalene sulfonate organic matter from naphthol wastewater, which avoids the process route of using expensive resin adsorption or solvent extraction to treat naphthol wastewater. The present application utilizes the characteristics of sodium sulfate and sodium sulfite to form hydrates at room temperature. When the wastewater is concentrated to a near-saturated state at low temperature, the sodium sulfate hydrate mixed salt and the naphthalene sulfonate organic matter can be effectively separated by using the characteristics of sodium sulfate to form pure decahydrate crystals at room temperature and low temperature. The colorless solid-state hydrate mixed salt obtained is used as a raw material for producing sodium sulfite or sodium pyrosulfite, which improves the added value of the sodium sulfate mixed salt. The naphthalene sulfonate organic matter separated from the wastewater is also recycled as a solid-state intermediate for producing a-naphthol and returned to the naphthol production workshop for reuse, which is the best way for resource utilization of naphthol wastewater. SUMMARY

[0006] According to the solubility characteristics of sodium sulfate, sodium sulfite and naphthalene sulfonate organic matter in water in the naphthol wastewater, the solubility tables of sodium sulfate and sodium sulfite, and the solubility table of sodium β-naphthalene sulfonate in the sulfate solution are listed. Figure 2 、 Figure 3 、 Figure 4The properties of sodium sulfate and sodium sulfite in the handbook can be found that the solubility (wt%) of sodium sulfate and sodium sulfite is maximum 32.80 and 28.20 respectively at 30.0-40.0℃, the solubility of sodium β-naphthol sulfonate and other organic matters in sodium sulfate near-saturated solution is almost zero at 30.0-40.0℃, therefore, the organic matters and water in the wastewater can be removed by heat preservation and filtration at the temperature, and the pure sodium sulfate hydrate mixed salt can be precipitated, so that the organic matters in the wastewater can be separated from the sodium sulfate hydrate mixed salt, and then the organic matters adsorbed on the surface of the sodium sulfate hydrate mixed salt can be removed by alkali washing, thus the pure sodium sulfate mixed salt and the naphthalene sulfonic acid organic matters with low salt content can be obtained.

[0007] To achieve the above object, the present application adopts the following technical scheme:

[0008] The method for directly separating and purifying sodium sulfate hydrate mixed salt from naphthol wastewater and recycling naphthalene sulfonic acid organic matters comprises the following steps: firstly, filtering the naphthol wastewater cooled to the ambient temperature of 15-25℃ to remove naphthalene sulfonate organic precipitate A; concentrating the filtrate to a near-saturated state by low-temperature evaporation with an evaporator, and measuring the concentration of the filtrate with a hydrometer to be 1.25-1.38 g / cm 3 ; discharging the filtrate into an aging tank to stand for 1.0-6.0 hr at 30-35℃ to precipitate naphthalene sulfonic acid organic matters; filtering the organic matters B at 30-35℃; moving the filtrate into a crystallizer to precipitate salt by water cooling at ≤24℃, so that the sodium sulfate mixed salt is precipitated in the form of decahydrate and heptahydrate crystals; centrifugally spinning and drying the crystals; washing the sodium sulfate hydrate mixed salt with sodium hydroxide solution and centrifugally spinning and drying the mixed salt to obtain pure and decolorized sodium sulfate hydrate mixed salt crystals ①; continuously evaporating and concentrating the mother liquor to a near-saturated state under reduced pressure; standing the concentrated liquid for 1.0-6.0 hr at 30-35℃, and filtering naphthalene sulfonic acid organic matters C at the temperature; moving the filtrate into a crystallizer to precipitate salt by water cooling at ≤24℃, so that the sodium sulfate mixed salt is precipitated in the form of hydrate crystals; centrifugally spinning and drying the crystals; washing the sodium sulfate hydrate mixed salt with sodium hydroxide solution and centrifugally spinning and drying the mixed salt to obtain pure and decolorized sodium sulfate hydrate mixed salt crystals ②; adding 50% sulfuric acid to the remaining filtrate to adjust the pH value of the mother liquor to 2.0-4.5 to remove SO2; mixing the alkali washing liquid of the first and second times with the acidified mother liquor to neutralize the mixture; continuously evaporating and concentrating the mixture to a near-saturated state under low temperature; filtering the organic matters D at 30-35℃; returning the naphthalene sulfonic acid organic matter filter cakes A, B, C and D to the α-naphthol workshop for reuse; freezing and precipitating salt from the filtrate at ≤10℃ for 1.0-4.0 hr; centrifugally spinning and drying the precipitated sodium sulfate hydrate mixed salt and washing the mixed salt with dilute alkali to obtain pure and decolorized sodium sulfate hydrate mixed salt crystals ③; sending the remaining mother liquor to a spray dryer to obtain naphthalene sulfonic acid organic matter dry powder E with a salt content of ≤20%, which is used as a naphthalene sulfonic acid water reducing agent, a surfactant or an additive for coal water slurry; and mixing the purified and decolorized sodium sulfate hydrate mixed salt crystals ①, ② and ③ to obtain a mixture, which is used as a raw material for preparing sodium sulfite or sodium pyrosulfite.

