Fixed bed reactor for synchronously fixing cadmium in water body and capturing carbon dioxide

Abstract

The invention relates to the technical field of environmental engineering, and discloses a fixed bed reactor for synchronously fixing cadmium in a water body and capturing carbon dioxide. The reactor aims at solving the problems that in the prior art, water distribution and gas distribution are not uniform, a catalyst is prone to loss and blockage, the CO2 capture rate is low, and pollutants cannot be cooperatively treated. The reactor main body adopts a modular design and is sequentially integrated with a water distribution module, an exhaust assembly, a protective filtering assembly and a sectional type catalyst bed layer from top to bottom, a gas distribution module is arranged at the bottom of the reactor main body, and the reactor main body is matched with a multi-height sampling and tail gas collection circulating system. According to the method, efficient fixation of Cd < 2 + > and collaborative capture of CO2 are achieved, the concentration of Cd < 2 + > in effluent can be reduced to 0.01 mg / L or below, the system can continuously and stably run for 180 days or above, the comprehensive treatment cost is reduced by 30%-40%, and the method is suitable for collaborative resourceful treatment of various industrial cadmium-containing wastewater and carbon dioxide waste gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental engineering, and particularly relates to a fixed bed reactor for synchronously fixing cadmium and capturing carbon dioxide in a water body. BACKGROUND

[0002] Industrial activities, especially electroplating, non-ferrous metal smelting and battery manufacturing, discharge cadmium-containing wastewater, which poses a serious threat to the water environment. Cadmium, as a heavy metal with strong biological toxicity and accumulation, can be enriched through the food chain even at trace levels (such as more than 0.01 mg / L), causing irreversible damage to the human kidney, skeleton and nervous system. In response to this risk, the Surface Water Environmental Quality Standard (GB 3838-2002) of China sets a strict limit of not more than 0.005 mg / L for the cadmium content of centralized drinking water surface water sources. At the same time, a large amount of carbon dioxide (CO2) is discharged in the process of industrial production as a major greenhouse gas.

[0003] Currently, the treatment of cadmium-containing wastewater mainly relies on chemical precipitation and adsorption. Chemical precipitation forms Cd(OH)2 or CdS precipitate by adding alkali or sulfide, although the cost is low, but there is a large consumption of chemical agents, a large amount of cadmium-containing sludge needs to be safely disposed of, and the effluent quality is difficult to stabilize to meet the above strict standard, especially not suitable for deep purification of low concentration wastewater. Although the adsorption method is effective in specific scenarios, the commonly used activated carbon, zeolite and other adsorbents generally have limited adsorption capacity, poor selectivity for Cd 2+ (easily interfered by coexisting Ca 2+ , Mg 2+ and other cations), difficult regeneration and inability to co-treat gaseous pollutants.

[0004] Layered double hydroxides (LDHs) have been considered as an ideal material for synchronously fixing Cd 2+ and capturing CO2 (ultimately fixed in the form of stable cadmium carbonate) in recent years due to their unique layered structure, exchangeable interlayer anions and high selective complexing capacity for Cd 2+ . However, existing technologies are mostly limited to applying the material in powder form to laboratory-scale batch stirring experiments. If the powdered LDH is directly used in a fixed bed reactor that needs to be continuously operated, the following engineering problems will inevitably arise: 1) excessively high bed pressure drop and plugging: fine powder accumulation leads to a huge fluid resistance; 2) severe material loss: water flow erosion easily makes the fine powder penetrate the downstream filtration unit and be lost with the effluent, not only causing loss of active components, but also leading to secondary pollution; 3) low mass transfer efficiency: disordered accumulation of powder will lead to uneven gas-liquid distribution, forming dead zones, and making it difficult for Cd 2+CO2 cannot fully contact the active sites of the material, making it difficult to exert its synergistic fixation potential. On the other hand, the capture technology of CO2 in industrial exhaust gas (such as amine liquid absorption, membrane separation, etc.) has been relatively mature, but these technology systems run independently and are incompatible with heavy metal wastewater treatment processes, have the disadvantages of high energy consumption, complex process flow, large equipment investment, etc., and cannot achieve the goal of synergistic treatment of "waste treatment with waste".

