Photo-reduction treatment system and treatment method of hexavalent chromium-containing wastewater

Abstract

The invention provides a photo-reduction treatment system and a treatment method of hexavalent chromium-containing wastewater, and relates to the technical field of sewage treatment. The photo-reduction treatment system comprises a conveying pipeline, a water conveying pump, and a reaction tank, a recovery tank and a sedimentation tank which are sequentially connected based on the conveying pipeline and the water conveying pump; and the reaction tank comprises a light reaction device. According to the photoreduction treatment system, hexavalent chromium is efficiently reduced through ultraviolet light and a photoreducing agent, toxicity is reduced, and secondary pollution is reduced. The method has the advantages of mild reaction conditions, low energy consumption and short treatment period. And the recovery tank and the sedimentation tank realize trivalent chromium recovery and light reducing agent cyclic utilization, so that the cost is reduced, and the resource utilization rate is improved. The system is simple and convenient to operate, high in automation degree, compact in equipment and suitable for large-scale wastewater treatment, and has remarkable 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, as 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, chemical industry and pigment production. The discharge of hexavalent chromium wastewater is becoming increasingly prominent. Due to its high water solubility and oxidizability, hexavalent chromium can exist stably in water bodies for a long time and pose a serious threat to the ecological environment and human health through bioaccumulation in the food chain. Relevant studies have shown that hexavalent chromium is highly carcinogenic, teratogenic and mutagenic. Long-term exposure may lead to skin inflammation, respiratory diseases, nervous system damage and other health problems. Therefore, how to efficiently and safely remove hexavalent chromium from wastewater has become a key issue that needs to be urgently solved in the field of environmental governance.

[0003] At present, the treatment technologies for hexavalent chromium wastewater mainly include chemical reduction precipitation, adsorption, electrochemical and biological treatment. Among them, although the adsorption method is easy to operate, the adsorbent is easily saturated and needs to be frequently regenerated and replaced, which undoubtedly increases the additional treatment cost; the electrochemical method has high requirements on the performance of electrode materials, and the electrode is prone to passivation during use, and the power consumption is large, which to a certain extent limits its wide application in large-scale wastewater treatment; although the biological treatment method has certain environmental friendliness, the treatment cycle is long, and microorganisms are more sensitive to changes in environmental conditions. In practical applications, it is often necessary to build a large-scale biological reaction system, which to a certain extent limits its promotion and application. The chemical reduction method is widely used in industrial wastewater treatment because of its relatively mature process and high removal efficiency. This method usually uses a reducing agent (such as sulfite, iron salt, sulfide, etc.) to reduce hexavalent chromium to low-toxic, insoluble trivalent chromium, and then removes it by 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, the high treatment cost, and the risk of secondary pollution. These problems have, to a certain extent, limited its promotion and application in large-scale industrial wastewater treatment.

[0004] In addition, the traditional technical processes commonly used in the treatment of hexavalent chromium wastewater in China mainly include processes such as adjustment, reaction, precipitation, coagulation precipitation, inclined plate precipitation, sludge thickening, and pressure filtration. Although this traditional treatment process can achieve the treatment of hexavalent chromium wastewater to a certain extent, there are many problems, such as high treatment costs, complex processes, long treatment cycles, large equipment floor areas, and large chemical consumption. These problems not only increase the treatment burden on enterprises but also affect the further development and optimization of hexavalent chromium wastewater treatment technology to a certain extent. Against the background of increasingly strict environmental governance requirements and continuously enhanced awareness of resource recycling, the challenges faced by traditional hexavalent chromium wastewater treatment technologies have become increasingly obvious. There is an urgent need to develop more efficient, economical, environmentally friendly, and easy-to-operate new treatment technologies to meet the growing wastewater treatment needs, achieve the 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 specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a photoreduction treatment system and a method for treating hexavalent chromium-containing wastewater. The photoreduction treatment system efficiently reduces hexavalent chromium through photoreduction reactions, reduces toxicity, and reduces secondary pollution. Using an ultraviolet light source and a photoreducing agent, the reaction conditions are mild, the treatment cycle is short, and the energy consumption is low. The recovery pool and the sedimentation pool achieve the separation and recovery of trivalent chromium and the recycling of the photoreducing agent, reducing costs and improving resource utilization rates. The system is easy to operate, has a high degree of automation, and the equipment is compact, suitable for large-scale wastewater treatment, with significant environmental and economic benefits.

[0007] In order to achieve the above object of the present invention, the following technical solutions are specifically adopted: In a first aspect, the present invention provides a photoreduction treatment system, which includes a delivery pipeline and a delivery pump, and a reaction tank, a recovery tank, and a sedimentation tank that are sequentially connected based on the delivery pipeline and the delivery pump; The reaction tank includes a photoreaction device; the photoreaction device can add a photoreducing agent to the hexavalent chromium-containing wastewater, and through a photoreduction reaction, reduce the hexavalent chromium in the hexavalent chromium-containing wastewater to trivalent chromium to obtain a reaction solution; The recovery tank and the sedimentation tank can receive the reaction solution based on the delivery pipeline and the pump, and separate the trivalent chromium precipitate from the reaction solution.

[0008] In an optional embodiment, the photoreduction treatment system further includes an adjustment tank connected to the reaction tank through the delivery pipeline; The adjustment 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.

[0009] In an alternative embodiment, the reaction tank includes a tank body and the photoreaction device connected to the tank body; wherein, the tank body is a tank body made of a transparent material; The photoreaction device includes a reducing agent supplement unit, a first stirring and mixing unit, and a light source unit, all of which are connected to the tank body.

[0010] In an alternative embodiment, the first stirring and mixing unit includes a first paddle provided at the bottom inside the tank body and a first motor provided outside the tank body; the rotating shaft of the first motor is connected to the first paddle.

[0011] In an alternative embodiment, the light source unit includes a tube sleeve provided in the tank body and a light source part provided in the tube sleeve. Wherein, the light source part is selected from at least one of an ultraviolet light source, a visible light source, and a xenon light source.

[0012] In an alternative embodiment, the reducing agent supplement 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 tank body for inputting the photoreducing agent in the reducing agent container into the tank body.

[0013] In an alternative embodiment, 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.

