Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iva metal
Patent
1999-09-16
2000-11-21
Griffin, Steven P.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iva metal
423240R, C01G 1700, C01G 1704, C22B 4100
Patent
active
06149884&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of treating gaseous waste containing germanium and coming from a unit for manufacturing an optical fiber preform.
In conventional manner, a unit for manufacturing an optical fiber preform causes gases of the silicon chloride SiCl.sub.4 and germanium tetrachloride GeCl.sub.4 type to react with oxygen at high temperature. The resulting silicon oxide SiO.sub.2 is deposited in successive layers to form a cylindrical preform. Germanium oxide is deposited in the central layers of the preform so as to form a core that has a refractive index different from that of the silica.
Only a small fraction of the germanium tetrachloride reacts with oxygen. The germanium tetrachloride that has not reacted, and the germanium oxide that is not deposited, are discharged by the manufacturing unit together with hydrogen chloride HCl. These gases cannot be discharged as such into the environment. That is why it is necessary to treat them.
Furthermore, it is also desirable to recover the germanium, not only to preserve environment, but also to recycle the germanium for subsequent reuse in the manufacture of optical fiber preforms so as to reduce manufacturing costs.
A method known from document U.S. Pat. No. 4,385,915 serves to treat such gaseous waste and to recover the germanium. It comprises the following steps in particular: gaseous waste to react with caustic soda; the liquid effluent then contains not only germanium, but also hypochlorite; adding magnesium sulfate.
The precipitation of the germanium contained in the effluent by means of the magnesium sulfate releases sulfates in the supernatant phase, which sulfates are compounds that are harmful to the environment.
SUMMARY OF THE INVENTION
The object of the present invention is thus to develop a method of processing germanium-containing gaseous waste, whereby, after precipitation, the release of environmentally-harmful compounds is avoided.
To this end, the invention provides a method of treating gaseous waste containing germanium and coming from a unit for manufacturing an optical fiber preform, the method comprising the following steps: adding magnesia MgO to said liquid effluent.
The addition of magnesia makes it possible to cause the germanium contained in the effluent to be precipitated so that it can be recovered for recycling purposes, without releasing environmentally-harmful compounds such as sulfates.
The germanium precipitates in the form of germanates. The quantity of magnesia introduced into the effluent corresponds to a stoichiometric ratio of magnesium to germanium that is typically 1.5 to 1, and gives rise to low magnesia consumption for precipitating the germanium.
In an aspect of the invention, the gaseous waste contains germanium in the form of germanium tetrachloride GeCl.sub.4 and the step of forming a liquid effluent consists in causing caustic soda to react with said gaseous waste so that the liquid effluent contains germanium and hypochlorite.
In order to reduce the hypochlorite, it is possible to use formic acid, for example.
By way of example, the magnesia used can be nonpurified and in the form of a powder. It is introduced into the effluent in a proportion such that it raises its pH to a value lying in the range 8 to 10 so that the germanium precipitates in the effluent. Provision is made to treat the effluent without prior addition of caustic soda, its pH being about 4, or to treat it after caustic soda has been added to raise its pH to about 7. In the first case, the possibility of working in an acid medium makes it possible to reduce the consumption of caustic soda.
By a buffer effect of the magnesia, the supernatant phase of the effluent after the germanium has been precipitated is at substantially the same pH, equal to 9.5, as that obtained at the beginning of precipitation. Where necessary, an acid is added to reduce this pH value to a value that is acceptable for discharging the surface matter into the environment.
The precipitate is in the form of a sludge containing the ge
REFERENCES:
patent: 4385915 (1983-05-01), Amelse et al.
patent: 4578253 (1986-03-01), Gill et al.
patent: 6054104 (2000-04-01), Lankewicz et al.
Appriou Andre
Calvo Laurent
Lavanant Gerard
Alcatel
Griffin Steven P.
Ildebrando Christina
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