CN114751425A

CN114751425A - Preparation method and application of zeolite soil passivator with high iron content

Info

Publication number: CN114751425A
Application number: CN202210340778.1A
Authority: CN
Inventors: 余江; 皇甫卓曦; 杨韬; 常凯威; 吴玥蓉
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2022-04-02
Filing date: 2022-04-02
Publication date: 2022-07-15
Anticipated expiration: 2042-04-02
Also published as: CN114751425B

Abstract

The invention provides a preparation method of a zeolite soil passivator with high iron content, which comprises the steps of crushing, sieving and roasting coal gangue in sequence, then uniformly mixing the coal gangue with NaOH powder, then calcining, then adding sodium metaaluminate and water, stirring and aging, and finally carrying out hydrothermal crystallization reaction. According to the invention, the zeolite with high iron content can be prepared by selecting the inferior coal gangue with high iron content in the slag storage yard without additionally adding an iron source in the preparation process. The prepared Fe-NaX zeolite contains partial hydroxyl, can interact with heavy metal in soil to form a coordinate bond, is a porous material, and can achieve the purpose of stabilizing the heavy metal in the soil through two main modes of cation exchange and electrostatic interaction.

Description

Preparation method and application of zeolite soil passivator with high iron content

Technical Field

The invention relates to the technical field of soil heavy metal pollution treatment, in particular to a preparation method of a zeolite soil passivator with high iron content and application of the passivator in repairing heavy metal soil.

Background

In recent years, with the rapid development of the urbanization process and the adjustment of the industrial layout in China, the rapid development of industrial and agricultural industries and the mining of mines, the heavy metal pollution of soil is more and more serious. Heavy metals, as persistent toxic pollutants, can enter the soil through different ways, and can not be biodegraded and exist in the soil for a long time, so that soil pollution is caused, and public health and surrounding environment are harmed.

The remediation of the soil polluted by heavy metals mainly comprises physical remediation, biological remediation and chemical remediation. The physical method has high treatment cost and large engineering quantity for high-concentration heavy metal polluted sites; the bioremediation method has long restoration period and certain selectivity on pollutant restoration. The chemical remediation method has the advantages of passivation and thoroughness in treatment effect, suitability for treatment of heavily polluted soil and the like, so that the chemical remediation method is widely concerned and applied.

At present, chemical remediation methods for heavy metal pollution mainly adopt a chemical leaching technology and a passivation remediation technology. However, for the leaching technique, since the eluent has some selectivity for heavy metals, the soil fertility is destroyed, the soil properties are affected, and the eluent needs further treatment. The passivation technology can effectively reduce the migration performance of soil pollutants, and the operation is simple and easy. The materials which can be used as the heavy metal passivator comprise ammonium salt, turf, ground phosphate rock, quicklime and the like, have higher cost and poor application universality, and can seriously change the physical and chemical properties of soil after being applied. It is therefore desirable to provide a new heavy metal passivator which should have a lower material cost and a better passivation capability.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention provides a preparation method and application of a zeolite soil passivator with high iron content.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to a preparation method of a zeolite soil passivator with high iron content, which comprises the following steps:

the method comprises the following steps: sequentially crushing, sieving and roasting the coal gangue to obtain coal gangue powder;

preferably, the mass percentage content of the iron oxide in the coal gangue is more than 10%. Different from the prior art, the method has the advantages that the iron in the coal gangue can be retained to the maximum extent by directly roasting the coal gangue without acid washing and iron removal after the coal gangue is crushed, and the zeolite soil passivator with high iron content is obtained without adding an iron source in the preparation process.

In one embodiment of the present invention, the coal gangue is from a coal mine slag storage yard in south china, and the main components of the coal gangue comprise: silicon oxide (the mass percentage content is more than or equal to 40 percent), aluminum oxide (the mass percentage content is more than or equal to 15 percent) and iron oxide (the mass percentage content is more than or equal to 10 percent), wherein the iron oxide is a mixture of ferroferric oxide and ferric oxide.

Generally, coal gangue can be divided into micro-iron coal gangue (the mass percentage of iron element is less than 1%), low-iron coal gangue (the mass percentage of iron element is 1% -3.5%), medium-iron coal gangue (the mass percentage of iron element is 3.5% -5%), and high-iron coal gangue (the mass percentage of iron element is more than 5%) according to the iron content. The iron content in the coal gangue determines the thermal processing process mode and the industrial utilization range, the sintering of the coal gangue as the masonry is the main direction of resource recycling of the coal gangue, and when the high-iron coal gangue is used for making bricks, the coal gangue cannot be used as the main material of the baked bricks due to excessive iron elements and can only be used as an auxiliary material.

Preferably, the size of the sieve used for sieving is 100-500 meshes, and preferably 200 meshes.

