Chromium-containing wastewater treatment and recovery treatment line and recovery treatment method thereof

Abstract

The invention discloses a chromium-containing wastewater treatment and recovery treatment line and a recovery treatment method thereof. The ion exchange system is used for carrying out ion exchange adsorption on the hexavalent wastewater; the alkali washing system is used for outputting alkali liquor to the ion exchange system; the washing system is used for outputting washing water to the ion exchange system; the pickling system is used for outputting acid liquor to the ion exchange system; the chromium recovery treatment branch line is used for receiving the hexavalent wastewater of the ion exchange system, mixing the hexavalent wastewater with sulfur powder and alkali liquor to prepare chromium hydroxide, then carrying out filter pressing on the chromium hydroxide, outputting a chromium hydroxide filter cake to the recovery calcination treatment line, and outputting a press filtrate to the press filtrate recovery branch line; the press filtrate recovery branch line is used for recovering sodium thiosulfate from the press filtrate; and the recycling and calcining treatment line is used for calcining the chromium hydroxide filter cake into Cr2O3. According to the scheme, the purposes of micro discharge and even zero discharge of the chromium-containing wastewater are achieved, and the problem that a large amount of chromium-containing hazardous waste sludge is generated by depending on a chemical reduction-precipitation method in traditional chromium-containing wastewater treatment is solved.

Description

Technical Field

[0001] This invention relates to the field of chromium-containing wastewater treatment, and more particularly to a chromium-containing wastewater treatment and recycling line and its recycling method. Background Technology

[0002] Chromium-containing wastewater, a typical highly toxic and difficult-to-treat waste liquid in the industrial sector, is widely generated in production processes such as electroplating, leather making, pigment synthesis, stainless steel pickling, and chemical catalysis. In electroplating workshops, chromic acid solutions are used extensively during the surface treatment of metal parts, resulting in hexavalent chromium (Cr(VI)) concentrations in the cleaning wastewater often reaching hundreds to thousands of mg / L. The pH is generally below 3.0, presenting as a strongly acidic, dark yellow liquid with strong oxidizing and cell-penetrating properties. Cr(VI) readily passes through cell membranes as chromate (CrO4²⁻). - When chromium (Cr(III)) enters the body, it can generate reactive oxygen species during reduction, causing DNA breaks and mutations. It is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), and its environmental hazards far exceed those of trivalent chromium (Cr(III)). Even low-concentration emissions can accumulate in aquatic sediments over long periods, threatening ecosystems and human health through bioaccumulation in the food chain.

[0003] Currently, the mainstream treatment technology is still chemical precipitation, with a typical process of "reduction-neutralization-flocculation sedimentation": sodium metabisulfite or ferrous salt is added to the dosing tank, and Cr(VI) is reduced to Cr(III) under pH 2-3 conditions, followed by raising the pH to 8-9 to generate Cr(OH)3 precipitate. Although this method is simple to operate and has low construction costs, it can generate about 10 kg of chromium-containing sludge per ton of wastewater, which belongs to HW21 hazardous waste in the "National Hazardous Waste List" and must be disposed of by a qualified unit, resulting in high annual operating costs. Moreover, the sludge has a high water content and is prone to caking, posing a risk of heavy metal leaching, and landfill or solidification treatment still poses a risk of secondary pollution. In addition, the effluent quality is greatly affected by fluctuations in the influent, making it difficult to consistently and stably meet the special limit requirement of ≤ 0.1 g / L in the "Electroplating Pollutant Discharge Standard" (GB 21900-2008).

[0004] Traditional ion exchange methods rely on strongly basic anion exchange resins for Cr2O7²⁻ - The selective adsorption of the resin can reduce Cr(VI) in the effluent to below 0.1 mg / L, making it suitable for advanced treatment applications. However, after resin saturation, it requires high-concentration NaOH or NaCl for desorption and regeneration, resulting in regeneration wastewater containing Cr(VI) and Cl. - SO4² -The eluent contains organic leachates with complex compositions, high color, and significantly increased COD. Subsequent treatment requires multi-stage membrane separation or advanced oxidation units, leading to a dramatic increase in system energy and reagent consumption. More importantly, existing processes generally lack effective conversion and productization pathways for chromium in the eluent, resulting in severe resource loss and failing to achieve true closed-loop treatment. Summary of the Invention

[0005] The purpose of this invention is to propose a chromium-containing wastewater treatment and recycling line, which includes a resin regeneration treatment line, a chromium recycling treatment line, a filtrate recycling line, and a recycling calcination treatment line. This process not only effectively blocks the risk of hexavalent chromium migration and bioaccumulation in the environment, but also avoids the long-term ecological hazards and regulatory pressure caused by chromium-containing sludge landfill.

[0006] The present invention also proposes a method for treating and recycling chromium-containing wastewater, which uses the aforementioned chromium-containing wastewater treatment and recycling line.

[0007] To achieve this objective, the present invention adopts the following technical solution: A chromium-containing wastewater treatment and recycling line includes: a resin regeneration treatment line, a chromium recovery treatment line, a filtrate recovery line, and a recovery calcination treatment line; The resin regeneration process includes: an ion exchange system, an alkaline washing system, a water washing system, and an acid washing system; The ion exchange system is used to receive hexavalent wastewater and perform ion exchange adsorption on the hexavalent wastewater; the alkaline washing system is connected to the ion exchange system and is used to output alkaline solution to the ion exchange system; the water washing system is connected to the ion exchange system and is used to output washing water to the ion exchange system; the acid washing system is connected to the ion exchange system and is used to output acid solution to the ion exchange system. The input end of the chromium recovery and treatment branch line is connected to the output end of the ion exchange system; the output end of the chromium recovery and treatment branch line is connected to the filtrate recovery branch line and the recovery calcination treatment line respectively; the chromium recovery and treatment branch line is used to receive the hexavalent wastewater from the ion exchange system, and mix the hexavalent wastewater with sulfur powder and alkaline solution to produce chromium hydroxide, then filter the chromium hydroxide, the chromium hydroxide filter cake is output to the recovery calcination treatment line, and the filtrate is output to the filtrate recovery branch line; The filter press recovery line is used to recover sodium thiosulfate from the filter press; The recycling and calcination process line is used to calcine chromium hydroxide filter cake into Cr2O3.

[0008] Optimally, the ion exchange system is provided with an ion exchange column, the interior of which is filled with ion exchange resin; a column bottom water distributor and a column bottom aerator are provided below the ion exchange column; the column bottom water distributor is provided with a porous distribution plate; the column bottom aerator is provided with a microporous aeration pipe for introducing compressed gas. The alkaline washing system includes: an alkaline solution storage tank, an alkaline washing pipe, and an alkaline solution output pump; The alkali storage tank is connected to the column bottom water distributor via the alkali washing pipe for discharging alkali solution to the column bottom water distributor. The alkali solution is then discharged into the ion exchange column through the porous distribution plate. The alkali solution output pump is installed in the column bottom water distributor. The water washing system is connected to the ion exchange column and is used to output washing water to the ion exchange column; the acid washing system is connected to the ion exchange column and is used to output acid solution to the ion exchange column. The ion exchange system also includes: a differential pressure sensor and a bubble control valve; The detection end of the differential pressure sensor is located inside the ion exchange column and close to the ion exchange resin; the differential pressure sensor is communicatively connected to the bubble control valve; the bubble control valve is installed in the microporous aeration pipe.

[0009] Optimally, the ion exchange system includes: a series tube, an inner valve, an outer connecting tube, an outer valve, an adsorption monitoring device, a first column valve, and multiple ion exchange columns; Multiple ion exchange columns are connected in series, and one output end of one ion exchange column is connected to the input end of another ion exchange column through the series tube; the series tube is equipped with the internal valve. The ion exchange column has at least two input ends, one of which is used to connect to the series tube, and the other input end is equipped with the first column valve; the column bottom water distributor is connected to the alkaline washing tube through the external connecting pipe; the external valve is installed on the external connecting pipe; the ion exchange column is equipped with the adsorption monitoring device; the adsorption monitoring device is communicatively connected to the inner valve and the outer valve.

[0010] Optimally, the chromium recovery processing line includes: a recovery reactor, a reducing agent feeder, an alkali feeder, and a recovery filter press system; The recovery reactor is used to receive the hexavalent chromium wastewater from the resin regeneration treatment line; the output end of the reducing agent feeder is connected to the recovery reactor and is used to output sulfur powder to the recovery reactor; the output end of the alkali feeder is connected to the recovery reactor and is used to output alkali to the recovery reactor, so that the hexavalent chromium wastewater in the recovery reactor is treated into chromium hydroxide wastewater. The output end of the recovery reactor is connected to the recovery filter press system, and is used to output chromium hydroxide wastewater to the recovery filter press system; The recycling filter press system includes: a primary filter press, a filter crushing device, a washing tank, and a secondary filter press; The primary filter press is used to receive the chromium hydroxide wastewater from the recovery reactor, perform filter press treatment on the chromium hydroxide wastewater, output the filtrate to the filter filtrate recovery branch line, and output the chromium hydroxide to the filtration and pulverizing device; The filtration and pulverizing device is used to pulverize chromium hydroxide and output the chromium hydroxide to the cleaning tank; The cleaning tank is used to clean chromium hydroxide and output the chromium hydroxide to the secondary filter press; The secondary filter press performs filter pressing on the chromium hydroxide in the washing tank to obtain chromium hydroxide.

