CN108624326A - The preparation method and method of modifying of a kind of soil passivator and application - Google Patents

Abstract

The invention discloses a preparation method, a modification method and an application of a soil passivation agent. Coal gangue is used as a raw material to synthesize a NaY type zeolite molecular sieve, and the influence of various factors on the synthesis of the NaY type zeolite molecular sieve is discussed. The obtained zeolite molecular sieve is modified with iron sulfide, and the synthetic zeolite and the modified zeolite are respectively applied to the passivation and repair of heavy metal contaminated soil, and the heavy metal is passivated in the soil to reduce its mobility and biological activity. In the process of soil remediation It does not cause secondary pollution, and has wider practicability in soil remediation projects.

Description

Preparation method, modification method and application of a soil passivating agent

technical field

The invention belongs to the technical field of soil heavy metal pollution control, and in particular relates to a preparation method, modification method and application of a soil passivation agent.

Background technique

In recent years, with the rapid development of my country's urbanization process and the adjustment of industrial layout, the vigorous development of industry and agriculture, and the mining of mines, soil heavy metal pollution has become more and more serious. As persistent toxic pollutants, heavy metals can enter the soil through different channels and remain in the soil for a long time because they cannot be biodegraded, causing soil pollution and endangering public health and the surrounding environment.

The remediation of soil contaminated by heavy metals mainly includes physical remediation, biological remediation and chemical remediation. Physical methods are expensive to deal with, and require a large amount of work for high-concentration heavy metal-contaminated sites. Bioremediation has a long remediation period and is selective for remediation of pollutants. The chemical remediation method has gained wide attention and application due to its advantages of passivation of treatment effect, thoroughness, and suitability for the treatment of heavily polluted soil.

At present, chemical remediation methods for heavy metal pollution mainly use chemical rinsing technology and passivation remediation technology. However, for leaching technology, since the eluent has a certain selectivity to heavy metals, it will destroy soil fertility and affect soil properties, and the eluate needs to be further processed. Passivation technology can effectively reduce the migration performance of soil pollutants, and is easy to operate. Materials that can be used as passivators for heavy metals include ammonium salts, peat, phosphate rock powder, quicklime, etc. These materials have high costs and poor applicability, and will seriously change the physical and chemical properties of the soil after application.

Contents of the invention

The invention provides a preparation method, modification method and application of a soil passivation agent to overcome the problems existing in the prior art. The present invention uses mercapto-containing compounds in food additives as a heavy metal adsorbent, thereby solving the problem of soil passivation agents The technical problems of low adsorption capacity, weak passivation ability and secondary pollution during use.

To achieve the above object, the present invention adopts the following technical solutions:

A kind of preparation method of soil passivating agent, comprises the following steps:

Step 1: Thermally activate the coal gangue raw material, then fully mix the thermally activated coal gangue and sodium carbonate powder by grinding, and roast the mixture to obtain an alkali fusion product;

Step 2: adding the alkali fusion product into the sodium hydroxide solution, stirring and filtering to obtain the filtrate;

Step 3: adding Y-type zeolite seed crystals and disodium edetate to the filtrate, adding sodium silicate at the same time to adjust the silicon-aluminum ratio to 3-8, and then aging to obtain the precursor;

Step 4: Crystallize the precursor, then cool, filter, wash, and dry to obtain NaY zeolite as a soil passivation agent.

Further, the thermal activation temperature in step 1 is 650°C-1000°C, and the time is 1h-3h; the mass ratio of heat-activated coal gangue to sodium carbonate powder is (0.5-1.5):1; the roasting temperature is 700°C-1000°C ℃, the time is 1h ~ 3h.

Further, in step 2, the alkali fusion product is added to the sodium hydroxide solution at a temperature of 70°C to 100°C, so that the liquid-solid ratio is 30mL/g to 50mL/g, and the concentration of the sodium hydroxide solution is 1mol/L ～5mol/L; stirring time 0.5h～1.5h.

