3,942,765 Static mixing apparatus

Patent Number/Link:

United States Patent [19]

Henrickson

[11] 3,942,765

[45] Mar. 9, 1976

Primary Examiner-Robert W. Jenkins

Attorney, Agent, or Firm-Sheridan, Ross & Fields

[52] U.S. CI 259/4 R

[51 ] Int. CI............................................. BOlf 15/00

[58] Field of Search 259/4, 18, 36; 138/38,

138/42; 48/180 R, 180 M, 180 B; 239/476;

. 23/252 R

[54] STATIC MIXING APPARATUS

[75] Inventor: Angus V. Henrickson, Golden, Colo.

[73] Assignee: Hazen Research, Inc., Golden, Colo.

[22] Filed: Sept. 3, 1974

[21] App!. No.: 502,871

There is provided an improved static mixing apparatus

which comprises in combination a tubular body and a

static mixing element preferably coextensive in length

with the tubular body and disposed therein in fluid

flow intercepting relation. The static mixing element is

characterized by a plurality of alternately oppositely

extending first triangular elements from a common

center line whereby the laterally extending first triangular

elements are in axially staggered relation, and a

plurality of second triangular members each having

one apex on the common center line and each having

a side in common with a first triangular element, and

each of the second triangular elements lying in a plane

angularly related to the first triangular element with

which it has a side in common.

The second triangular elements lie in sectors about the

common center line. These devices are particularly

useful for mixing a plurality of materials in the same

or different states, miscible or immiscible, soluble or

insoluble, and reactive or nonreactive.

16 Claims, 9 Drawing Figures

[57] ABSTRACT

References Cited

UNITED STATES PATENTS

6/1934 Durkee 138/38

6/1952 Heyl 259/4

2/1953 Rogers : 239/476

11/1953 Morrow 138/38

9/1958 Lynn 138/38

8/1965 Mosey 259/4

[56]

1,961,744

2,601,018

2,628,864

2,660,198

2,852,042

·3,203,371

u.s. Patent March 9, 1976 3,942,765

·1 "

"I"

16" r.~/8 srI. '\'~J 201l

26 ~[,

20g:::-r-'/ 20f.

20e \17 38d

,fl71 20d

20c" 38b

38c . 20b

, 380

~ORGA:~: Fig_;4

AQUEOUS

86)(

Fig_7

I--.."..=---l.--j---l---.,,----, 60

3,942,765

BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION OF THE DRAWINGS

oppositely extending first triangular elements are in

axially staggered relation. There is also provided a

plurality of second triangular members each having an

apex on the common center line and each having a side

5 in common with at least a portion of a side of a first

triangular element, each of the second triangular elements

lying in a plane angularly related to the plane of

the first triangular element with which it has a side in

least in part in common. In a preferred embodiment of

10 the present invention, the first triangular elements all

lie in a common plane. The second triangular elements

each lie in a plane which is at right angles to the plane

of the first triangular member with which it has a side in

common. Conveniently, although not essentially, the

15 triangular elements are right triangles, for example 30°

right triangles.

BRIEF STATEMENT OF THE INVENTION

STATIC MIXING APPARATUS

BACKGROUND OF THE INVENTION AND PRIOR

ART

The concept of mixing materials by utilizing "static"

or motionless mixing has been known for sometime. In

the past 4 years, two designs have been available on the

market one of which consists of a series of helical elements

in a tube or pipe, and the other of which utilizes

a complex series of tubular channels. Both of these

structures divide and recombine a stream in geometric

progression, and within a relatively short distance, feed

stock material is thoroughly and predictably mixed.

("Automation", February 1972 "Motionless Mixers").

