JPH0483590A - Method and apparatus for treating cyan compound-containing solution - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to the treatment of a cyanide compound-containing liquid, in which a ferrous salt is added to a cyanide-containing liquid and reacted, and the cyanide compound is separated and removed as a water-insoluble salt. The present invention relates to a method and a processing apparatus.

[Conventional technology]

Conventionally, as a method for separating and removing cyanide compounds 1, for example, metal cyanide complex ion-containing liquids, by reacting them with ferrous salts to generate water-insoluble salts, Japanese Patent Publication No. 51-28939 deals with iron cyanide complexes, After two-stage decomposition using the chlorine method, the oxidation-reduction potential (hereinafter referred to as ORP) was 200.
Ferrous salt is added so that the voltage is ~300 mV. This method is based on the reaction of the following formula: 3Fe2" + 2Fe (CN) knee → Fe, (Fe
(CN)slz↓ ・(1)2Fe" + OCQ'
−+ 2H” →2Fe” + Cj)−+ LO・・
・(2) Here, equation (1) takes precedence over equation (2),
The reaction to make the iron cyanide complex less soluble occurs, and then the residual chlorine is reduced, so the ORP value at the time the residual chlorine disappears,
That is, if the ferrous salt was added until the voltage reached 200 to 300 mV, the reaction to make it difficult to solubilize would be completed, and it was thought that the treatment was theoretically complete.

Also, JP-A-1-30693 and JP-A-1-355
In No. 3, ferrous salt and copper salt are added in an amount equal to or more than the amount of iron cyanide complex or silver cyanide complex contained. In this method, a water-insoluble complex salt is generated according to the following formula.

xFa"+yCu"+zFe(CN)4-*FexCu
y(Fe(CN), ), ↓ ・(3)xFe”+yCu
”+zAg(CN)i-+FexCuy(Ag(CN)
, ), ↓ ・(4) However, even if proper ORP control or more than equivalent amounts of ferrous salt and copper salt are added,
The cyanide concentration in treated water may exceed 1 mg/Ω,
In such a case, the treatment liquid must be returned to the raw water tank for reprocessing, which poses a problem in that stable water treatment cannot be performed.

[Problem to be solved by the invention]

The purpose of this invention is to solve the above-mentioned problems by controlling the dissolved oxygen (hereinafter referred to as DO) in the liquid to be treated to a certain level, adding just the right amount of ferrous salt, and cyanide compound treatment. It is an object of the present invention to provide a method and apparatus for treating a cyanide-containing liquid, which can treat cyanide at a high level and stably, and can lower the cyanide concentration of the treatment liquid.

[Means to solve the problem]

The present invention provides the following method and apparatus for treating a cyanide-containing liquid.

(1) In a method of adding a ferrous salt to a cyanide compound-containing liquid and separating and removing the cyanide compound as a water-insoluble salt, while or after adding the ferrous salt to the cyanide compound-containing liquid, 1. A method for treating a cyanide-containing liquid, the method comprising measuring the dissolved oxygen concentration, and determining the end point of addition of ferrous salt when the dissolved oxygen concentration value sharply decreases.

(2) In a method in which a ferrous salt is added to a reaction tank into which a cyanide compound-containing liquid continuously flows, and the cyanide compound is separated and removed as a water-insoluble salt, the dissolved oxygen concentration in the reaction tank is measured, and the dissolved oxygen concentration in the reaction tank is measured. A method for treating a cyanide-containing liquid, which comprises adding a ferrous salt so that the dissolved oxygen concentration reaches a predetermined value.

(3) A reaction tank for introducing a cyanide compound-containing liquid to react with a ferrous salt, a means for adding the ferrous salt to the reaction tank, and a dissolved oxygen meter for measuring the dissolved oxygen concentration in the reaction tank. and a control device for controlling the amount of ferrous salt added based on the dissolved oxygen concentration value measured by the dissolved oxygen meter.

As a result of examining the causes of variations in conventional treatment methods, we found that there is a close relationship between the cyanide concentration of the treatment solution and Do, and that ferrous salt injection should be controlled to keep DO at a constant level. It has become clear that a stable processing solution can be obtained.

Ferrous salt and Do easily react at pH 5 or higher, and ferrous iron is easily oxidized to ferric iron according to the following formula.