Further, the addition amount of Y-type zeolite seed crystals in step three is 2g-10g per mL of filtrate, the addition amount of disodium edetate is 2g-10g per mL of filtrate; the aging temperature is 60°C-90 ℃, the aging time is 12h~16h.

Further, the temperature of the crystallization treatment in step 4 is 60°C-150°C, and the time is 6h-10h.

A method for modifying the soil passivating agent prepared by the above-mentioned preparation method, comprising the following steps:

Step a: dissolving ferrous sulfate in ultrapure water to obtain a ferrous sulfate solution, adding NaY type zeolite to the ferrous sulfate solution, stirring until evenly mixed, then filtering, washing, and drying the filter residue;

Step b: Roasting the dried filter residue, cooling to room temperature, grinding and sieving to obtain Fe-NaY zeolite as a modified soil passivation agent.

Further, the concentration of ferrous sulfate solution in step a is 0.2mol/L～3mol/L, after adding NaY type zeolite to ferrous sulfate solution, make liquid-solid ratio be 2mL/g～4mL/g, stirring time is 2h～18h; the drying temperature is 40℃～120℃, and the drying time is 4～24h.

Further, in step b, the calcination temperature is 200°C-800°C, and the calcination time is 2h-24h.

An application of the soil passivation agent prepared by the above method in removing heavy metals in polluted soil. When in use, the contaminated soil, water and soil passivation agent are mixed uniformly to obtain a mixture, so that the solid content in the mixture is 10% to 90% %, and the mass fraction of the soil passivator in the solid is 0.1% to 10%, and then cured for 3 months to remove heavy metals in the polluted soil.

Further, the heavy metals include copper, nickel, lead, cadmium and chromium.

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

The present invention selects coal gangue as a raw material to prepare high-purity NaY zeolite with high silicon-aluminum ratio, provides a new high-efficiency and low-cost passivating agent for the chemical passivation repair technology of heavy metals, and solves the massive accumulation of coal gangue solid waste to achieve the ideal goal of "treating waste with waste", the NaY-type zeolite prepared by the present invention contains some hydroxyl groups, which can interact with heavy metals in the soil to form coordination bonds, and the NaY-type zeolite is a porous material , NaY zeolite can also adsorb heavy metals in two main ways, cation exchange and electrostatic interaction, to achieve the purpose of stabilizing heavy metals in soil.

Compared with the NaY type zeolite, the Fe-NaY type zeolite prepared by modification in the invention has more pores, larger pore diameter, uniform distribution of pores, and a porous shape lamellar structure formed on the crystal surface.

The NaY type zeolite prepared by the present invention and the Fe-NaY type zeolite are applied to the test, and the results show that the NaY type zeolite and the Fe-NaY type zeolite have a certain passivation effect on Pb, Cd, Cu and Ni in the soil. Under the situation (10%), the passivation effect of Fe-NaY type zeolite to heavy metal is better than that of NaY type zeolite, especially to the passivation effect of Ni, Cu and Cd, the passivation effect of two kinds of passivators to heavy metal in soil The main effect is to change the existing forms of various heavy metals in the soil and reduce the migration ability of various heavy metals in the soil.

Description of drawings

Figure 1 is the speciation analysis of heavy metal Cr before and after passivation;

Figure 2 is the speciation analysis of heavy metal Cu before and after passivation;

Figure 3 is the speciation analysis of heavy metal Ni before and after passivation;

Figure 4 is the speciation analysis of heavy metal Pb before and after passivation;

Figure 5 is the speciation analysis of heavy metal Cd before and after passivation;

Fig. 6 is a flow chart at the time of application.

