JPH0975954A - Method of removing seleno sulfate ion in selenium-containing waste solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing selenium dissolved as seleno sulfate ion from a selenium-containing waste solution which has conventionally been said difficult, in the method for removing selenium from the selenium-containing waste solution. SOLUTION: The waste solution is made acidic of pH<=1.2 by adding H2 SO4 thereto and heated and aerated. It is preferable that the heating temp. is >=60 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a selenosulfate ion (

[Chemical formula 1] And a method for removing the selenosulfate ion from selenium-containing wastewater containing

[0002]

2. Description of the Related Art Generally, selenium may be contained in a relatively high concentration in a waste liquid discharged from a process for treating electrolytic precipitates such as copper refining, and selenium is harmful and causes environmental pollution. The permissible limit in the wastewater is 0.1 ppm, and it is necessary to remove these harmful selenium from the wastewater.

Conventionally, as a method of removing selenium in the waste water, for example, Japanese Patent Publication No. 48-30558 discloses that the Fe water and the Cu ion are added to the waste water while adjusting the pH of the waste water containing selenium. Mainly dissolved

[Chemical formula 2] A method of recovering selenium together with hydroxide for the purpose of removing selenium dissolved as (hereinafter, referred to as SeO ₃ ion) is disclosed. Further, in JP-A-5-78105 and JP-A-6-79286, the inventions described in the above publications are

[Chemical formula 3] Since it was difficult to remove selenium dissolved as (hereinafter referred to as SeO ₄ ion), it is aimed to remove both selenium dissolved in the waste liquid as SeO ₃ ion and SeO ₄ ion, Add metal salt,
Then, a method of removing selenium dissolved as SeO ₃ ions and SeO ₄ ions from the selenium-containing wastewater by adding an iron salt to adjust the pH and performing solid-liquid separation as a coprecipitate of the iron salt and selenium Is disclosed.

However, in the process of recovering selenium, red selenium (amorphous selenium) was obtained by blowing sulfurous acid gas (SO ₂ ) into a purified selenite solution (H ₂ SeO ₃ ).
The selenosulfate ion is contained in the scrubber water of the scrubber, which has been reduced to, but at which time excess sulfurous acid gas has been absorbed and removed.

Further, selenosulfate ions are also contained in the exhaust gas scrubber water in the divisional silver process. In this, the slime containing gold and silver is roasted for the purpose of removing selenium in the slime treatment step, but selenium cannot be completely removed and a small amount remains in the roasted slime. The roasted slime is then dissolved and reduced in a smelting furnace. At that time, sulfur remains in the slime and volatilizes as SO ₂ , and at the same time Se also volatilizes. Exhaust gas containing SO ₂ and Se is collected in a scrubber, and selenosulfate ion (

[Chemical formula 1]) is contained.

[0006]

However, according to the conventional method as described above, it is possible to remove selenium dissolved as SeO ₃ ions and selenium dissolved as SeO ₄ ions, but JP-B-48-30558. issue,
In the inventions described in JP-A-5-78105 and JP-A-6-79286, removal of selenium dissolved as selenosulfate ions is not intended. Actually, these conventional methods include wastewater containing selenosulfate ions. It is not sufficient to remove selenium dissolved as selenosulfate ions from the inside, and there is a demand for the development of a method capable of efficiently treating selenosulfate ions in wastewater in a short time.

[0007]

The present invention provides a method for removing selenosulfate ions from selenium-containing wastewater containing selenosulfate ions, and removing selenium dissolved as selenosulfate ions. The feature is that H ₂ SO ₄ is added to the waste water to make the waste liquid acidic with a pH of 1.2 or less, and then heated and aerated. The heating temperature is preferably 60 ° C. or higher.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for removing selenosulfate ions from selenium-containing wastewater containing selenosulfate ions according to the present invention will be described in more detail below. In the processing flow of FIG. 1, Se process scrubber water or slime reduction process scrubber water is generated from a scrubber that absorbs process exhaust gas while maintaining pH 7 or higher with a basic salt such as Na ₂ CO ₃ . The scrubber water is supplied to the treatment tank of the present invention, and sulfuric acid is added to the treatment tank. The addition of sulfuric acid has a function of moving the reversible reaction equilibrium of the following chemical formula 4 to the right and precipitating selenosulfate ions as metal selenium. For that purpose, the pH of the liquid is adjusted to 1.2 or less by adding sulfuric acid. Liquid p
When H exceeds 2, the precipitation of metal selenium becomes insufficient.

