RNS Number : 9455A
Rainbow Rare Earths Limited
08 February 2022
8 February 2022
Rainbow Rare Earths Limited
("Rainbow" or "the Company")
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
The results of the test work to date are set out in a technical
report accessible on the Company's website at
text from which is included in Appendix A. The key findings include
-- 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
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
For further information, please contact:
Rainbow Rare Earths George Bennett
Ltd Company Pete Gardner +27 82 652 8526
SP Angel Corporate Ewan Leggat
Finance LLP Broker Charlie Bouverat +44 (0) 20 3470 0470
Tavistock Communications PR/IR Charles Vivian +44 (0) 20 7920 3150
Limited Tara Vivian-Neal email@example.com
Appendix A: Technical Report on the Phalaborwa Processing Flow
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
-- The gamma results of the phosphogypsum sample confirm a very
low uranium content of 1.7ppm that is not in secular
-- The thorium content also very low at 48ppm and in secular
equilibrium, probably associated with the detected monazite
-- 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
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
-- Moderately elevated temperatures do not impact on the total
extraction extent but significantly improve the dissolution
-- Increased slurry density in the leach impacts marginally on
the extraction of rare earths due to suspected solubility
-- 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
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
-- 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
-- Significant fluoride levels in the leach due to the targeted
dissolution of the rare earth rich calcium aluminium fluoride
-- 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
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
-- 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
-- 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
-- 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
K-Tech also considered various alternative options that can
support the front-end leach circuit pending further test work
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
-- 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
-- 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
-- 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
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
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
Continuous ion chromatography Rare earth separation as individual
(CIC) groups or elements in continuous
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
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
ppm Parts per million
Pregnant Leach Solution (PLS) A solution that contains the
extracted valuable metal
Water Neutralisation Water treatment employing lime
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
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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February 08, 2022 01:59 ET (06:59 GMT)
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