Green recyclable method for efficiently reducing and recycling vanadium (V) in wastewater

Abstract

The invention discloses a green and recyclable method for efficiently reducing and recovering vanadium (V) in wastewater. According to the method, titanomagnetite with magnetism and high reduction activity is used for reducing soluble V (V) into V (IV) / V (III) in a precipitation form, and resource reutilization of precious metal V is achieved through magnetic separation and recovery. The method comprises the following steps: synthesizing titanomagnetite nanoparticles with different doping amounts of titanium atoms by a coprecipitation method, adding the titanomagnetite nanoparticles into V (V)-containing simulated wastewater to realize surface adsorption and reduction immobilization of V (V), separating a V (V)-containing reduction product and a titanomagnetite solid part from a solid-liquid two-phase through magnetic adsorption separation, and then V is separated and recovered from the surfaces of titanomagnetite particles from the reduction product in a low-concentration acid pickling mode, and recycling of the titanomagnetite is achieved. The method is suitable for treating wastewater containing V (V) ions with different concentrations, the reduction degree can reach 100%, the recovery efficiency reaches 90% or above, and the method is low in treatment cost, environmentally friendly and wide in application prospect.

Description

Technical Field

[0001] This invention belongs to the field of vanadium (V) ion treatment and recovery technology in wastewater, specifically relating to a green and recyclable method for the efficient reduction and recovery of vanadium (V) in wastewater. Background Technology

[0002] Vanadium-titanium magnetite is a complex magnetic mineral containing multiple metallic elements such as iron, vanadium, and titanium. It possesses extremely high comprehensive utilization value, and its development and utilization play a crucial role in national infrastructure construction and strategic development. Southwest my country contains billions of tons of vanadium-titanium magnetite resources, making it an important iron ore region in my country. However, during the mining and smelting process of vanadium-titanium magnetite, large amounts of vanadium-containing waste residue and wastewater enter the environment, leading to serious environmental risks. Vanadium (V) is a variable-valence metallic element, mainly existing in the +3, +4, and +5 forms in the natural environment. The occurrence form of vanadium is mainly affected by the redox state and pH value of the environment. Under reducing conditions, vanadium exists stably in the trivalent and tetravalent forms with lower mobility and toxicity. However, once exposed to an aerobic environment, low-valent vanadium oxidizes to form soluble pentavalent vanadium, whose toxicity and mobility are significantly enhanced. Vanadium is an essential trace element for life, but excessive vanadium intake can lead to damage to the respiratory, digestive, and nervous systems, and seriously harm organs such as the kidneys, spleen, and intestines. Furthermore, excessive vanadium in soil and surface water can accumulate bioaccumulate and enter the human body through the food chain, posing a threat to the health of local residents. In addition, the demand for the precious metal vanadium has been increasing in recent years due to the development and application of energy storage materials (especially vanadium batteries). Therefore, developing efficient and environmentally friendly theories and technologies for vanadium pollution control, and researching new pathways for vanadium pollution reduction and the recycling of precious metals, are essential for achieving the rational development and utilization of vanadium resources in parallel with ecological environmental protection, and are in line with the major needs of national sustainable development.

