JPS583690A - Treatment of waste water containing iron cyanide complex salt - Google Patents

Abstract

PURPOSE:To remove an iron cyanide complex salt in waste water in a good efficiency, by the action of a acting thiosulfate on waste water containing an iron cyanide complex salt including a ferricyanide compound in the presence of a zinc salt and an ammonium salt to expedite formation of zinc ferrocyanide. CONSTITUTION:To waste water containing an iron cyanide complex salt including a ferricyanide compound, 2.1-5mol of a zinc salt, 1X10<-4>-1M (in terms of an ammonium ion) of an ammonium salt and 1-2mol of a thiosulfate per mol of a ferricyanide ion are added to precipitate the ferricyanide ion as zinc ferrocyanide. The formed precipitate is removed by a conventional solid-liquid separation method and the cyanide concn. in the treated liquid can be easily reduced to 1ppm or less which is a regulation value and the reduction thereof to 0.1ppm or less can also be attained within a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for precipitation treatment of wastewater containing iron cyano complexes containing ferricyanide, which uses zinc salt as a precipitant and thiosulfate as a reducing agent.

Wastewater containing iron cyano complex salts such as ferricyanide and ferrocyanide is used in photo labs, plating plants, steel carburizing plants, nitriding plants, and fruit and vegetable fumigation warehouses.

Cyanide is discharged from cyanide smelting plants, etc., and must be treated so that the concentration of cyanide in the wastewater is below the regulatory value of 1 ppm.

Conventionally known methods for removing iron cyano complexes from wastewater include chemical, electrochemical, or photochemical decomposition treatment methods, physical concentration methods such as ion exchange, electroosmosis, and reverse osmosis, and activated carbon. Examples include an adsorption treatment method using an adsorbent and a precipitation treatment method using a precipitant.

The above decomposition treatment method requires harsh reaction conditions because iron cyano complex salts are chemically stable, and the decomposition rate is low even if high valence energy such as electric energy and light energy and special equipment are used. Physical concentration methods have the disadvantage of being uneconomical.

Not only is the equipment expensive, but the concentrated liquid obtained by this method must be subjected to post-treatment such as decomposition treatment or precipitation.Furthermore, the adsorption treatment method is inexpensive, has large adsorption power, and is highly selective. It is not practical because good adsorbents have not yet appeared.

The precipitation treatment method is suitable for large-scale treatment, but 9i! Even in the Prussian method, which uses iron salts as a precipitant, which is the only method currently used, accurate analysis of ferricyanide and ferrocyanide ions is required for the production and precipitation separation of insoluble ferrocyanide and ferrocyanide. Effect of oxygen in the air, PH
In addition to many difficult problems such as fluctuations in solubility due to
It is extremely difficult to suppress the cyanide concentration in the treated water to a few ppm or less, not to mention the regulatory value, and the current situation is that even stricter process control is required.

As another precipitation treatment method, a method is disclosed in JP-A-55-59886 in which a reducing agent is applied to wastewater containing iron cyano complex salts containing ferricyanide in the presence of zinc salt to precipitate and remove iron cyano complex salts as zinc ferrocyanide. It is proposed in the Publication No.

The method according to the above publication in which thiosulfate, sulfite, pyrosulfite, dithionite, hydrazine salt, hydroxylammonium salt, etc. is used as a reducing agent, uses the reducing agent to convert ferricyanion to -tamferrocyanide. This process is characterized in that it can be processed relatively more quickly than in the case where a zinc 7-erocyanide precipitate is produced using a zinc salt after reduction to ions, and that the residual cyanide concentration can be easily reduced to IPPm or less.

However, among the above-mentioned reducing agents, hydrazine salts and hydroxylamine salts are expensive and have poor practical use.

Furthermore, sulfites, pyrosulfites, and dithionites have the disadvantage that they are very susceptible to oxidation by dissolved oxygen from the air. In contrast, thiosulfates have the characteristic of not being oxidized by dissolved oxygen.

