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Sept. '24, î[946.
' |_. c'. sTu'RBELLE
2 4, 0 82’ 4 l
File@ Jan. fle, 1945
v2 Sheets-,sheet 2
Luc/AN. c. „S'TUR-BH LE
' BY
Patented Sept. 24, 1946
_Y Lucien C. Sturbelle, New York, N. Y.
Application January 1s, 1943, serial No. 472,586
5 Claims. (Cl. 23--141)
This invention relates to the production of me
tallic aluminum and particularly tothe produc
material, such as fbauxites, clays, and coalv ashes.
Metallic aluminum heretofore has been common
ly obtained from sources of material which vare
The lime is .used in an amount' calcu--
lated to give a slag containing a substantial
amount of calcium ‘aluminate and preferably'acomposition falling within the area shownby the
dot and dashlines in the phase equilibrium dia
not plentiful in this country, but Which are rela
to at least reduce the SiOz, FezOa and TiOz _to
the elements silicon, iron, andtitanium respec-j
" tion of the same from lowv grade sources of» raw
tively rich in alumina.
erous material is used in an amount calculated
An object of this invention is to provide an
improved, simple and inexpensive method of -pre
paring metallic aluminum from low grade sources
- gram of Fig. 2.- When the lime is calculated _to
produce a slag that will fall Within this selected
area of the phase diagram, the slag so produced
of raw material, which will require a minimum
of outside energy and of additional reagents; with
will disintegrate into a fine powder when the slag
has been cooled, such as to about 96 degrees C.
which the by-productswill also be useful mate
and is mainly a cli-silicate of calcium> and alu_-`
rials of commercial value, and which will require 15 minum and a calcium aluminate. The propor
only relatively simple and inexpensive apparatus.
tion of lime» can be easily precalculatedby ref
Another object of the invention is to provide
erence to said phase diagram, so as to producea
an improved, simple and inexpensive process of
which will have these characteristics.r
obtaining aluminum oxide and aluminum hydrox
This mixture of the aluminum-containing ma-ide of relatively pure grades, which may be em 20
terial, the carboniferous material, and the lime
ployed .by any of the Well-known processes for
is smelted, either continuously or in batches >as
the production of metallic aluminum.
desired, in a suitable furnace, and an electric
Other objects and advantages Will be apparent
furnace is very suitable for this purpose. When
from the following description of an example of
the mixture has been smelted, the result is a
the invention, and the novel features will be par-v
metal alloy and a slag, which are tapped from
ticularly pointed out hereinafter in connection
time to time from- the bottom of the furnace into
with the appended claims. f
\ _»
ï '
a tapping mold which -is preferably conical in
shape, the temperature of the smeltedmass be
Fig. 1V is a flow sheet illustratingr the successive
ing approximately 1600 to 1800 degrees C. The
steps in one example of the process according
Inthe drawings:
to this invention; and
f .
mold with the tapped mixture of' metal and slag ,
therein is allowed to cool by itself, during which
Fig. 2 is a diagram of a'portio-n of a phase
equilibrium diagram of refractory oxides, which
is advantageously .employedin connection With
this invention.
The diagram of Fig. 2 is knownas a compost-`
tion~temperature phase equilibrium> diagram of
the refractory oxides, which is published by the
United States Steel Corporation, Research Lab
oratory, and identified as Plate 2. Similar dia
grams have been published by other concerns
covering approximately the same subject matter,
and this diagram illustrates the characteristics
and properties of'compositions of the oxides of
calcium, aluminum andsilicon, and changes in
such characteristics and properties which occur
as relative proportions of the -different compo
nents vary. Only that portion of the chart to
Which this invention relates has been illustrated.
Low grade bauxites are characterized by their
10W content of alumina, which is usually between
30% and 55% aluminum oxide, A1203, with a
high content of silica or iron oxide, or both.
the slag stratii’ies separately from vthe metal al
-lo'y,~and when the ’temperature reaches about 96
degrees C. this slag swells and disintegrates into
a powder which is easily separated from the
metal. The metal is largely a ferro-silicon alloy,
plus impurities such as titanium, and the slag
has an appearance very much like a basalt rock.
