Synthesis method and application of nano zero-valent iron loaded struvite mineral composite material for selective recovery of copper ions

Abstract

The invention discloses a synthesis method and application of a nano zero-valent iron loaded struvite mineral composite material for selective recovery of copper ions, and the method comprises the following steps: oxidizing ferric iron into nano zero-valent iron by using an oxidant in an aqueous solution of an organic solvent, and then synthesizing struvite with a wrapping structure in a solution containing the nano zero-valent iron, and separating and drying to obtain the nano zero-valent iron supported struvite mineral composite material. The functionalized struvite mineral composite material synthesized by the method has the characteristics of good separation effect, high selectivity and difficulty in desorption on copper ions, and copper can be selectively enriched and separated from Cu-Co-Ni waste liquid. The used struvite synthesis raw material is cheap and easy to obtain, the chemical synthesis process is simple to operate and mild in reaction, and the obtained mineral composite material is excellent in passivation capability and relatively simple and convenient to store and use, and has a relatively wide application prospect in selective enrichment and separation of copper resources in specific composite precious metal polluted wastewater.

Description

Technical Field

[0001] The present invention relates to a selective enrichment and separation material for heavy metal copper, and in particular to a synthesis method and application of a nanometer zero-valent iron-loaded struvite mineral composite material for selective adsorption of copper ions. Background Art

[0002] The global trend towards new energy and electrification has led to a significant increase in the demand for Co / Ni / Cu, and issues such as its mineral sources, distribution, processing, and secondary recycling have received widespread attention. Co / Ni often forms composite deposits with elements such as Cu, leading to serious Co-Ni-Cu heavy metal composite pollution during the mining process. In addition, the production process of Co / Ni / Cu metal also produces a large amount of industrial wastewater (containing heavy metals such as Co, Ni, and Cu). Its substandard treatment or arbitrary discharge will cause huge economic losses and serious environmental pollution problems. Although heavy metals are pollutants, they are also a potential mineral resource. However, the separation and extraction of copper from the Co-Ni-Cu heavy metal composite system is relatively difficult, and there is currently no better treatment method.

[0003] Studies have found that struvite, a metastable phosphate mineral material with excellent passivation ability for a variety of heavy metals, shows broad application prospects in the field of heavy metal passivation and pollution remediation research. However, the vast majority of studies only focus on the passivation effect of heavy metals and their environmental effects, and do not focus on the selective separation and extraction of specific heavy metals in specific complex heavy metal systems. Therefore, studying the separation and extraction of copper elements in the Co-Ni-Cu heavy metal complex system using struvite mineral materials has important economic value and environmental significance. At the same time, the precipitates formed after struvite immobilizes heavy metals are currently separated by centrifugation, filtration, and natural sedimentation, but the separation cost is high and the time is long. Summary of the Invention

[0004] Purpose of the invention: In response to the problems existing in the prior art, the present invention provides a method for synthesizing a multifunctional struvite mineral composite material for selective recovery of copper ions. The present invention is a method for synthesizing and preparing a multifunctional struvite mineral composite material using a two-step chemical method. The present invention can use common chemical reagents as raw materials and adopt a chemical method to prepare a special core-shell structure to prepare a copper ion selective recovery mineral composite material with excellent enrichment effect, which can efficiently recover copper ions in a Co-Ni-Cu heavy metal composite system.

[0005] The present invention also provides a multifunctional struvite mineral composite material for selective copper ion recovery and its application. The present invention synthesizes and prepares a highly efficient, easy-to-operate struvite composite material with magnetic recovery properties, which can be used for efficient and selective copper ion recovery.

[0006] Technical solution: In order to achieve the above-mentioned purpose, the present invention provides a method for synthesizing a nano-zero-valent iron-loaded struvite composite material for selective recovery of copper ions, comprising the following steps: using an oxidant to oxidize trivalent iron or divalent iron into nano-zero-valent iron in an aqueous solution of an organic solvent, then synthesizing struvite with an encapsulated structure in a solution containing nano-zero-valent iron, and obtaining a mineral composite material of nano-zero-valent iron-loaded struvite after separation and drying.

