3,890,425 Redox treatment of alunite ore

Patent Number/Link:

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

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

SECOND SEPARATION ",/

DESILICATION ,

'-/

PREtl PilAT/ON

ALUNITE

ORE

WATER OF HYDRATION

SULFUR

DIOXIDE

SULFUR

OXIDE

AL (OH) 3

LIQUID

SOLIDS

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REDOX TREATMENT OF ALUNITE ORE

FIELD OF THE INVENTION

3,890,425

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

3,890,425

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-

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

* * * * *

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. 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.

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

(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;

in (b) as ammonium tetramolybdate by adjust