A photoreduction treatment system and a method for treating hexavalent chromium-containing wastewater

Abstract

The present invention provides a photoreduction treatment system and a method for treating hexavalent chromium-containing wastewater, and relates to the technical field of sewage treatment. The photoreduction treatment system includes a delivery pipeline and a water delivery pump, and a reaction tank, a recovery tank, and a sedimentation tank connected in sequence based on the delivery pipeline and the water delivery pump; the reaction tank includes a photoreaction device. The photoreduction treatment system efficiently reduces hexavalent chromium through ultraviolet light and a photoreductant, thereby reducing toxicity and secondary pollution. The reaction conditions are mild, the energy consumption is low, and the treatment cycle is short. The recovery tank and the sedimentation tank realize the recovery of trivalent chromium and the recycling of the photoreductant, thereby reducing costs and improving resource utilization. The system is easy to operate, has a high degree of automation, and is compact in equipment. It is suitable for large-scale wastewater treatment and has significant environmental and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a photoreduction treatment system and a method for treating hexavalent chromium-containing wastewater. Background Art

[0002] Hexavalent chromium, a typical heavy metal pollutant, is widely present in many industrial fields, especially in industries such as electroplating, leather making, metal smelting, printing and dyeing, chemicals, and pigment production. The discharge of hexavalent chromium wastewater is becoming increasingly prominent. Due to its high water solubility and oxidizability, hexavalent chromium can persist stably in water bodies for long periods of time and, through bioaccumulation in the food chain, poses a serious threat to the ecological environment and human health. Relevant research has shown that hexavalent chromium is highly carcinogenic, teratogenic, and mutagenic. Long-term exposure may lead to a variety of health problems such as skin inflammation, respiratory diseases, and neurological damage. Therefore, how to efficiently and safely remove hexavalent chromium from wastewater has become a key issue that needs to be urgently addressed in the field of environmental governance.

[0003] Currently, treatment technologies for hexavalent chromium wastewater primarily include chemical reduction precipitation, adsorption, electrochemical, and biological treatment. While adsorption is simple to operate, the adsorbent easily saturates and requires frequent regeneration and replacement, which undoubtedly adds additional treatment costs. Electrochemical treatment places high demands on the performance of electrode materials, which can easily lead to electrode passivation during use and consumes significant amounts of electricity, limiting its widespread application in large-scale wastewater treatment. While biological treatment offers some environmental benefits, it suffers from long treatment cycles, and microorganisms are sensitive to changes in environmental conditions. In practice, large-scale biological reaction systems are often required, which also limits its widespread adoption. Chemical reduction is widely used in industrial wastewater treatment due to its relatively mature process and high removal efficiency. This method typically uses a reducing agent (such as sulfite, iron salt, or sulfide) to reduce hexavalent chromium to less toxic, insoluble trivalent chromium, which is then removed through precipitation or adsorption. However, the chemical reduction method also has some problems that cannot be ignored, such as the large consumption of chemical reagents, the production of more by-products during the reaction process, the high treatment cost, and the risk of secondary pollution. These problems have to some extent limited its promotion and application in large-scale industrial wastewater treatment.

[0004] Furthermore, the traditional technical process commonly used in China for treating hexavalent chromium wastewater primarily includes conditioning, reaction, sedimentation, coagulation and sedimentation, inclined plate sedimentation, sludge concentration, and filter press filtration. While this traditional process can treat hexavalent chromium wastewater to a certain extent, it presents numerous challenges, such as high treatment costs, complex processes, long treatment cycles, large equipment footprint, and high chemical consumption. These issues not only increase the treatment burden on companies but also, to a certain extent, hinder the further development and optimization of hexavalent chromium wastewater treatment technology. Against the backdrop of increasingly stringent environmental governance requirements and growing awareness of resource recycling, the challenges facing traditional hexavalent chromium wastewater treatment technology are becoming increasingly apparent. There is an urgent need to develop new, more efficient, economical, environmentally friendly, and easy-to-operate treatment technologies to meet the growing demand for wastewater treatment, achieve efficient treatment and resource recovery of hexavalent chromium wastewater, and promote the sustainable development of related industries.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide a photoreduction treatment system and a method for treating hexavalent chromium-containing wastewater. The photoreduction treatment system efficiently reduces hexavalent chromium through a photoreduction reaction, reducing toxicity and minimizing secondary pollution. Utilizing an ultraviolet light source and a photoreducing agent, the system offers mild reaction conditions, a short treatment cycle, and low energy consumption. Recovery tanks and sedimentation tanks separate and recover trivalent chromium and recycle the photoreducing agent, reducing costs and improving resource utilization. The system is easy to operate, highly automated, and compact, making it suitable for large-scale wastewater treatment and offering significant environmental and economic benefits.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0008] In a first aspect, the present invention provides a photoreduction treatment system, comprising a delivery pipeline and a water delivery pump, and a reaction tank, a recovery tank, and a sedimentation tank sequentially connected based on the delivery pipeline and the water delivery pump;

[0009] The reaction tank includes a photoreaction device; the photoreaction device can add a photoreducing agent to the hexavalent chromium-containing wastewater, and reduce the hexavalent chromium in the hexavalent chromium-containing wastewater to trivalent chromium through a photoreduction reaction to obtain a reaction solution;

[0010] The recovery tank and the sedimentation tank can receive the reaction liquid based on the delivery pipeline and the pump, and separate trivalent chromium precipitate from the reaction liquid.

[0011] In an optional embodiment, the photoreduction treatment system further comprises a regulating tank connected to the reaction tank via the delivery pipeline;

[0012] The regulating tank is used to adjust the pH of the hexavalent chromium-containing wastewater to acidic hexavalent chromium-containing wastewater, and transport the acidic hexavalent chromium-containing wastewater to the reaction tank.

[0013] In an optional embodiment, the reaction pool includes a pool body and the light reaction device connected to the pool body; wherein the pool body is a pool body made of a transparent material;

[0014] The photoreaction device includes a reducing agent replenishing unit, a first stirring and mixing unit, and a light source unit, all of which are connected to the cell body.

[0015] In an optional embodiment, the first stirring and mixing unit includes a first paddle disposed at the bottom of the pool body, and a first motor disposed outside the pool body; a rotating shaft of the first motor is connected to the first paddle.

[0016] In an optional embodiment, the light source unit includes a sleeve disposed in the cell body and a light source portion disposed in the sleeve, wherein the light source portion is selected from at least one of an ultraviolet light source, a visible light source, and a xenon light source.

[0017] In an optional embodiment, the reducing agent replenishing unit includes a reducing agent container and a reducing agent delivery pipe connected to the reducing agent container; the reducing agent delivery pipe is connected to the cell body and is used to input the light reducing agent in the reducing agent container into the cell body.

[0018] In an optional embodiment, the recovery tank includes a recovery body and a recovery pipeline connected to the recovery body;

[0019] The other end of the recovery pipeline is connected to the reducing agent delivery pipe.

[0020] In an optional embodiment, the recovery body includes an upper phase device, an interface interception device and a lower phase device connected in sequence from top to bottom;

[0021] The upper phase device is connected to the reaction cell via the transport pipeline, and is also connected to the recovery pipeline and the electrolyte salt input pipeline; the upper phase device is a constriction structure, and a constriction port is provided at the lower end;

[0022] The interface interception device is a columnar structure, the upper end of which is connected to the upper phase device through the constriction port, and the lower end is connected to the lower phase device;

[0023] The lower phase device is connected to the sedimentation tank through the conveying pipeline.

