Method for recovering calcium and magnesium precipitates from high-salinity wastewater and application of calcium and magnesium precipitates

Abstract

The invention provides a method for recovering calcium and magnesium precipitates from high-salinity wastewater and application of the calcium and magnesium precipitates. The mass concentration of salt in the high-salinity wastewater is 10g / L-300g / L; the method comprises the following steps: placing pretreated high-salinity wastewater under a first microwave condition, heating, and irradiating for 1-5 minutes to obtain a supersaturated solution; heating the supersaturated solution under a second microwave and ultrasonic condition, irradiating for 5-20 minutes, and stirring to obtain a mixed solution; and carrying out post-treatment on the mixed solution to obtain a solid substance, namely the calcium-magnesium precipitate, wherein the power of the first microwave is greater than or equal to that of the second microwave; the power of the first microwave is greater than or equal to 100W; the heating temperature ranges from 20 DEG C to 60 DEG C. The method is simple in process step and high in nucleation rate, low-cost and large-scale preparation can be achieved, and the recycled calcium-magnesium precipitate has good application in building materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-salt wastewater treatment, and particularly relates to a method for recovering calcium and magnesium precipitates from high-salt wastewater and its application. Background Art

[0002] With the rapid development of industrialization, the discharge of high-salt wastewater continues to increase, and its composition is complex. High-salt wastewater often contains high concentrations of Na + , Cl - , SO4 2- and Ca 2+ , Mg 2+ and other ions. The processes for recovering calcium and magnesium precipitates from high-salt wastewater mainly include the caustic soda-soda ash softening process and the lime-soda ash softening process. These processes can remove all the hardness in the wastewater, but the softened wastewater needs to be coagulated, flocculated and clarified, and then enter the subsequent concentration and reduction section after sand filtration and ultrafiltration. The entire pretreatment softening and clarification process is relatively complex and the operating cost is high. Although traditional chemical precipitation methods and evaporation crystallization processes are widely used, they generally have a long crystal nucleation induction period, a low crystal growth rate, and are prone to form fine aggregates, resulting in increased energy consumption and costs in the solid-liquid separation stage. In addition, the precipitation effect of amorphous calcium and magnesium ions is not good, and it is easy to form colloids in the wastewater, which will block the pipelines of the reactor during the flow with water, further restricting the process efficiency.

[0003] To overcome the above problems, researchers have tried to use microwave heating and ultrasonic strengthening technologies. Among them, microwave realizes synchronous heating inside and outside the solution through high-frequency electromagnetic fields, improving the system temperature and local supersaturation. The ultrasonic cavitation effect and microjet action can effectively inhibit crystal aggregation and strengthen the mass transfer process. However, the microwave technology has problems such as a long reaction time, a high required heating temperature, thus increasing energy consumption and equipment costs, and its application in large-scale high-salt wastewater treatment is limited and difficult to meet the demand for treating a large amount of wastewater in actual industrial production. When ultrasonic technology is used to treat high-salt wastewater, it is easy to affect the viscosity and density of the water body, resulting in a weakened cavitation effect, and it is difficult to ensure stable treatment effects, with large fluctuations in crystallization efficiency and quality, and it cannot meet the requirements for efficient and stable high-salt wastewater treatment.

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

[0005] The main object of the present invention is to provide a method for recovering calcium and magnesium precipitates from high-salt wastewater and its application, aiming to solve the technical problems in the prior art that the rate of recovering calcium and magnesium precipitates from high-salt wastewater is slow, the energy consumption is high, the process is complex, and it is not suitable for large-scale treatment.

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

[0007] Placing the pretreated high-salt wastewater under the first microwave condition for heating and irradiating for 1 to 5 minutes to obtain a supersaturated solution.

[0008] Placing the supersaturated solution under the second microwave and ultrasonic conditions for heating, irradiating for 5 to 20 minutes, and stirring to obtain a mixed solution.

[0009] After the mixed solution is post-treated, a solid substance is obtained, 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 100 W; the heating temperature is 20 to 60 °C.

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

[0012] According to an embodiment of the present application, the power of the first microwave is 100 to 300 W; the power of the second microwave is 100 to 200 W; the power of the ultrasonic wave is 50 to 200 W, and the frequency is 20 to 40 kHz.

