Note: Descriptions are shown in the official language in which they were submitted.
2~10~95
SPECIFICATION ~ ~
METHOD FOR PRODUCING IRON-MANUFACTURING RAW ~ ~:
MATERIAL COMPRISING DISSOLUTION RESIDUE OF BAUXITE
FIELD OF THE INVENTION ~:
The present invention relates to a method for producing .
an iron-manufacturing raw material comprising a dissolution residue
of bauxite. In particular, the present invention relates to a method ~ ~
for producing a dissolution residue of bauxite which can be used as a ~ ~;
raw material or an auxiliary material in iron manufacturing ~ j
(hereinafter, both may be referred to as an iron manufacturing raw ~:
material collectively), in a so-called Bayer process in which bauxite
is treated with a solution of sodium aluminate to obtain alumina.
PRIOR ART
As is well known, in the ~ayer process in which alumina
is extracted from bauxite, a large amount of dissolution residue is
discharged. Effective use of such residue has been studied and
discussed from various views for a long time.
For example, the dissolution residue is decomposed to
recover valuable components (Japanese Patent KOKAI Publication No.
261350/1988), the dissolution residue is consolidated and
advantageously used for the production of concrete, tiles or paving
material (Japanese Patent KOKAI Publication No. 319259/1987), or a
special component in the dissolution residue is used as a catalyst or
a catalyst support.
Although the various utilities have been proposed in the
literatures as above, only a small amount of the dissolution residue
is used as road construction material besides being used as a land-
fill material.
,,,~' .
-` 211059~
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Reasons for such situation are (1) that the dissolution
residue is in a slurry state having a solid content of about 450 g/l, -
and it is difficult to dehydrate the slurry, (2) that it is a mixture
containing various components some of them are not suitable for the ~ ~;
intended use, and it is difficult to make full use of properties of all
the components, (3) that a soda content in the dissolution residue is
high, so that it is not suitable as a raw material of a refractory or
ceramics, and (4) that particles are very fine, so that handing of the
residue is difficult. Consequently, the most of the dissolution
residue is used as the land-fill material.
However, these days, a sea shore or an inland area which :~
can be land-filled is decreasing. In addition, the dissolution residue
contains considerable amounts of iron oxides, silicon oxide and the
like. In view of the preserve of resources, more serious solutions on
the effective use of dissolution residue of bauxite are desired.
As is weil known, while it is not uniform depending on a
kind of bauxite to be used or treating conditions in the Bayer
process, a composition of dried dissolution residue (hereinafter
referred to as "red mud" somewhere) is 8 to 12 % by weight of loss
on ignition (L01), 18 to 25 % by weight of Al2O3, 15 to 20 % by
weight of SiO2, 30 to 40 % by weight of Fe2O3, 8 to 12 % by weight
of Na20, and 2 to 8 % by weight of TiO2 (see Jiro Kitagawa,
"ALUMINUM INDUSTRIES" (published by Seibundo-Shinko-sha), page
76).
When attention is given to the iron oxide in view of the
effective use of dissolution residue of bauxite, the above content of
iron oxide is acceptable, while Na20 should be 3 % by weight or less,
preferably 1 % by weight or less, and the L01 should be 10 % by ...
2110595
- 3 ~
weight or less, preferably about 8 % by weight or less as other
ingredients.
When a large amount of sodium material is present in the
iron manufacturing raw material, it is evaporated in a blast furnace
to generate vapor, which is deposited and accumulated in a low
temperature area at an upper part of the furnace and has adverse
effects such as weakening of the refractories, and also interferes
the flow o' furnace gas.
When an amount of the L01 is large, the L01 tends to
decrease a furnace temperature in a sintering equipment for sintered
iron or pellets, which lead to great loss of energy.
When an amount of Al203 is large, the slug is acidified,
which makes desulfuration and dephosphorization difficult, so that
an amount of an alkaline flux such as calcined lime increases, and
thereby the productivity is decreased. In addition, when the amount
of Al203 is large, reduction disintegration index (RDI) of sintered
iron or pellets increases to cause the strength reduction of blocks,
whereby uniform and smooth gas flow in the blast furnace is
interfered, and quality and productivity of pig iron are adversely
affected. Accordingly, the content of Al203 is usually 20 % by ~ -
weight or less, preferably 10 % by weight or less.
