A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater.

Abstract

This utility model discloses a treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater. The system is sequentially connected to a pretreatment system, an ion exchange system, an evaporation and concentration system, a purification system, and an evaporation and crystallization system. The pretreatment system removes suspended solids. The ion exchange system contains at least four ion exchange columns and an eluent tank; the coordinated operation of multiple columns ensures sufficient adsorption and elution of chromium, increasing the concentration of hexavalent chromium in the eluent, reducing the load on subsequent evaporation equipment, and shortening processing time. The evaporation and concentration system uses an MVR evaporator and integrates an online density meter. The purification system is equipped with a purification reaction vessel with a detachable pH meter probe, which can quantitatively remove sulfate, reducing the difficulty of salt separation and crystallization, increasing the number of mother liquor circulations, and thus improving the chromium recovery rate. The feed to the eluent tank allows for reasonable adjustment of the alkali dosage according to different concentrations of components, avoiding waste and reducing costs. The detachable pH meter probe facilitates maintenance, ensures accurate monitoring, and improves the stability of sulfate removal rate and the quality of sodium chromate products.

Description

Technical Field

[0001] This utility model relates to the field of wastewater treatment technology, and in particular to a treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater. Background Technology

[0002] The electroplating industry generates large amounts of chromium-containing wastewater during production. Hexavalent chromium, in particular, is highly toxic and environmentally hazardous. Direct discharge without effective treatment can severely pollute water bodies, soil, and ecosystems, threatening human health. Therefore, recycling and treating chromium-containing electroplating wastewater to reuse chromium resources has significant environmental and economic benefits. Industrial-grade sodium chromate, as an important chemical raw material, has wide applications in electroplating, tanning, and dyeing. Recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater not only reduces chromium waste but also lowers production costs for enterprises, achieving resource recycling.

[0003] Traditional ion exchange systems typically operate using single-column adsorption. In this mode, the concentration of hexavalent chromium in the eluent is low, generally ≤20 g / L. Due to the low eluent concentration, the subsequent evaporation equipment needs to process a large amount of liquid, significantly increasing the load on the evaporation equipment. This not only prolongs the processing time and reduces the overall processing efficiency but also increases energy consumption and equipment operating costs. In sodium chromate concentrate, the presence of sulfate complicates the salt separation and crystallization process. Existing salt separation and crystallization equipment requires multiple recrystallizations to achieve effective separation of sulfate and sodium chromate. However, multiple recrystallizations lead to a significant increase in wastewater volume, prolonging the process flow, increasing the amount of treatment equipment, making process control difficult, and resulting in high treatment costs.

[0004] In existing technologies, eluents are typically treated using a mixed collection method. Because it's impossible to distinguish between high and low concentration components in the eluent, excessive alkali solution is often added during subsequent processing to ensure treatment effectiveness, based on the requirements for high-concentration components. This leads to significant waste of alkali solution and increases processing costs. Furthermore, excessive alkali solution can adversely affect subsequent processing equipment and processes, such as corroding equipment and increasing acid consumption. Utility Model Content

[0005] The purpose of this invention is to disclose a treatment system that solves the problems of low treatment efficiency, increased costs, and unstable product quality in the process of recovering industrial-grade sodium chromate from electroplating chromium-containing wastewater.

[0006] To achieve the above objectives, this utility model discloses a treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater, comprising, in sequence: a pretreatment system for removing suspended solids; an ion exchange system including a transfer tank, a regeneration tank, a washing tank, at least four sets of ion exchange columns, and at least four sets of eluent tanks, with each ion exchange column and eluent tank connected in a corresponding manner; an evaporation and concentration system including an MVR evaporator and an online density meter, the online density meter being integrated into the feed and discharge pipes of the MVR evaporator; a purification system including a purification reaction vessel with a detachable pH meter probe for quantitatively removing sulfates; and an evaporation and crystallization system including a single-effect evaporator, a cooling crystallization tank, and a centrifuge; wherein a pH meter, a flow meter, and a transparent observation tube are installed on the feed pipe of the eluent tank.

