A mercury removal agent, its preparation method and application

Abstract

The present invention discloses a mercury removal agent, its preparation method, and application. The preparation method comprises the following steps: starch and a calcium source are mixed to obtain a mixture, the mixture is stirred evenly, and then shaped and granulated using a molding device. After drying, the mixture is calcined and carbonized under an inert atmosphere to obtain the mercury removal agent. The starch used in the preparation of the mercury removal agent serves as a carbon precursor, which, after calcination and carbonization, produces a carbon material that provides a high specific surface area and disperses calcium oxide nanoparticles. Furthermore, the carbon material itself, after calcination and carbonization, also exhibits mercury removal properties. Furthermore, the starch has a certain viscosity and can be used as a binder to shape the mercury removal agent, facilitating subsequent separation and recovery. The mercury removal agent provided by the present invention has the characteristics of a high specific surface area, uniform calcium dispersion, separable and recyclable properties, and excellent mercury adsorption properties.

Description

Technical Field

[0001] The present invention relates to the field of mercury removal agents, and in particular to a mercury removal agent, a preparation method thereof and an application thereof. Background Art

[0002] Mercury and its compounds are highly toxic and pose serious risks to both humans and the environment. When absorbed by the body, mercury can damage the central nervous system and, in severe cases, cause brain death. Mercury in the environment can remain in the ecosystem for long periods of time, polluting not only the atmosphere but also water and soil. With the release of a series of national policies and regulations restricting mercury emissions, the need for mercury control is urgent.

[0003] Adsorption is a common method for mercury removal in industry, making the development of adsorbents crucial. Mercapto ion exchange resins are a commonly used adsorbent on the market, but their preparation is complex and expensive. Another class of adsorbents, carbon-based materials, offer high surface area and low cost, but their adsorption performance is poor, requiring modification by loading them with precious metals or alkaline earth metals to enhance their adsorption performance.

[0004] Calcium-based mercury removers offer advantages such as high capture efficiency, energy conservation, low raw material prices, low cost, and high economic efficiency, and are also widely used in the field of gas-liquid phase mercury removal. Patent CN107376826B uses an impregnation method to load calcium oxide onto a carrier such as aluminum oxide to produce a calcium oxide-based adsorbent. However, this simple impregnation method is difficult to disperse large calcium oxide particles. Current calcium-based mercury removers typically suffer from low specific surface area and large calcium nanoparticles, which make it difficult to fully expose the active components in the calcium-based mercury removers, resulting in a low effective adsorption area and poor adsorption performance. Furthermore, since most calcium-based mercury removers are in powder form, their recovery is difficult. If the calcium-based mercury removers could be prepared into a shaped mercury remover with a high specific surface area, solid-liquid separation could be easily achieved, significantly improving their efficiency. Summary of the Invention

[0005] In response to the above-mentioned technical problems existing in the prior art, the present invention aims to provide a mercury removal agent, a preparation method thereof, and applications thereof. The mercury removal agent provided by the present invention has the characteristics of high specific surface area, uniform dispersion of the active component calcium oxide, and excellent mercury adsorption performance. In addition, the mercury removal agent is in granular form, which has great advantages in the field of gas-solid phase mercury removal.

[0006] The technical solution adopted in the present invention is as follows:

[0007] The method for preparing a mercury removal agent comprises the following steps: mixing starch and a calcium source to obtain a mixture, wherein the mixture further contains water capable of sticking the starch (sticking the starch facilitates subsequent molding by equipment), stirring the mixture evenly, shaping and granulating the mixture by molding equipment, drying the mixture, and then calcining and carbonizing the mixture under an inert atmosphere to obtain the mercury removal agent.

[0008] Furthermore, the starch is natural starch and / or modified starch, the natural starch is one or more of corn starch, potato starch, tapioca starch, and wheat flour, preferably wheat flour and / or tapioca starch, and the modified starch is one or more of cationically modified starch, anionically modified starch, and amphoteric starch.