[0011] Optimally, it also includes: a calcination atmosphere control system and a waste gas treatment branch line; The recycling and calcination processing line includes: a calcination pulverizer, a conveyor, and a calcination kiln; The calcining pulverizer is used to receive chromium hydroxide from the secondary filter press and pulverize the chromium hydroxide; the conveyor end of the conveyor is used to receive chromium hydroxide from the calcining pulverizer and convey the chromium hydroxide to the calcining kiln. The calcining kiln is used for calcining chromium hydroxide; the calcining kiln is provided with a heating zone, a heat preservation zone and a cooling zone in sequence from the inlet to the outlet; The temperature of the heating zone is 500-680℃; the temperature of the heat preservation zone is 1050-1100℃; and the temperature of the cooling zone is 20-80℃. The calcination atmosphere control system includes: a protective gas output device, an oxygen detection device, and an infrared gas analysis device; The exhaust gas treatment line, oxygen detection device, and infrared gas analysis device are communicatively connected; the input end of the exhaust gas treatment line is connected to the insulation zone for discharging exhaust gas from the insulation zone; the detection ends of the oxygen detection device and the infrared gas analysis device are located in the insulation zone; the output end of the protective gas output device is connected to the insulation zone for outputting protective gas to the insulation zone.

[0012] Optimally, the waste gas treatment branch line includes: a main waste gas pipe, a desulfurization tower, and a waste gas fan; One end of the exhaust gas main pipe is connected to the insulation zone, and the other end of the exhaust gas main pipe is connected to the input end below the desulfurization tower; the exhaust gas fan is installed at the output end above the desulfurization tower, and when the exhaust gas fan is started, a negative pressure is formed inside the desulfurization tower and the exhaust gas main pipe; The desulfurization tower is equipped with a spraying device inside, which is used to spray alkaline droplets into the interior of the desulfurization tower.

[0013] Optimally, the filtrate recovery line includes: a multi-effect evaporator, a recovery crystallizer, a recovery centrifuge, and a recovery drying device; The multi-effect evaporator is provided with a single-effect evaporation unit and multiple sub-effect evaporation units in sequence along the steam conveying direction; the multi-effect evaporator is used to receive the filtrate from the chromium recovery treatment line, and the filtrate enters the separation chamber of the single-effect evaporation unit after passing through the separation chambers of the multiple sub-effect evaporation units in sequence. The separation chamber of the single-effect evaporation unit is connected to the recovery crystallization vessel and is used to output the filtrate to the recovery crystallization vessel; The recovery crystallization kettle is used to cool and crystallize the filtrate, so that sodium thiosulfate precipitates out of the filtrate to form sodium thiosulfate slurry. The recovery centrifuge device is used to receive the sodium thiosulfate slurry from the recovery crystallization vessel, separate the sodium thiosulfate slurry into solid and liquid phases, and output the sodium thiosulfate solid to the recovery drying device. The recovery and drying device is used for drying solid sodium thiosulfate.

[0014] Optimally, it may also include: a water storage mechanism; The water storage mechanism includes: a water storage pipe, a system water storage tank, and a cleaning connecting pipe; The input end of the water storage pipe is connected to the heating chamber of the multi-effect evaporation unit and the heating chamber of the single-effect evaporation unit, respectively; the output end of the water storage pipe is connected to the system water storage tank, which is used to receive the condensate from the multi-effect evaporator and output the condensate to the system water storage tank; the input end of the cleaning pipe is connected to the system water storage tank, and the cleaning pipe is equipped with a cleaning pump body.

[0015] A method for treating and recycling chromium-containing wastewater, using the aforementioned chromium-containing wastewater treatment and recycling line, includes the following steps: S1: When the Cr ion concentration in the ion exchange column rises to the preset threshold, the alkali washing system is connected to the ion exchange system; the alkali output pump is turned on, and the alkali storage tank outputs alkali to the ion exchange column through the alkali washing pipe. The alkali is output to the bottom of the ion exchange column through the column bottom water distributor, and the alkali liquid flows from bottom to top through the ion exchange resin. S2: Open the column bottom aerator and output compressed gas to the ion exchange column through the microporous aeration tube. The compressed gas forms bubbles in the alkaline solution through the microporous aeration tube. After the Cr ion concentration in the ion exchange column stabilizes, disconnect the alkaline washing system. S3: Connect the water washing system to the ion exchange system. The water washing system outputs cleaning water to the ion exchange column to remove the alkaline solution in the ion exchange column. Disconnect the water washing system when the liquid in the ion exchange column is colorless. Connect the acid washing system to the ion exchange system. The acid washing system outputs acid to the ion exchange column until the pH of the liquid in the ion exchange column is stable and weakly alkaline. Disconnect the acid washing system. Connect the water washing system to the ion exchange system and use cleaning water to perform slow and fast washing on the ion exchange column in sequence. S4: Output the hexavalent chromium wastewater to the recovery reactor; add sulfur powder to the hexavalent chromium wastewater in the recovery reactor via the reducing agent feeder, stir, and the sulfur powder will cause Cr to... 6+ Reduced to Cr 3+ The alkali feeder adds alkali solution to the recovery reactor, generating Cr(OH)3 precipitate. S5: The chromium hydroxide wastewater is transported to a primary filter press, which filters the chromium hydroxide wastewater to form a filter cake. The filtrate is output to the recovery filter press system to recover sodium thiosulfate. The filter pulverizer pulverizes the chromium hydroxide filter cake. The chromium hydroxide is then placed in a washing tank for washing. S6: Chromium hydroxide is fed to a secondary filter press, where it is filtered to form a filter cake, yielding Cr(OH)3. S7: Cr(OH)3 material is fed into the calcining kiln via a conveyor to generate Cr2O3; Compared with the prior art, one of the above technical solutions has the following beneficial effects: This solution provides a chromium-containing wastewater treatment and recycling line that selectively reduces highly toxic hexavalent chromium to trivalent chromium under acidic conditions, and further converts it into high-purity chromium trioxide (Cr2O3), realizing the resource transformation from pollutant to functional material. This process not only effectively blocks the migration and bioaccumulation risks of hexavalent chromium in the environment, but also avoids the long-term ecological hazards and regulatory pressure caused by chromium-containing sludge landfill. It achieves the goal of "micro-discharge" or even near-zero discharge of chromium-containing wastewater, and solves the problem of large amounts of hazardous chromium-containing sludge generated by the chemical reduction-precipitation method in traditional chromium-containing wastewater treatment. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of one embodiment of a chromium-containing wastewater treatment and recycling line; Figure 2 This is a schematic diagram of the structure of one embodiment of the resin regeneration processing line; Figure 3 This is a schematic diagram of the structure of one embodiment of the ion exchange column 11; Figure 4 This is a top view of one embodiment of the porous distribution plate; Figure 5 This is a schematic diagram of one embodiment of the filtrate recovery line; Figure 6 This is a schematic diagram of the structure of one embodiment of the chromium recycling and processing branch line to the recycling and calcination processing line; Figure 7 This is a schematic diagram of one embodiment of the recycling and calcination treatment line. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more comprehensive description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0018] like Figure 1-7 A chromium-containing wastewater treatment and recycling line includes: a resin regeneration treatment line 1, a chromium recycling treatment line 5, a filter press recycling line 6, and a recycling calcination treatment line 55. The resin regeneration treatment line 1 includes: an ion exchange system 1, an alkaline washing system 2, a water washing system 3, and an acid washing system 4. The ion exchange system 1 is used to receive hexavalent wastewater and perform ion exchange adsorption on the hexavalent wastewater; the alkaline washing system 2 is connected to the ion exchange system 1 and is used to output alkaline solution to the ion exchange system 1; the water washing system 3 is connected to the ion exchange system 1 and is used to output washing water to the ion exchange system 1; the acid washing system 4 is connected to the ion exchange system 1 and is used to output acid solution to the ion exchange system 1. The input end of the chromium recovery treatment line 5 is connected to the output end of the ion exchange system 1; the output end of the chromium recovery treatment line 5 is connected to the filtrate recovery line 6 and the recovery calcination treatment line 55 respectively; the chromium recovery treatment line 5 is used to receive the hexavalent wastewater from the ion exchange system 1, and mix the hexavalent wastewater with sulfur powder and alkaline solution to produce chromium hydroxide, then filter the chromium hydroxide, the chromium hydroxide filter cake is output to the recovery calcination treatment line 55, and the filtrate is output to the filtrate recovery line 6; The filter press recovery line 6 is used to recover sodium thiosulfate from the filter press; The recycling and calcination treatment line 55 is used to calcine chromium hydroxide filter cake into Cr2O3.

[0019] This solution provides a chromium-containing wastewater treatment and recycling line that selectively reduces highly toxic hexavalent chromium to trivalent chromium under acidic conditions, and further converts it into high-purity chromium trioxide (Cr2O3), realizing the resource transformation from pollutant to functional material. This process not only effectively blocks the migration and bioaccumulation risks of hexavalent chromium in the environment, but also avoids the long-term ecological hazards and regulatory pressure caused by chromium-containing sludge landfill. It achieves the goal of "micro-discharge" or even near-zero discharge of chromium-containing wastewater, and solves the problem of large amounts of hazardous chromium-containing sludge generated by the chemical reduction-precipitation method in traditional chromium-containing wastewater treatment.

[0020] The communication connection method described in this application refers to the communication established between connected devices through signal transmission and interaction, which can be divided into wired connection and wireless connection; wired connection is such as conventional data cable connection; wireless connection is such as conventional WiFi, Bluetooth, infrared, NFC, etc.