Detailed ways

The present invention is described in further detail below:

A kind of preparation method of soil passivating agent, comprises the following steps:

Step 1: thermally activate the coal gangue raw material at a temperature of 650°C-1000°C for 1h-3h, then thoroughly mix the heat-activated gangue and sodium carbonate powder by grinding at a mass ratio of (0.5-1.5):1, and The mixture is calcined at a temperature of 700°C to 1000°C for 1h to 3h to obtain an alkali fusion product;

Step 2: Add the alkali fusion product to the sodium hydroxide solution at a temperature of 70°C to 100°C, so that the liquid-solid ratio is 30mL/g to 50mL/g, and the concentration of the sodium hydroxide solution is 1mol/L to 5mol/ L, magnetically stirred for 0.5h to 1.5h, and filtered to obtain the filtrate;

Step 3: Add Y-type zeolite seed crystals and EDTA disodium to the filtrate, the addition amount of Y-type zeolite crystal seeds and EDTA disodium is 2g-10g per mL of filtrate, and add silicon Adjust the silicon-aluminum ratio to 3-8 with sodium nitrate, and then age at a temperature of 60°C-90°C for 12h-16h to obtain the precursor;

Step 4: Carry out crystallization treatment on the precursor, the temperature of the crystallization treatment is 60°C-150°C, the time is 6h-10h, and then rapidly cool, filter, wash, and dry to obtain the soil passivation agent NaY zeolite.

A modification method of the above-mentioned soil passivator, comprising the following steps:

Step a: Dissolve ferrous sulfate in ultrapure water to obtain a ferrous sulfate solution with a concentration of 0.2mol/L-3mol/L, and add NaY-type zeolite to the ferrous sulfate solution so that the liquid-solid ratio is 2mL/g- 4mL/g, stir for 2h to 18h until evenly mixed, then filter, wash, and dry the filter residue at a drying temperature of 40°C to 120°C and a drying time of 4h to 24h;

Step b: roasting the dried filter residue at a temperature of 200° C. to 800° C. for 2 hours to 24 hours, then cooling to room temperature, grinding and passing through a 300-mesh sieve to obtain a modified soil passivator Fe-NaY zeolite.

An application of a soil passivation agent to remove heavy metals in polluted soil. When used, the contaminated soil, water and soil passivator are mixed uniformly to obtain a mixture, so that the solid content in the mixture is 10% to 90%, and the solid content The mass fraction of the soil passivation agent is 0.1% to 10%, and then it is maintained for 3 months to remove heavy metals in the polluted soil, and the heavy metals include copper, nickel, lead, cadmium and chromium.

Below in conjunction with embodiment the present invention is described in further detail:

Example 1

A kind of preparation method of soil passivating agent, comprises the following steps:

Step 1: Thermally activate the coal gangue raw material at a temperature of 650°C for 3 hours, then thoroughly mix the heat-activated coal gangue and sodium carbonate powder by grinding at a mass ratio of 0.5:1, and roast the mixture at a temperature of 700°C for 1 hour An alkali fusion product is obtained;

Step 2: adding the alkali fusion product into the sodium hydroxide solution at a temperature of 70° C., so that the liquid-solid ratio is 50 mL/g, and the concentration of the sodium hydroxide solution is 5 mol/L, magnetically stirred for 1.5 h, and filtered to obtain the filtrate;

Step 3: Add Y-type zeolite seed crystals and EDTA disodium to the filtrate, the addition amount of Y-type zeolite crystal seeds and EDTA disodium is 2g per mL of filtrate, and add sodium silicate at the same time Adjust the silicon-aluminum ratio to 8, and then age at a temperature of 60°C for 12 hours to obtain a precursor;

Step 4: Carry out crystallization treatment on the precursor, the temperature of the crystallization treatment is 60° C., the time is 6 hours, and then rapid cooling, filtration, washing, and drying are carried out to obtain NaY type zeolite as a soil passivation agent.

A modification method of the above-mentioned soil passivator, comprising the following steps:

Step a: Dissolve ferrous sulfate in ultrapure water to obtain a ferrous sulfate solution with a concentration of 0.2mol/L, add NaY type zeolite to the ferrous sulfate solution to make the liquid-solid ratio 2mL/g, stir for 2h until mixed uniform, then filter and wash, and dry the filter residue at a drying temperature of 40°C and a drying time of 24 hours;

Step b: Roast the dried filter residue at 200° C. for 24 hours, then cool to room temperature, grind and pass through a 300-mesh sieve to obtain the modified soil passivator Fe-NaY zeolite.

