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Mineral Engineering Technical Services
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A division of Midas Engineering Group
Technical Options for Producing Premium Quality Zircon
j ENVIRONMENTALPROCESSINGDESIGN&VERIFICATIONPRODUCTINNOVATIONPROJECTMANAGEMENTOPERATIONSTRAININGSKILLSHIRE
• DISCLAIMERWith respect to all the information contained herein, neither Mineral Engineering Technical Services Pty
Ltd, nor any officer, servant, employee, agent or consultant thereof make any representations or give
any warranties, expressed or implied, as to the accuracy, reliability or completeness of the information
contained herein, including but not limited to opinions, information or advice which may be provided to
users of the document. No responsibility is accepted to users of this document for any consequence of
relying on the contents hereof.
• COPYRIGHT ©Passing of this document to a third party, duplication or re-use of this document, in whole or part,
electronically or otherwise, is not permitted without the expressed written consent of Mineral
Engineering Technical Services Pty Ltd.
• ACKNOWLEDGEMENTSThis document is a dynamic record of the knowledge and experience of personnel at Mineral
Engineering Technical Services. As such it has been built upon over the years and is a collaborative
effort by all those involved. We are thankful for the material supplied by and referenced from various
equipment manufacturers, vendors, industry research and project partners.
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Key Attributes
• Working globally since 1988
• Dynamic and innovative niche consultancy
• Dedicated team providing customised service
• Specialist in mineral processing & engineering projects
• Unique solution finder
Pragmatic, efficient, complete engineering through
quality, personalised & exceptional service delivery
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The Midas Family
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Introduction
• Zircon is a valuable by-product from mineral sands operations
• The demand for zircon is growing as evidenced by increasing prices.
• Natural zircon contains uranium and thorium in varying quantities -
problematic from an environmental perspective
• The industry accepted standard is U+Th <500 ppm
• High brightness is a significant marketing advantage
• Removal of uranium and thorium achieves the production of a
premium product
• Sell a zircon sand to the ceramic market where “clean and green” is
highly desirable
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Mineral Sands - Zircon By-Product
Product
For Sale
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Zircon Uses
• Pure zircon is ZrSiO4
• Usually impurities Zr,U, Fe,Th,TiO2,
Al2O3, SiO4
• Very inert and refractory
• Opacifier in ceramics, zircon flour,
zircon wash, fired in a kiln
• Kitchen crockery
• Floor tiles
• Minor zircon chemicals
• Minor zircon metal
Zircon concentrate
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Global Production
• Recovered as a by-product from
mineral sands
• Very high unit value $/t
• Very few producers - tight supply
market
• Production, prices and demand
have been rising
• Company’s like Iluka and Rio are
brilliant at marketing and can
effect market prices for zircon
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Global Zircon Production
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Global Inventory Overhangs the Market
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Zircon Price & Market
Stability returning after extreme highs
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Uranium & Thorium Radioactivity
• Contains from 10 ppm up to 1% uranium & thorium
− Highly variable depending on source of zircon
− Cation substitution at the time of formation in original host rock
• Market requirements of <500 ppm total uranium & thorium
• Transport limits of 50 Bq/gram and if exceeded radioactive stickers are
required
• The aim is to have the zircon classed as non radioactive to minimise
all the issues that arrive from a radioactive classification
• The uranium and thorium recovered can be precipitated and sold to a
nuclear authority so there is no environmental issue with waste storage
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Are Your Glazes Food Safe?
• Live in a no fault generation
• US FDA (Food & Drug Administration) test ceramics for leaching of
metals
• Zircon flour or wash is the base of ceramic glazes
• Reducing radioactivity and impurities is market desirable-premium
product
• If fired at the correct temperature, the risks should be very low
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• An imaging technique using backscattered electrons to identify mineral
phases in a ore / rock sample
− Need to be coupled with energy dispersive spectrometry (EDS) for
definitive identification
• Image contrast used to identify the ore minerals and their associations
with other minerals
− Higher the atomic number, the brighter the image
Silver mineral acanthite
Ag2S (bright) in a copper
mineral malachite
Cu2CO3(OH)2 (dark)
Back-scatttered electron
image (BS)
Scanning Electron Microscopy
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QEMSCAN – A Technology for Rapid
Mineralogical Analysis
• Third generation of automated mineral analysis
system began with the QEM*SEM and CSIRO
• The system consists of:
− Scanning electron microscope
− Four X-ray detectors
− Software package based on procedures
developed by CSIRO
• Capable of identifying ore- and rock-forming
minerals in milliseconds
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Mineralogy & SEM
• (Zr,Hf,U,Th,Y)SiO4
• The uranium and thorium based on
SEM work is associated around the
surface of the zircon grains or in micro
cracks
• SEM is brilliant at detecting the
radioactivity
• The zircon is inert but has some
porosity
• Leaching removes the uranium and
thorium to varying extents
Zircon at 5 m
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Historical Work
• Westralian Sands 1992
• Rio Tinto WIM project studies and testwork
• Hydrometallurgical studies by Hart, 1993; Hawkins & Aral, 1995 –
CSIRO
• Patent search reveals numerous patents
• Hot acid leaching more effective than ambient leaching
• Zircon inert – small losses
• Mineralogical differences (porosity, impurities, age) result in different
efficiencies
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Process Review
• Various patented processes are referred to in the public domain
− CSIRO pure zircon process
− Pressure alkaline leaching
− Acid leaching & hot acid leaching
− PlaTCOM process
− Alkane process-Dubbo Zirconia process
− METS Engineering “Zirclean” process
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CSIRO Pure Process
• CSIRO has developed a process which reduces the
radiation level of zircons by using a heat process
followed by leaching to extract the radio nuclides.