[0013] According to an embodiment of the present application, the ultrasonic wave includes one of continuous ultrasonic wave and pulsed intermittent multi-frequency ultrasonic wave.

[0014] Wherein, the duty cycle of the ultrasonic wave is 10 to 50%.

[0015] According to an embodiment of the present application, the ions in the high-salt wastewater include Li + , Na + , K + , Cl - , SO4 2- and at least one of them.

[0016] According to an embodiment of the present application, the pretreatment steps of the high-salt wastewater include:

[0017] Adding an alkali regulator to the high-salt wastewater to adjust it to an alkaline state, and then adding sodium carbonate and mixing evenly to obtain the pretreated high-salt wastewater.

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

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

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

[0021] According to an embodiment of the present application, the post-treatment includes: cooling, centrifuging to obtain the lower-layer solid, washing, and drying.

[0022] Application of the calcium and magnesium precipitate prepared by the above method in building materials.

[0023] The beneficial effects of the present invention are:

[0024] In the method for recovering calcium and magnesium precipitate from high-salt wastewater according to the present invention, the pretreated high-salt wastewater is heated under the first microwave condition and irradiated for 1 - 5 min to achieve rapid heating of the high-salt wastewater and strengthen the local supersaturation degree, thereby promoting the rapid combination of Ca 2+ , Mg 2+ with CO3 2- ions to obtain a supersaturated solution, realizing the rapid nucleation of amorphous calcium and magnesium in high-salt wastewater and the transformation into crystal state, so as to reduce the energy consumption in subsequent steps. Then, combined with heating under the second microwave and ultrasonic conditions, irradiated for 5 - 20 min and stirred to form strong turbulence, which has an obvious promoting effect on the formation of calcium and magnesium precipitate and is beneficial to the complete development of calcium and magnesium precipitate crystals in the mixed solution. After the mixed solution is post-treated, a solid substance is obtained, which is the calcium and magnesium precipitate.

[0025] Moreover, the application of the calcium and magnesium precipitate prepared by the method of the present application in building materials can realize resource recycling and reduce environmental pollution. The process steps of the present application are simple, the nucleation rate is fast, and large-scale preparation at low cost can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0027] Figure 1 is a flowchart of the method for recovering calcium and magnesium precipitate from high-salt wastewater in the present application;

[0028] Figure 2 is an SEM image of recovering calcium and magnesium precipitate from high-salt wastewater by different methods.

[0029] The realization, functional characteristics, and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0031] Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

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

[0033] Heat the pretreated high-salt wastewater under the first microwave condition and irradiate for 1 to 5 minutes to obtain a supersaturated solution.

[0034] In some embodiments, a microwave reactor is selected. The reactor is equipped with a high-precision temperature sensor to enable real-time temperature monitoring and is internally provided with a magnetic or mechanical stirring device to ensure sufficient mixing of various substances in the high-salt wastewater during the reaction process. Place the pretreated high-salt wastewater in the microwave reactor, set the power of the first microwave to 300 W, irradiate for 1 to 5 minutes, and the heating temperature is 20 to 60 °C for 3 to 5 minutes. Achieve a short-time increase in the local temperature of the high-salt wastewater and obtain a supersaturated solution, thereby ensuring the nucleation rate and uniformity.

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

[0036] In some embodiments, calcium and magnesium ions in the high-salt wastewater are prone to form an amorphous state. Since most of the amorphous state is calcium carbonate precipitate, due to the instability of the precipitate, it is easy to form a colloid in water and run with the water in the equipment, easily blocking the pipeline, thus affecting the recovery effect. Therefore, under the condition of the first microwave, the amorphous state of calcium and magnesium precipitates is reduced within a few minutes and converted into a crystalline state, which is beneficial to the stability of the precipitate and subsequent separation.

[0037] In some embodiments, a microwave emission device is selected, which is suitable for large-scale recovery of calcium and magnesium precipitates from high-salt wastewater. The reaction vessel in the microwave emission device is made of borosilicate glass or quartz, which has high temperature resistance and good microwave penetration. The filling volume of high-salt wastewater per time does not exceed 70% of the maximum capacity of the vessel, preferably 50% - 70%. During the reaction process, it is necessary to avoid the foam or steam generated by the boiling of the solution along the vessel wall from overflowing, improve the transfer efficiency of microwave and ultrasound, and reduce the potential safety hazards of the experiment. Among them, borosilicate glass or quartz can ensure 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 the loss or reflection of microwave energy as much as possible.