However, as seen from the above cited "ALUMINUM -
INDUSTRIES", the conventional dissolution residue of bauxite does
not necessarily satisfy the composition required for the iron
manufacturing raw material in not only the Na2O content but also in
the L01 and the Al203 content. Accordingly, though the attention is
paid on the content of Fe2O3 in the composition, its utilization has
been given up.
--` 2110~95
- 4 -
SUMMARY OF THE INVENTION
In view of the above situations, the inventors have made
study to obtain a dissolution residue of bauxite which can be used as
a raw or auxiliary material for iron manufacture and, as the result,
found a method for producing an iron manufacturing raw material
comprising a dissolution residue of bauxite which satisfies the
composition necessary for the raw or auxiliary material for iron -~
manufacture without sacrificing the inherent object of the Bayer
process, namely without decreasing a production unit of alumina.
Then, the present invention has been completed.
That is, the present invention provides a method for
producing an iron manufacturing raw material comprising a
dissolution residue of bauxite containing 3 % by weight or less of
Na20 and 10 % by weight of loss of ignition, which process comprises
steps of:
mixing bauxite and an alkaline solution to form a slurry,
charging said slurry in an extractor,
extracting alumina under conditions that most of the
alumina which is extractable from bauxite is extracted while
dissolution of reactive silica is suppressed as much as possible,
separating an extract and a dissolution residue while the
reactive silica which is dissolved in the extract is no precipitated
substantially as a desilication product, and
washing and dehydrating said separated dissolution .. ~.
residue .
The present invention further provides a method for
producing an iron manufacturing raw material comprising a
dissolution residue of bauxite containing 3 % by weight or less of
'
:
`- 211059~
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Na20, 10 % by weight or less of loss on ignition and 10 % by weight
or less of Al203, which process comprises mineral processing and/or
chemically treating the separated dissolution residue obtained in the
above method.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow sheet of the Bayer process for producing
the dissolution residue of bauxite according to the present invention,
and
Fig. 2 is a flow sheet of the conventional Bayer process.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the composition of bauxite
dissolution residue as the iron manufacturing raw material
comprises 3 % by weight or less of Na20, 20 % by weight or less of
Al203, and 10 % by weight or less of LOI (all dry material base).
Depending on the bauxite raw material, the contents of other major
components are 35 % or more of Fe203, 20 % or less of SiO2, and 10 %
by weight or less of TiO2, preferably, 40 % or more of Fe203, 1 % by
weight or less of Na20, 8 % by weight or less of LOI, 10 % by weight
or less of Al203, 15 % by weight or less of SiO2, and 10 % by weight
or less of TiO2.
The bauxite dissolution residue having the above
composition can be obtained by mixing bauxite and an alkaline
solution to form a slurry, charging the slurry in an extractor,
extracting alumina under conditions that most of the alumina which
:. . .
is extractable from bauxite is extracted while dissolution of -
reactive silica is suppressed as much as possible, separating an
extract and a dissolution residue while the reactive silicon which is
dissolved in the extract is not precipitated substantially as a
r~ ~ ~
` 2110~95 :
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desiliconized material, and washing and dehydrating said separated
dissolution residue.
The bauxite which is used as the raw material is bauxite
in which a crystal structure of contained alumina is mainly
aluminium trihydrate (usually a content of aluminium trihydrate
being about 50 % by weight ore more, preferably about 70 % by
weight or more based on the whole weight of alumina contained in
the ore). Although the content of reactive silica in the ore is not
limited usually, it is from about 0.1 to about 15 % by weight based on
the weight of ore. -
The raw material bauxite is, as such or after coarse ~ -
grinding, mixed with the alkaline solution to form the slurry. The
slurry is, as such or after water grinding, charged in the extractor.
Instead of directly charging the slurry to the extractor,
the slurry can be charged in the extractor by a method known as a
binary fluid method, in which bauxite is slurried with a small amount
of a slurrying solution, and it is, as such or after water grinding,
preheated in one preheater, while a large amount of circulating
alkaline solution such as a sodium aluminate solution is preheated in
another preheater, and both are charged in the extractor. ;~
As the extractor for extracting alumina, a tubular reactor
in which back mixing rarely occurs is used. A type of extractor is
not limited. For example, a pipe through which the slurry is
transferred to the subsequent separation step is heat insulated and
used as the reactor, insofar as the binary flows consisting of the
preheated bauxite slurry and the preheated alkaline solution can be
mixed and the alumina can be extracted from the bauxite.