2Fe" + O+ HzO→2Fe" + 208-
...(5) Therefore, the iron salts in the precipitates of formulas (1), (3), and (4) are all ferrous salts (Fe2+
), and if the amount of ferrous salt added is slightly excessive, it will be oxidized by DO and redissolved according to the following formula.

Fe, [Fe(CN)s)a →3Fe”+2Fe(
CN) knee - (6) FexCuy (Fe
(CN), )z →xFe"+yCu"+zFe(CN
)'5-(7)FexCuy(Ag(CN)2), -
) xFe”+yCu” zAg(CN)i −(8
) In order to prove the above point, when a deep blue method processing using ORP control was performed, cyan processing failure occurred.

This result will be shown in the example below, but in order to completely make the cyanide complex insoluble, more ferrous salt than the reaction figure is required, and the excess amount must be added until DO falls below a certain level. I found out that I needed a lot.

The cyanide compound-containing liquid to be treated in the present invention is a liquid containing free cyanide ions and metal cyanide complex ions, specifically, ferrocyanide ions (Fe(CN
)2-), ferricyanion [Fe(CN)ffi-
Water containing iron cyanide complex ions of grade 3 and silver cyanide complex ions (
In addition to water containing Ag(CN)i), examples include water in which other metal ions such as potassium, sodium, copper, nickel, and zinc coexist with cyanide ions.

The ferrous salt added to the cyanide-containing solution is as follows:
Ferrous chloride, ferrous sulfate, etc. can be used.

In the present invention, in order to convert the cyanide compound in the liquid to be treated into a water-insoluble salt, a ferrous salt is added and reacted. In this case, although the ferrous salt can be added alone to the cyanide-containing liquid, it is preferable to add the copper salt together with the ferrous salt.

The copper salt may be any water-soluble salt, and may be either a monovalent copper salt or a divalent copper salt, but monovalent copper salts are generally poorly soluble and easily oxidized by air, so they are not commercially available. divalent copper salts such as copper sulfate, copper chloride, and copper nitrate are available.

If ferrous salt is oxidized to ferric iron during or after the reaction, it becomes difficult to form a water-insoluble salt, so it is desirable to avoid air oxidation during the reaction.

When adding and reacting ferrous salts, in order to efficiently generate water-insoluble salts, a pH adjuster is added to adjust the reaction solution to pH 5.
It is preferable to adjust the pH to 11. As the pH adjuster, acids such as hydrochloric acid and sulfuric acid, and alkalis such as sodium hydroxide and calcium hydroxide can be used.

If the reaction solution has a pH lower than P) 15, the reaction between ferrous ions and dissolved oxygen tends to occur, and if the pH is higher than 11, it becomes difficult to form water-insoluble salts.

[For production]

In the treatment of a cyanide-containing liquid according to the present invention, a cyanide-containing liquid is introduced into a reaction tank, a ferrous salt is added thereto, and the ferrous salt is reacted with the cyanide compound in the liquid to be treated to produce a water-insoluble salt. When the treatment is carried out in a batch manner, the operation of measuring the DO concentration using a DO meter while adding the ferrous salt, or adding the ferrous salt appropriately and then measuring the Do concentration is repeated. The end point of the addition of ferrous salt is when the value of DO concentration suddenly decreases.

In the case of a continuous type, the DO concentration is adjusted to a predetermined value, that is, when the DO concentration suddenly decreases in batch processing.

Ferrous salts can be added to efficiently generate water-insoluble salts so that the concentration values are the same.

The water-insoluble salts thus generated in the reaction solution are separated into solid-liquid as they are, but it is preferable to perform coagulation-sedimentation separation by adding a flocculant such as a polymer flocculant. They may be added at the same time or may be added later. Further, the above reaction and aggregation treatment may be performed simultaneously in one reaction tank or may be performed at different times. Solid-liquid separation can be performed by known separation means such as precipitation and filtration.

In the present invention, when free cyanide or easily decomposable cyanide compounds coexist in the cyanide-containing liquid, separation and removal efficiency can be improved by decomposing these ions in advance by an alkali chlorine method or the like. In the case of the alkali chlorine method, a two-stage treatment method is preferred, in which a chlorine agent is first added at pH 10 or higher to perform primary decomposition, and then the pH is lowered and a chlorine agent is added again to perform secondary decomposition.

