CN110697745A - Modified hydrotalcite and preparation method and application thereof - Google Patents

Abstract

The invention provides a preparation method of modified hydrotalcite, which comprises the steps of putting aluminum-magnesium hydrotalcite into a muffle furnace at 5 ℃ for min^‑1The temperature is increased to 480 ℃ at a speed, and the mixture is roasted for 5 hours; grinding and sieving with a 200-mesh sieve to obtain roasted modified hydrotalcite; and (3) carrying out intercalation modification on the roasted modified hydrotalcite by using sodium dodecyl benzene sulfonate or diethyl triaminepentaacetic acid. The modified hydrotalcite and the preparation method thereof provided by the invention have the advantages that the hydrotalcite is properly modified, the agglomeration can be reduced, and the dispersibility is enhanced; change interlayer ions, promote the proceeding of ion exchange reaction and endow the ion exchange material with stronger ion exchange capacity.

Description

Modified hydrotalcite and preparation method and application thereof

Technical Field

The invention belongs to the technical field of soil pollution treatment, and particularly relates to modified hydrotalcite, and a preparation method and application thereof.

Background

In general, fluorine in groundwater, drinking water and food is derived from soil, and thus research on remediation of fluorine contamination of soil is receiving wide attention. At present, the technology for restoring the fluorine-polluted soil focuses on the aspects of chemical passivation restoration, soil leaching restoration, electric restoration, plant restoration and the like, wherein the chemical passivation restoration technology is widely applied due to the advantages of simple and convenient operation, low cost, high adsorption efficiency and the like, and the clay mineral is widely concerned as a passivator for restoring the fluorine pollution in the soil.

Clay minerals are the main minerals constituting soil and widely present in soil. Due to the special layered structure and chemical characteristics, the organic silicon-inorganic composite material has good ion exchange performance and can adsorb anions and cations in soil. The modified clay mineral has better ion adsorption effect due to the change of the crystal structure. In recent years, modified hydrotalcite mostly needs to remove anions in water, and related reports on soil anion passivation repair are lacked.

Disclosure of Invention

Aiming at the technical problems, the invention provides a modified hydrotalcite and a preparation method and application thereof, wherein the hydrotalcite is modified by adopting a roasting method and an intercalation method, and the modified hydrotalcite material has a repairing effect on fluorine-polluted soil.

The specific technical scheme is as follows:

the preparation method of the modified hydrotalcite comprises the following steps:

(1) putting the aluminum-magnesium hydrotalcite into a muffle furnace at 5 ℃ for min^-1The temperature is increased to 480 ℃ at a speed, and the mixture is roasted for 5 hours; the molar ratio of aluminum to magnesium in the magnesium-aluminum hydrotalcite is 1: 3;

(2) grinding and sieving with a 200-mesh sieve to prepare roasted modified hydrotalcite (CLDH);

(3) and (3) carrying out intercalation modification on the roasted modified hydrotalcite by using sodium dodecyl benzene sulfonate or diethyl triaminepentaacetic acid.

The intercalation modification method is prepared according to the following substance proportion,

1g of calcined modified hydrotalcite was added with 50ml of 0.1 mol. L^-1Stirring for 5h at 85 ℃ in sodium dodecyl benzene sulfonate, filtering, drying for 24h at 80 ℃, grinding and sieving with a 200-mesh sieve to obtain DSO-LDHs; (ii) a

Alternatively, 1g of calcined modified hydrotalcite was added with 50ml of 0.1mol. L^-1Oscillating in diethyltriaminepentaacetic acid at constant temperature for 12h, filtering, drying at 55 ℃ for 24h, grinding and sieving with a 200-mesh sieve to obtain DTPA-LDHs.

The modified hydrotalcite and the preparation method and application thereof provided by the invention have the advantages that the hydrotalcite is properly modified, so that the agglomeration can be reduced, and the dispersibility can be enhanced; change interlayer ions, promote the proceeding of ion exchange reaction and endow the ion exchange material with stronger ion exchange capacity.