...
211059~
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A temperature and period of time required for the
extraction vary with the kind and particle size of bauxite, a Na20
concentration of the alkaline solution, the Al2O3 concentration, a
molar ratio of Alz03 to Na20, and the like, and an economically
optimum condition is set in view of the units and unit prices of
bauxite and sodium hydroxide, equipment costs, a performance of
separator, and a performance of the desilication step, and the like.
In general, the Na20 concentration of the extract is from about 100
to about 160 g/l, the extracting temperature (an exit temperature of
the extractor) is from about 110 to about 1 60C, the extracting time
is within 10 minutes, and preferably the extracting temperature is
from about 120 to about 1 50C, and the extracting time is within 5
minutes. Within this temperature range and extracting time, the
extraction ratio of alumina from the bauxite can be made high while `
the dissolution of reactive silica can be suppressed as much as
possible. ;
In the extraction step, the conditions are set so that the
extraction ratio of alumina is made as high as possible while the
dissolution of reactive silica is suppressed as much as possible.
Usually, the extraction ratio is at least about 70 %, preferably at
least about 80 %, and the dissolution of reactive silica is not more
than about 70 % by weight, preferably not more than 50 % by weight.
The slurry after the alumina extraction is immediately
transferred to the solid-liquid separator, in which the slurry is
separated into the extract and the dissolution residue. The liquid-
solid separation is carried out at substantially the same as the
extraction temperature. Insofar as the solid-liquid contact time is
short and the reactive silica is not dissolved from the dissolution
2110395
- 8 -
residue or the reactive silica dissolved in the extract is not
desilicated in the treating step, it is possible to carry out the solid-
liquid separation after decreasing the slurry temperature by, for
example, flash cooling.
As the solid-liquid separator used in the present
invention, any apparatus, which can shorten the solid-liquid contac~
time, in particular, the residence time of dissolution residue and
also decrease an amount of extract to be carried in the dissolution
residue, may be used. In general, a high speed separation type
thickener, a centrifugal separator (a decanter), and the like can be
used. The separation should be carried out in as short time as
possible. Usually, it is carried out within 10 minutes, preferably
within 5 minutes after the extraction. Under such condition, the
requirement of the present invention, that is, "separating an extract
and a dissolution residue while the reactive silica which is dissolved
in the extract is not precipitated substantially as a desilication
product" is satisfied.
The dissolution residue which is separated in the solid~
liquid separator is cooled, if the slurry has not been cooled
immediately after the extraction, and washed to recover the extract
carried in the residue.
To cool the dissolution residue, a flash evaporator or an
indirect heat exchanger is employed usually. Apparatuses used for
washing and deliquidizing the dissolution residue are not limited. To
wash the dissolution residue having the high soda content, a high
speed thickener, a centrifugal separator, a filter, and the like which
can prevent the dissolution of reactive silica from the residue in the
washing step are used independently or in suitable combination.
-- 2110~9~
g
The dissolution residue obtained from the bauxite
contains substantially no desilication product such as sodalite or
zeolite, and the Na20 content therein is not larger than 3 % by
weight, and the L01 is not larger than 10 % by weight. When the more
efficient operation is desired, the bauxite dissolution residue
obtained by the above described method is subjected to the mineral
processing and/or chemical treatment, to reduce the Al203 content
in the residue to 10 % by weight or less.
From bauxite dissolution residue obtained by the above
Bayer process, Fe203 and other components can be separated by
mineral processing, such as magnetic separation, floatation, gravity
concentration, and the like. Examples of the other components are
Al203-containing materials such as gibbsite, boehmite, diaspore,
kaolinite, etc.; SiO2-containing materials such as quartz, kaolinite,
etc.; TiO2-containing materials such as rutile, anatase, etc.; and
,. ;., ~
Na20-containing materials such as sodalite, zeolite, etc.
The mineral processing conditions depend on the kind of
bauxite, the type of mineral processing, a kind of apparatus to be
used, and a desired degree of mineral processing, and the like. For
example, in the magnetic separation, the bauxite slurry is adjusted
to the solid content of 1 to 30 % by weight and pH of at least 9, and
then magnetically separated in a magnetic field intensity of 1 to 10
kGauss.
