Membrane-free electrochemical calcium and magnesium selective removal and recovery system and method

Abstract

The invention belongs to the technical field of electrochemistry, and relates to a membrane-free electrochemical calcium-magnesium selective removal and recovery system and method. The membrane-free electrochemical calcium-magnesium selective removal and recovery system comprises a water inlet tank, a direct-current power supply, an electrolytic bath, a water pump and a crystallization granulation column; the anode cylinder is internally provided with a porous cathode filter element, the anode of the direct-current power supply is electrically connected with the anode, and the cathode of the direct-current power supply is electrically connected with the porous cathode filter element; a water outlet of the water inlet tank is connected with the electrolytic bath, the top in the porous cathode filter element cylinder is communicated to the bottom of the crystallization granulation column, and a water outlet is formed in the upper part of the crystallization granulation column; a membrane-free electrochemical method is adopted, OH <-> is generated by pumping the porous cathode, and the problem of membrane pollution is completely avoided; by regulating and controlling electrochemical parameters and cathode configuration, the purpose of graded calcium and magnesium removal can be achieved, and meanwhile efficient recovery of calcium and magnesium ions can be achieved by combining with a crystallization and granulation system; the membrane-free design reduces the operation and maintenance cost of the system, and calcium and magnesium ions are efficiently removed and recycled in a graded manner, so that the economical efficiency of the process is improved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and relates to a membraneless electrochemical calcium and magnesium selective removal and recovery system and method, which can efficiently and selectively remove and recover calcium and magnesium ions in water without using a diaphragm. Background Art

[0002] Under the "dual carbon" strategy and energy crisis, water, as an important carrier of energy in industry, seeks efficient use of water, which is an important strategic need to achieve low-carbon transformation of industrial water system and break through water resource constraints. 2+ and Mg 2+ When the concentration is too high, it will react to form CaCO 3 and Mg(OH) 2 Insoluble precipitates such as precipitates can cause pipeline blockage, resulting in increased system pressure and reduced flow. From an economic and environmental perspective, recycling and utilizing Ca in circulating cooling water, mine water, seawater desalination and other industrial water is a good choice. 2+ and Mg 2+ It can not only reduce the exploitation of natural resources and alleviate environmental pressure, but also provide raw materials for various industrial processes and has important economic value.

[0003] At present, the methods of scale prevention and descaling widely used in industry mainly include dosing method, ultrasonic method, ion exchange softening method, reverse osmosis method and electrochemical descaling method. Dosing method is the most widely used method in industry at present. The advantages of this method are time-saving and labor-saving, simple operation and obvious effect. There are two main types of dosing methods: scale inhibitor method and lime softening method. The principle of scale inhibitor is that it can complex with calcium and magnesium ions in water, so that these ions are not easy to deposit on the wall of the heat exchanger, and it can also disperse some existing scale grains in the water body. However, scale inhibitor cannot remove hardness ions, but can only delay the occurrence of precipitation. At the same time, the organic phosphorus scale inhibitor introduced will also cause the P content of circulating cooling water to exceed the standard, further causing pollution. The method of using lime to soften hard water is called lime softening method. The main principle of this method is to use lime milk to react with calcium bicarbonate in the solution, so that the scale ions are converted into insoluble precipitates and deposited. However, chemical agents are expensive and will produce a lot of sludge, which needs further treatment. The principle of ultrasonic scale inhibition is based on the characteristic that ultrasonic waves can generate mechanical vibrations when passing through the medium, thus causing changes in the physical structure of the medium (such as cracks). The circulating cooling water is subjected to ultrasonic waves, and the shearing, cavitation and activation effects produced by them loosen and fall off the scale already formed on the heat exchanger wall. However, the cost of ultrasonic equipment is relatively high, and long-term operation may cause the equipment to loosen. The most widely used ion exchange method is sodium ion exchange resin, which uses the Na in the resin to + With Ca2 + Exchange, reduce calcium ion concentration, and thus inhibit scale formation. However, this method requires regular replacement of resin columns, which is too expensive, and due to the Na + As the concentration increases, the treated water needs to be reprocessed to avoid secondary pollution. Reverse osmosis is achieved by applying pressure to the solution on one side of the membrane so that its pressure exceeds the solution penetration. The solvent penetration direction will change from high pressure to low pressure side, and the solute will remain on the high pressure side because it cannot pass through the membrane, thereby achieving the purpose of separating ions. Although the scale removal rate of reverse osmosis technology is very high, after a long period of operation, high concentrations of scale-forming ions will be deposited on the surface of the membrane due to ion concentration, blocking the micropores of the membrane, resulting in a decrease in scale removal rate and an increase in energy consumption. At present, most methods can only remove hardness ions in water, and it is difficult to achieve the separate removal and recovery of calcium and magnesium ions and their resource recycling.

