Method for preparing soil As passivation material by utilizing supercritical water-carbon-based solid waste to cooperatively treat red mud and application of soil As passivation material

Abstract

The invention discloses a method for preparing a soil As passivation material by utilizing supercritical water-carbon-based solid waste to cooperatively treat red mud and application of the soil As passivation material. The method comprises the following steps: (1) uniformly mixing the red mud, water and carbon-based solid waste; (2) putting the mixture obtained in the step (1) into a supercritical water reaction device, and carrying out supercritical hydrothermal reaction to complete the dealkalization of the red mud and the synthesis of a passivation material; and (3) washing the product in the step (2) with water, and drying to obtain the soil As passivation material. The application refers to the application of the passivating material in passivating soil As. According to the method disclosed by the invention, alkali release of the red mud is accelerated by utilizing the carbon source and the decomposition product thereof through strong permeation and high reaction activity of supercritical water, meanwhile, iron-containing minerals in the red mud are activated and decomposed into high-activity iron components, and the red mud is dealkalized, so that treatment of the red mud solid waste and the carbon-containing solid waste is realized; the resource utilization of the solid waste is also realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil arsenic treatment, and particularly relates to a method for preparing soil As passivation material by using supercritical water-carbon-based solid waste to cooperatively treat red mud and application thereof. BACKGROUND

[0002] The artificial pollution sources of soil arsenic include mining and smelting, application of arsenic-containing pesticides and fertilizers, coal combustion, etc. Arsenic has the characteristics of high toxicity, great harm and difficult degradation. Passivation and barrier are the mainstream technologies for remediation of soil arsenic pollution. The passivation and barrier materials for As currently include aluminum-based, calcium-based, biochar-based and iron-containing materials. The iron-containing materials become the core category because they can efficiently fix arsenic and are widely used for the passivation of As. Liu Yaoci et al. developed a preparation method of an iron-based arsenic passivation material, with the publication number CN108358290A. The patent is prepared by mixing silicate minerals with composite salt, roasting, water immersion treatment, and then hydrothermal activation with iron-based materials such as zero-valent iron to prepare the iron-based arsenic passivation material. However, the consumption of iron-based materials leads to high production cost of the technology.

[0003] Red mud is a large solid waste in the production of alumina industry, which is rich in iron content and has a wide source. However, the original iron component of red mud does not have the ability to fix arsenic. Therefore, how to jointly use red mud and other solid wastes to achieve waste control and waste, and realize the resource utilization of solid wastes and the remediation of soil arsenic pollution is an effective way to reduce costs and increase efficiency. Therefore, it is necessary to develop a method for preparing soil As passivation material by using supercritical water-carbon-based solid waste to cooperatively treat red mud. SUMMARY

[0004] To solve the technical problem of large consumption of zero-valent iron in the preparation process of the existing technology of iron-based arsenic passivation material, the purpose of the present application is to provide a method for preparing soil As passivation material by using supercritical water-carbon-based solid waste to cooperatively treat red mud. The core of the present application is to use the strong penetration and high reactivity of supercritical water, carbon source and its decomposition products to accelerate the alkali release of red mud, and to activate and decompose the iron-containing minerals in red mud into high-activity iron components, and to realize the dealkalization of red mud. The present application not only realizes the treatment and disposal of red mud and carbon-containing solid waste, but also realizes the resource utilization of solid waste.

[0005] The second purpose of the present application is to provide a passivation material prepared by the method for preparing soil As passivation material by using supercritical water-carbon-based solid waste to cooperatively treat red mud. The passivation material synchronously realizes the resource utilization of red mud and carbon-based solid waste and the efficient and stable passivation of As.

[0006] The third purpose of the present application is to provide the application of the passivation material in passivating soil As.

[0007] The first purpose of the present application is achieved by the following steps: (1) Mix red mud, water, and carbon-based solid waste evenly; (2) The mixture obtained in step (1) is placed in a supercritical water reactor to carry out a supercritical hydrothermal reaction to complete the dealkalization and passivation material synthesis of red mud; (3) The product from step (2) is washed and dried with water to obtain soil As passivation material.

[0008] Carbon-based solid waste refers to carbon-containing solid waste from agriculture and forestry (straw), domestic waste (kitchen waste), etc. Supercritical water refers to water in a special state where both temperature and pressure exceed the critical temperature and critical pressure of water. Water breaks through the critical temperature and becomes a supercritical state that has both gas diffusion and liquid solubility.