By the chemical treatment, the Al203 cornponents can be
separated from the dissolution residue. For example, acid treatment
with, for example, hydrochloric acid, sulfuric acid, nitric acid, etc.
is most popular, though the chemical treatment is not limited to this
method.
,.~ . .,
~` 2110~9~
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But, it is difficult to apply the mineral processing to the
dissolution residue containing sodalite, which is prepared by the
conventional method comprising extracting the alumina component
from the bauxite with the alkaline solution, the dissolved silica is
desilicated in the form of sodalite without separating the .
undissolved residue, and separating the solid and liquid. This is
because, in the conventional method, the crystal of sodalite which is
precipitated in the desilication step may partly grow from a mineral
particle constituting the undissolved residue as nucleus to form a
single particle, whereby the separation of sodalite may be difficult.
In the dissolution residue obtained according to the
present invention, substantially no Na20-containing material such as ~;
sodalite is contained. Further, the Al203-containing materials are
undissolved gibbsite, boehmite and clay minerals such as kaolinite,
they can be easily separated by water grinding the dissolution
residue slurry, whereby the Al203-containing materials are removed
from the residue.
Accordingly, the bauxite dissolution residue obtained in
the present invention is a slurry containing 100 g/l to 800 g/l,
usually 300 g/l to 600 g/ of the bauxite dissolution residue
comprising 3 % by weight or less of Na20, 10 % by weight or less of
L01, and 20 % by weight or less of Al203.
To dehydrate the bauxite dissolution slurry which is -
separated by the above process and obtain a dry material, the slurry
is concentrated by a multi-stage thickener, a cyclone, a magnetic
force, and the like, filtrated by a filter press, and dried by solar
drying or a rotary kiln or drier to a water content required for the
iron manufacturing raw material.
;`` 21~039~
However, the solar drying requires a large drying yard and
a transportation cost, while forced drying using the rotary kiln or
drier requires a large amount of equipment investment and energy,
whereby they may cause some economical problems.
According to the investigations on a used form of the iron
manufacturing raw material, when the iron manufacturing raw and
auxiliary materials is used in iron manufacture, the various powder
ores are blended and bulked and then charged in the furnace. As the
bulking method, there are known 1 ) a sintering process, 2) a ;~:
pelletizing process. 3) a briqueting process, and the like.
As the sintering process, a continuous Dwight-Lloyd type
equipment which is suitable for mass produc~ion has been developed
and used mainly. In the Dwight-Lloyd type equipment for producing
the sintered ore, from various raw material tanks, iron ore having a `
size of about 5 mm as the main raw material, various auxiliary
materials, cokes for sintering and about 5 to 10 % by weight of
water as a binder are supplied in a mill or mixer, mixed and
granulated, the obtained mixture is spread over a pallet through a
surge hopper, and the cokes are ignited while the mixture is passed
through a sintering furnace to self-burn the mixture to obtain the
sintered body. The sintered body is crushed and sieved to obtain the
raw material with a size of +5 mm for the blast furnace.
In the pelletizing process, to the mixture of the fine
powder iron ore and various ores as the auxiliary materials,
bentonite is added to suppress shatter strength of green pellets and ~
bursting during drying, also water as a binder is added in an amount
of about 5 to 10 % by weight based on the weight of raw ma~erials,
and the mixture is granulated by a disc or drum granulating machine
` 2110S9S
- 12-
to produce green pellets. The green pellets are sintered by a
traveling grate furnace, a grate kiln, a shaft furnace or a rotary kiln
and used as the raw material for the blast furnace.
Here, it is to be noted that, in either of the sintering
process and the pelletizing process, the materials are shaped using a
some amount of water to form the lump ore from the powder ore, and
then sintered to obtain the raw material for the blast furnace.
According to the present invention, it has been found
that, when the bauxite dissolution residue having the composition
obtained in the present invention is not dried and mixed with other
iron manufacturing materials and shaped by the use of water ~ `;
contained in the residue as water to be added and used in the ~ ;
sintering or pelletizing process, the bauxite dissolution residue
which is washed, filtered and discharged from the Bayer process can
be used without predrying. : ~ -
In the case of the Dwight-Lloyd type sintering equipment, ~:
the undried bauxite dissolution residue is used in place of the
addition of water as the binder when the raw materials are mixed in
the mill or mixer. Of course, the components such as iron oxide
contained in the bauxite dissolution residue can be used as the iron
manufacturing raw materials with the calculation of their amounts.
