DE2637048A1 - METHOD OF REMOVING FLUORIONS FROM WATER - Google Patents

Description

KRAUS & WEISERT 2637Q48

FATE NATIONAL LAWYERS

DR. WALTER KRAUS DIPLOMA CHEMIST DR.-1NG. ANNEKÄTE WEISERT DlPL-INE. SPECIALIZATION CHEMISTRY IRMSARDSTRASSE 15 D-8OOO MUNICH 71 TELEPHONE 089 / 797077-79 7078 TELEX O5-212156 kpat d

TELEGRAM CRAUS PATENT

1336 AW / MY

KOHEI DEGÜCHI, Suita / Japan

Process for removing fluorine ions from water

The invention relates to a method of removal of fluorine from water, at danman aluminum ions in water ionized so that they form insoluble aluminum fluorides react with the fluorine ions. The aluminum fluorides can easily be removed from the water *

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The invention relates to a method for removing of fluorine from water and its conversion into drinking water.

For the removal of the fluorine content from waste water It is common to use calcium and form insoluble calcium fluorides, which usually form deposits drop. However, it has been found that using this method the residual water still contains 15 to 50 ppm fluorine. This level is too high for the water to flow into a river because of the risk of environmental pollution permit. More effective methods have therefore been proposed. One of these processes uses activated alumina used as an adsorbent, and in another process aluminum sulfate is used as an aggregating agent. However, these methods must use the Reagents are regenerated, which is labor and costly, and it is difficult to keep track of the quantities of these Control reagents. Therefore, these methods have not found wide use.

It is widely believed that the fluorine content in water is not a health hazard, it is serves as a prevention against dental caries. However, if the fluorine content is over 0.5 ppm, there is a risk that the tooth enamel will be damaged damaged. If it is above 0.8 ppm, the water is no longer suitable for drinking. So that water is drinkable is, the fluorine content must be kept below 0.8 ppm and preferably below 0.5 ppm.

In general, river water contains 1.0 to 2 ppm fluorine at the surface, and when subsurface pollution occurs, it will the undesired content is 3.0 to 10.0 ppm or even more be higher. In such cases, known methods such as precipitation, filtration, the pasteurization, etc. is insufficient, and accordingly the water cannot be used as drinking water will.

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The present invention is now based on the object of eliminating the disadvantages of the known methods and an improved method for removing fluorine from water using activated alumina.

The invention relates to a method for removal of fluorine from water, with aluminum sulfate or aluminum chloride and sodium aluminate in the water to be treated and the solution is stirred while the pH is adjusted to a value in the range of 6.6 to 6.9 will. The formed aluminum fluorides are then removed, and thereby the fluorine content becomes 5 ppm or less humiliated.

The invention also relates to a method for removing fluorine ions from water, which is characterized is that an aluminum anode is installed opposite a copper or iron cathode in the water to be treated, Direct current passed through to ionize the aluminum ions from the anode, aluminum sulfate or aluminum chloride and adding sodium aluminate to the water to be treated and stirring the solution while the pH is at a value is set in the range of 6.0 to 7.0. In the process, aluminum fluoride hydrates are formed, and the aluminum fluoride hydrates are adsorbed in flakes of aluminum hydroxides.

The invention also relates to a method for removing fluorine ions from water, which is characterized in that is to add polyaluminum chloride and sodium aluminate to the water to be treated, the solution while adjusts its pH to a value in the range from 6.5 to 6.8, stirs, 1 part polyaluminum chloride and 1/3 part sodium aluminate to form aluminum fluoride to the solution while maintaining the pH in the same range, wherein

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the aluminum fluoride is adsorbed in flakes of aluminum hydroxides will.

According to the invention, the fluorine content is effectively reduced to such an extent that the water is of drinking quality.

The invention is explained in more detail with reference to the accompanying drawings; show it:

Fig. 1 is a schematic view of a device, which is used for treating the water according to a first embodiment of the invention;

Fig. 2 is a graph showing the changes in pH values in the water to be treated are;

Figure 3 is a schematic view of an apparatus used in accordance with the second embodiment of the invention can be;

Fig. 4 is a schematic view of an apparatus used in accordance with the third embodiment of the invention can be.

