Improvements in and connected with the Manufacture of Alkali Aluminates.
Year: 1891

page_text: Date of Application, 29th Apr., 1891
Complete Specification Left, 30th Dec., 1891-Accepted, 13th Feb., 1892
PROVISIONAL SPECIFICATION.
Improvements in and connected with the Manufacture of Alkali
Aluminates.
I Dr. EMIL FLEISCHER of Wiesbaden Germany do hereby declare the nature
of this invention to be as follows:-
The present invention relates to the production of alkali aluminate, alumina,
caustic alkalies, and carbonates (soda, potash) by a special method whereby alkali
aluminate (potash
or soda alumina) is obtained from aluminous substances by means
of alkali sulphates.
This alkali-aluminate process will therefore affect both the manufacture of
alumina and its compounds as well as that of caustic alkalies and carbonates
(soda, potash) to such extent as to constitute it the starting point in these
industries.
In addition to the method of producing alkali-aluminate, the invention also
relates to the treatment of lixiviated residues.
The essential feature, however, of the present application is the new mode of
producing alkali aluminate (potash or soda alumina) from substances containing
alumina (such as bauxite, clay, blast furnace slags, and the like) by means of
alkali sulphates and certain other substances.
It has been frequently attempted to obtain sodium aluminate by fusing bauxite
and sulphate of soda (instead of soda which is usually employed) with the addition
of charcoal, but, as iron is always present in bauxite and mostly in considerable
quantity, the formation of liquors containing much sulphur and colored deep black
by dissolved iron sulphide has rendered the adoption of such process impracticable.
This statement may be confirmed by reference to Lunge's Handbuch der
Sodafabrikation 2nd volume, page 295, where he says "It is true that the soda
of Glauber salt can easily be converted into aluminate by adding charcoal to the
mixture with alumina and then igniting. Bauxite, however, which invariably
contains oxide of iron is not available for this method because the known noxious
sulphur-iron-sodium compound is formed."
66
In the first volume of Muspratt (Stohmann-Kerl) 1888, page 820, the following
occurs By igniting sulphate of soda with bauxite alone no reaction takes place.
If, however, steam or charcoal be added, sodium-aluminate is formed (in the latter
case with the greatest facility) which contains the noxious compound of sodium
and iron sulphides, as the mineral never occurs entirely free from iron. It is
consequently necessary to eliminate the iron before employing bauxite, and this
could only be effected economically if the alumina result as a bye or intermediate
product."
Similar evidence is furnished by other authorities, all of which, taken in con-
junction with the fact that sulphate of soda has never yet been used on a
manufacturing scale for the treatment of bauxite and that only carbonate of
soda is employed, bears out the accuracy of
my assertion.
As a matter of fact, in the treatment of bauxite with sulphates of the alkalies
and charcoal, not only are inky black liquors obtained containing, along with iron
sulphide, much alkali sulphide, but the product of aluminate, as stated by Muspratt,
is scarcely half that obtained by the soda process.
Moreover, the fused mass containing iron seriously attacks the furnace or melting
pot, thus absorbing many impurities and necessitating frequent repairs.
Now, the iron contained in bauxite being generally admitted to constitute the
main obstacle to be removed to admit of alkali sulphates being employed, instead
of carbonates, for obtaining aluminate, if I add iron to the alkaline sulphates and

page_text: thus obtain perfectly colorless liquors containing no iron and very little sulphur
and almost all the aluminate, without the igniting vessel being in the least attacked
by the charge, it will be admitted that for such results a special chemical process.
had to be invented which will teach what treatment is necessary and substances
are required in order to successfully manufacture aluminate from bauxite or any
other aluminous crude substance by means of alkaline sulphates instead of
carbonates. I therefore claim as my invention, the employment of iron or its
oxygen compounds for converting alumina contained in aluminous substances into
aluminate by means of alkali sulphates.
Although iron or its oxides in proper proportion are very suitable for adding
with alkali sulphates for making aluminate, a still better result will be obtained if
lime, either quick or carbonate (limestone or chalk) be also added. I have, more-
over, ascertained that very good aluminate can be got from bauxite and the like
without adding any iron (apart from what may be naturally contained in the
mineral) by means of alkali sulphates and charcoal if a proper quantity of lime or
chalk be added.
