A recovery treatment line and recovery treatment method for chromium-containing wastewater

Abstract

A recovery treatment line and method for chromium-containing wastewater; the recovery treatment line comprises a recovery reactor, a reducing agent feeder, a lye feeder and a recovery filter pressing system; the output end of the recovery reactor is communicated with the recovery filter pressing system, and is used for outputting chromium hydroxide wastewater to the recovery filter pressing system; a primary filter press is used for receiving the chromium hydroxide wastewater of the recovery reactor, and performing filter pressing treatment on the chromium hydroxide wastewater, outputting filtrate to a liquid phase recovery device, and outputting chromium hydroxide to a filter crushing device; the filter crushing device is used for performing crushing treatment on the chromium hydroxide, and outputting the chromium hydroxide to a cleaning tank; the cleaning tank is used for cleaning the chromium hydroxide, and outputting the chromium hydroxide to a secondary filter press; the secondary filter press performs filter pressing treatment on the chromium hydroxide of the cleaning tank, and obtains chromium hydroxide. The scheme solves the problem of high treatment difficulty of chromium-containing wastewater.

Description

Technical Field

[0001] This invention relates to the field of chromium wastewater recycling and treatment, and more particularly to a recycling and treatment line and method for chromium-containing wastewater. 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(VI)) 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. Therefore, Cr(VI) needs to be recycled and utilized.

[0003] Traditional chromium-containing wastewater treatment generates large amounts of hazardous chromium-containing sludge from the treatment of hexavalent chromium, resulting in high disposal costs and the risk of secondary pollution. Furthermore, industrial wastewater quality and quantity fluctuate greatly, while discharge standards are becoming increasingly stringent (e.g., chromium...). 6+ (≤0.2 mg / L), traditional processes struggle to consistently meet the standards, leading to significant challenges in treating traditional chromium-containing wastewater. Summary of the Invention

[0004] The purpose of this invention is to provide a recycling and treatment line for chromium-containing wastewater, which includes a recycling reactor, a reducing agent feeder, an alkali feeder, a recycling filter press system, and a recycling calcination system. This line can recycle and treat hexavalent chromium wastewater into chromium hydroxide, thereby transforming it from hazardous waste into functional inorganic materials.

[0005] The present invention also proposes a method for recycling and treating chromium-containing wastewater, which uses the above-mentioned recycling and treatment line for chromium-containing wastewater.

[0006] To achieve this objective, the present invention adopts the following technical solution: A recycling and treatment line for chromium-containing wastewater includes: a recycling reactor, a reducing agent feeder, an alkali feeder, and a recycling filter press system; The recovery reactor is used to receive hexavalent chromium wastewater; 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 liquid phase recovery device, a filter pulverizing 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, and to perform filter press treatment on the chromium hydroxide wastewater, outputting the filtrate to the liquid phase recovery device and outputting 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.

[0007] Optimally, the recovery reactor is equipped with a redox potential probe; the redox potential probe is equipped with an Ag / AgCl reference electrode and a platinum indicator electrode.

[0008] Alternatively, the sidewall of the recovery reactor may be equipped with an interface detector.

[0009] Alternatively, the recovery reactor may be equipped with an anchor-type stirrer; the top of the recovery reactor may be equipped with a protective gas inlet for introducing protective gas.

[0010] Optimally, it may also include: a recovery calcination system; The input end of the recovery calcination system is connected to the output end of the recovery filter press system; The recycling and calcining system includes: a calcining pulverizer, a conveyor, and a calcining 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℃.

[0011] Optimally, it may also include: a calcination atmosphere control system; The calcination atmosphere control system includes: a calcination exhaust device, a protective gas output device, an oxygen detection device, and an infrared gas analysis device; The calcination exhaust device, oxygen detection device, and infrared gas analysis device are communicatively connected; the input end of the calcination exhaust device is connected to the heat preservation zone for discharging the exhaust gas from the heat preservation zone; the detection ends of the oxygen detection device and the infrared gas analysis device are located in the heat preservation zone; the output end of the protective gas output device is connected to the heat preservation zone for outputting protective gas to the heat preservation zone.

