Method for recovering calcium and magnesium precipitate from high-salinity wastewater and applications thereof

Abstract

The application provides a method for recovering calcium-magnesium precipitate from high-salt wastewater and application thereof, the mass concentration of salt in the high-salt wastewater is 10-300 g / L; the steps comprise the following: the pretreated high-salt wastewater is heated under the first microwave condition, and irradiated for 1-5 min to obtain a supersaturated solution; the supersaturated solution is heated under the second microwave and ultrasonic condition, irradiated for 5-20 min, and stirred to obtain a mixed solution; the mixed solution is post-treated to obtain solid substances, namely the calcium-magnesium precipitate; wherein the power of the first microwave is greater than or equal to the power of the second microwave; the power of the first microwave is greater than or equal to 100 W; and the heating temperature is 20-60 DEG C. The process steps are simple, the nucleation rate is fast, large-scale preparation at low cost can be realized, and the recovered calcium-magnesium precipitate has good application in building materials.

Description

Technical Field

[0001] This invention belongs to the field of high-salinity wastewater treatment technology, and particularly relates to a method for recovering calcium and magnesium precipitates from high-salinity wastewater and its application. Background Technology

[0002] With rapid industrial development, the discharge of high-salinity wastewater has continued to increase, and its composition is complex. High-salinity wastewater often contains high concentrations of sodium (Na). + Cl - SO4 2- and Ca 2+ Mg 2+ Plasma. The main processes for recovering calcium and magnesium precipitates from high-salt wastewater are caustic soda softening and lime soda softening. These processes can remove all hardness from the wastewater, but the softened wastewater requires coagulation, flocculation, and clarification before passing through sand filtration and ultrafiltration to enter the subsequent concentration and reduction stage. The entire pretreatment softening and clarification process is relatively complex and has high operating costs. While traditional chemical precipitation and evaporation crystallization processes are widely used, they generally suffer from long nucleation induction periods, low crystal growth rates, and a tendency to form small agglomerates, leading to increased energy consumption and costs in the solid-liquid separation stage. Furthermore, amorphous calcium and magnesium ions are poorly precipitated and easily form colloidal substances in the wastewater, which, while flowing with the water, clog the reactor pipes, further limiting process efficiency.

[0003] To overcome these challenges, researchers have attempted to employ microwave heating and ultrasonic enhancement technologies. Microwaves use high-frequency electromagnetic fields to simultaneously heat the solution inside and outside, increasing the system temperature and local supersaturation. Ultrasonic cavitation and microjets effectively suppress crystal aggregation and enhance mass transfer. However, microwave technology is limited in its application in large-scale high-salinity wastewater treatment due to its long reaction time, high required heating temperature, increased energy consumption, and high equipment costs, making it difficult to meet the demands of large-scale wastewater treatment in actual industrial production. Ultrasonic technology, when treating high-salinity wastewater, easily affects the viscosity and density of the water, leading to weakened cavitation and inconsistent treatment results. Crystallization efficiency and quality fluctuate significantly, failing to meet the requirements for efficient and stable high-salinity wastewater treatment.

[0004] Based on this, the present invention proposes a method for recovering calcium and magnesium precipitates from high-salinity wastewater and its application. Summary of the Invention

[0005] The main objective of this invention is to provide a method for recovering calcium and magnesium precipitates from high-salinity wastewater and its application, aiming to solve the technical problems of slow recovery rate, high energy consumption, complex process, and unsuitability for large-scale treatment in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for recovering calcium and magnesium precipitates from high-salinity wastewater, wherein the high-salinity wastewater contains salts with a mass concentration of 10 g / L to 300 g / L; the steps include:

[0007] The pretreated high-salt wastewater was heated under the first microwave condition and irradiated for 1–5 min to obtain a supersaturated solution.

[0008] The supersaturated solution was heated under second microwave and ultrasonic conditions for 5–20 min and stirred to obtain a mixed solution.

[0009] After post-processing, the mixed solution yields a solid substance, which is the calcium and magnesium precipitate.