The metal’alloy is marketable because it has
usefulness in various industries and is not an
economic loss. The slag is disintegrated into
ñnely divided particles which are then leached
with a sodium carbonate (NazCOs) solution, which
gives a solution of sodium aluminate and a pre
cipitate of calcium carbonate. After the leaching
has been completed, the solid residue is sepa
rated from the liquid in any suitable manner,
such as by filtration. Preferably, the residue
after separation of the liquid is Washed in order
to recover as much as possible of the excess of
the sodium carbonate and of solutions of sodium
aluminateV which may adhere to the residue.
Clays and ashes have a content of approximately
While any suitable leaching, filtering and Washing
30% to 50% of SiO2, 30% to 50% of A1203, the 55 aparatus may, of course, be employed, one suit-y
remaining content including _Fe-203, TiOz, etc.
able for this purpose ,is disclosed in my copending
This raw material (loW grade bauxite, clay or
application Ser. No. 331,265, ñled April 23, 1940.l
ashes), according to Athis invention is mixed with
The composition _ofthe desired slag, as explained,
a carboniferousv material, rsuch as co_al„` carbon,
is largelya ldil-silicate of calcium and aluminum
cokeor charcoal, and with lime.“ The Ycarbonit 60 and. a Calcium aluminate, and when such apoW
der is leached by the sodium carbonate, the re~
one which disintegrates upon cooling to facilitate
its separation from the metal alloy, and be in
easily leachable condition, a slag of modified com
actions are as follows:
20a (OH) 2+Na2O~Al2Os-l-CaCO3
While the composition of the slag is preferably
position, but contatining calcium aluminate, may
be reduced to powder form in any suitable man
ner, such as by atomizing it while fluid, or cru-she
ing it, but this entails additional operations and
expense that can be avoided by selecting the pro~
The residue from the leaching operation after 10 portion of lime-to produce a slag that yswells and
it has been washed, as explained, is calcined,
disintegrates upon cooling. The lime should,
which converts it into carbon dioxide gas andV a
therefore, preferably be calculated to give a slag
residue containing lime. The lime so formed is
that melts at a temperature not materially above
used in place of fresh lime for mixing with fresh
approximately 1600 degrees C., contains not in
aluminum bearing materials and carbon to pI'o
excess of approximately 52% or less than ap
vide fresh charges to. be smelted, as above ex
proximately 30% of alumina, a silica content‘less
plained. The carbon dioxide gas> is used in a later
than approximately 20% and a lime content. of
step of the. process., which will be explained
47% to 70%. Such a slag on coolingv should cause
The solution from the filtration operation may
contain s-ome silicious material which preferably
crystallization of lone or more of tricalcium lsili
20 cate, tricalcium aluminate, 5:3' calciumalunii~
should be removed. Therefore, this solution from
the filtration operation is preferably heated to a
temperature approximately from 100 to 125 de
grecsl C. and with 29 to 34 pounds per square inch
pressure, with the -result that the silicious con
tent is coagulated and settles. The mixture is
then allowed to settle, and by adding to this set
tung mixture 9» Small partv 0f the cake remaining
upon the filter in the preceding operation, the set
tling out is aided. It is difficult to ñlter out a 30
gelatinous silica, and for that reason, the gelati
nous material is settled out andv with some of the
solution is cycled or sent backwardsl to and mixed
with the source of the sodium carbonate solution
for the leaching operation. The clear liquid from
.the settling operation is then reacted upon with
the carbon dioxide obtained' from the calcination
of the filtration residue.
This reaction isA as Yfol'
This precipitates aluminum hydroxide inr rela
nate, calcium aluminate, and' alpha and beta di
calcium silicate, which are crystals appearing
within the area deñned by the dot and dash line
in the phase diagram of Fig. 2. A slag of this
composition will disintegrate automatically as it
cools, such as around 96 to 100 degrees C.
