A method and apparatus for treating heavy metal ion wastewater

Abstract

This invention provides a method and apparatus for treating heavy metal ion wastewater. By precisely controlling the pH value, this invention combines the advantages of chemical precipitation and adsorption methods, not only efficiently and maximally removing heavy metal ions from the wastewater to be treated, ensuring the treated water meets the discharge requirements of the "Electroplating Pollutant Discharge Standard," but also regenerating the adsorbent through the chelating effect of disodium ethylenediaminetetraacetate (EDTA). Simultaneously, the disodium EDTA is recycled, significantly reducing operating costs and aligning with the concepts of green environmental protection and resource recycling.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method and apparatus for treating heavy metal ion wastewater. Background Technology

[0002] Electroplating is currently the most widely used, most numerous, and most influential surface treatment technology in industrial manufacturing. Therefore, the electroplating industry also generates a large amount of wastewater, especially from Cu plating. 2+ Zn 2+ Wastewater containing heavy metal ions. Due to the high toxicity, non-degradability, and bioaccumulation of heavy metal ions, these ions in wastewater may pose a significant threat to human survival and health through bioaccumulation in the food chain.

[0003] Industrially, methods for removing heavy metal ions mainly include adsorption, chemical precipitation, ion exchange, membrane separation, and biological treatment. Among these, adsorption utilizes the specific surface area, pore structure, and surface active sites of adsorbent materials to bind with heavy metal ions, thus immobilizing them in wastewater and achieving removal. While adsorption is simple and convenient to operate, long-term use of the adsorbent can lead to a drastic decrease in adsorption capacity, resulting in increased operating costs and uncontrollable heavy metal recovery. Therefore, how to achieve effective heavy metal recovery while simultaneously enhancing the recycling of adsorbents and reducing operating costs is a problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a method and apparatus for treating heavy metal ion wastewater. Through the coordinated control of each step, it can not only efficiently remove heavy metal ions from wastewater, but also realize the recycling of adsorbent and regenerator of regenerated adsorbent, thereby reducing operating costs and saving resources.

[0005] This invention provides a method for treating heavy metal ion wastewater, comprising the following steps:

[0006] The pH value of the wastewater to be treated was adjusted to 8-9 for the first sedimentation treatment, resulting in the first supernatant and the first sludge.

[0007] The first sludge is subjected to a first solid-liquid separation treatment to obtain a second supernatant and a second sludge.

[0008] The first supernatant and the second supernatant were combined to obtain a mixture;

[0009] The pH of the mixture is adjusted to 4-6, and then it is mixed with the adsorbent for adsorption treatment to obtain treated water.

[0010] After the adsorbent is saturated, the saturated adsorbent is mixed with disodium ethylenediaminetetraacetate and the pH is adjusted to 6-8 for regeneration treatment to obtain regenerated adsorbent and regeneration solution. The regeneration conditions include: temperature of 40-55℃, ultrasonic power of 200-400 W, ultrasonic frequency of 30-50 kHz, and time of 50-70 min.

[0011] The pH of the regeneration solution was adjusted to 7-8 for a second precipitation treatment, resulting in a third supernatant and a third sludge.

[0012] The third sludge is subjected to a second solid-liquid separation treatment to obtain a fourth supernatant and a fourth sludge.

[0013] The second and fourth sludge ...

[0014] The third and fourth supernatants were combined to obtain regenerated disodium ethylenediaminetetraacetate.

[0015] In the treatment method described above, the adsorbent is a metal-organic framework-aerogel composite material.

[0016] In the treatment method described above, the metal-organic framework of the adsorbent is ZIF-8, the aerogel is a hydrophobically modified silica aerogel, and the aerogel contains functional groups, including amino, carboxyl and sulfonic acid groups.

[0017] In the treatment method described above, the adsorbent has a particle size of 0.5-10 mm and a specific surface area of ​​350-700 m². 2 / g, pore volume is 0.05-0.6 mL / g, and average pore size is 0.2-3 nm.

[0018] The treatment method described above includes the following conditions for the first precipitation treatment and the second precipitation treatment: a temperature of 10-35℃ and a time of 30-240 min.

[0019] The processing method described above includes the following conditions for the first solid-liquid separation treatment and the second solid-liquid separation treatment: temperature of 10-35℃, pressure of 0.6-1.6 MPa, and time of 30-240 min; or, temperature of 10-35℃, rotation speed of 1500-4000×g, and time of 0.1-10 min.

[0020] The treatment method described above includes the following conditions for adsorption treatment: temperature of 20-40℃ and time of 15-90 min.

[0021] In the treatment method described above, the amount of disodium ethylenediaminetetraacetate used is 35-65 wt% based on the mass of the saturated adsorbent.

[0022] The present invention provides an apparatus for implementing the above-described processing method, comprising a first precipitation device, a first solid-liquid separation device, an intermediate device, an adsorption device, a regeneration device, a second precipitation device, and a second solid-liquid separation device connected in sequence; the first precipitation device is also connected to the intermediate device, the regeneration device is also connected in reverse to the adsorption device, and the second precipitation device and the second solid-liquid separation device are also connected in reverse to the regeneration device.

