AN IMPROVED METHOD OF TREATING BLAST FURNACE SLAG TO OBTAIN THERE- FROM CERTAIN PRODUCTS USEFUL FOR VARIOUS PURPOSES
Year: 1883

page_text: LETTERS PATENT to Edward Gardner Colton of Victoria Chambers, Chancery
Lane, in the County of Middlesex Patent Agent for an Invention of "AN
IMPROVED METHOD OF TREATING BLAST FURNACE SLAG TO OBTAIN THERE-
FROM CERTAIN PRODUCTS USEFUL FOR VARIOUS PURPOSES." Communicated
to him from abroad by Alexander Daniel Elbers, of Hoboken, in the County
of Hudson and State of New Jersey, United States of America
PROVISIONAL SPECIFICATION left by the said Edward Gardner Colton
at the Office of the Commissioners of Patents on the 3rd May 1883.
"
EDWARD GARDNER COLTON of Victoria Chambers, Chancery Lane, in the
County of Middlesex, Patent Agent, AN IMPROVED METHOD OF TREATING BLAST
FURNACE SLAG TO OBTAIN THEREFROM CERTAIN PRODUCTS USEFUL FOR VARIOUS
PURPOSES"
(A communication to me from abroad by Alexander Daniel Elbers,
of Hoboken in the County of Hudson, and State of New Jersey United States of
America).
This invention has reference to an improved method of treating blast furnace slag,
in such a manner that finely friable white silicates are obtained that may be
utilized for various applications in the keramic and other arts as a paint as a plastic
material and by admixture with other substances.
This invention consists in changing the blast furnace slag by the steam or air
blast into slag fibres, known as slag wool, mineral wool or silicate cotton then
beating and fritting the said slag fibres until the fibres are reduced to white
friable silicates which are then pulverized.
It is a well known fact that the dark coloration of slags is mainly due to their
earthy sulphides and incidentally to slight metallic admixtures also that slags
containing earthy sulphides and sulphurets will evolve sulphurous acid vapours
if they are roasted in contact with atmospheric air. If therefore granulated or
pulverized slag of suitable composition be exposed to a high temperature-but below

page_text: the fusing point,-it would seem that then the so called opening of the slag and
the fritting together of the silicates, freed from volatile sulphur would take place
and thereby the desired desulphurized whitish silicates be obtained.
But this reduction cannot be satisfactorily accomplished in practice, owing either
to the lack of a sufficient quantity of atmospheric air or because the fusion of n
part of the charge cannot be prevented before the remaining part has been
desulphurized or fritted.
To supply therefore the required quantity of air to the slag I prefer to change
the slag first in the well known manner by a steam or air blast into slag fibres, in
the loose condition of which the intermediate space is filled with air, so that the
slag fibres besides having already undergone a slight chemical change in their
composition are therefor better adapted for reduction.
These slag fibres are placed into an ordinary crucible and pressed by hand into the
same until their density is about one half that of solid slag and so that the crucible
contains about one volume or more of air to one volume of slag fibres. The crucible
is then heated to a temperature somewhat above red-heat and retained at this high
temperature for about half an hour or more, care being taken that the fusing
point is not reached. During this continuous heating the slag fibres emit sulphurous
fumes and are thereby desulphurized, then being finally fritted down into a soft
white crumbling mass. The metallic admixtures become concentrated in spots of
darker colour which are separated by scraping from the fritted mass, when the
same is taken out and broken up or separated by gravity when the mass is washed.
After assorting the broken up mass, the finished or perfectly reduced particles are
pulverized and the incompletely reduced parts reheated with the next charge.
The product thus obtained consists according to the composition. used of com-
paratively pure silicates of lime alumina and magnesia of whitish color which can be
still more improved by washing and bleaching. It forms either singly or by proper
admixture with other pigments a paint of considerable covering and spreading
power, that possesses a high resistance against deterioration by atmospheric
influences. By mixing these silicates with diluted sulphuric acid, sulphate of lime
or gypsum is formed and silica is set free in a gelatinous state, which when
thoroughly mixed renders the mass plastic. This readily hardens into a compara-
tively insoluble compound.
:
This action of the sulphuric acid may be utilized in the arts and thereby an
improved plastic material for statuary and other ornamental or useful purposes be
obtained.
The pulverized unfinished mass of incompletely reduced parts which still
contains sulphurous acid may also be treated with diluted nitric acid which will
yield oxygen to the sulphurous acid, thereby changing the latter into diluted
sulphuric acid which will then also form sulphate of lime and gelatinous silica. It is
obvious that when the slag fibres are to be reduced on a larger scale they may be
heated in retorts, muffles and ovens of proper construction so that the silicates may
be obtained in larger quantities and that the fibres as well as the unfinished mass
may be mixed with such substances that facilitate reduction.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Edward Gardner Colton in the Great Seal Patent Office on the
3rd November 1883.
