6,092,665
Jui. 25, 2000
[11]
[45]
111111111111111111111111111111111111111111111111111111111111111111111111111
US006092665A
Patent Number:
Date of Patent:
United States Patent [19]
Schmidt et ai.
FOREIGN PATENT DOCUMENTS
3816061 8/1989 Germany 423/206.2
Primary Examiner-Tuan N. Nguyen
Attorney, Agent, or Firm---8heridan Ross P.e.
A process is provided for recovering a saline mineral from
an ore containing the saline mineral and impurities. In one
aspect, the process generally includes the steps of separating
a first portion of impurities from the ore by density
separation, electrostatically separating a second portion of
impurities from the ore, and magnetically separating a third
portion of impurities from the ore. The process can further
include the steps of crushing the ore and dividing the
crushed ore into a plurality of size fractions before the
above-referenced separating steps. In another aspect, the
process includes the steps of calcining the ore and subsequently
separating a first portion of impurities by density
separation. Indirect heating may be utilized for the calcining
process and, preferably, calcining gases are recycled and
utilized for heating fluidizing another portion of ore. Water
vapor may be condensed from the calcining gas and utilized
for other purposes.
ABSTRACT
3/1975 Sproul et al. 423/206.2
7/1982 Brison et al. 209/127.1 X
3/1983 Imperto et al. 423/206.2
7/1990 Gilbert et al. 209/40 X
11/1995 Schmidt et al. 209/131 X
7/1997 Schmidt et al. 423/206.2 X
3,869,538
4,341,744
4,375,454
4,943,368
5,470,554
5,651,465
[57]
Related U.S. Application Data
[54] BENEFICIATION OF SALINE MINERALS
[75] Inventors: Roland Schmidt, Lakewood; Dale L.
Denham, Louisville, both of Colo.;
Ralph B. Tacoma, Green River, Wyo.;
Allen H. Moore, Parker; Allan L.
Thrner, Lakewood, both of Colo.
[73] Assignee: Environmental Projects, Inc, Casper,
Wyo.
[21] Appl. No.: 08/737,871
[22] PCT Filed: May 25,1994
[86] PCTNo.: PCT/US94/05918
[56] References Cited
U.S. PATENT DOCUMENTS
[63] Continuation-in-part of application No. 08/066,871, May
25, 1993, Pat. No. 5,470,554.
[51] Int. CI? B03B 1/00
[52] U.S. CI. 209/3; 209/11; 209/39;
209/127.1; 209/214; 423/206.2
[58] Field of Search 209/3, 12.1, 12.2,
209/17, 30-37, 39, 40, 127.1, 128, 131,
214, 11; 423/121, 206.2; 241/19, 24, 25
§ 371 Date: JuI. 3, 1997
§ 102(e) Date: JuI. 3, 1997
[87] PCT Pub. No.: W094/27725
PCT Pub. Date: Dec. 8, 1994
3,244,476 4/1966 Smith 423/206.2 X 38 Claims, 1 Drawing Sheet
HEATER
CALCINED
TRONA ORE
HIGH-EffiCIEHCY
PARTICUlATE
SCRUBBER
HIGH
PURIlY
WATER
PARTICUlATE
WATER
COMBUSTION
GASES
ANAL PRODUCT
FUEL
HIGH
HIGH-EmCIENCY 2ND STAGE LpURITY
~ PARTICULATE CONDENSER I -WATER
SCRUBBER
~ ITO STACK
COMBUSTION
GASES
~ SLUSH PROCESS I II I
(- 200 MESH)
d•
•'JJ.
~
~..... ~=.....
N
~Ul
N
C
CC
~
~
FINAL PRODUCT
DENSITY I I MAGNETIC
SEPARATION r--I SEPARATION I(+
65 MESH)
MAGNETIC
SEPARATION
(65 X200 MESH)
STEAM
BOILER ~FUEL r
1
FLUIDIZED BED
REACTOR
1ST STAGE I--PARTICULATE
CONDENSER I - WATER
I 'CALCINING
GASES CALCINED
TRONA ORE
- I
RAW....--_
O~ CR~SH I
-6 MESH
FRESH GAS a
HEATER
...0. \ =\C
...N.
0\
0\
Ul
6,092,665
1
BENEFICIATION OF SALINE MINERALS
REFERENCE TO RELATED APPLICATIONS
This application is filed under 35 U.S.c. §371 based on 5
PCT/US94/05918, filed on May 25, 1994, which is a CIP of
U.S. patent application Ser. No. 066,871, filed on May 25,
1993, now U.S. Pat. No. 5,470,554.
FIELD OF THE INVENTION
10
2
ciation processes typically do not consistently produce such
a purity. Consequently, these industries generally use trona
purified by the more expensive and complex wet beneficiation
processes.
Accordingly, it is an object of the present invention to
provide a dry process for the beneficiation of saline minerals
and in particular, trona, resulting in higher purities than
existing dry beneficiation processes and which is simpler
and less expensive than known wet beneficiation processes.
The present invention relates generally to the beneficiation
of saline minerals and, more specifically, trona. The
invention further relates to a dry process for recovering
saline minerals from an ore containing saline minerals and
impurities.
BACKGROUND OF THE INVENTION
Many saline minerals are recognized as being commercially
valuable. For example, trona, borates, potash and
sodium chloride are mined commercially. After mining,
these minerals need to be beneficiated to remove naturally
occurring impurities.
With regard to trona (Na2C03.NaHC03 .2H2 0), highpurity
trona is commonly used to make soda ash, which is
used in the production of glass and paper. Naturallyoccurring
trona, or crude trona, is found in large deposits in
the western United States, such as in Wyoming and
California, and also in Egypt, Kenya, Botswana, Tibet,
Venezuela and Turkey. Crude trona ore from Wyoming is
typically between about 80% and about 90% trona, with the
remaining components including shortite, halite, quartz,
dolomite, mudstone, oil shale, kerogen, mica, nahcolite and
clay minerals.
The glass and paper making industries generally require
soda ash produced from trona having a purity of 99% or
more. In order to obtain such a high purity, wet beneficiation
processes have been used. Such processes generally involve
crushing the crude trona, solubilizing the trona, treating the
solution to remove insolubles and organic matter, crystallizing
the trona, and drying the trona which may subsequently
be calcined to produce soda ash. Alternatively, the
crude trona can be calcined to yield crude sodium carbonate,
which is then solubilized, treated to remove impurities,
crystallized and dried to produce sodium carbonate monohydrate.
Not all industries which use trona require such a highly
purified form of trona. For example, certain grades of glass
can be produced utilizing trona having less than 97% purity.
For this purpose, U.S. Pat. No. 4,341,744 discloses a dry
beneficiation process which is less complex and less expensive
than the above-described wet beneficiation process.
Such a dry beneficiation process generally includes crushing
the crude trona, classifying the trona by particle size, electrostatically
separating certain impurities, and optionally
magnetically separating other impurities. Such a process can
yield trona having up to about 95% to 97% purity, depending
on the quantity and type of impurities present in the crude
trona ore. The lower resulting purities of known dry processes
is partially due to the presence of impurities, such as
shortite and halite, which have similar electrostatic and
magnetic properties as the trona. Further, halite has a similar
density as the trona and, therefore, is difficult to remove even
utilizing known wet density separation processes.
There are uses for trona, for example, in certain applications
in the glass industry, requiring a purity of at least 97%,
yet not needing a purity over 99%. The known dry benefi-
SUMMARY OF THE INVENTION
The present invention is embodied in a process for
recovering a high-purity saline mineral from an ore containing
the saline mineral and impurities. In one aspect of the
15 present invention, the process generally includes separating
a first portion of impurities from the ore by a density
separation method, electrostatically separating a second
portion of impurities from the ore, magnetically separating
a third portion of impurities from the ore.
20
In one embodiment, the density separation step can
include air tabling or dry jigging to separate impurities
having a different density than the saline mineral. In another
embodiment, the process of the present invention is used for
25 beneficiating trona from an ore containing trona and impurities.
In this embodiment, the first portion of impurities
removed by the density separation step comprises shortite.
In another embodiment of the present invention, a process
is provided for the production of purified soda ash for
30 production of caustic soda by the lime-soda process. The
process generally includes the steps of separating a first
portion of impurities from a trona-containing ore by a
density separation method, electrostatically separating a
second portion of impurities from the ore, magnetically
35 separating a third portion of impurities from the ore. The
product of the above-mentioned separation processes is used
to produce caustic soda. The process further includes solubilizing
aluminum hydroxide in bauxite by contacting the
bauxite with the caustic soda to produce a solution and
40 recovering alumina from the solution.
In another aspect of the present invention, a process is
provided which includes calcining the saline mineral prior to
density separation. The process generally includes calcining
the ore to alter the apparent density of the saline mineral and
45 separating a first portion of impurities from the calcined ore
by density separation to produce a recovered saline mineral.
This process is particularly suitable for separating impurities
which have densities similar to the density of the saline
mineral prior to calcination, but which have different appar-
50 ent densities after calcination. In one embodiment, the saline
mineral comprises trona and the first portion of impurities
comprises halite. The process also improves the separation
of a saline mineral from other impurities by widening the
difference in apparent densities between the saline mineral
55 and such other impurities.
In yet another aspect of the present invention, a process is
provided for effectively removing impurities from about a
-65 mesh size fraction. The process generally comprises the
steps of sizing the ore to generate about a -65 mesh fraction
60 and about a +65 mesh fraction and separating iron from the
-65 mesh fraction to produce a first recovered portion. In
one embodiment, the separating step comprises a wet separation
process, such as the slush process. In another
embodiment, the separating step comprises magnetic sepa-
65 ration. In addition to iron, shaley components, such as
dolomitic and oil shales, may also be removed during the
separating step. Preferably, a second portion of impurities is
6,092,665
3 4
that materials of different densities physically separate from
each other. Thereby, certain impurities having a different
density than the desired saline mineral can be separated. The
density separation step of the present invention is most
5 preferably a dry process, however, wet density separation
processes, such as heavy media separation, can be used as
well. In dry density separation processes, the need for
processing in a saturated brine solution, solid/brine
separation, and drying of the product is eliminated.
10 Consequently, the process according to the present invention
is much cheaper and less complex. Any known density
separation technique could be used for this step of the
present invention, including air tabling or dry jigging.
As discussed above, density separation is conducted by
15 subjecting an ore to conditions such that materials of different
densities separate from each other. The mineral stream
having materials of varying densities is then separated by a
first or rougher pass into a denser and a lighter stream, or
into more than two streams of varying densities. Typically,
20 in the case of beneficiating trona, trona is recovered in the
lighter stream. The purity of a saline mineral recovered from
density separation can be increased by reducing the weight
recovery of the recovered stream from the feed stream. At
lower weight recoveries, the recovered stream will have a
25 higher purity, but the rougher stage process will also have a
reduced yield because more of the desired saline mineral
will report to the impurity stream. Such a "high purity"
process may be beneficial in that it requires less subsequent
processing (e.g., separation) of the ore and, in addition, may
30 be of higher value because it can be used in other applications
where high purity saline minerals are required.
In the case of beneficiating trona, for example, the weight
recovery (weight of trona recovered/weight of trona in the
feed stream) from the density separation step is between
35 about 65% and about 95%. More preferably, the weight
recovery is between about 70% and about 90% and, most
preferably, the weight recovery is about 80%.
