A method for treating thallium-containing wastewater by piezoelectric enhanced heterogeneous Fenton oxidation-adsorption

Abstract

The present invention discloses a method for piezoelectric enhanced heterogeneous Fenton oxidation-adsorption treatment of thallium-containing wastewater, which comprises the following steps: 1) Prepare the catalyst BiFeO3; 2) Put the catalyst BiFeO3 into the thallium-containing wastewater to be treated, add hydrogen peroxide, and react for more than 1 h under stirring conditions to complete the oxidation and stabilization of Tl(I). Using nano-BiFeO3 as the catalyst, the piezoelectric potential of BiFeO3 accelerates the interfacial charge migration of the catalyst in the Fenton reaction process, improves the Fenton oxidation rate, so it has high catalytic performance and has an outstanding effect on the removal of Tl(I) in water bodies; The method of the present invention has the advantages of simple and easy operation of the treatment process and convenient recovery and regeneration of the catalyst. As a carrier, BiFeO3 will not cause secondary pollution to water bodies; It can achieve long-term treatment of thallium-containing wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal-containing wastewater treatment, and particularly relates to a method for piezoelectric-enhanced heterogeneous Fenton oxidation-adsorption treatment of thallium-containing wastewater. Background Art

[0002] Thallium (Tl) is a typical toxic heavy metal element. In nature, it mainly occurs as an associated element in minerals such as galena, pyrite, and sphalerite. It dissolves from rock minerals into groundwater or surface water through chemical weathering or the interaction of water-rock phases. Thallium in industrial wastewater from processes such as the mining, processing, and smelting of thallium-containing ores also enters environmental water bodies. Thallium pollution in water mainly exists in the form of migratory Tl(I). Thallium can seriously threaten the ecological safety of water environment and soil, and cause organ lesions in the digestive and respiratory systems after accumulating in the human body.

[0003] Conventional treatment methods for heavy metals in wastewater include ultrafiltration, reverse osmosis, electrodialysis, precipitation method, adsorption method, etc. These methods often rely on large equipment and high-energy-consuming materials, and have problems such as high cost and difficulty in application in many actual sites. Due to the easy migration and diffusion of Tl(I) with the flow of water, and the characteristic that Tl(III) is easy to form stable precipitates, after oxidizing Tl(I) to Tl(III), the efficiency of adsorption and precipitation treatment has been greatly improved. Researchers oxidize Tl(I) through Fenton catalysts such as Fe 2+ 、Fe 0 、Fe 3 O 4 、Fe 2 O 3 and then adsorb and remove it, realizing the in-situ treatment of Tl(I). Among them, the homogeneous Fenton method (Fe 2+ ) treatment depends on an acidic environment and introduces new reagent pollution, resulting in a relatively high comprehensive cost, and is only suitable for the emergency treatment of large-scale industrial Tl pollution. For example, the literature "Simultaneous Removal of Thallium and EDTA by Fenton Process (Earth and Environmental Science 111 (2018) 012034)" published by Ruibing Xu, Xuexia Huang, etc. uses the Fenton method. Under the conditions of pH 2.5, adding 21.58 mmol / L Fe 2+ , 53.96 mmol / L H 2 O 2 to remove thallium ions in water, and the removal efficiency reaches 96.64% after 2 hours. This method belongs to the homogeneous Fenton method and depends on an acidic environment. The heterogeneous Fenton method (Fe 0 、Fe 3 O 4, Fe 2 O 3 etc.) improve the shortcomings in the above method on the oxidation-stabilized heavy metals, but the interfacial charge migration and the rate of conversion to Fe 3+ to Fe 2+ are slow, resulting in a low Fenton catalytic rate. Summary of the Invention

[0004] The object of the present invention is to provide a simple and mild enhancement strategy to improve the Fenton oxidation performance for the above problems. For the first time, BiFeO 3 heterogeneous Fenton catalyst is used for the oxidation and stabilization of Tl(I) in thallium-containing wastewater. By inducing piezoelectric potential in BiFeO 3 through hydrodynamic shear force, the problems of low catalyst activity and slow reaction rate in traditional Fenton reactions are solved.