[0007] By employing the above-mentioned scheme, multiple ion exchange columns work synergistically, which, compared to single-column adsorption, can more fully adsorb and elute chromium from chromium-containing wastewater, increasing the concentration of hexavalent chromium in the eluent, reducing the amount of liquid that subsequent evaporation equipment needs to process, thereby reducing the load on the evaporation equipment, shortening the processing time, and improving the overall treatment efficiency. The impurity removal system can quantitatively remove sulfate, reducing the sulfate content entering the salt separation and crystallization stage, reducing the difficulty of salt separation and crystallization, increasing the number of mother liquor circulations, and thus improving the chromium recovery rate. The pH meter probe on the impurity removal reactor can reasonably adjust the pH value of the reaction system according to different concentration components, avoiding excessive use of reagents and reducing treatment costs. The use of a detachable pH meter probe allows for easy disassembly, cleaning, or replacement when scale buildup affects the monitoring effect, ensuring that the pH meter can accurately monitor the pH value of the solution, thereby improving the stability of sulfate removal rate and ultimately improving the quality of sodium chromate products.

[0008] Furthermore, the ion exchange columns are connected in parallel via a shared inlet and a shared outlet pipe, and each set of exchange columns is equipped with an independent metering pump and valve at the inlet and outlet.

[0009] By adopting the above scheme, each ion exchange column can independently control its influent and effluent. Chromium-containing wastewater can enter any ion exchange column through a shared influent pipe, or be discharged into a transfer tank or enter any ion exchange column through a shared effluent pipe. The number of exchange columns that can be operated is flexible; for example, when the wastewater treatment volume is small, only some exchange columns can be operated, avoiding resource waste caused by all exchange columns operating simultaneously. If a group of ion exchange columns malfunctions or requires maintenance, simply close the inlet and outlet valves of that group of exchange columns to stop its operation without affecting the normal operation of other exchange columns. For exchange columns with better adsorption performance, the influent flow rate can be appropriately increased to improve treatment efficiency; for exchange columns with slightly weaker adsorption performance, the influent flow rate can be reduced to ensure adsorption effect. The parallel structure can prevent the slow processing speed of one link from affecting the overall system's treatment progress, thereby improving the overall treatment efficiency.

[0010] Furthermore, the pretreatment system includes a homogenizing tank, a pretreatment filter press, and a filtrate tank connected in sequence, and the filtrate tank is connected to the ion exchange system via a common inlet pipe.

[0011] By adopting the above scheme, the homogenizing tank fully mixes and stirs the collected wastewater, making the wastewater quality more uniform. After the pretreatment filter press separates the solid and liquid in the wastewater, the filtrate enters the filtrate tank, which can buffer the water quality and further stabilize the filtrate quality.

[0012] Furthermore, both the regenerated liquid tank and the washing tank are connected to the common inlet pipe, and the transfer pool is connected to both the common inlet pipe and the common outlet pipe.

[0013] By adopting the above scheme, compared with the decentralized and independent pipeline connection method, the number of pipelines and connection points are reduced, making the entire treatment system structure more compact and simple. The regenerator tank and the washing tank share a common inlet pipeline, allowing the regenerator and washing solution to be precisely delivered to the appropriate ion exchange column according to the actual needs of the ion exchange column. Accurate delivery of the regenerator and washing solution to the ion exchange column through the shared inlet pipeline ensures that the ion exchange column is fully regenerated and washed.

[0014] Furthermore, the evaporation and concentration system also includes a transfer tank, which is connected between the four sets of eluent tanks and the MVR evaporator.

[0015] By adopting the above solution, in actual production, some unexpected situations may occur that cause changes in the eluent flow rate, such as an abnormality in the elution process of a certain ion exchange column, resulting in the discharge of a large amount of eluent in a short period of time. The existence of the transfer tank can accommodate these sudden flow rate changes and avoid adverse effects on the MVR evaporator.

[0016] Furthermore, the impurity removal system also includes an impurity removal reagent tank, an impurity removal filter press, and a filtrate tank. The impurity removal reagent tank is connected to the impurity removal reaction vessel, and the impurity removal filter press and the filtrate tank are sequentially connected between the impurity removal reaction vessel and the evaporation crystallization system.

[0017] By adopting the above scheme, the impurity removal agent tank is connected to the impurity removal reaction vessel, allowing for precise control of the amount of impurity removal agent added. When treating chromium-containing wastewater, different water qualities and impurity contents require different proportions of impurity removal agents. The impurity removal filter press is connected sequentially between the impurity removal reaction vessel and the evaporation crystallization system, enabling efficient solid-liquid separation of the mixture after the impurity removal reaction. The effective operation of the impurity removal system significantly reduces the impurity content entering the evaporation crystallization system. Pure filtrate helps improve the quality of the product after evaporation crystallization.