As an example of the use of such a phase dia
gram, let it be supposed that there is a slag of
the following composition:
Per cent
SlOz ____________________________________ _- 20
A1203 ___________________________________ __ 30
CaO ____________________________________ __ 50
This would locate the» slag on the. phase diagram
(Fig. 2) at approximately the point “0.” From
the diagram and by reference, it- will` be observed
that such a slag lies betweenl the isotherms 1600
and 1500, so that the melting point. will be about
1530 degrees C. If such a, slag is tapped olf at
40 1600 degrees C., it will be liquid and the elements
are mixed together as a homogeneous solution,
but when it cools, as soon as a temperature of
about 15.30 degrees C. is reached. some of the
elements will` begin to crystallize in accordance
This mixture, after this reaction, is then filtered
45 with well established laws shown by the diagrams,
to remove the sodium carbonate solution which
.and the ñrst. crystals formed will be 2CaO.SiO2,
is returned to the source of sodium- carbonate
because this compound has a melting point of
used for the leaching operation, and since sub
2130 degrees C. andr this slag isv located in the
stantially all ofthe sodium carbonate is recov~
di-silicate zone. The equilibrium of the slag is de
ered and re-usedv for this purpose, it is only neces
tively pure form in a solution of sodium carbonate.
sary to add a small amount of fresh sodium car 50 stroyed, more crystals are formed, and aY liquidus
of a lower melting point is separated, the compo
bonate as a make-up solvent» Similarly the lime
sition of the liquid part following the arrows on
recovered by the calcination of the solids residue
linesl shownA in the drawings.l The. separated crys
following the leaching is nearly suñicient to pro
tals being mostly 2CaO.SiOz with little A1203, the
vide the li-me required for treating afresh (111211
tity of rawv material containing aluminum,- and 55 quantity of the latter in the liquidus increases.
The. eutectic of this zone has a melting pointv of
only a small amount of make-up lime need be
aboutI 1336 degrees C. and will freeze last, but be
cause many crystals of di-silicate have been
formed and the quantity of silica present is lowy
minum hydroxide is then calcined so as to con- 60 a large part of the alumina will crystallize as alu
minate of calcium. When all of the slag is crys
vert it into a relatively pure aluminum oxide,
tallized, one obtains a mixture of t
A1203, which is then converted into. metallic alu
minum in any suitable manner, such as by an elec
1. Crystals of ZCaQSiOz
trolytic aluminum cell, and the metallic alu
2. Eutectic containing CaO.A12O3.SiO2
minum4 may then be formed into suitable insots
3. Aluminate of’calcium.
for marketing.
added and that lime can> be added as limestone to
solids residue from the leaching step and calcined
therewith. This separated precipitate of alu
During this calcination of the aluminum hy
The first of these components of this crystal
lized mass h'as the property of swelling at about
droxide, hot gases are driven off, and these gases
96 degrees C., the second is insoluble in soda ash,
may be used in the purification of the solution
received from the leaching operation. Such gases 70 or sodium carbonate, and the third is soluble in
soda ash, giving a solution of sodium aluminate
do not enter into the chemical reaction, but are
land a precipitate of carbonate of lime.
used to heat the leached liquid and coagulate the
Ifv now, for example, the lime is calculated to
, impurities therein, such as the silicious material.
give a slag of nearly the same composition but
'_I'hus very little, if any, heat is lost by such cal»
75 situated at' “0'” at the other side- of the bound
cination of the aluminum hydroxide.
>bon dioxide resulting from such calcination as
the source of carbon dioxide employed to pre
cipitate the alumina, and returning the calcined
solid residue to new batches of charging stock
increase in lime and the eutectic will melt at 1265
degrees C. with a composition of:
5 together with sufficient fresh lime and carbon to
maintain the proportionsr stated for the forma
tion of ferrosilicon and said slag.
A1203 _____ __
3. In the process set forth in claim 1, the fur
ary line, the first crystals formed would be
Gehlenite >at 1596 degrees C., which is richer in
A1203 than the slag. Th'eremaining liquidus will
__ __
ther steps of purifying the sodium aluminate
solution obtained by leaching the slag by heat
This will give a separation of some lime and
the whole product will be insoluble in sodium
carbonate.` Therefore, to get a leachable prod
ing said solution to a temperature of from 120°
to 125° C., and under a pressure of from 29 to 34
pounds per square inch, thereby to coagulate the
uct, it is important to have the composition of
the slag fall approximately within the area en
closed by the dot and dash lines, which is the
boundary of th'e ternary crystallization ñeld joinf
ing the point 2CaO.SiOz to 5CaO.3Al2Oa and toV Y
CaO.Al2O3. For practical reasons, it is better to
avoid going over the 1600 degrees C. isotherm be
cause that would give too vhigh a melting point
with too low a content of A1203 and too low a v
fluidity. In other words, the compositionshould
silica therein, and separating the silica by set
4. In the process set forth in claim 1, the fur
ther-steps of purifying the sodium aluminate
solution obtained by leaching the slag which
comprise heating said solution under pressure,
adding to the solution a small part of the leached
slag, and settling the separated silica and said
leach'ed slag.
