Preparation method and application of iron-phosphorus composite soil heavy metal passivator

Abstract

The present invention provides a preparation method and application of an iron-phosphorus composite soil heavy metal passivator, which relates to the technical field of soil remediation. Specifically, a dispersion containing coal gangue, ferrous salt and phosphate is prepared, an oxidant is added and fully reacted, solid-liquid separation is carried out to obtain a solid-phase material; then the solid-phase material is immersed in a concentrated alkali solution, and then the solid-liquid separation and drying are carried out to obtain an iron-phosphorus composite soil heavy metal passivator. The present invention uses coal gangue as a loading material for the iron-phosphorus complex, removes the coal gangue by alkali dissolution to obtain an iron-phosphorus composite heavy metal passivation material with a flaky structure, which has excellent heavy metal ion adsorption and solidification capabilities; at the same time, the present invention uses waste coal gangue as a raw material, realizes the recycling of resources, and has good environmental and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a preparation method and application of an iron-phosphorus composite soil heavy metal passivator. Background Art

[0002] Heavy metal contamination of soil is a global environmental problem, seriously impacting soil safety and crop quality, and consequently threatening human health. Traditional methods for soil heavy metal remediation, including physical, chemical, and biological remediation, often suffer from high costs, low efficiency, and secondary pollution. Therefore, efficient, economical, and environmentally friendly soil heavy metal remediation technologies are of great practical significance.

[0003] Gangue is a solid waste generated during coal mining and washing. It accompanies coal seams during coal formation. It is a dark gray rock with a low carbon content and is harder than coal. Its primary components are Al2O3 and SiO2, but it also contains a complex array of oxide impurities and trace amounts of rare elements. Gangue accumulates in large quantities, occupies land, and pollutes the environment. Therefore, its resource utilization has been a hot topic of research.

[0004] Currently, coal gangue is primarily used as a building material, soil conditioner, and chemical raw material. However, the resource utilization of coal gangue still needs to be further expanded. In the field of soil heavy metal remediation, an iron-phosphorus composite soil heavy metal passivator is a new type of soil heavy metal remediation material with excellent passivation effect and stability. Its principle is to form a stable iron-phosphorus mineral phase in the soil, fixing heavy metal ions in the mineral phase, thereby reducing the bioavailability of heavy metals and reducing their harm to the environment and human body. If coal gangue can be used as a raw material to prepare an iron-phosphorus composite soil heavy metal passivator, it will further expand the application of coal gangue.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first purpose of the present invention is to provide a method for preparing an iron-phosphorus composite soil heavy metal passivator, which, on the one hand, provides a high-efficiency, high-value resource application channel for coal gangue, and on the other hand, provides a passivator material with good heavy metal passivation performance and low cost.

[0007] A second object of the present invention is to provide a soil reagent that achieves the heavy metal passivation performance and stability of the iron-phosphorus composite material while having good designability or functionality.

[0008] The third purpose of the present invention is to provide a method for resource processing of coal gangue, so as to turn waste into treasure and realize the economical recycling of waste.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0010] A method for preparing an iron-phosphorus composite soil heavy metal passivator comprises the following steps:

[0011] A dispersion containing coal gangue, ferrous salt and phosphate is prepared, an oxidant is added and fully reacted, and solid-liquid separation is performed to obtain a solid phase material;

[0012] The solid phase material is soaked in concentrated alkali solution, and then the solid-liquid is separated and dried to obtain an iron-phosphorus composite soil heavy metal passivator.

[0013] A reagent for soil, comprising a passivator prepared by the method for preparing the iron-phosphorus composite soil heavy metal passivator.

