JP2580610B2 - Treatment method for water containing iron cyanide complex - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating water containing an iron cyanide complex, and more particularly to a method for treating water containing an iron cyanide complex that can simultaneously remove heavy metals coexisting with the iron cyanide complex. Things.

[Conventional technology]

As a method for treating water containing an iron cyanide complex such as a ferrocyanide ion or a ferricyan ion, a navy blue method in which a ferrous salt is added to react with water is known.
In this method, a weakly acidic (pH 4 to 6) and hardly soluble iron cyanide complex is precipitated, and then a high alkali (pH 9 to 12) is used to precipitate excess ferrous salt and coexisting heavy metals as hydroxide.

Further, ferrous salt is added to the water containing iron cyanide complex, alkali is added to adjust the pH to 7 to 8, and then ferric salt is added to adjust the pH to 6.5.
A method is known in which the iron cyanide compound is separated by precipitation at a temperature of from 7.3 to 7.3 (JP-B-56-51835). This method turns ferrocyan ion, which is generated by adding a ferrous salt to water containing an iron cyanide complex and partially dissolving by adding an alkali to ferrocyanide ions, to be inactive Berlin blue with a ferric salt. is there.

[Problems to be solved by the invention]

However, in the navy blue method, since the region where the hardly soluble iron cyanide complex is generated is weakly acidic, the iron cyanide complex is used at pH 4-6.
And a second step of precipitating excess ferrous salt and coexisting heavy metals at pH 9-12.

Also in the method of JP-B-56-51835, two-stage treatment was necessary because the coexisting heavy metals such as nickel and zinc do not form hydroxide precipitates when the pH is neutral.

The present invention has been made to solve the above-mentioned problems. The iron-cyan complex-containing water, which makes the iron-cyan complex hardly soluble at a high pH, whereby excess iron, copper and coexisting heavy metals can be removed at the same time in a single-stage treatment. The purpose of the present invention is to propose a processing method.

[Means for solving the problem]

In the present invention, a ferrous salt and a copper salt are reacted with water containing an iron cyanide complex in the presence of a reducing agent other than the ferrous salt and the copper salt to form a hardly soluble salt under alkaline conditions, This is a method for treating water containing iron cyanide complex, which is characterized by liquid separation.

Iron cyanide complex-containing water to be processed in the present invention, ferrocyanide ion ^{_{(Fe (CN) 6 4-)}} , with water containing an iron cyanide complexes such as ferricyanide ion ^{_{(Fe (CN) 6 3-)}} , Other heavy metals such as nickel and zinc may be included.

As the ferrous salt to be reacted with the iron cyanide complex, ferrous chloride, ferrous sulfate and the like can be used. The copper salt may be any water-soluble salt, and may be a monovalent copper salt or a divalent copper salt. In general, monovalent copper salts are poorly soluble and are easily oxidized by air, so that they are industrially used. It is difficult to obtain, and divalent copper salts such as copper sulfate, copper chloride, and copper nitrate can be used.

In the treatment method, a ferrous salt and a copper salt are added to water containing an iron cyanide complex, and the reaction is carried out in the presence of a reducing agent other than the ferrous salt and the copper salt, thereby producing a sparingly soluble ferrocyanide salt.
In this case, it is necessary to react the iron salt in the state of a ferrous salt, and if it is oxidized to ferric at the time of the reaction or thereafter, it becomes difficult to generate a sparingly soluble salt. Therefore, it is desirable to avoid air oxidation during the reaction. Further, when ferricyan ion is contained as the iron cyanide complex, the added ferrous salt is oxidized when reducing the ferricyan ion to ferrocyanide ion. Therefore, the reduction is performed by adding a reducing agent. If ferrous salts and copper salts are used as reducing agents, the amount of sludge increases, so that other reducing agents such as sulfites and thiosulfates can be simultaneously added and reacted.

The amounts of the ferrous salt and the copper salt to be reacted with the iron cyanide complex are (Fe + Cu) / Fe (CN) ₆ = 2 or more (molar ratio), Cu / Fe
= 0.2 to 2 (molar ratio), and even if added in excess, it is later removed as hydroxide. If the raw water contains ferricyanide or chlorine, or if it is in an oxidizing atmosphere, the ferrous salt will be oxidized, so adding ferrous salt to the work or adding another reducing agent is not an option. preferable. Ferrous salt,
When the copper salt, the reducing agent and the like are contained in the raw water, the amount of addition can be reduced.

