Aluminum-based composites for sustainable control of internal phosphorus release from sediments

Abstract

The application discloses an aluminum-based composite material capable of continuously controlling release of endogenous phosphorus in bottom mud. The aluminum-based composite material is prepared by mixing activated carbon, Al powder and FeCl3 powder under inert gas condition through ball milling, and the weight percentage of the activated carbon powder, the Al powder and the FeCl3 powder is 4-6:1:0.1-0.3. The aluminum-based composite material forms a local alkaline environment in the bottom mud, and the continuously dissolved and non-passivated active zero-valent aluminum continuously fixes the released phosphorus in the bottom mud. + The dense oxide film formed by the aluminum powder after being contacted with water is dissolved to expose the zero-valent aluminum inside the oxide film, then the local alkaline environment formed around the aluminum-based composite material through the galvanic cathode effect continuously promotes the activation of the zero-valent aluminum in the inner layer of the aluminum powder, and the activated zero-valent aluminum is used to form flocculation and precipitation with the released endogenous phosphorus in the bottom mud under the local alkaline environment, so that the purpose of continuously fixing the released phosphorus in the bottom mud is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water pollution treatment, in particular to an aluminum-based composite material capable of sustainable control of internal source phosphorus release in sediment. BACKGROUND

[0002] Excessive phosphorus content in water can cause water eutrophication. Sediment, which deposits a large amount of phosphorus-containing pollutants, acts as an internal source to continuously release phosphorus to the overlying water, so blocking and controlling the release of pollutants in sediment to the outside becomes the key to water treatment.

[0003] There are many phosphorus removal agents and phosphorus locking agents for sediment remediation on the market today. However, the iron salt in the phosphorus removal agent is prone to black odor during sediment remediation, causing secondary pollution to the environment; and the phosphorus locking agent contains rare earth metals, which has a high material preparation cost.

[0004] Aluminum is abundant in nature, easy to obtain, and Al 3+ has good phosphorus fixation capacity. However, when aluminum powder is directly contacted with water, a dense oxide film will quickly form on the surface of the aluminum powder, and the zero-valent aluminum inside the oxide film cannot continuously react and dissolve due to the presence of the oxide film, resulting in the loss of the phosphorus fixation capacity of the aluminum powder.

[0005] Currently, the common method for removing the oxide film on the surface of aluminum is acid washing and mechanical treatment, but the treated aluminum usually still needs to be in a strong acidic or alkaline condition (pH < 4 or pH > 10) to continuously maintain activity, and the continuous acidic or alkaline condition cannot be achieved in actual engineering applications. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides an aluminum-based composite material capable of sustainable control of internal source phosphorus release in sediment, which generates a galvanic cathodic effect in the sediment to form a local alkaline environment, and uses active zero-valent aluminum that continuously dissolves and does not passivate to continuously fix the released phosphorus in the sediment.

[0007] To achieve the above purpose, the present application provides an aluminum-based composite material capable of sustainable control of internal source phosphorus release in sediment, which is used to be put into sediment to control the release of internal source phosphorus in the sediment, and has the following special features: the aluminum-based composite material is prepared by mixing activated carbon, Al powder and FeCl3 powder under inert gas conditions and ball milling, and the weight percentage of the activated carbon powder, Al powder and FeCl3 powder is 4-6:1:0.1-0.3; the aluminum-based composite material put into the sediment forms a local alkaline environment, and uses active zero-valent aluminum that continuously dissolves and does not passivate to continuously fix the released phosphorus in the sediment.

[0008] Further, the particle size of the Al powder before ball milling is 100-2000 mesh.

[0009] Furthermore, the activated carbon is selected from one or more of coconut shell activated carbon, wood activated carbon, fruit shell activated carbon, and coal-based activated carbon.

[0010] Furthermore, the inert gas is selected from one or more of nitrogen, argon, and helium.

[0011] Furthermore, the aluminum-based composite material is mixed and ball-milled using a planetary ball mill with a rotation speed of 200–400 r / min and a milling time of 4–8 h.