[0021] Optimally, the ion exchange system 1 is provided with an ion exchange column 11, the interior of which is filled with ion exchange resin 110; a column bottom water distributor 111 and a column bottom aerator 112 are provided below the ion exchange column 11; the column bottom water distributor 111 is provided with a porous distribution plate 1111; the column bottom aerator 112 is provided with a microporous aeration pipe 1121 for introducing compressed gas. The alkaline washing system 2 includes: an alkaline solution storage tank 21, an alkaline washing pipe 22, and an alkaline solution output pump 23; The alkali storage tank 21 is connected to the column bottom water distributor 111 through the alkali washing pipe 22, and is used to output alkali to the column bottom water distributor 111. The alkali is output to the ion exchange column 11 through the porous distribution plate 1111. The alkali output pump 23 is installed in the column bottom water distributor 111. The water washing system 3 is connected to the ion exchange column 11 and is used to output washing water to the ion exchange column 11; the acid washing system 4 is connected to the ion exchange column 11 and is used to output acid solution to the ion exchange column 11. The ion exchange system 1 further includes: a differential pressure sensor 17 and a bubble control valve 18; The detection end of the differential pressure sensor 17 is located inside the ion exchange column 11 and close to the ion exchange resin 110; the differential pressure sensor 17 is communicatively connected to the bubble control valve 18; the bubble control valve 18 is installed on the microporous aeration pipe 1121.

[0022] Specifically, the ion exchange system 1 is equipped with an ion exchange column 11, which is filled with ion exchange resin 110 for ion exchange adsorption with chromium in chromium-containing wastewater. The alkali storage tank 21 stores alkali solution. When the alkali solution output pump 23 is started, the alkali solution is output to the bottom of the ion exchange column 11 through the alkali washing pipe 22. The bottom of the ion exchange column 11 is equipped with a column bottom water distributor 111 and a column bottom aerator 112. The column bottom water distributor 111 is connected to the alkali washing pipe 22 and is used to receive the alkali solution and pass the alkali solution from bottom to top through the ion exchange resin 110. The column bottom water distributor 111 is equipped with a porous distribution plate 1111. When the alkali solution enters the column bottom water distributor 111, it is uniformly diffused through multiple diffusion holes 1112 of the porous distribution plate 1111, thereby forming a stable upward flow and ensuring that the alkali solution and the particles of the ion exchange resin 110 are in full contact. As the alkali solution continues to flow in, the liquid level gradually rises. Once the liquid surface stabilizes above the ion exchange resin 110, a liquid seal environment is formed, effectively preventing the formation of gas channels. This prevents air from entering the resin bed and causing gas resistance, ensuring liquid phase continuity and sufficient contact with the resin. It also prevents small bubbles from entering the gas channels and affecting the aeration function. A bottom aerator 112 is also provided below the ion exchange column 11. The bottom aerator 112 can be located below or above the porous distribution plate 1111. The bottom aerator 112 has a microporous aeration tube 1121 for inputting compressed air. The microporous aeration tube 1121 releases microbubbles through the micropores, which continuously disturb the alkali solution. Specifically, the bubbles rise between the resin layers, breaking the local concentration gradient and promoting OH- ion exchange. - Ions diffuse into the micropores of the resin, significantly enhancing mass transfer efficiency. Simultaneously, when bubbles rupture inside the ion exchange resin 110, the local shear force generated at the moment of rupture helps to remove colloidal or organic deposits attached to the resin surface, restoring the activity of functional groups. Furthermore, trace amounts of dissolved oxygen can participate in redox side reactions in a strongly alkaline environment, inhibiting the potential damage to the resin structure caused by reducing impurities such as sulfides. Moreover, continuous aeration maintains the loose structure of the ion exchange resin 110, avoiding channeling caused by particle compaction and ensuring uniform penetration of the alkaline solution across the entire cross-section.

[0023] The differential pressure sensor 17 is located inside the ion exchange column 11 and is used to detect the pressure change of the ion exchange resin 110 per unit time in real time, thereby monitoring the bed resistance change in real time; because the microporous aeration tube 1121 releases tiny bubbles through micropores, it promotes OH- - Ions diffuse into the interior of the resin micropores, significantly enhancing mass transfer efficiency. In this scheme, the differential pressure sensor 17 is connected to the bubble control valve 18. When the differential pressure sensor 17 detects an abnormal increase in ΔP per unit time, the differential pressure sensor 17 controls the bubble control valve 18 to increase the opening ratio, thereby increasing the aeration rate and making the resin bed of the ion exchange resin 110 more porous.

[0024] Optimally, the ion exchange system 1 includes: a series tube 12, an inner valve 13, an outer connecting tube 14, an outer valve 15, an adsorption monitoring device 16, a first column valve 19, and a plurality of the ion exchange columns 11; Multiple ion exchange columns 11 are connected in series, and one of the output terminals of one ion exchange column 11 is connected to the input terminal of another ion exchange column 11 through the series tube 12; the series tube 12 is provided with the internal valve 13; The ion exchange column 11 is provided with at least two input terminals, one of which is used to connect to the series tube 12, and the other input terminal is provided with the first column valve 19; the column bottom water distributor 111 is connected to the alkaline washing tube 22 through the external connecting pipe 14; the external valve 15 is installed on the external connecting pipe 14; the ion exchange column 11 is equipped with the adsorption monitoring device 16; the adsorption monitoring device 16 is communicatively connected to the internal valve 13 and the external valve 15.

[0025] There are multiple ion exchange columns 11. Adjacent ion exchange columns 11 are connected by a series tube 12. The first ion exchange column 11 bears the main adsorption load. As the running time goes by, the front ion exchange column 11 gradually becomes saturated, and trace amounts of Cr(VI) begin to be transported to the rear ion exchange column 11 through the series tube 12. The ion exchange column 11 continues to capture Cr ions, thus forming a Cr gradient adsorption zone and maximizing the utilization of the system resin capacity.

[0026] Multiple ion exchange columns 11 are connected in series. Generally, chromium wastewater stably passes through the series column group. As the operating time progresses, the front-end ion exchange column 11 gradually approaches saturation, and Cr(VI) begins to penetrate and be captured by the downstream ion exchange column 11. When the ion exchange column 11 reaches the breakthrough critical point, and the adsorption monitoring device 16 of a certain ion exchange column 11 detects a continuous upward trend in the Cr(VI) concentration approaching the process threshold (e.g., 3 mg / L), the adsorption monitoring device 16 immediately triggers a saturation alarm. Through a preset program, it controls the inner valve 13 between the two ion exchange columns 11 to close and controls the first column valve 19 to close, thus physically isolating the saturated ion exchange column 11 from the alkaline washing system 2. Simultaneously, the outer valve 15 of the first column external connecting pipe 14 is opened, and alkaline solution is introduced into the external connecting pipe 14 through the alkaline washing pipe 22 to regenerate the saturated ion exchange column 11. The next isolated ion exchange column 11 becomes the first column, the first column valve 19 is opened, and chromium-containing wastewater continues to be input into the first column ion exchange column 11.

[0027] Optimally, the ion exchange resin 110 is a D201 type styrene-based basic anion exchange resin. The chemical formula of the D201 type styrene-based basic anion exchange resin is P-[N + (CH3)3]Cl- P represents the polymer backbone; the polymer backbone is formed by suspension polymerization using styrene-divinylbenzene copolymer as the matrix, with divinylbenzene (DVB) as the crosslinking agent and a crosslinking degree of 6-8%. This ion exchange resin 110 employs a macroporous design with pore sizes ranging from 20-100 nm, forming a continuous pore network with a specific surface area >50 m² / g, effectively absorbing large-sized ions (HCr₂O₇). - Adsorption.

[0028] Optimally, the porous distribution plate 1111 is provided with a plurality of diffusion holes 1112 arranged in an array. The porous distribution plate 1111 is provided with a plurality of diffusion holes 1112; the porous distribution plate 1111 is used to pass alkali solution, which first enters the column bottom water distributor 111, and then diffuses evenly into the interior of the ion exchange column 11 through the diffusion holes 1112 of the porous distribution plate 1111, forming a stable upward flow to ensure that the alkali solution and resin particles are in full and uniform contact.

[0029] Optimally, the pickling system 4 includes: a concentrated sulfuric acid storage tank 41 and a sulfuric acid dilution tank 42; The output end of the concentrated sulfuric acid storage tank 41 is connected to the sulfuric acid dilution tank 42 for discharging concentrated sulfuric acid into the sulfuric acid dilution tank 42; one output end of the water washing system 3 is connected to the ion exchange column 11; the other output end of the water washing system 3 is connected to the sulfuric acid dilution tank 42 for discharging water into the sulfuric acid dilution tank 42 to dilute the concentrated sulfuric acid into dilute sulfuric acid; the output end of the sulfuric acid dilution tank 42 is connected to the ion exchange column 11 for discharging dilute sulfuric acid into the ion exchange column 11. The ion exchange column 11 is provided with water inlets 113 at its upper and lower ends for connecting to the water washing system 3.

[0030] Ion exchange system 1 is disconnected from water washing system 3 and connected to acid washing system 4. Sulfuric acid dilution tank 42 can draw in water from water washing system 3 under negative pressure. Concentrated sulfuric acid is transported from concentrated sulfuric acid storage tank 41 to sulfuric acid dilution tank 42. The concentrated sulfuric acid is diluted into dilute sulfuric acid in the presence of water, and a 6-8% dilute sulfuric acid solution is prepared immediately. With the temperature controlled below 35°C, the dilute sulfuric acid passes through ion exchange column 11 at a uniform rate, and the contact time with ion exchange resin 110 can be greater than 2 hours. Using dilute sulfuric acid can prevent the ion exchange resin 110 from dehydrating and aging, and also facilitates subsequent recovery into Na2S2O3.

