A composite slow-release material for repairing organic matter contaminated groundwater and a preparation method and application thereof

Abstract

This invention relates to the fields of environmental protection and groundwater remediation technology, and discloses a composite slow-release material for remediating organically contaminated groundwater, its preparation method, and its application. The method includes: pretreatment of sludge; mixing sludge powder with RuCl3 solution, calcining with carbon dioxide to obtain modified biochar powder; calcining an organic nitrogen source to obtain carbon nitride powder; mixing cobalt salt, manganese salt, copper salt, ammonium fluoride, modified biochar powder, urea, and water, and reacting with sodium percarbonate to obtain a catalyst biochar material; mixing carbon nitride powder, catalyst biochar material, iron salt, and an oxygen-removing solvent, and reacting with a reducing agent to obtain modified nano-zero-valent iron; mixing modified nano-zero-valent iron, sodium percarbonate, and sodium persulfate, and adding to a binder to obtain the composite slow-release material. The composite slow-release material prepared by this method can continuously exert adsorption, Fenton-like catalytic oxidation, and micro-electrolysis effects to effectively remove pollutants from groundwater.

Description

Technical Field

[0001] This invention relates to the fields of environmental protection and groundwater remediation technology, specifically to a composite slow-release material for remediating organic polluted groundwater, its preparation method, and its application. Background Technology

[0002] Groundwater remediation technologies include ex-situ remediation and in-situ remediation. Ex-situ remediation primarily involves pumping groundwater to the surface and treating it using wastewater treatment technologies, requiring the construction of above-ground wastewater treatment facilities. In-situ remediation technologies include in-situ chemical oxidation, bioremediation, in-situ aeration, and permeable reactive barrier (PRB) technology. For operating industrial enterprises, due to limitations imposed by production operations and above-ground structures, in-situ remediation is more suitable for controlling groundwater pollution risks. Permeable reactive barrier (PRB) technology, which originated in the United States in the 1980s, involves installing a permeable reactive barrier filled with reactive materials perpendicular to the direction of groundwater flow. When contaminants migrate along the water flow direction and pass through the PRB, they react with the filling material within the barrier, leading to the degradation or in-situ fixation of the contaminants. Since the contaminated water flows through the reactive barrier by gravity, no additional power or above-ground treatment systems are required. Therefore, selecting appropriate reactive materials for different contaminants in groundwater is crucial for groundwater remediation.

[0003] Iron is a common, inexpensive, and readily available metallic element. Its application in environmental remediation is not only cost-effective but also avoids secondary pollution. Nano-zero-valent iron (nZVI), a novel environmental remediation material commonly used in recent years, is one of the fillers frequently used in groundwater remediation (PRB). nZVI possesses a unique core-shell structure, offering advantages such as large specific surface area, low toxicity, low cost, and ease of preparation. It can remove various types of pollutants from groundwater through chemical reduction and adsorption-precipitation, attracting widespread attention in the field of groundwater remediation. However, nZVI exhibits limitations in groundwater remediation due to its tendency to aggregate, passivate, and leak, as well as poor electron selectivity.

[0004] Biochar typically refers to a loose, porous material with high carbon content, formed by the pyrolysis of biomass resources under anaerobic conditions, followed by dehydration, pyrolysis, and aromatization. It is mainly composed of elemental carbon, aromatized carbon, and graphitic carbon, and is one of the commonly used fillers in biochar remediation (PRB). Common raw materials for biochar preparation include straw, wood, sludge, and core shells. Existing research and applications have shown that biochar possesses numerous advantages, including a large specific surface area, well-developed pore structure, abundant surface functional groups, high cation exchange capacity, low bulk density, and strong chemical and thermal stability. It can be used simultaneously as an adsorbent and catalyst for pollutant control in the environment. Furthermore, its wide availability and low economic cost make it a widely used adsorbent and carrier material for treating various organic pollutants such as organic dyes, polycyclic aromatic hydrocarbons, antibiotics, pesticides, and insecticides. Although biochar has many advantages in environmental remediation, for single-phase biochar, its adsorption capacity and kinetic rate are generally insufficient to meet the requirements for efficient removal of organic pollutants from the environment. When applied to adsorb organic pollutants, biochar exhibits the drawback of difficulty in achieving solid-liquid separation, and its long-term effectiveness and stability in pollutant removal also face some challenges. Therefore, the preparation of composite materials with unique remediation functions using biochar as a carrier or auxiliary catalyst is attracting increasing attention.

[0005] In-situ chemical oxidation (ISCO) remediation technology for organically contaminated sites has become increasingly widely used due to its advantages of broad applicability, good remediation effect, and short remediation cycle. Commonly used oxidants include Fenton's reagent (H₂O₂) and permanganate (MnO₄). - ), persulfate (S2O8) 2- Examples of oxidants include oxidants such as permanganate and ozone (O3). Fenton's reagent can react with most organic matter, including adsorbed pollutants, but its stability is relatively poor. Ozone can also react with most organic matter, but its treatment effect is easily limited by mass transfer and solubility, and it is also affected by the toxicity of byproducts. Permanganate is relatively stable in underground environments, but its reaction is selective, and permanganate reacts rapidly with natural organic matter in the soil. The resulting manganese dioxide precipitate can clog soil pores and affect the transport of oxidants.

[0006] Persulfate, as a novel in-situ chemical oxidative remediation agent, exhibits advantages such as good stability, wide pH applicability, and being green and non-toxic. Its oxidation mechanism involves the cleavage of its -OO- groups under activation, generating highly oxidizing sulfate free radicals (SO4). - SO4 -(E0 = 2.60V) It has a lone pair of electrons, and its oxidizing power exceeds that of persulfate itself (E0 = 2.10V), approaching that of the hydroxyl radical ·OH (E0 = 2.80V). SO4 - The long half-life of · (4s, 40℃) allows for more complete contact with pollutants. Persulfate, upon activation, can also generate ·OH, which can oxidize recalcitrant organic pollutants such as polychlorinated biphenyls (PCBs).

[0007] Chinese patent application CN201510191672.X discloses a permeable reactive wall material for remediating chromium contamination in groundwater. This material includes a reducing agent and an adsorption medium, and its composition and manufacturing method are complex. It is mainly used to reduce hexavalent chromium in groundwater, but it has great limitations in the remediation of organically contaminated groundwater.

[0008] Chinese patent application CN201410408865.1 discloses a method for preparing a biocarbon adsorbent for the remediation of organic pollution. This material only has the function of adsorbing pollutants and is difficult to completely degrade pollutants. Moreover, the removal effect of the material on pollutants is limited after the adsorption is saturated, and it does not have the function of long-term degradation of pollutants.

