Note: Descriptions are shown in the official language in which they were submitted.
~6q~
The Prior ~rt
G~rman Patent No. ~14,128 (1921) propos~s the use
of HCl solutions for the leaching oE ~1203 fr~m minerals, such as
bauxite, clay or other sources, for the product.ion of pure alumina
especially for the aluminum indust.ry. The need for such a process
has become more important over the years, since the better grade
and higher quali-ty bauxites, needed for the Bayer process have
~ecome rarer. U.S. Patent No. 2,24g,761 proposes leaching clay
with hydrochloric acid on a continuous countercurrent basis, in
which the separation of iron contained in the clay is by organic
` solvents and the aluminum chloride crystals are washed with a
; mother liquor. These prior proposed methods of a hydrochloric
acid leaching have several disadvantagesO One difficulty is the
~ complications of.these proposed methods which make them prohibit-
"! ively expensive and which, in combination with the corrosiveness
;}, of ~1, result in high equipment cost and expensive maintenance
costs.
~ _bjects of The Invention
i It is an object of the present invention to prov.ide
;~ 20 an economical process and apparatus for producing pure alumina
from alumina and silicate containing raw materials comprising
~, conta tïng this raw material with a leaching liquor containing HCl.
-,- Another object is to provide process and apparatus
' :1 .
`~ for producing pure alumina from raw material containing alumina
and silicate in which the decomposition of ALC13. 6 H~0 into
Al(OH)3, HCl and water provides fresh aqueous solution of HCl
~ which is recycled baek to the leaching tower to be utilized as
`~ leaching liquor.
. -, , .
'; A further object of the invention is to provide a
~olution rich in AlC13 which also contains an amount of FeC13
su~ficient to perm.it the crystalliza-tion and separatiQn o:E AlC13
i in sub~tantial quantities by merely lowering the temperature of
. . i.
;~ the solution and recycle the HCl and H20 formed during A1C13O~
:, : - -.-
~66~372
6 1120 decomposition.
These and other objects of the present invention
will become apparent as the description thereof proceeds~
Description Of The Invention
The above-mentioned disadvantages of the prior art
processes can be overcome by the present invention in which the
~ raw material may first be treated, for example, by calcination
.~ and disaggregation, in order to sufficiently increase its A1203
solubility and then extracted with HCl preferably by counter
current leaching.
.~
As an embodiment of the invention there is provided
a process for the recovery of alumina from A1203 and silicate
containing raw materials which comprises continuous.ly extracting
.~ . , .
said raw material by counter-current leaching in an essentially
vertical tower, with a solution containing essentially HCl and -
. FeC13, to extract AlC13 from said raw material, crystallizing
ALC13.6H20 from said leach solution by the substantially continuous : .
:l washing with concentrated hydrochloric acid, moving said ~ : :
, ~ . . .
AlC13 . 6H20 crystals upwards through a closed essentially :~
,~
horizontal, slightly inclined crystallizer-washer thermal decomposer ..
~ with conveyor meansl washing said moving AlC13 ~ 6H20 crystals by a
.~, counter-current flow of pure concentrated hydrochloric acid con~
densate in said crystallizer-washer thermal decomposer, heating
said moving AlC13 . 6H20 crystals in said thermal decomposer to .~.
~: convert them into AltOH)3 and recovering the pure alumina.
_e Drawings
My invention will be described by reerence to the
accompanying drawings which illustrate preferred embodimeints of
~;~ the invQntiOn but ara not intended to limit the invention to the
~`30 em~odiments shown. .
Fig~ 1 shows the acid leaching and aluminum oxide
recovery`system as a whole.
.
.~ Fig. 2 shows the liquid-solid-separator in greater
~ 2 -
.~
'~06
detail.
Fig. 3 is a sectional view alony thc line 2-2 of Fig~ 2.
` Fig, ~ shows a modiEied leachinc~ tower and th~ heat
;~ exchang~r Eor pre~leating the motll~r li~uor ~rom the crystallizer.
Fig. 5 shows a modified form of raw material charging
; chute and leaching tower.
Fig. 6 shows a modified form of washing crystallizer.
Fig. 1 shows a vertical leaching tower 1 open to the
atmosphere at its top lined with acidproof material such as
- 10 bric]c or other acidproof material. Its horizontal cross
~ection is smaller at the top than near the bottom. A pre-
pared (calcined) solid raw material, such as clay, is fed
continuously or semi-continuously into the top of the tower
1 through the feeder 10. The leached solid residue goes to
the bottom of tower 1 and is continuously or semi-continuously
, removed.
An HCl containiny leaching liquor is introduced contin-
uously through the screen-pipe 6 near the bottom of towér 1.
~j The leaching liquor flows upwards through the particles of
the solid raw material in the tower 1 and is heated by the
dissolution heat of A1203 in the acid, while the solid raw ~`
material moves slowly downward countercurrently. The solution
leaves the tower 1 throùgh the overflow pipe 7 located at
least 1.5 $o 2 meters below the raw material feeder 10, which
open at its top and which is maintained full o~ solid raw
~ ~ ~aterial up to thP level 39. The overflow solution is a hot
,~ solution of AlC13; and, after passing through the balancing
containPr 8 or surge *ank and the backwashable sand filter 9,
îs introduced through pipe 36 into the AlC13 crystalli~er 19.
~ ,~
~, 30 The leaching tower 1 is operated at a very low upward flow
-~ ~ velocity of the leaching liquor through the solid raw material.
;' The advantage of this low velocity i~ that the entire 601id
!
b/ ~ 3 -
.. . .