The rate of formation of zinc ferrocyanide precipitate is relatively slow (1. In other words, in the case of the above reducing agents except thiosulfate, it is within a few minutes). The formation of a precipitate is almost completed, but in the case of thiosulfate, "if the amount of thiosulfate added is about 1 to 2 times the molar amount of ferricyanion, the formation of a precipitate will gradually progress and it will take more than 60 minutes to complete the reaction." Furthermore, the rate of formation of zinc ferrocyanide precipitates is significantly reduced in the presence of salts.Thus, thiosulfate-containing When using wastewater from a photographic fixing facility that uses a fixing solution, processing time is required due to coexisting salts that are added as subcomponents (5 problems). As a result of extensive research into the method of reducing ferricyanion with thiosulfate in the presence of zinc salt and precipitating it as zinc ferrocyanide in order to increase the production rate of zinc ferrocyanide, we unexpectedly found that ammonium salt was present. The inventors have discovered that this increases significantly under the following conditions, leading to the present invention.

That is, the present invention consists of treating iron cyano complex-containing wastewater containing ferricyanide with thiosulfate in the presence of zinc salts and ammonium salts to precipitate and remove iron cyano complexes as zinc 7-erocyanide.

In the present invention, if the ammonium salt is soluble and does not form a poorly soluble salt with zinc ions, there is almost no difference in effectiveness depending on the acid group, but it is most economical to include it in the form of ammonium chloride or ammonium sulfate. It is. Furthermore, in the treatment of wastewater from photographic bleaching facilities, it is advantageous to use ammonium thiosulfate as a fixer component when the thiosulfates contained in the wastewater from photographic fixing facilities are utilized as a reducing agent. The required concentration of ammonium salt varies depending on the processing conditions, but p
When processing within 2 hours at H3.5 to pH 8.5, ammonium ions must be 1 x 1a-' M or more and 1 M or less, preferably 0.5 x 10" M or more and 0.
．． It is 1M or less. It is most efficient to set the pH around neutrality. Under the above conditions, the amount of zinc salt and thiosulfate added is sufficient to be 2.1 to 5 times mole and 1 to 2 times mole relative to IJ cyan ion, respectively. The rate of formation of zinc ferrocyanide precipitate increases significantly as the concentration of ammonium ions increases from 1x10-'M to 0.1M. The effect of ammonium salts is
This was not observed in other ordinary salts, and although the cause is not clear, it indicates the presence of some specific synergistic action of ammonium ions and zinc ions.

In addition, in the region where the concentration of ammonium salt added is higher than around 0.1M, the formation rate of zinc ferrocyanide precipitate gradually decreases to 1.
4, but this seems to be due to the influence of the acid radical, which has a greater influence on the acid radical whose complex with zinc ions is more stable.

In the present invention, it is easy to reduce the cyanide concentration in the treatment liquid to the regulatory value of 1 ppm or less by removing the generated zinc ferrocyanide precipitate by solid-liquid separation using a conventional method, and furthermore, it is possible to reduce the cyanide concentration in the treatment liquid to 1 ppm or less, which is the regulatory value. Even reductions to below .1 ppm can be achieved in a short period of time. In addition.

Zinc ions may remain in the treatment solution at levels greater than the regulatory value of 5 ppm. In such cases, zinc ions in the treatment solution can be removed using various precipitation methods and ion exchange methods.

It can be easily removed by conventional methods such as adsorption and ion flotation. Further, after the process of the present invention has been completed to produce zinc ferrocyanide precipitate, alkali is added and zinc hydroxide is produced by a conventional method at a pH of around 9.

It may be removed simultaneously with zinc ferrocyanide precipitation.

Therefore, it goes without saying that the present invention is not limited by the method of removing residual zinc ions.

