Treatment methods for cyanide-containing water

Abstract

High-quality treated water with significantly reduced total cyanide concentration is obtained by stably and efficiently treating cyanide-containing water containing metal cyanide complexes and a large amount of inorganic carbon. A pH adjuster is added to the cyanide-containing water to adjust the pH to below 7.5. Then, a ferrous salt as a reducing agent and a copper compound are added to separate the insoluble salts of the generated cyanide. The cyanide-containing water contains metal cyanide complexes and contains inorganic carbon of 100 mg-C / L or more, as measured by total inorganic carbon based on total organic carbon as described in Japanese Industrial Standard K0102 Item 22.

Description

Technical Field

[0001] This invention relates to a method and apparatus for treating cyanide-containing water that contains metal cyanide complexes and a large amount of inorganic carbon, thereby obtaining high-quality treated water with a sufficiently reduced total cyanide concentration. Prior Technology

[0002] Previously, as a method for treating cyanide-containing water containing free cyanide or metal cyanide complexes, methods included treatment based on sodium hypochlorite (NaClO) under alkaline conditions (hereinafter referred to as "alkaline-hypochlorite treatment"), the Tirion blue method using ferrous sulfate, and treatment using copper (I) ions to generate sparingly soluble salts (hereinafter referred to as "total cyanide method") (Non-Patent Document 1).

[0003] The alkaline-sub-cyanochemical treatment is as follows: as shown in the reaction formula below, firstly, sodium cyanate is produced by adding NaClO to free cyanide under alkaline conditions (first stage), and then, by adding NaClO, it is finally decomposed into nitrogen gas (second stage). First stage: NaCN + NaOCl → NaCNO + NaCl Second stage: 2NaCNO + 3NaOCl → N2 + 3NaCl + 2NaHCO3 (NaHCO3 ⇔NaOH+CO2)

[0004] This method is effective for treating free cyanide, but it is not sufficiently effective for treating metal cyanide complexes such as ferrocyanide.

[0005] The Tirion blue method is as follows: by adding ferrous sulfate to cyanide-containing water containing ferrous cyanide, as shown in the following reaction formula, a water-insoluble metal cyanide complex is formed and removed. 3[Fe(CN)6 ]4- +4Fe3+ →Fe4 [Fe(CN)6 ]3 Iron-colored (Prussian blue) 2[Fe(CN)6 ]3- +3Fe2+ →Fe3 [Fe(CN)6 ]2 Ferrous iron oxide (Teng's blue) [Fe(CN)6 ]4- +2Fe2+ →Fe2 [Fe(CN)6 ] Ferroferroferrochrome (Berlin Blue)

[0006] In the Tirion process, when the pH of the water is higher than 6.0, the Fe2+ ions in ferrous sulfate become unstable and readily become hydroxides of Fe(OH)3, as shown in the following reaction formula. Therefore, treatment is required under conditions below pH 6.0. Fe4[Fe(CN)6]3 +12OH- →3[Fe(CN)6]4- +4Fe(OH)3 Regarding the Iron Blue method, based on the aforementioned reaction mechanism, it can be said that it is less effective for metal cyanide complexes other than iron (metal cyanide complexes of zinc, copper, silver, nickel, etc.).

[0007] As a total cyanide method, for example, there is a method as follows: copper and magnesium compounds are added to cyanide-containing water, and in the presence of a reducing agent such as sodium bisulfite, an insoluble salt of cyanide is generated and removed according to the following reaction formula (Patent Document 1).

[0008] [Chemistry 1]

[0009] According to this method, even any metal cyanide complex forms a sparingly soluble salt with Cu, which can stably treat cyanide.