As the treatment of substances containing alumina by means of alkali-sulphates
and lime without the addition of a flux, viz. fluor spar (fusing I purposely avoid)
has neither been recommended nor technically employed, I also claim as my
invention the employment of lime or chalk, without fluor spar as an addition, for
the production of aluminate, by igniting it with aluminous substances together
with alkali sulphates and charcoal. I should also consider it as my invention if,
with much lime or chalk, so little fluor spar were added that the ignited mass did
not become fluid, etc.
It is not necessary to particularly specify the action that lime and iron or either
of them (added in various proportions) have upon the treatment of clay, bauxite,
and the like, with alkali sulphates; but it may be stated generally that the treat-
ment with lime alone yields liquors not too sulphurous or black if for every
equivalent of alumina at least 13rds equivalent of lime or chalk be added.
This large quantity of lime fixes a considerable amount of alumina so that the
yield of aluminate is less than from the normal process presently to be described
wherein lime and iron are employed together. Iron alone behaves similarly, but
too small quantities of iron yield black liquors, while too large quantities consume
much alkali and consequently give too small a yield of aluminate. If therefore it
is desired to use iron or its oxides only, the best proportion is also 133rds
equivalent metallic iron to one equivalent of alumina or alkali-sulphate.
The most satisfactory results, however, are obtained if lime and iron be simul-
taneously present in proper proportion in the mixture to be ignited. For pure
alumina one equivalent of metallic iron (or its oxide) one quarter equivalent of
lime or chalk per equivalent of alumina and alkali sulphate (together with charcoal)
may be employed. These proportions, however, may be varied without very great
disadvantage, so that if per equivalent of alumina one equivalent of lime and one
and a half equivalent of iron be used, fairly good results will still be obtained. In
these additions, the iron acts as a desulphurizer, FeS being formed; the lixiviated
burnt mass containing lime and iron sulphide only imparts traces of sulphur to
sal-ammoniac solution. The chief function of the lime is to unite with the silicic
acid of the silicate containing the alumina.
Even with pure alumina, the addition of lime or chalk to the iron is very
useful, as it obviates the necessity for a great excess of iron which diminishes the
yield.
The following general rule may be laid down for obtaining the most favorable
results: Add to the aluminous substance (clay or bauxite) for every equivalent
of alumina one equivalent of alkali-sulphate and ensure by the addition of iron or
its oxides that fully one equivalent of iron (including that already contained in the
clay) be present for the formation of FeS, for every equivalent of alkali sulphate
or alumina. The lime or chalk is to be reckoned as two equivalents for every
three equivalents of silica and a further quarter equivalent of lime or chalk is to

page_text: be added for every equivalent of alumina. Or what is much the same when adding
chalk, add as much as the silicic acid in the mass weighs plus a quarter equivalent
of chalk per equivalent of alumina. These mixing proportions (with the addition
of the necessary charcoal) yield the best results, but they may be considerably
varied as before mentioned without very greatly deteriorating the result. If a
high yield, recovery of sulphur etc., is not essential, satisfactory results may be
obtained with lime or iron alone.
I now proceed to describe my process for the manufacture of alkali-aluminate
(potash or soda alumina) from aluminous substances (clay, bauxite, etc.,) by means
of alkali sulphate, iron (or its oxides) lime (chalk or limestone) and charcoal.
All the silica (sand) which can be washed out is preferably so removed from the
aluminous substance (clay, bauxite, etc.). The alumina, (Al,O,) iron, silica and
lime, (when present in any considerable quantity) contained in the substance to be
treated are to be estimated. The presence of small quantities of magnesia in the
clay is as harmless to the aluminate process as are small quantities of alkalies,
phosphoric acid, or heavy metals, and compounds thereof. Having completed the
analysis the ingredients for the mixture are weighed and finely ground to form an
intimate mixture thereof.