In an alternative embodiment, the impurity stream from
40 density separation can go through one or more scavenger
density separation step(s) to recover additional trona to
improve the overall recovery. The scavenger separation is
similar to the above-described density separation step. The
scavenger step recovers a portion of the impurity stream
45 from the rougher pass having the saline mineral in it and
combines that portion with the above-described recovered
stream to increase the overall yield from density separation
or recycles it to other steps in the process, with or without
further size reduction.
In a further alternative embodiment, the recovered stream
from the rougher pass density separation can go through one
or more cleaning density separation steps to further remove
impurities from the recovered stream and improve the purity
of the final product. The cleaning step is similar to the
55 above-described density separation process in that impurities
are removed from the stream by density separation. In
both scavenging and cleaning passes, the feed stream into
those passes can undergo further size reduction, if desired,
for example, to achieve higher liberation.
With regard to the beneficiation of trona, which has a
density of 2.14, impurities that are removed during the
density separation step of the present invention include
shortite, having a density of 2.6, dolomite, having a density
of 2.8-2.9 and pyrite, having a density of 5.0. Each of these
65 is separable from the trona ore because of differences in
density from trona. By practice of the present invention, of
the total amount of shortite, dolomite, pyrite and, if present,
DETAILED DESCRIPTION OF THE
INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of one embodiment
of the present invention.
separated from the +65 mesh fraction to produce a second
recovered portion, and the first and second recovered portions
are combined to produce a recovered saline mineral.
In another aspect of the present invention, a novel process
for calcining saline minerals is provided. The process generally
comprises heating the saline mineral in a calcining
vessel above its calcining temperature with a heat source to
calcine the saline mineral, wherein said heat source is not in
direct fluid communication with said saline mineral. The
saline mineral may comprise, for example, trona. In one
embodiment, the heating step includes heating a fluid (e.g.,
steam) and bringing the fluid into thermal communication
with the calcining vessel (e.g., utilizing a steam coil heat
exchanger positioned within the interior of the vessel). In
another embodiment, the calcining gases produced by the
calcining process are recycled back to the vessel inlet, such
as to provide a medium for fluidizing. To accomplish this, at
least a portion of calcining gas must be removed from the
process stream to accommodate for the gas produced by the
calcining process.
In yet another embodiment, water vapor may be removed
from the calcined gas to reduce significantly the amount of
gas emitted from the system. For example, water may be
condensed from the calcining gas utilizing a scrubber, which
also aids in removal of particulates from the gas stream.
The processes of the present invention are designed to
recover saline minerals from naturally occurring ores to
produce commercially valuable purified minerals. As used in
the mineral processing industry, the term "saline mineral"
refers generally to any mineral which occurs in evaporite
deposits. Saline minerals that can be beneficiated by the
present process include, without limitation, trona, borates,
potash, sulfates, nitrates, sodium chloride, and preferably,
trona.
The purity of saline minerals within an ore depends on the
deposit location, as well as on the area mined at a particular
deposit. In addition, the mining technique used can significantly
affect the purity of the saline minerals. For example,
by selective mining, higher purities of saline minerals can be
achieved. Deposits of trona ore are located at several locations
throughout the world, including Wyoming (Green
River Formation), California (Searles Lake), Egypt, Kenya, 50
Venezuela, Botswana, Tibet and Turkey (Beypazari Basin).
For example, a sample of trona ore from Searles Lake has
been found to have between about 50% and about 90% by
weight (wt. %) trona and a sample taken from the Green
River Formation in Wyoming has been found to have
between about 80 and about 90 wt. % trona. The remaining
10 to 20 wt. % of the ore in the Green River Formation
sample comprised impurities including shortite (1-5 wt. %)
and the bulk of the remainder comprises shale consisting
predominantly of dolomite, clay, quartz and kerogen, and 60
traces of other impurities. Other samples of trona ore can
include different percentages of trona and impurities, as well
as include other impurities.
In the first aspect, the present process includes removing
a first portion of impurities from an ore containing saline
minerals by a density separation method. Density separation
methods are based on subjecting an ore to conditions such
6,092,665
5 6
higher magnetic susceptibility than trona. By practice of the
present invention, the use of an induced roll magnetic
separation technique can remove at least about 5 wt. %,
more preferably, about 50 wt. %, and most preferably about
5 90 wt. % of the shale from the material being treated by
magnetic separation.
As noted above for the density and electrostatic separation
steps, the impurity stream from the rougher pass of the
magnetic separation process can go through one or more
10 scavenger steps to improve the overall recovery. The scavenger
step recovers a portion of the impurity stream from the
rougher pass through magnetic separation and combines it
with the above-described recovered stream or recycles it to
the process with or without further size reduction to increase
15 the overall yield of the magnetic separation step.
Furthermore, the recovered stream from magnetic separation
can go through one or more magnetic cleaning steps to
further remove impurities from the recovered stream and
improve the purity of the final product.
It should be appreciated that the above-identified process
steps could be performed in any order. Preferably, however,
the density separation is performed first, followed by electrostatic
separation and finally magnetic separation.
25 In a further embodiment of the present invention, the
saline mineral-containing ore can be crushed to achieve
liberation of impurities prior to the separation steps. The
crushing step of the present invention can be accomplished
by any conventional technique, including impact crushing
30 (e.g., cage or hammer mills), jaw crushing, roll crushing,
cone crushing, autogenous crushing or semi-autogenous
crushing. Autogenous and semi-autogenous crushing are
particularly beneficial because the coarse particles of ore
partially act as the crushing medium, thus requiring less cost
35 in obtaining grinding media. Moreover, because saline minerals
are typically soft, these methods are suitable for use in
the present process. In addition, these two crushing methods
allow for the continuous removal of crushed material and
high grade potentially saleable dust.
In general, crushing to smaller particle size achieves
better liberation of impurities and thus, improved recovery.
However, if the particle size after crushing is too fine, there
may be adverse effects upon subsequent separation steps. In
addition, over-crushing is not needed for many applications
45 of the present invention and merely increases the costs
associated with the crushing step. It has been found that
acceptable liberation for the present process can be achieved
by crushing the ore to at least about 6 mesh. Preferably, the
particle size range after crushing is from about 6 to about
50 100 mesh and, more preferably, from about 6 to about 65
mesh.
In another embodiment of the present invention, the ore is
sized into size fractions prior to the separation steps. Each
size fraction is subsequently processed separately. In
55 general, the narrower the range of particle size within a
fraction, the higher the efficiency of removal of impurities.
On the other hand, a larger number of fractions will increase
the efficiency, but may increase the cost of the overall
process. The use of between 3 and 10 fractions has been
60 found to be acceptable. Preferably, the number of fractions
is between 4 and 10 and, more preferably, the number of
fractions is 8. Any conventional sizing technique can be used
for the present process, including screening or air classification.
For dividing into 8 fractions, the fractions typically
65 have the following particle size ranges: 6 to 8 mesh; 8 to 10
mesh; 10 to 14 mesh; 14 to 20 mesh; 20 to 28 mesh; 28 to
35 mesh; 35 to 48 mesh; 48 to 65 mesh (Tyler mesh).
potentially valuable heavy minerals in the trona ore, the
density separation step can remove at least about 10 wt. %
and more preferably, about 50 wt. %, and most preferably,
about 90 wt. % of the heavy impurity.
In an alternative embodiment, impurities removed during
the density separation process can be recovered as a product
for commercial use. For example, in the beneficiation of
trona, the impurities removed during the air tabling step can
comprise as much as 90% shortite. Such shortite may be
acceptable, for example, for certain applications in the glass
industry. The acceptability of the shortite in the glass industry
will depend upon the consistency and the relative lack of
iron in the product. In addition, for some trona deposits,
potentially valuable heavy minerals may be present. Such
minerals can be separated in the method and recovered.
The present invention further includes removing a second
portion of impurities by an electrostatic separation method.
Electrostatic separation methods are based on subjecting the
ore to conditions such that materials of different electrical
conductivities separate from each other. The electrostatic 20
separation of the present invention can be accomplished by
any conventional electrostatic separation technique. U.S.
Pat. No. 4,341,744 discloses standard electrostatic separation
processes suitable for use in the present invention in col.
4, line 62 through col. 6, line 32, which is incorporated
herein by reference in its entirety. As discussed in the
above-identified patent, saline mineral ore particles are first
differentially electrified and then separated into a recovered
stream from an impurity stream by various electrostatic
separation processes.
As noted above for the density separation step, the impurity
stream from the rougher pass of an electrostatic separation
process can go through a scavenger step to improve
the overall recovery. The scavenger step recovers a saline
mineral-containing portion of the impurity stream from the
rougher pass through electrostatic separation and combines
it with the above-described recovered stream to increase the
overall yield of the electrostatic separation step or otherwise
cycles it to other steps in the process. Furthermore, the 40
recovered stream from the rougher pass of the electrostatic
separation can go through one or more electrostatic cleaning
steps to further remove impurities from the recovered stream
and improve the purity of the final product.
For example, electrostatic separation can be used to
separate trona from impurities having a higher electrical
conductivity, such as shale, mudstone or pyrite. It should be
appreciated, however, that electrostatic separation could also
be used to separate impurities that have a lower electrical
conductivity than the saline mineral being recovered. By
practice of the present invention, utilizing electrostatic separation
can remove at least about 10 wt. %, more preferably,
about 50 wt. %, and most preferably, about 90 wt. % of the
more conductive mineral impurities from the is material
being treated by electrostatic separation.
The present process further includes a magnetic separation
step which subjects the ore to conditions such that
materials of different magnetic susceptibilities separate from
each other into a recovered stream and an impurity stream.
The magnetic separation step can be accomplished by any
conventional technique, such as induced roll, cross-belt, or
high intensity rare earth magnetic separation methods.
Preferably, induced roll is used in the present invention for
the finer fractions and high intensity rare earth magnets are
used for the coarser fractions. With regard to the beneficiation
of trona, typical impurities that can be removed during
the magnetic separation step include shale which has a
7
6,092,665
8
In yet another embodiment of the present invention, the
ore is dried prior to the separation processes set forth above.
The drying step removes surface moisture from the ore to
better enable the ore to be separated. Drying can be accomplished
by any conventional mineral drying technique,
including rotary kiln, fluid bed or air drying. The ore can be
dried to less than about 2%, and preferably less than about
1% surface moisture content. During the drying process, it
is preferred that the saline mineral is not raised to such a
temperature for such a period of time that is it calcined. In
the case of trona, the drying temperature should remain
below about 40 degrees centigrade to avoid calcination.
In still another embodiment of the present invention, a
de-dusting step is added to the basic beneficiation process to
remove fines before the electrostatic and magnetic separation
steps. De-dusting can be particularly important before
electrostatic separation because the dust can otherwise interfere
with effective electrostatic separation. Such a
de-dusting step can be conducted before, during or after one
or more of the crushing, sizing and/or density separation
steps. The fines produced during the processing of trona are
relatively high purity trona and are useful in several industrial
applications. For example, trona recovered by
de-dusting can have a purity of greater than about 94%,
preferably greater than about 96% and more preferably
greater than about 98%. Fines can be collected in de-dusting
steps by use of a baghouse, or other conventional filtering
device, and sold as purified trona without further processing.