[0003] Currently, non-biological treatment methods for vanadium-containing wastewater both domestically and internationally mainly include: 1) Adsorption: such as using adsorbents like activated carbon, resin, and natural minerals to adsorb and remove vanadium ions from water; 2) Precipitation: by adding precipitants or reducing agents, soluble vanadium ions are converted into precipitates, reducing their migration ability. For example, Tiina et al. investigated the removal efficiency of six iron-containing materials for vanadium in actual industrial wastewater. Through batch testing, they found that ferric hydroxide had the highest vanadium removal efficiency, mainly due to its highest iron content and weakly crystalline form of iron, which provides the most reactive sites, and the adsorption process conforms to the Langmuir isotherm. However, during wastewater treatment, ferric hydroxide gradually transforms into less reactive ferric oxide species, affecting long-term treatment effectiveness and resulting in high operation and maintenance costs (Leiviskä T., Khalid MK, Sarpola A., et al., 2017. Removal of vanadium from industrial wastewater using ironsorbents in batch and continuous flow pilot systems. Journal of Environmental Management, 190: 231-242.). Zhu et al. used chelating resin D851 to remove and recover tetravalent and pentavalent vanadium from acidic solution systems. They found that at pH < 1.5, the adsorption efficiency of D851 for vanadium exceeded 98%, and the equilibrium adsorption capacity of tetravalent vanadium was 162 mg / g. After regeneration using resin D851, the adsorption efficiency of vanadium remained above 97% even within a 10-fold range. However, the resin regeneration process requires high concentrations of acid, which causes significant secondary pollution (Zhu X., Yang X., Li W., et al., 2022. Efficient removal and recovery of vanadium (IV and V) from high acidic wastewater with resins D851 and D201: A comparative study. Journal of Water Process Engineering, 49: 103153.). In general, non-biological vanadium treatment and recovery methods suffer from high costs, poor long-term effectiveness, and a high risk of secondary pollution, resulting in significant limitations in practical applications. Therefore, increasing research is focusing on biological treatment technologies that offer lower maintenance costs and are more environmentally friendly.

[0004] Microbial synergistic mineral removal of vanadium from wastewater has become a research hotspot in recent years due to its environmentally friendly characteristics. At the phylum level, vanadium-reducing bacteria are mainly Proteobacteria, and all strains have been identified as Gram-negative bacteria. *Geobacterium* and *Shewanella* are widely accepted model strains for microbial V(V) reduction. In addition, *Bacillus* and *Pseudomonas* have also been found to be prevalent in vanadium-contaminated sites. Microbial V(V) reduction mainly involves two mechanisms: reduction via electron transfer using V(V) as an electron acceptor, and reduction by binding to reductases with other electron acceptors. The former is the focus of research, involving the synergistic use of various minerals (such as Maginotite, pyrrhotite, and siderite) as electron donors to reduce V(V) to the lower valence state V(IV). Although microbial V(V) reduction has been proven to be an efficient and sustainable method, the high operating costs, long growth cycles, low V recovery rates, and secondary pollution associated with microbial cultivation still restrict the application of related technologies. There is an urgent need to develop more efficient, green, and recyclable V(V) treatment and recovery technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for the resource-based disposal of valuable waste by efficiently reducing and fixing V(V) through the adjustment of the reduction potential of nano-minerals and achieving resource recovery and recycling of reducing materials through physical methods such as magnetic adsorption and rinsing. This method solves the problems of low recovery efficiency, serious secondary pollution, poor environmental compatibility, and high treatment costs in current methods for removing and recovering V(V) ions from wastewater. This invention utilizes the high reactivity and reduction potential of titanomagnetite nanoparticles with controllable redox potentials and different stoichiometric ratios to rapidly adsorb and efficiently reduce V(V) to lower valence states V(IV) and V(III), achieving V(V) removal from wastewater. V and titanomagnetite are separated using low-cost magnetic field separation and dilute hydrochloric acid rinsing, enabling metal resource recovery. The titanomagnetite is recyclable, environmentally friendly, and cost-effective.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A green and recyclable method for efficiently reducing and recovering V(V) from wastewater includes the following steps: using highly reactive and reducing titanomagnetite nanoparticles to adsorb V(V) ions from wastewater onto a solid surface to achieve rapid reduction and fixation of V(V); then using magnetic adsorption to separate the solid and liquid phases, followed by acid elution to remove V species from the surface of the nanoparticles, and adjusting the pH value to achieve V precipitation and recovery and recycling of the titanomagnetite nanoparticles.

[0007] In the above method, the general formula of the titanomagnetite is Fe. 3-x Ti x O4, where x takes values ​​from 0.17 to 0.46, and can further be from 0.31 to 0.46, specifically 0.17, 0.31, or 0.46.