[0018] Furthermore, it also includes a mother liquor tank, which is connected to a centrifuge for collecting the solution.

[0019] By adopting the above scheme, the mother liquor tank acts as a buffer, receiving and temporarily storing the mother liquor from the centrifuge. The mother liquor tank also facilitates the monitoring of its composition. Regular sampling and analysis of the mother liquor in the tank allows for understanding the changes in the content of target components, impurities, etc.

[0020] Furthermore, it also includes a condensate pool, which is connected to the MVR evaporator and the single-effect evaporator respectively.

[0021] By adopting the above scheme, the evaporation and concentration system, including the MVR evaporator and the single-effect evaporator, generates a large amount of condensate during operation. This condensate is essentially water that has been heated and vaporized in the evaporator and then condensed, and its water quality is relatively good. A condensate tank is connected to both evaporators to collect this condensate, thereby reducing energy costs and improving energy efficiency.

[0022] Furthermore, the detachable pH meter probe includes a quick-release buckle structure, and the probe surface is coated with a polytetrafluoroethylene anti-scaling coating.

[0023] By adopting the above solution, the quick-release snap-fit ​​structure allows operators to quickly install and remove probes without the need for complex tools, simply by using the snap-fit ​​mechanism. This quick-release snap-fit ​​structure also makes probe replacement much easier, allowing operators to quickly switch to the appropriate probe according to actual needs, thus improving the flexibility and adaptability of the equipment.

[0024] Furthermore, a flash tank is provided on the steam pipe between the MVR evaporator and the single-effect evaporator.

[0025] By adopting the above scheme, the MVR evaporator generates secondary steam during operation. Although the temperature and pressure of this steam are lower than those of the main MVR steam, it still contains a certain amount of energy. A flash tank is installed on the steam pipelines of both. When the secondary steam discharged from the MVR evaporator enters the flash tank, because the pressure inside the tank is lower than the saturation pressure of the secondary steam, flash evaporation occurs, further releasing latent heat and generating more low-grade steam. By releasing the energy of the secondary steam in stages through the flash tank, the high-grade energy can be used in high-energy-consuming processes such as the circulating heating of the MVR evaporator itself, while the low-grade steam generated by flash evaporation is used in processes with relatively lower temperature and pressure requirements, such as single-effect evaporators, thus improving the overall energy utilization efficiency.

[0026] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0027] 1. Multiple ion exchange columns work in synergy, enabling more thorough adsorption and elution of chromium in chromium-containing wastewater compared to traditional single-column adsorption methods. This significantly increases the concentration of hexavalent chromium in the eluent, reducing the volume of liquid that subsequent evaporation equipment needs to process, thereby lowering the load on the evaporation equipment, shortening the processing time, and improving overall treatment efficiency.

[0028] 2. The impurity removal system uses a reaction vessel with a detachable pH meter probe, which can quantitatively remove sulfate. This reduces the sulfate content entering the salt separation and crystallization stage, lowers the difficulty of salt separation and crystallization, and allows the salt separation and crystallization equipment to effectively separate sulfate and sodium chromate without multiple recrystallizations. This avoids a significant increase in wastewater volume caused by multiple recrystallizations, which not only prolongs the process flow and increases the amount of treatment equipment, but also makes process control more difficult and the treatment cost higher.

[0029] 3. A pH meter, flow meter, and transparent observation tube are installed on the feed pipe of the eluent tank, allowing for reasonable adjustment of the amount of alkali added based on different concentrations of components in the eluent. This avoids adding excessive alkali to meet the processing requirements of high-concentration components, significantly reducing alkali waste and lowering processing costs. Furthermore, the increased hexavalent chromium concentration in the eluent reduces the liquid volume processed by subsequent evaporation equipment, lowering the load on the evaporation equipment and thus reducing energy consumption.