[0005] Therefore, there is an urgent need in the art for a technical solution that can combine the excellent performance of LDH materials with the advantages of continuous flow reactor engineering. Although previous studies have confirmed the feasibility of CaAl-LDH simultaneous fixation of Cd 2+ and CO2 at the material level, so far there is still a lack of a reactor-level equipment designed specifically for this synergistic reaction that can achieve long-term stable and efficient operation. The existing technical blank is how to solve the bottleneck of the engineering application of powdered materials through innovative design of reactor internals and system integration, so as to realize the leap from "material science verification" to "equipment technology implementation". SUMMARY

[0006] Based on the above background technology, the present application aims to solve the key problems existing in the prior art, including: 1. The powdered hydrotalcite material has the engineering problems of easy clogging of the bed layer, easy loss of the material, and low mass transfer efficiency when applied in a continuous flow fixed bed reactor; 2. The existing heavy metal wastewater treatment technology and carbon dioxide capture technology are independent of each other, and cannot achieve the synergistic treatment and resource utilization of "waste treatment with waste" in an intensive device; 3. There is a lack of reactor equipment designed specifically for the simultaneous fixation of Cd 2+ and the capture of CO2 by hydrotalcite material, which can ensure efficient contact of gas, liquid and solid phases and long-term stable operation. In order to overcome the shortcomings of the prior art, the present application provides a fixed bed reactor for simultaneous fixation of cadmium in water and capture of carbon dioxide.

[0007] It comprises a water distribution module, a top exhaust assembly, a protective filtration assembly, a bed layer main body, a sampling module, a gas distribution module and a tail gas collection and circulation system. The water distribution module is arranged on the inside top of the reactor body and above the protective filtration assembly. The top exhaust assembly comprises an exhaust port arranged in the center of the top of the reactor body, a polytetrafluoroethylene gas-liquid separation membrane and a stainless steel one-way anti-backflow valve. The protective filtration assembly is arranged below the top exhaust assembly and above the bed layer main body of the reactor body, and is fixed by the annular clamping groove of the inner wall of the reactor body. The bed layer main body is divided into two layered structures along the direction of wastewater flow. Each bed layer is provided with a catalyst layer and a support layer from top to bottom. The sampling module is composed of multiple height sampling assemblies, and the gas distribution module is arranged at the bottom of the bed layer main body.

[0008] Preferably, the water distribution module comprises a ring-shaped porous pipe and an umbrella-shaped flow guide, both made of polytetrafluoroethylene, the ring-shaped porous pipe is arranged around the inner wall of the reactor body, with a pore diameter of 1-5 mm, and the ring-shaped porous pipe is provided with water outlets facing the umbrella-shaped flow guide.

[0009] Preferably, the umbrella-shaped flow guide is located directly above the ring-shaped porous pipe, with an inclination angle of 20-40°, and the gap between the edge of the umbrella-shaped flow guide and the ring-shaped porous pipe is ≤2 mm, the water distribution module comprises a plurality of 316L stainless steel support columns fixed to the inner wall of the reactor body, the support columns are uniformly distributed, with a diameter of 5-20 mm and a length of 10-15 cm, for resisting deviation caused by water flow impact.

[0010] Preferably, the top exhaust assembly comprises an exhaust port arranged at the top center of the reactor body, with an inner diameter of 10-15 mm, and the exhaust port is provided with a polytetrafluoroethylene gas-liquid separation membrane and a 316L stainless steel one-way anti-backflow valve, and the pore diameter of the polytetrafluoroethylene gas-liquid separation membrane is 0.22-0.45 μm, the protective filtration assembly is composed of a double-layer 316L stainless steel filter screen and a quartz sand cushion layer, the upper filter screen of the double-layer stainless steel filter screen is a 100-mesh stainless steel screen arranged on the upper part of the ring-shaped clamping groove, the middle cushion layer is composed of a 1-5 cm thick quartz sand cushion layer with a particle size of 2-5 mm, and the lower filter screen is a 20-mesh stainless steel screen provided with a stainless steel support rib with a diameter of 3-5 mm, which is uniformly distributed along the radial direction of the reactor body and is fully welded to the filter screen.

[0011] Preferably, the reactor body is provided with a reaction cavity, and a liquid redistributor is arranged between adjacent two bed layers, the support layer is composed of a 316L stainless steel filter screen and a stainless steel support rib, and the liquid redistributor is made of a polytetrafluoroethylene porous sieve plate with a pore diameter of 3-5 mm and an opening rate of 30%-50%.

[0012] Preferably, the catalyst layer is composed of a hydrotalcite-based porous ceramic filler with a height of 10-50 cm, the filler is loaded with hydrotalcite-based material in the pores of an α-alumina porous ceramic carrier by in-situ hydrothermal method, the pore diameter of the α-alumina porous ceramic carrier is 5-50 μm, the porosity is 40%-60%, and the particle size is 3-10 mm, the hydrothermal conditions are 100-200 ℃ for 1-50 h, then the carrier is taken out and washed with deionized water until the pH of the filtrate is neutral, and then dried at 60-80 ℃ for 2-12 h, and the loading amount of the hydrotalcite-based porous ceramic filler is 8%-20% m / m.

