Improvements relating to the Reduction of Sodium, Potassium, and like Metals from their Salts, and to Apparatus therefor.
Year: 1898

page_text: Date of Application, 18th Mar., 1898-Accepted, 26th Nov., 1898
COMPLETE SPECIFICATION.
Improvements relating to the Reduction of Sodium, Potassium, and
like Metals from their Salts, and to Apparatus therefor.
I, CHARLES ERNEST ACKER, of East Orange, Essex, County and State of New
Jersey, United States of America, Chemical Engineer, 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 statements:-
My invention consists of an improved process and apparatus for reducing
metals from their salts more particularly for the manufacture of sodium and
potassium. Briefly stated, the process consists in forming electrolytically an
alloy of some heavy metal such as lead, with sodium or potassium, and then dis-
tilling the latter.
In the accompanying drawings I have shown one form of electrolytic furnace
which may be used in carrying out my process.
Figure 1 is a vertical section;
Figure 2 is a section along line 2-2 of Figure 1;
Figure 3 is an enlarged detail view of the screw in elevation, and,
Figure 4 is a plan view of the screw partly in section, on the same scale as
Figure 3.
Similar letters of reference refer to corresponding parts in the several views
of the drawings.
K is a cast iron hearth, supporting by suitable lugs the cast iron pan or
partition L, and wrought iron cylindrical chamber G. Upon the rim of the
hearth is the magnesia lining J, and surrounding the chamber is a magnesia
cylinder H.
A tile cover rests on the magnesia cylinder I, and on the lining and is provided
with openings for a suitable number of anodes as at R, and openings for feeding
salt W, as at V, side walls J being provided on the salt receptacle. Through
the center of the hearth, a tube 0 projects upwardly to a point above the intended
level of alloy in the chamber, and surrounding this tube in the furnace is an
inverted cup 4, carrying at the bottom a screw M, the blades of which are designed
to force the liquid outwardly and away from the axis. The cup with the screw
is mounted rigidly on the shaft N, supported, and having its bearings below
the furnace.
Suitable pipes for feeding lead, collecting the products, etc., are provided as
described later, and the whole is suitably encased in brickwork or equivalent
heat insulating material. In starting the furnace, sufficient molten lead is run
in to seal the chamber G and cover the pan or partition L. The anodes having
been previously placed in position with one of them lowered into the molten
lead, the full current is turned on, passing down through the one anode, through
the lead to the exterior of the furnace and from the furnace by any suitable
connection, as at Z, or at X, when sodium is being produced. Dry salt is quickly
fed in on top of the lead and around the anodes. The anode carrying the full
D917

page_text: current is then raised slightly above the lead, as indicated by the volt meter,
thereby forming an arc,-the surrounding salt quickly melts and thereafter
conducts the current,--the melt soon extends to the anodes on either side, until
the entire charge is fluid, and the furnace works steadily at nearly the normal
voltage, the salt is decomposed by the current, chlorine being liberated at the
anodes and passing off through channel and pipe to the point where it is
utilized; the sodium is. liberated at the cathode surface, where it forms an alloy.
The screw M is set in motion, and by a comparatively slow but positive action
pulls the surface alloy continuously down between the pan or partition and
chamber, when the lighter portion rises to the surface in the chamber and the
heavier alloy sinks and follows the pull of the screw, and passes up under the
pan or partition to the surface, where it comes in contact with the molten electro-
Tyte, becomes the true cathode, and takes up the liberated sodium as it passes
over the pan toward the chamber. The screw is turned fast enough to produce
a definite movement toward and into the chamber of the shallow body of alloy
in contact with the electrolyte. The forced circulation of this surface alloy
continuously removes that part which is richest in sotlium away from the molten
salt. Salt is fed at regular intervals until the desired working depth is obtained,
and to replace that decomposed. The alloy becoming richer and lighter and
more bulky, rises in the chamber to a height dependent on the height of the
column of salt outside and the relative specific gravity of the alloy and the salt.
An overflow pipe which projects upwardly in the chamber to a point previously
determined, or which runs from the exterior of the furnace thereto, may be used
whenever the alloy is to be removed bodily. Down it the alloy will overflow,
almost continuously of nearly uniform richness, provided appropriate charges of
lead and salt are fed at frequent and regular intervals. Lead is introduced in
small charges, either in the molten state or in pigs of uniform weight, at definite
intervals into the pipe S which is sufficiently close to the highly heated interior
of the furnace to insure the fluidity of its contents. The charge therefore enters
the furnace from below, the oxide and scum remaining on the surface in the
feed pipe. A branch T extending to the bottom of the feed pipe provides for
emptying the furnace completely at the end of a run. The salt is heaped up on
top of the furnace and surrounding the anodes to a considerable depth, and thus
serves to keep in the heat, to effect a packing around the anodes by bridging
over the small annular spaces surrounding them where they pass through the
cover, and to utilize what heat would otherwise be lost to thoroughly dry and
heat the salt before it is introduced into the furnace. I consider this utilization
of the salt for purposes specified as being of great value, dispensing as it does
with packings, lutes, etc., beside conserving the heat of the furnace.
After the furnace has been in operation for several hours, and the walls have
become thoroughly heated, it will thenceforth work at maximum economy and
the volt meter needle will remain stationary as long as the proper operating
conditions are fulfilled.
I am unwilling to be confined to the details of the furnace which I have illus-
trated. Various arrangements of parts other than those illustrated may be used
without departing from the essential principle of operation described in the
specification; namely, the removal of the lighter and richer alloy from the
cathode surface into a chamber where it is no longer in contact with the molten
electrolyte. The object is, when producing alloy only, to work at the lowest
temperature consistent with proper fluidity of the bath, but I have found when
making particularly rich alloy, with the furnace working at approximately the
correct temperature or slightly higher, that the space above the alloy in the
chamber is frequently filled with the purple or violet vapor of sodium, which may
be easily observed by placing a small mirror at the bottom of pipe P. The
sodium thus vaporized may he condensed and separately collected by providing
the vapor pipe C, leading from the top of the chamber laterally and downwardly,
connecting with a vertical pipe D having a receptacle F at the bottom.

