Method for removing high-ligand-concentration complex-state lead under ultraviolet light and aeration conditions by using phosphorus-modified nano zero-valent iron

Abstract

The invention discloses a method for removing complexed lead with high ligand concentration by using phosphorus modified nano zero-valent iron under ultraviolet light and aeration conditions, ultraviolet light irradiation promotes the replacement process of Fe (III) on complexed lead,-COOPb (II) is replaced by Fe (III) to form-COOFe (III), after the-COOPb (II) is irradiated by the ultraviolet light, the transfer process of electrons from ligand to metal is generated, and the purpose of removing the complexed lead with high ligand concentration is achieved. The-COOFe (III) can be decomposed into CO2 and Fe (II); the high dissolved oxygen can quickly oxidize Fe (II) reduced from-COOFe (III) into Fe (III), and the oxidized Fe (III) can participate in the replacement reaction again and is recombined with the ligand to form-COOFe (III), so that the high removal efficiency of the nanoscale zero-valent iron on high-ligand-concentration complex-state lead is realized, and the treatment of water pollution is efficiently and cleanly realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wastewater treatment, and particularly relates to a method for removing complex-bound lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano zero-valent iron. Background Art

[0002] Complex-bound heavy metals are a special form of the existence of heavy metals. They are formed by the complexation of ligands and heavy metal ions and have extremely strong solubility and stability. At present, there is less attention paid to complex-bound heavy metals. However, research shows that 90% of heavy metals in nature exist in complex forms. Most current studies use advanced oxidation methods to oxidize and break the complex for their removal. However, the advanced oxidation methods not only have relatively high costs, but are also severely affected by coexisting anions and protonation, and have certain limitations. The traditional methods such as adsorption and chemical precipitation have little effect on the removal of complex-bound heavy metals. Therefore, there is an urgent need for an efficient method to meet the growing demand for removing complex-bound heavy metals.

[0003] Some studies have applied nano zero-valent iron to the treatment of complex heavy metals and achieved good results. For example, Guan X. et al. used a magnetic field to enhance the removal of complex copper by nano zero-valent iron (Guan X. et al. Decomplexation and subsequent reductive removal of EDTA-chelated CuII by zero-valent iron coupled with a weak magnetic field: Performances and mechanisms[J]. Journal of Hazardous Materials, 2015, 300: 688-694.). Li R. et al. used sulfur-modified nano zero-valent iron to remove complex cadmium (Li R. et al. Low dose of sulfur-modified zero-valent iron for decontamination of trace Cd (II)-complexes in high-salinity wastewater[J]. Science of The Total Environment, 2021, 793: 148579.). Nano zero-valent iron has excellent performance for complex heavy metals. However, in actual wastewater, the concentrations of organic ligands and heavy metals are often not proportional. Under the condition of high organic ligand concentration, excessive organic ligands will compete with complex heavy metals for the adsorption of nano zero-valent iron, resulting in a significant decrease in the removal rate of heavy metals. Therefore, how to exert the performance of nano zero-valent iron under the condition of high organic ligand concentration remains a challenge.

[0004] Therefore, the present invention proposes a method for removing complex lead with high ligand concentration by using phosphorus-modified nano zero-valent iron under ultraviolet light and aeration conditions. Summary of the Invention

[0005] Technical problems to be solved: Aiming at the above technical problems, the present invention provides a method for removing complex lead with high ligand concentration by using phosphorus-modified nano zero-valent iron under ultraviolet light and aeration conditions, which can effectively solve the defect that it is difficult to achieve an ideal removal effect under the condition of high organic matter concentration in the process of removing complex lead by nano zero-valent iron in the prior art; realize a high removal efficiency of nano zero-valent iron for complex lead with high ligand concentration, so as to efficiently and cleanly achieve the treatment of water pollution.

[0006] Technical solution: A method for removing complex-bound lead with high ligand concentration by using phosphorus-modified nano-zero-valent iron under ultraviolet light and aeration conditions, comprising the following steps: adding phosphorus-modified nano-zero-valent iron to a complex-bound lead solution containing a ligand and mixing evenly, while aerating and irradiating the reaction solution with ultraviolet light to achieve the removal of complex-bound lead.

[0007] Preferably, the concentration of the ligand in the complex-bound lead solution containing the ligand is ≥ 1 g / L, and the concentration of the complex-bound lead is ≤ 200 mg / L.

[0008] Preferably, during the aeration process, the dissolved oxygen concentration is adjusted to 0.4 - 8.5 mg / L by oxygen blowing or air blowing.

[0009] Preferably, the light source for ultraviolet light irradiation is a mercury lamp with a power of 100 w - 500 w.

[0010] Preferably, the complex-bound lead is any one or more of ethylenediaminetetraacetic acid complex-bound lead (EDTA-Pb), diethylenetriaminepentaacetic acid complex-bound lead (DTPA-Pb), citrate complex-bound lead (Citrate-Pb), nitrilotriacetic acid complex-bound lead (NTA-Pb), or glycine complex-bound lead (Glycine-Pb).

[0011] Preferably, the phosphorus-modified nano-zero-valent iron is prepared from ferric chloride, sodium borohydride, and sodium dihydrogen phosphate. The specific process is as follows: first, nano-zero-valent iron is prepared from ferric chloride and sodium borohydride according to a molar ratio of 1:4; then, according to a molar ratio of nano-zero-valent iron to sodium dihydrogen phosphate of 1:0.3, the nano-zero-valent iron is ultrasonically dispersed in a sodium dihydrogen phosphate solution and ultrasonically treated for 15 minutes to obtain phosphorus-modified nano-zero-valent iron.

[0012] Beneficial effects: 1) In the method of the present invention, ultraviolet light irradiation is introduced while using phosphorus-modified nano-zero-valent iron to decomplex complex-bound lead, which promotes the replacement process of Fe(III) for complex-bound lead. After -COOPb(II) is replaced by Fe(III), -COOFe(III) is formed, and -COOFe(III) is a photo-unstable group. After being irradiated with ultraviolet light, an electron transfer process from the ligand to the metal will occur, and -COOFe(III) will decompose into CO2 and Fe(II). This process will promote the replacement process of Fe(III) for complex-bound lead, causing the chemical equilibrium to shift towards the release of lead under the interference of complex water quality conditions, and achieving a higher replacement efficiency under complex water quality conditions; 2) In the method of the present invention, ultraviolet light irradiation and an aeration environment are introduced while using phosphorus-modified nano-zero-valent iron to decomplex lead. A relatively high dissolved oxygen level will rapidly oxidize Fe(II) reduced from -COOFe(III) to Fe(III), and the oxidized Fe(III) will re-participate in the substitution reaction and re-combine with the ligand to form -COOFe(III). This reaction forms a cyclic process of Fe(III) during the reaction process, reducing the leaching of Fe(III) in the phosphorus-modified nano-zero-valent iron. At the same time, it can cope with the competition of excessive ligands for Fe(III) under high ligand concentrations, enabling -COOPb(II) to still be converted into free Pb(II) in a high-concentration ligand environment. Meanwhile, the continuously formed -COOFe(III) will also continuously photolyze into CO2, reducing the TOC concentration in the wastewater; 3) The core mechanism of the method of the present invention is to utilize the high stability of the binding of Fe(III) with carboxyl ligands to release Pb(II). The generated -COOFe(III) generates CO2 and Fe(II) under photolysis. Therefore, it has a wide range of applications and can achieve good removal effects for lead complexed with different ligands. Theoretically, it can be applied to all Pb(II) complexed with carboxyl ligands and has potential application value; 4) The solid residue after treating complexed lead with phosphorus-modified nano-zero-valent iron by the method of the present invention has high stability, is not easily leached, and has a very low probability of causing secondary pollution. Since the solubility product constant of the combination of phosphate and lead is extremely low, this compound is very stable. The lead content in the solid residue after the reaction is 243.2 mg / g, and the leaching of Pb(II) does not exceed 1.5 mg / L in a continuous 45-day leaching experiment. Description of the Drawings

[0013] Figure 1 Shows the differences in the removal of complexed lead by phosphorus-modified nano-zero-valent iron under ultraviolet light sources with different powers; Figure 2 Shows the differences in the removal of complexed lead by phosphorus-modified nano-zero-valent iron at different dissolved oxygen concentrations; Figure 3 Shows the performance differences in the removal of complexed lead with different concentrations by phosphorus-modified nano-zero-valent iron; Figure 4 Shows the differences in the removal of lead complexed with different ligands by phosphorus-modified nano-zero-valent iron; Figure 5 Shows the stability test of the solid residue after phosphorus-modified nano-zero-valent iron removes complexed lead. Detailed Embodiments

[0014] The present invention will be described in detail below with reference to the drawings and specific embodiments: Embodiment

[0015] This example explores the difference in the removal effect of phosphorus-modified nano zero-valent iron on EDTA-Pb(II) under ultraviolet light sources with different powers: The EDTA-Pb(II) used in this example was prepared by mixing ethylenediaminetetraacetic acid and lead nitrate in a molar ratio of 1:1 and boiling to obtain a 500 mg Pb / L EDTA-Pb(II) stock solution; Take 40 mL of the stock solution as the target pollutant, adjust the pH of the solution to 3.5 using 1 M hydrochloric acid or sodium hydroxide, then add phosphorus-modified nano zero-valent iron at a dosage of 0.5 g / L, and simultaneously introduce nitrogen or air into the solution. By adjusting the flow rate, the dissolved oxygen concentration is controlled at a level of 5.4 mg / L.

[0016] Ultraviolet light irradiation is an important parameter affecting the removal process in this study, which directly provides energy for the photolysis of -COOPb(II). Figure 1 The removal of EDTA-Pb(II) by phosphorus-modified nano zero-valent iron under dark conditions, natural light conditions, and ultraviolet light irradiation of 100 W, 300 W, and 500 W. It can be seen from the figure that under dark conditions, the coexisting organic ligands greatly inhibited the removal process of EDTA-Pb(II), and the residual Pb was as high as 14.78 mg / L after 60 min of reaction. This is due to the high concentration of EDTA 2- Competing with EDTA-Pb(II) for Fe 3+ resulting in; while under natural light conditions, due to the existence of a certain ultraviolet light intensity, it promoted the photolysis of a part of EDTA-Fe(III), promoted the iron cycle process, more lead was transformed into the free state, and could be fixed by zero-valent iron, and the residual lead concentration decreased to 6.33 mg / L; while under the irradiation of mercury lamps with different powers, EDTA-Pb(II) was quickly removed, and it can also be seen that the removal rate was the fastest under the irradiation of the 500 W mercury lamp, and almost all of it was removed in 10 min. This all proves that the rapid photolysis of EDTA-Fe(III) under ultraviolet light irradiation promoted the lead fixation process. Example

[0017] This example explores the difference in the removal effect of phosphorus-modified nano zero-valent iron on EDTA-Pb(II) under different dissolved oxygen concentrations: Since it involves the process of oxidizing Fe(II) generated by the photoreduction of EDTA-Fe(III) to Fe(III), the concentration of dissolved oxygen in the solution is crucial for the removal process of EDTA-Pb(II). Figure 2The removal of EDTA-Pb(II) by phosphorus-modified nano-zero-valent iron under anoxic (dissolved oxygen concentration = 0.4 mg / L), aerobic (dissolved oxygen concentration = 5.2 mg / L), and oxic (dissolved oxygen concentration = 8.5 mg / L) conditions. It can be seen from the figure that when removing EDTA-Pb(II) in the presence of a high concentration of organic ligands, ultraviolet light alone is not enough. When the ultraviolet mercury lamp is 300 W and the dissolved oxygen in the solution is 0.4 mg / L, the residual Pb concentration reaches 11.13 mg / L. This is because although photolysis of EDTA-Fe(III) occurs under ultraviolet light irradiation to generate Fe(II), the dissolved oxygen concentration in the solution is too low to fully complete the transformation process of Fe(II) to Fe(III). The Fe(III) released by nano-zero-valent iron is competed by EDTA-Pb(II) and EDTA 2- and cannot complete the complete replacement of lead, resulting in a part of lead still existing in the complex form and unable to be removed by nano-zero-valent iron. When the dissolved oxygen concentration in the solution is increased to 5.2 mg / L and 8.5 mg / L, EDTA-Pb(II) is rapidly removed, proving that the increase in dissolved oxygen concentration enables Fe(II) to be oxidized to Fe(III) and then re-participate in the replacement process to generate EDTA-Fe(III), which is then photolyzed by ultraviolet light again, thus forming a cycle process of iron and enhancing the release of lead. Example

[0018] This example explores the difference in the removal effect of phosphorus-modified nano-zero-valent iron on complex-bound lead with different initial concentrations: The initial concentration of complex-bound lead is also a key factor affecting removal. In actual wastewater, the concentration of complex-bound heavy metals is usually not high. In this example, initial concentrations of 20 - 200 mg / L are selected. As Figure 3 shown, under high organic ligand concentration, with the intervention of ultraviolet light and dissolved oxygen, phosphorus-modified nano-zero-valent iron can almost completely remove 200 mg / L of complex-bound lead, proving the applicability of this process. At the same time, if there is a higher concentration of complex-bound lead in actual wastewater, the dosage of phosphorus-modified nano-zero-valent iron can be increased or the power of ultraviolet light irradiation can be enhanced. Example

[0019] This example explores the difference in the effect of phosphorus-modified nano-zero-valent iron on removing lead complexed with different ligands: Considering the diversity of ligands in actual wastewater, common ligands in industry are selected to complex with lead to explore the applicability of P-NZVI. As Figure 4As shown, phosphorus-modified nano zero-valent iron has good removal effects on 5 kinds of complex-bound lead. Although the complexing ability of diethylenetriaminepentaacetic acid is stronger than that of ethylenediaminetetraacetic acid, phosphorus-modified nano zero-valent iron can almost completely remove the lead bound by diethylenetriaminepentaacetic acid. The figure shows that the ligand with the strongest binding ability, diethylenetriaminepentaacetic acid, has a slower removal rate than glycine with the weakest binding ability. This is because the ligand with a stronger complexing ability has a slower dissociation rate than the ligand with a weaker complexing ability, resulting in a slower release process of lead. However, even for a ligand with an extremely strong complexing ability like diethylenetriaminepentaacetic acid, phosphorus-modified nano zero-valent iron can still almost completely remove lead in about 30 minutes, showing great application prospects. Example

[0020] This example explores the stability of the solid residue after phosphorus-modified nano zero-valent iron removes complex-bound lead: The toxicity characteristic leaching procedure was used to evaluate the mobility of lead in the residue after the reaction, as Figure 5 shown. The contents of lead and phosphorus (calculated as phosphate) in the residue after the reaction were determined to be 243.2 mg / g and 312.6 mg / g respectively. Through a 1080-hour continuous leaching experiment, it was found that phosphorus was extremely stable and no leaching of phosphorus was detected in the supernatant. The leaching of lead was relatively obvious. As time increased, the leaching concentration of lead gradually increased, reaching a peak of 0.32 mg / L at 540 h and fluctuating around this level within the subsequent 540 h. Compared with the total amount of Pb, 243.2 mg / g, this is a relatively low leaching level, far lower than the leaching limit of Pb, 5 mg / L, in hazardous waste identification. Therefore, it can be considered that the solid residue after the reaction of phosphorus-modified nano zero-valent iron is relatively stable and safe.

[0021] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for removing complexed lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron, characterized in that, It includes the following steps: Add phosphorus-modified nano zero-valent iron into the complexed lead solution containing ligands, stir evenly, and at the same time aerate and irradiate the reaction solution with ultraviolet light to achieve the removal of complexed lead.

2. The method for removing complexed lead with high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano zero-valent iron according to claim 1, characterized in that: In the complexed lead solution containing ligands, the concentration of the ligand ≥ 1 g / L, and the concentration of the complexed lead ≤ 200 mg / L.

3. A method for removing complex-bound lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron according to claim 1, characterized in that: During aeration, adjust the dissolved oxygen concentration to 0.4 - 8.5 mg / L.

4. A method for removing complex-bound lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron according to claim 1, characterized in that: The light source for ultraviolet light irradiation is a mercury lamp with a power of 100 w - 500 w.

5. A method for removing complexed lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron according to claim 1, characterized in that: The complexed lead is any one or several of ethylenediaminetetraacetic acid complexed lead, diethylenetriaminepentaacetic acid complexed lead, citric acid complexed lead, nitrilotriacetic acid complexed lead, or glycine complexed lead.

6. A method for removing complexed lead with a high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron according to claim 1, characterized in that: The phosphorus-modified nano zero-valent iron is prepared from ferric chloride, sodium borohydride, and sodium dihydrogen phosphate.

7. A method for removing complex-bound lead with high ligand concentration under ultraviolet light and aeration conditions by using phosphorus-modified nano-zero-valent iron according to claim 6, characterized in that: The preparation method of the phosphorus-modified nano zero-valent iron is as follows: Dropwise add sodium borohydride into the ferric chloride solution under nitrogen conditions, with a molar ratio of 4:1, to obtain nano zero-valent iron. Subsequently, disperse the nano zero-valent iron in the dihydrogen phosphate solution under nitrogen conditions and stir for 24 hours, with a molar ratio of phosphorus to iron of 0.3:1.

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