[0010] Wherein, the power of the first microwave is greater than or equal to the power of the second microwave; the power of the first microwave is greater than or equal to 100W; and the heating temperature is 20–60°C.

[0011] According to an embodiment of this application, the pretreated high-salt wastewater contains hydroxide and carbonate ions.

[0012] According to the embodiments of this application, the power of the first microwave is 100-300W; the power of the second microwave is 100-200W; the power of the ultrasound is 50-200W, and the frequency is 20-40kHz.

[0013] According to an embodiment of this application, the ultrasound includes one of continuous ultrasound and pulse intermittent multi-frequency ultrasound.

[0014] The duty cycle of ultrasound is 10-50%.

[0015] According to embodiments of this application, the ions in the high-salinity wastewater include Li. + Na + K + Cl - SO4 2- At least one of them.

[0016] According to an embodiment of this application, the pretreatment step of the high-salinity wastewater includes:

[0017] First, add an alkali adjuster to adjust the alkalinity of the high-salt wastewater to alkalinity, then add sodium carbonate and mix well to obtain pretreated high-salt wastewater.

[0018] The molar concentration of the alkali adjuster is 0.1 mol / L; the alkali adjuster includes at least one of sodium hydroxide, potassium hydroxide, and calcium oxide.

[0019] According to an embodiment of this application, the particle size of the calcium-magnesium precipitate is 6-12 μm.

[0020] According to an embodiment of this application, the stirring speed is 400-600 rpm.

[0021] According to an embodiment of this application, the post-processing includes: cooling, centrifugation to obtain a lower solid layer, washing, and drying.

[0022] Application of calcium and magnesium precipitates prepared according to the above method in building materials.

[0023] The beneficial effects of this invention are:

[0024] The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to the present invention involves heating the pretreated high-salinity wastewater under a first microwave condition and irradiating it for 1-5 minutes. This achieves rapid heating of the high-salinity wastewater and enhances local supersaturation, thereby promoting the precipitation of calcium and magnesium precipitates. 2+ Mg 2+ With CO3 2- Ions rapidly combine to form a supersaturated solution, facilitating the rapid nucleation and transformation of amorphous calcium and magnesium in high-salt wastewater into crystalline forms, thus reducing energy consumption in subsequent steps. Further heating under microwave and ultrasonic conditions for 5–20 min with stirring creates strong turbulence, significantly promoting calcium and magnesium precipitation and ensuring complete crystal development in the mixed solution. After post-treatment, the mixed solution yields a solid substance, the calcium and magnesium precipitate.

[0025] Furthermore, the calcium and magnesium precipitates prepared by the method of this application can be used in building materials to achieve resource recycling and reduce environmental pollution. The process steps of this application are simple, the nucleation rate is fast, and it can achieve low-cost large-scale preparation. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a flowchart of the method for recovering calcium and magnesium precipitates from high-salinity wastewater according to this application;

[0028] Figure 2 These are SEM images of calcium and magnesium precipitates recovered from high-salt wastewater using different methods.

[0029] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] This invention provides a method for recovering calcium and magnesium precipitates from high-salinity wastewater, wherein the salt concentration in the high-salinity wastewater is 10 g / L to 300 g / L; the steps include:

[0033] The pretreated high-salt wastewater was heated under the first microwave condition and irradiated for 1–5 min to obtain a supersaturated solution.

[0034] In some embodiments, a microwave reactor is selected, equipped with a high-precision temperature sensor for real-time temperature monitoring, and a built-in magnetic or mechanical stirring device to ensure thorough mixing of substances in the high-salt wastewater during the reaction. The pretreated high-salt wastewater is placed in the microwave reactor, with the first microwave power set to 300W, irradiated for 1–5 minutes at a temperature of 20–60°C, for a period of 3–5 minutes. This achieves a rapid increase in the local temperature of the high-salt wastewater, resulting in a supersaturated solution, thereby ensuring the nucleation rate and uniformity.