[0014] In an alternative 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; The upper phase device is connected to the reaction tank through the delivery pipeline, and the upper phase device is also connected to the recovery pipeline and an electrolyte salt input pipeline; the upper phase device is a constricted structure with a constricted port 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 constricted port, and the lower end is connected to the lower phase device; The lower phase device is connected to the sedimentation tank through the delivery pipeline.

[0015] In an alternative 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.

[0016] In an alternative embodiment, the interface interception device further includes an interface sensor; and / or, The columnar body of the interface interception device is made of a transparent material; and / or, The area of the cross-section of the columnar body is smaller than the area of the maximum cross-section of the upper-phase device.

[0017] In an alternative embodiment, a second stirring and mixing unit is further included in the recovery body and is disposed in the upper-phase device; Wherein, the second stirring and mixing unit includes a second paddle disposed inside the upper-phase device and a second motor disposed outside the upper-phase device; the rotating shaft of the second motor is connected to the second paddle.

[0018] In an alternative embodiment, the sedimentation tank includes a sedimentation tank body and a sodium hydroxide feeding device connected to the sedimentation tank body; and / or, pH meters are provided in both the reaction tank and the sedimentation tank; and / or, pH sensors are provided in both the reaction tank and the sedimentation tank; and / or, The conveying pipeline includes a water inlet pipe and a water outlet pipe disposed at both ends of the water pump; and / or, A flow meter and an input pressure gauge are provided on the water inlet pipe; and / or, An output pressure gauge and a water outlet valve are provided on the water outlet pipe.

[0019] In a second aspect, the present invention provides a method for treating hexavalent chromium-containing wastewater, including: Inputting the hexavalent chromium-containing wastewater into a regulation tank, adjusting the pH to an acidic state by using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater, and pumping it into a reaction tank; Adding a photoreducing agent to the reaction tank through a photoreaction device, and after mixing and treating, obtaining a mixed solution; wherein, the addition amount of the photoreducing agent is: adding 5 g to 600 g of the photoreducing agent per liter of acidic hexavalent chromium-containing wastewater; Performing a photoreduction reaction on the mixed solution by using the photoreaction device to obtain a reaction solution containing trivalent chromium, and pumping the reaction solution into a recovery tank; Adding an inorganic strong electrolyte salt to the recovery tank, after mixing and stratifying, recovering the upper phase to the reaction tank, and taking the target mixed phase of the lower phase and pumping it into a sedimentation tank; wherein, the addition amount of the inorganic strong electrolyte salt is: adding 100 g to 200 g of the inorganic strong electrolyte salt per liter of the reaction solution; In the sedimentation tank, using sodium hydroxide to adjust the target mixed phase to an alkaline state, so that trivalent chromium ions in the target mixed phase form a precipitate, and after separation, obtaining chromium hydroxide precipitate.

[0020] In an alternative embodiment, the photoreducing agent is polyethylene glycol; and / or, The weight-average molecular weight of the photoreducing agent is 1000 to 5000; and / or, The reaction time of the photoreduction reaction is 30 minutes to 40 minutes; and / or, The conditions of the mixing treatment include: the blade rotation speed of stirring 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.

[0021] The photoreduction treatment system provided by this application has significant beneficial effects. First, this system reduces hexavalent chromium to trivalent chromium through the photoreduction reaction, effectively reducing the toxicity of harmful heavy metals in the wastewater and reducing the environmental pollution risk. The use of the photoreducing agent and the cooperation of the ultraviolet light source make the reaction conditions mild and efficient, and the reduction of hexavalent chromium can be completed in a short time, greatly shortening the wastewater treatment cycle. In addition, the design of the recovery tank and the sedimentation tank in the system not only realizes the separation and recovery of trivalent chromium, but also can recycle the photoreducing agent, reducing the treatment cost and improving the resource utilization rate. The whole system is easy to operate, has a high degree of automation, reduces the complexity and labor intensity of manual operation, and at the same time the equipment structure is compact and the floor area is small, which is suitable for large-scale industrial wastewater treatment and has broad application prospects and popularization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a schematic diagram of the overall structure of the photoreduction treatment system in the embodiment of this application; Figure 2 It is a schematic diagram of the structure of the reaction tank in the photoreduction treatment system in the embodiment of this application; Figure 3 It is a schematic diagram of the structure of the recovery tank in the photoreduction treatment system in the embodiment of this application; Figure 4 It is a schematic diagram of the connection relationship and structure of the conveying pipeline and the water pump in the photoreduction treatment system in the embodiment of this application; Figure 5 It is a schematic diagram of the process flow of the treatment method of the wastewater containing hexavalent chromium in the embodiment of this application.

[0024] Description of 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 - tube sleeve; 2132 - light source part; 22 - tank body; 3 - recovery tank; 31 - recovery body; 311 - upper phase device; 3111 - electrolyte salt input pipeline; 3112 - constricted port; 312 - interface interception 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 - delivery pipeline; 51 - water inlet pipe; 511 - flowmeter; 512 - input pressure gauge; 52 - water outlet pipe; 521 - output pressure gauge; 522 - water outlet valve; 6 - water pump; 7 - pH meter. Detailed implementation manners

[0025] The implementation manners of the present invention will be described in detail below in conjunction with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0026] Reference Figure 1 In the embodiments of the present application, a photoreduction treatment system 100 is provided. The photoreduction treatment system 100 includes a delivery pipeline 5 and a water pump 6, and a reaction tank 2, a recovery tank 3, and a sedimentation tank 4 that are sequentially connected based on the delivery pipeline 5 and the water pump 6; 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 through a photoreduction reaction, reduce the hexavalent chromium in the hexavalent chromium-containing wastewater to trivalent chromium to obtain a reaction solution; The recovery tank 3 and the sedimentation tank 4 can receive the reaction solution based on the delivery pipeline 5 and the pump, and separate trivalent chromium precipitates from the reaction solution.

[0027] In this embodiment, a photoreduction treatment system 100 is provided. The core of the system lies in treating hexavalent chromium-containing wastewater through photoreduction technology to achieve the reduction of hexavalent chromium and the recovery of chromium resources. The photoreduction treatment system 100 mainly includes a conveying pipeline 5, a water pump 6, a reaction tank 2, a recovery tank 3, and a sedimentation tank 4. These components are sequentially connected through the conveying pipeline 5 and the water pump 6 to form a complete wastewater treatment process.

