Treatment method for cyanide-containing wastewater

Abstract

The present invention aims to provide a method for treating cyanide-containing wastewater to which an oxidizing agent is added, which effectively reduces the cyanide component in cyanide-containing wastewater without adding heavy metals, or by reducing the amount of heavy metals added. [Solution] A method for treating cyanide-containing wastewater, comprising adding an oxidizing agent and an organic catalyst simultaneously or separately to the cyanide-containing wastewater.

Description

Technical Field

[0001] The present invention relates to a method for treating cyanide-containing wastewater.

Background Art

[0002] Since cyanide has a strong adverse effect on the ecosystem, cyanide-containing wastewater (hereinafter also referred to as "cyanide wastewater") cannot be directly discharged into nature. Depending on the origin of the wastewater, cyanide exists in the wastewater in three forms: hardly decomposable cyanide complexes and their ions, easily decomposable cyanide complexes and their ions, and cyanide ions (free cyanide), although the content varies.

[0003] Conventionally, various methods have been proposed and put into practical use for the removal treatment of cyanide in cyanide-containing wastewater, but each has its advantages and disadvantages and is used appropriately according to the situation of the wastewater. For example, (1) the alkaline chlorine method in which cyanide-containing wastewater is adjusted to be alkaline and then chlorine is injected to oxidize and decompose cyanide; (2) the ozone oxidation method in which cyanide is oxidized and decomposed into nitrogen gas and bicarbonate by the strong oxidizing power of ozone; and (3) oxidation decomposition methods such as the electrolytic oxidation method (electrolysis method) in which cyanide is electrolyzed using an insoluble electrode to perform an oxidation reaction; (4) the Prussian blue method in which, for example, ferrous sulfate is added as a supply compound of iron ions to cyanide-containing wastewater to generate insoluble ferro / ferricyanide, which is then removed by precipitation; (5) the zinc white method in which zinc chloride and a reducing agent are added and the generated insoluble complex is removed by precipitation; and (6) the reduced copper salt method in which a copper salt and a reducing agent are added and the generated insoluble complex is removed by precipitation; (7) the biological treatment method in which cyanide is decomposed by microorganisms (cyanide-decomposing bacteria) acclimated to cyanide; (8) the thermal hydrolysis method in which cyanide-containing wastewater is maintained at a high temperature to hydrolyze cyanide compounds into ammonia and formic acid, and coexisting heavy metals are precipitated as simple substances or oxides; and (9) hot water reactions such as the wet oxidation method in which organic pollutants are also oxidized and decomposed in addition to the decomposition of cyanide. Therefore, various chemicals have been used appropriately according to the situation of the wastewater for the removal treatment of cyanide in cyanide-containing wastewater.

[0004] Regarding the treatment methods for removing cyanide from cyanide-containing wastewater as described above, the following disclosures exist regarding treatment methods using oxidizing agents. For example, Patent Document 1 discloses a wastewater treatment method in which hydrogen peroxide, a copper salt, and a reducing agent are added to wastewater containing at least one of free cyanide, a zinc cyano complex, a nickel cyano complex, and a copper cyano complex, as well as an iron cyano complex, and the reaction is carried out by solid-liquid separation of the reaction solution to separate and remove the sparingly soluble cyanide compounds produced in the reaction solution. The method discloses the use of hydrogen peroxide in the treatment of wastewater containing cyanide compounds.

[0005] Furthermore, Patent Document 2 describes a method for removing cyanide from cyanide-containing wastewater by using chlorine dioxide in combination with one or more metal compounds selected from manganese compounds, iron compounds, zinc compounds, and copper compounds. Specifically, Patent Document 2 discloses that by using a reducing agent in addition to chlorine dioxide and the above metal compounds in combination with cyanide-containing wastewater, a COD (chemical oxygen demand) removal effect can be obtained, and that chlorine dioxide, which is an oxidizing agent, is used.