In the pelletizing process, the undried bauxite dissolution
residue can be used in place of the addition of water as the binder
when the raw materials are mixed in substantially the same way as
in the Dwight-Lloyd type sintering equipment.
That is, the undried bauxite dissolution residue is mixed
with other iron manufacturing raw materials, molded and used as the -
molded iron manufacturing raw materials.
211059~
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The extract which is separated in the solid-iiquid
separation step of the Bayer process is, as such or after optional
indirect heating or heating with live steam blowing, charged in a ~ -
desilication reactor (desilication step). In the desilication step, the
extract is, as such or after optional addition of a seed comprising a :
solid silica~e material, transferred to the desilication reactor, in
which silica dissolved in the extract is reacted with alumina and a
part of the alkaline solution to form insoluble silicate materials
such as sodalite or zeolite.
To separate the desilication product from the extract, a
thickener, a centrifugal separator or a filter is used independently or
in combination thereof. Since the recovered sodalite is highly pure,
it can be used as a raw material of zeolite, a filler, a recovering
material of soda or alumina, and the like.
The present invention will be explained in detail by
making reference to the accompanying drawings, which do not limit
the present invention.
Fig. 1 shows a flow sheet of one embodiment of the Bayer
process for producing the bauxite dissolution residue according to
the present invention, and Fig. 2 shows a flow sheet of one
embodiment of the conventional Bayer process. In the Figures, 50 `
stands for a slurry-preparation tank such as a ball mill, 51 through
56 stand for preheaters, 57 stands for an extractor, 58 stands for a
solid-liquid separator, 59 stands for a desilication reactor, 60, 61
and 62 stand for flash evaporators for cooling, 63 stands for a solid-
liquid separator, 64 stands for a grinder, 1 stands for bauxite, 2
stands for a circulating resolving liquid, and 3 through 47 stand for
lines (conduits).
2~10S9~
1 ~
in Fig. 1, the circulating resolving liquid 2 is separately
supplied in the lines 3 and 4. The bauxite is supplied from the line 1
to the ball mill 50, and ground and mixed in the ball mill together
with a part of the circulating resolving liquid supplied from the line
3 to form a slurry which is transportable. Then, the slurry is
transported through the line 5 to the preheaters 51 and 52 each
comprising a double-pipe heat exchange to which heat is supplied
from the flash evaporators 62 and 61, respectively through the lines
31 and 30, and preheated to a desired temperature. ~
The main flow of the circulating resolving liquid supplied -~ ;
in the line 4 passes through the lines 8, 9 and 10 and preheated by
the preheaters 53, 54 and 55 each comprising a shell and tube heat
exchanger to which heat is supplied from the flash evaporators 62,
61 and 60 through the lines 29, 28 and 27. Further, the circulating : ; `
resolving liquid passes through the line lO and is preheated by the
preheater 56 comprising a double-pipe heat exchanger to which heat
is supplied by live steam through the line 26. While a part of the live
steam from the line 26 may be directly supplied in the resolving
liquid, it is preferred to uses the live steam in the indirect heating
form in the preheater 56 since the size of evaporator, which
balances an amount of water in the system, can be made small. The
preheating temperature in the preheater 56 is not limited. Usually,
the resolving liquid is preheated to reach a desired alumina
extraction temperature, when it is supplied in the extractor and :
mixed with the bauxite-containing slurry from the line 7.
After preheating, the bauxite slurry and the main flow of
resolving liquid are withdrawn frorn the lines 7 and 11, respectively
21~0~95
- 15-
and mixed, and the mixture is supplied to the extractor 57 through
the line 1 2. ~ `
As the extractor, a tubular reactor in which back mixing ;~
rarely occurs is used, and the extraction temperature is usually from
about 1 20C to about 1 60C.
The slurry, in which the alumina component from the ore
is extracted in the form of sodium aiuminate in the extractor 57, is
immediately supplied in the solid-liquid separator S8 through the
line 13, and separated into the dissolution residue and the extract to
prevent the dissolution of silica in the extract from the dissolution
residue.
