Method for reducing arsenic-containing wastewater by ultraviolet light and extracting and separating elemental arsenic

Abstract

The invention relates to the technical field of arsenic-containing wastewater treatment, in particular to a method for reducing arsenic-containing wastewater by ultraviolet light and extracting and separating elemental arsenic. According to the method for reducing the arsenic-containing wastewater through the ultraviolet light and extracting and separating the elemental arsenic, after the arsenic-containing wastewater and a reducing agent are mixed, photo-reduction is conducted under the normal-temperature and normal-pressure conditions, and the elemental arsenic is obtained; adding a surfactant into the dispersion phase containing the elementary substance arsenic, and extracting and separating the product elementary substance arsenic through cloud point extraction; the reducing agent is sulfite and halide. The method disclosed by the invention is mild in condition, high in arsenic reduction rate and wide in pH range of applicable wastewater, and the prepared product is high in purity.

Description

Technical Field

[0001] The invention relates to the technical field of arsenic-containing wastewater treatment, and in particular to a method for reducing arsenic-containing wastewater by ultraviolet light and extracting and separating elemental arsenic. Background Art

[0002] At present, chemical precipitation and coagulation precipitation are widely used in industry to treat arsenic-containing wastewater. In addition, other methods such as adsorption and ion exchange also have certain treatment potential. However, these methods inevitably produce a large amount of dangerous arsenic residues, which pose the risk of arsenic release and secondary pollution, and do not truly eliminate the environmental risks of arsenic.

[0003] The existing technology uses zero-valent iron and sodium formate hydrothermal method to convert trivalent arsenic (As(III)) in acidic arsenic-containing solution into zero-valent arsenic (As(0)), but this method requires a high-temperature and high-pressure hydrothermal environment and can only treat acidic wastewater. The treatment cost is high and it is not easy to promote and apply.

[0004] In the prior art, UV / TiO 2 Photoreduction methods such as ionization / methanol and UV / dithionite can reduce arsenic to As(0). However, the products obtained in these heterogeneous catalytic systems are mixtures of catalyst and As(0), such as As(0) / TiO 2 、As(0) / As 4 S 4 Therefore, it is difficult to separate pure As(0) and its value is not high. Summary of the invention

[0005] The purpose of the present invention is to provide a method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic in view of the above-mentioned deficiencies in the prior art.

[0006] The present invention discloses a method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic. The arsenic-containing wastewater is mixed with a reducing agent and then subjected to photoreduction at normal temperature and pressure to obtain elemental arsenic. A surfactant is added to a dispersed phase containing elemental arsenic, and extraction and separation of the product elemental arsenic is achieved through turbidity point extraction. The reducing agent is sulfite and halide.

[0007] Furthermore, the molar ratio of the sulfite to the halide is 0.25-6:1.

[0008] Furthermore, the pH of the arsenic-containing wastewater is 4-10.

[0009] Furthermore, the molar ratio of the amount of the reducing agent added to the arsenic in the arsenic-containing wastewater is in the range of (10-100):1.

[0010] Furthermore, the extractant is TX-114, and the extraction temperature is 40°C.

[0011] Furthermore, the amount of the extractant used is 0.5-2% of the total reaction system mass.

[0012] Furthermore, the light source for the photoreduction is a mercury lamp with a wavelength of 100-400 nm.

[0013] Furthermore, the photoreduction time is 1 to 5 hours.

[0014] Furthermore, the purity of elemental arsenic in the dispersed phase containing elemental arsenic is greater than 95%.

[0015] Furthermore, the extraction rate of elemental arsenic in the dispersed phase containing elemental arsenic is greater than 95%.

[0016] The technical solution of the present invention is the first to reduce arsenic-containing wastewater in one step by photoreduction combined with turbidity extraction to prepare high-purity arsenic element. The photoreduction reaction mechanism is: under ultraviolet light excitation, reducing substances such as halides and sulfites are activated by ultraviolet light to produce strongly reducing hydrated electrons, and arsenic is gradually reduced from pentavalent or trivalent to zero-valent arsenic element. By using sulfites and halides in combination, the intermediate products produced by the process of two reducing agents producing hydrated electrons can react with each other, thereby avoiding the consumption of hydrated electrons and improving the generation and utilization efficiency of hydrated electrons. Since the arsenic element generated by the above reaction has a small particle size and is difficult to separate when dispersed in the reaction solvent, after the introduction of a surfactant, the product can be separated by turbidity extraction. The separation process is carried out directly in the reaction device without the need for other operations such as filtration or centrifugation, which not only ensures the separation efficiency, but also avoids the exposure of arsenic element to the air in other separation operations, thereby improving the purity of the product.