[0013] Preferably, the sampling module consists of a multi-height sampling component, including three independent sampling units. Each sampling unit consists of a PTFE sampling tube with an inner diameter of 3-5 mm, a PTFE shut-off valve, and a sampling bottle interface. The three sampling units are positioned as follows: the first group is located 5-10 cm above the top of the first bed catalyst layer; the second group is located 5-8 cm below the liquid redistributor between the two bed sections; and the third group is located 5-10 cm below the bottom of the second bed catalyst layer.

[0014] Preferably, the gas distribution module is located at the bottom of the main body of the bed and below the bottom support layer. The gas distribution module includes a spiral porous tube made of 316L stainless steel. The spiral porous tube extends spirally around the central axis of the reactor body, covering the entire cross-section of the reactor. The pore diameter is 0.5~5 mm, the spiral spacing is 3~15 cm, and the opening is only on the side facing the catalyst bed. The opening rate is 30%~50%. A 5μm precision filter and a pulse backflushing device are provided upstream of the gas distribution module.

[0015] Preferably, the exhaust gas collection and circulation system includes a 316L stainless steel exhaust gas delivery pipeline, a CO2 concentration sensor, a high-precision gas flow meter, a variable frequency air pump, a 316L stainless steel check valve, a gas buffer tank, and a PLC control system. One end of the exhaust gas delivery pipeline is connected to the top exhaust assembly, and the other end is connected to the gas distribution module via a three-way valve. When the CO2 concentration of the exhaust gas is higher than the threshold, the variable frequency air pump delivers the exhaust gas to the gas distribution module for recycling after the buffer tank stabilizes the pressure. When the concentration is lower than the threshold, it switches to a fresh gas source for replenishment.

[0016] Preferably, the following applications are included: 1. for treating cadmium-containing wastewater and simultaneously capturing carbon dioxide; 2. for co-treating industrial tail gas containing carbon dioxide and cadmium-containing wastewater; 3. for pretreatment or reaction devices for the production of cadmium carbonate; and the cadmium-containing wastewater needs to be pretreated to a suspended solids concentration ≤10 mg / L and a pH ≥4.0.

[0017] As can be seen from the above technical solution, the fixed-bed reactor provided by the present invention for simultaneously fixing cadmium in water and capturing carbon dioxide has the following beneficial effects compared with the prior art: 1. This fixed-bed reactor, used for simultaneously fixing cadmium in water and capturing carbon dioxide, can flexibly switch the treatment capacity for cadmium-containing wastewater from industries such as electroplating, non-ferrous metal smelting, and battery manufacturing by adjusting the amount of catalyst filling in the bed and the wastewater flow rate. It can also be adapted to low-concentration industrial exhaust gas emitted from thermal power plants and steel plants, or pure CO2 gas sources in laboratory settings. Through three-way valve switching and variable frequency gas pump pressure regulation, it can adapt to different CO2 inlet gas concentrations without modifying the main structure of the reactor. In addition, the inner diameter of the reactor can be designed in different specifications according to the site space, taking into account small-scale research and development, pilot-scale verification, and industrial-grade applications, thus solving the limitation of traditional reactors that are "adapted to a single operating condition".

[0018] 2. This fixed-bed reactor, used for simultaneously fixing cadmium in water and capturing carbon dioxide, ensures long-term continuous operation through multi-dimensional structural protection and material adaptation design. Firstly, the catalyst uses an α-alumina porous ceramic carrier, loaded with hydrotalcite via an in-situ hydrothermal method. The granular structure prevents powder loss, and the carrier's resistance to acid and alkali corrosion ensures a catalyst lifespan of ≥6 months. Secondly, a bottom aeration module is connected in series with a 5μm precision filter and a pulse backflushing device, combined with a spiral porous tube with oblique openings, significantly reducing the clogging rate of the aeration holes and extending the maintenance cycle compared to traditional bottom aeration modules. Thirdly, the protective filter components intercept residual suspended solids after pretreatment, preventing clogging of the bed pores and aeration holes. The addition of multi-height sampling modules for real-time monitoring allows for timely adjustment of operating parameters, enabling the reactor to operate continuously and stably for over 180 days.

[0019] 3. This fixed-bed reactor, used for simultaneously fixing cadmium in water and capturing carbon dioxide, achieves a dual improvement in environmental and economic benefits through its integrated design of "simultaneous water and gas treatment." Economically, it eliminates the need for a separate CO2 capture device, and the exhaust gas recirculation system increases CO2 utilization, reducing the amount of fresh CO2 required (or the cost of industrial exhaust gas treatment). The overall treatment cost is lower than the traditional solution of "separate wastewater treatment + separate CO2 capture." Simultaneously, the extended maintenance cycle and enhanced continuous operation capability further reduce labor and consumable replacement costs. Environmentally, the exhaust gas emission concentration is ≤30%~40% of the initial inlet CO2 concentration, achieving both cadmium-containing wastewater treatment and contributing to greenhouse gas emission reduction for industrial enterprises.