[0024] In an optional embodiment, the interface interception device includes a columnar body, and an upper interface control valve and a lower interface control valve respectively provided at the upper and lower ends of the columnar body.

[0025] In an optional embodiment, the interface interception device further includes an interface sensor; and / or,

[0026] The columnar body of the interface interception device is made of a transparent material; and / or,

[0027] The cross-sectional area of the columnar body is smaller than the maximum cross-sectional area of the upper phase device.

[0028] In an optional embodiment, the recovery body further includes a second stirring and mixing unit provided in the upper phase device;

[0029] Wherein, the second stirring and mixing unit includes a second paddle arranged in the upper device and a second motor arranged outside the upper device; the rotating shaft of the second motor is connected to the second paddle.

[0030] In an optional embodiment, the sedimentation tank includes a sedimentation tank body and a sodium hydroxide feeding device connected to the sedimentation tank body; and / or,

[0031] The reaction tank and the sedimentation tank are both provided with a pH meter; and / or,

[0032] The reaction tank and the sedimentation tank are both provided with pH sensors; and / or,

[0033] The delivery pipeline includes a water inlet pipe and a water outlet pipe provided at both ends of the water delivery pump; and / or,

[0034] The water inlet pipe is provided with a flow meter and an input pressure gauge; and / or,

[0035] The water outlet pipe is provided with an output pressure gauge and a water outlet valve.

[0036] In a second aspect, the present invention provides a method for treating hexavalent chromium-containing wastewater, comprising:

[0037] The hexavalent chromium-containing wastewater is fed into a regulating tank and the pH is adjusted to an acidic state using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater, which is then pumped into a reaction tank;

[0038] A photoreducing agent is added to the reaction tank through a photoreaction device, and after mixing, a mixed solution is obtained; wherein the amount of the photoreducing agent added is: 5g~600g of the photoreducing agent is added per liter of acidic hexavalent chromium-containing wastewater;

[0039] Using the photoreaction device to perform a photoreduction reaction on the mixed solution to obtain a reaction solution containing trivalent chromium, and pumping the reaction solution into a recovery tank;

[0040] An inorganic strong electrolyte salt is added to the recovery tank, mixed and separated, and the upper phase is recovered to the reaction tank, and the target mixed phase of the lower phase is removed and put into a sedimentation tank; wherein the amount of the inorganic strong electrolyte salt added is: 100g~200g of the inorganic strong electrolyte salt is added per liter of the reaction solution;

[0041] In the precipitation tank, sodium hydroxide is used to adjust the target mixed phase to an alkaline state, so that the trivalent chromium ions in the target mixed phase form a precipitate, and chromium hydroxide precipitate is obtained after separation.

[0042] In an optional embodiment, the photoreducing agent is polyethylene glycol; and / or,

[0043] The weight average molecular weight of the photoreducing agent is 1000-5000; and / or,

[0044] The reaction time of the photoreduction reaction is 30 minutes to 40 minutes; and / or,

[0045] The mixing conditions include: the stirring blade speed is 20 r / min to 25 r / min; and / or,

[0046] The acidic solvent is sulfuric acid; and / or,

[0047] The acidic state is pH < 5; and / or,

[0048] The inorganic strong electrolyte salt is sodium sulfate.

[0049] The photoreduction treatment system provided by the present application has significant beneficial effects. First, the system reduces hexavalent chromium to trivalent chromium through a photoreduction reaction, effectively reducing the toxicity of harmful heavy metals in wastewater and reducing the risk of pollution to the environment. The use of a photoreductant and the coordination of an ultraviolet light source make the reaction conditions mild and efficient, and the reduction of hexavalent chromium can be completed in a relatively short time, greatly shortening the wastewater treatment cycle. In addition, the design of the recovery tank and sedimentation tank in the system not only realizes the separation and recovery of trivalent chromium, but also can recycle the photoreductant, reducing processing costs and improving resource utilization. The entire system is easy to operate and has a high degree of automation, which reduces the complexity and labor intensity of manual operation. At the same time, the equipment has a compact structure and occupies a small area, making it suitable for large-scale industrial wastewater treatment and has broad application prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 This is a schematic diagram of the overall structure of the photoreduction processing system in the embodiment of the present application;

[0052] Figure 2 This is a schematic diagram of the structure of the reaction pool in the photoreduction treatment system in the embodiment of the present application;

[0053] Figure 3 This is a schematic diagram of the structure of the recovery pool in the photoreduction treatment system in the embodiment of the present application;

[0054] Figure 4 This is a schematic diagram of the connection relationship and structure of the delivery pipeline and the water delivery pump in the photoreduction treatment system in the embodiment of the present application;

[0055] Figure 5 Schematic diagram of the process for treating hexavalent chromium-containing wastewater in the embodiment of the present application.

[0056] Explanation of the main component symbols: 100-photoreduction treatment system; 1-regulating tank; 2-reaction tank; 21-photoreaction device; 211-reducing agent replenishing unit; 2111-reducing agent container; 2112-reducing agent delivery pipe; 212-first stirring and mixing unit; 2122-first motor; 2121-first paddle; 213-light source unit; 2131-pipe sleeve; 2132-light source part; 22-tank body; 3-recovery tank; 31-recovery body; 311-upper phase device; 3111-electrolyte salt input pipeline; 3112-reduction port; 312-interface Retention device; 3121-columnar body; 3122-upper interface control valve; 3123-lower interface control valve; 3124-interface sensor; 313-lower phase device; 314-second stirring and mixing unit; 3141-second paddle; 3142-second motor; 32-recovery pipeline; 4-sedimentation tank; 41-sedimentation tank body; 42-sodium hydroxide feeding device; 5-transport pipeline; 51-water inlet pipe; 511-flow meter; 512-input pressure gauge; 52-water outlet pipe; 521-output pressure gauge; 522-water outlet valve; 6-water pump; 7-pH meter. DETAILED DESCRIPTION

[0057] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0058] refer to Figure 1 In an embodiment of the present application, a photoreduction treatment system 100 is provided, the photoreduction treatment system 100 comprising a delivery pipeline 5 and a water delivery pump 6, and a reaction tank 2, a recovery tank 3 and a sedimentation tank 4 sequentially connected based on the delivery pipeline 5 and the water delivery pump 6;

[0059] The reaction tank 2 includes a photoreaction device 21; the photoreaction device 21 can add a photoreducing agent to the hexavalent chromium-containing wastewater, and reduce the hexavalent chromium in the hexavalent chromium-containing wastewater to trivalent chromium through a photoreduction reaction to obtain a reaction solution;

[0060] The recovery tank 3 and the sedimentation tank 4 can receive the reaction liquid based on the delivery pipeline 5 and the pump, and separate the trivalent chromium precipitate from the reaction liquid.

[0061] This embodiment provides a photoreduction treatment system 100, which uses photoreduction technology to treat hexavalent chromium-containing wastewater, achieving hexavalent chromium reduction and chromium resource recovery. This photoreduction treatment system 100 primarily comprises a delivery pipeline 5, a water delivery pump 6, a reaction tank 2, a recovery tank 3, and a sedimentation tank 4. These components are sequentially connected via the delivery pipeline 5 and the water delivery pump 6, forming a complete wastewater treatment process.

