A method for removing divalent manganese from water

Abstract

The application discloses a method for removing divalent manganese in water, which comprises the following steps: adding NaClO into a water body containing Mn 2+ to obtain a mixed solution, and stirring and reacting under long-wave ultraviolet irradiation to obtain the method. The application innovatively introduces long-wave ultraviolet (UVA-LED) to activate NaClO, and breaks through the bottleneck of oxidation kinetics. NaClO has a high molar absorption coefficient and quantum yield in the UVA band, and can be photolyzed after absorbing light energy. HO• and active chlorine species (RCS) can be generated, and oxygen atoms generated by photolysis can also react with O2 to generate O3. The application generates key intermediate trivalent manganese Mn(III) through the single-electron transfer mechanism driven by ClO• and the double-electron transfer mechanism mediated by O3. The strong oxidation of ClO• and O3 rapidly oxidizes Mn(III) to Mn(IV), forming a high-efficiency multi-path oxidation network.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for removing divalent manganese from water. Background Technology

[0002] Manganese, an essential trace element for the human body, exists widely in drinking water sources in the form of dissolved divalent manganese (Mn(II)). However, excessive intake can pose serious health risks. With the continuous improvement of drinking water quality standards, controlling the concentration of manganese in water to a low level (e.g., below 0.1 mg / L) has become an important goal in the water treatment field. However, traditional removal technologies, such as biological filtration, ion exchange, and adsorption, are difficult to effectively remove Mn(II) from water. In contrast, oxidation technology is a more efficient and economical removal method. This technology uses strong oxidants to oxidize dissolved Mn(II) into insoluble manganese dioxide (MnO2) precipitate, which is then removed through solid-liquid separation. Commonly used oxidants include liquid chlorine (NaClO), ozone (O3), chlorine dioxide (ClO2), and permanganate. Among these, NaClO is widely used as an oxidant in water treatment due to its low cost, wide availability, and ease of addition. However, studies have shown that NaClO alone has limited oxidation capacity for Mn(II), with a slow reaction rate, making it difficult to meet the requirements for efficient removal.

[0003] Therefore, there is an urgent need to develop a system with higher oxidation efficiency for the removal of divalent manganese. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a method for removing divalent manganese from water, which has high oxidation efficiency and high divalent manganese removal efficiency.

[0005] According to a first aspect of the present invention, a method for obtaining divalent manganese in water is provided, comprising the following steps: To contain Mn 2+ NaClO is added to water to obtain a mixed solution, which is then stirred and reacted under long-wave ultraviolet irradiation to obtain the final product.

[0006] According to a preferred embodiment of the present invention, the wavelength of the long-wave ultraviolet light is 365~405 nm.

[0007] According to a preferred embodiment of the present invention, the light intensity of the long-wave ultraviolet light is 8.6~31.2 mW / cm².

[0008] According to a preferred embodiment of the present invention, the concentration of NaClO is 200~1000 μM.

[0009] According to a preferred embodiment of the present invention, the concentration of NaClO is 500~700 μM.

[0010] According to a preferred embodiment of the present invention, the Mn 2+ The concentration is 10~100 μM.

[0011] According to a preferred embodiment of the present invention, the Mn 2+ The corresponding compounds include at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0012] According to a preferred embodiment of the present invention, the stirring reaction time is 10 to 60 minutes.

[0013] According to a preferred embodiment of the present invention, the reaction temperature of the stirring reaction is 20~30°C.

[0014] According to a preferred embodiment of the present invention, the stirring speed is 300 r / min to 1000 r / min.

[0015] According to a preferred embodiment of the present invention, the pH value of the mixture is 4.0 to 9.0.

[0016] According to a preferred embodiment of the present invention, the long-wave ultraviolet light source is an LED lamp. Therefore, compared to traditional 254 mercury lamps, LEDs offer advantages such as being environmentally friendly, mercury-free, having a longer lifespan, and adjustable wavelength. The removal method according to embodiments of the present invention has at least the following beneficial effects: This invention innovatively introduces long-wave ultraviolet (UVA) light to activate NaClO, overcoming its oxidation kinetic bottleneck. NaClO exhibits high molar absorptivity and quantum yield in the UVA band (especially at 365 nm). After absorbing light energy, it undergoes photolysis, generating not only HO• and active chlorine species (RCS, such as Cl•, Cl2•-, and ClO•), but also oxygen atoms produced by photolysis reacting with O2 to generate O3. This invention induces the generation of the key intermediate trivalent manganese Mn(III) through a ClO•-driven single-electron transfer and an O3-mediated two-electron transfer mechanism. ClO•, in conjunction with the strong oxidizing effect of O3, rapidly oxidizes it to Mn(IV), forming a highly efficient multi-pathway oxidation network. The specific equations are as follows: (1); (2); (3); (4); (5); (6); Therefore, this invention features higher efficiency, energy saving, environmental friendliness, and safety. UVA-LED replaces traditional low-pressure mercury lamps, eliminating the environmental risk of mercury leakage, offering a longer operating life, and being more environmentally friendly and safer. UVA-LED efficiently activates NaClO, promoting the generation of active chlorine species (RCS) and O3, significantly improving the removal efficiency of Mn(II). It has a wide applicable pH range (pH 4.0 to 9.0), and is suitable for Cl... - HCO3 - Even under complex water matrix conditions such as coexistence with humic acid (HA), it can still achieve effective removal of Mn(II).