[0020] 4. This fixed-bed reactor, used for simultaneous fixation of cadmium in water and capture of carbon dioxide, achieves Cd filtration and carbon dioxide removal through "gas-liquid-solid three-phase flow field optimization + catalyst functional adaptation". 2+ Highly efficient synergistic removal with CO2, targeting cadmium-containing wastewater (initial Cd). 2+ (Concentration 1~200 mg / L), after a two-stage bed catalytic reaction, the effluent Cd 2+ Concentration stable ≤0.01 mg / L, Cd 2+With a fixation rate of ≥90%, the reactor overcomes the limitations of traditional technologies in treating "single pollutants" and achieves a synergistic effect of "treating waste with waste and recycling resources". Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments of the present invention or the prior art will be briefly introduced and explained below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a three-dimensional structural diagram of a fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide, according to the present invention. Figure 2 This is a schematic cross-sectional view of a fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide, according to the present invention. Figure 3 This is a schematic diagram of a fixed-bed reactor filtration assembly for simultaneously fixing cadmium in water and capturing carbon dioxide, according to the present invention. Figure 4 This is a schematic diagram of the main structure of a fixed-bed reactor bed used for simultaneously fixing cadmium in water and capturing carbon dioxide, according to the present invention. Figure 5 The effects of hydrotalcite-based materials used in this invention on Cd under different pH conditions 2+ A schematic diagram showing the changes in adsorption capacity and removal rate; Figure 6 The effects of hydrotalcite-based materials used in this invention on Cd under different temperature conditions 2+ Adsorption capacity trend graph; Figure 7 The hydrotalcite-based multimaterials used in this invention are effective against Cd under various coexisting cation conditions. 2+ Comparison of selective adsorption and anti-interference performance; Figure 8 The hydrotalcite-based material used in this invention is effective against Cd under various coexisting anionic conditions. 2+ The adsorption stability test results are shown in the figure. Figure 9 A comparison of X-ray diffraction (XRD) spectra of different Ca / Al ratio hydrotalcite-based materials used in this invention before and after reaction in a CO2 atmosphere; Figure 10 This is a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDS) analysis of the hydrotalcite-based material used in this invention after the reaction.

[0023] AppendixFigure 1 -Appendix Figure 10 The correspondence between the components is as follows: 1. Reactor body; 2. Tail gas delivery pipeline; 3. Exhaust pipe; 4. Exhaust port; 5. Top cover; 6. Bottom support layer; 7. Umbrella-shaped guide plate; 8. Bed body; 9. Lower stainless steel mesh; 10. Quartz sand cushion layer; 11. Upper stainless steel mesh; 12. Annular porous tube; 13. Liquid redistributor; 14. Support ribs; 15. 100-mesh stainless steel filter screen; 16. Hydrotalcite-based porous ceramic packing; 17. 20-mesh stainless steel filter screen; 18. Spiral porous tube. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. In order to provide a clearer explanation and description of the technical solutions and implementation methods of the present invention, the following describes specific embodiments that implement the preferred technical solutions of the present invention.

[0025] Example 1: Please refer to Figures 1-4 A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide includes a water distribution module, a top exhaust assembly, a protective filter assembly, a bed body 8, a sampling module, a gas distribution module, and a tail gas collection and circulation system. The water distribution module is located on the top inner side of the reactor body 1, above the protective filter assembly. The top exhaust assembly includes an exhaust port 4 located at the center of the top of the reactor body 1, a polytetrafluoroethylene gas-liquid separation membrane, and a stainless steel one-way anti-backflow valve. The protective filter assembly is located below the top exhaust assembly and above the bed body of the reactor body 1, and is fixed by an annular groove on the inner wall of the reactor body 1. The bed body is divided into two layered structures along the wastewater flow direction. Each bed layer consists of a catalyst layer and a support layer arranged sequentially from top to bottom. The sampling module consists of multi-height sampling components. The gas distribution module is located at the bottom of the bed body.

[0026] In one embodiment of the present invention, the water distribution module includes an annular porous pipe 12 and an umbrella-shaped guide plate 7, both of which are made of polytetrafluoroethylene. The annular porous pipe 12 is arranged around the inner wall of the reactor body 1 across the entire cross section, and its pore diameter is 1~5mm. The annular porous pipe 12 has water outlet holes facing the umbrella-shaped guide plate 7.