[0023] The first precipitation device is used for the first precipitation treatment; the first solid-liquid separation device is used for the first solid-liquid separation treatment; the intermediate device is used to adjust the pH of the mixed liquid; the adsorption device is used for the adsorption treatment; the regeneration device is used for the regeneration treatment; the second precipitation device is used for the second precipitation treatment; and the second solid-liquid separation device is used for the second solid-liquid separation treatment.

[0024] In the apparatus described above, the first sedimentation device and the second sedimentation device are sedimentation tanks; the first solid-liquid separation device and the first solid-liquid separation device are selected from at least one of plate and frame filter press and centrifuge; the intermediate device is an intermediate tank; the adsorption device includes several parallel fixed bed adsorbers with a diameter of 15-35 cm and a height of 0.5-1.5 m; and the regeneration device is a reaction vessel.

[0025] This invention provides a method for treating heavy metal ion wastewater, which has the following advantages:

[0026] This invention combines the advantages of chemical precipitation and adsorption methods by precisely controlling the pH value. It not only efficiently and maximally removes heavy metal ions from the wastewater to be treated, enabling the treated water to meet the emission requirements of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008), but also regenerates the adsorbent through the chelating effect of disodium ethylenediaminetetraacetate. At the same time, disodium ethylenediaminetetraacetate is recycled, significantly reducing operating costs and conforming to the concepts of green environmental protection and resource recycling. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the heavy metal ion wastewater treatment method in Embodiment 1 of the present invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To achieve effective recovery and utilization of heavy metals while enhancing the recycling of adsorbents and reducing operating costs, the first aspect of this invention provides a method for treating heavy metal ion wastewater, comprising the following steps:

[0030] The pH value of the wastewater to be treated was adjusted to 8-9 for the first sedimentation treatment, resulting in the first supernatant and the first sludge.

[0031] The first sludge is subjected to a first solid-liquid separation treatment to obtain a second supernatant and a second sludge.

[0032] The first supernatant and the second supernatant were combined to obtain a mixture;

[0033] The pH of the mixture is adjusted to 4-6, and then it is mixed with the adsorbent for adsorption treatment to obtain treated water.

[0034] After the adsorbent is saturated, the saturated adsorbent is mixed with disodium ethylenediaminetetraacetate and the pH is adjusted to 6-8 for regeneration treatment to obtain regenerated adsorbent and regeneration solution. The regeneration conditions include: temperature of 40-55℃, ultrasonic power of 200-400 W, ultrasonic frequency of 30-50 kHz, and time of 50-70 min.

[0035] The pH of the regeneration solution was adjusted to 7-8 for a second precipitation treatment, resulting in a third supernatant and a third sludge.

[0036] The third sludge is subjected to a second solid-liquid separation treatment to obtain a fourth supernatant and a fourth sludge.

[0037] The second and fourth sludge ...

[0038] The third and fourth supernatants were combined to obtain regenerated disodium ethylenediaminetetraacetate.

[0039] Specifically, this invention first adjusts the pH of the wastewater to be treated to 8-9 for a first precipitation treatment, obtaining a first supernatant and a first sludge. Most heavy metal ions (e.g., Cu) in the wastewater are removed. 2+ Zn 2+ Cr 3+ Pb 2+ Fe 3+ Under alkaline conditions (pH 8-9), heavy metals will form hydroxide precipitates (e.g., Cu(OH)2, Zn(OH)2, Cr(OH)3, Pb(OH)2, Fe(OH)3, etc.), which are known as the first sludge. Therefore, the first precipitation treatment can remove most of the heavy metal ions in the wastewater, thereby reducing the load on subsequent adsorption treatments.

[0040] In the above steps, the first precipitation treatment can be carried out under stirring to improve precipitation efficiency.

[0041] In the above steps, a pH adjuster can be used to adjust the pH value, such as ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, sodium carbonate, ammonium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. Preferably, it can be sodium hydroxide or calcium oxide.

[0042] In the above steps, the pH adjuster can be slowly added under stirring until the pH meter in the wastewater to be treated reads 8-9. It is understood that the amount of pH adjuster added is determined by the pH value of the wastewater to be treated.

[0043] In the above steps, after the precipitation treatment is completed, if OH - Excessive concentration can cause premature precipitation of hydroxides. Flocculants can be added to help with precipitation. Preferably, the flocculant can be anionic polyacrylamide.

[0044] In practice, a power pump can be used to pump the wastewater to be treated into a sedimentation tank. A pH adjuster is slowly added under stirring until the pH meter shows 8-9. After a period of reaction, a flocculant is added to help the sedimentation. After settling, the first supernatant on the upper layer and the first sludge at the bottom are obtained.

