Sulfate purification process and system

Abstract

The invention belongs to the field of treatment of industrial wastewater, and relates to a sulfate purification process which comprises the following steps: sequentially carrying out dosing reaction treatment, denitrification nitrogen removal treatment, reverse osmosis treatment, evaporation treatment, purification treatment and sodium sulfate crystallization treatment on high-salinity wastewater to finally obtain a sodium sulfate product. The invention also provides a system for the sulfate purification process. The system comprises a dosing unit, a denitrification unit, a reverse osmosis unit, an evaporation unit, a purification unit and a crystallization unit according to a material flow. According to the method, phosphate and sodium hydroxide are used for jointly treating high-salinity wastewater, and fluorine hardness and calcium hardness are efficiently removed. In addition, softening treatment including hardness removal, COD removal and deep softening is conducted on the wastewater again after evaporation and concentration operation, and the hardness and COD enriched again in the concentration processes such as the reverse osmosis process and the evaporation process are effectively reduced. In a word, the industrial wastewater in a high-salt environment can be treated with low energy consumption, and meanwhile, the yield of a sodium sulfate product is high.

Description

Technical Field

[0001] The invention relates to the technical field of chemical resource recycling, and in particular to a sulfate purification process and system for removing nitrate impurities from high-salinity wastewater. Background Art

[0002] Coal chemical industry, pickling and other production processes produce a large amount of industrial by-product salts containing high concentrations of sulfates and nitrates. The high salt content and heavy metal ions limit the application of treatment methods such as biochemical degradation, resulting in limited sulfate resource utilization, and some are even listed as hazardous waste. The presence of nitrates not only affects the purity of sulfates and increases treatment costs, but also increases the boiling point of wastewater and increases energy consumption. The existing nitrate treatment methods mainly include physical and chemical methods, biological denitrification methods and catalytic reduction methods.

[0003] At present, the treatment methods for nitrate in wastewater mainly include physical and chemical methods, biological denitrification and chemical catalytic reduction. Although physical and chemical methods such as ion exchange, reverse osmosis, electrodialysis and evaporation can effectively concentrate or transfer nitrates, the operating costs are high, and the nitrates are not completely removed, which poses a risk of secondary pollution. Although biological denitrification technology is environmentally friendly, it is inefficient under high salinity conditions and requires the addition of a large amount of carbon source, which increases operating costs and greenhouse gas emissions. The chemical catalytic reduction method is limited in its widespread application due to problems such as complex catalyst preparation, insufficient activity and difficult process control.

[0004] In view of the above technical bottlenecks, it is urgent to develop a sulfate purification process that can effectively remove nitrate salts in high-salinity wastewater environments and achieve efficient resource utilization of sulfate. This process should not only significantly reduce the output of salts and solve the problem of salt disposal as hazardous waste, but also take into account economic benefits, by recovering high-purity sulfate to reduce the operating costs and energy consumption of the overall treatment process, and provide strong support for the sustainable development of industries such as coal chemical industry. Summary of the invention

[0005] The purpose of the present invention is to solve the problem mentioned in the background technology that nitrates in high-salt wastewater are difficult to effectively remove and affect the resource utilization of sulfates, and to provide a sulfate purification process and system for removing nitrates and impurities.

[0006] To achieve the above-mentioned object of the invention, the first aspect of the present invention provides a sulfate purification process, comprising the following steps:

[0007] (S1) subjecting the high-salinity wastewater to a drug-adding reaction treatment to obtain drug-adding effluent;

[0008] (S2) subjecting the effluent to denitrification treatment to obtain denitrified effluent;

[0009] (S3) subjecting the denitrification effluent to reverse osmosis treatment to obtain reverse osmosis concentrated water;

[0010] (S4) evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water;

[0011] (S5) purifying the evaporated concentrated water to obtain purified water;

[0012] (S6) subjecting the purified water to sodium sulfate crystallization to obtain a sodium sulfate product.

[0013] The second aspect of the present invention provides a system for the above-mentioned sulfate purification process, wherein the system comprises the following units according to the material flow:

[0014] A dosing unit is used to perform a dosing softening treatment on the high-salinity wastewater to obtain dosing effluent;

[0015] A denitrification unit is used to perform denitrification treatment on the effluent from the dosing to obtain denitrified effluent;

[0016] A reverse osmosis unit is used to perform reverse osmosis treatment on the denitrification effluent to obtain reverse osmosis concentrated water;

[0017] An evaporation unit, used for evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water;

[0018] A purification unit, used for purifying the evaporated concentrated water to obtain purified water;

[0019] The crystallization unit is used to perform sodium sulfate crystallization treatment on the purified water to obtain a sodium sulfate product.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention uses phosphate and sodium hydroxide to jointly treat high-salt wastewater, efficiently generates Ca5(PO4)3F precipitate with low solubility product, and simultaneously removes fluoride ions and calcium hardness, significantly improving the fluoride and hardness removal effects.

[0022] 2. The purification treatment of the present invention effectively reduces the hardness and COD that are re-enriched by concentration processes such as reverse osmosis and evaporation processes, and in the hardness removal process, the magnesium hydroxide colloid formed by the magnesium agent is used to adsorb the free silicon in the wastewater, thereby efficiently removing the hardness such as silicon and fluorine in the wastewater.

