A method for treating complexed heavy metal wastewater

Abstract

The present application relates to wastewater treatment technical field, specifically to a kind of removal method of complex heavy metal in wastewater, including metal organic framework material reaction adsorption, pH adjustment and the formation of heavy metal precipitate.Compared with prior art, the present application adopts segmented treatment process, one-stage type desorption adsorption process adopts metal organic framework material to induce desorption to complex heavy metal, and simultaneously adsorbs ligand;Two-stage type alkaline precipitation process removes free state heavy metal precipitate generated after desorption, can deeply remove complex heavy metal in wastewater, reaches the sewage discharge standard stipulated by our country;The present application has the advantages such as simple process, environment-friendly, high removal efficiency and low energy consumption, and has good popularization and application prospect in electroplating wastewater advanced treatment technical field.

Description

Technical Field

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

[0002] The treatment of complexed heavy metal wastewater has been a major concern, as its sources are widespread. Wastewater from industries such as leather tanning, electroplating, dyeing and printing, metal smelting, and printed circuit boards contains large amounts of complexing agents. Heavy metal ions typically combine with organic substances such as ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, and formic acid to form various heavy metal complexes. my country generates approximately 40 billion tons of industrial wastewater annually, with electroplating wastewater alone accounting for 10% of the total industrial wastewater discharge. Furthermore, the vast majority of wastewater discharged from processes in the electroplating industry contains complexed heavy metals.

[0003] Compared to free heavy metal ions, complexed heavy metals are highly water-soluble, stable across a wide pH range, and exhibit complex forms, increasing their diffusion in environments such as groundwater. Therefore, they are readily absorbed by organisms. Complexed heavy metals typically have higher potential toxicity than both individual organic ligands and free heavy metals, and are more difficult to remove. Traditional chemical precipitation methods often fail to achieve satisfactory treatment results, and the effluent often fails to meet discharge standards. If improperly treated, they can accumulate in high concentrations in the human body once they enter the food chain, leading to serious health risks. Therefore, the treatment of wastewater containing complexed heavy metals has become one of the most pressing environmental protection issues.

[0004] Currently, common treatment technologies for complexed heavy metal wastewater mainly include chemical precipitation, oxidation, membrane separation, ion exchange, biological methods, and adsorption. Each method has its own characteristics and advantages, but also some shortcomings in practical applications. For example, chemical precipitation requires a large amount of flocculant and suffers from difficulties in solid-liquid separation of the precipitate colloid, sulfur source odor, and environmental stability issues. Oxidation methods have very limited removal efficiency for complexed heavy metals at concentrations close to the new special emission limits for water pollutants, and even at the surface water and drinking water standard limits (μg / L). Ion exchange methods are generally not directly used for treating complexed heavy metal wastewater due to drawbacks such as easy saturation of exchange resins, easy contamination or aging of exchange resins by complexes, and frequent resin regeneration; instead, they are used as a follow-up safeguard. Membrane separation methods are limited in practical application due to problems such as short membrane lifespan, high cost, difficult cleaning, and easy clogging of membrane modules. Adsorption methods have good application prospects in the treatment of complexed heavy metal wastewater due to their advantages such as simple operation, low energy consumption, low cost, high efficiency, and no secondary pollution.

[0005] Metal-organic frameworks (MOFs) possess high specific surface area, abundant active sites, tunable pore size, and ease of modification, and have been recognized in recent years as a new generation of ion exchange and adsorption materials, widely used for the purification and removal of pollutants in water. Among them, the UiO (University of Oslo) series materials are typical zirconium-based MOFs. Their hydroxyl-containing zirconium clusters can bind to pollutant molecules through coordination and other interactions. Furthermore, their organic ligands can bind to environmental pollutants through various mechanisms such as acid-base interactions, electrostatic interactions, hydrogen bonding, π-π interactions, hydrophobicity, and the "breathing" effect of the flexible framework, thereby achieving separation and removal. The UiO series materials have been used to remove Cr(VI), Se(IV), Cd(II), dyes, organic arsenic, and PO4. 3- It exhibits excellent adsorption performance for various pollutants, including [list of pollutants].

