Application of biochar in adsorbing heavy metal thallium in water

Abstract

This invention belongs to the field of water treatment technology and discloses an application of biochar for adsorbing the heavy metal thallium in water. The biochar is obtained from the pyrolysis of camellia oleifera shells. Camellia oleifera shell biochar is added to water containing thallium at a concentration of 1 μg / L to 100 mg / L, and adsorption is achieved by constant-temperature shaking. This invention uses camellia oleifera shell biochar as an adsorbent, which is readily available and can be used to adsorb the heavy metal thallium in wastewater, especially showing excellent results in adsorbing trace amounts of thallium in wastewater. The removal effect can reach the Class III standard for groundwater, and it can be repeatedly recycled and reused.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and in particular relates to the application of biochar in adsorbing the heavy metal thallium in water. Background Technology

[0002] Thallium (Tl) is a typical highly toxic, rare, and dispersed heavy metal element, widely present in various natural environments. Thallium plays important roles in various industries such as chemicals, pharmaceuticals, aerospace, and superconducting materials. However, it inevitably leaks into the environment from various sources, including mining, ore processing, and smelting, leading to elevated thallium levels in natural water bodies. Thallium is more toxic to mammals than common heavy metals such as mercury, cadmium, lead, and zinc. The lethal dose of thallium for adults is only 8–10 mg / kg. -1 However, even lower doses absorbed by the human body can cause acute or chronic poisoning, accompanied by various symptoms such as vomiting, diarrhea, hair loss, and liver and kidney failure. To minimize these health risks, my country's drinking water standards stipulate that thallium content should not exceed 0.1 μg / L, and industrial discharge standards stipulate that thallium content in industrial wastewater should not exceed 5 μg / L, with some provinces specifying a limit of 2 μg / L. Furthermore, compared to other toxic heavy metals, thallium is more dispersed and mobile in the environment, posing greater technical challenges to its effective removal.

[0003] With the development of thallium removal technologies by researchers, more and more of these technologies are being applied in the field of water treatment. Commonly used methods such as precipitation, oxidation, ion exchange, and membrane separation have certain thallium removal effects, but they are generally characterized by high cost, large amounts of waste residue, and high energy consumption. Adsorption, on the other hand, has advantages such as abundant potential sources, low cost, simple operation, good adsorption effect, wide application, low secondary pollution, and the availability of potentially biodegradable biosorbent materials, making it a promising technology for water treatment.

[0004] Adsorption for the removal of hydrogen sulfide (Tl) from wastewater has become a research hotspot in recent years. Currently, the main reported adsorbents capable of removing Tl include titanium-based, iron-based, aluminum-based, manganese-based, zinc-based, activated carbon-based, and biochar-based materials. Titanium, iron, and aluminum-based adsorbents generally have poor regeneration and recycling performance. Activated carbon is a widely used heavy metal adsorbent with a well-developed pore structure, offering advantages such as large specific surface area, high adsorption efficiency, environmental friendliness, and ease of operation. However, activated carbon adsorption typically suffers from low selectivity and high operating costs. Biochar materials made from agricultural or forestry byproducts have attracted attention due to their waste resource utilization properties and are also used for heavy metal pollution control. Various biomass raw materials, such as eucalyptus wood, grapefruit peel, areca leaves, crayfish, and watermelon rind, have been used to prepare biochar-based functional materials.

[0005] Camellia oleifera shells are a high-quality source for biochar production. Camellia oleifera shells are a byproduct of processing camellia fruit into camellia oil, generally accounting for 50-60% of the total fresh weight of the fruit. Aside from a small amount used for fertilizer and energy, most of the waste from processing camellia oleifera shells is discarded or burned, resulting in serious resource waste and environmental pollution. Camellia oleifera shells, with cellulose, hemicellulose, and lignin as their main components, are an excellent raw material for biochar production. However, the application of camellia oleifera shell-based biochar in adsorbing heavy metal thallium from water has been rarely reported. Summary of the Invention

[0006] The purpose of this invention is to provide an application of biochar for adsorbing the heavy metal thallium in water, aiming to quickly and effectively solve the problem of excessive thallium ions in wastewater. This invention uses camellia oleifera shell biochar as an adsorbent, which is readily available and can be used to adsorb the heavy metal thallium in wastewater, especially showing excellent results in adsorbing trace amounts of thallium-containing wastewater. The removal effect can reach the Class III standard for groundwater, and it can be repeatedly recycled and reused.