In the first embodiment, the fluorine ions react with the aluminum ions obtained by ionizing an aluminum salt in the water to be treated, that comes from a river or from underground sewage or from sewage fields. Aluminum fluoride hydrates are thereby used formed, which are deposited in the water. The fluorine ions can do so. easily as aluminum fluoride hydrates or with the Aluminum fluoride hydrates are removed. Is preferred an aggregating agent of suitable molecular weight is used. To carry out this process, aluminum sulfate or aluminum chloride and sodium aluminate are added and mixed. The amount of aluminum ions that are released from the aluminum salt are given off as ions, the removal of the fluorine ions affects critically.

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As shown in FIG. 1, waste water 2 obtained from a factory is put in a 500 ml beaker 1. Above that, two burettes 3 and 4 are attached in a suitable manner; these contain aluminum chloride (or aluminum sulfate) and sodium aluminate. The pH value is determined with a pH meter 5. The water 2 in the beaker 1 is mixed with a stirrer 6, while the burettes 3 and 4 allow drop by drop of liquid to run in. With the pH meter 5, the pH values are checked so that they do not exceed a range from 6.6 to 6.9. For example, certain amounts of each liquid are added and mixed at the same time. If the pH value exceeds the stated value _s , the aluminum ions are less reactive and performance is reduced.

Table I lists the values for comparison which are obtained in this test for various samples. In Fig. 2, curves of each of these samples are plotted for pH changes specified.

Tabel,! ,,

Sample (A) (B) Order of aggregate- F "

No. aluminum sodium d. Addition medium hal-

chloride (ppm) aluminate (ppm) th.

- (ppm) pH

1 100

2 100

3 100

4 100

5 '100

Each sample is received and owned from the same factory a pH of 6.76 and a fluorine ion content of 26.1 ppm;

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210 first
Secondly (B) 5 6.90 10.20 210 first
Secondly f ) 5 6.82 8.50 210 first
Secondly
then 1/2 tr 5 6.77 8.80 210 (A) Sc (B)
in time same- 5 6.88 5.10 210 dito 5 6.79 4.60

⁺⁺ F ~ means the remaining fluorine ions, expressed as ppm ..

Add liquids (A) and (B) to the samples as described above while checking their pH value, it is preferred that the dose of each reagent according to the pH, acidity and alkalinity of the water to be treated is varied. In the present invention, the appropriate dose depending on the desired pH value determined »

In the second preferred embodiment shown in FIG. 3, water 12 to be treated is contained in a 500 ml beaker 11. The anode 13 made of aluminum and the cathode made of copper (or iron) are located in this beaker 11. A voltage of 5 to 10 V is applied across the electrodes so that a 30 mA direct current is obtained. As a result, hydrogen gas is generated from the cathode 14 and aluminum ions are ionized at the anode 13 while a small amount of oxygen gas is generated. At this point the pH of the water is adjusted and maintained to be in the range of 6.0 to 7.0. In this area the aluminum ions are reactive and aluminum fluoride hydrates are easily formed by chemical reaction with the fluorine ions. The aluminum fluoride hydrates are insoluble in water and disperse in the form of a colloid that is adsorbed by aluminum hydroxides, which are also formed from the aluminum ions. By removing the aluminum hydroxides from the water, the fluorine ions contained therein are removed at the same time. In this way, as indicated in Table II, 60 to 90% of the fluorine ions are removed. In order to have an excessive amount of aluminum ions _t compared with the fluorine ions, aluminum sulfate or aluminum chloride and sodium aluminate are previously added in amounts of 30 to 200 ppm to such an extent that the pH of the drinking water is between 6.0 and 7.0 . Usually increases

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the pH as the electrolysis progresses, and accordingly aluminum sulfate or aluminum chloride are added to adjust the pH, so that the process proceeds with high performance and yield. This also reduces the amount of aluminum ions that are ionized at the anode, reduced. However, the added aluminum ions are less active and only react with a small part of the Fluorine ions.

For comparison, Table III lists values which obtained in experiments in which an anode made of aluminum or carbon is used together with a cathode made of copper will. These experiments show that aluminum ions ionized from the anode are more effective than those derived from an added aluminum compound.