[0062] In the reaction tank 2, the photoreaction device 21 is the core part of the system. The photoreaction device 21 can add a photoreductant to the hexavalent chromium-containing wastewater and reduce the hexavalent chromium in the wastewater to trivalent chromium through a photoreduction reaction. This process utilizes the redox ability of the photoreductant under light conditions to convert highly toxic, water-soluble hexavalent chromium into low-toxic, poorly soluble trivalent chromium, thereby reducing the polluting nature of the wastewater. After the photoreduction reaction, the hexavalent chromium in the wastewater is reduced to trivalent chromium to form a reaction solution. The reaction solution contains components such as trivalent chromium ions and a photoreductant, which require further treatment to achieve resource recovery and wastewater purification.

[0063] Recovery tank 3 receives the reaction liquid from reaction tank 2 and separates the trivalent chromium precipitate. Sedimentation tank 4 receives the trivalent chromium-containing mixed phase liquid discharged from recovery tank 3 and, by adjusting the pH, completely converts the trivalent chromium into chromium hydroxide precipitate. The precipitated trivalent chromium can be recovered through filtration and other methods, achieving the recycling of chromium resources and simultaneously purifying the wastewater to meet discharge standards.

[0064] The photoreduction reaction utilizes light energy as a driving force, has mild reaction conditions, low energy consumption, high efficiency, and can complete the reduction of hexavalent chromium in a relatively short period of time; through the design of the recovery tank 3 and the sedimentation tank 4, the recycling of the photoreductant and the recovery of chromium resources are achieved, thereby reducing treatment costs and improving resource utilization; the photoreduction treatment process avoids the use of a large amount of chemical reagents, reduces the risk of secondary pollution, and meets environmental protection requirements; the system realizes automatic transportation and treatment of wastewater through the conveying pipeline 5 and the water pump 6, is easy to operate, has a high degree of automation, and is suitable for large-scale industrial wastewater treatment.

[0065] In summary, the photoreduction treatment system 100 provided in this embodiment efficiently treats hexavalent chromium-containing wastewater through photoreduction technology, realizes the reduction of hexavalent chromium, the recovery of chromium resources and the purification of wastewater, and has significant environmental and economic benefits.

[0066] In some embodiments, the photoreduction treatment system 100 further includes a regulating tank 1 connected to the reaction tank 2 via the transport pipeline 5;

[0067] The regulating tank 1 is used to adjust the pH of the hexavalent chromium-containing wastewater to acidic hexavalent chromium-containing wastewater, and transport the acidic hexavalent chromium-containing wastewater to the reaction tank 2.

[0068] The regulating tank 1 is a key component of the photoreduction treatment system 100. Its primary function is to pretreat hexavalent chromium-containing wastewater by adjusting its pH to achieve acidic conditions suitable for the photoreduction reaction. This pretreatment step is beneficial for the subsequent photoreduction reaction because the acidic environment improves the reduction efficiency of hexavalent chromium, ensuring the smooth progress of the reaction.

[0069] In actual wastewater treatment, the pH of wastewater can fluctuate significantly due to varying industrial processes and discharge conditions. Adjusting tank 1 adjusts the pH of the wastewater by adding an acidic substance (such as sulfuric acid), ensuring a stable acidic environment before entering reaction tank 2. This pretreatment not only improves the efficiency of the photoreduction reaction but also reduces interference from pH fluctuations, thereby enhancing the stability and reliability of the entire system.

[0070] Besides pH adjustment, regulating tank 1 also plays other important roles. For example, it serves as a buffer for wastewater, balancing its flow and quality, thereby reducing the impact of fluctuations in wastewater discharge on subsequent treatment units. Furthermore, regulating tank 1 can further enhance wastewater treatment effectiveness by mixing wastewater from different sources and homogenizing the water quality.

[0071] refer to Figure 2In some embodiments, the reaction pool 2 includes a pool body 22 and the light reaction device 21 connected to the pool body 22; wherein the pool body 22 is a pool body 22 made of a transparent material;

[0072] The photoreaction device 21 includes a reducing agent replenishing unit 211 , a first stirring and mixing unit 212 , and a light source unit 213 , all of which are connected to the cell body 22 .

[0073] As mentioned above, the reaction pool 2 mainly includes a pool body 22 and a photoreaction device 21 connected thereto. The pool body 22 provides a physical space for the reaction, while the photoreaction device 21 is a key component for realizing the photoreduction reaction.

[0074] The photoreaction device 21 is composed of a reducing agent replenishing unit 211 , a first stirring and mixing unit 212 and a light source unit 213 . These components work together to ensure efficient photoreduction reaction.

[0075] The reducing agent replenishing unit 211 is responsible for adding the photoreducing agent to the reaction tank 2 to ensure the stability of the concentration of the photoreducing agent during the reaction process and provide the necessary chemical conditions for the reduction of hexavalent chromium; the first stirring and mixing unit 212 fully mixes the photoreducing agent with the hexavalent chromium-containing wastewater through stirring, increases the contact area between the reactants, and improves the reaction rate; the light source unit 213 is used to provide light energy to excite the photoreducing agent so that it can undergo an oxidation-reduction reaction with hexavalent chromium and reduce the hexavalent chromium to trivalent chromium.

[0076] The cell body 22 is made of a transparent material. This design facilitates the light emitted by the light source unit 213 to evenly penetrate the reaction cell 2, ensuring that the wastewater in the entire reaction cell 2 receives sufficient light, thereby improving the efficiency of the photoreduction reaction. The transparent cell body 22 also facilitates observation of the reaction process, allowing for the timely identification and resolution of potential problems.

[0077] In some embodiments, the first stirring and mixing unit 212 includes a first paddle 2121 disposed at the bottom of the pool body 22 and a first motor 2122 disposed outside the pool body 22 ; a rotating shaft of the first motor 2122 is connected to the first paddle 2121 .

[0078] The first blade 2121 is located at the bottom of the reaction tank 2 and is used to stir the liquid in the reaction tank 2 to ensure that the photoreducing agent and the hexavalent chromium-containing wastewater are fully mixed. The design and installation position of the blade are crucial to improving stirring efficiency and mixing uniformity.

[0079] A first motor 2122 is mounted outside of the reaction tank 2 and provides power for stirring. The motor selection must consider the power and speed required for stirring to ensure effective stirring. The rotating shaft of the first motor 2122 is mechanically connected to the first paddle 2121 via the rotating shaft, transmitting the motor's power to the paddle, enabling it to rotate and achieve stirring.

[0080] The primary function of the first stirring and mixing unit 212 is to thoroughly mix the photoreducing agent with the hexavalent chromium-containing wastewater through stirring, increasing the contact area between the reactants and thereby improving the rate and efficiency of the photoreduction reaction. Stirring not only accelerates the diffusion of the reactants but also prevents local concentrations of the reactants from being too high or too low, ensuring uniformity of the reaction.

[0081] In some embodiments, the light source unit 213 includes a sleeve 2131 disposed in the pool body 22 and a light source portion 2132 disposed in the sleeve 2131;

[0082] The light source 2132 is selected from at least one of an ultraviolet light source, a visible light source and a xenon light source.