[0023] 3. Denitrification treatment adopts sulfur autotrophic denitrification pathway to convert nitrate nitrogen and nitrite nitrogen in wastewater into N2, which is the full name of CO2 and NO X This process is not only energy-saving, but also uses sulfur-containing minerals as a bacterial bed to promote the attachment of sulfur autotrophic bacteria, improve denitrification efficiency, and produce additional sulfate, thereby improving resource recovery benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of treating high-salt wastewater in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific embodiments, but such description is not intended to limit the scope of protection of the present invention. Those skilled in the art should know that certain process steps and equipment used in the specific embodiments of the present invention can be properly adjusted or replaced without affecting the implementation of the present invention.

[0026] A first aspect of the present invention provides a sulfate purification process for removing nitrate from coal chemical wastewater, characterized in that the sulfate purification process comprises the following steps:

[0027] (S1) subjecting the high-salinity wastewater to a drug-adding reaction treatment to obtain drug-adding effluent;

[0028] (S2) subjecting the effluent to denitrification treatment to obtain denitrified effluent;

[0029] (S3) subjecting the denitrification effluent to reverse osmosis treatment to obtain reverse osmosis concentrated water;

[0030] (S4) evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water;

[0031] (S5) purifying the evaporated concentrated water to obtain purified water;

[0032] (S6) subjecting the purified water to sodium sulfate crystallization to obtain a sodium sulfate product.

[0033] The high-salt wastewater is wastewater obtained after various types of wastewater generated in the direct coal liquefaction process have undergone quality separation treatment, biochemical treatment and various forms of primary concentration treatment in this field. The parameters of the high-salt wastewater include: pH 6-9, COD content ≤200mg / L, total nitrogen content ≤230mg / L, total hardness content ≤500mg / L, ammonia nitrogen content ≤30mg / L, TDS content 5000-10000mg / L, silicon content ≤250mg / L, and fluorine content ≤130mg / L.

[0034] In step (S1), the dosing reaction treatment refers to removing fluorine and hardness from the high-salinity wastewater to obtain dosing reaction effluent, which includes the following steps:

[0035] (S1a) mixing phosphate with the high-salt wastewater, and separating the solid and liquid after the reaction is completed to obtain a first dosing mixed solution;

[0036] (S1b) mixing sodium hydroxide with the first dosing mixed solution, and separating the solid and the liquid after the reaction is completed to obtain the dosing effluent.

[0037] In some embodiments, in step (S1a), phosphate is added to the high-salinity wastewater to form a precipitate containing fluorapatite (K sp is 3.19×10 -61 ) of the first dosing mixture.

[0038] Further, the phosphate is selected from at least one of orthophosphate, pyrophosphate and metaphosphate, preferably trisodium phosphate;

[0039] Furthermore, the amount of phosphate added is such that the pH of the first dosing mixed solution is 7-8, and the amount added is about 0.5‰ of the high-salinity wastewater.

[0040] The inventors found that calcium and fluoride coexist in the high-salt wastewater, and the ratio of calcium ions to fluoride ions is (5-10):1. The traditional double-alkali method for removing hardness (i.e., removing hardness by adding alkaline substances such as lime and sodium carbonate) has the disadvantage of a low calcium hardness removal rate. However, the present invention selects phosphate as a precipitating agent. When calcium ions and phosphate are sufficient, the reaction conditions are controlled to be neutral conditions, which can effectively form a Ca5(PO4)3F precipitate with a lower solubility product, remove fluoride hardness and calcium hardness at the same time, and the calcium hardness removal rate is high.

[0041] In some embodiments, in step (S1b), sodium hydroxide is added to the first dosing mixture to form a precipitate containing Ca3(PO4)2 (K sp 2.07×10 -29 ) of the second dosing reaction mixture, i.e., dosing effluent;

[0042] Furthermore, the sodium hydroxide can be solid or solution, and the amount added is such that the pH of the dosing water is 10-11. When the mass fraction of the solution is 32%, the amount added is about 0.5% of the first dosing mixed solution.

[0043] In some embodiments, after the dosing reaction treatment in step (S1), the removal rate of fluorine and calcium in high-salinity wastewater can reach more than 90%. The total hardness content of the dosing effluent is ≤50 mg / L, and the pH is 10-11.

[0044] In step (S2), the denitrification treatment refers to the process in which sulfur autotrophic bacteria, under anoxic conditions, use low-valent sulfur (S, S 2- 、S2O3 2- ) as electron donor, CO3 2- , CO2 as an inorganic carbon source, converting nitrate nitrogen and nitrite nitrogen in wastewater into nitrogen gas, including the following steps:

[0045] (S2a) using special fillers as carriers to acclimate biochemical sludge enriched with sulfur autotrophic bacteria to adapt to the treatment environment;

[0046] (S2b) After the acclimation is completed, the effluent from the dosing is continuously introduced into the system, and the nitrogen element in the effluent from the dosing is removed by the denitrification action of the sulfur autotrophic bacteria to obtain the denitrified effluent;

[0047] In some embodiments, in step (S2a), in a sulfur autotrophic biochemical pond in the art, a special filler is used to acclimate the biochemical sludge containing sulfur autotrophic bacteria for more than 10 hours.

[0048] Furthermore, the special filler comprises 60-80 parts by weight of sulfur-containing minerals (exemplarily pyrite and / or pyrite), 5-8 parts by weight of alkaline substances (exemplarily sodium carbonate), 20-40 parts by weight of kaolin tailings and 10-20 parts by weight of adhesives (exemplarily bentonite and / or cement calcium silicate).