[0009] Furthermore, the calcium source is one or more of calcium carbonate, acetate, nitrate, metal oxide, hydroxide, gluconate and industrial calcium-containing waste, and the mass ratio of the calcium source to starch is 1-3:5.

[0010] Furthermore, the starch can be mixed with a calcium source after undergoing hydrothermal pretreatment. The hydrothermal pretreatment includes the following steps: placing the starch in an aqueous solution with a pH of 3-12 for hydrothermal treatment. The starch undergoes hydrothermal treatment in an acidic / alkaline environment to catalytically depolymerize the starch, or undergoes hydrothermal treatment in a neutral environment to break up the starch granules and expose their internal hydroxyl structures. The starch does not require additional treatment after the hydrothermal treatment. The treated starch is in a paste-like state, and the residual water in the paste can gelatinize the starch, increasing its viscosity. The mixture after mixing with the calcium source can then be formed using equipment.

[0011] Furthermore, the aqueous solution with a pH of 3-12 is one or more of hydrochloric acid solution, nitric acid solution, acetic acid solution, sulfuric acid solution, sodium hydroxide solution, potassium hydroxide solution, ammonia water, and deionized water; and the solid-liquid ratio of starch to the aqueous solution is 5g:1-3mL.

[0012] Furthermore, the temperature of the hydrothermal treatment is 90-120° C., and the treatment time is 0.5-3 h.

[0013] Furthermore, the forming equipment is one of an extruder, a granulator or a pelletizer.

[0014] Furthermore, the specific process of the calcination carbonization treatment is: in a flowing nitrogen, helium or argon atmosphere, the material is heated to 750-900° C. in a pyrolysis furnace, and then calcined at a constant temperature for 1-4 hours.

[0015] The mercury removal agent prepared by the method of the present invention has a specific surface area of 300-600m 2 / g, pore volume is 0.20~0.50cm 3 / g; the size of calcium oxide is 5-30nm. The mercury removal agent of the present invention can be well applied to remove mercury in sewage.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The active component calcium oxide in the mercury remover prepared by the method of the present invention is nano-sized and uniformly dispersed, and the specific surface area of the mercury remover is high. In addition, since the mercury remover undergoes shaping and granulation during the preparation process, the final mercury remover product has a certain macroscopic shape, which has the advantage of being easy to recover and separate when used for mercury removal treatment in wastewater.

[0018] (2) Starch is used as a raw material in the preparation of the mercury remover of the present invention. On the one hand, starch, as a carbon precursor, has a high specific surface area after calcination and carbonization. On the other hand, starch and its catalytic depolymerization products under a hydrothermal environment have a certain viscosity. During the preparation of the mercury remover, starch itself can be used as a binder to facilitate shaping and granulation. This allows the prepared mercury remover to be easily separated and recovered in subsequent applications.

[0019] (3) The present invention uses starch as a raw material. The starch surface is rich in hydroxyl groups, which can well anchor the active component calcium oxide and promote the effective dispersion of calcium oxide (the hydroxyl groups of starch can also disperse large particles of CaO, making the CaO size smaller). The hydroxyl-rich starch can be decomposed at high temperature during calcination and carbonization to generate water vapor, forming a large number of microporous structures, providing a high specific surface area, and increasing more accessible mercury adsorption active sites, thereby improving mercury removal performance.

[0020] (4) The starch of the present invention is hydrothermally pretreated and then mixed with a calcium source to prepare a mercury removal agent. The starch depolymerizes under the hydrothermal environment, causing large starch particles to break up and expose their internal hydroxyl structures. This allows more active functional groups, such as hydroxyl groups, to be exposed on the starch surface, which can anchor active components and facilitate the subsequent full dispersion of the active component, calcium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The N2 adsorption isotherm of the mercury removal agent obtained in Example 1 of the present invention is shown in FIG.