[0031] In hexavalent chromium wastewater, Cr(VI) mainly exists as the binuclear anion Cr₂O₇²⁻. - It exists in a form carrying two negative charges, readily interacting with the functional groups of the resin through electrostatic attraction. When hexavalent chromium wastewater flows through ion exchange column 11, the exchangeable chloride ions (Cl-) in the resin phase... - ) with Cr2O7² in the liquid phase- Two-site ion exchange reactions occur: 2R≡N + Cl - + Cr2O7² - (R≡N + )2Cr2O7² - + 2Cl - This reaction system can selectively retain and enrich hexavalent chromium in the solid resin matrix, while simultaneously promoting the formation of Cl... - The adsorption is carried out into the purified aqueous phase. During the adsorption process, the color change of the resin phase shows a clear concentration dependence: as the chromium loading increases, the ion exchange resin 110 gradually changes from light yellow to a characteristic deep orange-red. This visualized color gradient change provides an intuitive qualitative criterion for process monitoring.

[0032] Optimally, the chromium recovery processing line 5 includes: a recovery reactor 51, a reducing agent feeder 52, an alkali feeder 53, and a recovery filter press system 54; The recovery reactor 51 is used to receive the hexavalent chromium wastewater from the resin regeneration treatment line 1; the output end of the reducing agent feeder 52 is connected to the recovery reactor 51 and is used to output sulfur powder to the recovery reactor 51; the output end of the alkali feeder 53 is connected to the recovery reactor 51 and is used to output alkali to the recovery reactor 51, so that the hexavalent chromium wastewater in the recovery reactor 51 is treated into chromium hydroxide wastewater. The output end of the recovery reactor 51 is connected to the recovery filter press system 54, and is used to output chromium hydroxide wastewater to the recovery filter press system 54; The recycling filter press system 54 includes: a primary filter press 541, a filter crushing device 543, a washing tank 544, and a secondary filter press 545; The primary filter press 541 is used to receive the chromium hydroxide wastewater from the recovery reactor 51, and to perform filter press treatment on the chromium hydroxide wastewater, outputting the filtrate to the filter filtrate recovery branch line 6, and outputting the chromium hydroxide to the filter pulverizer 543. The filter pulverizing device 543 is used to pulverize chromium hydroxide and output the chromium hydroxide to the cleaning tank 544. The cleaning tank 544 is used to clean chromium hydroxide and output the chromium hydroxide to the secondary filter press 545; The secondary filter press 545 performs filter pressing on the chromium hydroxide in the washing tank 544 to obtain chromium hydroxide.

[0033] Specifically, the recovery reactor 51 receives hexavalent chromium wastewater, which contains Cr. 6+For example, Na₂CrO₄ has strong oxidizing properties and is carcinogenic and mutagenic; the reducing agent feeder 52 is equipped with sulfur powder with reducing properties; the reducing agent feeder 52 outputs sulfur powder to the recovery reactor 51, Cr 6+ It reacts with sulfur powder, and the specific reaction formula is as follows: 4CrO4 2- + 6S + 7H2O → 4Cr(OH)3↓ + 3S2O3 2- + 2OH - ; Cr recovery reactor 51 6+ Reduced to Cr 3+ After the reduction reaction is complete, trivalent chromium is converted into Cr. 3+ The ions are uniformly dispersed in the alkaline aqueous system; to achieve efficient solid-liquid separation, soluble Cr must be... 3+ It is converted into chromium hydroxide precipitate, which is sparingly soluble in water. To address this, after Cr(OH)3 is generated in the recovery reactor 51, the alkali feeder 53 can supply alkali solution to the recovery reactor 51, maintaining the pH value of the reaction system in the alkali feeder 53 at 9.5-10.8, thus preventing Cr from forming. 3+ All of the wastewater forms a colloidal Cr(OH)3 precipitate. The recovery reactor 51 outputs the wastewater containing the Cr(OH)3 precipitate to a primary filter press 541; the primary filter press 541 filters the chromium hydroxide wastewater, and the filtrate is output to the filtrate recovery line 6. The filtrate recovery line 6 mainly treats S2O3. 2- Recycling, can yield S2O3 2- Cooling and crystallization can be performed, for example, to recover sodium thiosulfate (Na2S2O3·5H2O). The Cr(OH)3 solid from the primary filter press 541 is output to the filtration and pulverizing device 543, which pulverizes the filter cake-like Cr(OH)3 solid to facilitate Cr(OH)3 washing and remove impurities. After Cr(OH)3 washing, it is output to the secondary filter press 545, which performs pressure filtration on Cr(OH)3, pressing it into a filter cake and discharging the liquid phase of Cr(OH)3. The moisture content of the filter cake can be reduced to 34.7±0.8%, obtaining a high-purity Cr(OH)3 filter cake that meets the standards for calcined raw materials.

[0034] Alternatively, the recovery reactor 51 may be equipped with a redox potential probe 511; the redox potential probe 511 may be equipped with an Ag / AgCl reference electrode and a platinum indicator electrode.

[0035] The recovery reactor 51 is equipped with a redox potential probe 511 consisting of an Ag / AgCl reference electrode and a platinum indicator electrode. The recovery reactor 51 records the system's ORP value. At the start of the reaction, a large amount of hexavalent chromium is present in the solution, and the system has a high oxidizing capacity, exhibiting a high positive potential, typically >400mV. The ORP gradually decreases as reduction proceeds. When the ORP stabilizes below +250mV and remains unchanged for 30 minutes, the reduction endpoint is considered reached. Upon identification of the reduction endpoint, alkaline solution can be discharged into the wastewater to allow the Cr to return to its normal value. 3+ All of it formed a gelatinous Cr(OH)3 precipitate.

[0036] Alternatively, the sidewall of the recovery reactor 51 may be provided with an interface detector 512.

[0037] An interface detector (such as interface detector 512) is installed on the side wall of the recovery reactor 51. It can be the inner side wall or the outer side wall of the recovery reactor 51 (a transparent glass can be installed at the corresponding outer side wall position). The interface detector 512 installed on the side wall of the recovery reactor 51 can dynamically identify a clear solid-liquid stratification interface. When the interface descent rate is less than a preset value (e.g., 0.5 cm / min), it can be determined that the sedimentation of chromium hydroxide is basically completed, providing a basis for the next stage of discharge to the recovery filter press system 54.

[0038] Alternatively, the recovery reactor 51 is equipped with an anchor stirrer 513; the top of the recovery reactor 51 is provided with a protective gas inlet 514 for introducing protective gas.

[0039] The anchor stirrer 513 can keep chromium hydroxide in a fully suspended state throughout the reaction process, which can prevent local sedimentation and uneven nucleation. The top of the recovery reactor 51 is equipped with a protective gas port 514, which is used to continuously introduce protective gas (such as nitrogen, argon, helium, etc.) from top to bottom during the precipitation stage to suppress the possible surface oxidation of Cr(III) above the recovery reactor 51 and ensure the chemical stability of the product.

[0040] Optimally, it also includes: a calcination atmosphere control system 56 and a waste gas treatment sub-line 7; The recycling and calcining treatment line 55 includes: a calcining pulverizer 551, a conveyor 552, and a calcining kiln 553; The calcining pulverizer 551 is used to receive chromium hydroxide from the secondary filter press 545 and pulverize the chromium hydroxide; the conveying end of the conveyor 552 is used to receive chromium hydroxide from the calcining pulverizer 551 and convey the chromium hydroxide to the calcining kiln 553. The calcining kiln 553 is used for calcining chromium hydroxide; the calcining kiln 553 is provided with a heating zone 5531, a heat preservation zone 5532 and a cooling zone 5533 in sequence from the inlet to the outlet; The temperature of the heating zone 5531 is 500-680℃; the temperature of the heat preservation zone 5532 is 1050-1100℃; and the temperature of the cooling zone 5533 is 20-80℃. The calcination atmosphere control system 56 includes: a protective gas output device 562, an oxygen detection device 563, and an infrared gas analysis device 564; The exhaust gas treatment branch line 7, the oxygen detection device 563, and the infrared gas analysis device 564 are communicatively connected; the input end of the exhaust gas treatment branch line 7 is connected to the insulation zone 5532 for discharging the exhaust gas from the insulation zone 5532; the detection ends of the oxygen detection device 563 and the infrared gas analysis device 564 are located in the insulation zone 5532; the output end of the protective gas output device 562 is connected to the insulation zone 5532 for outputting protective gas to the insulation zone 5532.

[0041] The input end of the recycling calcination treatment line 55 is connected to the output end of the recycling filter press system 54. The recycling calcination treatment line 55 is used to receive chromium hydroxide from the secondary filter press 545. The calcination pulverizer 551 first receives the chromium hydroxide. The blade assembly of the calcination pulverizer 551 can shear and crush the chromium hydroxide filter cake at a speed of 250-300 rpm, which can control the particle size of chromium hydroxide to below 5 mm. The crushed chromium hydroxide is fed into the input end of the calcination kiln 553 at a uniform speed by the conveyor 552. The output end of the conveyor 552 drives the chromium hydroxide through the heating zone 5531, the heat preservation zone 5532 and the cooling zone 5533 in sequence. In the heating zone 5531 (500-680℃), after the chromium hydroxide enters the heating zone 5531 from room temperature, it undergoes rapid heating (e.g., within 60 minutes). During this stage, the temperature curve can rise linearly, minimizing the cracking of chromium hydroxide caused by thermal stress concentration. Upon exiting heating zone 5531, the residual moisture content of chromium hydroxide can be reduced to below 1.2%. In holding zone 5532 (1050-1100℃), Cr(OH)3 undergoes deep dehydration and lattice reconstruction, generating Cr2O3 and a large amount of water vapor. After calcination to generate Cr2O3, the red-hot Cr2O3 material enters the cooling section. A gradual temperature reduction can be adopted, with the initial cooling air temperature not exceeding 80℃ and the final temperature approaching room temperature. The cooling rate is controlled at a decrease of 15-20℃ per minute to avoid lattice distortion or microcrack propagation caused by rapid cooling. Movable gates can be installed between heating zone 5531, holding zone 5532, and cooling zone 5533 to maintain mutual isolation during calcination.

