Preparation method and application of arsenic-cadmium solid solution resistant to electric field stress and acid dissolution

Abstract

The invention discloses a preparation method and application of an arsenic-cadmium solid solution resistant to electric field stress and acid dissolution. The method comprises the following steps: preparing a cadmium chloride solution and a calcium chloride solution into a mixed solution according to a fixed molar ratio, taking a sodium arsenate solution as a basic solution, then adding the mixed solution into the basic solution, and controlling the molar ratio of the mixed solution, the concentration of the basic solution and the reaction temperature to obtain the arsenic-cadmium solid solution. The arsenic-cadmium solid solution synthesized by the method is low in arsenic-cadmium dissolution amount under different pH conditions and electric field stress conditions, and particularly has the strongest cadmium stability. Technical support can be provided for solidification and stabilization repair of arsenic-cadmium combined polluted soil and stable storage of tailings containing arsenic and cadmium.

Description

Technical Field

[0001] The present invention belongs to the field of environmental safety and technology, and relates to a method for preparing an arsenic-cadmium solid solution that is resistant to electric field stress and acid dissolution and its application. The method uses cadmium chloride solution and sodium arsenate solution as cadmium source and arsenic source, adds calcium chloride solution as calcium source, and adjusts the initial pH value of aging to prepare arsenic-cadmium solid solution, providing technical support for the simultaneous solidification / stabilization remediation of arsenic-cadmium composite heavy metal pollutants in water and soil. Background Art

[0002] Arsenic is a highly toxic metalloid that exists in the form of arsenite and arsenate, with trivalent arsenic being more toxic. Cadmium is a toxic heavy metal with high mobility that exists in the soil in the form of divalent ions. Both affect plant photosynthesis and nutrient absorption, hindering growth, and are not easily degraded and easily accumulate in the soil. Arsenic and cadmium can enter the human body through the food chain. Long-term intake of arsenic increases the risk of diabetes and cancer, while cadmium damages the kidneys and bones and increases the risk of cardiovascular disease. Natural factors such as rock weathering and geological activities release arsenic and cadmium, but the amount is limited by the environmental background. Human activities such as mining, smelting, use of agricultural chemicals, and discharge of industrial waste are the main causes of soil pollution, leading to large accumulations of arsenic and cadmium, resulting in large amounts of soil being contaminated by arsenic and cadmium, with serious excesses.

[0003] Arsenic-cadmium solid solution is usually composed of two elements, arsenic and cadmium, and its chemical formula is CdAs or Cd 3 As 2 , depending on the composition ratio of the solid solution. In terms of crystal structure, the arsenic-cadmium solid solution exhibits a complex cubic or hexagonal crystal system. This structural feature makes it uniquely stable in electric fields and acid-base environments. Due to its semi-metallic properties, arsenic plays a key doping role in semiconductor materials and can significantly affect the conductivity and band structure of the material. The cadmium element, with its good metallic properties and plasticity, provides a stable structural basis for the solid solution.

[0004] In recent years, with the accelerated development of industrialization and urbanization, the problem of heavy metal pollution in soil has become increasingly serious. Heavy metal pollution not only affects soil quality, but may also enter the human body through the food chain, posing a threat to human health. Therefore, it is particularly important to find effective soil heavy metal remediation technology. Arsenic-cadmium solid solution shows unique advantages in solidifying and stabilizing heavy metals in soil. Its stable crystal structure and excellent chemical stability enable it to form stable compounds in the soil, thereby effectively fixing heavy metal ions and preventing their migration and diffusion. In addition, through technical means, the acid resistance and electric field stress resistance of arsenic-cadmium solid solution can be improved, which can enhance the solidification / stabilization effect of arsenic-cadmium solid solution on arsenic-cadmium composite pollution (especially cadmium pollution). Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method and application of an arsenic-cadmium solid solution that is resistant to electric field stress and acid dissolution. The prepared solid solution is subjected to X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) solid phase characterization before and after dissolution to explore the formation mechanism of the arsenic-cadmium solid solution and the dissolution process under electric field stress.

[0006] The method for preparing arsenic-cadmium solid solution by chemical coprecipitation method has the following characteristic steps:

[0007] (1) Prepare fresh ultrapure water and weigh appropriate amounts of calcium chloride, cadmium chloride and sodium arsenate solids in turn. Use these raw materials to prepare calcium chloride solution, cadmium chloride solution and sodium arsenate solution with a concentration of 0.025 mol / L respectively and set aside.

[0008] (2) In a clean beaker, accurately measure 60 mL of the cadmium chloride solution and 240 mL of the calcium chloride solution prepared in step (1) at a molar ratio of cadmium to (calcium + cadmium) of 0.2, and mix them into a 300 mL solution for later use.