The type of solid-liquid separator 58 is not limited
insofar as the solid and the liquid are separated in as short time as
possible, usually within about 10 minutes from the start of ~`
treatment. In general, the high speed separation thickener or the
centrifugal separator is used.
The slurry supplied in the solid-liquid separator 58 is
separated into the dissolution residue (red mud) and the extract. The
dissolution residue (red mud) is transferred to the dissolution-
residue treating step through the line 15 to recover the heat and
alkaline components, followed by washing with water and
dehydration. Then, the residue is, as such or after optional shaping,
dried and recovered as the iron manufacturing raw material. The
extract is transferred through the line 14 to thé desilication reactor
59 and maintained therein till the silica component dissolved in the
liquid is converted to the desired desilication product. As the
desilication reactor 59, a tank having a stirring function is used in
general. In the desilication step, a solid silicate material as a seed
21~0~9~
- 1 6 - .
is added from the line 25 for promotion of the reaction. While a
commercially sold solid silicate material can be supplied as the seed
from outside the system, the desilication product which is separated
in the subsequent step is recycled and used as such or after
activation treatments necessary for the preparation of seed such as
washing, grinding, and the like. A reaction temperature in the
desilication reactor 59 is from about 11 5C to about 1 60~C, and a
reaction time is from about 15 minutes to about 5 hours. The
desilication product used as the seed has an average particle size of
about 1 ~,lm to about 30 llm, and an amount of the seed is from about 5
g/l to about 150 g/l.
The extract from which the dissolved silica is
precipitated as the desilication product and in which the silica
concentration is reduced to the desired concentration in the
desilication reactor 59 is withdrawn with the desilication product
from the line 16, passed through the lines 17 and 18 and cooled in
the flash evaporators 60, 61 and 62 for cooling. Thereafter, the
extract is transferred to the solid-liquid separator 63 through the
line 1 9.
The vapor recovered in the flash evaporators 60, 61 and
62 is used as a preheating source for preheating the main flow of the
circulating resolving liquid which is the alkaline solution, and the
bauxite-containing slurry.
After the slurry is charged from the line 19 to the solid-
Iiquid separator 63 for separating the desilication product, it is
separated into the desilication product and a clear extract (a sodium
aluminate solution), and the desilication product is passed through :~`
the line 21 and recovered from the line 23.
` 17 2110~95
Since the obtained desilication product contained only
small amounts of impurities such as iron oxide, titanium oxide, etc.,
it can be discharged from the line 23 and used in the conventional
applications such as a catalyst, an inorganic filler, and the like. A
part of the desilication product is passed through the line 22 and
introduced in the grinder 64 and ground to a particle size desirable
for use in the desilication reactor 59.
The clear extract which is recovered from the solid-
liquid reactor 63 is transferred to a step for precipitating aluminum
hydroxide (not shown) through the line 20. In the precipitating step,
a seed is added to precipitate aluminum hydroxide, and precipitated
aluminum hydroxide is separated. The resolving liquid from which
aluminum hydroxide has been separated is recycled to the line 2.
Fig. 2 shows an embodiment of the conventional Bayer
process. In Fig. 2, the circulating resolving liquid is introduced in
the slurry-preparation tank 50 from the line 2. In the tank 50, the
bauxite supplied from the line 1 is ground to prepare the slurry, and
the slurry is transferred to the preheaters 51 and 52 and then to the
extractor 57 through the lines 32, 33 and 34. As in Fig. 1, to the
preheaters 51 and 52 and the extractor 57, heat which is recovered
from the slurry after extraction in the flash evaporators 62, 61 and
60 for cooling is supplied through the lines 47, 46 and 45. In
addition, to the extractor 57, the live steam is introduced from the
line 44, and the slurry is heated to the temperature suitable for the
alumina extraction, whereby alumina is extracted from the bauxite.
