Highly mineralized mine water circulating freezing-thermal method salt separation treatment process and device

Abstract

The application discloses a high-mineralization mine water circulating freezing-thermal method salt separation treatment process and device, and belongs to the technical field of high-mineralization mine water treatment and recovery. The process adopts a modified sodium sulfate decahydrate freezing crystallization device, the bottom of the tank body is a W-shaped structure, which is beneficial to crystal suspension and circulation, a filter screen is arranged at the upper portion and is used for filtering fine crystals, freezing crystallization is carried out at about-5 DEG C, and high-purity anhydrous sodium sulfate is prepared through hot melting, hot crystallization and centrifugal drying of the obtained sodium sulfate decahydrate. The freezing mother liquor is subjected to evaporation crystallization to obtain sodium chloride, and the mother liquor of the two is combined and introduced into a miscellaneous salt crystallizer, temperature and pH value are regulated and controlled based on the miscellaneous salt rate (when the miscellaneous salt rate is greater than 5%), and potassium, magnesium and calcium salts are sequentially recovered. The process realizes efficient recovery of sodium sulfate and sodium chloride (the recovery rates are greater than or equal to 98% and 99% respectively, and the particle diameters are 0.4 mm and 0.5 mm), and completes miscellaneous salt resource utilization, and the mine water recovery efficiency is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high salinity mine water treatment and recovery, in particular to a circulating freezing-thermal method salt separation treatment process and device for high salinity mine water. BACKGROUND

[0002] At present, domestic research mainly focuses on membrane separation technology (double membrane method) or evaporation crystallization technology for treating high salinity wastewater. Among them, the double membrane method refers to combining ultrafiltration and reverse osmosis to remove suspended solids and large molecular organic matter by ultrafiltration, and further desalination by reverse osmosis. Although the double membrane method can significantly reduce the salinity of water, the salt or organic matter in the reverse osmosis concentrate is enriched, which causes subsequent disposal difficulties, and the salt in the concentrate is complex, with low resource utilization value; at the same time, membrane pollution is easily produced during the treatment process, resulting in frequent chemical cleaning, high operation and maintenance cost, and the inability to realize salt separation and recovery. The evaporation crystallization technology refers to concentrating wastewater through multi-stage evaporation, and finally crystallizing and separating salt. Although the evaporation crystallization technology can avoid the problem of salt enrichment, it also has limitations such as poor quality of crystallized salt, which cannot meet the industrial salt standard; the crystallization process is easily disturbed by high-concentration organic matter (COD>1000mg / L); and high energy consumption. Therefore, these two traditional high salinity mine water treatment technologies can achieve partial desalination, but have problems such as disposal difficulty of concentrate, high energy consumption, and low salt resource utilization rate. SUMMARY

[0003] The purpose of the present application is to provide a circulating freezing-thermal method salt separation treatment process and device for high salinity mine water, which selectively separates single salts such as sodium sulfate and sodium chloride by precisely controlling the crystallization conditions (temperature, pH, additives), and realizes salt resource recovery and wastewater "near-zero discharge" by coupling the freezing-thermal method circulation process, thereby breaking through the limitations of traditional high salinity mine water treatment technology.

[0004] To achieve the above purpose, the present application provides a circulating freezing-thermal method salt separation treatment process for high salinity mine water, comprising the following steps:

[0005] (1) Pretreating the high salinity mine water concentrate to reduce its COD and TDS content; sending the pretreated concentrate into an improved sodium sulfate decahydrate freezing crystallization device for freezing crystallization, and then centrifugally separating to obtain sodium sulfate decahydrate;

[0006] (2) Introducing the sodium sulfate decahydrate obtained in step (1) into a molten salt device for thermal melting to form a sodium sulfate saturated solution, and then performing thermal crystallization to obtain anhydrous sodium sulfate salt by centrifugal drying;

[0007] (3) Evaporating and crystallizing the mother liquor containing sodium chloride discharged after centrifugal separation in step (1) to obtain sodium chloride by centrifugal drying;

[0008] (4) Combine the mother liquor produced in step (2) and step (3), and pass into a miscellaneous salt crystallizer, and determine the subsequent flow direction according to the calculated miscellaneous salt rate:

[0009] When the miscellaneous salt rate is ≤5%, the solution is refluxed to the refrigeration crystallization step for reprocessing;

[0010] When the miscellaneous salt rate is >5%, potassium salt, magnesium salt and calcium salt are sequentially precipitated and recovered by adjusting the temperature and pH value.