[0045] Next, the present invention performs a first solid-liquid separation treatment on the first sludge to obtain a second supernatant and a second sludge. The solid-liquid separation treatment can completely separate the remaining solution and hydroxide precipitate in the first sludge to obtain recyclable heavy metal sludge, while the remaining solution is further processed to maximize the recovery of heavy metal ions.

[0046] In the above steps, the first solid-liquid separation treatment can be achieved by using a plate and frame filter press to filter the first sludge, or by using a centrifuge to centrifuge the first sludge.

[0047] Subsequently, the first and second supernatants are combined to obtain a mixed solution for centralized subsequent processing. This step improves processing efficiency and ensures that any residual heavy metal ions that have not been completely precipitated enter the subsequent adsorption process.

[0048] Next, the pH of the above mixture is adjusted to 4-6, and then mixed with the adsorbent for adsorption treatment to obtain treated water. The adsorbent usually has stronger adsorption activity under acidic to weakly acidic conditions (pH 4-6). At this time, the functional groups on the surface of the adsorbent are more likely to bind with heavy metal ions, so as to deeply remove heavy metal ions in the wastewater to be treated, so that the effluent (treated water) meets the standards.

[0049] In the above steps, a pH adjuster can be used to adjust the pH value, such as sulfuric acid, hydrochloric acid, or acetic acid. Preferably, it can be sulfuric acid.

[0050] The amount of adsorbent used can be determined by the volumetric flow rate of the wastewater to be treated, the total mass of heavy metal ions in the wastewater, and the residence time of the wastewater in the adsorbent. Specifically, the expression for the amount of adsorbent used is as follows: (W×Y×T) / (X×K); where W is the volumetric flow rate of the wastewater to be treated (i.e., the volumetric flow rate of water in the entire treatment method), Y is the total mass of heavy metal ions in a unit volume of mixed solution, T is the residence time of the mixed solution in the adsorbent, X is the saturated capacity of the adsorbent, and K is the margin coefficient. In this invention, the saturated capacity of the adsorbent is 50-200 mg / g, and the margin coefficient is 100%-200%.

[0051] After the adsorbent becomes saturated, the present invention mixes the saturated adsorbent with disodium ethylenediaminetetraacetate (EDTA-2Na) and adjusts the pH to 6-8 for regeneration, obtaining regenerated adsorbent and regeneration solution. Disodium ethylenediaminetetraacetate (EDTA-2Na) is a strong chelating agent; its amino and carboxyl groups can form stable chelates with heavy metal ions, and this chelating effect is strongest at pH 6-8. The stability of the resulting chelate is higher than the binding force between the adsorbent and heavy metal ions, thus desorbing heavy metal ions from the adsorbent, regenerating the adsorbent, and achieving the cyclic regeneration of the adsorbent. It also allows the enriched heavy metal ions to be transferred to the regeneration solution for subsequent recovery. Furthermore, adjusting the pH to 6-8 not only ensures that EDTA-2Na is in its optimal chelating state but also prevents the adsorbent structure from being damaged.

[0052] Through extensive experiments, this invention has found that the regeneration conditions include: a temperature of 40-55℃, an ultrasonic power of 200-400 W, an ultrasonic frequency of 30-50 kHz, and a time of 50-70 min. These conditions can effectively improve the recovery of heavy metal ions and enhance the adsorption capacity retention rate of the adsorbent.

[0053] Preferably, the temperature for the regeneration process can be 45-51°C.

[0054] In practice, the concentration of heavy metal ions in the treated water is monitored. When a breakthrough of the outlet concentration (i.e., Cu) is detected, the monitoring is initiated. 2+ Concentration > 0.5 mg / L, Zn 2+When the concentration is >0.5 mg / L, shut down the original fixed-bed adsorber and start the new fixed-bed adsorber to ensure continuous operation of the device. Next, start the automatic discharge system connected to the original fixed-bed adsorber to transfer the saturated adsorbent from the original adsorber to the regeneration reactor. The regeneration reactor contains EDTA-2Na solution. After adjusting the pH to 6-8, regeneration is performed at a controlled temperature of 40-55℃, with ultrasonic treatment (ultrasonic power 200-400 W, ultrasonic frequency 30-50 kHz) for 50-70 minutes. After regeneration, allow to stand and separate to obtain the regenerated adsorbent and regeneration solution. The automatic discharge system returns the regenerated adsorbent to the original fixed-bed adsorber, while the regeneration solution is used for subsequent processing.

[0055] Optionally, the concentration of the EDTA-2Na solution in the regeneration reactor is 0.05-0.15 mol / L, which can produce a good matching effect with the saturated adsorbent, thereby achieving a better regeneration effect.

[0056] In this invention, the adsorbent can be regenerated and recycled multiple times, and EDTA-2Na can also be recycled, which greatly reduces the cost of consumables. Furthermore, the heavy metal hydroxides generated throughout the process are effectively collected and recovered, turning waste into treasure and avoiding secondary pollution.