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The effects of pH under experimental and simulated conditions on the oxidation of Mn(II) in the UVA-LED / NaClO system, the concentration of active substances in the system at different pH values, and the contribution of active substances to the oxidation of Mn(II) at different pH values ​​are investigated.

[0019] Figure 2 It is Cl - HCO3 - The effect of humic acid (HA) concentration on the removal of manganese ions in Example 1 is shown in the figure. Detailed Implementation

[0020] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0021] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0022] In some embodiments of the present invention, a method for obtaining divalent manganese in water is provided, comprising the following steps: To contain Mn 2+ NaClO is added to water to obtain a mixed solution, which is then stirred and reacted under long-wave ultraviolet irradiation to obtain the final product.

[0023] Understandably, NaClO is an economical, readily available, and widely used chemical oxidant, often used in water treatment processes for disinfection and oxidation to remove inorganic pollutants. It can oxidize dissolved divalent manganese (Mn(II)) in water into insoluble MnO2 precipitate, which can then be removed from drinking water sources through precipitation or filtration. Based on its low cost and mature engineering applications, the NaClO oxidation method has become an important method in waterworks and groundwater treatment. However, the oxidation capacity of NaClO alone for Mn(II) is limited, and the reaction kinetics are relatively slow, making it difficult to achieve the desired Mn(II) removal effect within the actual contact time required for water treatment.

[0024] This invention innovatively introduces long-wave ultraviolet (UVA) light to activate NaClO, overcoming its oxidation kinetic bottleneck. NaClO exhibits high molar absorptivity and quantum yield in the UVA band (especially at 365 nm). After absorbing light energy, it undergoes photolysis, generating not only HO• and active chlorine species (RCS, such as Cl•, Cl2•-, and ClO•), but also oxygen atoms produced by photolysis reacting with O2 to generate O3. This invention induces the generation of the key intermediate trivalent manganese Mn(III) through a ClO•-driven single-electron transfer and an O3-mediated two-electron transfer mechanism. ClO•, in conjunction with the strong oxidizing effect of O3, rapidly oxidizes it to Mn(IV), forming a highly efficient multi-pathway oxidation network. The specific equations are as follows: (1); (2); (3); (4); (5); (6); Therefore, this invention features higher efficiency, energy saving, environmental friendliness, and safety. UVA-LED replaces traditional low-pressure mercury lamps, eliminating the environmental risk of mercury leakage, offering a longer operating life, and being more environmentally friendly and safer. UVA-LED efficiently activates NaClO, promoting the generation of active chlorine species (RCS) and O3, significantly improving the removal efficiency of Mn(II). It has a wide applicable pH range (pH 4.0 to 9.0), and is suitable for Cl... - HCO3 - Even under complex water matrix conditions such as coexistence with humic acid (HA), it can still achieve effective removal of Mn(II).

[0025] In some embodiments of the present invention, the wavelength of the long-wave ultraviolet light is 365~405 nm. For example, it includes 365 nm, 370 nm, 375 nm, 380 nm, 385 nm, 390 nm, 395 nm, 400 nm, 405 nm, or any sub-range composed of any two of the above values.

[0026] In some embodiments of the present invention, the intensity of the long-wave ultraviolet light is 8.6 to 31.2 mW / cm². For example, it includes 8.6 mW / cm², 9 mW / cm², 10 mW / cm², 12 mW / cm², 14 mW / cm², 16 mW / cm², 18.4 mW / cm², 20 mW / cm², 24 mW / cm², 26 mW / cm², 30 mW / cm², 31.2 mW / cm², or any combination of two of the above values.

[0027] In some embodiments of the present invention, the concentration of NaClO is 200~1000 μM. For example, it includes 200 μM, 300 μM, 400 μM, 500 μM, 600 μM, 700 μM, 800 μM, 900 μM, 1000 μM or any two of the above values.

