JP2000246270A - Waste water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment method capable of efficiently recovering and removing anions such as oxoanions of Se(IV), As and Sb or cations such as Cd2+, Mn2+ or the like contained in waste water and excellent in economical efficiency. SOLUTION: An iron salt and alkali are added to waste water in which anions and cations comprising metal oxoanions and metal ions are present to adjust the pH of waste water to 4-8 and alkali is further added to the waste water to adjust the pH thereof to 9-12 and metal oxoanions or metal ions are adsorbed on an iron precipitate or co-precipitated along with iron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater, and more particularly, to a method for efficiently removing metal ions such as tetravalent selenium contained in wastewater generated during the treatment of electrolytic precipitates and the like in nonferrous smelting. The present invention relates to a method for treating wastewater that can be removed at low cost.

[0002]

2. Description of the Related Art In a non-ferrous smelting process, particularly in a copper electro smelting process, selenium contained in copper sulfide ore is concentrated in anode slime for electrolytic refining of copper, and selenium is recovered in a subsequent metal selenium manufacturing process. Is done. However, in the wastewater generated in the process of recovering selenium, it is dissolved in the aqueous solution,
Selenium that could not be recovered is contained at a relatively high concentration as selenous acid or selenic acid. Therefore, since such wastewater cannot be discharged to the outside of the factory as it is, it is necessary to collect and remove selenium from the wastewater.

Further, selenium, arsenic, antimony, cadmium and manganese are contained in the wastewater in the nonferrous smelting in the form of oxoanions or metal ions of metals, and oxoanions or metal ions of these metals are also contained. In addition, it is necessary to collect and remove.

Heretofore, as a method for treating wastewater containing oxo anions or metal ions of these metals, it has been known to add an iron salt and recover as a coprecipitate of these metal ions and iron (iron precipitation). ). For example, regarding wastewater treatment containing selenium, Japanese Patent Publication No. 48-30558 and Japanese Patent Application Laid-Open No. 9-249922 disclose techniques using iron precipitation.

When the iron is removed by the iron precipitation method, Se (IV),
As and Sb are SeO ₃ ^2- , AsO ₄ ^3- and SbO, respectively.
₄ present an anion such as ^3, the optimum pH to which they are adsorbed 6-8, whereas Cd, Mn respectively Cd ^2+, Mn
It exists as a ²⁺ cation, and its optimum pH for adsorption is said to be 9 or more.

[0006] These Se (IV), As, Sb, Cd, M
When n is removed only by the iron precipitation method, first, pH 6 is removed in the first step.
Adjusted to ８8, and the oxo anions of Se (IV), As, and Sb are adsorbed by iron coprecipitation. If the pH is raised to pH 9 or higher, these anions adsorbed will be desorbed and redissolved. Therefore, after solid-liquid separation using a thickener, the pH is adjusted to pH 9 or higher in the second step, and Cd and Mn are coprecipitated with iron. It has been considered necessary to remove it.

This process requires solid-liquid separation equipment such as a thickener after adsorbing anions and after adsorbing cations, and has a problem that capital investment becomes large and the steps become complicated.

Further, the method of treating Sb with sulfide has been studied in detail, and S ²⁻ is 1.5 to 2
It is reported that the Sb sulfide forms a complex and re-dissolves when the Sb sulfide is present in an excess of twice or more, so that the application range of the S ²⁻ amount is narrow and it is difficult to control industrially (““ from aqueous solution ”). Removal of Antimony (V) and Antimony (III) ", Wasser Abbasser, Reiner Enders, Martin Jeckel, No. 12, 199
4, 690-695 ").

Accordingly, an object of the present invention is to efficiently collect and remove anions such as oxo anions of Se (IV), As and Sb and cations such as Cd ²⁺ and Mn ²⁺ contained in wastewater. It is an object of the present invention to provide a wastewater treatment method that is excellent in economic efficiency.

[0010]

Means for Solving the Problems As a result of the examination, the present inventors have found that, in the above-mentioned iron precipitation, the pH is changed, and the coprecipitation residue of iron is used as an iron source in the further iron precipitation.
It has been found that the above object can be achieved.