[0007] Wherein, the oxidant is KBH4 or NaBH4.

[0008] Wherein, the trivalent iron is provided by FeCl3·6H2O, and the divalent iron is provided by ferrous chloride.

[0009] The aqueous solution of the organic solvent is an ethanol aqueous solution or a propanol aqueous solution, and the concentration range is 70-80% by volume.

[0010] Wherein, 1-2g KBH4 and 3-4g FeCl3·6H2O were added to every 200mL ethanol aqueous solution.

[0011] The struvite synthetic material includes Na2HPO4·12H2O, NH4Cl and MgCl2·6H2O in a mass ratio of 1-1.5:0.5-1:0.2-0.5, and is formed by reacting at room temperature for 10-20 minutes.

[0012] Preferably, the oxidant and the trivalent iron ion are analytically pure KBH4 and FeCl3·6H2O.

[0013] Preferably, the ethanol-water solution is an ethanol solution with a certain percentage concentration.

[0014] Preferably, 1-2 g KBH4 and 3-4 g FeCl3·6H2O are added to every 200 mL of ethanol solution.

[0015] Preferably, the struvite synthetic materials are analytically pure Na2HPO4·12H2O (1-1.5 g), NH4Cl (0.5-1 g) and MgCl2·6H2O (0.2-0.5 g).

[0016] Preferably, the freeze-drying temperature is -55°C, and the drying is carried out for 3 days. The mineral complex is collected and ground through a 60-mesh sieve to obtain a nano-zero-valent iron-loaded struvite mineral composite material.

[0017] The nanometer zero-valent iron loaded struvite mineral composite material is prepared by the synthesis method of the multifunctional struvite composite material for selective recovery of copper ions described in the present invention.

[0018] The nanometer zero-valent iron loaded struvite mineral composite material of the present invention is used in the selective enrichment and separation of copper ions or in the preparation of a specific copper ion passivator.

[0019] The selective passivator for recovering heavy metal copper ions described in the present invention comprises the nano zero-valent iron loaded struvite mineral composite material.

[0020] The present invention slowly adds a specific oxidant solution to an ethanolic liquid solution (containing ferric chloride hexahydrate). After a sufficient chemical reaction, beaded black nano-zero-valent iron is obtained. Disodium hydrogen phosphate, ammonium chloride, and magnesium chloride are then added to the aqueous solution (containing the synthesized nano-zero-valent iron) to synthesize a core-shell structured nano-zero-valent iron-loaded struvite mineral composite material through a precipitation reaction. The first step, synthesizing the solution, is an ethanol-water solution at a certain concentration. The present invention's synthesis system is complex, and differences in the order and quality of chemical elements added can lead to significant differences in the composition of the synthesized material. For example, the material prepared by adding sodium phosphate and magnesium chloride first, followed by ammonium chloride, according to the method of Example 1, exhibits significantly inferior performance to that of Example 1.

[0021] The nano zero-valent iron loaded struvite mineral composite material of the present invention is a nano zero-valent iron loaded struvite mineral composite material with a core-shell structure synthesized by utilizing the chemical reaction principle and crystal growth theory and the order in which they occur. This characteristic can be utilized to enable insoluble compounds to form organic-inorganic mineral complexes containing struvite crystals of a specific structure. The raw materials of the present invention are derived from analytically pure chemical reagents, and the method adopted is a two-step chemical method for sequential synthesis. The composite material synthesized by the present invention has selective enrichment and separation characteristics for copper ions, and can selectively recover copper from mixed heavy metal waste liquid. The chemical raw materials used in the present invention are cheap and easy to obtain, can be synthesized at room temperature, and are simple to operate. The obtained struvite mineral composite material is easy to store and use, and has broad application prospects for the selective recovery of copper resources in composite heavy metal contaminated wastewater. In addition, in the present invention, phosphate and magnesium ions need to be added successively for the synthesis of struvite minerals. If added at the same time, magnesium phosphate compounds will be generated, and struvite cannot be generated.