[0027] In one embodiment of the present invention, the umbrella-shaped guide plate 7 is located directly above the annular porous pipe 12, with an inclination angle of 20°~40°, and the gap between the edge of the umbrella-shaped guide plate 7 and the annular porous pipe 12 is ≤2 mm. The water distribution module includes multiple 316L stainless steel support columns fixed on the inner wall of the reactor body 1. The support columns are evenly distributed, with a diameter of 5~20 mm and a length of 10~15 cm, and are used to resist the displacement caused by the impact of water flow.

[0028] In one embodiment of the present invention, the top exhaust assembly includes an exhaust port 4 located at the center of the top of the reactor body 1, with an inner diameter of 10-15 mm. The exhaust port 4 is equipped with a polytetrafluoroethylene gas-liquid separation membrane and a 316L stainless steel one-way anti-backflow valve. The pore size of the polytetrafluoroethylene gas-liquid separation membrane is 0.22-0.45 μm. The protective filter assembly consists of a double-layer 316L stainless steel filter screen and a quartz sand pad 10. The upper layer of the double-layer stainless steel filter screen is a 100-mesh stainless steel mesh 15, located on the upper part of the annular groove. The middle pad is composed of a quartz sand pad 10 with a particle size of 2-5 mm and a thickness of 1-5 cm. The lower layer of the filter screen is a 20-mesh stainless steel mesh 17. The bottom of the lower layer is provided with stainless steel support ribs 14 with a diameter of 3-5 mm, which are evenly distributed radially along the reactor body 1 and fully welded to the filter screen.

[0029] In one embodiment of the present invention, a reaction chamber is provided inside the bed body 8, and a liquid redistributor 13 is provided between two adjacent bed sections. The support layer is composed of a 316L stainless steel filter screen and stainless steel support ribs. The liquid redistributor 13 is made of polytetrafluoroethylene porous sieve plate with a pore diameter of 3~5 mm and an opening rate of 30%~50%.

[0030] In one embodiment of the present invention, the catalyst layer is composed of a hydrotalcite-based porous ceramic packing 16 with a height of 10-50 cm. The packing uses α-alumina porous ceramic as a carrier, and the hydrotalcite-based material is loaded into the pores of the carrier by an in-situ hydrothermal method. The pore size of the α-alumina porous ceramic carrier is 5-50 μm, the porosity is 40%-60%, the particle size is 3-10 mm, and the hydrothermal conditions are 100-200 °C for 1-50 h. After that, the packing is taken out and washed with deionized water until the pH of the filtrate is neutral, and then dried at 60-80 °C for 2-12 h. The loading of the hydrotalcite-based porous ceramic packing is 8%-20% m / m.

[0031] In one embodiment of the present invention, the sampling module is composed of a multi-height sampling component, including three independent sampling units. Each sampling unit consists of a PTFE sampling tube with an inner diameter of 3-5 mm, a PTFE shut-off valve, and a sampling bottle interface. The three sampling units are positioned as follows: the first group is located 5-10 cm above the top of the first bed catalyst layer; the second group is located 5-8 cm below the liquid redistributor between the two bed sections; and the third group is located 5-10 cm below the bottom of the second bed catalyst layer.

[0032] In one embodiment of the present invention, the gas distribution module is located at the bottom of the main body of the bed and below the bottom support layer 6. The gas distribution module includes a spiral porous tube 18, which is made of 316L stainless steel. The spiral porous tube 18 extends spirally around the central axis of the reactor body 1, covering the entire cross section of the reactor. The pore diameter is 0.5~5 mm, the spiral spacing is 3~15 cm, and the opening is only on the side facing the catalyst bed. The opening rate is 30%~50%. A 5 μm precision filter and a pulse backflushing device are provided upstream of the gas distribution module.

[0033] In one embodiment of the present invention, the exhaust gas collection and circulation system includes a 316L stainless steel exhaust gas delivery pipeline 2, a CO2 concentration sensor, a high-precision gas flow meter of 0.1~5 L / min, a variable frequency air pump of 0.12~0.20 MPa, a 316L stainless steel check valve, a gas buffer tank of 5~10 L, and a PLC control system. One end of the exhaust gas delivery pipeline 2 is connected to the top exhaust assembly, and the other end is connected to the gas distribution module via a three-way valve. When the CO2 concentration of the exhaust gas is higher than the threshold, the variable frequency air pump delivers the exhaust gas to the gas distribution module for recycling after the buffer tank is stabilized. When the concentration is lower than the threshold, it switches to a fresh gas source for replenishment.