[0012] Furthermore, the ball mill beads in the ball mill have a particle size of 6–20 mm.

[0013] Furthermore, the grinding beads have particle sizes of 6mm, 10mm, and 15mm, and the corresponding grinding bead ratio is 15:5:1.

[0014] Furthermore, the grinding beads are made of one or more of the following materials: zirconium oxide, agate, corundum, and stainless steel.

[0015] Furthermore, the amount of the aluminum-based composite material added to the sediment is 1–50 g / kg.

[0016] Furthermore, the phosphorus released from the sediment includes bound phosphorus, exchangeable phosphorus, occluded phosphorus, authigenic calcium phosphorus, detrital phosphorus, and organic phosphorus.

[0017] The principle behind the aluminum-based composite material designed in this invention's ability to continuously control the release of endogenous phosphorus from sediment is as follows:

[0018] 1. By mixing and ball milling, lattice dislocations are generated during the collision of aluminum powder and ferric chloride, which destroys the passivation layer on the aluminum surface and exposes fresh, active zero-valent aluminum, ensuring that the aluminum powder added to the bottom mud is active.

[0019] 2. When an active aluminum-based composite material is added to the bottom sediment, a dense oxide film quickly forms on the surface of the aluminum powder upon contact with water; ferric chloride hydrolyzes to release a certain amount of H+ upon contact with water. + H + Dissolve the oxide film on the aluminum surface to leach Al. 3+ The dissolved Al 3+ In an acidic environment, the endogenous phosphorus released from the sediment forms flocculation and precipitation, which plays a role in controlling the endogenous phosphorus in the sediment. At the same time, the aluminum oxide film on the surface dissolves and exposes the active zero-valent aluminum inside.

[0020] 3, the active carbon material has the characteristics of large specific surface area and strong electron transfer ability, the active zero-valent aluminum inside the oxide film and the active carbon form a micro corrosion primary cell in the aqueous solution, that is, the active zero-valent aluminum gradually dissolves out and releases electrons as an anode, the active carbon transfers the electrons released by the zero-valent aluminum to the surface of the active carbon as a cathode, and then hydrolysis reaction occurs, and OH - , OH - The active carbon surface PH rises (this phenomenon is "galvanic cathode effect"), so that a local alkaline environment is formed around the aluminum-based composite material, the activated zero-valent aluminum in the inner layer of Al promotes the activation of the zero-valent aluminum, and the activated zero-valent aluminum and the endogenous phosphorus released in the sediment form a flocculent precipitate in the local alkaline environment, so that the endogenous phosphorus in the sediment is controlled; and the activated zero-valent aluminum has a larger potential difference with the active carbon, and the surface of the active carbon as a cathode will produce more OH - , which can continuously promote the activation of the zero-valent aluminum in the inner layer of Al, and continuously form a flocculent precipitate with the endogenous phosphorus released in the sediment, so that the endogenous phosphorus in the sediment is continuously controlled.

[0021] The advantages of the present application are:

[0022] 1, the present application firstly produces H + The dense oxide film formed after the aluminum powder is exposed to water is dissolved, and the zero-valent aluminum inside the oxide film is exposed; then the local alkaline environment formed around the aluminum-based composite material by the galvanic cathode effect continuously promotes the activation of the zero-valent aluminum in the inner layer of the aluminum powder, effectively solving the practical problem of poor activation sustainability of zero-valent aluminum when the aluminum-based composite material is applied to sediment remediation;

[0023] 2, the present application not only utilizes the rich functional groups on the surface of the active carbon to alleviate the PH value in water, but also utilizes the hydrolysis product of the aluminum powder to stabilize the PH value in water, so that the designed aluminum-based composite material can effectively maintain the PH value in solution while treating sediment pollutants, without increasing the alkalinity of the water body;

[0024] 3, the active carbon with large specific surface area in the present application not only can adsorb organic pollutants in water, but also can attach microorganisms to grow, and the microbial film fixed by the active carbon can convert the difficult-to-decompose macromolecular organic matter in water into easily-degradable small molecular organic matter;

