REG - Rainbow Rare Earths - Phalaborwa Test Work Update & Process Flow Sheet

Rainbow Rare EarthsAnnouncement

08/02/2022 07:00

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RNS Number : 9455A  Rainbow Rare Earths Limited  08 February 2022

 

8 February 2022

 

Rainbow Rare Earths Limited

("Rainbow" or "the Company")

LSE: RBW

 

Phalaborwa Rare Earths Test Work Update and Process Flow Sheet Development
Demonstrates Robust Fundamentals

 

Rainbow Rare Earths is pleased to announce positive results from the ongoing
phased test work programme at the Phalaborwa Project, in South Africa
("Phalaborwa" or the "Project"). The test work is being conducted in
conjunction with ANSTO Minerals in Australia, a world-leading critical and
strategic metals processing expert ("ANSTO"), and K-Technologies Inc, the
processing technology developer located in the USA ("K-Tech").

 

The results of the test work are enabling Rainbow to develop an economic rare
earths extraction flowsheet currently as part of the feasibility study for the
Project.  Results to date have provided the Company with additional
optimisation opportunities to explore, which can reduce both operating and
capital costs for the Project.  The next phase of the test work programme is
now underway, which includes a number of trade-off and project optimisation
studies.

 

The results of the test work to date are set out in a technical report
accessible on the Company's website at
https://rainbowrareearths.com/investors/corporate-documents/
(https://rainbowrareearths.com/investors/corporate-documents/) the text from
which is included in Appendix A.  The key findings include the following:

 

·    Strong recoveries and optimisation opportunities:

o  The test work at ANSTO has confirmed that a simple acid leaching process
is expected to allow 65-70% of the rare earths contained in the Phalaborwa
gypsum stacks to be recovered in solution, with an average 66% leach recovery
reported from preliminary metallurgical variability test work.

o  The K-Tech purification and separation desktop study has confirmed the
ability to deliver separated rare earths with over 99% purity oxides from the
leach solution.  Phalaborwa will be unique in producing separated Neodymium
and Praseodymium (NdPr) oxide, Dysprosium (Dy) oxide and Terbium (Tb) oxide on
site.  This will allow the full value of the rare earths to be realised - a
47% increase in revenue over the expected sales price for a mixed rare earth
carbonate.

o  Trade-off studies have started at both ANSTO and K-Tech to determine the
optimal method to maximise the grade of rare earth elements in the leach
solution prior to the final K-Tech separation step, whilst managing the
build-up of impurities present in the gypsum stacks that could impact overall
rare earth recovery.  Increasing the leach solution grade by recycling the
leach solution will significantly reduce both operating and capital costs.

·    Reduced capital and operating costs, with flexibility in terms of
project development

o  The Phosphogypsum will be hydraulically reclaimed from the stacks and
pumped into the processing facility, reducing cost per tonne compared to
traditional hard rock mining.

o  Nano filtration will successfully recycle over 60% of the sulphuric acid
required to recover the rare earths to the leach solution, reducing operating
and capital costs and minimising leach solution flows into the downstream
K-Tech separation circuit.

o  Potential identified for phased development providing versatility: the
K-Tech study has shown that a cerium-depleted mixed rare earth carbonate could
be produced at Phalaborwa as an initial phase if required at a lower up-front
capital cost.

o  Sulphuric acid remains the lixiviant (leaching liquid) of choice following
this test work, owing to the low cost and availability of the reagent in the
local area, and the simpler materials of construction requirements.

o  With a slight elevation to the temperature of the sulphuric acid leach
solution, recovery is optimised with a 12-hour leach residence period,
providing significant operating and capital cost savings compared to the
initial 24-hours leach residence period originally envisaged at atmospheric
temperature.

·    Environmental benefits

o  Water neutralisation test work has confirmed the ability to treat the
existing water from the stacks and reuse it in a closed circuit as plant
process water. This not only reduces the substantial legacy issue of acid
water from historic work (prior to the Company's involvement) but will also
reduce overall freshwater usage in the flowsheet.

o  Very low levels of radioactivity have been confirmed within the gypsum
extracted, significantly below the International Atomic Energy Agency ("IAEA")
guidelines, therefore exempting the Project from regulation pertaining to
radioactivity.

