Improvements relating to the Extraction of Aluminium from Cryolite and other Substances.
Year: 1889

page_text: Date of Application, 8th Jan., 1889
Complete Specification Left, 8th Oct., 1889-Accepted, 16th Nov., 1889
PROVISIONAL SPECIFICATION.
Improvements relating to the Extraction of Aluminium from Cryolite
and other Substances.
I, Professor CURT NETTO, of 16 Lindenaustrasse, Dresden, in the Empire of
Germany, Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to the extraction of metallic aluminium from cryolite and
other aluminium compounds by the reduction of the same by means of sodium or
similar reducing agents, or by the aid of electricity.
In the Specifications of former Letters Patent No. 4228 dated 21st March 1887
and No. 17532 dated 20th December 1887, I have described processes whereby I
provide for obtaining metallic aluminium containing a small per-centage of impurities
as compared with the aluminium produced by the processes employed previous to the
date of the said former Letters Patent No. 4228.
The object of my present invention is to provide for the production of practically
pure aluminium from cryolite and other aluminium compounds containing silicon,
iron or other impurities.
My said invention is based upon the discovery that nearly all the silicon, iron or
other impurities which are capable of combining with aluminium, are reduced during
the first stage or stages of the reduction process for the extraction of the aluminium,
and that, by interrupting the process when such impurities have been reduced, and
withdrawing the impure aluminium thus formed, the impurities contained in the
charge can be eliminated so that, in the subsequent stage or stages of the process, pure
aluminium will be extracted.
According to my said invention therefore, I obtain the aluminium by fractional
reduction, that is to say, I first separate or extract part of the aluminium with
practically all of the impurities contained in the charge which are capable of combining
with aluminium, and I then extract from the charge (which has, in the manner above
indicated, been freed from the said impurities) the remainder of the aluminium
in a pure state. For example, I proceed as follows, viz. :-I first smelt, in a crucible
or other suitable receptacle, a charge consisting of cryolite and rock-salt in equal, or
about equal proportions, I then introduce into the molten compound (in the manner
described in the said former Specifications or in any other convenient manner) about
one third of the quantity of sodium theoretically required for the complete reduction.
When the desired decomposition has taken place, I pour the charge from the said
crucible slowly into a second crucible which has been previously heated to a red heat,
taking care that the metallic bottom which is collected in the lower part of the first
crucible does not fall into the second crucible.
After nearly the whole charge is thus transferred into the second crucible, I pour
the metallic bottom from the first crucible, together with a small quantity of the slag,
into an iron mould for cooling.
I put the second crucible again into the furnace and complete the reduction therein,
using for this purpose the balance of the theoretical quantity of sodium required for
the reduction of the entire charge. I then empty the contents of this crucible into a
convenient mould.
In this manner, from the ordinary commercial cryolite, about one-third of the
aluminium produced is extracted in the first stage of the process in an impure state,
whilst the remaining two-thirds are obtained as practically pure metal (containing
only from say one-half to one per cent. of impurities).
It is not essential that the entire operation should be performed in crucibles, as it

page_text: can be carried into effect in other vessels; for instance, in reverberatory furnaces. I
sometimes effect the first stage of the reduction process in a reverberatory furnace and
the subsequent stage or stages in crucibles.
My invention is applicable to the extraction of aluminium by the introduction,
into the molten aluminium compound, of the sodium either in a solid or a liquid
state..
Although I have herein before described my invention, by way of example, as
applied to the reduction of cryolite by means of sodium for the purpose of producing
pure aluminium from impure or contaminated raw material, my improved process of
fractional reduction can also be applied to the extraction of aluminium from other
substances by means of the same or other reducing agents (such as magnesium or
potassium); for instance, in cases where chloride of aluminium or the double chloride
of aluminium and sodium are to be treated. Moreover, in cases where the decom-
position is effected, by electricity, or by electricity and carbon, a fractional reduction
can be applied with advantage for the purpose of removing or eliminating, during the
first stage or stages of the process, the impurities contained in the charge, and
subsequently completing the reduction from the material thus purified.
It is evident that I can divide the quantity of sodium required for the complete
reduction into other fractional parts than those above stated, that is to say, instead
of using one-third of the reducing agent in the first stage and the remaining two-
thirds thereof in the subsequent stage of the process, I can use one-fourth or any
other desired fraction of the reducing agent for obtaining the impure aluminium and
the remainder for the production of the practically pure metal.
In some instances I may divide the reduction process into three or more stages.
To more effectually ensure the purity of the aluminium, 1 line the crucibles or
other receptacles in which the reduction is performed with basic materials of such a
nature that the aluminium cannot gather from the wall of the crucible or other
receptacle, silicon, iron or other impurities.
TY
1
011
1
"
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
"
COMPLETE SPECIFICATION.
Improvements relating to the Extraction of Aluminium from Cryolite
and other Substances.
1, Professor CURT NETTO, of 16 Lindenaustrasse, Dresden, in the Empire of
Germany, 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 statement :-
My invention relates to the extraction of metallic aluminium from cryolite
and other aluminium compounds by the reduction of the same by means of sodium
or similar reducing agents or by the aid of electricity.
.
In the specifications of former Letters Patent No. 4228 dated 21st March 1887
and No. 17,532 dated 20th December 1887, I have described processes whereby I
provide for obtaining metallic aluminium containing a small percentage of impurities
as compared with the aluminium produced by the processes employed previous to
the date of the said foriner Letters Patent No. 4228.
The object of my present invention is to provide for the production of practically
pure aluminium from cryolite and other aluminium compounds containing silicon, iron
or other impurities.
My said invention is based upon the discovery that nearly all the silicon, iron or
other impurities which are capable of combining with aluminium are reduced during
the first stage of the reduction process for the extraction of the aluminium, and that,
by interrupting the process when such impurities have been reduced, and withdrawing