[0010] As a method for treating cyanide-containing water containing both iron and copper compounds, the following method is proposed. Patent Document 2: A method for separating the insoluble silver cyanide complex formed by adding ferrous compounds such as ferrous sulfate and copper compounds such as copper sulfate to water containing silver cyanide complex and adjusting the pH to 3-8. Patent Document 3: A method for separating ferrous and copper salts in water containing ferric cyanide complexes under alkaline conditions of pH 9-11 in the presence of a reducing agent other than ferrous and copper salts to form an insoluble salt. Patent Document 4: A method for adding ferric salt and cuprous salt to cyanide-containing water, then adjusting the pH to 6-8, and removing the resulting water-insoluble salts. [Existing technical documents] [Patent Literature]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2013-226510 [Patent Document 2] Japanese Patent Publication No. 64-3553 [Patent Document 3] Japanese Patent Application Publication No. 1-30693 [Patent Document 4] Japanese Patent Application Publication No. 2005-313112 [Non-patent literature]

[0012] [Non-Patent Literature 1] Yoshihiro Eto and Toshitsugu Nakahara, "Inorganic Wastewater Treatment Technology Useful on-site", First Edition, Second Printing, Industrial Research Institute Co., Ltd., May 13, 2007, pp. 151-157 Summary of the Invention

[0013] [The problem that the invention aims to solve]

[0014] None of the aforementioned treatment methods have achieved sufficient cyanide removal for cyanide-containing water that contains metal cyanide complexes and a large amount of inorganic carbon.

[0015] The purpose of this invention is to provide a method and apparatus for treating cyanide-containing water that contains metal cyanide complexes and a large amount of inorganic carbon in a stable and efficient manner to obtain high-quality treated water with a sufficiently reduced total cyanide concentration. [Methods for solving problems]

[0016] To solve the aforementioned problem, the inventors conducted repeated research and found that by adding a pH adjuster to cyanide-containing water containing metal cyanide complexes and a large amount of inorganic carbon, and adjusting the pH to below 7.5 beforehand, and then adding ferrous salts and copper compounds to react, insoluble cyanide salts can be efficiently generated, thereby obtaining high-quality treated water with a sufficiently reduced total cyanide concentration. This invention is based on this insight, and the following is set as the main theme.

[0017] [1] A method for treating cyanide-containing water, wherein a pH adjuster is added to the cyanide-containing water to adjust the pH to below 7.5, and then a ferrous salt as a reducing agent is added, and a copper compound is added, thereby separating the insoluble salt of the generated cyanide, wherein the cyanide-containing water contains a metal cyanide complex and contains inorganic carbon of 100 mg-C / L or more as measured by the total inorganic carbon (TIC) based on the total organic carbon (TOC) as described in Japanese Industrial Standards (JIS) K0102 22.

[0018] [2] A treatment apparatus for cyanide-containing water includes: a pH adjustment mechanism for adding a pH adjuster to adjust the pH to below 7.5 to the cyanide-containing water, the cyanide-containing water containing a metal cyanide complex and containing inorganic carbon of 100 mg-C / L or more as measured by TIC based on TOC as described in JIS K0102 22; a reaction tank for adding a ferrous salt as a reducing agent to the water whose pH has been adjusted by the pH adjustment mechanism and adding a copper compound to carry out the reaction; and a solid-liquid separation mechanism for separating the insoluble salt of cyanide generated in the reaction tank. [The effects of the invention]

[0019] According to the present invention, cyanide-containing water containing metal cyanide complexes and a large amount of inorganic carbon can be stably and efficiently treated to obtain high-quality treated water with a sufficiently reduced total cyanide concentration. Simple Explanation of the Diagram

[0020] Figure 1 is a system diagram showing an example of an embodiment of the cyanide-containing water treatment apparatus of the present invention. Implementation

[0021] The following is a detailed description of the embodiments of the method and apparatus for treating cyanide-containing water according to the present invention.