[0028] In the reaction tank 2, the photoreaction device 21 is the core part of the system. The photoreaction device 21 can add a photoreducing agent 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 photoreducing agent under light conditions to convert highly toxic and water-soluble hexavalent chromium into low-toxic and poorly soluble trivalent chromium, thereby reducing the pollution of the wastewater. After the photoreduction reaction, the hexavalent chromium in the wastewater is reduced to trivalent chromium, forming a reaction solution. The reaction solution contains components such as trivalent chromium ions and photoreducing agents, and further treatment is required to achieve resource recovery and wastewater purification.

[0029] The function of the recovery tank 3 is to receive the reaction solution generated in the reaction tank 2 and separate the trivalent chromium precipitate from it. The sedimentation tank 4 is used to receive the mixed-phase liquid containing trivalent chromium discharged from the recovery tank 3, and the trivalent chromium can be completely converted into chromium hydroxide precipitate by adjusting the pH value. The precipitated trivalent chromium can be recovered and utilized through methods such as filtration, realizing the recycling of chromium resources, while purifying the wastewater to meet the discharge standards.

[0030] The photoreduction reaction uses light energy as the driving force, with mild reaction conditions, low energy consumption, high efficiency, and can complete the reduction of hexavalent chromium in a short time; through the design of the recovery tank 3 and the sedimentation tank 4, the recycling of the photoreducing agent and the recovery of chromium resources are realized, reducing the treatment cost and improving the resource utilization rate; the photoreduction treatment process avoids the use of a large amount of chemical reagents, reduces the risk of secondary pollution, and meets the environmental protection requirements; the system realizes the automatic transportation and treatment of wastewater through the conveying pipeline 5 and the water pump 6, with simple operation and high automation degree, suitable for large-scale industrial wastewater treatment.

[0031] In summary, the photoreduction treatment system 100 provided in this embodiment efficiently treats hexavalent chromium-containing wastewater through photoreduction technology, achieving the reduction of hexavalent chromium, the recovery of chromium resources, and the purification of wastewater, with significant environmental and economic benefits.

[0032] In some embodiments, the photoreduction treatment system 100 further includes an adjustment tank 1 connected to the reaction tank 2 through the conveying pipeline 5; The adjustment 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.

[0033] The regulating tank 1 is an important component of the photoreduction treatment system 100. Its main function is to pre-treat the wastewater containing hexavalent chromium and adjust the pH value of the wastewater to make it reach the acidic condition suitable for the photoreduction reaction. The role of this pre-treatment step in the subsequent photoreduction reaction is that because the acidic environment can improve the reduction efficiency of hexavalent chromium and ensure the smooth progress of the reaction.

[0034] In the actual wastewater treatment process, the acidity and alkalinity of the wastewater may vary greatly due to different industrial production processes and discharge conditions. The regulating tank 1 adjusts the pH of the wastewater by adding acidic substances (such as sulfuric acid) to ensure that the wastewater entering the reaction tank 2 has a stable acidic environment. This pre-treatment not only improves the efficiency of the photoreduction reaction but also reduces the interference to the reaction process caused by the pH value fluctuation, thereby improving the stability and reliability of the entire system.

[0035] In addition to adjusting the pH value, the regulating tank 1 can also play other important roles. For example, it can serve as a buffer tank for the wastewater, balancing the flow rate and water quality of the wastewater and reducing the impact on the subsequent treatment units caused by the fluctuation of the wastewater discharge volume. In addition, the regulating tank 1 can also homogenize the water quality by mixing wastewater from different sources, further improving the effect of wastewater treatment.

[0036] Reference Figure 2 , in some embodiments, the reaction tank 2 includes a tank body 22 and the photoreaction device 21 connected to the tank body 22; wherein, the tank body 22 is a tank body 22 made of a transparent material; The photoreaction device 21 includes a reducing agent supplement unit 211, a first stirring and mixing unit 212, and a light source unit 213, all of which are connected to the tank body 22.

[0037] As described above, the reaction tank 2 mainly includes a tank body 22 and the photoreaction device 21 connected thereto. The tank body 22 provides a physical space for the reaction, while the photoreaction device 21 is the key component for realizing the photoreduction reaction.

[0038] The photoreaction device 21 is composed of a reducing agent supplement unit 211, a first stirring and mixing unit 212, and a light source unit 213. These components work together to ensure the efficient progress of the photoreduction reaction.

[0039] The reducing agent supplement unit 211 is responsible for adding a photoreducing agent to the reaction tank 2 to ensure a stable concentration of the photoreducing agent during the reaction process, providing the necessary chemical conditions for the reduction of hexavalent chromium; the first stirring and mixing unit 212 makes the photoreducing agent and the wastewater containing hexavalent chromium fully mixed through stirring, increasing the contact area between the reactants and improving 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 to reduce hexavalent chromium to trivalent chromium.

[0040] The pool body 22 is made of a transparent material. This design is conducive to the light emitted by the light source unit 213 evenly penetrating the reaction pool 2, ensuring that the wastewater in the entire reaction pool 2 can receive sufficient light, thereby improving the efficiency of the photoreduction reaction. The transparent material of the pool body 22 also facilitates observing the reaction process and promptly discovering and handling possible problems.

[0041] In some embodiments, the first stirring and mixing unit 212 includes a first paddle 2121 disposed at the inner bottom of the pool body 22, and a first motor 2122 disposed outside the pool body 22; the rotating shaft of the first motor 2122 is connected to the first paddle 2121.

[0042] The first paddle 2121 is located at the inner bottom of the reaction pool 2 and is used to stir the liquid in the reaction pool 2 to ensure that the photoreducing agent and the wastewater containing hexavalent chromium are fully mixed. The design and installation position of the paddle are crucial for improving the stirring efficiency and mixing uniformity.

[0043] The first motor 2122 is installed outside the reaction pool 2 to provide power for stirring. The selection of the motor needs to consider the power and rotation speed required for stirring to ensure the stirring effect. The rotating shaft of the first motor 2122 is mechanically connected to the first paddle 2121 through a rotating shaft to transmit the power of the motor to the paddle, enabling it to rotate and achieve the stirring function.