It is presumed that when the ferrous cyanide complex-containing water is added with a ferrous salt, a copper salt, and a reducing agent and reacted with stirring, a sparingly soluble salt is formed by the following formula.

Here, the product is in the form of a double salt of Fe _x Cu _y [Fe (CN) ₆ ] _z , or —Fe—O—Cu— or And compound nucleus complex represented in either a Fe (CN) ₆ ^4- and reactants is not known.

The above reaction proceeds in a wide pH range from the acidic region to pH 11. Therefore, when the reaction is carried out under alkaline conditions, particularly at pH 9 to 11, the iron cyanide complex is precipitated as an insoluble compound, and at the same time, excess ferrous salts and copper salts and heavy metal ions such as nickel and zinc coexist with water. It precipitates as an oxide, and at the same time enables solid-liquid separation. In this case, the reaction may be carried out by adjusting the pH to the alkaline side from the beginning, but in order to reduce the rate at which the cuprous salt is oxidized by the dissolved enzyme, the ferrous salt and the copper salt are acidified or neutralized. After the reaction with the iron cyanide complex, it is desirable to adjust the pH to the alkali side to precipitate another metal.

The hardly soluble salt thus formed is subjected to solid-liquid separation as it is, but it is preferable to perform coagulation precipitation separation by adding a coagulant such as a polymer coagulant. The coagulant may be added simultaneously with the ferrous salt or the like, or may be added later. Further, the above reaction and aggregation treatment may be performed simultaneously in one reaction tank, or may be performed with a time lag. Solid-liquid separation can be performed by known separation means such as precipitation and filtration.

In the above-described treatment method, the resulting hardly soluble salt does not redissolve the cyan complex even at a high pH, and thus is precipitated and separated at a high pH together with other coexisting metals. The treated water thus obtained is free of cyan, iron, copper and other heavy metals,
It can be released as it is.

〔The invention's effect〕

As described above, according to the present invention, a ferrous salt and a copper salt are reacted with water containing an iron cyanide complex, and a sparingly soluble salt is separated under alkalinity.
The iron cyanide complex, excess iron, copper, coexisting heavy metals, and the like can be simultaneously removed at a high removal rate, and the amount of chemicals used and the amount of sludge generated can be reduced.

〔Example〕

Sodium ferricyanide Na ₃ [Fe (CN) ₆ ] 35mg /
(As CN) raw ferrous sulfate containing (FeSO ₄ · 7H
₂ O), copper sulfate (CuSO ₄ .5H ₂ O) and sodium sulfite (Na ₂ SO ₃ ) were added as shown in Table 1, adjusted to a predetermined pH, reacted for 10 minutes, and filtered through filter paper No. 5A. The water quality of the filtrate obtained is shown in Table 1.

As a comparative example, Table 2 shows the results of a similar test conducted without adding a ferrous salt and / or a copper salt or adding zinc chloride (ZnCl ₂ ).

In Table 1, in Comparative Example 1, when ferrous salt is used as a reducing agent, the removal rate of cyan and the like is increased, but it is necessary to add a large excess of ferrous salt, and the amount of sludge also increases. . When a small excess of ferrous salt is reacted in the absence of a reducing agent as in Comparative Example 2, ferrous deficiency is consumed due to oxidation to ferric iron by the dissolved enzyme and reduction of ferricyan, It is estimated that the effect will be worse. Thus, it can be seen that when a reducing agent is used in combination as in Example 1, the removal rate of cyan and the like increases.

On the other hand, in Comparative Examples 3 to 7 in Table 2, when only the ferrous salt or the copper salt is added alone, or when these are used in combination with the reducing agent or zinc, the cyan removal rate decreases at pH 9 or more. I understand. Comparative Example 8 shows the case where the ferrous salt was oxidized by the combined use of aeration, which indicates that the cyanide removing effect was deteriorated.

Claims (2)

(57) [Claims] 1. A ferrous salt and a copper salt are reacted with water containing an iron cyanide complex in the presence of a reducing agent other than the ferrous salt and the copper salt to form a poorly soluble salt under alkaline conditions. A method for treating iron-cyan complex-containing water, comprising performing solid-liquid separation. 2. The method according to claim 1, wherein the pH for forming the hardly soluble salt is 9 to 11.