IMPROVEMENTS IN THE METHOD OF UTILIZING SLAGS OBTAINED IN THE DEPHOSPHORIZATION OF IRON
Year: 1882

page_text: LETTERS PATENT to Carl Pieper, Civil Engineer and Patent Agent resident
at 109-110 Gneisenaustrasse Berlin S.W. Prussia for an Invention of
"IMPROVEMENTS IN THE METHOD OF UTILIZING SLAGS OBTAINED IN THE
DEPHOSPHORIZATION OF IRON A communication to him from Carl Scheibler,
Professor of Chemistry, residing in Berlin, kingdom of Prussia
"
PROVISIONAL SPECIFICATION left by the said Carl Pieper at the Office '
of the Commissioners of Patents on the 7th December 1882.
CARL PIEPER, Civil Engineer and Patent Agent, resident at 109-110 Gneisenau-
strasse, Berlin S.W. Prussia, Germany IMPROVEMENTS IN THE METHOD OF
UTILIZING SLAGS OBTAINED IN THE DEPHOSPHORIZATION OF IRON, a communication
from Carl Scheibler, Professor of chemistry, residing in Berlin, kingdom of Prussia,
This invention relates to the utilization of slags obtained in the dephosphorization
of iron, and it consists in an improved method of treating such slags, the object of
which is, firstly, to convert certain phosphates of the slags into more soluble
compounds of phosphoric acid, and secondly, to produce from the slags calcic and
magnesic phosphates and oxides of iron (iron ore).
The first part of the invention is based on the reaction at elevated temperature of
the lime or magnesia or certain compounds thereof contained in the slags, on the
phosphates of iron and manganese, and the formation thereby of phosphates of
lime respectively of magnesia, while the second part has for its point of issue the
hitherto unknown fact that, when diluted acids act in limited quantity on the
powdered slag, they will dissolve the phosphates of lime and magnesia, whereas
iron and manganese will substantially remain undissolved.
For carrying out the first part of the invention, the slag is reduced to a fine
powder. Particles of metallic iron or of steel inclosed in the same should be
separated during this operation. The powder is hereupon heated to a suitable
temperature (or roasted) in oxidizing flame while being stirred. It is thereby
rendered fit for being used with advantage as manure.

page_text: The first operation of the second part of the invention consists in treating the
powder, whether previously roasted or not, by muriatic acid, the quantity and
dilution whereof must be such that only the phosphates of lime and magnesia
together with some other compounds of the same metals will be dissolved. The
quantity of acid to be employed is determined by calculation based on chemical
analysis of the powder, or by experiment, while the degree of dilution may be carried
as far as convenience will allow. The solid residue remaining after the separation
of the liquid, may be utilized in the same manner as iron ore.
Instead of muriatic acid, other suitable acids may be used, as for instance acetic
acid, which can be re-obtained by distillation.
The next operation consists in neutralizing the liquid by lime or magnesia or by
a mixture or combination of both, such as burnt dolomite. The precipitate thereby
formed and which is substantially phosphate of lime or magnesia or of both metals,
is finally separated from the lye, and washed. In case acetic acid has been used, so
much muriatic acid is added to the lye as is required to liberate the quantity of
the former combined with a base, whereupon distillation is proceeded with as
hereinbefore mentioned.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Carl Pieper in the Great Seal Patent Office on the 18th April
1883.
"
CARL PIEPER, Patent Agent and Civil Engineer residing at 109/110 Gneisenau-
strasse Berlin S W. Prussia "IMPROVEMENTS IN THE METHOD OF UTILIZING
a communication to me
SLAGS OBTAINED IN THE DEPHOSPHORIZATION OF IRON
from Carl Scheibler, professor of chemistry, residing in Berlin, Kingdom of Prussia
This invention relates to the utilization of slags obtained in the dephosphorization
of iron in the converter by the process of Thomas Gilchrist, or of other slags
having a similar composition, and it consists in improvements in the method of
treating such slags for the purpose of producing therefrom calcic and magnesic
phosphates and oxides of iron and manganese.