[0022] Figure 2 The XRD patterns of the mercury removal agents of Example 1, Comparative Example 1, and Comparative Example 3 of the present invention are compared;

[0023] Figure 3 The SEM scanning electron microscope image of the mercury removal agent obtained in Example 1 is shown in the figure;

[0024] Figure 4 This is a transmission electron microscope image of the mercury removal agent obtained in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] Example 1

[0027] 50 g of wheat flour and 20 g of calcium oxide powder were weighed and mixed uniformly by solid-phase grinding. 30 mL of deionized water was added and stirred uniformly. The mixture was compressed using an extruder, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated to 850°C, where it was maintained at this temperature for 2 hours. The mixture was then naturally cooled to room temperature to obtain a mercury removal agent.

[0028] The N2 adsorption isotherm of the mercury removal agent obtained in Example 1 of the present invention is shown in FIG. Figure 1 It can be seen that it conforms to the IV type adsorption isotherm, rises rapidly at the relative pressure P / P0=0.1, and there is a hysteresis loop within the relative pressure P / P0 of 0.5-1.0, indicating that the demercuration agent contains micropores and mesopores.

[0029] The SEM scanning electron microscope image of the mercury removal agent obtained in Example 1 is as follows: Figure 3 As shown, it can be seen that the pore structure of the mercury removal agent of Example 1 is rich ( Figure 3 The black area in the circle mark is the pore structure. The TEM transmission electron microscope image of the mercury removal agent obtained in Example 1 is as follows: Figure 4 As shown, the CaO is in the form of particles of about 10 nm attached to the surface of the biochar.

[0030] Example 2

[0031] 50 g of wheat flour and 20 g of industrial calcium-containing waste powder (primarily CaO, with a CaO content of 90%) were weighed and mixed uniformly by solid-phase grinding. 30 mL of deionized water was added and stirred uniformly. The mixture was shaped using a granulator, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated to 850°C, where it was maintained at this temperature for 2 hours. The mixture was then naturally cooled to room temperature to obtain a mercury removal agent.

[0032] Example 3

[0033] 50g of wheat flour was weighed, added to 30mL of aqueous ammonia (pH = 9), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed. The mixture was then compressed using an extruder, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated until the temperature in the tube reached 850°C, where it was maintained at this temperature for 2 hours. Finally, the mixture was naturally cooled to room temperature to obtain a mercury removal agent.

[0034] Example 4

[0035] 50g of wheat flour was weighed, added to 10mL of aqueous ammonia (pH = 9), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed. The mixture was then compressed using an extruder, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated until the temperature in the tube reached 850°C, where it was maintained at this temperature for 2 hours. Finally, the mixture was naturally cooled to room temperature to obtain a mercury removal agent.

[0036] Example 5

[0037] 50g of wheat flour was weighed, added to 10mL of deionized water (pH=7), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed. The mixture was then compressed using an extruder, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated until the temperature in the tube reached 850°C, where it was maintained at this temperature for 2 hours. Finally, the mixture was naturally cooled to room temperature to obtain a mercury removal agent.

[0038] Example 6

[0039] 50g of wheat flour was weighed, added with 30mL of hydrochloric acid (pH=3), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed, and pelletized using a pelletizer. After air drying, the mixture was placed in a pyrolysis tube, purged with nitrogen, and heated until the temperature in the tube reached 850°C. This temperature was maintained for 2 hours, and then naturally cooled to room temperature to obtain a mercury removal agent.

[0040] Comparative Example 1

[0041] Commercial calcium oxide powder was selected as the mercury removal agent.

[0042] Comparative Example 2

[0043] Weigh 50g of dried corn stalks, add 30mL of aqueous ammonia (pH=9), and place in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1h. Weigh 20g of calcium oxide powder and add it to the mixture from the previous step, mixing thoroughly. Pelletize the mixture using a pelletizer, air dry, and place in a pyrolysis tube. Heat the mixture in the tube while purging it with nitrogen until it reaches 850°C and maintains this temperature for 2h. Finally, cool the mixture naturally to room temperature to obtain a mercury removal agent.