[0030] 4. The detachable pH meter probe accurately monitors the pH value of the solution. When scale buildup on the probe affects monitoring results, it can be easily disassembled, cleaned, or replaced, ensuring the pH meter always accurately monitors the solution's pH value. This helps improve the stability of sulfate removal rate, making the sodium chromate product more stable in subsequent evaporation and crystallization processes. Quantitative removal of sulfate through the impurity removal system reduces the impurity content entering the evaporation and crystallization system, allowing equipment such as cooling crystallizers and centrifuges to more effectively separate pure sodium chromate crystals, thus improving the purity and quality of the sodium chromate product. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a system connection block diagram of an embodiment of the present utility model;

[0033] Figure 2 This is a structural block diagram of the ion exchange system according to an embodiment of the present invention.

[0034] Key reference numerals in the attached drawings: 1. Pretreatment system; 11. Homogenization tank; 12. Pretreatment filter press; 13. Filtrate tank; 2. Ion exchange system; 21. Transfer tank; 22. Regenerated liquid tank; 23. Washing tank; 24. Ion exchange column; 25. Eluent tank; 251. pH meter; 252. Flow meter; 253. Transparent observation tube; 26. Metering pump; 27. Valve; 3. Evaporation and concentration system; 31. Transfer tank; 32. MVR evaporator; 4. Impurity removal system; 41. Impurity removal reaction vessel; 411. Detachable pH meter probe; 42. Impurity removal filter press; 43. Filtrate tank; 44. Impurity removal reagent tank; 5. Evaporation and crystallization system; 51. Single-effect evaporator; 52. Cooling crystallization tank; 53. Centrifuge; 6. Common inlet water pipe; 7. Common outlet water pipe; 8. Mother liquor tank; 9. Condensate tank. Detailed Implementation

[0035] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0036] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0037] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this utility model according to the specific circumstances.

[0038] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this utility model based on the specific circumstances.

[0039] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0040] The technical solution of this utility model will be further described below with reference to the embodiments and accompanying drawings.

[0041] Please refer to Embodiment 1 of this utility model. Figures 1 to 2 As shown, a treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater is provided. The system includes a pretreatment system 1, an ion exchange system 2, an evaporation and concentration system 3, a purification system 4, and an evaporation and crystallization system 5 connected in sequence. The pretreatment system 1 is used to remove suspended solids and particles from the chromium-containing electroplating wastewater. In one embodiment, the pretreatment system 1 includes a homogenization tank 11, a pretreatment filter press 12, and a filtrate tank 13. The homogenization tank 11 has a volume of not less than 50 m³. 3 The tank is equipped with a twin-shaft agitator, and the wastewater retention time is not less than 2 hours. The pretreatment filter press 12 is located between the homogenization tank 11 and the filtrate tank 13. The pretreatment filter press 12 can be a chamber filter press. The filtrate tank 13 has a volume of not less than 20m³. 3Its outlet is connected to ion exchange system 2 via a DN100 pipe. Ion exchange system 2 includes a transfer tank 21, a regeneration tank 22, a washing tank 23, at least four sets of ion exchange columns 24, and at least four sets of eluent tanks 25. It is used to adsorb hexavalent chromium from chromium-containing electroplating wastewater and elute it to obtain a sodium chromate solution. The ion exchange columns 24 and eluent tanks 25 are connected one-to-one. All four sets of ion exchange columns 24 use strongly basic anion exchange resin columns. Each set of ion exchange columns 24 has an independent pneumatic butterfly valve and a metering pump 26 at its inlet and outlet. The ion exchange columns 24 are connected in parallel via a shared inlet pipe 6 and a shared outlet pipe 7. The filtrate tank 13 is connected to the shared inlet pipe 6 of the ion exchange system 2. Each set of exchange columns has an independent metering pump 26 and a valve 27 at its inlet and outlet. This design allows each ion exchange column to independently control its influent and effluent. Chromium-containing wastewater can enter any ion exchange column 24 through a shared influent pipe 6, or be discharged into a transfer tank 21 or into any ion exchange column 24 through a shared effluent pipe 7. The number of exchange columns that can be activated is flexible; for example, when the wastewater volume is small, only some exchange columns can be activated, avoiding resource waste caused by all exchange columns operating simultaneously. The parallel structure prevents the slow processing speed of one stage from affecting the overall system's processing progress, thereby improving overall treatment efficiency.