Drawings

FIG. 1(a) FT-IR spectrum of DSO-LDHs;

FIG. 1(b) XRD spectrum of DSO-LDHs;

FIG. 1(c) FT-IR spectrum of DTPA-LDHs;

FIG. 1(d) XRD spectrum of DTPA-LDHs;

FIG. 1(e) FT-IR spectrum of CLDH;

FIG. 1(f) XRD pattern of CLDHs;

FIG. 2(a) Effect of initial fluorine concentration on pH of the adsorption solution;

FIG. 2(b) influence of initial fluorine concentration on the amount of fluorine ion adsorption;

FIG. 2(c) effect of initial fluorine concentration on fluoride ion fixation rate;

FIG. 2(d) effect of initial fluorine concentration on desorption amount;

FIG. 3(a) effect of adsorption time on the amount of fluoride ion adsorbed in soil;

FIG. 3(b) is a graph showing the influence of the amount of the material added on the amount of fluorine ion adsorbed in soil.

Detailed Description

The specific technical scheme of the invention is described by combining the embodiment.

The soil to be tested in this example was sandy loam of both prosperity towns of kaisha 37025, sichuan province, and the type of land utilization was cultivated land. The method has the advantages that the method is characterized in that the combination of the shish 37025, the coal with high fluorine and a large amount of phosphorus chemical industry are combusted in an open mode for a long time, so that the shish 37025is polluted by soil fluorine, and the shish 37025is a endemic fluorosis disease area. The soil was collected and air dried, and sieved through 10 mesh, 60 mesh and 100 mesh sieves, respectively, for use, and the soil physicochemical properties were measured as shown in table 1. The magnesium aluminum hydrotalcite is purchased from Shandong Yousio chemical Co.

TABLE 1 basic physicochemical Properties of the soil tested

The preparation method of the modified hydrotalcite comprises the following steps:

putting the aluminum-magnesium hydrotalcite into a muffle furnace, wherein the molar ratio of aluminum to magnesium in the aluminum-magnesium hydrotalcite is 1: 3; at 5 ℃ min^-1The temperature is raised to 480 ℃, roasting is carried out for 5 hours, grinding and sieving with a 200-mesh sieve are carried out, thus obtaining the CLDH.

Sodium Dodecyl Benzene Sulfonate (SDBS) and diethyltriaminepentaacetic acid (DTPA) are selected^5-) And (5) carrying out intercalation modification. Weighing 1g of roasted modified hydrotalcite, adding 50ml of 0.1 mol.L^-1Stirring the mixture in SDBS at 85 ℃ for 5h, carrying out suction filtration, drying the mixture for 24h at 80 ℃, grinding the mixture and sieving the ground mixture with a 200-mesh sieve to prepare DSO-LDHs. 1g of calcined modified hydrotalcite was weighed and 50ml of 0.1mol. L was added^-1DTPA^5-And oscillating at constant temperature for 12h, filtering, drying at 55 ℃ for 24h, grinding and sieving with a 200-mesh sieve to obtain the DTPA-LDHs.

All hydrotalcite samples were stored sealed in a dry dish.

2g of soil was weighed into a 50ml centrifuge tube at 0.02 mol. L^-1KCl solution as supporting electrolyte, fluorine concentration of 0, 200, 400, 600, 800, 1000, 1500, 2000 mg.L^-10.15g of the modified material was added to each of the NaF solutions. At 200 r.min^-1Oscillating for 24h at 25 ℃, 4000 r.min^-1Centrifuge for 10 min. 20ml of the supernatant was taken and 10ml of TISAB buffer (1 mol. L)^-1Sodium citrate), measuring the fluorine concentration by using a fluorine ion selective electrode (DDS-307, Shanghai Ramat magnetic), and calculating the fluorine adsorption quantity of the soil by a subtraction method. Data were fitted using the Langmuir model and the Freundlich model.

50ml of 0.02 mol.L is added into the soil sample after isothermal adsorption^-1KCl solution at 200 r.min^-1The rotating speed of the device is oscillated at 25 ℃ for 24 hours, the concentration of the fluorine ions in the supernatant is measured, and the desorption amount is calculated.