[0006] Furthermore, Patent Document 3 discloses a method for treating cyanide wastewater in which hydrogen peroxide solution is used as an oxidizing agent and manganese is added as a catalyst for this hydrogen peroxide solution. Furthermore, Patent Document 4 discloses a method for detoxifying an aqueous solution containing cyanide and / or cyano complexes by oxidizing the solution with a peroxide compound, using at least one equivalent of a peroxide compound per equivalent of cyanide in the presence of a heavy metal compound, at a pH of 8 to 12 and a temperature of around 80°C where the solution freezes. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6474472 [Patent Document 2] Japanese Patent Publication No. 2021-53620 [Patent Document 3] Japanese Patent Application Publication No. 58-34083 [Patent Document 4] Japanese Patent Application Publication No. 5-68979 [Overview of the project] [Problems that the invention aims to solve]

[0008] As mentioned above, there are several methods for adding oxidizing agents in the treatment of cyanide-containing wastewater, but in conventional treatment of cyanide-containing wastewater, oxidizing agents have mainly been used together with or in the presence of heavy metals such as manganese compounds, iron compounds, zinc compounds, and copper compounds. Therefore, when adding an oxidizing agent in the treatment of cyanide-containing wastewater, if the amount of heavy metals present in the wastewater is insufficient for cyanide treatment, both the oxidizing agent and heavy metals are added to the cyanide-containing wastewater. If the amount of heavy metals present in the wastewater is sufficient for cyanide treatment, the oxidizing agent is added alone. However, since the amount of heavy metals present in cyanide-containing wastewater does not always remain constant and fluctuates, when an oxidizing agent is used to treat cyanide-containing wastewater, heavy metals are generally also added. However, heavy metals are regulated by wastewater standards due to concerns about their adverse effects on ecosystems, and heavy metals used in wastewater treatment are difficult to recover. Recently, their use has also become a challenge from the perspective of promoting the efficient use of resources.

[0009] Therefore, the object of the present invention is to provide a method for treating cyanide-containing wastewater to which an oxidizing agent is added, which effectively reduces the cyanide component in cyanide-containing wastewater without adding heavy metals, or by reducing the amount of heavy metals added. [Means for solving the problem]

[0010] The inventors of this invention diligently studied methods for treating cyanide-containing wastewater using oxidizing agents and, as a result, unexpectedly discovered that using an organic catalyst together with the oxidizing agent significantly improved the effect of reducing cyanide components in cyanide-containing wastewater, leading to the completion of this invention. This invention can also improve the effect of reducing cyanide components in the treatment of cyanide-containing wastewater that also contains heavy metals.

[0011] In other words, the present invention is not limited to the following, but relates to a method for treating cyanide-containing wastewater.

[0012] [1] A method for treating cyanide-containing wastewater, comprising adding an oxidizing agent and an organic catalyst simultaneously or separately to the cyanide-containing wastewater. [2] The treatment method described in [1] above, wherein the cyanide in the wastewater is reduced by oxidation of the cyanide component in the wastewater. [3] The treatment method according to either [1] or [2] above, wherein the organic catalyst is a compound having the function of catalyzing an electron transfer reaction. [4] The treatment method according to any one of [1] to [3] above, wherein the oxidizing agent is added to the cyanide-containing wastewater so that the concentration of the oxidizing agent in the cyanide-containing wastewater is 0.01 mmol / L or more. [Effects of the Invention]

[0013] According to the present invention, in a method for treating cyanide-containing wastewater to which an oxidizing agent is added, it is possible to provide a method for treating cyanide-containing wastewater that effectively reduces the cyanide component in the wastewater without adding heavy metals, or by reducing the amount of heavy metals added. Furthermore, according to the present invention, in a method for treating cyanide-containing wastewater to which an oxidizing agent is added, the cyanide component can be effectively reduced even in the treatment of cyanide-containing wastewater that already contains heavy metals. [Modes for carrying out the invention]

[0014] The present invention relates to a method for treating cyanide-containing wastewater, characterized by adding an oxidizing agent and an organic catalyst to the cyanide-containing wastewater simultaneously or separately.

[0015] In the present invention, the method for treating cyanide-containing wastewater preferably reduces the amount of cyanide in the wastewater by oxidation of the cyanide components in the wastewater. While it is believed that the treatment method of the present invention decomposes the cyanide in the wastewater through oxidation, the mechanism of cyanide decomposition is not clear. The inventors of the present invention believe that the cyanide is oxidized and decomposed by the added oxidizing agent and organic catalyst. As described above and as is clear from the results of the examples, the method for treating cyanide-containing wastewater of the present invention, by using an oxidizing agent and an organic catalyst in combination, effectively decomposes the cyanide components in cyanide-containing wastewater. Therefore, even when using an oxidizing agent with weaker oxidizing power than conventional oxidizing agents such as hypochlorite (for example, chlorite, chlorine dioxide, hydrogen peroxide) used in the treatment of cyanide-containing wastewater, it is considered that the effect of reducing cyanide components in cyanide-containing wastewater can be significantly improved. Furthermore, for oxidizing agents with relatively strong oxidizing power, such as hypochlorite, it is believed that by using them in combination with organic catalysts, the reduction in cyanide components in cyanide-containing wastewater can be achieved even with a reduced amount of oxidizing agent used.