[0028] In some embodiments of the present invention, the concentration of NaClO is 500~700 μM. For example, it includes 500 μM, 550 μM, 600 μM, 650 μM, 700 μM, or any sub-range consisting of two of the above values.

[0029] In some embodiments of the present invention, the Mn 2+ The concentration is 10~100 μM. For example, it includes 10μM, 20μM, 30μM, 40μM, 50μM, 60μM, 70μM, 80μM, 90μM, 100μM or any two of the above values.

[0030] In some embodiments of the present invention, the stirring reaction time is 10 to 60 minutes.

[0031] In some embodiments of the present invention, the reaction temperature of the stirring reaction is 20~30°C.

[0032] In some embodiments of the present invention, the stirring speed is 300 r / min to 1000 r / min.

[0033] In some embodiments of the present invention, the pH value of the mixture is 4.0 to 9.0.

[0034] Example 1 This example provides a method for removing divalent manganese from water, including the following steps: Add 500 µM NaClO solution to deionized water containing 50 µM MnSO4, and then apply the solution to a UVA-LED (wavelength 365 nm, light intensity 18.4 mW / cm²). 2 The reaction was carried out under continuous irradiation with stirring for 15 min to complete the removal of Mn(II); the initial pH of the reaction solution was adjusted to 7.0, the reaction temperature was controlled at about 25℃, and the stirring speed was 600 r / min.

[0035] Example 2 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the initial pH of the reaction solution is 4.0.

[0036] Example 3 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the initial pH of the reaction solution is 9.0.

[0037] Example 4 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the wavelength of the long-wave ultraviolet light is 385 nm.

[0038] Example 5 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the wavelength of the long-wave ultraviolet light is 395 nm.

[0039] Example 6 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the wavelength of the long-wave ultraviolet light is 405 nm.

[0040] Example 7 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that the light intensity is 8.6 mW / cm².

[0041] Example 8 This example provides a method for removing divalent manganese from water, which is the same as that in Example 1, except that the light intensity is 31.2 mW / cm².

[0042] Example 9 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that a 200 µM NaClO solution is added.

[0043] Example 10 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that a 300 µM NaClO solution is added.

[0044] Example 11 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that a 700 µM NaClO solution is added.

[0045] Example 12 This example provides a method for removing divalent manganese from water, which is the same as in Example 1, except that a 1000 µM NaClO solution is added.

[0046] Comparative Example 1 This example provides a method for removing divalent manganese from water, and the steps are as follows: Add 500 µM NaClO solution to deionized water containing 50 µM MnSO4 and stir for 15 min to remove Mn(II); the initial pH of the reaction solution is 7.0, the reaction temperature is controlled at about 25℃, and the stirring speed is 600 r / min.

[0047] Comparative Example 2 This example provides a method for removing divalent manganese from water, and the steps are as follows: Add 500 µM NaClO solution to deionized water containing 50 µM MnSO4 and stir for 15 min under continuous UV (wavelength 254 nm) irradiation to remove Mn(II). The initial pH of the reaction solution is adjusted to 7.0, the reaction temperature is controlled at about 25℃, and the stirring speed is 600 r / min.

[0048] Comparative Example 3 This example provides a method for removing divalent manganese from water. The removal method is the same as in Example 1, except that a 500 µM NaClO solution is not added.

[0049] Performance testing The removal rates of manganese ions were tested for 15 minutes using the removal methods of Example 1 and Comparative Example 1, and the results are shown in Table 1 below: Table 1

[0050] Furthermore, Examples 1-3 of this invention investigated the effect of different pH values ​​on removal efficiency, and the results are shown in […]. Figure 1 ,like Figure 1As shown in (a), in the UVA-LED / NaClO system, the reaction rate and oxidation efficiency of Mn(II) increase significantly with increasing pH. When the pH increases from 4.0 to 9.0, the oxidation efficiency of Mn(II) increases from 84.4% to 98.1%. This pH dependence may be attributed to the changes in the contribution and concentration of active species at different pH values ​​in the UVA-LED / NaClO system. Calculations show that in the 365 nm UV emission band, the quantum yield of ClO- (0.743 mol / Einstein) is higher than that of HOCl (0.388 mol / Einstein), and the increase in pH promotes the generation of active species, thereby leading to the increase in the oxidation efficiency of Mn(II).