[0044] The main function of the first stirring and mixing unit 212 is to fully mix the photoreducing agent and the wastewater containing hexavalent chromium through stirring, increasing the contact area between the reactants, thereby improving the rate and efficiency of the photoreduction reaction. Stirring can not only accelerate the diffusion of the reactants but also prevent the concentration of the reactants from being too high or too low in a local area, ensuring the uniformity of the reaction.

[0045] In some embodiments, the light source unit 213 includes a tube sleeve 2131 disposed in the pool body 22, and a light source part 2132 disposed in the tube sleeve 2131; wherein, the light source part 2132 is selected from at least one of an ultraviolet light source, a visible light source, and a xenon light source.

[0046] The above-mentioned tube sleeve 2131 is disposed in the pool body 22 of the reaction pool 2 and is used to accommodate and protect the light source part 2132. The design of the tube sleeve 2131 needs to ensure that the light source part 2132 can stably emit light and the light can evenly irradiate the wastewater in the reaction pool 2.

[0047] The above-mentioned light source part 2132 is disposed in the tube sleeve 2131 and is the core part of the light source unit 213, responsible for emitting the light used for the photoreduction reaction. Among them, the light source part 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.

[0048] For example, an ultraviolet light source can be selected. This light source can play an important role in the photoreduction reaction, and its wavelength and energy can effectively excite the photoreducing agent and promote the reduction reaction of hexavalent chromium. The specific reaction process can be as follows: 。

[0049] Ultraviolet light has higher energy and can more effectively excite the photoreducing agent, thereby improving the reduction efficiency of hexavalent chromium. Compared with other types of light sources, ultraviolet light sources usually have higher photon energy and can complete the reduction reaction in a shorter time, reducing the treatment time and energy consumption. The combination of the ultraviolet light source and the transparent material of the cell body 22 can ensure that the light irradiates evenly on each part in the reaction cell 2, improving the uniformity of the reaction.

[0050] The cell body 22 is preferably made of a transparent material, which can ensure that the light emitted by the ultraviolet light source penetrates evenly through the entire reaction cell 2, enabling the photoreducing agent and the hexavalent chromium wastewater to come into full contact and improving the reaction efficiency. The transparent material facilitates the operator to observe the reaction process, promptly discover and handle possible problems, and ensure the smooth progress of the reaction. The transparent material can reduce the loss of light during propagation, improve the utilization rate of light energy, and further optimize the effect of the photoreduction reaction.

[0051] In some embodiments, the reducing agent supplement 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 cell body 22 and is used to input the photoreducing agent in the reducing agent container 2111 into the cell body 22.

[0052] The reducing agent container 2111 is used to store the photoreducing agent to ensure that there is enough photoreducing agent available for supplementation. The design of the container needs to consider the storage capacity, sealing performance, and connection method with the delivery system.

[0053] 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 transport the photoreducing agent from the container to the reaction cell 2. The delivery pipe needs to have good corrosion resistance and sealing performance to ensure that the photoreducing agent does not leak or become contaminated during transportation.

[0054] The main function of the reducing agent supplement unit 211 is to keep the addition of the photoreducing agent controllable, ensure the stable concentration of the photoreducing agent in the reaction cell 2, and thus ensure the efficient progress of the photoreduction reaction. The photoreducing agent will gradually be consumed during the reaction, so it is necessary to timely supplement the photoreducing agent through the reducing agent supplement unit 211 to maintain the continuous progress of the reaction.

[0055] Reference 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.

[0056] The above-mentioned recovery tank 3 is an important component in the photoreduction treatment system 100, and its main function is to separate trivalent chromium precipitate from the reaction solution and recover the photoreducing agent.

[0057] The recovery body 31 is used to hold the reaction solution and separate and recover the trivalent chromium precipitate. The recovery pipeline 32 is connected to the recovery body 31 and is used to transport the recovered photoreducing agent to the reducing agent replenishment unit 211. The other end of the recovery pipeline 32 is connected to the reducing agent delivery pipe 2112, forming a closed-loop system to realize the recycling of the photoreducing agent.

[0058] The main function of the recovery tank 3 is to separate trivalent chromium precipitate from the reaction solution and recover the photoreducing agent. According to the reduction principle adopted, its structure can have different choices. For example, in this embodiment, the extraction separation method can be used to recover the photoreducing agent. The separated photoreducing agent is transported to the reducing agent replenishment unit 211 through the recovery pipeline 32 and re-enters the reaction tank 2 for recycling. In addition, the remaining mixed phase containing trivalent chromium is transported to the sedimentation tank 4 through the delivery pipeline 5 for subsequent sedimentation treatment.

[0059] The photoreducing agent is recovered through the recovery pipeline 32 and re-transported to the reaction tank 2, realizing the recycling of the photoreducing agent and reducing the treatment cost. The design of the recovery tank 3 can effectively separate the trivalent chromium precipitate and the photoreducing agent, improving the efficiency of resource recovery. The recovery tank 3 is connected to the reaction tank 2 and the sedimentation tank 4 through the delivery pipeline 5, forming a complete treatment system and improving the operation efficiency and stability of the entire system.

[0060] 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 in sequence from top to bottom; The upper phase device 311 is connected to the reaction tank 2 through the delivery pipeline 5, and the upper phase device 311 is also connected with the recovery pipeline 32 and an electrolyte salt input pipeline 3111; the upper phase device 311 is a constricted structure with a constricted port 3112 at the lower end; The interface interception device 312 is a columnar structure, its upper end is connected to the upper phase device 311 through the constricted port 3112, and its lower end is connected to the lower phase device 313.

[0061] The lower phase device 313 is connected to the sedimentation tank 4 through the delivery pipeline 5.

[0062] As described above, the recovery tank 3 is a key component in the photoreduction treatment system 100 for separating and recovering reaction products. Through the upper-phase device 311, the interface interception device 312, and the lower-phase device 313, the recovery of the photoreducing agent and the extraction and collection of the trivalent chromium product after the reaction are realized.

[0063] The upper-phase device 311 is located at the top of the recovery tank 3 and is connected to the reaction tank 2 through a delivery pipeline 5 to receive the reaction solution transported from the reaction tank 2. The upper-phase device 311 is also connected with a recovery pipeline 32 and an electrolyte salt input pipeline 3111 for recovering the photoreducing agent and adjusting the properties of the reaction solution. Its structure is a constricted structure, and a constricted port 3112 is provided at the lower end, which helps to guide the liquid flow direction and the separation process.

