Mr. Jaye Pickarts reports
RARE ELEMENT RELEASES RARE EARTH METALLURGICAL TEST RESULTS AND BEGINS PILOT PLANT TESTING
Rare Element Resources Ltd. has completed the bench-scale metallurgical test program
for near-surface, oxidized high-grade, rare-earth-mineralized vein
material from the Bull Hill deposit at the Bear Lodge project, Wyoming.
The test program resulted in the development of a process flowsheet
that will become the basis for a pilot plant operation and a
preliminary feasibility (prefeasibility) study. Additional studies
are also being conducted on the high-grade oxide-carbonate
mineralization type, and on the low-grade stockwork mineralization that
envelops the high-grade material. The pilot plant test is currently
under way to further define an economical ore process and to develop
design criteria that can be used to scale up to commercial operation.
Completion of the initial pilot plant testing is scheduled for the end
of October, 2011. The low-grade stockwork mineralization (generally less
than 1.5 per cent rare earth oxides (REO)) surrounds the resource area and is not included in the
company's NI 43-101 resource estimate (see news release of June
14, 2011). Much of this material will be mined in the current pit design in
order to access the high-grade areas. These tests will determine
whether the low-grade rare earth element (REE) mineralization can be
upgraded and recovered from these areas in a simple cost-effective
manner.
Bench-scale high-grade oxide testing
Rare earth mineralized bodies occur as high-grade dikes and veins within
the Bull Hill deposit. They include a well-defined, near-surface
oxidized zone that has been the subject of most metallurgical testing
to date. The oxide mineralization contains essentially no matrix
carbonates or sulphides. The sulphides are completely oxidized to hydrous
iron oxides, and the non-REE-bearing carbonate minerals (calcite and
strontianite) are completely leached from the zone, which ranges from
the surface to depths of about 500 feet. These conditions created a
loose and friable oxide material that allows for a simple physical
mineral processing method.
In parts of the high-grade zone, the sulphides are oxidized but matrix
carbonate is partially and variably leached. This zone is termed the
oxide-carbonate zone. A thin transitional zone occurs at the base
of the oxide and/or oxide-carbonate zone at a depth of approximately
500 feet (150 metres). The transitional zone passes relatively abruptly into
the sulphide-bearing zone with typical carbonatite characteristics.
Tests on the high-grade oxide mineralization indicate that recoveries of
80 to 85 per cent of REO are expected using a
two-stage process. The first stage is mineral concentration, also known
as physical upgrading (PUG). The second stage is a chemical leaching
process using hydrochloric acid that produces a mixed rare earths
leachate that is precipitated as a bulk carbonate concentrate. The
series of bench-scale testing programs was completed by Mountain States
R&D International (MSRDI), Vail, Ariz., under the direction of Dr.
Roshan Bhappu. The test results show that 80 to 90 per cent REO can be
recovered in 50 to 60 weight per cent of the original mass weight by
employing a simple washing, scrubbing and screening process that
produces a mineral preconcentrate of sand size and finer particles.
The washing and screening process uses only water as a process media
and is similar to gravel washing plants that are commonly employed
throughout the United States. Using a 5- to 8-per-cent REO head grade
sample, the preconcentrate can be upgraded to 16 to 19 per cent REO using
this process. A parallel series of tests to verify the process has been
conducted by Nagrom of Perth, Australia, under the direction of Tony Wilkinson, general manager.
Mineral concentration by physical
upgrading of high-grade oxide
material*
Sample Assay Distribution
Weight REO REO (recovery)
(%) (%) (%)
-500 mesh 28.60 21.68 79.10
-325 mesh 32.30 20.60 84.80
-200 mesh 35.60 19.49 88.60
-100 mesh 38.10 18.54 90.20
-48 mesh 40.10 17.83 91.10
* Using a head grade of approximately 8
per cent REO
The preconcentrate will be trucked to a hydrometallurgical facility
located approximately 40 miles from the Bull Hill mine site. The plant
site will be selected from several sites identified in the area that
are located on a railway line with existing infrastructure. Such a
location will help reduce the environmental impact associated with
chemical processing.
The subsequent leaching process consists of dissolving the
preconcentrate in a 15- to 17-per-cent hydrochloric acid leach solution at
a temperature of 90 C. This updated acid concentration
for leaching is a significant reduction from the 21-per-cent
concentration used in modelling costs in the preliminary economic
assessment filed in November, 2010. In addition, the leach temperature
of 90 C is lower than many other REE leach projects and allows
for lower energy consumption.
Once the rare earth minerals are dissolved, iron is precipitated using
sodium carbonate and sodium hydroxide. A mixed rare earth carbonate
precipitate is produced by adding sodium carbonate to the rare earth
leach solution. Approximately 95 per cent of the REO in the
preconcentrate is dissolved by the hydrochloric acid and recovered in
the precipitate, with an upgraded concentration of approximately 40
per cent REO. Optimization of the leaching and precipitation process is
under way. The hydrochloric acid is regenerated in a distillation
circuit using sulphuric acid and sodium chloride. This regeneration
process is commonly used in the steel industry.
CHEMICAL CONCENTRATION RESULTS FROM BENCH-SCALE LEACHING TESTWORK
Sample Ce2O3 La2O3 Nd2O3 Pr2O3 Sm2O3 Y2O3 REO Fe
% % % % % % % %
Leach residue 0.35 1.06 0.63 0.19 0.11 0.01 2.35 1.81
Iron precipitate 3.00 1.82 1.01 0.45 0.14 0.00 6.43 17.70
Mixed carbonate precipitate 18.59 11.47 6.11 2.90 0.84 0.02 39.93 0.15
Pilot plant test program of the high-grade oxide REE bulk sample
The following data are used as the basis for the pilot scale plant that
commenced in early September, 2011. Hazen Research Inc., of Golden,
Colo., is contracted to conduct pilot testing of this flowsheet.