page_text: the impure aluminium thus formed, the impurities contained in the charge can be
eliminated so that, in the subsequent stage or stages of the process, pure aluminium
will be extracted.
According to my said invention, therefore, I obtain the aluminium by fractional
reduction, that is to say, I first separate or extract part of the aluminium with
practically all of the impurities contained in the charge which are capable of com-
bining with aluminium, and I then extract from the charge (which has, in the
manner above indicated, been freed from the said impurities) the remainder of the
aluminium in the pure state.
For example, I proceed as follows, viz. :-I first smelt in a crucible or other suitable
receptacle a charge consisting of cryolite and rock-salt in equal, or about equal
proportions. I then introduce into the molten compound (in the manner described
in either of the said former specifications, or in any other convenient manner) about
one third of the quantity of sodium theoretically required for the complete reduction.
When the desired decomposition has taken place, pour the charge from the said
crucible slowly into a second crucible which has been previously heated to a red
heat, taking care that the metallic bottom which is collected in the lower part of the
first crucible and which contains the impurities, does not fall into the second
crucible.
After nearly the whole charge is thus transferred into the second crucible, I pour
the metallic bottom from the first crucible together with a small quantity of the slag
into an iron mould in which I allow it to cool.
I put the second crucible again into the furnace and complete the reduction therein,
using for this purpose the balance of the quantity' of sodium required for the
reduction of the entire charge. I then empty the contents of this crucible into a
convenient mould.
In this manner, from the ordinary commercial cryolite, about one third of the
aluminium produced is extracted in the first stage of the process, in an impure state,
whilst the remaining two thirds are obtained in the second stage of the process, as
practically pure metal (containing only from say one-half to one per cent. of
impurities).
It is not essential that the entire operation should be performed in crucibles, as it
can be carried into effect in other vessels; for instance, in reverberatory furnaces
or in iron converters. I sometimes effect the first stage of the reduction process in
a reverberatory furnace and the subsequent stage or stages in crucibles.
My invention is applicable to the extraction of aluminium by the introduction
of the sodium either in a solid or in a liquid state into the molten aluminium
compound.
It is not always necessary that any aluminium should be reduced in the first stage
of the process. In some cases, I add, in the first crucible, a quantity of sodium just
sufficient to reduce the impurities with the exclusion of aluminium. I then allow
the said impurities to settle at the bottoni, pour the remaining purified charge into
another crucible, taking care that none of the impurities collected at the bottom of the
first crucible fall into the second crucible.
After nearly the whole charge is thus transferred into the second crucible, I
proceed as above described, that is to say, I pour the impurities from the first crucible
together with a small quantity of the slag into an iron mould for cooling; and I put
the second crucible again into the furnace and complete the reduction therein, using
for this purpose the balance of sodium required for the reduction of the whole charge;
I then empty the contents of this crucible into a convenient mould.
Although I have hereinbefore described my invention, by way of example, as
applied to the reduction of cryolite by means of sodium for the purpose of producing
pure aluminium from impure or contaminated raw material, my improved process
of fractional reduction can also be applied to the extraction of aluminium from other
substances, by means of the same or other suitable reducing agents (such as inagnesium
or potassium), for instance in cases where chloride of aluminium, or the double chloride

page_text: of aluminium and sodium are to be treated. Moreover in cases where the decom-
position is effected by electricity, or by electricity and carbon, a fractional reduction
can be applied with advantage for the purpose of removing or eliminating, during
the first stage or stages of the process, the impurities contained in the charge, and
subsequently completing the reduction from the material thus purified.
It is evident that I can divide the quantity of sodium required for the complete
reduction into other fractional parts than those above stated, that is to say, instead
of using one third of the reducing agent in the first stage and the remaining two
thirds thereof in the subsequent stage of the process, I can use one fourth or any
other desired fraction of the reducing agent for obtaining the impure aluminium
or extracting the impurities, and the remainder for the production of the practically
pure metal.
In some instances, I divide the reduction process into three or more stages.
To more effectually ensure the purity of the aluminium, I line the crucibles or
other receptacles in which the reduction is performed, with basic materials of such a
nature that the aluminium cannot gather from the wall of the crucible or other
receptacle, silicon or other impurities."
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed I wish it understood
that I claim :-
First. The extraction of aluminium from cryolite or other aluminium compounds
by fractional reduction, for the purpose above specified.
Second. In the manufacture of aluminium, the fractional reduction of the aluminium
compounds in such a manner that first a part of the aluminium contained in the
charge is precipitated together with the impurities (or the metals reduced from such
impurities) and then the remainder of the aluminium is obtained in a practically pure
state, from the part of the charge thus purified, substantially as hereinbefore
described.
Third. In the manufacture of aluminium, the treatment of the aluminium
compounds in such a manner that first the impurities contained in the charge are
precipitated and removed, and then the aluminium is reduced from the purified
charge in a practically pure state, substantially as hereinbefore described.
Fourth. The treatment of cryolite or other aluminium compounds by a decomposing
metal in a vessel lined with a basic material, as, and for the purpose, above
specified.
Unted this 5th day of Ostahau 1880