JP3825537B2 - Treatment method for wastewater containing As - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for treating wastewater containing As (arsenic) discharged from various factories, and more specifically, the As content of wastewater after treatment is below a reference value of about 0.1 mg / L (liter). It is related with the processing method of the wastewater containing As characterized by removing until.
[0002]
Conventionally, as an As removal method in wastewater, as disclosed in a method of removing as a precipitate by a neutralization method of slaked lime, quick lime, or the like, or Japanese Patent Publication No. 55-37955 “Method of treating wastewater containing hazardous metals” In addition, a method of performing a flotation process, etc. along with smelting of As-containing wastewater generated from a copper smelting process is known.
[0003]
However, the neutralization method has disadvantages such that the amount of neutralized starch produced by the reaction is large, the secondary treatment is difficult, and the cost of the neutralizing agent is high. Furthermore, the treatment method described in the above Japanese Patent Publication No. 55-37955 is effective when a harmful metal other than As is contained in a high concentration, but in other cases, the treatment method is expensive.
[0004]
Further, as a treatment method for reaction removal in the presence of iron, as disclosed in JP-A-59-162897, it can be reacted with ferric ions to precipitate and remove as iron arsenate, or JP-A-52-52 As disclosed in Japanese Patent No. 120547, a method in which an extraction solvent in which magnetic particles are dispersed and water to be treated are mixed using ultrasonic waves and then magnetically separated, or as disclosed in Japanese Patent Laid-Open No. 54-41270. A method is known in which the pH of waste water is adjusted to alkaline in the presence of ferrous salt and the ferritization reaction is performed by mixing air or the like.
[0005]
However, in general, a method using a commercially available ferric sulfate solution has a high cost such as reagent costs. Therefore, a method of oxidizing ferrous ions in waste water to ferric iron by adding an oxidizing agent or bacteria is also proposed. However, in the treatment method simply by adding a ferric sulfate solution, ferric iron must be reacted with arsenic 1 at an equivalent ratio of about 30 to 50 times, and the reaction time is also long. There was a drawback that it took.
[0006]
The applicant previously reduced the consumption of the ferric sulfate solution to about 1/10 of the conventional usage and added ferric sulfate in the presence of ferrite fine particles as a method that can be processed in a short time. Then, it was found that the arsenic precipitate could be removed in a short time, and it was proposed as Japanese Patent Publication No. 1-28633, and a considerable result was obtained as a method for treating low concentration As-containing wastewater.
[0007]
[Problems to be solved by the invention]
However, in the above processing method, when processing an As-containing liquid having a low concentration, the As concentration can be finally reduced to 0.1 mg / L or less, but the processing stock solution has a high concentration of As. When it contains, there was a problem that application was difficult.
[0008]
In the present invention, As-containing wastewater containing As at a high concentration is reduced to an As concentration of 0.1 mg / L or less in accordance with the “Prime Ministerial Ordinance for Establishing Wastewater Standards” enforced in February 1994, by relatively simple treatment. It aims at providing the processing method of wastewater containing As which makes it possible.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention of claim 1 is a method for treating As-containing wastewater, and the amount of addition to the As-containing wastewater is controlled so that the oxidation-reduction potential of the wastewater is 120 mV or less. First, after adding the iron starch and the neutralizing agent to the product obtained in the first step and adding the sulfurizing agent to the product obtained in the first step , the first treated water and the starch a second step and, the first to the treated water, the third step of obtaining a second processed water by further neutralizing agent is added as inclusions precipitate removal obtained in the second step of bets to solid-liquid separation And a method for treating As-containing wastewater.
[0010]
The invention of claim 2
The method for treating an As-containing wastewater according to claim 1, wherein the addition of the iron starch in the second step is to coprecipitate As at a pH of 3 or more.