When a cyanide-containing solution is treated as described above, the Do concentration in the reaction solution is reduced, so that the ferrous iron in the water-insoluble salt is not oxidized to ferric iron by dissolved oxygen and can be redissolved. do not have. Therefore, cyan ions do not leak into the processing liquid, and high-level processing can be performed stably.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a system diagram showing a cyanide compound-containing liquid processing apparatus according to an embodiment. In the figure, reference numeral 1 denotes a reaction tank, in which a liquid to be treated is introduced from a liquid to be treated tube 2, reacted with ferrous salt, and a reaction liquid 3 is taken out from a treated liquid tube 4 as a treatment liquid. The reaction tank 1 includes a ferrous salt supply pipe 5 and a copper salt supply pipe 6.
, acid supply pipe 7, and alkali supply pipe 8 communicate with each other, and pumps P1, P2, P3 . P4 is the control device 9
It is now controlled by. In reaction solution 3,
Stirrer 10 rotated by motor M, DO meter 11, pH
A total of 12 are provided, each connected to the control device 9.

The method for treating a cyanide-containing liquid using the above-mentioned processing apparatus is to introduce the liquid to be treated into the reaction tank 1 from the liquid to be treated pipe 2, and to supply ferrous salt by driving the pumps P□ and P2 by the control unit 9. Ferrous salt is added through tube 5, copper salt is added through copper salt supply tube 6, and the stirrer 10 is rotated to cause a reaction and produce a water-insoluble salt. During this time, the pH of the reaction solution 3 was measured by the pH meter 12.
is measured, and depending on the p)I value, pump p3 or P is driven to add acid or alkali, and the p)I of reaction solution 3 is
is controlled to 5-11.

The DO meter 11 measures the DO concentration of the reaction solution 3 and calculates the DO concentration.
The concentration value is input to the control device 9. The control device 9 is set in advance by a beaker test or the like to set the DO concentration at the point in time when the DO concentration value rapidly decreases, and the pump P1 is controlled so that the point at which the Do concentration is reached is the end point of ferrous salt addition. do. It can also be controlled so that the end point is the point in time when the DO becomes 6 mg/Q or less, preferably 3 ml g/Q or less, more preferably 2 rag/Q or less.

The addition of the ferrous salt and the measurement of the Do concentration value may be performed continuously, or after adding an appropriate amount of the ferrous salt and reacting,
After the 0 reaction, the operation of measuring the Do concentration may be repeated.
The reaction liquid 3 is taken out as a treatment liquid from the treatment liquid pipe 4, and a water-insoluble salt is generated by solid-liquid separation.

The above reaction may be carried out batchwise or continuously. The batch type is suitable for detecting the point of sudden decrease in the Do concentration value. In the case of a continuous type reaction tank, if the reaction tank is a complete mixing type, ferrous salt should be added so that the DO concentration value becomes the specified value, and if the reaction tank is a push-flow type, ferrous salt should be added along the flow of the liquid. The amount of ferrous salt added can be controlled by installing a plurality of DO meters and adding ferrous salt so that the DO concentration value of the most downstream DO meter becomes a predetermined value.

Example 1 and Comparative Example 1 Metsuki wastewater containing dark blue treated iron cyanide complex ions (total CN 65wa
g/Q, Zn 28IIgIQ, Fg 8B/Q)
was subjected to the usual alkali-chlorinated two-stage treatment (-Next: pH 10,
5, ORP 500 ■■, reaction for 20 minutes, secondary: p) 1
8. ORP 750■■, 30 minutes reaction)
After making the total CN 25 rag/(l), F as ferrous salt
e50.・7H20 was added, the pH was adjusted to 6, and a dark blue treatment was performed. At this time, Do concentration value, ORP value, treated water total cyanide and Fe50. - Figure 2 shows the relationship with the amount of 7H20 added.

Comparative Example 1 is a method based on ORP control, and the ON-OFF potential setting of ferrous salt addition is selected from a steep range of ORP value ratio change distribution. For example, in FIG.

The set potential is selected in the range of 300 to 70 (laV, 3
Control was performed such that the addition of ferrous salt was turned off at 00■■ and turned on at 400■■. However, when such a setting value is selected, as is clear from FIG. 2, cyanide is not yet completely rendered insoluble. Therefore, it is necessary to select an ORP value that allows further addition of ferrous salt.
When the ORP value is less than 300■■, the change in ORP with respect to the amount of ferrous salt added is slow and control is difficult. If a low ORP value is set in consideration of the safety of cyanogen treatment, excessive ferrous salt will be injected, which is impractical.