The present invention provides a process for the separation
of saline minerals from an ore utilizing a dry beneficiation
technique, resulting in a high purity product, typically
greater than 85% purity, produced at low cost
compared to wet beneficiation processes. Utilizing the
above-described process, trona having about 98.8% purity
from an ore containing 90% trona has been obtained, compared
to less than about 97% purity for the prior art dry
beneficiation processes. The purity of recovered product can
be greater than about 97%, preferably greater than about
97.5%, and more preferably greater than about 98%. In
addition, by utilizing selective mining techniques and lower
weight recoveries for the separation steps, higher purities
can be obtained.
Utilizing the process of the present invention, recoveries
of greater than about 55% can be obtained. More preferably,
recoveries are greater than about 65% and, most preferably,
greater than about 75a. In the case of trona, the resulting
trona product can be used in many applications, especially
those requiring a purity of about 97.5% or greater, such as
in certain areas of the glass industry.
In the second aspect of the present invention, a process is
provided whereby impurities having the same or similar
density, magnetic properties and/or electrostatic properties
as a saline mineral in an ore can be effectively removed. As
used herein, the term "saline minerals" has the same meaning
as it is used in the description of the first aspect of the
present invention. The process recognizes and relies on the
fact that the apparent density of saline minerals, such as
trona, changes during calcining, while the apparent densities
of many impurities remain relatively constant during calcining.
A reduction in apparent density of the saline mineral
allows the impurities to be removed utilizing density
separation, even if the pre-calcined density of the trona is the
same as or similar to that of the impurity.
Accordingly, the second aspect of the present invention
comprises a process for recovering a saline mineral from an
ore containing the saline mineral and impurities. A schematic
diagram of a process embodying the second aspect of
the present invention is illustrated in the accompanying
FIGURE. The process may be performed utilizing each of
the illustrated process or, alternatively, bypassing some of
5 the illustrated processes. The process generally comprises
the steps of calcining the ore to alter the apparent density of
the saline mineral and separating a first portion of impurities
from the calcined ore by density separation to produce a
recovered saline mineral. As noted above, the impurities
10 may have a density which is similar to the density of the
un-calcined saline mineral, but which is sufficiently different
than the apparent density of the calcined saline mineral to be
readily susceptible to density separation.
The calcining step can be performed utilizing any appro-
15 priate calcining process. For example, direct heating utilizing
a rotary kiln or fluidized bed reactor can be utilized. In
a preferred embodiment, the calcining step is performed
utilizing an indirect heating process in a calcining vessel
such as a fluidized bed reactor at a temperature of at least
20 about 120° C. In the indirect heating process, the combustion
gases from the heat source are not in direct fluid
communication with the ore containing the saline mineral,
but rather provide heat to the ore by conduction through, for
example, heating coils, as described in more detail below. In
25 one embodiment, the calcining occurs at least about 140° C.
with a 20 minute residence time within a fluidized bed
reactor. Other calcining times and temperatures may also be
utilized as is known in the art.
The density separation step is based on subjecting the ore
30 to conditions such that materials of different apparent densities
physically separate from each other. In the case of
beneficiating uncalcined trona, having a density of about
2.14, density separation is relatively effective in removing
shortite, having a density of about 2.6; dolomite, having a
35 density of about 2.8-2.9; and pyrite, having a density of
about 5.0, as described above in more detail. On the other
hand, density separation of uncalcined trona is generally not
effective in separating impurities having a density close to
that of uncalcined trona, such as halite, which has a density
40 of about 2.17.
Therefore, in accordance with the second aspect of the
present invention, it has been discovered that the calcining
process reduces the apparent density of saline minerals. In
the case of trona, the apparent density reduces to less than
45 about 2.0. It is believed that such reduction in apparent
density is caused by the formation of voids within the trona
particles without a significant change in the particle size.
Thus, when a calcined trona particle is subjected to density
separation, such as on an air table, the particle will behave
50 approximately as if it were a particle of the same shape with
a uniform actual density lower than the actual density of
calcined trona. With such a reduction in the apparent density
of calcined trona, impurities such as halite can be separated
utilizing density separation methods based upon differences
55 in apparent density. Furthermore, the density separation of
other impurities, such as shortite, dolomite and pyrite is
significantly improved due to the larger difference between
the apparent densities of the trona and these impurities. The
density separation step may remove as much as 50%,
60 preferably 75%, and more preferably 90%, of these impurities.
The resulting purity of the trona is preferably at least
about 95%, and more preferably about 98%.
As noted above in more detail, the density separation step
is preferably a dry process; however, wet density separation
65 processes such as heavy media separation may be used as
well. Any known density separation technique could be used
for this step of the invention, including air tabling or dry
6,092,665
9
jigging. Further details of the density separation step are set
forth above in the description of the first aspect of the
invention.
In one embodiment of the second aspect of the invention,
as noted above, the step of heating the ore for calcining 5
includes indirect heating which comprises the steps of
heating a fluid and bringing the heated fluid into thermal
communication with the ore in the calcining vessel. This
step can be accomplished utilizing a heat source which
provides the heated fluid to coils positioned within the 10
interior of the calcining vessel. In one embodiment, the heat
source is a steam boiler and the fluid is steam. Alternatively,
the fluid may comprise oil or any other appropriate medium.
The step of heating the fluid can comprise the steps of
combusting an energy source to produce heat and combustion
gas, transferring at least a portion of the heat to the fluid, 15
and directing at least a portion of the combustion gas
through a combustion gas outlet which is not in direct fluid
communication with the calcining vessel.
The utilization of indirect heating for calcining the saline
mineral provides significant benefits in that it significantly 20
reduces the amount of gas flowing through the fluidized bed
because no combustion gas flows through the bed. In this
manner, a significantly lower amount of particulates from
the ore are entrained and need to be removed from exhaust
gas from the calcining operation. More specifically, the 25
amount of gas required for fluidization is about 80% less
than the amount of gas produced during the combustion
necessary to produce sufficient heat for the calcining process
(e.g., utilizing natural gas in a steam boiler). Accordingly, by
utilizing a source of gas for fluidization which is different 30
than the combustion gases, a smaller amount of fluidizing
gas can be used. Further, the smaller amount means that the
fluidizing gas will flow at lower velocities, thereby potentially
reducing particulate entrainment even further. In
addition, less fluidizing gas means that less gas needs to be
scrubbed for particulates before emission, thereby reducing 35
the costs of the calcining process.
It is well known that the calcining process produces
calcining gas having a significant amount of water vapor.
For example, calcining three moles of trona produces five
moles of water and one mole of carbon dioxide. In order to 40
reduce the amount of calcining gas exiting the system, the
process may further comprise the step of condensing at least
a portion of the water vapor from the calcining gas by, for
example, cooling the calcining gas. Such condensation step
will reduce the calcining gas volume by as much as %ths, 45
thereby reducing the amount of calcining gas which must be
treated. In addition to reducing the volume of gas exiting the
system, the condensing step also has a scrubbing effect on
the calcining gas by removing particulates from the calcining
gas. It is believed that the amount of particulates 50
removed is proportional to the amount of gas removed (i.e.,
as much as %ths or more). It is estimated that the particulate
emission from a process for calcining trona ore in a directfired
rotary calciner is typically about 6 lbs/ton of feed. By
practice of the present process, including indirect calcination
55 and condensing water from calcining gas, the particulate
emissions from calcination of trona ore can be less than
about 3 lbs/ton of feed, more preferably less than about 1.5
lbs/ton of feed and most preferably less than about 1 lbs/ton
of feed.
In a preferred embodiment, the condensing step for con- 60
densing water from gas produced during calcining comprises
two stages. In the first stage, a small amount (e.g., less
than about 5%) of the water vapor within the calcining gas
is condensed to significantly reduce the particulate content
of the gas. The first stage can be performed utilizing a 65
water-cooled condenser, such as a tubed condenser. In the
second stage, as much as 80% of the water vapor is
10
condensed. Because of the reduction in particulate content
resulting from the first stage, the water condensed from the
second stage is essentially distilled water grade. A third stage
may be added to further scrub particulates from the gas. For
example, a high-efficiency venturi scrubber or electrostatic
precipitator may be used.
The water which is removed during the condensing steps
can be utilized for other processes. For example, the condensed
water may be cooled (e.g., using air coolers) and then
recycled and used as the cooling medium to condense
further water vapor from the calcining gas by bringing the
cooled water into thermal communication with the precondensed
calcining gas. Further, the condensed water could
be utilized for wet separation processes in other areas of the
facility such as for treating fines, as described below. The
condensed water may also be treated and utilized for almost
any other appropriate purpose, such as for general water
usage in the facility (e.g., for cleaning, drinking water, etc.).
Calcining gas which is produced during the calcining
process may be removed from the calcining vessel through
a calcining gas outlet, and at least a portion of the calcining
gas (proportional to the amount of CO2 produced in the
calcining process) may be expelled through a stack. The
expelled gas is preferably heated prior to exiting through the
stack to inhibit condensation and plume formation at the
stack outlet. For example, the expelled gas can be mixed
with hot combustion gas from heating fluid for indirect
calcination.
Another portion of the calcining gas may be recycled back
to the inlet of the calcining vessel and utilized for heating
and fluidizing additional ore for calcining. Preferably, this
gas is recycled after the above-noted condensation step,
thereby resulting in dry CO2 as the heating and fluidizing
medium. The recycled gas may be heated (e.g., by steam
coils) in order to bring the gas up to a temperature prior to
entry into the calcining vessel. In one embodiment, the
recycled gas temperature is between about 1200 C. and about
2000 c., and is preferably about 1400 C. This recycling of
gas is beneficial in that it utilizes latent heat within the
calcining gas as part of the energy required for calcining,
rather than heating ambient temperature gas up to calcining
temperature. Further, such recycling reduces the gas requirements
and emissions of the process by eliminating the need
for fresh gas.
In another embodiment of the second aspect of the present
invention, the process further includes removing a second
portion of impurities by a magnetic separation method such
that materials of different magnetic susceptibilities separate
from each other into a recovered stream and an impurity
stream. With regard to the beneficiation of trona, typical
impurities that can be removed during the magnetic separation
step include shaley components, such as dolomitic
shale and oil shale, iron associated with the shaley
components, complex iron silicates, iron-bearing
carbonates, as well as other impurities having different
magnetic susceptibilities. Such shaley components typically
have a higher magnetic susceptibility than trona. Further
details of the magnetic separation step are set forth above in
the description of the first aspect of the invention.
It should be appreciated that the magnetic separation step
could be performed at any point in the separation process.
For example, magnetic separation may occur prior to calcining
and/or prior to the density separation step.
Furthermore, the ore may be subjected to density separation
prior to calcining to remove some impurities and then
subjected to another density separation step after calcining
to remove more impurities. Other separation techniques,
such as electrostatic separation, could also be incorporated
into the second aspect of the invention.
In another embodiment of the present invention, the saline
mineral-containing ore is crushed to achieve liberation of
11
6,092,665
12
impurities prior to the calcining step. Preferably, the ore is
crushed to at least about 6 mesh during the crushing step.
Further details of the crushing step are set forth above in the
description of the first aspect of the invention.