[0009] Chinese patent application CN201711294049.2 discloses an in-situ remediation material and method for soil and groundwater in organically contaminated sites. This patent uses surfactants to increase the solubility and dispersibility of organic pollutants in groundwater and activates zero-valent iron to form a Fenton-like system to oxidize and degrade organic pollutants. However, this material is difficult to inhibit the aggregation, oxidation and scaling of zero-valent iron, and does not have a slow-release function or long-term effect. Summary of the Invention

[0010] The purpose of this invention is to overcome the problems of poor electronic selectivity, poor long-term effectiveness and stability of pollutant removal in existing groundwater remediation materials, and to provide a composite slow-release material for remediating organic polluted groundwater, its preparation method and application. The composite slow-release material prepared by this method can continuously exert adsorption, Fenton-like catalytic oxidation and micro-electrolysis to effectively remove pollutants from groundwater. Moreover, the composite material is granular, not easy to clog or scale, and has high permeability, so it can be used as a filler for permeable reactive grids (PRBs) to treat polluted groundwater.

[0011] To achieve the above objectives, the present invention provides a method for preparing a composite slow-release material for remediating organically contaminated groundwater, the method comprising the following steps:

[0012] (1) The sludge is pretreated to obtain sludge powder;

[0013] (2) The sludge powder is mixed with RuCl3 solution, and after solid-liquid separation, the solid part is heated in an inert atmosphere and then calcined by passing carbon dioxide through it, and then cooled in an inert atmosphere to obtain modified biochar powder.

[0014] (3) The organic nitrogen source is calcined to obtain carbon nitride powder;

[0015] (4) Cobalt salt, manganese salt, copper salt, ammonium fluoride, the modified biochar powder, and optional urea are mixed with deoxygenated deionized water under an inert atmosphere. Sodium percarbonate is added to adjust the pH of the solution to greater than 10 before the reaction is carried out to obtain catalyst biochar material.

[0016] (5) The carbon nitride powder, the catalyst biochar material, iron salt and deoxygenating solvent are mixed, and then a reducing agent is added under an inert atmosphere to react and obtain biochar catalyst supported modified nano zero-valent iron.

[0017] (6) The biochar catalyst is loaded with modified nano-zero valent iron, sodium percarbonate and sodium persulfate, mixed together, and then the resulting mixture is added to the binder and extruded and granulated to obtain a composite slow-release material.

[0018] Preferably, in step (1), the pretreatment includes: allowing the sludge to settle, centrifuging, solid-liquid separation, drying, and sieving.

[0019] More preferably, the centrifugal separation conditions include: a rotation speed of 3000-5000 r / min and a centrifugation time of 5-15 min.

[0020] More preferably, the drying temperature is 100–120°C.

[0021] More preferably, the mesh size of the sieve is ≥100 mesh.

[0022] Preferably, in step (2), the mass ratio of the sludge powder to the RuCl3 in the RuCl3 solution is 1:0.1 to 2, more preferably 1:1 to 1.5.

[0023] Preferably, the concentration of the RuCl3 solution is 1–6 mol / L, more preferably 2.8–3.2 mol / L.

[0024] Preferably, in step (2), the mixing method is ultrasonic oscillation mixing.

[0025] More preferably, in step (2), the mixing conditions include: a temperature of 20 to 40°C and a time of 12 to 36 hours.

[0026] Preferably, step (2) further includes drying the solid portion after solid-liquid separation.

[0027] More preferably, the drying conditions include a temperature of 120–150°C and a time of 36–48 hours.

[0028] Preferably, in step (2), the calcination process includes: heating to 500-800°C under an inert atmosphere and then introducing carbon dioxide for calcination for 60-120 minutes.

[0029] More preferably, the temperature is raised to 500-800°C at a heating rate of 4-6°C / min.

[0030] Preferably, step (2) further includes: washing, centrifuging, drying and sieving after cooling.

[0031] More preferably, the washing process includes washing with hydrochloric acid solution and deionized water in sequence.

[0032] More preferably, the concentration of the hydrochloric acid solution is 2-4 mol / L.

[0033] More preferably, the drying temperature is 100–110°C.

[0034] More preferably, the mesh size of the sieve is ≥100 mesh.

[0035] Preferably, in step (3), the organic nitrogen source is at least one of dicyandiamide, melamine, and thiourea.

[0036] Preferably, in step (3), the calcination conditions include: a heating rate of 3-7℃ / min, preferably 5-6℃ / min; a calcination temperature of 500-600℃ / min, preferably 500-550℃; and a calcination time of 2-3h.

[0037] Preferably, step (3) further includes: cooling and sieving after calcination.

[0038] More preferably, the mesh size of the sieve is ≥100 mesh.

[0039] Preferably, in step (4), the mass ratio of the cobalt salt, the manganese salt, the copper salt, the ammonium fluoride, the modified biochar powder, and the urea is 2-5:2:1:10:10:5.

[0040] More preferably, the cobalt salt is selected from at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0041] More preferably, the manganese salt is selected from at least one of manganese nitrate, manganese sulfate, and manganese chloride.

[0042] More preferably, the copper salt is selected from copper nitrate and / or copper sulfate.

[0043] Preferably, in step (4), the mixing method is stirring; more preferably, the stirring time is 20 to 40 minutes.

[0044] Preferably, in step (4), the reaction is carried out under isothermal oscillation conditions; more preferably, the reaction conditions include: a temperature of 20-30°C and a time of 12-24 hours.

[0045] Preferably, step (4) further includes: performing solid-liquid separation after the reaction and washing, drying and sieving the obtained solid portion.

[0046] More preferably, the washing process includes washing with deionized water and ethanol alternately.

[0047] More preferably, the drying conditions include a temperature of 50–80°C and a time of 8–15 hours.

[0048] More preferably, the mesh size of the sieve is ≥100 mesh.

[0049] Preferably, in step (4), the iron salt is a divalent iron salt and / or a trivalent iron salt.

[0050] More preferably, the ferrous salt is selected from at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

[0051] More preferably, the trivalent iron salt is selected from at least one of ferric sulfate, ferric nitrate and ferric chloride.

[0052] Preferably, in step (5), the mass ratio of the carbon nitride powder, the catalyst biochar material and the iron salt is 0.2-2:0.1-1:1, more preferably 0.8-1.2:0.3-0.8:1.

[0053] Preferably, in step (5), the deoxygenating solvent is a mixed solution of water and ethanol.

[0054] More preferably, the volume ratio of water to ethanol is 1 to 4:1, more preferably 3:1.

[0055] Preferably, the ratio of iron salt to water is 0.25 to 0.1 mol / L, more preferably 0.5 mol / L.

[0056] Preferably, in step (5), the mixing is ultrasonic oscillation mixing.

[0057] More preferably, the mixing time is 20 to 30 minutes.

[0058] Preferably, in step (5), the reducing agent is NaBH4 solid or NaBH4 solution.

[0059] More preferably, the concentration of the NaBH4 solution is 10–20 mol / L, and even more preferably 12–16 mol / L.

[0060] Preferably, the amount of reducing agent is based on a molar ratio of Fe to NaBH4 of 1:2 to 4.

[0061] Preferably, the reducing agent is added at a time of 30 to 40 minutes.

[0062] Preferably, step (5) further includes: performing solid-liquid separation after the reaction and washing, drying, grinding and sieving the obtained solid powder.

[0063] More preferably, the washing process includes washing with deionized water and anhydrous ethanol multiple times, more preferably washing 2 to 4 times.

[0064] More preferably, the drying conditions include: a temperature of 50–80°C and a time of 6–8 hours.