``l ~ ' , . .~
, - - -
1~6~
material wi.~h all its leach~d out, ~i.n~ parti(~:Lcs move~ down
toward the bottom o~ tower 1 at a regulatecl outlet speed
controlled by one or more screw conveyor~ 2, preferably hori-
zontal in position. By the use of low flow velocity, very
~ew fine, r~sidue particles are carried up and out of the top
of tower 1 into the sand-filter 9 so that backwashing o~ filter
need only be performed after long time intervals. The level
indicators 37 and 38 continuously indicate the-pressure drop
in filter to show if backwashing of the sand-filter 9 is needed.
An alternative way to provide a clear AlC13 solution is
to maintain in the upper region of the leaching tower 1 such
an excess amount o~ the solid raw material, that the rising
:.
leach liquor solution will have already lost practically all
of its free HCl content before it reaches the overflow level 7,
The additional thick layer of unreacted new raw material, such
as clay or bauxite, functions as a mechanical filter, which
is not influenced by chemical disintegration of the raw material.
.~1 . . .
: In order to monitor the operating conditions in the upper part ~-
; .::
~-~ of the leaching tower 1, one or more sampler tubes 76 and 77
,. . .
lFig. 5~ may be provided at different levels for the removal
o~ leach solution for analysis of its free ~Cl or AlC13 at ~-
these levels. ~
! The raw material for the leaching step, should be thoroughly ~ -
i ~dried,~before being fed into the feeder shaft 10 of the leaching
"~ to~er 1, in order to avoid intxoducing an excess of water into
the AlC13 ~olution and in order to provide a margin for the ~;
~3~ quan~it~ of wash water need~d for the solid residue ~as will be
described later).
, ~ ~ . . -
-Sl Total calcination of all the raw material is unnecessary
. ,~ . .
and some uncalcined material is desirable from the po:int of ~-
view o~ A1203 dissolution due to the high concentration o~
~eC13 in the leaching li~uid and to preven~ing an extended
''~1 .
~ .... ..
~ cb/
;' ' ' .
~a~661~2
residence time in the leachincJ tow~r 1. In c~rtain cases a
lesser amount o~ washincJ wclt~r ~or t:he sol.i.d residue ma~ b~
used as a conse~uence of re~idual w~ter of crystallization
o~ the caolinite which dissolves in the ~lC~13 solution.
It is useful first to drive. off all free moisture from
the raw material, for example, by utili~inq the hot combustion
~aste ~ases from the decomposer 23 for the AlC13. 6 H20 crys~als
or from other heat sources o~ the process. There are at least
two elements of apparatus in which water vapor is ~ormed.. ~he
.~ ., .
first is in the AlC13 . 6 H2n decomposer 23, in whi~h in the ...
formation of Al(OH)3, three mols of water are liberated, and
in the formation of A1203, 4.5 mols of water are liberated ...
~rom one mol of AlC13 . 6 H20. The second is in the dryer 26 .. .
for the evaporation of HCl and ~2 from the resulting fraction .~ -
o~ mother liquor. About 4.7 mols of.water are formed per 1 :~ -
i mol o$ A1203 produced, based upon a content of 11.7% FeC13
.~i in the mother liquor and a content of 2.6~ Fe203 and 34% A1203 ::
in.the raw material.
. ............. An additional st.ripper column ~1 ~Fig. 5) may be provided : ~
on column 1 to insure complete prevention of HCl solution or ..
i~ vapor escaping from the top of tower 1. ` . .
.i Hot HCl-H20 vapor mixture from furnace dryer 26 may be
passed through the stripping layer 66, shown in Fig. 5, composed
.l~ of dxy pieces of calcinated bauxite or cal~inated clay. The
introduction of the hot H20-HCl vapors from dryer furnace 26
is made through conduit 72 into the ring space ~3. Condensation
".
o~ waker from these vapors happens only initially when a new
charge of cold calcinaked bauxite or clay is fed in. Feeding
hot calcinated material, condensation o~ water can be nearly
fullx avoidedO
Absorption o~ HCl on the other hand is possible, because
~ chemically active A1203 reaction sites are available. The
.. ~ ,
:`~ Cb~
,',' : - . ' '
i~ , .
6i~37;Z~
vapors rise upwards throu~h the layer 66, whiah is supplied
at such a ra-te w:ith new cal~inatecl material as to never exhaust
perfectly its reacting A1203 cont~llt. Irhus the llCl ~apors
can reack with the A1203 contained therein, while the vapors
are too hot to allow considerable amounts of water to condense.
The bulk of water vapor passes through the layer 6~ free of HCl
and into the atmosphere, or through an exhaust stack.
It is preferable that the raw material in layer 66 not
` be completely exhausted of A1203 when it finally joins the layer
:`; 10 71. The vertical dimension of layer 66 must be such to provide
- a sufficient thickness of the raw material, which thickness ..
depends upon the ra-te of absorption of the ~Cl vapors. The ~ .
.:.-:
~ amount of HCl vapor in question is only about 2% of the total
~ ~Cl required for the A1203 dissolution reaction.
~ It is also preferable that the horizontal cross section - -
,':~ ' .
r 0~ the stripper layer 66 is such that the speed of the HCl .:~.
'.! Yapors is kept low therethrough. Thus the volume of layer 66
~ should provide a sufficient residence time for these vapors. .:
~i . .. : : :
~ Depending.upon size and shape of the equipment, the linear .. ~.
., 20 speed of the vapors should not exceed more than about 5cm/sec,
~ll corres~onding to a diameter of the stripper layer of about 2.8 .-
- meters, and based upon a.production of 100 tons per day of .::
.:1 ~roduct.
' The most efficient method for the elimination of water ... -::
~ the raw material is by calcining the clay or bauxite, which
ij . .