[0038] Heat the supersaturated solution under the second microwave and ultrasonic conditions, irradiate for 5 - 20 min, and stir to obtain a mixed solution. Among them, 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; the heating temperature is 20 - 60 °C.

[0039] In some embodiments, the supersaturated solution is placed under the second microwave and ultrasonic conditions. Among them, the power of the second microwave is 150 W, irradiated for 10 minutes, the ultrasonic frequency is 20 - 40 kHz, the power of the ultrasound is 100 W, and the stirring speed is 400 - 600 rpm for uniform stirring to ensure sufficient contact of ions in the supersaturated solution, reduce the crystallization defects caused by local undersaturation or uneven nucleation, and promote crystal formation.

[0040] In some embodiments, the power of the second microwave is relatively low, which is used to maintain the temperature of the supersaturated solution, promote the growth of crystal nuclei and the perfection of crystals. It can also avoid crystal aggregation or decomposition caused by overheating, contribute to the formation of uniform calcium and magnesium precipitates. And microwave heating can also reduce energy consumption.

[0041] Ultrasound can produce a cavitation effect. By ultrasonic oscillation impacting the supersaturated solution and cooperating with a suitable rotation speed to form turbulence, it can improve the ion mass transfer effect, promote the uniform dispersion of crystal nuclei, prompt the supersaturated solution to be transformed into a mixed solution, and then increase the precipitation rate of calcium and magnesium. Under the combined action of the second microwave and ultrasound, it accelerates the migration of ions to the surface of crystal nuclei and inhibits the secondary aggregation or fragmentation of crystals due to violent collision, and reduces the energy consumption of the post-treatment steps, obtaining crystals with large particle size and regular morphology.

[0042] In some embodiments, a temperature sensor can be selected for heating, such as a probe with high precision and fast response speed like a thermocouple, a thermistor, an optical fiber thermometer, etc., and continuously monitor the temperature change in the microwave reactor. Among them, the heating temperature is preferably 25 - 50 °C. At this heating temperature, in combination with the first microwave condition, it can take into account the rapid formation of amorphous calcium carbonate and the stability of subsequent crystallization, and effectively regulate the crystal growth kinetics.

[0043] In some embodiments, when the heating temperature is too high, the temperature of the high-salt wastewater can be reduced to an appropriate range by intermittently turning off the microwave or increasing the external cooling water jacket. When 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 power of the ultrasound can be appropriately adjusted to keep the heating temperature within an appropriate temperature range.

[0044] The mixed solution is post-treated to obtain a solid substance, which is the calcium and magnesium precipitate.

[0045] In some embodiments, the mixed solution is naturally cooled or cooled, and then centrifuged to obtain a lower-layer solid. The lower-layer solid is 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 method for recovering calcium and magnesium precipitate from high-salt wastewater heats the treated high-salt wastewater under the condition of the first microwave and irradiates for 1 - 5 min, realizing rapid heating of the high-salt wastewater and strengthening the local supersaturation degree, thereby promoting the rapid combination of Ca 2+ , Mg 2+ with CO3 2- ions to obtain a supersaturated solution. Then, heating is carried out in combination with the second microwave and ultrasonic conditions, irradiating for 5 - 20 min and stirring to form strong turbulence, which has an obvious promoting effect on crystal formation, increasing the number of nuclei in the supersaturated solution and making them evenly dispersed, and being beneficial to the complete development of crystals in the later mixed solution. After the mixed solution is post-treated, a solid substance is obtained, which is the calcium and magnesium precipitate. The process steps of the present application are simple, the nucleation rate is fast, and large-scale preparation at low cost can be realized.

[0047] In some embodiments, the pretreated high-salt wastewater contains hydroxide and carbonate ions, which can effectively promote the precipitation of calcium and magnesium ions and realize the effective recovery of calcium and magnesium precipitate.