The helical element type of device is clearly disclosed

in U.S. Pat. No. 3,286,992 to Armeniades et al. dated

Nov. 22, 1966. These devices are called motionless

mixers because they have no moving parts. Relative The present invention may be better understood by

movement of the fluid with respect to the motionless 20 having reference to the annexed drawings wherein;

mixing elements is, however, achieved by the flow of FIG. 1 is a cross sectional view of a motionless mixing

fluid within the conduit. apparatus of the present invention employing a pre-

Other efforts at blending various materials include ferred motionless element therein.

the patent to Heyl et al. No. 2,601,018 wherein the FIGS. 2a and 2b are perspective views of the motionblending

tube contains a single perforated sheet metal 25 less mixing element shown in FIG. 1.

spiral member substantially throughout its length, the FIG. 3 is a top plan view of the motionless mixing

perforated surface ofthe spiral member extending from member shown in FIG. 2.

wall to wall of the blending tube. Rogers in U.S. Pat. FIG. 4 is an end view on an enhirged scale of the

No. 2,628,864 is disclosing an aerosol paint spraying apparatus shown in FIG. 1.

device taught the use within the spray tube of a spiral 30 FIG. 5 is a top plan view on an enlarged scale of a

form member formed either of twisted wire or a helical portion of the mixing element shown in FIG. 3.

ribbon of metal. Andrews et al. in U,S. Pat. No. FIG. 6 is a side elevation ofthe portion shown in FIG.

2,710,250 taught the mixing of fluids with a series of 5.

orifice members in a conduit. Grubb et al. U.S. Pat. No. FIG. 7 is a schematic illustration of a single stage

2,863,649 taught an apparatus for mixing on a small 35 solvent extraction unit employing a motionless mixing

scale of compositions having a short period of coexis- apparatus in accordance with the present invention.

tence when mixed and utilizing a rotating mixing rod FIG. 8 shows a portion of a blank from which the

having a small wire spirally wound around it and in- preferred motionless mixing elements may be formed

cluding at regularly spaced intervals spiral notches. by bending along the diverging diagonals of successive

Another device is taught in the patent to Thomas et al. 40 oppositely extending rectangular member according to

U.S. Pat. No. 3,089,683 wherein an elongated tubular a predetermined pattern.

body is provided with a series of diffusers which create

a turbulent flow of the liquids thereby ensuring a complete

mixture of the liquids prior to ejection through Referring now more particularly to FIG. 1, there is

the outlet. U.S. Pat. No. 3,203,371 to Mosey teaches a 45 here shown a tubular member 10 having an inlet end 12

machine for whipping of confectionary filling utilizing and an outlet end 14. The tubular member 10 may be

in the nozzle thereof a baffle which comprises a strip of formed of any suitable material which will not be afchrome

steel twisted into a helical form and having a fected by or reactive with the materials or anyone of

plurality of transverse slits to provide a multplicity of them being mixed. In some cases, therefore, the tubular

teeth or tongues which extend more or less radially 50 member may be formed of plastic, or glass, or a section

from the axis of the helical bent strip. of iron or cast iron pipe, or clay, as may be described.

The present invention is distinguished from these The cross section is desirably circular although a rectprior

art devices in that the motionless mixing element angular cross section may as well be used. The materiis

a singular structure of far simpler geometric configu- als to be mixed are conveniently introduced through a

ration then that heretofore proposed and therefore 55 Y-fitting at the inlet end as will be illustrated in FIG. 7.

much less costly in either fabrication or disassembly The mixing element 16 is positioned within the tubular

and cleaning than prior art structures. member in fluid flow intercepting relation.

Referring now to FIGS. 2a, 2b, 3, 4, 5 and 6, FIGS. 2a

and 2b show in perspective the mixing element gener-

Briefly stated, therefore, the present invention is in a 60 ally indicated by the numeral 16. For convenience, a

motionless mixing apparatus which comprises in com- center line 18 is shown and provides a reference from

bination a tubular body and a motionless mixing ele- which conveniently to describe the illustrated embodiment

disposed within the tubular body in fluid flow ment of the present invention. The center line 18 lies in

intercepting relation therein. The mixing element com- a plane. What will be designated for convenience as

prises an elongated member having a plurality of alter- 65 first triangles 20 also lie in the same plane. The first

nately oppositely extending first triangular elements triangles 20 alternately oppositely extend from the

from a common center line which forms a side of each center line 18. Thus, first triangles 20a, 20b, 20c and

said first triangular elements whereby the alternately 20d alternately extend first to the left then to the right,