.
Before entering upon a description of the invention, I have to premise that the
said slags are mainly constituted of proto-phosphates of iron and manganese,
phosphates and silicates of lime and maguesia, sulphide of calcium and magnesium
and caustic lime and magnesia.
The process which my correspondent employs, consists substantially in a roasting
of the powdered slag, in the subsequent treatment of the same by a limited
quantity of highly diluted muriatic acid for the purpose of dissolving phosphates
of lime and magnesia, while the oxides of iron and manganese remain undissolved,
and finally, in precipitating the said phosphates from their solution by means of
lime or magnesia.
For carrying out the invention, the slag is reduced to a fine powder. Particles of
iron and steel inclosed in the same, should be separated during this operation. The
powder is hereupon heated to a red heat, or roasted; in oxidizing flame (i.e. in
flames containing an excess of air) while being stirred; but the temperature should
not be allowed to rise to the point at which the powder would begin to slag. By
this process the lime and magnesia present in caustic state and in certain compounds,
are caused to decompose the proto-phosphates of iron and manganese, and to
combine with the phosphoric acid of the same to phosphates of lime and magnesia,
while protoxides of iron and manganese are set free and converted by the
oxidizing action of the air into sesquioxides or combinations of protoxide and
sesqui oxide, which are not so easily affected by acids as the protoxides. Besides,
the sulfides of line and magnesia are decomposed under the influence of the air
into sulphurous acid, which escapes, and caustic lime which contributes to the
decomposition of the phosphates of iron and manganese. Also, any sulphide of
iron will be decomposed in the same manner. The process may be carried out in a
reverberatory furnace with inclined hearth, or in revolving furnaces, or other
furnaces of suitable construction.
The next step consists in the treatment of the roasted slag by diluted muriatic
acid, the quantity whereof should be just sufficient to dissolve all the phosphates
and silicates of lime and magnesia together with the caustic lime and magnesia
which are yet present. This quantity is determined by calculation based on
chemical analysis of the powder, or experimentally, in treating equal quantities of
powder by gradually increasing quantities of acid, or by continuing to add acid
from a determined quantity thereof until iron and manganese commence to be
dissolved.
'
In many cases 11%. part by weight of the muriatic acid of commerce to one part
by weight of powdered slag will be a suitable proportion. As regards the degree of
dilution, I have to observe that, if the slag is treated by muriatic acid but little

page_text: diluted, the silicic acid of the slag will not be completely dissolved; the same will
separate out in gelatinous state and thereby render the separation of the liquid
from the undissolved residue so difficult that it cannot be carried out in practice.
Besides, though the oxides of iron and manganese have acquired by the roasting
the property of being less readily affected by acids than before that process, never-
theless when acids are used which are but little diluted, the process is likely to
take place in too rapid a manner with development of heat, in consequence whereof
a considerable quantity of iron will at the beginning be dissolved. By the influence
of the lime contained in the slag, this iron subsequently separates out again as a
gelatinous and bulky precipitate of hydrated ferric oxide, which impedes, in a
similar manner as the gelatinous silicic acid, the separation of the liquid from the
undissolved residue.
If, on the other hand, highly diluted acid is employed, the silicic acid instead of
gelatinizing, will be dissolved, and the solution will contain nearly all the
phosphoric acid, whereas the quantity of iron and manganese entering into the
same is but insignificant. The inventor therefore adds so much water to the acid
as to produce a liquid not containing above 3 per cent of gaseous hydrochloric
acid, which corresponds to a specific gravity of 1,0172. This degree of dilution will
ordinarily be obtained by mixing 1 part by volume of the common muriatic
acid of commerce having a strength of 21° Baumé with about 9 parts of water.
By preference, however, a quantity of water is added sufficient to reduce the titre
of the liquid in gaseous hydrochloric acid to 21 per cent, which requires about
15 parts of water to 1 part of acid of 21° Baumé. Higher degrees of dilution
may be applied, but they present the inconvenience that unnecessarily large
quantities of water have to be dealt with.
