KR0149933B1 - Fluorine-contained waste water treatment - Google Patents

Abstract

The present invention relates to the composition of soluble rare earth compounds used for treating fluorine using soluble rare earth compounds to selectively and effectively remove dissolved fluorine ions from waste water containing fluorine. A treatment agent treated with a compound, wherein the cerium (Ce) component in the rare earth component is less than 10% by weight.

Description

Fluorine-containing wastewater treatment agent

The accompanying drawings are graphs showing the removal of fluorine ion concentration according to Ce content.

The present invention relates to a method for the selective and effective removal of dissolved fluorine ions in wastewater containing fluorine, and more particularly, to the composition of a soluble rare earth compound used for treating fluorine using a soluble rare earth compound. .

Wastewater containing fluorine is discharged from all factories that use fluorine compounds, such as semiconductor manufacturing plants, metal surface treatment plants, and ceramic manufacturing plants. Recently, environmental concerns are expected to increase and environmental regulations will be strengthened. There is a need to develop a method for removing fluorine at low concentrations in an effective and economic manner.

In this regard, fluorine is removed by various methods. Most commonly, a Ca compound or an Al compound is added to waste water to insolubilize fluorine ions and to separate solid-liquid (Japanese Patent Laid-Open No. 60-117, No. 62-125894). Is proposed.

This method is not suitable for removing fluorine at low concentration because the amount of chemicals used and the amount of sludge generated are high, and fluorine ions of up to 8mg / l are theoretically retained in the solution when removing fluorine as a Ca compound.

In addition, the method of removing fluorine by adsorption method rather than deposition method has been proposed in Korean Patent 89-3882. However, since the adsorbent used is an insoluble rare earth compound, the manufacturing cost of the rare earth hydroxide from the raw material is expensive and the amount to be added is excessive. However, there is a disadvantage that the ion exchange action is performed only in an acidic solution, and the reaction rate is slow because the ion exchange reaction must be dependent upon the desorption.

In addition, this method does not use the existing equipment, it is cumbersome to intermittently work in a number of vessels containing a large amount of adsorbent, and when treating the resulting alkali fluoride with Ca (OH) ₂ , a considerable amount of CaF ₂ residues are generated, and when treated with Ca (OH) ₂ , fluorine remaining in the solution is always present at a concentration of about 8 mg / l or more.

In addition, Japanese Patent Laid-Open No. 3-186393 proposes to insolubilize fluorine ions in wastewater containing fluorine using a soluble rare earth compound and an alkali and alkaline earth metal compound, followed by solid-liquid separation.

In this method, fluorine can be removed relatively easily and with high efficiency compared to the above-mentioned methods. However, depending on the liquidity of the waste water, the filtrate becomes colloidal or does not settle well even if the coagulant is excessively added. Has become a big problem.

In other words, since a large amount of waste water is generated, the ease of separation of solid-liquid is a very important factor, and thus a treatment method for improving the fluorine ion removal effect and having a very high floc rate and settling rate is required.

That is, in the case of a semiconductor factory that occupies a large part of wastewater containing fluorine, the wastewater contains hydrogen peroxide (H ₂ O ₂ ).

In treating fluorine-containing wastewater containing hydrogen peroxide with a soluble rare earth compound, when the content of cerium (Ce) which is highly reactive with hydrogen peroxide in the rare earth component is high, it does not react with fluorine ions and binds with hydroxide ions to precipitate as rare earth hydroxide. This decreases the fluorine removal efficiency and forms a yellow precipitate at pH3.

The reaction scheme is shown below.

H ₂ O ₂ + 2H ⁺ + 2Ce ³⁺ + 2H ₂ O + 2Ce ⁴⁺

^{4OH - + Ce 4+ → Ce (} OH) 4 ↓ ( yellow precipitate)

In this case, rare earth ions form a mixture with hydroxide ions and fluorine ions, which collide to cause turbidity.

In addition, such deposits are attached to the sensor, stirrer, reactor wall, etc. due to the high adhesion has raised many problems.

Even when hydrogen peroxide is not included, the precipitation reacts with the oxygen in the air to make it yellow.

Accordingly, an object of the present invention is to provide a method for solving the problems described above and increasing the fluorine removal efficiency of the soluble rare earth compound.

The present invention for achieving the above object comprises a fluorine-containing wastewater treatment agent in which the Ce component in the rare earth component is less than 10% by weight in the treatment agent for treating the fluorine-containing wastewater with a soluble rare earth compound.

