15 Claims, 2 Drawing Figures
Primary Examiner-Herbert T. Carter
Attorney, Agent, or Firm-Van C. Wilks; Herbert M.
Hanegan; Stanley L. Tate
This invention relates toa method for recovering aluminum
hydroxide from alunite ore by roasting the ore
to remove water of hydration, roasting it again in a reducing
atmosphere to remove sulfate, roasting a third
time in an oxidizing atmosphere to convert any sulfides
formed in the second roast, leaching with water
to remove potassium and sulfate, extracting the aluminum
content with a mixture of sodium hydroxide and
potassium hydroxide, removing contaminant silica
from the leach solution, and precipitating aluminum
hydroxide by cooling and seeding the solution.
United States Patent [19]
Stevens et al.
[54] REDOX TREATMENT OF ALUNITE ORE
[75] Inventors: Douglas Stevens, Golden, Colo.;
H~e O. Forberg, Owensboro, Ky.;
Larry D. Jennings, Arvada, Colo.;
Frank M, Stephens, Jr., Lakewood,
Colo.; Francis J. Bowen, Golden,
Colo.; David L. Thompson; Julian
V. Copenhaver, Jr., both of Arvada,
Colo.
[73] Assignees: Southwire Company, Carrollton,
Ga.; National Steel Corporation,
Pittsburgh, Pa.; Earth Sciences, Inc.,
Golden, Colo.
[22] Filed: Mar. 21, 1974
[21] Appl. No.: 453,234
[52] U.S. CI 423/127; 423/111; 423/118;
423/120; 423/131; 423/629; 423/339;
423/567; 423/530; 423/122
[51] Int. CI COlf7/06; COif 7/02
[58] Field of Search 423/111, 118, 120, 127,
423/131,629,122; 75/97 R, 101 R
[56] References Cited
UNITED STATES PATENTS
1,070,324 8/1913 Chappell 423/131
1,189,254
1,191,105
1,195,655
2,120,840
2,398,425
3,652,208
[57]
7/1916
7/1916
8/1916
6/1938
4/1946
3/1972
[ II ] 3,890,425
[45] June 17, 1975
Hershman et al... 423/120
Hershman 423/122
Chappell. 423/131
McCullough 423/127
Haft' 423/120
Burk et al.. 423/127
ABSTRACT
WATER OF HYDRATION
SULFUR
DIOXIDE
SULFUR
OXIDE
ALl1HITe
OAE LIQUID
SOLIDS
Al(OHh
'i' ,i' "" --
.. DEHYDRATION " REDUCTION , OXI DATION I "- LEACHING- "- FIRST ,
~ ROASTING- --; ROASTING- ' ROASTING I .I .I SEPARATION ,
"'I'
"" '"
CARBON MONOXIDE,
HYDROGEN DIGESTION
1
SECOND SEPARATION ",/
v
,
DESILICATION ,
'-/
PREtl PilAT/ON
ALUNITE
ORE
WATER OF HYDRATION
SULFUR
DIOXIDE
SULFUR
OXIDE
AL (OH) 3
LIQUID
SOLIDS
SOLIDS
C/':l :..:..r.=,
rTl
-<
...
~>--t
I"T'1 z:
--t
I"T'1
I:::::'
Cc=
::IE
~
'
I:> CJ'I
CJ
(l)
o
-4.
N
U1
PATENTEDJUN17 1~5
SHEET 2
; r"-
et:
w
ti .--..
U. ell
0
W~
ze
;1' 2\-
~g
uo
-0
:::tlC
til 0...
w
0
Z
0
~ ,
u- ... ....l
in
LU
0 , ,
L z
~ 0
u-O- zl:(
OOC£:
,5....Wu o<..!
'-"V)uJ
:::i V}
UJ
~
«
---7$
o
\-
1
REDOX TREATMENT OF ALUNITE ORE
FIELD OF THE INVENTION
3,890,425
2
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
The present invention concerns a method for recovering
aluminum hydroxide from ore containing alunite
by calcination, roasting the calcined ore in a reducing
atmosphere, further roasting the reduced ore in an oxidizing
atomsphere, leaching with water and subsequent
digestion of the solids resulting from the water leach
with a mixture of alkali metal hydroxides.