[0004] Electrochemical precipitation is an active hardness removal technology with the advantages of high efficiency, environmental friendliness, low cost and easy operation, and has attracted extensive attention in recent years. - Ca 2+ and Mg 2+ The reaction produces CaCO 3 and Mg(OH) 2 Precipitation, thereby achieving the removal of hardness ions. This method promotes the precipitation of hardness ions through electrochemical reactions, thereby achieving hardness removal without the use of chemical additives. However, the current conventional electrochemical descaling efficiency is low, generally maintained between 15% and 25%, making it difficult to remove the hardness in water in a one-time and relatively thorough manner. This low efficiency is mainly caused by the following factors: (1) The surface area of ​​conventional electrodes is limited, which limits the reaction rate and efficiency. (2) The mass transfer rate of ions between the electrode surface and the solution may be slow, thereby limiting the reaction rate. (3) The generated precipitate accumulates on the electrode surface, further hindering the reaction. In order to improve the descaling efficiency and achieve resource recycling, researchers have developed a diaphragm electrochemical method to treat wastewater. The core of the diaphragm electrochemical method is to use an ion exchange membrane to separate the electrolytic cell into an anode chamber and a cathode chamber. Through this method, the migration path of ions in the electrolytic cell can be more effectively controlled, thereby improving the reaction efficiency. The ion exchange membrane allows specific ions to pass through while preventing the migration of other ions. In this way, the reaction environment can be more precisely controlled, improving the selectivity and efficiency of the reaction. By using membrane materials, the mixing between the anode chamber and the cathode chamber can be reduced, thereby reducing the occurrence of side reactions. This helps to improve the efficiency of the main reaction and the purity of the product. At the same time, through the separation of membrane materials, a higher ion concentration gradient can be formed between the anode chamber and the cathode chamber, further promoting the migration and reaction of ions.

[0005] Existing electrochemical water treatment technology has the following objective disadvantages:

[0006] 1. Membrane fouling problem:

[0007] Existing technical solutions: Traditional electrochemical water treatment technology usually relies on membrane separation technology, using various types of membranes to separate and recover ions. The membrane is easily contaminated during use, resulting in a decrease in its filtration efficiency, requiring frequent replacement and cleaning, and increasing operating and maintenance costs. In addition, membrane contamination may also lead to reduced system treatment efficiency and fluctuations in treatment effects.

[0008] 2. It is difficult to achieve selective graded removal:

[0009] Most existing water treatment technologies cannot achieve selective phased removal of calcium and magnesium ions, and can usually only treat all ions at once. The inability to remove calcium and magnesium ions in phases makes it difficult to optimize the removal conditions of different ions during the treatment process, affecting resource recovery and treatment effects.

[0010] 3. Spontaneous homogeneous precipitation takes a long time:

[0011] In traditional precipitation methods and some electrochemical treatment technologies, the spontaneous homogeneous precipitation process of calcium and magnesium ions is usually slow (usually takes 90 to 180 minutes). The long spontaneous homogeneous precipitation time leads to a longer overall treatment cycle, reduced system treatment efficiency, and increased operating costs.

[0012] 4. The precipitate is difficult to separate:

[0013] Traditional precipitation methods generate fine precipitates, which usually require complex post-processing steps to separate and recover. Fine precipitates are difficult to separate and recover, increasing the difficulty and cost of processing. In addition, the precipitates generated by traditional precipitation methods are of low purity, which limits their resource utilization value.

[0014] Therefore, there is an urgent need for a method or device with high stability, high efficiency, and the ability to improve resource recovery rate and treatment effect to solve the above technical problems and achieve efficient removal of calcium and magnesium ions and recycling of resources. Summary of the invention

[0015] The present invention combines the "pumping porous cathode OH - The membraneless electrochemical method and crystallization granulation technology are designed to efficiently remove and recover calcium and magnesium ions in brine and realize their resource recovery. - The membraneless electrochemical method can achieve the effect of selective graded removal of calcium and magnesium ions by controlling the operating parameters of the electrochemical process and the pore size of the porous cathode and regulating the pH value of the pumped water.