[0007] The technical solution of the present invention is as follows:

[0008] This invention provides a biochar, wherein the biochar is camellia oleifera shell biochar, which is obtained by pyrolysis of camellia oleifera shell as raw material. The camellia oleifera shell biochar comprises a solid powder with a heterogeneous structure and active functional groups on its surface.

[0009] The present invention also provides a method for preparing the Camellia oleifera shell biochar, comprising the following steps:

[0010] After drying the camellia oleifera shell raw material, it is ground into powder and sieved. Then it is placed in a muffle furnace for pyrolysis. After pyrolysis, it is naturally cooled to room temperature and then subjected to acid washing, water washing, and drying to obtain the camellia oleifera shell biochar.

[0011] Preferably, the pyrolysis temperature is 350–600℃, the heating rate is 3–30℃ / min, and the pyrolysis time is 4–8 h. More preferably, the pyrolysis temperature is 400℃, the heating rate is 5℃ / min, and the pyrolysis time is 6 h.

[0012] Preferably, the pyrolysis is carried out in an oxygen-deficient environment.

[0013] Preferably, the pickling is performed using an aqueous hydrochloric acid solution for 5–15 hours. More preferably, a 1 M aqueous hydrochloric acid solution is used for pickling for 12 hours.

[0014] Preferably, the preparation method of the camellia oleifera shell biochar specifically includes the following steps:

[0015] (1) Clean the raw material of camellia shell, dry it in an oven at 100-120℃, then grind it into powder and pass it through a 60-140 mesh sieve to obtain camellia shell powder.

[0016] (2) Place the camellia shell powder in a crucible and compact it, then transfer it to a muffle furnace and heat it to 350-600℃ at a heating rate of 3-30℃ / min. Keep it in an oxygen-deficient environment for 4-8 hours, and then cool it naturally to room temperature to obtain biochar powder.

[0017] (3) The obtained biochar powder is acid-washed with hydrochloric acid solution for 5-15 h to remove impurities, then washed with water until neutral, and dried and stored at 70-120℃.

[0018] This invention also provides an application of biochar for adsorbing the heavy metal thallium in water. The application method includes the following steps: adding camellia oleifera shell biochar to thallium-containing water with a thallium concentration of 1 μg / L to 100 mg / L, and adsorbing by constant temperature shaking.

[0019] Preferably, the thallium-containing water body is a thallium-containing water body with trace amounts of thallium, specifically with a thallium concentration of 1 to 100 μg / L, and more preferably with a thallium concentration of 10 to 100 μg / L.

[0020] Preferably, the dosage of the camellia oleifera shell biochar is 0.2–0.8 g / L, and more preferably 0.4–0.6 g / L.

[0021] Preferably, the initial pH of the thallium-containing water is 5–9, the adsorption temperature is 293–303 K, and the adsorption time is 1–120 min. More preferably, the initial pH of the thallium-containing water is 6–8, the adsorption temperature is 298 K, and the adsorption time is 2–60 min. Even more preferably, the initial pH of the thallium-containing water is 8, the adsorption temperature is 298 K, and the adsorption time is 20 min.

[0022] Preferably, the rotational speed of the oscillation is 100-200 r / min, and more preferably 170 r / min.

[0023] Among them, camellia shell biochar can directly adsorb thallium. After the adsorption reaction is completed, the reaction solution can be filtered to obtain the corresponding camellia shell biochar. It can be desorbed with 0.1 M dilute nitric acid, washed with water and dried for reuse.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) The raw materials required for the preparation of Camellia oleifera shell biochar of the present invention are commonly used and simple to prepare, with a high carbon yield. No other chemical reagents need to be added. Camellia oleifera shell is directly selected as the raw material and pyrolyzed to obtain Camellia oleifera shell biochar.