In accordance with the above mentioned rule, the best mixing proportions for
one hundred parts by weight of alumina (Al2O3) contained in the clay or bauxite
are the following:-(Respecting the figures for sulphate of potash and soda, it is
almost unnecessary to remark that they refer to the analogous aluminates to be
obtained by means of the one or the other sulphate.) For one hundred parts
alumina (Al,O.) add—
Sulphate of soda (reckoned as anhydrous) 140 parts by weight
Iron oxide or other oxygen compounds thereof (or metallic iron) containing
an equivalent quantity of iron including that contained in the clay, etc.
80 parts by weight
Charcoal (for reducing at least three equivalents per equivalent of Al₂03)
40 parts by weight
Carbonate of lime (exclusive of an amount equal to the weight of the silica)
equivalent per equivalent Al₂O, 25 parts by weight.
The charcoal may be employed in the form of carbonizing substances (saw-
dust, etc.). The carbonate may be replaced by an equivalent quantity of quick
lime, but in that case for every part by weight of silica there must be added
either the like weight of silica or 56 per cent. of quicklime. For instance, if the
bauxite contain twenty parts by weight of silica to one hundred parts by weight
of alumina, twenty parts more of chalk (corresponding to 11-2 parts CaO) should
be added besides the twenty-five parts of chalk, (or fourteen parts of quicklime).
Of impure substances, such as limestone, etc., it will of course be necessary to use
more. Double the quantity of lime, as already mentioned, would not do any great
practical harm, whereas with the given quantity of iron, black liquors, which are
to be avoided, would result from the use of too little chalk. The lime or the
chalk therefore to a certain extent regulates the iron; for the latter alone always
forms black liquors when at least 13rds equivalent of iron to one equivalent of
alumina or alkali sulphate is not present. The addition of lime, however, permits
this large quantity of iron to be considerably reduced. It is evident that a clay
containing the given quantity of iron (like equivalent to alumina) per hundred
parts by weight of Al2O3 requires no additional iron, but if on the other hand
clays containing much less iron and having even a 15 per cent. content of silica,
are to be treated with only lime or chalk (with the addition of course of alkali
sulphate) as much lime will suffice as will make the total equivalents thereof and
of the metallic iron together, equal to about 13rds of the alumina equivalents
present. Even pure alumina free from iron requires at least 1½rds equivalent of

page_text: lime to produ
-with a deficit
combining
lime.
the
aluminate liquors not too sulphurous so that in a certain degree
of iron-this equivalent proportion indicates the minimum for
phur. Clays containing much silica of course require more
It is evident from these facts, which I have ascertained by experiment, that,
should the iron already present in the clay be insufficient, it is always best, in
accordance with the above given table, to add the lime and iron simultaneously,
according to the general rule "like equivalents of alumina and iron."
Before passing to the further description of the above normal-mixture, I would
remark in regard to the quantity of alkali sulphate to be added that as in the
process of heating, each equivalent of alumina combines with only one equivalent
of alkali and thus produces a compound soluble in water without decomposition,
eg. KOAl2O3 the employment of more alkali sulphate than is equivalent to
the alumina is unnecessary-in fact it is harmful because very sulphurous liquors
are easily produced thereby. If it is desired to leach out the alumina from the
ignited mass as completely as possible, a little carbonate of potash or soda is
added to the leaching water which becomes caustic, owing to the quicklime
produced and thus dissolves any alumina that might become soluble. These
precautions will very soon be found superfluous. As a matter of course, alkali
thio-sulphates or sulphides may be used in place of sulphates.