[0035] In some embodiments, microwave heating has the characteristic of "simultaneous heating inside and outside". By adjusting the power of the first microwave to be relatively high, the temperature of high-salt wastewater can be rapidly increased to a supersaturated state, promoting the nucleation of calcium and magnesium ions and transforming most amorphous states into crystalline states.

[0036] In some embodiments, calcium and magnesium ions in high-salinity wastewater tend to form amorphous states. Since amorphous states are mostly calcium carbonate precipitates, these precipitates are unstable and easily form a gel-like substance in the water, which can clog pipes as it flows through the equipment, thus affecting the recovery effect. Therefore, under the first microwave condition, the amorphous state of calcium and magnesium precipitates is reduced and transformed into a crystalline state within a few minutes, which is beneficial to the stability of the precipitate and subsequent separation.

[0037] In some embodiments, a microwave emitting device is selected, suitable for large-scale recovery of calcium and magnesium precipitates from high-salinity wastewater. The reaction vessel in the microwave emitting device is made of borosilicate glass or quartz material that is heat-resistant and has good microwave penetration. The amount of high-salinity wastewater filled at one time does not exceed 70% of the vessel's maximum capacity, preferably 50%–70%. During the reaction, foam or steam generated by boiling of the solution is prevented from overflowing along the vessel wall, improving microwave and ultrasonic transmission efficiency and reducing experimental safety hazards. The borosilicate glass or quartz material ensures good chemical and mechanical stability under high temperature and long-term microwave irradiation conditions. The thickness and shape of the vessel wall should match the microwave waveguide structure to minimize microwave energy loss or reflection.

[0038] The supersaturated solution is heated under a second microwave and ultrasonic environment for 5–20 minutes, and stirred to obtain a mixed solution. The power of the first microwave is greater than or equal to the power of the second microwave; the power of the first microwave is greater than or equal to 100W; and the heating temperature is 20–60°C.

[0039] In some embodiments, the supersaturated solution is placed under a second microwave and ultrasonic condition, wherein the power of the second microwave is 150W and the irradiation is 10 minutes, the ultrasonic frequency is 20-40kHz and the ultrasonic power is 100W, and the solution is stirred evenly at a stirring speed of 400-600rpm to ensure that the ions in the supersaturated solution are in full contact, reduce crystallization defects caused by local undersaturation or uneven nucleation, and promote crystal formation.

[0040] In some embodiments, the second microwave has lower power and is used to maintain the temperature of the supersaturated solution, promoting crystal growth and crystal maturation. It also avoids crystal agglomeration or decomposition caused by overheating, contributing to the formation of uniform calcium and magnesium precipitates. Furthermore, microwave heating reduces energy consumption.

[0041] Ultrasound can generate cavitation, and by impacting a supersaturated solution with ultrasonic vibrations and using appropriate rotation speed to create turbulence, it enhances ion mass transfer, promotes uniform dispersion of crystal nuclei, and transforms the supersaturated solution into a mixed solution, thereby increasing the precipitation rate of calcium and magnesium. Under the combined action of microwave and ultrasound, ion migration to the crystal nucleus surface is accelerated, and secondary agglomeration or breakage of crystals due to violent collisions is inhibited. Furthermore, energy consumption in post-processing steps is reduced, resulting in large-diameter crystals with regular morphology.

[0042] In some embodiments, heating can be performed using temperature sensors, such as thermocouples, thermistors, fiber optic thermometers, and other probes with high accuracy and response speed, to continuously monitor temperature changes in the microwave reactor. The preferred heating temperature is 25–50°C. At this heating temperature, combined with the first microwave condition, both the rapid formation of amorphous calcium carbonate and the stability of subsequent crystallization can be achieved, thus realizing effective control of crystal growth kinetics.

[0043] In some embodiments, if the heating temperature is too high, the temperature of the high-salinity wastewater can be reduced to a suitable range by intermittently shutting off the microwave or adding an external cooling water jacket. If the heating temperature is too low or the heating rate is too slow, the power of the first microwave can be appropriately increased, or the power of the second microwave and the ultrasonic power can be appropriately adjusted to keep the heating temperature within a suitable temperature range.

