Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~763~i6
This invention relates to a process for recovering
aluminium values from aluminium-containing minerals.
Aluminium is widely distributed about the surface
of the earth, mainly in the form of clays from which it
S has hitherto not proved economic to extract the metal or
its compounds. It is known to -form aluminium chloride by
sintering a mixture of bauxite, which is a hydra-ted oxide
of aluminium, and powdered coal at a high temperature and
then passing gaseous chlorine over the mixture. This
tO process has been applied industrially, but is limited
by the relatively low yield of aluminium chloride and the
high cost of the starting materials.
'I`he present invention enables aluminium values to
be recovered from aluminium-containing minerals, and in
particular from materials containing minerals which have
hitherto been regarded as industrial waste products.
The present invention provides a process for recovering
~lunlinium values from an aluminium-containing mineral,
which process comprises heating a dried paper sludge,
2~ said dried paper sludgecontaining a carbonisable organic
material in the form of organic fibres in intimate
association with an aluminium-containing mineral selected
from the group consisting of an oxide of aluminium and an
aluminosilicate in finely divided form, to a temperature
2~ of 500 to 1000C to carbonise the organic fibers,
chlorinating the solid residue from the carbonisation step,
and recovering a chlorination product containing aluminium and
chlorine.
The invention may be applied to a wide range of
~0 aluminium-containing minerals in which aluminium is in
combination with oxygen and/or silica.
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- Thus the invention may be applied -to oxides of aluminium,
for example hydrated oxides such as bauxite, and alumino-
silicates, for example aluminium-containing glasses and
clay minerals such as kaolinite (sometimes referred to
as china clay), montmorillonite, bentonite, halloysite,
allophane and mica. The aluminium-containing mineral is
~`inely divided in order to make possible intimate mixing
with the carbonisable organic fibres, particle sizes down
to 20 microns, especially down to 10 microns, are preferred.
The mineral can, if desired, be calcined before the
carbonisation step.
The organic material should be one that can be
~arbonised without complete volatilisaion although some
production of volatile material can be tolerated and may
1~ indeed be desirable in that it can help to distribute fine
particles of carbon throughout the aluminium-containing
mineral. The carbonisable organic material is in fibrous
form so that, upon carbonisation, a very finely divided
form of carbon is obtained in intimate contact with the
aluminium-containing mineral.
The process of the invention utilises dried paper
sludge as carbonisable organic material. Paper sludge
is the effluent from paper making processes and consists
of a dilute slurry of organic fibres of vegetable origin,
2~ usually cellulosic fibres, and of non-fibrous fillers or
loading agents. The organic fibres in the sludge are
extremely fine, since they have passed through the paper-
making wire, and upon carbonisation provide very finely
divided carbon. The fillers or loading agents can con-tain
a high proportion of aluminium-containing minerals, for
example clays such as bentonite and china clay. Paper
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7~;3~;~
sludge thus can contain a carbonisable organic mineral, in
the form of organic fibres, and also an aluminium-con-taining
mineral, and a paper sludge containing both may be used
directly in the process of the invention. Additional
carbonisable material, such as shredded waste paper, and/or
an aluminium-containing mineral may be added to a paper sludge
and incorporated therein by simple mixing techniques. Paper
sludge can contain as much as 10% by weight of solid material,
but usually the proportion is typically around 500 ppm to
100 ppm in the effluent as it leaves the paper mill. The
sludge is preferably allowed to settle, concentra-ted, for
example to 20 to 25% by weight solids content, and then dried
~o 90 to 95% by weight solids content for use in the process
o~` the present invention.
In the next stage of the process, the paper sludge or
other mixture of aluminium-containing mineral and carbonisable
organic material is heated to carbonise the organic material
present. The mixture can be shaped, for example by pelletising
or briquetting, before the carbonisation. The carbonisation
can be carried out entirely in a non-oxidising atmosphere
which may for example be nitrogen or carbon dioxide or i-t is
possible to supply a limited amount of oxygen or gas containing
molecular oxygen in order to burn some of the organic material
and supply heat for the carbonisation reaction. Clearly in
the latter case it is necessary to use sufficient organic
material to allow for that which is burnt while leaving a
suitable amount to undergo carbonisation. The temperature
of carbonisation will of course depend upon the organic
material being used, but is usually in the range of from
500C to 1000 C, and preferably from 750 C -to 900C. The
636~
organic material is converted upon carbonisation to finely
divided carbon which is distributed throughout the aluminium-
containing mineral and provides for a high interfacial area
of contact between the aluminium-containing mineral and the
carbon. l`he surface area and reactivity of this carbon is
many times greater than that of the powdered coal which has
hitherto been used.
