A method for modifying red clay for heavy metal pollution remediation

Abstract

The application discloses a red clay modification treatment method for heavy metal pollution remediation, which comprises the following steps: dispersing natural red clay in deionized water, and obtaining a clay suspension after fully stirring the natural red clay and the deionized water; sequentially adding sodium citrate solution and sodium bicarbonate solution into the clay suspension, and adding sodium disulfite during water bath heating. The red clay modification treatment method for heavy metal pollution remediation removes free iron oxide, complex iron oxide and amorphous iron oxide and other colloidal oxides existing in the original red clay by a selective chemical dissolution method, eliminates the shielding effect of the colloidal oxides on the active sites of clay minerals in the red clay, and adds different proportions of aluminum oxide colloids in the red clay from which the colloidal oxides are removed, so that the active sites, the specific surface area and the cation exchange capacity of the clay minerals in the red clay are improved, thereby effectively improving the adsorptivity of the red clay, and the soil environment is not polluted.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution remediation technology, specifically to a method for modifying red clay for the remediation of heavy metal pollution. Background Technology

[0002] With the rapid development of my country's industrial and agricultural production, various environmental pollution problems are becoming increasingly serious, mainly due to the unreasonable discharge and disposal of pollutants. The main components of inorganic pollutants are various heavy metals. Once heavy metals enter water bodies and soil, they will accumulate and thus harm the ecological environment. Some organic pollutants are also highly toxic, widely distributed, and difficult to be absorbed, excreted, or degraded by organisms in nature, posing potential hazards such as teratogenicity, carcinogenicity, and mutagenicity. Therefore, finding adsorption materials with large adsorption capacity, good adsorption effect, and recyclability has become an important way to adsorb heavy metal wastewater and organic pollutants.

[0003] Red clay is widely distributed and abundant in nature. Due to its high surface area, porosity, surface charge, cation exchange capacity, acidity, and various types of active sites, it is used as a commonly used adsorbent material. The adsorption characteristics of clay minerals have been extensively studied. The presence of iron and aluminum oxides in soil can enhance the adsorption of certain heavy metals, such as Cu²⁺ and Pb. Red clay, containing active functional groups such as hydroxyl and carboxyl groups, exhibits good removal effects on heavy metal pollutants. Furthermore, the adsorption capacity of red clay depends primarily on the chemical and mineral composition of the soil, and secondly, it is generally related to the active sites of the effective functional groups and the interlayer cation exchange capacity. Existing natural red clay has poor adsorption effects as an adsorbent for heavy metal and organic pollutants; currently, modified natural clay is often used to prepare clay composites for application as adsorbents in practical engineering. Clay composites demonstrate significantly higher adsorption capacity for heavy metals and organic pollutants than natural clay. Therefore, researching simple and effective ways to improve the adsorption capacity of red clay, enabling its wider application as an adsorbent across multiple fields, has significant scientific and practical value and greatly promotes the development of novel, cost-effective adsorbents with high adsorption capacity. Summary of the Invention

[0004] The purpose of this invention is to provide a method for modifying red clay for the remediation of heavy metal pollution, in order to solve the problem mentioned in the background art that the existing natural red clay has poor adsorption effect on heavy metal pollution and organic pollutants.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for modifying red clay for the remediation of heavy metal pollution, comprising the following steps:

[0006] Step 1: Disperse natural red clay in deionized water, and stir the natural red clay and deionized water thoroughly to obtain a clay suspension;

[0007] Step 2: Add sodium citrate solution and sodium bicarbonate solution to the clay suspension in sequence. Add sodium disulfite while heating in a water bath. Then place the mixture in a constant temperature water bath shaker and shake until the soil turns grayish-white. Stop heating and let it cool to room temperature for half a month to allow it to react fully. Then add distilled water dropwise to the mixture and wash it multiple times with a centrifuge until the upper liquid is clear. This gives you mixture A.

