From Big Medical Encyclopedia

DEFLUORINATION OF WATER — decrease in content of fluorine in water. Of century carry out in cases when natural waters or in drains of the industrial enterprises contaminating water sources contain the increased amount of fluorine.

Of century 20 century when data that fluorine at excess receipt in an organism can be the cause patol, processes (see appeared acquired big relevance from 30th. Fluorosis ).

In practice it is necessary to meet need of defluorination more often drain waters (see), but sometimes there is a need for D. of century and natural sources.

Defluorination of drain waters

Drain waters of glass, cryolite, superphosphate and other productions may contain a significant amount of various fluorochemicals, napr, sodium fluosilicate, fluorsilicate calcium, hydrofluoric and hydrofluosilicic to - you. Because zhidkostnofazny waste contains also significant amount of suspended matters and other chemical connections, the general scheme of cleaning of such drains provides their neutralization, sedimentation of fluorine, upholding.

A little tekhnol is developed. schemes and ways of defluorination of drain waters. One of the most widespread ways of neutralization of drains — processing by their agstone and lime milk. Drain waters come to contact tanks where the agstone and lime milk moves. In the beginning there is a neutralization present at drains salt to - you lime milk:

2HCl+CaCO 3 = CaCl 2 + H 2 O + CO 2 .

Then sodium fluosilicate is formed:

H 2 SiF 6 + 2NaCl = Na 2 SiF 6 + 2HCl

(NaCl usually is present at drain waters of these productions). Further fluorine by means of lime milk is emitted from fluorsilicate salts:

Na 2 SiF 6 + 3Ca (OH) 2 = 3CaF 2 + SiO 2 + 2NaOH + 2H 2 O,

CaSiF 6 + 2Ca (OH) 2 = 3CaF 2 + SiO 2 + 2H 2 O.

After completion of these reactions waste liquid is pumped over in an osadkonakopitel where CaF 2 and other insoluble impurity drop out in a deposit.

Release of water from fluorochemicals by filtering of drain waters through a layer of the shattered limestone shell rock or method of their electrochemical processing is possible.

Defluorination of drinking waters

Defluorination of drinking waters is made by reagent and filtrational methods. The principle of reagent methods consists in formation of almost insoluble compounds of fluorine which in the subsequent are removed in a deposit.

Processing of water salts of aluminum is most rational (aluminum sulfate, sodium aluminate, alumina, etc.). The compounds of aluminum which are widely applied to coagulating of water form the aluminum hydroxide having well-marked sorption properties in water solution. Process of removal from solutions of compounds of fluorine is based on it. It is possible to apply two to an intensification of process of defluorination - and even three-phase processing of water salts of aluminum. In this case enter into water at first a smaller part of aluminum sulfate and lime. At the same time in water the set of fine particles of the occluding reagent deleting a part of fluorine from solution forms. Then the suspension is filtered, and add the new dose of reagents giving the chance to reduce the content of fluorine to 1 mg/l to a filtrate. Such method is especially shown at low water temperatures when coagulating is connected with great difficulties.

For loading of filters at D. century by a filtrational method it is possible to use the activated alumina, the granulated tricalcium phosphate crushed and the burned bone, ion-exchange resins. Use of the activated alumina is the most effective.

It is possible to apply also other methods, in particular a method of natural freezing of water. It is established that the content of fluorine in a melt water decreases by 10 — 45 times. This decrease in concentration of fluorine is most expressed at a mineralization of the initial water which is not exceeding 500 mg/l. Natural winterizing as the simplest and available method D. of century for the decentralized water supply is recommended in the 1,2 and 3 climatic zones of the USSR.

Process of defluorination of drinking waters is controlled a dignity. bodies. During control the size of residual concentration of fluorine is defined. In process a dignity. supervision of operation of installations for D. century control reagents which shall not support strangers of toxic impurity, check a duty of installations, investigate the conditioned water.

See also Water , Water treatment , Fluoration of water .

Bibliography: Aglitsky S. S., Hait K. B. and Lyashchev K. V. Drain waters of superphosphate production and a condition of their descent in a reservoir, in book: Vopr, improvements of superphosphate production, under the editorship of I. Ya. Deyneki, page 52, Odessa, 1961; B of e d N about in and I. N., Sh at - a bin. Page irivkinde. The item Elektroio-nitnaya sewage treatment from compounds of fluorine, in book: A fluorosis and its prevention, under the editorship of S. V. Miller and M. S. Sadi-lova, page 216, M., 1967; Gabovichr., Nikoladze G. I. and Savelyeva N. P. Fluoration and defluorination of drinking water, M., 1968, bibliogr.; M e y N to F., Sh t about f f G. and Kolshyutter of. Purification of industrial sewage, the lane with it., L., 1963; The Guide to hygiene of water supply, under the editorship of S. N. Cherkinsky, page 186, M., 1975, bibliogr.

I. I. Belyaev.