[0016] The technical solution adopted by the present invention to solve the technical problem is: a membraneless electrochemical calcium and magnesium selective removal and recovery system, comprising: a water inlet tank, a DC power supply, an electrolytic cell, a water pump, and a crystallization granulation column;

[0017] An electrolytic cell is provided with a long cylindrical anode with a vertical rotating axis, and a side cylinder wall of the anode is in a mesh shape, and the mesh holes of the side cylinder wall of the anode are connected to the inside and outside of the cylinder of the anode; a long cylindrical porous cathode filter element with closed upper and lower ends is provided in the cylinder of the anode, and the filter holes of the cylinder wall of the porous cathode filter element are connected to the inside and outside of the cylinder of the porous cathode filter element; the positive pole of the DC power supply is connected to the anode, and the negative pole of the DC power supply is electrically connected to the porous cathode filter element; the filter hole diameter range of the porous cathode filter element is: 10μm~15mm;

[0018] The crystallization granulation column is in the shape of a water tank, and is filled with fillers, the filling height of which does not exceed one third of the depth of the water tank of the crystallization granulation column; the fillers include: calcite, garnet, quartz sand, brucite;

[0019] The water outlet of the water inlet tank is connected to the lower part of the electrolytic cell, the top of the porous cathode filter is connected to the water inlet of the water pump, the water outlet of the water pump is connected to the bottom of the crystallization granulation column, and the upper part of the crystallization granulation column is provided with a water outlet;

[0020] The incoming water flows from the water inlet tank into the electrolytic cell. The incoming water in the electrolytic cell completely immerses the anode and the porous cathode filter element. The water pump extracts the electrolytic separation water in the porous cathode filter element and pumps it to the bottom of the crystallization granulation column. The treated water is discharged from the water outlet on the top of the crystallization granulation column.

[0021] Preferably, the anode includes: a titanium-coated ruthenium-iridium electrode, a lead dioxide electrode, a titanium-coated tin-antimony electrode, a boron-doped diamond electrode, a graphite electrode, and a titania electrode; the porous cathode filter element includes: a stainless steel filter element, a nickel-plated copper powder sintered filter element, a copper mesh filter element, a titanium powder sintered filter element, and a stainless steel sintered filter element.

[0022] Preferably, an overflow return pipe is provided on the upper portion of the electrolytic cell and is connected to the water inlet tank.

[0023] Preferably, the removal and recovery system is provided with multiple groups, and the multiple groups of removal and recovery systems are connected in sequence by head and tail water channels, and the water outlet of the crystallization granulation column of the previous group of removal and recovery systems is connected to the water inlet tank of the next group of removal and recovery systems.

[0024] More preferably, the removal and recovery system is provided with two groups;

[0025] The pore size range of the porous cathode filter element of the previous group of removal and recovery systems is: 1 to 15 mm, the porous cathode filter element of the previous group of removal and recovery systems is a stainless steel filter element; the filler of the previous group of removal and recovery systems is calcite;

[0026] The pore size range of the porous cathode filter element of the latter group of removal and recovery systems is 10 to 500 μm. The porous cathode filter element of the latter group of removal and recovery systems is a nickel-plated copper powder sintered filter element. The filler of the latter group of removal and recovery systems is garnet.

[0027] The present invention also discloses a membraneless electrochemical calcium and magnesium selective removal and recovery method, which is used for the membraneless electrochemical calcium and magnesium selective removal and recovery system. The method comprises the following steps:

[0028] Step S1: The electrolyte flows from the water inlet tank into the lower end of the side of the electrolytic cell and is electrolyzed in the electrolytic cell;

[0029] Step S2: When the electrolyte fills the electrolytic cell, a portion of the electrolyte overflows from the upper side of the electrolytic cell, and the overflow water flows back to the water inlet tank to mix with the raw water; a portion of the electrolyte is pumped out from the top of the porous cathode filter element by a water pump;

[0030] Step S3: pump the water to the crystallization granulation column, the water flows in from the lower end of the crystallization granulation column, and flows out from the upper end of the crystallization granulation column after passing through the filler; in this step, the water flow must have a certain flow rate to flush the filler in the crystallization granulation column to achieve a suspended state, and the water flow is fully in contact with and mixed with the filler; the crystallization granulation column is divided into a granulation zone, a separation zone, and a clear water zone from bottom to top, wherein the filler filling density in the granulation zone is the largest, and the filler filling density in the separation zone is second, the clear water zone is used to store the water recovered after the selective removal of calcium and magnesium, and the water outlet of the crystallization granulation column is arranged at the upper part of the clear water zone.

[0031] Preferably, in step S2, when removing and recovering Ca 2+ When the pH value of the pumped water is adjusted to 9.5-10, the Mg 2+ When the pump is used, adjust the pH value of the water sucked out by the pump to >11.5.

[0032] Better, when removing and recycling Ca 2+ and Mg 2+ When two groups of membraneless electrochemical calcium and magnesium selective removal and recovery systems are connected in series, the first group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Ca 2 The latter group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Mg 2+ ;

[0033] After repeating steps S1 to S3 in the previous group of membraneless electrochemical calcium and magnesium selective removal and recovery systems, the water flowing out of the upper end of the crystallization granulation column enters the water inlet tank of the next group of membraneless electrochemical calcium and magnesium selective removal and recovery systems, and repeats steps S1 to S3 in the next group of membraneless electrochemical calcium and magnesium selective removal and recovery systems. The beneficial effects of the present invention are:

[0034] 1. Solve the membrane pollution problem; the present invention adopts a membrane-free electrochemical method to generate OH by pumping a porous cathode. - , completely avoiding the problem of membrane contamination. The membrane-free design makes the system no longer rely on the filtration function of the membrane, thus eliminating the possibility of membrane contamination. This will significantly reduce the operation and maintenance costs of the system, improve the stability and efficiency of the treatment, and extend the service life of the equipment.