[0025] 4, the active carbon, aluminum powder and ferric chloride used in the present application are all industrial-grade raw materials, which are low in price and easy to obtain, and can be used on a large scale;

[0026] 5, the aluminum-based composite material in the present application is prepared by mixing and ball milling under inert gas conditions, the preparation method is simple, the production conditions are easy to achieve, and it is suitable for industrial production;

[0027] The aluminum-based composite material capable of continuously controlling the release of endogenous phosphorus in the sediment in the application first dissolves the compact oxide film formed by the aluminum powder after encountering water to expose the zero-valent aluminum inside the oxide film, and then continuously promotes the activation of the zero-valent aluminum in the inner layer of the aluminum powder through the local alkaline environment formed around the aluminum-based composite material by the galvanic cathode effect, and uses the activated zero-valent aluminum to form flocculation and precipitation with the endogenous phosphorus released in the sediment under the local alkaline environment to achieve the purpose of continuously fixing the released phosphorus in the sediment. + The compact oxide film formed by the aluminum powder after encountering water is dissolved to expose the zero-valent aluminum inside the oxide film, and then a local alkaline environment is formed around the aluminum-based composite material by the galvanic cathode effect, continuously promoting the activation of the zero-valent aluminum in the inner layer of the aluminum powder, and using the activated zero-valent aluminum to form flocculation and precipitation with the endogenous phosphorus released in the sediment under the local alkaline environment to achieve the purpose of continuously fixing the released phosphorus in the sediment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Mechanism diagram for the application capable of continuously fixing the released phosphorus in the sediment;

[0029] Figure 2 Schematic diagram of the sediment repair device applied in the embodiment of the application;

[0030] Figure 3-1 Total phosphorus concentration change graph in the comparative example;

[0031] Figure 3-2 Total phosphorus concentration change graph applied in the embodiment of the application;

[0032] Figure 4-1 Light wave number change graph in the comparative example;

[0033] Figure 4-2 Light wave number change graph applied in the embodiment of the application;

[0034] Figure 5-1 Concentration change graph of specific organic pollutants humic acid in the comparative example;

[0035] Figure 5-2 Concentration change graph of specific organic pollutants humic acid applied in the embodiment of the application. DETAILED DESCRIPTION

[0036] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0037] In the description of the application, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application.

[0038] The aluminum-based composite material for continuously controlling release of endogenous phosphorus in bottom mud of the application is used for being put into the bottom mud to control release of endogenous phosphorus in the bottom mud, the aluminum-based composite material is prepared by mixing and ball milling active carbon (AC), Al powder and FeCl3 powder under inert gas condition, and the weight percentage of the active carbon powder, the Al powder and the FeCl3 powder is 4-6:1:0.1-0.3; the aluminum-based composite material put into the bottom mud forms a local alkaline environment, and the active zero-valent aluminum continuously dissolves and does not passivate to continuously fix the released phosphorus in the bottom mud.

[0039] The particle size of the Al powder before ball milling is 100-2000 mesh. The Al powder with too small particle size has too high activity, and there is a risk in storage and transportation process; the Al powder with too large particle size has low reaction activity and is not easy to activate.

[0040] The active carbon is selected from one or more of coconut shell active carbon, wooden active carbon, fruit shell active carbon and coal active carbon. The active carbon material has large specific surface area and rich functional groups.

[0041] The inert gas is selected from one or more of nitrogen, argon and helium. In addition, the aluminum-based composite material after ball milling needs to be collected and stored in an inert gas atmosphere and sealed.

[0042] The aluminum-based composite material is mixed and ball milled by using a planetary ball mill, the rotation speed of the ball mill is 200-400 r / min, and the ball milling time is 4-8 h.

[0043] The particle size of the ball milling beads in the ball mill is 6-20 mm.