[0017] The method of the invention has mild conditions, high arsenic reduction rate, is applicable to a wide pH range of wastewater, and has a high purity of the prepared product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The appearance and scanning electron microscope images of the preparation of elemental arsenic by photoreduction in Example 1;

[0019] Figure 2 The energy spectrum and X-ray photoelectron spectrum of the elemental arsenic prepared by photoreduction in Example 1;

[0020] Figure 3 It is a flow chart of the steps of enriching and separating elemental arsenic by turbidity point extraction in the present invention and an optical photograph of the solution during the separation process;

[0021] Figure 4 The photoreduction effect of wastewater with different pH values;

[0022] Figure 5 The effect of the concentration of sodium sulfite and iodide ion on the photoreduction effect;

[0023] Figure 6 The influence of interference factors on the photoreduction effect of wastewater;

[0024] Figure 7 The photoreduction effect of the method of the present invention on actual factory wastewater;

[0025] Figure 8 The figure is a comparison of the photoreduction effects of UV / sulfite, UV / potassium iodide and UV / sulfite / potassium iodide systems. DETAILED DESCRIPTION

[0026] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0027] Example 1

[0028] (1) Sodium arsenate or sodium arsenite was used as raw material to prepare simulated arsenic wastewater, and the mass concentration of arsenic was controlled to be 50 mg L -1 , using NaOH or H 2 SO 4 Adjust the solution pH to 10;

[0029] (2) adding reducing agents sodium sulfite and potassium iodide at concentrations of 9 mM and 2 mM respectively and mixing well;

[0030] (3) Use ultraviolet light (254 nm, 30 W) to evenly irradiate the arsenic-containing wastewater for 1-5 h while stirring to keep the solution uniform;

[0031] (4) After the reaction is completed, a portion of the reaction dispersion is taken for vacuum filtration and washed with ultrapure water to obtain a solid product.

[0032] The solid product obtained in Example 1 was characterized by scanning electron microscopy. Figure 1 As shown in the figure, it can be seen that the obtained solid product is particles with smaller particle size, and the above small particles are agglomerated to obtain clustered particles.

[0033] The solid product obtained in Example 1 was characterized by energy spectrum and X-ray photoelectron spectrum. The results are as follows: Figure 2 As shown, from the energy spectrum results, it can be seen that the main element of the solid product is arsenic, and its mass percentage is greater than 96%. There is a small amount of oxygen in the product, which may be related to the partial oxidation of arsenic during sample preparation and characterization. From the results of X-ray photoelectron spectroscopy, it can be seen that the solid product is mainly zero-valent arsenic, and its content exceeds 95%.

[0034] Figure 3The flowchart of the steps of separating elemental arsenic by turbidity point extraction is as shown in the figure. To the dispersion obtained after the photoreaction in Example 1, surfactant TX-114 (the added amount is 0.1% by mass) is added, and after being fully stirred for 5 minutes, it is allowed to stand for 30 minutes.

[0035] The obtained elemental arsenic-rich phase is the lower layer. The upper and lower dispersed phases containing elemental arsenic are separated and their masses are weighed respectively, and the extraction rate is calculated to be greater than 95%.

[0036] Example 2

[0037] The pH of the wastewater in Example 1 was modified to 2, 4, 6, 8, and 12, and the photoreduction effects were compared.

[0038] like Figure 4 As shown, the UV / sulfite / potassium iodide system is applicable in a wide pH range (pH 4-10), and the reduction efficiency is low only at pH = 2 or pH = 12.

[0039] Example 3

[0040] In the modified example 1, the concentrations of sodium sulfite and potassium iodide are 0-13 mM and 0-10 mM, respectively, that is, the concentration ratio is 0.25:1-6:1.

[0041] Figure 5 As can be seen from Figures a and b, when the concentration of potassium iodide is 2 mM, it is found that with the increase in the amount of sulfite, the reduction efficiency of As(V) and As(III) increases from 0 to almost 100%, and gradually stabilizes at a concentration of 9 mM. This shows that the concentration of potassium iodide is one of the key factors affecting the efficiency of arsenic reduction.

[0042] Figure 5 As can be seen from Figures c and d, when the sodium sulfite concentration is 9 mM, with the increase of potassium iodide dosage, the removal efficiency of As(V) and As(III) increases from 0 to almost 100%, and gradually stabilizes at a concentration of 2 mM. This shows that the sodium sulfite concentration is also one of the key factors affecting the arsenic reduction efficiency.