[0035] 2. Accelerate precipitation: The present invention uses a membraneless electrochemical method to increase the pH of the pumped water, significantly increase the supersaturation of calcium and magnesium ions, and at the same time combines a crystallization granulation system to promote the rapid precipitation of calcium and magnesium ions. This greatly shortens the time of spontaneous homogeneous precipitation and reduces the overall processing cycle. At the same time, accelerating the precipitation process improves the processing efficiency of the system and reduces operating costs. Due to the shortened precipitation time, the entire processing process is more efficient, saving time and resources.

[0036] 3. Selective staged removal of calcium and magnesium ions: The present invention can achieve selective staged removal of calcium and magnesium ions by precisely controlling the electrochemical reaction parameters and the pore size of the porous cathode filter. In view of the difference in solubility of calcium and magnesium ions at different pH values, the pH value is increased step by step and the reaction conditions are adjusted to allow different ions to precipitate separately. This will optimize the removal conditions of different ions, achieve efficient selective removal and recovery, and improve resource recovery rate and treatment effect.

[0037] 4. Efficient separation and resource recovery of precipitates: The crystallization granulation technology of the present invention promotes the crystallization of calcium and magnesium ions into larger particles by regulating crystallization conditions. These particles are easier to separate and recover than the fine precipitates generated by traditional precipitation methods. This will significantly reduce the difficulty and cost of post-processing, and the recovered particles have higher purity and resource utilization value, realizing the recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of a membraneless electrochemical calcium and magnesium selective removal and recovery system and method;

[0039] Figure 2 This is a schematic diagram of the membrane-free electrochemical descaling process of the present invention;

[0040] Figure 3 It is the operating principle diagram of the crystallization granulation process of the present invention;

[0041] Figure 4 It is a schematic diagram of the coupled process of calcium and magnesium ion removal, granulation and densification of the present invention;

[0042] Figure 5 This is a comparison chart of the descaling rates of the conventional electrochemical process and the coupling process of the present invention;

[0043] Figure 6 This is a comparison chart of the descaling efficiency between the membraneless electrochemical process and the coupling process of the present invention;

[0044] Figure 7 It is a comparison diagram of water hardness at each stage of the coupling process of the present invention.

[0045] In the figure, 1. water inlet tank; 2. DC power supply; 3. electrolytic cell; 4. water pump; 5. crystallization granulation column; 6. anode; 7. porous cathode filter element; 8. filler; 9. overflow return pipe. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] like Figure 1 As shown in the figure, it is a membraneless high-efficiency electrochemical calcium and magnesium separation and recovery system, which mainly includes two parts: calcium hardness removal and recovery and magnesium hardness removal and recovery. Each part is connected in series by a membraneless electrochemical system and a crystallization granulation system. A single group of membraneless electrochemical calcium and magnesium selective removal and recovery system can be selected to remove and recover Ca 2+ You can also choose a single group of membraneless electrochemical calcium and magnesium selective removal and recovery system to remove and recover Mg 2+ ; Flexible combination according to actual needs. The recovery system of the present invention can also be used to recover other ions.

[0048] When removing recycled Ca 2+ and Mg 2+ When two groups of membraneless electrochemical calcium and magnesium selective removal and recovery systems are connected in series, the first group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Ca 2 The latter group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Mg 2+ ;

[0049] In the previous group of membraneless electrochemical calcium and magnesium selective removal and recovery systems, Ca 2+ The removal and recovery system includes: a raw water inlet tank 1, a DC power supply 2, an electrolytic cell 3, a mesh anode 6, a large mesh (1-15 mm) porous cathode filter 7, a water pump 4 and a primary crystallization granulation column 5. 2+ Removal of Ca from the recovery system 2+ Electrolyzer 3 is connected to raw water inlet pool 1, Ca 2+An anode 6 is arranged in the electrolytic cell 3, a large-mesh porous cathode filter 7 is arranged in the anode 6, the anode 6 is connected to the positive electrode of the DC power supply 2, and the large-mesh porous cathode filter 7 is connected to the negative electrode of the DC power supply 2. 2+ The top outlet of the electrolytic cell 3 is also connected to the inlet of the water inlet tank 1, Ca 2+ The overflow water in the electrolytic cell 3 flows back to the raw water inlet tank 1. The water pump 4 pumps the electrochemical system effluent into the Ca 2+ In the crystallization column 5, the influent first passes through the Ca 2+ The removal and recovery system raises the pH of the pumped water to between 9.5 and 10 to achieve Ca 2+ Supersaturated precipitation without causing Mg 2+ A precipitate is produced, and then Ca 2+ The membraneless electrochemical system pumps out water from the bottom of the removal recovery system to connect the Ca 2+ Crystallization granulation system, water flows through the crystallization column and flows out from the upper clarification area to complete Ca 2+ Removal and recycling.