[0016] While methods for treating cyanide-containing wastewater using chlorine dioxide are already known, for example, Japanese Patent Publication No. 52-123976 discloses a method for treating cyanide-containing wastewater using chlorine dioxide. However, reducing the total cyanide concentration in cyanide-containing wastewater to 1 mg / L or less requires the use of a large amount of chlorine dioxide (for example, 10% of the total volume in the above-mentioned publication), and a method for reducing the amount of chlorine dioxide used while reducing the cyanide component in wastewater was desired for practical application. On the other hand, there have been few studies on the treatment of cyanide-containing wastewater using chlorite as the main agent. This is because chlorite has weaker oxidizing power compared to hypochlorite, and it was thought that its effect on reducing cyanide components in cyanide-containing wastewater was low or almost nonexistent. However, although both chlorine dioxide and chlorite have weaker oxidizing power compared to hypochlorite, during treatment, it is possible to obtain treated wastewater without the risk of halogenated salts without controlling the pH, and thus they have the effect of being reusable. Therefore, in addition to hypochlorite, a method for treating cyanide-containing wastewater using such oxidants is also desired.

[0017] <Cyanide-containing wastewater> In the present invention, the cyanide-containing wastewater to be treated includes cyanide-containing wastewater containing cyanide components such as metal cyanide compounds, cyanide ions, cyanide complexes, and cyano complex ions discharged from steel mills, chemical factories, plating factories, coke manufacturing factories, metal surface treatment factories, etc., cyanide-containing wastewater discharged in the treatment process of radioactive contaminated water, and cyanide-containing wastewater discharged from soil treatment devices.

[0018] In the present invention, the cyanide content in the cyanide-containing wastewater to be treated is not particularly limited, but the above-mentioned cyanide-containing wastewater generally has a total cyanide concentration of about 1 to 500 mg / L. The total cyanide concentration can be measured in accordance with JIS K0102. Further, the method for treating cyanide-containing wastewater of the present invention is suitable for treating wastewater containing cyanide ions (free cyanide), and for example, it may be wastewater in which easily decomposable cyanide complexes and their ions, as well as hardly decomposable cyanide complexes and their ions, are present.

[0019] In the present invention, the concentration of suspended substances in the cyanide-containing wastewater to be treated is not particularly limited, but it is preferably less than 10000 mg / L, and more preferably less than 5000 mg / L. The cyanide-containing wastewater that is the treatment target of the present invention may not contain suspended substances. That is, the suspended substances may be below the detection limit.

[0020] In the present invention, the oxidation-reduction concentration (ORP) of the cyanide-containing wastewater to be treated is not particularly limited, but since the ORP of cyanide-containing wastewater is an indicator of the effect of the oxidizing agent, the ORP of cyanide-containing wastewater may be used for the treatment management of the oxidizing agent. In the present invention, the ORP of the cyanide-containing water after the addition of the oxidizing agent is preferably an oxidizing atmosphere of 0 mV or higher, more preferably an oxidizing atmosphere of 0 mV to 500 mV, and even more preferably an oxidizing atmosphere of 10 mV to 400 mV. Furthermore, the ORP of cyanide-containing wastewater to which the treatment method of the present invention is applied is preferably 500 mV or less, and more preferably 400 mV or less. This is because if the cyanide-containing wastewater before the addition of the oxidizing agent is in a sufficiently oxidizing atmosphere, there is no need to apply the present invention.

[0021] <Oxidizing agent> The oxidizing agent used in the treatment method of the present invention is not particularly limited as long as it is a compound that oxidizes cyanide in cyanide-containing wastewater. Examples include hypochlorite, hypobromite, chlorite, bromite, chlorine dioxide, bromine dioxide, ozone, hydrogen peroxide, hydrogen peroxide adducts, persulfates, peracetic acid, percarbonates, perborates, superphosphates, and persilicates. Among these, the oxidizing agent is preferably at least one selected from the group consisting of hydrogen peroxide, chlorite, chlorine dioxide, and persulfates, more preferably at least one selected from the group consisting of hydrogen peroxide, chlorite, and chlorine dioxide, and even more preferably hydrogen peroxide. Furthermore, the oxidizing agent used in the treatment method of the present invention may be a single agent or a mixture of two or more agents. In the case of a mixture of two or more agents, the component ratio of the mixed oxidizing agent can be appropriately changed depending on the cyanide-containing wastewater that is the target of the treatment method of the present invention.

