Application of charcoal to adsorption of heavy metal thallium in water

Abstract

The invention belongs to the technical field of water treatment, and discloses an application of biochar to adsorption of heavy metal thallium in water, the biochar is obtained by pyrolysis of camellia oleifera shells, the camellia oleifera shell biochar is added into thallium-containing water with the concentration of 1 microgram / L-100 mg / L, and constant-temperature oscillation adsorption is performed. The camellia oleifera shell charcoal is used as the adsorbent, the source of the camellia oleifera shell charcoal is simple, the camellia oleifera shell charcoal can be used for adsorbing heavy metal thallium in wastewater, especially the effect of adsorbing trace thallium-containing wastewater is excellent, the removal effect can reach the underground water III-class standard, and the camellia oleifera shell charcoal can be recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to an application of biochar in adsorbing heavy metal thallium in water. Background Art

[0002] Thallium (Tl) is a typical highly toxic and rare heavy metal element that is widely present in various natural environments. Thallium plays an important role in different industries such as chemistry, pharmaceuticals, aerospace, and superconducting materials. At the same time, it is inevitable that it leaks into the environment from various sources such as mining, ore processing, and smelting, resulting in increased thallium content 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 to 10 mg.kg -1 , but even if the human body absorbs a lower dose, it may cause acute or chronic poisoning, accompanied by various symptoms such as vomiting, diarrhea, hair loss, and liver and kidney failure. In order to minimize these health risks, my country's drinking water hygiene standards stipulate that the thallium content shall not exceed 0.1 μg / L, and the industrial emission standards stipulate that the thallium content in industrial discharge water shall not exceed 5 μg / L. Some provinces stipulate that the thallium content shall not exceed 2 μg / L. In addition, compared with other toxic heavy metals, thallium is more dispersed and mobile in the environment, which brings more technical obstacles to its effective removal.

[0003] With the development of thallium removal technology by researchers, more and more thallium removal technologies are applied in the field of water treatment. Commonly used treatment methods such as precipitation, oxidation, ion exchange, membrane separation, etc. have certain thallium removal effects, but they generally have the characteristics of high cost, large amount of waste residue, and high energy consumption. The adsorption method has the advantages of rich potential sources, low cost, simple operation, good adsorption effect, wide application, low secondary pollution, and potential biodegradable biological adsorption materials, and has great application prospects in the field of water treatment.

[0004] The removal of Tl from wastewater by adsorption has been a hot topic in recent years. The main adsorption materials reported to remove Tl include titanium-based, iron-based, aluminum-based, manganese-based, zinc-based, activated carbon-based, and biochar-based. The regeneration and recycling performance of metal-based adsorption materials such as titanium, iron, and aluminum is generally poor. Activated carbon is a widely used heavy metal adsorbent with a well-developed pore structure, large specific surface area, high adsorption efficiency, environmental friendliness, and simple operation. However, activated carbon adsorption usually has problems such as low selectivity and high operating costs. Biochar materials made from agricultural or forestry by-products have attracted attention due to their waste resource properties and have also been used for heavy metal pollution control. Various biomass raw materials such as eucalyptus, grapefruit peel, betel nut leaves, crayfish, watermelon peel, etc. have been prepared into biochar-based functional materials.

[0005] Camellia oleifera shell is one of the high-quality sources for preparing biochar. Camellia oleifera shell is a byproduct of tea oil processing from camellia oleifera fruit, generally accounting for 50-60% of the fresh weight of the entire tea fruit. Most of the camellia oleifera shell waste generated by processing is discarded or burned, except for a small amount of fertilizer and energy, which not only causes serious waste of resources but also pollutes the environment. Camellia oleifera shell, which is mainly composed of cellulose, hemicellulose and lignin, is a high-quality raw material for preparing biochar, and there are few reports on the application of camellia oleifera shell-based biochar in the adsorption of heavy metal thallium in water. Summary of the invention

[0006] The purpose of the present invention is to provide an application of biochar to adsorb heavy metal thallium in water, aiming to quickly and effectively solve the problem of excessive thallium ions in wastewater. The present invention uses camellia oleifera shell biochar as an adsorbent, which has a simple source and can be used to adsorb heavy metal thallium in wastewater, especially in adsorbing trace amounts of thallium-containing wastewater. The removal effect can reach the groundwater Class III standard and can be recycled and reused.