[0065] More preferably, the mesh size of the sieve is ≥100 mesh.

[0066] Preferably, in step (6), the mass ratio of the biochar catalyst-supported modified nano-zero valent iron, the sodium percarbonate, and the sodium persulfate is 5-10:1-3:3, more preferably 6:2:3.

[0067] Preferably, in step (6), the mass ratio of the mixture to the adhesive is 1:2 to 5, more preferably 1:3 to 4.

[0068] Preferably, in step (6), the preparation process of the adhesive includes: mixing polyvinyl alcohol and sodium alginate, and then adding water and stirring to mix.

[0069] More preferably, the mass ratio of polyvinyl alcohol to sodium alginate is 5 to 12:1, and even more preferably 8 to 10:1.

[0070] More preferably, the mass ratio of the total amount of polyvinyl alcohol and sodium alginate to the amount of water is 2 to 6:100, and more preferably 3 to 5:100.

[0071] Preferably, step (6) further includes: stirring and mixing and constant temperature oscillation before extrusion granulation; and drying after extrusion granulation.

[0072] More preferably, the conditions for the isothermal oscillation include: a rotation speed of 150–180 r / min, a temperature of 20–25°C, and a time of 8–12 h.

[0073] More preferably, the particle size of the particles obtained by extrusion granulation is 5 to 10 mm.

[0074] More preferably, the drying conditions include: a temperature of 50–80°C and a time of 2–4 hours.

[0075] Preferably, the inert atmosphere used in steps (2), (4) and (5) is composed of one or more gases selected from nitrogen, helium, neon and argon.

[0076] A second aspect of the present invention provides a composite sustained-release material prepared by the method described above.

[0077] A third aspect of this invention provides the application of the aforementioned composite slow-release material in the remediation of organically contaminated groundwater.

[0078] Compared with the prior art, the present invention has the following technical effects:

[0079] 1) The composite material prepared in this invention utilizes the activation effect of modified nano-zero valent iron and catalyst biochar on sodium persulfate to increase the sulfate radical SO42- content. - · production efficiency;

[0080] 2) Biochar prepared from wastewater treatment plant sludge can realize waste resource utilization. At the same time, after modification, biochar can not only effectively improve its specific surface area and adsorption performance, but also significantly improve the catalytic activity of biochar particles and enhance the oxidation capacity of oxidants, thereby achieving the effect of synergistic adsorption and oxidative degradation of organic pollutants.

[0081] 3) The prepared nitrogen carbide / catalyst biochar / nano zero-valent iron composite slow-release material has a large specific surface area and pore volume, which can provide more active reaction sites. Compared with the shell of iron oxide, it has stronger conductivity, making the micro-electrolysis environment composed of composite materials have a higher electron transfer capacity than the ordinary "iron / carbon" micro-electrolysis environment. It can transfer electrons to the reaction interface more quickly, improving the selectivity (targeting) of target pollutants. In addition, the modification treatment can also inhibit the agglomeration, oxidation and scaling of nano zero-valent iron, as well as side reactions with non-target pollutants, thereby improving the pollutant removal efficiency.

[0082] 4) The composite slow-release material, after being encapsulated in binder, can continuously remove pollutants from groundwater through adsorption, Fenton-like catalytic oxidation, and micro-electrolysis during the treatment process.

[0083] 5) This composite material is granular, not easy to clog or scale, and has high permeability. It can be used as a filler for permeable reactive grids (PRBs) to treat polluted groundwater. Attached Figure Description

[0084] Figures 1-14The graphs show the removal rates of benzene, toluene, and ethylbenzene in benzene-contaminated groundwater by the composite material particles prepared in Examples 1-9 and Comparative Examples 1-5, respectively.

[0085] Figure 15 This is a SEM image of composite material particle A1. Detailed Implementation

[0086] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0087] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0088] This invention provides a method for preparing a composite slow-release material for remediating organically contaminated groundwater, the method comprising the following steps:

[0089] (1) The sludge is pretreated to obtain sludge powder;

[0090] (2) The sludge powder is mixed with RuCl3 solution, and after solid-liquid separation, the solid part is heated in an inert atmosphere and then calcined by passing carbon dioxide through it, and then cooled in an inert atmosphere to obtain modified biochar powder.

[0091] (3) The organic nitrogen source is calcined to obtain carbon nitride powder;

[0092] (4) Cobalt salt, manganese salt, copper salt, ammonium fluoride, the modified biochar powder, and optional urea are mixed with deoxygenated deionized water under an inert atmosphere. Sodium percarbonate is added to adjust the pH of the solution to greater than 10 before the reaction is carried out to obtain catalyst biochar material.

[0093] (5) The carbon nitride powder, the catalyst biochar material, iron salt and deoxygenating solvent are mixed, and then a reducing agent is added under an inert atmosphere to react and obtain biochar catalyst supported modified nano zero-valent iron.

[0094] (6) The biochar catalyst is loaded with modified nano-zero valent iron, sodium percarbonate and sodium persulfate, mixed together, and then the resulting mixture is added to the binder and extruded and granulated to obtain a composite slow-release material.

[0095] This invention uses sludge as the source of biochar. First, the biochar is modified with Ru and carbon dioxide. Ru-modified biochar exhibits higher catalytic activity, while carbon dioxide modification increases its porosity and specific surface area, reduces surface oxygen content, enhances surface reducing capacity, and improves the C=O / CO group ratio and carbon defects, thus improving its catalytic performance against persulfate. Then, cobalt, manganese, and copper are supported on the modified biochar to obtain a catalyst biochar material. Next, carbon nitride, the catalyst biochar, iron salts, and a reducing agent are reacted to obtain biochar catalyst-supported modified nano-zero-valent iron. Finally, the biochar catalyst-supported modified nano-zero-valent iron is mixed with sodium percarbonate and sodium persulfate to promote the activation of sodium persulfate and increase the sulfate radical SO42-. - By increasing the efficiency of the production process and then encapsulating it with a binder, the composite slow-release material can continuously exert its functions of adsorption, Fenton-like catalytic oxidation, and micro-electrolysis to remove pollutants from groundwater.

[0096] In this invention, the source of the sludge is not limited, as long as it can be calcined to obtain biochar. In a specific embodiment, the sludge can be the residual sludge discharged from the bottom of the secondary sedimentation tank of a sewage treatment plant.

[0097] When using sludge, it can first undergo sludge-water separation. In a specific embodiment, in step (1), the pretreatment includes: allowing the sludge to settle, centrifuging, solid-liquid separation, drying, and sieving. In a preferred embodiment, the centrifugation conditions include: a rotation speed of 3000–5000 r / min, for example, 3000 r / min, 3500 r / min, 4000 r / min, 4500 r / min, or 5000 r / min; and a centrifugation time of 5–15 min, for example, 5 r / min, 10 r / min, or 15 r / min. In this invention, in step (1), the method and conditions for drying the sludge can be conventionally selected in the art. In a preferred embodiment, the drying temperature is 100–120°C, for example, 100°C, 105°C, 110°C, 115°C, or 120°C. In this invention, in step (1), in order to ensure that the sludge reacts sufficiently to obtain high-performance modified biochar powder, the particle size of the sludge powder can be controlled. In a preferred embodiment, the sieve mesh number after grinding the sludge is ≥100 mesh.

