JPS60241988A - Treatment of waste water containing fluorine - Google Patents

Abstract

PURPOSE:To reduce the required amt. of a calcium compd. and the concn. of fluorine in the waste water in the treatment of waste water contg. fluorine by using a clacium compd. and an inorg. coagulant in combination and reutilizing a part of generated precipitate for the treatment of the feed water. CONSTITUTION:Calcium fluoride is formed by adding an optional calcium compd. selected from Ca(OH)2, CaCl2, CaCO3, etc. in combination with an optional inorg. coagulant selected from an aluminium coagulant such as aluminium sulfate, and iron coagulant such as ferrous sulfate. Further, if the waste water treatment is executed reutilizing at least a part of generated precipitate, the concn. of fluorine in the waste water may be reduced to <=15mg/l by only adding ca. five times weight of the calcium compd. basing on the amt. of F ion in the waste water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating fluorine-containing wastewater, and particularly to a method for highly removing fluorine ions from wastewater by calcium precipitation.

Manufacturing factories for semiconductors, aluminum, glass, etc. discharge wastewater containing fluorine ions. Conventionally, as a method for treating fluorine-containing wastewater, a method has been adopted in which a calcium compound is added to the wastewater and fluorine is removed from the wastewater as calcium fluoride. However, adding calcium compounds alone does not necessarily reduce the fluorine concentration to 15/jN.
I couldn't drop it below 21. In addition, in order to reduce the fluorine concentration to 15μ/e or less just by adding a calcium compound, it is necessary to add a calcium compound with a ratio of 10 to 1
Five equivalents had to be added.

For this reason, the current situation is that operating costs are high.

An object of the present invention is to provide a method for treating fluorine-containing wastewater that eliminates the drawbacks of the prior art, significantly reduces the amount of calcium compounds added, removes fluorine to an extremely low concentration, and provides stable treated water quality. Our goal is to provide the following. This object is achieved according to the invention by using an inorganic flocculant together with a calcium compound and by reusing the resulting precipitate for the treatment of raw water.

That is, the method for treating fluorine-containing wastewater according to the present invention is characterized by adding a calcium compound and an inorganic flocculant to fluorine-containing wastewater, and reusing at least a portion of the generated precipitate for treatment of raw water.

The calcium compound used in the method of the invention may be any calcium compound conventionally used to produce calcium fluoride, such as calcium hydroxide, calcium chloride, calcium carbonate, calcium sulfate, and the like.

Examples of inorganic flocculants used in the method of the present invention include aluminum-based flocculants, such as aluminum sulfate and sodium aluminate, and iron-based flocculants, such as ferrous sulfate, ferric sulfate, and ferric chloride. It will be done.

By using the method of the present invention in combination with a calcium compound and an inorganic flocculant, and reusing at least a portion of the generated precipitate to treat raw water, the amount of calcium compound added can be reduced to about 5 times the amount of fluorine. This makes it possible to reduce the concentration of fluorine in wastewater to below 15 μ/l.

Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

Example I Calcium hydroxide and aluminum sulfate were added to fluorine-containing wastewater discharged from Factory A in the amounts shown in Table 1 below, and the fluorine concentration in the treated water was measured. The results are shown in Table 1.

Table 1 A part of the generated sludge was reused for the treatment of raw water, and calcium hydroxide was added to the raw water with a fluorine concentration of 760 μ/p at an equivalent ratio of 5 to fluorine, as shown in Table 2 below. amount of aluminum sulfate was added, and the fluorine concentration in the treated water was measured, and the results are shown in Table 2. Table 2 also shows the operating costs in each experiment, with the operating costs in the case of not reusing sludge being set at 100.

(Left below) Table 2 As is clear from Table 2, the amount of flocculant added can be significantly reduced by reusing sludge, and if 50% of sludge is reused, operating costs can be reduced by 40%. I was able to save money.

In the examples, aluminum sulfate was used as a flocculant, but even if an iron-based flocculant is used, good effects similar to those described above can be obtained.

patent applicant Hitachi Plant Construction Co., Ltd.

Claims (1)

[Claims] (1) A method for treating fluorine-containing wastewater, which comprises adding a calcium compound and an inorganic flocculant to fluorine-containing wastewater, and reusing at least a portion of the generated precipitate for treatment of raw water.