.l: not only eliminates the water of hydration in the caolinite,
but also increases the reactivity of the A1~03 toward HClo
~ he stripper layer 66 has to absorb only about 2~ of the
totally reacting HCl, and so it is useul to provide for the
. :,~ . .
absorption of HCl the mentioned separate stripper layer 66 -.
~j~ : at a level above the ~eeder shafk 10. This separate layer
66 is se~arated from layer 71 b~ a sluice gate 67, which i~
.
,. . .
c~/ . . .- 6 -
: i .
6872
preerentially ~ed with calcinated r~w material. Il~t HCl-~l20-
vapors are passcd throucJh tllis lclycr 66, while the fee~der shat
10 is fed with calcined or non calc:ined ra~ materia:l ~rom ~he
top and HCl solution from the bottom of the leaching tower 1.
This has the advanta~es: thai-t if the raw material is to
be substantially non-calcined,then only about 4-6~ of the total
raw materia:l fed into feeder 10 has to be calcined. There is
apartial hydration of only a~mall fraction of the stripper
raw material by the water vapor to be elim:inated. There is
no need for the hot HC1-H20-vapors from dryer 26 to heat up
*he total amount of feed material; so the temperature rise of
the small amount of stripper material is larger and its select-
., .
ivity to the HCl-H20-mixture is better. The hot HC1-H2~-
vapors coming from furnace 26 can be removed by partial vacuum
' on the upper end of the stripper 66, with only negligible inter- -
'iJ ference with the raw material feeding.
Before the stripper capacity of column 66 is exhausted
the sluice gates 67 are opened for a moment and the nearly
exhausted stripper load enters the feed shaft 10 to become
~art of the total feed material.
The hot AlC13 solution from the top of tower 1 afte~
~, passing through the filter 9 flows with a temperature of
about 120C through line 36 to a crystallizer thermal decomposer
tube 19 - 23 in which the AlC13 solution is crystallized and
therma1ly decomposed to Al~OH)3 by the following reactions
2AlC13 . 6 H2D ~ heat ) 2Al~O~)3 + 6 HCl . 6H2o
The crys*allizer-thermal-decomposer tube, or "hot-cold
tube~ composed o~ the hot zone 19 and cold zone 23 and
is pre~erably made of densely impreg~ated graphite, titanium,
30; taDtalum or other HCl resistant materials with the exception
of those component parts which cause the rotation of the
"hot-cold tube". A olear solution of AlC13, at about 120C
~ 668'~2
leaves the sandfllter 9 by ~.ravlty flow, or by pump pressure,
and flows throuc.lh pipe 36 into the relativcly colcl crystallizer
zone 19 of the "hot-cold tube" opcrating at about 10C -to
60C, p.referably at 55C. There it mixes with the mother
uor already present in ~he crystallizer, whi.cll remains
. after the AlC13 . 6 H20 crystallization from prior solution
of ~lC13 flowed throuyh crys~alliæer 19. ~he AlC13 present
in the solution entering through pipe 36 is caused to crystallize
out as AlC13 . 6 H20 by the combined actions of lower temper-
ature and reaction with the HCl-H20 vapors coming from the
relatively hot zone decomposer 23 of the "hot-cold tube",
eliminating in this manner the maj.or portion of the AlC13 ` ..
content of the AlC13 solution introduced through pipe 36. These - :
`1 . . .
. AlC13 . 6 H20 crystals are moved forward in the crystallizer :.
1 . ,: . :
zone 19 towards and into the relatively hot zone decomposer 23 -
by the action of the flights of screw conveyor 24 o the rotat-
;~ ing cr~stallizer 19. These crystals pass through the prefer- . -
`. . entially conical intermedia~e washing zone 25 between the rela~
. ~ .
3j tively cold portion 19 and the relatively hot portion 23 of . .
the rotating "hot-cold tube". The average temperature of
~: the relatively cold portion 1~ is about 55C, while the temper-
' ature of the hot zone 23 is from 300C to 400C with the average
being about 350C. The junction of the decomposer 23 and the
~a~hiny zone 25 is e~uipped with a heat insulating gasket 44.
.., ~
~ Tubes 19 and 23 are connected so as to rotate at the same speed. ..
... .
In the hot decomposer zone 23 the AlC13 crystals are
converted into Al~OH)3 and moved by the flight 24 to the
3 collecting bin 43.
! The excess o~ cold mother liquor flows from the cool
3a cr~stallizer zone 19 into the U-tube 59 and the overflow pipe
42 and is pumped in~o the heat exchanger 35 and into the
collec~ing tank 33 at about 50C. Pipe 59 ha~ the branch
.,
'.;' ~ :.,
.~, cb/ . - 8 - ::
.,~. , .
; ~ .,:
,.1 ,~ ,, . . . ' ~ . I ' ~ ' .
3L06G87Z
pipe 60 with the valve 61 and an enlar~ed pipe with the hydro~
meter or density indicator 49. The density indicator 49 per-
mits the detection of changes ln the coMposikion of the effluent
mother licluor, especially with re~ard ~o ~eC13 content. It i.s
then possible to coxrespondingl~ d.ivert la.rger or smaller
amounts of this mother liquor ~hro~gh valve ~9, flowmeter 30
and the pipe 31 in-to the rotating dryer furnace 26 which is
at a temperature of between 250C to 350C pre~erably about
300C, in which HCl and water are then evaporated. The HCl ~.
and water are condensed and incorporated in-to the ~ain part
of mother liquor flowing to the heat exchanger 35 while the
residue remaining after evaporation, rich in Fe203 crystals
. ia transported by screw conveyor 27 into container 28.
'J, The AlC13 . 6 H20 crystals move upwards through the : :
.. conical intermediate washing section 25 of the "hot-cold .
~; tube'' ~23 - l9); which is kept relatively cold by cooling ..
.