[0014] A method for resource processing of coal gangue includes a method for preparing the iron-phosphorus composite soil heavy metal passivator.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides an iron-phosphorus composite soil heavy metal passivator and a preparation method thereof. By using coal gangue as a filling carrier for loading the iron-phosphorus composite material, and removing the coal gangue by alkali dissolution, a flaky iron-phosphorus composite material is prepared. That is, by converting the discarded coal gangue into a flaky structure passivator with a high specific surface area and porosity, on the one hand, the resource utilization of waste is realized, which has good environmental and economic benefits; on the other hand, the adsorption and solidification ability of the passivator for heavy metal ions is significantly improved, thereby improving the soil remediation effect. Specifically, the iron-phosphorus composite soil heavy metal passivator not only has high passivation efficiency and good stability for heavy metals, but also can effectively reduce the bioavailability of heavy metals, reduce environmental and human hazards, and its flaky structure design further enhances the remediation efficiency.

[0017] The preparation method and its derivative applications provided by the present invention have the advantages of low cost, simple production process, and easy promotion and application, which have significant cost advantages compared with traditional soil remediation methods. In addition, the production process of this method is environmentally friendly, without secondary pollution, and has no adverse effects on soil and crops after use, ensuring the safety and quality of crops. The passivation material produced by this method is highly applicable and suitable for the remediation of various heavy metal-contaminated soils. By adjusting the process parameters, passivators of different specifications and performance can be prepared to meet diverse remediation needs, demonstrating good universality. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments, but those skilled in the art will understand that the embodiments described below are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially. In addition, the terms "first", "second" and "third" are only used for descriptive purposes and are not to be understood as indicating or implying relative importance.

[0019] The first aspect of the present invention is to provide a preparation method of an iron-phosphorus composite soil heavy metal passivator, which specifically includes the following steps: first preparing a dispersion containing coal gangue, ferrous salt and phosphate, adding an oxidant and fully reacting, solid-liquid separation, to obtain a solid phase material; then soaking the solid phase material in a concentrated alkaline solution, and then solid-liquid separation and drying to obtain the iron-phosphorus composite soil heavy metal passivator.

[0020] As a preferred embodiment, the preparation method includes: pre-treatment of the gangue, and the pre-treatment mainly includes crushing, screening, and cleaning, etc., to remove impurities in the gangue raw material and obtain low-particle-size gangue fine powder, thereby ensuring the quality and fineness of the gangue to meet the requirements of subsequent uniform loading of iron and phosphorus. In some feasible embodiments in this field, the crushing includes but is not limited to one or more of crushing, splitting, grinding, impact, etc., and in actual application, crushing equipment is selected based on several of the above crushing processes for combined use; the screening is mainly achieved by screening with a sieve corresponding to the expected particle size of the gangue.

[0021] As a preferred embodiment, the particle size of the coal gangue is 0.1mm~0.3mm.

[0022] As a preferred embodiment, in the dispersion, the concentration of the gangue is 1 g / L~20 g / L, including but not limited to any one of 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 18, 20 (g / L) or a numerical range consisting of any two.

[0023] As a preferred embodiment, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, ferrous citrate or ferrous acetate, and the phosphate includes at least one of sodium phosphate, potassium phosphate, ammonium phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate or ammonium dihydrogen phosphate.

[0024] As a preferred embodiment, the dispersion is prepared by first preparing a solution of the ferrous salt, adjusting the pH to 1-3 to promote the dissolution of ferrous sulfate, and then sequentially adding the coal gangue and the phosphate to the ferrous salt solution, followed by thorough mixing to obtain the dispersion. In some optional embodiments, the acid used to adjust the pH can be selected based on the anion of the ferrous salt. For example, when ferrous sulfate is used as the ferrous salt, sulfuric acid (e.g., a dilute sulfuric acid solution, concentrated sulfuric acid, etc.) is used as the pH adjuster.

[0025] As a preferred embodiment, any adding step in the preparation of the dispersion and the reaction step can be assisted by oscillation, stirring, shaking, centrifugation, ultrasound, heating, etc., which helps to accelerate dispersion and obtain a relatively uniform dispersion system or promote the full progress of the chemical reaction.

[0026] As a more preferred embodiment, for the preparation of the dispersion, stirring treatment is carried out after the addition of the coal gangue, the stirring frequency is 80rpm~200rpm, and the stirring time is 5min~30min; it can be understood that the time point for the above-mentioned stirring treatment is only set to after the addition of the coal gangue, but this embodiment does not impose any restrictions on the timing of adding the coal gangue.