The dissolving process may be carried out in wooden vessels or in iron tanks
lined with lead, or in cemented cisterns of masonry. In order to promote the
action of the acid on the powder, the mixture should be agitated by a mechanical
stirrer or by jets of steam or air introduced into the same. Although the disso-
lution of the phosphates, &c., will take place whether the temperature be high or
low, it is accelerated by heat.
i
The solid residue remaining after the separation of the liquid, and which
contains almost all the iron and manganese of the slags together with a small
portion of the silicic acid thereof, may be utilized for the manufacture of iron.
Instead of muriatic acid, other acids may be used in the process, but the inventor.
does not attach any importance to them, as they are either inconvenient in their
application or too expensive for the purpose.
The third operation consists in neutralizing the liquid by caustic lime or
magnesia, or by a mixture or combination thereof, such as burnt dolomite, which
substances are, by preference employed after having been stirred with water to
milk of lime, &c. (Instead of caustic lime and magnesia, the carbonates thereof
might be. used, but the former are to be preferred.) A precipitate is thereby
formed, which possesses a different character according to the particular mode of
operating. If lime is added in excess, the precipitate will consist of a mixture of
bibasic and tribasic phosphates of lime, &c., together with almost the whole quantity
of silicic acid contained in the solution. If the solution is gradually and accurately
neutralized, it is substantially the bibasic phosphate which falls to the bottom with
the silicic acid.
But, if so much lime only is added, as to leave the solution slightly acid, the
bulk of the silicic acid remains in solution. In all cases, however, the precipitate
contains but very little iron or manganese. Another mode of proceeding in order.
to obtain phosphates with but little silicic acid consists in first treating the powdered
and roasted slag by a part only of the acid required for dissolving the phosphates
of the same, and subsequently by the remaining part. The solution obtained first;
will then contain the greater portion of the silicic acid with. a comparatively low
amount of phosphates, whereas the second solution comprises the main part of the
phosphates with but little silicic acid.

page_text: The precipitate obtained is separated from the lye by means of filter-presses or
other suitable means, whereupon it is washed and dried. It then forms a tender
white powder, especially adapted to be used as manure.
Having thus described the nature and object of this invention, and, the manner
in which it is to be carried out in practice, as communicated to me by my corre-
spondent, I wish it to be understood that I am aware that heretofore attempts
have been made to produce calcic phosphates from phosphatic slags by a process
of dissolution in an acid and subsequent precipitation; but these attempts have been
unsuccessful; as they were based on the wrong opinion that the peroxides of iron
and manganese and also the silica in the roasted slags were insoluble in acids; but
on account of the too great strength and quantity of the acid employed it was found
impossible to avoid dissolving iron and manganese and to prevent more or less of
the silicic acid from gelatinizing in the solution. In consideration, however, of
such attempts I do not broadly claim the combination of the roasting, dissolving
and precipitating operations, but what I claim is:
The treatment of slags obtained in the dephosphorization of iron by the Thomas-
Gilchrist process, or of other basic slags having a similar composition, which
consists in roasting the powdered slags by oxidizing flame, in submitting the
material thus prepared to the action of muriatic acid, the quantity whereof is so
determined as to be sufficient only for dissolving caustic lime and magnesia
together with the silicates and the phosphates thereof (or whichsoever of these
substances are present) while its dilution is such as is attained by adding at least
9 parts of water to 1 part of the acid of commerce of 21 degrees Baumé, and
finally, in precipitating phosphate of lime or magnesia, or of both, by addition to
the liquor separated from the residue, of lime or magnesia whether caustic or in the
state of carbonate, or of a mixture or combination thereof, substantially as and for
the purpose specified.
In Witness whereof, I, the said Carl Pieper, have hereunto set my hand and
seal this twenty-first day of March in the year of our Lord One thousand
eight hundred and eighty-three.
CARL PIEPER (L.S.)