JP2013123655A - Method for treating cyanide-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating cyanide-containing wastewater, efficiently and surely removing cyanide components compared with the case of treating cyanide-containing wastewater by a conventional method and detoxifying treated matter obtained by treating cyanide components with higher reliability while excelling in economical efficiency.SOLUTION: The method for treating cyanide-containing wastewater includes maintaining pH of wastewater in treatment at 6 or more; adding together, to the cyanide-containing wastewater, an iron compound (A) producing iron ions in wastewater, a compound (C) reacting on cyanide ions to produce a nitrile compound, and metallic salts (B) producing metallic ions of either Zn, Mnor Cuat least in wastewater, thereby complexing most of cyanide ions so as to be converted into a hexacyanoferrate complex while converting cyanide ions remaining uncomplexed, into a nitrile compound to adsorb the nitrile compound to suspended matter in wastewater, and insolubilizing the cyano complex; and then carrying out solid-liquid separation of the suspended matter and the insolubilized cyano complex.

Description

  The present invention relates to a method for treating cyanide-containing wastewater for removing cyanide components from cyanide-containing wastewater, and in particular, cyanide-containing products produced in chemical factories that perform plating, coal factories, coke factories, factories that use a large amount of coke, and the like. The present invention relates to a method for treating cyanide-containing wastewater that can remove cyanide components in wastewater containing wastewater more efficiently, economically and safely.

As described above, wastewater from a plating factory, a coal factory, a coke factory, an iron factory that uses a large amount of coke, or the like may contain a cyan-containing compound (cyan component). Conventionally, as a method for treating cyanide ions (CN ⁻ ) in waste water containing cyanide, the alkali chlorine method has been practiced for a long time. There are problems such as inconvenience. As a treatment method free of such problems, there is known a method of detoxifying cyanide by treating formaldehyde-containing wastewater with a treating agent containing formaldehyde to produce formaldehyde cyanohydrin, which is one of toxic cyanohydrins. (See Patent Document 1). Furthermore, in order to enhance the reduction effect of cyanide compounds in the above method and enhance safety, a specific amount of hydrogen peroxide is added after the first reaction after adding formaldehyde, and the second reaction is performed at pH 7.0 or higher. Has been proposed (see Patent Document 2).

  However, although formaldehyde cyanohydrin is weak in toxicity, its toxicity is relatively high, and in some cases, it may be dissociated into formaldehyde and cyanide. Furthermore, according to the study by the present inventors, in order to sufficiently treat cyanide ions in a large amount of waste water from the above-listed factories with the above-mentioned chemicals, it depends on the concentration of cyanide ions. In addition to the problem of safety in treated water and treated products, the above-described conventional methods are difficult to say economically because they require a large amount of chemicals. For these reasons, there is room for improvement in the conventional method for treating cyan-containing wastewater described above.

According to the study by the present inventors, in the cyanide-containing wastewater containing the waste liquid from the factory as listed above, the cyan component contains cyanide ions (CN ⁻ , also referred to as free cyanide) as well as phenotype. It is contained in the form of complex ions such as Russian ion and ferricyanide ion. And among these, ferrocyanide ions are known to form poorly soluble metal complexes by the action of metal ions, and conventionally, using this, ferrocyanide ions are included. The waste liquid is reacted with metal ions such as manganese and zinc to precipitate and remove the resulting metal salt. In addition, ferricyanide ions are also removed by precipitation in the same manner as described above after being converted to ferrocyanide ions with a reducing agent.

  Patent Document 3 discloses a method in which the above prior art is improved and sodium hydroxide is added to simultaneously remove ferrocyanide ions and ferricyanide ions from the waste liquid.

Japanese Patent Publication No. 45-36 JP-A-2-35991 JP-A-7-124570

However, in the conventional method for removing cyan components in the waste water containing cyanide including the waste liquid from the factory as listed above, toxic free cyanide (CN ⁻ ) which becomes a problem particularly when remaining in the treated water. Therefore, the following processing is generally performed. First, free cyanide is removed using a treating agent containing formaldehyde by the method described above, and then there is a complex ion such as ferrocyanide ion or ferricyanide ion that is not treated by the above method. Is insolubilized and solid-liquid separated. In other words, in the conventional method for removing cyan components from waste water containing cyanide, the treatment of free cyan is the first, followed by the treatment of cyan ions coordinated to complex cyan, and the treatment is stepwise. Has been done.

