Preparation method and application of suspension agent for passivating soil heavy metals based on ball-milled modified fly ash

Abstract

The invention discloses a preparation method of a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash, which comprises the following steps: sieving fly ash to remove larger particles, and drying to constant weight; uniformly mixing the dried fly ash, quick lime and monopotassium phosphate; uniformly mixing the uniformly mixed solid with clean water; and transferring the solid-liquid mixture into a ball mill, grinding for 1-3 hours according to the ball-milling rotating speed of 300-400rpm to obtain the suspension medicament, and sub-packaging the suspension medicament in a container for normal-temperature storage. The invention also discloses an application of the suspension agent prepared by the preparation method in passivating soil heavy metals. The prepared ball-milled modified fly ash suspension agent is added into heavy metal contaminated soil according to 0.1-0.4% of the mass of the contaminated soil for 45 days, so that the heavy metal activity of the soil can be remarkably reduced. The invention develops a novel suspension agent which is green in preparation, low in cost, free of pollution and suitable for passivating heavy metals in polluted soil.

Description

Technical Field

[0001] The invention relates to the field of soil heavy metal passivation and restoration, and in particular to a preparation method and application of a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash. Background Art

[0002] Soil is the foundation of sustainable agricultural development. The situation of heavy metal pollution in farmland soil in my country is not optimistic. It is urgent to remediate farmland soil contaminated by heavy metals. At present, the passivation remediation method is widely used in farmland soil heavy metal pollution in my country due to its high remediation efficiency, simple operation and low cost. The research and development of heavy metal passivation materials has a long history, such as fly ash, hydroxyapatite, biochar, zeolite, bentonite, etc. Usually, the passivation effect of the passivator can be greatly improved after a simple modification. Taking fly ash as an example, many researchers have used the hydrothermal alkaline dissolution modification method to improve the adsorption effect of fly ash on heavy metals, but most of the studies are solid-liquid separation at the end of the modification process, and then the solid is dried to obtain the modified fly ash passivator. The separated liquid often contains other modifiers with high alkalinity and may contain, if not treated, it may pollute the environment again. In addition, the ball milling method is also widely used in the research and development of passivation materials because it can activate the passivation material and increase the specific surface area of ​​the modified material.

[0003] Related research:

[0004] Ji Puhui (CN202211709276.8) modified fly ash with NaOH solution to prepare artificial zeolite to passivate Cd and Pb in the soil. The material needs to be washed with water many times until it is neutral during the preparation process. Lu Yongping et al. (CN202311294139.7) prepared a curing agent geopolymer slurry by mixing NaOH solution with fly ash and adding quicklime, encapsulating heavy metal pollutants in the structure of the geopolymer matrix. Although the problem of drying the solid state and treating the liquid after solid-liquid separation is avoided, it also makes the soil unable to be reused. Zhang Tingting et al. (202211451743.1) activated soluble calcium salts, magnesium salts and iron-based materials by ball milling to form a powdered calcium carbonate passivator with the property of slow release of iron elements. In addition, Huang Di et al. (202010225937.4) also prepared a powdered heavy metal passivator after drying the cellulose powder modified by wet ball milling.

[0005] At present, most of the final products of soil passivators are stored, transported and used in powder form. The research results of a few final forms of slurry also make the soil unable to be reused. Practice shows that there are two main practical applications of powder passivators: one is to directly sprinkle it into polluted farmland in powder form. This method is simple and convenient but has obvious disadvantages, such as large material loss and low operating safety; the other is to use a solid-liquid mixing device to mix fly ash with water and then spray it on the polluted farmland. This type of mechanical mixing wet spraying method is more suitable for open areas and has a high cost. Therefore, it is particularly necessary to explore a method to prepare a liquid or solid-liquid mixed passivator that has good effect, is easy to operate, has no secondary pollution and is environmentally friendly. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a preparation method and application of a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash, while ensuring a passivation effect not less than that of a powdered passivator, to achieve resource recycling, avoid secondary pollution, improve economic benefits, and solve the drawbacks of powdered passivators in practical applications, especially the drawbacks of powdered passivators based on fly ash modification in applications.

