A NEW OR IMPROVED PROCESS FOR THE DEPHOSPHORISATION OF IRON IN THE BLAST FURNACE
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Charles Denton Abel at the Office
of the Commissioners of Patents on the 22nd August 1881. A communi-
cation from abroad by Henri Jean Baptiste Pellet and Jules Cahen, both of
Paris, France.
CHARLES DENTON ABEL, of No. 28, Southampton Buildings, Chancery Lane,
in the County of Middlesex. "A NEW OR IMPROVED PROCESS FOR THE
DEPHOSPHORISATION OF IRON IN THE BLAST FURNACE." [A communication from
abroad by Henri Jean Baptiste Pellet and Jules Cahen, both of Paris, France.]
This Invention relates to a process for dephosphorising iron in the blast furnace,
wherein such dephosphorisation is effected in acting upon the ore, while in the
process heretofore employed, the smelted metal only has been operated upon for
this purpose. By this new process the use of expensive apparatus, such as has
been heretofore necessary for acting upon the metal, is obviated.
Various attempts have been made to dephosphorize the materials before its
introduction into the blast furnace, the phosphorus being generally found to exist
in the form of phosphates of lime or alumina and not as phosphate of iron, and it
has been endeavoured to treat the phosphatic materials with acids, principally
sulphuric acid, whereby the percentage of phosphorus has been considerably
diminished.
It has no doubt occurred to manufacturers to treat the phosphatic ores and
materials in the. furnace, but it appeared preferable to operate upon one ton of
phosphatic cast iron than upon two or three tons of materials, and it was known
that the phosphates of alumina or of lime were reduced in the presence of the
silicates of carbon and carbonic oxide, and that the phosphorus then combined
with the iron, from which fact it would not appear possible to arrive at a useful
result by this means.
On the other hand the endeavours made up to the present time to dephosphorise
cast iron, and which have partly succeeded, are based on the use of magnesia in a
more or less pure condition as a lining to the furnaces, in which the purification of
cast iron is carried on. In this operation, in which the phosphoric acid combines
with the bases, forming slags, it has been proved that the magnesia operates in a
different manner to the other bases, and that it alone is capable of retaining in a
special degree the phosphoric acid produced by the smelting.

page_text: These considerations have led my correspondents to conclude that this property
of magnesia of retaining energetically the phosphoric acid would subsist in the
blast furnace even in the presence of the reducing gases and other agents, and that
the phosphate of magnesia even in the presence of silica would not be reduced, or
only slightly, by the carbon, oxide of iron, and other matters.
According to the present Invention therefore magnesia is added in certain
proportions to the charge in the blast furnace in order to act upon the phosphatic
earths (lime and alumina) contained in the iron ores so as to produce phosphate of
magnesia.
It has been found that when heating phosphate of lime and silica in the presence
of magnesia a double decomposition is effected (that is to say, phosphate of
magnesia and silicate of lime are produced), and this at a temperature below that
required for the reduction of the oxide of iron into metallic iron. This addition of
magnesia in any desired quantity in the blast furnace effects a considerable
reduction of the percentage of phosphorus in the cast iron produced.
The quantity of magnesia to be added cannot be definitely given, as it will vary
considerably, depending entirely upon the percentage of phosphorus contained in
the ores, which must be ascertained beforehand by analysis, the proportion of
magnesia being increased or decreased according to the degree of dephosphorisation
desired, and according as the ore or the reducing agents themselves contain more
or less magnesia.
The magnesia may be added to the blast furnace charge either in the form of
dolomite or of carbonate of magnesia, or in some cases in the form of silicate of
magnesia if the ore is too calcareous, as some clays contain as much as from 20 to
24 per cent. of magnesia.
The magnesia may be added either directly after the iron ore or together with
the calcareous or siliceous materials.