JPH01171690A - Removal of iron cyan complex - Google Patents

Abstract

PURPOSE:To remove iron cyan complex with high efficiency in a form of water- insoluble precipitate by adding an equimolar amt. of Cu(II) ion to iron cyan complex to an aq. soln. contg. iron cyan complex having <=7pH and removing separated precipitate. CONSTITUTION:An equimolar amt. of Cu(II) ion to iron cyan complex is added to an aq. soln. contg. iron cyan complex having a pH adjusted to <=7pH, and the iron cyan complex is removed from the aq. soln. by removing the generated precipitate. The addition of the Cu(II) ion is finished pref. at a point where jumping of an oxidation-reduction potential happens while measuring the oxidation-reduction potential of the aq. soln. contg. the iron cyan complex. Suitable iron cyan complex is hexacyano iron(II), etc., and suitable Cu(II) compd. for producing the Cu(II) ion to be added is CuSO4(II), Cu(NO3)2(II), CuCl2(II), CuBr2(II), etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for separating and removing an iron cyanide complex from an aqueous solution containing the iron cyanide complex.

[Conventional technology]

Free cyanide or the cyanide compounds that easily generate it are generally easily decomposed by oxidation, and various treatment methods such as the alkali chlorine method, ozone oxidation method, and electrolytic oxidation method are available to detoxify wastewater containing such cyanide compounds. It has been developed and put into practical use. The most common treatment method at present is the alkali chlorine method. However, when heavy metal ions are contained, the heavy metal ions generally form a cyanide complex, making decomposition by the above method difficult. In particular, cyanide complexes of iron and nickel are known to be highly stable. Nickel cyanide complexes can be decomposed by the alkali chlorine method if sufficient processing time is allowed, but iron cyanide complexes are difficult to decompose even by the alkali chlorine method, and the hexacyanoferrate (I [) Only oxidation to acid ions occurs. Iron cyanide complexes are relatively stable complex ions and are considered harmless to the human body.However, iron cyanide complexes gradually decompose under sunlight and liberate hydrogen cyanide, so even at low concentrations iron cyanide complexes are considered harmless to the human body. Discharging wastewater containing cyanide complexes into rivers should be avoided. Therefore, the iron cyanide complex must be thoroughly removed.

In the case of iron-cyanide complexes, efficient oxidative decomposition of cyano groups is difficult, so methods are being considered that conversely produce insoluble iron-cyanide complexes and remove them as precipitates. As methods for removing iron cyanide complexes as precipitates, methods using cationic surfactants such as quaternary ammonium salts and methods using heavy metal salts are known. Quaternary ammonium salts are not common because the drug is expensive and it is difficult to reuse the drug after precipitation. On the other hand, methods using heavy metal salts include iron (I[) salt, zinc (IT
) salt and copper(II) salt are known, but the so-called Prussian method using iron(II) salt is difficult to completely separate the iron cyanide complex by precipitation. It is not easy to reduce the total cyanide concentration of the solution after precipitation separation to a level that passes wastewater standards, and it has the disadvantage that a large amount of sludge is generated. Also, it>(
II) The so-called self-determination of zinc using salt is effective against hexacyanoferrate(II) ions, but is less effective against hexacyanoferrate(II[) ions due to the high solubility of the precipitate formed. . Therefore, iron hexacyano (
III) Excess zinc(II) to treat acid ions
) It is necessary to carry out the reduction in the presence of salt, and methods using sodium sulfite or sodium thiosulfate as the reducing agent have been proposed, but the reduction reaction is slow and the reducing agent is wasted due to air oxidation. Not only does this have the disadvantage that the reduction reaction may be inhibited depending on the coexisting salt. On the other hand, the precipitation removal method of iron cyanide complexes using copper(II) salts is effective against hexacyanoferrate(It) ions, but precipitates are formed against hexacyanoferrate(I[I) ions. Since this is incomplete, it was necessary to add slaked lime and sodium sulfite as a reducing agent to precipitate and remove hexacyanoferrate(1) ions using copper(I[) salts. Even so, no examples have been found in which the total cyanide concentration in the final treated solution was lower than the wastewater standard (0.1 mg/I!). Therefore, a solution containing hexacyano(III) acid ion? No method has been established for completely and effectively precipitating and separating these hexacyanoferrate ions overnight or from a solution containing hexacyanoferrate (III) ions and hexacyanoferrate (II) ions.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the conventional problems and to
loss (II) acid ion and/or iron hexacyano (lT
() An object of the present invention is to provide a method for forming and separating iron cyanide complexes such as acid ions as a sufficiently insoluble precipitate from an aqueous solution containing the iron cyanide complexes.