[0083] The sleeve 2131 is provided in the body 22 of the reaction tank 2 to accommodate and protect the light source 2132. The sleeve 2131 is designed to ensure that the light source 2132 can emit light stably and evenly onto the wastewater in the reaction tank 2.

[0084] The light source 2132 is disposed within the housing 2131 and is the core component of the light source unit 213. It is responsible for emitting light for the photoreduction reaction. The light source 2132 can be selected from at least one of an ultraviolet light source, a visible light source, and a xenon light source. For example, it can be an ultraviolet light source.

[0085] For example, an ultraviolet light source can be selected. This light source can play an important role in the photoreduction reaction. Its wavelength and energy can effectively excite the photoreducing agent and promote the reduction reaction of hexavalent chromium. The specific reaction process can be:

[0086] .

[0087] Ultraviolet light has a high energy content, effectively stimulating the photoreductant, thereby increasing the efficiency of hexavalent chromium reduction. Compared to other light sources, ultraviolet light sources typically have higher photon energy, enabling the reduction reaction to be completed in a shorter timeframe, reducing processing time and energy consumption. The combination of the ultraviolet light source and the transparent cell body 22 ensures uniform illumination of all areas within the reaction cell 2, improving reaction uniformity.

[0088] The cell body 22 is preferably made of a transparent material to ensure that the light emitted by the UV light source evenly penetrates the entire reaction cell 2, allowing sufficient contact between the photoreducing agent and the hexavalent chromium wastewater, thereby improving reaction efficiency. The transparent material facilitates operator observation of the reaction process, allowing for timely identification and resolution of potential problems, ensuring smooth reaction progress. The transparent material also reduces light loss during propagation, improving light energy utilization and further optimizing the effectiveness of the photoreduction reaction.

[0089] In some embodiments, the reducing agent replenishing unit 211 includes a reducing agent container 2111 and a reducing agent delivery pipe 2112 connected to the reducing agent container 2111; the reducing agent delivery pipe 2112 is connected to the pool body 22 for inputting the photoreducing agent in the reducing agent container 2111 into the pool body 22.

[0090] The reducing agent container 2111 is used to store the light reducing agent to ensure that there is enough light reducing agent for replenishment. The design of the container needs to consider the storage capacity, sealing performance and connection method with the delivery system.

[0091] The reducing agent delivery pipe 2112 connects the reducing agent container 2111 and the cell body 22 of the reaction cell 2, and is used to deliver the photoreducing agent from the container to the reaction cell 2. The delivery pipe needs to have good corrosion resistance and sealing properties to ensure that the photoreducing agent will not leak or be contaminated during delivery.

[0092] The main function of the reducing agent replenishing unit 211 is to maintain a controlled addition of the photoreducing agent, ensuring a stable concentration of the photoreducing agent in the reaction tank 2, thereby ensuring the efficient progress of the photoreduction reaction. The photoreducing agent is gradually consumed during the reaction process, so the reducing agent replenishing unit 211 needs to replenish the photoreducing agent in a timely manner to maintain the continuous progress of the reaction.

[0093] refer to Figure 3 In some embodiments, the recovery tank 3 includes a recovery body 31 and a recovery pipeline 32 connected to the recovery body 31 ; the other end of the recovery pipeline 32 is connected to the reducing agent delivery pipe 2112 .

[0094] The recovery tank 3 is an important component of the photoreduction treatment system 100 , and its main function is to separate the trivalent chromium precipitate from the reaction solution and recover the photoreducing agent.

[0095] The recovery unit 31 is used to hold the reaction solution and separate and recover the trivalent chromium precipitate. A recovery line 32 is connected to the recovery unit 31 to transport the recovered photoreducing agent to the reducing agent replenishment unit 211. The other end of the recovery line 32 is connected to the reducing agent delivery pipe 2112, forming a closed-loop system for recycling the photoreducing agent.

[0096] The main function of the recovery tank 3 is to separate the trivalent chromium precipitate from the reaction solution and recover the photoreducing agent. Depending on the reduction principle employed, its structure can vary. For example, in this embodiment, an extraction separation method can be used to recover the photoreducing agent. The separated photoreducing agent is transported via the recovery line 32 to the reducing agent replenishment unit 211, where it re-enters the reaction tank 2 for recycling. The remaining trivalent chromium-containing mixed phase is then transported via the delivery line 5 to the sedimentation tank 4 for subsequent precipitation.

[0097] The photoreducing agent is recovered via recovery line 32 and re-delivered to reaction tank 2, enabling its recycling and reducing processing costs. The design of recovery tank 3 effectively separates trivalent chromium precipitate from the photoreducing agent, improving resource recovery efficiency. Recovery tank 3 is connected to reaction tank 2 and sedimentation tank 4 via delivery line 5, forming a complete treatment system that improves overall system efficiency and stability.

[0098] In some embodiments, the recovery body 31 includes an upper phase device 311, an interface interception device 312, and a lower phase device 313 connected sequentially from top to bottom;

[0099] The upper phase device 311 is connected to the reaction cell 2 via the delivery pipeline 5, and is also connected to the recovery pipeline 32 and the electrolyte salt input pipeline 3111; the upper phase device 311 is a constriction structure, and a constriction port 3112 is provided at the lower end;

[0100] The interface interception device 312 is a columnar structure, the upper end of which is connected to the upper phase device 311 through the constriction port 3112 , and the lower end of which is connected to the lower phase device 313 .

[0101] The lower phase device 313 is connected to the sedimentation tank 4 through the conveying pipeline 5 .

[0102] As mentioned above, the recovery tank 3 is a key component for separating and recovering reaction products in the photoreduction treatment system 100. The upper phase device 311, the interface interception device 312 and the lower phase device 313 are used to recover the photoreducing agent and extract and collect the trivalent chromium product after the reaction.

[0103] The upper phase device 311 is located at the top of the recovery tank 3 and is connected to the reaction tank 2 via the delivery line 5. It receives the reaction liquid from the reaction tank 2. The upper phase device 311 is also connected to the recovery line 32 and the electrolyte salt input line 3111, which are used to recover the photoreducing agent and adjust the properties of the reaction liquid. It has a constricted structure with a constriction port 3112 at the lower end to help guide the liquid flow and the separation process.

[0104] Interface retention device 312 is located in the middle of recovery tank 3 and is a columnar structure. Its upper end is connected to upper phase device 311 via constriction port 3112, and its lower end is connected to lower phase device 313. Interface retention device 312 stabilizes the interface between the two phases, preventing emulsification or mixing of the mixed liquid during the separation process, thereby ensuring effective separation.

[0105] The lower phase device 313 is located at the bottom of the recovery tank 3 and is connected to the sedimentation tank 4 through the delivery pipeline 5 to deliver the separated mixed phase containing trivalent chromium to the sedimentation tank 4 for subsequent treatment.

[0106] The main function of recovery tank 3 is to separate trivalent chromium precipitate from the reaction liquid and recover the photoreducing agent. The specific process may include the following: the reaction liquid enters the upper phase device 311 of recovery tank 3 from reaction tank 2 through conveying pipeline 5. Within recovery tank 3, the addition of auxiliary agents such as electrolyte salts (such as sodium sulfate) promotes the separation of trivalent chromium and photoreducing agent in the reaction liquid, forming a two-phase system. The upper layer is the photoreducing agent phase, and the lower layer is a mixed phase containing trivalent chromium. The photoreducing agent in the upper layer is transported to the reducing agent replenishing unit 211 via recovery pipeline 32 and re-enters the reaction tank 2 for recycling. The lower layer containing the trivalent chromium mixed phase is transported to the sedimentation tank 4 via conveying pipeline 5 for subsequent precipitation treatment.