[0008] Step 3: Dissolve sodium pyrophosphate in deionized water to obtain sodium pyrophosphate solution, and add sodium pyrophosphate solution to mixture A in proportion. Then place it on a constant temperature water bath shaker and shake to react. Add distilled water and centrifuge until the upper liquid is clear to obtain mixture B.

[0009] Step 4: Dissolve oxalic acid-ammonium oxalate in deionized water to obtain oxalic acid-ammonium oxalate buffer solution, and add the oxalic acid-ammonium oxalate buffer solution to mixture B in proportion. Then place it on a constant temperature water bath shaker and shake to react. Add distilled water and centrifuge until the upper liquid is clear. Finally, wash repeatedly with deionized water to remove residual oxalic acid-ammonium oxalate buffer solution, and dry to obtain soil sample with removed colloidal oxides.

[0010] Step 5: Mix the soil sample (after removing colloidal oxides) with alumina in a specific ratio and stir thoroughly. Place the mixture in a soil container and add a certain amount of distilled water. Stir the mixture in a mixer to obtain alumina colloidal reconstituted soil. Seal the container with plastic wrap and place it in an open-air location protected from rain. Add distilled water to the reconstituted soil every 20 days. After 20 days and 40 days of cultivation, remove the reconstituted soil, dry it at 60℃, grind it, and sieve it to obtain a clay / alumina colloidal composite adsorbent.

[0011] As a preferred embodiment of the present invention, sodium disulfite is added in step two when the water bath is heated to 80°C.

[0012] As a preferred embodiment of the present invention, the mixing liquid in step two is shaken and stirred in a constant temperature water bath for 12-16 minutes.

[0013] As a preferred embodiment of the present invention, the ratio of sodium pyrophosphate solution to mixture A in step three is 1:20.

[0014] As a preferred technical solution of the present invention, in step three, the mixture is kept at a constant temperature of 25°C and shaken for 2 hours in a constant temperature water bath shaking box.

[0015] As a preferred embodiment of the present invention, in step four, the ratio of oxalate-ammonium oxalate buffer to mixture B is 1:50, and the pH of the oxalate-ammonium oxalate buffer is 3.1.

[0016] As a preferred technical solution of the present invention, in step four, the mixture is kept at a constant temperature of 40°C and shaken for 4 hours in a constant temperature water bath shaking box.

[0017] As a preferred embodiment of the present invention, the mass-to-volume ratio of the soil sample from which colloidal oxides are removed to alumina in step five is 9:1-3.

[0018] As a preferred embodiment of the present invention, the stirring time in step five is 5.5-6.5 hours.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The red clay modification treatment method for heavy metal pollution remediation removes colloidal oxides such as free iron oxide, complexed iron oxide and amorphous iron oxide present in the original red clay by selective chemical dissolution, thereby eliminating the shielding effect of colloidal oxides on the active sites of clay minerals in the red clay. Different proportions of alumina colloid are added to the red clay after the removal of colloidal oxides, which modifies and improves the active sites, specific surface area and cation exchange capacity of clay minerals in the red clay, thereby effectively improving its adsorption capacity without causing pollution to the soil environment.

[0020] The preparation method and operation process are simple, the synthesis time is short, the yield is large, and there are significant advantages such as no violent chemical reaction and no release of harmful substances during the preparation process, thus avoiding the formation of secondary pollutants.

[0021] Sodium bicarbonate solution, sodium pyrophosphate, and oxalic acid-ammonium oxalate were used to remove some of the cementing substances from red clay. Colloidal alumina was used to modify the clay to increase its pore volume, specific surface area, and active sites. This method has a good adsorption effect on pollutants such as heavy metals, providing an efficient and low-cost treatment approach for wastewater, soil, and other environmental pollution. For example, it can adsorb and purify water bodies polluted with heavy metals such as phosphorus and lead. The treatment operation is relatively simple but does not affect the improvement of the treatment effect, which is key to the healthy and sustainable development of industry and agriculture.