[0008] The titanomagnetite nanoparticles used in this invention are prepared by an improved method. Compared with traditional methods, this method can synthesize titanomagnetite nanoparticles with a large x-value without introducing impurities. The method is simple and effective. The main steps include: (1) Prepare a mixed solution containing (1+x) mol / L FeCl2·4H2O, (2-2x) mol / L FeCl3·6H2O and x mol / L TiCl4 in an oxygen-free glove box using prepared oxygen-free deionized water, which also includes 0.3 mol / L HCl; the oxygen-free glove box is in a nitrogen atmosphere with O2 < 1 ppm; (2) After the solid particles are fully dissolved using a magnetic stirrer, NaOH solution (concentration can be 1 mol / L) is rapidly added dropwise to the solution until the color of the suspension changes from brownish-gray to black. The final pH value is 7.0±0.5. (3) Centrifuge (e.g., at a speed of 5000 rpm) to separate the solid and liquid phases. After thoroughly washing away the inorganic salt ions adsorbed on the surface of the titanomagnetite particles with oxygen-free deionized water, bring the solid particles to a suitable volume and adjust the pH of the suspension to 8.5 for later use.

[0009] In the above-mentioned method for synthesizing titanomagnetite nanoparticles, titanomagnetite particles with different stoichiometric ratios can be synthesized by adjusting the concentration of added titanium ions (different x values). Compared with the traditional ammonia method, when synthesizing titanomagnetite with larger x values, ilmenite (FeTiO4) impurities are not introduced on the surface of titanomagnetite. This method is suitable for treating wastewater containing V (V) with a wider concentration range. For example, when the V (V) concentration is high, it is preferable to use titanomagnetite particles with larger x values, thereby increasing the reduction capacity of titanomagnetite and achieving better reduction and fixation of V (V).

[0010] In the above-mentioned method for synthesizing titanomagnetite nanoparticles, the particle size of titanomagnetite particles can also be controlled. After synthesis, micron-sized particles can be obtained by heating and aging at 60°C. Preferably, nano-sized titanomagnetite is used for V (V) reduction and recovery. The average particle size of the nano-sized titanomagnetite is 10-15 nm.

[0011] In the method for treating and recovering V(V) ions from wastewater provided by this invention, the treatment effect on V(V) is better when the amount of titanomagnetite nanoparticles added and the V(V) concentration satisfy the molar ratio Fe(II) / V(V)>10. As the stoichiometric ratio of titanomagnetite Fe(II) / Fe(III) increases, the amount of titanomagnetite added can have an even lower concentration. For example, when the concentration of titanomagnetite (x=0.3) added to wastewater containing V(V) is 1.14 g / L, the highest corresponding treated V(V) concentration is approximately 20 mg / L.

[0012] In the above-mentioned method for treating and recovering V(V) ions in wastewater provided by the present invention, the added titanomagnetite nanoparticles reduce soluble V(V) ions to V(IV) / V(III). According to the pH-Eh phase diagram, when pH>6, V(IV) and V(III) will exist in solid form, and the precipitate adsorbed on the surface of titanomagnetite is beneficial for subsequent separation and recovery.

[0013] In the method for treating and recovering V(V) ions in wastewater provided by the present invention, the solid form of V and the pH range in which titanomagnetite is stably present require the solution to be near neutral. Therefore, it is necessary to control the pH value of the wastewater containing V(V) to be 6 or above (such as pH value 6-8.5 or 7-8.5 or 7.0, 8.0, 8.5). Before the reaction, the wastewater should be prepared to a suitable pH range with acid or alkali solution in advance, and the pH change should be monitored during the reaction to maintain pH stability.

[0014] In the method for treating and recovering V(V) ions in wastewater provided by the present invention, after V(V) is reduced and fixed on the surface of titanium magnetite, given the strong magnetic properties of titanium magnetite, a strong magnetic field separation method with low energy consumption is directly selected to separate the solid and liquid phases, which is efficient and energy-saving.

[0015] In the method for treating and recovering V(V) ions from wastewater provided by this invention, after use, the surface-fixed V species of the recovered titanomagnetite material are removed by leaching with 20 mM HCl, which effectively removes V from the surface of the titanomagnetite. The titanomagnetite can be recycled after being washed with oxygen-free water. The leaching solution obtained in the above process is collected, and the pH of the leaching solution is adjusted to >6 with a weak alkali, causing V(IV) / V(III) to precipitate again in solid form, thus realizing the resource recovery of V.