[0011] Preferably, in step (1), the pretreatment includes ozone oxidation, flocculation precipitation, filtration and two-stage reverse osmosis, and the COD content of the effluent after pretreatment is less than 100 mg / L, and the TDS content is 2500-3000 mg / L.

[0012] Preferably, in step (1), the operating temperature of the improved sodium sulfate decahydrate refrigeration crystallization device is -5°C, and ethylene glycol is used as a refrigerant, and when the solid-liquid ratio of the crystallization device reaches 20%-25%, centrifugal separation is performed.

[0013] Preferably, in step (2), the hot melting is performed under the condition of 200 r / min stirring, and the crystal growth time is 90 min; the hot crystallization temperature is 32.4°C.

[0014] Preferably, the specific operation of step (3) is: under the condition of 200 r / min stirring, the crystal growth time is 60 min to obtain a sodium chloride concentrate, which is then introduced into a sodium chloride evaporation crystallizer, and the evaporation crystallization temperature is 162°C, and sodium chloride is precipitated when the concentration reaches 40%.

[0015] Preferably, in step (4), the conditions for recovering potassium salt, magnesium salt and calcium salt are: the temperature is controlled at 50°C, and the pH value is adjusted to sequentially precipitate, wherein the pH value is 7-8 when recovering potassium salt, the pH value is 8-9 when recovering magnesium salt, and the pH value is 10.5 when recovering calcium salt.

[0016] Preferably, in step (4), when the miscellaneous salt rate is ≤5%, steps (1)-(4) are repeated until the miscellaneous salt rate is >5%, and then evaporation crystallization is performed with potassium chloride and sodium citrate as additives, and then potassium salt, magnesium salt and calcium salt are sequentially recovered at a temperature of 50°C and pH values of 7-8, 8-9 and 10.5, respectively.

[0017] Preferably, in step (4), the miscellaneous salt rate is determined by a sensor in the miscellaneous salt crystallizer, and the calculation formula of the miscellaneous salt rate is as follows:

[0018] ;

[0019] Wherein, C(miscellaneous) represents the concentration of the solubility solid determined as impurities after the concentrate is evaporated and concentrated, and TDS represents the total dissolved solid concentration in the concentrate.

[0020] The application also provides an improved sodium sulfate decahydrate freezing crystallization device for implementing the above-mentioned treatment process, comprising:

[0021] a crystallization tank body with a W-shaped bottom structure at the bottom;

[0022] a freezing converter arranged around the inner wall of the crystallization tank body for freezing treatment of the feed liquid to reduce the temperature;

[0023] a flow guide cylinder coaxially arranged inside the crystallization tank body for guiding the feed liquid to form a circulating flow path;

[0024] a temperature sensor arranged on the side wall of the flow guide cylinder for determining whether the feed liquid after freezing treatment is lower than-5℃;

[0025] a stirring assembly with stirring paddles extending into the flow guide cylinder for driving the movement of the feed liquid;

[0026] a clarification zone which is a diameter expansion section arranged at the upper part of the crystallization tank body;

[0027] a fine crystal filtration assembly arranged in the clarification zone for separating and discharging fine crystals;

[0028] a feed inlet arranged at the upper part of the crystallization tank body for introducing new concentrated liquid to mix with the circulating mother liquor in the tank body;

[0029] a discharge outlet arranged at the bottom of the flow guide cylinder for discharging sodium sulfate decahydrate obtained by freezing crystallization treatment.

[0030] Preferably, the fine crystal filtration assembly comprises:

[0031] a fine crystal filtration screen horizontally arranged at the upper part of the clarification zone;

[0032] a fine crystal discharge outlet arranged on the side wall or top of the clarification zone and located above or in communication with the fine crystal filtration screen for discharging the intercepted fine crystals and impure salts.

[0033] Therefore, the high salinity mine water circulating freezing-thermal method desalination treatment process and device provided by the application have the following beneficial effects:

[0034] (1) In the field of industrial wastewater "zero discharge", the thermal method desalination technology can well realize the resource separation of Na2SO4, NaCl and K + , Mg 2+ , Ca 2+ inorganic salts, effectively solve the problems of impure salt pollution and high energy consumption, etc.