DESCRIPTION OF THE PRIOR ART
Various techniques have been proposed for recovering
alumina from ore containing alunite. Ofthe various
techniques disclosed by the prior art the general
method involves treating alunite ore with concentrated
sulfuric acid following by roasting or vice versa, with
S03 recovered as a bi-product and subsequently converted
into sulfuric acid and reused in the process, the
aluminum being retained in solution as a sulfate. Potash
(KzO) is then added at a pH of between I and 2 to precipitate
alum [KzS04.Alz(S04h18HzO]. After precipitation
the alum is then roasted to disassociate the aluminum
sulfate, with the production of S03 and aluminum
oxide which are then recovered by crystallization.
Ordinarily the prior art practioners have used much effort
and expense to eliminate potash. U.S. Pat. No.
1,948,887 (Saunders) is representative of the prior art
techniques. U.S. Pat. No. 1,406,890 (Pedersen) further
discloses the precipitation of "potash alumn" by the
addition of potassium sulfate to an acidic leach solution.
Loevenstein, U.S. Pat. No. 2,958,580, teaches the
recovery of aluminum as aluminum sulfate by digesting
aluminum ore with sulfuric acid.
Although each of the aforementioned techniques
may be useful for the particular application referred to,
none of these conventional techniques is suitable for
recovering aluminum hydroxide from a low grade aluminum
ore containing alunite, which consists of aluminum,
potassium, sodium, sulfate and water. Such ore
being domestic to the United States in large quantities
offers a relatively untouched source of aluminum.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to
provide a method for overcoming the aforementioned
disadvantages of the prior art techniques for recovering
aluminum hydroxide from ore containing alunite.
It is a further object of the present invention to provide
a novel method for economically extracting aluminum
hydroxide from ore containing alunite.
Another object of this invention is to provide a novel
and economical method for separating aluminum hydroxide
and other valuable components from ore containing
alunite, which consists of aluminum, potassium,
sodium, sulfate and water.
This and other objects, features and advantages of
the present invention will be apparent from the following
description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general diagramatic representation of an
embodiment of this invention.
FIG. 2 is a diagramatic representation of an embodiment
of this invention depicting an optional method of
silica removal.
Referring to FIG. 1, which is a general diagramatic
5 flow sheet of an embodiment of this invention, ore containing
what is commonly known as alunite, which has
an approximate empirical formula of (KzAI6( OH) IZ(
S04)4] (NazAI6(OH)lz (S04)4] and or combinations
thereof, is roasted to remove the water of hydration,
10 roasted again in a reducing atmosphere to liberate a
portion of the sulfate present as SOz, roasted a third
time in an oxidizing atmosphere to convert any sulfides
formed in the reduction roast, and leached with water
and the liquid and solid portions of the resultant slurry
15 are separated. The solid component is then digested
with a mixture of alkali metal hydroxides and the liquid
and solid portions are separated in a second separation
step. The liquid portion is heated and/or seeded to remove
silica by precipitating sodium aluminum silicate,
20 the remaining liquid is then cooled and/or seeded to
precipitate and recover aluminum hydroxide.
Advantageously, the ore containing alunite is roasted
in the dehydration, reduction and oxidation steps at a
temperature offrom about 400°C to about 850°C to ef-
25 feet the removal of the water of hydration and sulfates
existing as Alz(S04h. Preferably the ore is roasted in
the dehydration, reduction and oxidation steps at a
temperature of from about 500°C to about 650°C. Advantageously,
the roasting steps are carried out at at-
30 mospheric pressure in fluidized-bed reactors, rotating
kilns or the like, and the preferred temperatures maintained
for from about one-half minute to about six
hours in each step. The residence time within each step
varying greatly depending upon the type equipment
35 used.
The reducing atmosphere in the reduction roast can
be reducing gases such as hydrogen, hydrocarbons, carbon
monoxide or mixtures thereof. The sulfur dioxide
emitted from the reduction roast can then be converted
40 to commercial products such as elemental sulfur, sulfuric
acid and the like.
The oxidizing atmosphere of the oxidation roast can
be air, oxygen or mixtures of air and other oxidizing
gases. The sulfur oxides emitted from the oxidation
45 roast can also be converted to commercial products
such as elemental sulfur, sulfuric acid and the like.
The roasted ore is then leached with a solvent, preferably
water or an alkaline solution. The liquid and
50 solid portions of the resultant slurry are then separated
in a first separation step by conventional means such as
thickener tanks, filters, belt extractor filters and the
like.
The solid portion therein separated is then digested
55 with a mixture of alkali metal hydroxides having a concentration
of up to about 300 grams per liter caustic expressed
as NazC03. Preferably the alkali metal hydroxides
used are sodium hydroxide and potassium hydroxide.
