JPS586553B2 - Method for removing fluorine ions in water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing fluorine ions dissolved in water.

Fluorine ions (F-) are present in water sources such as groundwater or surface water.
may be contained in excess (0.8 ppm or more),
When this water is used as a water supply source for drinking purposes, excess fluoride ions in the water cause dental diseases such as mottled teeth.

And the method to remove this excess fluorine ion is as follows:
There are activated alumina methods, electrolytic methods, bone charcoal methods, etc., but none of these methods can be said to be easy to operate, efficient, and economical if they remain as conventional methods, and they do not allow excessive fluoride ions to be used. Even if water is included in water, valuable water resources may be left unused.

That is, in the conventional activated alumina method, water containing fluoride ions is passed through the activated alumina layer to adsorb and remove fluoride ions, but in order to regenerate activated alumina, alkali and acid or a large amount of aluminum sulfate are used to regenerate the activated alumina. Therefore, a large amount of these processing liquids are produced as by-products, and as a result, a large amount of chemicals and equipment are required to reprocess this processing liquid, which is complicated to operate and is economically disadvantageous.

Furthermore, when the water to be treated contains impurities such as turbidity components and iron, there are many drawbacks such as the possibility that activated alumina cannot be recycled.

In addition, the electrolytic method uses metallic aluminum as an anode and elutes aluminum by electrolysis to generate active aluminum hydroxide, and this aluminum hydroxide adsorbs and removes fluorine ions in water. This method requires a large amount of electric power, generates a large amount of sludge based on aluminum hydroxide, and has the disadvantage that the aluminum electrode is consumed more than necessary.

In addition, the bone charcoal method uses hydroxyapatite [Ca, (P
Bone char whose main component is O4)3OH) is used, and water is passed through this bone char to adsorb and remove fluorine ions, and the principle behind this is the selective ion exchange of fluorine ions with respect to hydroxyabatite. It is said that

However, this method also requires a large amount of alkali to regenerate bone charcoal, requires a lot of cost to regenerate this treatment solution, and depending on the raw water, after several cycles of use and regeneration,
There are cases where bone char is difficult to regenerate for unknown reasons, and there are concerns about its practical use.

The present invention has been made in view of the above points, and provides a practical and economical method for removing fluorine ions in water, which eliminates the drawbacks of the conventional bone char method, facilitates the reuse and reuse of bone char in a simple and efficient manner. It provides:

That is, hydroxyapatite is generated by adding phosphate ions and calcium ions to the water to be treated.

In order to carry out this reaction, phosphorus (P) and calcium (C
The atomic ratio with a) is 3:5 or less, and the pH is 8.
Phosphate and calcium hydroxide are added to the water to be treated so that the amount of colloidal hydroxyapatite crystals is 9 to 9.

Next, after stirring, the water to be treated is passed through a bone char layer, and the hydroxyapatite produced is immediately crystallized on the bone char surface.

Then, the hydroxyl ions of the hydroxyapatite crystals crystallized on the bone char surface undergo ion exchange with fluorine ions in the water, and the fluorine ions in the water are captured and removed by the crystals crystallized in the bone char as fluoroapatite. .

Furthermore, by subsequently passing treated water containing hydroxyapatite through the bone char layer, hydroxyapatite crystals accumulate in the bone char layer and grow while capturing fluorine ions in the treated water.

In this way, fluorine ions can be continuously removed by generating hydroxyapatite crystals in the water to be treated, crystallizing them in the bone char layer, and ion-exchanging the fluoride ions with the hydroxyapatite in the water to be treated. This is how it was done.

Furthermore, when the pH is below 8, when the water to be treated is passed through the bone and coal bed at a relatively high superficial velocity of about 20 m3/m3h, there is a sufficient amount of water to form hydroxyapatite crystals in the water to be treated. If the reaction is difficult to take place and the pH is above 9, the aggregation reaction occurs preferentially, and an efficient crystallization reaction of hydroxyapatite does not occur.

Next, one embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 designates a chemical adjustment tank, which has a stirrer 2 and is connected to a chemical addition tank 5 through a conduit 4 having a pump 3, into which liquid chemicals are fed.