[0005] To achieve its object, the technical solution adopted by the present invention is as follows:

[0006] A method for piezoelectric-enhanced heterogeneous Fenton oxidation-adsorption treatment of thallium-containing wastewater, comprising the following steps:

[0007] 1) Prepare the catalyst BiFeO 3 ;

[0008] 2) Put the catalyst BiFeO 3 into the thallium-containing wastewater to be treated, add hydrogen peroxide, and react for more than 1 h under stirring conditions to complete the oxidation and stabilization of Tl(I).

[0009] The BiFeO 3 is prepared by the molten salt method; the mixed salt used in the molten salt method is a mixture of potassium salt and sodium salt, and the mixed salt is a mixture of K 2 SO 4 and Na 2 SO 4 or a mixture of KCl and NaCl. Preferably, the mixed salt is K 2 SO 4 and Na 2 SO 4 . Preferably, the synthesis raw materials of BiFeO 3 are Bi 2 O 3 , Fe 2 O 3 .

[0010] Take the synthesis raw materials of BiFeO 3 and the mixed salt, mix them evenly, grind to make the raw materials evenly mixed. Preferably, the grinding time is 2 - 6 h, and then calcine at 600 - 800 °C for 9 - 20 h to obtain a solid-phase product. Wash with water, wash away the salts, and then dry to obtain BiFeO3 Catalyst

[0011] BiFeO 3 In the synthesis raw materials of BiFeO, the molar ratio of Bi:Fe is 1 to 1.15:1, the total molar amount of the mixed salts is 30 to 60 times the molar amount of Bi, and the molar ratio of potassium salt:sodium salt in the mixed salts is 1:0.8 - 1.2, preferably 1:1.

[0012] BiFeO 3 The synthesis raw materials of BiFeO are Bi 2 O 3 、Fe 2 O 3 ,and the mixed salts are a mixture of K 2 SO 4 and Na 2 SO 4 Weigh Bi 2 O 3 、Fe 2 O 3 、K 2 SO 4 、Na 2 SO 4 in a molar ratio of 1:1:30:30, grind for 2 - 6 h, calcine at 700 - 800 °C for 9 - 17 h or 9 - 15 h or 9 - 13 h or 9 - 11 h to obtain a solid-phase product, wash it with deionized water to remove salts, and dry it in an oven at 50 - 80 °C.

[0013] In step 2), the addition amount of BiFeO 3 is 0.1 - 2 g / L, and the addition amount of hydrogen peroxide is added according to its concentration in the wastewater of 5 - 70 mM, preferably 10 - 70 mM or 20 - 70 mM or 30 - 70 mM or 40 - 70 mM or 40 - 60 mM or 50 mM.

[0014] In step 2), the addition amount of BiFeO 3 is 0.2 - 1.5 g / L or 0.2 - 1.3 g / L or 0.2 - 1.0 g / L or 0.3 - 0.8 g / L or 0.3 - 0.6 g / L or 0.4 - 0.6 g / L, and the addition amount of hydrogen peroxide is added according to its concentration in the wastewater of 10 - 70 mM or 20 - 60 mM or 30 - 60 mM or 40 - 60 mM or 45 - 55 mM.

[0015] In step 2), the reaction is carried out for 1 to 10 h under the stirring condition of 300 - 800 rpm, preferably for 1 to 8 h or 1 to 6 h or 1 to 4 h or 1 to 2 h or 1 h under the stirring condition of 300 - 700 rpm or 400 - 700 rpm or 400 - 600 rpm or 400 - 500 rpm or 500 - 600 rpm; preferably, electric rod stirring or magnetic stirring is adopted.

[0016] In step 2), the pH of the thallium-containing wastewater is adjusted to 3.5 - 10, and then BiFeO 3 and hydrogen peroxide are added, preferably the pH is adjusted to 3.5 - 9 or 4 - 8 or 4 - 7 or 5 - 6.

[0017] In step 2), stirring is carried out using an electric stirring rod, and grinding is carried out using a ball mill.