The present invention is applicable to the treatment of wastewater from bleaching facilities in color photo labs, wastewater from thiosulfate-containing fixing facilities, and wastewater from photographic processing facilities using Farmer-reduced liquids in which iron cyano complexes and thiosulfates coexist. It is clear that it would be very useful if applied to the treatment of. In addition, sulfite-based reducing agents are easily susceptible to air oxidation, and especially when they contain trace amounts of copper ions, such as wastewater from plating processing facilities, air oxidation is significantly accelerated and the amount required increases. hand.

Since the method of the present invention overcomes the disadvantage of thiosulfate, which is the slow reaction rate, it is possible to take advantage of the advantage of thiosulfate, which is not subject to air oxidation, and - iron cyano complexes in wastewater from plating facilities. can be efficiently removed.

This will be explained below using Examples. In the following treatment experiments, the precipitation treatment was performed in a constant temperature bath (25° C.). Also,
The total cyanide concentration was analyzed by the pyridine-pyrazolone method or the atomic absorption spectrophotometry (converted from the iron analysis value), and the ferrin anion was analyzed by the colorimetric method (420 nm). The pH was adjusted using dilute sulfuric acid or hydroxide solution.

The resulting increase in liquid volume was 5% or less.

Example 1 To 100 ml of an aqueous solution containing 50 ppm red blood salt and 0.001N ammonium chloride as cyanide was stirred with a magnetic stirrer, and 1 ml of a zinc sulfate solution with a molar ratio of 2.5 times the red blood salt was added. After adjusting the pH to 6.5, 1.6 ml of a solution of thiosulfuric acid in an equimolar amount to red blood salt was added, and the pH was maintained at 6.5 using a pH stat. Collect the liquid at predetermined intervals and immediately place it on Toyo Okishi (Mu5).
C) to measure the total cyanide concentration in the p solution. The results are shown in fil of FIG. Total cyan concentration is 0
．． It was after about 80 minutes of processing time that it became 1 ppm or less. Comparative Example 1 100 ml of red blood salt solution containing 50 PPm as cyanide was stirred with magnetic starde, so it was 2.5 times the red blood salt. Add 1 ml of molar zinc sulfate solution.

After adjusting the pH to 6.5, add 1.6 ml of an equimolar sodium thiosulfate solution to red blood salt, and check the pH with a pH stat.
It was held at 6.5. The solution was sampled at predetermined intervals, immediately filtered using Toyo Oki paper (Mu5C), and the total cyanide concentration in the 'f5 solution was measured. The results are shown in FIG. 1 (2). It took about 250 minutes for the total cyanide concentration in the furnace liquid to drop to 0.1 ppm or less.

After stirring with a magnetic stirrer, 1.6 ml of an equimolar sodium thiosulfate solution was added to the red blood salt mixture, and the pH was maintained at 6.5 using a pH stat.

Felicia after 2 hours and after being left at room temperature (20-27°C) for 1 day; ion concentration is 49.5 in terms of cyanide.
ppm, 46.2 PPm (Both undiluted solution amount 5Q
(in terms of ml), and the reduction reaction rate of ferricyanion ions was extremely low.

Example 2 To 100 ml of an aqueous solution containing 50 ppm red blood salt as cyanide and ammonium chloride at various concentrations was stirred with a magnetic starde, 2 ml of a zinc sulfate solution with a molar ratio of 5 times the red blood salt was added, and the pH was adjusted. After adjusting to 6.5, add 1.6 ml of equimolar sodium thiosulfate solution to red blood salt.
and maintained at pH 6.5 using a pH stat. The yellow coloring that indicates the presence of ferricyanion ions completely disappears,
The time required for the residual cyanide concentration to be 1ppm or less is when the ammonium chloride concentration is 0.001N, 0.01N,
0. When IN, it was 15 minutes, 2.5 minutes, and 3 minutes, respectively.