[0022] Further modifications and designs to the chemically treated clay mineral surface and composite clay structure will provide potential and broader application value for the remediation of heavy metal pollution in water and soil. In addition, they will greatly promote the development of new high-performance, cost-effective adsorbents with high adsorption capacity and unique selectivity for different heavy metals. Attached Figure Description

[0023] Figure 1Infrared spectra of undisturbed red clay (UC), decolloidal oxide removed (RC), and clay / alumina composite adsorbent cultured for 20 days are shown in this invention.

[0024] Figure 2 Infrared spectra of undisturbed red clay (UC), decolloidal oxide removed (RC), and clay / alumina composite adsorbent cultured for 40 days are shown in this invention.

[0025] Figure 3 The graph shows the adsorption capacity of N2 on the original red clay (UC), the clay / alumina composite adsorbent with removed colloidal oxides (RC), and the soil sample cultured for 20 days.

[0026] Figure 4 The graph shows the adsorption capacity of N2 on the original red clay (UC), the clay / alumina composite adsorbent after removing colloidal oxides (RC), and the soil sample after 40 days of cultivation.

[0027] Figure 5 This is an adsorption diagram of various heavy metals by the clay / alumina composite adsorbent of the present invention;

[0028] Figure 6 This is a comparison table of the specific surface areas of the three types of composite adsorbents of the present invention.

[0029] Figure 7 This is a comparison table of the adsorption capacities of the three types of composite adsorbents of this invention.

[0030] Figure 8 This is a table showing the adsorption capacity of various heavy metals by the clay / alumina composite adsorbent of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0032] Please see Figure 1-8 The technical solution of this invention is: a method for modifying red clay for the remediation of heavy metal pollution, comprising the following steps:

[0033] Step 1: Disperse 200g of sieved natural red clay in deionized water, and stir the natural red clay and deionized water thoroughly to obtain a clay suspension.

[0034] Step 2: Add 400 mL of 0.3 mol / L sodium citrate solution and 50 mL of 1 mol / L sodium bicarbonate solution to the clay suspension in sequence. When the mixture is heated to 80°C in a water bath, add 10 g of sodium disulfite. Then place the mixture in a constant temperature water bath shaker and shake for 15 min until the soil turns grayish-white. Stop heating and let it cool to room temperature for half a month to allow it to react fully. Then add distilled water dropwise to the mixture and wash it multiple times using a centrifuge until the upper liquid is clear. This gives you mixture A, which removes free iron oxide.

[0035] Step 3: Dissolve sodium pyrophosphate in deionized water to obtain sodium pyrophosphate solution, and add 0.1 mol / L sodium pyrophosphate solution to mixture A at a ratio of 1:20. Then place it on a constant temperature water bath shaker and shake at a constant temperature of 25℃ for 2 hours. Add distilled water and centrifuge until the upper liquid is clear to obtain mixture B, thus removing complexed iron oxide.

[0036] Step 4: Dissolve oxalic acid-ammonium oxalate in deionized water to obtain oxalic acid-ammonium oxalate buffer solution. Add 0.2 mol / L oxalic acid-ammonium oxalate buffer solution with pH 3.1 to mixture B at a ratio of 1:50. Then place the mixture in a constant temperature water bath shaker and shake at 40℃ for 4 hours. Add distilled water and centrifuge until the upper liquid is clear. Finally, wash repeatedly with deionized water to remove residual oxalic acid-ammonium oxalate buffer solution. Dry the soil sample to obtain soil sample with removed colloidal oxides, thus achieving the removal of amorphous iron oxide.

[0037] Step 5: Mix the soil sample (excluding colloidal oxides) with alumina at a ratio of 9:1, stir thoroughly, put into a soil container, add a certain amount of distilled water, and stir on a mixer for 6 hours to obtain remolded soil containing 10% alumina colloid. Seal the container with plastic wrap to prevent impurities from entering the remolded soil, and place it in an open-air, rain-protected location to allow the alumina to interact with the soil particles, thereby generating more active sites for the effective component clay minerals in the red clay. Add 200g of distilled water to the remolded soil every 20 days to ensure that the alumina and soil particles can fully interact. After 20 days and 40 days of cultivation, take out the remolded soil, dry it at 60℃, grind it, and sieve it to obtain the clay / alumina colloid composite adsorbent. Example

[0038] Please see Figure 1-8 The technical solution of this invention is: a method for modifying red clay for the remediation of heavy metal pollution, comprising the following steps:

[0039] Step 1: Disperse 200g of sieved natural red clay in deionized water, and stir the natural red clay and deionized water thoroughly to obtain a clay suspension.