 

Rainbow Rare Earths CEO, George Bennett, commented:

"We are delighted by this positive test work and are very reassured that
results received to date continue to demonstrate Phalaborwa's robust
fundamentals. The studies have identified several key opportunities for
capital and operating cost savings as well as underscoring the significant
environmental benefits of the Project. The potential to participate further
downstream in the value chain and produce rare earth oxides with 99.5-99.9%
purity has been confirmed by K-Tech's study, which also highlights flexibility
for phased project development if required.

As a team, we have led numerous projects through this vital development phase
and recognise the enormous benefits of implementing the correct trade-offs and
optimising to the greatest extent possible in order to deliver a successful
end result. I firmly believe that we have the right people in place to take
Phalaborwa's development forward, with significant experience throughout the
asset lifecycle from optimisation, feasibility and development to plant
construction and commissioning. By getting this stage of process flow sheet
definition right, investigating the highlighted optimisation and trade-off
opportunities identified by our considerable work to date, we aim to realise
the full value of Phalaborwa and develop a responsible, independent Western
rare earths supply chain.

I am proud that we have delivered significant progress in unlocking this
opportunity at Phalaborwa for Rainbow's stakeholders in an exceptionally short
time frame since the Project was first secured in December 2020."

Market Abuse Regulation

This announcement contains inside information as defined in the Market Abuse
Regulation (EU) No. 596/2014, as amended, as it forms part of UK law by virtue
of the European Union (Withdrawal) Act 2018.

**ENDS**

 

For further information, please contact:

 

 Rainbow Rare Earths Ltd           Company  George Bennett     +27 82 652 8526

                                            Pete Gardner
 SP Angel Corporate Finance LLP    Broker   Ewan Leggat        +44 (0) 20 3470 0470

                                            Charlie Bouverat
 Tavistock Communications Limited  PR/IR    Charles Vivian     +44 (0) 20 7920 3150

                                            Tara Vivian-Neal   rainbowrareearths@tavistock.co.uk (mailto:rainbowrareearths@tavistock.co.uk)

 

Appendix A: Technical Report on the Phalaborwa Processing Flow Sheet
Development

Rainbow initiated a phased test work programme at ANSTO Minerals in Sydney,
Australia to develop a feasible, rare-earth extraction, flowsheet for
processing the phosphogypsum ("PG") deposit located at Phalaborwa, South
Africa.

 

The ANSTO Minerals test work programme was supported by various other studies
and test campaigns at various facilities. The key programs can be summarised
as follows:

·    Filtration test work at Roytec Global in Johannesburg, South Africa

·    Nano filtration desktop study at Chimerical in Cape Town, South
Africa

·    Site water analysis and basic neutralisation testing at SGS
Johannesburg, South Africa

·    K-Tech rare earth purification and separation desktop study carried
out in Florida, USA

 

The initial test work programme, at ANSTO Minerals, has been designed as a two
phased programme with the phase 1 programme completed July 2021.

 

The phase 1 programme covered the following milestones:

·    Material characterisation and mineralogy

·    Radiological classification

·    Leach conditions and lixiviant selection

·    Resin in leach evaluation

·    Preliminary metallurgical variability response

 

Material characterisation and mineralogy

·   Mineralogical evaluation indicates 96 weight % (wt.%) as calcium
sulphate and a 3 wt.% calcium aluminium, rare earth rich, fluoride phase that
contains the bulk of the rare earth minerals. The remainder of the rare earths
are associated with refractory phases, for example monazite, and no rare earth
association with the calcium sulphate phase was detected.

·    Rare earths are not preferentially upgraded to any size fraction and
are evenly distributed with particle size.

·    Maximum rare earth leach recovery possible at mild to medium acid
conditions will be in the range of 70 to 75% of contained total rare earths,
with a similar response for the light rare earth group.

 

Radiological classification

·    The gamma results of the phosphogypsum sample confirm a very low
uranium content of 1.7ppm that is not in secular equilibrium.