[0022] The method for treating cyanide-containing water according to the present invention is characterized by: adding a pH adjuster to adjust the pH to below 7.5 to the cyanide-containing water, then adding a ferrous salt as a reducing agent and adding a copper compound to separate the insoluble salt of the generated cyanide, wherein the cyanide-containing water contains a metal cyanide complex and contains inorganic carbon of 100 mg-C / L or more as measured by TIC based on TOC as described in JIS K0102 22.

[0023] The apparatus for treating cyanide-containing water according to the present invention is characterized by comprising: a pH adjustment mechanism for adding a pH adjuster to adjust the pH to below 7.5 to cyanide-containing water containing a metal cyanide complex and containing inorganic carbon of 100 mg-C / L or more as measured by TIC based on TOC as described in JIS K0102 22; a reaction tank for adding a ferrous salt as a reducing agent to the water whose pH has been adjusted by the pH adjustment mechanism and adding a copper compound to carry out the reaction; and a solid-liquid separation mechanism for separating the insoluble salts of cyanide generated in the reaction tank.

[0024] [mechanism] For cyanide-containing water (hereinafter, sometimes referred to as "the water to be treated in this invention") containing metal cyanide complexes and containing inorganic carbon with a TIC value (hereinafter referred to as "TIC value") of 100 mg-C / L or more based on TOC as described in JIS K0102 22, the prior method could not achieve sufficient cyanide removal effect.

[0025] The water to be treated in this invention is usually weakly alkaline to alkaline with a pH of 8 to 10. However, a pH adjuster is added to this cyanide-containing water in advance to adjust the pH to below 7.5. Then, ferrous salt and copper compound are added as reducing agents. Fe2+ is used to stabilize the ferrous salt and effectively exert its reducing effect, thereby stably and reliably generating insoluble cyanide salts and achieving good cyanide removal effect.

[0026] As a method for treating cyanide-containing water containing both iron and copper compounds, Patent Document 2 proposes a method of adding iron compounds such as ferrous sulfate and copper compounds such as copper sulfate to water containing silver cyanide complexes, and adjusting the pH to 3-8 to separate the resulting insoluble silver cyanide complexes. In Patent Document 2, pH adjustment is performed simultaneously with the addition of iron and copper compounds. As described above, in the method of simultaneously adding iron and copper compounds and adjusting pH, Fe2+ is not stabilized, and the ferrous salt cannot function as a reducing agent. Therefore, the effect of the present invention cannot be obtained, and cyanide remains.

[0027] During the research of this invention, the inventors discovered that, as shown in Comparative Examples 1 to 3 described below, when measuring the total cyanide concentration of the treated water obtained by performing cyanide removal treatment, if the sample water contains interfering components for total cyanide analysis (e.g., sodium hyposulfite), the correct analytical value cannot be obtained.

[0028] Regarding this type of sample water, the inventors believe that it is effective to dilute the sample water to reduce the influence of interfering components before analysis, and to calculate the total cyanide concentration by multiplying the obtained analytical value by the dilution factor. In the examples and comparative examples described later, analyses related to the diluted sample water were also performed.

[0029] [Treatment methods for cyanide-containing water] <Water to be treated in this invention> The target water for treatment in this invention is cyanide-containing water containing metal cyanide complexes and with an inorganic carbon content of 100 mg-C / L or more based on a TIC value. For cyanide-containing water with an inorganic carbon content of less than 100 mg-C / L based on a TIC value, sufficient cyanide removal can be achieved even without applying this invention. To more effectively obtain the effects of this invention, the TIC value of the target water for treatment is preferably 200 mg-C / L or more. On the other hand, if the TIC value is too high, a large amount of pH adjusting agents such as H₂SO₄ is required, which presents an economic problem. Therefore, the TIC value of the target water for treatment in this invention is preferably 500 mg-C / L or less.

[0030] The M alkalinity of the target water for treatment according to this invention, with such a TIC value, is typically 400 mg-CaCO3 / L or higher, preferably 400 mg-CaCO3 / L to 5000 mg-CaCO3 / L, and even more preferably 400 mg-CaCO3 / L to 1000 mg-CaCO3 / L. The M alkalinity of the target water for treatment according to this invention can be determined using the method described in one of the following examples.

