Improvements in Utilizing Spent Iron Pyrites, and Apparatus therefor.
Year: 1894

page_text: Date of Application, 14th Mar., 1891
Complete Specification Left, 14th Jan., 1895-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
Improvements in Utilizing Spent Iron Pyrites, and Apparatus
therefor.
IWALTER MILLS of 20 Anstey Road Peckham London S.E. Analyst do hereby
declare the nature of this invention to be as follows:-
In the process of manufacturing sulphuric acid large quantities of iron pyrites
are burnt, after which ferric oxide with a quantity of ferrous sulphide, silica, and
sometimes salts of other metals remain. I grind this mixture to a fine powder and
remove any ferrous sulphide that it may contain by passing it over a magnetic.
separator.
I then mix with the residue finely divided iron in the proportion of about 35 parts
of iron to every 100 parts of the ferric oxide that it may contain. The substance
so prepared is rammed into a convenient receptacle and heated to a dull red heat
out of contact with air. I thus convert the ferric into ferrous oxide.
When cold the ferrous oxide mixture is mixed with finely powdered anthracite
coal, coke, or charcoal, or similar carbonaceous matter and heated out of contact
with air to redness. Carbonic oxide gas is given off and metallic iron produced.
This is crushed to powder and separated from silica or other foreign substances by
being passed over a magnetic separator.
I prefer however to reduce the ferrous oxide by agitating it at a red heat in
presence of carbonic oxide, or a similar reducing gas, in an apparatus of special
construction which I call a "revolver." This is an iron cylinder revolving in a
hollow fixed shaft which is closed in the centre. When carbonic oxide gas is used
it is admitted at one end of the shaft, while carbonic acid is pumped out at the
other end, and then forced through red hot coke; from this the reduced gas passes
again into the revolver, until complete reduction of the ferrous oxide has taken
place.
1 1044
WALTER MILLS.
Improvements in Utilizing Spent Iron Pyrites, and Apparatus
therefor.
I, WALTER MILLS, of 20, Anstey Road, Peckham, in the County of London,
Analyst, 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 :-
My invention relates to the utilization of the large quantities of comparatively
worthless refuse produced when iron pyrites are burnt in order to prepare sulphuric
acid, and consisting chiefly of ferric oxide, but also containing ferroso ferric oxide,
ferrous sulphide, silica, and sometimes salts of other metals.
According to my invention the greater part of the substance is converted into
ferrous oxide which may be reduced to metallic iron or used as a pigment or in

page_text: In carrying out my invention I first pass the refuse over a screen or by any other
suitable mechanical contrivance remove the stones which it contains. The
remainder of the substance is ground up or crushed to a fine powder and passed
through a magnetic separator which removes the ferroso ferric oxide and the greater
part of, and in some cases all, the ferrous sulphide. The substance after this treat-
ment is mixed with amorphous metallic iron in about the proportion of 35 pounds
of iron to every 100 pounds of ferric oxide which the substance contains, and this
mixture is rammed into a crucible, heated to redness out of contact with air, and
then cooled under the like conditions to the ordinary temperature, whereby 1
convert the ferric oxide into ferrous oxide, in accordance with the formula
Fe,O, + Fe = 3 FeO.
In working on a commercial scale I substitute for the crucible an iron tube,
having a closely fitting cover at each end, one of these covers having inserted into
it an iron tap, so as to allow any air that may be present in the mixture to escape
while it is being heated; the said tap, however, being closed. before removing the
tube from the furnace in which it is heated so as to prevent access of air to the
contents of the tube as it cools.
The ferrous oxide thus obtained may be treated with a reducing gas, such as
hydrogen, coal gas, water gas or carbonic oxide gas in the apparatus shewn in the
accompanying drawing, in which:
Figure 1 is a sectional elevation of the apparatus :
Figure 2 an end view of part of the same; and,
Figure 3 a sectional view of a detail.
a is a cylinder having journals aº, a mounted in bearings a', a' in the ends of a
casing a carried upon legs or standards a³. a is a gear wheel upon one of the
journals aº, and as is a pinion engaging therewith adapted to be operated by a
handle a. The said cylinder which is made of iron or copper, and so arranged that
it can be heated to any required temperature, while supporting a pressure of
about 30 lbs. to the square inch, has baffle plates b, b fixed to its interior in order to
agitate its contents as it revolves. c and d are pipes or tubes which pass through
the journals aº, aº, the pipe c admitting the reducing gas while the pipe d carries off
the oxidized gas, the said pipes extending towards the walls of the cylinder as I
find this arrangement is slightly more advantageous than carrying the central shaft
straight through the cylinder as described in my Provisional Specification, while the
principle on which the apparatus is constructed is the same. e is an opening closed"
by a plug through which the cylinder a is charged.
The casing a enclosing the cylinder is open at the bottom so that the cylinder
may be heated, for instance, by gas burners e', el.
fis the reducing gas producing apparatus which comprises a chamber 7 fixed in a
furnace, the upper part of the said chamber being connected by a pipe i with
the gas inlet pipe c of the revolving cylinder a; whilst the gas discharge pipe d of
the said revolving cylinder is connected to a pipe ; which' extends down into the
chamber 9 as far as a perforated plate k near the bottom thereof. A pump (not
shewn in the drawing) is placed in connection with the pipe to cause the circula-
tion of the gas, a filter, such for instance as that shewn in Figure 3, being arranged
between the suction valve of the pump and the pipe d for preventing dust from
entering the pump.
In working the apparatus the substance to be reduced is introduced into the
cylinder a which is hermetically closed and the air exhausted therefrom, it is then
heated and the chamber g is filled with coke and rendered incandescent by the heat
of the furnace h. Carbonic oxide gas generated in the chamber g is then admitted
through the pipe from the chamber g. As the carbonic oxide gas enters the
cylinder a it comes in contact with the hot ferrous oxide contained therein, whereby
the ferrous and also the copper oxides, if any, are reduced to metallic iron and
copper respectively, while the carbonic oxide gas is oxidized to carbonic acid.
The temperature at which this reaction takes place is comparatively low; l'estimate