[0012] Optimally, the calcination exhaust device includes: a desulfurization device; The insulation zone is connected to the desulfurization device via a pipeline and is used to output exhaust gas to the desulfurization device.

[0013] A method for recycling and treating chromium-containing wastewater, using the aforementioned chromium-containing wastewater recycling and treatment line, includes the following steps: S1: Output the hexavalent chromium wastewater to the recovery reactor; S2: The reducing agent feeder adds sulfur powder to the hexavalent chromium wastewater in the recovery reactor and stirs. The sulfur powder then removes the chromium... 6+ Reduced to Cr 3+ The alkali feeder adds alkali solution to the recovery reactor, generating Cr(OH)3 precipitate. S3: The chromium hydroxide wastewater is transported to a primary filter press, which performs filter pressing treatment on the chromium hydroxide wastewater, pressing the chromium hydroxide into a filter cake. The filtrate is output to the recovery filter press system for recycling. The filter pulverizer pulverizes the chromium hydroxide filter cake. S4: Chromium hydroxide is placed in a cleaning tank for washing; S5: Chromium hydroxide is fed to a secondary filter press, where it is filtered to form a filter cake, yielding Cr(OH)3.

[0014] Optimally, it may also include: step S6; Step S6 includes the following steps: S61: 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. S62: 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%. S63: Cr(OH)3 enters the heat preservation zone of the calcining kiln, where the temperature is 1050-1100℃. Cr(OH)3 is calcined to produce Cr2O3. S64: 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.

[0015] Optimally, in step S63, an oxygen detection device is used to detect the O2 content in the heat preservation zone in real time, and an infrared gas analysis device is used to detect 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 calcination exhaust device.

[0016] Compared with the prior art, one of the above technical solutions has the following beneficial effects: This solution provides a chromium-containing wastewater recycling and treatment line, which includes a recycling reactor, a reducing agent feeder, an alkali feeder, a recycling filter press system, and a recycling calcination system. It can recycle and treat hexavalent chromium wastewater into chromium hydroxide, realizing the transformation from hazardous waste to functional inorganic materials, and solving the problem of the difficulty in treating chromium-containing wastewater. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of one embodiment of the recycling line; Figure 2 This is a schematic diagram of one embodiment of the recycling and calcination system.

[0018] in: Recovery reactor 51, reducing agent feeder 52, alkali feeder 53, recovery filter press system 54; recovery calcination system 55; calcination atmosphere control system 56; Primary filter press 541, liquid phase recovery device 542, filter pulverizing device 543, washing tank 544, secondary filter press 545; 511 Oxidation-reduction potential probe; 512 Interface detector; 513 Anchor stirrer; 514 Protective gas interface; Calcination pulverizer 551, conveyor 552, calcination kiln 553; Heating zone 5531, insulation zone 5532, cooling zone 5533; Calcination exhaust device 561, protective gas output device 562, oxygen detection device 563, infrared gas analysis device 564; desulfurization device 5611. Detailed Implementation

[0019] 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.

[0020] like Figure 1-2 A chromium-containing wastewater recycling and treatment line includes: a recycling reactor 51, a reducing agent feeder 52, an alkaline solution feeder 53, and a recycling filter press system 54; The recovery reactor 51 is used to receive hexavalent chromium wastewater; 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 liquid phase recovery device 542, a filter pulverizing 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 liquid phase recovery device 542 and outputting the chromium hydroxide to the filtration and pulverizing device 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.

[0021] This solution provides a chromium-containing wastewater recycling and treatment line, which includes a recycling reactor 51, a reducing agent feeder 52, an alkali feeder 53, a recycling filter press system 54, and a recycling calcination system 55. It can recycle and treat hexavalent chromium wastewater into chromium hydroxide, realizing the transformation from hazardous waste to functional inorganic materials, and solving the problem of the difficulty in treating chromium-containing wastewater.

[0022] 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 a liquid phase recovery device 542, which mainly recovers S2O3. 2- Recycling, can yield S2O3 2- Cooling and crystallization are performed, for example, to recover sodium sulfate and 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.

[0023] 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.

[0024] 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.