[0031] The inorganic carbon contained in the water to be treated by this invention is carbonate ions (CO3 2-), bicarbonate ions (HCO3-), and carbonic acid (H2CO3).

[0032] The metal cyanide complexes contained in water that are the target of treatment in this invention are not particularly limited, and examples include: iron cyanide complexes, silver cyanide complexes, nickel cyanide complexes, copper cyanide complexes, zinc cyanide complexes, etc. The water to be treated by the present invention may contain only one of these metal cyanide complexes, or it may contain two or more.

[0033] In addition to metal cyanide complexes, the water to be treated by this invention may also contain free cyanide.

[0034] There are no particular limitations on the content of metal cyanide complexes in the water to be treated by this invention. The content of metal cyanide complexes in the water to be treated by this invention, expressed as a cyanide concentration, is typically around 0.5 mg / L to 30 mg / L, and the total cyanide concentration in the water to be treated by this invention, including cyanides other than free cyanide and other metal cyanide complexes, is typically around 0.5 mg / L to 10 mg / L. The total cyanide concentration in the water to be treated by this invention can be determined using the method described in one of the following examples.

[0035] Examples of the water to be treated in this invention include: electroplating factory wastewater, ore dressing and smelting treatment plant wastewater, city gas manufacturing factory wastewater, chemical factory wastewater, petroleum factory wastewater, gas factory wastewater, metal refining factory wastewater, metal surface treatment plant wastewater such as chromate treatment, petroleum / carbon thermal decomposition process wastewater, photo factory wastewater, pharmaceutical factory wastewater, precious metal mining wastewater, gold plating wastewater, gold plating fixture cleaning wastewater, etching wastewater, metal surface treatment plant wastewater, ammonia synthesis factory wastewater, etc.

[0036] The pH of the water to be treated in this invention is usually about 8 to 12. In order to make it below pH 7.5, a pH adjuster needs to be added.

[0037] <pH adjustment> In this invention, first, a pH adjuster is added to the water to be treated in this invention to adjust the pH to below pH 7.5. As described above, the pH of the water to be treated in this invention is usually 8 to 12. Therefore, in order to make it below pH 7.5, an acid is usually added as the pH adjuster.

[0038] The acid used in the pH adjustment is not particularly limited, and inorganic acids such as sulfuric acid and hydrochloric acid can be used.

[0039] In terms of the cyanide removal effect, it is advisable to adjust the pH value to be low, preferably below pH 7. In terms of the cost of the pH adjuster and the safety of free cyanide gasification when the pH is too low, it is preferable to adjust the pH value to be above pH 5, more preferably above pH 5.5.

[0040] Regarding this pH adjustment, it can be implemented by adding a pH adjuster to the water to be treated in this invention. From the perspective of stably and uniformly adjusting the water to be treated in this invention to a specified pH value, it is preferable to set up a pH adjustment tank, for example. In the pH adjustment tank, the water to be treated in this invention and the pH adjuster are fully stirred and mixed, and then supplied to the next reaction step using ferrous salts and copper compounds.

[0041] In order to make the pH value of the water to be treated in this invention uniform and stable, when a pH adjustment tank is set up, the residence time in the pH adjustment tank is preferably set to about 5 minutes to 60 minutes. When the mixing time can be fully ensured, the pH adjuster can also be mixed online with the water to be treated in this invention for pH adjustment.

[0042] <Reaction using ferrous salts and copper compounds> In this invention, as described above, a ferrous salt as a reducing agent is added to the water to be treated, which has been pre-adjusted to stabilize its pH value, and a copper compound is added to generate an insoluble salt of cyanide.