Table II

Sample " ¹ " F "(ppm) Agents added Auxiliary agent " ¹ " ¹ "

No. before after the aluminum (bentonite) treatment, sulphate aluminate

(ppm) (ppm) (ppm)

11 26.1 9.6 -

12 26.1 6.8 200 + 50 30

13 26.1 2.9 200 + 50 30 100

14 2.88 1.21

15 2.88 0.66 50 + 20 10

16 2.88 0.28 50 + 20 10 50

Sample Nos. 11 to 13 are from the same Factory and samples 14 to 16 come from the same well and are considered drinking water. For samples 13 to 16, the treatment was carried out for 2 hours, for the others only 1h.

⁺⁺ The aid is used to facilitate the aggregation of aluminum hydroxides; this increases their adsorption effect for the adsorption of aluminum fluoride hydrates

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improved The removal of the fluorine ions is thus carried out in an effective manner * Alternatively, kieselguhr can be used.

Table III

Sample F ".CRP.nÜ Material Aluminum- Sodium- Calcium-

Nr = before "after Her d.Anode ⁺⁺ sulfate aluminate carbonate

Treatment (ppm) (ppm) (ppm)

17 20 _s 0 7 ₉ 0 aluminum - -

18 2OpO 10.4 carbon 200 +50 .20 -

19 20.0 17.8 »-

20 2 * 0 0.62 aluminum 50 + 20 8

21 2.0 1 _S 78 carbon - -

22 2.0 1.94 η - -

⁺ Each sample is prepared by adding sodium fluoride according to its equivalent weight to purified

Add water j

The cathode is made of copper.

Samples 17-19 are electrolyzed with a 50 mA current for 50 minutes, and Samples 20-22 become Electrolyzed with a 20 mA current for 2 h.

The dissociation of aluminum ions from the anode can be controlled by adjusting the current flow, which for example, is done by rotating a knob. This prevents electricity from being lost, and this leads to an increased economy of the treatment process. Since it is not necessary to add calcium, there is no risk of deposits on the cathode are formed. The aluminum ions ionized at the anode are active enough that they combine with hydroxyl groups, and thereby the formation of aluminum hydroxides is favored, which, as described above, the fluorine ions of the Adsorb water.

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In Fig. 4, the third preferred embodiment is shown in more detail. The water to be treated flows into one Tank 22 via an inlet passage 21, where the water with stirrers with the addition of polyaluminum chloride and sodium aluminates, which are supplied from the corresponding containers 24, is stirred. The fluorine ions in the water combine with the aluminum ions that are added by ionization of the Reagents are formed and aluminum fluorides are formed in the colloidal state. The aluminum ions will mainly consumed for the formation of aluminum hydroxides, and accordingly it is necessary that the aluminum ions are present in excess so that a sufficient amount is available for the fluorine ions. the colloidal aluminum fluorides are adsorbed by the aluminum hydroxides existing around the former, and the adsorbed material is left to stand in the settling tank 23. This way the fluorine content in the water is related removed with a sludge taken from the settling tank.

Table IV shows the values obtained using the apparatus described above. As shown in FIG. 4, the treatment is in three process stages distributed. These procedural steps are called Stage in the first chamber, the second chamber and the third chamber designated.

In the first chamber are given amounts of polyaluminum chloride and sodium aluminate simultaneously poured into the water to be treated. Its pH will be up to 6.5 6.8 set. While water from the first chamber is in the third chamber running over the second chamber will be polyaluminium chloride and sodium aluminate were added in amounts of 3 parts to 1 part while maintaining the pH at 6.5 to 6.8 will. In this way one achieves that the water is tri akbar.