[0044] Comparative Example 3

[0045] 50 g of activated carbon as a carbon source, 20 g of calcium oxide powder as a calcium source, and 30 g of potassium humate as a binder were weighed and mixed uniformly. 70 mL of deionized water was added and stirred uniformly. The mixture was shaped using a granulator, air-dried, and placed in a pyrolysis tube. Nitrogen was introduced and heated to 850°C in the pyrolysis tube, where it was maintained at this temperature for 2 hours. The mixture was then naturally cooled to room temperature to obtain a mercury removal agent.

[0046] Comparative Example 4

[0047] 50g of wheat flour was weighed, added with 30mL of hydrochloric acid (pH=2), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed, and pelletized using a pelletizer. After air drying, the mixture was placed in a pyrolysis tube, purged with nitrogen, and heated until the temperature in the tube reached 850°C. This temperature was maintained for 2 hours, and then naturally cooled to room temperature to obtain a mercury removal agent.

[0048] Comparative Example 5

[0049] 50g of wheat flour was weighed, added to 30mL of aqueous ammonia (pH=13), and placed in a hydrothermal autoclave for a hydrothermal reaction at 110°C for 1 hour. 20g of calcium oxide powder was weighed and added to the hydrothermal reaction mixture, further mixed uniformly, and pelletized using a pelletizer. After air drying, the mixture was placed in a pyrolysis tube, purged with nitrogen, and heated until the temperature in the tube reached 850°C, where it was maintained at this temperature for 2 hours. Finally, the mixture was naturally cooled to room temperature to obtain a mercury removal agent.

[0050] The XRD comparison results of the mercury removal agents of Example 1, Comparative Example 1 and Comparative Example 3 are summarized in Figure 2 In the XRD patterns of the mercury removers of Comparative Examples 1 and 3, the main peaks of CaO gradually become sharper, indicating that their CaO crystals are large. In contrast, the CaO crystals of the mercury remover of Example 1 are relatively small. This suggests that starch can promote the dispersion of calcium oxide on the mercury remover.

[0051] Application Examples

[0052] 0.02 g of the prepared mercury removal agent was weighed and placed in 50 mL of a 200 ppm mercury solution at 25°C for 24 hours of adsorption. After adsorption, the filtrate was filtered and the mercury concentration, Ce, in the filtrate was measured using an atomic fluorescence spectrometer. The maximum mercury adsorption per unit mass of the mercury removal agent in the liquid phase was calculated using the formula (200 - Ce) * 50 / 0.02. The mercury removal agents prepared in Examples 1-5 and Comparative Examples 1-3 were used to remove mercury from the mercury solution using the above-described adsorption method. The calculated maximum mercury adsorption per unit mass of the mercury removal agents in the liquid phase is summarized in Table 1.

[0053] The physical properties of the mercury removal agents prepared in Examples 1-6 and Comparative Examples 1-5 are shown in Table 1 below. As shown in Table 1, Example 1 exhibits considerable mechanical strength, a high specific surface area, and CaO content, and exhibits excellent liquid-phase mercuric chloride adsorption performance. In Example 2, industrial calcium-containing waste was selected as the calcium source, and it was found that changing the calcium source did not affect the structure of the mercury removal agent or its mercury adsorption capacity. In Examples 3, 5, and 6, starch was hydrothermally treated with ammonia water, deionized water, and hydrochloric acid solution, respectively. It was found that within the pH range of 3-9, hydrothermal treatment further promoted the dispersion of calcium oxide on the mercury removal agent and increased its mercury adsorption capacity. In Example 4, the volume of ammonia water was reduced, which affects the exposure of hydroxyl groups on the starch surface and, consequently, the dispersion of CaO. As shown in Table 1, the CaO size in Example 4 is larger than that in Example 3, and its mercury adsorption capacity is slightly lower than that in Example 3. The commercial calcium oxide in Comparative Example 1 exhibited lower mercury adsorption than that of Examples 1-4 prepared using the method of this patent. Furthermore, commercial calcium oxide is often in powder form, making it difficult to separate and recover. Furthermore, commercial calcium oxide is very large, resulting in a very low specific surface area. In Comparative Example 2, corn straw was used as the carbon source. While the dispersion of calcium oxide in the mercury remover and the mercury adsorption were similar to those in Example 3, the straw itself was not sticky, resulting in a very poor crush strength, making it difficult to meet the requirements of the working condition test. In Comparative Example 3, commercial activated carbon was used as the carbon source. The CaO in the mercury remover exhibited a size of 79.3 nm, indicating that the activated carbon was unable to effectively disperse the CaO. Despite its high crush strength, the binder required during the preparation process clogged the pore structure of the mercury remover and partially covered the active components, resulting in poor mercury adsorption. Comparative Examples 4 and 5 controlled the pH of the solution during the hydrothermal process. Excessively high or low pH values can lead to excessive starch hydrolysis, thereby affecting the dispersion of CaO and the strength of the mercury removal agent. As shown in Table 1, the CaO size in Comparative Examples 4 and 5 was larger than that in Examples 3 and 6, and their crushing strength and mercury adsorption were also lower than those in Examples 3 and 6.