[0107] Through the design of the interface interception device 312, the interface of the two-phase liquid can be stabilized, the separation efficiency can be improved, and the effective separation of the photoreductant and trivalent chromium can be ensured; the recovery tank 3 realizes the recovery and recycling of the photoreductant, reduces the processing cost, and improves the resource utilization rate; the recovery tank 3 is connected with the reaction tank 2 and the sedimentation tank 4 through the transmission pipeline 5, forming a complete treatment system, which improves the operating efficiency and stability of the entire system; the design of the upper phase device 311 with a constriction structure and the columnar interface interception device 312 helps to optimize the liquid flow and separation process, and reduce the equipment footprint and energy consumption.

[0108] In summary, the specific structure of recovery tank 3 demonstrates the mechanism for photoreducing agent recovery and trivalent chromium precipitation separation in photoreduction treatment system 100. This design not only achieves efficient recovery and recycling of the photoreducing agent, but also improves the overall operational efficiency and stability of the system, providing a key guarantee for the efficient treatment of hexavalent chromium-containing wastewater.

[0109] In some embodiments, the interface interception device 312 includes a cylindrical body 3121, and an upper interface control valve 3122 and a lower interface control valve 3123 respectively provided at the upper and lower ends of the cylindrical body 3121;

[0110] Furthermore, the interface interception device 312 also includes an interface sensor 3124;

[0111] Furthermore, the columnar body 3121 of the interface interception device 312 is made of a transparent material.

[0112] As mentioned above, the interface interception device 312 is a key component in the recovery tank 3, which is used to stabilize the interface of the two-phase liquid and ensure the separation effect.

[0113] The columnar body 3121 serves as the main structure of the interface interception device 312, and is used to contain liquid and provide a stable separation environment. The design of the columnar body 3121 helps optimize the liquid flow and separation process.

[0114] Upper interface control valve 3122 and lower interface control valve 3123 are located at the upper and lower ends of cylindrical body 3121, respectively. These valves regulate the flow of liquids, ensuring a stable interface between the two phases during separation. By precisely controlling the opening and closing of these valves, mixing of the two phases can be effectively prevented, improving separation efficiency.

[0115] Furthermore, an interface sensor 3124 is a preferred feature of the interface interception device 312, used to monitor the position of the interface between the two phases of liquid in real time. This interface sensor 3124 enables precise control of the interface position, further optimizing the separation process. Interface sensor 3124 can be integrated with an automated control system to automatically adjust the opening and closing of the upper interface control valve 3122 and the lower interface control valve 3123 based on the interface position, achieving automated operation.

[0116] The main function of the interface interception device 312 is to stabilize the interface of the two-phase liquid to ensure the effective separation of the photoreducing agent and the mixed phase containing trivalent chromium. For example, the specific process may include the following:

[0117] (1) Keep the upper interface control valve 3122 open and the lower interface control valve 3123 closed.

[0118] (2) The reaction liquid is passed from the reaction tank 2 through the conveying pipe 5 into the upper phase device 311 of the recovery tank 3. In the upper phase device 311, by adding auxiliary agents such as electrolyte salts (such as sodium sulfate), the trivalent chromium in the reaction liquid and the photoreducing agent are separated to form a two-phase system (during which appropriate stirring and mixing can be performed to avoid emulsification, sufficient extraction, and the part of the mixed liquid trapped in the columnar body 3121 can be fully mixed with the reaction liquid). After stratification, the upper layer is the photoreducing agent phase, and the lower layer is the mixed phase containing trivalent chromium.

[0119] (3) Slowly open the lower interface control valve 3123 of the interface retention device 312 so that the stratified interface in the stratified reaction liquid reaches the columnar body 3121, and close the upper interface control valve 3122 and the lower interface control valve 3123 so that the stratified interface is in the columnar body 3121 between the upper interface control valve 3122 and the lower interface control valve 3123.

[0120] (4) The upper layer portion in the upper phase device 311, i.e., the photoreducing agent portion, is controlled and transported to the reducing agent replenishing unit 211 through the recovery pipeline 32 and re-enters the reaction tank 2 for recycling.

[0121] (5) The lower layer portion in the lower phase device 313, i.e., the trivalent chromium mixed phase, is controlled and transported to the sedimentation tank 4 through the transport pipeline 5 for subsequent sedimentation treatment.

[0122] (6) The next batch of reaction liquid is fed into the upper phase device 311 and the upper interface control valve 3122 is opened to allow the mixed liquid therein to contact and mix with the reaction liquid, and step (1) is repeated.

[0123] Through the adjustment of the upper interface control valve 3122 and the lower interface control valve 3123, and the real-time monitoring of the interface sensor 3124, the interface retention device 312 can stably retain the stratified interface of the two-phase liquid, so that the upper phase and the lower phase can avoid the appearance of impurities during separation, thereby improving the separation efficiency and purity, and preventing the part that prevents emulsification or mixing from entering the upper phase or the lower phase.

[0124] The design of the cylindrical body 3121 helps optimize liquid flow, reducing turbulence and disturbance during the separation process, further improving separation efficiency. The integration of the interface sensor 3124 with the automated control system enables automated operation of the interface interception device 312, reducing manual intervention and improving the system's operational efficiency and stability.

[0125] Through the synergistic effect of the interface control valve and interface sensor 3124, the interface interception device 312 stabilizes the interface between the two phases of liquid, significantly improving separation efficiency. The combination of interface sensor 3124 and the automated control system enables automated operation of the interface interception device 312, reducing manual intervention and improving the system's operational efficiency and stability. The columnar body 3121 is constructed of a transparent material, allowing operators to observe the separation process, promptly identify and address potential issues, and ensure effective separation. The design of the columnar body 3121 helps optimize liquid flow, reduce equipment footprint and energy consumption, and improve overall system performance.

[0126] In summary, this embodiment provides a key mechanism for two-phase liquid separation in the photoreduction treatment system 100. This design not only improves separation efficiency but also reduces manual intervention through automated control, improving system operational efficiency and stability, and providing a key guarantee for the efficient treatment of hexavalent chromium-containing wastewater.

[0127] Furthermore, the cross-sectional area of the columnar body 3121 is smaller than the maximum cross-sectional area of the upper phase device 311 .

[0128] In the recovery tank 3, the reaction liquid is separated to form a two-phase liquid, namely the photoreducing agent phase in the upper layer and the trivalent chromium-containing mixed phase in the lower layer. By designing the cross-sectional area of the columnar body 3121 to be smaller than the maximum cross-sectional area of the upper phase device 311, the area of the stratification interface can be reduced. This means that in the horizontal direction, the stratification interface is formed by the constriction structure of the upper phase device 311, and reaches and enters the columnar body 3121 based on the premise that the constriction port 3112 can remain horizontal. The stratification interface can better adapt to the shape of the columnar body 3121, thereby more accurately controlling the separation process of the two-phase liquid. In addition, a smaller stratification interface area helps to reduce the mixing and emulsification of the two-phase liquid during the separation process. Due to the reduction in the interface area, the contact area between the two-phase liquid is also reduced accordingly, which makes the two-phase liquid easier to separate and improves the separation efficiency.