[0098] In a specific embodiment, in step (2), the mass ratio of the sludge powder to the RuCl3 in the RuCl3 solution can be 1:0.1 to 2. In a preferred embodiment, in step (2), the mass ratio of the sludge powder to the RuCl3 in the RuCl3 solution is 1:1 to 1.5, for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, or 1:1.5. In a specific embodiment, the concentration of the RuCl3 solution can be 1 to 6 mol / L, for example, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L, preferably 2.8 to 3.2 mol / L.

[0099] In this invention, the mixing method in step (2) is not limited and can be a conventional choice in the art. In a specific embodiment, the mixing method in step (2) is ultrasonic oscillation mixing. In a preferred embodiment, the mixing conditions in step (2) include: a temperature of 20–40°C, for example, 20°C, 25°C, 30°C, 35°C, or 40°C; and a time of 12–36 hours, for example, 12 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, or 40 hours.

[0100] In this invention, step (2) further includes drying the solid portion after solid-liquid separation. In specific embodiments, the drying method and conditions can be conventionally selected in the art. In a preferred embodiment, in step (2), the drying conditions include: a temperature of 120–150°C, for example, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, or 150°C; and a time of 36–48 hours, for example, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 38 hours.

[0101] In this invention, in step (2), Ru can be loaded onto biochar through calcination, which simultaneously creates pores in the biochar, effectively improving its specific surface area and adsorption performance. In a specific embodiment, the calcination process in step (2) includes: heating under an inert atmosphere to a temperature of 500–800°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, followed by calcination with carbon dioxide for 60–120 min, for example, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min. In a preferred embodiment, the temperature is raised to 500–800°C at a heating rate of 4–6°C / min (e.g., 4°C / min, 5°C / min, or 6°C / min).

[0102] In the method described in the invention, step (2) further includes: washing, centrifuging, drying, and sieving after cooling. In a specific embodiment, the washing process in step (2) includes: washing sequentially with hydrochloric acid solution and deionized water. Preferably, the concentration of the hydrochloric acid solution can be 2-4 mol / L, for example, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L. In a more preferred embodiment, the cooled solid powder can be washed 3-5 times with a hydrochloric acid solution of concentration 2-4 mol / L, and then washed with deionized water until the pH value is neutral.

[0103] In this invention, the drying temperature in step (2) can be a conventional selection in the art. In a preferred embodiment, the drying temperature in step (2) can be 100-110°C, for example, 100°C, 105°C, or 110°C. In this invention, the mesh size of the sieve used in step (2) is ≥100 mesh.

[0104] In this invention, the organic nitrogen source serves as the raw material source for carbon nitride powder. In a specific embodiment, in step (3), the organic nitrogen source is at least one of dicyandiamide, melamine, and thiourea. In a preferred embodiment, in step (3), the organic nitrogen source is dicyandiamide.

[0105] In a preferred embodiment, in step (3), the calcination conditions are as follows: the heating rate can be 3 to 7 °C / min, for example 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min or 7 °C / min, more preferably 5 to 6 °C / min; the calcination temperature can be 500 to 600 °C / min, for example 500 °C / min, 550 °C / min or 600 °C / min, more preferably 500 to 550 °C; and the calcination time can be 2 to 3 h, for example 2 h, 2.5 h or 3 h.

[0106] In this invention, step (3) further includes: cooling after calcination and sieving. In a specific embodiment, in step (3), the mesh size of the sieve is ≥100 mesh.

[0107] In this invention, in step (4), the mass ratio of the cobalt salt, the manganese salt, the copper salt, the ammonium fluoride, the modified biochar powder from step (2), and the urea can be 2 to 5:2:1:10:10:5, for example, 2:2:1:10:10:5, 3:2:1:10:10:5, 4:2:1:10:10:5, or 5:2:1:10:10:5.

[0108] In a specific embodiment, in step (4), the cobalt salt is selected from at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride, preferably cobalt nitrate. In another specific embodiment, the manganese salt is selected from at least one of manganese nitrate, manganese sulfate, and manganese chloride, preferably manganese nitrate. In other specific embodiments, the copper salt is selected from copper nitrate and / or copper sulfate, preferably copper nitrate.

[0109] In this invention, the mixing method in step (4) can be a conventional choice in the art, such as stirring. In a specific embodiment, the stirring time can be 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0110] In this invention, in step (4), the reaction is carried out under isothermal oscillation conditions. In a specific embodiment, the reaction conditions include: the temperature can be 20-30°C, for example 20°C, 25°C or 30°C; the time can be 12-24h, for example 12h, 15h, 20h or 24h.

[0111] In this invention, step (4) further includes: performing solid-liquid separation after the reaction and washing, drying, and sieving the resulting solid portion. In a specific embodiment, in step (4), the washing includes: washing with deionized water and ethanol alternately. In a specific embodiment, in step (4), the drying conditions include: a temperature of 50–80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C; and a time of 8–15 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours. In a specific embodiment, in step (4), the sieve mesh size is ≥100 mesh.

[0112] In a specific embodiment, in step (4), the iron salt is a ferrous salt and / or a ferric salt. In a preferred embodiment, the ferrous salt is selected from at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride. In a preferred embodiment, the ferric salt is selected from at least one of ferric sulfate, ferric nitrate, and ferric chloride.

[0113] In this invention, in step (5), the mass ratio of the carbon nitride powder, the catalyst biochar material and the iron salt can be 0.2-2:0.1-1:1, preferably 0.8-1.2:0.3-0.8:1, for example 0.8:0.3:1, 0.9:0.4:1, 1:0.6:1, 1.2:0.8:1, 1.1:0.5:1.

[0114] In this invention, in step (5), the deoxygenating solvent is a mixed solution of water and ethanol. In a preferred embodiment, the volume ratio of water to ethanol is 1 to 4:1, for example 1:1, 2:1, 3:1 or 4:1, more preferably 3:1.

[0115] In this invention, in step (5), the ratio of the iron salt to water can be 0.25 to 0.1 mol / L, for example 0.25 mol / L, 0.5 mol / L, 0.75 mol / L or 1 mol / L, more preferably 0.5 mol / L.

[0116] In a specific embodiment, in step (5), the mixing is ultrasonic oscillation mixing. In a preferred embodiment, the mixing time is 20 to 30 minutes, for example, 20 minutes, 25 minutes, or 20 minutes.

[0117] In this invention, the reducing agent can be a conventional choice in the art. In a specific embodiment, in step (5), the reducing agent is solid NaBH4 or a NaBH4 solution. When the reducing agent is a NaBH4 solution, the concentration of the NaBH4 solution is 10-20 mol / L, for example, 10 mol / L, 15 mol / L, or 20 mol / L, preferably 12-16 mol / L. In a specific embodiment, the amount of reducing agent used is based on a molar ratio of Fe to NaBH4 of 1:2-4, for example, a molar ratio of Fe to NaBH4 of 1:2, 1:3, or 1:4. In a preferred embodiment, the reducing agent can be added slowly and uniformly, and the addition time of the reducing agent can be controlled to be 30-40 min, for example, 30 min, 35 min, or 40 min.