[0022] The present invention adopts the design principle of regulating the sequence of different chemical reactions and their occurrence in different liquid solutions, and successfully synthesizes a new organic-inorganic mineral composite material with efficient and selective adsorption of copper ions. The material can enrich and separate copper ions from a composite heavy metal solution. The material prepared by the present invention can efficiently and selectively recover copper ions. The existing struvite mineral material has poor recovery capacity and cannot efficiently recover specific heavy metals under field environmental conditions. Moreover, the material prepared by the present invention can extract specific heavy metals through magnetic separation characteristics. In addition, the material of the present invention has an irregular morphology. The different affinities of the struvite composite material to heavy metals result in its selective extraction of copper, which can achieve physical and chemical passivation. The existing materials have less difference in affinity to common heavy metals and most of them are physical adsorption.

[0023] The present invention combines redox reaction and crystal growth to synthesize a core-shell structure of struvite-coated nano-zero-valent iron, ensuring the long-term stability of part of the nano-zero-valent iron, which is beneficial to the subsequent magnetic separation and can be applied to complex field environments to passivate heavy metal pollution and extract and separate pollutants. The present invention proposes for the first time to use metastable crystalline struvite minerals as a wrapping material to form a core-shell structure with nano-zero-valent iron inside and struvite outside, achieving long-term stability of the internal part of the nano-zero-valent iron while having the high reactivity of struvite, greatly expanding the application scenarios of heavy metal recovery. In the present invention, the struvite mineral is used to protect the nano-zero-valent iron and form a core-shell structure, thereby achieving the purpose of selectively passivating heavy metal copper and passing the passivation product through magnetic separation, and can be applied to complex field environments.

[0024] In the present invention, zero-valent iron is simple to synthesize and has high reaction activity, while struvite is difficult to synthesize. The combination of the two can achieve selective enrichment of copper and then passivate the product through magnetic separation, which has good application prospects in complex field environments.

[0025] The present invention focuses on efficiently recovering copper ions from a Co-Ni-Cu heavy metal composite system, followed by treatment of the Co and Ni. This effectively achieves the goal of selectively recovering and reusing copper ions in the composite system, reducing wastewater treatment costs while also generating economic value. The material constructed in this invention is the first to efficiently and rapidly separate and extract copper from a Co-Ni-Cu heavy metal composite system, a goal not achieved with either zero-valent iron or struvite alone.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0027] The synthesis method of the nano zero-valent iron loaded struvite mineral composite material of the present invention utilizes the regulation of the order of occurrence of different chemical reactions and the crystal growth theory to synthesize it. It is a mineral composite material containing only crystalline struvite mineral and hydroxyl organic compound. It is an organic-inorganic mineral composite material developed based on the chemical reaction principle and crystal growth theory with the characteristics of efficient and selective enrichment and separation of copper. It is a new mineral synthesis method for efficiently separating copper ions under conditions of complex heavy metal pollution.

[0028] The nano-zero-valent iron-loaded struvite mineral composite material of the present invention has a maximum copper removal capacity of approximately 166.67 mg / g, significantly exceeding the corresponding values ​​of most currently available mineral adsorption materials. In a simulated aqueous solution of Cu-Co-Ni, the mineral composite material efficiently and selectively enriches and separates copper, while exhibiting a weaker adsorption effect on the Co / Ni mixture. Furthermore, the composite material can convert nitrate into nitrogen gas, allowing the material prepared by the present invention to rapidly remediate copper contamination.

[0029] The raw materials in the synthesis method of the present invention are cheap and easily available, the synthesis is carried out at room temperature, the operation is simple, and the application range is wide. The obtained nano zero-valent iron loaded struvite mineral composite material has good stability, is easy to store and use, and has great application prospects for the recovery and utilization of copper resources in composite heavy metal contaminated wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Elemental and morphological characterization of mineral materials (A, B) SEM; (C) electron image; (D) EDS.

[0031] Figure 2 Physical and chemical properties of mineral materials (A) XRD; (B) FTIR; (C) magnetic curve.

[0032] Figure 3 The adsorption isotherms of heavy metals on struvite composite materials (A) Cu (B) Co (C) Ni.

[0033] Figure 4 Adsorption kinetics of heavy metals on struvite complexes (A)Cu (B)Co (C)Ni.

