CN109592698B - Method for preparing funnel-shaped sodium sulfate from high-salinity wastewater - Google Patents
Method for preparing funnel-shaped sodium sulfate from high-salinity wastewater Download PDFInfo
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Abstract
The invention relates to a method for preparing funnel-shaped sodium sulfate from high-salinity wastewater; heating the wastewater to 50-80 ℃, adding sodium hydroxide to adjust the pH of the wastewater to 11-14, and controlling the stirring speed to be 100-400 rpm; adopting a negative pressure evaporation crystallization mode, wherein the vacuum degree is 0.04-0.07 MPa, until the volume of the evaporated water is 20-30% of the volume of the original wastewater; the obtained product is filtered and dried to obtain funnel-shaped anhydrous sodium sulfate crystals. The sodium sulfate product with funnel-shaped special crystal form is prepared, the cone angle of the funnel is 120-150 degrees, and the purity of the sodium sulfate is more than or equal to 95 percent; the particle size is larger and the distribution is uniform, and the particle size of the product is more than or equal to 300 mu m.
Description
Technical Field
The invention relates to a crystallization desalination process of pharmaceutical wastewater mainly containing sodium sulfate, in particular to funnel-shaped sodium sulfate capable of being efficiently recycled from pharmaceutical wastewater and a preparation method thereof.
Background
Sodium sulfate (Sodium sulfate), chemical formula Na2SO4Also called as thenardite, as a common inorganic salt, its solubility shows a decreasing inverse solubility trend with increasing temperature, and the solid-liquid balance is maintained in saturated aqueous solution at normal temperature in the form of sodium sulfate decahydrate. Therefore, the anhydrous sodium sulfate product is usually obtained by evaporation crystallization in industry.
At present, the domestic sodium sulfate is mainly produced by comprehensively exploiting and preparing sulfate ore and salt lake brine resources. Meanwhile, in industrial production, the main constituent substances in the wastewater finally obtained in the production process related to the desulfurization process comprise sulfate. For example, the inorganic salt component in wastewater from coal chemical industry and some pharmaceutical industries is mainly sodium sulfate. With the current increasingly strict water resource management mechanism and environmental protection requirements, the recovery of the simple salt in the wastewater becomes the key content of the three wastes treatment in the current factory, how to efficiently extract and prepare high-quality salt products from the wastewater is a necessary way to open the outlet of the waste salt, and is the development direction of the future high-salt wastewater treatment.
Under industrial production conditions, sodium sulfate is mainly granular crystals of an orthorhombic system and a monoclinic system. The evaporation process is easy to nucleate, the particles are fine and easy to gather into loose clusters, the fluidity is poor, and the phenomenon of mother liquor entrainment is aggravated. Meanwhile, in the solid-liquid separation process after wastewater desalination, the sodium sulfate obtained by improper control is in a powder shape, the particle size of the product is small (as in comparative example 1 in the application), a compact filter cake is easily formed, the filtration difficulty is increased, and the production cost is increased finally. Therefore, changing the shape of the product and improving the particle size distribution of the crystals become measures for effectively improving the separation efficiency of the wastewater and the quality of the product. For example, in the Chinese patent application CN1986406, a surfactant is added to assist in evaporating the clear liquid to prepare granular sodium sulfate with large particle size, and the particle size can reach 200-1000 μm. Due to the complexity of the components in the process of wastewater desalination, the addition of the additive introduces new impurities into the system on one hand, increases the difficulty of wastewater treatment, and on the other hand, the effect of the additive on crystallization is limited by the influence of other impurities in the system. From the current research reports, the existence of organic impurities in the wastewater can generate a certain inhibiting effect on the nucleation and growth of crystals, easily causes the occurrence of unfavorable phenomena such as explosive nucleation and fine crystal growth limitation in the crystallization process, and causes great difficulty in the treatment of high-salt wastewater. Therefore, there is still a need for continued development and research on how to prepare large particle size sodium sulfate from wastewater.
In the aspect of downstream process of products, domestic sodium sulfate is mainly used in industries of detergent fillers, sulfate pulping, glass preparation by replacing soda ash and the like, and the consumption structure proportion of the three aspects is over 90 percent. The dissolution property of the product directly affects the operating efficiency and the product quality of the subsequent industry. From some previous research reports, the large particle sodium sulfate product has the disadvantages of slow dissolution and inhibition of the mixing effect of sodium sulfate as a filler and pulping aid. Therefore, the production of the large-particle sodium sulfate product with uniform particle size distribution and easy dissolution is of great significance for expanding the application field of sodium sulfate.
