Preparation method and application of phytic acid modified zero-valent iron

Abstract

The invention discloses a preparation method and application of phytic acid modified zero-valent iron. The method comprises the following steps: (1) mixing phytate and liquid phytic acid according to a molar ratio of (5: 5)-(8: 2), and preparing a buffer solution with the concentration of 0.05-0.5 mol / L; (2) adding micron or nano zero-valent iron into a buffer solution according to a solid-to-liquid ratio of 1: 10 to 1: 50 (g / mL), and transferring to a polytetrafluoroethylene reaction kettle; (3) under the protection of nitrogen, reacting for 6-48 hours under the conditions that the temperature is 20-80 DEG C and the oscillation rate is 100-1000 rpm, and controlling the pH value to be 3.5-5.5; and (4) after the reaction, carrying out suction filtration, ethanol-water alternate washing and vacuum drying to prepare the modified zero-valent iron with the surface coated with the phytic acid iron complex. A stable chelation layer is formed on the surface of phytic acid molecules and zero-valent iron, the oxidation resistance, dispersity and heavy metal adsorption capacity of the material are remarkably improved, and the material is suitable for efficient repair of industrial wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal pollution control, and more specifically to a preparation method and application of plant acid modified zero-valent iron. Background Art

[0002] With the rapid development of my country's mining, electroplating, leather and textile industries, a large amount of heavy metal wastewater including lead, cadmium, mercury and chromium has been discharged. These heavy metals in polluted water or soil are easy to accumulate, highly toxic and highly mobile, which seriously threatens my country's ecological environment and human health. Therefore, the restoration of heavy metal polluted water has become an important environmental problem that needs to be solved urgently in my country at this stage. The restoration methods of heavy metal polluted water include chemical precipitation, flocculation, electrodeposition, membrane filtration and adsorption. Among them, adsorption is considered to be the most effective method because of its simple operation and high efficiency.

[0003] The core of the adsorption method for remediation of heavy metal polluted water bodies is the development of efficient adsorption materials. Compared with clay minerals, zeolites, metal sulfides and metal-organic framework materials (MOF), zero-valent iron has attracted extensive attention in the remediation of heavy metal polluted water bodies due to its environmental friendliness, low price and high heavy metal removal reactivity. However, due to the high reactivity of the surface of zero-valent iron, it is easily deactivated by reaction with oxygen, and its own magnetism causes agglomeration, which limits the application of zero-valent iron. At the same time, the side reaction of zero-valent iron with water will also reduce its reactivity.

[0004] In order to improve the reactivity of zero-valent iron, surface modification to regulate the surface microstructure and charge properties of zero-valent iron is an effective way to improve the performance of zero-valent iron. At present, the use of oxygen-containing anions to modify zero-valent iron is an effective method to improve the performance of zero-valent iron. These oxygen-containing anions include oxalic acid, phosphoric acid and boric acid, but these methods have the disadvantages of high cost and potential secondary pollution. Therefore, it is urgent to find a low-cost, simple and non-secondary pollution method to prepare high-performance modified zero-valent iron to enhance the remediation of heavy metal-contaminated water bodies. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems that the existing zero-valent iron is easily oxidized and deactivated, and agglomerates seriously, and the existing modification methods are costly and have the risk of secondary pollution. The present invention provides a preparation method and application of phytic acid-modified zero-valent iron. The present invention selects low-cost and environmentally friendly phytic acid as a modification reagent. The method obtains phytic acid-modified zero-valent iron, which has rich active sites and high heavy metal removal efficiency.

[0006] The technical solution adopted by the present invention is as follows: A method for preparing plant acid-modified zero-valent iron, comprising the following steps:

[0007] (1) preparing a phytic acid-phytate buffer solution: mixing phytate and liquid phytic acid in a molar ratio of 5:5 to 8:2, adding deionized water to prepare a buffer solution with a concentration of 0.05-0.5 mol / L, and mixing with a magnetic stirrer at a speed of 300-500 rpm for 15-30 minutes;

[0008] (2) Surface modification: micronized zero-valent iron with a particle size of 10-50 μm or a specific surface area of ​​20-50 m 2 / g of nano zero-valent iron was added into the buffer solution at a solid-liquid ratio of 1:10 to 1:50 (g / mL), and transferred to a closed reactor with a polytetrafluoroethylene liner;

[0009] (3) Dynamic modification reaction: Under nitrogen protection, the reaction was carried out in a constant temperature water bath at 20-80°C with an oscillation rate of 100-1000 rpm for 6-48 hours, and the pH value of the solution was maintained in the range of 3.5-5.5 during the reaction;

[0010] (4) Post-treatment process: After the reaction is completed, the product is vacuum filtered through a 0.22 μm microporous filter membrane, washed three times with anhydrous ethanol and deionized water alternately, and dried in a vacuum drying oven at 50-80° C. for 12-24 hours to obtain a modified zero-valent iron with a surface coated with a phytic acid iron complex.

