Arsenic adsorbent generated in situ from mine wastewater as well as preparation method and application of arsenic adsorbent

Abstract

The invention relates to an arsenic adsorbent generated in situ from mine wastewater and a preparation method and application thereof, and the preparation method comprises the following steps: (1) placing acidic mine wastewater in an electrooxidation system of a ruthenium-iridium-titanium mixed metal anode and a pure titanium mesh cathode, and synchronously adding montmorillonite for stirring reaction; and (2) separating the suspension after the reaction, recovering the solid, and drying to obtain the montmorillonite-based composite arsenic adsorbent. According to the method, the TFe precipitation rate is high, the reaction speed is high, and the efficient adsorbent capable of being used for arsenic removal is recycled by combining montmorillonite resources with abundant resource reserves. According to the pretreatment method, the application amount of the neutralizer in the subsequent neutralization stage can be remarkably reduced, and the reduction amplitude can reach 17.6-68.1%. Meanwhile, the recycled composite adsorbent has good arsenic adsorption performance, and the adsorption capacity reaches 6.67-11.93 mg g <-1 >.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical wastewater treatment and resource recovery, and particularly relates to an arsenic adsorbent generated in situ from mine wastewater, a preparation method thereof, and an application thereof. Background Art

[0002] Acid mine drainage (AMD) is a kind of wastewater with low pH (2.0-4.0) and rich iron ions (0.4-1gL) formed by the chemical and biological oxidation of sulfur-containing minerals exposed to air and water with the action of oxygen and microorganisms. -1 ) and toxic heavy metals (As, Cd, and Pb). With the increasing demand and development of mineral resources, AMD has become a major environmental issue that urgently needs to be addressed globally due to its high acidity and heavy metal contamination risks.

[0003] Currently, AMD treatment technologies mainly include source control and end-of-pipe treatment. Among them, limestone neutralization is widely used due to its advantages such as simple operation, low cost, and quick effect. However, in actual treatment, there are the following technical bottlenecks: (1) High concentration of iron ions significantly increases limestone consumption; (2) The iron hydroxide precipitate generated by the reaction easily coats the surface of limestone, reducing reaction efficiency; (3) The by-product is gypsum-iron hydroxide mixed sludge containing heavy metals, which is difficult to dispose of. Therefore, it is urgent to introduce a pretreatment step before the neutralization process to enhance the removal efficiency of iron and sulfate ions, so as to improve the sustainability and resource utilization level of the limestone neutralization method.

[0004] Existing AMD pretreatment technologies are primarily based on chemical or biological mineralization mechanisms, simultaneously removing iron ions and sulfate ions by generating mineral precipitation. Chemical methods, such as the hydrogen peroxide oxidation and antimony co-precipitation process proposed in Chinese invention patent CN119591232A, can effectively purify wastewater, but the large amount of oxidant required leads to high transportation and storage costs and safety risks. The Schmidt mineral generation technology proposed in CN111186933A is innovative, but the oxidant it relies on presents safety risks. Biological methods, such as the indigenous microbial coupling system developed in CN111620444A and the "aerobic-anaerobic" composite reactor designed in CN119306356A, can both achieve resource-recovery treatment. However, these methods suffer from issues such as poor strain adaptability, severe niche competition, long reaction cycles, and low mineralization efficiency, limiting their practical application. In summary, developing a novel pretreatment technology that combines high efficiency, safety, and resource recovery capabilities to reduce neutralizer consumption and improve pollution control effectiveness has become a key technical issue urgently needed to be addressed in the AMD treatment field. Summary of the Invention

[0005] Technical problems to be solved: The existing AMD pre-processing technology has Fe 2+The present invention addresses the problems of slow oxidation rate, low iron ion removal efficiency, complex operation process and potential safety hazards. The present invention provides an arsenic adsorbent generated in situ from mine wastewater, its preparation method and application. This method has a high TFe precipitation rate and a fast reaction speed, and combines with the abundant montmorillonite resources to recover a highly efficient adsorbent for arsenic removal. This pretreatment method can significantly reduce the amount of neutralizer applied in the subsequent neutralization stage, with a reduction of up to 17.6-68.1%. At the same time, the recovered adsorbent has good arsenic adsorption performance, with an adsorption capacity of 6.67-11.93 mg g -1 .