[0042] In some embodiments, both the regenerated liquid tank 22 and the washing tank 23 are connected to the common inlet pipe 6, and the transfer tank 21 is connected to both the common inlet pipe 6 and the common outlet pipe. Compared to a decentralized and independent pipe connection method, this reduces the number of pipes and connection points, making the entire treatment system more compact and simpler. The connection of the regenerated liquid tank 22 and the washing tank 23 to the common inlet pipe 6 allows the regenerated liquid and washing liquid to be precisely delivered to the corresponding ion exchange column according to the actual needs of the ion exchange column 24. Accurate delivery of the regenerated liquid and washing liquid to the ion exchange column 24 via the common inlet pipe 6 ensures that the ion exchange column 24 receives sufficient regeneration and washing.

[0043] In this embodiment 1, the evaporation and concentration system 3 includes an MVR evaporator 32 and an online densitometer for evaporating and concentrating the sodium chromate solution obtained by elution. The online densitometer is integrated into the feed and discharge pipes of the MVR evaporator 32 and is used to measure the density of the evaporated concentrate, thereby controlling the endpoint of evaporation and concentration. The impurity removal system 4 includes a purification reaction vessel 41 with a detachable pH meter probe 411 for quantitatively removing sulfate from the sodium chromate concentrate. The detachable pH meter probe 411 is an pH meter 251 that can be inserted into the reaction solution and is easy to remove and clean, used to control the pH value during the reaction process. The evaporation and crystallization system 5 includes a single-effect evaporator 51, a cooling crystallization tank 52, and a centrifuge for further evaporating the sodium chromate concentrate after sulfate removal and cooling and crystallizing to separate sodium chromate crystals. The waste heat from the steam in the single-effect evaporator 51 can be piped to the MVR evaporator 32 for use. The eluent tank 25 is equipped with a pH meter 251, a flow meter 252, and a transparent observation tube 253 on its feed pipe. The eluent can be classified and collected by observing changes in pH, volume, and color. Multiple ion exchange columns 24 work in tandem, enabling more thorough adsorption and elution of chromium from chromium-containing wastewater compared to single-column adsorption. This increases the concentration of hexavalent chromium in the eluent, reduces the amount of liquid that subsequent evaporation equipment needs to process, thereby reducing the load on the evaporation equipment, shortening processing time, and improving overall treatment efficiency. The impurity removal system can quantitatively remove sulfate, reducing the sulfate content entering the salt separation and crystallization stage, lowering the difficulty of salt separation and crystallization, increasing the number of mother liquor circulations, and thus improving chromium recovery. The pH meter probe 411 on the impurity removal reactor can rationally adjust the pH of the reaction system according to different concentrations of components, avoiding excessive use of reagents and reducing treatment costs. The use of a detachable pH meter probe 411 allows for easy disassembly, cleaning, or replacement when scale buildup on the probe affects monitoring performance. This ensures that the pH meter 251 can accurately monitor the pH value of the solution, thereby improving the stability of sulfate removal rate and ultimately enhancing the quality of sodium chromate products.

[0044] In some embodiments, the evaporation and concentration system 3 further includes a transfer tank 31, which is connected between the four sets of eluent tanks 25 and the MVR evaporator 32. In actual production, some unexpected situations may occur that cause changes in the eluent flow rate, such as an abnormality in the elution process of a certain set of ion exchange columns 24, resulting in the discharge of a large amount of eluent in a short period of time. The existence of the transfer tank 31 can accommodate these sudden flow rate changes and avoid adverse effects on the MVR evaporator 32.

[0045] In this embodiment 1, the impurity removal system 4 further includes an impurity removal agent tank 44, an impurity removal filter press 42, and a filtrate tank 43. The impurity removal agent tank 44 is connected to the impurity removal reaction vessel 41. The impurity removal filter press 42 and the filtrate tank 43 are sequentially connected between the impurity removal reaction vessel 41 and the evaporation crystallization system 5. The connection between the impurity removal agent tank 44 and the impurity removal reaction vessel 41 allows for precise control of the amount of impurity removal agent added. When treating chromium-containing wastewater, different water qualities and impurity contents require different proportions of impurity removal agents. The impurity removal filter press 42, sequentially connected between the impurity removal reaction vessel 41 and the evaporation crystallization system 5, enables efficient solid-liquid separation of the mixture after the impurity removal reaction. The effective operation of the impurity removal system 4 can significantly reduce the impurity content entering the evaporation crystallization system 5. Pure filtrate is beneficial for improving the quality of the product after evaporation crystallization.