[0018] Piezoelectric potential can achieve the rapid transfer of charges at the catalyst bulk phase and interface. Therefore, introducing a catalytic system with piezoelectric enhancement design can greatly improve the reaction rate. Bismuth ferrite (BiFeO 3 ) as a bismuth-based layered piezoelectric material can respond to the fluid shear force formed under high-speed stirring, generate piezoelectric potential, and thus accelerate the electron transport on the catalyst. The Fe 3+ sites of nano-bismuth ferrite can activate H 2 O 2 , S 2 O 8 2- , making it have broad application prospects in the field of advanced oxidation. At the same time, as an iron-based metal oxide, the surface of bismuth ferrite can form relatively stable bonds with some heavy metal ions, which helps to further stabilize heavy metals at its interface. Combining its advantages in piezoelectric response, Fenton reaction activity, and heavy metal adsorption, the developed piezoelectric enhanced Fenton oxidation technology based on nano-bismuth ferrite has important application value for the efficient treatment of Tl-containing heavy metal wastewater.

[0019] The beneficial effects of the present invention are:

[0020] 1. The piezoelectric potential of nano-BiFeO 3 accelerates the interfacial charge migration of the catalyst in the Fenton reaction process, improves the Fenton oxidation rate, and thus has high catalytic performance, showing excellent effects on the removal of Tl(I) in water.

[0021] 2. The synthesized nano-BiFeO 3 catalyst has a large specific surface area, retains the adsorption characteristics of multi-metal oxides for heavy metal ions, integrates the oxidation and adsorption processes in the Tl(I) treatment process on the solid-phase catalyst, has the advantages of simple and easy operation of the treatment process and convenient recovery and regeneration of the catalyst, and will not cause secondary pollution to the water body as a carrier.

[0022] 3. Due to the promoting effect of rapid charge transfer on the Fe 3+ / Fe 2+ cycle in the technology of the present invention, the problem of gradually decreasing catalytic activity caused by the imbalance of Fe 3+ / Fe 2+ conversion in the traditional heterogeneous Fenton system is properly solved, and the long-term treatment of thallium-containing wastewater can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the powder X-ray diffraction pattern of the catalyst sample prepared in Example 1.

[0024] Figure 2 It is the morphology diagram of the catalyst sample prepared in Example 1 obtained by scanning electron microscope.

[0025] Figure 3 It is the time-removal rate curve of catalytic oxidation-adsorption treatment of Tl under the same conditions with different rotation speeds in Example 4.

[0026] Figure 4 It is the time-removal rate curve of catalytic oxidation-adsorption treatment of Tl in the multi-round cycle experiment in Example 5.

[0027] Figure 5 It is the time-removal rate curve of catalytic oxidation-adsorption treatment of Tl under the same conditions in Examples 1-3 and Comparative Examples 1-2. The numbers 1-3 in the figure correspond to Examples 1-3, and the numbers 4-5 correspond to Comparative Examples 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described below in conjunction with examples, but the present invention is not limited thereto.

[0029] The experimental methods in the following examples are all conventional methods unless otherwise specified; the experimental reagents and materials used are all conventional reagents and materials in the art and can be commercially obtained unless otherwise specified.

[0030] Example 1 Preparation of BiFeO by molten salt method 3 and its piezoelectric enhanced Fenton oxidation-adsorption treatment as a catalyst

[0031] 1. Experimental method

[0032] 1) Preparation of BiFeO by molten salt method 3 : Weigh 2.329 g, 0.888 g, 26.656 g, and 21.306 g of Bi 2 O 3 , Fe 2 O 3 , K2 SO 4 、 Na 2 SO 4 was put into a nylon ball milling jar and milled in a planetary ball mill for 4 h. The raw materials were transferred to a crucible and calcined in a muffle furnace at 750 °C for 10 h to obtain a solid-phase product, which was washed 3 times with deionized water to remove salts and then placed in an oven and dried at 60 °C for 12 h to obtain the catalyst sample. Figure 1 is the powder X-ray diffraction pattern of the catalyst sample prepared in Example 1, Figure 2 and is its SEM morphology diagram.