[0006] Technical solution: A method for recovering iron ions from acidic mine wastewater and generating an arsenic adsorbent in situ, comprising the following steps: (1) placing the acidic mine wastewater in an electro-oxidation system comprising a ruthenium-iridium-titanium mixed metal anode and a pure titanium mesh cathode, and simultaneously adding montmorillonite to carry out a stirring reaction; (2) separating the suspension after the reaction, recovering the solid and drying it to obtain a montmorillonite-based composite arsenic adsorbent.

[0007] The above-mentioned Fe 2+ The concentration is 0.4-1g L -1 , SO4 2- The concentration is 1-4 g L -1 .

[0008] In step (1), HCl or NaOH is used to adjust the initial pH value of the wastewater to 2.0-4.0.

[0009] The electro-oxidation system is powered by a DC power supply with an operating voltage of 5 V and a reaction time of 10 hours.

[0010] The dimensions of the anode and cathode are both 3 cm×3 cm, and the distance between the electrodes is 3 cm.

[0011] The stirring speed in step (2) is 500 rpm, and the amount of montmorillonite added is 1-12 g L -1 .

[0012] The separation in step (3) is carried out by centrifugation, and the drying is carried out by freeze drying.

[0013] The arsenic adsorbent prepared by the above method is a composite of montmorillonite loaded with iron oxyhydroxide, and its specific surface area is 35.8-74.1m 2 g -1 , the adsorption capacity for arsenic is 6.67-11.93 mg g -1 .

[0014] The application of the above arsenic adsorbent in the treatment of acid mine drainage.

[0015] The application step includes a pretreatment step, which is applied before the limestone neutralization process to reduce the amount of neutralizer used.

[0016] Beneficial effects: (1) A method for efficiently recovering iron ions from acidic mine wastewater and generating arsenic adsorbent in situ, innovatively generating an electrochemical system that couples anodic oxidation and cathode alkali production, combined with the alkaline buffering and adsorption properties of montmorillonite, to achieve Fe 2+ During the reaction, the dynamically controlled pH environment significantly enhances the co-precipitation effect of iron ions and sulfate ions, with the TFe precipitation efficiency reaching 58.2-89.4% and the sulfate precipitation rate simultaneously increasing to 6.38-12.01%. 2+ In the slightly alkaline environment formed by cathode hydrolysis and the alkaline buffer system of montmorillonite, it is converted into Fe by direct oxidation at the anode or indirect oxidation by dissolved oxygen. 3+ .Fe 3+ During the oxidation process, it undergoes structural coupling with montmorillonite through surface adsorption and interlayer intercalation, ultimately forming a composite adsorbent based on modified montmorillonite, achieving efficient recovery of iron resources and synergistic generation of functional materials, and providing a sustainable solution for AMD's green governance that combines pollution control and resource recovery.

[0017] (2) The arsenic adsorbent prepared by the method of the present invention was identified by X-ray diffraction (XRD) technology, and its crystal structure was confirmed to have the characteristic diffraction peak of iron oxyhydroxide. Scanning electron microscopy (SEM) observation showed that the surface of montmorillonite was covered with fine spherical particles. The results of specific surface area analysis (BET) showed that the specific surface area, micropore surface area and pore volume of the adsorbent increased significantly after treatment, indicating that its void structure was effectively optimized. The adsorbent can be used as a resource material recycled in the AMD purification process and has good environmental utilization potential. In terms of arsenic pollution control, its adsorption capacity for arsenic can reach 6.67-11.93 mg g -1 .

[0018] (3) After the adsorbent is generated, the present method neutralizes the separated filtrate by adding a neutralizing agent dropwise while stirring to adjust its pH to neutral. Compared with direct neutralization of AMD without pretreatment, this method significantly reduces the amount of neutralizing agent used by 17.6-68.1%, effectively improving treatment efficiency and reducing operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Energy dispersive spectrometry (EDS) analysis results and morphology of the precipitates (i.e., adsorbents) generated after electrooxidation reaction with different amounts of montmorillonite. (a) CKMMT represents the original montmorillonite without any treatment, and (b) 1MMT represents the addition of 1gL -1 The precipitate obtained after the reaction of montmorillonite, (c) 6MMT and so on.

