Targeted and long-lasting passivation material for soil cadmium immobilization, and preparation method and use thereof

Abstract

Disclosed are a targeted and long-lasting passivation material for soil cadmium immobilization, and a preparation method and use thereof. In the disclosure, the passivation material is a mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite, which is prepared by hydrothermal co-precipitation of a metal salt dispersion and an intercalation solution in an alkaline environment.

Claims

1. A method for preparing a targeted and long-lasting passivation material for soil cadmium, comprising steps of: (1) preparing a metal salt dispersion A, a precipitant solution B, and an intercalation solution C; wherein the metal salt dispersion A comprises a divalent metal salt dispersion and a trivalent metal salt dispersion, the precipitant solution B is a sodium hydroxide solution, and the intercalation solution C is a mercaptosuccinic acid solution; and the divalent metal salt dispersion, the trivalent metal salt dispersion, the sodium hydroxide solution, and the mercaptosuccinic acid solution each are prepared with carbon dioxide-free water; wherein the divalent metal salt dispersion is a solution of calcium salts, and the trivalent metal salt dispersion is a solution of iron salts and aluminum salts; the molar ratio of the calcium salts, the iron salts and the aluminum salts in the metal salt dispersion A is 4:1:1; and the metal salt in the metal salt dispersion A is any one selected from the group consisting of a nitrate, a chloride, and a sulfate; and the mercaptosuccinic acid solution has a concentration of 0.025 mol/L to 0.50 mol/L; (2) adding the metal salt dispersion A in a container, constantly introducing nitrogen into the container, and subjecting the metal salt dispersion A to water bath heating at a temperature of 65 C.5 C. under magnetic stirring at a speed of 150 r/min to 240 r/min at the same time; (3) pumping the precipitant solution B and the intercalation solution C into the container at a controlled pumping speed to form a mixed system, and monitoring a pH value of the mixed system in real time such that the pH value is in a range of 10.50.5 during the pumping; (4) subjecting the mixed system to hydrothermal stirring for 6 h to 8 h, and then subjecting a resulting system to aging to obtain an aged system; and (5) subjecting the aged system to solid-liquid separation, washing an obtained solid phase until a resulting effluent is neutral, and then drying and grinding a resulting washed solid phase to obtain a mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

2. The method of claim 1, wherein in step (1), the precipitant solution B has a concentration of 0.50 mol/L to 1.70 mol/L.

3. The method of claim 2, wherein in step (2), the water bath heating is conducted at a temperature of 65 C.2 C., and the magnetic stirring is conducted at a speed of 180 r/min.

4. The method of claim 3, wherein in step (3), the precipitant solution B is pumped at a pumping speed of 1.0 mL/min to 3.0 mL/min, and the intercalation solution C is pumped at a pumping speed of 0.5 mL/min to 2.0 mL/min.

5. The method of claim 4, wherein in step (4), the aging is conducted at ambient temperature for 8 h to 12 h.

6. The method of claim 5, wherein in step (5), the washing is conducted alternately with deionized water and absolute ethanol; and the drying is conducted at a temperature of 35 C. to 45 C.

7. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 1, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

8. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 2, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

9. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 3, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

10. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 4, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

11. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 5, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

12. A targeted and long-lasting passivation material for soil cadmium prepared by the method of claim 6, wherein the targeted and long-lasting passivation material for soil cadmium is the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows a solid powder of a calcium aluminum hydrotalcite;

(2) FIG. 1B shows a solid powder of a calcium iron aluminum hydrotalcite;

(3) FIG. 1C shows a solid powder of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite as prepared in Example 2 of the present disclosure;

(4) FIG. 2 shows removal efficiencies of heavy metal ions in a soil extraction liquid by different hydrotalcite materials as prepared in Example 3 of the present disclosure;

(5) FIG. 3A shows immobilization effects of Cd by different hydrotalcite materials as prepared in Example 4 of the present disclosure on cadmium-contaminated paddy soil;

(6) FIG. 3B shows immobilization effects of Fe by different hydrotalcite materials as prepared in Example 4 of the present disclosure on cadmium-contaminated paddy soil;

(7) FIG. 3C shows immobilization effects of Mn by different hydrotalcite materials as prepared in Example 4 of the present disclosure on cadmium-contaminated paddy soil;

(8) FIG. 3D shows immobilization effects of Zn by different hydrotalcite materials as prepared in Example 4 of the present disclosure on cadmium-contaminated paddy soil;

(9) FIG. 4 shows acid dissolution rates of cadmium adsorbed by different materials as prepared in Example 5 of the present disclosure; and

(10) FIG. 5 shows immobilization effects of cadmium by different materials as prepared in Example 6 of the present disclosure under periodic flooding and drainage conditions.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) The following examples are intended to illustrate the present disclosure, but not to limit the scope of the present disclosure. Modifications or substitutions made to methods, procedures, conditions, instruments, or reagents of the present disclosure without departing from the spirit and essence of the present disclosure would fall within the scope of the present disclosure.