5. In a process of producing metallic aluminum
preferably remain in the zone alpha 2CaO.SlO2
from low ,grade sources of alumina containing
and within the limited area defined by the dot
substantial amounts of silica, such as low grade
and dash lines.
bauxites, clays, and coal ashes, the steps of mix
To express the matter in a slightly different
ing the alumina bearing material from said
manner, the lime sh'ould be calculated to give a
sources with carboniferous material and lime,
slag which has a composition varying from
with the carboniferous material present in an
3CaO.Al2Oa to 5CaO.AlzO3 with a silica compo
amount approximately suilicient to reduce the
nent not greatly exceeding more than one mole. 30 silica, iron oxide and titanium oxide to silicon,
It will be understood that various changes in
iron and titanium and the'formation of silicon
the details and materials, as well as proportions,
alloys, and with the lime present in an amount
which have been herein described and illustrated
sufñcient to give, upon smelting of the mixture,
in order to explain the nature of the invention,
a slag which contains calcium aluminate and di
may be made by those skilled in the art within
calcium silicate’and wherein the calcium alumi
the principle and scope of th'e invention as ex
nate is present as tricalcium aluminate and 5:3
pressed in the appended claims.
calcium aluminate and mixtures thereof, said
' I claim as my invention:
slag further'being such as to disintegrate auto
y 1. In a process of producing alumina by fusion
matically upon cooling, smelting th'e mixture,
of low grade and silicious alumina-bearing mate 40 cooling the same to effect a separation of the
rial with carbon and lime and subsequent extrac
alloyed metals from the slag and the solidiñca
tion of the alumina from the resulting slag by
tion of the yslag with disintegration at low tem
leaching with sodium carbonate, the steps com
peratures, leaching the disintegrated slag with
prising adding to the low grade alumina-bearing
- a sodium carbonate solution to form a solution
material enough carbon to convert iron and sili
con contained therein to the metallic state with
of sodium aluminate and a residue of dicalcium
the formation of a ferrosilicon, and enough lime /
to form a, slag separating on cooling from said
ferrosilicon composed essentially of dicalcium
silicate and calcium aluminate in which the ra- ’
tio of lime to alumina is between three parts of
lime to‘one of alumina and five parts of lime to
th'ree of alumina, heating the mixture to fusion
and for a time sufficient to form said ferrosilicon
and slag, cooling the mass to effect separation
of the ferrosilicon from the slag,'leaching the
slag with a solution of sodium carbonate, thereby
to extract substantially all of the alumina there
in as sodium aluminate in solution and leave a
residue composed essentially of dicalcium sili
cate and calcium carbonate, purifying the solu
tion from colloidal silica contained therein, pre
cipitating the alumina from the purified solution
by adding thereto carbon dioxide and thereby
regenerating sodium carbonate, returning the
regeneratedsodium carbonate solution to leach
further quantities of slag, vand recovering the
precipitated alumina.
,_ 2. In th'e process set forth in claim 1, the fur
ther steps of calcining the residue of dicalcium
silicate and calcium carbonate, utilizing the car-_
silicate and precipitated calcium carbonate,
heating the liquid from the leaching step to coag
ulate the silicious content thereof, separating the
coagulated silica by settling, treating the so pur
ified liquid with carbon dioxide to precipitate
aluminum hydroxide and form a solution of so
dium carbonate, separating th'e aluminum hy
droxide from said solution to form aluminum hy
droxide with the liberation of hot gases, using
the heat of said gases to heat the liquid from
the leaching operation to effect the coagulation
of -the silicious content, calcining the residue of
dicalcium silicate and calcium carbonate to re
lease carbon dioxide and recover'a lime-silica
mixture, using the released carbon dioxide as lthe
precipítant for the aluminum hydroxide, return
ing. the lime-silica mixture to fresh charges of
alumina bearing material together with such
quantities of lime and carbon as are required to
“ form the said auoys and slag, returning the solu
tion of sodium carbonate` regenerated by the pre
cipitation of the aluminum hydroxide to the
f leaching step, and treating the precipitated alu
minum hydroxide to recover aluminum there
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