EDWARD GARDNER COLTON, of Victoria Chambers, Chancery Lane, in the
county of Middlesex, Patent Agent "AN IMPROVED METHOD OF TREATING BLAST
FURNACE SLAG TO OBTAIN THEREFROM CERTAIN PRODUCTS USEFUL FOR VARIOUS
PURPOSES (Communicated by Alexander Daniel Elbers, of Hoboken, in the
county of Hudson, and State of New Jersey, United States of America.
"
This invention has reference to an improved method of treating blast furnace
slag, in such a manner that finely friable white silicates are obtained that may be
utilized for various applications in the keramic and other arts, as a paint, as a
plastic material and by admixture with other substances.
The invention consists in changing the blast furnace slag by the steam or air
blast into slag-fibres, known as slag-wool, mineral-wool, or silicate cotton, then
heating and fritting the said slag-fibres until the fibres are reduced to white friable
silicates which are then pulverized.
It is a well-known fact, that the dark coloration of slags is mainly due to their
earthy sulphides and incidentally to slight metallic admixtures, also that slags
containing earthy sulphides and sulphurets will evolve sulphurous acid vapors if
they are roasted in contact with atmospheric air. If therefore granulated or
pulverized slag of suitable composition be exposed to a high temperature, but
below the fusing point, it would seem that then the so-called "opening" of the slag
and the fritting together of the silicates, freed from volatile sulphur, would
take place, and thereby the desired desulphurized whitish silicates be obtained.
But this reduction cannot be satisfactorily accomplished in practice, owing
either to the lack of a sufficient quantity, of atmospheric air or because the fusion
of a part of the charge cannot be prevented before the remaining part has been
desulphurized or fritted. To supply therefore the required quantity of air to the
slag I prefer to change the slag first in the well known manner by a steam or air
blast into slag fibres, in the loose condition of which the intermediate space is
filled with air, so that the slag-fibres besides having already undergone a slight
chemical change in their composition are therefore better adapted for reduction.
In carrying out my invention slag fibres are placed into suitable crucibles and
pressed by hand into the same until their density is about one half that of solid
slag and so that the crucible contains about one volume or more of air to one volume of
slag fibres. The crucible is then heated to a temperature somewhat above red-heat and
retained at this high temperature for about half an hour or more, care being taken
that the fusing point is not reached. During this continuous heating the slag-
fibres emit sulphurous fumes and are thereby desulphurized, then being finally
fritted down into a soft white crumbling mass. The metallic admixtures become
concentrated in spots of darker color, which are separated by scraping from the
fritted mass, when the same is taken out and broken up or separated by gravity
when the mass is washed. After assorting the broken up mass, the finished or
perfectly reduced particles are pulverized and the incompletely reduced parts
reheated with the next charge. The product thus obtained, consists, according to
the composition used, of comparatively pure silicates of lime, alumina and
magnesia of whitish color which can be still more improved by washing and
bleaching. It forms, either singly or by proper admixture with other pigments a
paint of considerable covering and spreading power, that possesses a high
resistance against deterioration by atmospheric influences. By mixing these

page_text: silicates with diluted sulphuric acid, sulphate of lime or gypsum is formed and
silica is set free in a gelatinous state, which when thoroughly mixed renders the
mass plastic. This readily hardens into a comparatively insoluble compound.
This action of the sulphuric acid may be utilized in the arts and thereby an
improved plastic material for statuary and other ornamental or useful purposes
be obtained.
The pulverized unfinished mass of incompletely reduced parts which still
contains sulphurous acid, may also be treated with diluted nitric acid, which will
yield oxygen to the sulphurous acid, thereby changing the latter into diluted
sulphuric acid which will then also form sulphate of lime and gelatinous silica.
It is obvious that when the slag fibres are to be reduced on a larger scale, they may
be heated in retorts, muffles and ovens of proper construction so that the silicates
may be obtained in larger quantities and that the fibres as well as the unfinished
mass may be mixed with such substances that facilitate reduction.
according to the composition of the slag which is treated, the product will be
white or more or less dark colored, the former being the most desirable for general
purposes, and the properties of these desulphurised silicates will vary so as to
render them more or less suitable for one or the other of the following
applications:-
1. As a flux or glaze for china, pottery and enamelled ware, or as the body or
main-constituent in making new kinds of pottery and similar ware.
2. In the manufacture of glass.
3. In making ornamental plastering, stucco, statuary and artificial stone, it
may be used in admixture with lime &c. in about the same manner as these
products are now made from fine cements.