[0040] Step 2: Add 400 mL of 0.3 mol / L sodium citrate solution and 50 mL of 1 mol / L sodium bicarbonate solution to the clay suspension in sequence. When the mixture is heated to 80°C in a water bath, add 10 g of sodium disulfite. Then place the mixture in a constant temperature water bath shaker and shake for 15 min until the soil turns grayish-white. Stop heating and let it cool to room temperature for half a month to allow it to react fully. Then add distilled water dropwise to the mixture and wash it multiple times using a centrifuge until the upper liquid is clear. This gives you mixture A, which removes free iron oxide.

[0041] Step 3: Dissolve sodium pyrophosphate in deionized water to obtain sodium pyrophosphate solution, and add 0.1 mol / L sodium pyrophosphate solution to mixture A at a ratio of 1:20. Then place it on a constant temperature water bath shaker and shake at a constant temperature of 25℃ for 2 hours. Add distilled water and centrifuge until the upper liquid is clear to obtain mixture B, thus removing complexed iron oxide.

[0042] Step 4: Dissolve oxalic acid-ammonium oxalate in deionized water to obtain oxalic acid-ammonium oxalate buffer solution. Add 0.2 mol / L oxalic acid-ammonium oxalate buffer solution with pH 3.1 to mixture B at a ratio of 1:50. Then place the mixture in a constant temperature water bath shaker and shake at 40℃ for 4 hours. Add distilled water and centrifuge until the upper liquid is clear. Finally, wash repeatedly with deionized water to remove residual oxalic acid-ammonium oxalate buffer solution. Dry the soil sample to obtain soil sample with removed colloidal oxides, thus achieving the removal of amorphous iron oxide.

[0043] Step 5: Mix the soil sample (excluding colloidal oxides) with alumina in a 9:2 ratio, pour the mixture into a soil container, add a certain amount of distilled water, and stir for 6 hours to obtain remolded soil containing 20% ​​alumina colloid. Seal the container with plastic wrap to prevent impurities from entering the remolded soil, and place it in an open-air, rain-protected location to allow the alumina to interact with the soil particles, thereby generating more active sites for the effective component clay minerals in the red clay. Add 200g of distilled water to the remolded soil every 20 days to ensure that the alumina and soil particles can fully interact. After 20 days and 40 days of cultivation, remove the remolded soil, dry it at 60℃, grind it, and sieve it to obtain the clay / alumina colloid composite adsorbent. Example

[0044] Please see Figure 1-8 The technical solution of this invention is: a method for modifying red clay for the remediation of heavy metal pollution, comprising the following steps:

[0045] Step 1: Disperse 200g of sieved natural red clay in deionized water, and stir the natural red clay and deionized water thoroughly to obtain a clay suspension.

[0046] Step 2: Add 400 mL of 0.3 mol / L sodium citrate solution and 50 mL of 1 mol / L sodium bicarbonate solution to the clay suspension in sequence. When the mixture is heated to 80°C in a water bath, add 10 g of sodium disulfite. Then place the mixture in a constant temperature water bath shaker and shake for 15 min until the soil turns grayish-white. Stop heating and let it cool to room temperature for half a month to allow it to react fully. Then add distilled water dropwise to the mixture and wash it multiple times using a centrifuge until the upper liquid is clear. This gives you mixture A, which removes free iron oxide.

