An attapulgite-based passivator, a preparation method thereof and application thereof in passivating heavy metal ions

Abstract

The application discloses a preparation method of a palygorskite-based passivator. The preparation method comprises the following steps: mixing and reacting acid-modified palygorskite, biochar and an amino silane coupling agent in a solvent to obtain the palygorskite-based passivator, wherein the acid is phosphoric acid or nitric acid. Compared with the prior art, the palygorskite-based passivator prepared by the method can significantly improve the adsorption capacity of heavy metal ions, and can effectively meet the passivation and repair requirements of high-concentration heavy metal, especially lead and cadmium, contaminated soil.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal ion pollution control, specifically relating to an attapulgite-based passivating agent for adsorbing and passivating heavy metal ions, especially lead and cadmium ions. Background Technology

[0002] Heavy metal pollution has become a global environmental problem. Lead (Pb), in particular, poses a serious threat to the ecological environment and human health due to its high toxicity, recalcitrant nature, and tendency to accumulate. Therefore, there is a need to develop environmentally friendly and efficient remediation materials and technologies. Attapulgite is a hydrous magnesium-aluminate silicate clay mineral with a layered chain structure. Its surface contains abundant hydroxyl groups and exchangeable cations, giving it excellent adsorption properties. However, the number of its surface active sites is limited, and its pore structure is easily blocked by impurities, resulting in a specific surface area and adsorption capacity that are insufficient to meet the needs of high-concentration heavy metal pollution remediation. Summary of the Invention

[0003] The purpose of this invention is to provide an attapulgite-based passivating agent to enhance the adsorption capacity of attapulgite for heavy metal ions, thereby meeting the needs of high-concentration heavy metal pollution control, especially lead and cadmium pollution.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing an attapulgite-based passivating agent, comprising:

[0006] Acid-modified attapulgite, biochar, and an aminosilane coupling agent are mixed and reacted in a solvent to obtain the attapulgite-based passivating agent, wherein the acid is phosphoric acid or nitric acid.

[0007] Preferably, the mass ratio of the acid-modified attapulgite to biochar is 1:3 to 3:1.

[0008] More preferably, the mass ratio of the acid-modified attapulgite to biochar is 2:1.

[0009] Preferably, the aminosilane coupling agent is N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane.

[0010] Preferably, the amount of the aminosilane coupling agent is 2-5% of the total mass of acid-modified attapulgite and biochar.

[0011] Preferably, the reaction temperature is 50~80℃, the reaction time is 3~8 hours, and the solvent is ethanol.

[0012] Preferably, the concentration of the acid is 2 to 10 wt%.

[0013] Preferably, the acid-modified attapulgite is obtained by mixing attapulgite with acid and then letting it stand for a certain period of time.

[0014] Preferably, the solid-liquid ratio of attapulgite to acid is 10:0.1~2.5 g / mL.

[0015] More preferably, the solid-liquid ratio of attapulgite to acid is 10:0.15~1 g / mL.

[0016] An attapulgite-based passivating agent prepared according to the above method.

[0017] The application of the above-mentioned attapulgite-based passivating agent in the adsorption and passivation of heavy metal ions.

[0018] Preferably, the heavy metal ions are lead ions and / or cadmium ions. Attached Figure Description

[0019] Figure 1 The adsorption effect of lead ions on attapulgite modified with different acids was studied.

[0020] Figure 2 The effect of the ratio of acid-modified attapulgite to biochar on the adsorption of lead ions.

[0021] Figure 3 The infrared spectrum of the attapulgite-based passivating agent.

[0022] Figure 4 The passivation effect of attapulgite-based passivating agent on artificially simulated lead-contaminated soil.

[0023] Figure 5 The effect of attapulgite-based passivating agents on contaminated soil in mining areas. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0025] Attapulgite was mined from the Linze County mining area in Zhangye City, Gansu Province. After being air-dried, it was crushed and passed through an 80-mesh sieve for later use.

