AN IMPROVED METHOD OF TREATING SPENT MATERIALS FROM THE GAS WORKS BY RECOVERY OF SULPHUR
Year: 1876

page_text: LETTERS PATENT to Frank Wirth, of the Firm of Wirth & Co., Patent Agency,
of Frankfort-on-the-Maine, in the Empire of Germany, for the Invention of
ss
AN IMPROVED METHOD OF TREATING SPENT MATERIALS FROM THE GAS
WORKS BY RECOVERY OF SULPHUR." A communication from Gustav Theodor
Gerlach, Doctor of Philosophy, residing at Kalk, near Cologne (Germany).
PROVISIONAL SPECIFICATION left by the said Frank Wirth at the Office
of the Commissioners of Patents on the 26th September 1876.
FRANK WIRTH, of the Firm of Wirth & Co., Patent Agency, of Frankfort-on-the-
Maine, in the Empire of Germany. "AN IMPROVED METHOD OF TREATING SPENT
MATERIALS FROM THE GAS WORKS BY RECOVERY OF SULPHUR." A communication.
The spent compounds of iron which have been used in the purification of
illuminating gas contain often 40 per cent. and more of precipitated sulphur. This
sulphur has heretofore been employed for the manufacture of sulphuric acid by
burning the same directly to sulphurous acid, and the same has been extracted from
this spent oxide by means of carbon bisulphide, and by distilling off the latter and
recovering the sulphur itself.
My method of recovering the sulphur consists in heating this spent oxide in
retorts of iron or clay (for instance, retorts which are used in the manufacture of
illuminating gas) and in distilling off this sulphur, while at the same time super-
heated steam is introduced.
Without employing superheated steam the vapors of the sulphur evaporate slowly,
whilst by employing superheated steam the distillation of the sulphur is quick, and
the sulphur evaporates very easily.
My improved method of heating the spent oxide of iron by the recovery of
Prussian blue or prussiate of potash and sulphur is as follows:-
First. The humid material is ground in a mill to form a fine mass.
Second. This mass is then lixiviated by means of water. If the mass contains
ammonia or in a free state the lye can if it is necessary be neutralized by an acid.
By this lixiviation the soluble ammoniacal salts are obtained which are by evapora-

page_text: tion crystallized or employed in the usual manner by any suitable copper salt for
the precipitation of sulpho-cyanite of copper or distilled with lime to obtain volatile
ammonia.
Third. Water is again poured on the lixiviated mass and simultaneously caustic
soda in a quantity of about 5 to 6 per cent. of the weight of the original masses is
added; or a diluted solution of caustic soda or a solution of carbonate of soda is
added to the mass. Already by the cold digestion with such alkalies or with lime
the insoluble prussiates are converted into soluble prussiates. The clear liquid is
drawn off and treated with an acid till the same is neutralized or shows a weak acid
reaction. The weak acidified liquid is soon clouded by precipitated prussiates and
sulphur. This dirty green precipitate might afterwards injure the beautiful clear
color of the Prussian blue, and is therefore carefully removed. The clear solution,
which if necessary is filtered, is then acidified and treated by a solution of per-
chloride of iron or by a small surplus of any other soluble salt of oxide of iron, such
as sesqui-chloride of iron. I thus obtain Prussian blue, which in consequence of its
purity has a dark blue color and when dried shows a copper lustre on its fractures.
I employ this product as Prussian blue itself or couvert the same into prussiate of
potash. For the latter purpose I employ not only the pure Prussian blue but
also the prussiates which have been precipitated by the neutralisation of the
alkaline lye.
For the manufacture of prussiate of potash the spent oxide has hitherto been
treated directly by caustic or carbonic potash, and the lye evaporated or the lime
containing extract of the spent oxide treated with carbonate of potash, and after
filtering off the carbonate of lime the lye has been evaporated. In both cases great
masses of diluted lye' have to be treated, and there is danger of producing a
decomposition of the prussiate of potash. Consequently I prefer to precipitate the
acidified solution by a salt of oxide of iron (sesqui-chloride of iron) to wash out the
Prussian blue and to obtain by this washed Prussian blue the yellow prussiate of
potash. For this purpose I treat the Prussian blue directly by carbonate of potash,
or I heat the same together with carbonate of lime in order to be sure to obtain a
neutral solution. The prussiate of calcium is then carefully precipitated by car-
bonate of potash filtered and the concentrated solution is by a slow heat evaporated
until the same crystallizes.
Fourth. The spent oxide of iron lixiviated in this manner contains a great
quantity of sulphur in a free state. The mass is dried and then as above described
distilled for recovering the sulphur. During this distillation superheated steam is
lead over the heated mass, by which means the sulphur to be recovered is in a very
short time distilled off and recovered. My process distinguishes itself from those
heretofore used, as I do not employ any solvent (carbon bisulphide) for the sulphur
but distil off the sulphur together with steam. In the same manner the sulphur is
recovered from the gas lime, if lime in lieu of oxide of iron is used for desulphu-
rating the illuminating gas.
The lixiviated and desulphurated mass is heated whilst air is admitted and
the product is a beautiful brown colour caput mortuum which can be employed as
a paint.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Frank Wirth in the Great Seal Patent Office on the 22nd March
1877.
"
A com-
FRANK WIRTH, of the Firm of Wirth and Company, Patent Agency, of Frankfort-
on-the-Maine, in the Empire of Germany. AN IMPROVED METHOD OF TREATING
SPENT MATERIALS FROM THE GAS WORKS BY RECOVERY OF SULPHUR."
munication from Gustav Theodor Gerlach, Doctor of Philosophy, residing at Kalk,
near Cologne (Germany).