[0006] CN113019331A discloses a rare-earth-doped defective UiO-66 material, its preparation method, and its application, belonging to the field of wastewater treatment technology. The preparation method of the defective UiO-66 material includes the following steps: mixing zirconium tetrachloride, terephthalic acid, N,N-dimethylformamide, and rare earth oxides; subjecting the resulting mixture to a solvothermal reaction to obtain the rare-earth-doped defective UiO-66 material; the rare earth oxides are Sm₂O₃, Eu₂O₃, Er₂O₃, or Tm₂O₃; the molar ratio of zirconium tetrachloride, terephthalic acid, and rare earth oxides is 1:1:(0.25~0.5). The prepared rare-earth-doped defective UiO-66 material exhibits a large adsorption capacity for Sb as an adsorbent.

[0007] CN108905976A discloses a manganese ion-doped metal-organic framework material, its preparation method, and its application. The material comprises UiO-66(Zr) doped with manganese ions. The preparation method involves a solvothermal reaction of zirconium chloride, terephthalic acid, manganese chloride tetrahydrate, and N,N-dimethylformamide to obtain the manganese ion-doped metal-organic framework material. In this application method, the manganese ion-doped metal-organic framework material can efficiently adsorb and remove antibiotics and heavy metal pollutants from water.

[0008] The existing methods described above primarily utilize UiO-66(Zr) materials doped with other ions or modified in other ways to adsorb pollutants such as heavy metal ions. However, inventions related to the application of UiO-66(Zr) materials in the removal of complexed heavy metals are relatively limited. Complexed heavy metals are more toxic and more difficult to remove than heavy metal ions. Furthermore, low concentrations of complexed heavy metals are more difficult to remove than high concentrations. To address these issues, this invention provides a deep removal process for complexed heavy metals. Summary of the Invention

[0009] The purpose of this invention is to provide a method for treating complexed heavy metal wastewater. The method uses UiO-66 (Zr) adsorption combined with alkaline precipitation to treat complexed copper wastewater, so that the copper ion concentration in the wastewater is less than 0.5 mg / L, which meets the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] This invention provides a method for treating complexed heavy metal wastewater, comprising the following steps:

[0012] Preparation of zirconium-based metal-organic framework material UiO-66(Zr): Zirconium tetrachloride, terephthalic acid, N,N-dimethylformamide, acetic acid and deionized water were mixed and reacted to obtain UiO-66(Zr) material.

[0013] Adsorption / precipitation method for removing complexed heavy metal wastewater: UiO-66(Zr) material is added to the complexed heavy metal wastewater to be treated for adsorption. After reaching equilibrium, UiO-66(Zr) is filtered out. The pH of the remaining solution system is adjusted to maintain alkalinity, and the precipitated substances are filtered out.

[0014] Furthermore, the molar ratio of zirconium tetrachloride to terephthalic acid is 1:1 to 1:1.39.

[0015] Furthermore, the molar ratio of N,N-dimethylformamide, acetic acid, and deionized water is 111.86:1:9.65 to 177.43:1:4.09.

[0016] Furthermore, the reaction temperature is 80–120°C.

[0017] Furthermore, the reaction time is 15–90 min.

[0018] Furthermore, after the reaction, the reaction product obtained from the microwave reaction is cooled to room temperature, and then subjected to solid-liquid separation, solid washing, drying, and activation in sequence.

[0019] Furthermore, the activation is performed by vacuum drying, and the vacuum drying temperature is 100–150°C.

[0020] Furthermore, the ratio of the UiO-66(Zr) material to the complexed heavy metal wastewater is 0.5–1.0 g / L.

[0021] Furthermore, the complexed heavy metal wastewater is preferably complexed copper wastewater, and the concentration of the complexed copper is 1-5.58 mg / L [calculated as Cu], preferably 1-5 mg / L [calculated as Cu].