page_text: that ferrous oxide is so reduced at about 400 C. while it is well known that the
oxidės of copper are so reduced below that temperature.
The carbonic acid gas extracted from the revolving cylinder a by the pump is
forced by the said pump into the chamber g and through the red hot coke or char-
coal therein, whereby it is converted into carbonic oxide, its volume being at the
same time doubled or considerably augmented. This increase in volume enables
me to conduct the reducing operation within the cylinder a, under a slight pressure.
which I find very beneficial in producing uniformly satisfactory products. I there--
fore, attach at or some other convenient part of the apparatus a safety-valve
weighted to about 15 lbs. to the square inch; this valve is connected with a pipe.
through which the superfluous carbonic oxide gas is conducted to a gas holder.
The carbonic acid gas produced within the cylinder a having thus been reduced
to carbonic oxide again enters the said cylinder by the pipe . This operation is
continued until all the reducible metallic oxides within the cylinder a are converted
into metal. I find it advantageous to make the pipe i as short as is conveniently
practicable so as to utilize as much as possible all the heat contained in the carbonic
oxide gas as it issues from the chamber g whereby the heat that is applied to the
cylinder a may be greatly economized.
When carbonic acid gas ceases to be produced inside the cylinder a the operation
is stopped, the cylinder is allowed to cool somewhat, and then its contents are with-
drawn. These consist of amorphous metallic iron, ferrous sulphide, silica, and
sometimes other metals such as copper. From this mixture, the iron, which forms
the great bulk of the substance, is removed by a magnetic separator.
In carrying out the operation of converting ferrous oxide into metallic iron the.
use of a reducing gas is not essential; finely ground charcoal or coke will readily
reduce ferrous oxide at a red heat; but I prefer to use carbonic oxide gas because
it reduces ferrous oxide at a much lower temperature than is required when char-
coal or coke is employed as the reducing agent; the iron produced by the action of
carbonic oxide remains in an amorphous condition whereby its separation from
ferrous sulphide or other foreign substances is greatly facilitated.
In some cases the spent pyrites contain such a small quantity of silica and ferrous
sulphide that they become available for conversion into a black pigment in the-
following manner:-After being screened and ground up in the manner already
described the spent pyrites are straightway mixed with amorphous metallic iron
and heated to redness out of contact with air. The quantity of iron that has to he
used depends upon the amount of ferric and ferroso ferric oxides present in the
substance. Both these oxides are reduced to ferrous oxide by iron, but the latter
requires a much higher temperature than the former. Ferric oxide takes
about 35% of metallic iron for its reduction to ferrous oxide, ferroso ferric oxide.
requires about 25%. But the reaction :-
Fe,O,Fe 3 FeO
=
develops a great deal of heat which assists in reducing any ferroso ferric oxide.
with which it may be in contact. So that I find that practically the same external
heat is required for reducing to ferrous oxide the mixture of ferric and ferroso-
ferric oxides which occurs in spent iron pyrites as is necessary to be employed in
reducing ferric oxide per se.
When ferrous oxide is required in a practically pure state, for instance when
required for pharmaceutical purposes, the impure ferrous oxide prepared as afore-
said is dissolved in dilute sulphuric acid and filtered. The ferrous sulphide
contained in the impure substance is thus decomposed and a weak aqueous solution
of ferrous sulphate is produced. To this I add a weak aqueous solution of soda or
potash until no further precipitate is produced. This precipitate is placed upon a
filter paper and washed with water until the fluid that runs from it gives no
precipitate with an aqueous solution of barium chloride. The substance in the filter
is then dried at 100 C. and afterwards at 350 C. Pure ferric oxide is thus
produced; 100 grams of it are mixed with 35 grams of levigated iron; the mixture.

page_text: is tightly compressed into a 2 inch spun iron crucible which is then closed and
heated to redness in one of the " plate warmers" employed by dentists. Great
contraction of bulk ensues; ferrous oxide being produced. It has a specific gravity
of 5-566, does not oxidize at ordinary temperatures in the atmosphere, or even,
if
boiled in water, dissolves readily in muriatic or sulphuric acids with evolution of
much heat, and on being heated to about 400 C. in the air it spontaneously ignites,
passing into ferric oxide.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The method of producing and preparing ferrous oxide from ferric or ferroso
ferric oxide by the use of amorphous metallic iron, substantially as described herein.
2. The method of reducing ferrous oxide by carbonic oxide gas under pressure,
substantially as described.
3. The method of producing and preparing metallic iron from spent iron pyrites,
substantially as described herein.
4. The method of producing and preparing a black pigment from spent iron
pyrites, substantially as described herein.
5. In the reduction of metallic oxides by carbonic oxide gas, the use of the
apparatus herein described and illustrated in the accompanying drawing.
Dated this 14th day of January 1895.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.