[0044] The mixed solution was post-processed to obtain a solid substance, namely the calcium and magnesium precipitate.

[0045] In some embodiments, the mixed solution is naturally cooled or cooled down, then centrifuged to obtain a lower solid layer. The lower solid layer is then washed multiple times with ethanol, water, or other solvents to remove residual impurities and dried to obtain the calcium and magnesium precipitate.

[0046] The above-described method for recovering calcium and magnesium precipitates from high-salinity wastewater involves heating the treated wastewater under microwave conditions and irradiating it for 1–5 minutes. This rapid heating and enhanced local supersaturation of the wastewater promotes the precipitation of calcium and magnesium precipitates. 2+ Mg 2+ With CO3 2- Ions rapidly combine to form a supersaturated solution. This solution is then heated under microwave and ultrasonic conditions for 5–20 minutes with stirring to create strong turbulence, which significantly promotes crystal formation, increases the number of nuclei in the supersaturated solution, and ensures uniform dispersion, thus facilitating complete crystal development in the subsequent mixed solution. After post-treatment, the mixed solution yields a solid substance, namely the calcium-magnesium precipitate. This application features a simple process, rapid nucleation rate, and enables low-cost, large-scale preparation.

[0047] In some embodiments, the pretreated high-salinity wastewater contains hydroxide and carbonate ions. This effectively promotes the precipitation of calcium and magnesium ions, enabling the efficient recovery of the calcium and magnesium precipitate.

[0048] In some embodiments, the power of the first microwave is 100-300W; the power of the second microwave is 100-200W; and the power of the ultrasound is 50-200W with a frequency of 20-40kHz.

[0049] In some embodiments, the power of the first microwave is 100–300 W. In the initial stage of the high-salt wastewater reaction, i.e., the nucleation induction stage, the power of the first microwave is adjusted to a higher power to achieve rapid heating and local supersaturation in the shortest possible time, thereby promoting calcium carbonate nucleation and growth. The second microwave is adjusted to a lower power to avoid strong energy input causing crystal surface defects, while maintaining an appropriate heating temperature to promote ion migration to the crystal surface and promote crystal formation.

[0050] In some embodiments, the power of the first microwave is adjusted to 300W, the power of the second microwave is 150W, the power of the ultrasound is 100W, and the frequency is 20-30kHz to obtain a mixed solution.

[0051] In some embodiments, the ultrasound includes one of continuous ultrasound and pulsed intermittent multi-frequency ultrasound.

[0052] The duty cycle of ultrasound is 10-50%.

[0053] In some embodiments, during the step of converting the supersaturated solution into a mixed solution, i.e., the crystal growth period, continuous ultrasound is used with periodic switching cycles. The duty cycle of the ultrasound is 10-50%, for example, if the ultrasound is on for 10 seconds and off for 10 seconds, the duty cycle is 50%. Alternatively, pulsed intermittent multi-frequency ultrasound can be used, by alternately controlling multiple frequencies (e.g., 20kHz / 40kHz / 60kHz), with a pulse mode within each frequency band and a duty cycle of 20%-50%. The cavitation and turbulence of ultrasound can continuously enhance ion diffusion to the crystal surface, improving mass transfer, while avoiding excessive crystal fragmentation, secondary crystal agglomeration, and excessive energy consumption, thus maintaining crystal integrity. Moreover, although ultrasonic cavitation may attenuate somewhat in high salinity environments, by appropriately increasing the power and controlling the frequency, microjets sufficient to break the local concentration gradient of the supersaturated solution can still be generated, increasing the ion collision rate and promoting crystal growth.

[0054] In some embodiments, the ions in the high-salinity wastewater include Li + Na + K + Cl - SO4 2- At least one of them.

[0055] In some embodiments, the types and concentrations of anions and cations in the high-salinity wastewater can be flexibly proportioned according to the actual composition of the high-salinity wastewater, including but not limited to LiCl, NaCl, KCl, Na2SO4, and substances containing Ca. 2+ Mg 2+ Multiple salt combinations of ions with equal hardness.