[0064] The interface interception device 312 is located in the middle of the recovery tank 3 and is a columnar structure. Its upper end is connected to the upper-phase device 311 through the constricted port 3112, and its lower end is connected to the lower-phase device 313. The function of the interface interception device 312 is to stabilize the interface of the two-phase liquid, prevent emulsification or mixing of the mixed liquid during the separation process, and ensure the separation effect.

[0065] The lower-phase device 313 is located at the bottom of the recovery tank 3 and is connected to the sedimentation tank 4 through a delivery pipeline 5 to transport the separated mixed phase containing trivalent chromium to the sedimentation tank 4 for subsequent treatment.

[0066] The main function of the recovery tank 3 is to separate the trivalent chromium precipitate from the reaction solution and recover the photoreducing agent. The specific process can be as follows: The reaction solution enters the upper-phase device 311 of the recovery tank 3 from the reaction tank 2 through the delivery pipeline 5. In the recovery tank 3, by adding auxiliaries such as electrolyte salts (such as sodium sulfate), the separation of trivalent chromium and the photoreducing agent in the reaction solution is promoted to form a two-phase system. The upper layer is the photoreducing agent phase, and the lower layer is the mixed phase containing trivalent chromium. The photoreducing agent in the upper layer is transported to the reducing agent replenishment unit 211 through the recovery pipeline 32 and re-enters the reaction tank 2 for recycling. The mixed phase containing trivalent chromium in the lower layer is transported to the sedimentation tank 4 through the delivery pipeline 5 for subsequent sedimentation treatment.

[0067] 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 photoreducing agent and trivalent chromium can be ensured; the recovery tank 3 realizes the recovery and recycling of the photoreducing agent, reduces the treatment cost, and improves the resource utilization rate; the recovery tank 3 is connected to the reaction tank 2 and the sedimentation tank 4 through the delivery pipeline 5 to form a complete treatment system, improving the operation efficiency and stability of the entire system; the design of the constricted upper-phase device 311 and the columnar interface interception device 312 helps to optimize the liquid flow and separation process, reducing the floor area and energy consumption of the equipment.

[0068] In summary, based on the specific structure of the recovery tank 3, the separation mechanism of the photoreducing agent recovery and trivalent chromium precipitation in the photoreduction treatment system 100 is characterized. This design not only realizes the efficient recovery and recycling of the photoreducing agent, but also improves the overall operation efficiency and stability of the system, providing an important guarantee for the efficient treatment of hexavalent chromium-containing wastewater.

[0069] In some embodiments, the interface interception device 312 includes a columnar body 3121, and an upper interface control valve 3122 and a lower interface control valve 3123 respectively arranged at the upper and lower ends of the columnar body 3121; Furthermore, the interface interception device 312 further includes an interface sensor 3124; Furthermore, the columnar body 3121 of the interface interception device 312 is made of a transparent material.

[0070] As described 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.

[0071] The columnar body 3121, as the main structure of the interface interception device 312, is used to accommodate the liquid and provide a stable separation environment. The design of the columnar body 3121 helps to optimize the liquid flow and separation process.

[0072] The upper interface control valve 3122 and the lower interface control valve 3123 are respectively arranged at the upper and lower ends of the columnar body 3121. The main functions of these two control valves are to regulate the liquid flow and ensure a stable interface of the two-phase liquid during the separation process. By precisely controlling the opening and closing of the valves, the mixing of the two-phase liquid can be effectively prevented, and the separation efficiency can be improved.

[0073] In addition, the interface sensor 3124 is an optional configuration of the interface interception device 312, which is used to monitor the interface position of the two-phase liquid in real time. Through the interface sensor 3124, precise control of the interface position can be achieved, further optimizing the separation process. The interface sensor 3124 can be combined 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 according to the interface position, realizing automated operation.

[0074] The main function of the interface interception device 312 is to stabilize the interface of the two-phase liquid and ensure the effective separation of the photoreducing agent and the trivalent chromium-containing mixed phase. For example, the specific process can include the following: (1) Keep the upper interface control valve 3122 open and the lower interface control valve 3123 closed.

[0075] (2) Transfer the reaction solution from the reaction tank 2 to the upper-phase device 311 of the recovery tank 3 through the delivery pipeline 5. In the upper-phase device 311, by adding auxiliary agents such as electrolyte salts (such as sodium sulfate), promote the separation of trivalent chromium in the reaction solution from the photoreducing agent, forming a two-phase system (during this period, appropriate stirring and mixing can be carried out on the premise of avoiding emulsification, sufficient extraction, and enabling the partial mixed solution intercepted in the columnar body 3121 to be fully mixed with the reaction solution). After stratification, the upper layer is the photoreducing agent phase, and the lower layer is the mixed phase containing trivalent chromium.

[0076] (3) Slowly open the lower-interface control valve 3123 of the interface interception device 312 to make the stratification interface in the stratified reaction solution reach the columnar body 3121, and close the upper-interface control valve 3122 and the lower-interface control valve 3123 to make the stratification interface in the columnar body 3121 between the upper-interface control valve 3122 and the lower-interface control valve 3123.

[0077] (4) Control the upper part in the upper-phase device 311, that is, the photoreducing agent part, and transport it to the photoreducing agent replenishment unit 211 through the recovery pipeline 32 and re-enter the reaction tank 2 for recycling.

[0078] (5) Control the lower part in the lower-phase device 313, that is, the mixed phase containing trivalent chromium, and transport it to the sedimentation tank 4 through the delivery pipeline 5 for subsequent sedimentation treatment.

[0079] (6) Charge the next batch of reaction solution into the upper-phase device 311, and open the upper-interface control valve 3122 to enable the mixed liquid therein to contact and mix with the reaction solution, and re-execute the steps of step (1).

[0080] 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 interception device 312 can stably intercept the stratification interface of the two-phase liquid. During separation, impurities can be avoided in the upper and lower phases, improving the separation efficiency and purity, and at the same time preventing the part that causes emulsification or mixing from entering the upper or lower phase.