[0011] Preferably, in step (1), the phytate is selected from at least one of sodium phytate, potassium phytate and ammonium phytate, and when sodium phytate is used, the concentration of the buffer solution is 0.35±0.05 mol / L when the molar ratio of sodium phytate to liquid phytic acid is 7:3.

[0012] Preferably, a gradient temperature control method is used in step (3), specifically: the temperature is raised to 50°C at a rate of 2°C / min for the first 2 hours and maintained for 4 hours; then the temperature is raised to 70°C at a rate of 1°C / min for 12 hours, and the oscillation rate is maintained at 300±50rpm throughout the process.

[0013] Preferably, the surface of the nano zero-valent iron is pre-treated with acid activation, specifically: the nano zero-valent iron is placed in a 0.1 mol / L hydrochloric acid solution for ultrasonic treatment for 30 minutes, and then washed with deionized water to neutrality after solid-liquid separation.

[0014] An application of phytic acid-modified zero-valent iron prepared by any of the above methods in the remediation of heavy metal pollution includes the following process parameters:

[0015] (a) For Pb 2+ Wastewater: control pH = 4.0 ± 0.5, dosage 0.5 g / L, react at 25 ° C for 2 hours;

[0016] (b) For wastewater containing Cr(VI): adjust the pH to 3.0-4.5, add 1.2 g / L, and introduce nitrogen protection at 35°C for 3 hours;

[0017] (c) For wastewater with multiple metal complex pollution: When Pb 2+ , Hg 2+ 、Cd 2+ When coexisting, Pb is preferentially adsorbed 2+ The process conditions are: maintaining pH = 5.0 ± 0.3, dosage 0.8 g / L, reaction temperature 30°C, and adding 0.1 mmol / L of disodium EDTA as a complexing enhancer.

[0018] In another application, the initial concentration of 100 mg / L of Pb was treated. 2+ When treating wastewater, modified zero-valent iron has an effect on Pb 2+ The adsorption capacity reaches 480±15mg / g, the removal rate is ≥98.5%, and the adsorption capacity retention rate is >85% after 5 times of desorption and regeneration with 0.1mol / L HNO3.

[0019] In another application, when treating wastewater containing Cr(VI), Fe 3 O 4 @The phytic acid iron composite layer reduces Cr(VI) to Cr(III) through chemical reduction and coordination synergy, and then forms a stable hexadentate chelate with phytic acid. When the initial concentration is 50 mg / L, the removal rate is ≥95%.

[0020] In another application, the modified zero-valent iron can be used in combination with 2-5 wt% biochar or 0.1-0.3 wt% chitosan to form a porous composite material to enhance the degradation of Cd 2+ The adsorption capacity is increased by 30-45%.

[0021] In another application, when a fluidized bed reactor is used for continuous treatment, the hydraulic retention time is controlled to be ≥45 minutes, the ratio of the packing layer height to diameter is 3:1, and the backwash cycle is online regeneration with 0.5 mol / L citric acid solution every 8 hours of treatment.

[0022] A heavy metal pollution remediation system comprises the phytic acid-modified zero-valent iron prepared according to claim 1 as a core adsorption material, and is equipped with an automatic pH adjustment unit, an online redox potential monitoring module and a heavy metal ion selective electrode to achieve intelligent control of the treatment process.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. Green and environmentally friendly, no secondary pollution, using natural phytic acid as a modifier to avoid the introduction of toxic chemicals, the modification process has no harmful by-products, and meets the requirements of environmentally friendly materials;

[0025] 2. Significantly improve the stability of zero-valent iron. Phytic acid molecules are coated on the surface of zero-valent iron by chelation to form a dense protective layer, which effectively inhibits oxidative deactivation (isolation of oxygen / water contact) and particle agglomeration (negative charge repulsion), and the material stability is improved by more than 30%;

[0026] 3. Efficient adsorption and reduction synergistic effect on Pb 2+ , Hg 2+ The adsorption capacity of Cr(VI) is 400-500mg / g, and the removal rate is ≥98%. The adsorption capacity of Cr(VI) is ≥200mg / g, and the removal rate is ≥75%. It has both reduction (Cr(VI)→Cr(III)) and complexation dual removal mechanisms.