[0022] (Chlorite) The chlorite is not particularly limited as long as it is a compound that can generate chlorous acid or chlorite ions in water. Examples include alkali metal salts and alkaline earth metal salts of chlorous acid such as sodium chlorite, potassium chlorite, calcium chlorite, and magnesium chlorite, as well as hydantoin derivatives. In particular, sodium chlorite and potassium chlorite are readily available industrially and are suitably used in the present invention.

[0023] (Chlorine dioxide) Chlorine dioxide is an extremely unstable chemical substance, making its storage and transportation very difficult. Therefore, although chlorine dioxide or compounds capable of generating chlorine dioxide in wastewater may be added directly to wastewater, it is preferable to produce (generate) chlorine dioxide on-site by known methods, or to generate chlorine dioxide by adding a compound capable of generating chlorine dioxide in wastewater to water, and then adjust the concentration to the desired level before use. For example, chlorine dioxide can be produced by the following reaction, and commercially available chlorine dioxide generators (devices) can also be used. (1) Reaction of sodium hypochlorite, hydrochloric acid, and sodium hypochlorite NaOCl+2HCl+2NaClO2→ 2ClO2+3NaCl+H2O (2) Reaction of sodium chlorite with hydrochloric acid 5NaClO2+4HCl → 4ClO2+5NaCl+2H2O (3) Reactions with sodium chlorate, hydrogen peroxide and sulfuric acid 2NaClO3+H2O2+H2SO4→ 2ClO2+Na2SO4+O2+2H2O

[0024] (hydrogen peroxide) The hydrogen peroxide used in this invention mainly refers to commercially available aqueous solutions of hydrogen peroxide with a concentration of 3 to 60% for industrial use. In addition, hydrogen peroxide generated from hydrogen peroxide supply compounds (also called "hydrogen peroxide generators") or hydrogen peroxide generated by electrolysis of water or alkaline solutions can also be used. Examples of hydrogen peroxide-releasing compounds include inorganic peracids such as percarbonate, perboric acid, and peroxysulfuric acid, which can release hydrogen peroxide in water, organic peracids such as peracetic acid, and their salts. Examples of these salts include sodium percarbonate and sodium perborate. The hydrogen peroxide and hydrogen peroxide supply compound described above may be diluted or dissolved in water to achieve the desired hydrogen peroxide concentration before use.

[0025] (Persulfate) In the present invention, one or more persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate can be used, and preferably sodium persulfate and potassium persulfate.

[0026] <Organic catalyst> The organic catalyst used in the water treatment method of the present invention is not particularly limited as long as it is a compound that functions as a catalyst for the oxidation reaction of cyanide by the oxidizing agent in cyanide-containing wastewater. For example, the organic catalyst used in the water treatment method of the present invention is preferably a water-soluble organic catalyst and / or a compound that has the function of catalyzing an electron transfer reaction.

[0027] In the present invention, a water-soluble organic catalyst is a compound with a solubility of 0.01 g / L or more. Preferably, the water-soluble organic catalyst is at least one selected from the group consisting of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (H-TEMPO, TEMPOL), 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), hydroquinone-parabenzoquinone, N-tert-butyl-α-phenylnitrone (PBN), and ammonium 1,4-dihydroxy-2-naphthalenesulfonate.

[0028] Examples of compounds that have the function of catalyzing electron transfer reactions include compounds having radical scavenging function, polymerization termination function, spin trap function, spin probe function, etc. Preferably, it is at least one selected from the group consisting of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (H-TEMPO, TEMPOL), 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), hydroquinone, its derivatives, parabenzoquinone, N-tert-butyl-α-phenylnitrone (PBN), ammonium 1,4-dihydroxy-2-naphthalenesulfonate, N,N'-di-sec-butyl-1,4-phenylenediamine, triphenylphosphine oxide (TPPO), and proline.

[0029] The compound having the function of catalyzing the above electron transfer reaction is more preferably a compound having radical scavenging function, and even more preferably a water-soluble compound having radical scavenging function. As a water-soluble compound having radical scavenging function, it is preferable that it is at least one selected from the group consisting of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (H-TEMPO, TEMPOL)2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), hydroquinone, parabenzoquinone, N-tert-butyl-α-phenylnitrone (PBN), and ammonium 1,4-dihydroxy-2-naphthalenesulfonate.