[0007] The technical solution of the present invention is as follows: The invention provides a biochar, which is camellia oleifera shell biochar, obtained by pyrolysis of camellia oleifera shell as a raw material, and comprises a solid powder containing a heterogeneous structure and active functional groups on its surface.

[0008] The present invention also provides a method for preparing the camellia oleifera shell biochar, comprising the following steps: The camellia oleifera shell raw material is dried, ground into powder and sieved, and then placed in a muffle furnace for pyrolysis. After the pyrolysis is completed, it is naturally cooled to room temperature, and then acid-washed, water-washed, and dried in sequence to obtain the camellia oleifera shell biochar.

[0009] Preferably, the pyrolysis temperature is 350-600°C, the heating rate is 3-30°C / min, and the pyrolysis time is 4-8 h. More preferably, the pyrolysis temperature is 400°C, the heating rate is 5°C / min, and the pyrolysis time is 6 h.

[0010] Preferably, the pyrolysis is carried out in an oxygen-deficient environment.

[0011] Preferably, the pickling is performed with a hydrochloric acid aqueous solution for 5 to 15 hours, and more preferably, the pickling is performed with a 1 M hydrochloric acid aqueous solution for 12 hours.

[0012] Preferably, the method for preparing the camellia oleifera shell biochar comprises the following steps: (1) Clean the camellia oleifera shell raw material, dry it in an oven at 100-120°C, grind it into powder, and pass it through a 60-140 mesh sieve to obtain camellia oleifera shell powder.

[0013] (2) placing the camellia oleifera shell powder in a crucible and compacting it, then transferring it to a muffle furnace and pyrolyzing it at a temperature of 350-600°C at a heating rate of 3-30°C / min, keeping it warm for 4-8 hours in an oxygen-deficient environment, and then naturally cooling it to room temperature to obtain biochar powder; (3) The obtained biochar powder is acid-washed with hydrochloric acid solution for 5 to 15 h to remove impurities, then washed with water until neutral, and dried at 70 to 120 °C for storage.

[0014] The present invention also provides an application of biochar to adsorb heavy metal thallium in water, and the application method comprises the following steps: adding camellia oleifera shell biochar to a thallium-containing water body with a (thallium) concentration of 1 μg / L to 100 mg / L, and adsorbing under constant temperature oscillation.

[0015] Preferably, the thallium-containing water is a water body containing trace amounts of thallium, and the specific thallium concentration is 1 to 100 μg / L, and more preferably the (thallium) concentration of the thallium-containing water body is 10 to 100 μg / L.

[0016] Preferably, the dosage of the camellia oleifera shell biochar is 0.2-0.8 g / L, more preferably 0.4-0.6 g / L.

[0017] Preferably, the initial pH of the thallium-containing water is 5 to 9, the adsorption temperature is 293 to 303 K, and the adsorption time is 1 to 120 min. More preferably, the initial pH of the thallium-containing water is 6 to 8, the adsorption temperature is 298 K, and the adsorption time is 2 to 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.

[0018] Preferably, the oscillation speed is 100-200 r / min, preferably 170 r / min.

[0019] Among them, the camellia oleifera shell biochar can directly adsorb thallium. After the adsorption reaction is completed, the corresponding camellia oleifera shell biochar can be obtained by filtering the reaction solution, desorbing it with 0.1 M dilute nitric acid, washing it with water, and drying it for reuse.