[0057] Next, the pH of the regeneration solution is adjusted to 7-8 for a second precipitation treatment, yielding a third supernatant and a third sludge. Under weakly alkaline conditions (pH 7-8), the chelation equilibrium between heavy metal ions and EDTA-2Na is disrupted, and the heavy metal ions reform as hydroxide precipitates (i.e., the third sludge), while EDTA-2Na exists in a free state in the third supernatant. This step achieves the separation of heavy metal ions from EDTA-2Na, facilitating the recovery of heavy metals and the recycling of EDTA-2Na.

[0058] Subsequently, the present invention performs a second solid-liquid separation treatment on the third sludge to obtain a fourth supernatant and a fourth sludge, so as to realize the recovery of the fourth sludge containing heavy metals while promoting the fourth supernatant containing EDTA-2Na to enter the recovery process.

[0059] In the above steps, the second solid-liquid separation treatment can be achieved by using a plate and frame filter press to filter the third sludge to achieve solid-liquid separation, or by using a centrifuge to centrifuge the third sludge to achieve solid-liquid separation.

[0060] Finally, by combining the second and fourth sludge, this invention yields recyclable heavy metal sludge. This recyclable heavy metal sludge can be sent to a qualified unit for metal recovery as a sludge product. Furthermore, by combining the third and fourth supernatants, this invention yields regenerated disodium ethylenediaminetetraacetate (EDTA). This regenerated disodium EDTA can be further used in the regeneration of the adsorbent. Preferably, the regenerated disodium EDTA and fresh disodium EDTA can be mixed before being added to the adsorbent regeneration process.

[0061] This invention combines the advantages of chemical precipitation and adsorption methods by precisely controlling the pH value. It not only efficiently and maximally removes heavy metal ions from the wastewater to be treated, enabling the treated water to meet the emission requirements of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008), but also regenerates the adsorbent through the chelation effect of EDTA-2Na. At the same time, EDTA-2Na is recycled, significantly reducing operating costs and conforming to the concept of green environmental protection and resource recycling.

[0062] In one specific embodiment, the present invention has found through extensive experiments that the metal-organic framework-aerogel composite material selected as the adsorbent is highly compatible with the treatment method of the present invention, which helps to improve the adsorption efficiency and the adsorbent recovery effect.

[0063] Metal-organic frameworks (MOFs) possess high specific surface area and regular porous structure, providing numerous adsorption sites for precisely capturing trace heavy metal ions remaining in wastewater after precipitation. Aerogels, with their three-dimensional network structure and high porosity, not only serve as excellent carriers for MOFs, preventing their aggregation, but also further increase the specific surface area of ​​the composite material, enhancing its adsorption capacity for heavy metal ions. The combined composite material significantly improves the adsorption efficiency and capacity for residual heavy metal ions in the mixed solution, ensuring that the treated water meets standards.

[0064] The physicochemical properties of the aforementioned metal-organic framework-aerogel composite material are well matched with the pH adjustment and other conditions in the treatment method: in an environment where the pH of the mixed solution is 4-6, the active sites on its surface are more likely to interact with heavy metal ions, thereby improving the adsorption selectivity for heavy metal ions and reducing the interference of other ions.

[0065] Furthermore, the metal-organic framework-aerogel composite exhibits excellent chemical stability, and its structure is not easily disrupted during regeneration treatment involving mixing with disodium ethylenediaminetetraacetate (EDTA-2Na) and adjusting the pH to 6-8. EDTA-2Na can form more stable chelates with heavy metal ions adsorbed on the material, desorbing them from the adsorbent and restoring its adsorption performance. This allows the adsorbent to be reused in adsorption treatment steps, significantly improving adsorbent utilization and reducing operating costs.

[0066] Because metal-organic framework-aerogel composites have a certain stability in adsorbing heavy metal ions, heavy metal ions can enter the regeneration solution relatively completely during the regeneration process. Subsequent steps such as pH adjustment for precipitation and solid-liquid separation can concentrate the heavy metals into the sludge, facilitating their recycling. At the same time, EDTA-2Na can also be recycled after regeneration, further improving resource utilization and reducing treatment costs.

[0067] Furthermore, in the above-mentioned adsorbent, the metal-organic framework is ZIF-8, the aerogel is a hydrophobically modified silica aerogel, and the aerogel contains functional groups, including amino, carboxyl and sulfonic acid groups.

[0068] The adsorbent has a particle size of 0.5-10 mm and a specific surface area of ​​350-700 m². 2 / g, pore volume is 0.05-0.6mL / g, and average pore size is 0.2-3 nm.

[0069] This ZIF-8 hydrophobically modified silica aerogel composite material exhibits synergistic adsorption effects from multiple functional groups (amino, carboxyl, and sulfonic acid groups), demonstrating high efficiency and broad-spectrum adsorption. Specifically, the beneficial effects are as follows: ZIF-8 is an ultra-high specific surface area material, ensuring that the composite material has sufficient space to accommodate a large number of adsorption sites; the three-dimensional network structure of the silica aerogel forms interconnected macropores and mesopores, enabling heavy metal ions in the wastewater to rapidly diffuse to the ZIF-8 particles and functional group surfaces, while preventing ZIF-8 aggregation and deactivation; simultaneously, the hydrophobically modified aerogel framework can significantly slow down the erosion of the ZIF-8 framework by water molecules, improving the service life of the composite material in complex wastewater environments and facilitating aerogel recycling; furthermore, the abundant functional groups allow it to adapt to different water quality conditions.