[0044] The particle sizes of the ball milling beads are 6 mm, 10 mm and 15 mm respectively, and the corresponding proportions of the ball milling beads are 15:5:1.

[0045] The material of the ball milling beads is selected from one or more of zirconia, agate, corundum and stainless steel.

[0046] The active carbon, the Al powder and the FeCl3 used in the application are all industrial-grade raw materials, the material price is low and easy to obtain, and the materials can be used on a large scale; and the aluminum-based composite material is prepared by mixing and ball milling under inert gas condition, the preparation method is simple, the production condition is easy to achieve, and the method is suitable for industrial production.

[0047] The adding amount of the aluminum-based composite material put into the bottom mud is 1-50 g / kg.

[0048] The endogenous phosphorus in the bottom mud includes exchangeable phosphorus, bound phosphorus, occluded phosphorus, authigenic calcium phosphorus, detrital phosphorus and organic phosphorus.

[0049] In the above technical solution, the principle of the designed aluminum-based composite material for continuously controlling release of endogenous phosphorus in bottom mud is as follows:

[0050] First, by mixing ball milling, the lattice dislocation is generated in the process of aluminum powder colliding with iron chloride, the passivation layer of aluminum surface is destroyed, and fresh active zero-valent aluminum is exposed, so as to ensure that the aluminum powder put into the sediment has activity.

[0051] Second, the aluminum-based composite material with activity is put into the sediment, and after the aluminum powder meets water, a dense oxide film is quickly formed on the surface of the aluminum powder; after the iron chloride meets water, a certain amount of H + is hydrolyzed out. + The aluminum surface oxide film is dissolved, and Al 3+ is dissolved out, as shown in formulas 1-2. The dissolved Al 3+ forms flocculation and precipitation with the internal source phosphorus released in the sediment, thereby playing a role in controlling the internal source phosphorus in the sediment, and after the aluminum surface oxide film is dissolved, the internal active zero-valent aluminum is exposed, and the mechanism is shown in Figure 1 .

[0052] Anode reaction: Al2O3+H + =2Al 3+ +3H2O, Al-3e - =Al 3+ Formula 1

[0053] Cathode reaction: Fe 3+ +3H2O = Fe(OH)3+3H + , 2H + +2e - =H2 Formula 2

[0054] Third, using the characteristics of activated carbon material having a large specific surface area and strong electron transfer capacity, the active zero-valent aluminum inside the oxide film and the activated carbon form a micro-corrosion battery in the aqueous solution, that is, the active zero-valent aluminum gradually dissolves and releases electrons as the anode, and the activated carbon transfers the electrons released by the zero-valent aluminum to the surface of the activated carbon as the cathode, and then hydrolysis reaction occurs, producing OH - , OH - promotes the increase of PH on the surface of the activated carbon (this phenomenon is "Gavani cathode effect"), thereby forming a local alkaline environment around the aluminum-based composite material, promoting the activation of the zero-valent aluminum in the inner layer of Al, as shown in formulas 3-4. The activated zero-valent aluminum and the internal source phosphorus released in the sediment form flocculation and precipitation in the local alkaline environment, thereby playing a role in controlling the internal source phosphorus in the sediment, as shown in formula 5. The activated zero-valent aluminum and the activated carbon have a larger potential difference, and the surface of the activated carbon as the cathode will produce more OH - , which can continuously promote the activation of the zero-valent aluminum in the inner layer of Al, and continuously form flocculation and precipitation with the internal source phosphorus released in the sediment, thereby playing a role in continuously controlling the internal source phosphorus in the sediment, and the mechanism is shown in Figure 1 .

[0055] Anodic reaction: Al - 3e - =Al 3+ E 0 (Al 3+ / Al)=-1.66V Formula 3 Cathode reaction: 2H₂O + 2e⁻ - =H2 + 2OH - Formula 4

[0056] nAl 3+ + PO4 3- + (3n-3)OH - = Al n PO4(OH) 3n-3 Formula 5

[0057] The aforementioned localized alkaline environment exists within the microscopic corrosion galvanic cell reaction system and has little impact on the pH of the sediment.