[0049] Furthermore, the added amount of the special filler can be 0.02-0.08% of the effluent water after dosing.

[0050] The special filler of this scheme has the characteristics of strong hydrophilicity, efficient mass transfer, and internal porosity. It can adsorb and promote the growth of denitrifying bacteria. At the same time, the sulfur in the filler can provide electron donors for denitrifying bacteria, so that the denitrification system does not need to add additional carbon sources.

[0051] In step (S2a), the domestication is well known in the art, that is, through the regulation of specific environmental conditions and nutrients, the sulfur autotrophic bacteria gradually adapt to the environment and attach to the special filler, and then efficiently utilize the nutrients in the sewage for metabolic activities.

[0052] Furthermore, the denitrifying sulfur autotrophic bacteria is selected from at least one of Thiobacillus denitrificans, Thiobacillus thioparus, Thiobacillus naples, Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Thiobacillus novellas, Thiobacillus intermedius and Thiobacillus perometabolis, and may also be a denitrifying sulfur autotrophic bacteria that obtains at least one of the above-mentioned Thiobacillus after domestication.

[0053] In some embodiments, in step (S2b), the effluent after drug addition is added to the domesticated biochemical sludge, and denitrified effluent is obtained after denitrification by sulfur autotrophic bacteria.

[0054] Furthermore, the sludge separated during the denitrification process can be returned to the biochemical sludge of step (S2a) to maintain the quantity and activity of sulfur autotrophic bacteria.

[0055] In some embodiments, after the denitrification treatment in step (S2), the total nitrogen content in the (denitrification) wastewater is ≤20 mg / L, and the ammonia nitrogen content is ≤10 mg / L.

[0056] In some embodiments, in step (S3), the reverse osmosis treatment includes using an ultrafiltration device in the art to ultrafilter the denitrification effluent in a cross-flow filtration manner to obtain ultrafiltered effluent; and then using a high-pressure reverse osmosis device in the art to reverse osmosis concentrate the ultrafiltered effluent to obtain reverse osmosis produced water and reverse osmosis concentrated water.

[0057] Furthermore, the operating conditions of the ultrafiltration device include: water inlet pressure of 0.18-0.23 MPa, transmembrane pressure difference of 0.06-0.09 MPa, and recovery rate of more than 98%.

[0058] Furthermore, the dissolved solid content (i.e., salt content TDS) of the ultrafiltration effluent is greater than 10000 mg / L, the turbidity is ≤0.1 NTU, and the pollution index (SDI) is ≤2;

[0059] In some embodiments, in step (S3), the operating conditions of the high-pressure reverse osmosis device include: an inlet water pressure of 1.7-2.2 MPa, an interstage pressure of 0.18-0.23 MPa, and a recovery rate of more than 75%.

[0060] Furthermore, the conductivity of the reverse osmosis produced water is ≤150us / cm 2 ;

[0061] Furthermore, the parameters of the reverse osmosis concentrated water include: COD content ≤750 mg / L, total nitrogen content ≤100 mg / L, total hardness content ≤200 mg / L, and TDS content ≥40000 mg / L.

[0062] In step (S4), the evaporation treatment refers to further evaporating and concentrating the reverse osmosis concentrated water using an MVR evaporator in the art to obtain evaporated concentrated water. In some embodiments, the MVR evaporator uses a seed crystal falling film evaporation process in the art to further concentrate the reverse osmosis concentrated water by 4-5 times.

[0063] Furthermore, the operating conditions of the MVR evaporator include: a temperature of 100-105° C. and a pressure of 25-30 kPaG.

[0064] Those skilled in the art will appreciate that the evaporation treatment may also adopt a non-seed evaporation process, and the hardness removal and silicon removal in step (S5) need to be placed before step (S4), which will not be described in detail.

[0065] In some embodiments, in step (S4), the COD content of the evaporated concentrated water is ≤3000 mg / L, the total nitrogen content is ≤500 mg / L, and the TDS content is ≥200000 mg / L.

[0066] Those skilled in the art can understand that, for cost considerations, the denitrification effluent is first subjected to reverse osmosis concentration in step (S3) and then to evaporation concentration in step (S4). If the cost is not taken into account, the denitrification effluent can be directly subjected to evaporation concentration in step S4 and step (S3) can be omitted.

[0067] In step (S5), the purification treatment refers to removing fluorine and hardness, removing COD by ozone oxidation and deep softening the evaporated concentrated water, including the following steps:

[0068] (S5a) mixing the phosphate with the evaporated concentrated water, and separating the solid and the liquid after the reaction is completed to obtain a first softened effluent;

[0069] (S5b) mixing sodium hydroxide with the first softened water, and separating the solid and the liquid after the reaction is completed to obtain a second softened water;

[0070] (S5c) mixing the magnesium agent with the second softened water, and separating the solid and the liquid after the reaction to obtain a third desiliconized water;

[0071] (S5d) subjecting the third desiliconization effluent to ozone oxidation to remove COD, thereby obtaining fourth ozone oxidation effluent;

[0072] (S5e) The fourth ozone oxidation effluent is subjected to ultrafiltration and ion exchange treatment to obtain purified effluent.

[0073] The inventors have found that after the reverse osmosis treatment and evaporation treatment, the hardness of the concentrated evaporated water increases again, so it needs to be softened and COD removed again.