[0050] In the latter group of membraneless electrochemical calcium and magnesium selective removal and recovery systems, Mg 2+ Removal and recovery systems include: No Ca 2+ Water inlet tank 1, DC power supply 2, Mg 2+ Electrolytic cell 3, mesh anode 6, porous cathode filter element 7 with small mesh (10-500 μm), water pump 4 and Mg 2 + Crystallization granulation column 5. Mg 2+ Removal of Mg from the recovery system 2+ Electrolyzer 3 connected with or without Ca 2+ Inlet tank 1, Mg 2+ An anode 6 is arranged in the electrolytic cell 3, a small-mesh porous cathode filter 7 is arranged in the anode 6, the anode 6 is connected to the positive electrode of the DC power supply 2, and the small-mesh porous cathode filter 7 is connected to the negative electrode of the DC power supply 2. 2+ The top outlet of the electrolytic cell 3 is also connected to the inlet of the water inlet tank 1. 2+ The overflow water in the electrolytic cell 3 flows back to the raw water inlet tank 1. The water pump 4 pumps the electrochemical system effluent into the MgO 2+ In the crystallization granulation system 7, the influent water passes through the Ca 2+ The removal and recovery system can remove the Ca 2+ Completely removed, and then Ca 2+ Removal of Mg from the recovery system 2+ Remove the membraneless electrochemical system in the recovery system, and raise the pH of the pumped water to above 11.5 after treatment to achieve Mg 2+ The supersaturated precipitate was then added to the Mg 2+The effluent from the membraneless electrochemical system in the removal and recovery system is connected to the crystallization and granulation system from the bottom, and the water flows through the crystallization column and flows out from the upper clarification area to complete the Mg 2+ Removal and recycling.

[0051] like Figure 2 As shown, the principle of the membraneless electrochemical system in the present invention is to pump the cathode porous filter boundary layer water to remove the large amount of OH generated in the electrolysis process. - The bulk solution is extracted along with the nearby aqueous solution, and the OH produced at the cathode is separated without using any membrane material. - The H generated at the anode + , improve OH - Utilization rate, thereby improving the descaling efficiency. 2+ In the removal and recovery system, the use of a large mesh (1-15 mm) cathode filter can achieve the following benefits: (1) Control the pH at Ca 2+ Removal range (9.5 ~ 10) without Mg 2+ (2) The large-mesh cathode filter element can avoid frequent cathode blockage, and after blockage, the cathode can be regenerated by simple backflushing, simplifying the difficulty and cost of daily operation and maintenance. 2+ In the removal and recovery system, a cathode filter with a small mesh (90-500μm) is used. This is because Mg 2+ Removal requires a higher pH (>11.5), and the small mesh cathode filter has a larger specific surface area, so it will produce more OH - OH is also more likely to be absorbed by the cathode under the condition of cathode pumping. - At the same time, due to the Ca 2+ After removing the recovery system, the effluent is basically Mg 2+ ,Mg 2+ Formation of Mg(OH) 2 The process is generally slow, and less deposition is made on the cathode. Therefore, even if a cathode filter with a small mesh is used, it is not easy to cause clogging. After the treatment of the two-stage membraneless electrochemical system, efficient selective graded removal of calcium and magnesium can be achieved. In this process, the remaining solution in the electrolytic cell is + The pH value decreases slightly due to the effect, and the hardness of the solution remains basically unchanged. Therefore, the overflow water is returned to the water inlet tank 1 to be mixed with the raw water for further treatment.

[0052] Since the pumped water is alkaline, the solution will be supersaturated with calcium and magnesium ions, which will be in an unstable state, resulting in the precipitation of crystals. However, the spontaneous homogeneous precipitation process is generally slow, usually requiring more than 90 minutes, and the generated precipitate is difficult to collect effectively. Therefore, the present invention considers coupling a crystallization granulation system after the membraneless electrochemical system to accelerate the crystallization precipitation process of calcium and magnesium ions and form dense large particles.

[0053] like Figure 3 As shown in the figure, the principle of the crystallization granulation system of the present invention is that the electrochemical pump sucks out water from the lower part of the crystal column, so that the characteristic crystal seeds exist in the water in a suspended state, and the pH of the pumped water is accurately controlled by adjusting the electrochemical parameters, so as to improve the cohesion of calcium and magnesium ions on the surface of the crystal seeds, reduce the nucleation energy barrier, and induce Ca in the water. 2+ and Mg 2+ Rapid crystallization nucleation to generate CaCO 3 and Mg(OH) 2 Crystals attach to the surface of the seed crystals and become dense. As calcium and magnesium products continue to attach, the crystals grow slowly and eventually form large particles that are precipitated and discharged at the bottom of the water.