[0033] 2) Accurately weigh 50 mg of the catalyst and add it to 100 mL of thallium-containing wastewater sample according to the dosing amount of 0.5 g / L. In this example, the thallium-containing wastewater comes from the process wastewater tank of a smelter, and the concentration of Tl(I) is 1.0681 mg·L -1 , and the pH value is 5.8. Without adjusting the pH value of the wastewater, 0.5 mL of 30% hydrogen peroxide was added to make the concentration of H 2 O 2 in the system 50 mM, and it was stirred with an electric rod at a stirring speed of 400 rpm for 1 h.

[0034] 3) After the reaction, take 3 mL of the water sample and add 3 mL of methanol to terminate the Fenton reaction, and detect the thallium concentration in the water according to HJ / 748-2015 "Determination of Thallium in Water - Graphite Furnace Atomic Absorption Spectrophotometry".

[0035] 2. Experimental Results

[0036] The experimental results show that after 1 h of piezoelectric enhanced Fenton reaction and ion adsorption, the concentration of Tl(I) in the wastewater decreased to 0.0063 mg·L -1 , and the removal rate of Tl(I) in water by the piezoelectric enhanced Fenton oxidation-adsorption treatment method using BiFeO 3 prepared in this example as a catalyst is 99.41%. The crystallization of the sample prepared by the molten salt method has a preferred orientation, which can generate a large piezoelectric potential, so it can accelerate the charge transfer in the catalytic reaction process; at the same time, the crystal will also show more exposure of active surfaces, improving the reaction rate at the solid-liquid interface, which is beneficial to the oxidation and adsorption removal of Tl(I).

[0037] Example 2 Preparation of BiFeO 3 by the molten salt method and its piezoelectric enhanced Fenton oxidation-adsorption treatment as a catalyst

[0038] 1. Experimental Method

[0039] BiFeO 3 was prepared by the molten salt method using different potassium salts and sodium salts: BiFeO 3, the preparation method is the same as that of Example 1, except that K in the raw materials is 2 SO 4 、Na 2 SO 4 is replaced with the same molar amount of KCl and NaCl.

[0040] The BiFeO prepared in this example 3 is used for treating thallium-containing wastewater, and the treatment method is the same as steps 2) and 3) of Example 1.

[0041] 2. Experimental results

[0042] The experimental results show that after 1 h of piezoelectric enhanced Fenton reaction and ion adsorption, the concentration of Tl(I) in the wastewater drops to 0.0907 mg·L -1 , and the removal rate of Tl(I) in water by the piezoelectric enhanced Fenton oxidation-adsorption treatment method using the BiFeO prepared in this example 3 as a catalyst is 91.5%, which is lower than the Tl(I) removal rate of the BiFeO in Example 1 3 .

[0043] Example 3

[0044] 1. Experimental method

[0045] Prepare BiFeO 3 : The preparation method is the same as that of Example 1, except that the raw materials are only Bi 2 O 3 、Fe 2 O 3 , without adding the mixed salts K 2 SO 4 、Na 2 SO 4 .

[0046] The BiFeO prepared in this example 3 is used for treating thallium-containing wastewater, and the treatment method is the same as steps 2) and 3) of Example 1.

[0047] 2. Experimental results

[0048] The experimental results show that after 1 h of piezoelectric enhanced Fenton reaction and ion adsorption, the concentration of Tl(I) in the wastewater drops to 0.5052 mg·L -1 , and the removal rate of Tl(I) in water by the piezoelectric enhanced Fenton oxidation-adsorption treatment method using the BiFeO prepared in this example 3 as a catalyst is 52.7%. Compared with the BiFeO 3 sample synthesized by the molten salt method in Example 1, the BiFeO 3The specific surface area of the catalyst is small and the surface reaction activity is low, so its oxidation and adsorption removal performance for Tl(I) is low.