[0027] As a preferred embodiment, in the dispersion, the concentration of ferrous ions is 0.1 mol / L~0.5 mol / L, including but not limited to any one of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 (mol / L) or a numerical range consisting of any two of them.

[0028] As a preferred embodiment, in the dispersion, the concentration ratio of phosphate to ferrous ions is 10% to 30%, including but not limited to any one of 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and 30%, or a numerical range consisting of any two of them.

[0029] As a preferred embodiment, the oxidant includes at least one of oxygen, ozone, chlorine, hydrogen peroxide, sodium peroxide, potassium permanganate or potassium dichromate. In some more preferred embodiments, the oxidant is hydrogen peroxide.

[0030] As a preferred embodiment, the amount of the oxidant used is measured based on the complete oxidation of the ferrous ions in the dispersion to ferric ions. Usually, based on the expected usage (i.e., just completing the oxidation of the ferrous ions), the oxidant is in an excess molar amount of 10% to 30% compared to the expected usage.

[0031] As a preferred embodiment, the solid-liquid separation in the present invention includes but is not limited to decantation, filtration, centrifugation, filter or membrane separation, etc.; in a more preferred embodiment, the solid-liquid separation in the present invention uses suction filtration for solid-liquid separation in a low-yield production mode or a laboratory scenario, and in a large-scale batch production mode, solid-liquid separation can be performed by a filter or a combination of suction filtration.

[0032] As a preferred embodiment, the concentrated alkali solution includes at least one of an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, and the pH of the concentrated alkali solution is ≥12, more preferably 12-13.8.

[0033] As a more preferred embodiment, the concentrated alkali solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 10wt.% to 50wt.%.

[0034] As a preferred embodiment, the soaking time is 10 min to 30 min, including but not limited to any one of 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30 (min) or a numerical range consisting of any two of them.

[0035] As a preferred embodiment, the drying time is 2 hours to 6 hours, and the drying temperature is 50° C. to 100° C.

[0036] The second aspect of the present invention is to provide a reagent for soil, the components of which include a passivator obtained by the preparation method of the iron-phosphorus composite soil heavy metal passivator as described in the first aspect. It is understandable that the reagent for soil described in this aspect can be a passivator, a conditioner or an improver, etc., that is, any reagent used for soil remediation or solving soil conditioning problems, and its naming is not strictly limited in the present invention. For the reagent for soil, on the premise of including the iron-phosphorus composite soil heavy metal passivator, those skilled in the art can dope any component based on the characteristics of the soil conditions, or, those skilled in the art can further improve or upgrade based on the iron-phosphorus composite soil heavy metal passivator, or, those skilled in the art can use the iron-phosphorus composite soil heavy metal passivator alone as a reagent for soil, and the above-mentioned situations all belong to an embodiment of this aspect.

[0037] The third aspect of the present invention is to provide a method for resource-based treatment of coal gangue, including the preparation method of the iron-phosphorus composite soil heavy metal passivator as described in the first aspect. It is understandable that the resource-based treatment method described in the present invention may also include other processing steps or processes, that is, other operating steps may be introduced into the preparation method of the iron-phosphorus composite soil heavy metal passivator, or the process may be expanded based on the preparation method of the iron-phosphorus composite soil heavy metal passivator; under the premise of including the preparation method of the iron-phosphorus composite soil heavy metal passivator, any process based on coal gangue may belong to an embodiment of this aspect.

[0038] Example 1

[0039] a) Gangue pretreatment: The gangue is crushed and sieved to obtain uniform fine powder with a particle size of 0.2 mm.

[0040] b) Solution preparation: Mix ferrous sulfate with deionized water and add dilute sulfuric acid to adjust the pH to 2. Stir with a stirrer until the ferrous sulfate is completely dissolved to prepare a uniform solution with a ferrous sulfate concentration of 0.3 mol / L (83 g / L).

[0041] c) Slurry Preparation: The fine powder of coal gangue prepared in step a) was added to the solution prepared in step b) at a coal gangue addition amount of 10 g / L. The mixture was stirred thoroughly at 120 rpm using a high-speed stirrer for 10 minutes to form a suspension slurry.