[0074] In some embodiments, in step (S5a), the phosphate is selected from at least one of orthophosphate, pyrophosphate and metaphosphate, and is added in an amount such that the pH of the first softened effluent is 7-8, and the phosphate is more preferably trisodium phosphate;

[0075] In some embodiments, in step (S5b), the amount of sodium hydroxide added is such that the pH of the second softened water is 10-11. That is, the phosphate and sodium hydroxide in step (S5) can refer to step (S1).

[0076] In some embodiments, in step (S5c), the magnesium agent is added to the second softened effluent, and after the reaction is completed, the magnesium silicate precipitate is separated to obtain a third desiliconized effluent.

[0077] Furthermore, the magnesium agent can be magnesium chloride, magnesium oxide, magnesium sulfate, preferably magnesium chloride and / or magnesium sulfate. In addition to having better solubility, magnesium chloride and / or magnesium sulfate are hydrolyzed under alkaline conditions to form magnesium hydroxide colloid (rather than magnesium hydroxide precipitation) to adsorb free silicon in water, gradually forming insoluble magnesium silicate precipitation, removing free silicon in water, and achieving the purpose of removing fluorine and hardness.

[0078] Furthermore, the amount of magnesium agent added is such that the pH of the third desiliconization effluent is 10.5-11.5.

[0079] In some embodiments, in step (S5d), the ozone oxidation is a binary coordinated catalytic oxidation, consisting of a main excitation, an auxiliary excitation and an oxidation tower, and a multi-metal doped salt-tolerant catalyst is arranged in the oxidation tower. The core process of ozone oxidation is to add 0.3% hydrogen peroxide to the main excitation to cooperate with electrocatalysis to open the ring and break the chain of the refractory organic matter, and then add ozone to the oxidation tower at a concentration of about 6000 mg / L after generating ozone through auxiliary excitation. The oxidation tower is in reverse contact with gas and water, and the reflux volume is about 50% of the water intake, which can reduce the COD of the wastewater to below 300 mg / L.

[0080] Furthermore, the amount of ozone added to the oxidation tower directly affects the removal effect of ozone on COD. Generally speaking, the ratio of the amount of ozone added to the COD in the third desiliconization effluent (i.e., the O / C ratio in the art) is (2-4):1.

[0081] In some embodiments, in step (S5e), the ultrafiltration is performed in an ultrafiltration device in the art, and the process conditions include: the water inlet pressure is 0.15-0.22 MPa, the transmembrane pressure difference is 0.08-0.12 MPa, and the recovery rate is 96-97%;

[0082] The ion exchange treatment is carried out in an ion exchange resin (exemplified by a macroporous chelating resin) in the art, and the process conditions include: an inlet water pressure of 0.17-0.23 MPa, a pressure difference of 0.02-0.04 MPa, and an outlet water pH of 7.0-7.8.

[0083] The inventors have found that the conventional high-salt wastewater treatment process first removes COD from the reverse osmosis concentrate in step (S3). This process is relatively easy to process, but after evaporation and concentration in step (S4), the COD of the concentrate is enriched again, resulting in a higher COD in the subsequent crystallization unit, and ultimately a lower sulfate purity and an increased impurity salt ratio. However, the present invention places the COD removal process after the evaporation treatment in step (S4). Although the corresponding treatment process is more difficult, the COD removal effect is better.

[0084] In some embodiments, in step (S5), the purified water has a COD content of ≤300 mg / L, a total hardness content of ≤10 mg / L, a silicon content of ≤30 mg / L, a fluoride ion content of ≤15 mg / L, a turbidity of ≤1 NTU, and a TDS content of ≥200000 mg / L.

[0085] In step (S6), the sodium sulfate crystallization treatment refers to separating the sodium sulfate in the purified water by freezing crystallization, comprising the following steps:

[0086] (S6a) concentrating the purified water to obtain a nearly saturated solution of the purified water;

[0087] (S6b) subjecting the nearly saturated solution to freeze crystallization to obtain a sodium sulfate product.

[0088] In step (S6a), the concentration may be carried out by conventional methods in the art, such as heating and evaporation in a crystallizer.

[0089] In step (S6b), the freeze crystallization is carried out in a DTB crystallizer in the art, and the temperature of the freeze crystallization is -5 to 0°C.

[0090] In some embodiments, after the freezing crystallization, sodium sulfate mother liquor containing a large amount of sodium chloride solution and mirabilite are obtained. The mirabilite is sequentially subjected to conventional recrystallization and impurity removal processes such as melt crystallization, solid-liquid separation, and drying to obtain a sodium sulfate product that meets the Class A first-class product in "T / CCT001-2019".

[0091] Furthermore, the sodium sulfate mother liquor can be subjected to a sodium chloride crystallization process known in the art to obtain a sodium chloride product and a miscellaneous salt product.

[0092] The second aspect of the present invention provides a system for the above-mentioned sulfate purification process, wherein the system comprises the following units according to the material flow:

[0093] A dosing unit is used to perform a dosing softening treatment on the high-salinity wastewater to obtain dosing effluent;

[0094] A denitrification unit is used to perform denitrification treatment on the effluent from the dosing to obtain denitrified effluent;

[0095] A reverse osmosis unit is used to perform reverse osmosis treatment on the denitrification effluent to obtain reverse osmosis concentrated water;

[0096] An evaporation unit, used for evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water;

[0097] A purification unit, used for purifying the evaporated concentrated water to obtain purified water;

[0098] The crystallization unit is used to perform sodium sulfate crystallization treatment on the purified water to obtain a sodium sulfate product.