  In order to remove free cyanide that has been used in the past, the present inventors have conducted intensive studies on a method for removing cyanide component from cyanide-containing wastewater including cyanine-containing wastewater from the factory as listed above. The following problems have been recognized with respect to treatment agents containing formaldehyde. That is, as described above, in the conventional method, such a treatment agent is used to formaldehyde cyanohydrin to detoxify free cyanide, but although toxicity is weakened, the toxicity of formaldehyde cyanohydrin is reduced. Is relatively high, and in some cases, it may be dissociated into formaldehyde and cyanide. From these facts, the present inventors have recognized that it is necessary to develop a safer method for treating cyanide-containing wastewater. In order to make the treatment of cyanide-containing wastewater more efficient and economical, and to make the treated water and treated products safer, the above-described conventional method is used. It was recognized that it was necessary to comprehensively examine the above-mentioned stepwise processing method, and it was necessary to improve the basic configuration.

  Accordingly, an object of the present invention is to prevent the treatment of cyanide-containing wastewater containing a toxic cyan component by treating the cyan component, particularly free cyanide, in the treated water as compared with the case where the treatment is performed by a conventional method. Of course, it can be removed efficiently and reliably, and the treated product treated with the cyan component is more detoxified, the safety in the treatment is higher, and the cyan component in the waste water containing cyan is more treated. It is an object of the present invention to provide an excellent cyanide-containing wastewater treatment method that is efficient, economical, and industrially usable.

The above object is achieved by the present invention described below. That is, the present invention is a method for treating cyanide-containing wastewater for removing cyanide components from cyanide-containing wastewater, wherein the wastewater at the time of treatment is maintained at a pH of 6 or more, and the wastewater contains cyanide-containing wastewater. An iron compound (A) that generates iron ions (Fe ²⁺ ), a compound (C) that reacts with cyanide ions (CN ⁻ ) to generate nitrile compounds, and at least Zn ²⁺ or Mn ²⁺ or By adding together with the metal salt (B) that generates any metal ion of Cu ²⁺ , most of the cyanide ions in the cyanide-containing wastewater are complexed with the iron compound (A), and hexacyanocyanogen. In addition to the conversion to an iron complex, the compound (C) converts the cyanide ion remaining without being complexed into a nitrile compound, and the nitrile compound is adsorbed to a suspended substance in waste water. Characterized in that the metal salt (B) is used to insolubilize the cyano complex in the wastewater containing the hexacyanoiron complex converted as described above, and thereafter, the suspended substance and the insolubilized cyano complex are subjected to solid-liquid separation. A method for treating cyanogen-containing wastewater is provided.

The cyan-containing waste liquid treatment method is preferably configured as follows.
The pH of the waste water during the treatment is maintained in the range of 7.0 to 10.0, and the amount of the compound (C) added is the number of metal ions of Zn ²⁺ or Mn ²⁺ or Cu ²⁺ or the sum thereof. Is adjusted to be 0.05 molar equivalents or more with respect to all cyan components in wastewater (the sum of free cyan and cyanide ions coordinated to complex cyanide).
The compound (C) is selected from the group consisting of a compound having an aldehyde group or keto group, ascorbic acid or an optical isomer thereof, lignin or a derivative thereof, humic acid or a derivative thereof, acrylic acid and a derivative thereof, and a reducing sugar. It must be at least one of the compounds.
The metal salt (B) is at least one metal salt selected from the group consisting of zinc chloride, zinc sulfate, zinc ammonium chloride, zinc nitrate, manganese chloride, manganese sulfate, copper chloride, and copper sulfate.
Furthermore, with the addition of the compound (C), at least one compound selected from the group consisting of sulfurous acid or a salt thereof, thiosulfuric acid or a salt thereof, and nitrous acid or a salt thereof is added to the compound (C). In the range of 0.01 to 20 molar equivalents.
The cyan-containing wastewater contains waste liquid from a coke factory, a coal factory, or a plating factory.

  According to the present invention, the treatment of cyanogen-containing wastewater containing a toxic cyan component is performed so that cyan components in the treated water, particularly free cyanide, do not remain in the treated water as compared with the case where the treatment is performed by a conventional method. A method for treating cyanide-containing wastewater that can be efficiently and reliably removed is provided. Furthermore, according to the present invention, the treated product treated with the cyan component is more reliably detoxified, the safety in the treatment is high, and the treatment of the cyan component in the waste water containing cyan can be performed more efficiently. An excellent cyanide-containing wastewater treatment method that can be used industrially is provided.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the process of diligently studying to solve the problems in the above-described conventional cyanide-containing wastewater treatment methods, the present inventors treated a conventional treatment agent containing formaldehyde to formaldehyde cyanohydrin. Attention was paid to the detailed study of the improvement. Then, instead of a conventional treatment agent containing formaldehyde, a specific compound that is not formaldehyde is added to cyanogen-containing wastewater, and the cyanide component in the wastewater is reacted by reacting the compound with the cyanide component in the wastewater. The present inventors have newly found a useful treatment agent that is a cyanohydrin and can be a reaction product that is easily adsorbed on a suspended substance.