[0016] The reduction and recovery material used in this invention is nano-sized titanomagnetite with controllable reduction potential. The mineral potential is regulated by controlling the amount of titanium atoms incorporated, thereby altering the reduction rate and extent of V(V) by the nanoparticles. Simultaneously, due to the high specific surface area of ​​the nanoparticles, a large amount of V(V) ions can be adsorbed onto the particle surface, reducing soluble V(V) to solid V(IV) and V(III) under neutral conditions, achieving long-term fixation. This invention utilizes the stronger magnetic properties of titanomagnetite compared to ordinary magnetite, employing magnetic field separation to enrich and separate titanomagnetite nanoparticles. The surface V species are then eluted with dilute hydrochloric acid, regenerating the titanomagnetite for recycling. Subsequently, the pH of the elution solution is adjusted to near neutral with dilute alkali to recover solid V.

[0017] This invention is applicable to the treatment and recovery of V(V) and V(IV) in wastewater. In the embodiments of this invention, the removal process of V(V) in industrial / mining wastewater is simulated, and it can be adjusted according to the actual wastewater conditions.

[0018] The method for processing and recycling V(V) described in this invention has significant beneficial effects: The method for reducing, fixing, and recycling V(V) ions in wastewater provided by this invention improves the efficiency of V(V) recycling, reduces V(V) pollution, and achieves resource-based disposal. The reagents and methods used in this invention are relatively inexpensive and readily available, facilitating large-scale industrial production and overcoming the problems of high cost and long cycle in traditional methods. The treatment materials used in this invention have strong recycling capacity and can be reused multiple times after recycling and rinsing, making it green and environmentally friendly. Attached Figure Description

[0019] Figure 1 The images are high-resolution electron microscope (TEM) images and X-ray diffraction (XRD) patterns of common magnetite and titanomagnetite synthesized and used in Example 1 with x=0 and x=0.17, respectively. The synthesized materials were identified by comparison with the standard magnetite pattern (bottom) and the original pattern was refined and fitted.

[0020] Figure 2 The X-ray photoelectron spectroscopy (XPS) of the 2p orbital of V element and its fitting results are obtained by collecting solids after 7 days of the reduction reaction of V(V) by ordinary magnetite and x=0.17 titanomagnetite at pH 7.0 and V(V) ion concentration of 20 mg / L.

[0021] Figure 3 These are the product types and concentration change kinetic curves of magnetite and titanomagnetite reduction of V(V) at x=0 and x=0.17, as measured by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) in Example 1.

[0022] Figure 4 The images show TEM images and XRD patterns of the titanomagnetite with x=0.31 and x=0.46 synthesized and used in Example 2, as well as the identification of the synthesized material by comparison with the standard magnetite pattern (bottom) and the fine-fitting of the original pattern.

[0023] Figure 5 This is the XRD pattern of high stoichiometric titanomagnetite with x=0.46 synthesized by the conventional ammonia method in Example 2, which shows the diffraction characteristic peaks of the contained phases.

[0024] Figure 6 The figures are the open-circuit voltage (OCP) test curves of different x values ​​of titanomagnetite obtained by charge transfer medium testing under pH=7.0 conditions in Example 2. The charge transfer medium used for ordinary magnetite with x=0 is hexaammineruthenium chloride, the medium used for x=0.17 and x=0.31 is riboflavin, and the medium used for x=0.46 is diquat.

[0025] Figure 7 This refers to Example 2, where the relative proportions of different forms of V in the final product after the reduction of V(V) by titanomagnetite at different stoichiometric ratios are measured at pH 7.0 and V(V) ion concentration of 20 mg / L, with a reaction time of 7 days.

[0026] Figure 8 This refers to the degree of reduction of V(V) by titanomagnetite with different stoichiometric ratios under different pH conditions and V(V) ion concentrations of 20 mg / L in Example 3. The reduction products include V(IV) and V(III).

