Process of Treating Blast Furnace Slag for use in Cement, Mortar or the like.
Year: 1897

page_text: Date of Application (in United Kingdom), 12th June, 1897
Complete Specification Left, 10th Mar., 1898-Accepted. 14th May 1898
Date of Application (in United Kingdom), 12th June, 1897
Complete Specification Left, 10th Mar., 1898-Accepted 14th May 1898
PROVISIONAL SPECIFICATION.
Process of Treating Blast Furnace Slag for use in Cement, Mortar
or the like.
I, ALEXANDER DANIEL ELBERS, Industrial Chemist, of 418, Hudson Street,
Hoboken, County of Hudson, and State of New Jersey, United States of America;
do hereby declare the nature of this invention to be as follows;-
-
The invention has for its object to adapt slag that is suitable for my treatment
for use in admixture with hydraulic cement, as an ingredient for mortar, and for
similar purposes:
The invention consists in a novel process for treating sulphurous blast furnace
slag in its ground or pulverized state with a weak solution of nitric acid in such
manner that it becomes superficially desulphurized, as well as impregnated with
nitrosyl (NO); and the invention also consists in the improved material produced
by the said improved process, which may be chemically termed
slag," all as hereinafter more fully described.
66
' nitrosylized
As an admixture to hydraulic cement, such as Portland, Rosendale, etc., crude
blast furnace slag is considered an adulterant, chiefly for the reason that the slag,
which readily yields gelatinous silica and therefore is capable of promoting
cementation, also carries soluble and decomposable sulphides that are apt to impair
or even destroy the cohesion of the mass that contains themí, long after it has
become indurated, whereas the slag that does not contain such impurities is, as a
rule, too insoluble to promote cementation to any more appreciable extent than
ordinary sand does. Blast furnace slag can be completely desulphurized by roast-
ing it in a very intense heat. This process is, however, too expensive because its
successful operation involves many difficulties. Besides the intense heating has
the effect of rendering the slag less soluble than it is in the crude state. On the
other hand the crude slag is rendered available for cement, etc., in a comparatively
inexpensive manner and does not lose any of its solubility when it is treated after
the method hereinafter described.
By my improved treatment the slag becomes only superficially desulphurized,
but in such an effective manner that the still sulphurous interior of the slag
particles can not become disclosed by such chemical reactions as
take place in applied cement when it is either submerged or exposed to varying
are apt to
atmospheric influences. Moreover the absorption of nitrosyl prevents the.
[Price 8d.1

page_text: ferruginous slag particles from changing superficially to ferric hydrate, which is
an injurious reaction because it interferes with the progress of hydraulic cemen-
tation. The slag that is most suitable for the treatment has an oxygen ratio
somewhat above the singulo-silicate (1 : 1) standard, is high in lime and alumina,
and contains from 1% to 2% of calcium sulphide. The proportions of its essen-
tial constituents range within the following limits, viz.:-SiO2 equals 38% to 42%;
Cao equals 40% to 45%; A₁₂O₂+ Fe equals 16% to 18%; and when molten
slag of such composition is cooled suddenly it becomes vitrified and assumes a
dark greenish colour which is a certain indication that it is sufficiently ferruginous
for the treatment.
The term "ferruginous" as herein applied means that the slag contains an
appreciable proportion of ferrous silicate in constitutional combination and more
or less of oxide of iron or of partly reduced oxide in admixture.
When such slag is mixed in its ground or pulverised state with a weak solution
of nitric acid, the latter reacts most readily on the calcium sulphide with which
it forms calcium nitrate, but before this reaction which is accompanied by the
evolution of hydrogen-sulphide gas, can go very deep another portion of the acid
enters with the ferruginous matter of the slag into various and rather complex
reactions, the final outcome of which results in the formation of some ferrous or
even ferric nitrate as well as in the liberation of nitrosyl and the latter is eagerly
absorbed by the ferruginous slag particles and imparts to the mass a darker
colour. After removing the nitrates by leaching, the mass is dried at a moderate
heat and is then ready to be put up for use as nitrosylized slag.
As regards the usefulness of this material I find that mixtures of one part of
hydraulic cement and from one to five parts of nitrosylized slag shew much better
results within the same period of submergence than cement that is mixed with
corresponding proportions of sand, that mixtures consisting of one part of Portland
cement and of eleven parts of nitrosylized slag that has passed through a sieve
having 180 meshes to the linear inch harden still considerably under water within
seven days, and that the pats that contain nitrosylized slag stand the usual
shrinkage tests as well as those made of neat cement. I also find that ordinary
mortar hardens better when it is mixed with nitrosylized slag, especially when
the lime has been slaked in admixture with the slag, and that a fat or quick-
slaking lime can be rendered hydraulic by such admixture.
I will now proceed to describe how the process can be carried out:-In order
to prepare the slag for the treatment with acid, crude slag taken from the cinder
bank as well as granulated slag may be used. Either kind may be ground wet
or dry and the wet-ground slag may either be dried or used in its wet state for the
subsequent treatment. I prefer, however, to use only slag that has been vitrified
by casting it in cumulative layers. This method is best carried out by flushing
the molten slag from a lateral tap hole of a cinder car in a broad sheet about two
feet wide, over the inclined plane or side of the cinder bank and by moving the
car to and fro while flushing so that the slag spreads itself on the ground in layers
about half an inch thick. The layers that are thus cast on top of each other,
whether a few or a hundred, gradually detach themselves from each other and
break up into small pieces that can be easily shovelled and transported in bulk.
I prefer to grind this material dry and so fine that at least 90% of it will pass
through a sieve of 180 meshes to the linear inch. The slag thus pulverized I mix
with about one-fourth part by weight of a weak solution of nitric acid or with
just enough to have the slag thoroughly soaked without any liquor gathering on
the surface. The mixing is best done by charging a measured quantity of the
slag into tanks or vats that contain a corresponding portion of the solution. These
receivers should be provided with a hood and a draught chimney because a rather
copious evolution of hydrogen-sulphide gas sets in almost as soon as the slag comes
in contact with the solution. After letting the soaked mass stand about an hour
or two it should then be mixed with enough water to convert it into a thin pulp
and after allowing the slag particles to settle, the liquor that has gathered on