  However, the present inventors have made it clear that in the method for treating cyanide-containing wastewater, the detoxification of the cyan component, which is the final purpose of the present invention, can be used efficiently, economically and industrially. Has recognized that a sufficient effect cannot be obtained simply by replacing a new treatment agent capable of obtaining the excellent effect described above with a treatment agent used in a conventional treatment method. That is, if the treatment agent newly found by the present inventors is used in place of the treatment agent used in the conventional method, free cyanide in the cyanide-containing wastewater is reduced to toxic cyanohydrin, It can be a reaction product that is easily adsorbed by the suspended substance, and the cyanide component in the wastewater can be efficiently removed by solid-liquid separation of the suspended substance, but a large amount of treatment agent is required. In this respect, it is not different from the conventional method.

  From the above, the present inventors have recognized that a comprehensive review of the conventional method prioritizing removal of free cyanide is necessary. And, in the process of investigating the properties of the cyan component to be treated in the waste water containing cyanide, if there are complex ions after the removal of free cyan, which is finally performed in the conventional treatment method, this is insolubilized, Although solid-liquid separation was carried out, if this process could be used more actively, the amount of treatment agent used to remove free cyanide could be reduced, and further studies were conducted.

As a result, surprisingly, the cyanide-containing wastewater containing free cyanide is combined with the iron compound (A) that generates iron ions (Fe ²⁺ ) and the treatment agent (C) newly developed by the present inventors. It has been found that the addition of the following causes the following, which is more efficient and surely removes free cyanide, and can significantly reduce the amount of the treating agent (C) to be used. In addition, according to this method, the amount of the treating agent (C) to be used can be greatly reduced, but this also means that the amount of formaldehyde cyanohydrin to be generated is greatly reduced as compared with the conventional processing method. Means. Therefore, according to the method of the present invention, the amount of detoxified formaldehyde cyanohydrin generated in the treated product when the treatment with the treating agent (C) containing formaldehyde used in the conventional method is performed is slightly reduced. Therefore, the conventional problems described above can be solved by reducing the generation amount. Hereinafter, in the method for treating cyan-containing wastewater of the present invention, a reaction that is considered to occur in the cyan-containing wastewater in the process of removing the cyan component will be described.

First, in order to suppress the generation of hydrogen cyanide from the wastewater, the pH of the wastewater at the time of treatment is maintained at 6 or more, more preferably in the range of 7.0 to 10.0. Then, a cyanide-containing wastewater containing free cyanide whose pH is adjusted reacts with an iron compound (A) that generates iron ions (Fe ²⁺ ) in the wastewater and a cyanide ion (CN ⁻ ) to generate a nitrile compound. The treatment is carried out by adding together the compound (C) and a metal salt (B) that generates at least one metal ion of Zn ²⁺ or Mn ²⁺ or Cu ²⁺ in waste water. The term “together” here means that the treatment is not performed stepwise but in the state where the above-described compounds (A) to (C) coexist in the treatment tank.

It is known that when an iron compound (A) that generates iron ions (Fe ²⁺ ) is added to cyanide-containing wastewater, cyanide ions (CN ⁻ ) in the wastewater become ferrocyanide ions. In the method of the present invention, the compound (C) that reacts with cyanide ions to produce a nitrile compound is added to the cyanide-containing wastewater together with the iron compound (A). According to the study by the present inventors, when treated in this manner, most of the cyanide ions in the cyanide-containing wastewater are complexed and converted to a hexacyanoiron complex. That is, in the combined use state of the iron compound (A) and the compound (C), the cyanide ion (CN ⁻ ) in the wastewater does not react with the treating agent (C), but preferentially the iron compound (A). It was found that the reaction with

Further, according to the study by the present inventors, as described above, Fe ²⁺ can rapidly complex cyanide ions in cyanide-containing wastewater into ferrocyanide ions, but iron compounds (A ) Alone, it was found difficult to convert all cyanide ions in the actual waste liquid to ferrocyanide ions. In other words, when the theoretical amount of Fe ²⁺ required to convert cyanide ions into ferrocyanide ions is added to actual cyanogen-containing wastewater, the cyanide ions in the wastewater are rapidly increased until a certain low concentration is reached. Although ferrocyanide ions can be used, it has been found that if the cyanide ion concentration is further reduced, Fe ^{2+ in} an amount 3 to several times the theoretical amount may be required. Although the detailed reason is unknown, it is thought to be due to the influence of other ions and suspended substances contained in the waste liquid. The above tendency was the same even arose from as long as it results in a Fe ²⁺ is added to the water, such as iron sulfate or iron chloride is added Fe ²⁺ is what kind of compounds. The same was true when an iron compound producing a Fe ³⁺ having a different valence and a reducing agent were added.