In conclusion, the preparation of the sodium sulfate product with small bulk density and large specific surface area has important and obvious advantages for improving the desalination and separation efficiency of wastewater and the dissolution rate of a downstream process. However, the focus of the patent literature on the method for preparing sodium sulfate from wastewater is still in the feasibility of desalination process and development of evaporative crystallization device, and no report is found on the morphology regulation of sodium sulfate. In the traditional evaporation crystallization process, the influence of complex factors such as stirring, solution pH value and the like on the product morphology is not considered in the crystallization process, and the funnel-shaped sodium sulfate product with stable and controllable morphology is prepared mainly by regulating and controlling parameters such as evaporation intensity, stirring intensity, solution pH value and the like of wastewater in the evaporation process, so that the special advantages of the funnel-shaped sodium sulfate product in the aspects of solid-liquid separation and dissolution are further improved.
Disclosure of Invention
The invention aims to provide a method for preparing funnel-shaped sodium sulfate crystals from high-salinity wastewater containing sodium sulfate in the field of pharmacy. The obtained product has large particle size, is easy to filter, has good solubility, and has special advantages in the aspects of chemical separation, downstream application of the product and the like.
The invention aims to change the traditional granular or powdery sodium sulfate preparation method and develop a high-quality funnel-shaped sodium sulfate product with complete morphology by regulating and controlling key operation parameters of a sodium sulfate evaporation crystallization process in the wastewater desalination treatment process, thereby solving the problem of solid-liquid separation in the sodium sulfate-containing wastewater desalination process, effectively increasing the specific surface area of a solid phase and improving the dissolution rate of large-particle crystals.
The technical scheme of the invention is as follows:
a method for preparing funnel-shaped sodium sulfate from high-salinity wastewater; the method comprises the following steps:
1) heating the wastewater to 50-80 ℃, adding sodium hydroxide to adjust the pH of the wastewater to 11-14, and controlling the stirring speed to be 100-400 rpm;
2) adopting a negative pressure evaporation crystallization mode, wherein the vacuum degree is 0.04-0.07 MPa, until the volume of the evaporated water is 20-30% of the volume of the original wastewater;
3) the obtained product is filtered and dried to obtain funnel-shaped anhydrous sodium sulfate crystals.
In the wastewater, the mass percent of sodium sulfate is 28-30%.
The drying condition is that the normal pressure is 105 ℃, and the drying time is more than or equal to 8 hours.
The funnel-shaped anhydrous sodium sulfate prepared by the method is characterized in that the cone angle of the funnel is 120-150 degrees, and the purity of the sodium sulfate is more than or equal to 95 percent. The mass percentage of the product with the grain diameter more than or equal to 300 mu m is more than 90 percent.
The invention provides a preparation method of funnel-shaped anhydrous sodium sulfate, which has the creativity that:
1. the sodium sulfate product with funnel-shaped special crystal form is prepared, the cone angle of the funnel is 120-150 degrees, and the purity of the sodium sulfate is more than or equal to 95 percent (mass percentage).
2. The particle size is larger and the particle size is distributed evenly, the mass percentage of the product with the particle size of more than or equal to 300 mu m exceeds 90 percent, the special shape of the sodium sulfate particles is beneficial to filtration, the solid-liquid separation efficiency of wastewater desalination can be effectively improved, the moisture content of the filtered product is 4.3 to 7.0 percent, but the moisture content of the non-funnel-shaped sodium sulfate is about 8.5 percent, and is reduced by 15 to 45 percent compared with the moisture content of the product. Because a larger gap exists between funnel-shaped products and the particle size distribution of crystals is uniform, the filtration time is obviously shortened when solid-liquid separation is carried out by adopting a centrifugal or vacuum filtration mode (specific comparative data can be directly referred to example 2 and comparative example 1).
3. The invention effectively increases the specific surface area of the sodium sulfate solid, thereby improving the dissolution rate of large-particle crystals. In the experiment, the same mass (10g) of granular sodium sulfate and funnel-shaped sodium sulfate with the particle size of more than or equal to 300 mu m are selected by a screening method, the granular sodium sulfate and the funnel-shaped sodium sulfate are respectively placed in the same mass of deionized water (1000g), the time required for complete dissolution is measured, and the test is repeated for three times. The average dissolution times of the granular sodium sulfate and the funnel-shaped sodium sulfate were 157s and 70s, respectively. Experiments prove that funnel-shaped sodium sulfate is obviously superior in dissolution rate.