[0118] In this invention, step (5) further includes: performing solid-liquid separation after the reaction and washing, drying, grinding, and sieving the obtained solid powder. In a specific embodiment, the washing process in step (5) includes: washing with deionized water and anhydrous ethanol multiple times. In a preferred embodiment, the washing is performed 2 to 4 times, specifically by washing with deionized water 2 to 4 times and then washing with anhydrous ethanol 2 to 4 times. In a specific embodiment, the drying conditions in step (5) include: a temperature of 50 to 80°C, for example, 50°C, 60°C, 70°C, or 80°C; and a time of 6 to 8 hours, for example, 6 hours, 7 hours, or 8 hours. In a specific embodiment, the sieve mesh size in step (5) is ≥100 mesh.

[0119] In this invention, in step (6), the mass ratio of the biochar catalyst-supported modified nano-zero valent iron, the sodium percarbonate, and the sodium persulfate can be 5 to 10:1 to 3:3, for example 5:1:3, 5:2:3, 6:2:3, 7:1:3, 8:3:3, 9:2:3, or 10:1:3, preferably 6:2:3.

[0120] In this invention, in step (6), the mass ratio of the mixture to the adhesive can be 1:2 to 5, for example 1:2, 1:3, 1:4 or 1:5, preferably 1:3 to 4.

[0121] In this invention, the preparation process of the adhesive in step (6) includes: mixing polyvinyl alcohol and sodium alginate, and then adding water and stirring. In a preferred embodiment, the mass ratio of polyvinyl alcohol to sodium alginate can be 5 to 12:1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1 or 12:1, more preferably 8 to 10:1. In a preferred embodiment, the mass ratio of the total amount of polyvinyl alcohol and sodium alginate to the amount of water can be 2 to 6:100, for example, 2:100, 3:100, 4:100, 5:100 or 6:100, more preferably 3 to 5:100.

[0122] In this invention, step (6) further includes: stirring and mixing and constant-temperature oscillation before extrusion granulation; and drying after extrusion granulation. In a specific embodiment, the constant-temperature oscillation conditions in step (6) include: a rotation speed of 150–180 r / min, for example, 150 r / min, 160 r / min, 170 r / min, or 180 r / min; a temperature of 20–25°C, for example, 20°C, 21°C, 22°C, 23°C, 24°C, or 25°C; and a time of 8–12 h, for example, 8 h, 9 h, 10 h, 11 h, or 12 h. In a specific embodiment, the particle size of the particles obtained by extrusion granulation in step (6) can be 5–10 mm, for example, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm. In a specific implementation, the drying conditions in step (6) include: the temperature can be 50 to 80°C, for example 50°C, 60°C, 70°C or 80°C; the time can be 2 to 4 hours, for example 2 hours, 3 hours or 4 hours.

[0123] In a specific implementation, the inert atmosphere used in steps (2), (4) and (5) is independently selected from one or more of nitrogen, helium, neon and argon. For example, nitrogen is used as the inert atmosphere in step (2), helium is used as the inert atmosphere in step (4), and argon is used as the inert atmosphere in step (5), or nitrogen is used in all steps (2), (4) and (5).

[0124] In this invention, the solid-liquid separation in each step can be a conventional operation in the art. In a preferred embodiment, the solid-liquid separation is vacuum filtration.

[0125] A second aspect of this invention provides a composite slow-release material prepared by the method described above. This composite slow-release material can continuously exert adsorption, Fenton-like catalytic oxidation, and micro-electrolysis effects to effectively remove pollutants from groundwater. Moreover, the composite material is granular, not easily clogged or scaled, and has high permeability, making it suitable as a filler for permeable reactive grids (PRBs) to treat polluted groundwater.

[0126] A third aspect of this invention provides the application of the aforementioned composite slow-release material in the remediation of organically contaminated groundwater.

[0127] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0128] In this invention, benzene series compounds in groundwater are determined according to the "Determination of Benzene Series Compounds in Water by Headspace Chromatography" (HJ1067-2019), and the pH value of groundwater is determined according to the "Determination of pH Value in Water by Glass Electrode Method" (HJ 1147-2020).

[0129] Example 1

[0130] (1) Take the residual sludge discharged from the bottom of the secondary sedimentation tank of a municipal sewage treatment plant. After static sedimentation, take the lower sedimentation sludge for centrifugal separation to further remove the water in the sludge. The rotation speed is 5000 r / min and the centrifugation time is 10 min. After centrifugation, the sludge is filtered to separate the mud and water. The separated sludge is placed in an oven and dried at 110℃ to constant weight. After grinding, it is passed through a 100-mesh sieve to obtain sludge powder.

[0131] (2) Take 8g of sieved sludge powder and a 3mol / L RuCl3 solution (8g of RuCl3 was added to the RuCl3 solution, i.e., the mass ratio of sludge powder to RuCl3 was 1:1). Mix the mixture in a constant-temperature ultrasonic oscillator for 24h at a mixing temperature of 25℃. Then, filter the mixture to obtain solid powder and place it in an oven to dry at 130℃ for 36h. Take 5g of the dried powder and place it in a tube furnace. Under nitrogen atmosphere protection, heat the powder at a rate of 5℃ / min. The temperature was raised to 650℃, CO2 was introduced and maintained for 80 min at a rate of 1.5 L / min, then nitrogen was introduced and heating was stopped until the powder cooled to room temperature. The cooled powder was then washed four times with 3 mol / L hydrochloric acid and then washed with deionized water until the pH was neutral. The powder was centrifuged to remove water and then dried in an oven at 105℃ to constant weight. After passing through a 100-mesh sieve, modified biochar powder was obtained and placed in a centrifuge tube filled with inert gas for later use.

[0132] (3) Add 15g of dicyandiamide to the crucible, cover it and seal it with aluminum foil. Place the crucible in a muffle furnace and heat it to 550°C at a heating rate of 5°C / min. Keep the temperature constant for 2 hours. After the muffle furnace cools down to room temperature, take out the solid powder and pass it through a 100-mesh sieve to obtain carbon nitride powder for later use.

[0133] (4) Take 3g cobalt nitrate, 2g manganese nitrate, 1g copper nitrate, 10g ammonium fluoride, 5g urea and 10g of the modified biochar powder in step (2) and add it to 300ml of deionized water that has been deoxygenated by purging with nitrogen. Under nitrogen protection, stir thoroughly for 30min. Then, continuously add sodium percarbonate powder to the solution and stir thoroughly until completely dissolved until the pH of the solution is 11. The solution is then reacted in a constant temperature water bath shaker at 25℃ for 24h. After that, the precipitate is collected by vacuum filtration, washed alternately with deionized water and ethanol until neutral, and then placed in a vacuum drying oven. After drying at 60℃ for 12 hours, it is passed through a 100-mesh sieve to obtain the catalyst biochar material for later use.