3,942,765

shown in FIG. 4 being from the outlet end. The pattern

of disposing the second triangle members 38a, 38b, 38c

and 38d with respect to their respective contiguous first

triangular members 20a, 20b, 20c and 20d, and as

shown in FIGS. 5 and 6 is that the second triangular

member 38a is bent upwardly with respect to its contiguous

first triangular member 20a, the second triangular

member 38b is bent downwardly with respect to its

contiguous first triangular member 20d; the second

triangular member 38c is bent upwardly with respect to

its contiguous first triangular member 20c, and the

second triangular member 38d is bent downwardly with

respect to its contiguous first triangular member 20d.

Again regarding the device from the outlet end, in this

first group of four first triangular members 20, the

pattern of bending to form the second triangular members

38 is up-down-up-down. Thus, as one proceeds

axially toward the inlet end of the device, the bending

pattern is helical in a clockwise direction. With the next

20 set offour first triangle members 20e, 20f, 20g and 20h,

the bending pattern to form the second triangular

members 38e, 38f, 38g and 38h is just the opposite, i.e.,

counterclockwise and follows the pattern down-updown-

up.

The length of the motionless mixing element 16 is, in

the preferred embodiment, therefore, desirably divided

into segments of equal length wherein the bending

pattern alternates between·up and down ina clockwise

manner when viewed from the outlet end followed by a

bending pattern in the next adjacent segment in a counter-

clockwise fashion, followed by a bending pattern in

the next succeeding segment in a clockwise manner,

etc. The length of the individual segments as above

described is immaterial, and whereas in the preferred

embodiment, each segment is composed of four succeeding

first triangular members 20, the segment may

be composed of any even number of first triangular

members 20 in sequence with the bending pattern following

first upward then downward then upward, etc.

40 bending.

While reference has been had to "bending" in describing

mixing element 16, this is only occasioned by

reason that it has been found most convenient to form

the motionless mixing elements 16 from a flat piece of

metal, e.g., stainless steel sheet from a blank which

appears as shown in FIG. 8. The blank 58 shown in

FIG. 8 is conveniently slotted along alternately laterally

extending lines 60. With the centerline 18 extending

along the blank 58, it can readily be seen that the cen-

50 terline 18, the slit lines 60 andthe lower marginal edge

, 62 ofthe blank 58 define a series of rectangles lying

below the centerline 18. Likewise, the upper marginal

edge 64 of the blank 58 in combination with the centerline

18 and the radiating lines 60 define a series of

rectangular members. Since the lines 60 alternately

extend to the below and then above, the rectangular

members so defined are in alternating oppositely extending

staggered and overlapped relation. When the

rectangular members are bent along the diagonals 66

shown in dotted lines and converging upon the centerline

18, the bending being in the pattern above described

for each of the succeeding segments, the first

triangular members 20 and the second triangular members

38 are readily and conveniently formed. Bending

is desirably to an angular relationship with the first

triangular member 20 of 90°. When viewed from the

outlet end as shown in FIG. 4, it will be seen that there

is no clear path for the fluid to take as it proceeds from

then to the left and then to the right, for example,of

center line 18. This pattern persists for the length of the

mixing element 16, and illustrates what is meant by the

language "alternately oppositely extending first triangular

elements from a common center line 18." Consid- 5

ering, for the moment, the first triangle 20a, it will be

observed that it is composed of a base line 26, a radial

.line 28 and a hypotenuse 30, the first triangle 20a being

a right triangle. The base line 26 coincides with the

center line 18. Considering the first triangle 20b, it is 10

composed of a base line 32, a radial line 34, and a

hypotenuse 36. The base line 32 of the first triangle 20b

also coincides with the centerline 18. In the preferred

embodiment illustrated in FIGS. 2-6, the base line 32

of the first triangle 20b also coincides with a portion of 15

the base line 26 of the first triangle 20a. The extent of

the overlap or coincidence of the base line 32 with the

base line 26 is a matter of choice and, as shown in the

preferred embodiment is approximately one half the

length of the respective base lines 26 and 32. This

illustrates what is meant by the language "axially staggered

and overlapping relation." It should be understood

that while an overlap to the extent of one half of

the base line of contiguous first triangles is a preferred

arrangement, it is by no means an essential arrange- 25

ment, and the extent of overlapping may be zero or up

to 75%, with a 50% overlap being preferred.