[0007] In order to solve the above technical problems, a technical solution adopted by the present invention is: to provide a preparation method of a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash, comprising the following steps:

[0008] Step 1: sieve the fly ash to remove larger particles and dry it to constant weight;

[0009] Step 2: Mix the dried fly ash FA, quicklime CaO and potassium dihydrogen phosphate KH2PO4 in a mass ratio of 16: (1.8-2.5): 2.8;

[0010] Step 3: Mix the solid mixed in step 2 with clean water at a solid-to-liquid ratio of 1: (2-20);

[0011] Step 4: The solid-liquid mixture of step 3 is transferred to a ball mill, and ground at a ball mill speed of 300-400 rpm for 1-3 hours to obtain the suspension drug, which is packaged in containers and stored at room temperature.

[0012] In a preferred embodiment of the present invention, in step S1, fly ash is sieved through a 100-mesh sieve and dried at 100° C. to a constant weight.

[0013] In a preferred embodiment of the present invention, in step S2, the mass ratio of quicklime (CaO) to potassium dihydrogen phosphate (KH2PO4) is determined according to a chemical equation, which is as follows:

[0014] 3CaO + 3H2O + 2KH2PO4 → Ca3(PO4)2 + 2K + + 2OH - + 4H2O (1)

[0015] Therefore, the mass ratio of some raw materials to compounds is CaO:KH2PO4:Ca3(PO4)2=3×56.1:2×136.1:1×310.2=1.68:2.72:3.10, and the geometric conversion is CaO:KH2PO4:Ca3(PO4)2=1.73:2.80:3.20. Since the chemical equation can only be completed under the condition of excess alkali, the mass ratio of CaO to KH2PO4 is determined to be 1.8~2.5:2.8. Previous studies have shown that the ratio of fly ash to calcium phosphate is 5:1, which has the best adsorption effect on heavy metals (see the invention patent "A modified fly ash material and its preparation method and application", application number 202111659682.3), so the ratio of fly ash to calcium phosphate is set to 16:3.2. In summary, the mass ratio of raw materials is FA:CaO:KH2PO4=16:(1.8~2.5):2.8.

[0016] In a preferred embodiment of the present invention, in step S3, the clean water is deionized water.

[0017] In a preferred embodiment of the present invention, in step S4, the ball milling temperature is 15-25° C. The ball mill can be a planetary ball mill, a wet ball mill, or a stirring ball mill.

[0018] To solve the above technical problems, another technical solution adopted by the present invention is: to provide a suspension agent prepared by the preparation method of a suspension agent for passivating heavy metals in soil based on ball-milled modified fly ash as described in any of the above items, and to use the suspension agent in passivating heavy metals in soil.

[0019] In a preferred embodiment of the present invention, the heavy metals include Cd and Cu.

[0020] In a preferred embodiment of the present invention, the suspension agent can increase soil pH.

[0021] In a preferred embodiment of the present invention, the suspension agent can increase the content of available phosphorus and quick-acting potassium in the soil.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention provides a method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash. Compared with the preparation method of a powder passivating agent, the modified agent does not need to be dried at high temperature and then ground, but is stored in a solid-liquid mixed state, so the preparation cost is lower; after the modification, there is no need for solid-liquid separation or water washing to neutrality, and no waste liquid is generated during the preparation process, and there is no secondary disposal cost for the waste liquid generated during the preparation process;

[0024] (2) The passivating agent prepared by the method of the present invention is stored and used as a suspension agent (solid-liquid mixed state), and does not require drying and moisture-proofing conditions, which can solve the inconvenience of traditional powdered passivating agents in practical applications, especially improve the operating safety of workers;

[0025] (3) The passivating agent prepared by the method of the present invention has a flexible method of use. It can be directly applied to the contaminated soil after being shaken evenly by hand, or it can be applied by a pesticide spraying machine, such as a drone spraying operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic flow chart of the method for preparing a suspension agent for passivating heavy metals in soil by ball-milling modified fly ash according to the present invention;

[0027] Figure 2 is the adsorption effect of QMFA prepared with different ball milling times on Pb, Cd and Cu;

[0028] Figure 3 is the adsorption effect of QMFA prepared with different solid-liquid ratios on Pb, Cd and Cu;

[0029] Figure 4 is the passivation effect of different FA and QMFA addition amounts on soil heavy metal Pb;

[0030] Figure 5 is the passivation effect of different FA and QMFA addition amounts on soil heavy metal Cd;

[0031] Figure 6 is the passivation effect of different FA and QMFA addition amounts on soil heavy metal Cu;

[0032] Figure 7 It is the effect of different FA and QMFA addition amounts on soil available phosphorus and available potassium. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0034] See also Figure 1 , the embodiment of the present invention includes:

[0035] A method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash comprises the following steps:

[0036] Step 1: sieve the fly ash to remove larger particles and dry it to constant weight;

[0037] Step 2: Mix the dried fly ash FA, quicklime CaO and potassium dihydrogen phosphate KH2PO4 in a mass ratio of 16: (1.8-2.5): 2.8;

[0038] Step 3: Mix the solid (total mass g) mixed in step 2 with clean water (total volume mL) at a solid-liquid ratio of 1:5;

[0039] Step 4: The solid-liquid mixture of step 3 is transferred to a ball mill, and ground at a ball mill speed of 300-400 rpm for 1-3 hours to obtain the suspension drug, which is packaged in containers and stored at room temperature.