[0027] 4. Broad spectrum and high selectivity, suitable for Pb 2+ , Hg 2+ 、Cd 2+ , Cu 2+ 、Zn 2+ , Cr(VI) and other heavy metals, and preferentially adsorbs Pb in the coexistence system 2+ (Selective order: Pb 2+ >Hg 2+ >Cd 2+ );

[0028] 5. Low cost and convenient operation. Phytic acid-phytate buffer system is cheap and easy to obtain. The modification process is simple (normal temperature and pressure), with low energy consumption and suitable for industrial application.

[0029] 6. Widely applicable conditions, suitable for wastewater pH range of 2-6, rapid reaction (0.5-4 hours) at room temperature (20-40℃), no need for complex equipment support.

[0030] In summary, the synergistic mechanism of "surface protection-reduction-complexation" is achieved through phytic acid modification: surface protection layer prolongs the active life of zero-valent iron; reduction effect efficiently converts high-valent toxic heavy metals (such as Cr(VI)); complexation / electrostatic adsorption targets the removal of Pb 2+ , Hg 2+ Etc., to break through the technical bottleneck of poor selectivity and easy deactivation of traditional adsorption materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0032] Figure 1 The micron-scale modified zero-valent iron to Pb in Example 1 2+, Hg 2+ Removal effect comparison chart;

[0033] Figure 2 It is a rectangular diagram of the removal rate of multi-metal ions by modified zero-valent iron in Example 1;

[0034] Figure 3 The pH value of Pb in Example 1 2+ , Hg 2+ Comparison chart of the impact of removal rate;

[0035] Figure 4 This is a comparison chart of the improvement in adsorption capacity of nanoscale modified zero-valent iron in Example 2. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The technical solution of the present invention is described in detail below in conjunction with the embodiments and the accompanying drawings. The experimental data in all embodiments are averaged through three parallel experiments. Unless otherwise specified, the experimental conditions are implemented according to the parameters described in the claims.

[0039] Example 1

[0040] A method for preparing plant acid-modified micronized zero-valent iron comprises the following steps:

[0041] 1. Preparation of buffer solution: weigh 0.28 g of sodium phytate and 0.27 mL of liquid phytic acid (molar ratio 7:3), add 10 mL of deionized water, and stir magnetically (400 rpm, 25 minutes) to prepare a 0.35 mol / L phytic acid-sodium phytate buffer solution.

[0042] 2. Acid activation treatment: Immerse the micron zero-valent iron with a particle size of 30 μm in 0.1 mol / L hydrochloric acid solution, ultrasonically treat for 30 minutes, and wash until neutral.

[0043] 3. Modification reaction: Add activated micron zero-valent iron (0.5 g) to the buffer solution at a solid-liquid ratio of 1:30 (g / mL), transfer to a polytetrafluoroethylene reactor, and use gradient temperature control under nitrogen protection: increase the temperature to 50°C at 2°C / min for the first 2 hours and maintain for 4 hours; then increase the temperature to 70°C at 1°C / min for 12 hours, with an oscillation rate of 300 rpm, and control the pH to 4.5±0.2.

[0044] 4. Post-treatment: The reaction solution was filtered through a 0.22 μm filter membrane, washed alternately with anhydrous ethanol and deionized water for three times, and vacuum dried at 70°C for 18 hours to obtain phytic acid-modified micron zero-valent iron.

[0045] Experimental results:

[0046] SEM analysis: A uniform phytate iron coating layer (thickness 50-80 nm) was formed on the surface, which significantly reduced particle agglomeration.

[0047] BET specific surface area: 5m 2 / g increased to 28m 2 / g.

[0048] XPS analysis: Fe 2+ / Fe 3+ The ratio increased from 1.2 to 2.5, indicating that the modification effectively inhibited the oxidation of zero-valent iron.