[0070] In specific operation, the adsorbent can be placed in the adsorption bed of the fixed bed adsorber. Preferably, adsorbent particles of different sizes can be mixed evenly so that the particle size and number are distributed in a power law manner before being filled into the adsorption bed of the fixed bed adsorber. This helps to improve pore connectivity and reduce adsorption resistance.

[0071] Furthermore, the diameter of the fixed-bed adsorber can be 15-35 cm, and the height can be 0.5-1.5 m. The adsorption bed of the fixed-bed adsorber is filled with 2-5 g of adsorbent.

[0072] Specifically, after adjusting the pH of the mixture to 4-6, the mixture can be evenly introduced into several of the aforementioned fixed-bed adsorbers using a flow distributor, allowing the mixture to mix with the adsorbent for adsorption treatment. The feed flow rate for a single fixed-bed adsorber can be 50-100 L / h.

[0073] In one specific embodiment, the conditions for the first precipitation treatment and the second precipitation treatment include: a temperature of 10-35°C and a time of 30-240 min.

[0074] The above temperature range promotes the forward precipitation reaction, improves the removal rate of heavy metal ions, avoids excessively slow reaction rates and incomplete precipitation at low temperatures, and avoids energy waste and side reactions caused by high temperatures. The above time range ensures complete precipitation, laying the foundation for the solid-liquid separation step.

[0075] The first and second precipitation treatments are crucial steps in heavy metal enrichment and EDTA-2Na regeneration. Appropriate temperature and time ensure that heavy metals precipitate into the sludge (second and fourth sludge) as hydroxides as possible. The combined sludge forms high-purity, recyclable heavy metal sludge, providing high-quality raw materials for subsequent heavy metal recovery and reducing resource waste. Simultaneously, these conditions ensure complete precipitation and separation of heavy metals, resulting in higher purity EDTA-2Na in the combined third and fourth supernatants. This EDTA-2Na can be directly recycled for adsorbent regeneration, preventing heavy metal contamination of the reagent and reducing adsorbent regeneration efficiency, further lowering operating costs.

[0076] In one specific embodiment, the conditions for the first solid-liquid separation treatment and the second solid-liquid separation treatment include: a temperature of 10-35℃, a pressure of 0.6-1.6 MPa, and a time of 30-240 min; or, a temperature of 10-35℃, a rotation speed of 1500-4000×g, and a time of 0.1-10 min.

[0077] If the first and second solid-liquid separation processes use plate and frame filter press technology, the temperature can be 10-35℃, the pressure can be 0.6-1.6 MPa, and the time can be 30-240 min, which can produce sludge in the form of sludge cake; if the first and second solid-liquid separation processes use centrifugal separation, the temperature can be 10-35℃, the rotation speed can be 1500-4000×g, and the time can be 0.1-10 min.

[0078] In one specific embodiment, the adsorption treatment conditions include: a temperature of 20-40°C and a time of 15-90 min.

[0079] Within the aforementioned temperature and time range, it helps to increase adsorption capacity without requiring additional energy consumption, and enables the adsorbent to maintain good stability.

[0080] In one specific embodiment, the amount of disodium ethylenediaminetetraacetate is 35-65 wt% based on the mass of the saturated adsorbent.

[0081] For example, in this invention, the adsorption capacity of the adsorbent for heavy metal ions is 100-200 mg / g, and the amount of disodium ethylenediaminetetraacetate required to regenerate 10 g of saturated adsorbent is 4 g; that is, based on the mass of the saturated adsorbent, the amount of disodium ethylenediaminetetraacetate is 40 wt%.

[0082] Based on the above research, a second aspect of the present invention provides an apparatus for implementing the above-described processing method, which can be specifically referred to... Figure 1 It includes a first precipitation device, a first solid-liquid separation device, an intermediate device, an adsorption device, a regeneration device, a second precipitation device, and a second solid-liquid separation device connected in sequence; the first precipitation device is also connected to the intermediate device, the regeneration device is also connected to the adsorption device in reverse, and the second precipitation device and the second solid-liquid separation device are also connected to the regeneration device in reverse.

[0083] The first precipitation device is used for the first precipitation treatment; the first solid-liquid separation device is used for the first solid-liquid separation treatment; the intermediate device is used to adjust the pH of the mixed liquid; the adsorption device is used for the adsorption treatment; the regeneration device is used for the regeneration treatment; the second precipitation device is used for the second precipitation treatment; and the second solid-liquid separation device is used for the second solid-liquid separation treatment.