[0030] <Addition of compounds> The present invention provides a method for treating cyanide-containing wastewater, which includes a step of adding an oxidizing agent and an organic catalyst to the cyanide-containing wastewater simultaneously or separately. However, when adding the oxidizing agent and the organic catalyst separately to the cyanide-containing wastewater, the order of addition does not matter, as long as the oxidizing agent and the organic catalyst are added in a manner that allows them to coexist in the cyanide-containing wastewater.

[0031] In the treatment method of the present invention, it is preferable that the oxidizing agent is added to the cyanide-containing wastewater so that the concentration of the oxidizing agent in the cyanide-containing wastewater is 0.01 mmol / L or more. It is more preferable that the oxidizing agent is added to the cyanide-containing wastewater so that the concentration of the oxidizing agent in the cyanide-containing wastewater is 0.025 mmol / L or more, even more preferable that it is added so that it is 0.05 mmol / L or more, even more preferable that it is added so that it is 0.1 mmol / L or more, and even more preferable that it is added so that it is 0.3 mmol / L or more. Note that the concentration of the oxidizing agent in the cyanide-containing wastewater refers to the molar concentration of the pure oxidizing agent added.

[0032] The type and amount of oxidizing agent to be added are affected by the type and concentration (or cyanide content) of cyanide components contained in the cyanide-containing wastewater, and should be determined appropriately according to these conditions. Specifically, for example, the type and concentration (or cyanide content) of cyanide in the cyanide-containing wastewater may be measured in advance (from immediately before treatment to about 3 hours before treatment), and the type and amount of oxidizing agent to be used in the treatment method of the present invention may be determined based on these measurement results. Furthermore, in wastewater where the type and concentration (or cyanide content) of cyanide contained in the cyanide-containing wastewater do not change significantly over time, the type and amount of oxidizing agent to be added may be determined based on the type and concentration (or cyanide content) of cyanide that have already been measured.

[0033] As described above, the amount of oxidizing agent to be added varies depending on the type and amount of cyanide components contained in the cyanide-containing wastewater, but it is preferable that the total molar ratio of the oxidizing agent to the cyanide content (moles) in the wastewater be 0.025 times or more. For example, if one of chlorite, chlorine dioxide, hydrogen peroxide, or persulfate is used alone as the treatment method for cyanide-containing wastewater of the present invention, the total amount of any of the agents added should be determined so that the molar ratio to the cyanide content in the wastewater is 0.025 times or more. Also, if two or more selected from the group consisting of chlorite, chlorine dioxide, hydrogen peroxide, and persulfate are used, the total molar ratio obtained by summing the molar ratios of the two selected oxidizing agents to the cyanide content in the wastewater should be 0.025 times or more. The total molar ratio of the oxidizing agent to the cyanide content in the wastewater is more preferably 0.3 times or more, more preferably 0.5 times or more, more preferably 0.8 times or more, more preferably 0.9 times or more, more preferably 1 time or more, and may also be 5 times or more, or 10 times or more. Furthermore, the total molar ratio of the oxidizing agent to the cyanide content in the wastewater is preferably 200 times or less, more preferably 100 times or less, more preferably 50 times or less, more preferably 30 times or less, and may also be 20 times or less, or 10 times or less. This is because if the total molar ratio of the oxidizing agent to the cyanide content in the wastewater is less than 0.025 times, the effect of reducing cyanide components may be insufficient depending on the type of wastewater.

[0034] In the treatment method of the present invention, the amount of organic catalyst added to cyanide-containing wastewater is not particularly limited, but it is preferable that the amount is added such that the molar ratio (amount of oxidizing agent added (moles): amount of organic catalyst added (moles)) to the amount of oxidizing agent added to the cyanide-containing wastewater is 10000:1 to 1:10, more preferably 3000:1 to 1:10, more preferably 1500:1 to 1:10, more preferably 1000:1 to 1:10, more preferably 100:1 to 1:10, more preferably 10:1 to 1:10, more preferably 10:1 to 1:6, and more preferably 10:1 to 1:3. The organic catalyst is preferably added to the cyanide-containing wastewater so that the concentration of the organic catalyst in the cyanide-containing wastewater is 0.005 mmol / L or higher. Furthermore, it is more preferable that the organic catalyst is added so that the concentration of the organic catalyst in the cyanide-containing wastewater is 0.01 mmol / L or higher, even more preferable that it is 0.05 mmol / L or higher, even more preferable that it is 0.1 mmol / L or higher, even more preferable that it is 0.15 mmol / L or higher, and particularly preferable that it is 0.3 mmol / L or higher. Note that the concentration of the organic catalyst in the cyanide-containing wastewater refers to the molar concentration of the pure compound added.