[0058] This invention first utilizes H generated by the hydrolysis of ferric chloride + The dense oxide film formed when aluminum powder comes into contact with water is dissolved, exposing the zero-valent aluminum inside the oxide film; then, through the galvanic cathodic effect, a local alkaline environment is formed around the aluminum-based composite material, which continuously promotes the activation of the zero-valent aluminum in the inner layer of the aluminum powder, effectively solving the practical problem of poor activation sustainability of zero-valent aluminum when aluminum-based composite materials are used for sediment remediation.

[0059] The specific implementation method is as follows:

[0060] Devices for remediating sediment using acrylic glass as the raw material, such as... Figure 2 As shown, the cylindrical section of the sediment remediation device is divided into two parts: a sediment section (12 cm high) and an overlying water section (16 cm high), with an inner diameter of 8 cm. The sediment section is further divided into three zones from top to bottom: surface layer, transition layer, and bottom layer. The overlying water section is also divided into two zones from top to bottom: upper water and lower water. Sediment (1 kg, 70% water content) is filled into the sediment section according to the designated zones, and lake water (0.8 L) is filled into the overlying water section. To simulate natural conditions, the device is not sealed. Sampling ports are set up in the upper water, lower water, surface layer, transition layer, and bottom layer, and each sampling port is connected to a Rizhon sampler.

[0061] Comparative example:

[0062] Aluminum-based composite materials are not added to the sediment in the aforementioned sediment remediation device.

[0063] Example:

[0064] 6g of aluminum-based composite material was injected into the sediment of the aforementioned sediment remediation device. The preparation process of the aluminum-based composite material is as follows:

[0065] The first and fourth stainless steel ball mill jars (each with a volume of 100 mL) were each filled with 65 g of agate beads, 5 g of coconut shell activated carbon, 1 g of aluminum powder, and 0.2 g of ferric chloride powder, respectively. The mass ratio of activated carbon, aluminum powder, and ferric chloride powder was 5:1:0.2, and the mass ratio of the added materials to the agate beads was approximately 1:11. The diameters of the agate beads in each stainless steel ball mill jar were 6 mm, 10 mm, and 15 mm, respectively, and the ratio of the number of 6 mm, 10 mm, and 15 mm grinding beads in each jar was 15:5:1. The aluminum powder particles had a diameter of 80–150 μm and a purity of 99%. The ferric chloride powder had a purity of 98%.

[0066] Second, seal and evacuate the four stainless steel ball mill jars respectively, and then introduce argon gas.

[0067] Third, place the four stainless steel grinding jars into the planetary ball mill, set the ball mill speed to 400 r / min, and the ball milling time to 8 h.

[0068] Fourth, after ball milling, the obtained aluminum-based composite material is removed and stored in an argon atmosphere, sealed for preservation.

[0069] After the aluminum-based composite material was added, samples were taken at regular intervals from the five sampling ports in the comparative and example samples on days 1, 2, 4, 8, 15, 22, 29, and 36. The total phosphorus (TP) concentration of the samples taken from the comparative example was determined using the ammonium molybdate spectrophotometric method. Figure 3-1 As shown. The total phosphorus (TP) concentration of the samples taken in the examples was determined by ammonium molybdate spectrophotometry, as follows. Figure 3-2 As shown. By Figure 3-1 and 3-2 As can be seen, compared with the comparative example, the aluminum-based composite material in the embodiment effectively immobilizes the endogenous phosphorus in the surface layer, transition layer and bottom layer, thereby reducing the total phosphorus concentration in the upper and lower water layers.

[0070] After the aluminum-based composite material was added, samples were taken at regular intervals on days 1, 2, 9, 16, 23, 30, and 37 from the five sampling ports in the comparative and examples. The samples taken from the comparative examples were then analyzed according to UV... 254 Spectrophotometric determination of organic matter content, such as Figure 4-1 As shown. The samples taken in the examples were processed according to UV... 254 Spectrophotometric determination of organic matter content, such as Figure 4-2 As shown. By Figure 4-1 and 4-2 As can be seen, compared with the comparative example, the aluminum-based composite material in the embodiment absorbs the light wavenumbers of the surface layer, transition layer and bottom layer, effectively reducing the light wavenumbers of the upper and lower water layers.