After crushing, fines are preferably removed from the ore. 5
In one embodiment, particles having a size less than about
200 mesh are removed and processed separately from the
remaining size fractions. Such fines are removed because
they are typically not processable utilizing dry separation
processes, such as air tabling. The about -200 mesh fraction 10
subsequently can be treated utilizing a wet separation
process, such as the slush process. The slush process generally
comprises mixing the calcined trona fines in a saturated
brine solution at between 40° C. and 80° C. to convert
the anhydrous sodium carbonate to monohydrate form. The
slurry is then heated to between 112° C. and 120° C. under 15
pressure to convert back to anhydrous form. The slurry is
then cooled, causing the sodium carbonate to crystallize
back to the monohydrate form. The crystallization process
squeezes out impurities and forms coarse sodium carbonate
particles. The particles are then screened and washed to 20
remove impurities. Subsequent calcining of the particles
converts the sodium carbonate back to anhydrous form.
In addition to processing the -200 mesh fraction as
discussed above, saline mineral particles falling between
about 65 mesh and about 200 mesh are typically not able to 25
be readily separated from impurities in that size fraction
utilizing conventional dry density separation processes, such
as air tabling. This aspect includes separately processing the
65x200 fraction to remove iron and shale. Surprisingly, it
has been found that iron impurities are concentrated in about 30
the -65 fraction of saline mineral-containing ore and in
particular, trona-containing ore. Thus, by removing the -65
fraction and processing it separately, a significant portion of
the iron is removed from the ore. The 65x200 fraction can
be wet processed, as described above, or can be magneti- 35
cally separated to remove shaley components and iron
associated therewith. After separating the impurities, the
65x200 fraction can be recombined with the beneficiated
larger size fractions, or it can be used for a different purpose
more suited to its particle size and purity.
The +65 mesh particles are sized into size fractions before 40
the density separation step. Each size fraction is subsequently
processed separately. In general, the narrower the
range of particle size within a fraction, the higher the
efficiency of removal of impurities during the density separation
step. On the other hand, narrow size fractions requires 45
a large number of fractions which may increase the cost of
the overall process. Further details of the sizing step are set
forth above in the description of the first aspect of the
invention.
The number of size fractions required for a particular 50
separating step depends in part on the difference in properties
between the minerals sought to be separated. For
example, in the density separation step, the larger the
difference between the densities of the saline mineral and the
impurity, the smaller the number of size fractions required 55
(i.e., the larger the allowed size variation within a particular
fraction). In the case of beneficiating trona, the calcining
step increases the difference between the apparent density of
the trona and at least some of the impurities. Accordingly, it
is believed that the process according to the second aspect of
the invention will allow the use of between 3 and 10 size 60
fractions. In one embodiment, the process utilizes as few as
5 size fractions, each having a wider range of particle size
within the fraction. Such reduction in the number of fractions
decreases the cost of the overall process. In addition,
or alternatively, it is believed that the process according to 65
the second aspect of the present invention may be utilized to
produce a higher grade product and/or higher recoveries.
It has been found that the above-identified processes for
beneficiating trona are also particularly adaptable for use in
the production of caustic for use in alumina production. By
transporting beneficiated and calcined trona ore to alumina
processing facilities and producing caustic from the beneficiated
trona, the total cost for caustic can be significantly
below that of caustic currently used in the alumina industry.
For this application, the trona-containing ore is beneficiated
and the resulting beneficiated trona is calcined to produce
soda ash (Na2C03 ). The soda ash is then converted to caustic
soda by conventional processes at an alumina plant and can
then be used in conventional alumina processing. For
example, the Bayer process can be used in which caustic
soda is mixed with bauxite to solubilize the aluminum
hydroxide in the bauxite to produce a sodium illuminate
solution. Alumina hydrate can be precipitated from the
solution and calcined to remove water therefrom.
The foregoing description of the present invention has
been presented for purposes of illustration and description.
Furthermore, the description is not intended to limit the
invention to the form disclosed herein. Consequently, variations
and modifications commensurate with the above
teachings, and the skill or knowledge of the relevant art, are
within the scope of the present invention. The embodiment
described hereinabove is further intended to explain the best
mode known for practicing the invention and to enable
others skilled in the art to utilize the invention in such, or
other, embodiments and with various modifications required
by the particular applications or uses of the present invention.
It is intended that the appended claims be construed to
include alternative embodiments to the extent permitted by
the prior art.
EXAMPLES 1-8
Eight samples of trona-containing ore from Bed 17 of the
Green River Formation in Wyoming were beneficiated in
accordance with the first aspect of the present invention.
Each of the samples was crushed to -10 mesh on a roll
crusher. The samples were allowed to air dry until they
attained a constant weight (about 24 hours). The samples
were subsequently screened at 20 mesh, 35 mesh, 65 mesh
and 150 mesh Tyler. Each of the four 150 plus size fractions
was then subjected to electrostatic separation to generate a
conductive and non-conductive stream. The non-conductive
stream resulting from the electrostatic separation regime for
each of the size fractions was subjected to high intensity
magnetic separation to generate a magnetic and nonmagnetic
stream. The resulting non-conductive/nonmagnetic
streams from each of the size fractions were then
subjected to a density separation step. A heavy liquid separation
was used for density separation in these examples.
The heavy liquid used was a mixture of acetylene tetrabromide
and kerosene. Since the saline mineral being beneficiated
was trona, having a specific gravity of 2.14; the major
impurity was shortite, having a specific gravity of 2.6; and
other impurities having a specific gravity lighter than 2.0
were present, density separations were made at specific
gravities of 2.0 and 2.3 to generate a 2.0x2.3 fraction which
is the trona fraction.
The data generated from the foregoing beneficiation processes
is shown in Tables 1-8. As can be seen from the
Tables, the purity of trona recovered ranged from 95.3 in
Example 2 to 98.8 in Example 3 (shown as soluble % in
2.0x2.3 S.G. separation). In addition, the effectiveness of the
density separation in improving trona purity can be seen by
comparing the Soluble % in the "Plus 65 mesh trona" line
(before density separation) with the Soluble % in the "2.0x
2.3 S.G." line (after density separation).
6,092,665
13 14
TABLE 1 TABLE 2
Weight Percent Weight Percent
5
Bene- Assay Bene- Assay
Frac- Sam- ficiated Insoluble Soluble Frac- Sam- ficiated Insoluble Soluble
Fraction tion pIe Product % Distr. % Distr. 10 Fraction tion pIe Product % Distr. % Distr.
Electrostatic and Magnetic Separation of
Electrostatic and Magnetic Separation of
Trona-containing Waste Rock; Sample 1
Trona-containing Waste Rock; Sample 2
10 x 20 mesh
15 10 x 20 mesh
conductive stream 86.4 41.7 93.8 44.6 6.2 21.2
magnetic stream 2.0 1.0 67.3 0.7 32.7 2.6 conductive stream 57.6 27.6 87.7 40.9 12.3 8.3
non-conductive/ 11.6 5.6 24.6 69.5 4.4 30.5 14.0 magnetic stream 3.7 1.8 68.1 2.0 31.9 1.4
non-magnetic non-conductive/ 38.7 18.6 49.4 19.1 6.0 80.9 36.9
stream 20 non-magnetic
stream
Total 100.0 48.3 90.5 49.8 9.5 37.7
20 x 35 mesh Total 100.0 47.9 60.4 48.9 39.6 46.6
20 x 35 mesh
conductive stream 56.9 12.1 91.9 12.6 8.1 8.0 25
magnetic stream 9.5 2.0 83.6 1.9 16.4 2.7 conductive stream 30.0 3.7 81.3 5.0 18.7 1.7
non-conductive/ 33.6 7.1 31.3 83.2 6.8 16.8 9.8 magnetic stream 15.9 2.0 62.9 2.1 37.1 1.8
non-magnetic non-conductive/ 54.1 6.6 17.7 46.7 5.2 53.3 8.7
stream non-magnetic
30 stream
Total 100.0 21.2 88.2 21.3 11.8 20.5
35 x 65 mesh Total 100.0 12.3 59.6 12.4 40.4 12.2
35 x 65 mesh
conductive stream 28.6 3.9 91.5 4.1 8.5 2.7
magnetic stream 19.1 2.6 87.0 2.6 13.0 2.8 35 conductive stream 45.8 9.1 82.8 12.8 17.2 3.9
non-conductive/ 52.2 7.1 31.3 85.3 6.9 14.7 8.6 magnetic stream 13.5 2.7 69.3 3.2 30.7 2.0
non-magnetic non-conductive/ 40.7 8.1 21.6 47.7 6.5 52.3 10.4
stream non-magnetic
stream
Total 100.0 13.6 87.4 13.6 12.6 14.1 40
65 x 150 mesh Total 100.0 20.0 66.7 22.5 33.3 16.3
65 x 150 mesh
conductive stream 50.8 3.7 87.8 3.7 12.2 3.7
magnetic stream 8.9 0.7 82.7 0.6 17.3 0.9 conductive stream 22.0 1.6 82.9 2.2 17.1 0.7
non-conductive/ 40.3 2.9 12.9 77.4 2.6 22.6 5.4 45 magnetic stream 20.1 1.5 74.3 1.8 25.7 0.9
non-magnetic non-conductive/ 57.9 4.2 11.2 42.0 3.0 58.0 6.0
stream non-magnetic
stream
Total 100.0 7.3 83.2 6.9 16.8 10.0
Minus 150 mesh 9.6 77.4 8.4 22.6 17.7 50 Total 100.0 7.3 57.5 7.1 42.5 7.6
Plus 65 mesh trona 19.9 80.1 18.1 19.9 32.4 Minus 150 mesh 12.5 43.6 9.2 56.4 17.3
Trona Prod., 22.8 100.0 79.7 20.7 20.3 37.8 Plus 65 mesh 33.4 31.6 17.8 68.4 56.0
Calc. trona
Trona + 32.4 79.0 29.2 21.0 55.5 Trona Prod., Calc. 37.6 100.0 32.7 20.8 67.3 62.0
minus 55 Trona + minus 50.1 35.5 30.0 64.5 79.3
150 Calc. 150 Calc.
Sample Calc. 100.0 87.8 100.0 12.2 100.0 Sample Calc. 100.0 59.2 100.0 40.8 100.0
Heavy Liquid Density Separation of Plus 65 Mesh Heavy Liquid Density Separation of Plus 65 Mesh
Non-Magnetic/Non-Conductive Sample 1 Non-Magnetic/Non-Conductive Sample 2
60
<2.0 S.G. 0.2 0.0 <2.0 S.G. 6.0 2.0
2.0 x 2.3 S.G. 19.0 3.8 3.4 0.1 96.6 29.8 2.0 x 2.3 S.G. 63.0 21.0 4.7 1.7 95.3 49.1
>2.3 S.G. 80.8 16.1 98.3 18.0 1.7 2.5 >2.3 S.G. 31.0 10.3 92.3 16.1 7.7 6.9
Total 100.0 19.9 80.1 18.1 19.9 32.4 65 Total 100.0 33.4 31.6 17.8 68.4 56.0
6,092,665
15 16
TABLE 3 TABLE 4
Weight Percent Weight Percent
5
Bene- Assay Bene- Assay
Frac- Sam- ficiated Insoluble Soluble Frac- Sam- ficiated Insoluble Soluble
Fraction tion pIe Product % Distr. % Distr. 10 Fraction tion pIe Product % Distr. % Distr.