[0081] The design of the columnar body 3121 helps to optimize the liquid flow, reduce the turbulence and disturbance of the liquid during the separation process, and further improve the separation efficiency. The combination of the interface sensor 3124 and the automatic control system realizes the automatic operation of the interface interception device 312, reduces manual intervention, and improves the operation efficiency and stability of the system.

[0082] Through the synergistic effect of the interface control valve and the interface sensor 3124, the interface interception device 312 can stabilize the interface of the two-phase liquid, significantly improving the separation efficiency. The combination of the interface sensor 3124 and the automated control system enables the automated operation of the interface interception device 312, reducing manual intervention and enhancing the operation efficiency and stability of the system. The columnar body 3121 is made of a transparent material, facilitating the operator to observe the separation process, promptly detect and handle possible problems, and ensure the separation effect. The design of the columnar body 3121 helps optimize the liquid flow, reduce the floor area and energy consumption of the equipment, and improve the overall performance of the system.

[0083] In summary, in this embodiment, the key mechanism for separating the two-phase liquid in the photoreduction treatment system 100 is provided. This design not only improves the separation efficiency but also reduces manual intervention through automated control, enhancing the operation efficiency and stability of the system, providing an important guarantee for the efficient treatment of hexavalent chromium-containing wastewater.

[0084] Furthermore, the cross-sectional area of the columnar body 3121 is smaller than the maximum cross-sectional area of the upper-phase device 311.

[0085] In the recovery tank 3, the reaction liquid forms two-phase liquid after separation, namely the upper-layer photoreducing agent phase and the lower-layer trivalent chromium-containing mixed phase. 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 reaches and enters the columnar body 3121 through the constriction structure of the upper-phase device 311, 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, thus more precisely controlling the separation process of the two-phase liquid. In addition, the smaller stratification interface area helps reduce the mixing and emulsification phenomena of the two-phase liquid during the separation process. Due to the reduction of the interface area, the contact area between the two-phase liquids also decreases accordingly, making it easier for the two-phase liquids to separate and improving the separation efficiency.

[0086] If the cross-sectional area of the columnar body 3121 is too large, it may cause the stratification interface to not fully adapt to the shape of the columnar body 3121 in the horizontal direction, resulting in ineffective spaces at the edges of the columnar body 3121. These ineffective spaces may cause some liquids to not be effectively separated, resulting in volume loss. By reducing the cross-sectional area of the columnar body 3121, these ineffective 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 columnar body 3121 occupy a more compact space in the recovery tank 3, improving the space utilization rate of the entire recovery tank 3. This not only helps improve the separation efficiency but also reduces the overall volume of the equipment and the floor area occupied by the equipment.

[0087] 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, thereby more precisely controlling the separation process of the two-phase liquid, improving the separation efficiency, and avoiding volume loss. This design optimizes the function of the interface interception device 312, further enhancing the recovery of the photoreducing agent and the separation effect of trivalent chromium precipitation in the photoreduction treatment system 100.

[0088] In some embodiments, a second stirring and mixing unit 314 is further included in the recovery body 31 and is disposed in the upper-phase device 311; Furthermore, the second stirring and mixing unit 314 includes a second paddle 3141 disposed inside the upper-phase device 311 and a second motor 3142 disposed outside the upper-phase device 311; the rotating shaft of the second motor 3142 is connected to the second paddle 3141.

[0089] The second paddle 3141 is disposed inside the upper-phase device 311 for stirring the liquid. The design and installation position of the second paddle 3141 are crucial for improving the stirring efficiency and mixing uniformity. The second motor 3142 is disposed outside the upper-phase device 311 to provide power for stirring. The selection of the second motor 3142 needs to consider the power and rotational speed required for stirring to ensure the stirring effect. The rotating shaft connects the rotating shaft of the second motor 3142 and the second paddle 3141 through a mechanical connection to transmit the power of the motor to the paddle, enabling it to rotate and achieve the stirring function.

[0090] 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.

[0091] The sedimentation tank body 41 is the main part of the sedimentation tank 4 for accommodating the reaction liquid and carrying out the sedimentation process. The sodium hydroxide feeding device 42 is connected to the sedimentation tank body 41 for adding 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 reach 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 and adjust the pH value of the liquid to reach a suitable alkaline condition.

[0092] In some embodiments, pH meters 7 are provided in both the reaction tank 2 and the sedimentation tank 4; Furthermore, pH sensors are provided in both the reaction tank 2 and the sedimentation tank 4.

[0093] The above are used to monitor the pH values 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 and alkalinity of the liquid into an electrical signal.

[0094] In addition, a pH sensor can be employed to directly measure the pH value of the liquid. The pH sensor can be of various types, such as a glass electrode, a composite electrode, or an optical sensor, etc. The main function of the pH monitoring device is to monitor the pH values in the reaction tank 2 and the sedimentation tank 4 in real time to ensure that they are within an appropriate range. The pH monitoring device can be combined with an automated control system to automatically adjust the acidity and alkalinity according to the real-time monitored pH value, realizing automated operation.

[0095] Reference Figure 4 , in some embodiments, the conveying pipeline 5 includes a water inlet pipe 51 and a water outlet pipe 52 provided at both ends of the water pump 6; A flow meter 511 and an input pressure gauge 512 are provided on the water inlet pipe 51; An output pressure gauge 521 and a water outlet valve 522 are provided on the water outlet pipe 52.

[0096] Reference Figure 5 , in the embodiments of the present application, a method for treating hexavalent chromium-containing wastewater is provided, including: Step S1, input the hexavalent chromium-containing wastewater into the regulation tank 1, adjust the pH to an acidic state by using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater, and pump it into the reaction tank 2.

[0097] In this step, the hexavalent chromium-containing wastewater is input into the regulation tank 1, and the pH value of the wastewater is adjusted to an acidic state by using an acidic solvent to obtain acidic hexavalent chromium-containing wastewater. The acidic condition is beneficial to the subsequent photoreduction reaction because the photoreducing agent has higher activity in an acidic environment and can more effectively reduce hexavalent chromium. The adjusted acidic wastewater is conveyed to the reaction tank 2 to prepare for the photoreduction reaction.