[0134] (5) Weigh 8g of carbon nitride powder described in step (3), 4g of catalyst biochar material described in step (4), and 8g of FeCl3 and add them to a mixture of deoxygenated deionized water and ethanol in 300mL. The ratio of ethanol to deionized water is 2:1. Shake the mixture in an ultrasonic oscillator for 30min until the powder is evenly dispersed in the liquid phase. Then, during the process of thorough stirring, nitrogen gas is introduced to remove oxygen. At the same time, a 15mol / L NaBH4 solution is added dropwise to the mixture using a constant pressure funnel. The Fe:NaBH4 molar ratio is 1:2.5. During this process, stir continuously for 30min. After the reaction is completed, filter the mixture to separate the solid and liquid phases. Wash the obtained solid powder three times with deoxygenated deionized water and then three times with anhydrous ethanol. Then, dry the washed product at 60℃ for 8h in a vacuum drying oven to obtain biochar catalyst-supported modified nano-zero valent iron and store it in a nitrogen-filled centrifuge tube for later use.

[0135] (6) After mixing polyvinyl alcohol and sodium alginate, add a certain amount of deionized water and stir thoroughly until the mixture is uniform to make an adhesive. The mass ratio of polyvinyl alcohol to sodium alginate is 8:1, and the mass ratio of the mixture of polyvinyl alcohol and sodium alginate to deionized water is 1:20. Then, the biochar catalyst-supported modified nano-zero valent iron, sodium percarbonate and sodium persulfate described in step (5) are thoroughly mixed. The mass ratio of the biochar catalyst-supported modified nano-zero valent iron, sodium percarbonate and sodium persulfate is 6:2:3. Then, the resulting mixture is added to the binder and stirred thoroughly. The mass ratio of the mixture to the binder is 1:3.5. Then, it is placed in a constant temperature shaker and shaken at 25°C and 160 r / min for 10 h. Then, the bonded mixture is extruded and granulated to obtain spherical particles with a particle size of 5-10 mm. The composite material particles are placed in a constant temperature drying oven and dried at 60°C for 2 h to obtain composite material particles A1. The SEM image of composite material particles A1 is shown in Figure 15.

[0136] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles A1 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 27.5 mg / L (removal rate 85.5%), toluene 1.7 g / kg (removal rate 88.9%), ethylbenzene 0.5 mg / L (removal rate 93.4%), and the groundwater pH was 7.8.

[0137] Example 2

[0138] The method of Example 1 was implemented, except that in step (5), the mass ratio of carbon nitride powder, catalyst biochar material and ferric chloride was 0.2:0.1:1, that is, 1.6g of carbon nitride powder in step (3), 0.8g of catalyst biochar material in step (4) and 8g of FeCl3 were weighed and added to a mixture of 300mL of deoxygenated deionized water and ethanol to obtain composite material particles A2.

[0139] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles A2 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 28.9 mg / L (removal rate 84.8%), toluene 2.1 g / kg (removal rate 86.3%), ethylbenzene 0.9 mg / L (removal rate 88.2%), and the groundwater pH was 7.6.

[0140] Example 3

[0141] The method of Example 1 was implemented, except that in step (5), the mass ratio of carbon nitride powder, catalyst biochar material and ferric chloride was 0.6:0.2:1, that is, 4.8g of carbon nitride powder in step (3), 1.6g of catalyst biochar material in step (4) and 8g of FeCl3 were weighed and added to a mixture of 300mL of deoxygenated deionized water and ethanol to obtain composite material particles A3.

[0142] Groundwater contaminated with benzene series compounds was collected from a monitoring well of a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles A3 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 28.5 mg / L (removal rate 85.0%), toluene 2.0 g / kg (removal rate 86.9%), ethylbenzene 0.8 mg / L (removal rate 89.5%), and the pH of the groundwater was 7.4.

[0143] Example 4

[0144] The method of Example 1 was implemented, except that in step (5), the mass ratio of carbon nitride powder, catalyst biochar material and ferric chloride was 2:0.5:1. That is, 16g of carbon nitride powder described in step (3), 4g of catalyst biochar material described in step (4) and 8g of FeCl3 were weighed and added to a mixture of 300mL of deoxygenated deionized water and ethanol to obtain composite material particles A4.

[0145] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles (A4) were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 28.2 mg / L (removal rate 85.1%), toluene 1.9 g / kg (removal rate 87.6%), ethylbenzene 0.7 mg / L (removal rate 90.8%), and the groundwater pH was 7.5.

[0146] Example 5

[0147] The method of Example 1 was implemented, except that in step (2), the mass ratio of sludge powder to RuCl3 in RuCl3 solution was 1:0.5, that is, 8g of sieved sludge powder and RuCl3 solution with a concentration of 3mol / L (4g RuCl3 added to RuCl3 solution) were mixed by oscillation in a constant temperature ultrasonic oscillator to obtain composite material particles A5.

[0148] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 28.0 mg / L (removal rate 85.2%), toluene 1.8 g / kg (removal rate 88.2%), ethylbenzene 0.7 mg / L (removal rate 90.8%), and the groundwater pH was 7.6.

[0149] Example 6

[0150] The method of Example 1 was implemented, except that in step (2), the mass ratio of sludge powder to RuCl3 in RuCl3 solution was 1:2, that is, 8g of sieved sludge powder and RuCl3 solution with a concentration of 3mol / L (16g RuCl3 was added to RuCl3 solution) were mixed by oscillation in a constant temperature ultrasonic oscillator to obtain composite material particles A6.

[0151] Groundwater contaminated with benzene series compounds was collected from a monitoring well of a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 29.9 mg / L (removal rate 84.2%), toluene 2.3 g / kg (removal rate 85.0%), ethylbenzene 1.0 mg / L (removal rate 86.8%), and the pH of the groundwater was 7.3.

[0152] Example 7

[0153] The method of Example 1 was implemented, except that in step (6), the mass ratio of modified nano-zero valent iron, sodium percarbonate and sodium persulfate supported on the biochar catalyst was 5:1:3, and composite material particles A7 were obtained.

[0154] Groundwater contaminated with benzene series compounds was collected from a monitoring well of a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles A7 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 r / min and 25℃ for 72 h. Samples were then taken for testing. The results were: benzene 34.3 mg / L (removal rate 81.9%), toluene 2.6 g / kg (removal rate 83.0%), ethylbenzene 1.1 mg / L (removal rate 85.5%), and groundwater pH 7.2.

[0155] Example 8

[0156] The method of Example 1 was implemented, except that in step (6), the mass ratio of modified nano-zero valent iron, sodium percarbonate and sodium persulfate supported on the biochar catalyst was 10:3:3, and composite material particles A8 were obtained.

[0157] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles (A8) were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 33.2 mg / L (removal rate 82.5%), toluene 2.3 g / kg (removal rate 85.0%), ethylbenzene 0.9 mg / L (removal rate 88.2%), and the groundwater pH was 7.6.

[0158] Example 9

[0159] The method of Example 1 was implemented, except that in step (6), the mass ratio of the mixture to the binder was 1:5, and composite material particles A9 were obtained.

[0160] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles (A9) were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results were: benzene 35.3 mg / L (removal rate 81.2%), toluene 2.5 g / kg (removal rate 83.7%), ethylbenzene 0.9 mg / L (removal rate 88.2%), and the pH of the groundwater was 7.5.