[0009] The filtrate or mother liquor waste water evaporation concentration equipment is preferably MVR, multi-effect evaporator or other low-temperature vacuum evaporation concentration equipment, the evaporation concentration temperature is less than or equal to 80 DEG C, and distilled water is condensed and then returned to the workshop for recycling.

[0010] The sodium sulfate hydrate mixed salt caustic washing adopts 1.0-6.0% sodium hydroxide solution for countercurrent washing and decolorization, the caustic washing liquid dosage is 1 / 3-1 / 10 of the hydrate crystallization volume, and the caustic washing times of each batch of mixed salt are 2-3 times; the used caustic washing liquid is collected and used for neutralizing and acidifying the mother liquor and recycling.

[0011] After the naphthol waste water is separated for 4 times to obtain naphthalenesulfonic acid organic matter and 3 times to obtain salt, more than 82% sodium sulfate hydrate mixed salt can be purified from the naphthol waste water, and the concentration ratio of the original waste water volume to the mother liquor volume is 15-20 times.

[0012] The sodium sulfate mixed salt refers to anhydrous sodium sulfate containing anhydrous sodium sulfite; and the sodium sulfate hydrate mixed salt refers to ten-water sodium sulfate containing seven-water sodium sulfite.

[0013] SO2 discharged in the mother liquor acidification treatment is sent to an alkali absorption system for treatment.

[0014] The beneficial effects of the present application are as follows:

[0015] The present application aims at overcoming the series of problems in the naphthol waste water treatment process, such as large equipment investment, complex process, high energy consumption, difficult operation and the like, the traditional process has more organic matter and darker color in the anhydrous sodium sulfate mixed salt evaporated from the waste water, resulting in low added value, and the recovered naphthalenesulfonic acid organic matter has no secondary utilization value due to high salt content. The present application provides a method for directly separating pure sodium sulfate hydrate mixed salt and recovering low-salt naphthalenesulfonic acid organic matter from naphthol waste water. The method can obtain pure and decolorized sodium sulfate hydrate mixed salt and separated naphthalenesulfonic acid organic matter, which are returned to the workshop for secondary utilization, and the two are recovered and utilized as by-products, reducing the material consumption and energy consumption in the waste water treatment process, improving the utilization value of the by-product sodium sulfate mixed salt and the recovered naphthalenesulfonic acid organic matter, turning waste into treasure, saving energy and increasing efficiency; and the cost is low, the energy consumption is low, the benefit is high, the resource is realized and the zero emission target is achieved in the naphthol waste water treatment process.

[0016] 1) The method disclosed by the present application can purify and separate decolorized sodium sulfate hydrate mixed salt and recover naphthalene sulfonic acid organic matter from naphthol wastewater, so that it is resourceized and utilized, solves the problems of high investment and cost of naphthol wastewater treatment, deep color of byproduct sodium sulfate, and low secondary utilization value, realizes high value-added of byproducts while effectively treating wastewater; solves the problems of equipment fouling, pollution, and low energy efficiency caused by viscous material formed by naphthalene sulfonic acid organic matter and anhydrous sodium sulfate mixed salt during evaporation and concentration of wastewater; compared with the traditional resin adsorption or solvent extraction wastewater treatment process, the method omits the complicated process of resin adsorption desorption or solvent extraction regeneration, saves equipment investment and operation cost, greatly improves the wastewater treatment efficiency, and maximizes the economic benefit.

[0017] 2) The method disclosed by the present application is simple and easy to implement in industry. The decolorized sodium sulfate hydrate mixed salt and recovered naphthalene sulfonic acid organic matter can be purified by the method, the sodium sulfate hydrate mixed salt can be used to prepare sodium sulfite or sodium metabisulfite products, and the recovered pasty naphthalene sulfonic acid organic matter meets the quality requirements of production of a-naphthol. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the process flow chart of the method of the present application;

[0019] Figure 2 is the solubility table of sodium sulfate;

[0020] Figure 3 is the solubility table of sodium sulfite;

[0021] Figure 4 is the solubility table of sodium β-naphthalenesulfonate in sodium sulfate solution.