[0054] like Figure 4 As shown, high-hardness influent water can be treated by a two-stage membraneless electrochemical system coupled with a crystallization granulation system to achieve rapid and efficient selective graded removal of calcium and magnesium and resource recycling.

[0055] Due to the large mesh cathode filter (1-15mm) and small mesh cathode filter (10-500μm) OH - The enrichment capacity is different, so in Ca 2+ In the membraneless electrochemical system, due to the removal of Ca 2+ The pH required for precipitation is relatively low (pH = 9.5-10). At this time, by adjusting the operating parameters and combining with a large mesh cathode filter, Ca can be precipitated. 2+ But not for Mg 2+ Have an impact; in Mg 2+ In the membraneless electrochemical system for removal of 2+ The pH required for precipitation is relatively high (pH>11.5). By adjusting the operating parameters and combining a small mesh cathode filter, the system OH can be increased. - Enrichment capacity, Mg 2+Precipitation is performed. Through the configuration of the above process conditions, the pH of the effluent can be regulated to achieve the purpose of selective separation and precipitation of calcium and magnesium ions. However, its spontaneous homogeneous precipitation time is long, and it is difficult to perform efficient solid-liquid separation, which leads to a long overall processing cycle and difficulty in efficient and rapid resource recycling of the removed calcium and magnesium ions. Traditional crystallization and granulation technology can remove calcium and magnesium ions by adding characteristic crystal seeds and adjusting the pH at the same time, and form densified large particles for recycling, but a large amount of alkaline agents are required to control the pH of the inlet water during the process, which will lead to an increase in processing costs and will cause corresponding pollution, which is not conducive to the sustainable development of the environment. Therefore, the present invention not only achieves the complementarity and enhancement of technology through reasonable technical combination and optimization, but also ensures the optimal performance of each link through precise parameter control and optimized design, thereby achieving the goal of efficient removal and graded recovery. This innovative combination and optimization method enables the present invention to achieve a significant breakthrough on the basis of the prior art, and has high technical value and commercial potential.

[0056] Example

[0057] Example 1

[0058] (1) The hardness of the circulating water is 400 mg / L, of which the calcium hardness is 300 mg / L, the magnesium hardness is 100 mg / L, and the alkalinity is 230 mg / L.

[0059] (2) Anode 6 is made of titanium-coated ruthenium-iridium electrode; Ca 2+ Removal of the cathode 5 in the membraneless electrochemical electrolysis system using a stainless steel filter element, the current density is 14mA / cm 2 , electrolysis time is 1h; Mg 2+ Removal of the cathode 10 in the membraneless electrochemical electrolysis system using a nickel-plated copper powder sintered filter element with a current density of 25 mA / cm 2 , electrolysis time is 3h;

[0060] (3) Pumping scheme: The electrolyte flows from Ca 2+ The lower end of the side of the electrolytic cell 3 flows in, and the Ca 2+ Electrolysis is carried out in electrolytic cell 3. When the electrolyte is filled with Ca 2+ After electrolysis cell 3, part of the electrolyte is removed from Ca 2+ The electrolyte overflows from the upper side of the electrolytic cell 3, and a portion of the electrolyte is pumped out from the top of the large-mesh cathode filter 5 by the water pump 4, and the overflow water is returned to the water inlet tank 1 to be mixed with the raw water. 2+ The water flow rate of electrolytic cell 3 is 5400mL / h, the pump flow rate of water pump 4 is 2700mL / h, and the pumped water is connected to Ca 2 +In the crystallization granulation system 7, the filler is calcite, and water flows in from the lower end of the crystallization granulation column 7 and flows out from the upper end. The outflowing water flows into the Ca-free 2+ In water tank 1, as Mg 2+ Remove the water from the recovery system and continue processing. 2+ The lower end of the side of the electrolytic cell 3 flows in, and the Mg 2+ Electrolysis is carried out in electrolytic cell 3. When the electrolyte is filled with Mg 2+ After electrolysis cell 3, part of the electrolyte is removed from Mg 2+ The electrolyte overflows from the upper side of the electrolytic cell 3, and a portion of the electrolyte is pumped out from the top of the porous cathode filter 7 with small mesh by the water pump 4, and the overflow water is returned to the water inlet tank 1 to be mixed with the raw water. 2+ The water flow rate of electrolytic cell 3 is 5400mL / h, the pump flow rate of water pump 4 is 2700mL / h, and the water sucked out of the pump is connected to Mg 2+ In the crystallization granulation system 11, the filler is garnet, and water flows in from the lower end of the crystallization granulation column 7 and flows out from the upper end. The hardness of the water at this time is measured.