In addition to the first triangles 20, there is provided

a plurality of second triangular members 38 which

members are disposed out of the plane of the first tri- 30

angular members 20. Consider, therefore, second triangular

members 38a, 38b, 38c and 38d. Each of these

triangles 38a, 38b, 38c and 38d has an apex on the

common center line 18, and each of the second triangular

members 38a, 38b, 38c and 38d, has a side in 35

common with a first triangular element 20. Consider,

therefore, second triangular members 38a. It has an

apex 44 lying on the common centerline 18. Also, it has

a side 46 which is in common with the side 30 of the

first triangular member 20 a and in the embodiment

shown, in coextensive therewith. It has been found

convenient, and therefore illustrated in the preferred

embodiment that the second triangular members 38

should also be right triangles as are the first triangles

20. Thus the side 46 of the second triangular member 45

38a is indeed a hypotenuse and coincides with the

hypotenuse 30 of the first triangular member 20a. The

sides 48 and 50 of the second triangular member 38a

intersect at a 90° angle, and again, although not essentially,

the right triangle 38a is a 30, 60, 90° right triangle

as is the right triangle 20a.

As shown in FIGS. 2a and 2b, the right triangle 38a is

bent out of the plane of the right triangle 20a and extends

upwardly as it appears in FIGS. 5 and 6. In like

but opposite and staggered manner, the triangle 38b is 55

bent downwardly along the hypotenuse 36 ofthe first

triangular member 20b. Thus, the right triangle 38b is

bounded by the hypotenuse 52, the radial line 54 extending

from the centerline 18, and the side 56. The

triangles 38a and 38b are angularly related to the 60

planes of their respective contiguous first triangular

members 20a and 20b, that angle being in the preferred

embodiment shown in FIGS. 2-6 a 90° angle.

Considering the first triangle members 20a, 20b, 20c

and 20d, these first triangles 20 in the order named are 65

proceeding serially and axially in the direction toward

what I shall for convenience denominate "the inlet",

the vantage point of viewing the mixing element as

3,942,765

seconds. The fluid velocity in the settler 86 is approximately

0.28 feet per second and retention time 143

seconds. The volume· of solvent in the mixer 70 and

settler 86 is approximately 4000 gallons.

For comparative purposes, a conventional tank mixer-

settler system which will handle 1000 gallons per

minute of aqueous flow requires 2 minutes retention in

the mixer and 0.5 square feet of settler area per gallon

per minute of total flow. Assuming a solvent aqueous

ratio of 1.5 to 1 in the mixer and solvent depth of 8

inches in the settler, the volume of solvent in one stage

will be approximately 10,000 gallons. This difference

can be realized for a large size solvent extraction plant.

The capital cost for a system such as that shown in FIG.

7 has been extimated to be approximately 75% of the

conventional type mixer-settler system.

The conditions of extraction vary, of course, with

different systems and the mixer portion of the apparatus

may be relatively shorter or longer depending upon

20 these conditions, e.g. phase separation rate, solvent

power of organic phase with respect to the solute, ionexchange

rate between phases, etc. It should also be

noted that while, for convenience in description, referencehas

been made to an inlet end and an outlet end of

the motionless mixing element, fluid flow may be in

either direction relative to the mixing elements of the

present invention with equivalent results.

The invention has been described in detail with particular

reference to a referred embodiment thereof, but

30. it will be understood that variations and modifications

can be effected within the spirit and scope of the invention

as described hereinabove and within the scope of

the claims appearing below.