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to

Table IV

Sample " ¹ " Agent added First chamber Second chamber Third chamber Treated

No. Amount pH Amount pH Amount pH water

(ppm) (ppm) (ppm) pH F-

31 polyaluminum chloride 200 cn 50 / ■ Cr ₇ 50 c _7n cr? O sodium aluminate 50 ^{6 '60} 15 ⁶ ' ⁶⁷ 15 ^{6 '70 6} ' ⁷⁸

32 Polyalijminiumchlorid 200 r _Λη 100 _{A 7} «100 / - _{Ax A} Sodium aluminate 50 ^{6 '60} 30 ⁶ » ⁷² 35 ⁶ ' ^{63 6}

33 polyaluminum chloride 300 _{u 14} 100 5 21 ¹⁰ ° 6 55 6 ^ sodium aluminate 0 ⁴ » ¹⁴ 50 ⁵ ^ ¹ 100. ⁰ ^ ^b * ο

CD

- »The samples obtained are surface water from a river with a pH of

Z ^ 7.86 and a fluorine ion content of 1.23 ppm. '^ ο ο

K) CO

~ -J CD

26370Λ8

It is known to use polyaluminum chloride as an aggregating agent to use. To remove the fluorine, however, it is necessary to adjust the concentrations of aluminum ions in the to increase treating fluid. If fluorine ions are only removed using polyaluminum chloride (cf. Sample No. 33 in Table IV, column for the first chamber), thus, even with an increased amount of polyaluminum chloride, the pH lowers and is not within the required range from 6.5 to 6.8. This will make the subsequent treatments, in the second and third chambers adversely affected, and the. obtained for the fluorine standard value Border is not safe enough for drinking water.

Table V shows the values obtained from tests on two types of samples. No. 34 is out obtained from a deep well, and No. 35 is from underground water; both samples have a pH of 7 »52 and a fluorine content of 4.40 ppm.

During the treatment of sample 34, the pH is maintained in the range of 6.5 to 6.8, which is ₉ as mentioned above, so that the aluminum ions are uniformly reactive. In contrast, the pH of sample 35 is not controlled and it rises above the desired limit. This sample is therefore not suitable as drinking water.

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Table V

Sample Agent Added First Chamber Second Chamber Third Chamber Treated Water

No. Amount pH Amount pH Amount pH pH. P "

(ppm) (ppm) (ppm)

34 polyaluminum 600 r _{Λ (-} 100 Cr 100 ₇ * c cc c ,, c _{n ΛΛ} sodium 180 ^{6 '65} 30 ^{6' 71} 30 6.66 6.81 0.46

35 Polyaluminium Chloride 300 _{7 R} o 30 ₇ ca 30 "__" _ _n Sodium aluminate 120 " ^öö 10 ^» ^öb 10 "^ ^ ⁸⁰ 2.26

O CO OO

O CO

IV) I

cn

CO O

CO

Claims (3)

Claims 1. Process for removing fluorine ions from water, characterized in that one (a) aluminum sulfate or aluminum chloride and sodium aluminate to the water to be treated; (b) stir the solution and adjust its pH to a value in the range of 6.6 to 6.9; (c) the aluminum ions and the fluorine ions in the water with each other to form aluminum fluoride which is insoluble in the water lets react; '· .._ (d) removing the aluminum fluoride from the water. 2. Process for removing fluorine ions from water, characterized in that one (a) placing an anode made of aluminum opposite to a cathode made of iron or copper in the water to be treated; Cb) Direct current through the electrodes for ionization conducts of aluminum ions from the anode; Cq) aluminum sulfate or aluminum chloride and sodium aluminate adding to the water to be treated and stirring the solution; (d) adjusting the pH of the solution to a value in the range of 6.0 to 7.0; (e) allowing aluminum ions and fluorine ions in the water to react with one another to form aluminum fluorides; (f) Aluminum fluoride on flakes of aluminum hydroxides lets adsorb; (g) the flakes of aluminum hydroxide which the adsorbed Containing aluminum fluoride hydrates are removed. 3. A method for removing fluorine ions from water, characterized in that one 70 98 11/094 7 (a) polyaluminum chloride and sodium aluminate to the · adding water to be treated; (b) stir the solution to adjust its pH to a value in the range 6.5 to 6.8; (c) Add 1 part polyaluminum chloride and 1/3 part sodium aluminate to the solution while adjusting the pH in the specified range holds j (d) Aluminum ions and fluorine ions with each other in the allowed to react water to be treated to form aluminum fluoride; (e) the aluminum fluoride adsorbs onto flakes of aluminum hydroxide; (f) the aluminum hydroxide flakes present as sludge removed, the flakes of aluminum hydroxides containing the fluorine ions adsorbed. 70981 1/0947