[0034] Figure 5 NO3 - Effect of struvite composites on the adsorption of heavy metals (A) Specific removal capacity of elements (B) NH4 + Concentration; (C) pH.

[0035] Figure 6 The effect of different ratios of zero-valent iron and struvite on the selective passivation of copper by the material. DETAILED DESCRIPTION

[0036] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings.

[0037] Unless otherwise specified, the materials and reagents used in the examples can be obtained from commercial sources.

[0038] Example 1

[0039] The preparation method of the nano zero-valent iron loaded struvite mineral composite material is as follows:

[0040] 1. Preparation of Nano-Zero-Valent Iron: Prepare 200 mL of an 80% ethanol solution using anhydrous ethanol and ddH2O. Then, pipette 40 mL of this ethanol solution into a 50 mL EP tube. Using an analytical electronic balance, weigh 1.08 g of KBH4 and place it into the EP tube containing 40 mL of ethanol solution to dissolve it. Using an analytical electronic balance, weigh 1.62 g of FeCl3·6H2O and pour it into a glass beaker containing the remaining ethanol solution. Place the beaker on a magnetic rotator and stir (400 rpm). Use a pipette to remove all of the KBH4 solution and slowly add it to the ferric chloride solution. Continue stirring for 10 minutes. Wash the precipitate two to three times with ddH2O, fix it with a magnet, and pour off the supernatant to obtain the nano-Zero-Valent Iron precipitate.

[0041] 2. Preparation of Nano-Zero-Valent Iron-Loaded Struvite: Add 100 mL of ddH2O to the beaker containing the entire nano-Zero-Valent Iron precipitate prepared above and mix thoroughly using a magnetic stirrer. First, weigh 2.31 g of Na2HPO4·12H2O and 1.53 g of NH4Cl using an analytical electronic balance and add them to the beaker. Then, quickly add 0.78 g of MgCl2·6H2O to the beaker and stir continuously at 400 rpm for 10 minutes.

[0042] After stirring, secure the precipitated compound with a magnet and rinse several times with ddH2O. Place the precipitated compound in a new 50 mL EP tube. Finally, freeze-dry the mixture in a vacuum freeze dryer (-55°C for 3 days). Grind the powder through a 60-mesh sieve and set aside.

[0043] The morphology of the solid powder finally obtained in step (3) was identified by SEM-EDS. The mineral material synthesized by the present invention exhibits an irregular morphology ( Figure 1 A). The magnified image shows that the mineral surface is rough and contains nano-scale beaded structures in certain areas ( Figure 1 B), which should be nano-zero-valent iron. EDS results show that the mineral is composed of Mg, O, P, N, Fe and C ( Figure 1C and D), Mg, O, P, and N are the constituent elements of struvite. Fe is derived from nano-zero-valent iron or synthetic raw materials, and C is likely derived from carbon-based compounds such as ethanol during the nano-zero-valent iron synthesis process.

[0044] Example 2

[0045] Analysis of physical properties of nano-zero-valent iron loaded struvite mineral composites ( Figure 2 )

[0046] The mineral crystal structure of the nano-zero-valent iron-loaded struvite composite material obtained in Example 1 was analyzed using an X-ray diffractometer (XRD, BTX-526, Olympus, USA). The XRD results showed that the synthetic mineral material was mainly composed of crystalline struvite, but no peaks of nano-zero-valent iron were detected ( Figure 2 A), which indicates that the synthesized nano-zero-valent iron may be an amorphous mineral. Infrared spectrometry (FTIR, Nexus 670, Thermo Nicolet) was further used to explore the composition of mineral functional groups. FTIR results showed that in addition to phosphate groups and ammonium groups (struvite functional groups), the surface of the mineral material also contained functional groups such as hydroxyl and carbonyl groups ( Figure 2 B), which indicates that the material synthesized in this paper is an organic-inorganic mineral composite material. Finally, the magnetic intensity was characterized by a vibrating sample magnetometer (VSM, LakeShore7404, USA). The magnetic data showed that the saturation magnetic intensity was 22.12emu / g, the remanence was 7.13emu / g, the coercive force was 609.79Oe, and the hysteresis curve was elongated as a whole. This result indicates that the mineral composite material synthesized in this paper is a hard magnetic material ( Figure 2 C). Studies have shown that the material of the present invention can efficiently and selectively retain copper and possesses magnetic properties, facilitating its separation from the environment. Based on the above research results, the nano-zero-valent iron-loaded struvite mineral composite synthesized in Example 1 can be referred to as a Fe-struvite composite (FSC).