4. Compared with the patent literature, the application has the innovation points that the retention time of crystal nucleus suspension at the liquid level is prolonged mainly by controlling the stirring speed, and the evaporation process of the sodium sulfate wastewater solution is optimized by regulating and controlling the pH value of the solution, so that the funnel-shaped anhydrous sodium sulfate product is prepared. The evaporation liquid level is under the effect of higher supersaturation, and the crystal nucleus grows rapidly and forms new interface to form isotropic hourglass shape crystal at suspension in-process, along with the rising of solution pH value, the crystal surface nature changes, thereby is favorable to the stability of leaking hopper-shaped crystal and difficult emergence breakage.
Drawings
FIG. 1: a picture of funnel-shaped sodium sulfate crystals of the present application;
FIG. 2: a microscope photograph of funnel-shaped sodium sulfate crystals of the present application;
FIG. 3: scanning electron microscope photos of the sodium sulfate funnel-shaped crystals;
FIG. 4: scanning electron microscope photographs of granular sodium sulfate crystals obtained by evaporating the wastewater.
Detailed Description
The present invention will be described in further detail with reference to the following examples. It should not be understood that the scope of the above-described subject matter of the present invention is limited to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.
The determination of the purity of the sodium sulphate in the present invention is determined according to the sulphate gravimetric method provided in the standard GB/T13025.8-2012.
In the present invention, the filtration time was measured by vacuum filtration using a G4 crucible under the same pressure conditions.
The method for determining the moisture content of the product comprises the following steps: taking the filtered wet solid phase m1g, placing the mixture in a constant-temperature oven at 105 ℃, drying the mixture for more than 8 hours under normal pressure until the solid phase weight is constant, cooling the mixture to room temperature in a drier, and weighing the dry solid phase mass m2g. Thus, the moisture content of the product is (m)1-m2)/m1*100％。
The method for measuring the particle size distribution of the product comprises the following steps: taking dried solid phase m3g, screening in a clean and dry mesh screen with the aperture size of 300 mu m by gently shaking to prevent the crystals from colliding and breaking until no crystals fall down, and weighing the crystals (the particle size is more than or equal to 300 mu m) m in the screen4g, calculating to obtain the product with the mass ratio of m to the particle size of more than or equal to 300 mu m4/m3*100％。
The method for determining the cone angle of the funnel-shaped crystal is realized by a picture analysis method, and comprises the following specific steps: randomly selecting products with different particle sizes and complete crystal forms, reversely buckling the products on a horizontal plane, taking pictures at a side view angle, measuring through pictures and confirming the size range of the cone angle of the obtained products.
Example 1:
120mL of waste water (density: 1.2g/mL) containing 28 mass% of sodium sulfate is added into a 150mL crystallizer, the stirring speed is controlled at 200rpm, sodium hydroxide is added to adjust the pH value to be 11, the temperature is heated to 80 ℃, negative pressure evaporation is started after the temperature is constant, the vacuum degree is controlled to be 0.04MPa, and the distilled water amount is 30 mL. Then filtering, and drying the wet solid phase at 105 ℃ under normal pressure for 8h to constant weight to obtain the funnel-shaped sodium sulfate product. The moisture content of the product is 4.63%, the purity is 98.45%, the overall product photo, the single particle microscope photo and the electron microscope photo are shown in fig. 1 and fig. 2 (the short line at the lower right corner in the figure indicates that the length is 200 μm, and the edge and the end point of the funnel-shaped crystal are respectively marked by a white dotted line and a white dot), the product is obviously funnel-shaped, the cone angle distribution range of the funnel is 120-150 degrees, and the mass percentage of the product with the particle size of more than or equal to 300 μm is 94.64%.
Example 2:
adding 120mL of wastewater containing 28 mass percent of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 100rpm, adding sodium hydroxide to adjust the pH value to be 14, heating to 50 ℃ and keeping the temperature, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.07MPa, and controlling the distilled water amount to be 35 mL. And then completely filtering the solution for 50s, completely placing the wet solid phase at 105 ℃, and drying the wet solid phase for 8h under normal pressure until the weight is constant to obtain a funnel-shaped sodium sulfate product. The moisture content of the product is 5.56%, the purity is 96.63%, the cone angle distribution range of the funnel is 120-150 degrees, and the mass percentage of the product with the particle size of more than or equal to 300 mu m is 90.22%.