The chemical addition tank 5 has a stirrer 6 and is connected to an inlet passage 7 and an outlet passage 8, to which a filtration tank 9 is connected in communication.

In this filter tank 9, a bone char bed 11 filled with granular bone char at an appropriate density and volume is formed in a tank body 10, and spaces are formed in the upper and lower parts of this bone char layer 11, and the above-mentioned lead-out path 8 is formed. An inlet section 12 for water to be treated and an outlet section 13 for water to be treated are connected, and a conduit 1 is connected to this outlet section 13.
A treated water tank 15 is connected through 4, and an outflow path 16 is connected to this treated water tank 15.

Further, a conduit 18 having a pump 17 is connected to the treated water tank 15, and this conduit 18 is connected to the bottom of the tank body 10 of the filtration tank 9 in communication.

In addition, a discharge pipe 1 is connected to the introduction part 12 of the tank body 10 of the offshore tank 9.
A waste water storage tank 20 is connected through the pipe 9, and the waste water storage tank 20 is connected to the chemical addition tank 5 through a water pipe 21 at the upper part thereof, and has a sludge discharge port 22 at the lower part.

In such an apparatus, phosphate and calcium hydroxide are each stirred with water in a chemical adjustment tank 1 to form an aqueous solution, and a pump 3 sends these aqueous solutions via a conduit 4 to a chemical addition tank 5 .

On the other hand, the chemical addition tank 5 is previously filled with water to be treated via the introduction path 7, and predetermined amounts of the phosphate aqueous solution and calcium hydroxide aqueous solution are added while stirring the water to be treated.

Then, adjust the pH to 8-9.

At this time, crystal nuclei of hydroxyapatite are generated in the chemical addition tank 5, and the microcrystals of these crystal nuclei are dispersed in the water to be treated to produce colloidal matter. Immediately after stirring, for example for up to 10 minutes, it is led via outlet 8 to filtration bed 9 .

This filtration tank 9 maintains a constant amount of water in the introduction part 12 of the tank body 10, and this water has a flow time, that is, a residence time, in the bone and charcoal layer 11 by appropriately adjusting the filling capacity and packing density of the bone and charcoal layer 11. are adjusted and flow down sequentially.

In this process, colloidal hydroxyapatite microcrystals in the water to be treated are crystallized on the surface of hydroxyapatite crystals, the main component of bone char, while passing through the bone char layer 11, and the microcrystals are deposited on the surface of the bone char. Further crystals grow cumulatively from the crystal nucleus and gradually become coarser.

On the other hand, fluorine ions in the water to be treated are ion-exchanged with hydroxyl ions of hydroxyapatite crystals precipitated on the bone char surface, captured as fluoroapatite by the crystals crystallized on the bone char surface, and separated from the water to be treated.

The treated water from which fluoride ions have been removed flows down the bone and charcoal layer.

At this time, the hydroxyapatite crystals precipitated on the bone char surface are microcrystals and have a significantly large surface area, which can increase the efficiency of capturing fluorine ions.

Furthermore, the bone char is uniformly and widely distributed and filled in the tank body 10, and since it is in the form of particles, its surface area is large.Moreover, since the main component of bone char is hydroxyapatite, the hydroxyapatite crystal surface of the activated bone char A process in which colloidal microcrystals of hydroxyapatite in the water to be treated are crystallized over a wide area, and crystals grow by accumulating hydroxyapatite similar to the water to be treated, which is subsequently supplied to the crystallized microcrystals. The fluorine ions in the water to be treated are further captured by ion exchange, and the surface area of the hydroxyapatite crystals is made as large as possible over time, thereby increasing the fluorine ion removal efficiency.

In this sense, after mixing phosphate and calcium hydroxide with the water to be treated, it is preferable to flow the water into the filter tank 9 immediately after the crystals have not grown.

In order to maintain a high removal efficiency of fluorine ions, it is sufficient to slow down the flow time, that is, the residence time of the water to be treated in the filter tank 9, but the capacity of the bone char bed 11 can be adjusted as appropriate. It can be operated so that the fluorine ions in the treated water meet the desired fluorine ion content regulation value.