The substances well ground and mixed may now be ignited in the form of
powder (covered with a little charcoal) either in a reverberatory furnace or in
closed vessels. The temperature does not require to exceed a moderate red heat;
too great a heat (white heat) causes the mass to partly melt instead of lightly
fritting and renders the leaching out more difficult. Oxidation of the sulphide of
iron formed during the heating and cooling, which is preferably conducted in closed
vessels should be avoided. When working with reverberatory furnaces, the mass
should not be raked about more than necessary nor should the layer be too thick
as the heating should be uniform and thorough. Half an hour is sufficient for the
reduction, reckoning from the time the charge is thoroughly red-hot. The finished
mass is then placed in closed iron vessels to cool. Leaching out may be performed
in the manner usual in soda works, with cold or hot water, as, with the iron
addition, no decomposable calcic sulphide is present in the mass. The clear or
filtered liquor of alkali aluminate contains when properly made, but little alkali
sulphide and traces of lime. The latter can be precipitated by adding a little
carbonate of potash or soda, without precipitating alumina which is not precipitated
from aluminate solution by neutral alkali carbonates. If it be desired to dispose
of the aluminate liquor as such and therefore to eliminate the small quantity of
sulphur without introducing carbonic acid, this may be done by adding freshly-
precipitated ferrous oxide or ferric hydrate provided the sulphur is not more
highly oxidized (by chlorine, etc.). For most purposes however, the small amount
of sulphur in the aluminate liquor will be innoxious.
To obtain alumina and alkali carbonates (soda, potash) the colorless solution of
aluminate is saturated almost at boiling point with carbonic acid whereby the
sulphur is so completely driven off as sulphuretted hydrogen that only the least
traces of it are found in the resulting soda or potash solution. It is noteworthy
that no thio-sulphates are generated in this aluminate process. The carbonic acid
for saturating is produced by heating carbonate of lime (limestone). the burnt lime
being used not only for adding to the charge but for treating the leaching residues
and for various other purposes.
Alumina precipitated in a granular condition by means of the hot saturation can
be filtered and washed upon suction filters and is then perfectly free from iron and
silica, in fact so pure that it may be employed for the production of aluminium
The resulting soda or potash solution is also characterized by its purity so long
as the alkali sulphate used for the charge contained no material impurity of alkal
chlorides and which if present partially volatilize during the ignition. Much more
than 90 per cent. of pure soda or potash is obtained by the aluminate process from

page_text: the equivalent quantity of sulphate used. A small proportion of alkali, however,
remains behind as silicate with alumina and lime in the insoluble residue.
If it be desired to obtain caustic alkali liquor directly from the aluminate
solution the alumina may be precipitated by lime according to Löwig's process.
The precipitated lime aluminate after being dissolved in hydrochloric acid and
having the alumina precipitated therefrom with aluminate liquor is suitable for
obtaining easily soluble (gelatinous) alumina.
I found that instead of lime, strontium hydrate can be used, which, unlike
baryta, forms an insoluble aluminate. If however the whole object is to produce
caustic alkali and not gelatinous alumina, it is simpler to saturate alkali aluminate
solution and caustify the resulting solution of soda or potash by means of lime in
the usual way. As lime aluminate is tribasic, only a third the quantity of lime is
required. As the alkali aluminate liquor contains like equivalents of alumina and
alkali, it yields alum direct by saturation with sulphuric acid without excess of
alkali sulphate. Of course the alumina salts can be obtained direct by dissolving
the precipitated alumina in the respective acid. If desired to first extract the
small quantity of alkali still contained in the alumina, it is digested with a little
dilute hydrochloric acid.
of Amil 1001
DR. EMIL FLEISCHER,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.
COMPLETE SPECIFICATION.
Improvements in and connected with the Manufacture of Alkali
Aluminates.
I, Dr. EMIL FLEISCHER of Wiesbaden, Germany, 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:-
The present invention relates to the production of alkali-aluminates, alumina,
caustic alkalies, and carbonates (soda, potash.) by a special method whereby alkali
aluminate (potash or soda alumina) is obtained from aluminous substances by means
of alkali sulphates, &c.
This alkali-aluminate process will therefore affect both the manufacture of
alumina and its compounds as well as that of caustic alkalies and carbonates (soda,
potash) to such extent as to constitute it the starting point in these industries.
It has been frequently attempted to obtain sodium aluminate by fusing bauxite
and sulphate of soda (instead of soda which is usually employed) with the addition
of coal but as iron is always present in bauxite and mostly in considerable quantity,
the formation of liquors containing much sulphur and colored deep black by
dissolved iron sulphide has rendered the adoption of such process impracticable.