[0042] The calcination atmosphere control system 56 is equipped with a waste gas treatment line 7, a protective gas output device 562, an oxygen detection device 563, and an infrared gas analysis device 564. The waste gas treatment line 7 is used to discharge water vapor from the insulation zone 5532 outside the insulation zone 5532. The protective gas output device 562 is used to output protective gas, such as nitrogen, argon, or helium, to the insulation zone 5532 to form a stable protective atmosphere. The oxygen detection device 563 is used to detect the oxygen content in the insulation zone 5532 in real time, and the infrared gas analysis device 564 is used to detect the content of water vapor, carbon dioxide, carbon monoxide, methane, etc. in real time. The waste gas treatment line 7, the oxygen detection device 563, and the infrared gas analysis device 564 are connected in communication. Once the oxygen content or water vapor content deviates from the set threshold, the protective gas output device 562 increases the output of protective gas and increases the exhaust volume of the waste gas treatment line 7 to maintain the oxygen content in the furnace (e.g., below 0.1 Vol%), effectively preventing the infiltration of outside air.

[0043] The conveyor is a known mechanism with a conveying function, such as a trolley or conveyor roller.

[0044] Optimally, the exhaust gas treatment branch line 7 includes: exhaust gas main pipe 71, desulfurization tower 72 and exhaust gas fan 73; One end of the exhaust gas main pipe 71 is connected to the insulation zone 5532, and the other end of the exhaust gas main pipe 71 is connected to the input end below the desulfurization tower 72; the exhaust gas fan 73 is installed at the output end above the desulfurization tower 72, and when the exhaust gas fan 73 is started, a negative pressure is formed inside the desulfurization tower 72 and the exhaust gas main pipe 71; The desulfurization tower 72 is equipped with a spraying device 721 inside, which is used to spray alkaline droplets into the interior of the desulfurization tower 72.

[0045] The exhaust gas main pipe 71 is connected to the insulation zone 5532. When the exhaust gas fan 73 is started, water vapor, sulfur dioxide, and dust from the insulation zone 5532 enter the interior of the desulfurization tower 72 from the lower inlet end through the exhaust gas main pipe 71 and flow upwards. The desulfurization tower 72 is equipped with a spray device 721, which sprays alkaline droplets (such as sodium hydroxide) into the interior of the desulfurization tower 72. The alkaline droplets react with sulfur dioxide to generate SO3. 2- Salt and / or SO4 2- Salt is used to remove sulfur dioxide produced during chromium calcination, thus solving the problem of atmospheric pollution caused by impurities discharged during chromium wastewater recycling.

[0046] Alternatively, the exhaust gas treatment line 7 may further include an exhaust gas return pipe 74, an exhaust gas return valve 75, and an exhaust gas return pump 76; The calcining kiln 553 is provided with a pretreatment zone 5530; the pretreatment zone 5530, the heating zone 5531, the heat preservation zone 5532 and the cooling zone 5533 are arranged in sequence. The input end of the exhaust gas return pipe 74 is connected to the heat preservation zone 5532, and the output end of the exhaust gas return pipe 74 is connected to the pretreatment zone 5530; the exhaust gas return valve 75 and the exhaust gas return pump 76 are installed on the exhaust gas return pipe 74. The exhaust gas main pipe 71 is equipped with an exhaust gas regulating valve 77.

[0047] In this embodiment, the exhaust gas main pipe 71 is equipped with an exhaust gas regulating valve 77. By opening or closing the exhaust gas regulating valve 77, the connection between the exhaust gas main pipe 71 and the desulfurization tower 72 can be adjusted. At the same time, the exhaust gas return pipe 74 connects the insulation zone 5532 and the pretreatment zone 5530. By opening the exhaust gas return valve 75 and starting the exhaust gas return pump 76, the exhaust gas return pipe 74 outputs the tail gas from the insulation zone 5532 to the pretreatment zone 5530. The tail gas generated in the insulation zone 5532 can be used to preheat the chromium hydroxide in the pretreatment zone 5530, thus making reasonable use of the heat carried by the tail gas.

[0048] Alternatively, the calcining kiln 553 may be equipped with a natural gas burner 5534 in the heating zone 5531.

[0049] The heating zone 5531 is equipped with a natural gas burner 5534. The natural gas burner 5534 achieves thermal energy conversion through premixed air and fuel. The natural gas burner 5534 can proportionally adjust the air-fuel ratio to ensure a linear temperature rise, minimizing the cracking of chromium hydroxide particles caused by thermal stress concentration. Simultaneously, the exhaust gas return pipe 74 allows unburned natural gas from the insulation zone 5532 to flow back to the pretreatment zone 5530, where it re-enters the heating zone 5531 for re-combustion, thus improving thermal efficiency.

[0050] Alternatively, the recycling calcination treatment line 55 may further include: a calcination steam detector 70; The detection end of the calcination steam detector 70 is located in the heating zone 5531; the calcination steam detector 70 is communicatively connected to the conveyor 552. The calcination steam detector 70 can detect the residual moisture content of the Cr(OH)3 material in the heating zone 5531 in real time. Preferably, the residual moisture content of the Cr(OH)3 material needs to be reduced to below 1.2%, which can control the moisture content of the Cr(OH)3 material when it enters the heat preservation zone 5532, thereby preventing moisture from affecting the deep dehydration and lattice reconstruction of Cr(OH)3. The calcination steam detector 70 is communicatively connected to the conveyor 552, and can control the conveying speed of the conveyor 552. Before the residual moisture drops to a preset value, the calcination steam detector 70 controls the conveyor 552 to pass through the heating zone 5531 at a lower conveying speed until the residual moisture drops to the preset value, after which the calcination steam detector 70 controls the conveyor 552 to pass through the heating zone 5531 normally.

[0051] Optimally, the desulfurization tower 72 is equipped with a demister 722 near the output end. Sulfur dioxide reacts with alkaline droplets to produce sulfite and water. The alkaline droplets can remove a large amount of acidic substances in the exhaust gas in the desulfurization tower 72. Therefore, the desulfurization tower 72 is equipped with a demister 722 near the output end. Since the acidic substances have already reacted with the alkaline droplets below the desulfurization tower 72, the exhaust gas needs to pass through the demister 722 when it is output from the desulfurization tower 72. The demister 722 can remove the droplets entrained in the exhaust gas, ensuring that the emitted exhaust gas meets environmental protection requirements.

[0052] Optimally, the filtrate recovery line 6 includes: a multi-effect evaporator 61, a recovery crystallizer 62, a recovery centrifuge 63, and a recovery drying device 64; The multi-effect evaporator 61 is provided with a first-effect evaporation unit 611 and multiple sub-effect evaporation units 612 in sequence along the steam conveying direction; the multi-effect evaporator 61 is used to receive the filtrate from the chromium recovery treatment line 5, and the filtrate enters the separation chamber of the first-effect evaporation unit 611 after passing through the separation chambers of the multiple sub-effect evaporation units 612 in sequence. The separation chamber of the single-effect evaporation unit 611 is connected to the recovery crystallization vessel 62 and is used to output the filtrate to the recovery crystallization vessel 62; The recovery crystallization kettle 62 is used to cool and crystallize the filtrate, so that sodium thiosulfate precipitates out of the filtrate to form sodium thiosulfate slurry. The recovery centrifuge device 63 is used to receive the sodium thiosulfate slurry from the recovery crystallization vessel 62, and to separate the sodium thiosulfate slurry into solid and liquid phases, and to output the sodium thiosulfate solid to the recovery drying device 64. The recovery drying device 64 is used for drying sodium thiosulfate solid.

[0053] The generated Cr(OH)3 precipitate is filtered using a primary filter press 541 to press the Cr(OH)3 precipitate into a filter cake, thereby producing Na2S2O3 filtrate. The Na2S2O3 filtrate is output to a multi-effect evaporator 61. The multi-effect evaporator 61 can be a three-effect countercurrent evaporation system, which has a first-effect evaporation unit 611 and multiple sub-effect evaporation units 612 arranged sequentially in the direction of steam delivery. The direction of steam delivery is opposite to that of the Na2S2O3 filtrate. The steam is generated as saturated steam from the heating chamber of the first-effect evaporation unit 611 as a heat source, and passes sequentially through the heating chambers of multiple sub-effect evaporation units 612. The heat of the steam decreases step by step from the heating chamber of the first-effect evaporation unit 611 to the heating chamber of the last sub-effect evaporation unit 612. The Na2S2O3 filtrate enters the multi-effect evaporator 61 from the separation chamber of the last fractional-effect evaporation unit 612. After passing through the separation chambers of multiple fractional-effect evaporation units 612, it enters the separation chamber of the single-effect evaporation unit 611. The Na2S2O3 filtrate achieves energy cascade utilization in the multi-effect evaporator 61. After passing through the multi-effect evaporator 61, conditions for crystal nucleation are formed, and the filtrate is then discharged into the recovery crystallization kettle 62. The recovery crystallization kettle 62 cools and crystallizes the filtrate. Within this temperature drop range, the solubility of Na2S2O3·5H2O decreases sharply, resulting in significant supersaturation and inducing the precipitation of a large number of crystals, forming a sodium thiosulfate slurry. The sodium thiosulfate slurry is sent to the recovery centrifuge device 63, which performs solid-liquid separation. The centrifugal mother liquor is clear and transparent, while the solid sodium thiosulfate is output to the recovery drying device 64. The recovery drying device 64 dries the solid sodium thiosulfate, ultimately obtaining anhydrous sodium thiosulfate. Thus, this solution recovers sodium thiosulfate from chromium wastewater treatment, improves resource utilization during the chromium wastewater treatment process, thereby reducing the treatment cost of chromium wastewater and solving the problem of insufficient resource recovery in chromium wastewater treatment.