Weighing 2g of soil into a 50ml centrifuge tube, respectively adding 0.15g of three modified materials, namely CLDH, DSO-LDHs and DTPA-LDHs, and adding 300 mg.L^-150ml of NaF solution (2), at 200 r.min^-1Oscillating at constant temperature of 25 ℃ under constant frequency, sampling at 0.5, 1, 2, 4, 6, 8, 12 and 24h, and determining the concentration of fluorine ions in the supernatant.

Weighing 2g of soil into a 50ml centrifuge tube, and adding 0 g, 0.015 g, 0.03 g, 0.06 g and 0.15g (namely material) respectivelyAdding three modified materials of 0%, 0.5%, 1%, 2% and 5%), adding 300 mg.L^-150ml of NaF solution (2), at 200 r.min^-1The rotation speed of (2) was oscillated at 25 ℃ to sample at the optimum equilibrium time, and the fluoride ion concentration of the supernatant was measured.

FT-IR spectrum of DSO-LDHs, as shown in FIG. 1a, at 1000cm^–1～500cm^–1Within the range of hydrotalcite skeleton vibration. After the SDBS intercalation enters the hydrotalcite, the concentration is 1181cm^–1And 1038cm^–1The characteristic absorption peak of sulfonic acid group appears, which indicates that SDBS intercalation enters hydrotalcite. FIG. 1c shows the FT-IR spectrum of DTPA-LDHs at 3472cm^–1An absorption peak of-OH appears, and hydrogen bonds are generated among interlayer crystal water, anions and hydroxyl groups due to the fact that anions are absorbed by 'memory effect' of the hydrotalcite in the modification process. 1300cm^–1The presence of an absorption peak, indicating DTPA^5–The modified hydrotalcite exists between hydrotalcite layers in the form of anions, and carboxyl salt exists between the hydrotalcite layers after modification. As shown in FIG. 1e, 660cm of FT-IR spectrum of CLDH^–1And 1370cm^–1Treating CO₃ ^2–Absorption peak is substantially disappeared, interlayer CO₃ ^2–Decomposing; 1630cm^–1At H₂The absorption peak of O disappears, the crystal water between layers disappears after modification, the interlayer structure of the roasted product is destroyed, and the laminated structure is hollow.

Referring to FIG. 1b, the XRD pattern of DSO-LDHs shows hydrotalcite characteristic derived peaks 003 and 006, narrow and sharp peak shape, and structural features of organic anion intercalation product, which indicates that SDBS enters into hydrotalcite interlamination]And the regularity is better. Referring to FIG. 1d, the XRD pattern of DTPA-LDHs shows characteristic derivative peaks of 009, 110, 113, etc., which indicates DTPA^5–Present in hydrotalcite. As shown in FIG. 1f, the XRD pattern of CLDHs shows disappearance of the characteristic derivative peaks 003 and 006, and appearance of the characteristic derivative peaks 222, 400 and 422 of magnesium oxide, indicating that hydrotalcite loses interlayer ion CO during calcination₃ ^2–And water of crystallization.

As shown in FIG. 2a, the pH value of the adsorption equilibrium liquid is between 8 and 9, and the pH values of the adsorption equilibrium liquid of the three materials are not significantly different (p)>0.05), fluorine with fluoride ion (F)^–) In the form of fluorine in the material, the fluorine being present in the soil in two formsThe first is physical adsorption, and the second is chemical adsorption as intercalation anion entering into modified material interlamination (CLDH) or exchanging with intercalation ion of modified material (DSO-LDHs, DTPA-LDHs). 100 to 500 mg/kg^-1In this range, the initial fluorine concentration increases and the equilibrium pH increases, probably due to hydrolysis of fluoride ions in solution to ionize OH^–Resulting in an increase in pH. With OH^–The concentration increases and competition with fluorine ions for the adsorption sites increases, resulting in a decrease in the fluorine ion immobilization rate. At the same time, due to OH^–Adsorbed by soil and modified material, and the pH value is reduced.

