JPS6097091A - Treatment of fluoride ion-containing water - Google Patents

Abstract

PURPOSE:To remove a fluoride ion efficiently and inexpensively, by adding an Al-compound to fluoride ion-containing water to adjust the pH of said water to 5-8.5 and separating a precipitate from treated water while adding a Ca-compound to said precipitate. CONSTITUTION:Raw water is introduced into a reaction tank 1 from a raw water pipe 4 in a first process and the return reaction product from a fourth process is added to raw water while an aluminum compound is added thereto from a chemical agent injection pipe 5 if necessary and a pH controller is added from a chemical agent injection pipe 6 to adjust the pH of raw water to 5-8.5. By this method, Al(OH)3 is precipitated and the fluoride ion in raw water is adsorbed with the precipitate simultaneously with the formation of the precipitate and a part of the fluoride ion is immobilized as CaF2. The reaction solution in the reaction tank 1 is separated into a precipitate and a supernatant solution and a part of the precipitate is transferred to a precipitate reaction tank 3 where a calcium compound is added and formed reaction product is returned to the first process as the fourth process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating fluoride ion-containing water.

As a method for treating water containing fluoride ions, a method is known in which calcium ions or aluminum ions are added in an amount equivalent to about twice the amount of fluoride ions, and precipitates are generated and removed (for example, PPM June 1978 issue). 46
However, the fluoride ion concentration of the treated water obtained by this method was high, and it was not a satisfactory treatment method. Another drawback was that the amount of precipitate produced increased.

Furthermore, the above-mentioned known literature also describes an example in which fluoride ion-containing water is treated in two stages using a calcium compound or an aluminum compound. However, such a two-stage treatment method requires a sedimentation tank or the like for each stage, and has the disadvantage that the installation area of the plant becomes large.

This invention was developed as a result of intensive research to solve the drawbacks of these conventional examples.

That is, this invention provides that p in the presence of an aluminum compound in water containing fluoride ions.
A first step of adjusting H to 5 to 8.5, a second step of solid-liquid separation of the effluent suspension from the first step and separating it into treated water and precipitate, and precipitation from the second step. This is a method for treating fluoride ion-containing water, which includes a third step of adding a calcium compound to the product, and a fourth step of returning the third step reactant to the first step.

The fluoride ion-containing water to be treated in this invention is discharged from aluminum electrolytic smelting processes, phosphate fertilizer manufacturing processes, silicone and other electrical parts cleaning processes, uranium refining processes, surface treatment cleaning processes, etc. Examples include wastewater, flue gas desulfurization, and denitrification wastewater.

The present invention will be explained below with reference to embodiments of the drawings.

The drawing is a system diagram showing an embodiment of the present invention, in which 1 is a reaction tank, 2 is a precipitation tank, and 3 is a precipitation reaction tank.

1. In the first step, raw water is introduced from the raw water pipe 4 into the reaction tank 1, and reactants to be returned in the fourth step described below are added thereto, and aluminum compounds are added from the chemical injection pipe 5 as necessary. (3) pi (adjusting agent is added) and adjusted from the drug injection tube 6 to 5 to 8,5.

It is not necessary if a sufficient amount of aluminum compound is present in the raw water, but if it is insufficient or absent, aluminum compound is added from the outside.

Any known aluminum compound can be used as long as it is water-soluble, such as aluminum sulfate (sulfuric acid band), polyaluminum chloride, aluminum chloride, aluminum nitrate, and the like. Among these, aluminum sulfate is preferred in terms of performance and handling.

The required amount of the aluminum compound varies depending on the amount of fluoride ions, but as a guide, the weight ratio to the fluoride ions is 1:process (as aluminum ions). However, since the reactants introduced from the fourth step contain large amounts of calcium ions and aluminum ions, the amount can be reduced accordingly.

pH after adding aluminum compounds etc. is 5-85
It is necessary to adjust accordingly. If the pH of the reaction solution (4) naturally falls within this range, there is no need to add it from the outside, but in other cases, a pH adjuster is added.