[0054] Table 1

[0055]

[0056] The CaO content data in Table 1 of the present invention were obtained by measuring the ash content. Specifically, the mercury remover was calcined at 850°C in an air atmosphere to completely burn off the carbon in the mercury remover, leaving only calcium oxide. The CaO content was calculated from the mass difference before and after calcination.

[0057] The CaO size data in Table 1 of the present invention were measured in the following manner: After characterization by X-ray diffraction (XRD), the CaO particle size data was calculated based on the peak position and half-peak width of the corresponding signal peak in the XRD spectrum and the Scherrer formula.

[0058] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. Application of a mercury removal agent in removing mercury from sewage, characterized in that: The preparation method of the mercury removal agent comprises the following steps: mixing starch and a calcium source to obtain a mixture, wherein the mixture also contains water for sticking the starch, stirring the mixture evenly, shaping and granulating the mixture through a molding device, drying the mixture, and then calcining and carbonizing the mixture under an inert atmosphere to obtain the mercury removal agent; the specific surface area of the mercury removal agent is 300-600 m 2 / g, pore volume is 0.20~0.50cm 3 / g; calcium oxide size is 5-30nm.

2. The use according to claim 1, characterized in that The starch is natural starch and / or modified starch, the natural starch is one or more of corn starch, potato starch, cassava starch, and wheat flour, and the modified starch is one or more of cationically modified starch, anionically modified starch, and amphoteric starch.

3. The use according to claim 2, characterized in that The natural starch is wheat flour and / or tapioca starch.

4. The use according to claim 1, wherein The calcium source is one or more of calcium carbonate, acetate, nitrate, metal oxide, hydroxide, gluconate and industrial calcium-containing waste, and the mass ratio of the calcium source to starch is 1-3:

5.

5. The use according to claim 1, characterized in that The starch can be mixed with a calcium source after being subjected to hydrothermal pretreatment. The hydrothermal pretreatment includes the following process: placing the starch in an aqueous solution with a pH of 3-12 for hydrothermal treatment, thereby breaking the starch granules and exposing the internal hydroxyl structure thereof.

6. The use according to claim 5, characterized in that The aqueous solution with a pH of 3-12 is one or more of hydrochloric acid solution, nitric acid solution, acetic acid solution, sulfuric acid solution, sodium hydroxide solution, potassium hydroxide solution, ammonia water, and deionized water; the solid-liquid ratio of starch to the aqueous solution is 5g:1-3mL.

7. The use according to claim 5, characterized in that The temperature of the hydrothermal treatment is 90-120° C., and the treatment time is 0.5-3 hours.

8. The use according to claim 1, wherein The forming equipment is one of an extruder, a granulator or a pelletizer.

9. The use according to claim 1, wherein The specific process of the calcination carbonization treatment is: in a flowing nitrogen, helium or argon atmosphere, the material is heated to 750-900° C. in a pyrolysis furnace, and then calcined at a constant temperature for 1-4 hours.

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