[0020] Figure 2 Under the conditions of initial pH 3, voltage 5V, stirring rate 500rpm and room temperature for 10h, the reaction of TFe(a) and SO4 in AMD was simulated. 2- (b) Variation of concentration with power-on time.

[0021] Figure 3 Scanning electron microscopy (SEM) images of the precipitates (i.e., adsorbents) obtained after the electro-oxidation reaction with different montmorillonite addition amounts. (a) CKMMT represents montmorillonite without any treatment, and (b) 1MMT represents montmorillonite with 1 g L added to the system. -1 The precipitates obtained after the reaction of montmorillonite, (c) 3MMT and (d) 12MMT and so on.

[0022] Figure 4 XRD patterns of the precipitates (i.e., adsorbents) obtained after the electrooxidation reaction with different montmorillonite addition amounts. (a) XRD patterns of different precipitates; (b) Local XRD patterns of different precipitates and the change in the d001 interlayer spacing of montmorillonite in the precipitates. CKMMT represents untreated montmorillonite, and 1MMT represents the addition of 1 g L -1 The precipitate obtained after the reaction of montmorillonite, 3MMT and 6MMT and so on.

[0023] Figure 5 The pore size characteristics and adsorption-desorption spectra of the precipitates (i.e., adsorbents) obtained after the electro-oxidation reaction with different montmorillonite addition amounts. (a) The pore size characteristics and adsorption-desorption spectra of the montmorillonite without any treatment; (b) When 1 g L was added to the system -1 Pore size characteristics and adsorption-desorption spectra of the precipitate obtained from montmorillonite reaction.

[0024] Figure 6 The pore size characteristic spectrum of the precipitate (i.e. adsorbent) obtained after the electro-oxidation reaction with different montmorillonite addition amounts. CKMMT represents montmorillonite without any treatment, and 1MMT represents 1 g L added to the system. -1 The precipitate collected after the montmorillonite reaction.

[0025] Figure 7The adsorption behavior of the precipitate (i.e., adsorbent) obtained after the electro-oxidation reaction with different montmorillonite addition amounts. CKMMT represents montmorillonite without any treatment, PE represents the precipitate after pure electro-oxidation treatment, and 1MMT represents the addition of 1 g L -1 The precipitate obtained after the reaction of montmorillonite, 3MMT, 6MMT and 12MMT and so on.

[0026] Figure 8 Kinetic fitting curves of As(III) adsorption by precipitates (adsorbents) obtained after synergistic electrooxidation reaction with different montmorillonite addition amounts. (a) Pseudo-first-order kinetic fitting curves of As(III) adsorption by different precipitates (adsorbents); (b) Pseudo-second-order kinetic fitting curves of As(III) adsorption by different precipitates (adsorbents). CKMMT represents untreated montmorillonite, PE represents precipitate after pure electrooxidation treatment, and 1MMT represents 1 g L added to the system. -1 The precipitate obtained after the reaction of montmorillonite, 3MMT, 6MMT and 12MMT and so on.

[0027] Figure 9 Dynamic change curve of pH value of filtrate after different pretreatments and neutralization of CaO slurry. CK represents simulated acid mine wastewater without any pretreatment, PE represents filtrate after pure electro-oxidation treatment, and 1MMT represents the addition of 1g L -1 The filtrate after montmorillonite and electro-oxidation pretreatment is 3MMT, 6MMT and 12MMT and so on.

[0028] Figure 10 Characterization data of the precipitate (i.e., PE, adsorbent) obtained after pure electrooxidation reaction (without the addition of montmorillonite), including (a) SEM, (b) EDS, (c) XRD, and (d) Fourier transform infrared spectroscopy (FTIR).

[0029] Figure 11 Adsorption-desorption spectrum of the precipitate (i.e., adsorbent) obtained after pure electro-oxidation reaction (without adding montmorillonite), where PE represents the precipitate (adsorbent) after pure electro-oxidation treatment.