[Means for solving problems]

In order to solve the above-mentioned problems, the method of the present invention provides an aqueous solution containing an iron cyanide complex by keeping the pH of the aqueous solution at 5 or less.
The method is characterized in that lq(II) ions are added in an amount equal to or more than the equivalent molar amount to the iron cyanide complex, and the resulting precipitate is separated.

[For production]

The iron cyanide complexes include hexacyanoferrate (III) ions, hexacyanoferrate (II) u ions, or mixtures thereof, and examples of the aqueous solutions containing the iron cyanide complexes include various industrial wastewaters, test wastewaters, etc. It will be done.

In the present invention, the addition of copper (n) ions is not particularly limited as long as it dissolves to give copper (n) ions, but for example, as a water-soluble copper (II) compound, copper sulfate (
), copper nitrate (■), copper chloride (■), copper bromide (■), copper iodide (■), copper chlorate (■), copper perchlorate (■), copper hypochlorite (n ), copper (II) salts such as copper nitrite (■), copper acetate (n), and the like. Metallic copper, copper hydroxide (■
), copper oxide (■), basic copper carbonate (■), copper fluoride (■
), copper phosphate (■), copper (If) sulfide, etc., or copper chloride which produces copper(II) ions by oxidation reaction after dissolution or during precipitation with hexacyanoferrate ions. (■), copper(I) bromide, copper iodide (
I), copper oxide (■), copper sulfide (1), etc.
) compounds can also be used.

The amount of the IT (II) ion added must be equal to or more than the equivalent molar amount to the iron cyanide complex, and if the amount of the copper (IT) ion added is less than the equivalent molar amount, precipitation of the iron cyanide complex will occur. This is not good because it is not done enough.

When separating and removing the above-mentioned precipitate, the ρ11 of the aqueous solution must be set to 7 or less, but if the pit of the aqueous solution exceeds 7, the separation and removal of the precipitate will be incomplete, which is not good.

In order to adjust the pH of the aqueous solution to 7 or less, a general acid or alkali may be added according to a conventional method.

When adding political research (II) ions to the iron cyanide complex contained in the aqueous solution in an amount equal to or more than the same mole, the redox potential of the aqueous solution is measured, and the point at which a jump in the redox potential occurs. By ending the addition of the copper compound at this point, the present invention can be carried out accurately. A working electrode, a comparison electrode, a potentiometer, etc. are used to measure the redox potential. The working electrode includes a platinum electrode, a silver electrode,
Any non-reactive electrode, such as a gold electrode, that is not affected by the aqueous solution may be used, and examples of the reference electrode include a silver-silver chloride electrode, an agaric electrode, and a hydrogen electrode.

As Seikyo (II) ions are added to the aqueous solution, the redox potential becomes upper bound, and when two types of hexacyanoferrate (n) ions and hexacyanoferrate (I[I) ions are included] A jump in redox potential is observed at two locations. The jump in redox potential at the first location is due to iron hexacyano (
n) It was observed when 1.5 mol or more of copper(n) salt was added to 1 mol of acid ion, and a jump in the redox potential at the second location was observed when 1 mol of hexacyanoferrate(II[) acid ion was added. A jump in the oxidation-reduction potential at the first location was observed at the time when 1.5 mol or more of the copper(II) salt was further added. After the jump in the redox potential at the second location is completed, even if copper (II) salt is added, the redox potential increases slowly and no further increase occurs. Of course, when there is only one type of iron cyanide complex, the jump in redox potential occurs only at one location. The jump in the redox potential is particularly clearly observed when the pH of the aqueous solution is 7 or less.