page_text: top should be drawn off. This operation may be repeated one or twice within a
few hours but when the slag is of suitable composition one leaching, continued
for about twelve hours, will be found sufficient to entirely free the slag from
remnants of deliquescent matter. The slag thus treated may be dried in any con-
venient manner either in the open air or in a moderate artificial heat, always taking
care that it be not heated so highly as to render its contents of soluble silica
insoluble. The slag thus prepared is ready for use and may be packed, shipped,
and stored in any convenient manner inasmuch as its efficiency is not seriously
affected by dampness and moisture.
The strength of the solution that is to be employed is easily determined by
experiment. Apart from the superficial eradication of the decomposable sulphides,
the main object is to nitrosylize the slag with as little formation of additional
nitrates as possible and I find that in many cases an aqueous solution containing
about one and three-quarters per cent. of nitric acid (N₂O,,), or of a density some
what above 20 of Twaddell's scale answers the purpose. This is equivalent to the
use of about half a pound of 60% acid for the treatment of one hundred pounds
of slag.
In order to render the solution more productive of nitrosyl it may be partially
decomposed before the slag is mixed with it, which can be accomplished by allow-
ing the solution to react on wrought iron scrap which may be taken out as soon
as the decomposition has progressed far enough, and in many other well-known
ways.
Process of Treating Blast Furnace Slag for use in Cement, Mortar
or the like.
I, ALEXANDER DANIEL ELBERS, Industrial Chemist, of 418, Hudson Street,
Hoboken, in the County of Hudson and State of New Jersey, United States of
America, 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 invention has for its object to adapt slag that is suitable for my treatment
for use in admixture with hydraulic cement as an ingredient for mortar and for
similar purposes.
The invention consists in a novel process for treating sulphurous blast furnace
slag in its ground or pulverized state with a weak solution of nitric acid in such
manner that it becomes superficially desulphurized, as well as impregnated with
nitrosyl, (NO); and the invention also consists in the improved material pro-
duced by the said improved process which may be chemically termed "nitrosylized
slag," all as hereinafter more fully described and pointed out in the claims.
As an admixture to hydraulic cement, such as Portland, Rosendale, etc., crude
blast-furnace slag is considered an adulterant chiefly for the reason that the slag
which readily yields gelatinous silica, and therefore is capable of promoting
cementation, also carries soluble and decomposable sulphides that are apt to impair
or even destroy the cohesion of the mass that contains them long after it has
become indurated, whereas the slag that does not contain such impurities is, as
a rule, too insoluble to promote cementation to any more appreciable extent than