[0025] Alternatively, the sidewall of the recovery reactor 51 may be provided with an interface detector 512.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Optimally, it also includes: a recovery calcination system 55; The input end of the recovery calcination system 55 is connected to the output end of the recovery filter press system 54; The recycling and calcining system 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℃.

[0030] The input end of the recovery calcination system 55 is connected to the output end of the recovery filter press system 54. The recovery calcination system 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.

[0031] The conveyor is a known mechanism with a conveying function, such as a trolley or conveyor roller.

[0032] Optimally, it also includes: a calcination atmosphere control system 56; The calcination atmosphere control system 56 includes: a calcination exhaust device 561, a protective gas output device 562, an oxygen detection device 563, and an infrared gas analysis device 564. The calcination exhaust device 561, oxygen detection device 563, and infrared gas analysis device 564 are communicatively connected; the input end of the calcination exhaust device 561 is connected to the heat preservation zone 5532 for discharging the exhaust gas from the heat preservation zone 5532; the detection ends of the oxygen detection device 563 and the infrared gas analysis device 564 are located in the heat preservation zone 5532; the output end of the protective gas output device 562 is connected to the heat preservation zone 5532 for outputting protective gas to the heat preservation zone 5532.

[0033] The calcination atmosphere control system 56 is equipped with a calcination exhaust device 561, a protective gas output device 562, an oxygen detection device 563, and an infrared gas analysis device 564. The calcination exhaust device 561 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. 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 calcination exhaust device 561, 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 calcination exhaust device 561 to maintain the oxygen content in the furnace (e.g., below 0.1 Vol%), effectively preventing the infiltration of outside air.

[0034] The calcination exhaust device 561 is a known device that has exhaust gas treatment capabilities.

[0035] The communication connection method in this solution 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 Wi-Fi, Bluetooth, infrared, NFC, etc.

[0036] Optimally, the calcination exhaust device 561 includes: a desulfurization device 5611; The insulation zone 5532 is connected to the desulfurization device 5611 via a pipeline and is used to output exhaust gas to the desulfurization device 5611.

[0037] The desulfurization unit 5611 is connected to the insulation zone 5532 of the calcining kiln 553. The insulation zone 5532 outputs tail gas to the desulfurization unit 5611 through a pipeline. Since this application uses sulfur powder to reduce hexavalent chromium, the Cr(OH)3 fed into the calcining kiln 553 may contain sulfur powder. The calcining kiln 553 will convert the sulfur powder into sulfur dioxide. The desulfurization unit 5611 can react with the sulfur dioxide in the flue gas using an alkaline desulfurizing agent (such as limestone, magnesium oxide, etc.) to generate byproducts such as calcium sulfate or magnesium sulfate. A method for recycling and treating chromium-containing wastewater, using the above-mentioned chromium-containing wastewater recycling and treatment line, includes the following steps: S1: Output the hexavalent chromium wastewater to the recovery reactor 51; S2: 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; S3: The chromium hydroxide wastewater is transported to the primary filter press 541, where the chromium hydroxide wastewater is treated by filter pressing. The chromium hydroxide is pressed into a filter cake, and the filtrate is output to the recovery filter press system 54 for recovery. The filter pulverizer 543 pulverizes the chromium hydroxide filter cake. S4: Chromium hydroxide is washed in cleaning tank 544; S5: Chromium hydroxide is fed to a secondary filter press 545, where it is filtered to form a filter cake, yielding Cr(OH)3.

[0038] Alternatively, step S6 may include the following steps: S61: 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. 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).

[0039] S62: 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.

[0040] S63: 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. Under high temperature conditions, Cr(OH)3 undergoes deep dehydration and lattice reconstruction to generate Cr2O3. A large amount of water vapor is released during the reaction, which is discharged and condensed for recovery via a connected calcination exhaust device 561. The Cr2O3 produced in 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.

[0041] S64: 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.

[0042] 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.

[0043] Optimally, in step S63, 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 calcination exhaust device 561.

[0044] 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 inside 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 concentrations of oxygen and water in real time, respectively. If the concentrations deviate from the set thresholds, a nitrogen replenishment mechanism is immediately triggered.