As shown in FIG. 2c, the three materials have a fluorine ion fixation rate of 37-71% and a fluorine concentration of 100-300 mg/kg^-1The fluorine ion fixation rate is continuously increased in the range of (1), which shows that the three materials can better adsorb fluorine ions. The fluorine ion fixation rate is increased and then decreased, and as physical adsorption and chemical adsorption are performed simultaneously when the reaction starts, the combination probability of fluorine ions and soil adsorption sites is increased due to the increase of the initial concentration, and the adsorption amount of the soil to the fluorine ions is increased; when the concentration of the fluorine ions continues to increase, physical adsorption sites in the system are used up, chemical adsorption is still carried out, the adsorption quantity is still increased, and the fixation rate of the soil to the fluorine ions is reduced.

As shown in fig. 2d, the desorption rate indicates how firmly the soil is combined with the fluoride ions, and the lower desorption rate indicates that the soil can fix the fluoride ions better. The fluorine desorption rates for the three materials increased with increasing initial concentration. The three materials have the desorption law of fluoride ions at low concentration (<100mg/L) and high concentration of (>The desorption rate is higher when the concentration is 1000 mg/L: (>10 percent) and low desorption rate (4 to 7 percent) at medium concentration (300 to 700 mg/L). The lower and higher desorption rate at low concentration is caused by the lower adsorption amount and the larger desorption amount at low concentration. In the adsorption process of high-concentration fluorine, fluorine ions are adsorbed by static electricity and exchanged with hydroxyl ions^[31]The two physical adsorptions are reversible, the concentration of fluorinion is increased, the outer layer complex is increased, and the adsorption quantity is increased. As desorption proceeds, the complexation reaction proceeds in the reverse directionIn this case, the more fluorine ions physically adsorbed during adsorption, the larger the amount of fluorine ions desorbed during desorption.

As shown in FIG. 2b, the initial concentration is 100-300 mg/kg^-1When the fluorine ion adsorption capacity is substantially the same, the three materials adsorb fluorine ions. Initial concentration>1000mg·kg^-1The adsorption capacity of the soil added with DTPA-LDHs to fluoride ions is obviously higher than that of the soil added with other materials. The initial concentration was 2000mg kg^-1When the material is used, the adsorption rate of the DTPA-LDHs material to fluoride ions is 42.75 percent, and the adsorption rate of the CLDH material is only 35.67 percent. Because the intercalation ion of DTPA-LDHs is DTPA^5-Which is present between hydrotalcite layers in combination with positively charged ions, and the electronegativity of fluorine ions is greater than DTPA^5-More easily combined with positive charge ions and more fluorine ions with DTPA^5-And (4) exchanging and fixing by soil.

As shown in FIG. 3a, the initial fluorine concentration was 300mg kg^-1In time, the amount of fluorine ion adsorption by the DTPA-LDHs material increases with time. The adsorption of the DSO-LDHs material on fluorine ions can be divided into two stages of 'fast adsorption and slow equilibrium', wherein the fast adsorption stage is set between 0.5 and 6 hours, and the adsorption quantity is increased along with the time extension; after 6h, the slow equilibrium stage is carried out, and the adsorption capacity is basically unchanged. The adsorption reaction of the CLDH material is fast, and the maximum adsorption capacity is 139mg kg^-1。

Physical adsorption and chemical adsorption in soil are carried out simultaneously at the beginning, the three materials can quickly adsorb fluoride ions, physical adsorption sites are completely occupied at the middle and later stages, only the chemical adsorption is carried out, and the adsorption rate begins to decrease. The ion exchange capacity of the modified hydrotalcite interlaminar ion changes, and the adsorption time changes correspondingly. The DTPA-LDHs material has the largest adsorption amount to fluorine ions, and the intercalation ion DTPA is presumed^5–The exchange capacity with fluoride ion is strongest in three materials, the next is DSO-LDHs, and the last is CLDH, probably because the adsorption of the former two materials to fluoride ion is ion exchange, and the adsorption of the material CLDH is ion intercalation, the used time is longer.