[0027] Figure 9 This is a comparison of the reduction rates of two types of titanomagnetite with x=0.31 and x=0.46 in two cycles of reduction and recovery of V(V) when the V(V) ion concentration is 20 mg / L in Example 4. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0030] Example 1 Different stoichiometric ratios of titanomagnetite (Fe) were synthesized by co-precipitation in an oxygen-free glove box (nitrogen atmosphere, O2 < 1 ppm). 3-x Ti x (O4, x=0, 0.17). First, a mixed solution containing (1+x) mol / L FeCl2·4H2O, (2-2x) mol / L FeCl3·6H2O, and x mol / L TiCl4 was prepared in a glove box using deionized water, including 0.3 mol / L HCl. Second, after thoroughly dissolving the solid particles at 800 rpm using a magnetic stirrer, 1 mol / L NaOH was rapidly added dropwise until the suspension changed from brownish-gray to black, at which point the pH was approximately 7.0. Finally, the solid and liquid phases were separated by centrifugation at 5000 rpm. After thoroughly eluting the inorganic salt ions adsorbed on the surface of the titanomagnetite particles with deionized water, the solid particles were brought to a suitable volume, and the pH of the suspension was adjusted to 8.5 for later use. The synthesis equation for titanomagnetite by coprecipitation is as follows:

[0031] Figure 1 The TEM and XRD characterization results are for ordinary magnetite and titanomagnetite nanoparticles with x=0 and x=0.17 synthesized by the above method. TEM results show that the synthesized x=0.17 titanomagnetite has a similar particle size to ordinary magnetite, ranging from 10-15 nm. XRD results compared with the standard magnetite XRD pattern confirm that the synthesized mineral is magnetite, without other impurity phases. Furthermore, XRD pattern refinement confirms that the cell parameter increases after the incorporation of titanium atoms, indicating that titanium atoms were successfully incorporated into the magnetite to synthesize titanomagnetite.

[0032] 0.0368 g of sodium orthovanadate (Na3VO4) powder was dissolved in 40 mL of oxygen-free water to prepare a stock solution with a V(V) concentration of 250 mg / L. Batch experiments were conducted in a nitrogen-atmospheric glove box using 100 mL transparent glass serum bottles, sealed with rubber stoppers and wrapped in aluminum foil to protect from light. V(V) was first equilibrated in simulated wastewater at pH 7.0 for 12 h, then suspensions of ordinary magnetite (x=0) and titanomagnetite (x=0.17) were added to initiate the reaction. The final reaction system volume was 40 mL, with V(V) and titanomagnetite concentrations of 20 mg / L and ~1 g / L, respectively. Subsequently, at designated sampling points of 0.5, 1, 2, 3, 4, 5, 6, and 7 days, 1 mL of the liquid was transferred to centrifuge tubes, dissolved in 6 M concentrated hydrochloric acid, and the species and corresponding concentration of V in the system were analyzed by HPLC-ICP-MS. After the reaction, the 2p orbital XPS spectra of the solid V element were collected.

[0033] like Figure 2 As shown, after 7 days of reaction, ordinary magnetite reduced only about 10% of V(V), while x=0.17 titanomagnetite reduced about 60% of V(V). The reduction and removal efficiency of V(V) by titanium-doped magnetite is significantly improved compared with that of ordinary magnetite.

[0034] Figure 3 The figures show the reduction kinetics curves of ordinary magnetite and x=0.17 titanomagnetite for V(V). The reduction rate of ordinary magnetite to fix V(V) is slower than that of x=0.17 titanomagnetite, and V(III) appears in x=0.17 titanomagnetite. The incorporation of titanium atoms increases the reduction ability of magnetite.

[0035] Example 2 High-titanium-doped titanomagnetite nanoparticles with x=0.31 and x=0.46 were synthesized using the method described in Example 1. A reduction reaction was initiated by adding high-stoichiometric titanomagnetite to simulated wastewater containing V (V) at pH=7.0. The final reaction system volume was 40 mL, with V (V) and titanomagnetite concentrations of 20 mg / L and ~1 g / L, respectively. The speciation and relative proportion of V in the reaction system were quantified using HPLC-ICP-MS.

[0036] Figure 4 These are TEM images and XRD patterns of titanomagnetite at x=0.31 and x=0.46. The synthesized high stoichiometric titanomagnetite is still at the nanoscale, with a particle size range of 10-15 nm. The incorporation of titanium atoms did not change the magnetite particle size. The XRD pattern shows a single magnetite phase without impurity phases. After fitting the unit cell parameters, it was found that increasing the titanium incorporation further increased the unit cell parameters.