[0030] Figure 12 Pore size characteristic spectrum of the precipitate (i.e., adsorbent) obtained after pure electro-oxidation reaction (without adding montmorillonite). PE represents the precipitate (adsorbent) after pure electro-oxidation treatment.

[0031] Figure 13 The amount of precipitate (i.e., adsorbent) obtained after pure electro-oxidation reaction (without adding montmorillonite) under different conditions.

[0032] Figure 14Under the conditions of initial pH 3, voltage 3V, stirring rate 500rpm and room temperature for 5h, the Fe 2+ (a) and TFe (b) concentrations as a function of power-on time. DETAILED DESCRIPTION

[0033] To further illustrate the content of the present invention, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] Example 1 (The concentration of TFe in the simulated AMD was 1 g L -1 、SO4 2- The concentration is 4 g L -1 , the initial pH is 3, with Fe 2+ as the main form)

[0035] The present embodiment provides an electrochemical method for rapidly recovering iron ions from acid mine wastewater to generate an iron-containing arsenic adsorbent, comprising the following steps:

[0036] (1) Prepare the simulated solution: weigh 4.944g FeSO4·7H2O and 3.3815g Na2SO4 in a 1L beaker, add ultrapure water to completely dissolve, transfer to a 1L volumetric flask with a glass rod, and adjust the volume to 1L. Use 1mol L -1 Adjust the pH of the solution to 3 with HCl / NaOH. Dispense the prepared AMD solution into 300 mL electrolytic cells.

[0037] (2) Construction of an electro-oxidation reaction system: A ruthenium-iridium-titanium mixed metal electrode was constructed as the anode and a pure titanium mesh was constructed as the cathode. The electrodes were 3 × 3 cm in size and 3 cm apart. A DC power supply provided a constant voltage (5 V) for the electrical reaction.

[0038] (3) Adding montmorillonite: A magnetic stirring rotor was added to the electrolytic cell and placed on a magnetic stirrer with a stirring rate of 500 rpm. Different amounts of (1, 3, 6, and 12 g L -1 The pH of the solution was not additionally regulated during the entire reaction process.

[0039] (4) After the reaction, separation and recovery: After the reaction was completed for 10 hours, the suspension was centrifuged to obtain a yellow-brown to reddish-brown solid ( Figure 1 ). The solid is freeze-dried to obtain the prepared adsorbent.

[0040] (5) Neutralization treatment test: Take 50 mL of the filtrate obtained after centrifugation and place it in a 100 mL conical flask. Add CaO slurry dropwise while stirring until the pH reaches 7.5. Record the amount of neutralizer used.

[0041] Precipitation effect: The precipitation rate of TFe is 58.2-89.4%, SO4 2- The precipitation rate is 6.38-12.01% ( Figure 2 ), and with the increase of montmorillonite addition, the precipitation efficiency continues to improve.

[0042] Adsorbent appearance and composition ( Figure 1 and Figure 3 The adsorbent exhibits a yellow-brown to reddish-brown solid state, with color depth significantly positively correlated with iron content. SEM and EDS analysis revealed that the iron-based substances were uniformly distributed on the montmorillonite surface.

[0043] Crystal structure ( Figure 4 ): XRD showed that the characteristic diffraction peak of iron oxyhydroxide existed in the crystal structure of the recovered adsorbent, and the interlayer spacing of the montmorillonite changed significantly compared with that before the reaction, indicating that the iron-based substance had been intercalated into its structure.

[0044] Pore structure analysis ( Figure 5 and Figure 6 ): The specific surface area of the adsorbent is significantly improved compared with the original material, and the pore size distribution is more optimized, which is conducive to the adsorption and mass transfer process.

[0045] Adsorption performance ( Figure 7 and Figure 8 ):The adsorbent has a larger arsenic adsorption capacity than the original material, and the adsorption capacity can reach 6.67-11.93mg g -1 The adsorption performance is significantly positively correlated with its iron content, with chemical adsorption as the main adsorption and physical adsorption as the auxiliary.

[0046] Neutralizer saving effect ( Figure 9 ):The amount of CaO slurry required for neutralization of the pretreated filtrate is reduced by 17.6-68.1% compared with the unpretreated solution, and the higher the amount of montmorillonite added, the more obvious the neutralizer savings.