The above fact means that a large amount of chemical is required to convert ferricyanide ions into almost all cyanide ions in the wastewater using only the iron compound (A). On the other hand, cyanide ions are highly toxic and need to be removed from wastewater as much as possible. Acceptable wastewater standards are also 1 ppm or less. According to the study by the present inventors, although depending on the nature, the amount of the iron compound (A) as a drug required to make the concentration of cyanide ions in the wastewater about several ppm becomes large. Moreover, since it is necessary to remove excessively added Fe ²⁺ in a later step, it is not economical to add a large amount of Fe ²⁺ .

  In view of the above-mentioned facts, the inventors of the present invention incorporated an iron compound (A) for converting cyanide ions into a hexacyanoiron complex and a treating agent (for converting cyanide ions into nitrile compounds) in an actual cyanide-containing wastewater. It was found that it is effective to perform treatment in combination with C), and the present invention has been achieved. That is, when treated in this way, most of the cyanide ions in the wastewater quickly become ferrocyanide ions, and the cyanide ions remaining without being complexed react with the treating agent (C) to produce wastewater. It becomes a nitrile compound that is easily adsorbed by the suspended substances therein. By processing in this way, both the usage-amounts of an iron compound (A) and a processing agent (C) can be reduced.

Furthermore, in the present invention, in addition to the iron compound (A) and the treating agent (C), metal salts (B) that generate at least a metal ion of Zn ²⁺ or Mn ²⁺ or Cu ²⁺ are added. By processing in combination, the ferrocyanide ions generated above are quickly insolubilized. By comprising in this way, most of the cyanide ions in the actual cyanide-containing wastewater become cyano complexes insolubilized with the iron compound (A) and the metal salt (B), and remain without being complexed. The treated cyanide ion is converted into a nitrile compound that is easily adsorbed by the suspending substance in the wastewater by the treating agent (C). Further, after that, these suspended substances and the insolubilized cyano complex are separated by solid-liquid separation, which is a very simple and general method, so that cyanide ions in cyanide-containing wastewater are easily removed. As described above, according to the present invention, the amount of each drug to be used can be reduced, and the above-described two kinds of treatments are performed in the same process instead of stepwise treatment as in the past. In addition, since the final treatment can be performed by simple solid-liquid separation, it is extremely advantageous in terms of equipment.

Hereinafter, each chemical | medical agent used for the processing method of this invention is demonstrated.
[Iron compound (A)]
The iron compound (A) used in the present invention may be any compound that generates iron ions (Fe ²⁺ or Fe ³⁺ ) when added to waste water, most of which is water. Examples thereof include iron chloride (II), iron chloride (III), iron sulfate (II), iron sulfate (III), iron nitrate (II), iron nitrate (III) and the like. These may be added alone or in combination. The iron ion Fe ²⁺ reacts with the cyanide ion to form a complex ion (ferrocyanide ion), so iron that produces Fe ²⁺ such as iron chloride (II), iron sulfate (II), iron nitrate (II), etc. By adding the compound, most of the cyanide ions in the wastewater become ferrocyanide ions. When iron compounds that generate Fe ³⁺ such as iron (III) chloride, iron (III) sulfate, and iron (III) nitrate are added, ferricyanide ions are generated. However, by adding a reducing agent, Fe ³⁺ becomes Fe ^{2 +.} Reduced to ⁺ can be easily converted to ferrocyanide ion. In this case, the reducing agent may be added before the iron compound is added, or the reducing agent may be added after the iron compound is added. However, if the reducing agent is added simultaneously with the iron compound (A), ferrocyanide ions are formed. It is preferable because it is produced efficiently and the process is simple.

When the iron compound (A) is a substance that generates Fe ²⁺ such as iron (II) chloride, it is not necessary to add a reducing agent. However, ferricyanide ions may be contained in the wastewater. For the purpose of removing ferricyanide ions as ferrocyanide ions, it is preferable to add a reducing agent to cyanogen-containing wastewater. In some cases, the cyanide component in the wastewater is already present as ferrocyanide ions. In this case, the amount of iron compound (A) used can be further reduced, but in this case, ferricyanide ions are also included. Therefore, it is preferable to use the iron compound (A) and a reducing agent in combination.