[0009] (3) Pour the sodium arsenate solution prepared in step (1) into a 600 mL clean beaker and stir at 600 r / min at 25°C for 30 seconds. Then, take out 180 mL of the sodium arsenate solution and set aside.

[0010] (4) Add 300 mL of the cadmium chloride and calcium chloride solutions prepared in step (2) to the sodium arsenate solution in step (3) at a rate of 10 mL / min.

[0011] (5) Use step (4) to prepare three mixed solutions with different pH values. The pH values ​​of the three solutions are controlled by 0.01 mol / L HCl solution and 0.01 mol / L NaOH solution respectively.

[0012] (6) The solution system obtained in step (5) was subjected to contact reaction at room temperature for 10 minutes. After the reaction was completed, the solution was placed in a water bath at 25° C. for aging for 48 hours. Thereafter, the solution was taken out and cooled to room temperature.

[0013] (7) Solid-liquid separation was performed at room temperature to obtain a solid phase precipitate. The precipitate was washed with ultrapure water several times and then placed in a 50°C forced air drying oven for drying for 24 hours.

[0014] (8) The solid phase precipitate obtained in step (7) is the target arsenic-cadmium solid solution.

[0015] The main composition of the solid phase of arsenic-cadmium solid solution did not change significantly before and after electric field stress. The specific steps are:

[0016] (1) At room temperature, weigh 0.1 g of a series of samples of arsenic-cadmium solid solutions synthesized at pH 6, 7, and 8, and place them in three beakers containing 500 ml of 0.01 mol / L NaCl solution.

[0017] (2) Fix the electrode plate in the beaker, set the voltage gradient to 1 V / cm, and conduct the experiment at a temperature controlled at 25℃ ± 2℃.

[0018] (3) During the process, the pH value of the supernatant in each beaker was measured at 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, 168 h, 192 h, 216 h and 240 h, respectively. 10 ml of the supernatant was taken out from each beaker and filtered using a 0.45 μm syringe filter to measure the concentrations of arsenic, cadmium and calcium in the liquid phase.

[0019] The arsenic-cadmium solid solution prepared by the present invention is aged under the conditions of pH values ​​of 6, 7 and 8. After 240 hours, the Cd concentration in the liquid phase is 0.016-0.021 mmol / L, the As concentration is 0.432-1.106 mmol / L, and before and after the electrical enhanced dissolution, the changes in the Cd / (Ca+Cd) molar ratio and the (Ca+Cd) / As molar ratio are not significant. The Cd / (Ca+Cd) molar ratio ranges from 0.26 to 0.71, and the (Ca+Cd) / As molar ratio ranges from 1.29 to 3.81.

[0020] The arsenic-cadmium solid solution resistant to electric field stress and acid dissolution prepared by the present invention shows unique advantages and potential in the solidification, stabilization and remediation of arsenic-cadmium composite contaminated soil. Compared with traditional heavy metal treatment methods, solidification and stabilization technology can reduce the risk of secondary pollution. For example, it prevents heavy metals from being released into the air or water during the treatment process. By converting heavy metals into a stable solid solution form, the infiltration and diffusion of heavy metals in soil or water can be reduced, thereby reducing the risk of pollution of groundwater and surface water by the dissolution of arsenic-cadmium composite heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD diagram of the arsenic-cadmium solid solution prepared in Examples 1 to 6 of the present invention, wherein the arsenic-cadmium solid solution standard card is PDF#01-076-1635.

[0022] Figure 2 The FT-IR spectra of the arsenic-cadmium solid solutions prepared in Examples 1 to 6 of the present invention are shown.

[0023] Figure 3This is a scanning electron microscope (SEM) image of the arsenic-cadmium solid solution prepared in Example 1 of the present invention.

[0024] Figure 4 This is the full XPS spectrum of the arsenic-cadmium solid solution prepared in Examples 1 to 6 of the present invention.

[0025] Figure 5 The liquid phase composition changes during the electro-enhanced dissolution process of the present invention (01, 02, and 03 shown in the figure are a series of samples of arsenic-cadmium solid solution synthesized at pH values ​​of 6, 7, and 8, respectively) - (a) Cd 2+ Concentration liquid phase changes; (b) Ca in the process of electro-enhanced dissolution 2+ Concentration liquid phase change; (c) As in the process of electro-enhanced dissolution 5+ Concentration liquid phase changes.