[0020] The beneficial effects of the present invention are: (1) The raw materials required for preparing the camellia oleifera shell biochar of the present invention are commonly used, the preparation is simple, the carbon yield is high, and no other chemical reagents need to be added. The camellia oleifera shell is directly selected as the raw material and pyrolyzed to obtain the camellia oleifera shell biochar; (2) The oil tea shell biochar of the present invention has stable properties, is simple, convenient and efficient to use, and the materials for preparing the biochar are cheap and readily available; (3) The oil-tea camellia shell biochar of the present invention has high adsorption efficiency and is particularly suitable for adsorbing trace amounts of thallium ions in water, and has a large adsorption capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the camellia oleifera shell biochar obtained in Example 1 of the present invention; Figure 2 The SEM image and EDS spectrum of the camellia shell biochar after adsorption of thallium in Example 2 of the present invention ( Figure 2 middle: Figure 2 a is the SEM image, Figure 2 b is the EDS spectrum of Tl element, Figure 2 c is the EDS spectrum of the C element; Figure 2 d is the EDS spectrum of O element); Figure 3 FT-IR and XPS spectra of the camellia shell biochar before and after thallium adsorption in Examples 1 and 2 of the present invention ( Figure 3 middle: Figure 3 a is the FT-IR spectrum of the oil-tea camellia shell biochar before and after the adsorption of thallium. Figure 3 b is the XPS total spectrum of the tea shell biochar before and after the adsorption of thallium. Figure 3 c is the Tl 4f fine spectrum of the camellia shell biochar after adsorption of thallium; Figure 3 d is the O1s fine spectrum of the camellia shell biochar before and after the adsorption of thallium); Figure 4 The effect of different adsorption times on the adsorption of thallium by camellia oleifera shell biochar in Example 3 of the present invention; Figure 5 The effect of different addition amounts of camellia oleifera shell biochar on thallium adsorption in Example 4 of the present invention; Figure 6 The effect of different initial pH values ​​on the adsorption of thallium by camellia oleifera shell biochar in Example 5 of the present invention; Figure 7 The effect of different initial thallium concentrations (trace amounts) on the equilibrium adsorption amount of thallium by camellia oleifera shell biochar in Example 6 of the present invention; 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; Fig. 9 Based on Figure 7 The isothermal adsorption curve of Camellia oleifera shell biochar at 298 K (Q e : equilibrium adsorption capacity; C e : equilibrium concentration); Fig.10 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; Fig.11 This is the effect of different types of biochar on the adsorption of thallium in Example 7 of the present invention. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Unless otherwise specified, the reagents involved in the embodiments of the present invention are all commercially available products and can be purchased through commercial channels.

[0024] Example 1 Preparation of Camellia oleifera shell biochar (1) Clean the discarded camellia oleifera 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 oleifera shell powder.

[0025] (2) The camellia oleifera shell powder was placed in a crucible and compacted. It was then transferred to a muffle furnace and pyrolyzed at a heating rate of 5 °C / min to 400 °C. The mixture was kept in an oxygen-deficient environment for 6 h and then naturally cooled to room temperature to obtain biochar powder.

[0026] (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 at 80 °C for storage.

[0027] The SEM image of the camellia oleifera shell biochar prepared in this example is as follows: Figure 1 ,It can be observed that the surface of biochar is relatively rough and there are many irregularly shaped pore structures, which makes the material have higher adsorption performance.

[0028] Example 2 Application of Camellia oleifera shell biochar in adsorbing heavy metal thallium A solution with a thallium ion concentration of 10 μg / L was added to a 50 ml centrifuge tube, and the camellia oleifera shell biochar prepared in Example 1 was added at a concentration of 0.6 g / L. The solution was shaken in an oscillation box at pH 8, temperature 298 K, and 170 r / min for 2 h. After the reaction was completed, it was immediately filtered using a 0.22 μm filter membrane, and the filtrate was collected to detect the thallium ion content.