[0056] In some embodiments, the ions in the high-salinity wastewater are not specifically limited. The high-salinity wastewater contains OH-. - CO3 2- The high-salinity wastewater contains Ca. 2+ Mg 2+ At least one of the following; the high-salt wastewater also includes Li + Na + K + Cl- SO4 2- At least one of them.

[0057] In some embodiments, the pretreatment step of the high-salinity wastewater includes:

[0058] First, add an alkali adjuster to adjust the alkalinity of the high-salt wastewater to alkalinity, then add sodium carbonate and mix well to obtain pretreated high-salt wastewater.

[0059] The molar concentration of the alkali adjuster is 0.1 mol / L; the alkali adjuster includes at least one of sodium hydroxide, potassium hydroxide, and calcium oxide.

[0060] In some embodiments, 0.1 mol / L sodium hydroxide is first added to the high-salinity wastewater to make it alkaline, with a pH of 10-12. Then, sodium carbonate reagent is added at a rate of 1 mL / min and mixed thoroughly to obtain a pretreated high-salinity solution. The amount of sodium carbonate added is 1.2 times the theoretical amount required for calcium and magnesium precipitation to ensure complete precipitation of calcium and magnesium ions in the high-salinity wastewater.

[0061] In some embodiments, the particle size of the calcium-magnesium precipitate is 6–12 μm.

[0062] In some embodiments, the particle size and morphology of the calcium-magnesium precipitate can be controlled by adjusting the reaction conditions. For example, by heating the treated high-salt wastewater at the temperature and power of the first microwave condition, rapid heating and nucleation are achieved to obtain a supersaturated solution. Then, by adjusting the power of the second microwave and ultrasound, the migration of ions to the crystal nucleus surface is accelerated, and secondary agglomeration or breakage of the crystals due to violent collisions is suppressed. This also reduces the energy consumption of the post-processing steps, resulting in large-particle-size crystals with regular morphology. After post-processing, the particle size of the calcium-magnesium precipitate is 6–12 μm.

[0063] In some embodiments, the stirring speed is 400-600 rpm.

[0064] In some embodiments, excessively low stirring speeds will lead to a decrease in Ca in high-salinity wastewater. 2+ Mg 2+ With anion CO3 2- OH - Insufficient mixing leads to large local concentration differences, reducing the nucleation rate and prolonging the crystallization time. Simultaneously, the microwave thermal effect and ultrasonic cavitation effect are difficult to uniformly propagate throughout the solution, failing to effectively disperse the tiny crystal nuclei and causing secondary agglomeration.

[0065] In some embodiments, excessively high stirring speeds can generate shear forces that break down crystal nuclei in a supersaturated solution, leading to a reduction in effective nucleation sites and a decrease in crystallization rate. This also increases energy consumption and equipment wear.

[0066] In some embodiments, the post-processing includes: cooling, centrifugation to obtain a lower solid layer, washing, and drying.

[0067] In some embodiments, cooling can cause calcium and magnesium precipitates to fully precipitate from the mixed solution, reducing dissolution or redissolution at high temperatures, making the crystal structure of calcium and magnesium precipitates more stable, preventing deformation or dissolution of crystals during subsequent processing, and improving the crystallization rate of calcium and magnesium precipitates.

[0068] Centrifugation is a highly efficient solid-liquid separation method. It rapidly separates the precipitate from the upper solution, yielding the lower solid layer (the calcium and magnesium precipitate). This significantly improves separation efficiency, effectively removes impurities, and is suitable for large-scale industrial production, further enhancing the purity of the crystals.

[0069] Washing removes surface impurities from calcium and magnesium precipitates formed during their formation. These impurities may adsorb reaction byproducts, unreacted raw materials, or other impurities. Washing removes these surface impurities, improving crystal purity and preventing contamination or adverse effects on crystal properties during subsequent drying.

[0070] Drying removes moisture from calcium and magnesium precipitates, bringing them to the required level of dryness for easy storage and subsequent use.

[0071] In some embodiments, the calcium magnesium precipitate includes at least one of calcite, aragonite, spheroidalite, and calcium carbonate.