~ater ~or example sprayed onto its outside. During the ad-
vance of these crystals t they are contacted by the HCl-H20
Yapors flowing countercurrently downward from the decomposer
23. The va~ors condense partially on the relatively coLd AlC13. .
6 ~2 crystals moving through the throat of the washing zone
25 and on the relatively cold walls of the conical intermediate
ashing zone. These condensed vapors form a concentrated
solution of hydrochloric acid, which acts on the crystals as
a washing liquor wlth a ver~ high efficiency, as the condensed
liyuors flow continuousl~ countercurrently downward into the
relatively cold crystallizer zone 19 together with the mother
.~ . : .
l~ : li.~uor containing ~eC13 originally present on the crystal ..
~ur~aces. In this manner a washing action takes place, which
~ 30~ i~ repeated man~ tLmes und~r c.ountercurrent flow conditions by
:~ the extremel~ pure concentrated hydrochloric acid condensate :-
., j, ~ , . . .
durlng the entire time tha crystal~ of AlC13 .`6 H~0 are
~^ . ~ - : .'. '
~;~ Cb/ ~- 9 -
transported through the intcirmediate cone 25. Wllen the
crystals oE AlC13 6 1l20 fi~ lly arrive in khe decomposer 23
the~ are very pure ~nd produce a ver~ pure r iron free,
Al(OH)3. These crystals are thermally decomposed in the
crystalli7.er 23 according to the equation given above and
discharged into the collecting bin ~3.
. The above-described steps in the comb:ined "hot-cold tube"
`` 23 - 19 are promoted by a slight upward incl.ination o pre~er- :
ably ahout 5 from the entrance of tube 36 to the outlet of
decomposer 23.
As an alternative embodiment for us.e in very large pro- .
duction units it is preferable to utilize, instead of a rotat-
ing hot-cold tube 19 - 23, a stationary hot-cold tube, which
is e~uipped with one or more.rotating flight conveyor means
. for advancing the solid material therethrough. In this hot-
cold vessel the same chemical and physical process steps occur
as in the rotating hot-cold tube embodiment. The stationary
` vessel has the advantage, that large bearing and hous~in~s
are partially or completely eliminated.
Another alternative to the stationary hot-cold tube is
a hot-cold tube of large diameter which rotates very slowly
. and in addition contains internal conveyor means, to keep
the solidmaterial movingO
Metals, such as titanium alloys, tantalum, etc., which
~; are not corroded by HCl may be u~ed instead o impregnated
raphite in the hot-cold tubes 19 - 23 and in o*her parts o
jjl~ the process.
;: Stationary vessels o titanium can bP protected against .
i corrosion by the preisence o chlorine gas in ~ low concentration. ~ .
! ~: 30 The~presence of chlorine gas also keeps the iron chloride
i oxidized to ~eC13 . The chlorine gas should be of such low ~ ~ ~
aoncentration, that there is no reduction in the surface : :
b~ ~ - 10 - . :
. . . .
,. , . : .
66~'7~
condensAtion conc~itions for HCl and H~0 vapors.
A consiclerclble ~educt.ion of ~he heat recluiremen-~s for
the thermal decolTlposit:ion i.n the clecomposer ~one 23 ma~ be
ef~ected i~ washing of the crystals in the intermediate wash-
ing æone 25 is not made directly by the condensing HCl-~120
vapors bu~ instead the washing is made by the spraying of hydro-
chlor.ic acid,which forms, the HC1-H20 vapors, after having been
compressed by a heat pump into the washing zone 25 These
vapors transfer their heat of condensation to the AlC13 . 6 H20
cr~stals to be decomposed. This embodiment has the advantage
that the consumption of cooling water for the crystallizer
1~ is substantially reduced. The most convenient type of
heat pump, depending upon the cost relation of elec~ric energy
to heat energy, may be a liquid ring pump or a steam injector
.
pump.
In the case of liquid ring pumps, the HCl-H20 vapors
produced in the decomposer 23 are drawn in, compressed and
pumped into the heat exchange conduits of the crystal de-
~;~ composer 23. These conduits act as condensers r in which --~
the heat of condensation is transferred through their walls,
~:' ~hich walls may be composed of titanium, a titanium alloy or
~, .
tantalum, to the decomposer. This heat is absorbed by the
~ AlC13 . 6 ~2 crystals, whose thermal decomposition is initiat-
.~"!i ed at about 105C. The HCl~H20 vapors, newly generated, are
i ; ~ ai~o drawn in bX the heat pump and during their compression,
1~ the~ are again usea for heating and decomposing new AlC13 . 6 H20
crxs~als. The condensate of HCl and H2Q is used for washing
~,Jj ~ ` new AlC13 . 6 H20 crystals, while they pass ~hrough the inter-
mediate washing zone 25, wherein the condensate is sprayed
under its own pressur~ onto the crystals. The excess of con-
densate and the noncondensed HCl vapor i~ incorporated into ~-
'l - .
the mother li~uor of cr~stallizex 19.
", . , . '
~' ~b/
.. i - -.:
~i ` ~ ' .`... !
~6687~:
When steam injectors are used as heat pumps, a portion
of the IICl-H20 condensate ~o:rm~icl in t}le conduits o~ t.he
: condenser elements is pumped into a boiler, and t]lC ~IC 1 -~1120
vapor fo.rmed under pressure in ~he boiler is used in the steam
injector heat pumps for the compression of new IICl-H20 vapors
rom the decomposer 23 from atmospheric pressure up to thei.r
condensation pressure in the heat exc:hanger conduits of the .. ~. -
decom~oser 23. All the I~Cl H20 condensate is fully u-tilized
with a portion being the washing liquid for the AlC13 . 6H20
crxstals in the intermediate washing zone 25, and with the
remainder being directly incorporated into the mother liquor
of the crystallizer zone 19.