In this conventional process, the preheaters and the extractor
consist of autoclaves, and the slurry is maintained in the preheaters ~ -
and extractor for a time sufficient for dissolving the soluble alumina ~ :
d~:
- 1 8 - 2110~9 5 :
and soluble silica and for precipitating the soluble silica which has -
been dissolved in the solution as the desilication product The slurry
after extraction treatment is withdrawn from the extractor from the
line 35. The slurry after extraction is passed through the flash
evaporators 60, 61 and 62 in which the heat is recovered, introduced
in the solid-liquid separator ~8 through the line 38, and separated
into the extract and the dissolution residue. The extract is
transferred to a step for precipitating aluminum hydroxide (not
shown) through the line 40. In the precipitating step, a seed is added
to precipitate aluminum hydroxide, and precipitated aluminum
hydroxide is separated. The resolving liquid from which aluminum
hydroxide has been separated is recycled to the line 2. The
dissolution residue is discharged from the system through the line
39.
In Figs. 1 and 2, the number of the flash evaporators for
cooling, the preheaters of resolving liquid and the preheaters of
slurry is specified, while any number of such equipments may be
employed.
EXAMPLES
The present invention will be explained by making
reference to Examples, which is not limited the scope of the present
invention in any way.
Example 1
Using the system shown in Fig. 1, aluminum hydroxide
was precipitated from bauxi~e having the analyzed composition (Unit:
% by weight) shown in Table 1.
- 19 - 211059$
Table l
T-SiO2 R-SiO2 T-A1203 Fe203 TiO2
5.5 4.1 50.3 1 4.6 2.0
_ _ _
From the line l, bauxite was supplied, and from the line ~:
3, the alkaline solution was supplied so that Na20 and Al20
concentrations were 152 g/l and 600 g/l, respectively, and the
mixture was ground. Then, the ground bauxite slurry at a flow rate
of 1.7 m/sec. was preheated in the duple-pipe heat exchangers 51 and
52 having a pipe diameter of 25 mm and a total length (51 + 52) of
360 m from 70C to 95C at a heating rate of 7C/min. by the steam
which was recovered from the slurry after extraction and supplied
from the lines 31 and 30. The preheating time of the slurry was 3.5
minutes.
Separately, the circulating resolving liquid from the line
4 was preheated by the steam which was recovered from the slurry
after extraction and supplied through the lines 29, 28 and 27, and
further indirectly heated by the live steam which was blown from
the line 26 into the outer pipe of the double pipes up to 1 60C.
The bauxite slurry exiting from the double-pipe heat
exchanger 52 was passed through the line 7 and introduced in the line -
12 together with the circulating resolving liquid which had been
preheated in the double-pipe heat exchangers and passed through the ~ ~;
line l l, and the slurry and the resolving liquid were mixed. The ~;
mixture was introduced at a flow rate of 2.1 m/sec. in the extractor
57 consisting of a tubular reactor having a tube diameter of 40 mm ~ -
and a length of 290 m, in which alumina was extracted in a short
time.
2110S~5
- 20-
In the extractor 57, the exit temperature of slurry was
130C, and the extraction time was 2.3 minutes. To check an
extraction ratio of alumina from bauxite and a dissolution ratio of R-
SiO2, a sample of slurry was withdrawn from a sample takeoff outlet
provided at the exit of extractor 57, and quenched in the flasher to
separate out the bauxite residue. From chemical analysis of the
bauxite residue, the extraction ratio of Al203 and the dissolution
ratio of R-SiO2 were calculated. As the result, the extraction ratio
of Al203 at the exit of extractor was 91 %, and the corrected
extraction ratio of Al203, which was calculated by converting the
amount of R-SiO2 dissolved in the extract to that of the desilication
product and correcting the loss of alumina thereby (hereinafter ~ i
referred to as "effective extraction ratio"), was 88 %. The loss of
NazO was 27 kg/T-AI203. The loss of Na20 was calculated by
converting the amount of R-SiOz dissolved in the extract to that of
the desilication produce and obtaining the loss of soda.