·    The thorium content also very low at 48ppm and in secular
equilibrium, probably associated with the detected monazite phase.

·    The IAEA International guidelines for exemption from regulation
pertaining to radioactivity is that all radionuclides should be less than 1
Bq/g, so from this perspective the phosphogypsum would not be subject to the
requirements of any regulations.

 

Leach conditions and lixiviant selection

·    Hydrochloric and sulphuric acid stand out as the lixiviants of choice
and outperform the nitric acid and calcium nitrate leach system, as previously
postulated by Mintek.

·    Hydrochloric acid leaching, as expected, results in partial gypsum
dissolution, and as indicated by the mineralogy, does not improve the rare
earth extraction compared to less costly sulphuric acid.

·    Moderately elevated temperatures do not impact on the total
extraction extent but significantly improve the dissolution kinetics.

·    Increased slurry density in the leach impacts marginally on the
extraction of rare earths due to suspected solubility constraints.

·    Sulphuric acid control level in the leach must be in the region of
110-150g/L to ensure rare earth stability in the leach system but requires
further optimisation in the phase 2 programme.

 

Resin in leach ("RIL") evaluation

·    Various resins were evaluated and were effective in rare earth
absorption at mild acid conditions.

·    High impurity co-loading, mainly calcium, resulted in very low rare
earth loadings.

·    In order to improve selectivity, the slurry pH needed to be increased
and this impacted on the stability of the rare earths in the solution phase.

·    The forecast rare earth loadings indicate an impractically large
resin movement rate and associated elution system.

 

Preliminary metallurgical variability response

·    14 spatially distributed drill core samples were subjected to a
standard sulphuric acid leach test with resin addition. Resin, at this stage,
was still a contender but did not impact on the metallurgical response.

·    The overall metallurgical response yielded an average total rare
earth oxide extraction of 66% with associated minimum at 60% and maximum at
70%.

·    Further variability work will be concluded in future but from an
early stance the overall metallurgical response appears to be consistent,
indicative of a homogeneous deposit.

 

Key decisions and conclusions

·    Phosphogypsum will be hydraulically reclaimed from the stacks and
pumped to the processing facility.

·    In order to manage the leach slurry density and allow for reagent
recycling, pre- and post-leach filtration steps will be included. The
filterability of the material will need to be confirmed.

·    Significant fluoride levels in the leach due to the targeted
dissolution of the rare earth rich calcium aluminium fluoride phase.

·    Fluoride removal and or control needs to be considered in the phase 2
test work campaign

·    Sulphuric acid was initially selected as the lixiviant of choice due
to cost, materials of construction, availability in the region and targeted
dissolution of the rare earth rich calcium fluoride phase without significant
gypsum dissolution.

·    Although ambient leach conditions yielded acceptable results over a
24-hour leach period a moderate temperature adjustment may impact positively
on capital reduction and risk mitigation and will be further considered during
the phase 2 test work campaign.

·    Resin in leach, as a concentration step, will not be further
investigated due to the excessive impurity co-loading that was evident from
these early tests.

 

At the conclusion of the phase 1 leach programme at ANSTO Minerals, Roytec
Global in Johannesburg, South Africa was commissioned to complete pressure and
vacuum filtration testing on the phosphogypsum material.

 

Filtration test work at Roytec Global

A composite sample similar in nature to the tested composite at ANSTO Minerals
was divided and half the material was leached employing elevated temperature
sulphuric acid leaching.

 

The two samples were then handed over to Roytec Global to perform pre- and
post-leach filtration tests. The following key findings emanated from this
test work:

·    Material performed as expected and in line with original phosphoric
acid process filters at Phalaborwa.

·    Improvement in reclamation solids concentration will have a positive
impact on the filter operation and sizing.

·    Pre- and post-leach filters will yield an expected 25-27% cake
moisture and a competent cake.

·   Cake washing was tested and a three-stage counter current wash was
modelled, indicating an expected >99% recovery of soluble rare earth
elements.

·    The use of filters allows for acid recycling over the leach circuit
as well as the possibility of dry stack tailings deposition, that will have
positive tailings management and environmental implications in terms of
reduced capital and operating costs ("capex" and "opex", respectively).