[0099] In some embodiments, the dosing unit uses a high-density sedimentation tank to treat the high-salinity wastewater;

[0100] The denitrification unit uses a sulfur autotrophic biochemical pool to treat the dosing effluent;

[0101] The reverse osmosis unit sequentially uses an ultrafiltration device and a high-pressure reverse osmosis device to treat the denitrification effluent;

[0102] The evaporation unit uses an MVR evaporator to process the reverse osmosis concentrated water;

[0103] The purification unit sequentially uses a high-density sedimentation tank, an ozone oxidation device, an ultrafiltration device and an ion exchange resin to treat the evaporated concentrated water;

[0104] The crystallization unit uses a DTB crystallizer to treat the purified water.

[0105] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention will be described in detail below through specific embodiments and comparative examples.

[0106] In this document, unless otherwise specified, all percentages used are weight percentages.

[0107] The pH of the high-salinity wastewater is 7.0, the COD content is 180 mg / L, the total nitrogen content is 201 mg / L, the total hardness content is 451 mg / L, the ammonia nitrogen content is 30 mg / L, the TDS content is 10625 mg / L, the dissolved silicon content is 154 mg / L, and the F - The content is 54mg / L.

[0108] The biochemical sludge is the activated sludge of the deep treatment biochemical pool of Ordos Coal-to-Oil Company. After domestication, it will produce Thiobacillus denitrificans, Thiobacillus thioparus, Thiobacillus naples, Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Thiobacillus novellas, Thiobacillus intermedius and Thiobacillus perometabolis, and can be purchased from Ordos Coal-to-Oil Company.

[0109] Example 1

[0110] like Figure 1 As shown, the high-salinity wastewater is treated as follows:

[0111] (S1) subjecting the high-salinity wastewater to a drug-adding reaction treatment to obtain drug-adding effluent, comprising the following steps:

[0112] (S1a) In a high-density sedimentation tank, a trisodium phosphate solution (10%) is added to high-salinity wastewater, and after the reaction is completed, a first dosing mixed solution (pH=7.5) containing fluorapatite precipitation is obtained; wherein,

[0113] The dosage of the trisodium phosphate solution is 0.5‰ of the high-salt wastewater;

[0114] (S1b) The first dosing mixed solution is allowed to stand and then overflow into another high-density sedimentation tank, and sodium hydroxide solution (32%) is added thereto. After the reaction is completed, the Ca3(PO4)2 precipitate is removed by solid-liquid separation to obtain the dosing effluent; wherein,

[0115] The amount of sodium hydroxide solution added is 0.5% of the first dosing mixture;

[0116] The total hardness of the water after adding the drug was reduced from 451 mg / L to 42 mg / L, the pH was 10-11, and the total nitrogen content was 201 mg / L.

[0117] (S2) performing denitrification and denitrification treatment on the effluent from the dosing to obtain denitrified effluent, comprising the following steps:

[0118] (S2a) In a sulfur autotrophic biochemical pool, a special filler is used as a carrier to acclimate the biochemical sludge enriched with sulfur autotrophic bacteria for 16 hours; wherein,

[0119] The special filler comprises 70 parts by weight of pyrite, 7 parts by weight of sodium carbonate, 30 parts by weight of kaolin tailings, and 15 parts by weight of bentonite. The addition amount of the special filler is 0.05% of the effluent after the dosing.

[0120] (S2b) After the acclimation is completed, the effluent from the dosing is continuously introduced into the sulfur autotrophic biochemical pool, and the nitrogen element in the effluent from the dosing is removed by the denitrification action of the sulfur autotrophic bacteria to obtain the denitrification effluent and the sludge separated in the denitrification process; wherein,

[0121] The parameters of the denitrification effluent include: total nitrogen content of 21 mg / L, ammonia nitrogen content of 8 mg / L;

[0122] The sludge is returned to the sulfur autotrophic biochemical tank in step (S2a).

[0123] (S3) performing reverse osmosis treatment on the denitrification effluent to obtain reverse osmosis concentrated water, comprising the following steps:

[0124] (S3a) in an ultrafiltration device, under the conditions of an inlet pressure of 0.2 MPa, a transmembrane pressure difference of 0.08 MPa, and a recovery rate of 98%, the denitrification effluent is ultrafiltered by cross-flow filtration to obtain ultrafiltration effluent; wherein,

[0125] The TDS content of the ultrafiltration effluent is 10000 mg / L, the turbidity is 0.1 NTU, and the pollution index is 2.

[0126] (S3b) In a high-pressure reverse osmosis device, under the conditions of an inlet pressure of 2.0 MPa, an interstage pressure of 0.2 MPa, and a recovery rate of 80%, the ultrafiltration water is subjected to reverse osmosis concentration to obtain reverse osmosis concentrated water and a conductivity of 145 us / cm 2 of reverse osmosis water; among which,

[0127] The reverse osmosis concentrated water has a COD content of 711 mg / L, a total nitrogen content of 35 mg / L, a total hardness content of 165 mg / L, and a TDS content of 40580 mg / L.

[0128] (S4) In an MVR evaporator, the reverse osmosis concentrated water is further concentrated by 5 times at a temperature of 102° C. and a pressure of 29 kPaG to obtain evaporated concentrated water; wherein,

[0129] The evaporated concentrated water has a TDS content of 168,000 mg / L, a COD content of 3,000 mg / L, and a total nitrogen content of 130 mg / L.