Example 2

A kind of preparation method of soil passivating agent, comprises the following steps:

Step 1: thermally activate the coal gangue raw material at a temperature of 1000°C for 1 hour, then thoroughly mix the heat-activated gangue and sodium carbonate powder by grinding at a mass ratio of 1.5:1, and roast the mixture at a temperature of 1000°C for 3 hours An alkali fusion product is obtained;

Step 2: adding the alkali fusion product into the sodium hydroxide solution at a temperature of 100° C., so that the liquid-solid ratio is 30 mL/g, and the concentration of the sodium hydroxide solution is 1 mol/L, magnetically stirred for 0.5 h, and filtered to obtain the filtrate;

Step 3: Add Y-type zeolite seed crystals and EDTA disodium to the filtrate, the addition amount of Y-type zeolite crystal seeds and EDTA disodium is 5g per mL of filtrate, and add sodium silicate at the same time Adjust the silicon-aluminum ratio to 3, and then age at a temperature of 90°C for 14 hours to obtain a precursor;

Step 4: Carry out crystallization treatment on the precursor, the temperature of the crystallization treatment is 150° C., the time is 8 hours, and then rapid cooling, filtration, washing and drying are carried out to obtain NaY zeolite as a soil passivation agent.

A modification method of the above-mentioned soil passivator, comprising the following steps:

Step a: Dissolve ferrous sulfate in ultrapure water to obtain a ferrous sulfate solution with a concentration of 3 mol/L, add NaY type zeolite to the ferrous sulfate solution to make the liquid-solid ratio 4mL/g, stir for 18 hours until uniform , then filter, wash, and dry the filter residue at a drying temperature of 120°C and a drying time of 4 hours;

Step b: Roast the dried filter residue at 800° C. for 2 hours, then cool to room temperature, grind and pass through a 300-mesh sieve to obtain the modified soil passivator Fe-NaY zeolite.

Example 3

A kind of preparation method of soil passivating agent, comprises the following steps:

Step 1: Thermally activate the coal gangue raw material at a temperature of 800°C for 2 hours, then thoroughly mix the heat-activated coal gangue and sodium carbonate powder by grinding at a mass ratio of 1:1, and roast the mixture at a temperature of 800°C for 2 hours An alkali fusion product is obtained;

Step 2: adding the alkali fusion product into the sodium hydroxide solution at a temperature of 80° C., so that the liquid-solid ratio is 40 mL/g, and the concentration of the sodium hydroxide solution is 3 mol/L, magnetically stirred for 1 hour, and filtered to obtain the filtrate;

Step 3: Add Y-type zeolite seed crystals and EDTA disodium to the filtrate, the addition amount of Y-type zeolite crystal seeds and EDTA disodium is 10g per mL of filtrate, and add sodium silicate at the same time Adjust the silicon-aluminum ratio to 6, and then age at a temperature of 75°C for 16 hours to obtain a precursor;

Step 4: Carry out crystallization treatment on the precursor, the temperature of the crystallization treatment is 100° C., the time is 10 hours, and then rapid cooling, filtration, washing and drying are performed to obtain NaY zeolite as a soil passivation agent.

A modification method of the above-mentioned soil passivator, comprising the following steps:

Step a: Dissolve ferrous sulfate in ultrapure water to obtain a ferrous sulfate solution with a concentration of 1mol/L, add NaY type zeolite to the ferrous sulfate solution to make the liquid-solid ratio 3mL/g, stir for 10h until uniform , then filtered, washed, and dried the filter residue at a drying temperature of 105°C and a drying time of 18 hours;

Step b: Roast the dried filter residue at 500° C. for 16 hours, then cool to room temperature, grind and pass through a 300-mesh sieve to obtain the modified soil passivator Fe-NaY zeolite.