[0040] Preferably, in step S1, the fly ash is passed through a 100-mesh sieve and dried at 100° C. to a constant weight.

[0041] Preferably, in step S2, the mass ratio of the raw materials is FA:CaO:KH2PO4=16:2:2.8.

[0042] Preferably, in step S3, the clean water used is deionized water.

[0043] Preferably, in step S4, the ball milling time is 2 hours, the ball milling speed is 400 rpm, and the temperature is 25°C.

[0044] The method of using the passivating agent is as follows: adding the prepared suspension agent (based on the mass of the solid part thereof) to the soil at 0.1-0.4% of the mass of the polluted soil, and mixing and passivating the heavy metals for 45 days.

[0045] The specific steps of the method of the present invention are described below with specific embodiments.

[0046] 1. Preliminary experiments determine the best modification conditions:

[0047] The optimal modification conditions were determined by the adsorption effect of heavy metals in aqueous solution (we did not study the passivation effect of heavy metals in soil in the preliminary experiment stage. This is because the composition of soil is more complex than that of aqueous solution, so it is impossible to directly and quickly explore the passivation effect of heavy metals in soil treated with additives. Although there are some highly sensitive technologies that can be used to detect changes in heavy metal components in soil at the molecular level, such as synchrotron radiation technology, this technology is only used when the concentration of heavy metals is high, which is far higher than the concentration of heavy metals in contaminated soil):

[0048] Determine the optimal ball milling time: Figure 2 As shown, the experiment set up 6 treatments, control group: original fly ash; experimental group: ball milled for 1, 2, 3, 6, and 9 hours respectively. A planetary ball mill was used to add agate balls and material powder to four ball mills. The ball mills were placed symmetrically and the speed was 400rpm. The prepared modified fly ash was used for heavy metal adsorption test, and the ball milling time with the best adsorption effect was selected as the modified ball milling time.

[0049] Determine the optimal ball milling solid-liquid ratio: Figure 3 As shown, the experiment set up 5 treatments, control group: original fly ash; experimental group: ball milling solid-liquid ratios were 1:2, 1:5, 1:10, and 1:20 respectively. The solid-liquid ratio represents the ratio of the mass (g) of the passivation material to the volume (mL) of the liquid. A planetary ball mill was used to add agate balls and material powder to four ball mills. The ball mills were placed symmetrically and the rotation speed was 400rpm. The prepared modified fly ash was used for heavy metal adsorption test, and the solid-liquid ratio with the best adsorption effect was selected as the modified solid-liquid ratio.

[0050] The adsorption effects of QMFA prepared with different ball milling time and solid-liquid ratio on Pb, Cd and Cu are shown in Figure 2. Figure 2 , Figure 3 . The adsorption of Cd by fly ash increased significantly after ball milling. When the Cd concentration was lower than 200 mg / L, the difference in the adsorption of Cd and Cu by ball milling time was not significant within 1 to 3 hours. Therefore, the optimal ball milling time was determined to be 1 to 3 hours in combination with the adsorption effect and economic benefit. In this embodiment, the ball milling time was selected to be 2 hours. The adsorption effect of fly ash on Cu did not change significantly after ball milling with different solid-liquid ratios, but the adsorption of Cd increased significantly. The solid-liquid ratio of 1:5 had a high adsorption of Cd at different concentrations (100, 200, 300 mg / L). Therefore, the optimal solid-liquid ratio was determined to be 1:5.

[0051] After determining the ball milling time (2 h) and solid-liquid ratio (1:5), QMFA was prepared according to these conditions for soil heavy metal passivation culture.

[0052] 2. The passivation effect of suspension agent (QMFA) on soil heavy metals:

[0053] The test soil was collected from Guixi City, Yingtan City, Jiangxi Province. After removing plant roots and other residues, it was naturally air-dried and ground through a 20-mesh sieve for later use. The soil pH was 3.67, and the contents of Pb, Cd and Cu were 1216, 0.324 and 368.1 mg / kg, respectively.