[0043] Examples of ferrous salts include one or more inorganic ferrous salts such as ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous bromide, ferrous phosphate, ferrous bicarbonate, and ferrous carbonate. Among these, ferrous sulfate and ferrous chloride are preferred from the perspective of being commercially and inexpensively available.

[0044] The copper compound is a compound that generates copper(I) ions in the presence of a reducing agent. Generally, a water-soluble salt can be used. This copper compound can be either a copper(I) compound or a copper(II) compound. Generally, copper(I) compounds are poorly soluble and difficult to obtain; therefore, it is preferable to use a copper(II) compound and a ferrous salt as a reducing agent to reduce it to a copper(I) compound for reaction with a metal cyanide complex or free cyanide.

[0045] As copper(II) compounds, they can utilize water-soluble divalent copper salts such as copper(II) sulfate, copper(II) chloride, and copper(II) nitrate. As compounds of copper (I), copper chloride (I) and copper sulfate (I) can be used. These copper compounds can be used alone or in combination of two or more.

[0046] The amount of ferrous salt added to the pH-adjusted water of the present invention is preferably the amount required to create a reducing environment, specifically, the dissolved oxygen level is below 0.5 mg / L. For example, for water with a dissolved oxygen level of 6 mg / L as shown in JIS K0102 32.3, if the ferrous salt is ferrous sulfate, it is preferably about 50 mg / L to 100 mg / L in terms of purity; if the ferrous salt is ferrous chloride, it is preferably about 50 mg / L to 80 mg / L in terms of purity.

[0047] The amount of copper compound added is typically above the equivalent amount relative to the cyanide content in the water to be treated according to this invention. To improve the cyanide removal rate, it is preferable to add an excess amount. Generally, the amount of copper compound added is preferably set to 1.05 to 1.5 equivalents, particularly 1.1 to 1.3 equivalents, relative to the cyanide content in the water to be treated according to this invention.

[0048] In the case of adding excess copper compounds, in order to remove the copper compounds remaining after the reaction, it is preferable to add heavy metal scavenging agents such as dithiocarbamate or guanazine to form copper into a complex that makes it insoluble, and remove it together with the insoluble salt of cyanide.

[0049] The reaction to generate cyanide insoluble salts by adding ferrous salts and copper compounds after pH adjustment can be carried out, for example, by introducing the target water of the present invention with a pH adjusted to below pH 7.5 into the reaction tank and adding ferrous salts and copper compounds. In order to reliably generate cyanide insoluble salts for high cyanide removal, the residence time in the reaction tank is preferably ensured to be more than 1 minute, for example, about 1 minute to 10 minutes.

[0050] Solid-liquid separation After the reaction, the generated cyanide insoluble salt is separated into solid and liquid components to obtain treated water.

[0051] Alternatively, before solid-liquid separation, inorganic coagulants such as polyaluminum chloride and / or polymeric coagulants can be added to the reaction solution for coagulation treatment. In this invention, the ferrous salt added as a reducing agent becomes Fe(OH)3 sludge through a reduction reaction, thus becoming the nucleus of the flocculants. Therefore, the addition of inorganic coagulants is not necessary. Instead, it is preferred to add them according to the coagulation state, and to coarsen the flocculants by adding polymeric coagulants and stirring.

[0052] As a solid-liquid separation mechanism, a sedimentation tank is typically used, but it is not limited to any particular sedimentation tank.

[0053] [Cyanide-containing water treatment equipment] Next, the apparatus for treating cyanide-containing water according to the present invention will be described with reference to FIG1. Figure 1 is a system diagram showing an example of an embodiment of the cyanide-containing water treatment apparatus of the present invention.

[0054] In this cyanide-containing water treatment device, the water to be treated according to the present invention, which serves as the raw water, is introduced into a pH adjustment tank 1, and acid is added as a pH adjuster. The pH is adjusted to a specified pH of 7.5 or below by stirring with a stirrer 1B. In Figure 1, the pH of the solution in the pH adjustment tank 1 is measured using a pH meter 1A, and the amount of acid added is controlled based on this measurement to adjust to the specified pH value.