[0047] Example 3

[0048] Adsorption of heavy metals (Cu, Co, Ni) by nano-zero-valent iron loaded struvite mineral composites:

[0049] The nano-zero-valent iron-loaded struvite mineral composite material obtained in the above Example 1 was used for the adsorption of heavy metals: single heavy metal aqueous solutions of different concentrations (Cu: 4.88-397.96 mg / L; Co: 4.95-406.94 mg / L; Ni: 4.45-378.36 mg / L) were prepared using ddH2O, CuCl2·2H2O, CoCl2·6H2O and NiCl2·6H2O, respectively. Then, ddH2O and the aforementioned chemical reagents were used to prepare different binary heavy metal aqueous solutions of Cu (4.69-381.86 mg / L) + Ni (4.78-394.12 mg / L); Cu (4.71-387.74 mg / L) + Co (4.83-409.49 mg / L); Co (4.72-414.63 mg / L) + Ni (4.73-387.42 mg / L), and the binary heavy metal concentrations were compounded in similar concentrations from low to high. Finally, ddH2O and chemical reagents were used to prepare ternary heavy metal solutions of different concentrations of Cu (4.63-382.20 mg / L) + Co (4.80-395.3 mg / L) + Ni (4.86-415.66 mg / L), and the ternary heavy metal concentrations were compounded in similar concentrations from low to high.

[0050] Use a pipette to draw 20mL of the above-mentioned different composite heavy metal solutions of different concentrations into multiple 50mL EP tubes, and each concentration and each composite heavy metal are repeated three times. Use an analytical electronic balance to weigh multiple 0.01g of adsorbent (Example 1 Synthetic FSC). The adsorbent is added to the aforementioned 50mL EP tubes and quickly placed in a shaking table (100rpm, 25°C) and incubated for 24h. After the adsorption is completed, centrifuge (9000rpm, 25°C, 5min) is used to centrifuge and take the supernatant. Use a flame atomic spectrophotometer (AAS, AA-6300C, Shimadzu) to measure the concentrations of Cu, Co, Ni, Mg and Fe in the supernatant, and spectrophotometric determination of NH4 in the supernatant. + The concentration of heavy metals was calculated according to equation (1).

[0051] Q e =(C o -C e ) / M×V (1)

[0052] Q e : Unit adsorption capacity at adsorption equilibrium, mg / g; C o : initial concentration of heavy metals, mg / L; C e : heavy metal concentration in the solution when adsorption reaches equilibrium, mg / L; M: amount of adsorbent added, g; V: volume of adsorption solution, mL.

[0053] In different adsorption systems, the unit adsorption capacity of FSC for Cu(II) showed an overall trend of increasing with the increase of the initial concentration of Cu(II). The presence of Co(II) and Ni(II) reduced the adsorption capacity of FSC for Cu(II), but the reduction was small. The reason for this phenomenon is the competitive adsorption between heavy metals ( Figure 3 A). The adsorption of Co(II) and Ni(II) by FSC generally showed a trend of increasing first and then leveling off with the increase of initial metal concentration, but the presence of other ions significantly reduced the adsorption of Co(II) and Ni(II) by FSC ( Figure 3 B and C), this result indicates that the adsorption of Co(II) and Ni(II) is easily competed with Cu(II), further revealing that FSC has a low affinity for Co(II) and Ni(II). In addition, this example further uses an adsorption isotherm model to fit the adsorption isotherm data. The fitting results are shown in Table 1.