[0009] Preferably, in step (1), the mass ratio of red mud to carbon-based solid waste is 1~10:1, and the liquid-solid ratio of water to the mixture of red mud and carbon-based solid waste is 1mL~10mL:1g.

[0010] Preferably, before mixing in step (1), the red mud and carbon-based solid waste are crushed and sieved to a particle size of 100 mesh to 200 mesh.

[0011] Preferably, the hydrothermal reaction conditions in step (2) are 374℃~450℃, where 450℃ is the balance point between "efficiency and economy" in industrial applications, the pressure is 22.1Mpa~30MPa, and the reaction time is 2h~6h.

[0012] Preferably, in step (2), when maintaining the supercritical state, a stirring device is used for stirring, and the stirring rate is 100r / min to 300r / min.

[0013] Preferably, step (3) washing is performed with deionized water until the pH of the filtrate after washing is <8.

[0014] Preferably, step (3) drying is performed at 100℃~150℃ for 6h~10h, and then pulverized to 100 mesh~200 mesh.

[0015] The second objective of this invention is achieved by preparing a passivation material for soil using a method of co-processing red mud with supercritical water and carbon-based solid waste.

[0016] The third objective of this invention is achieved by the application of passivating materials in passivating soil As.

[0017] Preferably, the passivating material is added to the As-containing soil and mixed thoroughly, with an addition amount of 100kg to 1000kg per acre of soil, to achieve passivation of the heavy metal As in the soil.

[0018] The beneficial effects of this invention are as follows: This invention utilizes the synergistic effect of "supercritical water-carbon". Supercritical water provides a strong reaction environment, and the carbon source functions as both a "de-alkali promotion agent" and an "iron activation aid". This not only solves the problem of iron inertness in red mud, but also realizes the dual resource utilization of red mud and carbon-containing solid waste. The preparation process of this invention has no secondary pollution, and the resulting material has high passivation efficiency and low cost. When applied, it causes little disturbance to the soil and is suitable for large-scale soil arsenic pollution remediation. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0020] Example 1 This embodiment describes a method for preparing soil As passivation materials using supercritical water and carbon-based solid waste synergistic treatment of red mud, including the following steps: (1) Crush and sieve the red mud and carbon-based solid waste. The red mud particle size is 150 mesh and the carbon-based solid waste particle size is 120 mesh. The carbon-based solid waste is made from corn stalks. Mix the red mud, deionized water and carbon-based solid waste evenly and stir in a mixing tank at a stirring rate of 200 r / min for 25 min at room temperature. The mass ratio of red mud to carbon-based solid waste is 5:1, that is, weigh 250 g of red mud and 50 g of corn stalks. The liquid-solid ratio of deionized water to the mixture of red mud and carbon-based solid waste is 5 mL: 1 g, that is, the amount of deionized water used is 1500 mL. (2) Place the mixture obtained in step (1) into a supercritical water reaction device, seal it and heat it to 412℃ (heating rate 5℃ / min), pressure 26.05MPa, turn on the stirring device (speed 100r / min), keep the temperature and pressure for reaction, and the reaction time is 4h to complete the synthesis of red mud dealkalization and passivation materials. (3) After the reaction is completed, the temperature is naturally cooled to below 80°C, the pressure is released and the product is taken out. The product of step (2) is repeatedly washed with water. The pH value of the filtrate is checked each time it is washed until the pH is less than 8.0. Then the product is placed in a 125°C oven to dry for 8 hours, and then crushed to 150 mesh to obtain soil As passivation material.

[0021] Example 2 The method for preparing soil As passivation material by supercritical water-carbon-based solid waste synergistic treatment of red mud in this embodiment is based on Example 1, but differs from Example 1 in the following ways: Step (1) Wheat straw is selected as the carbon-based solid waste, the red mud particle size is 100 mesh, the carbon-based solid waste particle size is 100 mesh, the mass ratio of red mud to carbon-based solid waste is 10:1, that is, 200g of red mud and 20g of carbon-based solid waste are weighed, the liquid-solid ratio of water to the mixture of red mud and carbon-based solid waste is 10mL:1g, that is, 2100mL of deionized water is stirred in a high-speed mixer at a stirring rate of 200r / min and stirred at room temperature for 20min; Step (2) The hydrothermal reaction conditions are 374℃ (heating rate 4℃ / min), pressure 22.1Mpa, reaction time 6h, and stirring rate 100r / min; Step (3) Dry in a 100℃ forced-air drying oven for 10h, and then pulverize to 100 mesh.