On the other hand, Example 1 is a method in which the addition of ferrous salt is controlled by the Do concentration value, and in this method, after the cyanide complex ions are treated to a low level, the Do concentration value rapidly decreases. For example, it can be seen that if ferrous salt is added until the DO concentration becomes 3 mgIQ or less, treated water with a total cyanide concentration of 1 yag/Q or less can be obtained.

Example 2 and Comparative Example 2 Treatment of wastewater containing silver cyanide and iron cyanide After the metallurgical wastewater containing silver cyanide and iron cyanide was treated with alkaline chlorine as usual, it was treated with F as a ferrous salt at pH 8 to 8.5.
e50. - Treated by adding 7H20. Water quality after alkali chlorine treatment is pH 7-7.5, total CN 5.8-10
mg/Q, Cu 20mg/Q, Ag 5. Omg
/Q, Fe 3mg/Q, and the amount of treated water is 5 points/h
It is r.

In Comparative Example 2, 200 ■■ Te ferrous salt addition OFF, 30
The ON operation was performed at 0■■.

On the other hand, in Example 2, a DO meter was used instead of an ORP meter to control the addition of ferrous salt. FIG. 3 shows the relationship between the ORP value, the Do concentration value, and the amount of ferrous salt added.

Furthermore, based on the results shown in FIG. 3, the addition of ferrous salt was turned on at a DO concentration of 3BIQ, and turned off at a DO concentration of 2 mg#l. ORP
Table 1 shows the analysis results of the filtrate obtained by filtering the treated water at the outlet of the sedimentation tank through filter paper Nn5A when the water was controlled by a DO meter and when it was controlled by a DO meter.

Table 1 Table 2 Analytical values of treated water (liquid temperature 26°C) As shown in Table 1, the quality of treated water fluctuates widely when controlled with an ORP meter, but is stable and good when controlled with a DO meter. Treated water of high quality was obtained, demonstrating the effectiveness of control using the DO meter.

Example 3 Ferrous salt FeSO4.7H20 and copper salt CuSO4 were added to wastewater containing free cyanide 5 WAGED (as CN) and ferrocyanide 2 mg, 1 (as CN), and Do
The treatment was controlled by a meter. The results are shown in Table 2.

As shown in Table 2, it is found that it is possible to treat wastewater containing free cyanide if a copper salt is used in combination and the amount of ferrous salt added is controlled to an appropriate value using the DO concentration value as an index.

〔Effect of the invention〕

As described above, according to the present invention, since the amount of ferrous salt added is controlled using the Do concentration value as an index, the amount of ferrous salt added is just the right amount, and the cyanide-containing liquid is efficiently controlled. Processing can be carried out highly and stably, and a processing solution with a low cyan concentration can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the processing apparatus of the example, and FIGS. 2 and 3 are graphs showing the results of the example. 1: reaction tank, 2: treated liquid pipe, 3: reaction liquid, 4: treated liquid pipe, 5: ferrous salt supply pipe, 9: control device, 10: stirrer, 11: Do meter, 12: p) L total. Figure 3 ° Agent Patent attorney Sei Yanagihara

Claims (3)

[Claims] (1) In a method of adding a ferrous salt to a cyanide compound-containing liquid and separating and removing the cyanide compound as a water-insoluble salt, while or after adding the ferrous salt to the cyanide compound-containing liquid, 1. A method for treating a cyanide-containing liquid, the method comprising measuring the dissolved oxygen concentration, and determining the end point of addition of ferrous salt when the dissolved oxygen concentration value sharply decreases. (2) In a method in which a ferrous salt is added to a reaction tank into which a cyanide compound-containing liquid continuously flows, and the cyanide compound is separated and removed as a water-insoluble salt, the dissolved oxygen concentration in the reaction tank is measured, and the dissolved oxygen concentration in the reaction tank is measured. A method for treating a cyanide-containing liquid, which comprises adding a ferrous salt so that the dissolved oxygen concentration reaches a predetermined value. (3) A reaction tank for introducing a cyanide compound-containing liquid to react with a ferrous salt, a means for adding the ferrous salt to this reaction tank, and a dissolved oxygen meter for measuring the dissolved oxygen concentration in the reaction tank. and a control device for controlling the amount of ferrous salt added based on the dissolved oxygen concentration value measured by the dissolved oxygen meter.