 

The phase 1 test work campaign and successful filtration testing highlighted
the importance of acid recovery and recycling with an associated reduction in
Pregnant Leach Solution ("PLS") stream volume and improved rare earth solution
tenor to feed to a downstream purification and separation circuit.

 

Nano filtration was selected as a technology to recover and recycle sulphuric
acid and upgrade the downstream rare earth PLS grade. Chimerical Engineering,
in Cape Town, South Africa, was commissioned to complete a desktop study to
evaluate the application and performance of such a system using typical leach
PLS stream compositions from the phase 1 ANSTO test campaign.

 

Nano filtration ("NF") desktop study

The focus of the study was to model NF performance using speciation models
that Chimerical has developed and proved on similar projects with actual feed
stream compositions anticipated for Phalaborwa at the time of study.

 

The desktop study confirmed the following key findings:

·    Nano filtration, subject to confirmatory test work, will recover 65%
of the sulphuric acid for recycling to the front end of the leach circuit at
similar strength than the PLS feed stream.

·    Rare earth recovery to the retentate (concentrate) stream will be
99%.

·    Rare earths will be concentrated by a factor of 3 in the concentrate
stream.

·    Fluoride will report with the acid to the permeate stream and thus
recycle to the leach circuit.

·   Test work will need to be completed to confirm saturation limits and
maximum acid recovery, possible system scaling issues and membrane selectivity
under actual conditions.

 

The technology provides an opportunity to recycle acid to the leach circuit
that is critical due to the high levels of free acid required in the leach
system. It also allows for fluoride management options on a rare earth barren
stream and thus reduces the risk of rare earth losses during fluoride removal
treatment.

 

Pending test work confirmation, it should be possible to further reduce the
downstream processing volumes employing NF and optimise the overall circuit
design.  Test work will be initiated once an optimum leach regime has been
established.

 

The desktop study allowed Rainbow Rare Earths to confirm a plausible
conceptual design for the front-end processing circuit at Phalaborwa. The
circuit will employ the large volumes of typical stack water on site as
process water used for hydraulic reclamation and the bulk of the process water
requirements.

 

This implies that continuous water treatment will be required to improve the
water quality for use in the circuit. Water treatment options range from
simple two stage neutralisation that produces more gypsum that requires long
term stacking and/or focused treatment to yield saleable products.  It is
envisaged at this early stage that a hybrid water treatment facility will
provide all the water requirements for the project whilst improving the
overall site wide water quality over time.

 

Water neutralisation test work

Stack water samples from site were collected and sent to SGS Johannesburg to
perform basic neutralisation test work employing either slaked lime or
limestone. The intent was to evaluate water quality improvement at various pH
intervals as well as volumes of precipitate formed and reagent consumptions.

 

The following key findings emanated from this volume of work:

·    Neutralisation improves water quality and significantly reduces
fluoride present in the stack water.

·    Various water qualities are possible with a multistage circuit.

 

With all of the above in mind, the phase 2 test work campaign was initiated at
ANSTO Minerals to investigate the following objectives and scope:

·    Pre-leach impurity control

·    Optimise leach parameters

·    Optimise PLS quality and quantity

 

Pre leach impurity control

The key focus was to reduce impurities, mainly phosphates and fluoride, prior
to the leach circuit. The intended approach would then allow these impurities
to be dealt with in the water neutralisation circuit and not the leach
circuit.

 

Key findings can be summarised as follows:

·    Hydraulic reclamation will alter the hydration state of the long term
stored phosphogypsum prior to the leach.

·    Hydraulic reclamation and pumping at a 25 wt.% solids concentration
coupled to pre-leach filtration will significantly reduce potassium, magnesium
and sodium levels as well as to a lesser, but still significant extent, the
phosphates and fluorides present in the raw phosphogypsum feed. This step will
also reduce impurities present in the pore water in the stacks.

·    Historical work completed by Mintek postulated a fluoride removal
step that consisted of adding concentrated sulphuric acid to the filter cake
to reduce the fluoride through volatilisation. This technique did not prove to
add any value and no fluoride could be reduced though this process.