The composition of the HCl-H20 vapor mixture from the
decomposer 23 being about 66 weight % HCl and only 33 weight
H20, part of the EICl vapor ~rom the decomposer 23, which
cannot be absorbed in the concentrated acid, condenses under
the pressure and temperature conditions of the heat pu~p.
There is (usually) a quantitative excess of ~Cl over H20 in
~i ~
. the decomposition vapors, which are compressed by the heat pump
and which are then released by an automatic safety pressure ~ :
release valve into the head space of the crystallizer 19, ~ . -
i.'l ~ where the~ are cooled and dissolved in the mother liquor at .
about 55C. This release of the undissolved fraction of com-
ressed HCl gas means thermodynamically an energy loss. This
~i los~s is ~ept as low as possible by displacing the releasing . .:
of this HCl gas to a location do~n-stream from the coldest
zone of the decomposer because there the insoluble HCl
components are the least value at equal preissure. -
If the heat exchanger surface area of the crystallizer .~:
: ! ` .
decomposer xone 23 is sufficient, it is possible to reduce
the heat re~uirement.~or the cr~stallizer decompositi.on to
one-third or less, a fact which is .important for the economy
: ~: ,
3 eb~ ~ 12 - ~
~6f~
of the process. Tlle washing efficiency of the sprayed HC1-
II20 condcn~ate, instead o vapors condensing on the crystals,
on the ~lC13 . 6 II20 crystals in -the washing ~one 25, is a~
least as e~ficient as of the condensing vapors.
. There is an advantage to releasing the HCl-H20 vapors
into the decomposer zone 23 at a few points along its length,
because in this manner a much smaller diamete.r decomposer
tube 23 is sufficient for the flow of the vapors. Moreover
it is possible to condense the vapors from the different
sections of the decomposer length separately. The fi.rst vapors ~.
produced in the low decomposition temperature ran~e are rich
in water and poor in ~ICl, such that this constitutes an
I inexpensive method for eliminating water from the system with-
.. out consumption of added heat for evaporation. This embodiment
. ispreferably for a lengthy decomposer.
; In another alternative the mother liquor can be pre- :
concentrated using a heat pump with a boiler ~not shown), which .. : :
is positioned between the flowmeter 30 and the feed pipe 31 .. :~
of the dryer 26. The said pre-evaporation is terminated before . - .
I 20 the concentration of the FeC13 exceeds the maximum allowable : .
i; : lLmit of about ~5%; and consequently the viscosity of the solu-
ti~ will h~ve no negative effect on the evaporation. ..
~,~ There is also the possibility of extracting the bulk of
.i1
he FeC13 content of the diverted mother liquor or of the pre-
concentrated diverted mother liquid by isopropyl-ether or
another solvent, according to known procedures. : .
~nother advantage of the present invention is that the
: thermal decomposition of the AlC13 . 6 H20 cr~stals does not
roceed beyond the point which would produce an unsatisfactory
solid end product.- Also it is possible to avoid h~ving larger
:~ .
~ractions o~ water-produced by the decomposition of the AlC13.
' : 6 H2a join th~ mother liquor recycled into the crystallizer 19
~ ~. i . .
-' cb~ ~ ~3 ~
;i
6~72
than is needed.
Th~ c:lear ~lC13 so:l.ut:ion at about 120C, which l~av~
the sandfilter 9, usually contains a major amount oE ~lC13 .
and a ver~ m.inor amoun~ of HCl from the raw material. In
this case cooling alone cannot cause a suf~icient crystallization
o~ AlC13 . 6 H20 because the solubility of AlC13 is very slightly
dependent upon the temperature. The rate of crystalli~ation
can be increased, however, by u~ilizing a concentrated solu-
tion of hydrochloric acid, which is generated in the hot-cold
10 tube 23-19.
On the other hand, if the ore starting material in leach-
; in~ tower 1 is rich in Fe203, then a leaching solution rich in .
FeC13 is produced. Thus the AlC13 . 6 H20 crystallization can
then be carried out just by the cooling of the AlC13-FeC13 .
solution comin~ from filter zone 9. -. .
The solubility of AlC13 in pure water is as follows: ~ .
at - 4QC : 26.8% AlC13 :
!
. at + 25C : 31.6% " .
.. , .. ~ ' ..
~. at ~ 98C o 33.2%
-3'
This shows that the crystallization of AlC13 . 6 Hz0 -
from essentially pure aqueous solutions of AlC13 would be
eConomically unfeasible, if lowering of the solution temperature .. :
~ere the only crystallization st~p performed. For this reason
~æ~: : a concentrated solution of hydrochloric acid is needed for
~' a ~atisfactory crystallization.
Z~ However if the AlC13 solution contains sufficient amounts
o FeC13, cooling alone can cause sufficient crystallization : ::
:`t ~
to bring it closer to economical feasibility.
~; ~ substantial increase in the FeC13 content of the leaching .:~
~olu~ion, for example from 2~ up to 12%, gives the additional
~: advantage that for the elLmination of a certain amount of FeC13
i ~rom the circulating solution, only one-sixth o the amount of
~b~ .- 14 -
water has to be evaporated. The exccss o:E FeC13 altcrnatively
can be elimina~ed from thc le~chillcJ solu~ion by trea~ment w.i.th
iso~rop~l ether.
The xesidue rom the rotating furnace 26, accumulated in
tank 28, is primarily Fe203 And .c~n be used as refractory
material in a high temperature ~urnace or for the produc~ion
of ~i~ments.
Each of the three rotating chambers ~a) the "hot~cold
tube" 23-19 for the crystallization of and for the decomposition
o~ AlC13 . 6 H20, (b) the rotating tube 17 for the solld
extraction residue, and tc) the rotating tube 26 for the evapora~ .