[0022] Example 3 The method for preparing soil As passivation material by supercritical water-carbon-based solid waste co-processing red mud in this embodiment is based on Example 1, but differs from Example 1 in the following ways: Step (1) Kitchen waste is selected as the carbon-based solid waste, the red mud particle size is 200 mesh, the carbon-based solid waste particle size is 200 mesh, the mass ratio of red mud to carbon-based solid waste is 1:1, that is, 200g of red mud and 200g of kitchen waste, the liquid-solid ratio of water to the mixture of red mud and carbon-based solid waste is 1mL:1g, that is, 400mL of deionized water, and the mixture is stirred at 300r / min for 30min in a planetary mixer; Step (2) The hydrothermal reaction conditions are 450℃ (heating rate 6℃ / min), pressure 30MPa, reaction time 2h, stirring rate 250r / min, and rapid cooling to 60℃ after the reaction is completed; Step (3) The mixture is dried in a vacuum drying oven at 150℃ for 6h, and then pulverized to 200 mesh.

[0023] Example 4 This embodiment is the passivation material prepared by the method of preparing soil As passivation material by supercritical water-carbon-based solid waste synergistic treatment of red mud in Example 1.

[0024] Example 5 This embodiment is the passivation material prepared by the method of preparing soil As passivation material by supercritical water-carbon-based solid waste synergistic treatment of red mud in Example 2.

[0025] Example 6 This embodiment describes the passivation material prepared using the method described in Example 3, which involves the synergistic treatment of red mud with supercritical water and carbon-based solid waste to prepare soil As passivation material.

[0026] Example 7 The passivation material from Example 4 was added to As-contaminated soil at a rate of 550 kg per acre. The mixture was thoroughly stirred and left to stand naturally for 10 days. The test results showed that the content of available As in the soil decreased by 69% compared with that before treatment.

[0027] Example 8 The passivation material from Example 5 was added to As-contaminated soil at a rate of 1000 kg per acre. The mixture was thoroughly stirred and allowed to stand naturally for 12 days. The test results showed that the content of available As in the soil was reduced by 75% compared to before treatment.

[0028] Example 9 The passivation material from Example 6 was added to As-contaminated soil at a rate of 100 kg per acre. The mixture was thoroughly stirred and left to stand naturally for 8 days. The test results showed that the content of available As in the soil was reduced by 65% ​​compared with that before treatment.

Claims

1. A method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste, characterized in that... Includes the following steps: (1) Mix red mud, water, and carbon-based solid waste evenly; (2) The mixture obtained in step (1) is placed in a supercritical water reactor to carry out a supercritical hydrothermal reaction to complete the dealkalization and passivation material synthesis of red mud; (3) The product from step (2) is washed and dried with water to obtain soil As passivation material.

2. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1, characterized in that... Step (1) The mass ratio of red mud to carbon-based solid waste is 1~10:1, and the liquid-solid ratio of water to the mixture of red mud and carbon-based solid waste is 1mL~10mL:1g.

3. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1 or 2, characterized in that... Before mixing in step (1), the red mud and carbon-based solid waste are crushed and sieved to a particle size of 100-200 mesh.

4. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1, characterized in that... Step (2) The hydrothermal reaction conditions are 374℃~450℃, pressure 22.1Mpa~30MPa, and reaction time 2h~6h.

5. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1, characterized in that... In step (2), when maintaining the supercritical state, a stirring device is used for stirring at a speed of 100 r / min to 300 r / min.

6. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1, characterized in that... Step (3) Washing is performed with deionized water until the pH of the filtrate after washing is <8.

7. The method for preparing soil As passivation materials by co-processing red mud with supercritical water and carbon-based solid waste according to claim 1, characterized in that... Step (3) Drying is done at 100℃~150℃ for 6h~10h, and then pulverized to 100 mesh~200 mesh.

8. A passivation material prepared by the method for preparing soil As passivation material by supercritical water-carbon-based solid waste co-treatment of red mud according to any one of claims 1 to 7.

9. The application of the passivating material according to claim 8 in passivating soil As.

10. The application according to claim 9, characterized in that... Add the passivating material to the As-containing soil and mix thoroughly. The amount added is 100kg to 1000kg per acre of soil.