[0011]
The invention of claim 3
The method for treating As-containing wastewater according to claim 1 or 2, wherein the sulfiding agent in the first step is hydrogen sulfide or sodium sulfide.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1: is a figure which shows the flowchart of the processing method of As containing waste_water | drain concerning embodiment of this invention. Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0013]
As shown in FIG. 1, the water to be treated according to the embodiment of the present invention is obtained by subjecting a copper electrolysis leachate obtained by decoppering and leaching a copper electrolyzed starch to a copper electrolysis leachate to obtain copper. This is a mixture of the copper removal electrolytic tail solution after recovery and sulfuric acid factory effluent. In these wastewaters, As may be contained at a high concentration of about 2 to 10 g / L.
[0014]
The copper-free electrolytic tail solution is retained in the cushion tank and then led to the corn tank, where it is mixed with the sulfuric acid factory effluent. In the corn tank, the copper removal electrolytic tail liquor and the sulfuric acid factory effluent are mixed to remove the sulfuric acid precipitate, and the overflow water is guided to the sulfidation tank as treated water.
[0015]
In the sulfidation treatment tank, while measuring the oxidation-reduction potential (ORP), hydrogen sulfide gas is blown into the treated water, and the amount of hydrogen sulfide gas blown is adjusted so that the ORP value is not more than a predetermined value (No. 1). One step).
[0016]
It is necessary to blow in hydrogen sulfide gas so that the ORP value is 250 mV or less, preferably 150 mV or less. At this time, the pH in the sulfidation treatment tank is 1 or less.
[0017]
In the embodiment of the present invention, when the oxidation-reduction potential was set to 100 to 50 mV, it was confirmed that the As concentration after treatment was removed to 2 mg / L (raw sulfuric acid factory wastewater As concentration 5570 mg / L). In the conventional iron arsenate method alone, even when ferric sulfate is added so that the Fe / As ratio is 2.5 or more, the raw sulfuric acid factory wastewater As concentration is 4580 mg / L. Only about 10 mg / L could be removed.
[0018]
Furthermore, in this first step, underflow water in the sulfidation treatment tank is sucked up using a circulation pump or the like and is introduced into the upper part of the sulfidation treatment tank, and repeated, and sufficiently stirred using a stirrer or the like. It is important to improve the reaction rate.
[0019]
Next, the treated water that has passed through the first step is led to a neutralization pad, iron starch and calcium carbonate (carbon char) as a neutralizing agent are added, heavy metal starch is produced, and solid-liquid separation is performed. (Second step). In this case, the pH in the neutralization tank was adjusted to 4.0 by charcoal cal neutralization, and here, as iron starch, the iron starch separated by hydrometallurgical smelting ash The product was added as a starch by reacting with As and other heavy metals in the liquid so that 5 g / L of ferric oxide was added.
[0020]
Next, the treated water from which the starch has been separated in the neutralization tank is combined with the iron arsenate starch of the precipitate separated by wet smelting treatment of the smelter ash, and then led to the pump tank. This was introduced into a neutralization treatment plant as wet deironing process waste water, slaked lime was added as a neutralizing agent to adjust the pH to around 10.5, and the neutralized starch was separated by filtration (third step).
[0021]
Next, the treated water from which the neutralized starch was separated by filtration was guided to a clear pond, the As-containing material was removed by precipitation, and the swirl was used as discharge water. The As concentration in the treated water thus obtained was a numerical value of 0.1 mg / L or less that cleared the new drainage standard.
[0022]
The above-described embodiment is based on various examinations and test results, and some test examples will be described below.
[0023]
(Test Example 1)
Using sulfuric acid factory effluent containing 5570 mg / L of As as treated water, the removal change of the As concentration in the liquid was tested while controlling the ORP value with the oxidation-reduction potential while introducing hydrogen sulfide into a 3 liter tank.