 

Optimise leach parameters

The key leach parameters with respect to sulphuric acid were investigated and
optimised.

·    The acid concentration in the leach can be reduced to 110 g/L without
impact on the rare earth extraction or stability in the leach circuit.

·    The optimum temperature is 40(o)c that will result in a 12-hour leach
period significantly reducing Capex and Opex.

·    The practical designed leach slurry density will be 30 wt.% solids.

 

With these parameters confirmed the focus shifted to improving the PLS quality
and quantity though PLS recycle testing.

 

Improve PLS quality and quantity

Under optimised conditions, and using pre-washed phosphogypsum as feed, the
leach was tested in closed mode employing five cycles. The leached slurry was
filtered, and the primary filtrate used to repulp fresh feed for the next
cycle leach. Reagent levels was measured and adjusted as required.

 

The following are the key observations:

·    Key impurity levels spiked, most notably the fluoride levels, as
could be expected since the target mineral leached is a calcium aluminium
fluoride phase.

·    These impurity levels impacted on the rare earth extraction.

·    Offline precipitation tests were conducted employing process solution
that was dosed with HF and H(3)PO(4) to simulate various impurity levels. It
was established that the fluoride had the most pronounced effect on the rare
earth stability in solution.

 

This test work clearly highlighted the importance of fluoride management in
the leach and recycling solutions to successfully improve the PLS quality and
quantity from a downstream circuit efficiency and economic perspective.

 

Key decisions and conclusions

·    Pre-leach impurity control will be critical in the final flowsheet
and all future work will be completed with phosphogypsum washed with gypsum
saturated process water.

·    Testing that incorporates actual neutralised stack water as process
water will be scoped in the phase 3 programme.

·    Key, sulphuric acid, leach regime parameters established and
confirmed.

·    PLS recycling or other counter current leaching systems will need to
be critically investigated in a trade-off study to improve downstream PLS
volumes and grade in conjunction with fluoride control strategies.

·    Alternative fluoride control strategies will be tested over the next
phase of test work started in the week of 31(st) January 2022 to finalise the
front-end flowsheet for Phalaborwa.

 

In order to purify and separate the target rare earth elements and produce
final products for sale, a host of technologies have been investigated by
Rainbow Rare Earths. K-Technologies from Florida in the USA has been selected
as the best fit partner, to employ their technology, for the development of a
downstream solution for Phalaborwa.

 

K-Tech rare earth purification and separation desktop study

K-Tech was commissioned and delivered a desktop study late December 2021. The
report covered PLS stream concentration, purification and separation of the
targeted rare earth elements namely neodymium, praseodymium, dysprosium and
terbium up to final separated oxides.

 

K-Tech also considered various alternative options that can support the
front-end leach circuit pending further test work confirmation.

 

Key findings can be summarised as follows:

·    It is critical to reduce PLS volumes and improve rare earth grades in
the PLS to ensure a feasible long-term processing solution.

·   Product options that can be considered range from NdPr oxide, Dy
oxide, Tb oxide, low cerium mixed rare earth concentrate or a low cerium
Nd,Pr,Dy,Tb product. The balance of the rare earths can be stored for future
use.

·    The estimated opex and capex can be significantly improved if the PLS
volume can be reduced to the 40-60 m(3)/h range feeding K-Tech.

·    The desktop study includes a duplicate NF system to further reduce
the volumes predicted by Chimerical. K-Tech is confident that further
upgrading using NF should be possible based on their commercial experience.

·    They forecast, pending final test work, good purity levels for the
oxide products in the range of 99.5 to 99.9%.

·    They assumed a conservative circuit recovery of 80% for the oxide
products but are confident that this can be improved once final test work has
been concluded.

·    It might be possible to employ a cheaper carbonate intermediate
product and tailor the product suite to phases of project implementation with
deferred capex and opex impacts.

·    Can produce a cerium depleted mixed rare earth carbonate product with
significant capex and opex improvements as a starter project with a phased
move to the refined products.

·    K-Tech supports a pre-wash prior to the leach as currently planned
for Phalaborwa.