Electrostatic and Magnetic Separation of Electrostatic and Magnetic Separation of
Trona-Containing Waste Rock; Sample 3 Trona-containing Waste Rock; Sample 4
10 x 20 mesh 15 10 x 20 mesh
conductive stream 26.1 13.2 30.1 50.8 69.9 10.0 conductive stream 11.7 6.4 11.3 22.3 88.7 5.9
magnetic stream 4.4 2.2 4.6 1.3 95.4 2.3 magnetic stream 6.3 3.5 3.0 3.2 97.0 3.5
non-conductive/ 69.5 35.2 58.8 2.4 10.8 97.6 37.3 non-conductive/ 82.0 45.0 68.3 1.9 26.3 98.1 45.6
non-magnetic 20 non-magnetic
stream stream
Total 100.0 50.6 9.7 63.0 90.3 49.6 Total 100.0 54.8 3.1 51.8 96.9 54.9
20 x 35 mesh 20 x 35 mesh
25
conductive stream 24.9 4.0 25.0 12.7 75.0 3.2 conductive stream 15.4 2.2 14.3 9.5 85.7 1.9
magnetic stream 5.8 0.9 5.6 0.7 94.4 1.0 magnetic stream 10.8 1.5 5.4 2.5 94.6 1.5
non-conductive/ 69.3 11.1 18.5 3.0 4.3 97.0 11.7 non-conductive/ 73.8 10.3 15.7 2.6 8.3 97.4 10.4
non-magnetic non-magnetic
stream 30 stream
Total 100.0 16.0 8.6 17.7 91.4 15.9 Total 100.0 14.0 4.7 20.3 95.3 13.8
35 x 65 mesh 35 x 65 mesh
conductive stream 12.3 1.3 21.3 3.7 78.7 1.1 35 conductive stream 18.7 1.4 11.1 4.9 88.9 1.3
magnetic stream 4.0 0.4 6.6 0.4 93.4 0.4 magnetic stream 2.1 0.2 10.5 0.5 89.5 0.1
non-conductive/ 83.7 9.1 15.2 4.1 4.8 95.9 9.5 non-conductive/ 79.2 6.0 9.2 3.8 7.1 96.2 6.0
non-magnetic non-magnetic
stream stream
40
Total 100.0 10.9 6.3 8.8 93.7 11.1 Total 100.0 7.6 5.3 12.5 94.7 7.5
65 x 150 mesh 65 x 150 mesh
conductive stream 27.5 1.8 8.2 1.9 91.8 1.8 conductive stream 17.9 1.1 7.0 2.3 93.0 1.0
magnetic stream 3.9 0.3 4.4 0.1 95.6 0.3 45 magnetic stream 4.4 0.3 2.5 0.2 97.5 0.3
non-conductive/ 68.7 4.4 7.4 3.6 2.0 96.4 4.6 non-conductive/ 77.7 4.6 6.9 3.0 4.2 97.0 4.6
non-magnetic non-magnetic
stream stream
Total 100.0 6.5 4.9 4.0 95.1 6.7 50 Total 100.0 5.9 3.7 6.7 96.3 5.8
Minus 150 mesh 16.0 3.2 6.6 96.8 16.8 Minus 150 mesh 17.7 1.6 8.7 98.4 18.0
Plus 65 mesh trona 55.4 2.8 19.8 97.2 58.4 Plus 65 mesh trona 61.3 2.2 41.7 97.7 66.6
Trona Prod., Calc. 59.8 100.0 2.9 21.9 97.1 63.1 Trona Prod., Calc. 65.9 100.0 2.3 45.9 97.8 78.7
Trona + minus 75.9 2.9 28.4 97.1 79.9 Trona + minus 83.6 2.1 54.6 97.9 84.6
55
150 Calc. 150 Calc.
Sample Calc. 100.0 7.8 100 92.2 100 Sample Calc. 100.0 3.2 100.0 96.8 100.0
Heavy Liquid Density Separation of Plus 65 Mesh Heavy Liquid Density Separation of Plus 65 Mesh
Non-Magnetic/Non-Conductive Sample 3 Non-Magnetic/Non-Conductive Sample 4
60
<2.0 S.G. 0.2 0.1 <2.0 S.G. 0.4 0.0
2.0 x 2.3 S.G. 96.1 53.2 1.2 8.2 98.8 57.1 2.0 x 2.3 S.G. 98.6 60.5 2.0 37.3 98.0 61.2
>2.3 S.G. 3.7 2.1 44.5 11.7 55.5 1.4 >2.3 S.G. 1.0 0.6 23.3 4.4 76.7 5.3
Total 100.0 55.4 2.8 19.8 97.2 58.4 65 Total 100.0 61.3 2.2 41.7 97.7 66.6
6,092,665
17 18
TABLE 5 TABLE 6
Weight Percent Weight Percent
5
Bene- Assay Bene- Assay
Frac- Sam- ficiated Insoluble Soluble Frac- Sam- ficiated Insoluble Soluble
Fraction tion pIe Product % Distr. % Distr. 10 Fraction tion pIe Product % Distr. % Distr.
Electrostatic and Magnetic Separation of Electrostatic and Magnetic Separation of
Trona-Containing Waste Rock; Sample 5 Trona-Containing Waste Rock; Sample 6
10 x 20 mesh 15 10 x 20 mesh
conductive stream 23.0 10.9 37.8 48.0 62.2 7.4 conductive stream 28.3 14.1 18.0 47.7 82.0 12.2
magnetic stream 5.2 2.5 3.8 1.1 96.2 2.6 magnetic stream 4.4 2.2 2.8 1.1 97.2 2.2
non-conductive/ 71.9 34.2 56.2 3.0 11.9 97.0 36.3 non-conductive/ 67.3 33.4 57.3 2.1 13.2 97.9 34.5
non-magnetic 20 non-magnetic
stream stream
Total 100.0 47.6 11.0 61.0 89.0 46.4 Total 100.0 49.7 6.6 62.0 93.4 49.0
20 x 35 mesh 20 x 35 mesh
25
conductive stream 21.3 3.7 25.7 11.0 74.3 3.0 conductive stream 17.5 2.7 21.4 10.8 78.6 2.2
magnetic stream 10.2 1.8 5.2 1.1 94.8 1.8 magnetic stream 6.7 1.0 3.8 0.7 96.2 1.0
non-conductive/ 68.5 11.9 19.5 3.5 4.8 96.5 12.5 non-conductive/ 75.8 11.6 19.9 3.0 6.5 97.0 11.9
non-magnetic non-magnetic
stream 30 stream
Total 100.0 17.3 8.4 16.9 91.6 17.4 Total 100.0 15.3 6.3 18.1 93.7 15.1
35 x 65 mesh 35 x 65 mesh
conductive stream 19.8 2.2 17.0 4.4 83.0 2.0 35 conductive stream 13.0 1.1 16.2 3.5 83.8 1.0
magnetic stream 5.9 0.7 7.4 0.6 92.6 0.7 magnetic stream 6.0 0.5 6.7 0.7 93.3 0.5
non-conductive/ 74.3 8.4 13.8 4.6 4.5 95.4 8.7 non-conductive/ 81.0 7.1 12.3 2.8 3.8 97.2 7.3
non-magnetic non-magnetic
stream stream
40
Total 100.0 11.3 7.2 9.5 92.8 11.4 Total 100.0 8.8 4.8 7.9 95.2 8.9
65 x 150 mesh 65 x 150 mesh
conductive stream 19.7 1.6 11.0 2.1 89.0 1.6 conductive stream 16.5 1.3 6.6 1.6 93.4 1.3
magnetic stream 3.4 0.3 3.8 0.1 96.2 0.3 45 magnetic stream 4.2 0.3 3.6 0.2 96.4 0.3
non-conductive/ 76.8 6.4 10.5 4.4 3.3 95.6 6.7 non-conductive/ 79.3 6.1 10.5 2.2 2.5 97.8 6.3
non-magnetic non-magnetic
stream stream
Total 100.0 8.3 5.7 5.5 94.3 8.6 50 Total 100.0 7.7 3.0 4.3 97.0 7.9
Minus 150 mesh 15.5 4.0 7.2 96.0 16.3 Minus 150 mesh 18.5 2.2 7.7 97.8 19.1
Plus 65 mesh trona 54.5 3.4 21.2 96.5 64.3 Plus 65 mesh trona 52.1 2.4 23.5 97.6 60.1
Trona Prod., Calc. 60.8 100.0 3.5 24.5 96.6 72.0 Trona Prod., Calc. 58.3 100.0 2.4 26.0 97.6 71.3
Trona + minus 76.3 3.6 31.7 96.4 80.5 Trona + minus 76.8 2.3 33.7 97.7 79.2
55
150 Calc. 150 Calc.
Sample Calc. 100 8.6 100 91.4 100 Sample Calc. 100.0 5.3 100.0 94.7 100.0
Heavy Liquid Density Separation of Plus 65 Mesh Heavy Liquid Density Separation of Plus 65 Mesh
Non-Magnetic/Non-Conductive Sample 5 Non-Magnetic/Non-Conductive Sample 6
60
<2.0 S.G. 0.3 0.2 <2.0 S.G. 0.4 0.2
2.0 x 2.3 S.G. 92.6 50.4 2.5 14.6 97.5 53.8 2.0 x 2.3 S.G. 98.8 51.5 2.0 19.4 98.0 53.3
>2.3 S.G. 7.1 3.9 20.2 9.1 79.8 10.5 >2.3 S.G. 0.8 0.4 52.5 4.1 47.5 6.8
Total 100.0 54.5 3.4 21.2 96.5 64.3 65 Total 100.0 52.1 2.4 23.5 97.6 60.1
6,092,665
19 20
TABLE 7 TABLE 8
Weight Percent
Weight Percent
5 Bene- Assay
Bene- Assay
Frac- Sam- ficiated Insoluble Soluble
Frac- Sam- ficiated Insoluble Soluble
Fraction tion pIe Product % Distr. % Distr.
Fraction tion pIe Product % Distr. % Distr. 10 Electrostatic and Magnetic Separation of
Trona-Containing Waste Rock; Sample 8
Electrostatic and Magnetic Separation of
10 x 20 mesh
Trona-Containing Waste Rock; Sample 7
conductive stream 18.8 6.2 35.0 23.6 65.0 4.5
10 x 20 mesh 15 magnetic stream 1.3 0.4 28.7 1.4 71.3 0.4
non-conductive/ 79.9 26.5 40.9 4.4 12.6 95.6 27.9
conductive stream 0.0 0.0 0.0 0.0
non-magnetic
stream
magnetic stream 15.8 5.0 34.1 16.5 65.9 3.6
non-conductive/ 84.2 26.3 34.6 9.7 24.9 90.3 26.5 Total 100.0 33.2 10.5 37.6 89.5 32.7
non-magnetic 20
20 x 35 mesh
stream conductive stream 13.6 3.0 45.7 15.0 54.3 1.8
magnetic stream 2.1 0.5 40.9 2.1 59.1 0.3
Total 100.0 31.3 13.6 41.3 86.4 30.2 non-conductive/ 84.3 18.9 29.2 6.3 12.9 93.7 19.5
20 x 35 mesh
non-magnetic
stream
25
conductive stream 0.0 0.0 0.0 0.0 Total 100.0 22.4 12.4 30.0 87.6 21.6
magnetic stream 8.0 1.7 29.3 4.8 70.7 1.3 35 x 65 mesh
non-conductive/ 92.0 19.3 25.3 7.7 14.5 92.3 19.9
conductive stream 10.0 1.1 50.2 5.9 49.8 0.6
non-magnetic magnetic stream 3.2 0.3 48.9 1.8 51.1 0.2
stream 30 non-conductive/ 86.7 9.3 14.4 6.9 7.0 93.1 9.6
non-magnetic
Total 100.0 21.0 9.4 19.2 90.6 21.2
stream
35 x 65 mesh Total 100.0 10.8 12.6 14.7 87.4 10.4
65 x 150 mesh
conductive stream 0.0 0.0 0.0 0.0 35
magnetic stream 11.4 2.2 23.7 5.1 76.3 1.9
conductive stream 12.7 1.5 22.1 3.6 77.9 1.3
magnetic stream 2.5 0.3 32.0 1.0 68.0 0.2
non-conductive/ 88.6 17.0 22.3 6.4 10.6 93.6 17.8 non-conductive/ 84.8 10.0 15.4 3.6 3.9 96.4 10.6