  The amount of the iron compound (A) added to the wastewater is preferably in the range of 0.01 to 50 molar equivalents relative to the cyanide ions contained in the cyanide-containing wastewater, although it depends on the properties of the wastewater. (If the amount of the iron compound (A) is too small, the amount of cyanide ions remaining without complexing increases, and the amount treated with the compound (C) increases, which is more expensive than the iron compound (A). On the other hand, even if the iron compound (A) to be added is added in a large excess relative to the contained cyanide ions, not all of the cyanide ions can be removed. Therefore, it is not preferable because a process for removing excess iron compound is required, and the amount of cyanide ions in the wastewater is constantly monitored, and the iron compound (A ) Is considered effective for carrying out the reaction efficiently, but the present invention removes all of the cyanide ions in the wastewater only by the iron compound (A). Therefore, the amount of cyanide ion contained in the waste water containing cyanide is measured in advance, and an iron compound corresponding to the amount may be added, and there is an advantage that the management of the iron compound (A) to be added can be easily performed. .

  When the reducing agent is added simultaneously with the iron compound (A), as the reducing agent, those usually used for converting ferricyanide ions to ferrocyanide ions can be used. It is preferable to add in a range of 0.2 to 20 molar equivalents with respect to ferricyanide ions.

[Metal salts (B)]
As described above, the ferrocyanide ion generated from the added iron compound (A) and the cyanide ion in the wastewater is further insolubilized by adding the metal salt (B), and is hardly soluble. Precipitate as a metal complex. The hardly soluble metal complex salt thus precipitated can be solid-liquid separated by a simple method using a precipitation tank or the like, and as a result, cyanide ions in the wastewater are easily removed.

  As a metal which produces | generates an above-mentioned hardly soluble metal complex salt, if it is a metal which produces | generates a hardly soluble complex salt, any metal may be sufficient, However, A transition metal, especially zinc, manganese, copper, etc. are preferable. In addition, in the metal complex salt of ferrocyan, when the metal is an alkali metal such as potassium or sodium, the obtained metal complex salt is easily dissolved in water, and thus is not suitable for the present invention.

  As the metal salts (B), for example, salts that generate transition metal ions, particularly zinc ions, manganese ions, and copper ions are preferable. Specifically, zinc chloride, zinc sulfate, ammonium zinc chloride, zinc nitrate, manganese chloride, Examples include manganese sulfate, copper chloride, and copper sulfate. Any one of these may be used, or two or more may be mixed and used.

  In the metal salt (B), it is assumed that the cyanide ion contained in the cyanide-containing wastewater is converted to ferrocyanide ion by the iron compound (A) added above, and this ferrocyanide ion is all converted into a metal complex salt. It is preferable to add an amount that generates a sufficient amount of metal ions. Specifically, the metal salt (B) is preferably added in an amount of 0.3 molar equivalent or more with respect to the amount of cyanide ions contained in the cyanide-containing wastewater. Further, ferrocyanide ions other than those generated from cyanide ions in cyanide-containing wastewater, that is, ferrocyanide ions originally contained in wastewater, and ferrocyanide ions generated from ferricyanide ions by the above reducing agent In the case where ions are contained, ferrocyanide ions and ferricyanides contained in the cyanate-containing wastewater are further added by further adding metal salts (B) in an amount necessary to make the ferrocyanide ions into metal complexes. Ions can be removed at the same time.

  As described above, in the present invention, it is necessary to maintain the pH in the treatment tank during the reaction at 6 or more. This is because if the pH is less than 6, cyan gas is generated during the treatment and may be diffused into the atmosphere. On the other hand, if the pH value is too large, the amount of the drug used for neutralization thereafter increases, so the pH is preferably in the range of 7-10.

[Compound (C)]
Next, the compound (C) which reacts with the cyanide ion (CN ⁻ ) used in the present invention to produce a nitrile compound will be described. As described above, even if the iron compound (A) is added more than the theoretical amount, it is difficult to remove all the cyanide ions. Therefore, in the present invention, the compound (C) is added to the treatment system, and the treatment is performed together with the iron compound (A) and the metal salt (B). As a result, cyanide ions remaining in the wastewater without being complexed by the added iron compound (A) react with the compound (C) to be converted into a nitrile compound. Since it adsorbs easily to a suspended substance, it can be easily separated into solid and liquid thereafter.

  The compound (C) used in the present invention may be any compound as long as it can react with cyanide ions remaining without being complexed in cyanide-containing wastewater to form a nitrile compound. Specifically, at least any selected from the group consisting of a compound having an aldehyde group or keto group, ascorbic acid or an optical isomer thereof, lignin or a derivative thereof, humic acid or a derivative thereof, acrylic acid and a derivative thereof, and a reducing sugar. These compounds can be preferably used. Since these compounds have aldehyde groups or keto groups (carbonyl groups) in their structures, cyanide ions are easily added to these groups. At the same time, since the compound has a hydrophobic group in its structure, the obtained reaction product (adduct) can be rapidly converted into suspended matter such as coal fines present in wastewater. To be adsorbed. When a suitable suspending substance is not contained in the waste water or when it is small, for example, a porous body such as activated carbon, zeolite, or clay mineral may be contained as a suspending substance in the waste water.