[0026] (2) The biochar from camellia shells of the present invention is stable, simple, convenient and efficient to use, and the materials used to prepare the biochar are inexpensive and readily available;

[0027] (3) The biochar from camellia shells of the present invention has high adsorption efficiency, especially suitable for the adsorption of trace thallium ions in water, and the adsorption capacity is large. Attached Figure Description

[0028] Figure 1 This is a SEM image of the Camellia oleifera shell biochar obtained in Example 1 of the present invention;

[0029] Figure 2 The images shown are SEM images and EDS spectra of thallium adsorbed on Camellia oleifera shell biochar in Example 2 of this invention. Figure 2 middle: Figure 2 a is the SEM image. Figure 2 b is the EDS energy spectrum of the Tl element. Figure 2 c is the EDS energy spectrum of element C; Figure 2 d is the EDS energy spectrum of element O).

[0030] Figure 3 The images show the FT-IR and XPS spectra of Camellia oleifera shell biochar before and after adsorption of thallium in Examples 1 and 2 of this invention. Figure 3 middle: Figure 3 a shows the FT-IR spectra of camellia oleifera shell biochar before and after adsorption of thallium. Figure 3 b shows the total XPS spectra before and after thallium adsorption by camellia oleifera shell biochar. Figure 3 c is the fine Tl 4f spectrum after thallium adsorption by Camellia oleifera shell biochar; Figure 3 (d is the fine O1s spectrum before and after thallium adsorption by Camellia oleifera shell biochar).

[0031] Figure 4 This illustrates the effect of different adsorption times on the adsorption of thallium by Camellia oleifera shell biochar in Example 3 of the present invention.

[0032] Figure 5 This illustrates the effect of different amounts of Camellia oleifera shell biochar added on thallium adsorption in Example 4 of the present invention.

[0033] Figure 6 This illustrates the effect of different initial pH values ​​on the adsorption of thallium by Camellia oleifera shell biochar in Example 5 of the present invention.

[0034] Figure 7 This invention illustrates the effect of different initial thallium concentrations (trace amounts) on the equilibrium adsorption capacity of thallium on Camellia oleifera shell biochar in Example 6 of this invention.

[0035] Figure 8 The effect of different initial thallium concentrations (trace amounts) on the removal rate of thallium adsorbed by Camellia oleifera shell biochar in Example 6 of the present invention;

[0036] Figure 9 According to Figure 7 The isothermal adsorption curve (Q) of Camellia oleifera shell biochar at 298 K was plotted. e : Equilibrium adsorption capacity; Ce (equilibrium concentration);

[0037] Figure 10 This illustrates the effect of different initial thallium concentrations (trace amounts) on the adsorption of thallium by Camellia oleifera shell biochar in Example 6 of the present invention.

[0038] Figure 11 This illustrates the effect of different types of biochar on thallium adsorption in Example 7 of the present invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0041] Example 1: Preparation of Camellia oleifera shell biochar

[0042] (1) Clean the waste camellia shells, dry them in an oven at 105°C overnight, take them out of the oven and grind them into powder, and pass them through a 100-mesh sieve to obtain camellia shell powder.

[0043] (2) Place the camellia shell powder in a crucible and compact it. Then transfer it to a muffle furnace and heat it to 400℃ at a heating rate of 5℃ / min. Keep it in an oxygen-deficient environment for 6 h and then cool it naturally to room temperature to obtain biochar powder.

[0044] (3) The obtained biochar powder was acid-washed with 1 M hydrochloric acid solution for 12 h to remove impurities, then washed with water until neutral, and dried and stored at 80℃.

[0045] The SEM image of the camellia oleifera shell biochar prepared in this embodiment is as follows: Figure 1 It can be observed that the surface of biochar is relatively rough and has many irregularly shaped pore structures, which gives the material high adsorption performance.

[0046] Example 2: Application of Camellia oleifera shell biochar in adsorbing heavy metal thallium

[0047] A solution with a thallium ion concentration of 10 μg / L was added to a 50 mL centrifuge tube, and Camellia oleifera shell biochar prepared in Example 1 was added at a concentration of 0.6 g / L. The mixture was shaken for 2 h in a shaker at pH 8, temperature 298 K, and 170 r / min. After the reaction was completed, the mixture was immediately filtered through a 0.22 μm filter membrane, and the filtrate was collected to detect the thallium ion content.

[0048] After the adsorption reaction is complete, the reaction solution can be filtered to obtain the corresponding camellia shell biochar. It can be desorbed with 0.1 M dilute nitric acid, washed with water and dried for reuse.