[0130] (S5) the evaporated concentrated water is purified to obtain purified water, comprising the following steps:

[0131] (S5a) adding trisodium phosphate solution (10%) to the evaporated concentrated water, at which pH = 7.5, and then adding sodium hydroxide solution (32%) to obtain a first defluoridation and de-hardness effluent with pH = 11.5; wherein,

[0132] The amount of the trisodium phosphate solution added is 0.5‰ of the evaporated concentrated water, and the amount of the sodium hydroxide solution added is 0.5%.

[0133] (S5b) adding magnesium chloride solution (38%) to the first defluorination and dehardness removal effluent, separating the generated magnesium silicate precipitate, and obtaining a second desiliconization effluent with a pH of 11.

[0134] (S5c) catalytically oxidizing the second desiliconized water to obtain second purified water; wherein:

[0135] The catalytic oxidation conditions are as follows: adding 0.3% hydrogen peroxide to cooperate with electrocatalysis, and then adding ozone to the oxidation tower at a concentration of 6000 mg / L, and the reflux volume is 50% of the water inlet volume;

[0136] The COD of the second purified water is reduced to 240 mg / L.

[0137] (S5d) Under the conditions of an inlet pressure of 0.2 MPa, a transmembrane pressure difference of 0.1 MPa, and a recovery rate of 97%, the second purified water is subjected to ultrafiltration to obtain ultrafiltration water; under the conditions of an inlet pressure of 0.2 MPa, a pressure difference of 0.03 MPa, and an outlet pH of 7.5, the ultrafiltration water is subjected to ion exchange treatment to obtain purified water; wherein,

[0138] The purified water has a turbidity of 1 NTU, a hardness of 1 mg / L, a TDS content of 169000 mg / L, a COD content of 240 mg / L, a silicon content of 25 mg / L, and a fluoride ion content of 12 mg / L.

[0139] (S6) the purified water is subjected to sodium sulfate crystallization treatment to obtain a sodium sulfate product, comprising the following steps:

[0140] (S6a) in an evaporative crystallizer, at a pressure of 5 kPaG and a temperature of 98° C., concentrating the purified water to obtain a nearly saturated solution of the purified water; wherein:

[0141] The TDS content of the nearly saturated solution is 295000 mg / L.

[0142] (S6b) In a DTB crystallizer, the nearly saturated solution is subjected to freeze crystallization at a temperature of -4.1°C to obtain sodium sulfate and SO4 2- The concentration is 7500mg / L sodium sulfate mother solution;

[0143] The COD content in the sodium sulfate mother liquor is 530 mg / L.

[0144] (S6c) subjecting the mirabilite to melt crystallization, solid-liquid separation, recrystallization and drying in sequence to obtain a sodium sulfate product; wherein,

[0145] The sodium sulfate product has a content of 99.1%, a water-insoluble matter content of 0.05%, a chloride content of 0.3%, and a calcium and magnesium ion content of 0.1%, which meets the requirements of Class A first-class products in the group standard "T / CCT001-2019 Industrial Anhydrous Sodium Sulfate".

[0146] (S6d) in a sodium chloride crystallizer, the sodium sulfate mother liquor is subjected to sodium chloride crystallization treatment to obtain a sodium chloride product and a sodium chloride mother liquor; wherein,

[0147] The purity of the sodium chloride product is 99%, the total content of calcium and magnesium ions is 0.1%, SO4 2- The content is 0.2%, which meets the requirements of the first-class industrial dry salt of the group standard "T / CCT002-2019 Industrial Sodium Chloride as a Byproduct of Coal Chemical Industry";

[0148] The COD content in the sodium chloride mother liquor is 1050 mg / L;

[0149] (S6e) in a mixed salt crystallizer, the sodium chloride mother liquor is subjected to mixed salt crystallization treatment to obtain a mixed salt product and a mixed salt mother liquor; wherein,

[0150] The content of sodium nitrate in the miscellaneous salt is 6%;

[0151] The COD content in the mixed salt mother liquor is 2100 mg / L.

[0152] According to evaluation, the operation cycle of the crystallization system including sodium sulfate crystallizer, sodium chloride crystallizer and mixed salt crystallizer is about 90 days, which can remove more than 90% of nitrate before entering evaporation crystallization, and the mixed salt rate is 10.2%.

[0153] Comparative Example 1 (Double Alkali Method for Hardness Removal in the Field)

[0154] The method is carried out in accordance with Example 1, except that in step (S1), a double alkali method known in the art is used to remove hardness, including the following steps:

[0155] (S1a) In a high-density sedimentation tank, a sodium hydroxide solution (32%) is added to high-salinity wastewater, and after the reaction is completed, a first dosing mixed solution containing magnesium hydroxide and calcium carbonate precipitates is obtained; wherein,

[0156] The amount of sodium hydroxide solution added is 0.5% of the high-salt wastewater.

[0157] (S1b) The first dosing mixed solution is allowed to stand and then overflow into another high-density sedimentation tank, and sodium carbonate solution (mass fraction 16%) is added thereto, and after the reaction is completed, the dosing effluent overflows; wherein,

[0158] The amount of sodium carbonate solution added is 2‰ of the first dosing mixture;

[0159] The total hardness content of the water after adding the drug is reduced from 451 mg / L to 250 mg / L, the total hardness removal rate is less than 50%, and the total nitrogen content is 201 mg / L.