What is claimed is:

1.A motionlessrnixing apparatus comprising in combination:

a. a tubular body;

b. a motionless mixing element disposed within said

tubular body in fluid flow intercepting relation,

said mixing element comprising:

1. an elongated member having a plurality of alternately

.oppositely extending first triangular elements

from a common centerline which forms a

side of each said first triangular element, each of

said first triangular elements lying on one side of

said common centerline having a side in common

with a portion of the sides of two oppositely extending

first triangular elements lying on the

other side of said common centerline, whereby

said laterally extending first triangular elements

are in axially staggered and overlapping relation,

and .

2. a plurality of second triangular members each

having one apex on said common centerline and

each having a side in common with a first triangular

element, each of said second triangular elements

lying in a plane angularly related to the

first triangular element with which it has a side in

common.

60 2. A motionless mixing apparatus in accordance with

claim 1 wherein the second triangular members each

lie in a plane at right angles to the plane of the first

triangular member with which it has a side in common.

3. A motionless mixing apparatus in accordance with

claim 1 in which the first triangular elements are right

triangles.

4. A motionless mixing apparatus in accordance with

claim 3 in which the first triangular elements are 30°

the inlet to the outlet all quadrants are substantially

blocked by upstanding or depending second triangular

members 38. While a circular cross section has been

shown for the tubular member 10, and there is necessarily

some free space between the sides 50 and 56, for 5

example and the tubular member 10, this is not regarded

as material in the light of the convenience and

inexpensive mode of fabrication the motionless mixing

elements 16 in the preferred embodiment illustrated

and as described above. The tubular member 10 might 10

as well be provided with a square or rectangular cross

section. .

This apparatus has been tested and has demonstrated

superior mixing characteristics in liquid-liquid extraction

system, wherein, two immiscible phases are inti- 15

mately dispersed to permit transfer of a soluble constituent

from the aqueous phase to the organic phase.

FIG. 7 shows as apparatus incorporating a mixer in

accordance with the present invention. Thus, there is

shown in FIG. 7 in schematic and diagrammatic fashion

a mixer tube 70 which although it cannot be seen in

FIG. 7 contains an elongated mixing element such as

that shown in FIGS. 2-6. The inlet end n is attached to

one leg of a Y-fitting 74, one arm of which is connected

to a source of organic medium pumped therethrough 25

by means of a pump 76 and controlled by means of a

.flow meter 78, and wherein the other arm is connected

to an aqueous medium source pumped thereto by

means of a pump 80 through a flow meter 82.

By the time the immiscible organic and aqueous phases

have traversed the length ofthe tube 70 and emerge

at the outlet end 84, the degree of subdivision of the

organic phase in the aqueous phase is quite fine. The

dispersion or emulsion, as the case may be, enters the

settler portion 86, the fluid flows in to aT-shaped set- 35

tling tube of relatively large diameter with the laterally

extending arms in a vertical position. The organic

phase containing the solute being lighter than the water

rises to the top and is exhausted through the line 90.

The aqueous phase is exhausted through line 92. Be- 40

cause the fluid velocity in the mixer 70 can be set to

give uniform droplet size, coalescence is fast and requires

a shorter retention time. After the mixing section

70, the mixed solvent and aqueous phases are

discharged into the enlarged section of pipe 86 so that 45

turbulance is reduced to a minimum and the phases are

given an opportunity to separate. The length of the

settler 86 which is required is dependent on the phase

separation characteristic of the two fluids and is a function

of the specific gravity, viscosity and surface or 50

interfacial tension.

An apparatus of the type shown in FIG. 7 has been

used in the solvent extraction of copper from a dilute

aqueous copper sulphate solution with kerosene solution

of 2-hydroxybenzophenoxime whereby copper is 55

exchanged into the organic phase. Comparative studies

were made using the mixing device of the present invention

in a system as shown in FIG. 7, and using a

conventional tank mixer-settler system.