[0035] In the method for treating cyanide-containing wastewater of the present invention, it is preferable to have a stirring step after adding the oxidizing agent and the organic catalyst simultaneously or separately, so as to reduce the cyanide component, that the oxidizing agent, the organic catalyst, and the cyanide-containing wastewater are mixed. It is preferable to perform this stirring after each addition of the oxidizing agent and the organic catalyst. Furthermore, in order to promote the reaction during stirring, the liquid temperature of the cyanide-containing wastewater to be treated is preferably around 20 to 80°C, and more preferably 30 to 60°C.

[0036] For cyanide-containing wastewater, a pH of 6 to 9 is preferable in terms of reducing cyanide content. If the pH of cyanide-containing wastewater is below 6, there is a risk of harmful hydrogen cyanide gas being released. On the other hand, if the pH of cyanide-containing wastewater exceeds 9, it will exceed wastewater standards, and further pH adjustment will be necessary. Note that the cyanide-containing wastewater may be wastewater that has been adjusted to a pH of 6 to 9.

[0037] The present invention provides a method for treating cyanide-containing wastewater, which involves adding an oxidizing agent and an organic catalyst simultaneously or separately to the cyanide-containing wastewater. It does not particularly limit the presence or absence of heavy metals in the cyanide-containing wastewater, or whether or not heavy metals are added to the cyanide-containing wastewater. For example, even if the method includes a step of substantially adding heavy metals to the cyanide-containing wastewater, the amount of heavy metals used can be reduced according to the present invention. The present invention may also provide a method for treating cyanide-containing wastewater that does not include a step of substantially adding heavy metals to the cyanide-containing wastewater. The step of substantially adding heavy metals to cyanide-containing wastewater means adding heavy metals to the cyanide-containing wastewater to an extent that produces a cyanide treatment effect.

[0038] If the method for treating cyanide-containing wastewater of the present invention includes a step of substantially adding heavy metals to cyanide-containing wastewater, the concentration of the added heavy metals is affected not only by the type and concentration of cyanide contained in the cyanide-containing wastewater, but also by the type and concentration of the same or different metal compounds (ions) contained in the cyanide-containing wastewater. The concentration should be determined appropriately according to these conditions, but for example, it is preferably 150 mg / L or less, preferably 100 mg / L or less, preferably 30 mg / L or less, more preferably 10 mg / L or less, even more preferably 5 mg / L or less, and even more preferably 3 mg / L or less in the cyanide-containing wastewater. [Examples]

[0039] The present invention will be further described below using examples. However, the present invention is not limited to the following examples.

[0040] (Water quality of the test water) The cyanide-containing wastewater used in Test Examples 1 and 2 below had the water quality shown in Table 1. The cyanide-containing wastewater used was prepared by adding potassium cyanide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium chloride (manufactured by Kishida Chemical Co., Ltd.), sodium sulfate (manufactured by Kishida Chemical Co., Ltd.), ammonium chloride (manufactured by Kishida Chemical Co., Ltd.), and sodium bicarbonate (manufactured by Kishida Chemical Co., Ltd.) to pure water to prepare synthetic water. The cyanide ion concentration of the cyanide-containing wastewater used in Test Examples 1 and 2 below was 30 mg / L, and the pH was approximately 8.

[0041] [Table 1]

[0042] (Test Example 1: Examples 1-1 to 1-3, Comparative Examples 1-1 to 1-3) 100 mL of cyanide-containing wastewater was dispensed into 100 mL polyethylene containers, and the oxidizing agent and organic catalyst shown in Table 2 were added to obtain test water at concentrations shown in Table 2. The obtained test water was then stirred at 55°C for 3 hours using a constant-temperature shaker to obtain treated water. The pH of the obtained treated water was approximately 7-8, and the ORP was 180-370 mV. Next, the obtained treated water was filtered using quantitative filter paper No. 5C, and the total cyanide concentration (T-CN) in the obtained filtrate was measured in accordance with JIS K0102 to evaluate the cyanide reduction effect in each test water. Comparative Examples 1-1 to 1-3 are test examples conducted using the same procedure as the Examples, except that an organic catalyst was not added. The results obtained, along with the added compounds and their amounts, are shown in Table 2. The CN treatment amount was defined as the total cyanide concentration of the treated water filtrate minus the total cyanide concentration at the start of the test. A higher value indicated a greater effect in reducing the cyanide component.