[0026] Figure 6 This is a diagram of the device used in the electrical enhanced dissolution process of the present invention. DETAILED DESCRIPTION

[0027] Example 1

[0028] At room temperature, 500 mL of 0.025 mol / L calcium chloride solution and 200 mL of 0.025 mol / L cadmium chloride solution were prepared. The cadmium chloride solution and the calcium chloride solution were mixed evenly according to the molar ratio of Cd / (Ca+Cd) of 0.2. Then 1L of 0.025 mol / L sodium arsenate solution was prepared in a 600 mL beaker. The temperature was set to 25℃ and the speed was 600 r / min for stirring for 30 s. 180 mL of sodium arsenate solution was measured from it. Then 200 mL of the mixed solution of cadmium chloride and calcium chloride was measured and added to the sodium arsenate solution at 10 mL / min. The pH value of the solution was adjusted to 6. After the contact reaction for 10 min, it was placed in a water bath at 25℃ for 48 h. Finally, solid-liquid separation was performed and washed with ultrapure water for 3 times. The washed solid phase was placed in a drying oven at 50℃ for 24 h to obtain an arsenic-cadmium solid solution with an initial aging pH value of 6.

[0029] Example 2

[0030] At room temperature, 0.1 g of sample (01, i.e., arsenic-cadmium solid solution with an initial aging pH value of 6) was weighed into a 600 mL beaker, and then 500 mL of 0.01 mol / L sodium chloride solution was added thereto. After the electrode plate was fixed, the voltage gradient was set to 1 V / cm, and the electrical enhanced dissolution experiment was carried out at 25°C±2°C. At 15 sampling time points (1, 2, 4, 8, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h), the pH value of the supernatant in each beaker was measured and recorded, and 10 mL of the supernatant was taken from each beaker, filtered into a centrifuge tube with a 0.45 μm syringe filter, and used to determine the concentrations of arsenic, cadmium, and calcium in the liquid phase. After 240 h of electro-enhanced dissolution, the dissolved solid phase in the beaker was filtered, washed three times with ultrapure water, placed in a glass petri dish, and then dried in a 50°C forced air drying oven for 24 h.

[0031] Example 3

[0032] At room temperature, 500 mL of 0.025 mol / L calcium chloride solution and 200 mL of 0.025 mol / L cadmium chloride solution were prepared. The cadmium chloride solution and the calcium chloride solution were mixed evenly according to the Cd / (Ca+Cd) molar ratio of 0.2. Then 1L of 0.025 mol / L sodium arsenate solution was prepared in a 600 mL beaker. The temperature was set to 25℃ and the speed was 600 r / min for 30 s. Then 200 mL of the mixed solution of cadmium chloride and calcium chloride was added to the mixed solution at 10 mL / min. The pH value of the solution was adjusted to 7. After the contact reaction for 10 min, it was placed in a water bath at 25℃ for 48 h. Finally, the solid-liquid separation was performed and the solution was washed with ultrapure water for 3 times. The washed solid phase was placed in a drying oven at 50℃ for 24 h to obtain an arsenic-cadmium solid solution with an initial aging pH value of 7.

[0033] Example 4

[0034] At room temperature, 0.1 g of sample (02, i.e., arsenic-cadmium solid solution with an initial aging pH value of 7) was weighed into a 600 mL beaker, and then 500 mL of 0.01 mol / L sodium chloride solution was added thereto. After fixing the electrode plate, the voltage gradient was set to 1 V / cm, and the electro-enhanced dissolution experiment was carried out at 25°C±2°C. At 15 sampling time points (1, 2, 4, 8, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h), the pH value of the supernatant in each beaker was measured and recorded, and 10 mL of supernatant was taken from each beaker, filtered into a centrifuge tube with a 0.45 μm syringe filter, and used to determine the concentrations of arsenic, cadmium, and calcium in the liquid phase. After 240 h of electro-enhanced dissolution, the dissolved solid phase in the beaker was filtered, washed three times with ultrapure water, placed in a glass petri dish, and then dried in a 50°C forced air drying oven for 24 h.

[0035] Example 5

[0036] At room temperature, 500 mL of 0.025 mol / L calcium chloride solution and 200 mL of 0.025 mol / L cadmium chloride solution were prepared. The cadmium chloride solution and the calcium chloride solution were mixed evenly according to the Cd / (Ca+Cd) molar ratio of 0.2. Then 1L of 0.025 mol / L sodium arsenate solution was prepared in a 600 mL beaker. The temperature was set to 25℃ and the speed was 600 r / min for 30 s. Then 200 mL of the mixed solution of cadmium chloride and calcium chloride was added to the mixed solution at 10 mL / min. The pH value of the solution was adjusted to 8. After the contact reaction for 10 min, it was placed in a water bath at 25℃ for 48 h. Finally, the solid-liquid separation was performed and the solution was washed with ultrapure water for 3 times. The washed solid phase was placed in a drying oven at 50℃ for 24 h to obtain an arsenic-cadmium solid solution with an initial aging pH value of 8.