[Example 1] JIS K8801 special grade hexacyanoferrate (Ill) potassium was dissolved in water to prepare a 644 mg/J solution of hexacyanoferrate (II[) acid ion. Also, JIS 898
A 582 mg/ll solution of copper (II) ions was prepared by dissolving 3 special grade copper sulfate (■) pentahydrate in water. Hexacyanoferrate(III) acid ion solution 20m6, water, copper (U) ion solution O ~ 20mjl! were added in this order to make the total liquid volume 100 mj2. After adjusting the I)H of the solution to 3.0 with sulfuric acid and stirring for 10 minutes, suction filtration was performed using a membrane filter with a pore size of 0.05 μm. The iron concentration in the obtained filtrate was determined by atomic absorption spectrometry, and the total cyanide concentration was determined by 4-pyridinecarboxylic acid-virazolone absorption spectrophotometry after distilling the total cyanide according to the JrSKO102 factory wastewater test method. did. Total liquid volume 100mj
The total concentration of hexacyanoferrate (I[r) acid ions after setting 2 is 129 mg/II, while the total concentration of copper(II) ions is from 0 to 116 mg/e, and The ratio of the molar concentration of copper(n) ions to the molar concentration of ions is between 0 and 3.0. The relationship between the amount of copper (n) ions added and the iron and total cyanide concentrations in the filtrate is
Shown in the table. Table 1 shows that when the molar ratio of hexacyanoferrate (II) ions to 1ff (II) ions is equal to or higher than the equivalent molar ratio, the total cyanide concentration in the filtrate remains extremely small.

[Example 2] Dissolve JIS K8801 special grade hexacyanoferric (I[[) potassium] in water, and further dilute with water appropriately to obtain 652 mg/l and 65.2 mg/l of hexacyanoferric (I[[) acid ion.
1 and 6.52 mg/j! A solution was prepared. JISK
Dissolve 8802 special grade hexacyanoferric (n) potassium trihydrate in water, and further dilute with water appropriately to dissolve hexacyanoferric (n) potassium trihydrate.
) 644 mg/l and 6.44 mg/l of acid ions
l solution was prepared. Using the prepared hexacyanoferrate (III) ion solutions and hexacyanoferrate (If) ion solutions of various concentrations, the concentrations of both ions were changed stepwise until the total concentration of both ions was approximately 130 mg/ 100 ml of a mixed solution of both ions was prepared so that the ratio was 1/1.

In the prepared mixed solution of hexacyanoferrate (I) ion and hexacyanoferrate (II) ion, JISK8983
Copper prepared by dissolving special grade copper sulfate (■) pentahydrate in water (
II) A solution of 774 mg/(l) of ions was added in 0.5 ml portions at 1 minute intervals. During the addition of the copper(n) ion solution, the pH of the solution was adjusted to 4 using sulfuric acid or sodium hydroxide solution. Iron hexacyano (I[
l) Depending on the concentration of acid ions and hexacyanoferrate(II) ions, a total of 8 ml of 774 mg/H) ion solution, or 10 mj! After adding chlorine and stirring for 10 minutes, suction filtration was performed using a membrane filter with a pore size of 0.05 μm. Hereinafter, iron and total cyanide in the obtained filtrate were determined in the same manner as in Example 1. Hexacyanoferrate (III) [1 ion and hexacyanoferrate (
II) Concentration of acid ions, amount of copper(II) added,
The ratio of the molar concentration of copper (n) ions to the molar concentration of hexacyanoferrate ions (CCu”) / [[Fe(C
Table 2 shows the relationship between N)6]c) and the iron and total cyanide concentrations in the filtrate. From Table 2 - Xacyanoiron (II[)
Even in the case of an aqueous solution containing two types of acid ions and hexacyanoferrate(II) acid ions, the effects of the present invention are remarkable.