The NaY type zeolite and Fe-NaY zeolite prepared by embodiment 2 are used for soil passivation, and the specific implementation is as follows:

Implementation plan a:

Accurately weigh 3.074g kg ^-1 CrCl ₃ 6H ₂ O in 1.5kg sample soil with an analytical balance, add ultra-pure water to immerse, place on a magnetic stirrer and stir for 2 hours to mix evenly, and air-dry at room temperature. After a period of eight months of aging, pass through a 20-mesh sieve, weigh 40g of each portion of soil with an analytical balance and place it in a 250mL jar, add 0.1%, 0.25%, 0.4%, 1%, 2.5 %, 5% and 10% passivating agent NaY zeolite and Fe-NaY zeolite with a dry mass ratio of 10%, add ultrapure water to immerse, place on a magnetic stirrer and stir for 0.5h to make it evenly mixed, and air-dry at room temperature, Add ultrapure water regularly and control the soil moisture content at about 20%. Three groups of parallel experiments were set up for three-month passivation. After the reaction, the leaching concentration of heavy metal Cd in the soil was determined. The results are shown in Table 1. At the same time, the morphological analysis of the passivated soil was carried out, and the results are shown in Figure 1.

Table 1 Leach concentration and passivation efficiency of heavy metal chromium Cr after simulated soil passivation

Table 1 shows that NaY-type zeolite can reduce the concentration of Cr in the leachate, and has a certain passivation effect on Cr in polluted soil. When the NaY type zeolite is added more than 2.5%, the passivation rate of Cr in soil exceeds 50%. When the addition of NaY zeolite is 10%, the passivation rate of Cr is 57.47%, and when 10% of Fe-NaY zeolite is added, the passivation rate of Cr is 78.47%. It shows that the passivation effect of Fe-NaY zeolite on Cr is better than that of NaY zeolite. The passivation effect of NaY zeolite and Fe-NaY zeolite on Cr in soil is mainly to change the occurrence form of Cr in soil (Figure 1), and reduce the mobility of Cr in soil.

Implementation plan b:

Accurately weigh 3.058mg·kg ^-1 CdCl ₂ ·2.5H ₂ O, 1.510g·kg ^-1 Cu(NO ₃ ) ₂ , 1.201g·kg ^-1 Pb(NO ₃ ) ₂ , 1.336g·kg with an analytical balance ^-1 NiSO ₄ ·6H ₂ O in 1.5kg sample soil, add ultrapure water to immerse, place on a magnetic stirrer and stir for 2 hours to make it evenly mixed, air-dry at room temperature, and after a period of eight months of aging, pass 20-mesh sieve, weigh 40g of each portion of soil with an analytical balance and place it in a 250mL jar, add stabilizers according to the dry mass ratio of 0.1%, 0.25%, 0.4%, 1%, 2.5%, 5% and 10% respectively NaY zeolite and Fe-NaY zeolite with a dry mass ratio of 10%, add ultrapure water to immerse, place on a magnetic stirrer and stir for 0.5h to make it evenly mixed, air-dry at room temperature, add ultrapure water regularly and control the soil moisture content Around 20%. Three groups of parallel experiments were set up for three-month passivation. After the reaction, the leaching concentrations of heavy metals Cd, Cu, Pb and Ni in the soil were determined. The results are shown in Table 2. At the same time, the morphological analysis of the passivated soil was carried out, and the results are shown in Fig. 2 to Fig. 5 .

Table 2 The leaching concentration and passivation efficiency of heavy metals after simulated soil passivation

Table 2 shows that NaY-type zeolites and Fe-NaY-type zeolites have certain passivation effects on Pb, Cd, Cu and Ni in soil. NaY type zeolite has the best passivation effect on Pb, followed by Ni, and the worst passivation effect on Cd. With the addition of NaY zeolite increasing from 0.1% to 10%, the passivation rate of Pb increased from 31.32% to 65.06%, the passivation rate of Cu increased from 17.24% to 36.21%, and the passivation rate of Ni increased from 26.74% to 47.67%, while the passivation rate of Cd decreased from 22.72% to 13.63%, which was caused by competitive adsorption. In the case of the same addition amount (10%), the passivation effect of Fe-NaY zeolite on heavy metals is better than that of NaY zeolite, especially on Ni, Cu and Cd.