The present invention has been made on the basis of the above findings, and (1) an iron salt and an alkali are added to wastewater containing anions and cations composed of metal oxo anions and metal ions to adjust the pH to 4 to 8; And (2) providing a method for treating wastewater characterized by further adding an alkali to adjust the pH to 9 to 12, and adsorbing or coprecipitating the metal ion or metal oxide ion with iron precipitation or iron. Is what you do.

Further, the present invention provides a method for treating wastewater, wherein the coprecipitation residue of iron is added to wastewater in which the anions and cations are present, and the above steps (1) and (2) are repeated. Is provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wastewater treatment method according to the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing one embodiment of the method for treating wastewater of the present invention.

As shown in FIG. 1, an alkali (neutralizing agent) is added to wastewater containing anions and cations consisting of metal oxo anions and metal ions to adjust the pH to 4 to 4.
8, preferably 6 to 8, and an Fe source (iron salt) is added. At this time, a salt such as Mn, Cu, or Al may be added together with the iron salt. The wastewater used here is factory wastewater generated in various smelting processes, and is acidic wastewater. And, this wastewater contains Se as an anion.
(IV), oxo anions of As and Sb are contained,
Cd ²⁺ and Mn ²⁺ are contained as cations.

The oxo anion refers to an anion such as MO _n ^{(2n−x) −} (where x represents the oxidation number of the element M ⁾ formed by a certain element M combined with oxygen. S
In addition to oxo anions of non-metal elements such as O ₄ ²⁻ and PO ₄ ³⁻ , there are oxo anions of metal elements such as VO ₄ ³⁻ and MoO ₄ ²⁻ . Metal ions having a large oxidation number, such as vanadium (V) and molybdenum (VI), are unlikely to exist as aqua complexes, and dissociate protons of coordination water at ordinary pH to form oxo anions.

As the iron source, ferrous chloride or ferric chloride, or ferrous sulfate or ferric sulfate is used. Examples of the alkali include calcium hydroxide, sodium hydroxide, potassium hydroxide and the like.

In this pH range of 4 to 8, SeO ₃ ^2- , A
sO ₄ ^3-, SbO ₄ ^3- is, mainly to co-precipitation with iron. A residence time of 2-5 minutes is sufficient.

Next, an alkali (neutralizing agent) is further added to the wastewater having a pH of 4 to 8 to adjust the pH to 9 to 12, preferably 9 to 10. In this pH range of 9 to 12, Cd
²⁺ and Mn ²⁺ mainly co-precipitate with iron. The residence time is 2
5 minutes is enough. As the alkali used here, the same ones as described above are used.

The hydroxyl groups on the hydroxide surface such as iron precipitate are ionized as follows according to the pH of the solution. ^{M-OH + H + → M} -OH 2 + ( acidic ^{solution) M-OH + OH - →} M-O - + H 2 O ( basic solution) for example, adjusting the pH to 4-8, iron沈表surface to the positive When charged, the anions in the solution are attracted to the iron deposit surface by electrostatic forces. As shown in FIG. 2, general anions such as Cl ⁻ and NO ₃ ⁻ are non-specifically adsorbed because they can approach the solid surface only up to a certain distance. Non-specific adsorption is easily desorbed by washing or pH fluctuation

On the other hand, SeO ₃ ^2- , AsO ₄ ^3- , S
Anions such as bO ₄ ^3- are strongly and specifically adsorbed by a chemical action between Fe and anions on the surface of the iron precipitate, as shown in FIG. Since these specifically adsorbed anions are strongly adsorbed by a chemical action, they are not adsorbed at, for example, about pH 7 and are not desorbed or redissolved even if they are changed to about pH 9 to 12 as they are.

On the other hand, Cd and Mn as cations have a pH of 9
Above, specific adsorption on the surface of iron precipitation.

After that, the wastewater is settled and concentrated, and then subjected to solid-liquid separation using a thickener or the like. The treated wastewater (overflow) from which anions and cations have been removed and the coprecipitation residue (iron precipitation) which has been recovered by absorbing anions and cations. And separated. This treated wastewater is discharged out of the system.