Comparative Example 2 To 100 ml of an aqueous solution containing 50 ppm red blood salt as cyanide and various concentrations of water-soluble coexisting salts was stirred with a magnetic stirrer, 2 ml of a zinc sulfate solution with a molar ratio of 5 times the red blood salt was added, and the solution was adjusted to pH 6. After adjusting the pH to pH 6.5, 1 jml of thiosulfate (IJ) solution in an equimolar amount to the red blood salt was added, and the pH was maintained at pH 6.5 using a +PH slot.

FIG. 2 shows the relationship between the total cyanide concentration in the filtrate and the elapsed time.

The coexisting salts corresponding to the symbols in the figure and their concentrations (indicated in parentheses) are as follows.

(1): No additive, (2): MgC12 (0,01
N), f3i: CaC12 (0,01N), (4
1: LaCl5 (O button IN), (5): KCl0
4(0,IN), (61: KBr(0,IN),
(71: KCI (0, I N).

fsl2NaCl(0,IN)+f9):
K2S04(0,'N)+Ql: LiC1(0
, I N), (11): MgC12(0, I
N).

Q3: CaCl2 (0, IN) In addition, sodium bromide, acetate, IJium, sodium nitrate, sodium bicarbonate, sodium rhodanate, sodium dihydrogen phosphate, tetraoxalate) About IJium It was observed that as the concentration of zinc ferrocyanide increased, the rate of formation of zinc ferrocyanide precipitate decreased compared to when these coexisting salts were not included.

Example 3 To 50 ml of an aqueous solution containing 1100 pp of red blood salt as cyanide and ammonium sulfate at various concentrations was stirred with a magnetic stirrer, 1 ml of a zinc sulfate solution with a molar ratio of 2.5 times the red blood salt was added, and the pH was 6. 1.6 m of equimolar sodium thiosulfate solution to red blood salt after adjusting to 5.
1 was added and the pH was maintained at 6.5 using a pH stat. As a result, the time required for the yellow coloration indicating the presence of ferricyanide ions to completely disappear and for the residual cyanide concentration to be 1 ppm or less was 0.0005% for the ammonium sulfate concentration.
N, 0.001N, 0.01N, 0. IN
of,! 11 respectively 17 minutes, 6.5 minutes, 2.・2 minutes, 7
．． It was 2 minutes.

Comparative Example 5 To 50 ml of a red blood salt solution containing 100 ppm of cyanide was stirred with a magnetic nutara, then 1 ml of a zinc sulfate solution with a molar ratio of 2.5 times the red blood salt was added.

After adjusting the pH to 6.5, add 1.6 ml of an equimolar sodium thiosulfate solution to the red blood salt, and check the pH with a pH stat.
It was maintained at H6.5. As a result, the time required for the yellow coloration indicating the presence of ferricyan ions to completely disappear and the residual cyan concentration to be below IPP'' was 25 minutes.

Example 4 100 ppnl as cyan) red blood salt and 0.4 x 1
Stir with a magnetic stirrer to 50 ml of an aqueous solution containing O-3N ammonium chloride and 0.1N sodium chloride, add jml of a zinc sulfate solution of 2.5 times the mole of red blood salt, and adjust the pH to 6.5. 6 ml of a sodium thiosulfate solution J having an equimolar amount to the red blood salt was added, and the mixture was maintained at pH 6.5 for 2 hours using a pH stat, and then filtered. The total cyanide concentration in the furnace liquid is: o, uosPPm
Met.

Comparative Example 4 To 5Qml of an aqueous solution containing 1100 pp of red blood salt and 0.1N sodium chloride as cyan, stir with a magnetic stirrer and then add 1 ml of a zinc sulfate solution of 2.5 times the mole of red blood salt, After adjusting to pH 6.5, add equimolar amount of thiosulfate to red blood salt) IJum solution 1.6
Add ml, pH sp, y l-te pH 6,5 d 2
After holding for a period of time, it was filtered. The total cyanide concentration in the furnace liquid is
It was 14.2 ppm.

Example 5 Each ferricyanion ion is 50 ppm in terms of cyanide.