[0022] Furthermore, the complexed copper is copper citrate (CA-Cu), copper tartrate (TA-Cu), and copper hyponitrotriacetate (NTA-Cu).

[0023] Furthermore, the adsorption time is 12 to 24 hours, preferably 24 hours.

[0024] Furthermore, after adding UiO-66(Zr) material, the pH of the complexed heavy metal wastewater rapidly decreased to 3–4. At this pH, most of the complexed heavy metals dissociated into free metal ions and organic ligands, while a small portion of the complexed heavy metals remained in their entirety. Moreover, the lower the initial concentration of the complexed heavy metals, the higher the dissociation rate. During the adsorption process, organic ligands and complexed heavy metals can be adsorbed by UiO-66(Zr), while free metal ions are not adsorbed by the positively charged UiO-66(Zr) due to electrostatic repulsion.

[0025] Furthermore, after reaching adsorption equilibrium, UiO-66(Zr) is separated by filtration, and the pH of the remaining solution system is adjusted to maintain alkaline conditions of 8-10, preferably 10, for a duration of 0.5-12 hours, preferably 2 hours.

[0026] Furthermore, after reaching adsorption equilibrium, UiO-66(Zr) is separated by filtration, and the pH of the remaining solution system is adjusted to maintain alkaline conditions. The free metal ions present in the solution will generate metal hydroxide precipitates under alkaline conditions, ultimately achieving the purpose of removing complexed heavy metals.

[0027] Compared with the prior art, the present invention has the following technical advantages:

[0028] 1) Currently, traditional commercial adsorption materials, such as activated carbon, have low adsorption capacity for complexed heavy metals in water (generally less than 5 mg / g), short service life, and low treatment efficiency. This application is the first to use UiO-66 (Zr) adsorption technology combined with alkaline precipitation technology. After treatment by adsorption combined with precipitation, the concentration of Cu(II) in complexed copper wastewater is reduced to less than 0.5 mg / L, meeting the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industries" (GB25467-2010) (0.5 mg / L).

[0029] 2) The UiO-66(Zr) adsorption technology combined with alkaline precipitation technology in this application has a much better effect on the treatment of complexed heavy metals than either UiO-66(Zr) adsorption technology or alkaline precipitation technology alone.

[0030] 3) This application has the advantages of simple process, low cost, good removal effect and low energy consumption, and has good prospects for promotion and application in the field of deep treatment technology of electroplating wastewater. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall process flow of the present invention;

[0032] Figure 2 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method of the present invention on copper citrate (CA-Cu) of different concentrations in Examples 1-3.

[0033] Figure 3 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method on 5 mg / L of different types of complexed copper in Examples 3-5 of the present invention.

[0034] Figure 4 The figures show the removal efficiency of 2.5 mg / L of different types of complexed copper using the UiO-66(Zr)-NH2 adsorption method combined with alkaline precipitation method of the present invention in Examples 6-8.

[0035] Figure 5 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method of the present invention on 2.5 mg / L of different types of complexed nickel in Examples 9-11.

[0036] Figure 6 This is a graph showing the pH change trend of 1 mg / L copper citrate (CA-Cu) wastewater before and after the addition of UiO-66 (Zr) in this invention. Detailed Implementation

[0037] Overall, this invention relates to the field of wastewater treatment technology, and provides a method for treating complexed heavy metal wastewater. See also Figure 1 In this invention, the prepared UiO-66(Zr) is added to the complexed copper wastewater, and the pH of the system rapidly drops to 3-4 (see [reference]). Figure 6At this point, most of the complexed copper dissociates, existing as free copper ions and organic ligands, while a small portion of the complexed copper remains in its entirety. During adsorption, the organic ligands and the complexed copper can be adsorbed by UiO-66(Zr), while the free copper ions are not adsorbed by the positively charged UiO-66(Zr) due to electrostatic repulsion. Subsequently, by adjusting the pH of the system to alkaline, the free copper ions will precipitate as Cu(OH)2 under alkaline conditions, thus achieving the removal of the complexed copper. After treatment by adsorption combined with precipitation, the removal rate of complexed copper can approach 100%, and the residual copper ion concentration in the complexed copper wastewater is less than 0.5 mg / L, meeting the Chinese "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L). This application has the advantages of simple process, low cost, good removal effect and low energy consumption. It has good prospects for promotion and application in the field of deep treatment technology of electroplating wastewater and provides a new idea for the efficient removal of strong stable complexed heavy metals and complexing agents.