Advantageously, the digestion conditions are: at·
60 mospheric pressure, a temperature of from about 80°C
to about II OOC and a digestion time of from about five
minutes to about two hours.
The digestion product is then separated in a second
separation step by conventional means such as thick-
65 ener tanks, filters and the like. The separated liquid
portion is then treated to remove excess silica by heating
and/or seeding with sodium aluminum silicates. Advantageously
aggitation is applied to this liquid portion
3
3,890,425
4
25
of the extracted alumina had been precipitated and was
calcined at IOOO°C.
This invention has been described in detail with particular
reference to preferred embodiments thereof, it
5 should be understood that variations and modifications
can be effected within the spirit and scope of the invention
as described hereinbefore and as defined in the appended
claims.
What is claimed is:
10 1. A method for recovering aluminum hydroxide and
other valuable constituents from ore containing alunite,
comprising the steps of:
a. roasting the ore to remove water of hydration,
b. roasting the dehydrated ore resulting from Step (a)
in a reducing atmosphere to remove sulfate,
c. roasting the reduced ore resulting from Step (b) in
an oxidizing atmosphere to convert sulfides to sulfur
oxides,
d. leaching the oxidized ore resulting from Step (c)
with solvent to remove potassium and sulfate,
e. separating the liquid and solid portions of the
slurry resulting from Step (d),
f. digesting the solid portion resulting from Step (e)
with an aqueous mixture of alkali metal hydroxides
at a concentration and at a temperature sufficient
to extract the aluminum content from said solid
portion,
g. separating the liquid and solid portions of the digestion
mixture resulting from Step (f),
30 h. precipitating silica from the liquid portion resulting
from Step (g),
i. separating the supernatant from the precipitant resulting
from Step (h),
j. precipitating aluminum hydroxide from the super-
35 natant resulting from Step (i) and
k. separating the supernatant from the precipitated
aluminum hydroxide resulting from Step (j).
2. The method of claim 1 in which Step (a), Step (b)
and Step (c) are carried out at a temperature of from
40 about 400°C to about 850°C for a time of from about
one-half minute to about six hours for each step.
3. The method of claim 1 in which Step (a), Step (b)
and Step (c) are carried out at a temperature of from
about 500°C to about 650°C for a time of from about
45 one-half minute to about six hours for each step.
4. The method of claim 1 wherein the reducing atmosphere
of Step (b) is selected from the group consisting
hydrogen, hydrocarbons, carbon monoxide and mixtures
thereof.
50 5. The method of claim 1 wherein the oxidizing atmosphere
of Step (c) is selected from the group consisting
of air, oxygen and mixtures thereof.
6. The method of claim 1 wherein the solvent of Step
55 (d) is selected from the group consisting of water and
alkaline solutions.
7. The method of claim 1 wherein the alkali metal hydroxides
of Step (f) are selected from the group consisting
of sodium hydroxide and potassium hydroxide.
60 8. The method of claim 1 in which the precipitation
of silica of Step (h) is carried out by heating the liquid
to a temperature of about 90°C for at least one hour at
atmospheric pressure.
9. The method of claim 1 in which the precipitation
65 of silica of Step (h) is carried out by heating the liquid
at a pressure of from about 0.5 atmospheres to about
7 atmospheres at a temperature of from about 90°C to
about 200°C for at least fifteen minutes.
EXAMPLE I
A charge of alunite ore weighing about 200 grams
was placed in a Vycor retort. The retort was then
placed in a preheated electric furnace, the furnace lid
was closed and the temperature raised to about 580° to
about 600°C and held at this level for about 60 minutes.
During roasting, the retort was rotated continuously at
about one rpm and evolved gases were swept from the
retort by a stream of air.
After roasting under the conditions recited above the
ore was roasted for about 30 minutes at a temperature
of about 580°C in an atmosphere consisting of 50 percent
hydrogen gas and 50 percent carbon monoxide
gas. At the conclusion of this roast in a reducing atmosphere
the roasting chamber was purged with nitrogen
and the ore roasted for about 30 minutes in an air atmosphere.
The roasted ore was then ground to 35 mesh and
mixed with water at a 25 percent solids level and the
slurry was heated to between 75° and 80°C and mechanically
agitated while being held at this temperature
for one hour.