This statement may be confirmed by reference to Lunge's Handbuch der
Sodafabrikation, 2nd volume, page 295, where he says "The soda of Glauber salt
can easily be converted into aluminate by adding coal to the mixture with alumina
and then igniting. Bauxite however which invariably contains oxide of iron is not
available for this method because the known noxious ferro-sodic sulphide compound
would be thereby formed."
In the first volume of Muspratt (Stohmann-Kerl) 1888, page 820, the following
occurs "By igniting sulphate of soda with bauxite alone, no reaction takes place.
If however steam or coal be added, sodium-aluminate is formed (in the latter case
with the greatest facility) which contains the noxious compound of sodium and iron
sulphides, as the mineral never occurs entirely free from iron. It is consequently
necessary to eliminate the iron before employing bauxite and this could only be
effected economically, if the alumina result as a bye or intermediate product."

page_text: Similar evidence is furnished by other authorities all of which, taken in
conjunction with the fact that sulphate of soda has never yet been used on a
manufacturing scale for the treatment of bauxite and that only carbonate of soda is
employed, bears out the accuracy of my assertion.
As a matter of fact in the treatment of bauxite with sulphates of the alkalies
and coal, not only are inky-black liquors obtained containing along with iron
sulphide, much alkali sulphide, but the yield of aluminate, as stated by Muspratt, is
scarcely half that obtained by the soda process.
Moreover the fused mass containing iron seriously attacks the furnace or melting
pot, thus absorbing many impurities and necessitating frequent repairs.
Now, the iron contained in bauxite being generally admitted to constitute the
main obstacle to be removed for employing alkali sulphates instead of carbonates
for abtaining aluminate, if I add iron to the alkaline sulphates and thus obtain
perfectly colorless liquors containing no iron and very little sulphur and almost all
the aluminate without the vessel being in the least attacked by the charge, it will
be admitted that for such results a special chemical process had to be invented
which would teach what treatment is necessary and what substances are required
in order to successfully manufacture aluminate from bauxite or any other aluminous
crude substance by means of alkaline sulphates instead of carbonates.
If alumina be ignited with alkali-sulphate and oxide of iron with the addition of
coal, sulphide of iron and alkali-aluminate is formed but the process is not
sufficiently satisfactory for practical purposes. A considerable quantity of the
alkaline sulphide which forms, combines with the sulphide of iron with such
tenacity that the compound thus produced will not decompose even in the presence
of a large excess of iron. If such an ignited mass be lixiviated, an inky-black
solution of a double sulphide of iron and alkali is produced which is very trouble-
some to filter. And if the iron be separated from such an undesirable solution
(which is not a simple matter) still a considerable quantity (often exceeding 300°)
of alkaline sulphides (but only a little alkaline aluminate) is retained in solution.
From the above it is evident that it is in practice out of the question to treat
aluminiferous substances by means of alkali-sulphate and carbonaceous material
with the addition only of iron or its oxides, or to treat ferruginous bauxite with
only alkaline sulphate and carbonaceous material. In either case inky-black
liquors are obtained containing in solution not only sulphide of iron but also large
quantities of alkaline sulphide, whilst the yield of alkaline aluminate is very low.
The tendency of alkaline sulphides (forming on ignition) to combine with sulphide
of iron is actually so great that even an excess of alumina which might assist the
formation of aluminate does not overcome these drawbacks. The addition of
magnesia is equally ineffectual to prevent the formation of the troublesome double
sulphide compound.
As this sulphuretted alkali and iron compound forms on treating bauxite with
alkaline sulphates, not only if iron is purposely added but likewise when already
present as it always is in bauxite, it would be absolutely impossible (as above
indicated) to employ alkaline sulphates for this treatment, had I not discovered
means for effectually preventing the formation of the said noxious compound.
This consists in the employment of lime which is added in the form of quicklime
or carbonate to the mass to be ignited and causes part of the alkaline sulphide to
exchange its sulphur for the oxygen of the lime. Whilst the calcium sulphide
thus produced combines with the iron sulphide to form a substance quite
insoluble in water, the alkali liberated is rendered available for the formation of
aluminate. If therefore such mass after being heated together with the added lime
be dissolved in water, the whole of the iron sulphide (partially combined with
calcium sulphide) remains undissolved. A perfectly colorless liquor is thus
obtained which can be readily filtered and contains a high percentage of alkali-
aluminate but an exceedingly small amount of alkaline sulphide.