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0039] It should be noted that the preparation of the zirconium-based metal-organic framework material UiO-66(Zr) is not an innovation of this invention. The following existing techniques can be used for preparation: Zirconium tetrachloride, terephthalic acid, N,N-dimethylformamide, acetic acid, and deionized water are mixed, and the resulting mixture is reacted to obtain the UiO-66(Zr) material; the molar ratio of zirconium tetrachloride to terephthalic acid is 1:1 to 1:1.39. The molar ratio of N,N-dimethylformamide, acetic acid, and deionized water is 111.86:1:9.65 to 177.43:1:4.09. The reaction temperature is 80 to 120°C. The reaction time is 15 to 90 minutes. After the reaction, the reaction product obtained from the microwave reaction is cooled to room temperature, and then subjected to solid-liquid separation, solid washing, drying, and activation in sequence. The activation is vacuum drying at a temperature of 100 to 150°C.

[0040] Example 1

[0041] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0042] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated copper citrate (CA-Cu) wastewater with a concentration of 1.02 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Cu in the solution after adsorption was measured.2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0043] Figure 2 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method of the present invention on copper citrate (CA-Cu) of different concentrations in Examples 1-3.

[0044] Measurements showed that Cu was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 1.18 mg / L, the removal rate was 0, and the Cu in the solution after adding NaOH precipitation... 2+ The concentration was 0.01 mg / L, and the removal rate was 99.02%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0045] Example 2

[0046] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0047] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated copper citrate (CA-Cu) wastewater with a concentration of 2.85 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Cu in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0048] Measurements showed that Cu was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 2.71 mg / L, the removal rate was 4.91%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was 0.06 mg / L, and the removal rate was 97.89%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0049] Example 3

[0050] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0051] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated copper citrate (CA-Cu) wastewater with a concentration of 5.84 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Cu in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0052] Figure 3 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method on 5 mg / L of different types of complexed copper in Examples 3-5 of the present invention.

[0053] Measurements showed that Cu was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 4.36 mg / L, the removal rate was 25.34%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was 0.06 mg / L, and the removal rate was 98.97%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0054] Example 4

[0055] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0056] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated copper tartrate (TA-Cu) wastewater with a concentration of 5.37 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Cu in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0057] Measurements showed that Cu was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 6.24 mg / L, the removal rate was 0, and the Cu in the solution after adding NaOH precipitation...2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0058] Example 5

[0059] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0060] 100 mg of UiO-66(Zr) adsorbent was added to 100 ml of simulated wastewater containing 5.58 mg / L copper triacetate (NTA-Cu). The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66(Zr), and the remaining Cu in the solution was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0061] Figure 4 The figures show the removal efficiency of 2.5 mg / L of different types of complexed copper using the UiO-66(Zr)-NH2 adsorption method combined with alkaline precipitation method of the present invention in Examples 6-8.

[0062] Measurements showed that Cu was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 3.03 mg / L, the removal rate was 45.70%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was 0.46 mg / L, and the removal rate was 91.76%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0063] Example 6

[0064] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0065] 100 mg of UiO-66(Zr)-NH2 adsorbent was added to 100 ml of simulated copper citrate (CA-Cu) wastewater with a concentration of 2.63 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66(Zr)-NH2, and the remaining Cu in the solution after adsorption was measured. 2+Concentration. Then, the solution after separating the UiO-66(Zr)-NH2 adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0066] Measurements showed that only the solution treated with UiO-66(Zr)-NH2 adsorption contained Cu. 2+ The concentration was 2.44 mg / L, the removal rate was 7.22%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0067] Example 7