[0035] (2) Freeze-salting technology is beneficial to wastewater reduction, salt resource utilization and process greenization through the combination of low-temperature phase change and solubility difference. The multi-dimensional innovation framework of freeze-salting technology can help better integrate with other technologies in the future and promote the sustainable development of high-salinity wastewater treatment.

[0036] (3) In the process of salt separation and crystallization, freeze-salting and thermal-salting can not only solve the problem of mixed salt separation, but also transform high-salinity wastewater treatment from a "cost center" to a "resource income center". The salt separation and crystallization process, through the combination of thermal and freeze processes, can overcome the limitations of traditional methods, improve desalination efficiency, improve resource utilization, and reduce energy consumption, providing a method and experience for high-salinity mine water treatment. The salt separation and crystallization technology has great application value in the treatment of high-salinity mine water, and with the continuous development of technology in the future, the treatment technology can be better optimized to promote the green treatment and sustainable development of high-salinity mine water.

[0037] The technical solutions of the present application will be further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a flow chart of the circulating freeze-thermal crystallization process of the present application;

[0039] Figure 2 is a structure diagram of the improved sodium sulfate decahydrate freeze crystallization device;

[0040] REFERENCE NUMERALS

[0041] 1, crystallization tank body; 2, flow guide cylinder; 3, freeze heat exchanger; 4, temperature sensor; 5, stirring paddle; 6, stirring paddle blade; 7, clarification zone; 81, fine crystal filter screen; 82, fine crystal discharge outlet; 9, feed inlet; 10, discharge outlet. DETAILED DESCRIPTION

[0042] The present application provides an improved sodium sulfate decahydrate freeze crystallization device based on Figure 2 The process of the present application for the circulating freeze-thermal salt separation treatment of high-salinity mine water concentrate containing potassium salt, magnesium salt, calcium salt and having sodium sulfate, chloride and sodium ions as dominant ions, is shown in Figure 1 The process utilizes the coupling of freeze remelting, high-temperature evaporation crystallization and miscellaneous salt solid reflux, combined with the improved new sodium sulfate decahydrate freeze crystallization device, to ultimately achieve the purpose of separating and recycling the salt in the high-salinity mine water concentrate.

[0043] The improved sodium sulfate decahydrate freezing crystallization device mainly comprises a crystallization tank body 1, a flow guide cylinder 2, a stirring device and a fine crystal treatment system. The bottom of the crystallization tank body 1 is designed in a W-shaped bottom, which is beneficial to the suspension of the crystals and the circulating mixing of the material liquid. The flow guide cylinder 2 is coaxially arranged in the crystallization tank body 1, and a main flow channel is formed in the flow guide cylinder 2, and an annular gap flow channel is formed between the outer portion of the flow guide cylinder 2 and the tank wall. The crystallization tank body 1 is made of a heat preservation material except for the top cover, and four freezing heat exchangers 3 are arranged around the tank body. The new feed liquid enters the crystallization tank body 1 through a feed inlet 9, is mixed with the circulating mother liquor, and then is subjected to circulating freezing treatment. The temperature sensor 4 arranged on the side wall of the flow guide cylinder 2 is used for judgment. The heat preservation material ensures that the whole circulating freezing process is kept in a low temperature state, and only heat exchange is generated at the top of the tank. When the heat exchange of the material liquid reaches the specified freezing temperature, the material liquid enters the flow guide cylinder 2 and flows downward under the pushing of the stirring paddle 5, and then flows from the bottom to the top along the outside of the flow guide cylinder, forming a circulation. The stirring paddle 6 of the stirring device is arranged in the flow guide cylinder 2, and is used to drive the material liquid to flow from the upper portion of the flow guide cylinder 2 downward, and then to flow upward along the annular gap flow channel from the bottom, forming a circulation in the tank. A clarified zone 7 with an enlarged diameter is arranged at the upper portion of the crystallization tank body 1, and the starting position of the clarified zone 7 is higher than the upper end inlet of the flow guide cylinder 2, so that the upward flow velocity is reduced, and large particle crystals are difficult to enter the inside of the flow guide cylinder 2, thereby reducing the collision with the stirring paddle 5. A fine crystal filter assembly is arranged in the clarified zone 7 and is used for separating and discharging fine crystals. The fine crystal filter assembly comprises a fine crystal filter screen 81 and a fine crystal discharge outlet 82. The fine crystal filter screen 81 with a pore size of 0.2 mm is arranged in the upper layer of the clarified zone 7 and is used for intercepting fine crystals. The fine crystal discharge outlet 82 is arranged on the side wall of the upper layer of the clarified zone 7 and is used for discharging the intercepted fine crystals to an external fine crystal elimination system, and the fine crystals are mixed with the raw material liquid and then are returned to flow. A discharge outlet 10 is arranged at the bottom of the flow guide cylinder 2 and is used for discharging the sodium sulfate decahydrate crystals precipitated by freezing crystallization. The structure of the new crystallization device fully considers the influencing factors of the secondary nucleation of the continuous crystallizer, optimizes the structure of the traditional flow guide cylinder baffle crystallizer, reduces the occurrence of the secondary nucleation phenomenon, and correspondingly improves the crystal growth rate. Meanwhile, the structure for discharging fine crystals is introduced, so as to improve the average particle size of the crystalline particles. The recycling of the fine crystals adopts the method of mixing with the raw material, which pre-cools the raw material and eliminates the excess crystal nucleus by dissolving the fine crystals, thereby promoting the growth of the crystals.