[0084] Furthermore, the first sedimentation device and the second sedimentation device are sedimentation tanks; the first solid-liquid separation device and the first solid-liquid separation device are selected from at least one of plate and frame filter press and centrifuge; the intermediate device is an intermediate tank; the adsorption device includes several parallel fixed bed adsorbers with a diameter of 15-35 cm and a height of 0.5-1.5 m; the regeneration device is a reaction vessel.

[0085] Specifically, when breakthrough signs (i.e., Cu) are detected at the outlet concentration of the adsorption device... 2+ Concentration > 0.5 mg / L, Zn 2+ When the concentration is >0.5 mg / L, the original fixed-bed adsorber can be shut down and a new fixed-bed adsorber can be turned on to ensure the continuous operation of the device. Then, the automatic discharge system connected to the original fixed-bed adsorber is started to transport the saturated adsorbent in the original fixed-bed adsorber to the reaction vessel of the regeneration device. The reaction vessel contains a disodium ethylenediaminetetraacetate solution. After adjusting the pH to 6-8, regeneration treatment is carried out, and the temperature, ultrasonic power, ultrasonic frequency, and treatment time are controlled. After the regeneration treatment is completed, the adsorbent is allowed to stand and separate to obtain the regenerated adsorbent and regeneration solution. The regenerated adsorbent is sent back to the original fixed-bed adsorber by the automatic discharge system for later use, and the regeneration solution is used for subsequent processing.

[0086] The aforementioned fixed-bed adsorbers are numerous and small in size, which helps to reduce the volume of dead zones in the adsorption bed, thereby improving adsorption efficiency; moreover, adsorption treatment and regeneration treatment can be carried out simultaneously, enabling continuous treatment of wastewater; at the same time, the automatic discharge system facilitates the industrial application of this method.

[0087] The technical solution of this application will be further explained below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, all reagents used are commercially available or obtained through public channels.

[0088] Example 1:

[0089] This embodiment provides a method and apparatus for treating heavy metal ion wastewater, which can be referred to. Figure 1 It includes the following steps:

[0090] (1) First sedimentation treatment: The wastewater to be treated from the electroplating industry was pumped into the first sedimentation tank using a power pump. The volumetric flow rate was 251.2 L / h. Calcium oxide emulsion was slowly added under stirring until the pH meter showed 8.5 for the first sedimentation treatment. The reaction was carried out at a temperature of 25℃ for 40 min. Then anionic polyacrylamide flocculant was added (the amount of anionic polyacrylamide flocculant added was 3 mg / L based on the volume of the wastewater to be treated). After settling, the first supernatant and the first sludge at the bottom were obtained.

[0091] (2) First solid-liquid separation treatment: The first sludge was filtered by a plate and frame filter press at a temperature of 25°C, a pressure of 1.2 MPa, and a time of 100 min to separate the second supernatant and the second sludge.

[0092] (3) Combining: The first supernatant and the second supernatant are combined to obtain a mixed liquid; the mixed liquid flows into the intermediate tank by gravity.

[0093] (4) Adsorption treatment: After adjusting the pH of the mixed liquid in the intermediate tank to 5.0 with dilute sulfuric acid, it is evenly introduced into four parallel fixed-bed adsorbers (referred to as adsorption device 1, with a diameter of 20 cm and a height of 1.0 m) for adsorption treatment through a flow distributor; wherein, the feed flow rate of a single fixed-bed adsorber is 62.8 L / h, and the adsorption bed of a single fixed-bed adsorber is filled with 3 g of metal-organic framework-aerogel composite material with a particle size of 0.5-2 mm as adsorbent, and the specific surface area of ​​the adsorbent is 520 m². 2 The adsorbent has a pore volume of 0.5 mL / g and an average pore size of 1.2 nm. The metal-organic framework in the adsorbent is ZIF-8, and the aerogel is a hydrophobically modified silica aerogel containing functional groups of amino, carboxyl, and sulfonic acid groups. The temperature of the mixture in the fixed-bed adsorber is 25℃ and the residence time is 60 min. The treated water after adsorption is discharged from the outlet of the adsorption column.

[0094] (5) Regeneration treatment: Monitor the concentration of heavy metal ions in the treated water. When the concentration at the outlet shows signs of breakthrough (i.e., Cu... 2+ Concentration > 0.5 mg / L, Zn 2+ When the concentration is >0.5 mg / L, shut down the original fixed-bed adsorbent (adsorption device 1) and open the new fixed-bed adsorbent (denoted as adsorption device 2) to ensure continuous operation of the device. Then, start the automatic discharge system connected to the original fixed-bed adsorbent (adsorption device 1) to transport the saturated adsorbent in the original fixed-bed adsorbent (adsorption device 1) to the regeneration reactor. The regeneration reactor has a volume of 0.27 L. Introduce a 0.1 mol / L, 0.2 L solution of disodium ethylenediaminetetraacetate (EDTA) into the reactor (initially using fresh EDTA solution, followed by a mixture of regenerated and fresh EDTA solution). Adjust the pH to 7.0 and perform regeneration treatment. Control the temperature at 50℃ and activate ultrasound (ultrasound power 300 W, ultrasound frequency 40 kHz). Treat for 50 minutes. After regeneration, the adsorbent is allowed to stand for separation to obtain the regenerated adsorbent and regeneration solution. The regenerated adsorbent is then sent back to the original fixed-bed adsorbent (adsorption device 1) by the automatic discharge system for later use, and the regeneration solution is sent to subsequent processing.