[0047] Comparative Example 1 (In the simulated AMD, the concentration of TFe can be 1 g L -1 、SO4 2- The concentration is 4 g L -1 , the initial pH is 3, with Fe 2+ as the main form, without montmorillonite)

[0048] The electrochemical method of this comparative example for rapidly recovering iron ions from acid mine wastewater to generate an iron-containing arsenic adsorbent comprises the following steps:

[0049] (1) Prepare the simulated solution: weigh 4.944g FeSO4·7H2O and 3.3815g Na2SO4 in a 1L beaker, add ultrapure water to completely dissolve, transfer to a 1L volumetric flask with a glass rod, and adjust the volume to 1L. Use 1mol L -1 Adjust the pH of the solution to 3 with HCl / NaOH. Dispense the prepared AMD solution into 300 mL electrolytic cells.

[0050] (2) Construction of an electro-oxidation reaction system: A ruthenium-iridium-titanium mixed metal electrode was constructed as the anode and a pure titanium mesh was constructed as the cathode. The electrodes were 3 × 3 cm in size and 3 cm apart. A DC power supply provided a constant voltage (5 V) for the electrical reaction.

[0051] (3) Separation and recovery after the reaction: After the reaction was completed for 10 hours, the suspension was centrifuged and a dark brown solid ( Figure 10 b) The solid is freeze-dried to obtain the prepared adsorbent.

[0052] (5) Neutralization treatment test: Take 50 mL of the filtrate obtained after centrifugation and place it in a 100 mL conical flask. Add CaO slurry dropwise while stirring until the pH reaches 7.5. Record the amount of neutralizer used.

[0053] Precipitation effect: The precipitation rate of TFe is 54.2%, SO4 2- The precipitation rate reached 5.86% ( Figure 2 CK).

[0054] Adsorbent appearance and composition ( Figure 10 a and b): SEM and EDS analysis showed that the adsorbent was characterized by a solid state of fine spherical, dark brown particles with high contents of iron and sulfur.

[0055] Crystal structure ( Figure 10 b and c): XRD and FTIR showed that the recovered adsorbent was mainly composed of Schroederite and hydroxyl iron.

[0056] Pore structure analysis ( Figure 11 and Figure 12 ): The specific surface area of the adsorbent is significantly smaller than that of the original montmorillonite and montmorillonite composite adsorbent.

[0057] Adsorption performance ( Figure 7 、 Figure 8 and Figure 13 ):The adsorbent has a larger arsenic adsorption capacity than the original material, and the adsorption capacity can reach 19.65mg g -1 , with chemical adsorption as the main method and physical adsorption as the auxiliary method, but the amount of adsorbent produced is limited.

[0058] Neutralizer saving effect ( Figure 9):The amount of CaO slurry required for neutralization of the pretreated filtrate is reduced by 8.4% compared with the unpretreated solution, which can save neutralizer, but the saving degree is not as great as that of montmorillonite co-treatment.

[0059] Example 2 (The concentration of TFe in the simulated AMD was 1 g L -1 、SO4 2- The concentration is 4 g L -1 , Cu 2+ 10mg L -1 , Mn50mg L -1 , Zn is 150 mg L -1 The initial pH was 3, with Fe 2+ as the main form)

[0060] (1) Prepare the simulated solution: weigh 4.944g FeSO4·7H2O, 2.9046g Na2SO4, 0.0390g CuSO4·5H2O, 0.1539g MnSO4·H2O and 0.6595g ZnSO4·7H2O in a 1L beaker, add ultrapure water and dissolve them completely, then transfer them to a 1L volumetric flask with a glass rod and adjust the volume to 1L. Use 1mol L -1 Adjust the pH of the solution to 3 with HCl / NaOH. Dispense the prepared AMD solution into 300 mL electrolytic cells.

[0061] (2) Construction of an electro-oxidation reaction system: A ruthenium-iridium-titanium mixed metal electrode was constructed as the anode and a pure titanium mesh was constructed as the cathode. The electrodes were 3 × 3 cm in size and 3 cm apart. A DC power supply provided a constant voltage (3 V) for the electrical reaction.