[0044] The circulating freezing-thermal method salt separation treatment process of high salinity mine water specifically comprises the following steps:

[0045] (1) The pre-concentrated wastewater liquid enters the improved freezing crystallization device, is subjected to freezing crystallization, and is subjected to centrifugal separation operation to obtain sodium sulfate decahydrate.

[0046] (2) The sodium sulfate decahydrate obtained in step (1) is introduced into a molten salt device, steam heating is used to release the crystal water, a saturated sodium sulfate solution is formed at a stirring speed of 200 r / min and a crystal growth time of 90 min, and then the solution is introduced into a sodium sulfate crystallizer, the temperature is set to 32.4°C, and finally, sodium sulfate salt is obtained by centrifugal separation and drying.

[0047] (3) The mother liquor rich in sodium chloride discharged after the centrifugal separation operation after the freeze crystallization in step (1) is treated at a stirring speed of 200 r / min and a crystal growth time of 60 min to obtain a sodium chloride concentrate, which is introduced into a sodium chloride evaporation crystallizer, the temperature is increased to 162°C, and when the concentration reaches 40%, the sodium chloride saturation precipitation point is reached, and when the solid-liquid ratio of the crystal slurry reaches 20%-25%, the sodium chloride salt product is obtained by centrifugal separation and drying.

[0048] (4) The salt precipitation mother liquor in the sodium chloride evaporation crystallizer in step (3) and the mother liquor in the sodium sulfate crystallizer in step (2) are introduced together into a miscellaneous salt crystallizer, and the miscellaneous salt rate is determined by a sensor in the crystallizer. The calculation formula of the miscellaneous salt rate is as follows:

[0049] ;

[0050] Wherein, C (miscellaneous) represents the concentration of the dissolved solid determined as impurities after the concentrate is evaporated and concentrated, and TDS represents the total dissolved solid concentration in the concentrate.

[0051] A part of the miscellaneous salt solution with a miscellaneous salt rate greater than 5% will be recovered by adjusting the temperature, pH, etc. to sequentially precipitate various salt solids. When the temperature is adjusted to 50°C and the pH is adjusted to 7-8, potassium salt is first precipitated and recovered; when the temperature is adjusted to 50°C and the pH is adjusted to 8-9, magnesium salt is precipitated and recovered; when the temperature is adjusted to 50°C and the pH is adjusted to 10.5, calcium salt is finally precipitated and recovered. At the same time, the waste liquid recovered by adding an appropriate amount of hydrochloric acid solution to adjust the pH will be introduced into the molten salt device again, returned to the inlet of the freeze crystallization device through the reflux pipeline, and the liquid circulation process is completed. Another part of the miscellaneous salt solution with a miscellaneous salt rate less than 5% will be directly introduced into the molten salt device, returned to the inlet of the freeze crystallization device through the reflux pipeline, and the liquid circulation process is completed.