As the pH adjuster, sodium hydroxide, sodium carbonate, calcium hydroxide, etc. can be used as an alkaline agent, and calcium hydroxide is particularly preferred because it serves as a pH adjuster and a source of calcium ions. In addition, as an acid,
Use sulfuric acid, hydrochloric acid, etc.

As described above, when the reactant returned in the fourth step and the aluminum compound are added to the fluoride ion-containing water and the pH is adjusted to 5 to 8.5, the added aluminum ions become AI(OH )s, and fluoride ions in the raw water are mixed into the precipitation at the same time as precipitation is formed.
Fluoride ions are reduced by being adsorbed by flocs.

Furthermore, since the effluent introduced from the fourth step contains a large amount of calcium ions, some of the fluoride ions will be fixed as CaF.

The reaction time in the reaction tank 1vr is about several minutes to 1 hour, but in order to reduce fluoride ions as much as possible,
It is preferable to react for more than a minute.

The reaction liquid in reaction tank 1 is sent to precipitation tank 2, where it is separated into precipitate and supernatant water.

The settling tank used is of a known type.

The supernatant water is discharged from the system through a pipe 7 as treated water. Of course,
If necessary, the water may be further treated at a high level before being discharged. In addition, upon solid-liquid separation, a polymer flocculant such as a partial hydrolyzate of polyacrylamide may be used as necessary. A part of the sediment discharged from the settling tank 2 is discharged outside the system via the mud removal pipe 8 and disposed of by appropriate means.

On the other hand, the remainder of the precipitate is sent to the precipitate reaction tank 3. In the sediment reaction tank 3, a calcium compound is added from the chemical injection pipe 9, and if necessary, a PF (adjusting agent) is added from the chemical injection pipe 10.

As a calcium compound, any calcium AIl such as calcium oxide, calcium hydroxide, calcium chloride, etc.
k can be used. The same pH adjusters as those described above can be used.

Calcium compounds, such as Ca″(0)1) in the precipitate
2 and adjust the pH by adding pl (adjuster) as needed.
It is thought that the following reaction occurs when the is adjusted to 85-13.

A1 (0 old 3F + Ca (OH)t −k l (
OH) n−”−”ゝ+CaF.

Here, A 1 (Of()3-F' represents a fluoride fixed by being adsorbed or frozen to aluminum hydroxide as described above, and n represents an integer of 3 or more.

That is, the fluoride ions trapped in aluminum hydroxide are once eluted and then react with calcium hydroxide to become poorly soluble CaF and fixed again.

On the other hand, the higher the pH, the more aluminum hydroxide is released from the bath.
Comes to exhibit a solution state. For this reason (7), the pH in the precipitation reaction tank 3 is preferably 9 or higher. Further, the residence time is approximately several minutes to one hour.

In this way, from the precipitation reaction tank 3, precipitation of CaF,
Precipitates containing aluminum and galcium compounds, and suspended reactants containing aluminum ions and calcium ions are discharged.

In this invention, in order to effectively utilize the reactant discharged from the third step, this reactant is returned to the first step as the fourth step. The return location may be in the raw water or in the reaction tank 1.

By returning, aluminum ions and calcium ions are used to fix fluoride ions, and
CaF2 in the reaction product becomes the core of the reaction, and a precipitate with extremely good sedimentation properties can be obtained.

In addition, in the above explanation, the precipitate was discharged to the outside of the thread through the four pipes 8, but after dissolving the aluminum compound in the precipitate reaction tank 3, the precipitate mainly consisting of CaF2 was precipitated. It is also possible to pull out only the object.

As described above, according to the present invention, since the precipitate once generated is used after being detained and dissolved, the cost is low, and the fluoride ions are treated with the calcified compound and the aluminum compound. This makes it possible to remove fluoride ions extremely efficiently.