[0068] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0069] 100 mg of UiO-66(Zr)-NH2 adsorbent was added to 100 ml of simulated copper tartrate (TA-Cu) wastewater with a concentration of 2.43 mg / L [calculated as Cu]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66(Zr)-NH2, and the remaining Cu in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr)-NH2 adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0070] Measurements showed that only the solution treated with UiO-66(Zr)-NH2 adsorption contained Cu. 2+ The concentration was 2.36 mg / L, the removal rate was 2.88%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0071] Example 8

[0072] Treatment of Complexed Copper Simulated Wastewater by Adsorption Combined with Precipitation

[0073] 100 mg of UiO-66(Zr)-NH2 adsorbent was added to 100 ml of simulated wastewater containing 2.37 mg / L copper hyponitrotriacetate (NTA-Cu). The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66(Zr)-NH2, and the remaining Cu in the solution was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr)-NH2 adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Cu in the final solution was measured. 2+ concentration.

[0074] Measurements showed that only the solution treated with UiO-66(Zr)-NH2 adsorption contained Cu. 2+ The concentration was 2.03 mg / L, the removal rate was 14.35%, and the Cu in the solution after adding NaOH precipitation was... 2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed copper treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0075] Example 9

[0076] Adsorption combined with precipitation for treating simulated nickel complex wastewater

[0077] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated nickel citrate (CA-Ni) wastewater with a concentration of 2.86 mg / L [calculated as Ni]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Ni in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Ni in the final solution was measured. 2+ concentration.

[0078] Figure 5 The figures show the removal effects of the UiO-66(Zr) adsorption method combined with alkaline precipitation method of the present invention on 2.5 mg / L of different types of complexed nickel in Examples 9-11.

[0079] Measurements showed that Ni was only present in the solution after adsorption treatment. 2+ The concentration was 2.89 mg / L, the removal rate was 0, and the Ni concentration in the solution after adding NaOH precipitation was 0. 2+The concentration was 0.02 mg / L, and the removal rate was 99.30%, indicating that the simulated wastewater containing complexed nickel treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0080] Example 10

[0081] Adsorption combined with precipitation for treating simulated nickel complex wastewater

[0082] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated nickel tartrate (TA-Ni) wastewater with a concentration of 2.80 mg / L [calculated as Ni]. The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Ni in the solution after adsorption was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Ni in the final solution was measured. 2+ concentration.

[0083] Measurements showed that Ni was only present in the solution after UiO-66(Zr) adsorption treatment. 2+ The concentration was 2.87 mg / L, the removal rate was 0, and the Ni concentration in the solution after adding NaOH precipitation was 0. 2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed nickel treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0084] Example 11

[0085] Adsorption combined with precipitation for treating simulated nickel complex wastewater

[0086] 100 mg of UiO-66 (Zr) adsorbent was added to 100 ml of simulated wastewater containing 2.77 mg / L (Ni) of nickel triacetate (NTA-Ni). The adsorption time was 24 h at 25 °C. After adsorption, the system was filtered to separate UiO-66 (Zr), and the remaining Ni in the solution was measured. 2+ Concentration. Then, the solution after separating the UiO-66(Zr) adsorbent was adjusted to pH 10 with 0.1M NaOH solution and kept stable for 120 min. The precipitate was then separated by filtration, and the remaining Ni in the final solution was measured. 2+ concentration.

[0087] Measurements showed that Ni was only present in the solution after UiO-66(Zr) adsorption treatment.2+ The concentration was 2.61 mg / L, the removal rate was 5.78%, and the Ni concentration in the solution after adding NaOH precipitation was [missing information]. 2+ The concentration was below the instrument detection limit, and the removal rate was close to 100%, indicating that the simulated wastewater containing complexed nickel treated by adsorption combined with precipitation met the requirements of my country's "Emission Standard of Pollutants for Copper, Nickel and Cobalt Industry" (GB25467-2010) (0.5 mg / L).

[0088] Example 12

[0089] pH change trend of simulated wastewater with complexed copper before and after the addition of UiO-66(Zr).