[0072] Application of calcium and magnesium precipitates prepared according to the above method in building materials.

[0073] In some embodiments, calcite in calcium-magnesium precipitates is an important raw material in cement manufacturing, improving its strength and durability. It can also be used for interior and exterior building decoration, such as floors, walls, and columns. The application of calcium-magnesium precipitates in building materials can significantly improve their performance and quality while reducing production costs, aligning with the trend of green building development.

[0074] To further illustrate the present invention, the following examples are provided:

[0075] In the examples and comparative examples, the high-salt wastewater contained calcium chloride at a mass concentration ≥1.5 g / L and magnesium chloride at a mass concentration ≥0.2 g / L.

[0076] Example 1

[0077] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Li+, Ca2+, Ca2+, and Ca2+. 2 +, Mg 2+, Cl-. The pretreated high-salt wastewater was placed in a microwave reactor. The power of the first microwave was set to 300W, the irradiation time to 5min, and the heating temperature to 40℃. After 240 seconds, a supersaturated solution was obtained.

[0078] The supersaturated solution was then heated under a second microwave and ultrasonic environment and stirred. The power of the second microwave was set to 100W, the irradiation time to 5 minutes, the power of the ultrasonic environment to 100W, the frequency to 40kHz, and the stirring speed to 600rpm. After reacting for 15 minutes, a mixed solution was obtained.

[0079] The mixed solution was cooled, centrifuged to obtain the lower solid layer, washed, and dried to obtain a calcium-magnesium precipitate. Testing revealed that the calcium-magnesium precipitate had a particle size of 11.4 μm and a crystallinity of 92%.

[0080] Example 2

[0081] Compared to Example 1, the composition of the high-salinity wastewater was changed.

[0082] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Na+, Ca2+, and Ca2+. 2 +, Mg 2 +, Cl-. The pretreated high-salt wastewater was placed in a microwave reactor. The power of the first microwave was set to 300W, the irradiation time to 5min, and the heating temperature to 40℃. After 240 seconds, a supersaturated solution was obtained.

[0083] The supersaturated solution was then heated under a second microwave and ultrasonic environment and stirred. The power of the second microwave was set to 100W, the irradiation time to 5 minutes, the power of the ultrasonic environment to 100W, the frequency to 40kHz, and the stirring speed to 600rpm. After reacting for 15 minutes, a mixed solution was obtained.

[0084] The mixed solution was cooled, centrifuged to obtain the lower solid layer, and then washed and dried to obtain a calcium-magnesium precipitate. Testing revealed that the calcium-magnesium precipitate had a particle size of 7.13 μm and a crystallinity of 88%.

[0085] Example 3

[0086] Compared to Example 1, the mass concentration of salt in the high-salt wastewater was changed.

[0087] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the high-salinity wastewater is 10 g / L, and the ionic composition of the high-salinity wastewater is Na+, Ca2+, and Ca2+. 2 +, Mg 2+, Cl-. The pretreated high-salt wastewater was placed in a microwave reactor. The power of the first microwave was set to 300W, the irradiation time to 5min, and the heating temperature to 40℃. After 240 seconds, a supersaturated solution was obtained.

[0088] The supersaturated solution was then heated under a second microwave and ultrasonic environment and stirred. The power of the second microwave was set to 100W, the irradiation time to 5 minutes, the power of the ultrasonic environment to 100W, the frequency to 40kHz, and the stirring speed to 600rpm. After reacting for 15 minutes, a mixed solution was obtained.

[0089] The crystalline solution was cooled, centrifuged to obtain the lower solid layer, and then washed and dried to obtain a calcium-magnesium precipitate. Testing revealed that the calcium-magnesium precipitate had a particle size of 7.51 μm and a crystallinity of 96%.

[0090] Example 4

[0091] Compared to Example 1, the power of the first microwave was changed.

[0092] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Li+, Ca2+, Ca2+, and Ca2+. 2 +, Mg 2 +, Cl-. The pretreated high-salt wastewater was placed in a microwave reactor. The power of the first microwave was set to 200W, the irradiation time to 5min, and the heating temperature to 40℃. After 300 seconds, a supersaturated solution was obtained.