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

[0049] In some embodiments, the power of the first microwave is 100 - 300 W. In the initial stage of the high-salt wastewater reaction, that is, the nucleation induction stage, by regulating the power of the first microwave to a higher power, rapid heating is realized, and local supersaturation is achieved in the shortest time to promote the nucleation and growth of calcium carbonate. The second microwave is regulated to a lower power to avoid crystal plane defects caused by strong energy input, and at the same time, an appropriate heating temperature is maintained to promote the migration of ions to the crystal surface and promote the formation of crystals.

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

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

[0052] Among them, the duty cycle of the ultrasound is 10 - 50%.

[0053] In some embodiments, in the step of converting the supersaturated solution into a mixed solution, that is, the crystal growth period, continuous ultrasound is used with a periodic on-off cycle. Among them, the duty cycle of the ultrasound is 10 - 50%. For example, if the duration of ultrasound on is 10 seconds and the duration of ultrasound off is 10 seconds, the duty cycle is 50%. Or pulsed intermittent multi-frequency ultrasound is used, by alternately adjusting multiple frequencies (such as 20 kHz / 40 kHz / 60 kHz), and a pulsed mode is adopted within each frequency band, with a duty cycle of 20% - 50%. On the one hand, the cavitation and turbulence of the ultrasound can continuously strengthen the ion diffusion to the crystal surface and improve the mass transfer effect. On the other hand, it can avoid excessive crushing of the crystal, secondary agglomeration of the crystal, and excessive energy consumption, maintaining the integrity of the crystal. Moreover, in a high salinity environment, although the ultrasound cavitation will have a certain attenuation, by moderately 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-salt wastewater include Li + , Na + , K + , Cl - , SO4 2- and at least one of them.

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

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

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

[0058] Add an alkali-adjusting agent to the high-salt wastewater to adjust it to alkaline, and then add sodium carbonate and mix evenly to obtain the pretreated high-salt wastewater.

[0059] Among them, the molar concentration of the alkali-adjusting agent is 0.1 mol / L; the alkali-adjusting agent includes at least one of sodium hydroxide, potassium hydroxide, and calcium oxide.

[0060] In some embodiments, add 0.1 mol / L of sodium hydroxide to the high-salt wastewater to make the high-salt wastewater alkaline with a pH of 10 - 12. Then add the sodium carbonate reagent at a rate of 1 mL / min and mix evenly to obtain the pretreated high-salt solution. Among them, the addition amount of sodium carbonate is 1.2 times the amount required for theoretical calcium and magnesium precipitation to ensure complete precipitation of calcium and magnesium ions in the high-salt wastewater.

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

[0062] In some embodiments, the particle size and morphology of the calcium and magnesium precipitate can be controlled by adjusting the reaction conditions. For example, by heating temperature and power under the first microwave condition of the treated high-salt wastewater, rapid heating and nucleation are achieved to obtain a supersaturated solution. Then, by coordinating and controlling the power of the second microwave and ultrasound, the migration of ions to the surface of the crystal nucleus is accelerated, and the secondary aggregation or fragmentation of crystals due to violent collision is inhibited, and the energy consumption of the post-treatment step is reduced, obtaining crystals with large particle size and regular morphology. After post-treatment, the particle size of the calcium and magnesium precipitate is 6 - 12 μm.

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

[0064] In some embodiments, if the rotation speed of the stirring is too low, it will cause insufficient mixing of Ca 2+ and Mg 2+ in the high-salt wastewater with anions CO3 2- and OH - , large local concentration differences, reduced nucleation rate, and prolonged crystallization time. At the same time, the microwave thermal effect and ultrasonic cavitation effect are difficult to be evenly transmitted to the whole solution, and it is impossible to effectively disperse the tiny crystal nuclei, resulting in secondary aggregation phenomenon.

[0065] In some embodiments, if the rotation speed of the stirring is too high, the shear force generated will break the crystal nuclei in the supersaturated solution, resulting in a reduction in the effective nucleation points and a decrease in the crystallization rate. And it increases energy consumption and equipment wear.

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

[0067] In some embodiments, cooling can cause the calcium and magnesium precipitates to fully precipitate from the mixed solution, reduce the dissolution or re-dissolution phenomenon at high temperatures, make the crystal structure of the calcium and magnesium precipitates more stable, avoid deformation or dissolution of the crystals during subsequent processing, and improve the crystallization rate of the calcium and magnesium precipitates.