The solid residue from the carbonisation reaction is then
ch.lorinated, for example by passing chlorine gas (which need
not be pure and can contain, for example, hydrogen chloride,
hydrocarbons and chlorinated hydrocarbons) through the
carbonised material at an elevated temperature. The temper-
ature of` reaction may be up to about 1500C but is preferably
~ htly lower than the carbonisation temperature,for example
1~ in the range of from 500 C to 800 C. The main produc-ts of
the chlorination reaction are gaseous at the reaction temper-
ature and consist of the product containing aluminium and
chlorine, oxides of carbon and phosgene together with unreacted
chlorine, and minor amounts of impurities including silicon
~0 tetrachloride and ferric chloride. The chlorination products
can differ at different chlorination temperatures for example
greater amounts of silicon tetrachloride are produced at the
higher chlorination temperatures. The chlorination reaction
may be carried out in any suitable apparatus, for example a
~5 rotary kiln, fluidised bed, or indirect-fired system.
The chemical form of the chlorination product containing
aluminium and chlorine can depend upon the conditions of -the
chlorination reaction. The most usual chlorination product
is aluminium chloride, but other products could result, such
as aluminium oxychloride, aluminium hydroxychloride and mixed
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ehlorides such as sodium aluminium ehloride or potassium
aluminium chloride.
The reactions taking place during the chlorination step
involve simultaneous oxidation and reduetion. Two possible
reaetion sehemes when using an aluminium-containing mineral
such as a clay and producing aluminium chloride can be
summarised as follows:
(~) A1203 ~ 3C + 3C12 = 2AlC13 ~ 3CO
and
(B) 2A12 3 2 3 2
The first of these (A) can be termed the "carbon monoxide"
rout~, while the seeond (B) ean be the "earbon dioxide"
rou~. Whieh rou-te is the better to be followed will depend
upon the circumstances of a given situation since much ean
depend upon choice and form of starting materials and upon
energy requirements. The choice of route will affect the
theoretieal quantities of starting materials required for
stoiehiometric eonversion of -the aluminium values in the
aluminium-eontaining mineral into aluminium chloride. In
~0 enlculating the relative proportions of the starting ma-terials
aeeount must also be taken of the fact tha-t the organic
material usually suffers a large weight loss upon earbonisation,
whereas the aluminium-containing mineral is comparatively
unaffeeted. For example, eellulose suffers an approximately
~5 5-fold reduction in weight upon carbonisation. When taking
these factors into consideration it is ealculated -that -the
theoretical quantities (parts by weight) of -the starting
materials and product for the differen-t routes are as follows
~vhen using cellulose and china clay:-
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Cellulose (dry weight) China Clay Aluminium ChlorideRoute (A) 1 1.45 0.89
Route (B) 1 2.9 1.79
It is possible to employ an excess of the organic material
over tl~e stoichiometric requirements. When this is done the
c~cess carbon remaining after carbonisation and chlorination
rem<lins in the solid residue of the chlorination reaction and
is in highly active form, having become activated during -the
chlorination and also by moisture (either mois-ture introduced
by recycling products of combustion or carbonisation, or bound
moisture released by a clay during the final stages of carbon-
i~ation). Such active carbon may usefully be recovered.
~ lulllinium chloride may be separated from other products
vt` the chlorination reaction by dissolving in ethanol, passing
the resultant solution through a bed of active charcoal and
recovering the purified aluminium chloride from the ethanolic
solution. Alternatively it may be separated from the other
products by fractional distilla-tion or sublimation of the
condensed vapours emerging from the reaction zone.
Aluminium chloride produced by the process of the present
invention has a variety of uses as a ca-talyst in organic
chemistry, particularly in polymerisation reactions and organic
syntheses. It is also a useful intermedia-te in the production
ot` aluminium, for example by the TOTH and ALCOA processes, and
may have pharmaceutical applications.
The solid residue from the chlorination reaction is
depleted in aluminium ions and may therefore find application
as a solid adsorbent and as an ion exchange material. I-t
might also find use as an ingredient of cemen-t. Active
carbon contained therein can be separately recovered if desired.
The invention is illustrated by the following Example:
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~76366
c )
~: X ~ M P L E
Paper sludge containing china clay and cellulose fihres
in a ~eight ratio of 1:5 is dried to a moisture content o~
about 5% b~ wei~ht. The dried paper sludge is then fed into
a tu~ular he~ting chamber formed from passive alumina and
situated inside an electrically heated furnace. The tube may
be coated with metal to reduce oxygen di~usion into the
reaction æone or could be constructed of quartæ ox graphite.
~fter introduction of the drièd ma~erial, one end of the
tub~ is ~itted wlth an inlet for gas introduction and the
other end with an outlet for the products of the carbonisation
and chlorina~ion reac~ions. The temperature o the ~urnace
is gradually raised to $00C and maintained at 800C for one
hour, while passing a stream of nitrogen through the tube,
lS Volatile mater.ial produced by the carbonisation of the ce].lu~ose
~ibres is condensed and discarded. The temperature is the~
gradually lowered to 550C and chlorine passed through the tube
at approximately 1 litre per minute until chlorination is
complete. The rate of reaction may be controlled by varying
the temperature. The volatile products of the chlorination
reaction are bubbled through ethanol and passed through a bed
of active carbon. Finally the ethanol is separated from the
puri~ied aluminium chloride by fractional distillation.
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