[0055] Subsequently, pH-adjusted water, adjusted to a specified pH value below 7.5 in pH adjustment tank 1, is sent to reaction tank 2. Ferrous salt and copper compound are added under stirring using stirrer 2B. The copper compound and the metal cyanide complex react under reducing conditions to generate an insoluble salt of cyanide.

[0056] Subsequently, the reaction liquid from reaction tank 2 undergoes solid-liquid separation in sedimentation tank 3, and the separated water is removed as treated water. The separated sludge is pumped out of the system and treated using a dewatering machine, etc. 3A is a mixer.

[0057] Inorganic coagulants can be added to the reaction liquid from reaction tank 2 according to its coagulation state, and polymeric coagulants can also be added for coagulation treatment. In this case, a coagulation tank can also be set up between reaction tank 2 and sedimentation tank 3. [Example]

[0058] The present invention will be described in more detail below with reference to specific embodiments.

[0059] [Water quality testing] In the following examples and comparative examples, the water quality of raw water and treated water was measured in the following manner.

[0060] Total Cyanide (CN) The method described in JIS K0102-38 was used for determination. In the determination of cyanide-treated water, both undiluted and diluted values ​​using dilution water (diluted 10 times with distilled water) are performed. For raw water, only the value obtained using the diluted water (diluted 10 times) is measured. As mentioned above, the determination using dilution water is to reduce the influence of interfering components on the total CN analysis in the water. The value obtained using the diluted water (10 times) is expressed as the "measured value," and the value obtained by multiplying the measured value by 10 is expressed as the "determined value."

[0061] <Dissolved ions> Regarding Fe2+, Cu, and Zn, the filtrate obtained from filtering water (raw water and treated water) using a 0.45 μm filter was analyzed. Fe2+ was analyzed using the o-phenanthroline colorimetric method. Cu and Zn were analyzed using inductively coupled plasma (ICP) luminescence analysis as described in JIS K0102:2013 52-4 and 53-3.

[0062] <TOC value> Using the combustion oxidation-infrared TOC analysis method described in JIS K0102:2013 22.1, and measuring with a TOC meter.

[0063] <M alkalinity> Measured according to the acid consumption at pH 4.8 described in JIS K0102:2013 15-1.

[0064] [Examples from Example 1 to Example 6] Using the cyanide-containing water (including free cyanide) with the following water quality as raw water, and treating it according to the present invention.

[0065] <Raw water quality> pH: 8.0 Metal cyanide complexes (ferrocyanide, zinc cyanide complex salt, copper cyanide complex salt): 2.8 mg / L (cyanide equivalent content) Total CN: 4.0 mg / L Fe2+: 0.8 mg / L Zn: 1.4 mg / L Cu: 1.2 mg / L TOC value: 220 mg-C / L M alkalinity: 2400 mg-CaCO3 / L

[0066] First, in the pH adjustment tank, add sulfuric acid to the raw water to adjust the pH to that shown in Table 1. Then, send the pH-adjusted water to the reaction tank. In the reaction tank, add the ferrous salt shown in Table 1 as a reducing agent at the addition amount shown in Table 1, and add 130 mg / L of copper sulfate (CuSO4), and react with stirring to obtain cyanide-treated water. The residence time of the pH adjustment tank is set to 5 minutes, and the residence time of the reaction tank is set to 5 minutes. The addition amount of the ferrous salt shown in Table 1 is the addition amount at which the dissolved oxygen concentration in water measured by JIS K0102 32.3 becomes 0.5 mg / L. The addition amount of copper sulfate is the addition amount that becomes 0.7 equivalents relative to the cyanide in the raw water.

[0067] For the cyanide-treated water, measure the water quality using the above method, and show the results in Table 1.