[0037] This study compared the traditional ammonia injection method for synthesizing high stoichiometric titanomagnetite. Specifically, a fully dissolved mixed solution containing (1+x) mol / L FeCl2·4H2O, (2-2x) mol / L FeCl3·6H2O, and x mol / L TiCl4 (containing 0.3 mol / L HCl) was directly injected into a 25% w / v ammonia solution. The solution was stirred at 1400 rpm to precipitate titanomagnetite, which was then washed to obtain solid particles. Figure 5 The XRD pattern of the synthesized titanomagnetite at x=0.46 is shown. The results indicate that titanomagnetite prepared by the traditional ammonia method contains ilmenite (FeTiO3) impurity peaks. Rapid precipitation causes the ilmenite impurity phase to adhere to the surface of the titanomagnetite in a core-shell structure, thus affecting the reactivity of the titanomagnetite. Traditional methods introduce impurities when synthesizing titanomagnetite with high stoichiometry. In contrast, the improved method of this invention does not introduce other phases at x=0.46, resulting in better synthesis performance.

[0038] Figure 6 The open-circuit potentials of titanomagnetite with different stoichiometric ratios were measured using a charge-transfer medium. The intrinsic potential of titanomagnetite nanoparticles was lower than that of ordinary magnetite. Titanium doping reduced the reduction potential of magnetite, which is more conducive to the reduction of high-valence V. The potential of titanomagnetite is positively correlated with the amount of titanium doping. The more titanium atoms are incorporated, the more Fe(II) is required in the magnetite structure to neutralize the charge, and the lower the potential.

[0039] Figure 7These represent the relative proportions of different forms of V after reacting with V(V) at different stoichiometric ratios of IgM magnetite. IgM magnetite with x=0.31 exhibits a reduction rate of 82% for V(V). Further increasing the titanium doping content, IgM magnetite with x=0.46 achieves a reduction rate of 100% for V(V), demonstrating the superior reduction effect of high-titanium-doped IgM magnetite. The degree of V(V) reduction is also related to the titanium doping content. In the IgM magnetite systems with x=0.31 and x=0.46, the relative proportions of V(III) are 20% and 42%, respectively, significantly higher than those with x=0.17.

[0040] Example 3 Using the V(V) reduction parameters set in Example 1, the pH of the reaction system was adjusted to 7, 8, and 8.5 using 1 M HCl and 1 M NaOH, respectively. Different stoichiometric ratios of synthesized titanomagnetite were then added to initiate the reduction reaction. The final reaction system volume was 40 mL, with V(V) and titanomagnetite concentrations of 20 mg / L and ~1 g / L, respectively. pH fluctuations were monitored daily during the reaction, and the pH was adjusted back to the initial setting using 1 M HCl and 1 M NaOH. Figure 8 As shown, the reduction of V(V) by titanomagnetite gradually increases with the increase of pH in the reaction system. After 7 days of reaction, the reduction of V(V) in titanomagnetite with x=0.17 increased from 60% (pH=7) to 80% (pH=8.5), while the reduction of V(V) in titanomagnetite with x=0.31 showed a smaller change, increasing only from 80% to 90%, and the reduction of V(V) in titanomagnetite with x=0.46 remained unchanged at 100%. The pH of the reaction solution also affects the reduction potential of titanomagnetite, thus affecting the amount of V(V) reduced. Since the potential of titanomagnetite with high titanium doping is already sufficient to reduce V(V) to a large extent, changing the pH has a relatively small effect on the reduction of V(V) by titanomagnetite with high stoichiometric ratio.

[0041] Example 4 Using the V(V) reduction parameters set in Example 1, titanomagnetite with x=0.31 and x=0.46 was selected to reduce V(V) in simulated wastewater at pH=8.0. After 7 days of reaction, the solid and liquid phases were separated by strong magnetic attraction. The solid was washed twice with oxygen-free deionized water at pH=8.0, and then separated and collected again. The titanomagnetite solid was rapidly washed multiple times with 20 mM HCl, and the washing liquid was separated and collected. Then, the species and concentration of V in the solution were tested by HPLC-ICP-MS. The acid-washed titanomagnetite solid was washed with oxygen-free deionized water and added again to simulated wastewater containing V(V) to start the reduction reaction. After 7 days of reaction, the species and concentration of V in the eluent were collected and tested using the same treatment method, and the recovery rate of V(V) was calculated.