It can be seen from Figures 2 to 5 that the passivation effect of the two passivators on heavy metals in the soil is mainly to change the existing forms of the heavy metals in the soil and reduce the migration capacity of the heavy metals in the soil.

Claims (10)

1. a kind of preparation method of soil passivator, which is characterized in that include the following steps：

Step 1：Coal shale in brick making is subjected to thermal activation, it is then that thermal activated coal gangue and powdered sodium carbonate is abundant by grinding Mixing, mixture is roasted to obtain alkali fusion product；

Step 2：Alkali fusion product is added in sodium hydroxide solution, it is agitated, filtrate is obtained by filtration；

Step 3：Y-type zeolite crystal seed and disodium ethylene diamine tetraacetate are added into filtrate, while sodium metasilicate is added and adjusts silica alumina ratio To 3~8, then it is aged to obtain presoma；

Step 4：Presoma is subjected to Crystallizing treatment, then cools down, be filtered, washed, drying to get to soil passivator NaY types Zeolite.

2. a kind of preparation method of soil passivator according to claim 1, which is characterized in that thermal activation in step 1 Temperature is 650 DEG C~1000 DEG C, and the time is 1h~3h；The mass ratio of thermal activated coal gangue and powdered sodium carbonate be (0.5~ 1.5)：1；Calcination temperature is 700 DEG C~1000 DEG C, and the time is 1h~3h.

3. a kind of preparation method of soil passivator according to claim 1, which is characterized in that by alkali fusion in step 2 Product is added at a temperature of 70 DEG C~100 DEG C in sodium hydroxide solution, makes liquid-solid ratio for 30mL/g~50mL/g, and hydroxide A concentration of 1mol/L~5mol/L of sodium solution；Mixing time 0.5h~1.5h.

4. a kind of preparation method of soil passivator according to claim 1, which is characterized in that y-type zeolite in step 3 The addition of crystal seed is that 2g~10g is added per mL filtrates, the addition of disodium ethylene diamine tetraacetate be added per mL filtrates 2g~ 10g；Aging Temperature is 60 DEG C~90 DEG C, and digestion time is 12h~16h.

5. a kind of preparation method of soil passivator according to claim 1, which is characterized in that Crystallizing treatment in step 4 Temperature be 60 DEG C~150 DEG C, the time be 6h~10h.

6. a kind of method of modifying using soil passivator made from preparation method described in claim 1, which is characterized in that packet Include following steps：

Step a：Ferrous sulfate is dissolved in ultra-pure water and obtains ferrous sulfate solution, NaY types are added into ferrous sulfate solution Then zeolite, stirring are filtered, washed, to being uniformly mixed by filter residue and drying；

Step b：Filter residue roasts after will be dry, then cools to room temperature, and modified soil passivator Fe- is obtained after ground, sieving NaY zeolite.

7. the method for modifying of soil passivator according to claim 6, which is characterized in that ferrous sulfate solution in step a A concentration of 0.2mol/L~3mol/L, into ferrous sulfate solution be added NaY type zeolites after, make liquid-solid ratio be 2mL/g~ 4mL/g, mixing time are 2h~18h；Drying temperature be 40 DEG C~120 DEG C, drying time be 4~for 24 hours.

8. the method for modifying of soil passivator according to claim 6, which is characterized in that calcination temperature is 200 in step b DEG C~800 DEG C, roasting time is 2h~for 24 hours.

9. soil passivator prepared by a kind of any one of claim 1-8 the methods is on removal Heavy Metals in Contaminated Soils Using, which is characterized in that when in use, contaminated soil, water and soil passivator are uniformly mixed and obtain mixture so that is mixed It is 10%~90% to close the solid content in object, and the mass fraction of soil passivator is 0.1%~10% in solid, is then supported Shield 3 months, to remove the heavy metal in contaminated soil.

10. application according to claim 9, which is characterized in that the heavy metal includes copper, nickel, lead, cadmium and chromium.