[0071] After the aluminum matrix composite is added, the five sampling ports in the comparative example and the examples are sampled at the 1st day, the 2nd day, the 4th day, the 9th day, the 16th day, the 23rd day, the 30th day and the 37th day. The samples taken in the comparative example are used to determine the concentration of the specific organic pollutants humic acid by liquid chromatography, as shown in Table 1. The samples taken in the examples are used to determine the concentration of the specific organic pollutants humic acid by liquid chromatography, as shown in Table 2. Figure 5-1 Figure 5-2 Figure 5-1 5-2 It can be seen from Tables 1 and 2 that, compared with the comparative example, the aluminum matrix composite in the examples adsorbs and decomposes a large amount of organic matter in the surface layer, the transition layer and the bottom layer, and effectively reduces the organic matter concentration in the upper water and the lower water.

[0072] The activated carbon with a large specific surface area in the present application not only can adsorb organic pollutants in water, but also can attach microorganisms to grow, and the microbial membrane fixed by the activated carbon can convert the difficult-to-decompose macromolecular organic matter in water into easily-degradable small-molecular organic matter.

[0073] The aluminum matrix composite for continuously controlling the release of endogenous phosphorus in the sediment in the present application first generates H + The dense oxide film formed after the aluminum powder is exposed to water is dissolved to expose the zero-valent aluminum inside the oxide film, and then the local alkaline environment formed around the aluminum matrix composite through the galvanic cathodic effect continuously promotes the activation of the zero-valent aluminum in the inner layer of the aluminum powder, and the activated zero-valent aluminum and the released endogenous phosphorus in the sediment form flocculation and precipitation in the local alkaline environment, so as to continuously fix the released phosphorus in the sediment.

[0074] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.​​​

Claims

1. An aluminum-based composite material for sustainable control of internal phosphorus release in sediment, for being put into sediment to control internal phosphorus release in sediment, characterized in that: The aluminum-based composite material is prepared by mixing and ball milling of active carbon, Al powder and FeCl3 powder under inert gas condition, and the weight percentage of the active carbon powder, Al powder and FeCl3 powder is 4-6:1:0.1-0.3; the aluminum-based composite material put into the sediment forms a local alkaline environment, and the active zero-valent aluminum continuously dissolves and does not passivate to continuously fix the released phosphorus in the sediment; The rotation speed of the ball mill is 200-400 r / min, and the ball milling time is 4-8 h; The adding amount of the aluminum-based composite material put into the sediment is 1-50 g / kg; The released phosphorus in the sediment includes combined state phosphorus, exchangeable state phosphorus, closed storage state phosphorus, autogenous calcium phosphorus, detrital state phosphorus and organic phosphorus.

2. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 1, characterized in that: The particle size of the Al powder before ball milling is 100-2000 mesh.

3. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 2, characterized in that: The active carbon is selected from one or more of coconut shell active carbon, wooden active carbon, fruit shell active carbon and coal active carbon.

4. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 3, characterized in that: The inert gas is selected from one or more of nitrogen, argon and helium.

5. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 1, characterized in that: The aluminum-based composite material is mixed and ball milled by using a planetary ball mill.

6. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 5, characterized in that: The particle size of the ball milling beads in the ball mill is 6-20 mm.

7. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 6, characterized in that: The particle sizes of the ball milling beads are 6 mm, 10 mm and 15 mm respectively, and the corresponding ball milling bead proportions are 15:5:

1.

8. The aluminum-based composite material for sustainable control of internal loading of phosphorus in sediment according to claim 7, characterized in that: The material of the ball milling beads is selected from one or more of zirconia, agate, corundum and stainless steel.

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