[0052] (5) When the miscellaneous salt rate is ≤5%, steps (1)-(4) are repeated until the miscellaneous salt rate is greater than 5%, and the miscellaneous salt solution is evaporated and crystallized at a temperature of 50°C with potassium chloride and sodium citrate as additives. When the temperature is 50°C and the pH is 7-8, 8-9 and 10.5 respectively, potassium salt, magnesium salt and calcium salt are recovered in sequence.

[0053] (6) after completing all liquid circulation, recovering sodium sulfate, sodium chloride, potassium chloride, magnesium sulfate, calcium carbonate in turn, ensuring that the recovery rate of the five salts meets sodium sulfate 98%, sodium chloride 99%, potassium chloride 86%, magnesium sulfate 83%, calcium carbonate 92%, and the impurity salt rate is less than 5%, the remaining circulating liquid in the system is evaporated at 200 DEG C high temperature through the sodium chloride evaporation crystallizer, 0.3% of the impurity salt is obtained, the main component is sodium citrate, which can be used as an additive to participate in the next mine water recovery cycle.

[0054] The technical solutions of the present application are further described below by means of the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application, and any changes, modifications, substitutions, combinations, simplifications made without deviating from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application. In addition, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application, and are within the scope of protection of the present application.

[0055] In this paper, the term "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The term "embodiment" appearing at various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in this application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form a corresponding implementable technical solution.

[0056] Unless otherwise defined, the meaning of the technical terms used herein is the same as that generally understood by those skilled in the art to which the present application belongs; the use of related terms in this paper is only for the purpose of describing specific embodiments, and is not intended to limit the present application.

[0057] Unless otherwise specified, the reagents, instruments, equipment, etc. used in the present application are conventional reagents, instruments and equipment used by those skilled in the art; the test standards use national standards or international standards commonly used in the art, and no redundant description is made here.

[0058] Embodiment

[0059] The high salinity mine water concentrate liquid is configured, the TDS content of the concentrate liquid is 6000 mg / L, the content ratio of sulfate ion / chloride ion is 3.3, the sodium chloride and sodium sulfate salt account for 72% of the total salt content, and the COD content is 2350 mg / L. After the concentrate liquid is subjected to the pretreatment processes of the ozone oxidation device, the flocculation precipitation filtration device and the two-stage reverse osmosis in sequence, the COD content is controlled to be 85 mg / L and the TDS content is 2550 mg / L by connecting the sensor at the outlet. The sum of sodium ion, chloride ion and sulfate ion accounts for more than 90% of the total dissolved proportion in the high salinity mine water, and the dominant salt is sodium sulfate and sodium chloride, so the high-temperature evaporation crystallization can be used to separate the salt. The evaporation crystallization high-efficiency vertical pipe falling film evaporator is used, the heat exchange and crystallization surface are subjected to high-efficiency heat transfer treatment, the heat exchange pipe adopts a special pipe structure form, and the evaporator includes a sodium chloride evaporator and a sodium sulfate evaporator.

[0060] The pretreated concentrate liquid is injected into the improved sodium sulfate decahydrate freezing crystallization device Figure 2 The freezing crystallization device first changes the flow direction of the fluid in the draft tube 2 to downward flow, the new feed liquid is mixed with the circulating mother liquor to enter the heat exchanger, the heat exchange reaches the specified freezing temperature, so that the supersaturation degree is generated, and the fluid directly enters the draft tube 2 from the upper part, flows downward under the pushing of the stirring paddle 5, and then flows from the lower part to the upper part along the outer side of the draft tube 2 to form a circulation. The W-shaped bottom is adopted at the bottom of the tank body, which is beneficial to the suspension and circulation of the crystals. The crystal grains in the crystal slurry are in a suspended state and continuously grow by the uniform stirring of the stirrer. The design of the draft tube 2 and the tank body diameter and the selection of the stirring paddle rotation speed are all to make the crystals in the straight section of the tank body reach a good suspended state. The freezing agent is selected as ethylene glycol, the process temperature is controlled at-5 ℃, and the circulating concentration of the liquid is controlled to be not more than 1 g / L. When the sodium sulfate decahydrate in the crystallization device is continuously precipitated, the sodium sulfate decahydrate is separated out by the centrifugal separation device when the solid-liquid ratio of the crystal slurry reaches 25%.