It has been determined that a single stage of the extraction

circuit shown in FIG. 7 which handles 1000

gallons dilute aqueous copper sulphate (1 to 2 gms. per

liter) and 1500 gallons ofthe organic phase per minute

requires a mixer 70 which is 14 inches in diameter and

approximately 80 feet long. The settler 86 is then ap- 65

proximately 5 feet in diameter and approximately 40

feet long. This provides a fluid velocity of about 5.2

feet per second in the mixer 70 and a mixing time of 15

3,942,765

right triangles.

5. A motionless mixing apparatus in accordance with

claim 4 in which the 30° angle of the first triangular

members includes the side common to the common

centerline. 5

6. A motionless mixing apparatus in accordance with

claim 1 in which the first and second triangular elements

are right triangles.

7. A motionless mixing apparatus in accordance with

claim 6 wherein the common side between a first tri- 10

angular member and its second triangular member is

the hypotenuse of each.

8. A motionless mixing apparatus in accordance with

claim 6 in which the first and second triangular elements

are 30° right triangles. 15

9. A motionless mixing apparatus in accordance with

claim 8 in which the 30° angle of the first triangular

members includes the side common to the common

centerline.

10. A motionless mixing apparatus in accordance 20

with claim 1 wherein the second triangular members on

axially succeeding first triangular members occupy a

position in serial sectors about said common centerline.

11. A motionless mixing apparatus in accordance

with claim 10 in which the sectors are each 90°. 25

12. A "motionless mixing apparatus in accordance

with claim 1 wherein the first and second triangular

members are formed by folding staggered bilaterally

extending rectangular sections along a diagonal thereof 30

whereby the apices of successive first triangular members

alternately oppositely extending from said common

centerline also successively proceed along the

common centerline.

13. A motionless mixing apparatus in accordance 35

with claim 1 in which the first triangular members all lie

in a common plane.

14. A motionless mixing apparatus in accordance

with claim 1 in which the motionless mixing element is

formed from stainless steel sheet. 40

15. In a motionless mixing apparatus having a tubular

fluid conduit and stationary mixing means disposed in

said tubular fluid conduit, the improvement which

comprises: a single stationary mixing element coextensive

with said conduit comprising

a. an elongated member having a plurality of alternately

oppositely extending first triangular elements

from a common centerline which forms a

side of each said first triangular element, each of

said first triangular element, each of said first triangular

elements lying on one side of said common

centerline having a side in common with a portion

of the sides of two oppositely extending first triangular

elements lying on the other side of said common

centerline, whereby said laterally extending

first triangular elements are in axially staggered

and overlapping relation, and

b. a plurality of second triangular members each

having one apex on said common centerline and

each having a side in common with a first triangular

element, each of said second triangular elements

lying in a plane angularly related to the first triangular

element with which it has a side in common.

16. A motionless mixing apparatus comprising in

combination:

a. a tubular body;

b. a motionless mixing element disposed within said

tubular body in fluid flow intercepting relation,

said mixing element comprising:

I. an elongated member having a plurality of alternately

oppositely extending first triangular elements

from a common centerline which coincides

with a side of each of said first triangular

elements, whereby said alternately oppositely

extending first triangular elements"are in axially

staggered relation; and

2. a plurality of second triangular members each

having one apex on said common centerline and

each having a side in common with at least a

portion of a side of a first triangular element,

each of said second triangular elements lying in a

plane angularly related to the plane of the first

triangular element with which it has a side at

least in part in common.

* * * * *

gn:n�itx��0�ce:none'>pebble lime which reacts with the sulfur trioxide pro- 35

duced by the pyrolysis to form calcium sulfate. The ammonia

and water produced by the pyrolysis are also

passed through the lime column before being recycled

to the weak base leaching step. Calcium sulfate so produced

can then be either prepared for marketing or dis- 40

carded as a waste.