; tion o~ the diverted portion of mother liquor is necessarily
provided at each end thereof with bearing housings. It is :~ :
~referable to maintain these three rotating tubes under a
~ .
slight vacuum of about 2 mm of water, in order to prevent the ~ :
escaping of HCl containing vapors even in very small amounts. . :
This small vacuum is applied, for example, to the collecting
,. . .
! t~nk 33 for furnaces 26 and 17 and con-tainer 14 by maintaining
a continuous slight vacuum on the small washing tower 50. The
l 20 very small amounts of air drawn in finally reach the washing
tower 50 and therein are liberated f~om their HCl content by
Water~washing or a calcium hydroxide solution and are then
.~ discharged into the atmosphere wi~hout pollution. The vacuum
, .: '
in $he system is checked by the readings of .the three air
~lowmeters Sl~ 52 and 53 and is controlled by ~he vacuum intensity
~ ~ on the washing tower 50 of tank 33.
-' The small amount of acid, eventually discharged from the
;~ stuffing boxes of the three pumps 20, 40 a~d 54, is collected
to~ether with a little water and from time to time is recycled
30 back into the circulating liquid, in order to compensate for a
de~iciency of water eventually resulting from the production
; o~ ~l(OH)3 instead of A1203.
., .
,' ,
~/ 15
,
~66~372
Fig. 6 shows an altcrnative to the conical intermediate
washin~ section 25 oE the hot-cold tub~ :l9-23 shown :Ln
Fi~. 1. Fig. 6 shows the intermediate washillg secti.on 25a
made o~ densely .impreynated graphite, equiE)ped with external
metallic rein~orcing ribs 69, while E'iy. 1 shows a conical
sec~ion, made for example, of tantalum or lli~Pcl.
The heating of the rotating tubes 17, 26 and 23 is from
the outside by gas or oil fired burners respectively using
the above discussed heat pump systems at least in the lower
. ..
temperature zones. Tha cooling of the relatively cold rotating
crxstallizer 19 is by spraying water from outside, possibly
combined with the cooling effect of ~orced air, in the case ~ -
:
that the water temperature is not low enough.
If the concentration of FeC13 is about 10% to 1~% by
weight in the leaching liquor, then the AlC13 concentration
in the solution leaving the leaching tower 1 can reach about
`/ 27 weight % or more. This will result if the leaching liquor
be~ore its entrance into the heat insulated leaching tower
~ 1~ is preheated under the pressure of auxiliary pump 54, so ;-1~ 20 high that the leaching li~uor, due to the dissolution heat
; o~ A1~03 in hydrochloric acid, reaches a temperature of about
118C or more. The temperature to which the leaching liquor has
to be preheated for that purpose, depends upon the type and upon ~ -
the pretreatment of the solid raw material. For leaching calcined
ra~ material a ~ower preheating temperature is sufficient com-
ared with the case of noncalcined raw material, because the
i xeaction energy of calcined raw material is higher than that
~ o~ noncalcined material.
.~ The higher temperature in the leaching tower 1, which
, .
~ becomes possible by a high FeC13 cvntent, as well as by o~er-
pressure, results in the advanta~e of a higher rate o~ dissolu-
tion and o~ a higher percentage yield of A1203 leached out
., .
cb/ - 16 - ~
~, . . . .
~ 66872
of the cla~, baux.ite, etc. B~ .inCreasincJ the FeC13 concentra~
tion of ~he soluti.ons lo abollt 10 to 12~ the rcsult is an
increase in the boiling point of the soluti.on from about 106C
or solutions contailling small concentrations of FeC13, up
to 118 to 120C for solutions containing 10 to 12% FeC13.
In order to achieve more reaclily the maximum temperature
in the leaching tower 1, and to avoid boil.i.ng the AlC13
solution in the leaching tower, this soluti.on is kept under
a superatmospheric pressure in the leaching tower 1 as well as
in the sandfilter 9, preferably by a liquicl column in the feeder
sha~t 10 up to level 4 created by automatic throttling of valve
47, as shown in the alternative of Fig. 4. Above this liquid
column the open feeder shaft 10 contains the additional raw
material layer reaching level 39, as shown in Fig. 5 so that
i~ spite of the overpressure on the hot AlC13 solution leaving
the leaching tower 1 the open feeder shaft'10 for raw material
remains open ~o receive addi~ional raw material, :
j Be~ore the filter ~ becomes clogged, it is backwashed as
ollo~s. The valves 47 and 45 of the filter 9 are closed, so
that the passage of filtered AlC13-solution from valve 47 to
the pipe 36 of the crystalli~er 19 is intexrupted, Valves 46
and 48 are then opened; and the pump ~0 and the stirrer 55 are
put into operation, A high pressure stream of pure AlC13 ~;
;~ . -
solution backwash liquid then flows from container 8 through pump
20, valve 48 and sandfilter 9 and pipe 21l so as to lift the
, ~ cake from the filter bed. -The suspension created by the
tirrer 55 flows through pipe 21 and screen pipe 22 into the
lower part o~ tower lt close to the outlet scre~ conve~or 2
~ or ~he solid residue. Thexe the fine particles stick to the
t ~30 larger re~idue particles and are taken ~ff with them by the
~ outlet ~crew conveyor 2. After a few seconds o~ backwash ths '
.
above menkioned valves 47, 45, 46 and 48 are re~urned to their
~4 cb; ~ 17 ~
1; . ~' : '
7~'
original positions, pump 20 an~ stlrrer 55 are shut d~wn, so
tha~ ~h~ normal leaching proccss c~n cont:inue.