[0054] This embodiment has 7 treatment groups, including a blank control group (CK), a treatment group with different doses of FA addition, and a treatment group with different doses of QMFA addition. FA and QMFA (based on the mass of the solid part) were added to 1000g of contaminated soil through a 2mm sieve at 0.1%, 0.2% and 0.4% of the soil mass, respectively, and mixed thoroughly in a 1L polyethylene plastic dish. The treatments were set as follows: contaminated soil without passivation agent (CK); contaminated soil + 0.1% FA (FA-0.1); contaminated soil + 0.2% FA (FA-0.2); contaminated soil + 0.4% FA (FA-0.4); contaminated soil + 0.1% QMFA (QMFA-0.1); contaminated soil + 0.2% QMFA (QMFA-0.2); contaminated soil + 0.4% QMFA (QMFA-0.4), with three replicates in each group. The effect of adding ball-milled modified fly ash on soil pH changes and the effective state of heavy metals was investigated. On the 45th day of cultivation, samples were taken, air-dried, and sieved, and the soil pH and available heavy metal content were measured.

[0055] Example 1: Effects of different QMFA addition amounts on soil pH and passivation effect of heavy metal Pb

[0056] Figure 4 The results show the changes in soil pH and the available content of heavy metal Pb under flooding passivation culture conditions. pH is one of the important factors affecting the effectiveness of heavy metals in soil. When the soil pH is low, H + It will compete with heavy metal ions, which is not conducive to the passivation of heavy metals by the soil. + The content is reduced, and the soil's passivation ability for heavy metals is improved. As shown in the figure, the pH of each treatment has an upward trend during the 45-day culture period. Compared with CK, the pH value of the FA-0.1~0.4 treatment group increased by 0.03-0.16 units, while the pH value of the QMFA-0.1~0.4 treatment group increased by 0.13~0.40 units. Therefore, the addition of fly ash can increase the soil pH value, and the increase increases with the increase in its addition amount; under the same addition amount conditions, the effect of QMFA on soil pH is significantly higher than that of FA. This may be caused by the introduction of calcium oxide during the modification process.

[0057] During the 45-day incubation period, the available Pb content in the soil of CK was 180.4 mg / kg. Compared with CK, the addition of fly ash can significantly reduce the available Pb content in the soil, and the reduction increases with the increase of fly ash addition. This may be due to the high specific surface area of ​​fly ash that adsorbs heavy metals. Under the same addition conditions, QMFA is more effective in reducing the available Pb content in the soil than FA. When the addition amount was 0.4%, the available Pb content of FA and QMFA treatments was 0.4-9.1% and 14.7-43.0% lower than that of CK, respectively. In addition, on the 45th day of incubation, the available Pb content of the QMFA treatment group was 102.9 mg / kg at a 0.4% addition amount, which was 37% lower than that of the FA treatment group (163.4 mg / kg). This may be due to the increase in the specific surface area of ​​fly ash during ball milling and the introduction of P–O functional groups, which formed phosphate complex precipitation with lead.

[0058] Example 2: Effects of different QMFA addition amounts on soil pH and passivation effect of heavy metal Cd

[0059] Figure 5 The changes of soil pH and available heavy metal Cd content under flooding passivation culture conditions were shown. Compared with CK, the pH of the FA-0.1-0.4 treatment group increased by 1.9-4.0%, while the pH of the QMFA-0.1-0.4 treatment group increased by 3.2-9.9%. Therefore, the addition of fly ash can increase the soil pH, and the increase increases with the increase of its addition amount; under the same addition amount, the effect of QMFA on soil pH is significantly higher than that of FA, which may be caused by the introduction of calcium oxide during the modification process. During the 45-day culture period, the available Cd content of CK in the soil was 37.64ug / kg. Compared with CK, the addition of fly ash can significantly reduce the available Cd content in the soil, and its decrease increases with the increase of fly ash addition. This may be due to the high specific surface area of ​​fly ash that adsorbs heavy metals. Under the same addition amount, QMFA is more significant than FA in reducing the available Cd content in the soil. When the addition amount was 0.4%, the effective Cd content of FA and QMFA treatments was reduced by 15.4-30.9% and 34.1-39.4% respectively compared with CK. In addition, on the 45th day of cultivation, the effective Cd content of the QMFA treatment group was 22.82ug / kg at a 0.4% addition amount, which was 12% lower than that of the FA treatment group (25.6ug / kg). This may be due to the increase in the specific surface area of ​​fly ash during ball milling, the introduction of P-O functional groups, and the formation of phosphate complex precipitation with heavy metals.