[0047] Step 3: Dissolve sodium pyrophosphate in deionized water to obtain sodium pyrophosphate solution, and add 0.1 mol / L sodium pyrophosphate solution to mixture A at a ratio of 1:20. Then place it on a constant temperature water bath shaker and shake at a constant temperature of 25℃ for 2 hours. Add distilled water and centrifuge until the upper liquid is clear to obtain mixture B, thus removing complexed iron oxide.

[0048] Step 4: Dissolve oxalic acid-ammonium oxalate in deionized water to obtain oxalic acid-ammonium oxalate buffer solution. Add 0.2 mol / L oxalic acid-ammonium oxalate buffer solution with pH 3.1 to mixture B at a ratio of 1:50. Then place the mixture in a constant temperature water bath shaker and shake at 40℃ for 4 hours. Add distilled water and centrifuge until the upper liquid is clear. Finally, wash repeatedly with deionized water to remove residual oxalic acid-ammonium oxalate buffer solution. Dry the soil sample to obtain soil sample with removed colloidal oxides, thus achieving the removal of amorphous iron oxide.

[0049] Step 5: Mix the soil sample (excluding colloidal oxides) with alumina in a 9:3 ratio, stir thoroughly, put it into a soil container, add a certain amount of distilled water, and stir on a mixer for 6 hours to obtain remolded soil containing 30% alumina colloid. Seal the container with plastic wrap to prevent impurities from entering the remolded soil, and place it in an open-air, rain-protected location to allow the alumina to interact with the soil particles, thereby generating more active sites for the effective component clay minerals in the red clay. Add 200g of distilled water to the remolded soil every 20 days to ensure that the alumina and soil particles can fully interact. After 20 days and 40 days of cultivation, take out the remolded soil, dry it at 60℃, grind it, and sieve it to obtain the clay / alumina colloid composite adsorbent.

[0050] Fourier transform infrared spectroscopy was performed on the clay / alumina composite adsorbent, and the test results are as follows: Figure 1-2As shown, compared with natural red clay and red clay that removes colloidal oxides, the infrared spectrum of the clay / alumina colloidal composite adsorbent includes the characteristic infrared peaks of clay and oxide colloids. In addition, compared with the infrared spectrum of the adsorbent that removes colloidal oxides, it produces new absorption peaks at 3314 cm⁻¹ and 1400 cm⁻¹. These absorption peaks are caused by the stretching vibration of -OH in adsorbed water and the in-plane bending vibration of Al-OH, respectively. Furthermore, with the increase of alumina content, the absorption peaks at 795 cm⁻¹ and 694 cm⁻¹ gradually increase, indicating that the number of Al-OH groups increases. This is all related to the added alumina. The more alumina is added, the more groups it has. Carboxyl groups are active functional groups and have a better effect on the removal of heavy metal pollutants.

[0051] The clay / alumina composite adsorbent was tested for N2 adsorption capacity, and the test results are as follows: Figure 3-4 As shown, and from Figure 6 As can be seen, as the alumina content in the soil sample increases, the specific surface area of ​​the soil sample also increases. The red clay acts as an adsorbent because of its high specific surface area. The increase in specific surface area indicates that its adsorption performance has also increased. In addition, in the N2 adsorption test, the more N2 adsorbed, the higher the pore volume. Therefore, the modified red clay of this invention improves the adsorption effect of the clay / alumina composite material.

[0052] The clay / alumina composite adsorbent was used to treat wastewater containing heavy metals. Specifically, the adsorption capacity of the clay / alumina composite adsorbent and heavy metal wastewater was studied at a 1:3 ratio. The temperature of the constant-temperature shaker was controlled at 25℃, the rotation speed at 200 r / min, and the shaking reaction was carried out for 24 hours. After the shaking reaction was completed, the composite adsorbent was separated from the wastewater, obtaining the clay / alumina composite adsorbent containing adsorbed pollutants and the supernatant clear liquid. The heavy metal content in the solution before and after the reaction was tested, and the removal rates of various heavy metals were tested as follows: Figure 5 As shown, and from Figure 8 It is known that the clay / alumina composite adsorbent has good adsorption capacity for heavy metals (cadmium, chromium, copper, and zinc). The total heavy metal concentration (cadmium, chromium, copper, and zinc) in the raw wastewater can reach 12.502 mg / L. The heavy metal concentration in the clarified upper layer after adsorption by the clay / alumina composite adsorbent is reduced, especially for chromium and copper. With the increase of curing time, the active sites in the clay / alumina composite adsorbent further increase, and the adsorption efficiency for heavy metals will be further improved.