On the other hand, the coprecipitation residue (iron precipitation) recovered by adsorbing anions and cations can be repeatedly used as the iron source for the treatment of the wastewater. When this iron precipitation is used repeatedly as an iron source, it is preferable to supplementally add iron salts such as ferrous sulfate in addition to the iron precipitation.
The reason why the iron precipitation is used repeatedly is that the iron precipitation does not desorb the anions and cations once adsorbed, and that the iron precipitation has an adsorbing ability even when the iron precipitation is used repeatedly. As a result, the coprecipitation residue is reduced in volume, and is economically superior.

In this way, arsenic, antimony, cadmium and manganese, in addition to tetravalent selenium, can be efficiently recovered and removed from wastewater containing anions and cations. In addition, when co-precipitation residue (iron precipitation) is used repeatedly, it is economical.

[0025]

Embodiments will be described below with reference to embodiments.

[Examples 1 to 3 and Comparative Examples 1 to 3] (Test for confirming repetitive effect of iron precipitation) Wastewater containing metal oxo anions and metal ions as shown in Table 1 was used. The selenium drainage standard has been set at 0.2 since February 2000.
It is set to 1 ppm, and the treatment target of the wastewater is set as shown in Table 2 based on these reference values.

The pH of the waste water was adjusted to 6 to 8 with a 20% calcium hydroxide slurry (milk of lime), and the iron precipitation was repeated 1,000 ppm as Fe and 0 p, respectively.
pm, and ferrous sulfate as Fe, 5, 20, 100
ppm was added and kept for 2 minutes. Next, the pH was further adjusted to 9 to 10 with lime milk and kept for 2 minutes. Each reaction tank was performed by oxidizing Fe ²⁺ to Fe ³⁺ by aeration. Table 3 shows the concentration of each metal after the treatment.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[Examples 4 to 6 and Comparative Examples 4 to 6] (Effects of first-stage pH and second-stage pH) Effects of first-stage and second-stage set pH using wastewater shown in Table 1 A confirmation test was performed.

The pH of the first stage was adjusted with a 20% calcium hydroxide slurry (milk of lime), and iron precipitation was repeated
1,000 ppm as e and ferrous sulfate as 4
0 ppm was added and kept for 2 minutes. Next, the pH of the second stage was further adjusted with milk of lime, and the mixture was retained for 2 minutes. Each reaction tank was performed by oxidizing Fe ²⁺ to Fe ³⁺ by aeration. Table 4 shows the set pH of the first and second stages and the concentration of each metal after the treatment.

[0033]

[Table 4]

[0034]

As described above, according to the wastewater treatment method of the present invention, Se (IV), As,
Anions such as oxo anion of Sb and cations such as Cd ²⁺ and Mn ²⁺ can be efficiently collected and removed. In addition, by repeatedly using the generated coprecipitation residue (iron precipitation), the volume of the residue is reduced, and it is economically excellent.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a method for treating wastewater of the present invention.

FIG. 2 is a model diagram of a phenomenon of non-specific adsorption on an iron precipitation surface.

FIG. 3 is a model diagram of a phenomenon of specific adsorption on a surface of iron precipitation.

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[Procedure amendment]

[Submission date] March 10, 1999 (1999.3.1.
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

[0033]

[Table 4]

Continued on the front page F term (reference) 4D038 AA08 AB66 AB70 AB71 AB72 AB82 BB06 BB13 BB17 BB18 4D050 AA13 AB55 AB59 AB60 AB63 BA04 BA10 CA06 CA13 CA15 CA16 4K001 AA03 AA06 AA16 AA21 AA22 BA21 DB23 DB25

Claims (4)

[Claims] 1. A wastewater containing anions and cations consisting of metal oxo anions and metal ions, (1) iron salts and alkalis are added to adjust the pH to 4 to 8, and (2)
A method for treating wastewater, further comprising adding an alkali to adjust the pH to 9 to 12, and adsorbing or coprecipitating oxo anions and metal ions of the metal with iron precipitation. 2. The method for treating wastewater according to claim 1, wherein the coprecipitation residue of iron is added to the wastewater containing the anions and cations, and the steps (1) and (2) are repeated. 3. The method for treating wastewater according to claim 2, wherein an iron salt is supplementarily added to the wastewater in which the anions and cations are present. 4. The method according to claim 1, wherein the anion is Se (IV), As, Sb.
Wherein the cation is Cd ²⁺ , Mn
^The method for treating wastewater according to claim 1, 2 or 3, which is ²⁺ .