It might easily be supposed that by employing sufficient lime it would be
rendered unnecessary to add iron as moreover the lime might act as a desulphurizer

page_text: as in the Leblanc process, but the presence of the alumina absolutely bars the
addition of such a large quantity of lime as would be required for perfect
desulphurization.
During the heating the alumina combines with the lime to form insoluble lime
aluminate a great portion of the lime being thereby withdrawn from the alkali
desulphurization which necessitates a very large excess of lime in order to effect
even a tolerable desulphurization. I have found that 1 molecule of lime is
capable of desulphurizing a mixture of one molecule of pure alumina and the same
quantity of alkaline sulphate with an addition of carbonaceous material, but so
much lime aluminate was thus formed that scarcely half of the alumina used was
contained in the alkali-aluminate liquor. This tendency of the lime and alumina
to combine is diminished by the presence of silica but this is of no advantage as it
requires so much lime which it partly robbed by the alumina. If however the lime
does not alone form the chief desulphurizer but shares this function with the iron,
by adding such a quantity of lime that a part of it prevents the formation of the
objectionable compound of iron sulphide and alkali sulphide whilst the remainder
of the lime combines with the silica of the bauxite, the lime will serve a double
purpose without appreciably diminishing the yield of alkali-aluminate.
My invention consists essentially in the discovery that by a certain regulated
addition of lime and iron in the treatment of aluminiferous substances with alkaline
sulphates or sulphides and coal or other carbonaceous material liquors may be
obtained wherein the iron sulphide formed is insoluble yielding a high percentage
of alkali-aluminate. In order to solve the problem of "How much lime is at least
necessary to prevent the formation of the sulphuretted compound of iron and alkali"
I have performed many experiments with a mixture of equivalent quantities of pure
alumina, alkali sulphate, and iron (together with coal) with varying additions of
lime. These experiments shewed that for every molecule of alkali sulphate
(therefore of alumina also) at least molecule of line or chalk must be added in
order that the noxious iron compound may not form but that colorless liquors may
be obtained. It is true that pure liquors can be obtained if the quantity of lime
be increased without the excess being combined with silicic acid but the yield of
aluminate is thereby more or less seriously diminished. As in my process all the
sulphur of the alkali is given up to the iron it is evident that for every molecule of
alkali sulphate but one molecule of metallic iron or the corresponding amount of
oxide (including the iron contained in the crude material) is required. A large
excess of iron has a deleterious effect because uncombined oxide of iron combines
with alkali, thus diminishing the quantity of aluminate formed. According to my
experiments, to combine silica by means of lime two molecules of lime are required
for three of silica or just so much chalk as the silica contained in the mixture to be
ignited weighs. As the alkali aluminate which forms during the heating and is
soluble in water without decomposition is constituted according to the
formula R₂OA₁₂O₁, not more than one molecule of alkali-sulphate or alkali
sulphide must be added for every molecule of alumina. Hence the following
general rule "Add to the aluminous substance (clay or bauxite) for every
molecule of alumina one molecule of alkali sulphate and ensure by the addition of
iron or its oxides that fully one molecule of iron (including that already contained
in the clay) be present for the formation of FeS for every molecule of alkali
sulphate or alumina. The lime or chalk is to reckoned as two molecules for every
three molecules of silica and a further quarter molecule of lime or chalk is to be
added for every molecule of alumina. Or what is much the same when adding
chalk add as much as the silicic acid in the mass weighs plus a quarter of a
molecule of chalk for every molecule of alumina."
:
These mixing proportions (with the addition of the necessary charcoal) yield the
best results but they may be somewhat varied as before mentioned in reference to
5 lime without very greatly deteriorating the result.