[0046] Optionally, the system also includes a mother liquor tank 8, which is connected to a centrifuge 53 for collecting the solution. The mother liquor tank 8 acts as a buffer, receiving and temporarily storing the mother liquor from the centrifuge 53. The mother liquor tank 8 facilitates the monitoring of the mother liquor composition. By periodically sampling and analyzing the mother liquor in the mother liquor tank 8, the changes in the content of target components, impurities, etc., in the mother liquor can be understood.

[0047] In this embodiment 1, the system also includes a condensate tank 9, which is connected to the MVR evaporator 32 and the single-effect evaporator 51, respectively. The volume of the condensate tank 9 is not less than 30m³. 3 The MVR evaporator 32 and the single-effect evaporator 51 produce a large amount of condensate during operation. This condensate is essentially water that has been heated and vaporized in the evaporator and then condensed back down, and its water quality is relatively good. The condensate tank 9 is connected to both evaporators and can collect this condensate, which can reduce energy costs and improve energy efficiency.

[0048] In some embodiments, the detachable pH meter probe 411 includes a quick-release snap-fit ​​structure, and the probe surface is coated with a polytetrafluoroethylene (PTFE) anti-scaling coating. The quick-release snap-fit ​​structure uses an ISO standard interface, and the PTFE anti-scaling coating thickness is not less than 200 μm. The detachable pH meter probe 411 requires manual disassembly and cleaning every 24 hours. The quick-release snap-fit ​​structure allows operators to quickly install and remove the probe without the need for complex tools, simply by using the snap-fit ​​mechanism. This quick-release snap-fit ​​structure makes probe replacement more convenient, allowing operators to quickly replace the probe with the appropriate one according to actual needs, improving the flexibility and adaptability of the equipment.

[0049] Preferably, in some embodiments, a flash tank is provided on the steam pipe between the MVR evaporator 32 and the single-effect evaporator 51. The flash tank can be a cyclone separator combined with a 100-mesh 304 stainless steel wire mesh demister. The distance between the flash tank and the single-effect evaporator 51 does not exceed 2m to reduce heat loss. During the operation of the MVR evaporator 32, secondary steam is generated. Although the temperature and pressure of this steam are lower than those of the main MVR steam, it still contains a certain amount of energy. The flash tank is set on the steam pipe between the two. When the secondary steam discharged from the MVR evaporator 32 enters the flash tank, the secondary steam will undergo flash evaporation because the pressure inside the tank is lower than the saturation pressure of the secondary steam, further releasing latent heat and generating more low-grade steam. By releasing the energy of the secondary steam in stages through the flash tank, the high-grade energy can be used for high-energy-consuming links such as the circulating heating of the MVR evaporator 32 itself, while the low-grade steam generated by flash evaporation can be used for links such as the single-effect evaporator 51, which have relatively lower requirements for temperature and pressure, thereby improving the overall energy utilization efficiency.

[0050] The specific operating steps are as follows: The chromium-containing electroplating wastewater is mixed evenly in homogenization tank 11, then pumped into pretreatment filter press 12 for filtration. The filter residue obtained is handed over to a qualified unit for treatment, while the filtrate flows by gravity into filtrate tank 13. The filtrate in filtrate tank 13 is then pumped into the first ion exchange column 24 at a flow rate of 10-20 BV / h via metering pumps 26 equipped on the four ion exchange columns 24 for adsorption. Initially, the effluent can be directly discharged into transfer tank 21. When the hexavalent chromium content of the effluent exceeds 0.1 mg / L, the valve 27 discharging into transfer tank 21 is closed, and the effluent is pumped into the second ion exchange column 24 for adsorption. Similarly, the effluent is pumped into the third ion exchange column 24... Adsorption occurs in the first and fourth ion exchange columns 24. When the effluent is pumped into the fourth ion exchange column 24, the feed valve 27 of the first ion exchange column 24 is closed, and the filtrate in the filtrate tank 13 is directly pumped into the second ion exchange column 24. The first ion exchange column 24 is then eluted and regenerated. When the hexavalent chromium content in the effluent from the fourth ion exchange column 24 exceeds 0.1 mg / L, it is pumped into the regenerated first ion exchange column 24 for continued adsorption. At the same time, the feed valve 27 of the second ion exchange column 24 is closed, and the filtrate in the filtrate tank 13 is directly pumped into the third ion exchange column 24. This process is repeated alternately.