[0026] Biochar was purchased from Jiangxi Changyuan Biotechnology Co., Ltd., ground through an 80-mesh sieve, and is ready for use.

[0027] Artificial simulation of lead contamination in soil: Lead nitrate solution was precisely measured and added to soil samples (collected from Jingyuan County, Baiyin City, Gansu Province) according to a preset contamination gradient (three gradients were set: low, medium, and high, with values ​​of 100 mg / kg, 300 mg / kg, and 500 mg / kg, respectively), mixed well, and set aside.

[0028] The soil samples from the contaminated mining area were collected from a copper mine in the Dongdagou area of ​​Baiyin City, Gansu Province. The heavy metal content in the soil samples is shown in Table 1.

[0029] Table 1. Heavy metal content (mg·kg) in contaminated soil from the mining area -1 )

[0030] .

[0031] Lead ion adsorption experiment:

[0032] The adsorbent / passivating agent was added to 20 mL of lead nitrate solution, and the mixture was subjected to constant temperature and shaking for adsorption. Samples were taken at set time points to determine the remaining Pb in the solution. 2+ The concentration.

[0033] Adsorption capacity Qt (mg / g) = (C0 - C t V / m,

[0034] Where C0 and C t Pb in solution 2+ The initial concentration (mg / L) and final concentration (mg / L) are given, where m is the adsorbent mass (g) and V is the solution volume (L).

[0035] Passivation experiment of contaminated soil:

[0036] Passivating agents were added to contaminated soil at different proportions, and a blank control (CK) treatment without passivating agent was set up to assess changes in heavy metal bioavailability under natural conditions. The passivating agent was uniformly mixed with the contaminated soil and incubated for 30 days at a temperature of 25±1℃ and in the dark. During the incubation period, water was replenished regularly to maintain 70% field capacity. After cultivation, the bioavailable content of heavy metals was determined using the BCR sequential extraction method: The weakly acidic extractable form was easily absorbed by plants, exhibiting the highest bioavailability. However, it was sensitive to environmental changes and easily released into the environment when the pH decreased, requiring extraction with 0.11 mol / L acetic acid solution and shaking at room temperature for 16 hours. The reducible form was easily released under reducing conditions (such as flooding or hypoxia), exhibiting moderate bioavailability, requiring extraction with 0.5 mol / L hydroxylamine hydrochloride (pH=1.5) and shaking at room temperature for 16 hours. The oxidizable form was released under oxidizing conditions (such as organic matter decomposition), exhibiting low bioavailability, requiring extraction with 8.8 mol / L hydrogen peroxide (85℃ water bath) followed by 1 mol / L ammonium acetate (pH=2). The residual form was extremely difficult to release, exhibiting the lowest bioavailability, and almost did not participate in the biological cycle under natural conditions, requiring digestion with aqua regia and perchloric acid before concentration detection.

[0037] Example 1

[0038] Preparation of acid-modified attapulgite:

[0039] Phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid were diluted to prepare acid solutions with concentration gradients of 2 wt%, 4 wt%, 6 wt%, 8 wt%, and 10 wt%, respectively. Each acid solution was then uniformly mixed with attapulgite powder, allowed to stand at room temperature for 24 hours, and then transferred to a well-ventilated environment to air dry naturally. After grinding, the mixtures were passed through an 80-mesh sieve to obtain phosphoric acid-modified attapulgite (P-ATP), sulfuric acid-modified attapulgite (S-ATP), hydrochloric acid-modified attapulgite (CL-ATP), and nitric acid-modified attapulgite (N-ATP), respectively.