[0043] [Oxidizing agent] chlorine dioxide hydrogen peroxide Sodium persulfate (Na persulfate) [Organic catalyst] H-TEMPO:4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl

[0044] [Table 2]

[0045] From the results in Table 2, it was confirmed that in the test examples related to Examples 1-1 to 1-3, in which an oxidizing agent and an organic catalyst were added, the amount of cyanide component treated was increased compared to the test examples related to Comparative Examples 1-1 to 1-3, in which only an oxidizing agent was added, and the effect of reducing cyanide components in cyanide-containing wastewater was significantly improved.

[0046] (Test Example 2: Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-4) 100 mL of cyanide-containing wastewater was dispensed into 100 mL polyethylene containers, and the oxidizing agent and organic catalyst shown in Table 3 were added to obtain test water at concentrations shown in Table 3. The obtained test water was then stirred at 55°C for 3 hours using a constant-temperature shaker to obtain treated water. The pH of the obtained treated water was approximately 7-8, and the ORP was 20-350 mV. Next, the obtained treated water was filtered using quantitative filter paper No. 5C, and the total cyanide concentration (T-CN) in the obtained filtrate was measured in accordance with JIS K0102 to evaluate the cyanide reduction effect in each test water. Comparative Examples 2-1 to 2-4 are test examples conducted using the same procedure as the Examples, except that an organic catalyst was not added. The results obtained, along with the added compounds and their amounts, are shown in Table 3. The CN treatment amount was defined as the total cyanide concentration of the treated water filtrate minus the total cyanide concentration at the start of the test. A higher value indicated a greater reduction in cyanide components.

[0047] [Oxidizing agent] Sodium chlorite (Na chlorite) chlorine dioxide hydrogen peroxide Sodium persulfate (Na persulfate) [Organic catalyst] Hydroquinone

[0048] [Table 3]

[0049] From the results in Table 3, it was confirmed that in the test examples 2-1 to 2-4, in which an oxidizing agent and an organic catalyst were added, the amount of cyanide component treated was increased compared to the test examples 2-1 to 2-4, in which only an oxidizing agent was added, and the effect of reducing cyanide components in cyanide-containing wastewater was significantly improved.

[0050] (Test Example 3: Examples 3-1 to 3-6, Comparative Example 3-1) The cyanide-containing wastewater used in Test Example 3 was as follows:

[0051] (Water quality of the test water) The cyanide-containing wastewater used in Test Example 3 had the water quality shown in Table 4 below. The cyanide-containing wastewater used was prepared by adding potassium cyanide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium chloride (manufactured by Kishida Chemical Co., Ltd.), sodium sulfate (manufactured by Kishida Chemical Co., Ltd.), ammonium chloride (manufactured by Kishida Chemical Co., Ltd.), and sodium bicarbonate (manufactured by Kishida Chemical Co., Ltd.) to pure water to prepare synthetic water. The cyanide ion concentration of the cyanide-containing wastewater used in Test Example 3 was approximately 2 mg / L, and the pH was approximately 8.

[0052] [Table 4]

[0053] 100 mL of cyanide-containing wastewater was dispensed into each 100 mL polyethylene container, and the oxidizing agent and organic catalyst shown in Table 5 were added to obtain test water at concentrations shown in Table 5.

[0054] Next, the obtained test water was stirred at 55°C for 3 hours using a constant-temperature shaker to obtain treated water. The pH of the obtained treated water was approximately 8, and the ORP was 140-220 mV. Next, the obtained treated water was filtered using quantitative filter paper No. 5C, and the total cyanide concentration (T-CN) in the obtained filtrate was measured in accordance with JIS K0102 to evaluate the cyanide reduction effect in each test water. Comparative Example 3-1 is a test example in which the same procedure as in the Examples was followed, except that an organic catalyst was not added. The results obtained, along with the added compounds and their amounts, are shown in Table 5. The CN treatment amount was calculated by subtracting the total cyanide concentration of the treated water filtrate from the total cyanide concentration at the start of the test.