I now proceed to describe my process for the manufacture of alkali-aluminate
(potash or soda alumina) from aluminous substances (clay, bauxite, etc.,) by means

page_text: of alkali sulphate, iron (or its oxides) lime (chalk or limestone) and carbonaceous
matter. All the silica (sand) which can be washed out is preferably so removed
from the aluminous substance. The amount of alumina (Al,03) contained in the
substance to be treated is first to be estimated as well as the iron silica and lime
when present in any considerable quantity. The presence of small quantities of
magnesia in the clay is as harmless to the aluminate process as are small quantities
of alkalies, phosphoric acid, or heavy metals and compounds thereof. Having
completed the analysis, the ingredients for the mixture are weighed and finely
ground to form an intimate mixture thereof.
In accordance with the above mentioned rule the best mixing proportions for
one hundred parts by weight of alumina (Al2O3) contained in the clay or bauxite
are the following:-(Respecting the figures for sulphate of potash and soda, it is
almost unnecessary to remark that they refer to the analogous aluminates to be
obtained by means of the one or the other sulphate.) For one hundred parts of
alumina (Al,O) add
Sulphate of soda (reckoned as anhydrous) 140 parts by weight
Iron oxide [or other oxygen compounds thereof (or metallic iron) containing
an equivalent quantity of iron] including that contained in the clay, etc.
80 parts by weight
Charcoal (for reducing) at least three equivalents per equivalent of Al₂O,
40 parts by weight
Carbonate of lime (exclusive of an amount equal to the weight of the silica)
equivalent per equivalent of Al,0, 25 parts by weight.
The charcoal may be employed in the form of carbonizing substances (sawdust,
etc.). The carbonate may be replaced by an equivalent quantity of quick lime but
in that case for every part by weight of silica there must be added 56% of quick-
lime. For instance if the bauxite contain twenty parts by weight of silica to one
hundred parts by weight of alumina, twenty parts more of chalk (corresponding to
112 parts CaO) should be added besides the twenty-five parts of chalk (or fourteen
parts of quicklime). Of impure substances such as limestone, etc., it will of course
be necessary to use more. A somewhat larger quantity of lime as already mentioned
would not
do
any great practical harm whereas with the given quantity of iron,
black liquors (which must be avoided) would result from the use of too little chalk.
It is evident that a clay containing the given quantity of iron (molecular equivalent
to the alumina) per hundred parts by weight of Al,O, requires no additional iron
but if on the other hand clay's containing much less iron (containing even 15% of
silica) are to be treated with only lime or chalk (with the addition of course of
alkali sulphate) as much lime will suffice as will make the total molecules thereof
and of the metallic iron together equal to about 13rds of the molecules of alumina
present. Even pure alumina free from iron requires at least 13rds of a molecule of
Time to produce aluminate liquors not too sulphurous so that in a certain degree
(with a deficiency of iron) these molecular proportions indicate the minimum for
combining the sulphur. Clays containing much silica, of course require more lime.
It is evident from these facts which I have ascertained from experiment that
should the iron already present in the clay be insufficient it is always best to add
the lime and iron simultaneously in accordance with the above given table and in
conformity with the general rule "like number of molecules of alumina and iron "
as a large amount of lime reduces the yield of aluminate.
Before passing to the further description of the above normal or standard inixture
I would remark in regard to the quantity of alkali sulphate to be added that as in
the process of heating, the alumina forms only a monobasic compound with the
alkali and thus produces a compound soluble in water without decomposition, e.g.
K₂OA,O, the employment of more alkali sulphate than is equivalent to the
alumina is unnecessary-in fact it is harmful because very sulphurous liquors are

page_text: easily produced thereby. If it be desired to dissolve out the alumina from the
ignited mass as completely as possible a little carbonate of potash or soda is added
to the lixiviating water which becomes caustic, owing to the quicklime produced
and thus dissolves any alumina that might become soluble. These precautions will
very soon be found superfluous. Of course, alkali-thiosulphates or -sulphides may
be used in place of sulphates.