non-magnetic non-magnetic
stream stream
40
Total 100.0 11.8 6.7 8.5 93.3 12.1
Total 100.0 19.2 8.4 15.7 91.6 19.6 Minus 150 mesh 21.9 3.9 9.2 96.1 23.2
65 x 150 mesh Plus 65 mesh trona 54.7 5.5 32.5 94.5 57.0
Trona Prod., Calc. 64.7 100.0 5.2 36.4 94.8 67.6
conductive stream 0.0 0.0 0.0 0.0
Trona + minus 86.6 4.9 45.6 95.1 90.8
150 Calc.
magnetic stream 6.5 0.9 21.1 1.9 78.9 0.8 45 Sample Calc. 100.0 9.2 100.0 90.8 100.0
non-conductive/ 93.5 13.6 17.8 7.6 10.0 92.4 14.0 Heavy Liquid Density Separation of Plus 65 Mesh
non-magnetic Non-Magnetic/Non-Conductive Sample 8
stream <2.0 S.G. 0.3 0.2
2.0 x 2.3 S.G. 97.0 53.1 2.0 11.5 98.0 57.3
Total 100.0 14.5 8.5 12.0 91.5 14.8 50 >2.3 S.G. 2.7 1.5
Minus 150 mesh 14.0 8.7 11.8 91.3 14.2 Total 100.0 54.7 5.5 32.5 94.5 57.0
Plus 65 mesh trona 62.7 8.2 49.9 91.9 78.1
Trona Prod., Calc. 76.3 100.0 8.1 60.0 91.8 77.5
Trona + minus 90.2 8.2 71.8 91.8 92.4
55 EXAMPLE 9
150 Calc.
Sample Calc. 100.0 10.3 100.0 89.7 100.0 An ore sample containing trona, recovered from Bed 17
Heavy Liquid Density Separation of Plus 65 Mesh of the Green River Formation in Wyoming, was beneficiated
Non-Magnetic/Non Conductive Sample 7 using the process described below and the results are rep-
60 resented by the data in Table 9. The ore was a commercially
<2.0 S.G. 0.2 0.1 available trona-containing material identified as T-50, avail-
2.0 x 2.3 S.G. 93.0 58.3 4.2 23.8 95.8 62.2 able from Solvay Minerals S.A., Green River, Wyo. The
>2.3 S.G. 6.8 4.3 63.0 26.1 37.0 15.9 T-50 material has a trona purity of about 95% and a size
range of 20x150 mesh Tyler.
Total 100.0 62.7 8.2 49.9 91.9 78.1 65 The ore sample was first classified using a screening
process to divide the ore sample into three size fractions:
+35 mesh, 35x65 mesh, and -65 mesh. After screening, the
21
6,092,665
22
The cumulative products of the entire recovery process
are represented by the data in the third column at the end of
Table 9. The data represents the weight percentage of
non-magnetic, non-conductor material recovered from the
combined light and heavy density fractions and from the
ultra-heavy density fraction. As can be seen from the Table,
91.3% of the original sample was recovered as nonmagnetic,
non-conductive material. The trona purity of the
recovered material was determined. The trona product from
the lights plus heavies had a purity of 98.2%. The trona
product from the ultra-heavies, which contained the shortite,
had a purity of 88.9%. Comparison of these purities illustrates
the benefit of removing shortite.
individually magnetically separated utilizing an induced roll
magnetic separator. The conductors from each of the electrostatic
separation processes were not subjected to magnetic
separation. The magnetic separation process separated each
5 incoming sample into two fractions: magnetic and nonmagnetic.
The weights and weight percentages of each
magnetically separated fraction are listed in the three columns
of data in Table 9, as described above.
+35 mesh and 35x65 mesh fractions were each separated on
an air table into three density fractions: ultra-heavy, heavy
and light.
After air tabling, each of the density fractions which were
air tabled, and the -65 mesh size fraction that was not air
tabled, were electrostatically separated by a high tension
separator. To improve trona recovery, as seen in Table 9, the
light and heavy density fractions from the +35 mesh size
fraction were combined and electrostatically separated
together. Similarly, the light and heavy density fractions 10
from the 35x65 mesh size fraction were electrostatically
separated together. Electrostatic separation was further performed
on the ultra-heavy fraction from the +35 mesh size
fraction, the ultra-heavy fraction from the 35x65 mesh size
fraction, and the -65 mesh size fraction that was not air 15
tabled. Each of the above-identified electrostatic separation
processes divided the sample into three electrostatic fractions:
conductors, middlings, and non-conductors. The
respective weights and weight percentages of each electrostatic
fraction are listed in the three columns of data in Table 20
9, as noted above.
The non-conductors and middlings from each of the
above-referenced electrostatic separation processes were
TABLE 9
Density, Electrostatic and Magnetic Separation of Trona Ore, Sample 9
Weight (g, unless _----'-W""e"f.ig"'h"-.t",Pe""r",ce",n,,-t_ Purity
Separation otherwise noted) Fraction* Sample** (% trona)
SCREENING
plus 35 mesh
35 x 65 mesh
minus 65 mesh
362lb
482lb
140lb
36.8
49.0
14.2
36.8
49.0
14.2
Total 984lb
AIR TABLE SEPARATIONS
100.0 100.0
plus 35 mesh
Ull. Heavy
Heavy
Lights
Total
35 x 65 mesh
Ull. Heavy
Heavy
Lights
1605 4.2 1.5
1814 4.7 1.7
34960 91.1 33.5
38379 100.00 36.8
800 2.4 1.2
1603.5 4.7 2.3
31560 92.9 45.5
Total
minus 65 mesh
33963.5 100.0 49.0
not air tabled
HIGH TENSION ELECTROSTATIC SEPARATIONS (HI)
plus 35 mesh air table lights + heavies
Condo 190.8 7.4 2.6
Midd 230.5 8.9 3.1
Non-Cond. 2159.5 83.7 29.5
Total 2580.8 100.0 35.3
35 x 65 mesh air table lights + heavies
Condo 90.4 4.5 2.2
Midd 199.3 10.0 4.8
Non-Cond. 1709.5 85.5 40.9
Total 1999.2 100.0 47.8
plus 35 mesh air table ultra heavies
Condo 467.3 29.2 0.4
6,092,665
23
TABLE 9-continued
Density, Electrostatic and Magnetic Separation of Trona Ore, Sample 9
Weight (g, unless Weight Percent Purity
Separation otherwise noted) Fraction * Sample** (% trona)
Midd 188.7 11.8 0.2
Non-Cond. 943 59.0 0.9
Total 1599 100.0 1.5
35 x 65 mesh air table ultra heavies
Condo 97 12.1 0.1
Midd 106.8 13.4 0.2
Non-Cond. 595 74.5 0.9
Total 798.8 100.0 1.2
minus 65 mesh
Condo 23.4 1.4 0.2
Midd 96.9 6.0 0.9
Non-Cond. 1500.6 92.6 13.2
Total 1620.9 100.0 14.2
plus 35 mesh Non Condo from lights + heavies
HI Mag. 22.6 1.0 0.31
HI Non Mag. 2136.0 99.0 29.19
Total 2158.6 100.0 29.50
35 x 65 mesh Non Condo from lights + heavies
HI Mag. 61.1 4.1 1.67
HI Non Mag. 1438.1 95.9 39.23
Total 1499.2 100.0 40.90
plus 35 mesh Non Condo from ultra heavies
HI Mag. 11.2 1.2 0.01
HI Non Mag. 931.7 98.8 0.90
Total 942.9 100.0 0.91
35 x 65 mesh Non Condo from ultra heavies
HI Mag. 53.1 8.9 0.08
HI Non Mag. 541.7 91.1 0.78
Total 594.8 100.0 0.86
minus 65 mesh Non Condo
HI Mag. 59.9 3.5 0.46
HI Non Mag. 1649.0 96.5 12.71
Total 1708.9 100.0 13.17
plus 35 mesh HT Mid from lights + heavies
HI Mag. 15.6 7.8 0.25
HI Non Mag. 183.8 92.2 2.90
Total 199.4 100.0 3.15
35 x 65 mesh HT Mid from lights + heavies
HI Mag. 13.8 6.0 0.29
HI Non Mag. 216.9 94.0 4.48
Total 230.7 100.0 4.77
minus 65 mesh HT Mid
HI Mag. 11.8 12.2 0.02
HI Non Mag. 85.1 87.8 0.16
Total 96.9 100.0 0.18
plus 35 mesh HT Mid from ultra heavies
HI Mag. 7.6 4.0 0.01
HI Non Mag. 181.2 96.0 0.15
Total 188.8 100.0 0.15
24
6,092,665
25
TABLE 9-continued
Density, Electrostatic and Magnetic Separation of Trona Ore, Sample 9
Weight (g, unless __W-,-,-"e.·l g.",ht,-,P,-,e",rc",e",n,,-t_ Purity
26
Separation
35 x 65 mesh ill Mid from ultra heavies
otherwise noted) Fraction* Sample** (% trona)
HI Mag.
HI Non Mag.
Total
Recovered from lights + heavies
6.9
100.0
106.9
CUMULATIVE PRODUCTS
6.5
93.5
100.0
0.05
0.80
0.85
Primary non mag, non conductor
Scavo non mag, non conductor
Subtotal
Recovered from ultra heavies
Primary non mag, non conductor
Scavo non mag, non conductor
Subtotal
Total non mag, non conductor (inc!. - 65 mesh)
Total conductor
Total HI magnetics
Head Calc. from all test products
*Based on feed to separation as 100%
**Based on original sample as 100%
EXAMPLE 10
This example illustrates beneficiation of trona using air
tabling, electrostatic separation and magnetic separation,
and demonstrates a relationship between breadth of size
fractions and effectiveness of air tabling as the density
separation method by comparison with heavy liquid separation.
A sample of bulk trona from Bed 17 of the Green River
Formation in Wyoming was crushed to -6 mesh. The sample
was subsequently sized into size fractions of 6x10 mesh,
lOx20 mesh, 20x35 mesh, 35x65 mesh (Tyler mesh). Each
of the plus 65 mesh size fractions was then subjected to
initial density separation on an air table (Rougher Pass). The
Rougher Pass light fractions were subsequently sent through
a cleaner pass and for the 6x10 mesh fraction, the heavy
fraction was sent to a scavenger pass. The resulting separations
are shown in Table 10.1.
Each of the size fractions was then subsequently beneficiated
using either magnetic separation (in the case of 6xlO
mesh fraction) or electrostatic separation and magnetic
separation. The portions of material from each separation
reporting to various product streams are shown in Table
10.1.