[0040] Table 2. Amount of each acid solution at different concentrations (per 10g of attapulgite)

[0041]

[0042] The adsorption effects of lead ions on attapulgite modified with different acids are as follows: Figure 1 As shown (adsorption experiment conditions: temperature 298.15 K, adsorption time 60 min, Pb 2+ The initial concentration was 76.7 mg / L, pH=5, and the adsorbent dosage was 1 g / L. Figure 1 It can be seen that the adsorption capacity and adsorption efficiency of attapulgite modified with phosphoric acid and nitric acid are significantly better than those modified with sulfuric acid and hydrochloric acid, with phosphoric acid showing the best performance. When the phosphoric acid concentration is 4 wt%, the prepared P-ATP for Pb... 2+ The adsorption rate was 96.5%, corresponding to an adsorption capacity of 74.02 mg / g.

[0043] The P-ATP modified with 4wt% phosphoric acid was mixed with biochar (BC) at different mass ratios (1:1, 1:2, 1:3, 2:1, 2:3, 3:1, 3:2). The mixed powder was then added to ethanol (solid-liquid ratio of 5:1 g / mL) and ultrasonically dispersed for 1 hour. The mixture was then stirred and heated to 60°C and kept at that temperature for 6 hours. After settling, the mixture was filtered and separated. The filter residue was washed clean with anhydrous ethanol several times and then dried in a 60°C drying oven for 24 hours. After grinding and sieving, the attapulgite-based passivating agent without KH602 modification was obtained.

[0044] Figure 2 The ratio of P-ATP to biochar affects the adsorption of Pb by unmodified attapulgite-based passivating agents. 2+ The influence of Pb (adsorption experiment conditions: temperature 298.15 K, adsorption time 90 min) 2+The initial concentration was 136.1 mg / L, pH=5, and the passivating agent dosage was 1 g / L. The unmodified attapulgite-based passivating agent obtained at a P-ATP to BC mass ratio of 2:1 was effective against Pb. 2+ The adsorption capacity and adsorption rate were 106.2 mg / g and 78%, respectively.

[0045] Example 2

[0046] Phosphoric acid-modified attapulgite (P-ATP) was prepared according to the method in Example 1, using 4 wt% phosphoric acid as the acid solution.

[0047] P-ATP and biochar were mixed at a mass ratio of 2:1. The mixed powder was then added to ethanol (solid-liquid ratio of 5:1 g / mL) and ultrasonically dispersed for 1 hour. Silane coupling agent (KH602) was then added at 5 wt% of the mixed powder. The mixture was stirred and heated to 60°C and kept at that temperature for 6 hours. After the reaction was completed, the mixture was allowed to settle and precipitate. The residue was separated by filtration. The residue was washed clean with anhydrous ethanol several times and then dried in a 60°C drying oven for 24 hours. After grinding and sieving, the attapulgite-based passivating agent (P-ATP / BC) was obtained.

[0048] Figure 3 The infrared spectrum of P-ATP / BC is shown. Attapulgite-based passivating agents exhibit infrared spectra in the 3700-3000 cm⁻¹ range. -1 Location, approximately 1600cm -1 Approximately 1050 cm -1 The peak shape and intensity in the vicinity differ from the simple summation of P-ATP and BC, indicating that during the complexation process, biochar and phosphate-modified attapulgite were not simply physically mixed, but likely involved chemical interactions or bonds.

[0049] At a temperature of 298.15 K and an adsorption time of 90 min, Pb 2+ Under the conditions of an initial concentration of 87 mg / L, pH=5, and a passivating agent dosage of 0.6 g / L, the prepared attapulgite-based passivating agent showed a positive effect on Pb. 2+ The adsorption capacity and adsorption rate were 131.67 mg / g and 90.73%, respectively.

[0050] At 298.15K, Pb 2+ Under optimized conditions of an initial concentration of 200 mg / L, pH=4, and a passivating agent dosage of 0.25 g / L, the above-mentioned attapulgite-based passivating agent basically reached equilibrium after approximately 80 minutes of adsorption, and the adsorption capacity (Q) was [not specified]. t The concentration tended to stabilize over time (reaching 179.4 mg / g).