After separation of the liquid and solid portions of
the water leach slurry the solid portion thereof was digested
in a caustic solution comprising essentially sodium
and potassium hydroxides having a caustic concentration
of about 220 grams per liter as Na2C03' The
slurry was boiled at a pressure of one atmosphere with
mechanical agitation for one hour and the liquid and
solid portions thereof separated.
The digestion liquor was then introduced into a precipitation
assembly consisting of one liter graduated
cylinders equipped with paddles to stir the liquid from
top to bottom. The precipitations were maintained at
a constant temperature of 55°C and rotated constantly
at 125 to 150 rmp and stirred just enough to prevent
settling. After introduction of the digestion liquor into
the precipitation apparatus and stirring was started, 20
grams of wet seed ( 15 gm AI20 3 dry) were introduced
in small portions until all seed material had been added.
Precipitation was then allowed to proceed with constant
stirring. At the termination of the test 52 percent
during the removal of excess silica. If heating at atmospheric
pressure is used in this step, a temperature of
about 90°C for at least one hour is required. If heating
with pressure in excess of one atmosphere is used, a
temperature of from about 90°C to about 200°C for at
least fifteen minutes is required. Advantageously the
heating is carried out at a pressure of from about 0.5
atmosphere to about 7 atmospheres for a time of at
least fifteen minutes.
After removal of silica, which is precipitated as sodium
aluminum silicate, the resultant liquid is cooled to
precipitate crystalline aluminum hydroxide, which is
then separated from the liquid. Advantageously the liquid
is seeded with aluminum hydroxide crystals during
the cooling step to accelerate the rate of precipitation 15
and to control the particle size of crystalline aluminum
hydroxide.
The liquid from the first separation step may be processed
by vacuum or cooling crystallization to precipi-
20
tate potassium sulfate.
The following specific example is intended to be illustrative
of the invention herein described, but not limiting
of the scope thereof.
3,890,425
* * * * *
6
13. The method of claim 1 containing the additional
step of precipitating potassium sulfate from the liquid
resulting from Step (e).
14. The method of claim 1 containing the additional
5 step of converting the sulfate removed in Step (b) into
sulfuric acid.
15. The method of claim 1 containing the additional
step of converting the sulfate removed in Step (b) into
elemental sulfur.
10
5
10. The method of claim 1 in which the precipitation
of silica of Step (h) is accelerated by seeding with sodium
aluminum silicates.
11. The method of claim 1 in which the precipitation
of aluminum hydroxide of Step (j) is carried out by
cooling the liquid until crystalline aluminum hydroxide
is formed.
12. The method of claim 1 in which the precipitation
of aluminum hydroxide of Step (j) is accelerated by
seeding with aluminum hydroxide crystals.
15
20
25
30
35
40
45
50
55
60
65
t-f�Xfm0�(D�denHorzOCR'>References Cited
UNITED STATES PATENTS
7/10969 Litz , 23-15 W
7/1969 !Platzke et al. 23-15W
3/1959 Zimmerley et al. 23-18 X
7/1960 Zimmerley et al. 23-24
4/1966 Churchward , 23~15 W
211970 Ziegenbaly et al. 23-23 X
1/1971 Proter et al. 23-22
3,455,'677
3,45:8,277
2,876,065
2,945,743
3,244,475
3,495,934
3,558,268
23-23, 24 R, 51 R
7
(f) stripping the loaded agent of (e) with an alkali
metal hydroxide;
(g) extracting rhenium values from the strip solution
of (f) with pyridine or pyridine derivative; and
(h) recovering rhenium from the pyridine extractant 5
by distilling off the pyridine.
2. The process of claim 1 in which metal ion impurities
are removed from the strip solution of .(b) before
crystallizing ammonium tetramolybdate in (c).
3. The process of claim 1 in which the anion exchange 10
agent in (a) is a tertiary amine ion exchange resin and the
stripping solution of (b) is ammonium hydroxide.
4. A process for recovering molybdenum and rhenium
values from pregnant acid leach solutions containing these
values together with other metal impurities and derived 15
from dusts and flue gases resulting from roasting relatively
impure molybdenite concentrate, said process comprising:
(a) extracting molybdenum and rhenium values from
the pregnant acid solution with a liquid water in- 20
soluble amine ion exchange agent;
(b) stripping the molybdenum and rhenium values
from the exchange resin with ammonium hydroxide
solution to form a strip solution containing the molybdenum
as ammonium molybdate and the rhenium
as ammonium perrhenate;
(c) crystallizing the molybendum from the strip solution
in (b) as ammonium tetramolybdate by adjust