[0009]

[Chemical formula 4]

[Chemical formula 5]

Next, steam is introduced into the liquid, and the liquid is heated and aerated at the same time. In this heating aeration step, air may be introduced while heating the liquid with an appropriate heating means such as a hot starter. Aeration

[Chemical formula 6] (Hereinafter referred to as SO ₃ ion)

[Chemical formula 7] It is carried out to oxidize and fix it (hereinafter referred to as SO ₄ ion), and to accelerate the movement of the reversible reaction equilibrium of the chemical formula 4 to the right. Further, heating is performed in order to change the deposited amorphous selenium (red) into the most stable hexagonal selenium (gray) and to accelerate the oxidation of SO ₃ ions. If the heating step is insufficient, the metal selenium that has once been precipitated will react again with SO ₃ ions and redissolve, and the reaction of the above chemical formula 4 will shift to the left. Therefore, the heating temperature in the present invention is 60 ° C. or higher, more preferably 80 ° C. or higher.

After heating and aeration, it is subjected to filtration to separate the precipitate of selenium resulting from selenosulfate from the filtrate. The filtrate is the SeO ₃ ion, S remaining in the filtrate.
In order to remove eO ₄ ions, it is treated in the existing wastewater treatment process and is discharged as treated water having a selenium content of 0.1 mg / l or less, and the selenium precipitate is fixed in a harmless form.

In this way, selenium dissolved as selenosulfate ions in the selenium-containing waste liquid containing selenosulfate ions can be removed. It is also possible to remove the selenium dissolved as SeO ₃ ions and SeO ₄ ions in the liquid by further performing the method for treating a selenium-containing waste liquid as described above.

[0013]

EXAMPLE 1 The method of the present invention will be described below with reference to examples. Take 0.5 liters of scrubber water (selenium concentration 244 mg / l, Se is all present as selenosulfate ion) discharged from the selenium recovery process in a beaker, and add sulfuric acid to adjust the pH of the solution to 1.0 ± 0.1. After that, the solution was heated to 80 ° C. on the hot stirrer, and at the same time, aeration (air blowing, flow rate 0.5 liter / min) was performed for 1 hour. After cooling, the precipitate (selenium) was filtered off, the selenium concentration in the filtrate was analyzed by ICP, and the selenium concentration after treatment and the selenium removal rate were obtained. As a result, the selenium concentration in the stock solution
244mg / l is 3.0mg / l (removal rate 98.8%… 1st time) and 4.9mg / l
It was found that the method of the present invention was extremely effective in removing selenium dissolved as selenosulfate ions, even after the removal of 1 (removal rate 98.0% ... second time).

[0014]

Example 2 The same process as in Example 1 was carried out except that the heating temperature by the hot stirrer was changed, and the effect of the heating temperature was examined. Table 1 shows the results.

Table 1 Temperature (° C.) Selenium concentration (mg / l) Selenium removal rate (%) 60 24.4 90.0 70 22.2 90.9 70 15.4 93.7 80 3.0 3.0 88.8 80 4.9 98.0 90 2.0 99.2

From the results shown in Table 1, the selenium removal rate was in the range of 90 to 94% at the heating temperatures of 60 ° C. and 70 ° C. in the heat treatment performed with aeration, but 80
98% or more at 90 ° C, 99.2% at 90 ° C,
When the temperature is 80 ° C. or higher, a selenium removal rate of 98% or higher can be obtained.

[0017]

According to the present invention as described above, it becomes possible to remove selenium dissolved as selenosulfate ions, which has been conventionally difficult to treat, and to contain selenosulfate ions such as scrubber water in the selenium process. Selenium dissolved as selenosulfate ions in selenium-containing wastewater can be efficiently removed in a short time.

[Brief description of drawings]

FIG. 1 is a flow explanatory diagram of a processing method according to the present invention.

Claims (2)

[Claims] 1. A method for removing selenosulfate ions from selenium-containing wastewater containing selenosulfate ions, wherein H ₂ SO ₄ is added to the wastewater to make the waste solution acidic at a pH of 1.2 or less, and then heated and A method for removing selenosulfate ions in a selenium-containing waste liquid, which is characterized by aeration. 2. The method for removing selenosulfate ions in a selenium-containing waste liquid according to claim 1, wherein the heating temperature is 60 ° C. or higher.