In this way, the water to be treated is ion-exchanged with the hydroxyapatite crystallized in the bone char and fluorine ions are removed, and the water is led out to the outlet part 13 of the tank body 10 and stored in the treated water tank 15 via the conduit 14. The outflow channel 16 can be used as a water supply source, etc.

Next, the process of cleaning the bone charcoal layer 11 will be explained.

The water in the treated water tank 15 is sent from the pump 176 through the conduit 18 to the outlet part 13 of the tank body 10 of the sifting tank 9, and the water is passed through the bone charcoal bed 11 in the opposite direction to the flow direction of the water to be treated. coal seam 1
The coarse crystals consisting of hydroxyapatite and fluoroapatite that have grown cumulatively on the bone char particles 1 are desorbed from the bone char by the water pressure, and the bone char layer 11 is continued to be used as it is.

Further, the coarse particles separated from the bone and char bed 11 are carried by water, and this water is temporarily stored in the introduction part 12 of the tank body 10 and overflows to the wastewater storage tank 20 via the conduit 19.

Then, the washing water introduced into the waste water storage tank 20 is allowed to stand still, and the crystals of hydroxyapatite and fluoroapatite are sedimented and removed, and a substantially transparent supernatant liquid is obtained.

Then, this supernatant liquid can be returned to the chemical addition tank 5 to reuse the remaining phosphates, calcium hydroxide, etc.

Next, an experimental example based on the above embodiment of the present invention will be shown.

Experimental Example 1 Groundwater containing 190 ppm of fluorine ions (F-) (iron content: 0.02 ppm, hardness: 21.9, turbidity: 0.3, alkalinity: 18.6) was introduced into the chemical addition tank 5, and the water was introduced into the chemical adjustment tank 1 in advance.
40 ppm of the calcium dihydrogen phosphate aqueous solution prepared in above to the groundwater and 30 ppm of the slaked lime aqueous solution as calcium hydroxide to the above groundwater were added to the groundwater with stirring, and the atomic ratio of phosphorus and calcium was adjusted to P.
When /Ca=3/5.3, microcrystals of hydroxyapatite are precipitated.

This slightly turbid groundwater is immediately passed through the filter tank 9 at a rate of 20 times the capacity of the bone-charcoal bed 11 per hour.

In addition to this experimental example, as a comparative example, the above groundwater was added with the above chemicals and water was passed through it using sand, limestone, and anthracite as filtration layers. After passing the water to be treated for 24 hours, the water was taken from the outlet 13 of the filter tank 9, and the fluorine ions in this water were analyzed and compared. The results are as follows. It was as follows.

According to this result, except for the case of the present invention, the ability to remove fluoride ions from groundwater, which is the water to be treated, is weak, and even in the case of the bone and charcoal layer 11, this alone has a weak ability to remove fluoride ions.
After flowing the above groundwater for 24 hours, a considerable amount of fluoride ions remained, and only the method using bone char layer 11 using calcium dihydrogen phosphate and slaked lime according to the present invention showed remarkable ability to remove fluoride ions. ing.

Experimental Example 2 Surface water containing 1.2 ppm of fluorine ions (F-) (containing 0.3 ppm of iron) was used as the water to be treated, and 20 ppm of sodium dihydrogen phosphate and 30 ppm of slaked lime were added to the treated water.
are added respectively, and the atomic ratio of phosphorus and calcium is P/Ca=
As 3/9.4, hydroxyapatite was precipitated and immediately after stirring, the bone charcoal layer 11 was made into a furnace layer, and the capacity of the bone charcoal layer 11 was 200 liters, and the water flow rate was 4 m3/h (20 times the capacity of the bone charcoal layer).
An experiment was conducted using the same procedure as in Experimental Example 1 under the following conditions without adding sodium dihydrogen phosphate and slaked lime to the water to be treated.
The results of analyzing the fluorine ion content in the treated water were as shown in Figure 2.