[0061] The improved new sodium sulfate decahydrate freezing crystallization device fully considers the factors of reducing secondary nucleation in the crystallization process and promoting crystal growth. The crystal particles inside the crystallization device operate at different flow rates according to the size of the particle diameter. Smaller crystal particles operate synchronously with the circulating liquid to complete the complete circulation and continue to grow. For larger crystals, the flow rate of the liquid rising outside the draft tube 2 can only make them suspended. Because the diameter expansion section is added to the upper part of the crystallization device, the rising flow rate is reduced, so that larger crystal particles are difficult to pass through the upper end of the draft tube 2 and enter the inside of the draft tube 2, reducing the chance of large particles colliding with the stirring paddle 5. Crystal collision with the stirring paddle 5 is the main cause of secondary nucleation of crystallization. According to the empirical formula of secondary nucleation, the nucleation rate is proportional to the energy transfer rate to the crystal when colliding. For larger crystals, the collision produces a larger energy transfer. Therefore, reducing the collision probability of larger particles with the stirring paddle 5 can reduce the nucleation rate. The new structure not only reduces the breakage of large particles, but also maintains good crystal form, while the reduction of secondary nucleation can promote the growth of crystals in the entire crystallization device. The upper section of the crystallization device is the clarification zone 7, and a 0.2mm fine crystal filter screen 81 is arranged on the upper layer. Fine crystal particles with a particle diameter less than 0.2mm will be suspended into the filter layer and output to the treatment liquid to participate in the circulation. The setting of the fine crystal filter assembly 8 can ensure the crystal quality of the frozen crystallization product sodium sulfate decahydrate, and also ensure that the number of particles carried by the overflow circulating liquid is small and the particle size is very small, so that the circulating liquid can reduce secondary nucleation when contacting the impeller of the circulating pump; at the same time, the circulating pump selects an axial flow pump, which can reduce the impeller speed as much as possible while ensuring the flow rate and head. These measures all ensure that the circulating liquid can reduce the opportunity of secondary nucleation as much as possible during the circulation process.

[0062] The improved new type of sodium sulfate decahydrate freezing crystallization device is also provided with an outlet for discharging fine crystals in the crystallization device, so that the average particle size of sodium sulfate decahydrate crystals is increased. The crystals in the crystallizer are grown from crystal nuclei. In a certain volume of crystal slurry, the less the amount of crystal nuclei generated, the larger the product crystals grow. On the contrary, if the amount of crystal nuclei generated is too much, the solute in the solution will be deposited on the surface of the excessive crystal nuclei, and the particle size of the product crystals will inevitably be small. In actual production, the nucleation process is not easy to control, and the general situation is that the amount of crystal nuclei is excessive, so it is necessary to remove the excessive crystal nuclei to increase the average particle size of the crystals. In the clarification zone 7 at the upper part of the crystallization device, the crystal slurry flows upward at a low speed, so that the crystals larger than a certain "fine crystal cutting particle size" can all be precipitated from the solution and return to the main part of the crystallization device to participate in the internal circulation and grow again. The fine crystals smaller than the particle size will enter the fine crystal elimination circulation system through the fine crystal discharge outlet 82 provided in the clarification zone 7. The fine crystal elimination method is to mix the fine crystal liquid with the raw material without pre-cooling, which on the one hand reduces the temperature of the raw material to achieve the purpose of pre-cooling the raw material, and on the other hand dissolves the fine crystals to eliminate the total amount of crystal nuclei in the crystallization device. At the same time, this part of the fine crystal solute returns to the raw material and is reused, and finally the particle size and quality of the sodium sulfate decahydrate crystals are improved, and the sulfate ion index of the separated mother liquor is also guaranteed to fully meet the standard. The structure of the new type of crystallization device considers the influence factors of the secondary nucleation of the continuous crystallizer, introduces the fine crystal discharge structure, and makes the average particle size of sodium sulfate decahydrate reach 0.4 mm, and the precipitation rate is increased by 13.25%.

[0063] The sodium sulfate decahydrate is introduced into the molten salt container with a stirrer, heated by steam, and the crystallization water is released. After forming a saturated sodium sulfate solution at a stirring speed of 200 r / min and a crystal growing time of 90 min, it is introduced into the sodium sulfate evaporation crystallizer, the temperature is adjusted to 32.4℃, and when the concentration reaches about 30%, anhydrous sodium sulfate is precipitated. After centrifugal separation and drying, anhydrous sodium sulfate salt product is obtained, the crystalline particle size is 0.4 mm, the recovery rate is 98%, and the purity is 99%.