[0045] 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 recycling and treatment line for chromium-containing wastewater, characterized in that, include: Recovery reactor, reducing agent feeder, alkali feeder, and recovery filter press system; The recovery reactor is used to receive hexavalent chromium wastewater; 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 liquid phase recovery device, a filter pulverizing 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, and to perform filter press treatment on the chromium hydroxide wastewater, outputting the filtrate to the liquid phase recovery device and outputting 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.

2. The chromium-containing wastewater recycling and treatment line according to claim 1, characterized in that, The recovery reactor is equipped with a redox potential probe; the redox potential probe is equipped with an Ag / AgCl reference electrode and a platinum indicator electrode.

3. The chromium-containing wastewater recycling and treatment line according to claim 1, characterized in that, The sidewall of the recovery reactor is equipped with an interface detector.

4. The chromium-containing wastewater recycling and treatment line according to claim 1, characterized in that, The recovery reactor is equipped with an anchor-type agitator; the top of the recovery reactor is equipped with a protective gas inlet for introducing protective gas.

5. A chromium-containing wastewater recycling and treatment line according to any one of claims 1-4, characterized in that, Also includes: Recovery calcination system; The input end of the recovery calcination system is connected to the output end of the recovery filter press system; The recycling and calcining system includes: a calcining pulverizer, a conveyor, and a calcining kiln; The calcining pulverizer is used to receive chromium hydroxide from the secondary filter press and to pulverize the chromium hydroxide. The conveyor end is used to receive chromium hydroxide from the calcining pulverizer and transport 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℃.

6. The chromium-containing wastewater recycling and treatment line according to claim 5, characterized in that, Also includes: Calcination atmosphere control system; The calcination atmosphere control system includes: a calcination exhaust device, a protective gas output device, an oxygen detection device, and an infrared gas analysis device; The calcination exhaust device, oxygen detection device, and infrared gas analysis device are communicatively connected; the input end of the calcination exhaust device is connected to the heat preservation zone for discharging the exhaust gas from the heat preservation zone; the detection ends of the oxygen detection device and the infrared gas analysis device are located in the heat preservation zone; the output end of the protective gas output device is connected to the heat preservation zone for outputting protective gas to the heat preservation zone.

7. The chromium-containing wastewater recycling and treatment line according to claim 5, characterized in that, The calcination exhaust device includes: a desulfurization device; The insulation zone is connected to the desulfurization device via a pipeline and is used to output exhaust gas to the desulfurization device.

8. A method for recycling and treating chromium-containing wastewater, using the chromium-containing wastewater recycling and treatment line according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Output the hexavalent chromium wastewater to the recovery reactor; S2: The reducing agent feeder adds sulfur powder to the hexavalent chromium wastewater in the recovery reactor and stirs. The sulfur powder then removes the chromium... 6+ Reduced to Cr 3+ The alkali feeder adds alkali solution to the recovery reactor, generating Cr(OH)3 precipitate. S3: The chromium hydroxide wastewater is transported to a primary filter press, which performs filter pressing treatment on the chromium hydroxide wastewater, pressing the chromium hydroxide into a filter cake. The filtrate is output to the recovery filter press system for recycling. The filter pulverizer pulverizes the chromium hydroxide filter cake. S4: Chromium hydroxide is placed in a cleaning tank for washing; S5: Chromium hydroxide is fed to a secondary filter press, where it is filtered to form a filter cake, yielding Cr(OH)3.

9. The method for recycling and treating chromium-containing wastewater according to claim 8, characterized in that, It also includes: step S6; Step S6 includes the following steps: S61: 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. S62: 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%. S63: Cr(OH)3 enters the heat preservation zone of the calcining kiln, where the temperature is 1050-1100℃. Cr(OH)3 is calcined to produce Cr2O3. S64: 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.

10. The method for recycling and treating chromium-containing wastewater according to claim 9, characterized in that, In step S63, the oxygen detection device is used to detect the O2 content in the heat preservation zone in real time, and the infrared gas analysis device 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 increases the output of the protective gas and increases the exhaust volume of the calcination exhaust device.

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