page_text: ordinary sand does. Blast-furnace slag can be completely desulphurized by roast-
ing it in a very intense heat. This process is, however, too expensive because its
successful operation involves many difficulties. Besides the intense heating has
the effect of rendering the slag less soluble than it is in the crude state. On the
other hand the crude slag is rendered available for cement, etc., in a comparatively
inexpensive manner and does not lose any of its solubility when it is treated after
the method hereinafter described.
By my improved treatment the slag becomes only superficially desulphurized
but in such an effective manner that the still sulphurous interior of the slag
particles cannot become disclosed by such chemical reactions as are apt to take
place in applied cement when it is either submerged or exposed to varying atmo-
spheric influences. Moreover, the absorption of nitrosyl prevents the ferruginous
slag particles from changing superficially to ferric hydrate which is an injurious
reaction because it interferes with the progress of hydraulic cementation. The
slag that is most suitable for the treatment has an oxygen ratio somewhat above
the singulo-silicate (1:1) standard, is high in lime and alumina and contains
from one to two per cent., of calcium sulphide. The proportions of its essential
constituents range within the following limits viz.:-SiO2 equals 38% to 42%;
CaO equals 40% to 45%; Al₂0,-Fe equals 16% to 18%; and when molten
slag of such composition is cooled suddenly it becomes vitrified and assumes a
dark greenish colour which is a certain indication that it is sufficiently ferruginous
for the treatment. The term "ferruginous" as here applied means that the slag
contains an appreciable proportion of ferrous silicate in constitutional combina-
tion and more or less of oxide of iron or of partly reduced oxide in admixture.
When such slag is mixed in its ground or pulverized state with a weak solution
of nitric acid the latter reacts most readily on the calcium sulphide with which
it forms calcium nitrate; but before this reaction which is accompanied by the
evolution of hydrogen-sulphide gas, can go very deep, another portion of the
acid enters with the ferruginous matter of the slag into various and rather com-
plex reactions the final outcome of which results in the formation of some ferrous
or even ferric nitrate as well as in the liberation of nitrosyl, and the latter is
eagerly absorbed by the ferruginous slag particles and imparts to the mass a darker
colour. After removing the nitrates by leaching, the mass is dried at a moderate
heat and is then ready to be put up for use as nitrosylized slag.
As regards the usefulness of this material I find that mixtures of one part of
hydraulic cement and from one to five parts of nitrosylized slag shew much better
results within the same period of submergence than cement that is mixed with
corresponding proportions of sand, that mixtures consisting of one part of Portland
cement and of eleven parts of nitrosylized slag that has passed through a sieve
having 180 meshes to the linear inch, harden still considerably under water within
seven days, and that the pats that contain nitrosylized slag stand the usual shrink-
age tests as well as those made of neat cement, I also find that ordinary mortar
hardens better when it is mixed with nitrosylized slag especially when the lime
has been slaked in admixture with the slag, and that a fat or quick-slaking lime
can be rendered hydraulic by such admixture.
I will now proceed to describe how the process can be carried out.
In order to prepare the slag for the treatment with acid, crude slag taken from
the cinder bank, ag well as granulated slag, may be used. Either
kind may be ground wet or dry and the wet-ground slag may either
be dried or used in its wet state for the subsequent treatment. I
prefer, however, to use only slag that has been vitrified by cast-
ing it in cumulative layers. This method is best carried out by flushing the
molten slag from a lateral tap hole of a cinder car in a broad sheet, about two
feed wide, over the inclined plane or side of the cinder bank and by moving the
car to and fro while flushing, so that the slag spreads itself on the ground in
layers about half an inch thick. The layers that are thus cast on top of each
other, whether a few or a hundred, gradually detach themselves from each other

page_text: and break up into small pieces that can be easily shovelled and transported in
bulk. I prefer to grind this material dry, and so fine that at least 90% of it will
pass through a seive of 180 meshes to the linear inch. The slag thus pulverized
I mix with about one-fourth part by weight of a weak solution of nitric acid or
with just enough to have the slag thoroughly soaked without any liquor gather-
ing on the surface. The mixing is best done by charging a measured quantity
of the slag into tanks or vats that contain a corresponding portion of the solution.
These receivers should be provided with a hood and a draught chimney, because
a rather copious evolution of hydrogen-sulphide gas sets in almost as soon as the
slag comes in contact with the solution. After letting the soaked mass stand
about an hour or two it should then be mixed with enough of water to convert
it into a thin pulp and after allowing the slag particles to settle, the liquor that
has gathered on top should be drawn off. This operation may be repeated once
or twice within a few hours but when the slag is of suitable composition one
leaching, continued for about twelve hours, will be found sufficient to entirely
free the slag from remnants of deliquescent matter. The slag thus treated may
be dried in any convenient manner either in the open air or in a moderate
artificial heat, always taking care that it be not heated so highly as to render its
contents of soluble silica insoluble. The slag thus prepared is ready for use and
may be packed, shipped, and stored in any convenient manner inasmuch as its
efficiency is not seriously affected by dampness and moisture.
The strength of the solution that is to be employed is easily determined by
experiment. Apart from the superficial eradication of the decomposable sulphides,
the main object is to nitrosylize the slag with as little formation of additional
nitrates as possible, and I find that in many cases an aqueous solution containing
about 1 per cent. of nitric acid (N, O₂) or of a density somewhat above 2° of
Twaddell's scale, answers the purpose. This is equivalent to the use of about
half a pound of 60% acid for the treatment of 100 pounds of slag. In order to
render the solution more productive of nitrosyl, it may be partially decomposed
before the slag is mixed with it, which can be accomplished by allowing the
solution to react on wrought iron scrap which may be taken out as soon as the
decomposition has progressed far enough, and in many other well known ways.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:
1. The process of treating sulphurous blast-furnace slag in its ground or pulver-
ized state in the manner herein described.
2. The herein described process of treating sulphurous blast-furnace slag in its
ground or pulverized state, which consists in superficially desulphurizing the slag
and impregnating it with nitrosyl substantially in the manner set forth.
3. The herein described process of treating sulphurous blast-furnace slag in its
ground or pulverized state, which consists in superficially desulphuring the slag
and impregnating it with nitrosyl by the application of a weak solution of nitric
acid substantially as described.
4. An improved product consisting of superficially desulphurized and nitrosyl-
zed slag substantially as herein set forth.
Dated 1
1011 1
1000
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.