[0054] Optimally, it may also include: a water storage mechanism 66; The water storage mechanism 66 includes: a water storage pipe 661, a system water storage tank 662, and a cleaning connecting pipe 663; The input end of the water storage pipe 661 is connected to the heating chamber of the multi-effect evaporation unit 612 and the heating chamber of the single-effect evaporation unit 611, respectively; the output end of the water storage pipe 661 is connected to the system water storage tank 662, which is used to receive the condensate from the multi-effect evaporator 61 and output the condensate to the system water storage tank 662; the input end of the cleaning connecting pipe 663 is connected to the system water storage tank 662, and the cleaning connecting pipe 663 is equipped with a cleaning pump body 664.

[0055] The heating chambers of the single-effect evaporation unit 611 and the multi-effect evaporation unit 612 of the multi-effect evaporator 61 use steam to heat the separation chamber. After the heating chamber cools down, the steam liquefies and is pressurized by the pump body of the water storage pipe 661 or by the gravity of the condensate, and is output to the system water storage tank 662 through the water storage pipe 661. The cooling water is stored in the system water storage tank 662. When any system or device in the chromium-containing wastewater treatment and recycling line needs to be replenished or cleaned, it can be connected to the cleaning pipe 663. The cleaning pump body 664 of the cleaning pipe 663 outputs the cooling water from the system water storage tank 662 to the required location, thereby realizing the cascade utilization of water resources.

[0056] Alternatively, the recovery drying device 64 may include: a main drying tower 641, an air outlet 642, a moisture detector 643, and a recovery feeder 644; The air outlet 642 is installed inside the main drying tower 641 and close to the input end of the main drying tower 641. The air outlet 642 is used to output hot air to the main drying tower 641. The detection end of the moisture detector 643 is located at the input end of the main drying tower 641. The moisture detector 643 is communicatively connected to the air outlet 642 and the recovery feeder 644. The recovery feeder 644 is used to feed sodium thiosulfate solid to the input end of the main drying tower 641.

[0057] The drying tower 641 is a vertical structure. The air outlets 642 are located inside the drying tower 641, primarily outputting hot airflow towards the input end of the drying tower 641. The input end of the drying tower 641 can have more air outlets 642 than the output end, thus ensuring that the input temperature of the drying tower 641 is higher than the output temperature. After the recovery feeder 644 delivers sodium thiosulfate solids to the input end of the drying tower 641, the hot airflow output by the air outlets 642 fully disperses and dehydrates the sodium thiosulfate solids as they enter the input end of the drying tower 641. A moisture detector 6... 43 is used to detect the moisture content of the material at the input end of the drying main tower 641 and / or the moisture content of a local area. Since the moisture detector 643 is communicatively connected to the air outlet 642 and the recovery feeder 644, the moisture detector 643 can control the air volume or air temperature of the air outlet 642 to adjust the air inlet temperature; the moisture detector 643 can also control the feeding speed of the recovery feeder 644; when the moisture content of the material or the moisture content at the input end of the drying main tower 641 is greater than the threshold, the air volume of the air outlet 642 can be increased and / or the air temperature can be increased, or the feeding speed of the recovery feeder 644 can be slowed down.

[0058] The recovery feeder 644 can be replaced by a known feeding mechanism, such as a conveyor belt or a hopper, as long as it feeds material into the drying tower 641. The drying tower 641 can be replaced by a known drying mechanism, such as a drying chamber; in a preferred embodiment; Optimally, the recovery feeder 644 is an airflow vibrating screen; the drying main tower 641 is an airflow dryer; the output end of the recovery feeder 644 is connected to the input end of the drying main tower 641. The airflow vibrating screen utilizes the characteristics of sodium sulfate solid—small mass, light weight, easy floating, and good flowability—to fully diffuse it into the airflow. The sodium sulfate solid no longer agglomerates but passes through the screen as individual particles with the airflow, and is then output to the airflow dryer. The airflow dryer is internally and externally isolated; when connected to the airflow vibrating screen, the two combine to form a complete closed production line. This combination achieves continuous drying of sodium thiosulfate, shortens the transmission gap between the recovery feeder 644 and the drying main tower 641, reduces environmental pollution of sodium thiosulfate solid, and minimizes sodium thiosulfate solid loss.

[0059] Alternatively, the recovery centrifuge device 63 is connected to the multi-effect evaporator 61 via a centrifugal reflux pipe 65, for conveying the mother liquor after solid-liquid separation of sodium thiosulfate crystal slurry to the separation chamber of the fractional-effect evaporation unit 612.

[0060] Sodium thiosulfate slurry is fed into a recovery centrifuge 63. After solid-liquid separation, the sodium thiosulfate is solidified and output to a recovery drying device 64. The mother liquor after centrifugation is returned to the multi-effect evaporator 61 through the centrifuge reflux pipe 65. It then passes through the separation chambers of the multi-effect evaporation unit 612 and the single-effect evaporation unit 611. The mother liquor undergoes a re-crystallization process in the multi-effect evaporator 61, thereby recovering the residual sodium thiosulfate in the mother liquor and achieving closed-loop recycling to improve the recovery rate.

[0061] Alternatively, the water storage mechanism 66 may further include an activated carbon filter 67; The activated carbon filter 67 is disposed between the input end of the system water storage tank 662 and the output end of the water storage pipe 661.

[0062] The activated carbon filter 67 is equipped with activated carbon. When the water storage pipe 661 outputs condensate to the system water storage tank 662, the condensate is filtered through the activated carbon filter 67. The activated carbon adsorbs impurities in the condensate, thereby improving the water quality of the condensate. This improved water quality makes the condensate suitable for more institutions or systems that treat and recycle chromium-containing wastewater.

[0063] A method for treating and recycling chromium-containing wastewater, using the aforementioned chromium-containing wastewater treatment and recycling line, includes the following steps: S1: When the Cr ion concentration in the ion exchange column 11 rises to the preset threshold, the alkaline washing system 2 is connected to the ion exchange system 1; the alkaline output pump 23 is turned on, and the alkaline storage tank 21 outputs alkaline solution to the ion exchange column 11 through the alkaline washing pipe 22. The alkaline solution is output below the ion exchange column 11 through the column bottom water distributor 111, and the liquid surface of the alkaline solution flows from bottom to top through the ion exchange resin 110. Dilute acid is passed through ion exchange resin 110 at a constant flow rate of 1.5 BV / h for a contact time of no less than 2 hours. During this process, Na+ on the resin... + Ca² + Mg² + Isocations are subjected to H + Displacement: 2R-SO3 - Na + + H2SO4→ (R-SO3 - )2H2 + +Na2SO4; The functional groups are reprotonated, restoring them to a strongly acidic cation exchange state, thus creating conditions for the next adsorption cycle.

[0064] When a high concentration of NaOH solution is introduced, the pH of the system rapidly rises to above 12, and a large amount of OH-... - Not only do they compete for exchange sites, but they also trigger morphological transformations of chromium species in solution: Cr2O7² - + 2OH - 2CrO4² - + H2O; This shifts the equilibrium to the right, promoting the conversion of dichromate ions into monomeric chromate ions (CrO4²⁻). - Its higher charge density and lower steric hindrance make it easier to detach from the resin phase and enter the liquid phase. Simultaneously, the ion exchange reaction is reversed: (R≡N + )2CrO4² - + 2OH - → 2R≡N + OH - + CrO4² - ; That is, R2-CrO4+ 2OH - → 2R-OH + CrO4² - (where R represents the resin skeleton); this process is driven by strong thermodynamics, and combined with the enhanced hydrophilicity and increased swelling rate of the resin under alkaline conditions, it further accelerates the release of chromium. The final collected regenerated liquid is yellowish-brown and transparent, with a high Cr(VI) concentration, mainly existing in the form of Na2CrO4, providing high-grade raw materials for subsequent resource utilization.

[0065] S2: Open the column bottom aerator 112 and output compressed gas to the ion exchange column 11 through the microporous aeration tube 1121. The compressed gas forms bubbles in the alkaline solution through the microporous aeration tube 1121. After the Cr ion concentration in the ion exchange column 11 stabilizes, disconnect the alkaline washing system 2. S3: Water washing system 3 is connected to ion exchange system 1. Water washing system 3 outputs cleaning water to ion exchange column 11 to remove the alkaline solution in ion exchange column 11. Water washing system 3 is disconnected when the liquid in ion exchange column 11 is colorless. Acid washing system 4 is connected to the exchange system. Acid washing system 4 outputs acid to ion exchange column 11 until the pH of the liquid in ion exchange column 11 is stable and weakly alkaline. Acid washing system 4 is disconnected. Water washing system 3 is connected to ion exchange system 1, and cleaning water is used to perform slow washing and fast washing on ion exchange column 11 in sequence.

[0066] During the slow washing stage, the ion exchange resin 110 is rinsed with cleaning water at a low flow rate (≤1 BV / h) to fully displace the residual acid from the bed.