[0064] The concentrated mother liquor from the freezing crystallization is preheated, treated at a stirring speed of 200 r / min and a crystal growing time of 60 min to obtain a sodium chloride concentrate, and then introduced into a sodium chloride evaporation crystallizer. When the concentration reaches 40%, sodium chloride reaches the saturation precipitation point, the temperature is adjusted to 162℃, and the solid-liquid ratio of the crystal slurry reaches 25%. After centrifugal separation and washing with saturated salt solution, the sodium chloride salt product is obtained by drying, the crystalline particle size is 0.5 mm, the recovery rate is 99%, and the purity is 99%.

[0065] In addition, the concentrated mother liquor from the sodium chloride and sodium sulfate evaporation crystallizer is combined and introduced into a miscellaneous salt crystallizer. The sensor in the crystallizer is used to judge the miscellaneous salt rate, and the calculation formula of the miscellaneous salt rate is as follows:

[0066] ;

[0067] Wherein C (hetero) represents the concentration of dissolved solids determined as impurities after the concentrated solution is evaporated and concentrated, and TDS represents the total dissolved solids concentration in the concentrated solution. The evaporation and concentration of the mother liquor, also known as the salt-containing wastewater, is used to determine whether further solid recovery is required. The current evaporation and concentration technology produces wastewater with a salt content of 3-20%, and when the concentration of salt ions is too low, it is difficult to remove them efficiently and completely by chemical precipitation. The reaction kinetics is slow, the crystal growth is difficult, and the solid-liquid separation efficiency is low, which may result in substandard purity of the recovered product, forming "substandard salt", so the concentrated solution with a salt rate of less than 5% is reprocessed by refluxing, and is directly introduced into the molten salt tank through the reflux pipeline and returned to the frozen crystallization device inlet to complete the liquid circulation process. The salt solution with a salt rate greater than 5% is recovered by sequentially precipitating various salt solids by adjusting the temperature, pH and other specified conditions. When the temperature is adjusted to 50 DEG C and the pH is adjusted to 7.7, potassium chloride is first precipitated and recovered, with a recovery rate of 86% and a purity of 93.7%; when the temperature is adjusted to 50 DEG C and the pH is adjusted to 8.1, magnesium sulfate is precipitated and recovered, with a recovery rate of 83% and a purity of 97.1%; when the temperature is adjusted to 50 DEG C and the pH is adjusted to 10.5, calcium carbonate is finally precipitated and recovered, with a recovery rate of 92% and a purity of 97.5%. After completing all the liquid circulation and sequentially recovering sodium sulfate, sodium chloride, potassium chloride, magnesium sulfate and calcium carbonate, the recovery rates of the five salts are ensured to meet the requirements of sodium sulfate 98%, sodium chloride 99%, potassium chloride 86%, magnesium sulfate 83% and calcium carbonate 92%, and the remaining circulating liquid in the system is evaporated at a high temperature of 200 DEG C through the sodium chloride evaporation crystallizer to obtain 0.3% of the salt, which is mainly composed of sodium citrate and can be used as an additive for the next mine water recovery cycle.

[0068] In summary, the cyclic freezing-thermal method crystallization process of the present application reduces the enrichment effect of impurity ions and organic matter in wastewater, is conducive to the stable and long-period operation of the entire quality-based crystallization system, and the quality of the recovered salt product is stable and controllable. Finally, the salt in the salt-containing wastewater is effectively recovered by quality-based recovery, achieving the purpose of resource utilization and realizing near-zero discharge of wastewater.