[0068] Centrifugation is an efficient solid-liquid separation method. Through centrifugation, the precipitate can be quickly separated from the upper-layer solution to obtain the lower-layer solid (i.e., the calcium and magnesium precipitate). This greatly improves the separation efficiency, effectively removes impurities, is suitable for large-scale industrial production, and further improves the purity of the crystals.

[0069] Through washing, the surface impurities of the calcium and magnesium precipitate during formation can be removed. The surface may adsorb some reaction by-products, unreacted raw materials, or other impurities. Washing can remove surface impurities, improve the purity of the crystals, and prevent contamination of the crystals or affect their performance during subsequent drying.

[0070] Through drying, the moisture in the calcium and magnesium precipitate can be removed to reach the required drying degree, facilitating storage and subsequent use.

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

[0072] Application of the calcium and magnesium precipitate prepared by the above method in building materials.

[0073] In some embodiments, calcite in the calcium and magnesium precipitate is one of the important raw materials for manufacturing cement, which can improve the strength and durability of cement. It can also be used for interior and exterior decoration of buildings, such as floors, walls, and columns. When the calcium and magnesium precipitate is applied to building materials, it can significantly improve the performance and quality of building materials, while reducing production costs, in line with the development trend of green buildings.

[0074] For a further understanding of the present invention, examples are given below:

[0075] Among them, in the examples and comparative examples, the mass concentration of calcium chloride in the high-salt wastewater is ≥ 1.5 g / L, and the mass concentration of magnesium chloride is ≥ 0.2 g / L.

[0076] Example 1

[0077] Take 0.1 L of high-salt wastewater. Among them, the mass concentration of salts in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Li+, Ca 2 +, Mg 2+, Cl-. Place the pretreated high-salt wastewater in a microwave reactor, set the power of the first microwave to 300 W, the irradiation time to 5 min, and the heating temperature to 40 °C. After 240 seconds, a supersaturated solution is obtained.

[0078] Then, heat the supersaturated solution under the conditions of the second microwave and ultrasound, and stir it. Set the power of the second microwave to 100 W, the irradiation time to 5 minutes, the power of the ultrasound to 100 W, the frequency to 40 kHz, and the stirring speed to 600 rpm. After reacting for 15 min, a mixed solution is obtained.

[0079] Cool and centrifuge the mixed solution to obtain the lower-layer solid, wash and dry it to obtain the calcium and magnesium precipitate. After testing, it is found that the particle size of the calcium and magnesium precipitate is 11.4 μm and the crystallization rate is 92%.

[0080] Example 2

[0081] Compared with Example 1, the composition of the high-salt wastewater is changed.

[0082] Take 0.1 L of high-salt wastewater, in which the mass concentration of salt in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Na+, Ca 2 +, Mg 2 +, Cl-. Place the pretreated high-salt wastewater in a microwave reactor, set the power of the first microwave to 300 W, the irradiation time to 5 min, and the heating temperature to 40 °C. After 240 seconds, a supersaturated solution is obtained.

[0083] Then, heat the supersaturated solution under the conditions of the second microwave and ultrasound, and stir it. Set the power of the second microwave to 100 W, the irradiation time to 5 minutes, the power of the ultrasound to 100 W, the frequency to 40 kHz, and the stirring speed to 600 rpm. After reacting for 15 min, a mixed solution is obtained.

[0084] Cool and centrifuge the mixed solution to obtain the lower-layer solid, wash and dry it to obtain the calcium and magnesium precipitate. After testing, it is found that the particle size of the calcium and magnesium precipitate is 7.13 μm and the crystallization rate is 88%.

[0085] Example 3

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

[0087] Take 0.1 L of high-salt wastewater, in which the mass concentration of salt in the high-salt wastewater is 10 g / L, and the ion composition of the high-salt wastewater is Na+, Ca 2 +, Mg 2Li⁺, Ca²⁺, Mg²⁺, and Cl⁻. Place the pretreated high-salt wastewater in a microwave reactor, set the power of the first microwave to 300 W, the irradiation time to 5 min, and the heating temperature to 40 °C. After 240 seconds, a supersaturated solution is obtained.