[0054] Table 1 Adsorption isotherm parameters

[0055]

[0056] The results in Table 1 show that the adsorption energy of FSC for heavy metal Cu(II) is better fitted by the Freundlich equation (R 2 =0.9938 / 0.9363), which shows that the adsorption of heavy metal Cu(II) by FSC is multilayer adsorption. The adsorption of Co(II) and Ni(II) by FSC can be better fitted by the Langmuir equation (R 2 =0.9995 / 0.4990 and 1 / 0.9292), which indicates that the adsorption of Co(II) and Ni(II) by FSC is monolayer adsorption. L and 1 / n are both between 0 and 1, indicating that FSC is beneficial for the adsorption of Cu(II) / Co(II) / Ni(II). This example effectively demonstrates the number of distribution layers of heavy metals on FSC and the ease of adsorption, demonstrating that the FSC prepared by the present invention can efficiently recover Cu(II) from Cu(II) / Co(II) / Ni(II).

[0057] Example 4

[0058] Selective adsorption of copper by nano-zero-valent iron loaded struvite mineral composites ( Figure 4 ):

[0059] Heavy metal solutions with different composite systems of specific concentrations (374.21 mg / L Cu, 423.13 mg / L Co, 347.95 mg / LNi; 385.78 mg / L Cu+405.53 mg / L Co, 384.36 mg / L Cu+372.58 mg / LNi, 405.20 mg / LCo+379.83 mg / LNi; 379.06 mg / LCu+381.06 mg / L Co+377.78 mg / LNi) were prepared using ddH2O, CuCl2·2H2O, CoCl2·6H2O and NiCl2·6H2O, respectively. Use a pipette to draw appropriate amounts of 20 mL of different composite system heavy metal solutions into 50 mL EP tubes (three replicates for each treatment), use an analytical electronic balance to weigh appropriate amounts of 0.01 g of adsorbent, add the adsorbents to the above 50 mL EP tubes and place them in a shaker (25°C, 100 rpm) for shaking culture. Take out three EP tubes at different time points (time points: 5-720 min), centrifuge (25°C, 9000 rpm, 5 min) to collect the supernatant, and use AAS to measure the heavy metal concentration in the supernatant. The unit adsorption capacity of the adsorbent for heavy metals is calculated according to equation (1). Based on the experimental results, the experimental data are fitted using pseudo-first-order and pseudo-second-order kinetic equations, and the type of interaction force between the adsorbent and heavy metals is analyzed based on the relevant fitting parameters.

[0060] The adsorption of Cu(II) by FSC showed a trend of gradually increasing and then tending to parallel with the extension of adsorption time, but the presence of other ions promoted the adsorption of Cu(II) by FSC ( Figure 4 A), which may be related to the formation time and method of copper-containing phosphate compounds. The temporal changes of FSC adsorption of Co(II) and Ni(II) are similar to those of FSC adsorption of Cu(II), but the presence of other ions inhibits the adsorption of FSC on Co(II) / Ni(II) ( Figure 4 B and C), the results show that FSC has a high affinity for Cu (II). In addition, this example further uses a kinetic model to fit the experimental data, and the results are shown in Table 2.

[0061] Table 2 Adsorption kinetic parameters

[0062]

[0063] The results in Table 2 show that the adsorption of Cu, Co and Ni by FSC can be well fitted by pseudo-second-order kinetics (R 2=0.9944 / 0.9944, 0.9995 / 0.8829 and 0.9973 / 0.9896). The results show that the adsorption of Cu, Co and Ni by FSC is dominated by chemical adsorption. In addition, further analysis of the adsorption kinetics experimental results found that FSC has a selective retention capacity for Cu in the ternary composite system ( Figure 4 To further quantify the selective retention capacity of FSC for Cu, the selectivity coefficient and distribution coefficient results are shown in Table 3.

[0064] Table 3 Distribution coefficient and selectivity coefficient parameters

[0065]

[0066] Note: Cu-Co-Ni ternary composite system, distribution coefficient K d =Q t / C t , selectivity coefficient k = K d (Cu) / K d (x),x=Co / Ni.