[0037] Example 6

[0038] At room temperature, 0.1 g of sample (03, i.e., arsenic-cadmium solid solution with an initial aging pH value of 8) was weighed into a 600 mL beaker, and then 500 mL of 0.01 mol / L sodium chloride solution was added thereto. After fixing the electrode plate, the voltage gradient was set to 1 V / cm, and the electro-enhanced dissolution experiment was carried out at 25°C±2°C. At 15 sampling time points (1, 2, 4, 8, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h), the pH value of the supernatant in each beaker was measured and recorded, and 10 mL of supernatant was taken from each beaker, filtered into a centrifuge tube with a 0.45 μm syringe filter, and used to determine the concentrations of arsenic, cadmium, and calcium in the liquid phase. After 240 h of electro-enhanced dissolution, the dissolved solid phase in the beaker was filtered, washed three times with ultrapure water, placed in a glass petri dish, and then dried in a 50°C forced air drying oven for 24 h.

Claims

1. A preparation method and application of an arsenic-cadmium solid solution resistant to electric field stress and acid dissolution, wherein the characteristic steps are: (1) Prepare fresh ultrapure water, weigh an appropriate amount of calcium chloride solid, and prepare a 0.025 mol / L calcium chloride solution for later use; weigh an appropriate amount of cadmium chloride solid, and prepare a 0.025 mol / L cadmium chloride solution for later use; weigh an appropriate amount of sodium arsenate solid, and prepare a 0.025 mol / L sodium arsenate solution for later use; (2) In a clean beaker, measure 60 mL of the 0.025 mol / L cadmium chloride solution and 240 mL of the 0.025 mol / L calcium chloride solution prepared in step (1) to prepare 300 mL of a mixed solution with a cadmium / (calcium + cadmium) molar ratio of 0.2; (3) In a clean beaker, add the 0.025 mol / L sodium arsenate solution prepared in step (1) to a 600 mL beaker, set the temperature to 25°C, stir at 600 r / min for 30 s, and then measure 180 mL of the sodium arsenate solution; (4) In a clean beaker, add 300 mL of the mixed solution of cadmium chloride and calcium chloride prepared in step (2) to the sodium arsenate solution prepared in step (3) at a rate of 10 mL / min, adjust the pH value of the solution to 6, allow the solution to react for 10 min, place the reacted solution in a water bath at 25°C for 48 hours, remove it, and cool it to room temperature; (5) In a clean beaker, add 300 mL of the mixed solution of cadmium chloride and calcium chloride prepared in step (2) to the sodium arsenate solution prepared in step (3) at a rate of 10 mL / min, adjust the pH value of the solution to 7, allow the solution to react for 10 min, place the reacted solution in a water bath at 25°C for 48 hours, remove it, and cool it to room temperature; (6) In a clean beaker, add 300 mL of the mixed solution of cadmium chloride and calcium chloride prepared in step (2) to the sodium arsenate solution prepared in step (3) at a rate of 10 mL / min, adjust the pH value of the solution to 8, allow the solution to react for 10 min, place the reacted solution in a water bath at 25°C for 48 hours, remove it, and cool it to room temperature; (7) Carry out solid-liquid separation at room temperature, wash the obtained solid precipitate with ultrapure water for multiple times, and dry the washed solid precipitate in a 50°C forced air drying oven for 24 hours, thereby completing the preparation of the arsenic-cadmium solid solution.

2. An application of the method as claimed in claim 1 to synthesize arsenic-cadmium solid solution, characterized in that The main composition of the solid phase of arsenic-cadmium solid solution did not change significantly before and after electric field stress. The specific steps are: Under electric field stress: at room temperature, 0.1 g of arsenic-cadmium solid solution samples synthesized at pH 6, 7, and 8 were weighed and placed in three groups of 500 mL 0.01 mol / L NaCl solutions. After fixing the electrode plates, the voltage gradient was set to 1 V / cm, and the electrical enhanced dissolution experiment was carried out at 25℃ ± 2℃; the pH value of the supernatant in each beaker was measured and recorded at 1h, 2h, 4h, 8h, 12h, 24h, 48h, 72h, 96h, 120h, 144h, 168h, 192h, 216h and 240h, respectively. At the same time, 10 mL of supernatant was taken from each beaker and 0.45 The prepared arsenic-cadmium solid solution is aged at pH values ​​of 6, 7, and 8, and the Cd concentration in the liquid phase is 0.016-0.021 mmol / L, and the As concentration is 0.432-1.106 mmol / L after 240 hours. Before and after the electrical enhanced dissolution, the Cd / (Ca+Cd) molar ratio and the (Ca+Cd) / As molar ratio do not change significantly, the Cd / (Ca+Cd) molar ratio ranges from 0.26 to 0.71, and the (Ca+Cd) / As molar ratio ranges from 1.29 to 3.81.

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