The non-magnetic, in the case of the 6x10 mesh fraction,
and the non-magnetic/non-conductive fractions were then
further analyzed by conducting a second density separation
based on heavy liquid separation to identify what portion of
impurities which are separable by density separation had not
been removed in the earlier air tabling step. The results of
this analysis are shown in Table 10.2. The column entitled
">2.3 S.G., %" identifies the total amount of material
separated from the beneficiated ore by the additional heavy
81.13 98.2
7.54 94.4
88.67 98.0
1.68 85.0
0.94 95.7
2.62 88.9
91.30 97.7
5.56 55.2
3.14 80.3
100.00 94.8
30 liquid density separation step. Additionally, that column
shows subcolumns titled "Plus" and "Minus." These two
subcolumns represent a breakdown of the "Total" percentage
of material which is greater than 2.3 S.G. which falls
into either the coarser or finer portion of the particular
35 stream. For example, the 6xlO mesh fraction was broken
down into a 6x8 mesh fraction and an 8xlO mesh fraction.
Thus, by comparing the "Plus" and "Minus" subcolumns of
the ">2.3 S.G., %," it can be seen that inefficiency in the air
tabling density separation tended to be at smaller particle
40 sizes within each size fraction because most of the higher
specific gravity material left by air tabling was in the smaller
particle sizes (the "Minus" subcolumn).
The columns titled "Insoluble Assay" and "Soluble
Assay" provide data on the portion of each stream which is
45 insoluble (i.e., impurity) before heavy liquid separation
("Total" subcolumn) and after heavy liquid separation
(,,<2.3 S.G." subcolumn). Thus, for example, the purity of
products resulting from beneficiating ore using air tabling
can be seen in the "Total" subcolumn of the "Soluble Assay"
50 column for each of the different streams. This purity can be
compared with the subsequent column, having a higher
purity, which identifies the purity of the beneficiated material
with the subsequent heavy liquid separation to indicate
a theoretical purity based on perfect density separation. In
55 addition, the improvement in trona purity between the
non-magnetic/non-conductive product which was not air
tabled and the non-magnetic/non-conductive product which
was air tabled can be seen by comparing the "Total NonMagnetic/
Non-Conductive from Untabled Feed" line with
60 the "Total Non-MagneticlNon-Conductive from Cleaner
Lights" line in the "Cumulative Products" section of Table
10.2.
6,092,665
27 28
TABLE 10.1 TABLE 1O.1-continued
Data from Air Table Tests on Bulk Trona Sample Crushed to Minus 6
Mesh Data from Air Table Tests on Bulk Trona Sample Crushed to Minus 6
5
Weight. % of
Mesh
Product Feed Size Fraction Sample
Weight, % of
6 x 10 MESH
10
Rougher Pass Product Feed Size Fraction Sample
Heavies 17.7 17.7 7.9
Cleaner Pass
Lights 82.3 82.3 36.7
Feed Calc. 100.0 100.0 44.6
Scavenger Pass 15 Heavies 6.8 6.3 0.8
Heavies 2.8 3.1 0.2 Lights 93.2 85.9 10.6
Lights 97.2 17.2 7.7
Feed Calc. 100.0 92.2 11.3
Feed Calc. 100.0 20.3 7.9
Cleaner Pass 35 x 65 MESH
20
Heavies 1.5 1.2 0.6
Lights 98.5 81.1 36.2 Rougher Pass
Feed Calc. 100.0 82.3 36.7
10 x 20 MESH
Heavies 3.8 3.8 0.2
Rougher Pass 25 Lights 96.2 96.2 5.4
Feed Calc. 100.0 100.0 5.6
Heavies 7.6 7.6 0.9
Lights 92.4 92.4 11.4 Cleaner Pass
Feed Calc. 100.0 100.0 12.3
Cleaner Pass
30
Heavies 0.7 0.7 0.0
Heavies 2.5 2.3 0.3 Lights 99.3 95.5 5.3
Lights 97.5 90.1 11.1
Feed Calc. 100.0 96.2 5.4
Feed Calc. 100.0 92.4 11.4
20 x 35 MESH MINUS 65 MESH (not air tabled) 25.2
TOTAL FEED CALC. 100.0
Rougher Pass 35
Heavies 7.8 7.8 1.0
Lights 92.2 92.2 11.3
Feed Calc. 100.0 100.0 12.3
TABLE 10.2
Data from Electrostatic and Induced Roll Separations on Air Table Products
Feed Crushed to minus 6 mesh
Insoluble Soluble
Weight Percent >2.3 S.G.. % >2.3 S.G.. Dist.. % Assay, % of Assay, % of
Product Feed Sample Plus Minus Total Plus Minus Size Total <2.3 SG Total <2.3 SG
6 x 10 MESH
Not Tabled
Mag 9.0 4.0
Non Mag 91.0 40.6 0.47 0.74 1.21 100.0 100.0 100.0 3.8 2.3 96.2 97.7
Feed Calc. 100.0 44.6
Rougher Lights
Mag 12.2 4.5
Non Mag 87.8 32.2 0.17 0.86 1.03 28.7 92.3 67.6 3.2 2.3 96.8 97.7
Feed Calc. 100.0 36.7
Scavenger Lights
Mag 4.6 0.4
Non Mag 95.4 7.3 1.02 2.26 3.28 39.3 55.3 49.0 6.7 2.4 93.3 97.6
Feed Calc. 100.0 7.7
Cleaner Lights
Mag 11.6 4.2
Non Mag 88.4 32.0 0.1 0.86 0.96 16.8 91.6 62.5 3.2 2.3 96.8 97.7
6,092,665
29 30
TABLE lO.2-continued
Data from Electrostatic and Induced Roll Separations on Air Table Products
Feed Crushed to minus 6 mesh
Insoluble Soluble
Weight Percent >2.3 S.G., % >2.3 S.G., Dist., % Assay, % of Assay, % of
Product Feed Sample Plus Minus Total Plus Minus Size Total <2.3 SG Total <2.3 SG
Feed Calc. 100.0 36.2
10 x 20 MESH
Not Tabled
Condo 20.6 2.5
Mag 1.7 0.2
Non Mag/Non Condo 77.6 9.6 0.6 1.32 1.92 100.0 100.0 100.0 5.1 3.1 94.9 96.9
Feed Calc. 100.0 12.3
Rougher Lights
Condo 15.0 1.7
Mag 2.4 0.3
Non Mag/Non Condo 82.6 9.4 0.06 0.52 0.58 9.9 38.8 29.8 3.6 3.1 96.4 96.9
Feed Calc. 100.0 11.4
Cleaner Lights
Condo 9.9 1.1
Mag 2.1 0.2
Non Mag/Non Condo 88.0 9.8 0.01 0.55 0.56 1.7 42.6 29.8 3 2.5 97 97.5
Feed Calc. 100.0 11.1
20 x 35 MESH
Not Tabled
Condo 18.2 2.2
Mag 2.9 0.4
Non Mag/Non Condo 78.9 9.7 0.62 2.24 2.86 100.0 100.0 100.0 5.4 3.1 94.6 96.9
Feed Calc. 100.0 12.3
Rougher Lights
Condo 15.8 1.8
Mag 2.3 0.3
Non Mag/Non Condo 81.9 9.3 0.15 1.93 2.08 23.1 82.2 69.4 4.7 3.1 95.3 96.9
Feed Calc. 100.0 11.3
Cleaner Lights
Condo 14.2 1.5
Mag 2.8 0.3
Non Mag/Non Condo 83.0 8.8 0.1 0.71 0.81 14.6 28.8 25.7 4.4 3.1 95.6 96.9
Feed Calc. 100.0 10.6
35 x 65 MESH
Not Tabled
Condo 8.6 0.5
Mag 5.5 0.3
Non Mag/Non Condo 85.9 4.8 3.18 3.09 6.27 100.0 100.0 100.0 9.2 3.5 90.8 96.5
Feed Calc. 100.0 5.6
Rougher Lights
Condo 10.0 0.5
Mag 3.2 0.2
Non Mag/Non Condo 86.8 4.7 0.45 2.44 2.89 13.8 77.0 44.9 5.3 2.6 94.7 97.4
Feed Calc. 100.0 5.4
Cleaner Lights
Condo 13.0 0.7
Mag 4.8 0.3
Non Mag/Non Condo 82.2 4.4 0.24 1.73 1.97 6.8 50.7 28.5 4.9 2.8 95.1 97.2
Feed Calc. 100.0 5.3
CUMULATIVE
PRODUCTS
Total NMjNC from 64.7 100.0 100.0 100.0 4.6 2.6 95.4 97.4
Untabled Feed
Total NMjNC from 62.9 36.9 99.1 76.2 4.0 2.6 96.0 97.4
ROll. + Scavo
Lights 55.6 20.7 78.1 57.0 3.7 2.6 96.3 97.4
Total NMjNC from 54.9 11.3 58.9 41.4 3.5 2.5 96.5 97.5
Rou. Lights
6,092,665
31
TABLE lO.2-continued
Data from Electrostatic and Induced Roll Separations on Air Table Products
Feed Crushed to minus 6 mesh
32
Weight Percent _----'>"'2"'.3"--"-S."'G"'.,'-'I1"'0_ >2.3 S.G., Dist., %
Insoluble
Assay, % of
Soluble
Assay, % of
Product
Total NMjNC from
CI. Lights
Feed Sample Plus Minus Total Plus Minus Size Total <2.3 SG Total <2.3 SG
NOTE: The >2.3 sink products from the non mag., non condo were screened at intermediate mesh sizes to determine the
recoveries by particle size, i.e., the 6 x 10 m at 8 m, the 10 x 20 m at 14 m, the 20 x 35 m at 28 m, and the 35 x 65 mat
48 m.
15
EXAMPLE 11
This example illustrates beneficiation of trona using air
tabling, electrostatic separation and magnetic separation,
and demonstrates a relationship between breadth of size
fractions and effectiveness of air tabling as the density
separation method by comparison with heavy liquid separation.
A sample of bulk trona from Bed 17 of the Green River
Formation in Wyoming was crushed to -10 mesh. The
sample was subsequently sized into size fractions of 10 x20
mesh, 20x35 mesh and 35x65 mesh (Tyler mesh). Each of
the size fractions was then subjected to initial density
separation on an air table (Rougher Pass). The size fractions
were subsequently sent through a cleaner and for the lOx20
mesh fractions, a scavenger pass. The resulting separations
are shown in Table 11.1.
Each of the size fractions was then subsequently beneficiated
using electrostatic separation and magnetic separation.
The portions of material from each separation reporting
to various product streams are shown in Table 11.1.
The non-magnetic/non-conductive fractions were then
further analyzed by conducting a second density separation
based on heavy liquid separation to identify what portion of
impurities which are separable by density separation had not
been removed in the earlier air tabling step. The results of
this analysis are shown in Table 11.2. The column entitled
">2.3 S.G., %" identifies the total amount of material
separated from the beneficiated ore by the additional heavy
liquid density separation step. Additionally, that column
shows subcolumns titled "Plus" and "Minus." These two
subcolumns represent a breakdown of the "Total" percentage
of material which is greater than 2.3 S.G. which falls
into either the coarser or finer portion of the particular
stream. For example, the 10x20 mesh fraction was broken
down into a lOx14 mesh fraction and an 14x20 mesh
fraction. Thus, by comparing the "Plus" and "Minus" subcolumns
of the ">2.3 S.G., %," it can be seen that inefficiency
in the air tabling density separation tended to be at
smaller particle sizes within each size fraction because most
of the higher specific gravity material left by air tabling was
in the smaller particle size (the "Minus" column).
