Process for Utilizing the Silicic Fluoride Obtained by the Treatment of Certain Phosphates with Sulphuric Acid.
Year: 1890

page_text: Date of Application, 29th Sept., 1890
Complete Specification Left, 23rd June, 1891-Accepted, 8th Aug., 1891
PROVISIONAL SPECIFICATION.
Process for Utilizing the Silicic Fluoride Obtained by the Treatment
of Certain Phosphates with Sulphuric Acid.
I, ENGELBERT RICHTERS, Doctor of Philosophy, of Saarau, Silesia, in the
German Empire, do hereby declare the nature this invention to be
follows:-
If phosphates containing fluorine are rendered assimilable by means of sulphuric
acid, gaseous fluoride of silicon is produced, as is well known, and a portion of this
fluoride is decomposed by the water of the sulphuric acid, already during the said
process, so as to form silicic acid and fluosilicic acid, according to the following
equation:
follows:-
αν
трис
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If phosphates containing fluorine are rendered assimilable by means of sulphuric
acid, gaseous fluoride of silicon is produced, as is well known, and a portion of this
fluoride is decomposed by the water of the sulphuric acid, already during the said
process, so as to form silicic acid and fluosilicic acid, according to the following
equation:
3 Si F, 4 H₂O
4
-
2 Si F, H, H. Si O..
2
4
Hitherto these fluorides have been useless by-products, and it is the object of the
present invention, to utilise these by-products for the production of a double
Hluoride of alkali and aluminium, which, as shown by experiments, is a complete
substitute for natural cryolite in the manufacture of opaque or enamelled glass, or
of enamel.
The gases which are evolved during the treatment of the phosphate with
sulphuric acid, are conducted through receivers in which they are condensed.
These receivers may be made of any suitable material not liable to corrosion by
fluo-silicic acid, for instance of wood or of stone-ware, and may be similar to
the appliances used for the condensation of hydro-chloric acid (so-called tourilles,
or towers formed of wood or of stone-ware). If the gases contain silicon fluoride
besides fluosilicic acid, water or steam is introduced into the receiver, in order
to decompose the said fluoride. Otherwise, it is sufficient to cool the gases for the
purpose of condensing the fluosilicic acid.
Silicic acid containing fluosilicic acid collects in the receiver and is treated with
water, thereby forming a solution of fluosilicic acid which is separated from
the silicic acid by one of the known methods (decanting, treatment with wooden
filter presses etc.).
The solution of fluosilicic acid thus obtained, preferably in a strength of
12 to 15 per cent. by volume, is treated with alumina hydrate and caustic alkalies
or alkali carbonate in the manner represented by the following equation:

page_text: dilute liquid containing carbonic acid, and the cryolite compound forms a precipitate
free from silicic acid.
Dated this 27th day of September 1890.
ENGELBERT RICHTERS.
By Fairfax & Wetter,
433, Strand, London, Agents for the Applicant.
to the following equation:
3 Si F, 4 H, O = 2 Si F, H₂ + H. Si O.
6
2
Hitherto these fluorides have been useless by-products, and it is the object of the
present invention, to utilise the said by-products for the production of a double
Aluoride of alkali and aluminium, which, as shown by many experiments, is a
complete substitute for natural cryolite in the manufacture of opaque or enamelled
glass, or of enamel.
The gases evolved during the treatment of the phosphate with sulphuric acid,
are conducted through receivers, in which they are condensed. These receivers
may be made of any suitable material not liable to corrosion by fluosilicic acid, for
instance of wood or of stone-ware, and may be similar in construction to the
appliances used for the condensation of hydrochloric acid (so-called tourilles, or
towers formed of wood or of stoneware). If the gases contain silicic fluoride,
besides fluosilicic acid, which depends chiefly on the strength of the sulphuric acid
employed, water or steam is introduced into the receiver, in order to decompose the
said fluoride. Otherwise, it is sufficient, to simply cool the gases for the purpose
of coudensing the fluosilicic acid.
Silicic acid containing fluosilicic acid collects in the receiver and is treated with
water, thereby forming a solution of fluosilicic acid, which is separated from the
silicic acid by one of the known methods (decanting, treatment with wooden filter-
presses etc.).
The solution of fluosilicic acid thus obtained, preferably in a strength of
12 to 15 per cent. by volume, is treated with alumina hydrate and caustic alkalies
or alkali carbonate in the manner represented by the following equation :
The product is a mixture of silicic acid and a double fluoride of alkali and
aluminium, which corresponds to cryolite as regards its composition.
It is advantageous to employ the fluosilicic acid, the alumina and the alkali in
proportions corresponding to the above formula, but by varying the said proportions,
it is possible, to produce compounds richer or poorer in alumina or in alkali, in all
cases however a double fluoride of alkali and of aluminium is obtained.
The product obtained as described, may be advantageously employed in the
manufacture of opaque and enamelled glass or of enamel, for which purposes it

page_text: completely replaces the natural cryolite, owing to its high percentage (about
70 per cent.) of artificial double fluoride of alkali and aluminium.
The cryolite compound may also be obtained free from silicic acid, by using
alumina and alkali in the shape of a dilute solution of alkali-aluminate, which
should not contain more than 25 to 30 grammes of alumina in a litre of the solution,
and at the same time some alkali-carbonate. If such a solution is decomposed by
means of fluosilicic acid, the whole of the silicic acid remains in the dilute liquid
containing carbonic acid, and the cryolite compound forms a precipitate free from
silicic acid, which precipitate may be easily separated from the liquid by filter-
presses or other means.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare, that what I
claim is;
1. The utilization of the silicic fluoride obtained in the treatment of certain
phosphates with acid, which consists in producing with the silicic fluoride a solution
of fluosilicic acid by means of water, and treating the said solution with alumina
hydrate and caustic alkali or alkali carbonate, in order to obtain a mixture of
artificial cryolite and silicic acid, or artificial cryolite free from silica, substantially
as described.
Dated this 20th day of June 1891
E. RICHTERS.
By Fairfax & Wetter,
433, Strand, London, Agents.