[0049] Pb 2+ With Hg 2+ Adsorption performance test

[0050] Experimental conditions:

[0051] Adsorbent: Phytic acid-modified micronized zero-valent iron (10 mg) prepared in Example 1.

[0052] Solution parameters: 50mL containing Pb 2+ or Hg 2+ Wastewater (initial concentration 20 mg / L, pH = 5.0) was shaken at 25°C for 2 hours.

[0053] Control group: unmodified micronized zero-valent iron.

[0054] result:

[0055] Removal rate: modified materials for Pb 2+ and Hg 2+ The removal rates of the modified materials were 99.57% and 98.69%, which were significantly higher than those of the unmodified materials (75.29% and 67.82%) ( Figure 1 ).

[0056] Adsorption capacity: According to the formula q=(C 0 -C t)V / m calculation, Pb 2+ The adsorption capacity is 198.5 mg / g, Hg 2+ It is 197.4 mg / g.

[0057] Multi-metal composite pollution adsorption experiment

[0058] Experimental conditions:

[0059] - Adsorbent: phytic acid-modified micronized zero-valent iron (10 mg) prepared in Example 1.

[0060] -Solution parameters: 50mL containing Cd 2+ , Cu 2+ 、Zn 2+ , Cr(VI) 50 mg / L each, wastewater (pH=5.0), oscillate at 25°C for 2 hours.

[0061] result:

[0062] Removal rate: Cd 2+ (97.13%), Cu 2+ (98.26%), Zn 2+ (98.57%), Cr(VI)(75.29%)( Figure 2 ).

[0063] Mechanism verification: XPS detected that Cr(VI) was reduced to Cr(III) (binding energy 576.5 eV) and formed [Cr(C 6 H 6 O 24 P 6 )] 3- Chelate.

[0064] Effect of pH on adsorption performance

[0065] Experimental conditions:

[0066] Adsorbent: Phytic acid-modified micronized zero-valent iron (10 mg) prepared in Example 1.

[0067] Solution parameters: 50mL containing Pb 2+ or Hg 2+ Wastewater (initial concentration 50 mg / L), adjusted pH = 2-6, oscillated reaction at 25°C for 2 hours.

[0068] result:

[0069] pH dependence: Pb 2+ The removal rate increased from 11.23% at pH = 2 to 99.68% at pH = 6; Hg 2+ The removal rate increased from 9.58% to 99.29% ( Figure 3 ).

[0070] Optimized pH range: The adsorption efficiency was highest when pH = 4-6, which was related to the ionization state of the phytic acid phosphate group (pKa≈1.5-12) and the inhibition of zero-valent iron oxidation.

[0071] Example 2

[0072] A method for preparing plant acid-modified nano zero-valent iron comprises the following steps:

[0073] 1. Preparation of buffer solution: weigh 0.37 g of sodium phytate and 0.23 mL of liquid phytic acid (molar ratio 6:4), add 10 mL of deionized water to prepare a buffer solution.

[0074] 2. Modification reaction: Add nano-zero-valent iron (1 g) into the buffer solution at a solid-liquid ratio of 1:10 (g / mL) and shake at 25°C for 6 hours.

[0075] 3. Post-treatment: After filtration, vacuum drying was performed at 80°C for 10 hours to obtain phytic acid-modified nano-zero-valent iron.

[0076] Experimental results:

[0077] Adsorption performance: treatment of 50mg / L Pb 2+ and Hg 2+ wastewater (pH = 5.0), the adsorption capacity of modified nano zero-valent iron reached 482.46 mg / g and 428.78 mg / g, which was significantly higher than that of unmodified materials (198.68 mg / g and 226.19 mg / g) ( Figure 4 ).

[0078] Mechanistic advantage: high specific surface area of ​​nanomaterials (50m 2 / g) synergistically acts with phytic acid chelation to further improve the adsorption efficiency.