[0051] The specific steps for elution and regeneration of ion exchange resin are as follows: Add a pre-prepared 20-25% sodium hydroxide solution (twice the resin volume) to the regeneration tank 22; add tap water (twice the resin volume) to the washing tank 23; and pump the solution into the ion exchange column 24 to be regenerated at a flow rate of 3-5 BV / h, first adding the sodium hydroxide solution, then the tap water. The eluted liquid enters the eluent tank 25. The eluent is collected separately using a pH meter 251, a flow meter 252, and a transparent tube on the eluent tank 25. The eluent with a pH value similar to the original water, a yellow color, and approximately 0.5 times the resin volume (mainly residual chromium-containing original water on the resin bed) is collected in the eluent tank 25. The pH value begins to rise until it becomes... A neutral, orange-red eluent, approximately one-times the resin volume, is collected in eluent tank 25. A bright yellow eluent, with a pH greater than 7, approximately two-times the resin volume, is also collected in eluent tank 25. A strongly alkaline eluent, ranging from pale yellow to colorless, approximately 0.5 times the resin volume, is collected in eluent tank 25. The eluent in eluent tank 25 is pumped back to homogenizing tank 11 for reprocessing. The eluent in eluent tank 25 is also pumped into transfer tank 31. The eluent in eluent tank 25 can be used as regeneration solution and pumped into the next saturated ion exchange column 24 for regeneration. The eluent in eluent tank 25 can also be used to dissolve caustic soda flakes or dilute caustic soda, maintaining a sodium hydroxide concentration between 20% and 25%.

[0052] After sufficient eluent with a high concentration of hexavalent chromium has accumulated in the transfer tank 31, it is pumped into the MVR evaporator 32 for evaporation and concentration. The hexavalent chromium content in the MVR concentrate can be roughly controlled at around 400-500 g / L by an online density meter. The condensate obtained from evaporation and concentration enters the condensate pool 9 after heat exchange in a heat exchanger, and the concentrate is pumped into the impurity removal reactor 41 while it is still hot.

[0053] The impurity removal agent is prepared in the impurity removal agent tank 44. The pH value of the impurity removal reaction is controlled by the pH meter 251 equipped on the impurity removal reaction vessel 41. The impurity removal agent is quantitatively added to the impurity removal reaction vessel 41 and stirred for a period of time. Then, it is pumped into the impurity removal filter press 42. The filter residue obtained by filter pressing is handed over to a qualified unit for treatment, while the filtrate flows into the filtrate tank 43 by gravity.

[0054] The filtrate in the filtrate tank 43 is pumped into the single-effect evaporator 51 for further evaporation and concentration, so that the hexavalent chromium content in the concentrate reaches 800-900 g / L. The condensate obtained from evaporation is transferred to the condensate tank 9 after heat exchange in the heat exchanger. The concentrate is then pumped into the cooling crystallization tank 52 for cooling. When the temperature drops to about 40°C, the crystallized slurry is pumped into the centrifuge 53 for centrifugal separation. The sodium chromate crystals obtained are dried to obtain the product. The mother liquor obtained from centrifugal separation flows into the mother liquor tank 8. The mother liquor in the mother liquor tank 8 is then pumped into the impurity removal reaction vessel 41 for further processing steps.

[0055] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0056] 1. Multiple ion exchange columns work in tandem, enabling more thorough adsorption and elution of chromium in chromium-containing wastewater compared to traditional single-column adsorption methods. This significantly increases the concentration of hexavalent chromium in the eluent, reducing the volume of liquid that subsequent evaporation equipment needs to process, thereby lowering the load on the evaporation equipment, shortening the processing time, and improving overall treatment efficiency.

[0057] 2. The impurity removal system 4 uses an impurity removal reactor 41 with a detachable pH meter probe 411, which can quantitatively remove sulfate. This reduces the sulfate content entering the salt separation and crystallization stage, lowers the difficulty of salt separation and crystallization, and enables the salt separation and crystallization equipment to achieve effective separation of sulfate and sodium chromate without multiple recrystallizations. This avoids a significant increase in wastewater volume caused by multiple recrystallizations, which not only prolongs the process flow and increases the amount of treatment equipment, but also makes process control more difficult and the treatment cost higher.

