JPS6025584A - Treatment of fluorine-containing waste water - Google Patents

Abstract

PURPOSE:To prevent fine flocs from being formed at the time of flocculation and efficiently remove fluorine from a fluorine-containing waste water, by simultaneously adding a calcium salt and an iron salt to the fluorine-containing waste water, by simultaneously adding a calcium salt and an iron salt to the fluorine- containing waste water to effect sufficient reaction, followed by flocculation. CONSTITUTION:A calcium salt and an iron salt are simultaneously added to the fluorine-containing waste water, whereby the iron salt is converted into iron hydroxide, and fine flocs of calcium fluoride are adsorbed on flocs of iron hydroxide. A portion of complexes is also adsorbed on the flocs of iron hydroxide, and is separated by flocculation. As a result, the concentration of fluorine in the supernatant water in a settling tank approaches a theoretical solubility of calcium fluoride of 8mg/l (calculated as fluorine). The concentration of fluorine in the supernatant water flocculation is brought to a value appoximate to the theoretical value of 8mg/l by the addition of the iron salt as well as the calcium salt, as contrasted to the case of sole addition of the calcium salt wherein the fluorine concentration is 20mg/l.

Description

[Detailed description of the invention] This invention relates to a method for treating fluorine-containing wastewater.

In particular, the present invention relates to a method for treating fluorine-containing wastewater in which iron salts are added at the same time as calcium salts.

Conventional methods for treating fluorine-containing wastewater involve adding calcium salts to coagulate and precipitate calcium fluoride, which has low solubility.

However, due to the nature of wastewater, fine flocs of calcium fluoride react with fluorine during coagulation and precipitation, and the substance reacts with fluorine to form chains. Generally, the design value for this fluorine concentration is 151.
M1/ was set as below.

However, due to the above-mentioned influence, the amount often exceeded 15 tq/1.

For this reason, there was a drawback that the fluorine in the treated water could not be reduced to less than 15/l unless calcium salt was added about 10 times the amount of fluorine per liter.

An object of the present invention is to provide a wastewater treatment method that eliminates the drawbacks of the prior art and can prevent the formation of fine flocs during coagulation and sedimentation.

This invention is a method for treating fluorine-containing wastewater.

By simultaneously adding a calcium salt and an iron salt, the iron salt is converted into iron hydroxide, and at this time, the fine flocs of humidified calcium are adsorbed onto the iron hydroxide flocs, and a part of the complex is also converted into iron hydroxide. It is adsorbed onto the flocs and separated by coagulation and sedimentation in the subsequent stage. As a result, it was experimentally confirmed that the fluorine concentration in the clear water of the sedimentation pond approaches the theoretical solubility of fluorine in calcium butoxide, which is 8 mg/l.

With this treatment method, when only calcium salt was added, the fluorine concentration in the supernatant water after coagulation and sedimentation was 20 mg/l, but by adding iron salt, the fluorine concentration was 8 mg/l, which is close to the theoretical value.
I confirmed that it can be processed with my/Li.

FIG. 1 shows the processing results at Company A. If only calcium salt is added, will the fluorine concentration in the supernatant water (treated water) after coagulation and precipitation be 20m? /l. This was due to the high fluorine concentration due to the presence of many fine flocs of lumped calcium in the treated water. However, in addition to this, secondary chloride is added as an iron salt.
By adding iron and gradually increasing its amount, the above-mentioned fine flocs can be reduced! It was confirmed that the fluorine concentration in the treated water gradually decreased. This is hydroxide 2
This is thought to be because iron adsorbs fine flocs of lumped calcium.

Further, in the embodiment shown in FIG. 1, the anti-U3 pH was set to 10, but the p'H may be set to 7 to 8 if the amount of Cα/F2 is appropriate for the fluorine setting.

This invention involves adding calcium salts and iron salts to fluorine-containing wastewater at the same time, causing the iron salts to form iron hydroxide flocs, and the iron hydroxides adsorbing and precipitating fine lumped calcium flocs. This makes it possible to maintain a constant fluorine concentration in the treated water or to perform advanced treatment by adjusting the amount of iron salt added.

[Brief explanation of drawings]

Figure 1 shows the relationship between the amount of Fg+3 added and the fluorine concentration in treated water.

Claims (1)

[Claims] 1. A method for treating fluorine-containing wastewater, which is characterized by adding calcium salts and iron salts to fluorine-containing wastewater at the same time, allowing sufficient reaction to occur, and then coagulating and precipitating.