[0022] DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with examples. The specific examples described herein are only used to explain the present application, but the protection scope of the present application is not limited to the following examples.

[0024] Example 1

[0025] Example 1

[0026] Example 2

[0027] The 1000 L of the 2 times concentrated β-naphthol wastewater without resin adsorption was concentrated by MVR, and the naphthalene sulfonic acid organic precipitate A of 18.7 kg was filtered out at 30°C. The filtrate was moved to an evaporator to concentrate to a near saturated volume of 670.0 L, and the organic matter was precipitated at 33°C for 4.0 hr. The naphthalene sulfonic acid organic matter B of 14.3 kg was filtered out, and the filtrate was stirred at 23-24°C for 2.5 hr to precipitate the hydrate mixed salt. After centrifugal dewatering, the mixed salt was washed with 3.0% dilute lye of 17 L for 3 times. The total consumption of the lye was 51.0 L in the first lye washing, and the decolorized hydrate mixed salt ① of 276.7 kg was obtained. The remaining mother liquor had a volume of 410 L. The concentration was continued to a volume of about 350.0 L, and the precipitated organic matter was filtered to obtain the paste-like organic matter C of 38.5 kg after the mixture was kept at 33°C for 5.0 hr. The filtrate was precipitated at 23-24°C to obtain the mixed salt, which was washed with 2.0% lye for 3 times, 10.0 L each time, and the consumption of the lye was 30.0 L. The decolorized mixed salt ② of 186.5 kg was obtained, and the remaining mother liquor was about 160.0 L. 15.0 L of 50% sulfuric acid was added to acidify and remove SO2. The first, second and third lye washings of 51.0+30.0 L were combined with the mother liquor to continue the concentration to a near saturated state. The precipitated organic matter was filtered to obtain the paste-like organic matter D of 14.4 kg after the mixture was kept at 33°C for 4.0 hr. The naphthalene sulfonic acid organic matters A, B, C and D were combined to obtain a total of 85.9 kg, which was returned to the workshop for reuse. The filtrate was stirred in the water at ≤10°C for 4.0 hr to precipitate the hydrate mixed salt. The mixed salt ③ of 59.4 kg was obtained after centrifugal dewatering, washing with 2.0% dilute lye of 30.0 L for 3 times, 10.0 L each time, and centrifugal dewatering. The lye of 30.0 L was collected separately and used for the first lye washing of the mixed salt in the next batch. The concentrated liquid with a mixed salt concentration of ≤10% was obtained finally, and the solid organic matter E of 38.6 kg was obtained after drying and dewatering, which had a salt content of ≤20% and was used as a naphthalene water reducing agent, a surfactant or a coal water slurry additive. The sodium sulfate hydrate mixed salts ①, ② and ③ were combined to obtain a total of 522.6 kg, which was equivalent to the yield of 82.3% of anhydrous sodium sulfate.

[0028] Example 3

[0029] The 1000 L of the 2 times concentrated β-naphthol wastewater without resin adsorption was concentrated by MVR, and the naphthalene sulfonic acid organic precipitate A: 22.6 kg was filtered out at 31℃. The filtrate was moved to an evaporator to concentrate to a near saturated (density 1.34-1.36) volume of 690.0 L, and the organic matter was precipitated at 34℃ for 3.5 hr. The naphthalene sulfonic acid organic matter B: 12.5 kg was filtered out, and the filtrate was stirred at ≤20℃ for 2.0 hr to precipitate the hydrate mixed salt. After centrifugal dewatering, the mixed salt was washed with 2.5% dilute lye 19 L for 3 times, and the total consumption of lye was 57.0 L in the first lye washing to obtain the decolorized hydrate mixed salt ① 294.6 kg, and the remaining mother liquor had a volume of 450 L. The concentration was continued to a volume of about 350.0 L, and the precipitated organic matter was filtered to obtain the paste-like organic matter C: 50.4 kg after standing at 34℃ for 5.0 hr. The filtrate was precipitated at ≤20℃ to obtain the mixed salt, which was washed with 2.5% lye 3 times, 15.0 L each time, and the consumption of lye was 45.0 L to obtain the decolorized mixed salt ② 157.9 kg, and the remaining mother liquor was about 170.0 L. 12.0 L of 50% sulfuric acid was added for acidification to remove SO2, and the first and second lye 57.0+45.0 L was combined with the mother liquor and concentrated to a near saturated state. After standing at 33℃ for 4.0 hr, the precipitated organic matter was filtered to obtain the paste-like organic matter D: 25.3 kg, and the naphthalene sulfonic acid organic matters A, B, C and D were combined to return to the workshop for 110.8 kg of re-use. The filtrate was stirred in the frozen water at ≤10℃ for 3.0 hr to precipitate the hydrate mixed salt, which was centrifuged to remove water, washed with 2.5% dilute lye 36.0 L for 3 times, 12.0 L each time, and centrifuged to obtain the pure white hydrate mixed salt ③ 78.6 kg. The 36.0 L of lye was collected separately and used for the first lye washing of the mixed salt in the next batch. Finally, the concentrated liquid with a mixed salt concentration of ≤10% was obtained in a volume of 80.0-85.0 L, and the solid organic matter E: 33.2 kg was obtained after drying and dewatering, which had a salt content of ≤20% and was used as a naphthalene water reducing agent, a surfactant or a coal water slurry additive. The sodium sulfate hydrate mixed salts ①, ② and ③ were combined to obtain a total of 531.1 kg, which was equivalent to 83.6% of the yield of anhydrous sodium sulfate.