[0058] 3. A pH meter 251, a flow meter 252, and a transparent observation tube 253 are installed on the feed pipe of the eluent tank 25, allowing for reasonable adjustment of the amount of alkali added according to different concentrations of components in the eluent. This avoids adding excessive alkali to meet the processing requirements of high-concentration components, significantly reducing alkali waste and lowering processing costs. Furthermore, the increased hexavalent chromium concentration in the eluent reduces the liquid volume processed by subsequent evaporation equipment, lowering the load on the evaporation equipment and thus reducing energy consumption.

[0059] 4. The detachable pH meter probe 411 accurately monitors the pH value of the solution. When scale buildup on the probe affects the monitoring effect, it can be easily disassembled, cleaned, or replaced to ensure that the pH meter 251 can always accurately monitor the pH value of the solution. This helps improve the stability of sulfate removal rate, making the sodium chromate product more stable in subsequent evaporation and crystallization processes. The quantitative removal of sulfate by the impurity removal system 4 reduces the impurity content entering the evaporation and crystallization system 5, allowing equipment such as the cooling crystallizer 52 and centrifuge to more effectively separate pure sodium chromate crystals, thus improving the purity and quality of the sodium chromate product.

[0060] The technical means disclosed in this utility model are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of this utility model, and these improvements and modifications are also considered within the scope of protection of this utility model.

Claims

1. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater, characterized in that, Including those connected sequentially: A pretreatment system (1) for removing suspended solids; An ion exchange system (2) includes a transfer tank (21), a regeneration tank (22), a washing tank (23), at least four sets of ion exchange columns (24) and at least four sets of eluent tanks (25), wherein the ion exchange columns (24) and the eluent tanks (25) are connected in a one-to-one correspondence. An evaporation and concentration system (3) includes an MVR evaporator (32) and an online density meter, the online density meter being integrated into the feed pipe and discharge pipe of the MVR evaporator (32); The impurity removal system (4) includes an impurity removal reaction vessel (41) with a detachable pH meter probe (411) for quantitative removal of sulfate; An evaporation crystallization system (5) includes a single-effect evaporator (51), a cooling crystallization tank (52), and a centrifuge; The feed pipe of the eluent tank (25) is equipped with a pH meter (251), a flow meter (252), and a transparent observation tube (253).

2. The treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 1, characterized in that, The ion exchange columns (24) are connected in parallel through a common inlet pipe (6) and a common outlet pipe (7). Each set of exchange columns is equipped with an independent metering pump (26) and valve (27) at the inlet and outlet.

3. The treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 2, characterized in that, The pretreatment system (1) includes a homogenizing tank, a pretreatment filter press (12), and a filtrate tank (13) connected in sequence. The filtrate tank (13) is connected to the common inlet pipe (6) of the ion exchange system (2).

4. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 2, characterized in that, The regenerated liquid tank (22) and the washing tank (23) are both connected to the common water inlet pipe (6), and the transfer pool (21) is connected to the common water inlet pipe (6) and the common water outlet pipe respectively.

5. The treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 1, characterized in that, The evaporation and concentration system (3) also includes a transfer tank (31) which is connected between the four sets of eluent tanks (25) and the MVR evaporator (32).

6. The treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 1, characterized in that, The impurity removal system (4) also includes an impurity removal agent tank (44), an impurity removal filter press (42), and a filtrate tank (43). The impurity removal agent tank (44) is connected to the impurity removal reactor (41), and the impurity removal filter press (42) and the filtrate tank (43) are connected in sequence between the impurity removal reactor (41) and the evaporation crystallization system (5).

7. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 1, characterized in that, It also includes a mother liquor tank (8), which is connected to a centrifuge (53) for collecting the solution.

8. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 5, characterized in that, It also includes a condensate pool (9), which is connected to the MVR evaporator (32) and the single-effect evaporator (51) respectively.

9. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 1, characterized in that, The detachable pH meter probe (411) includes a quick-release snap-on structure and the probe surface is coated with a polytetrafluoroethylene anti-scaling coating.

10. A treatment system for recovering industrial-grade sodium chromate from chromium-containing electroplating wastewater according to claim 9, characterized in that, A flash tank is provided on the steam pipe between the MVR evaporator (32) and the single-effect evaporator (51).

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