[0095] (6) Second sedimentation treatment: The above regenerated solution is pumped into the second sedimentation tank using a power pump. Sodium hydroxide is added under stirring until the pH meter shows 7.5 to carry out the second sedimentation treatment. The reaction is carried out at a temperature of 25°C for 60 min to obtain the upper third supernatant and the bottom sedimented third sludge.

[0096] (7) Second solid-liquid separation treatment: The above-mentioned third sludge is filtered by a plate and frame filter press at a temperature of 25°C, a pressure of 1.2 MPa, and a time of 60 min to separate the fourth supernatant and the fourth sludge.

[0097] (8) Merging: Merge the second sludge and the fourth sludge to obtain recyclable heavy metal sludge, which can be sent to a qualified unit for metal recovery; merge the third supernatant and the fourth supernatant to obtain regenerated disodium ethylenediaminetetraacetate solution, which can be replenished with fresh disodium ethylenediaminetetraacetate solution to a concentration of 0.1 mol / L and a volume of 0.2 L before being put into regeneration treatment.

[0098] Example 2

[0099] This embodiment provides a method for treating heavy metal ion wastewater. It can be referred to in Embodiment 1, except that the temperature of the regeneration treatment in step (5) of this embodiment is 40°C.

[0100] Comparative Example 1

[0101] This embodiment provides a method for treating heavy metal ion wastewater. It can be referred to in Embodiment 1, except that the temperature of the regeneration treatment in step (5) of this embodiment is 60°C.

[0102] Test Example 1:

[0103] The wastewater used in the above embodiments and comparative examples was Cu-containing wastewater generated by an electroplating plant. 2+ Zn 2+ The wastewater has a pH of 3.0 and contains Cu. 2+ The concentration is 33 mg / L, Zn 2+ The concentration is 51 mg / L.

[0104] The wastewater to be treated was treated using the treatment methods in the above embodiments and comparative examples. Specifically, water quality analysis was performed on the mixture obtained in step (3) and the treated water obtained in step (4) after running for 24 hours. The analysis included: measuring the pH value with a pH meter and measuring the concentration of heavy metal ions with an atomic spectrophotometer. The water quality analysis results are shown in Table 1.

[0105] Table 1

[0106]

[0107] According to the results in Table 1, when the regeneration temperature is between 40-50℃, the residual heavy metal ions in the treated wastewater are all below 0.5 mg / L, meeting the requirements of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008) and can be discharged in compliance with the standard. When the regeneration temperature rises from 40℃ to 50℃, the residual heavy metal ions in the treated water decrease. However, when the regeneration temperature rises from 50℃ to 60℃, the residual heavy metal ions in the treated water increase significantly, to the point that the standard cannot be met.

[0108] Test Example 2:

[0109] The initial adsorption capacity of the adsorbent in the above examples and comparative examples was tested. After 10 adsorption-regeneration cycles, the adsorption capacity after 10 cycles was calculated, and the results are shown in Table 2. The formula for calculating the adsorption capacity is (AB) / C, where A is the total mass of metal ions in the mixture, B is the total mass of metal ions in the treated water, and C is the mass of the adsorbent. The adsorption capacity retention rate after 10 cycles is D / E×100%, where D is the adsorption capacity after 10 cycles and E is the initial adsorption capacity.

[0110] Table 2

[0111]

[0112] As shown in Table 2, the adsorption capacity using the treatment method of this invention remains at 55% or more of the initial adsorption capacity. Furthermore, it can be observed that when the regeneration temperature is 60°C, the pore structure and modifying groups of the regenerated adsorbent are easily damaged, leading to a significant reduction in the effective active sites for adsorbing heavy metal ions within it.

[0113] Test Example 3:

[0114] The recycling rate of disodium ethylenediaminetetraacetate (EDTA) in the above examples and comparative examples was tested after 24 hours of device operation. Note that during the 24-hour operation, no fresh EDTA was added; instead, water was added to 0.2 L when the volume of the regenerated EDTA solution was less than 0.2 L before regeneration. Specific results are shown in Table 3. In this test example, the concentration of the EDTA solution was determined by zinc oxide complexometric titration, and the recycling rate was calculated. The expression for the recycling rate is: F / G × 100%, where F is the molar concentration of the regenerated EDTA solution and G is the molar concentration of the initially added EDTA solution (0.1 mol / L).