[0067] In the rapid washing stage, cleaning water is used at a high flow rate (3-4 BV / h) to continuously wash until the pH of the effluent from ion exchange column 11 stabilizes at around 7.5 and there is no visible turbidity. At this point, the ion exchange resin 110 shows restored color, uniform particle size, and good mechanical strength. Thus, the ion exchange resin 110 completes its full cycle regeneration, and the system automatically switches back to standby mode, ready to start the next cycle of adsorption. This four-stage regeneration strategy of "alkali washing-water washing-acid washing-water washing" not only ensures the stability of the resin exchange capacity but also restores its original capacity. S4: The hexavalent chromium wastewater is discharged to the recovery reactor 51; sulfur powder is added to the hexavalent chromium wastewater in the recovery reactor 51 by the reducing agent feeder 52, and stirred. The sulfur powder will cause the Cr... 6+ Reduced to Cr 3+ Alkali feeder 53 adds alkali solution to recovery reactor 51, generating Cr(OH)3 precipitate; S5: The chromium hydroxide wastewater is transported to the primary filter press 541, where the chromium hydroxide wastewater is filtered and the chromium hydroxide is pressed into a filter cake. The filtrate is output to the recovery filter press system 54 to recover sodium thiosulfate. The filter pulverizer 543 pulverizes the chromium hydroxide filter cake. The chromium hydroxide is placed in the washing tank 544 for washing. S6: Chromium hydroxide is fed to a secondary filter press 545, where it is filtered to form a filter cake, yielding Cr(OH)3. S7: The Cr(OH)3 material is fed into the calcining kiln 553 via conveyor 552 and calcined to produce Cr2O3.

[0068] Alternatively, in step S1, multiple ion exchange columns 11 are connected in series, and an adsorption monitoring device 16 is installed on each ion exchange column 11. The adsorption monitoring device 16 monitors the chromium concentration output by the ion exchange column 11. When the detection value of the first ion exchange column 11 continuously exceeds 3 mg / L, it is determined that the ion exchange column 11 has reached the adsorption endpoint. The ion exchange column 11 at the adsorption endpoint is isolated from the ion exchange system 1, and steps S2-S3 are executed. The first column valve 19 of the next ion exchange column 11 at the adsorption endpoint is opened, and hexavalent chromium wastewater is continued to be introduced into the ion exchange column 11.

[0069] In step S3, the cleaning water flows from bottom to top through the ion exchange resin 110. After the pH of the ion exchange column 11 decreases to 7-9, the cleaning water flows from top to bottom through the ion exchange column 11, making the pH of the ion exchange column 11 ≤ 8.5. Concentrated sulfuric acid is transported from the concentrated sulfuric acid storage tank 41 to the sulfuric acid dilution tank 42. The water washing system 3 outputs the cleaning water to the sulfuric acid dilution tank 42, where a dilute sulfuric acid solution is prepared. The sulfuric acid dilution tank 42 then passes the dilute sulfuric acid solution through the ion exchange column 11. Step S7 includes the following steps: S71: The Cr(OH)3 filter cake from step S5 is conveyed to the calcining pulverizer 551 for crushing, and the Cr(OH)3 material is fed into the calcining kiln 553 via the conveyor 552. Beneficial effects: The loose, granular chromium hydroxide filter cake is conveyed to a calcining pulverizer 551 (e.g., a twin-shaft calcining pulverizer 551), which shears and crushes the filter cake, controlling the particle size to below 5 mm. The crushed chromium hydroxide is then uniformly fed into the heating zone of a calcining kiln 553 (e.g., a tunnel kiln) via a conveyor 552 (e.g., a closed belt conveyor 552).

[0070] S72: Cr(OH)3 material enters the heating zone 5531 of the calcining kiln 553. The temperature of the heating zone 5531 is 500-680℃, which reduces the moisture content to below 1.2%. After chromium hydroxide enters the heating zone 5531 from room temperature, it can undergo rapid heating within a specific time period (e.g., within 60 minutes). During this stage, multiple natural gas burners 5534 can be configured to proportionally adjust the air-fuel ratio, ensuring a linear temperature increase and minimizing particle cracking caused by thermal stress concentration. The residual moisture content of the chromium hydroxide upon exiting the heating zone 5531, as indicated by the calcination steam detector 70, has decreased to below 1.2%. At this point, X-ray diffraction analysis reveals no characteristic peaks for Cr(OH)3, indicating the initial dehydroxylation reaction of Cr(OH)3.

[0071] S73: Cr(OH)3 enters the heat preservation zone 5532 of the calcining kiln 553. The temperature of the heat preservation zone 5532 is 1050-1100℃. Cr(OH)3 is calcined to generate Cr2O3. The oxygen detection device 563 is used to detect the O2 content of the heat preservation zone 5532 in real time, and the infrared gas analysis device 564 is used to detect the H2O content in real time. When the oxygen content or water vapor content exceeds the preset threshold, the protective gas output device 562 increases the output of the protective gas and increases the exhaust volume of the waste gas treatment line 7. Under high-temperature conditions, Cr(OH)3 undergoes deep dehydration and lattice reconstruction, generating Cr2O3. A large amount of water vapor is released during the reaction, which is discharged and condensed for recovery via the connected waste gas treatment line 7. The Cr2O3 from this step can be characterized by a combination of XRD and Raman spectroscopy; the main phase of the product is generally α-Cr2O3 with a complete crystal structure. To prevent trivalent chromium from being oxidized to highly toxic hexavalent chromium under high-temperature, oxygen-rich conditions, a protective gas output device 562 continuously supplies high-purity nitrogen to maintain the oxygen content in the furnace below 0.1 vol%, forming a stable reducing protective atmosphere. An oxygen detection device 563 and an infrared gas analyzer 564 are installed inside the calcining kiln 553 to monitor the oxygen and water concentrations in real time. If the concentrations deviate from the set thresholds, an interlocking nitrogen replenishment mechanism is immediately triggered.

[0072] S74: Cr2O3 enters the cooling zone 5533 of the calcining kiln 553. The initial temperature of the cooling zone 5533 is less than 80℃, and the final temperature of the cooling zone 5533 is room temperature.

[0073] After calcination, the red-hot Cr2O3 enters cooling zone 5533. This cooling zone 5533 can employ a counter-current air-cooling design, gradually reducing the air temperature. The initial cooling air temperature does not exceed 80℃, and the final temperature approaches room temperature. The cooling rate can be controlled to decrease by 15-20℃ per minute to avoid lattice distortion or microcrack propagation caused by rapid cooling.

[0074] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A chromium-containing wastewater treatment and recycling line, characterized in that, include: Resin regeneration processing line, chromium recovery processing line, filtrate recovery line and recovery calcination processing line; The resin regeneration process includes: an ion exchange system, an alkaline washing system, a water washing system, and an acid washing system; The ion exchange system is used to receive hexavalent wastewater and perform ion exchange adsorption on the hexavalent wastewater; the alkaline washing system is connected to the ion exchange system and is used to output alkaline solution to the ion exchange system; the water washing system is connected to the ion exchange system and is used to output washing water to the ion exchange system; the acid washing system is connected to the ion exchange system and is used to output acid solution to the ion exchange system. The input end of the chromium recovery and treatment branch line is connected to the output end of the ion exchange system; the output end of the chromium recovery and treatment branch line is connected to the filtrate recovery branch line and the recovery calcination treatment line respectively; the chromium recovery and treatment branch line is used to receive the hexavalent wastewater from the ion exchange system, and mix the hexavalent wastewater with sulfur powder and alkaline solution to produce chromium hydroxide, then filter the chromium hydroxide, the chromium hydroxide filter cake is output to the recovery calcination treatment line, and the filtrate is output to the filtrate recovery branch line; The filter press recovery line is used to recover sodium thiosulfate from the filter press; The recycling and calcination process line is used to calcine chromium hydroxide filter cake into Cr2O3.

2. The chromium-containing wastewater treatment and recycling line according to claim 1, characterized in that, The ion exchange system is equipped with an ion exchange column, the interior of which is filled with ion exchange resin; a column bottom water distributor and a column bottom aerator are provided below the ion exchange column; the column bottom water distributor is equipped with a porous distribution plate; the column bottom aerator is equipped with a microporous aeration pipe for introducing compressed gas. The alkaline washing system includes: an alkaline solution storage tank, an alkaline washing pipe, and an alkaline solution output pump; The alkali storage tank is connected to the column bottom water distributor via the alkali washing pipe for discharging alkali solution to the column bottom water distributor. The alkali solution is then discharged into the ion exchange column through the porous distribution plate. The alkali solution output pump is installed in the column bottom water distributor. The water washing system is connected to the ion exchange column and is used to output washing water to the ion exchange column; the acid washing system is connected to the ion exchange column and is used to output acid solution to the ion exchange column. The ion exchange system also includes: a differential pressure sensor and a bubble control valve; The detection end of the differential pressure sensor is located inside the ion exchange column and close to the ion exchange resin; the differential pressure sensor is communicatively connected to the bubble control valve; the bubble control valve is installed in the microporous aeration pipe.

3. The chromium-containing wastewater treatment and recycling line according to claim 2, characterized in that, The ion exchange system includes: a series tube, an inner valve, an outer connecting tube, an outer valve, an adsorption monitoring device, a first column valve, and multiple ion exchange columns; Multiple ion exchange columns are connected in series, and one output end of one ion exchange column is connected to the input end of another ion exchange column through the series tube; the series tube is equipped with the internal valve. The ion exchange column has at least two input ends, one of which is used to connect to the series tube, and the other input end is equipped with the first column valve; the column bottom water distributor is connected to the alkaline washing tube through the external connecting pipe; the external valve is installed on the external connecting pipe; the ion exchange column is equipped with the adsorption monitoring device; the adsorption monitoring device is communicatively connected to the inner valve and the outer valve.