The liquid content separated in the first separation

step of FIG. 2 optionally may be processed by adding

a weak base, such as ammonia, thereby precipitating

potassium sulfate. The liquid may then be boiled in a 45

lime boil step in the presence of lime [Ca(OHhl. preferably

in excess of stoichiometric amounts at atmospheric

pressure, a reaction time of from about fifteen

minutes to about one and one-half hours. The product

of the lime boil step is then separated by conventional 50

means such as centrifuge, filter, thickener tanks, vacuum

distillation or crystallization, and the like. The liquid

portion then can be recycled to use in the leaching

step and the solid precipitated sulfate converted to 55

commercial products such as sulfuric acid, elemental

sulfur and the like.

Referring to FIG. 3 in more detail, the product

formed in the silica removal step optionally may be filtered

and the liquid solution containing aluminum hy- 60

droxide transferred to the precipitation step. The solid

content filtered is sodium aluminum silicate with or

without a sulfate ion depending upon the concentration

of silicon and sulfate in the solution.

After removal of silica (precipitated as sodium alumi- 65

num silicate) the resultant liquid is cooled to precipitate

crystalline aluminum hydroxide, which is then separated

from the liquid. Advantageously the liquid is

3,890,426

* * * * *

This invention has been described in detail with par- 9. The method of claim 1 wherein the alkali metal hyticular

reference to preferred embodiments thereof, it droxides of Step (d) are selected from the group conshould

be understood that variations and modifications sisting of sodium hydroxide and potassium hydroxide.

can be effected within the spirit and scope of the inven- 10. The method of claim 1 in which the precipitation

tion as described hereinbefore and as defined in the ap- 5 of silica of Step (f) is performed by heating the liquid

pended claims. to a temperature of about 90°C for at least one hour at

What is claimed is: atmospheric pressure.

1. A method for recovering aluminum hydroxide 11. The method of claim 1 in which the precipitation

from ore containing alunite comprising the steps of: of silica of Step (0 is performed by heating the liquid

a. roasting the ore to remove the water of hydration, 10 at a pressure of from about 0.5 atmosphere to about 7

b. leaching the roasted ore from Step (a) with a weak atmospheres at a temperature of from about 90°C to

base at a pH of from about 8 to about 12 to dissolve about 200°C and for at least fifteen minutes.

sulfate and alkali metals, 12. The method of claim 1 in which the precipitation

c. separating the liquid and solid portions of the of silica in Step (f) is accelerated by seeding with soslurry

resulting from Step (b), said liquid portion 15 dium aluminum silicates.

containing dissolved sulfate and alkali metals, 13. The method of claim 1 in which the precipitation

d. digesting the solid portion from Step (c) with an of aluminum hydroxide in Step (h) is performed by

aqueous mixture of alkali metal hydroxides at a cooling the liquid until crystalline aluminum hydroxide

concentration and at a temperature sufficient to is formed.

extract the aluminum content from said solid por- 20 14. The method of claim 1 further including accelertion,

ating the precipitation of aluminum hydroxide in Step

e. separating the liquid and solid portions of the (h) by seeding the liquid with aluminum hydroxide

slurry resulting from Step (d), crystals.

f. precipitating silica from the liquid portion resulting IS. The method of claim 1 including the additional

from Step (e), 25 step of washing the precipitation product of Step (i)

g. separating the liquid and solid portions resulting with water.

from Step (f), 16. The method of claim 1 including the additional

h. precipitating aluminum hydroxide from the liquid step of washing the precipitation product of Step (i)

portion resulting from Step (g), with an acid having a pH of about 4.5.

i. separating the aluminum hydroxide precipitate 30 17. The method of claim 1 including the additional

from the liquid portion resulting from Step (h). step of calcining the aluminum hydroxide precipitation

2. The method of claim 1 wherein Step (a) is per- product of Step (i).

formed at a temperature of from about 400°C to about 18. The method of claim 1 including the additional

850°C. step of crushing the ore containing alunite to a particle

3. The method of claim 1 wherein Step (a) is per- 35 size having a greatest distance between parallel oppoformed

at a temperature of from about 500°C to about site exterior surfaces of about one inch or less prior to

650°C. Step (a).