[0068] In Examples 1 to 6 and Comparative Examples 1 to 6, copper sulfate (CuSO4) was added in the form of a 20% solution of CuSO4·5H2O, ferrous sulfate (FeSO4) was added in the form of a 20% solution, ferrous chloride (FeCl2) was added in the form of a 32% solution, and sodium bisulfite (NaHSO3) was added in the form of a 10% solution. The amount of these solutions added relative to the original water is shown in Table 1.

[0069] [Comparative Example 1] Without adjusting the pH using sulfuric acid, only 1000 mg / L of sodium bisulfite (NaHSO3) as a reducing agent was added, and the reaction was carried out for 5 minutes. The water quality test results of the obtained cyanide-treated water are shown in Table 1.

[0070] [Comparative Example 2] In Comparative Example 1, 130 mg / L of copper sulfate was added along with sodium bisulfite, and the reaction was carried out in the same manner. The water quality determination results of the obtained cyanide-treated water are shown in Table 1.

[0071] [Comparative Example 3] In Comparative Example 2, sulfuric acid was added to adjust the pH to 5.5 before adding sodium bisulfite and copper sulfate, and the reaction was carried out in the same manner otherwise. The water quality test results of the obtained cyanide-treated water are shown in Table 1.

[0072] [Comparative Example 4] The reaction was carried out in the same manner as in Example 1, except that the pH adjustment using sulfuric acid was not performed. The water quality test results of the obtained cyanide-treated water are shown in Table 1.

[0073] [Comparative Example 5] The reaction was carried out in the same manner as in Example 3, except that copper sulfate was not added. The water quality test results of the obtained cyanide-treated water are shown in Table 1.

[0074] [Comparative Example 6] 400 mg / L of ferrous sulfate and 130 mg / L of copper sulfate were added to the raw water as reducing agents, and sulfuric acid was added to adjust the pH to 6.5. The reaction was carried out for 5 minutes. The water quality test results of the obtained cyanide-treated water are shown in Table 1.

[0075] [Table 1] Pretreatment pH adjustment reducing agent Copper sulfate addition amount [mg / L] Water quality of the treated water (mg / L) type Added amount [mg / L] Total CN Fe2+ Zn Cu TIC value ※1 M alkalinity ※2 Undiluted 10-fold dilution Measured values Measured values raw water 8.0 - - - - 4.0 0.4 0.8 1.2 1.4 220 2400 Comparative example 1 8.0 NaHSO3 1000 0 0.83 4.0 0.4 - - - 210 2200 2 8.0 NaHSO3 1000 130 0.81 2.3 0.23 - 0.5 0.3 210 2200 3 5.5 NaHSO3 1000 130 1.13 1.5 0.15 - 0.5 0.3 48 530 4 8.0 FeSO4 400 130 2.14 2.2 0.22 <0.1 0.5 0.4 210 2300 5 6.5 FeSO4 400 0 - 3.4 0.22 10.4 0.2 55 580 6 ※3 FeSO4 400 130 1.38 1.3 0.13 1.2 0.5 0.3 150 1500 Implementation Examples 1 7.5 FeSO4 400 130 0.95 1.2 0.12 0.34 0.4 0.3 75 750 2 7.0 FeSO4 400 130 0.95 <1.0 <0.1 0.54 0.2 <0.1 62 710 3 6.5 FeSO4 400 130 0.79 <1.0 <0.1 0.64 <0.1 <0.1 58 650 4 7.5 FeCl2 150 130 0.91 1.1 0.11 0.36 0.4 0.3 72 740 5 7.0 FeCl2 150 130 0.88 <1.0 <0.1 0.55 0.2 <0.1 55 590 6 6.5 FeCl2 150 130 0.75 <1.0 <0.1 0.66 <0.1 <0.1 48 520 ※1: Unit is "mg-C / L" ※2: The unit is "mg-CaCO3 / L" ※3: When adding reducing agent and copper sulfate, adjust the pH to 6.5.