  Specific examples of the compound (C) that can be used in the present invention include the following, and any of them can be used in the present invention. The compound having an aldehyde group or keto group and a hydrophobic group has an aromatic aldehyde having one aldehyde group, an aromatic ketone having one keto group, one aldehyde group and one or more unsaturated bonds. Unsaturated aldehyde, unsaturated ketone having 1 keto group and one or more unsaturated bonds, 1 saturated aldehyde having 1 aldehyde group and alkyl group having 2 to 28 carbon atoms, 1 keto group and 2 to 28 carbon atoms Saturated ketones having an alkyl group of Examples of the aromatic aldehyde include cinnamaldehyde, benzaldehyde, and vanillin. Examples of the unsaturated aldehyde include crotonaldehyde, and examples of the saturated aldehyde include pentanal and hexanal.

  Moreover, derivatives of acrylic acid such as acrylic acid and methyl acrylate, ascorbic acid or optical isomers thereof, lignin or derivatives thereof, humic acid or derivatives thereof, and reducing sugars can be used. Examples of reducing sugars include glucose and ribose.

  As an example of the compound (C), cinnamaldehyde, which is a kind of aromatic aldehyde, is used as an example, and cyanide ion remaining without being complexed in cyanate-containing wastewater reacts with cinnamaldehyde to form a nitrile compound. This will be explained. That is, when the aldehyde group of cinnamaldehyde reacts with the cyanide ion remaining in the waste liquid, the cyanohydrin derivative is generated. The derivatives include coal-derived suspended substances floating in the waste liquid, hexacyano iron complex salts in which cyanide ions are complexed with iron compounds (A) and insolubilized with metal salts (B), as described above, and the like. Is immediately adsorbed to the suspension. In the present invention, a cyanide ion remaining without being complexed in this way is added to the compound (C) to produce a reaction product, and the suspended material adsorbing the reaction product is By solid-liquid separation, all the cyanide ions in the waste water can be efficiently removed from the waste liquid. According to the present invention, not only the compound (C) but also the amount of each drug such as the iron compound (A) can be greatly reduced.

  The reaction between the cyanide ions in the cyanide-containing wastewater and the compound (C) such as cinnamaldehyde to be added is preferably performed under the following conditions. The added amount of the compound (C) to be added to the waste water is in the range of 0.8 to 1.2 molar equivalents, which are approximately equivalent to the cyanide ions that are considered to remain without being complexed. Although it is preferable to add, for safety, it is preferable to add and treat the compound (C) in an excess amount of about 2 to 20 times, for example.

  Furthermore, at the same time that compound (C) is added, at least one compound (D) selected from the group consisting of sulfurous acid or a salt thereof, thiosulfuric acid or a salt thereof, and nitrous acid or a salt thereof is added to compound (C). It is also preferable to add in the range of 0.01 molar equivalent to 20 molar equivalent, more preferably in the range of 0.05 molar equivalent to 5 molar equivalent. As the salt, sodium salt, potassium salt, calcium salt, ammonium salt and the like can be used. According to the study by the present inventors, an effect that the reaction proceeds more quickly and reliably by adding sodium bisulfite or the like into the treatment tank can be obtained.

  Moreover, although these compounds (D) may be added to cyanide-containing wastewater separately from the compound (C), it is also preferable to add them as a mixed drug mixed with the compound (C) such as cinnamaldehyde. If it does in this way, the addition ratio can be made into a stable state, and addition work will become easy. Furthermore, according to the study by the present inventors, there was a tendency that the stability of the treatment was ensured when added as a mixed drug rather than separately added. By using a mixed drug, the present inventors have ensured a compound such as sodium bisulfite that plays a catalytic role when a cyanide ion in a waste liquid reacts with a compound (C) such as cinnamaldehyde. I think that it will be possible to exist. The mixing ratio C: D in the case of a mixed drug with the compound (C) is, as a molar ratio, C: D = 1: 0.01 to 1:10, more preferably C: D = 1: 0. It is preferable to make it about 1-1: 1.