[0042] like Figure 9The diagram shows the recovery efficiency of V(V) by IgMA in two cycles. The recovery of V(V) by IgMA did not change significantly in either cycle. At x=0.46, the reduction and recovery of V(V) by IgMA remained around 100%, and at x=0.31, the second cycle maintained a similar recovery rate of 82% as the first. This indicates that the V(V) recovery process in this method has virtually no impact on the reduction capacity of IgMA. It is worth noting that since the reduction of V(V) consumes electrons in IgMA, a recharging treatment with Fe(II) solution should be considered during multiple cycles.

[0043] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A green and recyclable method for reducing and recovering vanadium (V) from wastewater, comprising the following steps: using titanomagnetite nanoparticles to adsorb vanadium (V) ions from vanadium (V)-containing wastewater onto a solid surface to achieve the reduction and fixation of vanadium (V); then using magnetic adsorption to separate the solid and liquid phases; then using acid elution to remove vanadium species from the surface of the nanoparticles; adjusting the pH value to achieve the precipitation and recovery of vanadium and the recycling of titanomagnetite nanoparticles.

2. The method according to claim 1, characterized in that: The general formula of the titanomagnetite is Fe. 3-x Ti x O4, where x ranges from 0.17 to 0.46; The method for preparing the titanomagnetite nanoparticles includes the following steps: (1) Prepare a mixed solution containing (1+x) mol / L FeCl2·4H2O, (2-2x) mol / L FeCl3·6H2O, x mol / L TiCl4 and HCl in an oxygen-free glove box using oxygen-free deionized water; the oxygen-free glove box is in a nitrogen atmosphere with O2 < 1 ppm; (2) After the solid particles are fully dissolved using a magnetic stirrer, NaOH solution is rapidly added dropwise to the solution until the color of the suspension changes from brownish-gray to black. The final pH value is 7.0±0.

5. (3) Centrifuge to separate the solid and liquid phases. After thoroughly washing away the inorganic salt ions adsorbed on the surface of the titanium magnetite nanoparticles with oxygen-free deionized water, adjust the nanoparticles to a suitable volume and adjust the pH of the suspension to 8.5 for later use.

3. The method according to claim 1 or 2, characterized in that: The average particle size of the titanomagnetite nanoparticles is 10-15 nm.

4. The method according to claim 1 or 2, characterized in that: The feeding ratio of the titanomagnetite nanoparticles to vanadium (V)-containing wastewater satisfies the following condition: the molar ratio of Fe(II) to vanadium (V) in the titanomagnetite nanoparticles is greater than 10.

5. The method according to claim 1 or 2, characterized in that: The titanomagnetite nanoparticles reduce soluble vanadium (V) ions in vanadium (V)-containing wastewater to solid vanadium (IV) / vanadium (III) and precipitate them from the solution. The precipitate is adsorbed on the surface of the titanomagnetite nanoparticles.

6. The method according to claim 5, characterized in that: The pH value of the vanadium (V)-containing wastewater is controlled to be 6 or above.

7. The method according to claim 1 or 2, characterized in that: The magnetic separation of solid and liquid phases is achieved by using a strong magnetic magnet to separate the two phases.

8. The method according to claim 1 or 2, characterized in that: The vanadium species immobilized on the surface of the nanoparticles were eluted using 20 mM HCl, and the eluted solution and the eluted titanomagnetite nanoparticles were collected.

9. The method according to claim 8, characterized in that: The pH of the eluent was adjusted to >6 using a weak alkali, so that V(IV) / V(III) in the eluent precipitated and recovered in solid form; And / or, the eluted titanomagnetite nanoparticles can be reactivated with Fe(II) solution to achieve continuous recycling.

10. The method according to claim 1 or 2, characterized in that: The vanadium (V)-containing wastewater is either industrial wastewater containing vanadium (V) or mining wastewater containing vanadium (V).

Images