[0160] The result is that the total hardness of the water discharged after the addition of the drug is relatively high, and there is no subsequent treatment measure, which leads to increased scaling of the membrane system of the subsequent ultrafiltration device and reverse osmosis device, and an increased cleaning frequency.

[0161] Comparative Example 2 (adding carbon source and using traditional denitrification)

[0162] The method is carried out with reference to Example 1, except that a carbon source is added in step (S2), and denitrification is carried out by the conventional A / O method, as follows:

[0163] In step (S2), 99% methanol is continuously added to the effluent to provide a carbon source for denitrifying heterotrophic bacteria to perform denitrification, thereby obtaining denitrified effluent; wherein,

[0164] The parameters of the denitrification effluent include: a total nitrogen content of 120 mg / L and an ammonia nitrogen content of 30 mg / L.

[0165] Calculation of methanol addition: total nitrogen in the inlet water is 201mg / L, COD is 100-150mg / L, and B / C ratio is 0.2; in addition, the total nitrogen content of the outlet water is 120mg / L and the COD content is 50mg / L. Therefore, the theoretical BOD supplementation is: (200-120)*4-(20-10)=230mg / l. Since the BOD content of methanol is 0.77, 99% methanol is supplemented: 230 / 0.77 / 0.99=301.7mg / l. The actual amount of methanol supplemented is less than the theoretical amount, but there are still problems of high operating costs and low total nitrogen removal rate (only 40%).

[0166] In step (S6e), after the carbon source is supplemented for denitrification, the content of sodium nitrate in the impurity salt is 18%. According to evaluation, the impurity salt ratio increases to about 14%.

[0167] Comparative Example 3 (Purification before entering the evaporator)

[0168] The same method is carried out with reference to Example 1, except that the purification treatment in step (S5) is performed first, and then the evaporation concentration in step (S4) is performed.

[0169] At this time, the COD content of the reverse osmosis concentrated water obtained in step (S3) is 711 mg / L. After the purification treatment in step (S5), the COD content of the purified water obtained is 350 mg / L (the water temperature is low, and the COD removal effect is poor). After the evaporation concentration in step (S4), the COD content of the evaporated concentrated water obtained is 1500 mg / L. In addition,

[0170] In step (S6b), the COD content in the sodium sulfate mother liquor is increased to 3300 mg / L.

[0171] In step (S6d), the COD content in the sodium chloride mother liquor is increased to 6500 mg / L, and the fluoride ion content is 200 mg / L.

[0172] In step (S6e), the COD content in the impurity salt mother liquor is increased to 14000 mg / L, and the fluoride ion content is 400 mg / L (significantly increased compared to the fluoride ion content of 12 mg / L in the purified water).

[0173] According to the evaluation, the solution in the impure salt crystallizer became sticky after running for about one month, and its heat exchange efficiency was significantly reduced. The longest operation cycle of the crystallization system was 40 days, and the discharge of the impure salt mother liquor increased, and the impure salt rate increased to 15.2%.

[0174] The present invention has described in detail the preferred embodiments of the present invention, but the embodiments are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other simple modifications and combinations within the scope of the present invention, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the scope of protection of the present invention.

Claims

1. A sulfate purification process, characterized in that: The sulfate purification process comprises the following steps: (S1) subjecting the high-salinity wastewater to a drug-adding reaction treatment to obtain drug-adding effluent; (S2) subjecting the effluent to denitrification treatment to obtain denitrified effluent; (S3) subjecting the denitrification effluent to reverse osmosis treatment to obtain reverse osmosis concentrated water; (S4) evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water; (S5) purifying the evaporated concentrated water to obtain purified water; (S6) subjecting the purified water to sodium sulfate crystallization to obtain a sodium sulfate product.

2. The sulfate purification process according to claim 1, characterized in that: In step (S1), the dosing reaction treatment refers to removing fluorine and hardness from the high-salinity wastewater to obtain dosing effluent, which includes the following steps: (S1a) mixing phosphate with the high-salt wastewater, and separating the solid and liquid after the reaction is completed to obtain a first dosing mixed solution; (S1b) mixing sodium hydroxide with the first dosing mixed solution, and separating the solid and the liquid after the reaction is completed to obtain the dosing effluent.

3. The sulfate purification process according to claim 2, wherein the phosphate is selected from at least one of orthophosphate, pyrophosphate and metaphosphate, and is preferably trisodium phosphate; The amount of phosphate added is such that the pH of the first dosing mixture is 7-8; The amount of sodium hydroxide added is such that the pH of the effluent after the addition of the drug is 10-11.

4. The sulfate purification process according to any one of claims 1 to 3, characterized in that: In step (S2), the sulfur autotrophic denitrification treatment comprises the following steps: (S2a) using special fillers as carriers to acclimate biochemical sludge enriched with sulfur autotrophic bacteria to adapt to the treatment environment; (S2b) After the acclimation is completed, the effluent from the dosing is continuously introduced into the reaction system, and the nitrogen element in the effluent from the dosing is removed by the denitrification action of the sulfur autotrophic bacteria to obtain the denitrified effluent; Preferably, the special filler comprises 60-80 parts by weight of pyrite and / or pyrite, 5-8 parts by weight of sodium carbonate, 20-40 parts by weight of kaolin tailings and 10-20 parts by weight of bentonite and / or cement calcium silicate. More preferably, the addition amount of the special filler is 0.02-0.08% of the effluent from the dosing. Preferably, the sulfur autotrophic bacteria is selected from at least one of Thiobacillus denitrificans, Thiobacillus thioparus, Thiobacillus naples, Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Thiobacillus novellas, Thiobacillus intermedius and Thiobacillus perometabolis.

