Improved Process for Extracting Iodine from Natural Saline Waters, Mother Liquors, or other Liquids Containing Iodine.
Year: 1892

page_text: Date of Application, 22nd Sept., 1892-Accepted, 29th Oct., 1892
COMPLETE SPECIFICATION.
Improved Process for Extracting Iodine from Natural Saline Waters,
Mother Liquors, or other Liquids Containing Iodine.
A communication by RAFFAELLO CAMPANI, of Pisa, in the Kingdom of Italy,
Professor.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6, Bank Street,
Manchester, both in the County of Lancaster and 323 High Holborn, in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
The process forming the object of this invention, which is an extremely simple
one and is very easily put in practice, may be directly employed for natural waters,
or other liquids, without concentrating them, even if but a very small quantity of
iodine be contained therein.
Gaseous chlorine, or an oxidising substance, such as nitric acid, hyponitrite, that
is to say combinations with nitric peroxide, permanganate of potash, hypochlorite
of lime, hypochlorite of soda, etcetera, etcetera, or even electricity, may be caused to
act directly, in large wooden vats or basins containing saline iodine water, to
which starch paste, prepared at a temperature of 70 degrees centigrade, has been
added.
Of all the substances hereinbefore enumerated, chlorine would be the most
suitable and the most economical; but, by reason of its deleterious action on the
respiratory organs, and the complicated apparatus necessary for obtaining it, and
its unpleasant smell, it is preferable to substitute for it a concentrated solution of
hypochlorite of lime (the commercial chloride of lime) which, by its double action,
chloridising and oxidising, serves very well for the purpose, whilst being quite as
economical as chlorine.
When the quantity of hypochlorite necessary for precipitating all the iodine
contained in the water in the form of iodide of amylum, has been added, the
whole is allowed to stand for about 10 hours, and the clear liquid is separated, by
decantation, from the deposit of iodide of amylum which is found at the bottom
of the vat. This deposit is then placed on a filter of more or less coarse cloth,
or preferably it is filtered by means of a filter press. The clear liquid decanted
off, which contains all the mineralising properties of the water, with the exception
of the iodine, may always be used for extracting sea salt, bromine, and other
chemical products therefrom. The precipitate of iodide of amylum, which has
been collected on the filter, is then placed in a vat containing pure water, where
it is washed by agitation, and it is afterwards subjected to a current of sulphurous
anhydride (obtained by the combustion of sulphur, pyrites, or the like) until the
iodide of amylum commences to be discoloured, being thus converted into hydriodic
acid which remains in solution, and into amylum which remains in an insoluble
condition. The whole is then allowed to stand about 10 hours, the liquid is
afterwards decanted off, and the deposit of amylum, which is collected on the
filter after washing, is steeped in water in order to convert it into amylum paste.
This paste may be employed again, almost without loss, in another subsequent
operation in order to precipitate the iodine contained in a similar quantity of
saline water. The water used in washing the amylum, when collected, is utilised
for other successive operations in place of the pure water employed in the first
operation of treating the iodide of amylum with sulphurous anhydride.
The liquid separated by decantation from the precipitate of amylum, which
contains hydriodic acid mixed with a little sulphuric acid, is neutralised by means

page_text: of carbonate of soda. The resulting solution, which contains iodide of sodium
with a little sulphate, being sufficiently concentrated, may be employed in this state
for preparing iodoform by the acetone process, or better still by treating it with a
mixture of 30 parts of bichromate of potash, 100 parts of water and 100 parts of
sulphuric acid of 66 degrees Beaumé, it speedily yields a precipitate of perfectly
pure iodine.
In place of employing sulphurous anhydride for treating iodide of amylum,
a saturated solution of sulphate of soda may be employed for this purpose, which,
at an ordinary temperature, quickly transforms iodide of amylum into soluble
iodide of sodium, and into amylum which remains in an insoluble condition, without
being in any way changed.
Instead of employing chlorine and the other above named oxidising substances
to precipitate the iodine from the iodide of sodium, it has been found preferable, as
well as simpler, and more hygienic, to employ a mixture of bichromate of potash
and sulphuric acid in the proportions herein before stated, because this mixture
completely precipitates the iodine in the solution of iodide of sodium, without
producing the inconveniences of the other oxidising agents.
The iodine, which is obtained as a precipitate by the method hereinbefore
described, after having been collected in funnels, and washed, and dried in the
ordinary manner, may be dealt with commercially in this condition, or it may be
sublimated at a very small expense.
The water used in washing the iodine is conveyed to the vats which contain the
natural water or other iodine liquid, which are to be treated by means of amylum
paste, etcetera.
By the process hercinbefore described, chemically pure iodine is obtained, and
without being sublimated it may be economically employed in the preparation of
its various compositions.
This process may be economically and industrially employed for the extraction
of iodine, not only from the mother liquors of the ashes of seaweed, but also from
the washings of kelp, and the mother liquors resulting from the refining of nitrate
of soda, and other residues containing iodine from various industrial processes.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is :-
An improved process for extracting iodine, which consists in treating saline
iodine waters, by means of amylum and hypochlorite of lime, and converting the
iodide of amylum, thus obtained, into hydriodic acid by means of sulphurous
anhydride and afterwards converting the hydriodic acid into iodide of sodium by
means of carbonate of soda, and finally in precipitating the pure iodine by treating
the iodide of sodium with a mixture of 30 parts of bichromate of potassium,
100 parts of water, and 100 parts of sulphuric acid of 66 degrees Beaumé,
substantially as described.
Dated this 21st day of September 1892.
WM. P. THOMPSON & Co.,
Agents for the Applicant.