[0051] like Figure 1 As shown in (b), a competition kinetics was established based on the experimental data of these four probes, which allowed for the calculation of H₂O•, Cl•, ClO•, and Cl₂•. - The concentrations of O3 were also analyzed. The results showed that at pH 7.0, the highest concentration of O3 was 3.96 × 10⁻⁷ M, followed by ClO• (8.34 × 10⁻¹⁰ M), H₂O• (1.35 × 10⁻¹² M), and Cl₂•. - (4.21 × 10⁻¹³ M) and Cl• (3.69 × 10⁻¹⁴ M). Specifically, as pH increases from 4 to 9, H₂O•, Cl•, and Cl₂• - The concentrations of H₂O, Cl, ClO, O₃, and Cl₂•- decreased by 49.1%, 48.4%, and 71.1%, respectively, while the concentrations of ClO• and O₃ increased by 6.88% and 97.7%, respectively. In summary, the concentrations of H₂O•, Cl•, ClO•, O₃, and Cl₂•- all showed a pH dependence.

[0052] Based on measured steady-state concentrations of reactive species, this study quantified the contributions of O3, ClO•, HO•, and free available chlorine (FAC) to the oxidation of Mn(II). The rate constants of the four reactive substances (ClO•, HO•, O3, and FAC) were calculated under UVA-LED / NaClO processes as follows. First, the rate constants of HO• on Mn(II) oxidation were calculated... k HO•-Mn(Ⅱ) = 3.0 × 10 7 M -1 s -1 ) and steady-state concentration calculation of HO• on the oxidation rate constant of Mn(II) ( k HO•-Mn(Ⅱ) ' Under three different pH UVA-LED / NaClO processes, k HO•-Mn(Ⅱ) 'The values ​​were 0.0035, 0.0024, and 0.0018 min, respectively. -1 Given the rate constants of O3 and Mn(II) ( k O3-Mn(Ⅱ) ) is 1.5×10 3 M -1 s -1 (Qian et al., 2023), and k O3-Mn(Ⅱ) ' The values ​​were 0.0026, 0.0356, and 0.1135 min, respectively. -1 Based on the oxidation rate of Mn(II) under NaClO treatment alone, the reaction rates of FAC were 0.0071, 0.0068, and 0.0043 min, respectively. -1 . , Known k ClO•-Mn(Ⅱ) 2.25×10 6 M -1 s -1 . k ClO•-Mn(Ⅱ) ' The values ​​were 0.1083, 0.1131, and 0.1163 min at the three pH values, respectively. -1 Finally, using the formula k ′ reactⅣe species-Mn(Ⅱ) / k obs The relative contribution of each reactive substance to the oxidation of Mn(II) was determined. Figure 1 c).

[0053] like Figure 1 As shown in (d), the relative contribution of each reactive substance to the oxidation of Mn(II) was determined. At pH = 7.0, the rate constants for the reactions of HO•, FAC, ClO•, and O3 with Mn(II) were 0.002, 0.007, 0.113, and 0.036 min, respectively. -1 Their relative contributions were 1.53%, 4.27%, 71.0%, and 22.4%, respectively. The contributions of ClO• and O3 at different pH values ​​were then calculated. During the oxidation of Mn(II) in the UVA-LED / NaClO system, as the pH increased from 4.0 to 9.0, the contribution of ClO• decreased from 88.2% to 48.6%, while the contribution of O3 increased from 2.14% to 47.4%. The fundamental reason is that during the UVA-LED irradiation of NaClO, the increased pH promotes the conversion of HOCl to ClO. - Under UVA irradiation, ClO -The photolysis pathway can more efficiently produce oxygen atoms O(3P), which rapidly combine with O2 in the solution to efficiently generate O3. Due to this transformation, the concentration of O3 produced by photolysis at high pH values ​​significantly exceeds the accompanying increase in ClO• concentration, ultimately causing their oxidation contributions to change in opposite directions.

[0054] Furthermore, this study investigated the effect of UVA wavelength on the oxidation of Mn(II) in the UVA-LED / NaClO system (Examples 1, 4-6). The results showed that the oxidation efficiency of Mn(II) decreased with increasing wavelength, from 91.9% at 365 nm to 65.0% at 405 nm. This phenomenon can be attributed to the higher molar absorptivity and quantum yield of NaClO at shorter wavelengths, which are beneficial for the oxidation of Mn(II). Compared with other UVA wavelengths, 365 nm showed superior efficiency in activating NaClO. Furthermore, the oxidation effects of UVA-LED alone (Comparative Example 3), NaClO alone (Comparative Example 1), and the UVA-LED / NaClO system (Example 1) were compared. Within 15 minutes, neither UVA-LED irradiation alone nor NaClO alone showed a significant oxidation effect on Mn(II), oxidizing only 3.7% and 8.7% of Mn(II), respectively. In addition, the pseudo-first-order reaction rate constants of NaClO alone and UVA-LED alone for the oxidation of Mn(II) were compared. k obs The time was only 0.007 min. -1 and 0.003min -1 In contrast, the oxidation efficiency of Mn(II) can reach 91.9% under the combined action of 500 μM NaClO and UVA-LED. k obs It is 0.159 min -1 This indicates that UVA-LED activation of NaClO can achieve rapid oxidation of Mn(II).