Preferably, the roasting is carried out in a muffle furnace, the roasting temperature is 750-950 ℃, and the roasting time is 1.5-3 h. The roasting function is to remove carbon impurities in the coal gangue.

Step two: uniformly mixing the coal gangue powder and NaOH powder, and then calcining to obtain a mixture;

in the prior art, the thermally activated coal gangue is added into a sodium hydroxide solution and then filtered to obtain a filtrate, which causes the loss of iron element. The invention makes the roasted coal gangue and sodium hydroxide powder perform solid phase reaction in a molten state, wherein the microstructure and particles of mineral crystals generate violent relative motion, and indissolvable silicon-aluminum crystal minerals are converted into soluble substances to promote the crystallization process.

Preferably, the mass ratio of the coal gangue powder to the NaOH powder is 1 (1.0-1.5).

Preferably, the calcination is carried out in a muffle furnace, the calcination temperature is 600-700 ℃, and the calcination time is 2.5-3.5 h.

Step three: sequentially adding sodium metaaluminate and water into the mixture, and stirring and aging to obtain a mixed solution;

preferably, the amount of the added sodium metaaluminate is the SiO in the coal gangue₂/Al₂O₃Adjusting the mass ratio of the substances to 3.5, then adding deionized water to adjust the alkalinity to 3.5mol/L, and stirring and aging for 6-8 h by using a magnetic stirrer at room temperature to obtain a mixed solution. The vessel is sealed during the process to prevent evaporation of water and loss of material during the agitation process.

Step four: and carrying out hydrothermal crystallization reaction on the mixed solution to obtain the Fe-NaX type molecular sieve, namely the zeolite soil passivator with high iron content.

Preferably, the hydrothermal crystallization reaction is to transfer the mixed solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallize the mixed solution in an oven at 100 ℃ for 8-12 hours.

The invention also relates to application of the zeolite soil passivator with high iron content prepared by the method, including application in removing heavy metals in polluted soil, wherein the heavy metals comprise lead and cadmium.

Preferably, the application comprises: the method comprises the steps of uniformly mixing contaminated soil, water and a soil passivator to obtain a mixture, wherein the solid content in the mixture is 10% -90%, the mass fraction of the soil passivator in the solid is 0.5% -2%, and then maintaining for one month to remove heavy metals in the contaminated soil.

Compared with the prior art, the invention has the following beneficial technical effects:

the invention selects local mining area coal gangue as a raw material, explores preparation conditions aiming at the original components of the coal gangue, prepares the Fe-NaX type zeolite with high iron content, provides a new high-efficiency and low-cost passivator for the chemical passivation and restoration technology of heavy metals, solves the problem of massive accumulation of solid waste of the coal gangue and achieves the ideal environmental management target of 'treating waste with waste'. According to the invention, the zeolite with high iron content can be prepared by selecting the inferior coal gangue with high iron content in the slag storage yard without additionally adding an iron source in the preparation process. The prepared Fe-NaX zeolite contains partial hydroxyl, can interact with heavy metal in soil to form a coordinate bond, is a porous material, and can achieve the purpose of stabilizing the heavy metal in the soil through two main modes of cation exchange and electrostatic interaction.

Compared with the traditional X-type zeolite, the Fe-NaX-type zeolite prepared by modification of the invention has the advantages of increased pores, increased aperture, uniform pore distribution and porous lamellar structure formed on the surface of the crystal.

The application test of the Fe-NaX zeolite prepared by the invention shows that the Fe-NaX zeolite has a good passivation effect on Pb and Cd in soil, and the passivation effect of the passivator on heavy metals in soil mainly changes the existence form of each heavy metal in soil and reduces the migration capability of each heavy metal in soil.

Drawings

FIG. 1 is an XRD pattern of Fe-NaX type zeolite obtained in example 1;

FIG. 2 is an FTIR spectrum of Fe-NaX type zeolite obtained in example 1;

FIG. 3 shows N of Fe-NaX type zeolite obtained in example 1₂Adsorption-desorption experimental spectrum.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It should be apparent that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A preparation method of a soil passivator comprises the following steps:

the method comprises the following steps: crushing and grinding the high-iron coal gangue into powder, sieving the powder by a 200-mesh sieve, and roasting the powder for 3 hours at 800 ℃ in a muffle furnace to obtain coal gangue powder. The coal gangue is from a certain coal mine slag storage yard in the south of Chuannan, and the coal gangue comprises the following main components: silicon oxide (45.82%), aluminum oxide (17.55%) and iron oxide (13.99%, all by mass percent), wherein the mass percent of the iron element in the coal gangue is 9.8%.