[0098] Step S2, add a photoreducing agent into the reaction tank 2 through the photoreaction device 21, and after mixing treatment, obtain a mixed solution. Among them, the addition amount of the photoreducing agent is: 5 g to 600 g of the photoreducing agent is added to each liter of acidic hexavalent chromium-containing wastewater. For example, the addition amount 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 of the photoreducing agent per liter of acidic hexavalent chromium-containing wastewater, etc.

[0099] Add a photoreducing agent into the reaction tank 2 through the photoreaction device 21, mix it with the acidic hexavalent chromium-containing wastewater to obtain a mixed solution. The photoreducing agent is a key substance for the photoreduction reaction. It can reduce hexavalent chromium to trivalent chromium under light irradiation conditions. The hexavalent chromium and the photoreducing agent in the mixed solution are in full contact, providing the necessary chemical conditions for the subsequent photoreduction reaction.

[0100] Step S3: Use the photoreaction device 21 to perform photoreduction reaction on the mixed solution to obtain a reaction solution containing trivalent chromium, and pump the reaction solution into the recovery tank 3. As described above, use the photoreaction device 21 to perform photoreduction reaction on the mixed solution. By irradiating the mixed solution with an ultraviolet light source, hexavalent chromium is reduced to trivalent chromium, obtaining a reaction solution containing trivalent chromium. The photoreduction reaction is the core step of the entire treatment process. By irradiating light to excite the photoreducing agent, it is made to have reducing ability, thereby reducing highly toxic hexavalent chromium to low-toxicity trivalent chromium, so that the hexavalent chromium in the reaction solution is reduced to trivalent chromium, and the reaction solution is transported to the recovery tank 3 for subsequent treatment.

[0101] Step S4: Add an inorganic strong electrolyte salt to the recovery tank 3. After mixing and stratifying, recover the upper phase into the reaction tank 2, and take the target mixed phase of the lower phase and pump it into the sedimentation tank 4. Among them, the addition amount of the inorganic strong electrolyte salt is: add 100 g to 200 g of the inorganic strong electrolyte salt per liter of the reaction solution. For example, the addition amount of the inorganic strong electrolyte salt can be 100 g, 120 g, 140 g, 160 g, 180 g, 200 g, etc. per liter of the reaction solution.

[0102] As described above, add an inorganic strong electrolyte salt to the recovery tank 3 to make the reaction solution mix and stratify, obtaining a two-phase system. Take the target mixed phase of the lower phase and pump it into the sedimentation tank 4. The addition of the inorganic strong electrolyte salt can promote the separation of trivalent chromium in the reaction solution from the photoreducing agent, forming a two-phase system. The upper layer is the photoreducing agent phase, and the lower layer is the target mixed phase, which contains trivalent chromium.

[0103] Through the stratification operation, the photoreducing agent can be recovered and recycled, and the target mixed phase is transported to the sedimentation tank 4 for further treatment.

[0104] Step S5: In the sedimentation tank 4, use sodium hydroxide 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.

[0105] As described above, in the sedimentation tank 4, use sodium hydroxide to adjust the target mixed phase to an alkaline state, so that trivalent chromium ions form chromium hydroxide precipitate. Among them, 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 ↓.

[0106] Through the separation operation, chromium hydroxide precipitate is obtained. An alkaline condition is favorable for the precipitation of trivalent chromium ions. Chromium hydroxide is a solid precipitate insoluble in water and can be separated and recovered by methods such as filtration. The trivalent chromium precipitates in the form of chromium hydroxide, achieving the recovery of chromium resources and the purification of wastewater.

[0107] The method for treating hexavalent chromium-containing wastewater provided in this embodiment efficiently reduces hexavalent chromium to trivalent chromium through a photoreduction reaction, reducing the toxicity of the wastewater. At the same time, the photoreducing agent is recovered and utilized, and the trivalent chromium is precipitated and recovered in the form of chromium hydroxide, reducing the treatment cost and achieving resource recycling. The entire process avoids the use of a large amount of chemical reagents, reduces the risk of secondary pollution, and meets environmental protection requirements. In addition, this method can be combined with an automated control system to achieve automated operation of wastewater treatment, improving the treatment efficiency and stability, and providing an economical, efficient, and environmentally friendly solution for the treatment of hexavalent chromium-containing wastewater.

[0108] Further, the photoreducing agent is polyethylene glycol.

[0109] Further, the weight-average molecular weight of the photoreducing agent is 1000 - 5000. For example, the weight-average molecular weight can be 1000, 1200, 1500, 2000, 3000, 4000, 5000, etc.

[0110] Further, the reaction time of the photoreduction reaction is 30 minutes - 40 minutes. For example, the reaction time can be 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, 40 minutes, etc.

[0111] Further, the conditions for the mixed treatment include: the rotational speed of the stirring paddle is 20 r / min - 25 r / min. For example, the rotational speed of the paddle can be 20 r / min, 21 r / min, 22 r / min, 23 r / min, 24 r / min, 25 r / min, etc.

[0112] In some embodiments, the acidic solvent is sulfuric acid; Further, the acidic state is pH < 5.

[0113] Further, the inorganic strong electrolyte salt is sodium sulfate.

[0114] The present invention will be further illustrated below through specific examples. However, it should be understood that these examples are only for more detailed illustration and should not be construed as limiting the present invention in any form.

[0115] Table 1. Process parameters in Examples 1 - 4

[0116] In Table 1, the dosage of the photoreducing agent is the amount of the photoreducing agent added to the acidic hexavalent chromium-containing wastewater per liter; the dosage of the inorganic strong electrolyte salt is the amount of the inorganic strong electrolyte salt added to the chromium-containing wastewater in Recovery Pond 3 per liter.

[0117] Example 1 In this example, the photoreduction treatment system 100 is used to treat the hexavalent chromium-containing wastewater. An industrial wastewater with a hexavalent chromium concentration of 30 mg / L is selected as the wastewater source for this method.

[0118] Experimental method: Step S1, the hexavalent chromium-containing wastewater is input into Regulation Pond 1 and the pH is adjusted to 4 with sulfuric acid to obtain acidic hexavalent chromium-containing wastewater, which is then pumped into Reaction Pond 2.

[0119] Step S2, 100 g of polyethylene glycol with a weight average molecular weight of 5000 is added to each liter of the acidic hexavalent chromium-containing wastewater in Reaction Pond 2 through the photoreaction device 21. After mixing treatment, a mixed solution is obtained.