[0042] d) Additive mixing: Add 20 g / L of dipotassium hydrogen phosphate to the slurry obtained in step c), and continue stirring until the dipotassium hydrogen phosphate is evenly dispersed in the slurry.

[0043] e) Oxidation treatment: hydrogen peroxide is added dropwise to the mixture obtained in step d) in an amount of 1% of the volume of the slurry to carry out an oxidation reaction.

[0044] f) Solid-liquid separation and soaking: solid-liquid separation is performed using a filter press to obtain a solid material after filtration. The solid material is then soaked in a 30% sodium hydroxide solution. After soaking for 20 minutes, the solid material is filtered again to obtain a solid material.

[0045] g) Drying: The solid material obtained in step f) is dried with hot air at a temperature of 70° C. for 3 hours to obtain the finished soil heavy metal passivator of this embodiment.

[0046] Example 2

[0047] a) Gangue pretreatment: The gangue is crushed and sieved to obtain uniform fine powder with a particle size of 0.15mm.

[0048] b) Solution preparation: Mix ferrous sulfate with deionized water and add dilute sulfuric acid to adjust the pH to 2. Stir with a stirrer until the ferrous sulfate is completely dissolved to prepare a uniform solution with a ferrous sulfate concentration of 0.4 mol / L (208 g / L).

[0049] c) Slurry Preparation: The fine powder of coal gangue prepared in step a) was added to the solution prepared in step b) at a coal gangue addition amount of 15 g / L. The mixture was stirred thoroughly at 180 rpm using a high-speed stirrer for 15 minutes to form a suspension slurry.

[0050] d) Additive mixing: Add 25 g / L of dipotassium hydrogen phosphate to the slurry obtained in step c), and continue stirring until the dipotassium hydrogen phosphate is evenly dispersed in the slurry.

[0051] e) Oxidation treatment: hydrogen peroxide is added dropwise to the mixture obtained in step d) in an amount of 1.5% of the volume of the slurry to carry out oxidation reaction.

[0052] f) Solid-liquid separation and soaking: solid-liquid separation is performed using a filter press to obtain a solid material after filtration. The solid material is then soaked in a 40% sodium hydroxide solution. After soaking for 25 minutes, the solid material is filtered again to obtain a solid material.

[0053] g) Drying: The solid material obtained in step f) is dried with hot air at a temperature of 80° C. for 4 hours to obtain the finished product of the soil heavy metal passivator of this embodiment.

[0054] Example 3

[0055] a) Gangue pretreatment: The gangue is crushed and sieved to obtain a uniform fine powder with a particle size of 0.25 mm.

[0056] b) Solution preparation: Mix ferrous sulfate with deionized water and add dilute sulfuric acid to adjust the pH to 1.5. Stir with a stirrer until the ferrous sulfate is completely dissolved to prepare a uniform solution with a ferrous sulfate concentration of 0.25 mol / L (53 g / L).

[0057] c) Slurry Preparation: The fine powder of coal gangue prepared in step a) was added to the solution prepared in step b) at a coal gangue addition amount of 5 g / L. The mixture was stirred thoroughly at 100 rpm using a high-speed stirrer for 20 minutes to form a suspension slurry.

[0058] d) Additive mixing: Add dipotassium hydrogen phosphate to the slurry obtained in step c) in an amount of 15 g / L and continue stirring until the dipotassium hydrogen phosphate is evenly dispersed in the slurry.

[0059] e) Oxidation treatment: hydrogen peroxide is added dropwise to the mixture obtained in step d) in an amount of 2% of the volume of the slurry to carry out an oxidation reaction.

[0060] f) Solid-liquid separation and soaking: solid-liquid separation is performed using a filter press to obtain a solid material after filtration. The solid material is then soaked in a 50% potassium hydroxide solution. After soaking for 20 minutes, the solid material is filtered again to obtain a solid material.

[0061] g) Drying: The solid material obtained in step f) is dried with hot air at a temperature of 60° C. for 5 hours to obtain the finished product of the soil heavy metal passivator of this embodiment.