[0051] Figure 4The results of the passivation experiment of the attapulgite-based passivating agent (P-ATP / BC) of the present invention in artificially simulated lead-contaminated soil at different dosages (AB1: 0.5 wt%, AB2: 1 wt%, AB3: 1.5 wt%, AB4: 2 wt%).

[0052] like Figure 4 As shown in Figure a, in low-concentration artificially simulated lead-contaminated soil, when the passivating agent dosage was 1.5%, the content of weakly acid-extractable (i.e., bioavailable) lead was significantly reduced by 25.9% compared to the control group, while the content of residual lead increased by 18.8%. In medium-concentration artificially simulated lead-contaminated soil (…),… Figure 4 In (b), when the dosage was 2%, the extractable lead in weakly acidic soil decreased by 28.3%, while the residual lead increased by 21.68%. This was observed in high-concentration artificially simulated lead-contaminated soil. Figure 4 In c), when the dosage is 1.5%, the weak acid extractable lead still decreases by 20.3%, while the residual lead increases by 19.62%.

[0053] Figure 5 This presents the results of passivation experiments on contaminated soil in mining areas using the attapulgite-based passivating agent (P-ATP / BC) of this invention at different dosages (AB1: 0.5 wt%, AB2: 1 wt%, AB3: 1.5 wt%, AB4: 2 wt%, AB5: 2.5 wt%), where α-lead (Pb), β-cadmium (Cd), β-chromium (Cr), γ-zinc (Zn), γ-copper (Cu), and γ-nickel (Ni).

[0054] like Figure 5 As shown, when the proportion of passivating agent added was increased to a higher level of 2% to 2.5%, compared with the blank control group, the acid-extractable contents of lead (Pb), cadmium (Cd), chromium (Cr), zinc (Zn), copper (Cu), and nickel (Ni) in the soil all showed a consistent and significant decreasing trend. The weakly acid-extractable content of lead decreased by 11.1%, while the residual content increased by 19%; the weakly acid-extractable content of cadmium decreased by 26.5%, while the residual content increased by 27.2%; the weakly acid-extractable content of chromium decreased by 5.5%, while the residual content increased by 7.3%; the weakly acid-extractable content of zinc decreased by 18.9%, while the residual content increased by 22.1%; the weakly acid-extractable content of copper decreased by 10.8%, while the residual content increased by 16.7%; and the weakly acid-extractable content of nickel decreased by 8.7%, while the residual content increased by 13.9%.

[0055] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an attapulgite-based passivating agent, comprising: Acid-modified attapulgite, biochar, and an aminosilane coupling agent are mixed and reacted in a solvent to obtain the attapulgite-based passivating agent, wherein the acid is phosphoric acid or nitric acid.

2. The preparation method according to claim 1, characterized in that: The mass ratio of acid-modified attapulgite to biochar is 1:3 to 3:1, preferably 2:

1.

3. The preparation method according to claim 1, characterized in that: The aminosilane coupling agent is N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane.

4. The preparation method according to claim 1 or 3, characterized in that: The amount of the aminosilane coupling agent is 2-5% of the total mass of acid-modified attapulgite and biochar.

5. The preparation method according to claim 1, characterized in that: The reaction is carried out at a temperature of 50-80°C for 3-8 hours, using ethanol as the solvent.

6. The preparation method according to claim 1, characterized in that: The concentration of the acid is 2~10wt%.

7. The preparation method according to claim 1, characterized in that: The acid-modified attapulgite is obtained by mixing attapulgite with acid and letting it stand for a certain period of time. Preferably, the solid-liquid ratio of attapulgite to acid is 10:0.1~2.5 g / mL, and more preferably, the solid-liquid ratio of attapulgite to acid is 10:0.15~1 g / mL.

8. An attapulgite-based passivating agent prepared according to the method of any one of claims 1 to 7.

9. The application of the attapulgite-based passivating agent according to claim 8 in the adsorption and passivation of heavy metal ions.

10. The application according to claim 9, characterized in that: The heavy metal ions are lead ions and / or cadmium ions.

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