[Solid-liquid separation]
As described above, in the present invention, the cyanide ion in the waste liquid is converted into a cyano complex (metal complex salt) insolubilized with the iron compound (A) and the metal salt (B), but remains without being complexed. The cyanide ion is converted into a nitrile compound by reaction with compound (C), and the nitrile compound is adsorbed to a suspended substance in waste water, and then these suspended substance and insolubilized cyano complex are converted into By performing solid-liquid separation, cyanide ions in the waste liquid are efficiently and reliably removed. As a method for solid-liquid separation of the above suspended substance and the insolubilized cyano complex, generally used methods such as precipitation using gravity sedimentation, pressurized flotation, filtration, and centrifugation are used. be able to. Further, an inorganic flocculant such as polyaluminum chloride (PAC) or an organic polymer flocculant such as polyacrylamide may be used before solid-liquid separation.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
Example 1
What added 20 mg / L (0.77 mM) sodium cyanide to tap water was prepared as a simulated waste liquid (raw water). In a 300 mL beaker, 200 mL of the prepared simulated waste liquid was taken, and the pH was adjusted to 8 by adding a pH adjuster (sodium hydroxide solution). The following chemicals were added to this cyanide-containing wastewater (raw water). Ferrous chloride is added in an amount such that Fe ²⁺ is 2 molar equivalents relative to cyanide ion, and zinc chloride is added so that the raw water contains 5 mg / L as Zn ^2+. Formaldehyde was added at 15 mg / L. And it stirred at room temperature for 60 minutes. After stirring was stopped, 200 mg of a polymer flocculant (KEA-520 (trade name), manufactured by Nippon Steel Environmental Engineering Co., Ltd.) was added and stirred so that the concentration in raw water was 1 mg / L. The solid content in the liquid was removed by filtration with 5C filter paper. And the density | concentration of the cyanide ion and all the cyanides was measured by the method of JISK0102 by making a filtrate into test water. Table 1 shows the results and processing conditions.

(Example 2)
Cyanide ions were removed from the raw water under the same conditions as in Example 1 except that manganese sulfate was used instead of zinc chloride, and the concentrations of cyanide ions and total cyanide were measured using the filtrate as a specimen. As in the case of Example 1, the results and processing conditions are shown in Table 1.

(Example 3)
Cyanide ions were removed from the raw water under the same conditions as in Example 1 except that 60 mg / L of cinnamaldehyde was added instead of 15 mg / L of formaldehyde, and the filtrate was used as a specimen. The concentrations of cyanide ion and total cyanide were measured. As in the case of Example 1, the results and processing conditions are shown in Table 1.

Example 4
Cyanide ions were removed from the raw water under the same conditions as in Example 2 except that 60 mg / L of cinnamaldehyde was added instead of 15 mg / L of formaldehyde, and the filtrate was used as a specimen. The concentrations of cyanide ion and total cyanide were measured. As in the case of Example 1, the results and processing conditions are shown in Table 1.

(Comparative Examples 1-3)
The same raw water as used in Example 1 was used, the pH was adjusted to each, stirring and filtration were performed in the same manner as in Example 1, and the concentrations of cyanide ions and total cyanide were measured using the filtrate as a specimen. did. As in the case of Example 1, the results and processing conditions are shown in Table 1.

(Comparative Examples 4 to 14)
Cyanide ions were removed from the raw water under the same conditions as in Example 1 except that the same raw water as used in Example 1 was used and the chemicals shown in Table 1 were added. Ion and total cyan concentrations were measured. As in the case of Example 1, the results and processing conditions are shown in Table 1.

(Results of processing of Examples 1 to 4 and Comparative Examples 1 to 14)
As is clear from Table 1, in the treatments of Examples 1 to 4, the cyanide ion concentration in the raw water was initially 20 mg / L, but in any case, 0.5 mg / L ( ppm) and the total cyan concentration was also reduced to 0.8 mg / L (ppm) or less, and it was confirmed that almost all cyan components in the raw water were removed by the treatment. On the other hand, only the iron compound (A), only the compound (C), only the metal salts (B), and only the iron compound (A) and the metal salts (B) of Comparative Examples 4 to 14 are compounds. In any case where only (C) and the metal salt (B) were added for treatment, both the cyanide ion concentration and the total cyan concentration in the treated water were reduced, but this was not sufficient.

  In Comparative Examples 1 to 3, the pH of the raw water was changed and stirred at room temperature for 60 minutes, and the influence of the pH of the raw water during the treatment was examined. As a result, as shown in Table 1, in Comparative Example 1 in which the pH was adjusted to 5.5, the cyanide ion and total cyan ion concentrations were slightly decreased as compared with the case where the pH was adjusted to 6 or more. The reason for this is considered that cyanide ions were diffused as hydrogen cyanide gas during the stirring treatment.

(Comparative Example 15)
To the tap water, sodium cyanide was added to 2 mg-CN / L, and potassium ferrocyanide was added to 5 mg-CN / L as a simulated waste liquid (raw water) with a total cyan concentration of 7 mg / L. Prepared. The pH of the prepared raw water was adjusted to 8, and the mixture was stirred and filtered at room temperature for 60 minutes in the same manner as in Example 1. The concentrations of cyanide ions and total cyanide were measured using the filtrate as a specimen. Table 2 shows the results and processing conditions.