[0062] Example 4

[0063] a) Gangue pretreatment: The gangue is crushed and sieved to obtain uniform fine powder with a particle size of 0.1 mm.

[0064] b) Solution preparation: Mix ferrous sulfate with deionized water and add dilute sulfuric acid to adjust the pH to 2.5. Stir with a stirrer until the ferrous sulfate is completely dissolved to prepare a uniform solution with a ferrous sulfate concentration of 0.5 mol / L (265 g / L).

[0065] c) Slurry Preparation: The fine powder of coal gangue prepared in step a) was added to the solution prepared in step b) at a coal gangue addition amount of 10 g / L. The mixture was stirred thoroughly at 200 rpm using a high-speed stirrer for 10 minutes to form a suspension slurry.

[0066] d) Additive mixing: Add 30 g / L of dipotassium hydrogen phosphate to the slurry obtained in step c), and continue stirring until the dipotassium hydrogen phosphate is evenly dispersed in the slurry.

[0067] e) Oxidation treatment: hydrogen peroxide is added dropwise to the mixture obtained in step d) in an amount of 0.5% of the volume of the slurry to carry out oxidation reaction.

[0068] f) Solid-liquid separation and soaking: solid-liquid separation is performed using a filter press to obtain a solid material after filtration. The solid material is then soaked in a 30% potassium hydroxide solution. After soaking for 30 minutes, the solid material is filtered again to obtain a solid material.

[0069] g) Drying: The solid material obtained in step f) is dried with hot air at a temperature of 90° C. for 2 hours to obtain the finished soil heavy metal passivator of this embodiment.

[0070] Example 5

[0071] a) Gangue pretreatment: The gangue is crushed and sieved to obtain uniform fine powder with a particle size of 0.2 mm.

[0072] b) Solution preparation: Mix ferrous chloride and deionized water, add dilute hydrochloric acid to adjust the pH to 2, and stir with a stirrer until the ferrous chloride is completely dissolved to prepare a uniform solution with a ferrous chloride concentration of 0.3 mol / L.

[0073] c) Slurry Preparation: The fine powder of coal gangue prepared in step a) was added to the solution prepared in step b) at a coal gangue addition amount of 10 g / L. The mixture was stirred thoroughly at 120 rpm using a high-speed stirrer for 10 minutes to form a suspension slurry.

[0074] d) Additive mixing: add sodium dihydrogen phosphate to the slurry obtained in step c) at an amount of 20 g / L and continue stirring until the sodium dihydrogen phosphate is evenly dispersed in the slurry.

[0075] e) Oxidation treatment: hydrogen peroxide is added dropwise to the mixture obtained in step d) in an amount of 1% of the volume of the slurry to carry out an oxidation reaction.

[0076] f) Solid-liquid separation and soaking: solid-liquid separation is performed using a filter press to obtain a solid material after filtration. The solid material is then soaked in a 30% sodium hydroxide solution. After soaking for 20 minutes, the solid material is filtered again to obtain a solid material.

[0077] g) Drying: The solid material obtained in step f) is dried with hot air at a temperature of 70° C. for 3 hours to obtain the finished soil heavy metal passivator of this embodiment.

[0078] Comparative Example 1

[0079] A 0.3 mol / L (83 g / L) ferrous sulfate solution was prepared, with a strictly controlled pH of 2. Stirring was continued at 120 rpm for 10 minutes to ensure thorough mixing. 20 g / L of dipotassium hydrogen phosphate was added to the system, and stirring continued until uniformly mixed. Hydrogen peroxide, representing 1% of the slurry volume, was added dropwise to the mixture to allow for reaction. After the reaction was complete, solid-liquid separation was performed using a filter press, and the separated solids were directly dried. The resulting product was the iron-phosphorus composite soil heavy metal passivator of this comparative example, without undergoing alkaline dissolution treatment.

[0080] Comparative Example 2

[0081] The process is basically the same as Example 1, with the only difference being that in step f) solid-liquid separation and soaking: solid-liquid separation is performed using a filter press, and the solid material obtained after filtration is directly used for drying in step g).