[0030] Example 4

[0031] Take 1000L of the β-naphthol wastewater which is not adsorbed by resin and concentrated 2 times by MVR, filter out the naphthalene sulfonic acid organic precipitate A: 17.8kg, move the filtrate into the evaporator to concentrate to near saturation (density 1.35-1.37) volume 700.0L, keep at 31℃ for 5.0hr, organic matter is precipitated, filter out the naphthalene sulfonic acid organic matter B: 15.0kg, the filtrate is water cooled and stirred for 2.5hr to precipitate the hydrate mixed salt, after centrifugal dewatering, wash the mixed salt with 3.5% dilute lye 18L for 3 times, the first alkali wash consumes lye 54.0L in total, get the decolorized hydrate mixed salt ① 374.0kg, the remaining mother liquor volume is 320L; continue to concentrate to volume about 250.0L, keep at 31℃ for 4.0hr, the precipitated organic matter is filtered to get the paste-like organic matter C: 47.5kg, the filtrate is water cooled to precipitate the mixed salt at ≤18℃, wash the mixed salt with 3.5% alkali 3 times, each time 16.0L, consume lye 48.0L, get the decolorized mixed salt ② 97.6kg, the remaining mother liquor is about 170.0L, add 18.0L 50% sulfuric acid to acidify and remove SO2, combine the first and second alkali wash liquid 54.0+48.0L into the mother liquor and continue to concentrate to near saturation, keep at 31℃ for 4.0hr, filter the precipitated organic matter to get the paste-like organic matter D: 18.4kg, combine A, B, C, D naphthalene sulfonic acid organic matter to get 98.7kg, return to the workshop for reuse; after stirring in ≤10℃ cold water for 2.5hr, centrifugal dewater the precipitated hydrate mixed salt, wash with 3.5% dilute lye 30.0L for 3 times, each time 10.0L, centrifugal dewater to get the pure white hydrate mixed salt ③ 76.7kg, collect the 30.0L alkali wash liquid separately for the first alkali wash of the mixed salt of the next batch, finally get the concentrated liquid containing mixed salt concentration ≤10% 80.0-85.0L, after drying and dewatering, get the solid organic matter E: 47.7kg, containing salt ≤20%, used as naphthalene water reducer, surfactant or coal water slurry additive; combine ①, ②, ③ sodium sulfate hydrate mixed salt to get 548.3kg, equivalent to anhydrous sodium sulfate yield 86.4%.

[0032] The above-mentioned embodiments utilize the characteristics that the concentration of sodium sulfate decahydrate and sodium sulfite heptahydrate in the wastewater is close to saturation, and the pure sodium sulfate hydrate mixed salt is precipitated at ≤24℃ water cooling, and the hydrate mixed salt crystals of sodium sulfate and sodium sulfite are centrifugally separated, and then the hydrate mixed salt is purified and decolorized by washing with dilute lye, and the sodium sulfate mixed salt after alkali washing and decolorization fully meets the technical index requirements of the double decomposition reaction of sodium sulfate + quicklime + SO2 to prepare sodium sulfite and sodium pyrosulfite, and the organic matter (TOC) such as α / β-naphthalene sulfonate contained in the wastewater is also separated from the sodium sulfate hydrate mixed salt according to the characteristics that the solubility of the organic matter in the sodium sulfate salt solution is very low; the industrial implementation of the process route can eliminate the traditional treatment method of removing naphthalenesulfonic acid organic matter by resin adsorption or extraction of naphthol wastewater, and the sodium sulfate mixed salt and naphthalenesulfonic acid organic matter in the wastewater can be directly recovered, which greatly reduces the treatment cost and equipment investment of the wastewater, solves the bottleneck problem of high investment and difficult treatment of naphthol wastewater and similar organic wastewater, and realizes the resource recycling of the three wastes of enterprises. Compared with the traditional naphthol wastewater treatment process route, the process route has the advantages of less investment, low running cost, small energy consumption and high economic benefit.