(Examples 5 to 9)
The same raw water prepared in Comparative Example 1 was used, the pH was adjusted to 8, and iron salts (ferrous chloride), cinnamaldehyde, and zinc chloride were used so that the concentrations were as shown in Table 2. The same processing as in Example 1 was performed. In the same manner as in Example 1, the filtrate was used as test water, and the concentrations of cyanide ions and total cyanide were measured. The results and treatment conditions are shown in Table 2.

(Examples 10 to 14)
The same raw water prepared in Comparative Example 1 was used, the pH was adjusted to 8, and iron salts (ferrous chloride), cinnamaldehyde, and manganese sulfate were used so that the concentrations were as shown in Table 2. The same processing as in Example 1 was performed. In the same manner as in Example 1, the filtrate was used as test water, and the concentrations of cyanide ions and total cyanide were measured. The results and treatment conditions are shown in Table 2.

(Examples 15 to 18)
Using the same raw water prepared in Comparative Example 1 and adjusting the pH to 6, 7, 9, and 10 so that the concentration is as shown in Table 2, iron salt (ferrous chloride), thinner The same treatment as in Example 1 was performed using mualdehyde and zinc chloride. In the same manner as in Example 1, the filtrate was used as test water, and the concentrations of cyanide ions and total cyanide were measured. The results and treatment conditions are shown in Table 2.

(Results of treatment of Examples 5 to 18 and Comparative Example 15)
In the treatments of Examples 5 to 14, the concentration and type of metal salts to be added were changed. As shown in Table 2, from the results of the treatments in Examples 5 to 14, the metal salt of zinc or manganese was added to the raw water so that the metal ion concentration was 0.05 equivalent or more with respect to all cyan. When added, a significant difference was observed as compared with the case where it was less. Moreover, in Examples 15-18, it processed by adjusting the pH of the raw | natural water at the time of processing to 6, 7, 9, and 10, respectively, and compared and examined. As a result, as is clear from Table 2, it was confirmed that the cyan component can be removed more favorably when the pH is adjusted in the range of 7 to 10.

Claims (6)

A method for treating cyanide-containing wastewater for removing cyanide components from cyanide-containing wastewater,
While maintaining the pH of the wastewater at the time of treatment at 6 or more,
An iron compound (A) that generates iron ions in the wastewater, a compound (C) that reacts with cyanide ions (CN ⁻ ) to generate a nitrile compound, and at least Zn ²⁺ or Mn in the wastewater ^By adding together with the metal salts (B) that give rise to either ²⁺ or Cu ²⁺ metal ions,
With the iron compound (A), most of the cyanide ions in the cyanide-containing wastewater are complexed and converted to a hexacyanoiron complex,
By the compound (C), the cyanide ion remaining without being complexed is converted into a nitrile compound, and the nitrile compound is adsorbed on a suspended substance in waste water,
The metal salts (B) insolubilize the cyano complex in the wastewater containing the hexacyanoiron complex converted above,
Thereafter, the method for treating cyanogen-containing wastewater is characterized by solid-liquid separation of the suspended substance and the insolubilized cyano complex. The pH of the waste water during the treatment is maintained in the range of 7.0 to 10.0, and the amount of the compound (C) added is the number of metal ions of Zn ²⁺ or Mn ²⁺ or Cu ²⁺ or the sum thereof. 2. The cyan content according to claim 1, wherein the cyan content is adjusted to be 0.05 molar equivalent or more with respect to all cyan components in the wastewater (the sum of free cyan and cyanide ions coordinated to complex cyanide). Wastewater treatment method.   The compound (C) is selected from the group consisting of a compound having an aldehyde group or keto group, ascorbic acid or an optical isomer thereof, lignin or a derivative thereof, humic acid or a derivative thereof, acrylic acid and a derivative thereof, and a reducing sugar. The method for treating cyanide-containing wastewater according to claim 1 or 2, which is at least one compound.   The metal salt (B) is at least one metal salt selected from the group consisting of zinc chloride, zinc sulfate, zinc ammonium chloride, zinc nitrate, manganese chloride, manganese sulfate, copper chloride, and copper sulfate. The processing method of cyanate containing wastewater of any one of 1-3.   Furthermore, with the addition of the compound (C), at least one compound selected from the group consisting of sulfurous acid or a salt thereof, thiosulfuric acid or a salt thereof, and nitrous acid or a salt thereof is added to the compound (C). The method for treating cyanide-containing wastewater according to any one of claims 1 to 4, which is added in a range of 0.01 to 20 molar equivalents.   The method for treating cyan-containing wastewater according to any one of claims 1 to 5, wherein the cyanine-containing wastewater contains waste liquid from a coke factory, a coal factory, or a plating factory.