[0067] The results in Table 3 show that the k value shows an overall increasing trend with the extension of adsorption time. This result indicates that FSC can efficiently and selectively enrich and separate Cu from a composite heavy metal solution with strong specificity. Although pure struvite alone has a strong ability to passivate heavy metals (prepared according to the method of Example 1 without the addition of nano-zero-valent iron), its ability to selectively enrich and separate specific heavy metals is relatively weak, and the separation of the passivated products is difficult. The FSC in the present invention can not only efficiently and selectively enrich copper in a Cu-Co-Ni composite system, but also has magnetic separation properties, which will provide a practical basis for the industrial application of FSC.

[0068] Example 5

[0069] Effect of nitrate on the selective passivation of Cu(II) Figure 5 ):

[0070] The quaternary composite system solution (NO3 -:9.00-44.69mg / L+81.28mg / L Cu+19.61mg / L Co+19.46mg / LNi). Use a pipette to draw 20mL of the composite solution of different nitrate concentrations into a 50mL EP tube (three replicates for each concentration), use an analytical electronic balance to weigh an appropriate amount of 0.01g of adsorbent, and add it to the above-mentioned 50mL EP tube. Then, the experimental system was placed in a shaking table (25°C, 100rpm) and incubated for 24h. After the shaking, centrifuge (9000rpm, 25°C, 5min) was used to collect the supernatant and the metal ion concentration in the supernatant was measured using AAS. The change in nitrate concentration was measured using ion chromatography (ICS-1100, Dionex, USA). Finally, the unit removal amount of nitrate and heavy metals by the adsorbent was calculated according to equation (1).

[0071] With the increase of the initial concentration of nitrate in the composite system, the unit immobilization capacity of Cu(II) by FSC showed an overall decreasing trend, but the amplitude was low; the effect on the unit immobilization capacity of Co(II) and Ni(II) was weak; the unit removal capacity of nitrate by FSC showed a slight increasing trend ( Figure 5 A). The results show that the presence of nitrate inhibits the selective passivation ability of FSC for Cu(II), which may be due to the competition between nitrate and Cu(II) for free electrons. After FSC adsorbs pollutants, NH4 + The concentration changes showed a trend of first decreasing and then increasing and were generally lower than the control group ( Figure 5 B) This result indicates that FSC is unlikely to reduce nitrate to form NH4 + After FSC adsorbed pollutants, the pH of the adsorption solution increased ( Figure 5 C), which may be related to the reduction of nitrate into nitrogen by nano-zero-valent iron (NO2 - The existence of H + This example proves that the effect of reducing substances represented by nitrate on the selective passivation of copper by FSC is relatively weak, and FSC has a strong anti-interference ability.

[0072] Example 6

[0073] Mechanism of FSC selective passivation of copper:

[0074] Using a pipette, 20 mL of a 347.12 mg / L Cu(II) solution was pipetted into a 50 mL EP tube. Three portions of 0.01 g each of Cu(PO)₄, Co(PO)₄, and Ni(PO)₄·xH₂O were weighed using an analytical electronic balance. 0.01 g of the adsorbent was added to the 50 mL EP tube, and the tube was shaken on a shaker (25°C, 100 rpm) for 24 h. After shaking, the supernatant was collected by centrifugation (25°C, 9000 rpm, 5 min). Finally, the metal ion concentration in the supernatant was determined using AAS, and the specific adsorption capacity of the adsorbent for heavy metals was calculated according to Equation (1).

[0075] Ternary composite heavy metal solutions (Cu: 8.84-83.58 mg / L, Co: 18.75 mg / L, and Ni: 19.26 mg / L) were prepared using ddH2O and related chemical reagents: copper chloride, cobalt chloride, and nickel chloride. 20 mL of each ternary composite heavy metal solution of varying concentrations was pipetted into a 50 mL EP tube. An appropriate amount of 0.01 g of adsorbent was weighed using an analytical electronic balance and added to the 50 mL EP tube. The tube was then shaken on a shaker (25°C, 100 rpm) for 24 h. After shaking, the supernatant was collected by centrifugation (25°C, 9000 rpm, 5 min). The metal ion concentration in the supernatant was determined by AAS. The specific adsorption capacity of the adsorbent for heavy metals was calculated according to Equation (1).