The slurry withdrawn from the tubular reactor 57 was
introduced in the high speed thickener 58, and immediately the
bauxite residue was separated. The SiO2 concentration in the extract
from which the bauxite residue had been separated was 3 g/l. The
extract was introduced in the desilication reactor 59. To the reactor
59, the desilication product the average particle size of which had
been adJusted to l O ,um was added as the seed in an amount of 50 g/l,
and the desilication was carried out at 1 26C for 120 minutes. The
desilication slurry was introduced in the flash evaporators 60, 61
and 62 to lower the temperature down to 1 00C by flashing, and then , -
the desilication produced was separated by the gravity type solid-
liquid separator 63. A part of the desilication product was separated
-:` ` 211059S
- 21 -
and ground in the ball mill 64 to adjust the particle size and recycled
to the desilication reactor. The rest of desilication product was
withdrawn through the lines 21 and 23 and cooled in a cooler (not
shown). The product was washed by multi-stage counterflow
washing (not shown) to recover the sodium aluminate solution
absorbed on the residue. The extract which had been separated in the
solid-liquid separator 63 was passed through the line 20 and
precision filtered by a filtration equipment for clarifying (not
shown). Then, the extract was introduced in the precipitating step to
precipitate aluminum hydroxide. The SiO2 concentration in the
extract which was withdrawn from the solid-liquid separator 63
was 0.6 g/l, which indicated that the desilication was sufficient.
The bauxite residue, which had been separated by the high
speed thickener 58, withdrawn from the line 15 and cooled by a
cooling apparatus (not shown), was washed by multi-stage
counterflow washing (not shown) to recover the sodium aluminate
absorbed on the residue. The composition of the obtained bauxite
dissolution residue is shown in the column of "Example", "Before
mineral processing" of Table 2.
Comparatiye Examrole 1
In the system of Fig. 2, the extraction was carried out in
the autoclave for 60 minutes using the same extraction liquid, `
bauxite, amount of bauxite and extraction temperature as those in
Example 1. Thereafter, the extract and the bauxite dissolution
residue were separated by the solid-liquid separator. The bauxite
residue was washed and dehydrated in the same manners as in
Example 1. The composition of obtained bauxite dissolution residue
211Ç1~9~
- 22
is shown in the column of "Comparative Example", "Before mineral
processing" .
The extraction ratio of alumina from the bauxite in the
slurry, and the dissolution ratio of R-SiO2 were measured. As the
result, the extraction ratio of A12O3 at the exit of extractor was 96 `
%, the effective extraction ratio was 88 %, and the loss of Na~O was ~ ~67 kg/T-AI2O3. `
Example 2
The slurry of bauxite dissolution residue obtained in
Example 1 having an average particle size of solid components of
about 3 ~lm was ground for 25 hours, and well dispersed in a wet ball
mill. Thereafter, the slurry was subjected to mineral processing
three times using a wet high-gradient magnetic selector (HGMS
manufactured by SALA) at a supplied slurry concentration of 5 % by .i~ ;
weight (solid content), at a liquid supply rate of 0.8 I/min. in a ~ ;
magnetic field intensity of 4700 Gauss, and a non-magnetic slurry ~ -
and a magnetic slurry were dried and caked.
The results of analysis after mineral processing are
shown in the column of "Example", "After mineral processing" of
Table 2.
The slurry of bauxite dissolution residue obtained in
Comparative Example 2 was subjected to the mineral processing in
the same manner as above, and the slurries after drying and caking
were analyzed. The results are shown in the column of "Comparative
Example", "After mineral processing" of Table 2. The yield of
magnetic materials after mineral processing was 65 % in Example 1
and 69 % in Comparative Example 1.
,~
211039~
- 23 -
Table 2
Composition Example (wt.%) Comp. Ex. (wt.%)
of ~auxite - -
dissolution ~efore After Before After
residue mineral mineral mineral mineral
processing processing processing processing
.
Fe203 52.7 63.5 45.2 48.9
Al23 17.2 9.6 17.1 16.2
TiO2 7.7 9.3 5.8 6.8
SiO2 14.2 9.2 14.5 11.5
Na20 <0.5 <0.5 6.0 5.1
L01 7.3 7.5 1 1.8 10.8
, .~
. .
Exam~le 3
The bauxite dissolution residue obtained in Example 1
was dipped in hydrochloric acid (concentration: 9 %) to extract
soluble components. Then, the liquid was separated off by filtration,
and the solid material was dried and caked. The result of analysis of
the solid material is shown in Table 3. In this case, the extraction
ratios of alumina and silica were 54 % and 57 %, respectively.
Table 3
Composition of bauxite Example 3
dissolution residue (wt.%)
Fe203 64.5
Alz03 9.6
TiO2 9 4
SiO2 7 5
Na20
L01 8.8
; - ,~' ~`. ` -,'.' ,,,., ' . ~ ~