[0093] The supersaturated solution was then heated under a second microwave and ultrasonic environment and stirred. The power of the second microwave was set to 100W, the irradiation time to 5 minutes, the power of the ultrasonic environment to 100W, the frequency to 40kHz, and the stirring speed to 600rpm. After reacting for 15 minutes, a mixed solution was obtained.

[0094] The mixed solution was cooled, centrifuged to obtain the lower solid layer, and then washed and dried to obtain a calcium-magnesium precipitate. Testing revealed that the calcium-magnesium precipitate had a particle size of 9.20 μm and a crystallinity of 90%.

[0095] Comparative Example 1

[0096] In Comparative Example 1, the first microwave, second microwave, and ultrasonic steps are omitted compared to Example 1.

[0097] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Li+, Ca2+, Ca2+, and Ca2+. 2 +, Mg 2 +、Cl-.

[0098] The high-salinity wastewater was cooled, centrifuged to obtain the lower solid layer, and then washed and dried to obtain a precipitate. Testing revealed that the precipitate had a particle size of 1.88 μm and a crystallization rate of 51%.

[0099] Comparative Example 2

[0100] In Comparative Example 2, the first microwave step was omitted compared to Example 1.

[0101] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Li+, Ca2+, Ca2+, and Ca2+. 2 +, Mg 2 +、Cl-.

[0102] The pretreated high-salt wastewater was heated under a combination of microwave and ultrasonic conditions and stirred. The power of the microwave was set to 100W, the irradiation time to 5 minutes, the power of the ultrasonic treatment to 100W, the frequency to 40kHz, and the stirring speed to 600rpm. After reacting for 15 minutes, a mixed solution was obtained.

[0103] The mixed solution was cooled, centrifuged to obtain the lower solid layer, washed, and dried to obtain the precipitate. Testing revealed that the precipitate had a particle size of 5.81 μm and a crystallinity of 71%.

[0104] Comparative Example 3

[0105] In Comparative Example 3, the second microwave and ultrasonic steps were omitted compared to Example 1.

[0106] Take 0.1 L of high-salinity wastewater, wherein the salt concentration in the wastewater is 300 g / L, and the ionic composition of the high-salinity wastewater is Li+, Ca2+, Ca2+, and Ca2+. 2 +, Mg 2 +、Cl-.

[0107] The pretreated high-salt wastewater was placed in a microwave reactor. The power of the first microwave was set to 300W, the irradiation time to 5 minutes, and the heating temperature to 40℃. After 240 seconds, a supersaturated solution was obtained.

[0108] The supersaturated solution was cooled, centrifuged to obtain the lower solid layer, washed, and dried to obtain the precipitate. Testing revealed that the precipitate had a particle size of 5.69 μm and a crystallinity of 74%.

[0109] Table 1 lists the particle size data of calcium and magnesium precipitates recovered from high-salinity wastewater using different methods in the examples and comparative examples. Figure 1 This is a flowchart of the method for recovering calcium and magnesium precipitates from high-salinity wastewater according to this application. Figure 2 These are SEM images of calcium and magnesium precipitates recovered from high-salt wastewater using different methods.

[0110] Table 1. Particle size data of calcium and magnesium precipitates recovered from high-salinity wastewater in the examples and comparative examples.

[0111]

[0112] Combination Figure 2 ,in, Figure 2 In the diagram, A1, B1, and C1 correspond to SEM images of calcium and magnesium precipitates recovered from high-salinity wastewater with a LiCl concentration of 300 g / L, using the methods of Comparative Example 1, Comparative Example 2, and Example 1, respectively. A2, B2, and C2 correspond to SEM images of calcium and magnesium precipitates recovered from high-salinity wastewater with a Na2SO4 concentration of 10 g / L, using the methods of Comparative Example 1, Comparative Example 2, and Example 1, respectively. A3, B3, and C3 correspond to SEM images of calcium and magnesium precipitates recovered from high-salinity wastewater with a NaCl concentration of 10 g / L, using the methods of Comparative Example 1, Comparative Example 2, and Example 1, respectively. A4, B4, and C4 correspond to SEM images of calcium and magnesium precipitates recovered from high-salinity wastewater with a NaCl concentration of 100 g / L, using the methods of Comparative Example 1, Comparative Example 2, and Example 1, respectively. Specific particle sizes are shown in Table 1.