[0055] Furthermore, this study investigated the effect of light intensity on the oxidation of Mn(II) in the UVA-LED / NaClO system (Examples 1 and 7-8). The results showed that when the UVA light intensities were 8.6, 18.4, and 31.2 mW / cm², the oxidation efficiencies of Mn(II) were 88.1%, 91.9%, and 95.0%, respectively. The study concluded that higher light intensities promoted the photolysis of NaClO, increased the generation of active species, and thus significantly accelerated the oxidation process of Mn(II).

[0056] In addition, this study investigated the effect of NaClO dosage on the oxidation of Mn(II) (Examples 1, 9-10). When the NaClO concentration increased from 200 μM to 700 μM, the oxidation efficiency of Mn(II) increased from 80.6% to 99.4%. This phenomenon is attributed to the higher NaClO dosage generating more active species, thus significantly enhancing the oxidation process of Mn(II). Notably, when the NaClO dosage was further increased from 700 μM to 1000 μM, the Kobs value of Mn(II) decreased from 0.298 min. - ¹ decreased to 0.153 min - ¹. This is because NaClO has limited light absorption capacity at specific wavelengths. When the NaClO concentration reaches a certain level, the generation rate of active species in the system cannot continue to increase, resulting in no further improvement in oxidation efficiency. In summary, appropriately increasing the amount of NaClO can improve the oxidation rate and efficiency of Mn(II), but excessive NaClO will weaken the oxidation effect of Mn(II).

[0057] Furthermore, this invention also explores Cl - HCO3 - The effect of humic acid (HA) concentration on the removal of manganese ions in this invention was investigated. Based on Example 1, different concentrations of Cl were added to the water. - HCO3 - and humic acid (HA), the results are as follows Figure 2 As shown, Figure 2 (a) Adding 1, 5, and 10 mM Cl - Effect of UVA-LED / NaClO system on the oxidation of Mn(II); Figure 2 (b) Add 1, 5, or 10 mM HCO3 - Effect of UVA-LED / NaClO system on the oxidation of Mn(II); Figure 2 (c) Effect of adding 1, 3, and 5 mg / L HA on the oxidation of Mn(II) in the UVA-LED / NaClO system; Figure 2 (d) Effect of adding 5 mg / L HA on the oxidation of Mn(II) by UVA-LED alone, NaClO alone and UVA-LED / NaClO system.

[0058] from Figure 2 Look, Cl - HCO3 - The concentration range of 1 to 10 mM had almost no effect on the oxidation efficiency of Mn(II) in the UVA-LED / NaClO system, while HA showed a slight promoting effect in the concentration range of 1 to 5 mg / L.

[0059] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for removing divalent manganese from water, characterized in that, Includes the following steps: To contain Mn 2+ NaClO is added to water to obtain a mixed solution, which is then stirred and reacted under long-wave ultraviolet irradiation to obtain the final product.

2. The method for removing divalent manganese from water according to claim 1, characterized in that, The wavelength of the long-wave ultraviolet light is 365~405 nm.

3. The method for removing divalent manganese from water according to claim 1, characterized in that, The intensity of the long-wave ultraviolet light is 8.6~31.2 mW / cm².

4. The method for removing divalent manganese from water according to claim 1, characterized in that, The concentration of NaClO is 200~1000 μM.

5. The method for removing divalent manganese from water according to claim 1 or 4, characterized in that, The concentration of NaClO is 500~700 μM.

6. The method for removing divalent manganese from water according to claim 1, characterized in that, The Mn 2+ The concentration is 10~100 μM.

7. The method for removing divalent manganese from water according to claim 1, characterized in that, The stirring reaction time is 10-60 min.

8. The method for removing divalent manganese from water according to claim 1, characterized in that, The reaction temperature of the stirring reaction is 20~30℃.

9. The method for removing divalent manganese from water according to claim 1, characterized in that, The stirring speed is 300 r / min to 1000 r / min.

10. The method for removing divalent manganese from water according to claim 1, characterized in that, The pH value of the mixture is 4.0~9.0.

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