[0034] In one embodiment of the present invention, the following applications are included: 1. for treating cadmium-containing wastewater and simultaneously capturing carbon dioxide; 2. for co-treating industrial tail gas containing carbon dioxide and cadmium-containing wastewater; 3. for a pretreatment or reaction device for producing cadmium carbonate; and the cadmium-containing wastewater needs to be pretreated to a suspended solids concentration ≤10 mg / L and a pH ≥4.0.

[0035] Example 2: This example aims to systematically evaluate the performance stability of the hydrotalcite-based material that constitutes the core function of the reactor described in Example 1 under different environmental conditions, and to provide a basis for optimizing the actual operating parameters of the reactor.

[0036] Test methods and conditions: To accurately evaluate the performance boundaries of the hydrotalcite-based material, a batch experiment with controlled variables was conducted. 250 mg of the hydrotalcite-based material was weighed and placed in a container containing 500 mL of Cd... 2+In a simulated wastewater reaction system with a concentration of 200 mg / L (prepared with cadmium nitrate), the initial pH value of the solution was adjusted (4.0, 5.0, 6.0, 7.0, 8.0, 9.0) and the reaction temperature was adjusted (15, 20, 25, 30, 35, 40, 45, 50 ℃) to investigate its effect on Cd. 2+ The effect of fixation.

[0037] Results and conclusions: Figure 5 and Figure 6 As shown, experimental data indicate that this hydrotalcite-based material exhibits good Cd efflorescence properties over a wide pH range from 4.0 to 9.0. 2+ The adsorption capacity remained at a high level, reaching 395-400 mg / g, corresponding to Cd 2+ The removal rate exceeded 99.5%, and the effluent concentration met stringent discharge standards. Regarding temperature adaptability, as the temperature increased from 15℃ to 50℃, the saturated adsorption capacity of the hydrotalcite-based material remained between 384 mg / g and 400 mg / g, with removal rates consistently above 95%. This indicates that the performance of the hydrotalcite-based material is minimally affected by temperature fluctuations and possesses good thermal stability. This embodiment demonstrates that the hydrotalcite-based material can maintain its Cd removal capacity under a wide range of pH and temperature conditions. 2+ Its high efficiency and stable fixation capability directly ensure that the fixed-bed reactor constructed with it can adapt to fluctuations in actual wastewater quality and temperature, exhibiting excellent operational reliability.

[0038] Example 3: This example aims to rigorously verify the performance of the fixed-bed reactor described in Example 1 (using its core hydrotalcite-based material as the test object) in treating simulated industrial wastewater containing multiple coexisting ions, particularly regarding Cd. 2+ Its selective fixing capability and anti-interference performance.

[0039] Test methods and conditions: Batch adsorption experiments were used to simulate the local reaction environment of the hydrotalcite-based material within the reactor. In Cd... 2+ In a solution with an initial constant concentration of 200 mg / L, high concentrations (200–10000 mg / L) of various competitive cations (K+) were introduced. + Na + Ca 2+ Mg 2+ Mn 2+ Ni 2+ Pb 2+ Cu 2+ Zn 2+ Fe 3+ Al 3+ ) or anion (Cl － NO3 －SO4 2－ PO4 3－ The effect of the hydrotalcite-based material on Cd was investigated under standard reaction conditions (25°C). 2+ The changes in adsorption capacity and removal rate.

[0040] Results and conclusions: Figure 7 and Figure 8 As shown, (1) resistance to interference from alkali metals and alkaline earth metals: coexisting ion is K + Na + Ca 2+ At that time, the effect of hydrotalcite-based materials on Cd 2+ The adsorption capacity and removal rate were not significantly different from those of the uninterrupted control group (change rate < 5%), demonstrating excellent resistance to background ion interference.

[0041] Competition for transition metals and heavy metals: When wastewater contains Mg 2+ Mn 2+ Ni 2+ Pb 2+ Cu 2+ Zn 2+ Fe 3+ Al 3+ At that time, competitive adsorption of varying degrees was observed, leading to different levels of adsorption of Cd. 2+ The adsorption capacity decreased by 10%-40% compared to the control group. This result also indicates that the hydrotalcite-based material has an affinity for a variety of heavy metal ions and can be extended to the synergistic remediation of water bodies polluted by complex heavy metals. (3) Stability to anions: except for high concentrations of Cl － Besides the possibility of forming complexes that could affect the fixation rate, NO3 － SO4 2－ PO4 3－ Common anions of Cd 2+ The removal effect is slightly affected (change rate < 8%).

[0042] This embodiment demonstrates that the core hydrotalcite-based material of the reactor is effective against Cd. 2+ It exhibits significant selective fixation advantages, particularly its ability to withstand high concentrations of alkali (earth) metals and common anions in real-world wastewater. Even in complex systems containing multiple competing heavy metals, it can effectively capture Cd. 2+ This provides crucial performance support for the reactor described in the claims to be able to stably treat "real industrial wastewater," clarifying its applicable water quality boundaries and competitive advantages.