[0043] Example 4

[0044] The effect of dissolved oxygen in actual wastewater on the reaction was simulated by deoxygenating or not the wastewater, and the effect of coexisting ions on arsenic reduction efficiency was explored by adding other coexisting ions into the wastewater.

[0045] like Figure 6 As shown, when dissolved oxygen and coexisting ions exist, the reduction effect of arsenic is less affected, indicating that this method is less affected by dissolved oxygen and coexisting ions.

[0046] Example 5

[0047] Arsenic-containing wastewater from a factory in Huangshi City, Hubei Province was taken, and its components are shown in Table 1. After adjusting the pH to 10, reduction was performed using the method of Example 1, and reducing agents sodium sulfite and potassium iodide were added at concentrations of 45 mM and 10 mM, respectively, and mixed evenly. The results are shown in Table 1. Figure 7 This method has a good arsenic reduction effect on actual arsenic-containing wastewater. When the irradiation time is 5 hours, about 95% of the arsenic in the wastewater is reduced.

[0048] Table 1

[0049] Components pH As <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[NO 3 - ]]> <![CDATA[PO 4 - ]]> <![CDATA[SO 3 2- ]]> <![CDATA[SO 4 2- ]]> Concentration (g / L) 12.8 5.2 0.017 0.031 0.29 0.04 73.3 0.14 2.09

[0050] Comparative Example 1

[0051] (1) Sodium arsenate or sodium arsenite was used as raw material to prepare simulated arsenic wastewater, and the mass concentration of arsenic was controlled to be 10 mg L -1 , using NaOH or H 2 SO 4 Adjust the solution pH to 10;

[0052] (2) adding the reducing agent sulfite (9 mM) alone;

[0053] (3) Use ultraviolet lamp (254nm, 30W) to evenly irradiate the arsenic-containing wastewater while stirring to keep the solution uniform.

[0054] Comparative Example 2

[0055] (1) Sodium arsenate or sodium arsenite was used as raw material to prepare simulated arsenic wastewater, and the mass concentration of arsenic was controlled to be 10 mg L -1 , using NaOH or H 2 SO 4 Adjust the solution pH to 10;

[0056] (2) adding the reducing agent potassium iodide (2 mM) alone;

[0057] (3) Use ultraviolet lamp (254nm, 30W) to evenly irradiate the arsenic-containing wastewater while stirring to keep the solution uniform.

[0058] Comparative Example 3

[0059] When the surfactant TX-114 in Example 1 was replaced with CTAB, it was found that arsenic extraction could not be achieved.

[0060] Figure 8 The figure is a comparison of the photoreduction effects of UV / sulfite, UV / potassium iodide and UV / sulfite / potassium iodide systems; Figure 8It can be seen that the UV / sulfite system and UV / potassium iodide have a certain reduction effect on arsenic, but the final efficiency is only 20% to 30%. The addition of potassium iodide significantly improves the efficiency of UV / sulfite reduction to remove arsenic, and As(V) and As(III) are completely reduced within 70 minutes.

[0061] For matters not mentioned above, the prior art applies.

[0062] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic, characterized in that: Arsenic-containing wastewater is mixed with a reducing agent and then photoreduced under normal temperature and pressure to obtain elemental arsenic; a surfactant is added to the dispersed phase containing elemental arsenic, and the product elemental arsenic is extracted and separated by turbidity point extraction; the reducing agent is sulfite and halide.

2. A method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The molar ratio of the sulfite to the halide is 0.25-6:

1.

3. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The pH of the arsenic-containing wastewater is 4-10.

4. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The molar ratio of the amount of the reducing agent added to the arsenic in the arsenic-containing wastewater is in the range of (10-100):

1.

5. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The extractant is TX-114, and the extraction temperature is 40°C.

6. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The amount of the extractant used is 0.5-2% of the total reaction system mass.

7. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The light source of the photoreduction is a mercury lamp with a wavelength of 100-400 nm.

8. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The photoreduction time is 1 to 5 hours.

9. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The purity of the arsenic in the dispersed phase containing the elemental arsenic is greater than 95%.

10. The method for ultraviolet light reduction of arsenic-containing wastewater and extraction and separation of elemental arsenic as claimed in claim 1, characterized in that: The extraction rate of elemental arsenic in the dispersed phase containing elemental arsenic is greater than 95%.

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