[0029] After the adsorption reaction is completed, the corresponding Camellia oleifera shell biochar can be obtained by filtering the reaction solution, desorbing it with 0.1 M dilute nitric acid, washing it with water, and drying it for reuse.

[0030] 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 aggregation of thallium ions was observed in b, indicating that thallium was evenly distributed on the surface of Camellia oleifera shell biochar.

[0031] 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 , the intensities of the absorption peaks of functional groups such as hydroxyl groups, aromatic rings CH and C=C, CH3 and C=O in the FT-IR spectrum all change ( Figure 3 a). The peak of thallium was detected in the XPS spectrum ( Figure 3 c), Figure 3 O 1s peaks of d showed oxygen-containing functional groups such as OH and OC=O, and the area ratio of each peak also changed before and after adsorption. The above results show that thallium ions were successfully adsorbed on the surface of biochar, and chemical adsorption occurred between thallium ions and the functional groups on the surface of biochar.

[0032] Example 3 Study on the effect of different adsorption times on the adsorption of thallium by camellia shell biochar 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, the rotation speed was 170 r / min, and the oscillation was performed for 0.5, 1, 2, 3, 5, 10, 15, 20, 40, and 60 min, respectively. The thallium ion concentration in the solution at different adsorption times was measured.

[0033] Results Figure 4 , 90% was adsorbed at 2 min, and 96% was adsorbed at 20 min, reaching adsorption equilibrium. The early adsorption was fast, which may be because the higher the initial thallium concentration, the stronger the driving force for its transfer from solution to biochar, resulting in more collisions between thallium ions and active sites on biochar, making the adsorption faster. The adsorption slowed down after 2 min, which may be because the thallium ion concentration became lower and the thallium ions could not quickly contact the adsorption sites.

[0034] Example 4 Study on the effect of different tea oil shell biochar dosage on thallium adsorption Camellia oleifera shell biochar with different dosages (0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L) was added into 10 μg / L (thallium concentration) thallium-containing water at pH 8 at 298 K, and samples were taken after oscillation in an oscillating box at 170 r / min for 60 min.

[0035] Results Figure 5 With the increase of the dosage of Camellia oleifera shell biochar, the adsorption efficiency is higher. The removal rate of thallium at the dosage of 0.2 g / L~0.8 g / L reaches more than 92%, and the concentration of residual thallium in the water is less than 1μg / L, which meets the industrial emission standard. When the dosage of Camellia oleifera shell biochar is ≥0.6 g / L, the concentration of residual thallium in the water is ≤0.1μg / L.

[0036] Example 5 Study on the effect of different initial pH of thallium-containing water on the adsorption of thallium by camellia shell biochar At 298 K, 0.4 g / L of camellia oleifera shell biochar was added to thallium-containing water with different initial pH (pH4, pH5, pH6, pH7, pH8, pH9) and 10 μg / L (thallium concentration), and samples were taken after oscillating in an oscillating box at 170 r / min for 60 min.

[0037] Results Figure 6 At pH 4, the removal rate of thallium was 41.36%; in 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 less than 1 μg / L.

[0038] Example 6 Study on the effect of different initial thallium concentrations on the adsorption of thallium by camellia oleifera shell biochar 1. Adsorption effect of water containing trace amounts of thallium 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 respectively. 12 mg of camellia oleifera shell biochar was weighed and added to 30 mL of the above-prepared solutions. The solutions were shaken in an oscillation box at pH 8, 298 K and 170 r / min for 60 min and then samples were taken.

[0039] Results Figure 7 , Figure 8 ,Depend on Figure 7 It can be seen that with the increase of the initial concentration of thallium ions, the adsorption of thallium ions by camellia shell biochar increased, but the growth rate became smaller and smaller. As the active sites were occupied, the adsorption material gradually tended to saturation. When the initial concentration of thallium ions was 70 mg / L, the adsorption capacity of camellia shell biochar was 22.89 mg / g. Figure 8 It can be seen that with the increase of initial thallium concentration, the removal rate shows a downward trend. When the initial concentration of thallium ions is 100 mg / L, the removal rate of thallium ions by camellia shell biochar is as low as 9.25%.

