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Патент USA US2405275

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Patented Aug. 6, 1946
Vernonv Monroe Stowe, Colllnsyill’aullll, assignor' , I ,
to Aluminum Company of America,“Pittsburgh,
IV’a., aicorporation of Pennsylvania" '
No Drawing. Application February 19,1944,
SerialNo. 523,101 ,
, This invention-relates to theremoval oi, im
cining operation mentioned. The term “alumi-i
produced; byfthfe successive cycles of calcination"
and-‘leaching; regardless of whether the parti
puritiesv from alumina-‘bearing material, andre
na” will be ‘used herein to refer'to the product
lates particularly to the production of aluminaof
low soda content.
Aluminum hydrate frequently contains small
cles still contain somelch‘e'mioally combined‘water
amounts ofa sodium compound or compounds
or' are ‘completely anhydrous._ “
usually calculated ‘and referred to as ‘soda
Water alone, or various solutions, maybe used
in carrying ou't‘the leaching operations, the par-'‘
ticular li'duid’br liquids employeddepending to
(NazO‘)—-—as a result of the method used to pro
duce it. For example, aluminum hydrate is prin
cipally produced in this country by the well‘ known 10 some extent, on? the characteristics" desired‘in the
Bayer process, which involves precipitation of the
?nal product; ‘Soda can be removed sufficiently
hydrate from a sodium aluminate solution,_and
effectively for many purposes by merely‘ using‘
the precipitated material contains soda values
equal to about 1.5-2.0 per cent by weight'of the
water indeaching ‘the material being treated,
Somewhat greater ireedom from soda can be jet:
alumina values. A portion of such soda can‘ be 15 fected by‘ employing .at least one ‘leach; with a
removed by washing with water; but evenafter
extensive washing, su?icient soda reinains’that
dilutesolutionof an acid, such“ as hydrochloric,
sulfuric,,,nitric; aceticfloxalic orformic acid, in
which case the, particles "should ordinarily be
treated to remove aoidjions from them after‘ such
upon cal'cination of the aluminum‘ hydrate ‘to
drive off combined water and produce alumina,
the calcined material contains sod'a‘in amounts
a leach. 'Insome ‘instances sufficient freedom
oithe particles from the acid ions can be at
whichv are considered objectionable‘in a number
of uses to which the alumina is put, such as the
use of alumina in producing certain ceramic arti
cles, or as a catalyst or catalyst support in hydro
It is an object of this invention to provide a
soda to produce alumina of low soda content
therefrom,~and it is a further object of the inven
tion to provide such amethod- which is economi
cal to use and does not leave objectionable mate
of even small; amounts of acid ionsin.v thev par
method of treating aluminum hydrate containing
rials in thealumina.
tained by washing. the. particles with water after
the treatment with acid. ' However, the. presence
' In carrying out the invention" aluminum hy-'
drate particles.- after being washed to remove
such soda as is easily removed by washing, are
subjected to a succession of calcining operations,
and after each of these calcinations the particles
are leached. _ In the leaching, sodium values are
removed. The process is so conducted that in
one of the calcining operations chemically com-—
bined water is driven off from the particles, but
the entire water content of the particles is not
ticles 'issometimes considered objectionable, .as
when they are used as a catalyst or catalyst sup-f
port in, hydrocarbon‘ conversion .processesfas,
disclosedv in copending application Serial No.
555,406if1ikewise, when. agglomerates of the types
mentioned hereinafter are treated in accordance
with the invention-,suchjacid ions have a dele
terious e?ect on thefagglomerates’; ?nal strength
andy'on their resistance to. erosion‘, of particles
there-frorniif. present. during calcination._ Acid
. ions can- be removed byleachingv the particles
with an alkaline solution, such, as a lime, ammo-v
nia, sodium hydroxide, sodium carbonate, or so}
dium ‘ bicarbonate solution, subsequent to the
leach with the acid, though preferably after. ?rst
washing out as much acidicv material asrpossible
with water.