[0049] SEM image of Camellia oleifera shell biochar after adsorption of thallium ions ( Figure 2 a) and EDS spectrum ( Figure 2 (b~2d) See Figure 2 , Figure 2 No thallium ion aggregation was observed in b, indicating that thallium is uniformly distributed on the surface of Camellia oleifera biochar.

[0050] FT-IR spectra of Camellia oleifera shell biochar before and after thallium ion adsorption ( Figure 3 a) and XPS spectra ( Figure 3 (b~3d) See Figure 3 In the FT-IR spectrum, the intensity of absorption peaks for functional groups such as hydroxyl groups, CH and C=C, CH3 and C=O of aromatic rings all change. Figure 3 a). A thallium peak was detected in the XPS spectrum ( Figure 3 c) Figure 3 The 1s fraction of the O ion concentration revealed oxygen-containing functional groups such as OH and OC=O, and the area ratio of each peak changed before and after adsorption. These results indicate that thallium ions were successfully adsorbed on the biochar surface, and that thallium ions underwent chemisorption with the functional groups on the biochar surface.

[0051] Example 3: Study on the effect of different adsorption times on the adsorption of thallium by Camellia oleifera shell biochar.

[0052] 12 mg of the Camellia oleifera shell biochar prepared in Example 1 was added to 30 mL of a solution with a thallium ion concentration of 10 μg / L. The temperature was 298 K, the pH was adjusted to 8, and the rotation speed was 170 r / min. The solution was shaken for 0.5, 1, 2, 3, 5, 10, 15, 20, 40 and 60 min respectively, and the thallium ion concentration in the solution was measured at different adsorption times.

[0053] See results Figure 4 At 2 minutes, 90% of the thallium was adsorbed, and at 20 minutes, 96% was adsorbed, reaching adsorption equilibrium. The rapid adsorption in the early stages is likely due to a higher initial thallium concentration, which strengthens the driving force for thallium transfer from the solution to the biochar, leading to more collisions between thallium ions and active sites on the biochar, thus accelerating adsorption. The slower adsorption after 2 minutes is likely due to a lower thallium ion concentration, making it more difficult for thallium ions to quickly reach the adsorption sites.

[0054] Example 4: Study on the effect of different amounts of Camellia oleifera shell biochar on thallium adsorption.

[0055] Different dosages (0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L) of Camellia oleifera shell biochar were added to thallium-containing water at 10 μg / L (thallium concentration) and pH 8 at 298 K. The mixture was shaken in a shaker at 170 r / min for 60 min before sampling.

[0056] See results Figure 5 The adsorption efficiency increases with the increase of the amount of Camellia oleifera shell biochar added. The removal rate of thallium reaches over 92% with an addition of 0.2 g / L to 0.8 g / L, and the concentration of residual thallium in the water is <1 μg / L, which meets the industrial emission standards. When the amount of Camellia oleifera shell biochar added is ≥0.6 g / L, the concentration of residual thallium in the water is ≤0.1 μg / L.

[0057] Example 5: Study on the effect of different initial pH values ​​of thallium-containing water on the adsorption of thallium by Camellia oleifera shell biochar.

[0058] Camellia oleifera shell biochar at a dosage of 0.4 g / L was added to thallium-containing water bodies with different initial pH (pH4, pH5, pH6, pH7, pH8, pH9) and thallium concentration of 10 μg / L at 298 K. The samples were taken after shaking in a shaker at 170 r / min for 60 min.

[0059] See results Figure 6 At pH 4, the removal rate of thallium was 41.36%; within the pH range of 5 to 9, the removal rate of thallium was higher than 94%, and the concentration of residual thallium in the water was <1 μg / L.

[0060] Example 6: Study on the effect of different initial thallium concentrations on the adsorption of thallium by Camellia oleifera shell biochar.

[0061] 1. Adsorption effect of water containing trace amounts of thallium

[0062] Thallium-containing solutions of 1 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, and 100 mg / L were prepared. 12 mg of Camellia oleifera shell biochar was weighed and added to 30 mL of each of the prepared solutions. The solutions were shaken in a shaker at pH 8, 298 K, and 170 r / min for 60 min before sampling.