[0060] Example 3: Effects of different QMFA addition amounts on soil pH and passivation effect of heavy metal Cu

[0061] Figure 6The changes in soil pH and the available content of heavy metal Cu under flooding passivation culture conditions are shown. The changes in soil pH are the same as before. The addition of fly ash can increase the soil pH value, and the increase increases with the increase of its addition amount; under the same addition amount conditions, the effect of QMFA on soil pH is significantly higher than that of FA, which may be caused by the introduction of calcium oxide during the modification process. During the 45-day culture period, the available Cu content in the soil of CK was 45.6 mg / kg. Compared with CK, the addition of fly ash can significantly reduce the available Cu content in the soil, and its decrease increases with the increase of fly ash addition amount. This may be due to the high specific surface area of ​​fly ash that adsorbs heavy metals. Under the same addition amount conditions, QMFA is more effective than FA in reducing the available Cu content in the soil. When the addition amount is 0.4%, the available Cu content of FA and QMFA treatments is 6.2-9.7% and 22.4-23.7% lower than that of CK, respectively. In addition, on the 45th day of cultivation, the effective Cu content of the QMFA treatment group was 35.5 mg / kg at a 0.4% addition, which was 17.3% lower than that of the FA treatment group (42.9 mg / kg). This may be due to the increase in the specific surface area of ​​fly ash during ball milling and the introduction of abundant functional groups, which formed complex precipitation with heavy metals.

[0062] Example 4: Effects of different QMFA addition amounts on soil available phosphorus and available potassium

[0063] Since potassium dihydrogen phosphate was introduced during the fly ash modification process, some fertilizer changes in the soil were detected after 45 days of passivation. Figure 7 The effect of different fly ash addition amounts on soil available phosphorus and available potassium. Compared with CK, after passivation for 45 days, the addition of FA did not significantly increase the content of soil available phosphorus and available potassium, while the addition of QMFA increased the content of soil available phosphorus and available potassium, and the increase increased with the increase in the amount of QMFA added. The content of soil available phosphorus and available potassium in QMFA treatment increased by 16.4-26.9% and 40.7-516.4% compared with CK, respectively. At 0.4% addition, the content of available phosphorus and available potassium in the QMFA treatment group was 77.72 and 327.34 mg / kg, respectively.

[0064] In summary, the novel suspension agent (QMFA) prepared by the method of the present invention can significantly improve the soil pH and the passivation effect of fly ash on heavy metals, and can significantly increase the potassium fertilizer and phosphorus fertilizer of the soil.

[0065] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0066] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash, characterized in that: The following steps are involved: Step 1: sieve the fly ash to remove larger particles and dry it to constant weight; Step 2: Mix the dried fly ash FA, quicklime CaO and potassium dihydrogen phosphate KH2PO4 in a mass ratio of 16: (1.8-2.5): 2.8; Step 3: Mix the solid mixed in step 2 with clean water at a solid-to-liquid ratio of 1: (2-20); Step 4: The solid-liquid mixture of step 3 is transferred to a ball mill, and ground at a ball mill speed of 300-400 rpm for 1-3 hours to obtain the suspension drug, which is packaged in containers and stored at room temperature.

2. The method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash according to claim 1, characterized in that: In step S1, fly ash is passed through a 100-mesh sieve and dried at 100° C. to a constant weight.

3. The method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash according to claim 1, characterized in that: In step S2, the mass ratio of quicklime CaO to potassium dihydrogen phosphate KH2PO4 is determined according to a chemical equation, which is as follows: 3CaO+3H2O+2KH2PO4→Ca3(PO4)2+2K + +2OH - +4H2O (1)。 4. The method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash according to claim 1, characterized in that: In step S3, the clean water is deionized water.

5. The method for preparing a suspension agent for passivating soil heavy metals based on ball-milled modified fly ash according to claim 1, characterized in that: In step S4, the ball milling temperature is 15-25°C.

6. Use of a suspension agent prepared by the method for preparing a suspension agent for passivating heavy metals in soil based on ball-milled modified fly ash as claimed in any one of claims 1 to 5 in passivating heavy metals in soil.

7. The use according to claim 6, characterized in that: The heavy metals include Cd and Cu.

8. The use according to claim 6, characterized in that: The suspension agent can increase soil pH.

9. The use according to claim 6, characterized in that: The suspension agent can increase the content of effective phosphorus and quick-acting potassium in the soil.

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