[0033] The above-mentioned only a few preferred embodiments of the present application, all with the process route described in the claims of the present application similar to the transformation, should belong to the scope of protection covered by the present application.

Claims

1. A method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic compounds from naphthol wastewater, characterized in that: The naphthol wastewater, cooled to ambient temperature (15℃~25℃), was filtered to remove naphthalene sulfonate organic precipitate A. The filtrate was then concentrated to near saturation using a low-temperature evaporator, and its concentration was measured to be 1.25~1.38 g / cm³ using a hydrometer. 3 The solution is discharged into an aging tank and kept at 30–35°C for 1.0–6.0 hours to allow naphthalene sulfonic acid organic compounds to precipitate. Organic compound B is then filtered out at 30–35°C. The filtrate is transferred to a crystallizer and cooled at ≤24°C to precipitate salts, causing sodium sulfate mixed salts to crystallize as decahydrate and heptahydrate. After centrifugation and dehydration, the hydrate mixed salts are washed with sodium hydroxide solution and centrifuged again to obtain pure, decolorized sodium sulfate hydrate mixed salt crystals ①. The mother liquor is further concentrated under reduced pressure until near saturation. The concentrated solution is then aged at 30–35°C for 1.0–6.0 hours, and then filtered out at this temperature to remove naphthalene sulfonic acid organic compound C. The filtrate is transferred to a crystallizer and cooled at ≤24°C to precipitate salts, causing sodium sulfate mixed salts to crystallize as hydrates. After centrifugation and dehydration, the hydrate mixed salts are washed with sodium hydroxide solution and centrifuged again to obtain pure, decolorized sodium sulfate mixed salt crystals ①. Sodium hydrate mixed salt crystallization ②; the remaining filtrate is acidified with 50% sulfuric acid to adjust the pH to 2.0-4.5 to remove SO2, and then the alkaline washing liquids from the first and second cycles are combined with the acidified liquid for neutralization and further low-temperature evaporation and concentration to near saturation. After filtering out organic matter D at 30-35℃, the filter cakes of naphthalene sulfonic acid organic matter A, B, C, and D are combined and returned to the workshop for reuse; the filtrate is frozen at ≤10℃ for 1.0-4.0 hours to precipitate salt, and the precipitated hydrate mixed salt is centrifuged and dehydrated and washed with dilute alkali to obtain pure and decolorized hydrate mixed salt crystals ③; the remaining mother liquor is sent for spray drying to obtain low-salt naphthalene sulfonic acid organic matter dry powder E with a salt content ≤20%, which is used as a naphthalene sulfonic acid water-reducing agent or an additive for coal-water slurry; the purified and decolorized sodium sulfate hydrate mixed salt crystals ①, ②, and ③ are combined, mixed, and homogenized and used as raw materials for the production of sodium sulfite or sodium metabisulfite.

2. The method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic compounds from naphthol wastewater according to claim 1, characterized in that: The preferred equipment for evaporating and concentrating filtrate or mother liquor is MVR, multi-effect evaporator, or other low-temperature vacuum evaporation and concentration equipment. The evaporation and concentration temperature is ≤80℃, and the distilled water is returned to the workshop for recycling after condensation.

3. The method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic compounds from naphthol wastewater according to claim 1, characterized in that: The sodium sulfate hydrate mixed salt is washed with 1.0-6.0% sodium hydroxide solution in a countercurrent manner for decolorization. The amount of alkali washing solution used is 1 / 3 to 1 / 10 of the hydrate crystal volume. Each batch of mixed salt is washed with alkali 2 to 3 times. The used alkali washing solution is collected and used to neutralize the acidification solution and is recycled.

4. The method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic compounds from naphthol wastewater according to claim 1, characterized in that: After four separations of organic matter and three salt precipitations, more than 82% sodium sulfate hydrate mixed salt can be purified from naphthol wastewater. The concentration ratio of the original wastewater volume to the mother liquor volume is 15 to 20 times.

5. The method for purifying sodium sulfate hydrate mixed salt and recovering naphthalene sulfonic acid organic compounds from naphthol wastewater according to claim 1, characterized in that: Sodium sulfate mixed salt refers to anhydrous sodium sulfate containing anhydrous sodium sulfite; sodium sulfate hydrate mixed salt refers to sodium sulfate decahydrate containing sodium sulfite heptahydrate.

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