The substances well ground and mixed may now be ignited in the form of powder
(covered with a little charcoal) either in a reverberatory furnace or in closed
vessels. The temperature does not require to exceed a moderate red heat; too
great a heat (white heat) causes the mass to partly melt instead of lightly fritting
and renders the lixiviation more difficult. Oxidation of the sulphide of iron formed
during the heating and cooling which is preferably conducted in closed vessels
should be avoided. When working with reverberatory furnaces, the mass should
not be unnecessarily raked about nor should the layer be too thick as the heating
should be uniform and thorough. Half an hour is sufficient for the reduction
reckoning from the time the charge is thoroughly red-hot. The finished mass is
then placed in closed iron vessels to cool. The lixiviation may be performed in the
manner usual in soda works with cold or hot water. The clear or filtered liquor of
alkali aluminate contains when the working is properly attended to but little alkali
sulphide and traces of lime. The latter can be precipitated by adding a little
carbonate of potash or soda without precipitating alumina which is not precipitated
from aluminate solution by neutral alkaline carbonates. If it be desired to dispose
of the aluminate liquor as such and therefore to eliminate the small quantity of
sulphur it may contain without introducing carbonic acid, this may be done by
adding freshly-precipitated ferrous oxide or ferric hydrate provided the sulphur is
not more highly oxidized (by chlorine, etc.). For most purposes however the small
quantity of sulphur in the aluminate liquor will be innoxious.
To obtain alumina and alkali carbonates (soda, potash) the colorless solution
of aluminate is saturated at nearly boiling point with carbonic acid whereby the
sulphur is so completely driven off as sulphuretted hydrogen that only the least
traces of it are found in the resulting soda or potash solution. It is noteworthy
that no thio-sulphates are generated in this aluminate process. The carbonic acid
for saturating is produced by heating carbonate of lime (limestone) the burnt lime
being used not only for adding to the charge but for treating the leached residues
and for various other purposes.
Alumina precipitated in a granular condition by means of the hot saturation can
be filtered and washed upon suction filters and is then perfectly free from iron and
silica in fact so pure that it may be employed for the production of aluminium.
The resulting soda or potash solution is also characterized by its purity so long
as the alkali sulphate used for the charge contained no material impurity of alkali
chlorides and which if present partially volatilize during the ignition. Much more
than 90% of pure soda or potash is obtained by the aluminate process from the
equivalent quantity of sulphate used. A small proportion of alkali however
remains behind as silicate with alumina and lime in the insoluble residue.
If it be desired to obtain caustic alkali liquor directly from the aluminate
solution the alumina may be precipitated by lime according to Löwig's process.
The precipitated lime aluminate after being dissolved in hydrochloric acid and
having the alumina precipitated therefrom with aluminate liquor is suitable for the
production of easily soluble (gelatinous) alumina.
I have found that, instead of lime, strontium hydrate can be used which, unlike
baryta, forms an insoluble aluminate. If however the whole object is to produce
caustic alkali and not gelatinous alumina it is simpler to saturate alkali aluminate
solution and causticise the resulting solution of soda or potash by means of lime in
the usual way. As lime aluminate is tribasic, only a third the quantity of lime is
required. As the alkali aluminate liquor contains equivalent quantities of alumina
and alkali, it yields alum direct by saturation with sulphuric acid without any
excess of alkali sulphate. Of course the alumina salts can be obtained direct by

page_text: dissolving the precipitated alumina in the respective acid. If desired to first
extract the small quantity of alkali still contained in the alumina, it is digested
with a little dilute hydrochloric acid.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what I
claim is
1. The herein described method of manufacturing alkali-aluminates from aluminous
substances and alkaline sulphates or alkaline thio-sulphates or alkaline sulphides
by the addition of iron and lime (or iron oxides, chalk, or limestone) in the presence
of a reducing agent in such manner that the main part of the sulphur in the mass
will combine with the iron whilst any excess of lime beyond the amount necessary
to combine with silicic acid will prevent the formation of soluble compounds of iron
sulphide with the alkalies.
2. The employment, in the above process, of a further addition of lime as a
substitute for a portion of the iron, to form an insoluble compound with part of the
sulphur whilst the remainder of the sulphur forms an insoluble compound with the
other portion of the iron as before described.
D
EMIL FLEISCHER,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.