[0055] [Oxidizing agent] Sodium persulfate (Na persulfate) [Organic catalyst] H-TEMPO:4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl

[0056] [Table 5]

[0057] The results in Table 5 show that in the test examples 3-1 to 3-6, in which both an oxidizing agent and an organic catalyst were added, the amount of cyanide component treated was increased compared to the test example 3-1, in which only an oxidizing agent was added, confirming the cyanide treatment effect of adding an organic catalyst.

[0058] (Test Example 4: Examples 4-1 to 4-10, Comparative Example 4-1) The cyanide-containing wastewater used in Test Example 4 is the same as that used in Test Example 3, except that the cyanide ion concentration was changed to 26 mg / L.

[0059] 100 mL of cyanide-containing wastewater was dispensed into each 100 mL polyethylene container, and the oxidizing agent and organic catalyst shown in Table 6 were added to obtain test water at concentrations shown in Table 6.

[0060] Next, the obtained test water was stirred at 55°C for 3 hours using a constant-temperature shaker to obtain treated water. The pH of the obtained treated water was approximately 8, and the ORP was 140-220 mV. Next, the obtained treated water was filtered using quantitative filter paper No. 5C, and the total cyanide concentration (T-CN) in the obtained filtrate was measured in accordance with JIS K0102 to evaluate the cyanide reduction effect in each test water. Comparative Example 4-1 is a test example in which the same procedure as in the Examples was followed, except that an organic catalyst was not added. The results obtained, along with the added compounds and their amounts, are shown in Table 6. The CN treatment amount was defined as the total cyanide concentration at the start of the test minus the total cyanide concentration of the treated water filtrate.

[0061] [Oxidizing agent] Sodium persulfate (Na persulfate) [Organic catalyst] H-TEMPO:4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl

[0062] [Table 6]

[0063] (Test Example 5: Examples 5-1 to 5-5, Comparative Example 5-1) The cyanide-containing wastewater used in Test Example 5 is the same as that used in Test Example 3, except that the cyanide ion concentration was changed to 25 mg / L.

[0064] 100 mL of cyanide-containing wastewater was dispensed into each 100 mL polyethylene container, and the oxidizing agent and organic catalyst shown in Table 7 were added to obtain test water at concentrations shown in Table 7.

[0065] Next, the obtained test water was stirred at 55°C for 3 hours using a constant-temperature shaker to obtain treated water. The pH of the obtained treated water was approximately 8, and the ORP was 0 to 260 mV. Next, the obtained treated water was filtered using quantitative filter paper No. 5C, and the total cyanide concentration (T-CN) in the obtained filtrate was measured in accordance with JIS K0102 to evaluate the cyanide reduction effect in each test water. Comparative Example 5-1 is a test example in which the same procedure as in the Examples was followed, except that an organic catalyst was not added. The results obtained, along with the added compounds and their amounts, are shown in Table 7. The CN treatment amount was calculated by subtracting the total cyanide concentration of the treated water filtrate from the total cyanide concentration at the start of the test.

[0066] [Oxidizing agent] Sodium persulfate (Na persulfate) [Organic catalyst] TEMPO:2,2,6,6-tetramethylpiperidine-1-oxyl p-Benzoquinone:1,4-Benzoquinone N,N'-di-sec-butyl-1,4-phenylenediamine PBN:N-tert-butyl-α-phenylnitrone 1,4-Dihydroxy-2-naphthalenesulfonate ammonium

[0067] [Table 7]

[0068] The results in Table 7 show that in the test examples 5-1 to 5-5, where an oxidizing agent and an organic catalyst were added, the amount of cyanide treated was increased compared to the test example 5-1, where only an oxidizing agent was added, confirming the cyanide treatment effect of adding an organic catalyst.

Claims

1. A method for treating cyanide-containing wastewater, comprising adding an oxidizing agent and an organic catalyst simultaneously or separately to the cyanide-containing wastewater.

2. The treatment method according to claim 1, wherein the cyanide in the wastewater is reduced by oxidation of the cyanide component in the wastewater.

3. The treatment method according to claim 1 or 2, wherein the organic catalyst is a compound having the function of catalyzing an electron transfer reaction.

4. The treatment method according to claim 1 or 2, wherein the oxidizing agent is added to the cyanide-containing wastewater so that the concentration of the oxidizing agent in the cyanide-containing wastewater is 0.01 mmol / L or more.

Images