4. As a paint or body for pigments its color and silicifying action may be
desirable under proper treatment.
Blast-furnace slag of the uni-silicate type is the most suitable raw material for
the treatment herein before described and for obtaining desulphurized silicates of
the most useful quality, but more acid or more basic slag may also be treated for
special purposes, or in fact all blast furnace slag, which can be desulphurized by
roasting, after having been previously reduced to a fibrous or air holding
condition.
$1
In the before named process, the first and well known operation is the reduction
of the slag to a finely fibrous condition, by subjecting it while in the fluid state, to
jets of steam. The product thus obtained is already commercially known as
Silicate-Cotton, Slag-Wool or Mineral-wool and will hereinafter be referred to as
fibrous-slag." The second operation is the roasting of this fibrous and very
voluminous slag until no further evolution of sulphurous acid vapors takes place;
this desulphurization generally occurs at about light cherry red heat and is
completed at and below ordinary white heat; during this heating (which may
be done in furnaces, ovens or pots of any suitable construction) the fibrous slag
breaks up or opens "and after it is freed from sulphur, the reuniting or fritting
together of its other constituents takes place.
"
By fibrous slag is to be understood the whole mass of fibres or short threads and
of less reduced slag particles or globules, into which the liquid crude-slag has been
converted by the steam blast and which become intermixed in settling. In roasting
the fibrous slag, the threads or fibres break up quickest and their mass, after being
desulphurised is then already in such a fine state, that it can be passed through a
sieve, having about 180 meshes to the linear inch.
The smaller globules in the fibrous mass also open, or break up and may become
desulphurized in the same heat, but the larger globules require a more protracted
heat and after being superficially desulphurized in the first heat they may be
crushed and then reheated, or may find utilization in their partially desulphurized
state. If pulverized crude slag were roasted in the same way, it would scorify or
melt without becoming desulphurized, because after expansion of its particles by heat,
the circulation of air around them is too much impeded for proper oxidization of the

page_text: comparatively small per centage of sulphur, which blast furnace slag contains.
Fibrous slag is in such a voluminous or air-holding condition, that it may be
compressed to one half one fourth or even less of its usual bulk and still, if roasted
in this compressed condition, admit sufficient air for proper reduction. The most
suitable state of air-holding capacity or porosity of the fibrous slag, varies of course
with its composition and has to be determined in practice, and it is most essential
during the first stages of oxidization, so much so, that an incompletely roasted or.
still sensibly sulphurous mass of fibrous slag may be re-roasted and thereby
completely desulphurized after having been powdered or reduced to the compact-
ness of crude pulverized slag, which, as before stated cannot be satisfactorily
reduced,in the same manner.
The main feature of this invention is therefore the manipulation of the fibrous
slag in such a manner as to obtain purified silicates from blast furnace slag, which
cannot be obtained by treating the crude slag in any other manner, and according
to convenience, the process of making fibrous slag and then roasting the same may
be treated as a continuous operation by having the still hot fibrous slag conveyed
directly into the roasting furnace, and by compressing it therein to the desired
consistency, or the fibrous slag may be shipped from where it is made to the
furnace where the roasting is to be done.
Fibrous slag which contains sulphates of lime may be first treated so as to reduce
the sulphates to sulphides, because the former are not directly decomposed by
contact with atinospheric air under heat; but this treatment forms no essential
part of the invention as it is a known metallurgical process, which may be used
when required. The fritting of the desulphurized fibrous slag must of course be
watched closely so as to prevent fusion. The desulphurized mass contains the
same silicates which were originally in the fibrous slag, but in a desulphurized
state usually as desulphurized silicates of lime, magnesia and alumina, which
however still contain free lime and perhaps free magnesia, which were set free by
oxidation of the calcium and magnesium sulphides. It also still contains other
minor impurities of slag, such as iron, manganese &c., which according to the
character of the slag are either in a chemically diffused condition, in which they
may not be separable by roasting, or they are only in a mechanical admixture and
then can be separated by gravity or washed out from the roasted mass.
Having thus described the said invention communicated to me, on behalf of
the said Alexander D. Elbers I claim as new and desire to secure by Letters
Patent-
1. The herein described method of treating blast furnace slag for industrial use,
which consists first in transforming the same into slag fibres, and then
desulphurizing or fritting the said slag fibres, substantially as set forth.
2. As a new product of manufacture for application in the manner described and
for similar purposes, desulphurized and fritted slag fibres, produced by such
process, substantially as described.
In witness whereof, I, the said Edward Gardner Colton, have hereunto set my
hand and seal, this 20 day of October, in the year of our Lord One thousand
eight hundred and eighty-three.
E GARDNER COLTON. (L.S.)