Approximately 13 tons of high-grade and stockwork mineralized material
will be processed over the next several months to develop data for the
prefeasibility study and to support the continuing environmental
permitting process.
The design criteria and flowsheet for this upcoming prefeasibility
study are as follows.
High-grade feed rate, stpd 1,000
Grade, % REO 3.5-6.0
Stockwork feed rate, stpd 1,000
Grade, % REO 0.5-1.5
Mass reduction from PUG plant, %
High-grade 30-50
Stockwork 80
Feed rate to hydrometallurgical plant, stpd 400-500
Grade, % REO 16-19
Hydrochloric acid concentration, % 15-17
Carbonate precipitation rate, stpd 80-100
Grade, % REO 40
Oxide-carbonate testing
The oxidized, but incompletely leached, oxide-carbonate zone in the Bull
Hill deposit generally occurs beneath the oxide zone, but may locally
breach the surface in select dikes and extend downward to the
transitional zone. It is characterized by an absence of sulphides, with
the residual iron oxides formed during the complete oxidation of the
former sulphide minerals, and by variable amounts of relict matrix
carbonates (calcite and/or strontianite). As now defined, the transitional
zone is relatively flat-lying and occurs at depth as a thin layer
immediately above the sulphide-bearing carbonatite zone. It contains
mixed iron oxides and sulphides, along with a significant amount of
relict matrix carbonates. The iron oxides in this zone are derived
primarily from the variable partial to complete oxidation of
constituent sulphide minerals. The unoxidized sulphide-bearing
carbonatite at depth has not been leached of matrix carbonates and
retains all of its initial sulphide content.
Metallurgy of the oxide zone REE mineralization is well established and
described above. Initial metallurgical testing of the oxide-carbonate
zone resource indicates that mineral preconcentration test results are
similar to those for the oxide zone mineralization. Bench-scale
testwork of the oxide-carbonate mineralization is continuing at both
MSRDI and Hazen Research. Preliminary results from the mineral
concentration testing are encouraging with recovery similar to the
oxide mineralization. The leach testwork results are expected within
the next few months.
The first set of test results indicate that rare earth recoveries
ranging from 85 to 93 per cent were achieved using the same leaching
criteria applied to the preconcentrated high-grade and stockwork oxide
materials.
PRELIMINARY METALLURGICAL RESULTS FOR THE OXIDE-CARBONATE MATERIAL
Experiment Residue analysis, % Extraction (solids basis), %
No. La Ce Pr Nd Eu La Ce Pr Nd Eu
Experiment 1 0.166 0.261 0.046 0.186 0.006 92 93 85 89 85
Experiment 2 0.144 0.239 0.038 0.167 0.006 93 93 88 90 85
Experiment 3 0.144 0.223 0.038 0.162 0.005 92 93 87 90 88
Experiment 4 0.167 0.256 0.042 0.185 0.006 91 93 86 89 85
Stockwork (lower grade) testing
Bulk-tonnage, lower grade stockwork mineralization averages
approximately 1 per cent REO and occurs as an envelope around the
higher grade oxide and oxide-carbonate zones. The stockwork zone is
extensive and only a small part of the potential has been tested by
drill holes. Scoping metallurgical testwork was completed for the lower
grade stockwork ore. Using the same upgrading and leaching parameters
as previously described, the REO content in the preconcentrate was
approximately doubled, with a mass reduction of nearly 80 per cent.
Subsequent hydrochloric acid leaching produced favourable rare earth
extractions. Further metallurgical testing may allow the addition of
this material to the resource base.
MINERAL CONCENTRATION BY PHYSICAL
UPGRADING OF STOCKWORK MINERALIZATION*
Sample Assay Distribution
Weight REO REO (recovery)
(%) (%) (%)
-500 mesh 4.60 6.01 43.3
-200 mesh 2.80 6.88 29.0
-100 mesh 1.30 9.67 18.9
-48 mesh 1.30 8.75 17.9
-1/4 inch 9.60 4.12 62.4
* Using a head grade of approximately 2.4 per cent REO.
Heavy rare earths testing plans
West of the Bull Hill resource area, the company discovered high grades
of heavy rare earth elements in the Whitetail Ridge resource area, and
in the East Taylor and Carbon target areas. All three of the
mineralized zones are located in the western half of an expanding
rare earth mineralized district (the Bear Lodge REE district).
Preliminary characterization of the western areas indicate high grades
(more than 3 per cent REO) and substantial quantities of the light rare earths,
along with some of the highest grades of heavy rare earths in North
American REE deposits. They are particularly enriched in europium,
terbium, dysprosium and gadolinium (Eu, Tb, Dy and Gd). The East
Taylor and Carbon targets also contain significant yttrium.
Metallurgical samples are being collected and testing of the heavy
rare earth mineralization will begin in the fourth quarter of 2011.
Jaye T. Pickarts, PE, serves the board of directors of the company as
an internal, technically qualified person. Technical information in
this news release has been reviewed by Mr. Pickarts and has been
prepared in accordance with Canadian regulatory requirements that are
set out in National Instrument 43-101.
We seek Safe Harbor.
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