[0043] Example 4: Verification of the Influence of Atmospheric Conditions and Material Structure-Property Relationships on the Synergistic Treatment Pathway. This example aims to explore and verify, from the perspectives of material synthesis and mechanism characterization, the effects of CO2 atmosphere on Cd.2+ The synergistic strengthening effect of the fixed process was investigated, and the influence of key synthesis parameters was examined.

[0044] Materials Preparation and Experimental Design: First, two hydrotalcite-based materials with different structural properties were prepared by controlling the hydrothermal synthesis conditions: the reactions were carried out at 100 ℃ and 120 ℃, respectively, using precursors with two Ca / Al molar ratios (8:3 and 2:1). Subsequently, using the above-mentioned different hydrotalcite-based materials, under strictly consistent batch experimental conditions, Cd-containing... 2+ A synergistic fixation experiment was conducted using simulated wastewater.

[0045] Characterization analysis and results: such as Figures 9-10 As shown, the phase and microstructure of the hydrotalcite-based material samples before and after the reaction were systematically characterized.

[0046] X-ray diffraction (XRD) analysis: Characteristic diffraction peaks of cadmium carbonate (CdCO3) were clearly visible in the XRD patterns of all samples reacted under a CO2 atmosphere. Notably, despite differences in hydrothermal temperature and Ca / Al ratio, CdCO3 formation was a common phenomenon, confirming the presence of a co-immobilization pathway (CdCO3). 2+ + CO3 2－ → CdCO3) is universally applicable to the aforementioned material series and does not change due to reasonable variations in the synthesis parameters. Subsequently, taking the 2:1 type hydrotalcite-based material prepared at 100 °C as an example, the hydrotalcite-based material after the reaction was analyzed by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS). High-resolution TEM images showed clear lattice fringes on the surface and within the pores of the hydrotalcite-based material after the reaction, which were identified as corresponding to the (110) and (104) crystal planes of CdCO3. The corresponding selected area electron diffraction pattern showed polycrystalline diffraction rings, which were further identified as the (110), (104), and (012) crystal planes of CdCO3. EDS surface scanning analysis showed that Cd, C, and O were uniformly distributed in the observation area. These results directly confirmed at the nanoscale the successful in-situ generation of high-purity, well-crystallized CdCO3.

[0047] This embodiment demonstrates, through a combination of controlled synthesis and multi-scale characterization, that Cd in the presence of CO2... 2+ The formation of stable CdCO3 crystals provides the core chemical basis for the efficient synergistic processing of this invention. Within the specified hydrothermal temperature range (100-120 °C) and Ca / Al ratio range (2:1~8:3), the prepared hydrotalcite-based materials effectively drive this synergistic pathway, demonstrating the good fault tolerance and repeatability of the synthesis process. This provides experimental support for the broad-range protection of the hydrotalcite-based materials in the claims.

[0048] This invention is not limited to the preferred embodiments described above. Anyone should understand that structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention. Finally, it should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of this application. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effects and objectives of this application, should still fall within the scope of the technical content disclosed in this application.

Claims

1. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide, comprising a water distribution module, a top exhaust assembly, a protective filter assembly, a bed body (8), a sampling module, an air distribution module, and a tail gas collection and circulation system, characterized in that: The water distribution module is located on the top of the inner side of the reactor body (1) and above the protective filter assembly. The top exhaust assembly includes an exhaust port (4) located in the center of the top of the reactor body (1), a polytetrafluoroethylene gas-liquid separation membrane, and a stainless steel one-way anti-backflow valve. The protective filter assembly is located below the top exhaust assembly of the reactor body (1) and above the bed body, and is fixed by an annular groove on the inner wall of the reactor body (1). The bed body is divided into two layered structures along the wastewater flow direction. Each bed layer is provided with a catalyst layer and a support layer from top to bottom. The sampling module consists of a multi-height sampling assembly. The gas distribution module is located at the bottom of the bed body.

2. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The water distribution module includes an annular porous pipe (12) and an umbrella-shaped guide plate (7), both of which are made of polytetrafluoroethylene. The annular porous pipe (12) is arranged around the inner wall of the reactor body (1) with a diameter of 1~5 mm. The annular porous pipe (12) has water outlet holes facing the umbrella-shaped guide plate (7).

3. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 2, characterized in that: The umbrella-shaped guide plate (7) is located directly above the annular porous pipe (12), with an inclination angle of 20°~40°, and the gap between the edge of the umbrella-shaped guide plate (7) and the annular porous pipe (12) is ≤2 mm. The water distribution module includes multiple 316L stainless steel support columns fixed on the inner wall of the reactor body (1). The support columns are evenly distributed, with a diameter of 5~20 mm and a length of 10~15 cm, to resist the displacement caused by water flow impact.

4. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The top exhaust assembly includes an exhaust port (4) located at the center of the top of the reactor body (1), with an inner diameter of 10-15 mm. The exhaust port (4) is equipped with a polytetrafluoroethylene gas-liquid separation membrane and a 316L stainless steel one-way anti-backflow valve. The pore size of the polytetrafluoroethylene gas-liquid separation membrane is 0.22-0.45 μm. The protective filter assembly consists of a double-layer 316L stainless steel filter screen and a quartz sand pad (10). The upper layer of the double-layer stainless steel filter screen is a 100-mesh stainless steel mesh (15) located on the upper part of the annular groove. The middle pad is composed of a quartz sand pad (10) with a particle size of 2-5 mm and a thickness of 1-5 cm. The lower layer of the filter screen is a 20-mesh stainless steel mesh (17). The bottom of the filter screen is equipped with stainless steel support ribs (14) with a diameter of 3-5 mm, which are evenly distributed radially along the reactor body (1) and fully welded to the filter screen.

5. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The bed body (8) is provided with a reaction chamber, and a liquid redistributor (13) is provided between two adjacent bed sections. The support layer is composed of a 316L stainless steel filter screen and stainless steel support ribs. The liquid redistributor (13) is made of polytetrafluoroethylene porous sieve plate with a pore diameter of 3~5 mm and an opening rate of 30%~50%.

6. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The catalyst layer is composed of hydrotalcite-based porous ceramic packing (16) with a height of 10-50 cm. The packing uses α-alumina porous ceramic as a carrier. The hydrotalcite-based material is loaded into the pores of the carrier by in-situ hydrothermal method. The pore size of the α-alumina porous ceramic carrier is 5-50 μm, the porosity is 40%-60%, the particle size is 3-10 mm, and the hydrothermal conditions are 100-200 ℃ for 1-50 h. Then, it is taken out and washed with deionized water until the pH of the filtrate is neutral, and dried at 60-80 ℃ for 2-12 h. The loading of the hydrotalcite-based porous ceramic packing is 8%-20% m / m.

7. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The sampling module consists of a multi-height sampling component, including three independent sampling units. Each sampling unit consists of a PTFE sampling tube with an inner diameter of 3-5 mm, a PTFE shut-off valve, and a sampling bottle interface. The three sampling units are positioned as follows: the first group is located 5-10 cm above the top of the first bed catalyst layer; the second group is located 5-8 cm below the liquid redistributor between the two bed sections; and the third group is located 5-10 cm below the bottom of the second bed catalyst layer.

8. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The gas distribution module is located at the bottom of the main body of the bed and below the bottom support layer (6). The gas distribution module includes a spiral porous tube (18) and is made of 316L stainless steel. The spiral porous tube (18) extends spirally around the central axis of the reactor body (1) and covers the entire cross section of the reactor. The pore diameter is 0.5~5 mm and the spiral spacing is 3~15 cm. The tube is only opened on the side facing the catalyst bed and the opening rate is 30%~50%. A 5μm precision filter and a pulse backflushing device are provided upstream of the gas distribution module.

9. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, characterized in that: The exhaust gas collection and circulation system includes a 316L stainless steel exhaust gas delivery pipeline (2), a CO2 concentration sensor, a high-precision gas flow meter (0.1~5 L / min), a variable frequency air pump (0.12~0.20MPa), a 316L stainless steel check valve, a gas buffer tank (5~10 L), and a PLC control system. One end of the exhaust gas delivery pipeline (2) is connected to the top exhaust assembly, and the other end is connected to the gas distribution module via a three-way valve. When the CO2 concentration of the exhaust gas is higher than the threshold, the variable frequency air pump delivers the exhaust gas to the gas distribution module for recycling after the buffer tank stabilizes the pressure. When the concentration is lower than the threshold, it switches to a fresh gas source for replenishment.

10. A fixed-bed reactor for simultaneously fixing cadmium in water and capturing carbon dioxide according to claim 1, comprising the following applications, characterized in that:

1. Used to treat cadmium-containing wastewater and simultaneously capture carbon dioxide; 2. Used for the co-treatment of industrial tail gas containing carbon dioxide and cadmium-containing wastewater; 3. Used as a pretreatment or reaction device for the production of cadmium carbonate; and the cadmium-containing wastewater must be pretreated to a suspended solids concentration ≤10 mg / L and a pH ≥4.0.

Images