(12) The technical solution of the present disclosure will be further described in detail below with reference to examples.

Example 1 Preparation of Solid Powder of Mercaptosuccinic Acid-Intercalated Calcium Iron Aluminum Hydrotalcite by Using Nitrate

(13) 11.81 g of Ca(NO.sub.3).Math.4H.sub.2O, 5.05 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, and 4.69 g of Al(NO.sub.3).sub.3.Math.9H.sub.2O were dissolved in 100 mL of carbon dioxide-free water to obtain a solution A. 6.80 g of NaOH was dissolved in 100 mL of carbon dioxide-free water to obtain a solution B. 3.75 g of mercaptosuccinic acid (purchased from Shanghai Macklin Biochemical Co., Ltd., China, product number 70-49-5) was dissolved in 100 mL of carbon dioxide-free water to obtain a solution C. The solution B and the solution C were added dropwise into the solution A through a peristaltic pump, and a pH value of a resulting mixed system was maintained at 10.50.5. In a nitrogen atmosphere, the mixed system was subjected to magnetic stirring in a water bath at 65 C. for 8 h and then aged for 12 h. An obtained mixed slurry was subjected to solid-liquid separation, and an obtained solid was washed alternately with ethanol and deionized water multiple times. Then the washed solid was dried at 45 C. for 8 h, and ground to obtain the solid powder of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

Example 2 Preparation of Solid Powder of Mercaptosuccinic Acid-Intercalated Calcium Iron Aluminum Hydrotalcite by Using Chloride

(14) 2.77 g of CaCl.sub.2), 3.17 g of FeCl.sub.2, and 3.33 g of AlCl.sub.3 were dissolved in 100 mL of carbon dioxide-free water to obtain a solution A. 6.80 g of NaOH was dissolved in 100 mL of carbon dioxide-free water to obtain a solution B. 3.75 g of mercaptosuccinic acid (purchased from Shanghai Macklin Biochemical Co., Ltd., China, product number 70-49-5) was dissolved in 100 mL of carbon dioxide-free water to obtain a solution C. The solution B and the solution C were added dropwise into the solution A through a peristaltic pump, and a pH value of a resulting mixed system was maintained at 10.50.5. In a nitrogen atmosphere, the mixed system was subjected to magnetic stirring in a water bath at 65 C. for 8 h and then aged for 12 h. An obtained mixed slurry was subjected to solid-liquid separation, and an obtained solid was washed alternately with ethanol and deionized water multiple times. Then, the washed solid was dried at 45 C. for 8 h, and then ground to obtain the solid powder of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite.

(15) FIG. 1A shows a solid powder of a calcium aluminum hydrotalcite; FIG. 1B shows a solid powder of a calcium iron aluminum hydrotalcite; and FIG. 1C shows a solid powder of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite as prepared in Example 2.

Example 3 Removal Effect of the Mercaptosuccinic Acid-Intercalated Calcium Iron Aluminum Hydrotalcite on Heavy Metals in Soil Extraction Liquid

(16) Cadmium-contaminated paddy soil (cadmium content: 2.77 mg/kg) was collected from Guixi City, Jiangxi Province, China, and extracted with deionized water for 24 h under shaking (a water-to-soil ratio was maintained at 1:2), and then subjected to centrifugation and filtration, to obtain a soil extraction liquid. The specific ion concentrations are shown in Table 1. The mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) as prepared in Example 1, the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH), and the reported calcium iron aluminum hydrotalcite (CA-LDH) were added separately into the soil extraction liquid at a solid-to-liquid ratio of 0.05 g/L, and shaken at room temperature for 24 h, and a remaining cadmium concentration in the soil extraction liquid was determined after treatment. The results are shown in FIG. 2.

(17) Where, the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH) was prepared according to the method of Example 1, except that mercaptosuccinic acid was not added. The calcium aluminum hydrotalcite (CA-LDH) was derived from the report of Chemical Engineering Journal 407 (2021) 127178.

(18) TABLE-US-00001 TABLE 1 Composition of the soil extraction liquid Type of cations Cd K Na Ca Mg Al Fe Zn Mn Concentration mg/L 0.1 6.8 5.6 12.5 2.6 3.4 2.0 0.3 0.2 Type of anions SO.sub.4.sup.2 Cl.sup. NO.sub.3.sup. Concentration mg/L 95.7 44.0 1.2

(19) Comparing the removal efficiencies of each ion in FIG. 2, it can be seen that the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite as prepared in the present disclosure has a removal efficiency on cadmium of up to 99.2% in a complex environment, which is 4 times that of the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH) and the calcium aluminum hydrotalcite (CA-LDH). At the same time, the removal effect of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) on iron, manganese, and zinc is weaker than that of the unintercalated hydrotalcite (CFA-LDH) and the reported calcium aluminum hydrotalcite (CA-LDH). This reflects that the intercalated hydrotalcite allows for target adsorption and removal of cadmium in complex soil solutions.