In the case of this experimental example, the content of fluorine ions in the treated water was 0.1 ppm or less regardless of the length of water passage time.

It is clear that when sodium hydrogen phosphate and slaked lime are not added, the amount of fluorine ions in the treated water increases with the passage time.

In addition, in the present invention, the reason why the atomic ratio of P and Ca is set to 3:5 or less is to generate hydroxyapatite, and by using calcium slightly in excess of the predetermined amount, chemical equilibrium is advantageously brought about. It is possible to keep the pH on the alkaline side.

The pH is preferably 8-9.

When the pH is set to 8 or more, even when the water to be treated is passed through the bone-char bed at a relatively high superficial velocity of about 20 m3/m3 h, a sufficient reaction occurs to precipitate hydroxyapatite in the water to be treated. be able to.

Moreover, when the pH becomes 9 or more, the aggregation reaction takes precedence over the crystallization reaction of hydroxyapatite, and the crystallization reaction does not occur effectively.

Note that pH adjustment is not limited to using calcium hydroxide; soda ash or caustic soda may be used as long as the atomic ratio of phosphorus (P) and calcium (Ca) is satisfied.

In addition, phosphates can be of any type as long as they react with calcium hydroxide to produce hydroxyapatite crystals and colloidal particles, but phosphates with a good production rate of hydroxyapatite or Calcium dihydrogen phosphate, sodium dihydrogen phosphate, etc., which are relatively harmless to residual metal ions in the water to be treated, are preferred.

However, the present invention is not limited to these, and for example, various phosphoric acid compounds that produce hydroxyapatite in combination with a calcium compound can be used.

According to the present invention, phosphate and calcium hydroxide are added to the treated water containing a small amount of fluorine ions so that the atomic ratio is 3:5 or less, and the pH is adjusted to 8 to 9. Generates hydroxyapatite in the water to be treated,
By passing this treated water containing hydroxyapatite through the bone charcoal layer, hydroxyapatite is crystallized on the surface of the bone charcoal, and fluorine ions in the water to be treated are crystallized from the hydroxyapatite on the surface of the bone charcoal. The fluoride ions in the water to be treated are captured by ion exchange with crystals, and as the crystals grow, the capture of fluoride ions in the water to be treated progresses, making it possible to remove fluoride ions from the water to be treated, reducing the content of fluoride ions in the water to approximately zero. It can be reduced to .1 ppm or less.

Bone char is simply crystallized microcrystals of hydroxyapatite,
It functions as a carrier for growing these microcrystals into larger crystals, and once these crystals grow to a certain extent, they can be physically removed from the bone char particles by the water pressure of washing water, and fluoride Since the ions are trapped in the crystals by ion exchange of this hydroxyapatite, fluoride ions are also removed along with the crystal grains, so the bone char bed can be immediately regenerated and reused with a simple operation. Continuous operation of the device is possible, and unlike conventional bone charcoal methods, fluoride ions are strongly adsorbed to bone charcoal, making it difficult to desorb, causing many obstacles to regenerating bone charcoal, and making it uneconomical. This method provides an extremely superior method for removing fluorine ions in water, compared to methods that are inefficient and have concerns about their practicality.

In this way, water resources that are left unused because they contain fluorine ions can be used as drinking water, such as a tap water source, and the resources can be used effectively.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram of an embodiment of the method of the present invention, and FIG. 2 is a measurement diagram of an experimental example thereof. 11... Bone charcoal layer.

Claims (1)

[Claims] 1. Phosphate and calcium hydroxide are added to the water to be treated that contains a small amount of fluorine ions, and the atomic ratio of phosphorus (P) to calcium (Ca) including the calcium (Ca) contained in the water to be treated is 3: 5 or less, and further adjust the pH to 8.
9 to produce hydroxyapatite in the water to be treated, and after stirring, water is passed through the bone char layer to continuously accumulate and crystallize hydroxyapatite crystals on the bone char surface, and the crystallized hydroxyapatite is A method for removing fluorine ions in water, which is characterized in that fluoride ions in the water to be treated are captured by apatite through ion exchange, and fluoride ions in the water to be treated are continuously removed.