·    Support the use of the existing gypsum stack water post
neutralisation as process water for large portion of the process (adding to
the ESG credentials of the Phalaborwa project), with the exception of high
purity water requirements for certain aspects in the continuous ion exchange
("CIX") and continuous ion chromatography ("CIC") sections. The high purity
requirements are low in terms of overall volumes.

·    K-Tech can also consider their water treatment technology that can
remove impurities and generate saleable products, and not just a mixed waste
that require storage, to improve opex costs.

·    K-Tech recommends the following to further optimise the capex and
opex of the Project ;

o  Investigate counter current leaching to improve PLS tenor and reduce
volumes

o  PLS recycle to improve PLS volumes

o  Alternative concentration technique that can negate the use of NF all
together or implicate a lot smaller NF circuit than the present anticipated
circuit

o  Consider various water treatment options

o  Kick-off a bench testing campaign to improve on the desktop study and firm
up assumptions that form the basis of the desktop study.

 

The detailed test work programme dealing with all the trade-off suggestions
highlighted above as well as test the K-Tech technology, namely continuous ion
exchange and continuous ion chromatography, for purification and separation of
the target products for Phalaborwa is already underway at K-Tech.

 

Prepared 7 February 2022

Chris Le Roux

Independent Metallurgical Consultant, South Africa

 

Glossary of terms

 Bq/g                                 Becquerel per gramme, a unit to measure radioactivity
 Cake washing                         Wash water applied to filtered solid to remove impurities or target solution
 Continuous ion chromatography (CIC)  Rare earth separation as individual groups or elements in continuous fashion.
 Continuous ion exchange (CIX)        Extract the rare earths from the PLS stream and produce a concentrated rare
                                      earth solution
 Filter cake                          Solid product produced as a result of filtration
 H(3)PO(4)                            Boric Acid
 HF                                   Hydrofluoric Acid
 Hydraulic reclamation                To recover a solid from a storage facility through the use of high pressure
                                      water
 Leach circuit                        System of tanks where a valuable element is recovered
 Lixiviant                            A liquid medium in hydrometallurgy used to selectively extract the desired
                                      metal from a mineral
 m(3)/h                               Measurement of flow in cubic meters per hour
 Nano filtration                      Pressure driven filtration through a membrane
 Neutralised stack water              Gypsum stack water that has been treated with a neutralising agent like lime
 Phosphogypsum                        Gypsum produced as a result of phosphoric acid production
 Pore water                           Water contained or locked in solids
 ppm                                  Parts per million
 Pregnant Leach Solution (PLS)        A solution that contains the extracted valuable metal
 Water Neutralisation                 Water treatment employing lime or limestone
 wt.%                                 Measurement of composition based on mass, weight percentage

 

 

Notes to Editors:

Rainbow Rare Earth's strategy is to become a globally significant producer of
rare earth metals. Nd/Pr are vital components of the strongest permanent
magnets used for the motors and turbines driving the green technology
revolution. Analysts are predicting demand for magnet rare earth oxides will
grow substantially over the coming years, driven by accelerating the adoption
of green technology, pushing the overall market for Nd/Pr into deficit.

 

The Phalaborwa Rare Earths Project, located in South Africa, comprises an
Inferred Mineral Resource Estimate of 38.3Mt at 0.43% total rare earths oxides
("TREO") contained within gypsum tailings stacked in unconsolidated dumps
derived from historic phosphate hard rock mining.  High value Nd/Pr oxide
represent 29.1% of the total contained rare earth oxides, with economic
Dysprosium and Terbium oxide credits enhancing the overall value of the rare
earth basket contained in the stacks.  The rare earths are contained in
chemical form in the gypsum dumps, which is expected to deliver a higher-value
rare earth carbonate, with lower operating costs than a typical rare earth
mineral project.

 

The Company's Gakara Project in Burundi has produced one of the highest-grade
concentrates in the world (typically 54% TREO) through trial mining
operations. The Gakara basket is weighted heavily towards Nd/Pr, which account
for over approximately 19.5% of the contained TREO and 85% of the value of the
concentrate.

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