[0129] If the cross-sectional area of the columnar body 3121 is too large, the stratified interface may not be able to fully adapt to the shape of the columnar body 3121 in the horizontal direction, thereby forming an invalid space at the edge of the columnar body 3121. These invalid spaces may cause some liquids to be unable to be effectively separated, resulting in volume loss. By reducing the cross-sectional area of the columnar body 3121, these invalid spaces can be reduced, ensuring that all liquids can participate in the separation process, thereby avoiding volume loss. The smaller cross-sectional area makes the space occupied by the columnar body 3121 in the recovery tank 3 more compact, thereby improving the space utilization of the entire recovery tank 3. This not only helps to improve the separation efficiency, but also reduces the overall volume of the equipment and reduces the equipment's footprint.

[0130] By designing the cross-sectional area of columnar body 3121 to be smaller than the maximum cross-sectional area of upper phase device 311, the area of the delamination interface can be reduced, thereby more precisely controlling the separation process of the two-phase liquid, improving separation efficiency, and avoiding volume loss. This design optimizes the function of interface interception device 312, further improving the recovery of photoreducing agent and the separation of trivalent chromium precipitate in photoreduction treatment system 100.

[0131] In some embodiments, the recycling body 31 further includes a second stirring and mixing unit 314 provided in the upper phase device 311;

[0132] Furthermore, the second stirring and mixing unit 314 includes a second paddle 3141 disposed in the upper device 311 and a second motor 3142 disposed outside the upper device 311 ; a rotating shaft of the second motor 3142 is connected to the second paddle 3141 .

[0133] The second paddle 3141 is arranged inside the upper device 311 and is used to stir the liquid. The design and installation position of the second paddle 3141 are crucial to improving the stirring efficiency and mixing uniformity. The second motor 3142 is arranged outside the upper device 311 to provide power for stirring. The selection of the second motor 3142 needs to consider the power and speed required for stirring to ensure the stirring effect. The rotating shaft connecting the second motor 3142 is mechanically connected to the second paddle 3141, transmitting the power of the motor to the paddle, enabling it to rotate and realize the stirring function.

[0134] In some embodiments, the sedimentation tank 4 includes a sedimentation tank body 41 and a sodium hydroxide feeding device 42 connected to the sedimentation tank body 41 .

[0135] The sedimentation tank body 41 is the main body of the sedimentation tank 4, used to accommodate the reaction liquid and perform the precipitation process. A sodium hydroxide feeding device 42 is connected to the sedimentation tank body 41 and is used to add sodium hydroxide to the sedimentation tank 4. The role of sodium hydroxide is to adjust the pH value of the liquid in the sedimentation tank 4 to achieve a suitable alkaline condition, thereby promoting the precipitation of trivalent chromium. The main function of the sodium hydroxide feeding device 42 is to add sodium hydroxide to the sedimentation tank 4 to adjust the pH value of the liquid to a suitable alkaline condition.

[0136] In some embodiments, a pH meter 7 is provided in both the reaction tank 2 and the sedimentation tank 4;

[0137] Furthermore, pH sensors are provided in both the reaction tank 2 and the sedimentation tank 4 .

[0138] The above is used to monitor the pH value in the reaction tank 2 and the sedimentation tank 4 in real time. The pH meter 7 generally includes an electrode and a signal conversion module, which can convert the acidity or alkalinity of the liquid into an electrical signal.

[0139] In addition, a pH sensor can be used to directly measure the pH value of the liquid. pH sensors can be of various types, such as glass electrodes, composite electrodes, or optical sensors. The primary function of the pH monitoring device is to monitor the pH values in the reaction tank 2 and sedimentation tank 4 in real time to ensure they are within the appropriate range. The pH monitoring device can be integrated with an automated control system to automatically adjust the pH based on the real-time pH values, achieving automated operation.

[0140] refer to Figure 4 In some embodiments, the delivery pipeline 5 includes a water inlet pipe 51 and a water outlet pipe 52 provided at both ends of the water delivery pump 6;

[0141] The water inlet pipe 51 is provided with a flow meter 511 and an input pressure gauge 512;

[0142] The water outlet pipe 52 is provided with an output pressure gauge 521 and a water outlet valve 522 .

[0143] refer to Figure 5 In an embodiment of the present application, a method for treating hexavalent chromium-containing wastewater is provided, comprising:

[0144] In step S1 , the hexavalent chromium-containing wastewater is input into the regulating tank 1 and the pH is adjusted to an acidic state using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater, which is then pumped into the reaction tank 2 .

[0145] In this step, hexavalent chromium-containing wastewater is fed into regulating tank 1, where its pH is adjusted to an acidic state using an acidic solvent, producing acidic hexavalent chromium-containing wastewater. Acidic conditions are beneficial for the subsequent photoreduction reaction, as the photoreducing agent exhibits higher activity in an acidic environment, enabling more efficient reduction of hexavalent chromium. The conditioned acidic wastewater is then transferred to reaction tank 2, where it is prepared for the photoreduction reaction.

[0146] In step S2, a photoreducing agent is added to the reaction tank 2 via the photoreaction device 21, and after mixing, a mixed solution is obtained. The photoreducing agent is added in an amount of 5 to 600 g per liter of acidic hexavalent chromium-containing wastewater. For example, the amount of photoreducing agent added can be 5 g, 10 g, 50 g, 80 g, 100 g, 200 g, 300 g, 400 g, 500 g, 520 g, 530 g, 550 g, 580 g, 600 g, and so on per liter of acidic hexavalent chromium-containing wastewater.

[0147] A photoreducing agent is added to the reaction tank 2 via the photoreaction device 21 and mixed with the acidic hexavalent chromium-containing wastewater to produce a mixed solution. The photoreducing agent is a key substance in the photoreduction reaction, capable of reducing hexavalent chromium to trivalent chromium under light conditions. The hexavalent chromium in the mixed solution is fully in contact with the photoreducing agent, providing the necessary chemical conditions for the subsequent photoreduction reaction.

[0148] Step S3, performing a photoreduction reaction on the mixed solution using the photoreaction device 21 to obtain a reaction solution containing trivalent chromium, and pumping the reaction solution into the recovery tank 3;

[0149] As described above, the mixed solution undergoes a photoreduction reaction using the photoreaction device 21. By irradiating the mixed solution with an ultraviolet light source, hexavalent chromium is reduced to trivalent chromium, yielding a reaction solution containing trivalent chromium. The photoreduction reaction is the core step of the entire treatment process. Illumination excites the photoreducing agent, giving it reducing power, thereby reducing the highly toxic hexavalent chromium to less toxic trivalent chromium. Consequently, the hexavalent chromium in the reaction solution is reduced to trivalent chromium. The reaction solution is then transported to the recovery tank 3 for subsequent treatment.

[0150] Step S4, adding an inorganic strong electrolyte salt to the recovery tank 3, mixing and stratifying, recovering the upper phase to the reaction tank 2, and taking the target mixed phase of the lower phase, and pumping it into the sedimentation tank 4; wherein, the amount of the inorganic strong electrolyte salt added is: adding 100g~200g of the inorganic strong electrolyte salt per liter of the reaction solution; for example, the amount of the inorganic strong electrolyte salt added can be 100g, 120g, 140g, 160g, 180g, 200g, etc. per liter of the reaction solution.