[0079] Experimental data summary table

[0080] heavy metal Initial Depth (mg / L) Removal rate (%) Adsorption capacity (mg / g) <![CDATA[Pb 2+ ]]> 20 99.57 198.5 <![CDATA[Hg 2+ ]]> 20 98.69 197.4 Cr(VI) 20 75.29 150.6 <![CDATA[Cd 2+ ]]> 20 97.13 194.3

[0081] in conclusion

[0082] The present invention significantly improves the adsorption performance of zero-valent iron to heavy metals through phytic acid modification, and its mechanism includes surface chelation coating, reduction precipitation and electrostatic adsorption. The data of the embodiment show that:

[0083] 1. Modified micronized zero-valent iron for Pb 2+ The adsorption capacity is up to 485mg / g, and the removal rate is >98%;

[0084] 2. Modified Nano Zero-Valent Iron for Pb 2+ The adsorption capacity increased to 482.46 mg / g, which was 143% higher than that of the unmodified material;

[0085] 3. When multiple metals coexist, the adsorption selectivity follows Pb 2+ >Hg 2+ >Cd 2+ , which is consistent with the order of phytic acid complexation constant (logK).

[0086] Combined with the accompanying drawings and experimental data, the phytic acid-modified zero-valent iron of the present invention has the technical advantages of high efficiency, stability and renewability in the remediation of heavy metal pollution.

[0087] The reaction principle of the present invention is: phytic acid is a small molecule organic acid that is ubiquitous in nature and has the characteristics of good antioxidant properties, metal ion complexing properties, and no secondary pollution. Based on these characteristics of phytic acid, under the interaction with zero-valent iron, a shell structure of phytic iron can be formed on the surface of zero-valent iron. This structure can effectively hinder the side reaction of zero-valent iron with water, and produce phosphoryl groups with rich active adsorption sites on the surface of zero-valent iron. These structural features promote the removal performance of zero-valent iron for heavy metal ions. The details are as follows:

[0088] 1. Phytic acid modification mechanism

[0089] Surface chelation coating: Phytic acid molecules contain 6 phosphate groups, which bind to the surface of zero-valent iron Fe 0 A stable chelate layer is formed by Fe-OP bond (reaction formula: Fe 0 +H 3 Phy→Fe-Phy complex).

[0090] Antioxidant: Isolate direct contact with oxygen and water, inhibit oxidation of zero-valent iron (Fe 0 →Fe 2+ / Fe 3+ ) caused by decreased activity;

[0091] Anti-aggregation: The phosphate group carries a negative charge, which reduces the magnetic aggregation between zero-valent iron particles through electrostatic repulsion.

[0092] 2. Heavy metal removal mechanism

[0093] Reduction precipitation (for high-valent heavy metals such as Cr(VI)): Zero-valent iron acts as an electron donor to reduce Cr(VI) to low-toxic Cr(III), while oxidizing itself to generate Fe 2+ / Fe 3+ (Reaction formula: Cr 2 O 7 2- +Fe 0 +H + →Cr 3+ +Fe 3+ +H 2 O).

[0094] Complex adsorption (for Pb 2+ , Hg 2+ etc.): Phytic acid phosphate groups and heavy metal ions form stable complexes (such as Pb-Phy, Hg-Phy) through coordination bonds and are adsorbed on the surface of the material (reaction formula: M 2+ +H 2 Phy→M-Phy+2H + ).

[0095] Electrostatic adsorption (for Cd 2+ , Cu 2+ etc.): The surface of the modified material is negatively charged (the phosphate group is ionized), and cationic heavy metals (such as Cd 2+ , Cu 2+ ).

[0096] 3. Principle of competitive adsorption selectivity

[0097] Phytic acid has significant differences in its complexing ability for different heavy metals, and the order of complexing constants is: Pb 2+ (logK≈18.2)>Hg 2+ (logK≈14.5)>Cd 2+ (logK≈10.3), resulting in adsorption priority for Pb 2+ >Hg 2+ >Cd 2+ .

[0098] 4. pH regulation mechanism

[0099] Acidic conditions (pH 2-6): promote the release of electrons from zero-valent iron (Fe 0 →Fe 2+ +2e - ), enhancing the reducing ability; the phytic acid phosphate group is partially protonated to balance the complexation and electrostatic adsorption efficiency and avoid excessive acidification leading to iron corrosion.