The shor~ conveyor scrcws 2 push the leached solld residue
from the bottom of tower 1 lnto the pipe 3, where a suf:Eiciently
rapid 1Ow of circula~ing carrier liquid propells the residue
up .into se~arator 5 whi.ch houses a cylindrical screen drum 11,
~igs 2 and 3, rotating about a substantially horizontal sligh-tly
inclined axis. This screen drum 11 rests on graphi~e bearings
56 and 57. It has a multilayer screen wall 12 and on its
inside conveyor flights 15. The carrier liquid filters through
the screen wall 12 of the rotating screen drum 11. Small
~mounts of fines, which leave the screen drum 11 together with
the carrier liquid are harmless. The filtered carrier liquid .. :
flows into the container 14 and out through discharge pipe 68
to the recirculation pump 40. The moist solid residue is
discharged from the end of drum 11 and carried through pipe 18 ..
into ~he rotating furnace 17 at 250C to 350C, preferably
at 300C, and made, for example, of densely impregnated graphite,
titanium alloy, tantalum or other HCl resistant material. The
HCl vapor and ~ater vapor formed in ~urnace 17 are condensed
in the heat exchanger 35 and flow into collecting tank 33 at
about 50C in the form of a concentrated solution of hydrQchloric
acld. This concentrated solution is pumped by means of pump
64 ox auxiliary pump 54 through screen pipe 6 into the lower
. pOrtion of leaching tower 1 as fresh leaching liquor.
~: ~he dry leached residue from furnace 17~ free of ~Cl and
rich.in sio2, is transported by the screw flights of conveyor
58 into the container 41 and can be used, for example, for the
~abrication of cement.
3~ The screw conveyor flights 15 in the separator 5 are
made o~ an acid resistant substance such as tantalum sheet, :~:
Ti-pd ~heet or pol~ester. Screen drum 11 has a li~uid per- ~
cbi ~ 18 - .
.
, .
~6~87~
meable multilay~r wall 12 preferably made of two layers o
acid ~roof perfoxclt~ sh~ct, exp~ndecl she~tor mcsh o;E tc~ Alum,
Ti~pd, h~rd poly~inyl chloride ~PVC) polyester or simiJar
material ~etween which one or more la~ers of an acid proo~
filter cloth such as PVC, ~eflon ~ or the like is enclosed.
The pipe 63, located beneath the rotating tube 11, serves
as an emergency over~low for the liquid from the pan 14, in
order to prevent any major amounts of liquid from reaching
the residue fallpipe 18 and the heated rotating tube 17.
The residue separator 5 is equipped with a second pipe
80 on the side opposite pipe 13 for the introduction of washing
li~uid, installed in a coaxial manner in a hollow axle within
the graphite bearing 57. Through this additional tube 80 is
periodically fed a washing liquid, such as a limited amount of
~ater, which has to be added to the system to compensate for
H20 losses, especially if calcined raw material is used. This
limited ~uantity of water 1s sufficient for washing the solid
residue, if it is dosed in a number of portionwise doses and
, . . .
v i$ the r.p.m. speed of the screen drum 11 is increased temporarily.
~ 20 The additional ~eed pipe 80 is loca~ed in such a manner that ; ~ -
'~J the ~ashing water is distributed over the entire amount of
xesidue present at that time in the separator 5. The separation
and ~ashing process is divided into three separate steps, and
~!: can be automatically controlled by programmed equipment..~ ~ These three steps are as follows:
J~ ~ ' The Separation Step A:
The carrier liquid containinq solid residue is fed through
t~e 3 into the screen drum 11. The screen drum 11 rotates at
,: :
such a speed, that the centrifugal acceleration upon the solid
residue is substantially higher than the force of ~ravity. The ~-
i .
~ hi~h speed rota~ion is ~rom 100 to 250 r.p~m., preferably from
.- 1~0 tv 150 x~p~m., in order to distribute the solid residue
.i :
" . ~: .
ob~ - 19 - ;
. ~ .-:
.,
;~ ~ . .. . . .
~:366~
unifoxmly over the cylindricAl periphery of filtex wall 12
o~ the screen drum 11 arld to holcl it in place. This avoids
~mbalancing and overloadin~ the bearin~s o~ the scxeen drwn 11,
~hich would o-therwise be unavoidable during the transition ~rom
l~w to high angular speed.
Wash S~
Washing of the solid residue in the screen drum 11 occurs
~hile the screen drum 11 is main-tained at a rapid ro~ation.
The circulation pump 40 is stopped; and the valve 7~ releases
wash water into the feed pipe 80, preferably in a number of
~ortionwise doses.
Separation Step C:
The valve 74 for wash water is closed. The screen drum 11
is returned to a slower rotation - in the range of 5 to 15 r.p.m.
such that the centrifugal acceleration on the solid residue is
aonsiderably still than the force of gravity. The screw conveyor
~lights 15 within screen drum 11 can advance the residue through
drum 11 and then discharge the same through outlet tube 18.
~ he washing steps are repeated as often as is necessary
during the separation procedure.
The transition from high revolution speed to low revolution ~ -
~
speed, or vice-versa, of screen drum 11 is made necessary, -
~ecause the tube 11 with its screw conveyor bands 15 at low
r . ~ Om . advances the residue through the length of drum 11 to
the outlet 16. However when drum 11 is rotated at a high r.p.m., ;~
the solid residue is held in place without advancing. `~
In the case of very lar~e scale production units it is
preferable to ins~all a number of residue separators in parallel~
operating with ~taggered separation and washing cycles. In
.
~30 this manner oversized separators are avoided and the residue
; can leave ~he leaching tower 1 semi-continuously or continuously.
Fil~ex~ or centxifuges may be used in place of screen drum 11-12.
,
: ,: .' .
~ - 20 - ~ ~
:, ' '' '~ -
.
