KR0142932B1 - Treatment of fluorine-containing wastewater - Google Patents

Abstract

The present invention relates to increasing the efficiency of fluorine removal by adjusting the pH of wastewater to neutrality and then adding soluble rare earth compounds in treating wastewater containing fluorine, and then treating fluorine-containing wastewater with soluble rare earth compounds. , A method for treating fluorine-containing wastewater, characterized in that fluorine is removed from the wastewater by adding an inorganic acid to the wastewater to adjust the pH to neutral and then adding a soluble rare earth compound.

Description

[Name]

Treatment of fluorine-containing wastewater

Detailed description of the invention

The present invention relates to a method for treating fluorine-containing wastewater, and more particularly, to increasing the fluorine removal efficiency by adding a soluble rare earth compound after adding an inorganic acid to adjust the pH to neutral.

Wastewater containing fluorine is emitted from all factories that use fluorine compounds, such as semiconductor manufacturing plants, metal surface treatment plants, and ceramic manufacturing plants. There is a need for development of a method that can be removed. Several methods are known in this regard. As the most common method, a method of solid-liquid separation by dissolving fluorine ions by adding a Ca compound or an Al compound to wastewater (Japanese Patent Laid-Open No. 60-117, No. 62-125894) has been proposed. And a large amount of sludge generation, and when removing fluorine as a Ca compound, theoretically, up to 8 mg / l of fluorine ions remain in the solution, which is not suitable for removing fluorine at low concentrations. In addition, the method of removing fluorine by adsorption method rather than precipitation method has been proposed in Korean Patent 89-3882. However, since the adsorbent used is an insoluble rare earth compound, the production cost of the rare earth hydroxide from the raw material is high and the amount to be added is excessive. There is a disadvantage that the ion exchange action is performed only in an acidic solution, and the reaction rate is slow because it has to rely on the ion exchange reaction when desorption. In addition, this method does not use the existing equipment, it is cumbersome to intermittently work in a large number of vessels containing a large amount of adsorbent, and a considerable amount of CaF when treating the produced alkali fluoride with Ca (OH) _{2 2} residues are generated, and when treated with Ca (OH) ₂ , F remaining in the solution is always present at a concentration of about 8 mg / l or more. In Korea, 93-12855 is used to remove dissolved fluorine using soluble rare earth compounds.In the case of high concentration fluorine-containing wastewater containing 30 ppm (mg / l) or more of fluorine in wastewater, It is quite disadvantageous. Therefore, economically effective amounts of soluble rare earth compounds in the treatment of fluorine wastewater should be used. The present invention is to provide such an efficient method, and to provide a treatment method for increasing the efficiency of fluorine removal by adding an inorganic acid to the wastewater to neutralize the pH in the fluorine wastewater treatment and then adding a soluble rare earth compound. have. In order to achieve the above object, the present invention treats fluorine-containing wastewater with a soluble rare earth compound, by adding an inorganic acid to the wastewater to adjust the pH to neutral and then adding a soluble rare earth compound to remove fluorine from the wastewater. to be. In the present invention, the inorganic acid is nitric acid, hydrochloric acid, sulfuric acid and the like, and the fluorine-containing wastewater applied in the present invention includes raw water of wastewater or primary treated water by slaked lime. The range of PH treated with the above inorganic acid is 7 or less, preferably PH 3-7. In the present invention, when the soluble rare earth compound is introduced in a state where the pH of the waste water is neutral, the soluble rare earth compound itself does not react with fluorine ions and binds with hydroxide ions to precipitate as a rare earth hydroxide, thereby reducing fluorine removal efficiency. Also, in this case, rare earth ions may form a comlex with hydroxide ions and fluorine ions to colloid to cause turbidity. Therefore, the inorganic acid, ie hydrochloric acid, nitric acid or sulfuric acid, is added before or after the time of introducing the rare earth compound into the wastewater, so that the pH is lowered to a neutral value, preferably 5 or less, thereby preventing the rare earth ions from being hydroxylated. It should be able to react. This applies both when the rare earth compound is added directly to the wastewater source, or when the filtrate is first treated with slaked lime. In particular, in the case of primary treatment using slaked lime, it is common to increase the reactivity of slaked lime and lower the pH to about 8-9 for the convenience of subsequent treatment, but in the case of secondary treatment by adding rare earth compounds to the mineral acid, Dropping the PH to lower than neutral using this can be said to be a more preferable treatment method in terms of reaction efficiency. It will be described in more detail through the following examples. The numerical values shown in the present embodiment are merely examples, and thus the present invention is not limited thereto.

Example 1 and Comparative Example 1

Experiments were conducted on the primary treatment of wastewater from semiconductor wafer manufacturers. At this time, the pH of the primary treated water was 9.5, and the fluorine concentration was 35 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, 0.6ml / L of a soluble rare earth compound was directly added to the wastewater, reacted for 10 minutes, and a flocculant was added, followed by measuring fluorine concentration (Comparative Example 1). Next, sulfuric acid was added to the same wastewater to adjust the pH to 4.5, and then the same amount of soluble rare earth compound was added to the reaction as in Comparative Example 1, followed by measurement of fluorine concentration (Example 1). As a result, it was found that in Comparative Example 1, the fluorine concentration of the treated water was 12.5 ppm, and in Example 1, the fluorine concentration was 5.3 ppm, which was superior to that of Comparative Example 1.

Example 2

An experiment was conducted to investigate the efficiency according to the pH conditions of the wastewater when the soluble rare earth compound was added to the first treatment water of the wastewater generated by the semiconductor manufacturer. At this time, the pH of the primary treated water was 9.13, and the fluorine concentration was 26 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. The pH of the wastewater was controlled by adding sulfuric acid. The experimental results are shown in the table below.

Example 3

An experiment was conducted to investigate the effect of acid type used to control the pH conditions of wastewater when the soluble rare earth compounds were injected into the first treatment water of wastewater generated by semiconductor manufacturers. At this time, the pH of the primary treated water was 9.13, and the fluorine concentration was 26 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. The pH of the wastewater at the time of introduction was set to 3.0 using sulfuric acid, hydrochloric acid, and nitric acid, respectively. The experimental results are shown in the table below.

Regardless of the acid type, the fluorine removal effect was superior to that without the acid.

Claims (4)

A method of treating fluorine-containing wastewater, wherein the treatment of fluorine-containing wastewater with soluble rare earth compounds comprises adding inorganic acid to the wastewater to adjust the pH to neutral and then adding soluble rare earth compounds to remove fluorine from the wastewater. The method for treating fluorine-containing wastewater according to claim 1, wherein the inorganic acid is nitric acid, hydrochloric acid or sulfuric acid. The method for treating fluorine-containing wastewater according to claim 1, wherein the pH treated with the inorganic acid is 3 to 7. The method for treating fluorine-containing wastewater according to claim 1, wherein the fluorine-containing wastewater is primary treated water by elemental or hydrated lime of the wastewater.