[0151] As mentioned above, a strong inorganic electrolyte salt is added to the recovery tank 3 to mix and separate the reaction liquid into two phases. The target mixed phase is removed and pumped into the sedimentation tank 4. The addition of the strong inorganic electrolyte salt promotes the separation of trivalent chromium and the photoreducing agent in the reaction liquid, forming a two-phase system. The upper phase is the photoreducing agent phase, and the lower phase is the target mixed phase containing trivalent chromium.

[0152] Through the layered operation, the photoreducing agent can be recovered and recycled, and the target mixed phase is transported to the sedimentation tank 4 for further treatment.

[0153] Step S5: In the precipitation tank 4, sodium hydroxide is used to adjust the target mixed phase to an alkaline state, so that the trivalent chromium ions in the target mixed phase form a precipitate, and chromium hydroxide precipitate is obtained after separation.

[0154] As mentioned above, in the precipitation tank 4, sodium hydroxide is used to adjust the target mixed phase to an alkaline state, so that the trivalent chromium ions form chromium hydroxide precipitation. The alkaline state can be pH>9, and the preferred pH range can be 9.5~11. The specific reaction formula can be: Cr 3+ +3OH - →Cr(OH)3↓.

[0155] Through the separation process, chromium hydroxide precipitate is obtained. Alkaline conditions favor the precipitation of trivalent chromium ions. Chromium hydroxide is a water-insoluble solid precipitate that can be separated and recovered through filtration and other methods. The trivalent chromium is precipitated as chromium hydroxide, achieving chromium resource recovery and wastewater purification.

[0156] The hexavalent chromium-containing wastewater treatment method provided in this embodiment efficiently reduces hexavalent chromium to trivalent chromium through a photoreduction reaction, reduces wastewater toxicity, and simultaneously realizes the recycling of the photoreductant and the precipitation recovery of trivalent chromium in the form of chromium hydroxide, thereby reducing treatment costs and realizing resource recycling. The whole process avoids the use of a large number of chemical reagents, reduces the risk of secondary pollution, and meets environmental protection requirements. In addition, the method can be combined with an automated control system to realize the automated operation of wastewater treatment, improve treatment efficiency and stability, and provide an economical, efficient, and environmentally friendly solution for the treatment of hexavalent chromium-containing wastewater.

[0157] Furthermore, the photoreducing agent is polyethylene glycol.

[0158] Furthermore, the weight average molecular weight of the photoreducing agent is 1000 to 5000. For example, the weight average molecular weight can be 1000, 1200, 1500, 2000, 3000, 4000, 5000, etc.

[0159] Furthermore, the reaction time of the photoreduction reaction is 30 minutes to 40 minutes. For example, the reaction time can be 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, 40 minutes, etc.

[0160] Furthermore, the mixing conditions include: a stirring blade speed of 20 r / min to 25 r / min. For example, the blade speed can be 20 r / min, 21 r / min, 22 r / min, 23 r / min, 24 r / min, 25 r / min, etc.

[0161] In some embodiments, the acidic solvent is sulfuric acid;

[0162] Furthermore, the acidic state is pH <5.

[0163] Furthermore, the inorganic strong electrolyte salt is sodium sulfate.

[0164] The present invention is further described below by way of specific examples. However, it should be understood that these examples are merely provided for more detailed description and are not to be construed as limiting the present invention in any form.

[0165] Table 1. Process parameters in Examples 1-4

[0166]

[0167] In Table 1, the amount of photoreducing agent used is the amount of photoreducing agent added per liter of acidic hexavalent chromium-containing wastewater; the amount of inorganic strong electrolyte salt used is the amount of inorganic strong electrolyte salt added per liter of chromium-containing wastewater in the recovery tank 3.

[0168] Example 1

[0169] In this embodiment, wastewater containing hexavalent chromium is treated using the photoreduction treatment system 100. Industrial wastewater with a hexavalent chromium concentration of 30 mg / L is selected as the wastewater source for this method.

[0170] Experimental methods:

[0171] In step S1, the hexavalent chromium-containing wastewater is input into the regulating tank 1 and the pH is adjusted to 4 using sulfuric acid to obtain acidic hexavalent chromium-containing wastewater, which is then pumped into the reaction tank 2.

[0172] Step S2: adding 100 g of polyethylene glycol with a weight-average molecular weight of 5000 to each liter of the acidic hexavalent chromium-containing wastewater in the reaction tank 2 through the photoreaction device 21, and mixing the mixture to obtain a mixed solution.

[0173] Step S3, performing a photoreduction reaction on the mixed solution using the photoreaction device 21, with a blade speed of 20 r / min and a reaction time of 35 minutes to obtain a reaction solution containing trivalent chromium, and pumping the reaction solution into the recovery tank 3;

[0174] Step S4, adding 100g of sodium sulfate into the recovery tank 3, mixing and layering, taking out the target mixed phase, and pumping it into the sedimentation tank 4.

[0175] Step S5: In the precipitation tank 4, sodium hydroxide is used to adjust the target mixed phase to an alkaline state, so that the trivalent chromium ions in the target mixed phase form a precipitate, and chromium hydroxide precipitate is obtained after separation.

[0176] After testing, the hexavalent chromium reduction rate in the treated wastewater reached 98.0%.

[0177] Example 2

[0178] In this embodiment, the photoreduction treatment system 100 is used to treat wastewater containing hexavalent chromium.

[0179] Experimental methods:

[0180] The method in this embodiment is basically the same as that in Example 1, and the differences are shown in Table 1.

[0181] Example 3

[0182] In this embodiment, the photoreduction treatment system 100 is used to treat wastewater containing hexavalent chromium.

[0183] Experimental methods:

[0184] The method in this embodiment is basically the same as that in Example 1, and the differences are shown in Table 1.

[0185] Example 4

[0186] In this embodiment, the photoreduction treatment system 100 is used to treat wastewater containing hexavalent chromium.

[0187] Experimental methods:

[0188] The method in this embodiment is basically the same as that in Example 1, and the differences are shown in Table 1.

[0189] Test method:

[0190] Standard chemical analysis methods, such as the diphenylcarbazide spectrophotometric method (DPC method), are used to measure the hexavalent chromium concentration in the wastewater before and after treatment. By measuring the hexavalent chromium concentration in the wastewater before and after treatment, the hexavalent chromium reduction rate is calculated to evaluate the efficiency of the photoreduction treatment system 100. The method includes:

[0191] (1) Sampling: Take a sample from the wastewater before treatment and mark it as “initial sample”.

[0192] (2) Treatment: After the wastewater is treated by the photoreduction treatment system 100, another sample is taken and marked as "treated sample".

[0193] (3) Determination: The concentration of hexavalent chromium in the initial sample and the treated sample was determined using the DPC method.

[0194] (4) Calculation: Calculate the reduction rate of hexavalent chromium based on the measurement results. The formula is:

[0195] .

[0196] Test results:

[0197] Table 2. Experimental results corresponding to Examples 1-4

[0198]

[0199] Referring to the data in Table 2, the present method can significantly improve the reduction efficiency of hexavalent chromium.