[0082] Test example

[0083] (1) The experimental soil was collected from a farmland in Guangxin District, Shangrao City, Jiangxi Province. Heavy metals were artificially added to the soil samples to make the cadmium and lead content in the soil exceed the Chinese soil environmental quality standards. The physical and chemical properties of the soil were measured and recorded as shown in Table 1.

[0084] The soil heavy metal passivators prepared in each example and comparative example were applied to heavy metal-contaminated soil at a 5 wt.% concentration and placed in a constant-temperature incubator at 25°C for 150 days. After 150 days, the soil was tested for the available Cd, Cr, As, and Pb contents. Available arsenic was determined according to the method disclosed in GB / T 44741-2024, and the contents of other heavy metals were determined according to the method disclosed in HJ804-2016. Available content refers to the chemical form in the soil that can be directly absorbed, utilized, or produce toxic effects by organisms (such as plants and microorganisms). This was used to evaluate the passivation effectiveness of each passivator material, as shown in Table 2. The removal rate in Table 2 was calculated as follows: Removal rate = (available content of heavy metal in untreated soil - available content of heavy metal in treated soil) × 100% / available content of heavy metal in untreated soil.

[0085] As can be seen from Table 2, the iron-phosphorus composite soil heavy metal passivator prepared by the present invention exhibits good absorption and removal effects on heavy metals represented by Cd, Cr, As and Pb during the 150-day soil treatment.

[0086] (2) The specific surface area and porosity of the soil heavy metal passivator materials prepared in each embodiment and comparative example were measured and recorded in Table 3.

[0087] As shown in Table 3, the specific surface area of ​​the iron-phosphorus composite soil heavy metal passivator prepared by the present invention is ≥150m 2 / g, porosity ≥60%, and has higher specific surface area and porosity than the comparative example.

[0088] Table 1

[0089]

[0090] Table 2

[0091]

[0092] Table 3

[0093]

[0094] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing an iron-phosphorus composite soil heavy metal passivator, characterized in that: The steps include: A dispersion containing coal gangue, ferrous salt and phosphate is prepared, an oxidant is added and fully reacted, and solid-liquid separation is performed to obtain a solid phase material; The solid phase material is immersed in concentrated alkali solution, and then the solid-liquid is separated and dried to obtain an iron-phosphorus composite soil heavy metal passivator; The particle size of the coal gangue is 0.1 mm to 0.3 mm; in the dispersion, the concentration of the coal gangue is 1 g / L to 20 g / L, the concentration of ferrous ions is 0.1 mol / L to 0.5 mol / L, and the ratio of phosphate to ferrous ions is 10% to 30%.

2. The preparation method according to claim 1, characterized in that The ferrous salt includes at least one of ferrous sulfate, ferrous chloride, ferrous citrate or ferrous acetate; And / or, the phosphate includes at least one of sodium phosphate, potassium phosphate, ammonium phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate or ammonium dihydrogen phosphate.

3. The preparation method according to claim 1, characterized in that The preparation of the dispersion comprises the following steps: The aqueous solution of the ferrous salt is prepared, the pH is adjusted to 1-3, and then the coal gangue and the phosphate are added in sequence, and the dispersion is obtained after thorough mixing.

4. The preparation method according to claim 1, characterized in that The pH of the concentrated alkali solution is ≥12; And / or, the concentrated alkali solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 10wt.% to 50wt.%.

5. The preparation method according to claim 1, characterized in that The soaking time is 10 min to 30 min.

6. The preparation method according to claim 1, characterized in that The drying time is 2 hours to 6 hours, and the drying temperature is 50° C. to 100° C.

7. A soil reagent, characterized in that The invention relates to a passivating agent prepared by the method for preparing the iron-phosphorus composite soil heavy metal passivating agent according to any one of claims 1 to 6.

8. A method for recycling coal gangue, characterized in that: The invention comprises a method for preparing the iron-phosphorus composite soil heavy metal passivator according to any one of claims 1 to 6.

Images