Step two: uniformly mixing coal gangue powder and NaOH powder, wherein the mass ratio of the coal gangue powder to the NaOH powder is 1:1.5, and calcining for 3 hours in a muffle furnace at 650 ℃ to obtain a mixture;

step three: adding sodium metaaluminate to the mixture, and adding SiO in the mixture₂:Al₂O₃Adjusting the quantity ratio of substances to 3.5, then adding deionized water to adjust the alkalinity of the mixture to 3.5mol/L, and stirring and aging for 8 hours by using a magnetic stirrer (the rotating speed is 350r/min) at room temperature to obtain a mixed solution;

step four: transferring the mixed solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing for 12 hours in an oven at the temperature of 100 ℃. After the hydrothermal reaction is finished, performing suction filtration, washing the product to be neutral by using deionized water, and drying at 120 ℃ to obtain a powdery red sample, wherein the obtained product is the Fe-NaX type molecular sieve.

Test example

The product obtained in example 1 was subjected to X-ray diffraction measurement, and fig. 1 is the XRD pattern obtained. The product is known to have a single crystal structure, and no obvious amorphous phase structure exists. The main diffraction peaks appear at 2 θ ═ 6.18, 10.08, 15.49, 20.15, 23.37, 26.72, 31.01, 32.06, and 33.67 °. The above peak positions are consistent with the characteristic peaks of type X molecular sieves and correspond to the diffraction peaks of standard JCPDS cards 38-0237.

The product was tested infra-red and figure 2 is the resulting FTIR spectrum. Wherein it appears at 3470cm^-1The broad transmission peak is caused by the stretching vibration of hydrogen bonding hydroxyl (-OH). These hydroxyl groups are derived from structural hydroxyl groups (Si-OH/Al-OH) or from hydroxyl groups in physically adsorbed water (H-OH) of the zeolite. 1637cm^-1The transmission peak at (A) may occur due to bending vibration of hydroxyl group (-OH) or H caused by incomplete dehydration of the sample₂The deformation of O vibrates. General structural information, e.g. Si (Al) O₄The basic vibrational position of the group can be in the mid-infrared region of the infrared spectrum (200-^-1) And finding. 976cm^-1And 756cm^-1The generation of the transmission peak can be attributed to the asymmetric stretching vibration of Si (Al) -O.

The product was subjected to a nitrogen adsorption test, and FIG. 3 shows the obtained N₂Adsorption-desorption experimental spectrum. As can be seen from the figure, the specific surface area of the experimentally synthesized zeolite molecular sieve is 37.63m ²In terms of a/g, the mean pore diameter is 13.56 nm.

The Fe-NaX zeolite prepared in example 1 was used for soil passivation, and the specific embodiment is as follows:

weighing appropriate amount of Pb (NO) by using an analytical balance₃) With Cd (NO)₃)·4H₂And adding ultrapure water into 9kg of sample soil, immersing, stirring for 2 hours to uniformly mix, and air-drying at room temperature. After aging for one month, sieving with a 20-mesh sieve, weighing 500g of soil by using an analytical balance, placing the soil in a small soil basin, respectively adding passivator Fe-NaX type zeolite with the dry mass ratio of 0.5%, 1%, 1.5% and 2%, adding ultrapure water, immersing, keeping the water content at 30%, uniformly stirring, air-drying at room temperature, periodically adding ultrapure water, and controlling the water content of the soil to be about 30%. Three sets of parallel experiments were set up to carry out the passivation for one month. And determining the effective state contents of heavy metals Pb and Cd in the soil after reaction, and simultaneously performing morphological analysis on the passivated soil, wherein the results are shown in tables 1-4.

TABLE 1 content of lead (Pb) as heavy metal after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Content of active state mg/kg	129.3	118.3	102.4	90.1	89.3

TABLE 2 heavy metal form of heavy metal lead (Pb) after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Can be exchanged for	19.56	16.69	13.50	11.78	10.87
Iron manganese oxidation state%	29.25	30.95	34.38	35.33	38.72
						Oxidizable state%	0.60	0.77	0.15	0.18	0.17
As residue as%	50.60	51.59	51.98	52.72	50.24

TABLE 3 content of heavy metal cadmium (Cd) in available state after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Content of active state mg/kg	1.56	1.23	1.16	0.98	0.95

TABLE 4 heavy metal form of heavy metal cadmium (Cd) after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Exchangeable states	32.00	29.25	28.00	27.50	25.00
Iron manganese oxidation state	28.00	32.20	40.50	43.66	45.75
						Reducible state	18.10	19.98	12.43	12.51	12.55
In the state of residue	21.90	18.57	15.00	16.34	18.25

The test results show that the Fe-NaX type zeolite can reduce the effective state contents of Pb and Cd in soil and has certain passivation effect on Pb and Cd in polluted soil. Taking Table 1 as an example, when the addition ratio of Fe-NaX zeolite is increased from 0 to 2%, the effective state content of lead in the soil is reduced from 129.3mg/kg to 89.3 mg/kg. When the addition amount of the Fe-NaX type zeolite is 2 percent, the reduction rate of the effective Pb in the soil is 30.9 percent, and the reduction rate of the effective Cd in the soil is 39.1 percent.