5. The sulfate purification process according to any one of claims 1 to 4, characterized in that: In step (S3), the reverse osmosis treatment refers to using an ultrafiltration device to perform ultrafiltration treatment in a cross-flow filtration manner to obtain ultrafiltration effluent, and then using a high-pressure reverse osmosis device to perform reverse osmosis concentration on the obtained ultrafiltration effluent to obtain reverse osmosis product water and reverse osmosis concentrated water; Preferably, the operating conditions of the ultrafiltration device include: water inlet pressure of 0.18-0.23 MPa, transmembrane pressure difference of 0.06-0.09 MPa, and recovery rate of more than 98%; Preferably, the operating conditions of the reverse osmosis device include: water inlet pressure of 1.7-2.2 MPa, interstage pressure of 0.18-0.23 MPa, and recovery rate of more than 75%; Preferably, the conductivity of the reverse osmosis produced water is ≤150us / cm 2 .

6. The sulfate purification process according to any one of claims 1 to 5, characterized in that: In step (S4), the evaporation treatment refers to using an MVR evaporator to further concentrate the reverse osmosis concentrated water by 4-5 times to obtain evaporated concentrated water; Preferably, the operating conditions of the MVR evaporator include: a temperature of 100-105° C. and a pressure of 25-30 kPaG.

7. The sulfate purification process according to any one of claims 1 to 6, characterized in that: In step (S5), the purification treatment refers to removing fluorine and hardness, catalytic oxidation and COD removal and deep softening of the evaporated concentrated water, including the following steps: (S5a) mixing the phosphate with the evaporated concentrated water, and separating the solid and the liquid after the reaction is completed to obtain a first softened effluent; (S5b) mixing sodium hydroxide with the first softened water, and separating the solid and the liquid after the reaction is completed to obtain a second softened water; (S5c) mixing the magnesium agent with the second softened water, and separating the solid and the liquid after the reaction to obtain a third desiliconized water; (S5d) subjecting the third desiliconization effluent to ozone oxidation to remove COD, thereby obtaining fourth catalytic oxidation effluent; (S5e) subjecting the fourth catalytic oxidation effluent to ultrafiltration and ion exchange treatment to obtain purified effluent; Preferably, the phosphate is selected from at least one of orthophosphate, pyrophosphate and metaphosphate, and the amount of the phosphate added is such that the pH of the first softened effluent is 7-8, and the phosphate is more preferably trisodium phosphate; Preferably, the amount of sodium hydroxide added is such that the pH of the second softened water is 10-11; Preferably, the magnesium agent is magnesium chloride, and the amount of magnesium chloride added is such that the pH of the third desiliconization effluent is 10-11.5; Preferably, when the ozone oxidation is performed, the ratio of the amount of ozone added to the chemical oxygen demand (COD) in the third desiliconization effluent (O / C value) is (2-4):

1. Preferably, the ultrafiltration conditions include: water inlet pressure of 0.15-0.22MPa, transmembrane pressure difference of 0.08-0.12MPa, and recovery rate of 96-97%; the ion exchange treatment conditions include: water inlet pressure of 0.17-0.23MPa, pressure difference of 0.02-0.04MPa, and outlet pH of 7.0-7.

8.

8. The sulfate purification process according to any one of claims 1 to 7, characterized in that: In step (S6), the sodium sulfate crystallization treatment refers to separating the sodium sulfate in the purified water by freezing crystallization, comprising the following steps: (S6a) concentrating the purified water to obtain a nearly saturated solution of the purified water; (S6b) freezing and crystallizing the nearly saturated solution to obtain a sodium sulfate product; Preferably, the temperature of the freezing crystallization is -5°C to 0°C.

9. A system for the sulfate purification process according to any one of claims 1 to 8, wherein the system comprises the following units according to the material flow: A dosing unit is used to perform a dosing softening treatment on the high-salinity wastewater to obtain dosing effluent; A denitrification unit is used to perform denitrification treatment on the effluent from the dosing to obtain denitrified effluent; A reverse osmosis unit is used to perform reverse osmosis treatment on the denitrification effluent to obtain reverse osmosis concentrated water; An evaporation unit, used for evaporating the reverse osmosis concentrated water to obtain evaporated concentrated water; A purification unit, used for purifying the evaporated concentrated water to obtain purified water; The crystallization unit is used to perform sodium sulfate crystallization treatment on the purified water to obtain a sodium sulfate product.

10. The system according to claim 9, characterized in that The dosing unit uses a high-density sedimentation tank to treat the high-salinity wastewater; The denitrification unit uses a sulfur autotrophic biochemical pool to treat the drug-dosed effluent; The reverse osmosis unit sequentially uses an ultrafiltration device and a high-pressure reverse osmosis device to treat the denitrification effluent; The evaporation unit uses an MVR evaporator to process the reverse osmosis concentrated water; The purification unit sequentially uses a high-density sedimentation tank, a catalytic oxidation device, an ultrafiltration device and an ion exchange resin to treat the evaporated concentrated water; The crystallization unit uses a DTB crystallizer to treat the purified water.

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