Example 4 Soil Immobilization Effect of the Mercaptosuccinic Acid-Intercalated Calcium Iron Aluminum Hydrotalcite

(20) Cadmium-contaminated paddy soil samples HS were collected in Guixi City, Jiangxi Province, China. The basic physical and chemical properties were: pH=5.34, total Cd 1.49 mg/kg. The mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) as prepared in Example 1, the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH) as prepared in Example 3, and lime alone (purchased from Guixi City, Jiangxi Province, China) were used as a passivator separately at 0.2% dosage to conduct soil incubation experiments, where soil moisture was maintained at 80% of water holding capacity of the field. After 14 days, the bioavailable cadmium, iron, manganese, and zinc in the soil were extracted by 0.01 M CaCl.sub.2) solution and measured by ICP-MS. The experimental results are shown in FIG. 3A to FIG. 3D.

(21) The results show that in the paddy soil HS, the calcium iron aluminum hydrotalcite (CFA-LDH), mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH), and lime alone (Lime) all show desirable cadmium immobilization effect, and the cadmium immobilization rates all were higher than 70%. However, regarding the reduction rate of available iron, manganese, and zinc, the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) is relatively mild, only 2/7, 5/7, and that of lime.

Example 5 Dissolution of Cadmium from Cadmium Adsorption Products of the Mercaptosuccinic Acid-Intercalated Calcium Iron Aluminum Hydrotalcite in Simulated Acidic Environment

(22) 0.06 g each of the different passivation materials in Example 3 was added into a 50 mL centrifuge tube, and then 30 mL of a 120 mg/L cadmium solution was added. A resulting mixture was subjected to adsorption under shaking for 24 h. The cadmium concentrations (C.sub.0, C.sub.e) of the solution before and after the adsorption were measured. An adsorption capacity q.sub.e was calculated by equation [1]. After each adsorption reached equilibrium, resulting products were subjected to solid-liquid separation, and obtained solids were put into 300 mL of an acidic solution with pH=4.5, which simulates an acidic soil environment, followed by magnetic stirring for 30 min, 60 min, 120 min, 180 min, 300 min, 420 min, and 660 min. Then, samples of the supernatant were collected, and the cadmium contents (C.sub.1, C.sub.2) in the solution before and after dissolution were measured, and a dissolution amount R.sub.e was calculated according to equation [2], where m represented a mass of the passivation materials added, and V.sub.1 and V.sub.2 represented a volume of the cadmium solution and a volume of the acidic solution, respectively. According to a ratio of the dissolution amount R.sub.e and the adsorption capacity q.sub.e, a dissolution rate D % was calculated using equation [3]. The results are shown in FIG. 4.

(23) $\begin{array}{cc}{q}_e=\frac{\left(c_0-c_e\right)v_1}{m}& \left[1\right]\end{array}$$\begin{array}{cc}{R}_e=\frac{\left(c_1-c_2\right)v_2}{m}& \left[2\right]\end{array}$$\begin{array}{cc}D\%=R_e/q_e& \left[3\right]\end{array}$

(24) Comparing the dissolution rates, it can be found that the cadmium adsorption product of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) has a cadmium dissolution rate of only 2.05% at pH=4.5, which is lower than 10.86% and 11.35% of the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH) and the reported calcium aluminum hydrotalcite (CA-LDH), and is much lower than 42.59% of the commercial hydrotalcite (LC-LDH).

Example 6 Stabilizing Effect of Cadmium Passivation in Mixed System of Soil and the Passivation Material Under Periodic Flooding and Drainage Environment

(25) The mixed system that had reached equilibrium in Example 5 was subjected to periodic flooding for 7 days and drainage for 7 days. After each period, the bioavailable cadmium was extracted using 0.01 M CaCl.sub.2) solution. FIG. 5 shows the changes in the bioavailable Cd concentration after the end of different period cycles.

(26) As shown in FIG. 5, in periodic flooding and drainage, the immobilization effect of lime (Lime) reduced from 70.9% to 60.3%, and the cadmium immobilization rate of the unintercalated calcium iron aluminum hydrotalcite (CFA-LDH) reduced from 67.8% to 50.2%. However, the cadmium passivation rate of the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite (MSA-LDH) was stably maintained at approximately 70%. Therefore, the mercaptosuccinic acid-intercalated calcium iron aluminum hydrotalcite could maintain low concentration of available cadmium for a long time, showing a long-lasting immobilization effect.

(27) The above examples are only intended to describe the preferred embodiments of the present disclosure, but not to limit the scope of the present disclosure. Various alterations and improvements made by those skilled in the art based on the technical solution of the present disclosure without departing from the design spirit of the present disclosure shall fall within the scope of the claims of the present disclosure.