Moreover, the obtained precipitate has many excellent advantages, such as extremely good sedimentation properties and easy treatment and disposal.

Example 1 51 m9/I3 of NaFeF was added to Yokohama city water to obtain raw water.

First, as a conventional example, aW & band 500my/1 is applied to raw water.
3 and 120 m of calcium hydroxide to adjust the pH to 97.5.
was set to 69, and after reacting for 20 minutes with stirring, the precipitate was separated (Case 1).

In addition, the treatment was performed in the same manner as in Case 1 except that the precipitate in Case 1 was added to the raw water. (Case 2) Next, as an example of the present invention, after obtaining a precipitate by the same method as in Case 1, 120 pumps of Ca (OH) 2/, 8 (converted to raw water amount) were added to the precipitate. pH 9,15)
, and was allowed to react for about 10 minutes. Next, this reaction product was added to the raw water, and at the same time, 500 μ/p of sulfuric acid was added, and the mixture was allowed to react for 20 minutes.

The pH at this time was 6.5. (Case 3) In Case 3, Ca (OR) 2 added to the precipitate is 30
omy/13 (pl-110,5) was treated in the same manner as Case 3, except that after adding the reactant to the raw water, the pH was adjusted to 7.2 with sulfuric acid (Case 4).

The results of Case 4 are shown in Table 1.

As shown in Table 1, it can be seen that by effectively utilizing the precipitate, fluoride ions were sufficiently removed even in one stage treatment.

Example 2 pi-12.0, F350 calls/g, Ca 5261%l
/#, A1370η/l flue gas desulfurization wastewater was used as raw water to carry out the invention method.

First, in the case of this raw water, there is already a sufficient amount of aluminum ions, so 1,500 μg of calcium hydroxide is added to the raw water.
/43 was added to adjust the pH to 7.1, and the precipitate formed after reaction for 0.5 hour was separated. The F content in the treated water obtained at this time was 40.3 m97.8.

The same treatment as above was carried out except that this precipitate was added to the raw water. As a result, F in the treated water was 37,'1rlU;l
'/, it was 8.

Next, 1 t of Ca (OH) was added to the precipitate obtained above.
．． After adding 500η/k (converted to the amount of raw water) and reacting for 1 hour, it was added to the raw water, and NaOH was further added to p
Adjusted to H6 and 7.

As a result, F in the treated water was reduced to 9.0η/13.

Thus, it can be seen that simply returning the precipitate hardly improves the quality of the treated water, but adding calcium compounds to the precipitate significantly improves the water quality.

Patent Applicant: Kurita Water Industries, Ltd. Procedural Amendment Written by the Commissioner of the Patent Office, 1982-7, 1. Indication of the case, Patent Application No. 204476, filed in 1982. 2. Name of the invention: Method for treating fluoride ion-containing water 3. Relationship with the case of the person making the amendment Patent applicant address 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo 1604
, date of the amendment order January 31, 19805, number of inventions increased by the amendment None 6, column 7 of "Brief explanation of drawings" of the specification subject to the amendment, page 12 of the description of the contents of the amendment Insert the following after the 6th line.

[Brief explanation of the drawing]

The drawing is a system diagram showing an embodiment of the present invention, in which 1 is a reaction tank, 2 is a sedimentation tank, 3 is a sediment reaction tank, 4 is a raw water pipe,
5.6.9.10 indicates a drug injection tube, 7 indicates a tube, and 8 indicates a conduit. ” (2)

Claims (1)

[Claims] In the presence of an aluminum compound in monofluoride ion-containing water,
The first step is to adjust pi to 5 to 8.5, the second step is to separate the effluent suspension from the first step into treated water and precipitate, and the precipitate from the second step. Method 2 for treating fluoride ion-containing water, comprising a third step of adding a calcium compound to the water, and a fourth step of returning the third step reactant to the first step.The aluminum compound is aluminum sulfate, and the calcium compound is The treatment method according to claim 1, which is calcium hydroxide.