[0076] Ion exchange occurred during the adsorption of Cu(II) by FSC, Ni-PO4, and Co-PO4. This result suggests that differences in solubility products between phosphate minerals contribute to the selective passivation of Cu(II) by FSC (Table 5). Further research revealed that the higher the initial Cu(II) concentration in the composite heavy metal solution, the stronger the selective passivation ability of FSC for Cu(II) (Table 6). This result indicates that the initial Cu(II) concentration of the mixed solution affects the selective retention of Cu(II) by FSC. These results provide a new approach for the design of selective adsorption materials for heavy metals.

[0077] Table 5 Effect of solubility product differences on the selective adsorption of copper by FSC

[0078]

[0079] Table 6 Effect of copper concentration on FSC selective adsorption

[0080]

[0081] Example 7

[0082] Effect of different raw material ratios on selective copper passivation

[0083] The preparation method of Example 1 is followed, except that the amount of nano zero-valent iron and struvite materials is (A) 2:2 (B) 1:1 (C) 1:2 (D) 0.5:2 (E) 0.5:4; wherein B is the amount of material in Example 1 of the present invention, with the amount of nano zero-valent iron synthetic material in Example 1 being 1 and the amount of struvite synthetic material being 1; the materials prepared by adjusting the amounts of A, C, D, and E are different.

[0084] The results of the heavy metal fixation were as follows: Figure 6 As shown. Figure 6 It can be seen that the FSC synthesized by the raw material ratio in Example 1 has a high unit adsorption capacity for copper and a low unit adsorption capacity for cobalt and nickel, showing a highly selective retention property for copper.

Claims

1. A method for synthesizing a nanometer zero-valent iron-loaded struvite composite material for selective recovery of copper ions, characterized in that: The method comprises the following steps: using an oxidant to oxidize trivalent or divalent iron into nano-zero-valent iron in an aqueous solution of an organic solvent, then synthesizing struvite with an encapsulated structure in the solution containing the nano-zero-valent iron, and obtaining a mineral composite material of nano-zero-valent iron loaded struvite after separation and drying.

2. The method for synthesizing a functionalized struvite composite material for selective recovery of copper ions according to claim 1, wherein: The oxidant is KBH4 or NaBH4.

3. The method for synthesizing a functionalized struvite composite material for selective recovery of copper ions according to claim 1, wherein: The trivalent iron is provided by FeCl3·6H2O, and the divalent iron is provided by ferrous chloride.

4. The method for synthesizing functionalized struvite mineral for selective recovery of copper ions according to claim 1, characterized in that: The aqueous solution of the organic solvent is an ethanol aqueous solution or a propanol aqueous solution, and the concentration range is 70-80% by volume.

5. The method for synthesizing a functionalized struvite composite material for selective recovery of copper ions according to claim 4, wherein: Preferably, 1-2 g KBH4 and 3-4 g FeCl3·6H2O or ferrous chloride are added to every 200 mL of ethanol aqueous solution and reacted at room temperature for 10-20 minutes.

6. The method for synthesizing a functionalized struvite composite material for selective recovery of copper ions according to claim 1, wherein: The struvite synthetic material comprises Na2HPO4·12H2O, NH4Cl and MgCl2·6H2O in a mass ratio of 1-1.5:0.5-1:0.2-0.5, and is formed by reacting at room temperature for 10-20 minutes.

7. The method for synthesizing a functionalized struvite composite material for selective recovery of copper ions according to claim 1, wherein: The separation and drying are magnetic separation, and the drying method is low-temperature vacuum freezing for 3-4 days.

8. A nano zero-valent iron-loaded struvite composite material prepared by the synthesis method of a nano zero-valent iron-loaded struvite composite material for selective recovery of copper ions according to any one of claims 1 to 7.

9. Use of the nano zero-valent iron loaded struvite mineral composite material according to claim 8 in the selective recovery of copper ions or the preparation of a specific copper ion adsorbent.

10. A selective passivating agent for recovering heavy metal copper ions, characterized in that: The invention comprises the nano zero-valent iron loaded struvite composite material according to any one of claims 1 to 7.

Images