4. The method of claim 1 wherein the weak base of 19. The method of claim 1 including the additional

Step (b) is selected from the group consisting of ammo- step of reducing the size of the product of Step (a) to

nium hydroxide and alkali metal hydroxides. 40 a particle size of about 8 mesh or less before proceed-

S. The method of claim 1 in which Step (b) is per- ing to Step (b).

formed at a temperature of from about 20°C to about 20. The method of claim 1 including the additional

120°C and for a time of at least five minutes. step of recovering Si02 from the solid content sepa-

6. The method of claim 1 in which the sulfate sepa- rated in Step (e).

rated in Step (c) is converted to sulfuric acid. 45 21. The method of claim 1 including the additional

7. The method of claim 1 in which the sulfate sepa- step of filtering the solution formed in Step (f) to yield

rated in Step (c) is converted to elemental sulfur. sodium aluminum silicate solids and sodium aluminum

8. The method of claim 1 in which potassium sulfate sulfate solids.

is recovered from the liquid content of Step (c).

ize:��btf��0�y:"Times New Roman","serif";mso-fareast-font-family: HiddenHorzOCR'>second oxidation zone.

* >I< >I< * *

About 7% of the molybdenum contained in the calcines

is also solubilized in the sulfurous acid leach.

The leached residue is separated from the leach solution

by filtration and after drying is ready for packaging 5

for sale. The leach solution joins the solutions from the

scrubbers on the flash roaster and re-roaster.

The effectiveness of the above-described process is

graphically illustrated by the high recovery of rhenium

and molybdenum achieved. it provides for the recovery 10

of up to 95% of rhenium and high recovery ofmolybdenum

in molybdenite with a minimum of process time

and a minimum of oxygen and added heat. The economic

advantages of these features are apparent. The

process is adaptable to either a batch or continuous op- is

eration.

It is an attractive side advantage of the. process that

a small volume of exhaust gas containing a high percentage

by volume of sulfur dioxide is produced. The

process is normally operated with an exhaust gas volume

discharge rate of 1,350 cubic feet per minute

(CFM) with up to 220% excess oxygen and 30-50% by

volume of sulfur dioxide in the exhaust gas. This high

volume percentage of sulfur dioxide makes its recovery

economically feasible for various commercial uses. In

contrast, present-day processes utilizing air for cooling

and for supplying oxygen are of necessity operated with

an exhaust volume discharge rate of 40,000 CFM, 16

volume percent excess oxygen and 1-2 volume percent

of sulfur dioxide. This volume percentage of sulfur dioxide

in the exhaust gas is so low that its recovery is not

economically feasible because it involves processing

such large volumes of gas. As a result the sulfur dioxide

is exhausted to the atmosphere creating a serious pollution

problem in heavily populated areas. The process of 35

this invention eliminates this problem.

The reduced volume of exhaust gas also results in a

much higher concentration of rhenium oxide in the exhaust

gas than is obtained in conventional processes.

As a result, recovery of substantially all of the rhenium

is far more feasible and economical than in present processes

using air with resultant large volumes of exhaust

gas to be processed for recovery of the rhenium oxide.

Reduction of the volume of gas processed through

the system by a factor of about 30resultsin a dr1!§jic: 45

reduction in the size of equipment require-d~ith~jgnificant

savings in equipment cost and floor space.

What is claimed is:

n. A method for recovering rhenium and molybdic

mdde from molybdenite concentrate which comprises:

a. pre-heating particles of said concentrate in an oxygen-

free atmosphere to a temperature not in excess

of about 750"C to raise the temperature of the particles

to promote flash oxidation of the molybdenite

when the particles are introduced into a flash

oxidation zone,

b. causing said pre-heated particles to fall through a

first oxidizing zone of heated oxygen with said particles

and heated oxygen moving countercurrent to

each other to disperse said pre-heated molybdenite

particles in said heated oxygen to provide maximum

particle surface contact with heated oxygen

for effective oxidation, said first oxidation zone

being heated substantially by the exothermic heat

of the reactions occurring in said first oxidation 65