[0053] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for modifying red clay for heavy metal pollution remediation, comprising the following steps: Step 1: Disperse natural red clay in deionized water, and stir the natural red clay and deionized water thoroughly to obtain a clay suspension; Step 2: Add sodium citrate solution and sodium bicarbonate solution to the clay suspension in sequence. Add sodium disulfite while heating in a water bath. Then place the mixture in a constant temperature water bath shaker and shake until the soil turns grayish-white. Stop heating and let it cool to room temperature for half a month to allow it to react fully. Then add distilled water dropwise to the mixture and wash it multiple times with a centrifuge until the upper liquid is clear. This gives you mixture A. Step 3: Dissolve sodium pyrophosphate in deionized water to obtain sodium pyrophosphate solution, and add sodium pyrophosphate solution to mixture A in proportion. Then place it on a constant temperature water bath shaker and shake to react. Add distilled water and centrifuge until the upper liquid is clear to obtain mixture B. Step 4: Dissolve oxalic acid-ammonium oxalate in deionized water to obtain oxalic acid-ammonium oxalate buffer solution, and add the oxalic acid-ammonium oxalate buffer solution to mixture B in proportion. Then place it on a constant temperature water bath shaker and shake to react. Add distilled water and centrifuge until the upper liquid is clear. Finally, wash repeatedly with deionized water to remove residual oxalic acid-ammonium oxalate buffer solution, and dry to obtain soil sample with removed colloidal oxides. Step 5: Mix the soil sample (after removing colloidal oxides) with alumina in a specific ratio and stir thoroughly. Place the mixture in a soil container and add a certain amount of distilled water. Stir the mixture in a mixer to obtain alumina colloidal reconstituted soil. Seal the container with plastic wrap and place it in an open-air location protected from rain. Add distilled water to the reconstituted soil every 20 days. After 20 days and 40 days of cultivation, remove the reconstituted soil, dry it at 60℃, grind it, and sieve it to obtain a clay / alumina colloidal composite adsorbent.

2. The method for modifying red clay for heavy metal pollution remediation according to claim 1, characterized in that, In step two, sodium disulfite is added when the water bath is heated to 80°C.

3. The method for modifying red clay for heavy metal pollution remediation according to claim 2, characterized in that, In step two, the mixture is shaken and stirred in a constant temperature water bath for 12-16 minutes.

4. The method for modifying red clay for heavy metal pollution remediation according to claim 3, characterized in that, In step three, the ratio of sodium pyrophosphate solution to mixture A is 1:

20.

5. The method for modifying red clay for heavy metal pollution remediation according to claim 4, characterized in that, In step three, the mixture is kept at a constant temperature of 25°C and shaken for 2 hours in a constant temperature water bath shaker.

6. The method for modifying red clay for heavy metal pollution remediation according to claim 5, characterized in that, In step four, the ratio of oxalate-ammonium oxalate buffer to mixture B is 1:50, and the pH of the oxalate-ammonium oxalate buffer is 3.

1.

7. The method for modifying red clay for heavy metal pollution remediation according to claim 6, characterized in that, In step four, the mixture is kept at a constant temperature of 40°C and shaken for 4 hours in a constant temperature water bath shaker.

8. A method for modifying red clay for heavy metal pollution remediation according to claim 7, characterized in that, In step five, the mass-to-volume ratio of the soil sample from which colloidal oxides are removed to alumina is 9:1-3.

9. A method for modifying red clay for heavy metal pollution remediation according to claim 6, characterized in that, The stirring time in step five is 5.5-6.5 hours.

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