[0120] Step S3, the photoreaction device 21 is used to perform a photoreduction reaction on the mixed solution. The paddle speed is 20 r / min and the reaction time is 35 minutes to obtain a reaction solution containing trivalent chromium, and the reaction solution is pumped into Recovery Pond 3; Step S4, 100 g of sodium sulfate is added to Recovery Pond 3. After mixing and stratifying, the target mixed phase in the lower phase is taken and pumped into Sedimentation Pond 4.

[0121] Step S5, in Sedimentation Pond 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.

[0122] After detection, the reduction rate of hexavalent chromium in the treated wastewater reaches 98.0%.

[0123] Example 2 In this example, the photoreduction treatment system 100 is used to treat the hexavalent chromium-containing wastewater.

[0124] Experimental method: The method in this example is basically the same as that in Example 1, and the differences are shown in Table 1 for reference.

[0125] Example 3 In this example, the photoreduction treatment system 100 is used to treat the hexavalent chromium-containing wastewater.

[0126] Experimental method: The method in this example is basically the same as that in Example 1, and the differences are shown in Table 1 for reference.

[0127] Example 4 In this embodiment, a photoreduction treatment system 100 is used to treat wastewater containing hexavalent chromium.

[0128] Experimental method: The method in this embodiment is basically the same as that in Embodiment 1, and the differences are shown in Table 1.

[0129] Testing method: Standard chemical analysis methods, such as diphenylcarbazide spectrophotometry (DPC method), are used to measure the concentration of hexavalent chromium in the wastewater before and after treatment. By measuring the concentration of hexavalent chromium in the wastewater before and after treatment, the reduction rate of hexavalent chromium is calculated to evaluate the efficiency of the photoreduction treatment system 100. The method includes: (1) Sampling: Sampling from the wastewater before treatment and labeling it as the "initial sample".

[0130] (2) Treatment: After the wastewater is treated by the photoreduction treatment system 100, sampling again and labeling it as the "sample after treatment".

[0131] (3) Measurement: Use the DPC method to measure the concentration of hexavalent chromium in the initial sample and the sample after treatment.

[0132] (4) Calculation: Calculate the reduction rate of hexavalent chromium according to the measurement results. The formula is: .

[0133] Test results: Table 2. Experimental results corresponding to Embodiments 1-4

[0134] Referring to the data in Table 2, through this method, the reduction efficiency of hexavalent chromium can be significantly improved.

[0135] The experimental results show that Embodiment 2 achieved the highest reduction rate of hexavalent chromium (99.3%) under all conditions. The main conditions include: the pH value is adjusted to 2, the dosage of the photoreducing agent is 300 g and the weight-average molecular weight is 1000, the stirring speed is 25 r / min, the reaction time is 40 minutes, and the dosage of the inorganic strong electrolyte salt is 150 g. The combination of these conditions indicates that a lower pH value, a higher dosage of the photoreducing agent and a lower weight-average molecular weight, a higher stirring speed, a longer reaction time, and an appropriate dosage of the inorganic strong electrolyte salt are all beneficial to improving the reduction efficiency of hexavalent chromium.

[0136] In addition, Embodiment 4 also achieved a relatively high reduction rate (99.1%). Its conditions are similar to those of Embodiment 2, but the pH value is slightly higher (2.5), the dosage of the photoreducing agent is slightly lower (200 g), the weight-average molecular weight is 2000, and the dosage of the inorganic strong electrolyte salt is 200 g.

[0137] This further demonstrates that within a certain range, the adjustment of these parameters has a significant impact on the reduction rate of hexavalent chromium, and there is a certain optimization interval.

[0138] In summary, by reasonably adjusting the pH value, the dosage and molecular weight of the photoreducing agent, the stirring speed, the reaction time, and the dosage of inorganic strong electrolyte salts, the reduction efficiency of hexavalent chromium can be significantly improved, providing an important basis for the optimized operation of the photoreduction treatment system 100.

[0139] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions 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 comprises a delivery pipeline and a water delivery pump, and a reaction tank, a recovery tank and a sedimentation tank which are sequentially connected based on the delivery pipeline and the water delivery pump; The reaction pool 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; The recovery tank and the sedimentation tank can receive the reaction liquid based on the delivery pipeline and the pump, and separate the trivalent chromium precipitate from the reaction liquid.

2. The photoreduction processing system according to claim 1, characterized in that: The photoreduction treatment system also includes a regulating tank connected to the reaction tank through 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, characterized in that: The reaction pool comprises 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; 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.

4. The photoreduction processing system according to claim 3, characterized in that: 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; the rotating shaft of the first motor is connected to the first paddle; and / or, The light source unit comprises 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; and / or, The reducing agent replenishing unit comprises 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.

5. The photoreduction processing system according to claim 4, characterized in that: The recovery pool 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 through 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.

6. The photoreduction processing system according to claim 5, characterized in that: The interface interception device comprises 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.

7. The photoreduction processing system according to claim 6, characterized in that: The interface interception device further comprises 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.

8. The photoreduction processing system according to claim 5, characterized in that: The recycling body also includes a second stirring and mixing unit disposed in the upper device; wherein the second stirring and mixing unit includes a second paddle disposed in the upper device and a second motor disposed outside the upper device; the 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 water inlet pipe is provided with a flow meter and an input pressure gauge; and / or, The water outlet pipe is provided with an output pressure gauge and a water outlet valve.

9. A method for treating hexavalent chromium-containing wastewater, characterized in that: include: The hexavalent chromium-containing wastewater is input 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 photoreductant is added to the reaction pool through a photoreaction device, and after mixing, a mixed solution is obtained; wherein the amount of the photoreductant added is: 5g to 600g of the photoreductant 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 pool; Adding an inorganic strong electrolyte salt to the recovery tank, mixing and stratifying, recycling the upper phase to the reaction tank, and taking the target mixed phase of the lower phase, and pumping it into a precipitation tank; wherein the addition amount of the inorganic strong electrolyte salt is: adding 100g to 200g of the inorganic strong electrolyte salt 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 precipitation, and chromium hydroxide precipitation is obtained after separation.

10. The method for treating hexavalent chromium-containing wastewater according to claim 9, characterized in that: 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 ~ 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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