[0024]
FIG. 2 is a graph showing the relationship between the ORP value and As concentration in Test Example 1. As shown in FIG. 2, it was found that almost no change was observed in the As concentration when the ORP value was 250 mV or more, but the As concentration began to drop sharply when the ORP value was 250 mV or less, and it decreased to several mg / L particularly at 100 mV. . Further, when the ORP value was set to −50 mV, the As concentration could be removed to 0.01 mg / L. However, in view of the balance with the amount of hydrogen sulfide blown, the ORP value was controlled to 250 mV or less, preferably 150 mV or less. It was found that by combining with an inexpensive treatment method, the As concentration of 0.1 mg / L or less of the new wastewater standard value can be reduced in terms of cost.
[0025]
(Comparative Test Example 1)
Use sulfuric acid factory effluent containing 4580mg / L of As as treated water, adjust to pH 4.5 using charcoal cal as neutralizer, lead to 3L capacity dredging, and add ferric sulfate as iron source However, ferric iron was increased so that the Fe / As (mol) ratio was 2 or more and removed as iron arsenate starch.
[0026]
FIG. 3 is a graph showing the relationship between the Fe / As ratio and the As concentration in Comparative Test Example 1. As shown in FIG. 3, it was found that even when the Fe / As ratio is 2.5 or more, As can be removed up to 10 to 13 mg / L, but it is almost impossible to make As below. Accordingly, it has been found that it is difficult for the iron arsenate method to make the As concentration 0.1 mg / L or less of the new drainage standard value.
[0027]
Next, a more specific example will be described. A copper electrolytic factory wastewater containing As concentration 2.9 / L and B sulfuric acid factory wastewater containing As concentration 6.2 g / L are subjected to sulfurization treatment with a capacity of 34 m ³ . The ORP value was controlled to 120 mV at the oxidation-reduction potential while introducing hydrogen sulfide into the tank. The pH value in the liquid at this time was 1.0, and the reaction efficiency was increased by extracting the liquid in the basket from the bottom and repeatedly circulating the liquid from the top (first step).
[0028]
The obtained 1st process water was led to the neutralization soot of 34 m < ³ > capacity | capacitance, while adding charcoal cal as a neutralizing agent, iron starch was added slightly excessively as an iron material, and was made to react (2nd process).
[0029]
Next, the obtained second step water is led to a neutralization pad, slaked lime is added as a neutralizing agent to adjust the pH to 10.5, and the concentration of As after solid-liquid separation of the produced neutralized starch is determined. As a result of analysis, it was 0.06 mg / L, which sufficiently satisfied the new wastewater standard value.
[0030]
【The invention's effect】
As described above in detail, the present invention includes a first step of adding a sulfiding agent to an As-containing wastewater that is treated water while controlling the addition amount so that the oxidation-reduction potential of the wastewater is 250 mV or less, A second step in which iron starch and a neutralizing agent are added to the liquid obtained in the first step for neutralization, and a third step in which a neutralizing agent is further added to the liquid obtained in the second step. In this way, the As concentration of treated water can be reduced to an As concentration of 0.1 mg / L or less as a new wastewater standard value.
[Brief description of the drawings]
FIG. 1 is a flowchart of an As-containing wastewater treatment method according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the ORP value and As concentration in Test Example 1;
FIG. 3 is a graph showing the relationship between Fe / As ratio and As concentration in Comparative Test Example 1;

Claims (3)

A method for treating As-containing wastewater ,
A first step of adding a sulfiding agent to the As-containing wastewater while controlling the addition amount so that the redox potential of the wastewater is 120 mV or less ;
The second step of solid-liquid separation into the first treated water and starch after adding the iron starch and neutralizing agent to the product obtained in the first step and performing neutralization treatment,
And a third step of adding a neutralizing agent to the first treated water obtained in the second step to precipitate and remove the As-containing material to obtain a second treated water. Wastewater treatment method.   The method for treating an As-containing wastewater according to claim 1, wherein the addition of the iron starch in the second step is to coprecipitate As at a pH of 3 or more.   The method for treating As-containing wastewater according to claim 1 or 2, wherein the sulfiding agent in the first step is hydrogen sulfide or sodium sulfide.

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