page_text: The spent compounds of iron which have been used in the purifycation of
illuminating gas contain often 40 per cent. and more of precipitated sulphur. This
sulphur has heretofore been employed for the manufacture of sulphuric acid by
burning the same directly to sulphurous acid, or the same has been extracted from
this spent oxide by means of carbon bisulphide or by other solvents, and by distil-
ling off the latter and recovering the sulphur itself.
My method of recovering the sulphur consists in heating this spent oxide in
retorts of iron or clay (for instance, retorts which are used by the manufacture of
illuminating gas) or in suitably constructed ovens of brickwork. At the same time
when the sulphur begins to distil superheated steam is introduced.
Without employing superheated steam the vapours of the sulphur evaporate
slowly, whilst by employing superheated steam the distillation of the sulphur is
quick, and the sulphur evaporates very easily. Whilst in closed steam boilers the
steam pressure is augmented in the same proportions as the temperature is raised;
superheated steam can be furnished of any desired temperature without any tension
or pressure. By superheated steam the temperature is quite independent of its
tension. If common steam is let through iron pipes heated to red heat the steam
leaves the said pipes having the same temperature as the red hot iron. Such super-
heated steam is invisible and is exactly like a gas. In a current of such superheated
steam, wood and paper become brown, and sealing wax and even lead and tin are
melted.
My improved method of treating the spent oxide of iron by recovery of sulphur
and by recovery of Prussian blue or prussiate of potash is as follows:-
The humid material is ground in a mill to form a fine mass.
This mass is then lixiviated by means of water. If the mass contains ammoniac
in a free state the lye can be neutralized by an acid. By this lixiviation the soluble
ammoniac salts are obtained which are by evaporation crystallized or employed in
the usual manner by any suitable copper salt for the precipitation of sulpho-cyanite
of copper or distilled with lime to obtain volatile ammoniac.
Water is again poured on the lixiviated mass and simultaneously caustic soda or
carbonate of soda or lime is added to the mass. Already by the cold digestion with
such alkalis the insoluble prussiates are converted into soluble prussiates. The
clear liquid is drawn off and treated with an acid until the same is neutralized or
gives a weak acid reaction. The weak acidified liquid is soon clouded by pre-
cipitated prussiates and sulphur. This dirty green precipitate might afterwards
injure the beautiful clear colour of the Prussian blue, and is therefore carefully
removed. The clear solution, which if necessary is filtered, is then acidified and
treated by a solution of perchloride of iron or by a small surplus of any other
soluble salt of oxide of iron, such as sesqui-chloride of iron. I thus obtain Prussian
blue, which in consequence of its purity has a dark blue color and when dried
shows a copper lustre on its fractures. I employ this product as Prussian blue
itself or convert the same into prussiate of potash.
For the manufacture of prussiate of potash the spent oxide has hitherto been
treated directly by caustic potash or by carbonate of potash, and the lye has been
evaporated; or the lime containing spent oxide has been treated with carbonate of
potash and after filtering off the carbonate of lime the lye has been evaporated. In
both cases great masses of diluted lye have to be treated, and there is danger of
producing a decomposition of the prussiate of potash. These lyes contain always
also sulpho-cyanide of potash, which is to be found again as a contamination in the
prussiate of potash. Consequently I prefer to precipitate the acidified solution by
sesqui-chloride of iron to wash out the Prussian blue and to obtain by this washed
Prussian blue the yellow prussiate of potash by any known manner.
The spent oxide of iron lixiviated in this manner contains a great quantity of
sulphur in a free state. The mass is dried and then as above described distilled for
recovering the sulphur. During this distillation superheated steam is led over the
heated mass, by which means the sulphur to be recovered is distilled off in a very
short time,

page_text: My process distinguishes itself from those heretofore used, as I do not employ any
solvent for the sulphur, but distil off the sulphur together with steam. In the same
manner the sulphur is recovered from the gas lime if lime in the place of iron is used
for desulphurating the illuminating gas, and in the like manner this method can be
employed for the recovery of sulphur from any other masses or ores containing
sulphur.
The lixiviated and desulphurated mass is heated whilst air is admitted, and the
product is a beautiful brown colouring mass, caput mortuum, which can be employed
as a paint.
If the sulphur only is to be recovered from the spent oxide and if the recovery of
the cyanides is dispensed with, it is advisable to dispense with the crushing or
pulverizing of the spent oxide in a mill. The desulphurated masses can be used
anew for the purification of the illuminating gas.
Having thus fully described the said Invention, and the manner of performing the
same, I wish it understood that I claim, the manufacture of pure Prussian blue free
from sulphur and of yellow prussiate of potash free from sulpho-cyanide of potash
principally by the use of superheated steam, for a quicker and more complete
recovery of the sulphur from spent oxide and other masses containing sulphur, and
the method of lixiviating spent oxides or fresh oxides coming directly from the gas
works for the recovery of sulphur.
In witness whereof, I, the said Frank Wirth, have hereunto set my hand and
seal, this Nineteenth day of March, in the year of our Lord One thousand
eight hundred and seventy-seven.