[Example 3] JISK8801 special grade hexacyanoferric (II) potassium and JISK8802 special grade hexacyanoferric (II) potassium trihydrate were each dissolved in water, and hexacyanoferric (II) potassium trihydrate was dissolved in water.
[[) 644 mg// each of acid ion and hexacyanoferrate(II) acid ion! A solution was prepared. In addition, 8983 special grade copper sulfate (■) pentahydrate was dissolved in JIS, and copper (n)
631mg/l and 850mg/A of ions! A solution was prepared. Hexacyanoferric (I[[) acid ion solution 201
Ill, 10ml of water, 10mj of copper(II) ion solution!
were added in this order to make a total liquid volume of 100ml, the pH of the solution was adjusted to between 5 and 11 using sodium hydroxide solution, and the precipitate was separated from the solution in the same manner as in Example 1. We investigated the influence of pH on this process. The total liquid volume is 100
mj! The total concentration of hexacyanoferrate (I [[) acid ion is 129 mg/j! , on the other hand, the total concentration of copper(II) ions was 63.7 mg/β, and the total concentration of copper(II) ions was 63.7 mg/β.
[I) The ratio of the molar concentration of copper(II) ions to the molar concentration of acid ions is 1.65.

In the case of hexacyanoferrate (II) ion, 644 mg of hexacyanoferrate (n) ion/β solution and copper (
n) The effect of pH on separating the precipitate from the solution was investigated in the same manner as in the case of hexacyanoferrate (III) ion, except that 850 mg of ion/6 solutions were used. The total liquid volume is 100n/! Iron hexacyano (I[) when
The total concentration of acid ions was 129 mg/i, while copper (I
I) The total concentration of ions is 85.0 mg/1% and copper(I) relative to the molar concentration of hexacyanoferrate(II) ions.
I) The ratio of molar concentrations of ions is 2.20. The effects of pH on hexacyanoferrate(III) ions and copper(n) ions are shown in Table 3, and the effects of pl+ on hexacyanoferrate(n) ions and tli(II) ions are shown in Table 4. .

Tables 3 and 4 show that in the case of aqueous solutions containing hexacyanoferrate (III) ions and hexacyanoferrate (II) ions alone, the total cyanide concentration in the filtrate decreases significantly at pH 7 or lower.

[Example 4] A leachate was prepared by immersing ores containing heavy metals such as gold, iron, and iron in a sodium cyanide solution. Gold and silver were adsorbed and separated from the leachate using activated carbon. The solution was then used as the sample stock solution. did.

Sodium hypochlorite solution (hypochlorite ion concentration 40.9 mg/ml) for 1000 ml of sample stock solution
By adding 1060 mg of hypochlorite ion, p
After stirring for 60 minutes while keeping the pH at 12.0 and stirring for 60 minutes while keeping the pH at 8.5, free cyanide and cyanide compounds that tend to generate it were oxidized and decomposed by the alkali chlorine method, and then a 1.0 μm membrane was removed. Suction filtration was performed using a filter to obtain a filtrate (2). 880 ml p of filtrate ■! Copper (II) ion (1.35 mg/
me) solution as copper(II) ions, 40.5 mg
The pH of the solution was adjusted to 6.8 with sulfuric acid and sodium hydroxide solution, stirred for 15 minutes, and the pH was adjusted to 1.0.
Suction filtration was performed using a μm membrane filter to obtain a treated solution.

Analysis of total cyanide in the sample stock solution, filtrate (1), and treated solution was conducted in the same manner as in Example-1. Furthermore, the amount of heavy metals in each solution was determined by ICP emission spectrometry.

Table 5 shows the quantitative results of total cyanide and heavy metals in each solution. According to Table 5, 3,'l+++g/e of iron contained in the filtrate (■) after the alkali chlorination treatment can be removed by adding copper (U) ions and separating the precipitate from the solution at a pt of 16.8. 0.05 mg/1. has been removed. It is clear that most of the hexacyanoferrate ions after the alkali chlorination treatment were present as mono-, xacyanoferrate ([[) acid ions, and were separated by precipitation by forming poorly soluble precipitates with 1fl(II) ions. The total cyanide concentration in the treatment solution was reduced to 0.1 mg71 or less.