[0113] Therefore, it can be seen that Comparative Example 1 omitted the first microwave, second microwave, and ultrasonic steps, and did not pretreat the high-salt wastewater. Due to the lack of rapid heating from microwaves and the cavitation effect of ultrasound, the calcium and magnesium precipitates were in an amorphous or non-crystalline state, easily forming colloidal and unstable precipitates, which could not effectively nucleate and grow, resulting in a precipitate particle size of 1.88 μm and a crystallization rate of only 51%. Comparative Example 2 omitted the first microwave step, which could not achieve rapid nucleation of calcium and magnesium ions, resulting in insufficient and unevenly distributed crystal nuclei, incomplete crystal development, a particle size of 5.81 μm, and a crystallization rate of 71%. Comparative Example 3 omitted the second microwave and ultrasonic steps, lacking the synergistic effect of ultrasonic turbulence and microwaves. The crystals were prone to agglomeration and breakage during growth, and could not form complete large-particle crystals, with a particle size of 5.69 μm and a crystallization rate of 74%. In contrast, in this embodiment of the invention, a supersaturated solution is first formed by rapid heating using a first microwave, and then crystal growth is enhanced by the synergistic effect of a second microwave and ultrasound. Although the corresponding process parameters are controlled, calcium and magnesium precipitation recovery with a particle size of 6-12 μm and a crystallization rate of over 90% is still achieved. This successfully overcomes the problems of crystal agglomeration and low nucleation rate in traditional processes. Furthermore, this demonstrates that the process of the present invention has significant advantages in terms of crystallization efficiency and improved crystal particle size.

[0114] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for recovering calcium and magnesium precipitates from high-salinity wastewater, characterized in that, The high-salinity wastewater has a salt concentration of 10 g / L to 300 g / L; the steps include: S1: Place the pretreated high-salt wastewater under the first microwave condition and heat for 1~5 minutes to obtain a supersaturated solution; S2: Place the supersaturated solution under second microwave and ultrasonic conditions, heat for 5-20 minutes, and stir to obtain a mixed solution; S3: After post-processing the mixed solution, a solid substance is obtained, which is the calcium and magnesium precipitate; Wherein, the power of the first microwave is greater than or equal to the power of the second microwave; the power of the first microwave is greater than or equal to 100W; and the heating temperature is 20~60℃. The pretreatment steps for the high-salinity wastewater include: First, add an alkalinity adjuster to the high-salinity wastewater to adjust it to alkalinity, then add sodium carbonate and mix well to obtain pretreated high-salinity wastewater; The pretreated high-salt wastewater contains hydroxide and carbonate ions.

2. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The power of the first microwave is 100~300W; the power of the second microwave is 100~200W; the power of the ultrasound is 50~200W, and the frequency is 20~40 kHz.

3. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The ultrasound includes one of continuous ultrasound and pulse intermittent multi-frequency ultrasound; The duty cycle of ultrasound is 10-50%.

4. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The ions in the high-salinity wastewater include Li. + Na + K + Cl - SO4 2- At least one of them.

5. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The molar concentration of the alkali adjuster is 0.1 mol / L; the alkali adjuster includes at least one of sodium hydroxide, potassium hydroxide, and calcium oxide.

6. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The particle size of the calcium and magnesium precipitate is 6~12μm.

7. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The stirring speed is 400~600 rpm.

8. The method for recovering calcium and magnesium precipitates from high-salinity wastewater according to claim 1, characterized in that, The post-processing includes: cooling, centrifugation to obtain the lower solid layer, washing, and drying.

9. The application of the calcium and magnesium precipitate prepared by the method according to any one of claims 1 to 8 in building materials.

Images