Example 3:
adding 120mL of wastewater containing 30 percent (mass percentage) of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 400rpm, adding sodium hydroxide to adjust the pH value to be 12, heating to 60 ℃, keeping the temperature constant, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.05MPa, and controlling the distilled water amount to be 30 mL. Then filtering, and drying the wet solid phase at 105 ℃ under normal pressure for 10h to constant weight to obtain the funnel-shaped sodium sulfate product. The moisture content of the product is 7.03%, the purity is 95.88%, the cone angle distribution range of the funnel is 120-150%, and the mass percentage of the product with the particle size of more than or equal to 300 mu m is 91.35%.
Example 4:
adding 120mL of wastewater containing 30 percent (mass percentage) of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 300rpm, adding sodium hydroxide to adjust the pH value to be 11, heating to 70 ℃, keeping the temperature constant, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.05MPa, and controlling the distilled water amount to be 30 mL. Then filtering, and drying the wet solid phase at 105 ℃ under normal pressure for 8h to constant weight to obtain the funnel-shaped sodium sulfate product. The moisture content of the product is 6.48%, the purity is 96.39%, the cone angle distribution range of the funnel is 120-150%, and the mass percentage of the product with the particle size of more than or equal to 300 mu m is 93.49%.
Example 5:
adding 120mL of wastewater containing 28 mass percent of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 300rpm, adding sodium hydroxide to adjust the pH value to be 13, heating to 80 ℃, keeping the temperature constant, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.05MPa, and controlling the distilled water amount to be 35 mL. Then filtering, and drying the wet solid phase at 105 ℃ under normal pressure for 10h to constant weight to obtain the funnel-shaped sodium sulfate product. The moisture content of the product is 6.99%, the purity is 95.26%, the cone angle distribution range of the funnel is 120-150 degrees, and the mass percentage of the product with the particle size of more than or equal to 300 mu m is 90.93%.
Example 6:
adding 120mL of wastewater containing 29 percent (mass percentage) of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 300rpm, adding sodium hydroxide to adjust the pH value to be 14, heating to 80 ℃, keeping the temperature, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.04MPa, and controlling the distilled water amount to be 25 mL. Then filtering, and drying the wet solid phase at 105 ℃ under normal pressure for 8h to constant weight to obtain the funnel-shaped sodium sulfate product. The moisture content of the product is 4.32%, the purity is 97.93%, the cone angle distribution range of the funnel is 120-150 degrees, and the mass percentage of the product with the particle size of more than or equal to 300 mu m is 96.87%.
Comparative example 1:
adding 120mL of wastewater containing 28 mass percent of sodium sulfate into a 150mL crystallizer, controlling the stirring speed to be 500rpm, adding sodium hydroxide to adjust the pH value to be 8, heating to 90 ℃, keeping the temperature constant, starting to evaporate by adopting negative pressure, controlling the vacuum degree to be 0.08MPa, and controlling the distilled water amount to be 35 mL. Then filtering for 75s, placing the wet solid phase at 105 ℃, drying for 12h under normal pressure to constant weight to obtain granular sodium sulfate, and scanning electron micrograph of the product is shown in figure 3. The moisture content of the product is 8.37 percent, the purity of the dried sodium sulfate is 90.20 percent, and the mass percentage of the product with the particle size of more than or equal to 250 mu m is 21.82 percent.
The funnel-shaped sodium sulfate and the preparation method thereof disclosed and provided by the invention can be realized by appropriately changing links such as raw materials, process parameters and the like by referring to the content in the text. While the methods and products of the present invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and products described herein may be made and equivalents employed to practice the techniques of the present invention without departing from the spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and content of the invention.
Claims (1)
1. A method for preparing funnel-shaped sodium sulfate from high-salinity wastewater; the method is characterized by comprising the following steps:
1) heating the wastewater to 50-80 ℃, adding sodium hydroxide to adjust the pH of the wastewater to 11-14, and controlling the stirring speed to be 100-400 rpm;
2) adopting a negative pressure evaporation crystallization mode, wherein the vacuum degree is 0.04-0.07 MPa, until the volume of the evaporated water is 20-30% of the volume of the original wastewater;
3) filtering and drying the obtained product to obtain funnel-shaped anhydrous sodium sulfate crystals;
in the wastewater, the mass percent of sodium sulfate is 28-30%; the cone angle of the funnel is 120-150 degrees, and the purity of the sodium sulfate is more than or equal to 95 percent; the mass percentage of the product with the grain diameter more than or equal to 300 mu m is more than 90 percent.
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