50 ml of a sample solution containing 0.005 N of ammonyl sulfate A in simulated wastewater containing ferrocyan ions and other ions with the composition shown in Table 1 was adjusted to pH 6.5 while stirring with a magnetic stirrer, and red blood salt was added to the solution. 1 ml of a 2.5 times molar zinc sulfate solution based on the total amount of yellow blood salt
After adjusting the pH to 6.5 again, add thiosulfate in an equimolar amount to the red blood salt) IJum solution 0.8m! Add r
The pH was maintained at 6.5 using a pH stat.

After 17 minutes, the coloration indicating the presence of ferricyan ions completely disappeared, so the mixture was immediately filtered. The total cyanide concentration in the furnace fluid was 0.065 ppm.

Comparative Example 5 After adjusting 50 ml of simulated wastewater having the composition shown in Table 1 to pH 6.5 while stirring with a magnetic stirrer, 1 ml of a zinc sulfate solution with a molar ratio of 2.5 times the total amount of red blood salt and yellow blood salt was added to the solution. After adjusting the pH to 6.5 again, add thiosulfate in an equimolar amount to the red blood salt) IJum solution 0.8tr+1
was added and maintained at pH 6.5 using a pH stat.

A portion of the liquid was collected after 17 minutes and 65 minutes, and the total cyanide concentration of the p liquid was measured, and the results were 22 ppm and 5.2 PP, respectively.
It was m. Furthermore, it took 90 minutes for the coloring caused by ferricyan ions to completely disappear and the residual cyan concentration to be below IPPm.

Example 6 7 Elysian ions, each 50 ppm in terms of cyanide.

Ammonium chloride was added at 0.001 N or 0 to simulated wastewater containing ferrocyanium ions and other ions with the composition shown in Table 2.
．． After adjusting the pH of 53 ml of the sample solution containing 005 N to 6.5 while stirring with a magnetic stirrer, 1 ml of a zinc sulfate solution of 2.5 times the molar amount relative to the total amount of red blood salt and yellow blood salt was added to the solution. , after adjusting the pH to 6.5 again, add equimolar amount of thiosulfate to red blood salt) IJum solution Q,
8 ml was added and the pH was maintained at 6.5 using a +PH stat. The coloration indicating the presence of ferricyanion ions completely disappeared after 57 minutes and 20 minutes in the case of ammonium chloride concentrations of 0.0[]IN and 0.005N, respectively. The total cyanide concentration in the filtrate filtered immediately after the coloring disappears is:
Ammonium chloride concentration 0.001N.

0°005N, each 0.50 ppm,
It was 0.13 ppm.

Table 2 Unit pp
Comparative Example 6 50ml of simulated wastewater having the composition shown in Table 2 was adjusted to pH 6.5 while being stirred with a magnetic stirrer, and then a zinc sulfate solution of 2.5 times the molar amount relative to the total amount of red blood salt and yellow blood salt was added to the solution. After adjusting the pH to 6.5 again, 0.8 ml of a solution of thiosulfuric acid in an equimolar amount to the red blood salt was added, and the pH was maintained at 6.5 using a pH stat. A portion of the liquid was sampled after 20 minutes, 60 minutes, and 130 minutes, and the total cyanide concentration of the filtrate was measured.

34.1 ppm, 19.5 ppm, 10 each
．． It was 2 ppm.

[Brief explanation of drawings]

Figure 1 shows the influence of ammonium ions on the precipitation processing rate, and Figure 2 shows the influence of various coexisting salts on the precipitation processing rate. Patent applicant Makoto Ishiita, Director of the Agency of Industrial Science and Technology

Claims (1)

[Claims] A method for precipitating and removing iron cyano complexes as zinc hepterocyanide by acting thiosulfate on iron cyano complex-containing wastewater containing ferricyanide in the presence of zinc, characterized in that the process is carried out in the presence of ammonium salts. Zero treatment method for wastewater containing complex salts.