[0090] The initial pH of 100 ml of simulated wastewater containing 1 mg / L copper citrate (CA-Cu) [calculated as Cu] was 5.75. When 100 mg of UiO-66 (Zr) adsorbent was added, the pH of the system rapidly decreased to 3.84 within 10 seconds after addition, and decreased to 3.50 within 60 seconds, reaching equilibrium.

[0091] Figure 6 This is a graph showing the pH change trend of 1 mg / L copper citrate (CA-Cu) wastewater before and after the addition of UiO-66 (Zr) in this invention.

[0092] In summary, when the prepared UiO-66(Zr) is added as an adsorbent to simulated wastewater containing complexed heavy metals, the pH of the system rapidly drops to 3–4 due to the deprotonation of Zr-OH / Zr-OH2 in the water at the defect sites of UiO-66(Zr). At this pH, the organic ligands in the complexed heavy metals react with H+ due to the acid effect. + The formation of corresponding organic ligand acids leads to a decrease in the stability of the complex, resulting in discomplexation. Most of the complexed heavy metals discomplex, existing as free metal ions and organic ligands, while a small portion remains in their entirety. During adsorption, both the organic ligands and the complexed heavy metals are adsorbed by the Zr-based MOF. According to the zeta potential curve, UiO-66(Zr) carries a positive charge at this pH and does not adsorb free metal ions due to electrostatic repulsion; therefore, a single adsorption treatment technique cannot effectively remove complexed heavy metals. However, by combining this with a precipitation method and adjusting the system pH to alkaline, free metal ions can be effectively removed by forming metal hydroxide precipitates. As shown in the examples, a single alkaline precipitation technique is also ineffective in removing complexed heavy metals because they can exist stably over a wide pH range and generally do not precipitate under alkaline conditions. Therefore, the Zr-based MOF adsorbent and the alkaline precipitant complement each other, both playing important roles in the removal of complexed heavy metals in this invention.

[0093] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for treating complexed heavy metal wastewater, characterized in that, Includes the following steps: UiO-66(Zr) material was added to the complexed heavy metal wastewater to be treated for adsorption. After reaching equilibrium, UiO-66(Zr) was filtered out. The pH of the remaining solution system was adjusted to maintain alkalinity, and the precipitated substances were filtered out. After adding UiO-66(Zr) material, the pH of the complexed heavy metal wastewater rapidly decreased to 3-4; When the pH drops rapidly to 3-4, most of the complexed heavy metals dissociate into free metal ions and organic ligands. A small portion of the complexed heavy metals remain in their whole form. The lower the initial concentration of the complexed heavy metals, the higher the dissociation rate. During the adsorption process, organic ligands and complexed heavy metals can be adsorbed by UiO-66(Zr), while free metal ions will not be adsorbed by the positively charged UiO-66(Zr) due to electrostatic repulsion. The complexed heavy metal wastewater is complexed copper wastewater, and the complexed copper is one or more of copper citrate, copper tartrate, and copper hyponitrotriacetate.

2. The method for treating complexed heavy metal wastewater according to claim 1, characterized in that, The ratio of the UiO-66(Zr) material to the complexed heavy metal wastewater is 0.5–1.0 g / L.

3. A method for treating complexed heavy metal wastewater according to claim 1, characterized in that, The concentration of the complexed copper is 1–5 mg / L.

4. A method for treating complexed heavy metal wastewater according to claim 1, characterized in that, The adsorption time is 12–24 h.

5. The method for treating complexed heavy metal wastewater according to claim 1, characterized in that, After reaching adsorption equilibrium, UiO-66(Zr) was separated by filtration, and the pH of the remaining solution system was adjusted to maintain alkaline conditions of 8-10 for 0.5-12 h.

6. The method for treating complexed heavy metal wastewater according to claim 5, characterized in that, After adjusting the pH of the remaining solution system to maintain alkaline conditions, the free metal ions present in the solution will form metal hydroxide precipitates under alkaline conditions, ultimately achieving the purpose of removing complexed heavy metals.

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