[0088] Then, heat the supersaturated solution under the conditions of the second microwave and ultrasonic waves and stir it. Set the power of the second microwave to 100 W, the irradiation time to 5 minutes, the power of the ultrasonic wave to 100 W, the frequency to 40 kHz, and the stirring speed to 600 rpm. After reacting for 15 min, a mixed solution is obtained.

[0089] Cool and centrifuge the crystal solution to obtain the lower-layer solid, wash and dry it to obtain the calcium and magnesium precipitate. It is found through testing that the particle size of the calcium and magnesium precipitate is 7.51 μm and the crystallization rate is 96%.

[0090] Example 4

[0091] Compared with Example 1, the power of the first microwave is changed.

[0092] Take 0.1 L of high-salt wastewater, where the mass concentration of salt in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Li⁺, Ca 2 ²⁺, Mg 2 ²⁺, and Cl⁻. Place the pretreated high-salt wastewater in a microwave reactor, set the power of the first microwave to 200 W, the irradiation time to 5 min, and the heating temperature to 40 °C. After 300 seconds, a supersaturated solution is obtained.

[0093] Then, heat the supersaturated solution under the conditions of the second microwave and ultrasonic waves and stir it. Set the power of the second microwave to 100 W, the irradiation time to 5 minutes, the power of the ultrasonic wave to 100 W, the frequency to 40 kHz, and the stirring speed to 600 rpm. After reacting for 15 min, a mixed solution is obtained.

[0094] Cool and centrifuge the mixed solution to obtain the lower-layer solid, wash and dry it to obtain the calcium and magnesium precipitate. It is found through testing that the particle size of the calcium and magnesium precipitate is 9.20 μm and the crystallization rate is 90%.

[0095] Comparative Example 1

[0096] Among them, in Comparative Example 1 compared with Example 1, the steps of the first microwave, the second microwave, and ultrasonic waves are omitted.

[0097] Take 0.1 L of high-salt wastewater, where the mass concentration of salt in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Li⁺, Ca 2 ²⁺, Mg 2 ²⁺, and Cl⁻.

[0098] After cooling, centrifuging to obtain the lower-layer solid, washing, and drying the high-salt wastewater, a precipitate is obtained. Through testing, it is found that the particle size of the precipitate is 1.88 μm and the crystallization rate is 51%.

[0099] Comparative Example 2

[0100] Among them, in Comparative Example 2 compared with Example 1, the first microwave step is omitted.

[0101] Take 0.1 L of high-salt wastewater, where the mass concentration of salt in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Li+, Ca 2 +, Mg 2 +, Cl-.

[0102] Place the pretreated high-salt wastewater under the conditions of the second microwave and ultrasound for heating, and stir. Set the power of the second microwave to 100 W, the irradiation time to 5 minutes, the power of the ultrasound to 100 W, the frequency to 40 kHz, and the stirring speed to 600 rpm. After reacting for 15 min, a mixed solution is obtained.

[0103] After cooling, centrifuging to obtain the lower-layer solid, washing, and drying the mixed solution, a precipitate is obtained. Through testing, it is found that the particle size of the precipitate is 5.81 μm and the crystallization rate is 71%.

[0104] Comparative Example 3

[0105] Among them, in Comparative Example 3 compared with Example 1, the second microwave and ultrasound steps are omitted.

[0106] Take 0.1 L of high-salt wastewater, where the mass concentration of salt in the high-salt wastewater is 300 g / L, and the ion composition of the high-salt wastewater is Li+, Ca 2 +, Mg 2 +, Cl-.

[0107] Place the pretreated high-salt wastewater in a microwave reactor, set the power of the first microwave to 300 W, the irradiation time to 5 min, and the heating temperature to 40 °C. After 240 seconds, a supersaturated solution is obtained.

[0108] After cooling, centrifuging to obtain the lower-layer solid, washing, and drying the supersaturated solution, a precipitate is obtained. Through testing, it is found that the particle size of the precipitate is 5.69 μm and the crystallization rate is 74%.

[0109] Among them, Table 1 lists the particle size data of calcium and magnesium precipitates recovered from high-salt wastewater by different methods in the examples and comparative examples. Figure 1 is the flow chart of the method for recovering calcium and magnesium precipitates from high-salt wastewater in this application, Figure 2 is the SEM image of calcium and magnesium precipitates recovered from high-salt wastewater by different methods.