[0063] See results Figure 7 , Figure 8 ,Depend on Figure 7It can be seen that with the increase of the initial thallium ion concentration, the adsorption capacity of Camellia oleifera shell biochar for thallium ions increases, but the increase rate becomes smaller and smaller, as the active sites are occupied and the adsorbent material gradually approaches saturation. When the initial thallium ion concentration is 70 mg / L, the adsorption capacity of Camellia oleifera shell biochar is 22.89 mg / g. Figure 8 It can be seen that the removal rate decreases with the increase of the initial thallium concentration. When the initial thallium ion concentration is 100 mg / L, the removal rate of thallium ions by Camellia oleifera shell biochar is as low as 9.25%.

[0064] right Figure 7 The adsorption data were subjected to isothermal fitting to obtain the isothermal adsorption curves shown below. Figure 9 As shown, the adsorption process of thallium by biochar conforms to the Ferundlich isothermal adsorption model, indicating that the adsorption of thallium by Camellia oleifera shell biochar is a heterogeneous process.

[0065] 2. Adsorption effect of water containing trace amounts of thallium

[0066] Thallium solutions of 1 μg / L, 2 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, and 100 μg / L were prepared. 12 mg of Camellia oleifera shell biochar was weighed and added to 30 mL of each of the prepared solutions. The solutions were shaken in a shaker at pH 8, 298 K, and 170 r / min for 60 min before sampling.

[0067] See results Figure 10 As the initial thallium concentration increased, the removal rate gradually increased, and the remaining thallium ion concentration was <1.2 μg / L, which met the industrial water thallium discharge standard, indicating that the biochar is suitable for removing trace thallium from water bodies.

[0068] Example 7: Study on the effect of different types of biochar on thallium adsorption

[0069] Pine sawdust, broadleaf forest biochar, coconut shell biochar purchased from the market, and homemade camellia shell biochar were compared. 12 mg of each biochar was added to 30 mL of a solution with a thallium ion concentration of 10 μg / L. The temperature was 298 K, the pH was adjusted to 8, the rotation speed was 170 r / min, and the solution was shaken in a shaker for 60 min before sampling.

[0070] See results Figure 11 The thallium removal rate of pine sawdust-based biochar was 90.58%, that of broadleaf forest-based biochar was 79.64%, and that of coconut shell-based biochar was 32.88%. It can be seen that the thallium removal rate of camellia shell-based biochar is better than the above three types of biochar.

[0071] The method for removing thallium from water according to this invention is simple to operate. Camellia husk biochar is directly added to thallium-containing water, simultaneously adsorbing both monovalent and trivalent thallium without the need for additional reagents. For complex thallium-containing water bodies with concentrations of 1–100 μg / L, the Camellia husk biochar of this invention requires only a dosage of 0.2–0.8 g / L, achieving industrial discharge standards within two hours. This Camellia husk biochar can rapidly and efficiently treat thallium-containing water bodies in neutral and slightly alkaline conditions to meet industrial discharge standards. Its high performance, low cost, pollution-free operation, and ease of operation make the thallium removal material and method of this invention highly valuable for practical applications.

[0072] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is 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. An application of biochar for adsorbing the heavy metal thallium in water, characterized in that: The biochar is camellia oleifera shell biochar, and the application method includes the following steps: To adsorb thallium-containing water at a concentration of 1–100 μg / L, add 0.2–0.8 g / L of Camellia oleifera shell biochar and allow it to oscillate at a constant temperature.

2. The application according to claim 1, characterized in that: The initial pH of the thallium-containing water body is 5–9, the adsorption temperature is 293–303 K, and the adsorption time is 1–120 min.

3. The application according to claim 1, characterized in that: The rotational speed of the oscillation is 100-200 r / min.

4. The application according to claim 1, characterized in that: The preparation method of the camellia oleifera shell biochar includes the following steps: After drying the camellia oleifera shell raw material, it is ground into powder and sieved. Then it is placed in a muffle furnace for pyrolysis. After pyrolysis, it is naturally cooled to room temperature and then subjected to acid washing, water washing, and drying to obtain the camellia oleifera shell biochar.

5. The application according to claim 4, characterized in that: The pyrolysis temperature is 350–600℃, the heating rate is 3–30℃ / min, and the pyrolysis time is 4–8h.

6. The application according to claim 4, characterized in that: The pyrolysis is carried out in an oxygen-deficient environment.

7. The application according to claim 4, characterized in that: The pickling process uses hydrochloric acid aqueous solution and the pickling time is 5 to 15 hours.

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