66~
The above-described resid~e washing m~thod is preferably
carried'out wi~h a number of por~ionwise injec~:ions of wasllincJ
~ater, which permits almost total separa~ion of the resiclual
s.olid from its content of IICl and AlC13 with a minimum of
wash water. Thls permits disposal of the re~idue without dry-
ing it, or to dr~ it by direct heating instead of the more
co~tly indirect heatiny, until it is used, for installce, as
an additive in cement production.
In the embodiment of Fig. 4 the solution pregnant with
AlC13 leaves the sandfilter 9 through pipe 36a and flows through
the heat exchanger 70 into the crystallizer tube 19. HCl
containing mother liquor at about 50C is pumped through heat
exchanger 70 by pump 54 which receives HCl solution from
collecting ~ank 33. Crystallization of AlC13 and conversion
to Al~OH)3 is performed in tubes 19 and 23 and mother liquor
and wash liquor, HCl condensate, etc. flows through pipe 59 ~'
and a part of it eventually into dryer furnace 26. "~
In the embodiment of Fig. 5 an extension feeder shaft 10 . '~-
~or tower 1 through which calcined or uncalcined raw material '. .
maX be fed into tower 1 through which HCl is 10wed counter- '
current to the r'aw materi.al feed. :.
The following examples are illustrative o the invention .~'
' without being deemed limitative in any manner. . '~
: EXAMPLE 1
' The mother liquor leaving the crystallizer 19 through
,~ conduit 59 had a temperature of about. 55C and has the follow-
.
ing composition: about 3.5~ AlC13., about 11.7% FeC13, about ~ -
22.9% HCl, and about 61.9% H20. :
It was used as leaching li~uor in tower 1 after ha~ing been ~:
: 30 preheated. The mother l~quor was pumped ~y the pump 54 through -~,:
'the.countercurrent .heat exchan~er 70. A solution of AlC13 at
:
~ ; 'a temperature o~ at least 120C coming from the pressure resistant -'
f ~
~:~ cb~ . - 21 - '
,
- . . . .
sand~ilter 9 flows thro~!gh th~ pipc 36a of hea~ exchanger 70
(Fig. 4). This system oE~ered the advantage that ~IIC A:l.C13
solution arr.ivecl in a pre-cooled sta~e in the crys-tallizer 19,
thus sav.ing cooling water, and that the leaching li~uor was
~reheated without further consumption of heat energ~. f Formation
o~ crystals stic]cing -to -the ins.ide wall of the central pipe
of heat exchanger 70 was not observed.
A leaching liquor with the above composition produced a
solution o~ AlC13 leaving the leaching tower 1 at about 118C
or higher and with the following composi.tion: about 27 weigh-t
% AlC13, about 10 weigh.t ~ FeC13, and about 63 weight % H20.
After heat exchange with the mother liquor, the AlC13
solution from sandfilter 9 entered the crystallizer 19 at a
temperature of about 85C, where it was cooled to about 55C.
The bulk of the AlC13 content was crystallized to produce AlC13 .
6 H20; and washed with the equivalent quantity of HCl~H20 vapors
from the thermal decomposition of previously crystallized AlC13 . :~
6 H20. In this manner the mother liqu~r was transformed into
`~ a new leaching liquor with the above-stated composition and
temperature. Contemporaneously the mother liquor, which had
: entered the heat exchanger at its original temperature of 55C
had been preheated under pressure from pump 54 and by heat
txansfer ~ith the AlC13 leach solution to about 60 to 90C.
.. This. preheated mother li~uor was introduced into the leaching
:~ .
~ to~er 1 through screen pipe 6 to be utilized as the new leaching
., .
uor.
The pump pressure during heating the mother liquid is
important, because at normal atmosphexic pressure the leaching :
'6 ~ uor containiny 22.9% ~Cl boils off HCl vapor at about 75C.
.~ 3~ A preferred pump pressure range is about 1 to 4 atmospheres
over pressure.
It had been found, that 1000 parts by weight of a solution
",
cb~ 22 -
.
.. .. . .
~66l~372
rich in AlC13 with the following approxima-te composition:
27~ AlCl3, 10~ FeC13 and 63~ llz0 y:ield~ about 434 parts by
weight o~ pure ~.LC13 . 6 H20, if cooled in the crystall:Lzer
19 ko about 55C. The equivalent quantity of HCl and ~12 vapors
enters the crystallizer and are absorbed in the mother liquor.
The mother li~uor leaving the crystallizer 19 had the following
composition: about 3.S% AlC13, 11.6~ FeC13, 22.9% HCl, and
62.1% H20, in spite of the fact that it had been cooled only
to about 55C.
Cooling of the mother liquor to only 55C is important,
because the heat transfer requirements of the cooling system
for the crystallizer 19 are substantially reduced both a~ to the ~:~uantity of cooling water and as to the required initial tempera~
ture of the water.
This invention has the advantages of ~1) a relatively non-
complicated method for leaching alumina from silicate containing ~ :
cla~vs, (2) substantially lower costs because of the continual -~
: recxclin~ of the mother li~uor from the crystallizer into the
leaching tower as a concentrated solution of hydrochloric acid ;~to be used as fresh leaching liquor, and ~3) the presence in ~the leaching liquOr of an effective amount of FeC13 which permits ~:
the crystallization and separation of AlC13 in substantial
: ` .
~uantities from a solution thereof, by onl~ lowering the tempera~
ture of the solution. Other advantages will also be apparent ; . -
to persons skilled in this art. ~::
Although the present invention has been disclosed in .
connection with a ew preerred embodiments thereof, variations
and~modifications may ~e resorted to and equivalent equipment
:us d in place of that specifically described without departing
.
~ xom the principles of the invention or the scope of the attached
~: : claimsO
cb/ - 23 - ~ .
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