[0062] (3) Adding montmorillonite: A magnetic stirring rotor was added to the electrolytic cell and placed on a magnetic stirrer with a stirring rate of 500 rpm. Different amounts of (3, 6, and 12 g L -1 The pH of the solution was not additionally regulated during the entire reaction process.

[0063] Precipitation effect: Fe 2+ The oxidation rate of α-Fe was 45.52-55.89%, and the precipitation rate of TFe was 24.88-48.42% ( Figure 14 ).

[0064] This method achieves the simultaneous recovery of iron and sulfur resources and in-situ generation of adsorbents by building an electrochemical system of anodic oxidation and cathode alkali production, synergizing the buffering and adsorption properties of montmorillonite. During the reaction process, the anodic oxidation reaction and the cathode electrolytic alkali production effect synergistically generate a dynamic pH control environment. Montmorillonite, with its alkaline buffering capacity and adsorption characteristics, significantly enhances the co-precipitation effect of iron ions and sulfate ions. 2+In the slightly alkaline environment formed by cathode electrolysis of water and the alkaline buffer system of montmorillonite, it is converted into Fe by direct oxidation at the anode or indirect oxidation by dissolved oxygen. 3+ The generated trivalent iron species undergoes structural coupling with montmorillonite through surface adsorption and interlayer intercalation, ultimately forming an adsorbent with montmorillonite as a carrier. This method simultaneously achieves the directional fixation of iron elements and the functional modification of montmorillonite adsorption materials, forming a sustainable treatment model that combines pollutant removal and resource recycling, overcoming the limitations of existing pretreatment technologies such as Fe 2+ The process overcomes technical problems such as slow oxidation rate, low removal efficiency, cumbersome operation and potential safety hazards, thus achieving a better pretreatment effect, avoiding the technical bottlenecks encountered in direct neutralization treatment, and significantly reducing the amount of neutralizer used.

[0065] The embodiment described above is merely a preferred embodiment of the present invention. Although the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various improvements, substitutions, and variations without departing from the technical principles of the present invention. Such improvements and variations are all within the scope of protection of the present invention.

Claims

1. A method for recovering iron ions from acid mine drainage and generating an arsenic adsorbent in situ, characterized in that: The following steps are involved: (1) placing acid mine wastewater in an electro-oxidation system consisting of a ruthenium-iridium-titanium mixed metal anode and a pure titanium mesh cathode, and simultaneously adding montmorillonite to carry out a stirring reaction; (2) separating the suspension after the reaction, recovering the solid and drying it to obtain a montmorillonite-based composite arsenic adsorbent.

2. The method according to claim 1, characterized in that The Fe in the acid mine drainage 2+ The concentration is 0.4-1gL -1 , SO4 2- The concentration is 1-4 g L -1 .

3. The method according to claim 1, characterized in that In step (1), HCl or NaOH is used to adjust the initial pH value of the wastewater to 2.0-4.

0.

4. The method according to claim 1, wherein The electro-oxidation system is powered by a DC power supply with an operating voltage of 5 V and a reaction time of 10 hours.

5. The method according to claim 1, wherein The dimensions of the anode and cathode are both 3 cm×3 cm, and the distance between the electrodes is 3 cm.

6. The method according to claim 1, characterized in that The stirring speed in step (2) is 500 rpm, and the amount of montmorillonite added is 1-12 g L -1 .

7. The method according to claim 1, characterized in that The separation in step (3) is carried out by centrifugation, and the drying is carried out by freeze drying.

8. The arsenic adsorbent prepared by the method according to any one of claims 1 to 7, characterized in that: The adsorbent is a composite of montmorillonite loaded with iron oxyhydroxide, and its specific surface area is 35.8-74.1m 2 g -1 , the adsorption capacity for arsenic is 6.67-11.93 mg g -1 .

9. Use of the arsenic adsorbent according to claim 8 in the treatment of acid mine wastewater.

10. The use according to claim 9, characterized in that The method comprises a pretreatment step which is applied before the limestone neutralization process to reduce the amount of neutralizer used.

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