According to the present invention, the amount of Ce in the components of the soluble rare earth compound to be injected into the wastewater regardless of the degree of alkali metal is less than 10% (preferably less than 5%), and the color of the precipitate can be removed. And turbidity and fluorine removal efficiency were improved.

This is because the rare earth ions are prevented from being hydrated by reducing the amount of Ce and increasing the amount of La, thereby selectively and efficiently reacting with fluorine ions.

Fortunately, Ce is easily oxidized to Ce ⁴⁺ , which can be easily removed in the following way.

That is, when rare earth hydroxide is heated to 120 ~ 130 ℃ in air to oxidize Ce to tetravalent and then dissolved in 5 ~ 10% nitric acid or hydrochloric acid, trivalent hydroxides are dissolved but tetravalent CeO ₂ · nH ₂ O is dissolved. It doesn't work.

In this way Ce can be removed.

As the soluble rare earth compound used in the present invention, chlorides, nitrates, sulfates and the like can be used.

Hereinafter, the present invention will be described in detail through examples.

[Examples 1-5 and Comparative Examples 1-5]

An experiment was performed on a solution in which 1 ml of hydrogen peroxide was added to artificial wastewater (fluorine concentration 30 ppm, pH7.7) prepared by dissolving 0.292 g of reagent-grade NH ₄ F in 5 L of tap water.

As the soluble rare earth compound to be added, a content of 200 g / L was used when the content of all rare earth oxides was used.

First, 0.6 ml of a soluble rare earth compound having 0.5, 10, 20, and 30% Ce oxide in the total rare earth oxide was added to the wastewater containing hydrogen peroxide, and then reacted for 10 minutes, and the pH was adjusted to 7.5 with caustic soda.

After the pH adjustment, the reaction was further reacted for 5 minutes, a flocculant was added, and the fluorine concentration, turbidity, and color of the sludge were measured (Examples 1 to 5).

Next, 0.6 ml of a soluble rare earth compound having 0.5, 10, 20, and 30% Ce oxide in the total rare earth oxide was added to the wastewater containing no hydrogen peroxide, and then reacted for 10 minutes, and the pH was adjusted to 7.5 with caustic soda.

After pH adjustment was completed, the reaction was further performed for 5 minutes, a flocculant was added, and fluorine concentration, turbidity, and color of sludge were measured (Comparative Examples 6 to 10).

The results are shown in Table 1 and the accompanying drawings.

Fluoride ion concentration was measured using ion metcr, and turbidity was measured using LaMotte water analyzer.

Turbidity indicates that the lower the number, the more solution.

As a result, when hydrogen peroxide was mixed, it was found that as the Ce content decreases, the fluorine removal effect and turbidity are improved, and the color of the precipitate does not occur.

In particular, in the case of turbidity, the situation is required to be 5 or less in the water treatment strictness of the user.

Example 6 and Comparative Example 11

An experiment was conducted to investigate the effects of the composition of soluble rare earth compounds on the first treatment water of wastewater generated by semiconductor manufacturers.

At this time, the pH of the primary treated water was 5.07, the fluorine concentration was 15 ppm, and the hydrogen peroxide concentration was 50 ppm.

As the soluble rare earth compound to be added, a content of 200 g / L was used when the content of all rare earth oxides was used.

First, 0.3 ml of a soluble rare earth compound having 55% of La oxide and 3.9% of Ce oxide in the rare earth oxide was added to the wastewater, followed by reaction for 10 minutes, and the pH was adjusted to 7.5 with caustic soda.

After the pH was adjusted, the reaction was carried out for 5 minutes, a flocculant was added, and the fluorine concentration, turbidity, and color of the sludge were measured (Example 6).

Next, soluble rare earth oxides containing 27% La oxide and 44% Ce oxide in the same wastewater were added in the same wastewater, and reacted in the same manner as in Example 1, and then fluorine concentration, turbidity, and color of sludge were measured. Example 11).

As a result, it can be seen that Example 6, which reduces the amount of Ce in the soluble rare earth compound, is superior to Comparative Example 11.

Claims (1)

A treatment agent for treating a fluorine-containing wastewater with a soluble rare earth compound containing one of chloride, nitrate, and sulfate salts, wherein the fluorine-containing wastewater treatment agent has a cerium (Ce) component of less than 10% by weight.