4. The chromium-containing wastewater treatment and recycling line according to claim 1, characterized in that, The chromium recovery processing line includes: a recovery reactor, a reducing agent feeder, an alkali feeder, and a recovery filter press system; The recovery reactor is used to receive the hexavalent chromium wastewater from the resin regeneration treatment line; the output end of the reducing agent feeder is connected to the recovery reactor and is used to output sulfur powder to the recovery reactor; the output end of the alkali feeder is connected to the recovery reactor and is used to output alkali to the recovery reactor, so that the hexavalent chromium wastewater in the recovery reactor is treated into chromium hydroxide wastewater. The output end of the recovery reactor is connected to the recovery filter press system, and is used to output chromium hydroxide wastewater to the recovery filter press system; The recycling filter press system includes: a primary filter press, a filter crushing device, a washing tank, and a secondary filter press; The primary filter press is used to receive the chromium hydroxide wastewater from the recovery reactor, perform filter press treatment on the chromium hydroxide wastewater, output the filtrate to the filter filtrate recovery branch line, and output the chromium hydroxide to the filtration and pulverizing device; The filtration and pulverizing device is used to pulverize chromium hydroxide and output the chromium hydroxide to the cleaning tank; The cleaning tank is used to clean chromium hydroxide and output the chromium hydroxide to the secondary filter press; The secondary filter press performs filter pressing on the chromium hydroxide in the washing tank to obtain chromium hydroxide.

5. The chromium-containing wastewater treatment and recycling line according to claim 4, characterized in that, Also includes: Calcination atmosphere control system and waste gas treatment sub-line; The recycling and calcination processing line includes: a calcination pulverizer, a conveyor, and a calcination kiln; The calcining pulverizer is used to receive chromium hydroxide from the secondary filter press and pulverize the chromium hydroxide; the conveyor end of the conveyor is used to receive chromium hydroxide from the calcining pulverizer and convey the chromium hydroxide to the calcining kiln. The calcining kiln is used for calcining chromium hydroxide; the calcining kiln is provided with a heating zone, a heat preservation zone and a cooling zone in sequence from the inlet to the outlet; The temperature of the heating zone is 500-680℃; the temperature of the heat preservation zone is 1050-1100℃; and the temperature of the cooling zone is 20-80℃. The calcination atmosphere control system includes: a protective gas output device, an oxygen detection device, and an infrared gas analysis device; The exhaust gas treatment line, oxygen detection device, and infrared gas analysis device are communicatively connected; the input end of the exhaust gas treatment line is connected to the insulation zone for discharging exhaust gas from the insulation zone; the detection ends of the oxygen detection device and the infrared gas analysis device are located in the insulation zone; the output end of the protective gas output device is connected to the insulation zone for outputting protective gas to the insulation zone.

6. The chromium-containing wastewater treatment and recycling line according to claim 5, characterized in that, The waste gas treatment line includes: a main waste gas pipe, a desulfurization tower, and a waste gas fan; One end of the exhaust gas main pipe is connected to the insulation zone, and the other end of the exhaust gas main pipe is connected to the input end below the desulfurization tower; the exhaust gas fan is installed at the output end above the desulfurization tower, and when the exhaust gas fan is started, a negative pressure is formed inside the desulfurization tower and the exhaust gas main pipe; The desulfurization tower is equipped with a spraying device inside, which is used to spray alkaline droplets into the interior of the desulfurization tower.

7. A chromium-containing wastewater treatment and recycling line according to claim 1 or 4, characterized in that, The filtrate recovery line includes: a multi-effect evaporator, a recovery crystallizer, a recovery centrifuge, and a recovery drying device; The multi-effect evaporator is provided with a single-effect evaporation unit and multiple sub-effect evaporation units in sequence along the steam conveying direction; the multi-effect evaporator is used to receive the filtrate from the chromium recovery treatment line, and the filtrate enters the separation chamber of the single-effect evaporation unit after passing through the separation chambers of the multiple sub-effect evaporation units in sequence. The separation chamber of the single-effect evaporation unit is connected to the recovery crystallization vessel and is used to output the filtrate to the recovery crystallization vessel; The recovery crystallization kettle is used to cool and crystallize the filtrate, so that sodium thiosulfate precipitates out of the filtrate to form sodium thiosulfate slurry. The recovery centrifuge device is used to receive the sodium thiosulfate slurry from the recovery crystallization vessel, separate the sodium thiosulfate slurry into solid and liquid phases, and output the sodium thiosulfate solid to the recovery drying device. The recovery and drying device is used for drying solid sodium thiosulfate.

8. The chromium-containing wastewater treatment and recycling line according to claim 7, characterized in that, Also includes: Water storage facilities; The water storage mechanism includes: a water storage pipe, a system water storage tank, and a cleaning connecting pipe; The inlet of the water storage pipe is connected to the heating chamber of the multi-effect evaporation unit and the heating chamber of the single-effect evaporation unit, respectively. The output end of the water storage pipe is connected to the system water storage tank, which is used to receive the condensate from the multi-effect evaporator and output the condensate to the system water storage tank; the input end of the cleaning pipe is connected to the system water storage tank, and the cleaning pipe is equipped with a cleaning pump body.

9. A method for treating and recycling chromium-containing wastewater, using a chromium-containing wastewater treatment and recycling line as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: When the Cr ion concentration in the ion exchange column rises to a preset threshold, the alkaline washing system is connected to the ion exchange system. Turn on the alkali output pump, and the alkali storage tank outputs alkali to the ion exchange column through the alkali washing pipe. The alkali is output to the bottom of the ion exchange column through the column bottom water distributor, and the liquid surface of the alkali flows from bottom to top through the ion exchange resin. S2: Open the column bottom aerator and output compressed gas to the ion exchange column through the microporous aeration tube. The compressed gas forms bubbles in the alkaline solution through the microporous aeration tube. After the Cr ion concentration in the ion exchange column stabilizes, disconnect the alkaline washing system. S3: The water washing system is connected to the ion exchange system. The water washing system outputs cleaning water to the ion exchange column to remove the alkaline solution in the ion exchange column. The water washing system is disconnected when the liquid in the ion exchange column is colorless. The acid washing system is connected to the exchange system. The acid washing system outputs acid to the ion exchange column until the pH of the liquid in the ion exchange column is stable and weakly alkaline. The acid washing system is then disconnected. Connect the water washing system to the ion exchange system and use cleaning water to perform slow and fast washing on the ion exchange column in sequence. S4: Output the hexavalent chromium wastewater to the recovery reactor; add sulfur powder to the hexavalent chromium wastewater in the recovery reactor via the reducing agent feeder, stir, and the sulfur powder will cause Cr to... 6+ Reduced to Cr 3+ The alkali feeder adds alkali solution to the recovery reactor, generating Cr(OH)3 precipitate. S5: The chromium hydroxide wastewater is transported to a primary filter press, which filters the chromium hydroxide wastewater to form a filter cake. The filtrate is output to the recovery filter press system to recover sodium thiosulfate. The filter pulverizer pulverizes the chromium hydroxide filter cake. The chromium hydroxide is then placed in a washing tank for washing. S6: Chromium hydroxide is fed to a secondary filter press, where it is filtered to form a filter cake, yielding Cr(OH)3. S7: Cr(OH)3 material is fed into the calcining kiln via a conveyor to generate Cr2O3.

10. The method for treating and recycling chromium-containing wastewater according to claim 9, characterized in that, In step S1, multiple ion exchange columns are connected in series. Each ion exchange column is equipped with an adsorption monitoring device to monitor the chromium concentration output from the column. When the detection value at the first ion exchange column consistently exceeds 3 mg / L, the column is determined to have reached its adsorption endpoint. The column at this endpoint is then isolated from the ion exchange system, and steps S2-S3 are executed. The first column valve of the next ion exchange column at this endpoint is opened, allowing hexavalent chromium wastewater to continue flowing into the column. In step S3, the washing water passes through the ion exchange resin from bottom to top. After the pH of the ion exchange column decreases to 7-9, the washing water flows down the ion exchange column from top to bottom to make the pH of the ion exchange column ≤ 8.

5. Concentrated sulfuric acid is transported from the concentrated sulfuric acid storage tank to the sulfuric acid dilution tank. The water washing system outputs the washing water to the sulfuric acid dilution tank, where a dilute sulfuric acid solution is prepared. The sulfuric acid dilution tank then passes the dilute sulfuric acid solution through the ion exchange column. Step S7 includes the following steps: S71: The Cr(OH)3 filter cake from step S5 is conveyed to a calcining pulverizer for crushing, and the Cr(OH)3 material is fed into the calcining kiln via a conveyor. S72: Cr(OH)3 material enters the heating zone of the calcining kiln, where the temperature is 500-680℃, causing the moisture content to drop to below 1.2%. S73: Cr(OH)3 enters the heat preservation zone of the calcining kiln, where the temperature is 1050-1100℃. Cr(OH)3 is calcined to generate Cr2O3. An oxygen detection device is used to monitor the O2 content in the heat preservation zone in real time, and an infrared gas analyzer is used to monitor the H2O content in real time. When the oxygen content or water vapor content exceeds a preset threshold, the protective gas output device increases the output of the protective gas and increases the exhaust volume of the waste gas treatment line. S74: Cr2O3 enters the cooling zone of the calcining kiln. The initial temperature of the cooling zone is less than 80℃, and the final temperature of the cooling zone is room temperature.

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