[0040] right Figure 7 The adsorption data were isothermally fitted and the isotherm adsorption curve was obtained. Fig. 9 As shown in the figure, the adsorption process of thallium by biochar conforms to the Ferundlich isotherm adsorption model, indicating that the adsorption of thallium by camellia shell biochar is a heterogeneous process.

[0041] 2. Adsorption effect of water containing trace amounts of thallium 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 respectively, and 12 mg of camellia oleifera shell biochar was weighed and added to 30 mL of the above prepared solutions. The samples were then oscillated in an oscillating box at pH 8, 298 K and 170 r / min for 60 min.

[0042] Results Fig.10 , with the increase of initial thallium concentration, the removal rate gradually increased, and the remaining thallium ion concentration was <1.2 μg / L, reaching the industrial water thallium discharge standard, indicating that the biochar is suitable for removing trace thallium in water.

[0043] Example 7 Study on the effect of different types of biochar on the adsorption of thallium Pine sawdust, broad-leaved forest, and coconut shell-based biochar purchased from the market were compared with homemade camellia shell-based biochar. 12 mg of different biochars were 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 samples were taken after oscillation in an oscillating box for 60 min.

[0044] Results Fig.11 The thallium removal rate of pine sawdust-based biochar was 90.58%, the thallium removal rate of broad-leaved forest-based biochar was 79.64%, and the thallium removal rate 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 that of the above three biochars.

[0045] The method for removing thallium from water bodies of the present invention is simple to operate. Camellia oleifera shell biochar is directly added to the thallium-containing water body, which can simultaneously adsorb monovalent thallium and trivalent thallium without adding other reagents. The camellia oleifera shell biochar of the present invention only requires a dosage of 0.2 to 0.8 g / L for complex water bodies containing 1 to 100 μg / L of thallium, and reaches industrial emission standards within two hours. The camellia oleifera shell biochar can be quickly and efficiently processed to industrial emission standards in neutral and alkaline thallium-containing water bodies. The excellent qualities of high performance, low cost, pollution-free, and easy operation make the thallium removal material and method of the present invention have great practical application value.

[0046] Finally, it should be noted that the above is only 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 aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An application of biochar to adsorb heavy metal thallium in water, characterized by: The biochar is camellia oleifera shell biochar, and the application method comprises the following steps: Add camellia oleifera shell biochar to thallium-containing water at a concentration of 1 μg / L to 100 mg / L, and perform adsorption by constant temperature oscillation.

2. The use according to claim 1, characterized in that: The concentration of the thallium-containing water body is 1-100 μg / L.

3. The use according to claim 1, characterized in that: The dosage of the camellia oleifera shell biochar is 0.2-0.8 g / L.

4. The use 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.

5. The use according to claim 1, characterized in that: The oscillation speed is 100-200 r / min.

6. The use according to claim 1, characterized in that: The method for preparing camellia oleifera shell biochar comprises the following steps: The camellia oleifera shell raw material is dried, ground into powder and sieved, and then placed in a muffle furnace for pyrolysis. After the pyrolysis is completed, it is naturally cooled to room temperature, and then acid-washed, water-washed, and dried in sequence to obtain the camellia oleifera shell biochar.

7. The use according to claim 6, characterized in that: The pyrolysis temperature is 350-600 °C, the heating rate is 3-30 °C / min, and the pyrolysis time is 4-8 h.

8. The use according to claim 6, characterized in that: The pyrolysis is performed in an oxygen-deficient environment.

9. The use according to claim 6, characterized in that: The pickling is carried out using a hydrochloric acid aqueous solution, and the pickling time is 5 to 15 hours.

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