[0049] Example 4

[0050] 1. Experimental method

[0051] Three groups of experiments with different stirring speeds were set up, and the stirring rates were 300, 600, and 800 rpm respectively. The preparation method of BiFeO 3 was the same as that in Example 1. The treatment method for treating thallium-containing wastewater with BiFeO 3 was the same as that in Example 1, except that the stirring rate during the reaction in step 2) was changed from 400 rpm to 300, 600, and 800 rpm.

[0052] 2. Experimental results

[0053] The experimental results showed that after 1 h of piezoelectric enhanced Fenton reaction and ion adsorption, the concentration of Tl(I) in the wastewater decreased to 0.1277 mg·L -1 , 0.0052 mg·L -1 , 0.4176 mg·L -1 at 300, 600, and 800 rpm respectively, and the corresponding removal rates of Tl(I) in the water body were 88.04%, 99.51%, and 60.90%. In the piezoelectric enhanced Fenton reaction induced by the water flow shear force, according to Newton's viscosity law, a higher rotation speed can apply a greater stress to the catalyst, form a higher piezoelectric potential, and promote charge transfer, thus improving the reaction rate. Therefore, the oxidation process of Tl(I) by the catalyst at a low rotation speed is slow, indirectly affecting its effective adsorption and removal at the catalyst interface. At a high rotation speed of 800 rpm, a large amount of H 2 O 2 will be decomposed and thus unable to supply the Fenton-like reaction, so the removal rate also decreases ( Figure 3 is the removal rate-time curve of Tl(I) at different rotation speeds).

[0054] Recycling and reuse of the catalyst in Example 5

[0055] 1. Recycling and regeneration of the catalyst

[0056] The catalyst in Example 1 was recycled and regenerated. The specific method was as follows: after the reaction in step 3) of Example 1 was completed, the reaction solution was dispersed conventionally in the recovery system to separate the wastewater and the catalyst, and then the catalyst was recovered. 25 mL of hydrochloric acid with a concentration of 0.01 mol / L was added and reacted for 5 min for desorption, and then washed with deionized water and dried to complete the regeneration and recovery of the catalyst. After detection, the final recovery rate was 92%.

[0057] 2. Removal Effect of Recycled Catalyst on Tl(I)

[0058] Using the recycled catalyst, the thallium removal experiment of wastewater was carried out according to steps 2) and 3) of Example 1, and the catalyst was recycled for the next round of wastewater treatment experiment. A total of three rounds of cycles were carried out. Samples were taken for testing at the end of each round of experiment. The experimental results showed that after 1 h of piezoelectric enhanced Fenton reaction and ion adsorption, the Tl(I) concentration in the wastewater decreased to 0.0195 mg·L -1 、0.0243 mg·L -1 and 0.0307 mg·L -1 at the end of the first, second, and third rounds of experiments respectively. The removal rates of Tl(I) in water by the piezoelectric enhanced Fenton oxidation-adsorption treatment method using the recycled BiFeO 3 as the catalyst were 98.17%, 97.72%, and 97.12% respectively ( Figure 4 is the removal rate-time curve of the initial experiment and three cycle experiments).

[0059] In Comparative Example 1, Fe 3 O 4 was used as the catalyst to treat thallium-containing wastewater by the Fenton oxidation-adsorption treatment method

[0060] 1. Experimental Method

[0061] The same as the scheme of Example 1, the difference is that the catalyst uses commercially available Fe 3 O 4 powder to replace the synthesized BiFeO 3 catalyst to carry out the performance experiment of Fenton-like catalyst-adsorption treatment of thallium-containing wastewater.

[0062] 2. Experimental Results

[0063] The experimental results showed that after 1 h of Fenton-like reaction and ion adsorption, the Tl(I) concentration in the wastewater decreased to 0.6547 mg·L -1 , and the removal rate of Tl(I) in water by the Fenton oxidation-adsorption treatment method using commercially available Fe 3 O 4 as the catalyst was 38.7%, with a low removal rate.