The columns titled "Insoluble Assay" and "Soluble
Assay" provide data on the portion of each stream which is
insoluble (i.e., impurity) before heavy liquid separation
("Total" subcolumn) and after heavy liquid separation
("<2.3 S.G." subcolumn). Thus, for example, the purity of
products resulting from beneficiating ore using air tabling
can be seen in the "Total" subcolumn of the "Soluble Assay"
column for each of the different streams. This purity can be
compared with the subsequent column, having a higher
purity, which identifies the purity of the beneficiated material
with the subsequent heavy liquid separation to indicate
a theoretical purity based on perfect density separation. In
addition, the improvement in trona purity between the
20 non-magnetic/non-conductive product which was not air
tabled and the non-magnetic/non-conductive product which
was air tabled can be seen by comparing the "Total NonMagnetic/
Non-Conductive from Untabled Feed" line with
the "Total Non-MagneticlNon-Conductive from Cleaner
25 Lights" line in the "Cumulative Products" section of Table
11.2.
TABLE 11.1
Data from Air Table Tests on Bulk Trona Sample Crushed to Minus 10
30 Mesh
Weight, % of
Product Feed Size Fraction Sample
35 10 x 20 MESH
Rougher Pass
Heavies 13.6 13.6 4.1
Lights 86.4 86.4 26.3
40
Feed Calc. 100.0 100.0 30.4
Scavenger Pass
Heavies 8.2 1.8 0.3
Lights 91.8 12.5 3.8
Feed Calc. 100.0 14.3 4.1
Cleaner Pass
45
Heavies 3.0 2.6 0.8
Lights 97.0 83.8 25.5
Feed Calc. 100.0 86.4 26.3
20 x 35 MESH
50 Rougher Pass
Heavies 1.3 1.3 0.3
Lights 98.7 98.7 20.1
Feed Calc. 100.0 100.0 20.4
Cleaner Pass
55
Heavies 4.4 4.3 0.9
Lights 95.6 94.4 19.2
Feed Calc. 100.0 98.7 20.1
35 x 65 MESH
60
Rougher Pass
Heavies 13.0 13.0 1.1
Lights 87.0 87.0 7.4
Feed Calc. 100.0 100.0 8.5
Cleaner Pass
65 Heavies 18.0 15.7 1.3
Lights 82.0 71.3 6.1
6,092,665
33 34
TABLE 1l.1-continued
Data from Air Table Tests on Bulk Trona Sample Crushed to Minus 10
Mesh
Product
Feed Calc.
MINUS 65 MESH (not air tabled)
TOTAL FEED CALC.
Weight. % of
Feed Size Fraction Sample
100.0 87.0 7.4
40.7
100.0
5
10
What is claimed is:
1. A process for recovering a saline mineral from an ore
containing the saline mineral and impurities, said process
comprising the steps of:
(a) calcining the ore to alter the apparent density of the
saline mineral; and
(b) separating a first portion of impurities, said impurities
having an apparent density different than that of the
saline mineral in the calcined ore, from the calcined ore
by density separation to produce a recovered saline
mineral.
2. A process, as claimed in claim 1, wherein the recovered
saline mineral comprises trona.
TABLE 11.2
Data from Electrostatic and Induced Roll Separations on Air Table Products
Feed Crushed to minus 10 mesh
Weight Percent _~>",2",.3"--"-S.",G,,.•,~'/1,,,o_ >2.3 S.G.. Dist.. %
Insoluble
Assay. % of
Soluble
Assay. % of
Product Feed Sample Plus Minus Total Plus Minus Size Total <2.3 SG Total <2.3 SG
10 x 20 MESH
Not Tabled
Condo
Mag
Non Mag/Non Condo
Feed Calc.
Rougher Lights
Condo
Mag
NonMag/NonCond.
Feed Calc.
Scavenger Lights
Condo
Mag
Non Mag/Non Condo
Feed Calc.
Cleaner Lights
Condo
Mag
Non Mag/Non Condo
Feed Calc.
24.7 7.5
1.6 0.5
73.7 22.4 0.59 1.19 1.78 100.0 100.0 100.0 4.0 2.6 96.0 97.4
100.0 30.4
16.6 4.4
3.6 0.9
79.8 21.0 0.06 0.7 0.76 9.5 55.1 40.0 2.7 2.4 97.3 97.6
100.0 26.3
23.1 0.9
3.7 0.1
73.1 2.8 0.51 3.05 3.56 10.7 31.8 24.8 6.5 2.3 93.5 97.7
100.0 3.8
23.1 5.9
3.7 1.0
73.1 18.6 0.02 0.63 0.65 2.8 44.1 30.4 2.5 2.3 97.5 97.7
100.0 25.5
45
3. A process, as claimed in claim 1, wherein the first
portion of impurities comprises halite.
4. A process, as claimed in claim 1, wherein the apparent
density of the first portion of impurities is greater than that
50 of the saline mineral.
5. A process, as claimed in claim 1, further comprising the
step of separating a second portion of impurities by magnetic
separation.
6. A process, as claimed in claim 5, wherein said magnetic
55 separation step occurs after said density separation step.
7. A process, as claimed in claim 5, wherein the second
portion of impurities is more magnetic than the saline
mineral.
8. A process, as claimed in claim 7, wherein the second
portion of impurities comprise minerals selected from the
60 group consisting of shale, complex iron silicates or ironbearing
carbonates.
9. A process, as claimed in claim 1, wherein the purity of
the recovered saline mineral is at least about 95% after said
separating step.
10. A process, as claimed in claim 9, wherein the purity
of the recovered saline mineral is at least about 98% after
said separating step.
EXAMPLE 12
This example illustrates beneficiation of trona using air
tabling, calcination, additional air tabling, and magnetic
separation in accordance with the second aspect of the
present invention.
A 25 kilogram sample of 8xlO mesh trona from air
tabling, having a purity of about 86.5%, was calcined at 3000
F. for 3 hours and subsequently subjected to additional air
tabling. The additional air tabling rejected impurities which
could not be separated by air tabling prior to calcination. The
purity of the trona increased from 86.5% to 93.1% after one
cleaning step of air tabling. Additional magnetic separation
increased the grade to 97.8%.
EXAMPLE 13
This example illustrates the effectiveness of the second
aspect of the present invention in removing halite from
trona. A sample of calcined trona was mixed with halite to
achieve a mixture comprising about 10% halite. Air tabling
of this mixture resulted in a sharp separation yielding a 65
virtually pure halite fraction and a calcined trona product
containing less than 1% halite.
35
6,092,665
36
* * * * *
5
20
10
(i) combusting an energy source to produce heat and
combustion gas;
(ii) transferring at least a portion of the heat to the fluid;
(iii) directing at least a portion of the combustion gas
through a combustion gas outlet which is not in direct
fluid communication with said calcining vessel.
26. A process, as claimed in claim 25, wherein said step
of heating the saline mineral produces calcining gas, and
wherein said process further comprises the steps of:
(d) removing the calcining gas from the calcining vessel
through a calcining gas outlet; and
(e) combining at least a portion of the calcining gas with
at least a portion of the combustion gas.
27. A process, as claimed in claim 22, wherein particulates
15 are removed from the calcining gas during said condensing
step.
28. A process, as claimed in claim 22, wherein said step
of condensing at least a portion of the water comprises the
step of condensing water by cooling the calcining gas.
29. A process, as claimed in claim 28, further comprising
the step of:
(d) cooling the condensed water, wherein said condensing
step comprises bringing the cooled water into thermal
communication with the calcining gas.
30. A process, as claimed in claim 22, wherein said
condensing step comprises reducing the water content of the
calcining gas to less than about 50%.
31. A process, as claimed in claim 22, wherein said
condensing step comprises reducing the volume of the
30 calcining gas by at least about 50%.
32. A process, as claimed in claim 27, wherein said
condensing step reduces the particulate content by at least
about 50%.
33. A process for recovering a saline mineral from an ore
35 containing the saline mineral and impurities, said process
comprising the steps of:
(a) sizing the ore to generate a first fraction of about -65
mesh and a second fraction of about +65 mesh; and
(b) separating iron from the first fraction to produce a first
recovered portion comprising a recovered saline mineral.
34. A process, as claimed in claim 33, wherein said
separating step comprises a wet separation process.
45 35. A process, as claimed in claim 34, wherein said wet
separation process comprises the slush process.
36. A process, as claimed in claim 33, further comprising:
(c) separating a second portion of impurities from the
second fraction to produce a second recovered portion;
and
(d) combining the first recovered portion with the second
recovered portion to produce a recovered saline mineral.
37. A process, as claimed in claim 33, further comprising,
55 before step (a), the step of reducing a particle size of said ore
before said separating steps.
38. A process, as claimed in claim 37, wherein said
reducing step reduces to particle size of said ore to less than
about 6 mesh.
11. A process, as claimed in claim 1, further comprising,
before step (b), the step of reducing a particle size of the ore.
12. A process, as claimed in claim 1, further comprising,
before step (b), the step of de-dusting the ore to recover
fines.
13. A process, as claimed in claim 1, further comprising,
before step (b), the step of sizing the ore into between 3 and
10 size fractions.
14. A process, as claimed in claim 1, wherein a maximum
particle size before said separating step is about 6 mesh.
15. A process, as claimed in claim 1, wherein a minimum
particle size before said separating step is about 100 mesh.
16. A process, as claimed in claim 1, wherein said
calcining step comprises heating the ore to a temperature of
at least about 120° C.
17. A process, as claimed in claim 16, wherein said
heating step occurs in a fluidized bed reactor.
18. A process, as claimed in claim 1, wherein said density
separation step comprises a process selected from the group
consisting of air tabling and dry jigging.
19. A process, as claimed in claim 18, wherein said
density separation step comprises air tabling.
20. A process, as claimed in claim 1, wherein said
calcining step comprises the step of heating the saline
mineral in a calcining vessel above its calcining temperature 25
with a heat source to calcine the saline mineral, wherein said
heat source is not in direct fluid communication with said
saline mineral.
21. A process for recovering trona from an ore containing
trona and impurities, said process comprising the steps of:
(a) reducing a particle size of the ore to a size to achieve
liberation of impurities;
(b) sizing the ore into between 3 and 10 size fractions;
(c) calcining the ore; and
(d) separating impurities comprising halite from a fraction
of the calcined ore by a density separation method, the
impurities having a higher apparent density than calcined
trona.
22. A process for calcining a saline mineral, said process 40
comprising the steps of:
(a) heating the saline mineral in a calcining vessel above
its calcining temperature with a heat source to calcine
the saline mineral, wherein said heat source is not in
direct fluid communication with said saline mineral and
wherein said step of heating the saline mineral produces
calcining gas having water vapor;
(b) removing the calcining gas from the calcining vessel
through a calcining gas outlet; and
(c) condensing at least a portion of water vapor from the 50
calcining gas.
23. A process, as claimed in claim 22, wherein the saline
mineral comprises trona.
24. A process, as claimed in claim 23, wherein said step
of heating comprises the steps of:
(i) heating a fluid; and
(ii) bringing the heated fluid into thermal communication
with the calcining vessel.
25. A process, as claimed in claim 24, wherein said step
of heating a fluid comprises the steps of: