Method for removing lead and zinc in underground water of mining area by using carboxymethyl cellulose modified nano zero-valent iron

Abstract

The invention discloses a method for removing lead and zinc in underground water of a mining area by using carboxymethyl cellulose modified nano zero-valent iron, which is characterized in that the underground water of the lead-zinc mining area is treated by using the carboxymethyl cellulose modified nano zero-valent iron, and the carboxymethyl cellulose modified nano zero-valent iron comprises nano zero-valent iron particles, the surface of the modified nano zero-valent iron is modified with carboxymethyl cellulose, and the mass ratio of the carboxymethyl cellulose to the iron element in the modified nano zero-valent iron is 1: (5-6). According to the invention, the adopted carboxymethyl cellulose modified nano zero-valent iron has the advantages of large specific surface area, many active sites, good mobility, good dispersibility, strong anti-interference capability and the like, can quickly adsorb lead and zinc in the water body, and can stably fix lead and zinc in the carboxymethyl cellulose modified nano zero-valent iron for a long time; the method has the advantages of simple process, low cost, high treatment efficiency, good removal effect, capability of ensuring long-term stability of heavy metal ions and the like, and is particularly suitable for long-term repair and treatment of lead and zinc pollution in underground water in mining areas.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental functional materials and groundwater remediation, and relates to a method for removing lead and zinc from groundwater in a mining area by utilizing carboxymethyl cellulose-modified nano zero-valent iron. Background Art

[0002] Heavy metal pollution of groundwater in lead-zinc mining areas is an urgent environmental problem that needs to be solved. It mainly comes from the leakage and migration of heavy metals and acidic wastewater during mining, ore dressing and smelting. Among these pollutants, lead (Pb 2+ ) and zinc (Zn 2+ ) are typical heavy metals. Lead, as a highly toxic heavy metal, can cause irreversible damage to the nervous system, especially negatively affecting children's intellectual development and behavioral performance, and may even lead to lifelong health problems. Although zinc is an essential trace element, it can also be toxic to organisms at high concentrations, affecting plant growth and the survival of aquatic organisms. Therefore, remediation of lead and zinc pollution in groundwater has become an important issue in the field of environmental protection.

[0003] Among the current remediation technologies, in-situ remediation has become a research hotspot due to its cost-effectiveness and applicability. Nano zero-valent iron (nZVI), as an emerging in-situ remediation material, has attracted much attention due to its large specific surface area, high reactivity and environmental friendliness. However, in actual engineering applications, it has defects such as easy agglomeration and poor mobility, making it difficult to promote and apply. In response to these problems, researchers have proposed a modification method for nano zero-valent iron. For example, by modifying the surface of nano zero-valent iron particles with sulfur, the reactivity and selectivity of nano zero-valent iron are effectively enhanced, while its dispersibility and stability are improved. It can efficiently remove heavy metals through the synergistic effect of adsorption-precipitation-reduction. However, the sulfur-modified nano zero-valent iron still produces toxic H2S gas during the preparation process, and its long-term stability has not yet been clarified. Excessive sulfidation will also reduce the degradation efficiency of some pollutants. In a more serious situation, the sulfur-modified nano zero-valent iron may undergo sulfur dissolution due to environmental factors during actual application, thereby causing secondary pollution problems. In addition, although the existing nano zero-valent iron material with biochar as the carrier can alleviate the occurrence of agglomeration to a certain extent, the material still has the defects of complex preparation process, strict control of pyrolysis and loading conditions, poor resistance to environmental interference, and easy secondary release of heavy metal ions. The existence of the above defects makes it difficult to use the existing modified nano zero-valent iron or loaded nano zero-valent iron to remove lead and zinc pollution in mining groundwater. Therefore, how to obtain a carboxymethyl cellulose modified nano zero-valent iron with a large specific surface area, multiple active sites, good mobility, good dispersibility, and strong anti-interference ability is of great significance for the rapid removal of lead and zinc in mining groundwater and the effective long-term stability of heavy metal ions. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for removing lead and zinc from mine groundwater by using carboxymethyl cellulose-modified nano zero-valent iron, which has a simple process, low cost, high treatment efficiency, good removal effect, and can ensure the long-term and stable utilization of heavy metal ions.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for removing lead and zinc from mine groundwater by using carboxymethyl cellulose-modified nano zero-valent iron, wherein the method uses carboxymethyl cellulose-modified nano zero-valent iron to treat the groundwater in the lead-zinc mine area; the carboxymethyl cellulose-modified nano zero-valent iron includes nano zero-valent iron particles, and the surface of the nano zero-valent iron particles is modified with carboxymethyl cellulose; the mass ratio of carboxymethyl cellulose to iron element in the carboxymethyl cellulose-modified nano zero-valent iron is 1:5-6.

[0007] In the above method, further improved, the nano zero-valent iron particles have a core-shell structure with zero-valent iron as the core and iron oxide or iron hydroxide as the shell; the particle size of the nano zero-valent iron particles is ≤100nm.

[0008] In the above method, further improved, the carboxymethyl cellulose-modified nano zero-valent iron is prepared by reducing carboxymethyl cellulose salt and iron salt with a reducing agent; the mass ratio of carboxymethyl cellulose salt to iron salt is 0.1:2.703.

[0009] In the above method, further improved, the preparation method of the carboxymethyl cellulose-modified nano zero-valent iron includes the following steps:

[0010] S1. Mix carboxymethyl cellulose salt with ethanol, add water, and perform ultrasonic treatment to obtain a carboxymethyl cellulose salt solution;

[0011] S2. Add iron salt to the carboxymethyl cellulose salt solution and perform ultrasonic treatment to obtain a carboxymethyl cellulose salt-iron mixed solution;

[0012] S3. Stir the carboxymethyl cellulose salt-iron mixed solution under a nitrogen atmosphere, and drop the reducing agent solution into the carboxymethyl cellulose salt-iron mixed solution at a dropping rate of 7.5 mL / min. After the dropping is completed, continue to stir to obtain carboxymethyl cellulose-modified nano zero-valent iron.

[0013] In the above method, further improved, the volume ratio of the reducing agent solution to the carboxymethyl cellulose salt solution is 1:1; the reducing agent solution is a sodium borohydride solution; the concentration of the reducing agent solution is 7.566 g / L.

[0014] In the above method, further improved, in step S1, the ratio of the carboxymethyl cellulose salt to ethanol is 0.1 g∶1 mL; the carboxymethyl cellulose salt is sodium carboxymethyl cellulose; the time of ultrasonic treatment is 20 min.

[0015] In the above method, further improved, in step S2, the time of ultrasonic treatment is 20 min.

[0016] In the above method, further improved, in step S3, the stirring time of the carboxymethyl cellulose salt-iron mixed solution under a nitrogen atmosphere is 30 min; the stirring time after the dropping is completed is 30 min; after the stirring is completed, it further includes: magnetically separating the product solution obtained after stirring to obtain crude carboxymethyl cellulose-modified nano zero-valent iron, washing the crude carboxymethyl cellulose-modified nano zero-valent iron with absolute ethanol, the number of washing times is 2 to 3 times, and drying at 60 °C under vacuum conditions for 15 h to obtain carboxymethyl cellulose-modified nano zero-valent iron.

[0017] In the above method, further improved, using carboxymethyl cellulose-modified nano zero-valent iron to treat the groundwater in the lead-zinc mining area, including the following steps: mixing the carboxymethyl cellulose-modified nano zero-valent iron with the groundwater in the lead-zinc mining area and stirring to complete the treatment of the groundwater in the lead-zinc mining area.

[0018] In the above method, further improved, the addition amount of the carboxymethyl cellulose-modified nano zero-valent iron is 0.5 g of carboxymethyl cellulose-modified nano zero-valent iron added per liter of groundwater in the lead-zinc mining area.

[0019] In the above method, further improved, the groundwater in the lead-zinc mining area contains at least one heavy metal ion of Pb 2+ , Zn 2+ ; the initial pH value of the groundwater in the lead-zinc mining area is 6; the initial concentration of Pb 2+ in the groundwater in the lead-zinc mining area is 10 mg / L to 100 mg / L, and the initial concentration of Zn 2+ is 10 mg / L to 100 mg / L.

[0020] In the above method, further improved, the stirring is carried out at a temperature of 25 °C; the stirring time is 2 h.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) Aiming at the deficiencies of existing nano zero-valent iron materials, such as easy agglomeration, small specific surface area, few active sites, poor dispersibility, poor mobility, and poor anti-interference ability, as well as the resulting defects of low adsorption rate, poor adsorption effect, and difficulty in long-term stability of heavy metal ions lead and zinc in water bodies, the present invention provides a method for removing lead and zinc in mine groundwater by using carboxymethyl cellulose-modified nano zero-valent iron. The carboxymethyl cellulose-modified nano zero-valent iron is used to treat the groundwater in lead-zinc mining areas. The carboxymethyl cellulose-modified nano zero-valent iron used includes nano zero-valent iron particles, and carboxymethyl cellulose is modified on the surface of the nano zero-valent iron particles. The mass ratio of carboxymethyl cellulose to iron element (iron content in the nano zero-valent iron particles) is 1:5 - 6. On the one hand, modifying carboxymethyl cellulose on the surface of nano zero-valent iron particles can increase the surface charge of the particles, provide double-layer electron repulsion or steric hindrance to inhibit the aggregation between particles and the attachment between particles and the surface, enhance the mobility of nano zero-valent iron particles, and also inhibit the agglomeration of nano zero-valent iron particles through steric hindrance and electrostatic stabilization under the action of carboxymethyl cellulose, which is beneficial to improving the dispersibility of nano zero-valent iron particles, increasing the specific surface area and the number of active sites of nano zero-valent iron particles, promoting the adsorption and fixation of lead and zinc by nano zero-valent iron particles. At the same time, carboxymethyl cellulose itself contains rich functional groups, which can enhance the fixation of heavy metals by modified nano zero-valent iron particles through chelation, facilitating the stable fixation of lead and zinc in the modified nano zero-valent iron and effectively avoiding the secondary release of heavy metal ions. On the other hand, by optimizing the mass ratio of carboxymethyl cellulose to iron element, not only can the content of nano zero-valent iron particles be increased, thereby strengthening the reduction effect of the modified nano zero-valent iron particles, and more Pb 2+ can be converted into zero-valent lead, but also more Zn 2+, More importantly, by optimizing their mass ratio, under the action of carboxymethyl cellulose, particle aggregation can be effectively avoided, and it is beneficial to obtain nano zero-valent iron with a smaller particle size. Moreover, under the protection of carboxymethyl cellulose, the particles can be effectively prevented from oxidation, and at the same time, it will not cause serious shielding of the active sites on the surface of nano zero-valent iron particles, nor will it increase the viscosity of the surface of modified nano zero-valent iron particles. Finally, it can ensure the formation of carboxymethyl cellulose-modified nano zero-valent iron with a large specific surface area, many active sites, good mobility, good dispersibility, and strong anti-interference ability. Therefore, when using carboxymethyl cellulose-modified nano zero-valent iron as a reducing agent and adsorbent to treat the groundwater in a lead-zinc mining area, under the combined action of nano zero-valent iron particles and carboxymethyl cellulose, lead and zinc in the water can be rapidly adsorbed, and the treatment efficiency is higher. Moreover, lead and zinc can be stably fixed in carboxymethyl cellulose-modified nano zero-valent iron for a long time and will not be released into the water environment again, which is more environmentally friendly. The method for removing lead and zinc in mine groundwater by using carboxymethyl cellulose-modified nano zero-valent iron in the present invention has the advantages of simple process, low cost, high treatment efficiency, good removal effect, and ensuring the long-term stability of heavy metal ions. It can not only rapidly remove lead and zinc in the water, but also stably fix lead and zinc in carboxymethyl cellulose-modified nano zero-valent iron when the water environment undergoes sudden changes (such as sudden changes in pH value and electrochemical characteristics), showing very excellent anti-interference ability, and is particularly suitable for the long-term remediation of lead and zinc pollution in mine groundwater.

[0023] (2) In the present invention, in the preparation method of the carboxymethyl cellulose-modified nano zero-valent iron adopted, by optimizing the dropping rate of the reducing agent solution, it is beneficial to form nano particles with a good dispersibility, small particle size and core-shell structure, thus being more conducive to preparing carboxymethyl cellulose-modified nano zero-valent iron with a larger specific surface area, a larger number of active sites and better mobility. This is because if the dropping rate is too fast, it will lead to intense nucleation and particle aggregation, forming coarse particles with uneven particle sizes. At the same time, the sudden increase in local pH will produce hydroxide impurities, and the intensification of side reactions will generate too many H2 bubbles; while if the dropping is too slow, the particles will continue to grow, resulting in too large particle sizes, increasing the oxidation risk and reducing the zero-valent iron content. In addition, in the preparation method of the carboxymethyl cellulose-modified nano zero-valent iron in the present invention, first mixing the carboxymethyl cellulose salt with ethanol can, under the promoting action of ethanol, promote the effective dispersion of the carboxymethyl cellulose salt, and then the carboxymethyl cellulose salt can be fully dispersed in the aqueous solution. Finally, it is also beneficial to uniformly modify the carboxymethyl cellulose on the surface of nano zero-valent iron particles, and finally it is beneficial to obtain carboxymethyl cellulose-modified nano zero-valent iron with strong anti-interference ability and better adaptability, which is more suitable for removing lead and zinc in mine groundwater. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention.

[0025] Figure 1 SEM images of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) prepared in Example 1 of the present invention.

[0026] Figure 2 XRD patterns of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) prepared in Example 1 of the present invention.

[0027] Figure 3 Comparison charts of the removal effects of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) on lead and zinc in pure water (PW) and simulated groundwater (GW) in Example 1 of the present invention.

[0028] Figure 4 Fitting charts of the adsorption kinetic models of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) on Pb / Zn in Example 1 of the present invention.

[0029] Figure 5 Variation charts of the removal efficiency of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) on Pb / Zn during long-term aging in Example 3 of the present invention.

[0030] Figure 6 Curves of the variation of pH and iron concentration in the solution over time during the long-term aging of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in Example 3 of the present invention.

[0031] Figure 7 Diagrams of the immediate removal efficiency and iron dissolution concentration of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) after adding humic acid (HA) and nitric acid in Example 4 of the present invention.

[0032] Figure 8 Variation charts of the long-term effects of the removal rate of Pb / Zn by carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) after environmental changes in Example 4 of the present invention. Detailed implementation manners

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] Example 1

[0035] A method for removing lead and zinc from mine groundwater using carboxymethyl cellulose modified nano-zero valent iron, specifically, using carboxymethyl cellulose modified nano-zero valent iron to treat the groundwater in lead-zinc mines, including the following treatments:

[0036] According to the addition amount of carboxymethyl cellulose modified nano-zero valent iron being 0.5 g / L, the carboxymethyl cellulose modified nano-zero valent iron was respectively added to lead ion solution, zinc ion solution, lead-zinc ion solution, lead ion simulated groundwater, zinc ion simulated groundwater, and lead-zinc ion simulated groundwater, mixed, and stirred at a temperature of 25 °C for 2 h to complete the treatment of different lead-zinc water bodies.

[0037] In this example, the lead ion solution, zinc ion solution, and lead-zinc ion solution used were prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) to pure water (PW) respectively. The concentration of lead ions in the lead ion solution was 10 mg·L -1 ; the concentration of zinc ions in the zinc ion solution was 10 mg·L -1 ; the concentration of lead ions in the lead-zinc ion solution was 10 mg·L -1 , and the concentration of zinc ions was 10 mg·L -1 .

[0038] In this example, the lead ion simulated groundwater, zinc ion simulated groundwater, and lead-zinc ion simulated groundwater used were prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) to simulated groundwater (GW) respectively. The concentration of lead ions in the lead ion simulated groundwater was 10 mg·L -1 ; the concentration of zinc ions in the zinc ion simulated groundwater was 10 mg·L -1 ; the concentration of lead ions in the lead-zinc ion simulated groundwater was 10 mg·L -1 , and the concentration of zinc ions was 10 mg·L -1; The simulated groundwater (GW) was prepared according to the ion types and concentration ranges of natural groundwater. Specifically, CaCl2, Na2SO4, and NaCl were added to ultrapure water and stirred until completely dissolved to obtain the simulated groundwater (GW). The concentration of CaCl2 in the simulated groundwater (GW) was 88.6 mg / L, the concentration of Na2SO4 was 141.9 mg / L, and the concentration of NaCl was 292.2 mg / L.

[0039] In this example, the carboxymethyl cellulose-modified nano zero-valent iron used includes nano zero-valent iron particles, and the surface of the nano zero-valent iron particles is modified with carboxymethyl cellulose. The mass ratio of carboxymethyl cellulose to iron element in the carboxymethyl cellulose-modified nano zero-valent iron is 1:5.585

[0040] In this example, the nano zero-valent iron particles in the carboxymethyl cellulose-modified nano zero-valent iron have a core-shell structure with zero-valent iron as the core and iron oxide or iron hydroxide as the shell, and the particle size of the nano zero-valent iron particles is ≤100 nm.

[0041] In this example, the carboxymethyl cellulose-modified nano zero-valent iron used was prepared by reduction with a reducing agent from carboxymethyl cellulose salt and iron salt. The mass ratio of carboxymethyl cellulose salt to iron salt is 0.1:2.703.

[0042] In this example, the preparation method of the carboxymethyl cellulose-modified nano zero-valent iron used includes the following steps:

[0043] S1. Mix 0.1 g of sodium carboxymethyl cellulose (CMC) with 1 mL of ethanol, add water to make up the volume to 200 mL, and perform ultrasonic treatment for 20 min to obtain a sodium carboxymethyl cellulose solution.

[0044] S2. Add 2.703 g of FeCl3·6H2O to the sodium carboxymethyl cellulose solution, and perform ultrasonic treatment for 20 min to fully dissolve the ferric chloride and form a uniform sodium carboxymethyl cellulose-iron mixed solution.

[0045] S3. Under a nitrogen atmosphere, stir the sodium carboxymethyl cellulose-iron mixed solution at a rotation speed of 250 rpm for 30 min. At a dropping rate of 7.5 mL / min, add 200 mL of a sodium borohydride solution with a concentration of 7.566 g / L to the sodium carboxymethyl cellulose-iron mixed solution. After the addition is completed, continue to stir at a rotation speed of 250 rpm for 30 min. Perform magnetic separation on the resulting product solution to obtain the crude carboxymethyl cellulose-modified nano zero-valent iron. Wash the crude carboxymethyl cellulose-modified nano zero-valent iron with absolute ethanol 3 times, and dry it under vacuum at a temperature of 60 °C for 15 h to obtain the carboxymethyl cellulose-modified nano zero-valent iron, denoted as CMC-nZVI.

[0046] Control group 1: Unmodified nano zero-valent iron was used instead of carboxymethyl cellulose modified nano zero-valent iron to remove lead and zinc in pure water (PW) and simulated groundwater (GW), with other conditions being the same.

[0047] The preparation method of the unmodified nano zero-valent iron used was basically the same as that of carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI), with the only difference being that sodium carboxymethyl cellulose (CMC) was not added.

[0048] The prepared unmodified nano zero-valent iron was denoted as nZVI.

[0049] Control 2: Sulfur-modified nano zero-valent iron was used instead of carboxymethyl cellulose modified nano zero-valent iron to remove lead and zinc in pure water (PW) and simulated groundwater (GW), with other conditions being the same.

[0050] The preparation method of the sulfur-modified nano zero-valent iron used mainly referred to the preparation method of carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI), and there were the following differences in the key steps: First, sodium carboxymethyl cellulose (CMC) was not added; second, sodium sulfide was introduced as a sulfur source in the sodium borohydride reduction system to form a sulfur precursor solution.

[0051] The prepared sulfur-modified nano zero-valent iron was denoted as S-nZVI.

[0052] Figure 1 SEM images of the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) prepared in Example 1 of the present invention. From Figure 1 it can be seen that the particle size is not greater than 100 nm; CMC-nZVI is mainly composed of spherical, cubic and irregular particles, and has a relatively high surface roughness.

[0053] Figure 2 XRD patterns of the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) prepared in Example 1 of the present invention. From Figure 2 it can be seen that the prepared CMC-nZVI material contains Fe 0 .

[0054] During the stirring process, samples were taken at preset time intervals. After filtration through a 0.22 μm filter membrane, the concentration of heavy metal ions in the filtrate was determined by air-acetylene flame atomic absorption spectrometry.

[0055] Figure 3This is a comparison chart of the removal effects of carboxymethyl cellulose modified nano zero valent iron (CMC-nZVI) and unmodified nano zero valent iron (nZVI) on lead and zinc in pure water (PW) and simulated groundwater (GW) in Example 1 of the present invention. As Figure 3 shown, in the PW system, the removal rates of both materials for Pb 2+ and Zn 2+ exceed 96%, and CMC-nZVI shows a faster heavy metal removal rate. In the GW environment, the removal rate of both for Pb 2+ can reach over 98% within 2 hours, and the removal rate for Zn 2+ exceeds 90%. Particularly, under the condition of Pb / Zn mixed pollution, due to Pb 2+ prioritizing to occupy the active sites, the removal of Zn 2+ is inhibited, and CMC-nZVI still shows the best comprehensive removal performance. At the same time, the present invention also selects S-nZVI for comparative experiments. In the PW system, the removal efficiency of CMC-nZVI for Zn 2+ can reach 95.36%, which is 16.09% and 19.85% higher than that of S-nZVI (79.27%) and nZVI (75.51%) respectively, showing significant performance advantages.

[0056] The experimental data was fitted using the pseudo-first-order kinetic and pseudo-second-order kinetic models. The model equations are as follows:

[0057]

[0058] In the formula, Q t (mg·g -1 ) and Q e (mg·g -1 ) are the adsorption amounts at time t and at equilibrium respectively, as Figure 4 shown; k1 (min -1 ) and k2 (g·mg -1 ·min -1 ) are the rate constants of the pseudo-first-order kinetic model and the pseudo-second-order kinetic model respectively, as shown in Table 1.

[0059] Figure 4 This is the fitting chart of the adsorption kinetic model of carboxymethyl cellulose modified nano zero valent iron (CMC-nZVI) and unmodified nano zero valent iron (nZVI) for Pb / Zn in Example 1 of the present invention.

[0060] In the PW and GW systems, the adsorption of Pb 2+ by CMC-nZVI provided in Example 1 of the present invention shows an extremely fast rate in the initial stage of the reaction. At 15 minutes of the reaction, Pb 2+The removal rate reaches over 98%. In contrast, the removal rate of nZVI is significantly lower, with a removal rate of 94.15% in 120 minutes in the PW system. In the GW system, the adsorption rate of nZVI for Pb 2+ has increased, and the removal rate can reach 99.64% in 15 minutes.

[0061] For Zn 2+ , in the PW system, CMC-nZVI reaches the adsorption equilibrium after 10 minutes of reaction, while the adsorption rate of nZVI is relatively slow. In the GW system, the removal rates of both materials for Zn 2+ have increased. Among them, CMC-nZVI reaches the adsorption equilibrium within 15 minutes, and nZVI takes 60 minutes to reach the adsorption equilibrium. These results fully demonstrate that the CMC-nZVI provided by the present invention has faster heavy metal removal kinetics performance compared with unmodified nZVI, can reach the adsorption equilibrium earlier, and maintains excellent removal effects in different water quality systems (PW / GW).

[0062] Table 1 Fitting parameters of kinetic models for the adsorption of Pb 2+ and Zn 2+

[0063]

[0064]

[0065] Example 2

[0066] Investigate the effects of carboxymethyl cellulose modified nano zero valent iron (CMC-nZVI) and unmodified nano zero valent iron (nZVI) on lead ion solutions and zinc ion solutions with different concentrations, including the following steps:

[0067] According to the addition amount of carboxymethyl cellulose modified nano zero valent iron being 0.5 g / L, add carboxymethyl cellulose modified nano zero valent iron into lead ion solutions and zinc ion solutions respectively, mix, and stir at a temperature of 25 °C and a rotation speed of 150 rpm for 6 h to complete the treatment of different lead-zinc water bodies.

[0068] In this example, the lead ion solutions and zinc ion solutions used are prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) to pure water (PW) respectively. The concentration of lead ions in the lead ion solution is 10 mg·L -1 , 30 mg·L -1 , 50 mg·L -1 , 70 mg·L -1 and 100 mg·L -1 ; the concentration of zinc ions in the zinc ion solution is 10 mg·L -1 ​, 30 mg·L -1 , 50 mg·L -1 , 70 mg·L -1 and 100 mg·L -1 .

[0069] Control group: The unmodified nano zero-valent iron (nZVI) prepared in Example 1 was used instead of the carboxymethyl cellulose modified nano zero-valent iron, and other conditions were the same.

[0070] After the reaction was completed, all samples were filtered through a 0.22 μm filter membrane, and air-acetylene flame atomic absorption spectrometry was used to determine the concentrations of Pb 2+ and Zn 2+ in the filtrate.

[0071] The experimental data were fitted with the Langmuir model and the Freundlich model:

[0072]

[0073] where Q m is the maximum adsorption capacity (mg·g -1 ); Q e is the amount of metal adsorbed at equilibrium (mg·g -1 ); C e is the metal concentration at equilibrium (mg·L -1 ), K L (L·mg -1 ) and K F (L·mg -1 ) are the Langmuir constant and the Freundlich constant, respectively; is the Freundlich model exponential parameter.

[0074] The experimental results are shown in Table 2. According to the Langmuir fitting results, the maximum adsorption capacity of CMC-nZVI for Pb 2+ reached 213.264 mg·g -1 , which was higher than that of nZVI (194.493 mg·g -1 ); the adsorption capacities for Zn 2+ were 191.329 mg·g -1 (CMC-nZVI) and 189.330 mg·g -1 (nZVI), respectively. In addition, the Freundlich constants (1 / n) of Pb 2+ and Zn 2+ were both between 0.1 and 1, indicating that the adsorption process was easy to occur. These results show that the carboxymethyl cellulose modified nano zero-valent iron adopted in the present invention has good application prospects in the remediation of Pb / Zn contaminated groundwater.

[0075] Table 2 Isothermal model parameters for the adsorption of Pb 2+ and Zn 2+ by different materials

[0076]

[0077]

[0078] Example 3:

[0079] To investigate the long-term stability of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in water, the following steps are included:

[0080] According to the addition amount of carboxymethyl cellulose-modified nano zero-valent iron being 0.5 g / L, the carboxymethyl cellulose-modified nano zero-valent iron was respectively added into the lead-zinc ion solution and the lead-zinc ion simulated groundwater, mixed, the initial pH value was adjusted to 6.0, sealed under N2 atmosphere, placed in a lightless environment and aged at 25 °C for 60 days. The suspension was manually shaken every day to ensure sufficient contact between the material and the pollutant. All experiments were set up with three parallel tests.

[0081] In this example, the lead-zinc ion solution used was prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) into pure water (PW) respectively. The concentration of lead ions in the lead-zinc ion solution was 10 mg·L -1 , and the concentration of zinc ions was 10 mg·L -1 .

[0082] In this example, the lead-zinc ion simulated groundwater used was prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) into simulated groundwater (GW) respectively. The concentration of lead ions in the lead-zinc ion simulated groundwater was 10 mg·L -1 , and the concentration of zinc ions was 10 mg·L -1 ; The simulated groundwater (GW) was prepared according to the ion types and concentration ranges of natural groundwater. Specifically, CaCl2, Na2SO4 and NaCl were added into ultrapure water and stirred until completely dissolved to obtain the simulated groundwater (GW). The concentration of CaCl2 in the simulated groundwater (GW) was 88.6 mg / L, the concentration of Na2SO4 was 141.9 mg / L, and the concentration of NaCl was 292.2 mg / L.

[0083] Control group: The unmodified nano zero-valent iron (nZVI) prepared in Example 1 was used instead of the carboxymethyl cellulose-modified nano zero-valent iron, and other conditions were the same.

[0084] Sampling was carried out at time points of 1, 3, 7, 14, 21, 40 and 60 days. The samples were filtered through a 0.22 μm membrane, and the residual heavy metal, iron ion concentration and solution pH value in the filtrate were measured, as Figure 5 and Figure 6 shown.

[0085] Figure 5 This is a graph showing the change in the removal efficiency of Pb / Zn by carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in Example 3 of the present invention during long-term aging.

[0086] Figure 6 This is a graph showing the change of pH and iron concentration in the solution with time during long-term aging of carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in Example 3 of the present invention.

[0087] As Figure 5 、 6 shown, the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) provided in Example 1 of the present invention has a removal rate of Pb 2+ and Zn 2+ maintaining above 95% in different water systems (PW and GW), and no secondary release of heavy metals was observed within 60 days; the solution pH value rose to about 8.5 and remained stable at the initial stage of the reaction, which was beneficial to maintaining a low heavy metal concentration; the total iron concentration showed a trend of first increasing and then decreasing, and finally dropped below the detection limit (<0.8 mg / L), indicating that most of the corrosion ions (such as Fe 2+ and Fe 3+ ) were mainly attached to the particle surface or formed precipitates. The above results prove that the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) provided by the present invention exhibits excellent long-term heavy metal removal performance, can effectively fix heavy metal ions during 60 days of aging, and is suitable for long-term remediation of groundwater environment.

[0088] Example 4:

[0089] To investigate the environmental adaptability of carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI), the following steps were included:

[0090] (1) According to the addition amount of carboxymethyl cellulose modified nano zero-valent iron being 0.5 g / L, the carboxymethyl cellulose modified nano zero-valent iron was respectively added into the simulated groundwater containing lead and zinc ions, mixed, the initial pH value was adjusted to 6.0, sealed under a N2 atmosphere, and placed in a lightless environment at 25 °C for aging for 3 days. The suspension was manually shaken every day to ensure sufficient contact between the material and the pollutants. All experiments were set with three parallel tests.

[0091] (2) After 3 days of aging, 247 μL of HA solution (to make the final concentration of HA in the solution 2 mg / L) and 5 μL of 0.5 M nitric acid solution (to cause a sudden drop in the pH of the system) were directly added under N2 protection, and samples were immediately taken for analysis.

[0092] (3) After the sampling in step (2) was completed, aging continued for 21 days in a light-shielded environment, and samples were taken regularly for analysis.

[0093] In this example, the lead- and zinc-ion-containing simulated groundwater used was prepared by adding lead salt (Pb(NO3)2) and zinc salt (Zn(NO3)2·6H2O) to simulated groundwater (GW) respectively. The concentration of lead ions in the lead- and zinc-ion-containing simulated groundwater was 10 mg·L -1 , and the concentration of zinc ions was 10 mg·L -1 ; The simulated groundwater (GW) was prepared according to the ion types and concentration ranges of natural groundwater. Specifically, CaCl2, Na2SO4, and NaCl were added to ultrapure water and stirred until completely dissolved to obtain simulated groundwater (GW). The concentration of CaCl2 in this simulated groundwater (GW) was 88.6 mg / L, the concentration of Na2SO4 was 141.9 mg / L, and the concentration of NaCl was 292.2 mg / L.

[0094] Control group: The unmodified nano zero-valent iron (nZVI) prepared in Example 1 was used instead of the carboxymethyl cellulose-modified nano zero-valent iron, and other conditions were the same.

[0095] Figure 7 It is the instant removal efficiency and iron dissolution concentration diagram of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in Example 4 of the present invention after adding humic acid (HA) and nitric acid.

[0096] Figure 8 It is the long-term effect change diagram of the Pb / Zn removal rate of carboxymethyl cellulose-modified nano zero-valent iron (CMC-nZVI) and unmodified nano zero-valent iron (nZVI) in Example 4 of the present invention after environmental changes.

[0097] As Figure 7 shown, on the one hand, no phenomenon of heavy metal secondary release was observed after HA was introduced into the system; on the other hand, when the pH of the system dropped suddenly, the removal rates of Pb 2+ by both materials were not affected, but it led to the secondary release of Zn 2+ , and the secondary release of Zn 2+The removal rate remained at 74.36%, significantly better than that of unmodified nZVI (41.09%). The results proved that the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) provided by the present invention had significantly better acid interference resistance than unmodified nZVI and could effectively maintain the stable fixation of heavy metals when environmental conditions changed. The long-term impact test results showed that( Figure 8 ), the precipitated Zn 2+ could be re-fixed by the nanomaterial, indicating that the carboxymethyl cellulose modified nano zero-valent iron (CMC-nZVI) provided by the present invention could adapt to environmental changes and effectively stabilize the released heavy metal ions.

[0098] From the above results, it can be seen that in the present invention, when treating the groundwater in the lead-zinc mining area with carboxymethyl cellulose modified nano zero-valent iron as a reducing agent and adsorbent, under the combined action of nano zero-valent iron particles and carboxymethyl cellulose, lead and zinc in the water body can be rapidly adsorbed, with higher treatment efficiency, and lead and zinc can be stably fixed in the carboxymethyl cellulose modified nano zero-valent iron for a long time without being released into the water environment again, which is more environmentally friendly. It has the advantages of simple process, low cost, high treatment efficiency, good removal effect, and ensuring the long-term stability of heavy metal ions. It can not only quickly remove lead and zinc in the water body, but also stably fix lead and zinc in the carboxymethyl cellulose modified nano zero-valent iron, showing very excellent anti-interference ability, and is particularly suitable for the long-term restoration and treatment of heavy metal pollution in the groundwater of mining areas.

[0099] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for removing lead and zinc from mine groundwater by using carboxymethyl cellulose modified nano zero-valent iron, which is characterized in that The method is to treat the groundwater in the lead-zinc mining area by using carboxymethyl cellulose modified nano-zero valent iron; the carboxymethyl cellulose modified nano-zero valent iron includes nano-zero valent iron particles, and the surface of the nano-zero valent iron particles is modified with carboxymethyl cellulose; the mass ratio of carboxymethyl cellulose to iron element in the carboxymethyl cellulose modified nano-zero valent iron is 1:5-6.

2. The method according to claim 1, wherein The nano-zero valent iron particles have a core-shell structure with zero valent iron as the core and iron oxide or iron hydroxide as the shell; the particle size of the nano-zero valent iron particles is ≤100 nm.

3. The method according to claim 2, wherein The carboxymethyl cellulose modified nano-zero valent iron is prepared by reducing carboxymethyl cellulose salt and iron salt with a reducing agent; the mass ratio of carboxymethyl cellulose salt to iron salt is 0.1:2.

703.

4. The method according to claim 3, wherein The preparation method of the carboxymethyl cellulose modified nano-zero valent iron includes the following steps: S1. Mix carboxymethyl cellulose salt with ethanol, add water, and perform ultrasonic treatment to obtain a carboxymethyl cellulose salt solution; S2. Add iron salt to the carboxymethyl cellulose salt solution and perform ultrasonic treatment to obtain a carboxymethyl cellulose salt-iron mixed solution; S3. Stir the carboxymethyl cellulose salt-iron mixed solution under a nitrogen atmosphere, and drop the reducing agent solution into the carboxymethyl cellulose salt-iron mixed solution at a dropping rate of 7.5 mL / min. After the dropping is completed, continue to stir to obtain carboxymethyl cellulose modified nano-zero valent iron.

5. The method according to claim 4, wherein The volume ratio of the reducing agent solution to the carboxymethyl cellulose salt solution is 1:1; the reducing agent solution is a sodium borohydride solution; the concentration of the reducing agent solution is 7.566 g / L.

6. The method according to claim 5, wherein In step S1, the ratio of carboxymethyl cellulose salt to ethanol is 0.1 g:1 mL; the carboxymethyl cellulose salt is sodium carboxymethyl cellulose; the time of ultrasonic treatment is 20 min; In step S2, the time of ultrasonic treatment is 20 min; In step S3, the stirring time of the carboxymethyl cellulose salt-iron mixed solution under a nitrogen atmosphere is 30 min; the stirring time after the dropping is completed and continued is 30 min; after the stirring is completed, it further includes: performing magnetic separation on the obtained product solution to obtain a crude product of carboxymethyl cellulose modified nano-zero valent iron, washing the crude product of carboxymethyl cellulose modified nano-zero valent iron with absolute ethanol, and the number of washing times is 2-3 times, and drying at 60 °C under vacuum for 15 h to obtain carboxymethyl cellulose modified nano-zero valent iron.

7. The method according to any one of claims 1 to 6, characterized in that Using carboxymethyl cellulose modified nano-zero valent iron to treat the groundwater in the lead-zinc mining area includes the following steps: mixing the carboxymethyl cellulose modified nano-zero valent iron with the groundwater in the lead-zinc mining area and stirring to complete the treatment of the groundwater in the lead-zinc mining area.

8. The method according to claim 7, characterized in that, The addition amount of the carboxymethyl cellulose modified nano-zero valent iron is 0.5 g of carboxymethyl cellulose modified nano-zero valent iron added per liter of groundwater in the lead-zinc mining area.

9. The method according to claim 8, wherein The groundwater in the lead-zinc mining area contains at least one heavy metal ion of Pb 2+ , Zn 2+ ; the initial pH value of the groundwater in the lead-zinc mining area is 6; the initial concentration of Pb 2+ in the groundwater in the lead-zinc mining area is 10 mg / L to 100 mg / L, and the initial concentration of Zn 2+ is 10 mg / L to 100 mg / L.

10. The method according to claim 7, wherein The stirring is carried out at a temperature of 25 °C; the stirring time is 2 h.

Images