[0064] In Comparative Example 2, Fe powder was used as the catalyst to treat thallium-containing wastewater by the Fenton oxidation-adsorption treatment method

[0065] 1. Experimental Method

[0066] The same as the scheme of Example 1, the difference is that the catalyst uses commercially available Fe powder to replace the synthesized BiFeO 3 catalyst to carry out the performance experiment of Fenton-like catalyst-adsorption treatment of thallium-containing wastewater.

[0067] 2. Experimental results

[0068] The experimental results show that after 1 h of Fenton-like reaction and ion adsorption, the concentration of Tl(I) in the wastewater decreases to 0.5265 mg·L -1 , and the removal rate of Tl(I) in water by the Fenton oxidation-adsorption treatment method using commercially available Fe powder as a catalyst is 50.7%, with a low removal rate. This is because in the traditional iron-based heterogeneous Fenton catalyst, with the progress of the reaction, the conversion of Fe 3+ / Fe 2+ is unbalanced, resulting in a large accumulation of Fe 3+ , which hinders the continuous and efficient progress of the catalytic reaction. Therefore, in terms of the treatment effect of thallium-containing wastewater, it is inferior to the BiFeO 3 catalyst proposed in the present invention.

[0069] Figure 5 It is the time-removal rate curve graph of catalytic oxidation-adsorption treatment of Tl under the same conditions for Examples 1-3 and Comparative Examples 1-2 (Numbers 1-3 correspond to Examples 1-3, and numbers 4-5 correspond to Comparative Examples 1-2).

Claims

1. A method for treating thallium-containing wastewater by piezoelectric enhanced heterogeneous Fenton oxidation-adsorption, characterized in that, it includes the following steps: 1) Prepare the catalyst BiFeO 3 ; The BiFeO 3 is prepared by the molten salt method; the mixed salt used in the molten salt method is K 2 SO 4 and Na 2 SO 4 mixture, and the synthesis raw materials of BiFeO 3 are Bi 2 O 3 , Fe 2 O 3 ; 2) Add the catalyst BiFeO 3 to the thallium-containing wastewater to be treated, add hydrogen peroxide, and react for more than 1 h under the stirring condition of 400 - 600 rpm to complete the oxidation and stabilization of Tl(I).

2. The method according to claim 1, characterized in that: Take the synthesis raw materials of BiFeO 3 and the mixed salts, mix them evenly, grind to make the raw materials evenly mixed, with the grinding time being 2 - 6 h, then calcine at 600 - 800 °C for 9 - 20 h to obtain a solid-phase product, wash it with water, wash away the salts and then dry it to obtain the BiFeO 3 catalyst.

3. The method according to claim 1, characterized in that: BiFeO 3 In the synthesis raw materials of 3 , the molar ratio of Bi to Fe is 1 to 1.15:1, the total molar amount of the mixed salts is 30 to 60 times the molar amount of Bi, and the molar ratio of potassium salt to sodium salt in the mixed salts is 1:0.8 - 1.

2.

4. The method according to claim 3, characterized in that: Weigh Bi according to the molar ratio of 1﹕1﹕30﹕30 2 O 3 、Fe 2 O 3 、K 2 SO 4 、Na 2 SO 4 , grind for 2 - 6 h, calcine at 700 - 800 °C for 9 - 17 h to obtain a solid-phase product, wash with deionized water to remove salts, and place in an oven to dry at 50 - 80 °C.

5. The method according to claim 1, characterized in that: The addition amount of BiFeO in step 2 3 is 0.1 - 2 g / L, and the addition amount of hydrogen peroxide is added according to its concentration in the wastewater of 5 - 70 mM.

6. The method according to claim 5, characterized in that: The addition amount of BiFeO in step 2 3 is 0.2 - 1.5 g / L, and the addition amount of hydrogen peroxide is added according to its concentration in the wastewater of 10 - 70 mM.

7. The method according to claim 1, characterized in that: The pH of the thallium-containing wastewater described in step 2) is adjusted to 3.5-10, and then BiFeO 3 and hydrogen peroxide are added.

8. The method according to claim 1, characterized in that: in step 2), stirring is carried out using an electric stirring rod, and grinding is carried out using a ball mill.

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