[Example 5] JIS K8801 special grade hexacyanoferrate (III) potassium was dissolved in water, and further diluted with water as appropriate to obtain 652 mg/l and 65.2 mg/l of hexacyanoferrate ([lI) acid ion.
It and 6.52 mg/E solutions were prepared. J.I.
Dissolve SK8802 special grade hexacyanoferric (■) potassium trihydrate in water, and further dilute with water as appropriate to dissolve hexacyanoferric (■) potassium trihydrate.
II) 644 mg of acid ions //! and 6.44 mg
/l solution was prepared. Hexacyanoferrate(III) acid ion solutions with various concentrations prepared and hexacyanoferrate(II)
) Using an acid ion solution, change the concentration of both ions stepwise so that the total concentration of both ions is about 130 mg/ffi, and prepare 100 ml of hexacyanoferrate ion solution.
was prepared. p of the prepared hexacyanoferrate ion solution
Dissolve special grade copper sulfate (■) pentahydrate in water in a hexacyanoferrate ion solution while maintaining o at 4.0.
I) 774 mg/rh of ion was added in 0.5 m7i at 1 minute intervals, during which time the redox potential of the solution was measured. A platinum electrode and a silver-silver chloride electrode using a saturated potassium chloride solution as the internal solution were used to measure the redox potential of the solution. The total amount of Ca(II) ions added is 11
．． 6 mg, i.e. the ratio of the molar concentration of copper(II) ions to the molar concentration of hexacyanoferrate ions ([Cu”]
The chloride-reduction potential was measured when /[[Fe(CN)i, ] ] ) was between 0 and 3.0. The respective concentrations of hexacyanoferrate (II) ions and hexacyanoferrate (1) ions in the prepared 100 ml hexacyanoferrate ion solution, and the concentration of hexacyanoferrate (III) ions relative to the total concentration of hexacyanoferrate ions. ratio ([[Fe(C
N) 6] 3-] / [[Fe(CN) 6]) In addition, copper (n) ions 774 mg/0.5 m of the 12 solution after a jump in redox potential at one or two locations was observed.
7! The total amount of copper(I[) ions added and the molar concentration of hexacyanoferrate ions at that time when the increase in redox potential due to the addition of
) ion molar concentration ratio ([Cu2°]/C[Fe(C
N) b ] ]) are shown in Table 6, respectively. Furthermore, [C
FIG. 1 shows the results with the horizontal axis representing the value of u2°]/[[Fe(CN),] ] and the redox potential representing the vertical axis.

As you can see from Figure 1, what are the types of iron cyanide complexes? A jump in the oxidation-reduction potential was confirmed depending on the solubility, and it was clearly understood where the amount of copper (II) ions added should end.

〔Effect of the invention〕

By using the method of the present invention, iron hexacyano (I
I) from an aqueous solution containing acid ions and/or iron cyanide complexes such as hexacyanoferrate (I[l) acid ions, the ions can be separated and removed as sufficiently insoluble precipitates;
By using the oxidation-reduction potential as a label, the effect is extremely large, such as being able to know the appropriate amount of addition of the copper compound and the end of addition.

[Brief explanation of the drawing]

FIG. 1 shows the change in redox potential obtained in Example 5 of the present invention. Patent applicant: Sumitomo Metal Mining Co., Ltd. No. 10 to 20

Claims (2)

[Claims] (1) In an aqueous solution containing an iron cyanide complex, the pH of the aqueous solution is
7 or less, adding copper (II) ions in an amount equal to or more than the equivalent molar amount to the iron cyanide complex, and separating the formed precipitate. (2) The addition of the copper (II) ions is terminated at the time when the redox potential of the aqueous solution increases while measuring the redox potential of the aqueous solution. Method for removing iron cyanide complex.