[0115] Table 3

[0116]

[0117] As shown in Table 3, the recycling rate of the disodium ethylenediaminetetraacetate solution treated by the method of the present invention is less than 65%. Since the adsorption capacity of the adsorbent remains in a good state after recycling, the loss of disodium ethylenediaminetetraacetate required for regeneration will inevitably be greater, resulting in a lower recycling rate of the desorbent disodium ethylenediaminetetraacetate. Therefore, this test example indirectly proves that the adsorbent adsorption capacity retention rate is higher when using the treatment method of the present invention.

[0118] Furthermore, the above test results indicate that during the operation of the device, fresh disodium ethylenediaminetetraacetate (EDTA) needs to be replenished according to the molar concentration of the regenerated disodium ethylenediaminetetraacetate solution. The expression for the amount of fresh disodium ethylenediaminetetraacetate to be replenished is: (GH) × I, where G is the molar concentration of the initially added disodium ethylenediaminetetraacetate solution (0.1 mol / L), H is the molar concentration of the regenerated disodium ethylenediaminetetraacetate solution, and I is the volume of the initially added disodium ethylenediaminetetraacetate solution (0.2 L).

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating heavy metal ion waste water, characterized by, The method comprises the following steps: adjusting the pH value of the wastewater to be treated to 8-9 for first precipitation treatment to obtain first supernatant and first sludge; carrying out first solid-liquid separation treatment on the first sludge to obtain second supernatant and second sludge; combining the first supernatant and the second supernatant to obtain a mixed solution; adjusting the pH value of the mixed solution to 4-6, and then mixing the mixed solution with a metal organic framework-aerogel composite adsorbent for adsorption treatment to obtain treated water; wherein in the adsorbent, the metal organic framework is ZIF-8, the aerogel is hydrophobically modified silica aerogel, and the aerogel contains functional groups, and the functional groups include amino groups, carboxyl groups and sulfonic acid groups; wherein the adsorbent particles of different particle sizes are uniformly mixed so that the particle size and quantity of the particles are in a power-law distribution, and then the particles are filled into the adsorption bed of a fixed bed adsorber; after the adsorbent is saturated, the saturated adsorbent is mixed with disodium ethylenediaminetetraacetate and adjusted to a pH value of 6-8 for regeneration treatment to obtain regenerated adsorbent and a regeneration solution; wherein the regeneration treatment conditions include a temperature of 40-55℃, an ultrasonic power of 200-400 W, an ultrasonic frequency of 30-50 kHz, and a time of 50-70 min; wherein the regenerated adsorbent is sent back to the adsorption treatment for recycling; adjusting the pH value of the regeneration solution to 7-8 for second precipitation treatment to obtain third supernatant and third sludge; carrying out second solid-liquid separation treatment on the third sludge to obtain fourth supernatant and fourth sludge; combining the second sludge and the fourth sludge to obtain recoverable heavy metal sludge; combining the third supernatant and the fourth supernatant to obtain regenerated disodium ethylenediaminetetraacetate; The adsorbent has a particle size of 0.5 to 10 mm, a specific surface area of 350 to 700 m 2 / g, a pore volume of 0.05 to 0.6 mL / g, and an average pore diameter of 0.2 to 3 nm. the conditions of the first precipitation treatment and the second precipitation treatment include a temperature of 10-35℃ and a time of 30-240 min; the conditions of the first solid-liquid separation treatment and the second solid-liquid separation treatment include a temperature of 10-35℃, a pressure of 0.6-1.6 MPa, and a time of 30-240 min, or a temperature of 10-35℃, a rotation speed of 1500-4000xg, and a time of 0.1-10 min.

2. The treatment method according to claim 1, characterized in that, the conditions of the adsorption treatment include a temperature of 20-40℃ and a time of 15-90 min.

3. The treatment method of claim 1, wherein The amount of disodium ethylenediaminetetraacetate is 35-65wt% based on the mass of the saturated adsorbent.

4. An apparatus for carrying out the treatment method according to any one of claims 1 to 3, characterized in that The method comprises sequentially connected first precipitation device, first solid-liquid separation device, intermediate device, adsorption device, regeneration device, second precipitation device and second solid-liquid separation device; the first precipitation device is further connected with the intermediate device, the regeneration device is further connected with the adsorption device in reverse, and the second precipitation device and the second solid-liquid separation device are further connected with the regeneration device in reverse. The first precipitation device is used for first precipitation treatment; the first solid-liquid separation device is used for first solid-liquid separation treatment; the intermediate device is used for adjusting the pH of the mixed liquid; the adsorption device is used for adsorption treatment; the regeneration device is used for regeneration treatment; the second precipitation device is used for second precipitation treatment; and the second solid-liquid separation device is used for second solid-liquid separation treatment.

5. The apparatus of claim 4, wherein, The first precipitation device and the second precipitation device are precipitation tanks; the first solid-liquid separation device and the second solid-liquid separation device are at least one selected from a plate-and-frame filter press and a centrifuge; the intermediate device is an intermediate tank; the adsorption device comprises a plurality of parallel fixed-bed adsorbers with a diameter of 15-35 cm and a height of 0.5-1.5 m; and the regeneration device is a reaction kettle.

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