[0076] [Inspection] The following information can be obtained from the results in Table 1. Comparative Example 1 is a system with only sodium bisulfite added. At first glance, it seems that sodium bisulfite alone can reduce total CN. However, after dilution, the total CN concentration in the treated water is the same as that in the raw water. It can be said that sodium bisulfite alone cannot remove cyanide. As mentioned above, the reason why the CN analysis value differs with or without dilution is that the analysis of total CN is interfered with by the sulfurous acid gas contained in sodium bisulfite. The concentration of sodium bisulfite is reduced by the dilution operation. If the influence of sulfurous acid gas is no longer present, the original CN concentration can be analyzed.

[0077] In Comparative Examples 2 and 3, it can be seen that although the previous method was to reduce copper sulfate to copper(I) ions by adding sodium bisulfite as a reducing agent, when the treatment water was diluted to reduce the effect of sodium bisulfite, an increase in the total CN concentration was observed, and the total CN remained.

[0078] In Comparative Example 4, it can be seen that adding ferrous sulfate and copper sulfate under alkaline conditions of pH 8.0 does not achieve sufficient CN removal effect under alkaline conditions. As can be seen from Comparative Example 6, even when the pH is adjusted to pH 6.5, sufficient CN removal effect cannot be obtained when the pH adjustment is carried out simultaneously with the addition of ferrous sulfate and copper sulfate.

[0079] In contrast, in Examples 1 to 6, by pre-adjusting the pH to below 7.5, the lower the pH, the better the CN removal effect, especially below 7.0, which resulted in good CN removal quality. Furthermore, as with the use of sodium bisulfite as a reducing agent, the analysis of total CN was not interfered with, and no significant change in the total CN analysis value was observed due to the presence or absence of dilution; approximately the same values ​​were obtained.

[0080] Furthermore, no residual Fe2+ ions were observed in Comparative Example 4, while residual Fe2+ was observed in Examples 1 to 6. Therefore, it is believed that Fe2+ is unstable under alkaline pH conditions, and the Fe2+ of the added ferrous salt becomes Fe3+, thereby becoming Fe(OH)3. That is, by lowering the pH, it is stabilized as Fe2+ ions and acts as a reducing agent for Cu1+, thus effectively maintaining the CN content of the treated water to meet water quality standards.

[0081] Comparative Example 5 uses the previous Tiramisu method, which at pH 6.5, makes it difficult to obtain sufficient cyanide to reach the water quality.

[0082] Based on these results, it can be seen that, according to the present invention, cyanide in cyanide-containing water containing metal cyanide complexes and a large amount of inorganic carbon can be significantly removed to obtain high-quality treated water with a sufficiently reduced total CN concentration.

[0083] Although the invention has been described in detail using specific examples, those skilled in the art will recognize that various modifications can be made without departing from the intent and scope of the invention. This application incorporates the entire contents of Japanese Patent Application 2020-138789, filed on August 19, 2020, by reference.

[0084] 1: pH adjustment tank 1A: pH meter 1B: Blender 2: Reaction tank 2A: Mixer 3: Sedimentation tank 3A: Mixer

Claims

1. A method for treating cyanide-containing water, wherein, A pH adjusting agent is added to the following cyanide-containing water in a pH adjustment tank to adjust the pH to below 7.

5. Then, the water adjusted to below pH 7.5 is introduced into a reaction tank. Ferrous salt as a reducing agent is added to the water introduced into the reaction tank in such a way that the dissolved oxygen is below 0.5 mg / L, and a copper compound is added, thereby separating the insoluble salt of the generated cyanide. The cyanide-containing water contains metal cyanide complexes and contains inorganic carbon of 100 mg-C / L or more as measured by total inorganic carbon based on total organic carbon as described in Japanese Industrial Standard K0102 Item 22. The amount of copper compound added is 0.7 to 1.5 equivalents relative to the cyanide content in the cyanide-containing water.

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