The alkaline material can thenv be
washed from the particlesrwith, water..
eliminated. After being washed or leached, the
If nitric acid or, one of the organicacidslmen
particles are further calcined sufficiently that
tioned, is the, leaching-acid used, acid-ions left in
the total water content thereof is lower than the 45 the material- treated-can also be volatilized read
water content of the particles at the end of the _
preceding calcination. The resulting material
then leached again.
Preferably in the second calcination mentioned
ily in a subsequent calcining operation-,= suchfas
the second calcination- described previously, al
though for best results- it' is desirablento wash; out
as much of theacid with vwater as possible before
only a part of the remaining water content of 50 such calcination; , ; »
the particles is driven off, for the more néarly--an-'
‘ ‘The calcination operations may becarried out
hydrous'f the particles are, the more difficult‘ itiis
in any manner which most economically drives‘
to remove soda from them by leaching. Con
off water from; the particles to; the desired; con
sequently, if it is desired to produce a ?nal mate
tent; The temperatures and length of. time which
rial which is anhydrous or which‘ has only a. small
may be employed ‘to drive off water from alumi-:
total‘ water content. it is advantageous to produce
num hydrate‘ particles to any particular content
such a water content by a ?nal calcination after
are well known. Preferably the initial calcula
successive cycles of calcinationand; leaching as
tion is effectedxat a relatively lowtemperature,
described above, rather than by‘ calcining the’ par
suchLas-55ll-7509 F., and the subsequent .calcina-v
ticles to such. a water contentin the second cal 60 tion is carried out. at a? higher temperaturelthan
4 .
between about 10 and ZSOper cent by‘weight. The
that employed in fine previous ‘calcining, step, in
order to secure a loweriwater ccntentin the par
calcined material was‘ then allowe‘d'to stand in
a 4 per cent solution of hydrochloric acid at 180°
ticles conveniently. It is preferred that in the
initial calcination su?'icient water be driven off‘
that the calcined particles contain about 8 to 20
for about 5 hours, after which it was leached
with water at 180° F. seven times by allowing it
per cent by weight of water values, and that after ‘ ~ l to stand in the water for 2 hours and then drain
ing off the water. It was next calcined at 750° F.
to a loss on ignition of the particles ranging from
the particles have been leached as; described
above, they be calcined again-until theycontain
~ _5_ to 10 per cent, by weight, and was then leached
' only about half of the'amount of water present
with a 5 per cent sodium bicarbonate solution at
at the end of the initial calcinatiomand then be‘
further leached. ,The particles of- aluminu'm'hy-?'
180° F. by allowing it to stand in the solution for
5 hours, and then draining off the solution. It
was thereafter washed seven times in water in
may be in the form of separate, individual bodies,
the manner described above, and calcined at
or they may be in the form of agglomerated mass
es of particles producedas describedin U. S. Pat 15 1000‘7 Fito ‘an average, loss on ignition of 3.3 per
cent by weight, The resulting material contained
out No. 2,352,867, or produced as. scale on the
drate treated in accordance with this invention“ '
soda; equal to only 0.05 per cent by' weight of the
walls off precipitation tanks‘ during the precipitav
tion of aluminum .hydratefrom sodium aluminate'
alumina values, and contained 0.03_per cent by
solution by the Bayer, process _
weight of chloride ions.
The following considerations may vexplain the
mechanism of the invention, but the explanation
is theoretical and is ‘not intended to limit the ap-;
pended claims.- When aluminum hydrate is. cal
cine-d. at asu?iciently high temperature to cause
_ a
_ As a second example, aluminum trihydr'ate
similar to that, describedin the preceding para
graph was treated in'the same manner,’ except
that it was not leached with a‘ sodium bicarbonate
. solution after the second calcination. The prod-_
not contained soda equal to 0.03 per cent by
weight of the alumina values, but contained 0.74
per cent by Weight of chloride ions.