[0161] Comparative Example 1

[0162] The method of Example 1 was implemented, except that carbon nitride powder and catalyst biochar material were not added in step (5), and composite material particles B1 were finally obtained.

[0163] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles B1 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results showed: benzene 38.3 mg / L (removal rate 79.8%), toluene 3.0 g / kg (removal rate 80.4%), ethylbenzene 1.4 mg / L (removal rate 81.6%), and the groundwater pH was 7.3.

[0164] Comparative Example 2

[0165] The method of Example 1 was followed, except that RuCl3 solution was not added in step (2) of the preparation process, and nitrogen gas was introduced instead of CO2 to obtain biochar powder, which ultimately yielded composite material particles B2. The specific operation of the biochar powder preparation process in step (2) is as follows:

[0166] (2) Take 8g of sieved sludge powder and mix it in a constant temperature ultrasonic oscillator for 24h at a mixing temperature of 25℃. Then, filter the mixture to obtain solid powder and place it in an oven to dry at 130℃ for 36h. Take 5g of the dried powder and place it in a tube furnace. Under nitrogen atmosphere protection, raise the temperature to 650℃ at a heating rate of 5℃ / min and hold for 80min. Then continue to pass nitrogen and stop heating until it cools to room temperature. Next, wash the cooled powder with 3mol / L hydrochloric acid 4 times and then wash it with deionized water until the pH value is neutral. Centrifuge to filter out the water and place the obtained powder in an oven to dry at 105℃ to constant weight. After passing through a 100-mesh sieve, obtain biochar powder and place it in a centrifuge tube filled with inert gas for later use.

[0167] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles B2 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results showed: benzene 39.9 mg / L (removal rate 79.0%), toluene 2.8 g / kg (removal rate 81.7%), ethylbenzene 1.2 mg / L (removal rate 84.2%), and the groundwater pH was 7.4.

[0168] Comparative Example 3

[0169] The method of Example 1 was implemented, except that the biochar catalyst-supported modified nano-zero valent iron was not added in step (6), and the composite material particles B3 were finally obtained.

[0170] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles B3 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results showed: benzene 62.8 mg / L (removal rate 66.9%), toluene 4.8 g / kg (removal rate 68.6%), ethylbenzene 2.2 mg / L (removal rate 71.1%), and the groundwater pH was 7.6.

[0171] Comparative Example 4

[0172] The method of Example 1 was implemented, except that no catalyst biochar material was added in step (5), and the composite material particles B4 were finally obtained.

[0173] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles B4 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results showed: benzene 68.2 mg / L (removal rate 64.0%), toluene 5.1 g / kg (removal rate 66.7%), ethylbenzene 2.3 mg / L (removal rate 69.7%), and the groundwater pH was 6.8.

[0174] Comparative Example 5

[0175] The method of Example 1 was implemented, except that sodium percarbonate and sodium persulfate were not added in step (6), and the composite material particles B5 were finally obtained.

[0176] Groundwater contaminated with benzene compounds was collected from a monitoring well at a chemical plant. The concentrations of pollutants in the groundwater were: benzene 189.7 mg / L, toluene 15.3 mg / L, and ethylbenzene 7.6 mg / L. The initial pH of the groundwater was 6.8. 300 mL of the contaminated groundwater and 8 g of composite material particles B5 were sealed in a brown wide-mouth bottle and reacted in a constant-temperature shaker at 150 rpm and 25°C for 72 hours. Samples were then taken for testing. The results showed: benzene 70.2 mg / L (removal rate 63.0%), toluene 5.5 g / kg (removal rate 64.1%), ethylbenzene 2.5 mg / L (removal rate 67.1%), and the groundwater pH was 7.9.

[0177] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a composite slow-release material for remediating organically contaminated groundwater, characterized in that, The method includes the following steps: (1) The sludge is pretreated to obtain sludge powder; (2) The sludge powder is mixed with RuCl3 solution, and after solid-liquid separation, the solid part is heated in an inert atmosphere and then calcined by passing carbon dioxide through it, and then cooled in an inert atmosphere to obtain modified biochar powder. (3) The organic nitrogen source is calcined to obtain carbon nitride powder; (4) Cobalt salt, manganese salt, copper salt, ammonium fluoride, the modified biochar powder and optional urea are mixed with deoxygenated deionized water under an inert atmosphere. Sodium percarbonate is added to adjust the pH of the solution to greater than 10 before the reaction is carried out to obtain catalyst biochar material. (5) The carbon nitride powder, the catalyst biochar material, iron salt and deoxygenating solvent are mixed, and then a reducing agent is added under an inert atmosphere to react and obtain biochar catalyst supported modified nano zero-valent iron. (6) The biochar catalyst is supported on modified nano-zero valent iron, sodium percarbonate and sodium persulfate, mixed together, and then the resulting mixture is added to the binder and extruded and granulated to obtain a composite slow-release material.

2. The method according to claim 1, characterized in that, In step (1), the pretreatment includes: allowing the sludge to settle, centrifuging, solid-liquid separation, drying, and sieving.

3. The method according to claim 2, characterized in that, The centrifugation conditions include: a rotation speed of 3000~5000 r / min and a centrifugation time of 5~15 min.

4. The method according to claim 2, characterized in that, The drying temperature is 100~120℃.

5. The method according to claim 2, characterized in that, The sieve mesh size is ≥100 mesh.

6. The method according to claim 1 or 2, characterized in that, In step (2), the mass ratio of the sludge powder to the RuCl3 in the RuCl3 solution is 1:0.1~2.

7. The method according to claim 6, characterized in that, In step (2), the mass ratio of the sludge powder to the RuCl3 in the RuCl3 solution is 1:1 to 1.

5.

8. The method according to claim 1 or 2, characterized in that, In step (2), the concentration of the RuCl3 solution is 1~6 mol / L.

9. The method according to claim 8, characterized in that, The concentration of the RuCl3 solution is 2.8~3.2 mol / L.

10. The method according to claim 1, characterized in that, In step (2), the mixing method is ultrasonic oscillation mixing.

11. The method according to claim 1, characterized in that, In step (2), the mixing conditions include a temperature of 20~40℃ and a time of 12~36h.

12. The method according to claim 1, characterized in that, Step (2) also includes drying the solid portion after solid-liquid separation.

13. The method according to claim 12, characterized in that, The drying conditions include a temperature of 120~150℃ and a time of 36~48h.

14. The method according to claim 1, characterized in that, In step (2), the calcination process includes: heating to 500~800℃ in an inert atmosphere and then introducing carbon dioxide for calcination for 60~120 minutes.

15. The method according to claim 14, characterized in that, The temperature is raised to 500-800℃ at a heating rate of 4-6℃ / min.

16. The method according to claim 1, characterized in that, Step (2) also includes: washing, centrifuging, drying and sieving after cooling.

17. The method according to claim 16, characterized in that, The washing process includes washing with hydrochloric acid solution and deionized water in sequence.

18. The method according to claim 17, characterized in that, The concentration of the hydrochloric acid solution is 2~4 mol / L.