[0200] Experimental results showed that Example 2 achieved the highest hexavalent chromium reduction rate (99.3%) under all conditions. The key conditions included: a pH of 2, a photoreducing agent dosage of 300 grams and a weight-average molecular weight of 1000, a stirring speed of 25 r / min, a reaction time of 40 minutes, and an inorganic strong electrolyte salt dosage of 150 grams. This combination of conditions demonstrates that a lower pH, a higher photoreducing agent dosage and lower weight-average molecular weight, a higher stirring speed, a longer reaction time, and an appropriate amount of inorganic strong electrolyte salt all contribute to improved hexavalent chromium reduction efficiency.

[0201] In addition, Example 4 also achieved a higher reduction rate (99.1%), and its conditions were similar to those of Example 2, but the pH value was slightly higher (2.5), the amount of photoreducing agent used was slightly lower (200 grams), the weight-average molecular weight was 2000, and the amount of inorganic strong electrolyte salt used was 200 grams.

[0202] This further illustrates that within a certain range, the adjustment of these parameters has a significant impact on the hexavalent chromium reduction rate, and there is a certain optimization range.

[0203] In summary, by reasonably adjusting the pH value, the amount and molecular weight of the photoreducing agent, the stirring speed, the reaction time and the amount of the inorganic strong electrolyte salt, the reduction efficiency of hexavalent chromium can be significantly improved, providing an important basis for the optimized operation of the photoreduction treatment system 100.

[0204] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photoreduction treatment system, characterized in that: The photoreduction treatment system includes a delivery pipeline and a water delivery pump, and a reaction tank, a recovery tank and a sedimentation tank connected in sequence based on the delivery pipeline and the water delivery pump; The reaction pool includes a pool body and a light reaction device connected to the pool body; wherein the pool body is a pool body made of a transparent material; The photoreaction device includes a reducing agent replenishing unit, a first stirring and mixing unit, and a light source unit, all of which are connected to the cell body; The reducing agent replenishing unit includes a reducing agent container and a reducing agent delivery pipe connected to the reducing agent container; the reducing agent delivery pipe is connected to the cell body and is used to input the light reducing agent in the reducing agent container into the cell body; The photoreaction device can add a photoreducing agent to the hexavalent chromium-containing wastewater, and reduce the hexavalent chromium in the hexavalent chromium-containing wastewater to trivalent chromium through a photoreduction reaction to obtain a reaction solution; The recovery tank and the sedimentation tank can receive the reaction liquid based on the delivery pipeline and the water delivery pump, and separate the trivalent chromium precipitate from the reaction liquid; The recovery tank includes a recovery body and a recovery pipeline connected to the recovery body; The other end of the recovery pipeline is connected to the reducing agent delivery pipe; The recovery body comprises an upper phase device, an interface interception device and a lower phase device connected in sequence from top to bottom; The upper phase device is connected to the reaction cell via the transport pipeline, and is also connected to the recovery pipeline and the electrolyte salt input pipeline; the upper phase device is a constriction structure, and a constriction port is provided at the lower end; The interface interception device is a columnar structure, the upper end of which is connected to the upper phase device through the constriction port, and the lower end is connected to the lower phase device; The lower phase device is connected to the sedimentation tank through the conveying pipeline.

2. The photoreduction processing system according to claim 1, wherein: The photoreduction treatment system further includes a regulating tank connected to the reaction tank via the delivery pipeline; The regulating tank is used to adjust the pH of the hexavalent chromium-containing wastewater to acidic hexavalent chromium-containing wastewater, and transport the acidic hexavalent chromium-containing wastewater to the reaction tank.

3. The photoreduction processing system according to claim 1, wherein: The first stirring and mixing unit includes a first paddle disposed at the bottom of the pool body, and a first motor disposed outside the pool body; a rotating shaft of the first motor is connected to the first paddle; and / or, The light source unit includes a tube sleeve disposed in the pool body, and a light source portion disposed in the tube sleeve; wherein the light source portion is selected from at least one of an ultraviolet light source, a visible light source, and a xenon light source.

4. The photoreduction processing system according to claim 1, wherein: The interface interception device includes a columnar body, and an upper interface control valve and a lower interface control valve respectively arranged at the upper and lower ends of the columnar body.

5. The photoreduction processing system according to claim 4, wherein: The interface interception device further includes an interface sensor; and / or, The columnar body of the interface interception device is made of transparent material; and / or, The cross-sectional area of the columnar body is smaller than the maximum cross-sectional area of the upper phase device.

6. The photoreduction processing system according to claim 1, wherein: The recycling body further includes a second stirring and mixing unit provided in the upper device; wherein the second stirring and mixing unit includes a second paddle provided in the upper device and a second motor provided outside the upper device; a rotating shaft of the second motor is connected to the second paddle; and / or, The sedimentation tank comprises a sedimentation tank body and a sodium hydroxide feeding device connected to the sedimentation tank body; and / or, The reaction tank and the sedimentation tank are both provided with a pH meter; and / or, The reaction tank and the sedimentation tank are both provided with pH sensors; and / or, The delivery pipeline includes a water inlet pipe and a water outlet pipe provided at both ends of the water delivery pump; and / or, The delivery pipeline includes a water inlet pipe and a water outlet pipe provided at both ends of the water delivery pump, and the water inlet pipe is provided with a flow meter and an input pressure gauge; and / or, The delivery pipeline includes a water inlet pipe and a water outlet pipe arranged at both ends of the water delivery pump, and the water outlet pipe is provided with an output pressure gauge and a water outlet valve.

7. A method for treating hexavalent chromium-containing wastewater based on the photoreduction treatment system according to any one of claims 1 to 6, characterized in that: include: The hexavalent chromium-containing wastewater is fed into a regulating tank and the pH is adjusted to an acidic state using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater, which is then pumped into a reaction tank; A photoreducing agent is added to the reaction tank through a photoreaction device, and after mixing, a mixed solution is obtained; wherein the amount of the photoreducing agent added is: 5g~600g of the photoreducing agent is added per liter of acidic hexavalent chromium-containing wastewater; Using the photoreaction device to perform a photoreduction reaction on the mixed solution to obtain a reaction solution containing trivalent chromium, and pumping the reaction solution into a recovery tank; An inorganic strong electrolyte salt is added to the recovery tank, mixed and separated, and the upper phase is recovered to the reaction tank, and the target mixed phase of the lower phase is removed and put into a sedimentation tank; wherein the amount of the inorganic strong electrolyte salt added is: 100g~200g of the inorganic strong electrolyte salt is added per liter of the reaction solution; In the precipitation tank, sodium hydroxide is used to adjust the target mixed phase to an alkaline state, so that the trivalent chromium ions in the target mixed phase form a precipitate, and chromium hydroxide precipitate is obtained after separation.

8. The method for treating hexavalent chromium-containing wastewater according to claim 7, wherein: The photoreducing agent is polyethylene glycol; and / or, The weight average molecular weight of the photoreducing agent is 1000-5000; and / or, The reaction time of the photoreduction reaction is 30 minutes to 40 minutes; and / or, The mixing conditions include: the stirring blade speed is 20 r / min to 25 r / min; and / or, The acidic solvent is sulfuric acid; and / or, The acidic state is pH < 5; and / or, The inorganic strong electrolyte salt is sodium sulfate.

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