it to-lose water of composition, :the loss of 'such
water opens up corridors orpassjages- which per
mit leach liquid to reach the interiorof the in
dividual particles ‘and remove soda. However,
I claim:
l. The process of producing alumina of low
to be more ?rmlyheld ‘by, the particles, andsuch 30 soda content from particles of aluminum hydrate
containing soda comprising the steps of calcining
is the caseto an increasing extent as the degree
the particles of aluminum hydrate su?ciently to
of'calcination isincreased'although whether this
such calcination also tends to cause soda values
effect is due to a strong chemical sorption of ions, a remove only a part of the. chemically combined
water'thereirom, subsequently leaching the re
or \to the formation of complex insoluble com-e,
pounds, or to other causeswisnot known. ‘Con 35 sulting particles with a liquid capable of remov
ing sodium values- therefrom, thereafter calcin
. sequently, it is desirable to remove soda by wash
ing said particles su?iciently that the total ‘water
ing before any calcinationis effected, and to Wash
content thereof is lower than the water content
out additional soda after only partial calcination
at a relatively’ low temperature, In. carrying out
of the particles'at the end of said ?rst mentioned
this invention the first calcination opens up cor 40 calcination, and subsequently leaching the result
ing particles with a liquid capable of removing
ridors in .the particles, vsufficiently to permit ac
cess of leach liquid to the interior of the particles,
sodium values therefrom.
but the above-mentioned e?ect‘of calcinationon
the soda content is restricted because of the lim
ited- nature of the‘ , calcination.
, 2. The process of producing alumina of low
soda content from particles of aluminum hydrate
containing soda comprising the steps of calcining
the particles of aluminum hydrate sufficiently to
Soda is then
leached out. , The second calcination, .driveso?
additional water from thesparticlea and although
it. increases the rtenacity with which the_remain
ing soda is held, it, also opens up additional ‘cor
ridorsfor soda removal by ‘leaching. The e?ec;
tiveness of acids in the leaching operation may
removeronly a part of the chemically combined
water therefrom, subsequently leaching the re~
sulting particles with a liquid capable of remov
ing sodium values therefrom, thereafter calcining
said particles, at a temperature higher than that
employed in said ?rst mentioned calcination, suf
?ciently that the total water content thereof is
be due, at least in part, to the fact that acids en
large the corridors opened up by calcination;
moreover, they mayv cause a base exchange in
which sodium ions are replaced by innocuous hy
drogen ions. @Surprisingly enough, when‘ solu
tions of sodium hydroxide, sodium carbonate 'or
lower than the Water content of the particles at
the end of said ?rst mentioned calcination, and
subsequently leaching the resulting particles with
a liquid capable of removing sodium values there
'sodium‘bicarbonate are used to remove acid ions
left in_the particles by an acid leach, little or no
' 3. The process of producing alumina of low
soda values from 'suchs'olutions' are retained when
sodacontent from particles of aluminum hydrate
containing soda comprising the steps of calcining
the particles of aluminum hydrate sufficiently to
theres'ults obtainable, are indicated in the follow
remove onlyya part of the chemically combined
ing examples, though the examples are given by
water therefrom, subsequently leaching the re
way of illustration only, and the‘invention can 65 sulting particles with a liquid capable of remov
be carried‘out other 'wa'ys'within the scope of
ing sodium values therefrom, thereafter calcining
the appended claims.
' ‘i
said particles suiflciently-to remove only‘ a part
vAluminum ftrihydrate scalev producedfon‘ the
of ‘the remaining water content thereof, subse
walls‘ of tanks used, in the‘ precipitation of ‘alué
minum trihydrateby the Bayer process, and con, 70 quently leaching ‘the resulting particles with a
liquid capable of removing sodium values there
taining sodae'qual'to"about*1.5 per cent of the
from, and thereafter calcining ‘such particles-suf
weight-‘of the’alu'min'a values of the aluminum
?ciently to remove remaining chemically com
trihydra'te; was washed thoroughly with hot
water’. ‘It was then calcined at 570°- E'Juntil the
‘ the "particles are subsequentlywashed’ with water.
_ ‘The ‘manner of carrying out the invention, and
bined water‘the'refrom;
loss‘ion ignition of‘tlie v‘various particles ranged
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