19. The method according to claim 16, characterized in that, The drying temperature is 100~110℃.

20. The method according to claim 16, characterized in that, The sieve mesh size is ≥100 mesh.

21. The method according to claim 1, characterized in that, In step (3), the organic nitrogen source is at least one of dicyandiamide, melamine and thiourea.

22. The method according to claim 1, characterized in that, In step (3), the calcination conditions include: a heating rate of 3~7℃ / min; a calcination temperature of 500~600℃ / min; and a calcination time of 2~3h.

23. The method according to claim 22, characterized in that, The heating rate for calcination is 5~6℃ / min.

24. The method according to claim 22, characterized in that, The calcination temperature is 500~550℃.

25. The method according to claim 1, characterized in that, Step (3) also includes: cooling and sieving after calcination.

26. The method according to claim 25, characterized in that, The sieve mesh size is ≥100 mesh.

27. The method according to claim 1, characterized in that, In step (4), the mass ratio of the cobalt salt, the manganese salt, the copper salt, the ammonium fluoride, the modified biochar powder and the urea is 2~5:2:1:10:10:

5.

28. The method according to claim 1, characterized in that, In step (4), the cobalt salt is selected from at least one of cobalt nitrate, cobalt sulfate and cobalt chloride.

29. The method according to claim 1, characterized in that, In step (4), the manganese salt is selected from at least one of manganese nitrate, manganese sulfate and manganese chloride.

30. The method according to claim 1, characterized in that, In step (4), the copper salt is selected from copper nitrate and / or copper sulfate.

31. The method according to claim 1, characterized in that, In step (4), the mixing method is stirring.

32. The method according to claim 31, characterized in that, The mixing time is 20-40 minutes.

33. The method according to claim 1, characterized in that, In step (4), the reaction is carried out under isothermal oscillation conditions.

34. The method according to claim 1, characterized in that, In step (4), the reaction conditions include: a temperature of 20~30℃ and a time of 12~24h.

35. The method according to claim 1, characterized in that, Step (4) also includes: performing solid-liquid separation after the reaction and washing, drying and sieving the obtained solid part.

36. The method according to claim 35, characterized in that, The washing process includes washing with deionized water and ethanol alternately.

37. The method according to claim 35, characterized in that, The drying conditions include a temperature of 50-80°C and a time of 8-15 hours.

38. The method according to claim 35, characterized in that, The sieve mesh size is ≥100 mesh.

39. The method according to claim 1, characterized in that, In step (4), the iron salt is a divalent iron salt and / or a trivalent iron salt.

40. The method according to claim 39, characterized in that, The ferrous salt is selected from at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

41. The method according to claim 39, characterized in that, The ferric salt is selected from at least one of ferric sulfate, ferric nitrate, and ferric chloride.

42. The method according to claim 1, characterized in that, In step (5), the mass ratio of the carbon nitride powder, the catalyst biochar material and the iron salt is 0.2~2:0.1~1:

1.

43. The method according to claim 42, characterized in that, In step (5), the mass ratio of the carbon nitride powder, the catalyst biochar material and the iron salt is 0.8~1.2:0.3~0.8:

1.

44. The method according to claim 1, characterized in that, In step (5), the deoxygenating solvent is a mixed solution of water and ethanol.

45. The method according to claim 44, characterized in that, The volume ratio of water to ethanol used is 1 to 4:

1.

46. ​​The method according to claim 45, characterized in that, The volume ratio of water to ethanol is 3:

1.

47. The method according to claim 44, characterized in that, The ratio of iron salt to water is 0.25~0.1 mol / L.

48. The method according to claim 44, characterized in that, The ratio of iron salt to water is 0.5 mol / L.

49. The method according to claim 1, characterized in that, In step (5), the mixing is ultrasonic oscillation mixing.

50. The method according to claim 49, characterized in that, The mixing time is 20-30 minutes.

51. The method according to claim 1, characterized in that, In step (5), the reducing agent is NaBH4 solid or NaBH4 solution.

52. The method according to claim 51, characterized in that, The concentration of the NaBH4 solution is 10~20 mol / L.

53. The method according to claim 52, characterized in that, The concentration of the NaBH4 solution is 12~16 mol / L.

54. The method according to claim 51, characterized in that, The amount of reducing agent used is based on a molar ratio of Fe to NaBH4 of 1:2~4.

55. The method according to claim 51, characterized in that, The reducing agent is added at a time of 30-40 minutes.

56. The method according to claim 1, characterized in that, Step (5) also includes: after the reaction, solid-liquid separation is performed and the resulting solid powder is washed, dried, ground and sieved.

57. The method according to claim 56, characterized in that, The washing process includes washing with deionized water and anhydrous ethanol multiple times.

58. The method according to claim 57, characterized in that, The washing process includes washing 2 to 4 times with deionized water and anhydrous ethanol, respectively.

59. The method according to claim 56, characterized in that, The drying conditions include: a temperature of 50~80℃ and a time of 6~8h.

60. The method according to claim 56, characterized in that, The sieve mesh size is ≥100 mesh.

61. The method according to claim 1, characterized in that, In step (6), the mass ratio of the biochar catalyst supported on modified nano-zero valent iron, the sodium percarbonate, and the sodium persulfate is 5~10:1~3:

3.

62. The method according to claim 1, characterized in that, In step (6), the mass ratio of the biochar catalyst supported on modified nano-zero valent iron, the sodium percarbonate, and the sodium persulfate is 6:2:

3.

63. The method according to claim 1, characterized in that, In step (6), the mass ratio of the mixture to the adhesive is 1:2~5.

64. The method according to claim 1, characterized in that, In step (6), the mass ratio of the mixture to the adhesive is 1:3~4.

65. The method according to claim 1, characterized in that, In step (6), the preparation process of the adhesive includes: mixing polyvinyl alcohol and sodium alginate, and then adding water and stirring to mix.

66. The method according to claim 65, characterized in that, The mass ratio of polyvinyl alcohol to sodium alginate is 5~12:

1.

67. The method according to claim 66, characterized in that, The mass ratio of polyvinyl alcohol to sodium alginate is 8~10:

1.

68. The method according to claim 65, characterized in that, The mass ratio of the total amount of polyvinyl alcohol and sodium alginate to the amount of water is 2~6:

100.

69. The method according to claim 68, characterized in that, The mass ratio of the total amount of polyvinyl alcohol and sodium alginate to the amount of water is 3~5:

100.

70. The method according to claim 1, characterized in that, Step (6) also includes: mixing and constant temperature oscillation before extrusion granulation; and drying after extrusion granulation.

71. The method according to claim 70, characterized in that, The conditions for the isothermal oscillation include: a rotation speed of 150~180 r / min, a temperature of 20~25℃, and a time of 8~12 h.

72. The method according to claim 70, characterized in that, The particle size of the extruded granules is 5~10mm.

73. The method according to claim 70, characterized in that, The drying conditions include: a temperature of 50~80℃ and a time of 2~4h.

74. The method according to claim 1, characterized in that, The inert atmospheres used in steps (2), (4) and (5) are each independently selected from one or more of nitrogen, helium, neon and argon.

75. The composite sustained-release material prepared by the method of any one of claims 1-74.

76. The application of the composite slow-release material of claim 75 in the remediation of organically contaminated groundwater.

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