[0061] Comparative Example 1: No Pumping

[0062] (1) The hardness of the circulating water is 400 mg / L, of which the calcium hardness is 300 mg / L, the magnesium hardness is 100 mg / L, and the alkalinity is 230 mg / L.

[0063] (2) The anode is titanium-coated ruthenium-iridium electrode; the cathode is nickel-plated copper powder sintered filter element, and the current density is 25mA / cm 2 , electrolysis time is 3h;

[0064] (3) Water flows in from the lower side of the electrolytic cell 3. When the electrolyte fills the electrolytic cell 3, all the electrolyte overflows from the upper side of the electrolytic cell 3. At this time, the water flow rate is 2700 mL / h. The hardness of the overflow water is measured after it has been left to stand for 3 hours.

[0065] The results are as follows Figure 5 As shown, after 1 hour of treatment, it was found that the hardness removal rate of the pumped water in Example 1 was relatively high, reaching 98%, and rapid and efficient recovery of calcium and magnesium ions could be achieved. However, in Comparative Example 1, the hardness removal rate was only 30% when no pumping was performed, and homogeneous precipitation of up to 3 hours was required, making it difficult to achieve graded removal and recovery of calcium and magnesium ions.

[0066] Example 2

[0067] Same as in Example 1, Ca 2+ Removal of effluent and Ca from membraneless electrochemical system 2+ Remove the hardness of the water discharged from the recovery system, Mg 2+ Membraneless electrochemical system and Mg removal 2+Remove the hardness of the water discharged from the recovery system.

[0068] The results are as follows Figure 6 As shown, after 3h treatment, Ca 2+ The removal rate of calcium hardness in the effluent of the membraneless electrochemical system was 70%, while the removal rate of calcium hardness in the effluent of the membraneless electrochemical system was 70%. 2+ The removal rate of calcium hardness in the water of the recovery system reaches 96.3%. 2+ The removal rate of magnesium hardness in the effluent of the membraneless electrochemical system was 7%, while the removal rate of magnesium hardness in the effluent of the membraneless electrochemical system was 7%. 2+ The removal rate of magnesium hardness in the water of the recovery system reached 89%, proving that the crystallization granulation process has the effect of accelerating the precipitation and recovery of calcium and magnesium ions.

[0069] Example 3

[0070] Same as in Example 1, Ca 2+ Removal of hardness and Mg in the effluent of the recovery system 2+ Remove the hardness of the water discharged from the recovery system.

[0071] The results are as follows Figure 7 As shown, after 3h treatment, Ca 2+ The calcium hardness of the water discharged from the removal and recovery system is only 11 mg / L, while the magnesium hardness remains unchanged at 100 mg / L. 2+ The calcium hardness of the effluent from the removal and recovery system is 0 mg / L, and the magnesium hardness is 8 mg / L.

[0072] In summary, the present invention adopts a membraneless electrochemical method to generate OH by pumping a porous cathode. - , completely avoiding the problem of membrane contamination. The membrane-free design makes the system no longer rely on the separation function of the membrane, thereby eliminating the possibility of membrane contamination, significantly reducing the operation and maintenance costs of the system, improving the stability and efficiency of the treatment, and extending the service life of the equipment. The present invention aims at the difference in solubility of calcium ions and magnesium ions at different pH values, gradually increases the pH value and adjusts the reaction conditions, so that different ions are precipitated separately, optimizes the removal conditions of different ions, and gradedly treats calcium ions and magnesium ions, achieving efficient selective removal and recovery, and improving resource recovery rate and treatment effect. The present invention is also provided with a crystallization and granulation link, which promotes the crystallization of calcium and magnesium ions to form larger particles by regulating the crystallization conditions, and effectively deposits calcium and magnesium. These particles are easier to separate and recover than the fine precipitates generated by the traditional precipitation method, and the possibility of subsequent resource utilization is improved; therefore, the present invention has broad application prospects.