As shown in FIG. 3b, the amount of the modified material is increased, so that more adsorption sites and ion intercalation and exchange vacancies can be provided, therefore, the adsorption amount of the three materials to fluorine ions is increased along with the increase of the addition amount of the materials, and the adsorption amounts of the three materials to fluorine are not obviously different (p > 0.05). The adsorption amount in the initial adsorption stage is increased sharply with the increase of the material dosage, and the soil added with CLDH shows the most obvious effect. When the material consumption is too large, the surface of the material is agglomerated, the adsorption space is reduced, the adsorption tends to be smooth, and the materials DTPA-LDHs and DSO-LDHs are embodied. Considering the application cost of the material and the influence of the application cost on the physical and chemical properties of the soil, DTPA-LDHs is a better choice.

The Langmuir model and the Freundlich model can well fit the adsorption capacity of the soil added with the modified material to fluoride ions, and the experimental results are obviously related to the simulation results of the two models as shown in Table 2. The Langmuir adsorption isothermal model can more reasonably describe the adsorption behavior of soil added with CLDHs and DSO-LDHs on fluorine, and the adsorption on the fluorine is mostly a monolayer adsorption process. The Freundlich model can describe the adsorption process of the soil added with DTPA-LDHs to fluorine more ideally, which shows that most of the reactions are the non-uniform adsorption process, and the isothermal adsorption models of the three materials have no significant difference (p is greater than 0.05).

TABLE 2 adsorption isotherm equation fitting parameters

The above examples illustrate:

the adsorption amount, desorption amount and desorption rate of the three materials to fluorine all show an ascending trend along with the increase of the initial concentration of the fluorine ions. At high fluorine concentration, the material added with DTPA-LDHs has the largest adsorption amount to fluorine.

The three materials are 300 mg/kg^-1The adsorption rate is highest, the desorption rate is lower in the range, and the optimum concentration of the soil fixed fluorine added with the three materials is 300mg kg^-1Left and right.

The three materials showed a tendency to increase the amount of fluoride ion adsorbed as time extended, with the shortest equilibration time for the materials to which DSO-LDHs were added.

The change of the addition amount of the material has great change on the fluorine adsorption amount of the soil, and the CLDH material is most obvious. The addition of DTPA-LDHs in consideration of actual conditions and treatment cost is a better choice for repairing the fluorine-polluted soil.

The adsorption isothermal equation of the three materials to fluoride ions can be described by Langmuir and Freundlich, the soil added with DTPA-LDHs and DSO-LDHs is mainly used for adsorbing and ion exchanging, and the soil added with CLDH is mainly used for adsorbing fluorine by interlayer intercalation and surface.

Claims (4)

1. The preparation method of the modified hydrotalcite is characterized by comprising the following steps:

(1) putting magnesium-aluminum hydrotalcite into a muffle furnace at 5 ℃ for min^-1The temperature is increased to 480 ℃ at a speed, and the mixture is roasted for 5 hours; the molar ratio of aluminum to magnesium in the magnesium-aluminum hydrotalcite is 1: 3;

(2) grinding and sieving with a 200-mesh sieve to prepare roasted modified hydrotalcite (CLDH);

(3) and (3) carrying out intercalation modification on the roasted modified hydrotalcite by using sodium dodecyl benzene sulfonate or diethyl triaminepentaacetic acid.

2. The method for preparing modified hydrotalcite according to claim 1, wherein the intercalation modification method comprises the following steps:

1g of calcined modified hydrotalcite was added with 50ml of 0.1 mol. L^-1Stirring for 5h at 85 ℃ in sodium dodecyl benzene sulfonate, filtering, drying for 24h at 80 ℃, grinding and sieving with a 200-mesh sieve to obtain DSO-LDHs; (ii) a

Alternatively, 1g of calcined modified hydrotalcite was added with 50ml of 0.1mol. L^-1Oscillating in diethyltriaminepentaacetic acid at constant temperature for 12h, filtering, drying at 55 ℃ for 24h, grinding and sieving with a 200-mesh sieve to obtain DTPA-LDHs.

3. Modified hydrotalcite, characterized by being obtained by the process according to claim 1 or 2.

4. Use of a modified hydrotalcite according to claim 3 for adsorbing fluorine in soil.

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