Claims

1. A method for preparing plant acid-modified zero-valent iron, characterized in that: The following steps are involved: (1) preparing a phytic acid-phytate buffer solution: mixing phytate and liquid phytic acid in a molar ratio of 5:5 to 8:2, adding deionized water to prepare a buffer solution with a concentration of 0.05-0.5 mol / L, and mixing with a magnetic stirrer at a speed of 300-500 rpm for 15-30 minutes; (2) Surface modification: micronized zero-valent iron with a particle size of 10-50 μm or a specific surface area of ​​20-50 m 2 / g of nano zero-valent iron was added into the buffer solution at a solid-liquid ratio of 1:10 to 1:50 (g / mL), and transferred into a closed reactor with a polytetrafluoroethylene liner; (3) Dynamic modification reaction: Under nitrogen protection, the reaction was carried out in a constant temperature water bath at 20-80°C with an oscillation rate of 100-1000 rpm for 6-48 hours, and the pH value of the solution was maintained in the range of 3.5-5.5 during the reaction; (4) Post-treatment process: After the reaction is completed, the product is vacuum filtered through a 0.22 μm microporous filter membrane, washed three times with anhydrous ethanol and deionized water alternately, and dried in a vacuum drying oven at 50-80° C. for 12-24 hours to obtain a modified zero-valent iron with a surface coated with a phytic acid iron complex.

2. The preparation method according to claim 1, characterized in that: In the step (1), the phytate is selected from at least one of sodium phytate, potassium phytate and ammonium phytate, and when sodium phytate is used, the molar ratio of sodium phytate to liquid phytic acid is 7:3 and the concentration of the buffer solution is 0.35±0.05 mol / L.

3. The preparation method according to claim 1, characterized in that: The step (3) adopts a gradient temperature control method, specifically: the temperature is raised to 50°C at a rate of 2°C / min for the first 2 hours and maintained for 4 hours; then the temperature is raised to 70°C at a rate of 1°C / min for 12 hours, and the oscillation rate is maintained at 300±50rpm throughout the process.

4. The preparation method according to claim 1, characterized in that: The surface of the nano zero-valent iron is pre-treated with acid activation, specifically: the nano zero-valent iron is placed in a 0.1 mol / L hydrochloric acid solution for ultrasonic treatment for 30 minutes, and then washed with deionized water to neutrality after solid-liquid separation.

5. An application of phytic acid modified zero-valent iron prepared by the method according to any one of claims 1 to 4 in the remediation of heavy metal pollution, characterized in that The following process parameters are included: (a) For Pb 2+ Wastewater: control pH = 4.0 ± 0.5, dosage 0.5 g / L, react at 25 ° C for 2 hours; (b) For wastewater containing Cr(VI): adjust the pH to 3.0-4.5, add 1.2 g / L, and introduce nitrogen protection at 35°C for 3 hours; (c) For wastewater with multiple metal complex pollution: When Pb 2+ , Hg 2+ 、Cd 2+ When coexisting, Pb is preferentially adsorbed 2+ The process conditions are: maintaining pH = 5.0 ± 0.3, dosage 0.8 g / L, reaction temperature 30°C, and adding 0.1 mmol / L of disodium EDTA as a complexing enhancer.

6. The use according to claim 5, characterized in that: Treatment of initial concentration of 100 mg / L Pb 2+ When treating wastewater, modified zero-valent iron has an effect on Pb 2+ The adsorption capacity reaches 480±15mg / g, the removal rate is ≥98.5%, and the adsorption capacity retention rate is >85% after 5 times of desorption and regeneration with 0.1mol / L HNO3.

7. The use according to claim 5, characterized in that: When treating wastewater containing Cr(VI), Fe 3 The O4@phytic acid iron composite layer reduces Cr(VI) to Cr(III) through the synergistic effect of chemical reduction and coordination, and then forms a stable hexadentate chelate with phytic acid. When the initial concentration is 50 mg / L, the removal rate is ≥95%.

8. The use according to claim 5, characterized in that: The modified zero-valent iron can be used in combination with 2-5 wt% biochar or 0.1-0.3 wt% chitosan to form a porous composite material. 2 +The adsorption capacity is increased by 30-45%.

9. The use according to claim 5, characterized in that: When a fluidized bed reactor is used for continuous treatment, the hydraulic retention time is controlled to be ≥45 minutes, the ratio of the packing layer height to the diameter is 3:1, and the backwashing cycle is online regeneration with 0.5 mol / L citric acid solution every 8 hours of treatment.

10. A heavy metal pollution remediation system, characterized in that: The invention comprises the phytic acid-modified zero-valent iron prepared in claim 1 as the core adsorption material, and is equipped with an automatic pH adjustment unit, an online redox potential monitoring module and a heavy metal ion selective electrode to realize intelligent control of the treatment process.

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