[0073] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A membraneless electrochemical calcium and magnesium selective removal and recovery system, characterized in that: include: Water inlet tank (1), DC power supply (2), electrolytic cell (3), water pump (4), crystallization granulation column (5); The electrolytic cell (3) is provided with a long cylindrical anode (6) with a vertical rotation axis, the side cylinder wall of the anode (6) is mesh-shaped, and the mesh holes of the side cylinder wall of the anode (6) communicate with the inside and outside of the cylinder of the anode (6); the cylinder of the anode (6) is provided with a long cylindrical porous cathode filter element (7) with closed ends, and the filter holes of the cylinder wall of the porous cathode filter element (7) communicate with the inside and outside of the porous cathode filter element (7); the positive electrode of the DC power supply (2) is electrically connected to the anode (6), and the negative electrode of the DC power supply (2) is electrically connected to the porous cathode filter element (7); the filter hole diameter range of the porous cathode filter element (7) is: 10μm to 15mm; The crystallization granulation column (5) is in the shape of a water tank, and is filled with a filler (8), wherein the filling height of the filler (8) does not exceed one third of the depth of the water tank of the crystallization granulation column (5); the filler (8) comprises: calcite, garnet, quartz sand, and brucite; The water outlet of the water inlet tank (1) is connected to the lower part of the electrolytic cell (3), the top of the porous cathode filter element (7) is connected to the water inlet of the water pump (4), the water outlet of the water pump (4) is connected to the bottom of the crystallization granulation column (5), and the upper part of the crystallization granulation column (5) is provided with a water outlet.

2. The membraneless electrochemical calcium and magnesium selective removal and recovery system according to claim 1 is characterized in that: The anode (6) comprises: a titanium-coated ruthenium-iridium electrode, a lead dioxide electrode, a titanium-coated tin-antimony electrode, a boron-doped diamond electrode, a graphite electrode, and a titanium oxide electrode; the porous cathode filter element (7) comprises: Stainless steel filter element, nickel-plated copper powder sintered filter element, copper mesh filter element, titanium powder sintered filter element, stainless steel sintered filter element.

3. The membraneless electrochemical calcium and magnesium selective removal and recovery system according to claim 1, characterized in that: An overflow return pipe (9) is provided at the upper portion of the electrolytic cell (3) and is connected to the water inlet tank (1).

4. The membraneless electrochemical calcium and magnesium selective removal and recovery system according to claim 1, characterized in that: The removal and recovery system is provided with a plurality of groups, and the plurality of removal and recovery systems are connected in sequence by head-to-tail water channels, and the water outlet of the crystallization granulation column (5) of the first group of the plurality of removal and recovery systems is connected to the water inlet tank (1) of the second group of the removal and recovery systems.

5. The membraneless electrochemical calcium and magnesium selective removal and recovery system according to claim 4 is characterized in that: The removal and recovery system is provided with two groups; The pore size range of the porous cathode filter element (7) of the previous group of removal and recovery system is 1 to 15 mm, and the porous cathode filter element (7) of the previous group of removal and recovery system is a stainless steel filter element; the filler (8) of the previous group of removal and recovery system is calcite; The filter pore size range of the porous cathode filter element (7) of the latter group of removal and recovery system is 10 to 500 μm, and the porous cathode filter element (7) of the latter group of removal and recovery system is a nickel-plated copper powder sintered filter element; the filler (8) of the latter group of removal and recovery system is garnet.

6. A membraneless electrochemical calcium and magnesium selective removal and recovery method, characterized in that: The membraneless electrochemical calcium and magnesium selective removal and recovery method is used in the membraneless electrochemical calcium and magnesium selective removal and recovery system according to any one of claims 1 to 5, and the method comprises the following steps: Step S1: the electrolyte flows from the water inlet tank (1) into the lower end of the side of the electrolytic cell (3) and is electrolyzed in the electrolytic cell (3); Step S2: When the electrolyte fills the electrolytic cell (3), part of the electrolyte overflows from the upper side of the electrolytic cell (3), and the overflowing water flows back to the water inlet tank (1) to mix with the raw water; part of the electrolyte is pumped out from the top of the porous cathode filter element (7) by the water pump (4); Step S3: The pump sucks out water and enters the crystallization granulation column (5). The water flows into the crystallization granulation column (5) from the lower end, passes through the filler (8), and flows out from the upper end of the crystallization granulation column (5).

7. The membraneless electrochemical calcium and magnesium selective removal and recovery method according to claim 6, characterized in that: In step S2, when removing and recovering Ca 2+ When the pH value of the pumped water is adjusted to 9.5-10, the Mg 2+ When the pump is used, adjust the pH value of the water sucked out by the pump to >11.

5.

8. The membraneless electrochemical calcium and magnesium selective removal and recovery method according to claim 7, characterized in that: When removing recycled Ca 2+ and Mg 2+ When two groups of membraneless electrochemical calcium and magnesium selective removal and recovery systems are connected in series, the first group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Ca 2 The latter group of membraneless electrochemical calcium and magnesium selective removal and recovery systems is used to remove and recover Mg 2+ ; After repeating steps S1 to S3 in the previous group of membraneless electrochemical calcium and magnesium selective removal and recovery system, water flowing out from the upper end of the crystallization granulation column (5) enters the water inlet tank (1) of the next group of membraneless electrochemical calcium and magnesium selective removal and recovery system, and steps S1 to S3 are repeated in the next group of membraneless electrochemical calcium and magnesium selective removal and recovery system.

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