page_text: The sodium vapor rises in pipe C above the chamber, condenses in the lateral
arm, flows down to the end thereof, and drops into the receptacle F.
The vaporization is facilitated by the continuous circulation in the direction
of the escaping vapor of the nitrogen contained in the pipes and above the alloy
(air deprived of oxygen by sodium). This circulation is accomplished by con-
necting the pipes 1) and P near the bottom by pipe E. Owing to the difference
in temperature of the two vertical legs of the system, the nitrogen rises through
the chamber and carries the sodium vapor along with it then descends through D,
losing some of its heat before entering P.
Since one of the causes influencing the rapidity of vaporization is the removal
of the vapor from the surrounding space, it is obvious that the continuous circu-
lation of the same volume of nitrogen is a material aid in the continuous pro-
duction of sodium.
The production of sodium, as considered in the foregoing method, is more or
less incidental to the production of alloy. That is, the rate of distillation may
be less than the rate of separation from the salt and alloying with the lead, the
excess of sodium remaining in the alloy, which continues to overflow into recep-
tacle Q. If, however, the whole temperature of the furnace be raised, by working
the furnace at a higher voltage, the rate of distillation approaches and equals
the rate of separation, and it becomes purely a sodium furnace. The heat
necessary to vaporize the sodium, is, of course, conducted from the electrolyte ;-
the same result may be accomplished without working the bath at this elevated
temperature by generating heat locally in the chamber at and near the exposed
surface of the alloy. I have successfully used for this purpose one or more
heating tubes"
as at A, B where B is an iron tube closed at the bottom,
containing a small quantity of lead which effects electrical contact with a cen-
trally located carbon or metal resistance A which is insulated from the walls of
the tube. The upper end of this resistance constitutes the negative terminal
of the furnace. The cross section of the resistance is so proportioned to the
current employed that the tubes are brought to a high temperature. This heat
is communicated directly to the alloy near its free surface, where the lighter
and richer alloy accumulates, and where it is comparatively quiescent, i.e.,
removed from the direct action of the screw.
Having now particularly described and ascertained the nature of my invention,
and in what manner the same is to be performed, what I claim is :-
1. The process of reducing metals from their fused salts, which consists in
subjecting the salts to the electrolytic action of an electric current in the presence
of a molten metallic cathode with which the liberated metal is adapted to form
an alloy, in imparting a forced circulation to the molten metal to conduct the
richer surface alloy to a separate chamber, and then volatilizing in an inert
atmosphere in said chamber the metal thus liberated from its salt from an exposed
surface of said cathode out of contact with the electrolyte, and collecting the
volatilized metal, substantially as specified.
2. The process of reducing metals from their salts, consisting in subjecting
the fused salts to the electrolytic action of an electric current in the presence
of a molten metallic cathode electro-negative to the metal to be reduced, and
with which the metal to be reduced is adapted to form an alloy, then volatilizing
in an inert atmosphere in a separate chamber the metal thus liberated from its
salt from an exposed surface of said cathode out of contact with the electrolyte,
and assisting in carrying off the volatilized metal by circulating the inert atmo-
sphere through said chamber, substantially as described.
3. In an apparatus for reducing metals from their fused salts, a chamber
in which salts are to be treated. means for electrolytically treating the said
salts in the presence of a molten metallic cathode with which the liberated metal
is adapted to form an alloy, means for circulating the molten metal to conduct
away the richer surface alloy, a separate chamber for receiving said richer surface

page_text: alloy, means for volatilizing the metal thus liberated, and means for collecting
the volatilized metal, substantially as specified.
4. In an apparatus for reducing metals from their fused salts, a chamber in
which salts are to be treated, means for electrolytically treating the said salts
in the presence of a molten metallic cathode with which the liberated metal is
adapted to form an alloy, means for circulating the molten metal to conduct
away the richer surface alloy, a separate chamber for receiving said richer sur-
face alloy, means for volatilizing the metal thus liberated, and means for circu-
lating an inert atmosphere through the said separate chamber to facilitate the
removal of the volatilized metal, substantially as specified.
Tatal the 10th 1 fl 1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.