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

[0111]

[0112] Combined with Figure 2 , wherein Figure 2 A1, B1, and C1 in correspond to SEM images of calcium and magnesium precipitates recovered from high-salt wastewater with a LiCl mass concentration of 300 g / L in 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-salt wastewater with a Na2SO4 mass concentration of 10 g / L in 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-salt wastewater with a NaCl mass concentration of 10 g / L in 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-salt wastewater with a NaCl mass concentration of 100 g / L in Comparative Example 1, Comparative Example 2, and Example 1, respectively. See Table 1 for specific particle size dimensions.

[0113] It can be seen from this that in Comparative Example 1, the first microwave, second microwave, and ultrasonic steps were omitted, and the high-salt wastewater was not pretreated. Due to the lack of the rapid temperature rise of the microwave and the cavitation effect of the ultrasound, the calcium and magnesium precipitates were in an amorphous or non-crystalline state, easily forming colloidal and unstable precipitates, unable to effectively nucleate and grow, resulting in a precipitate particle size of 1.88 μm and a crystallization rate of only 51%. In Comparative Example 2, the first microwave step was omitted, unable to achieve the rapid nucleation of calcium and magnesium ions, resulting in insufficient and unevenly distributed crystal nuclei and incomplete crystal development, with a particle size of 5.81 μm and a crystallization rate of 71%. In Comparative Example 3, the second microwave and ultrasonic steps were omitted, lacking the synergistic effect of ultrasonic turbulence and microwave, and the crystals were prone to agglomeration and fragmentation during growth, unable to form complete large particle crystals, with a particle size of 5.69 μm and a crystallization rate of 74%. In contrast, in the examples of the present invention, a supersaturated solution was first formed by rapid heating with the first microwave, and then the crystal growth was enhanced by the synergistic effect of the second microwave and ultrasound. Although the corresponding process parameters were regulated, the recovery of calcium and magnesium precipitates with a particle size of 6-12 μm and a crystallization rate of over 90% was still achieved. The problems of crystal agglomeration and low nucleation rate in the traditional process were successfully overcome. Further indicating that the process of the present invention has significant advantages in terms of improving crystallization efficiency and crystal particle size.

[0114] In the above technical solution of the present invention, the above is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for recovering calcium and magnesium precipitates from high-salt wastewater, characterized in that, The mass concentration of salt in the high-salt wastewater is 10 g / L to 300 g / L; the steps include: S1: Place the pretreated high-salt wastewater under the first microwave condition for heating and irradiate for 1 to 5 minutes to obtain a supersaturated solution; S2: Place the supersaturated solution under the second microwave and ultrasonic conditions for heating, irradiate for 5 to 20 minutes, and stir to obtain a mixed solution; S3: After post-treating the mixed solution, obtain a solid substance, which is the calcium and magnesium precipitate; Among them, 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; the heating temperature is 20 to 60 °C.

2. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, wherein The pretreated high-salt wastewater contains hydroxide ions and carbonate ions.

3. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, wherein, The power of the first microwave is 100 to 300 W; the power of the second microwave is 100 to 200 W; the power of the ultrasonic wave is 50 to 200 W, and the frequency is 20 to 40 kHz.

4. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, wherein The ultrasonic wave includes one of continuous ultrasonic wave and pulse intermittent multi-frequency ultrasonic wave; Among them, the duty cycle of the ultrasonic wave is 10 to 50%.

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

6. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, characterized in that, The pretreatment steps of the high-salt wastewater include: Add an alkali regulator to the high-salt wastewater to adjust it to alkaline, and then add sodium carbonate and mix evenly to obtain the pretreated high-salt wastewater; Among them, the molar concentration of the alkali regulator is 0.1 mol / L; the alkali regulator includes at least one of sodium hydroxide, potassium hydroxide, and calcium oxide.

7. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, wherein The particle size of the calcium and magnesium precipitate is 6 to 12 μm.

8. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, characterized in that, The rotation speed of the stirring is 400 to 600 rpm.

9. The method for recovering calcium and magnesium precipitates from high-salt wastewater according to claim 1, wherein, The post-treatment includes: cooling, centrifuging to obtain the lower-layer solid, washing, and drying.

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

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