In conclusion, the addition of the Fe-NaX type molecular sieve can obviously change the occurrence forms of heavy metals of lead and cadmium, can greatly increase the oxidation state (reducible state) contents of two heavy metals of iron and manganese, and the maximum rising amplitudes are respectively 32.39% (Pb) and 63.39% (Cd), so that the content of the effective lead and cadmium in the soil is reduced, and the maximum falling amplitudes are respectively 30.9% (Pb) and 39.1% (Cd), thereby effectively enhancing the stability of the heavy metals in the soil and reducing the migration capacity of the lead and the cadmium.

And changing the coal gangue source or the molecular sieve preparation method to obtain comparative examples 1-3.

Comparative example 1

The acid cleaning is carried out to remove the iron element in the coal gangue, the mass percentage content of the iron element after the acid cleaning is 1.9%, the preparation method of the molecular sieve is the same as that in the example 1, the obtained molecular sieve is used for passivating the soil in the same way as the example 1, and the content of the effective state of lead in the soil after one month is shown in a table 5.

TABLE 5 content of lead (Pb) as heavy metal in available state after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Content of available state mg/kg	167.6	144.3	128.9	116.9	107.5

Comparative example 2

The coal gangue with the iron element content of 4.8-5.0% in percentage by mass is adopted, the preparation method of the molecular sieve is the same as that of the example 1, the obtained molecular sieve is used for soil passivation in the same way as the example 1, and the content of the effective state of lead in the soil after one month is shown in a table 6.

TABLE 6 content of effective state of heavy metal lead (Pb) after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Content of available state mg/kg	150.6	131.2	116.9	107.8	102.6

Comparative example 3

The gangue source is the same as that in example 1, in the second step of the preparation method, gangue powder is added into NaOH aqueous solution with the mass fraction of 20%, the mixture is uniformly mixed and filtered, and the obtained solid is used for preparing the molecular sieve, and the preparation process is the same as that in example 1. The obtained molecular sieve was used for soil passivation in the same manner as in example 1, and the content of lead available state in soil after one month is shown in table 7.

TABLE 7 content of lead (Pb) as heavy metal in available state after soil passivation

Fe-NaX zeolite addition ratio%	0	0.5	1.0	1.5	2.0
						Content of active state mg/kgL	158.6	143.2	131.6	112.3	115.1

From comparative examples 1-3, the effective state content of the obtained molecular sieve on lead in soil is higher than that of example 1, which shows that the passivation effect of the molecular sieve is greatly reduced when the iron content of the coal gangue is reduced.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The preparation method of the zeolite soil passivator with high iron content is characterized by comprising the following steps:

step four: and carrying out hydrothermal crystallization reaction on the mixed solution to obtain the zeolite soil passivator with high iron content.

2. The method according to claim 1, wherein in the first step, the mass percentage content of the iron oxide in the coal gangue is more than 10%.

3. The method according to claim 1, wherein in step one, the screening uses a screen having a size of 100 to 500 mesh, preferably 200 mesh.

4. The method according to claim 1, wherein in the first step, the roasting is carried out in a muffle furnace, the roasting temperature is 750-950 ℃, and the roasting time is 1.5-3 h.

5. The method according to claim 1, wherein in the second step, the mass ratio of the coal gangue powder to the NaOH powder is 1 (1.0-1.5).

6. The method according to claim 1, wherein in the second step, the calcination is carried out in a muffle furnace, the calcination temperature is 600-700 ℃, and the calcination time is 2.5-3.5 h.

7. The method as claimed in claim 1, wherein in step three, sodium metaaluminate is added in an amount to dissolve SiO in the coal gangue₂/Al₂O₃The amount ratio of substances was adjusted to 3.5, and then deionized water was added to adjust the alkalinity to 3.5 mol/L.

8. The method as claimed in claim 1, wherein in the fourth step, the hydrothermal crystallization reaction is performed at 100 ℃ for 8-12 h.

9. Use of a high iron zeolitic soil passivator prepared according to the process of any one of claims 1 to 8 for the removal of heavy metals from contaminated soil.

10. The application according to claim 9, characterized in that it comprises: and uniformly mixing the contaminated soil, the water and the soil passivator to obtain a mixture, wherein the solid content in the mixture is 10-90%, the mass fraction of the soil passivator in the solid is 0.5-2%, and the maintenance time is more than or equal to 1 month.