[0069] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A process for the cyclic freeze-thermal fractional salt processing of high salinity mine water, characterised in that, The method comprises the following steps: (1) pretreating the high-mineralization mine water concentrate to reduce the COD and TDS content, feeding the pretreated concentrate into a modified sodium sulfate decahydrate freezing crystallization device to perform freezing crystallization, and then performing centrifugal separation to obtain sodium sulfate decahydrate; (2) introducing the sodium sulfate decahydrate obtained in step (1) into a molten salt device to perform hot melting, forming a sodium sulfate saturated solution, and then performing hot crystallization and centrifugal drying to obtain anhydrous sodium sulfate salt; (3) performing evaporation crystallization on the mother liquor containing sodium chloride discharged after centrifugal separation in step (1), and then performing centrifugal drying to obtain sodium chloride; (4) combining the mother liquor produced in steps (2) and (3), feeding the combined mother liquor into a miscellaneous salt crystallizer, and determining the subsequent flow direction according to the calculated miscellaneous salt rate: when the miscellaneous salt rate is less than or equal to 5%, the solution is returned to the freezing crystallization step for reprocessing; when the miscellaneous salt rate is greater than 5%, potassium salt, magnesium salt and calcium salt are sequentially precipitated and recovered by adjusting the temperature and pH value; the conditions for recovering the potassium salt, magnesium salt and calcium salt are as follows: the temperature is controlled at 50 DEG C, and the potassium salt, magnesium salt and calcium salt are sequentially precipitated by adjusting the pH value, wherein the pH value is 7-8 when the potassium salt is recovered, the pH value is 8-9 when the magnesium salt is recovered, and the pH value is 10.5 when the calcium salt is recovered; a modified sodium sulfate decahydrate freezing crystallization device for realizing the above processing process comprises: a crystallization tank body with a W-shaped bottom structure at the bottom; a freezing converter arranged around the inner wall of the crystallization tank body for freezing treatment of the feed liquid to reduce the temperature; a flow guide cylinder coaxially arranged in the crystallization tank body for guiding the feed liquid to form a circulating flow path; a temperature sensor arranged on the side wall of the flow guide cylinder for determining whether the feed liquid after freezing treatment is lower than-5 DEG C; a stirring assembly with stirring paddles extending into the flow guide cylinder for driving the feed liquid to move; a clarification zone which is a diameter expansion section arranged at the upper part of the crystallization tank body; a fine crystal filtration assembly arranged in the clarification zone for separating and discharging fine crystals; a feed inlet arranged at the upper part of the crystallization tank body for introducing new concentrate liquid to mix with the circulating mother liquor in the tank body; a discharge outlet arranged at the bottom of the flow guide cylinder for discharging the sodium sulfate decahydrate obtained by freezing crystallization treatment.

2. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: In step (1), the pretreatment includes ozone oxidation, flocculation precipitation, filtration and two-stage reverse osmosis, and the COD content of the effluent after pretreatment is less than 100 mg / L, and the TDS content is 2500-3000 mg / L.

3. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: In step (1), the operating temperature of the modified sodium sulfate decahydrate freezing crystallization device is-5 DEG C, and ethylene glycol is used as the refrigerant; when the solid-liquid ratio of the crystallization device reaches 20%-25%, centrifugal separation is performed.

4. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: In step (2), the hot melting is performed under the condition of 200 r / min stirring, and the crystal growth time is 90 min; the hot crystallization temperature is 32.4 DEG C.

5. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: The specific operation of step (3) is as follows: under the condition of 200 r / min stirring, sodium chloride concentrate liquid is obtained after crystal growth for 60 min, and then the sodium chloride concentrate liquid is introduced into a sodium chloride evaporation crystallizer; the evaporation crystallization temperature is 162 DEG C, and sodium chloride is precipitated when the concentration reaches 40%.

6. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: In step (4), when the impurity salt rate is ≤5%, steps (1) to (4) are repeated until the impurity salt rate is >5%. Potassium chloride and sodium citrate are used as additives for evaporation and crystallization. Then, potassium salt, magnesium salt and calcium salt are recovered in sequence at a temperature of 50°C and pH values ​​of 7~8, 8~9 and 10.

5.

7. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that: In step (4), the impurity salt rate is determined by a sensor inside the impurity salt crystallizer. The formula for calculating the impurity salt rate is as follows: ； Wherein, C (impurities) represents the concentration of dissolved solids that are identified as impurities after the concentrate has been evaporated and concentrated, and TDS represents the total dissolved solids concentration in the concentrate.

8. A process for the cyclic freezing- thawing fractional salt processing of high salinity mine water according to claim 1, characterized in that, The fine-crystal filter assembly includes: A fine-grained filter screen is horizontally positioned above the clarification zone; A fine crystal outlet is provided on the side wall or top of the clarification zone and is located above or in communication with the fine crystal filter screen, for discharging the trapped fine crystals.

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