• The stages involved in the Pure Zircon Process are:
− Grinding the sample to achieve a particle size of 15-20 m
− Calcining the sample with a colemanite mineral at 1200°C
for 4 hours
− 85% zircon + 15% colemanite by mass
− Leaching the calcine with a dilute acid solution
− Costs are high - no commercial plants
The new process
for treating zircon
reduces radiation
levels and removes
impurities.
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CSIRO Pure Process Flowsheet
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Pressure Alkaline leaching
• Pyrometallurgical methods include fusion with caustic soda and the
formation of acid soluble zirconate
• Followed by pressure leaching
• Time, temperature, grind size and caustic strength lead to the
conclusion it was chemically controlled
• No plants – probably not commercial and product not suitable for
ceramics industry
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Acid & Hot Acid Leaching
• Lots of work done in this area
• Heat pre-treatment
• Cold and hot acid leaching
• Nitric, sulphuric and hydrochloric acid
• Variable efficiency and practicality
• Materials of construction
• Acid recovery is an environmental issue
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Issues With Acid Slurry Leaching
• Acid cost and recovery
• Temperature limitations for each acid
• Bonded silicon carbide vessels for leaching – highly corrosive
• w/w % solids/acid limitations
• Bench scale ok but continuous piloting required
• For projects we have looked at, the handling of the acid and disposal
of uranium became significant issues
− Waste stream
− Neutralisation
− Handling of uranium
− Filtration difficulties
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Typical Feed & Leached Product
Results
ZrO2
%
Fe2O3
%
TiO2
%
Al2O3
%
SiO2
%
U
ppm
Th
ppm
U+Th
ppm
Feed 64.7 0.23 3.91 0.95 29.2 990 650 1640
Product 64.0 0.02 0.48 0.21 34.2 341 110 451
• U+Th below 500 ppm
• High recovery of zircon
• Grinding not required
• Premium brightness – removal of iron, alumina and titania
• Acid and conditions not quoted for confidentiality
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PlaTCOM Process
• A patented Malaysian process for removing radioactive elements from
zircon
• It reports minimal cost in removing radioactivity
• Does not involve grinding
• It suggests acid leaching is not cost effective
• Do not disclose how they process the zircon
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Alkane-Dubbo Zirconia Process
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Product Value Enhancements
• Continuing Product Development for Increased Return
• Rare Earths:
− MOU with Shin-Etsu Chemical to produce suite of separated rare earth oxides
− Sale of products to others excess to Shin-Etsu’s requirements
− Further work to improve recoveries proceeding at ANSTO
• Niobium:
− Treibacher JV to produce FeNb product for direct sale to end users
• Zirconium:
− Zr development to produce value added zirconium products of variable particle size
and quality for different applications: Production of yttria - stabilised zirconia
microsphere grinding media
• Production of PZT –piezoelectric lead zirconate titanate
• Ceramic colours, eg. yellow using praseodymium
• Glass and steel making refractories
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METS Engineering Zirclean Process
• Low CAPEX
• Low OPEX - $A100/t for 70,000 tpa plant. No grinding required as for
the CSIRO process.
• 95% zircon mass recovery – continuous not batch
• Reduction of U+Th<500 ppm
• Very clean zircon – high brightness
• No exotic materials of construction
• Atmospheric leach conditions
• Minimal reagent use
• Process is Proprietary knowledge
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ZrO2
%
HfO2
%
Zr+Hf
%
SiO2
%
Al2O3
%
Fe2O3
%
TiO2
%
U
ppm
Th
ppm
U+Th
ppm
Feed 64.48 1.42 65.90 31.97 0.13 0.08 0.99 446.3 375.6 821.9
Product 64.09 1.39 65.49 33.79 0.06 0.02 0.14 347.5 145.3 492.8
• Mass recovery 92%
• High brightness
METS Zirclean Results
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Zircon Leaching Batch Tests
• Batch tests are very good at achieving preliminary tests
• Optimisation of reagents and temperature is more time consuming
• Test parameters:
− Acid type
− Concentration
− Temperature
− Residence Time
− Leach density
− Effect grind size
− Product quality (brightness, U+Th)
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Zircon Leach Pilot Plant
• Scale up is an issue – what’s acceptable?
• Recycle streams
• How long to run?
• Engineering and sampling data generation
• Significant cost but provides confidence in the process
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CAPEX & OPEX Zircon Leach Plants
• CAPEX
− Tonnages are small
− Complexity can increase this significantly
− CAPEX similar to a small gold plant
− Country location can change this significantly (Malaysia vs Australia)
− Materials of construction – bonded silicon carbide expensive
− Environmental regulations
− OH&S impacts
• OPEX
− OPEX $/t high due to low throughput
− Assigned value for uranium?
− Will the market par for the premium?
− Possible OK during high zircon prices
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Zircon Leach Full Scale Plant
• Permitting & Licence
• Process Flowsheet
• Plant Layout
• Process Design
• P&ID’s
• Equipment List
• Mass Balance
• Water Balance
• Process Control
• OH&S
• Safety
• Environmental
• Project Implementation
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Zircon Leach Process Risks
• Never been done before at commercial scale
• Product acceptance
• Long term zircon price
• Variable geometallurgy
• Engineering & Scale up from bench scale
• Corrosion & materials of construction
• OH&S issues with radioactivity
• Social compliance and acceptance
Risk Assessment Tool
CONSEQUENCE
LIKELIHOOD INSIGNIFICANT MINOR MODERATE MAJOR CATASTR
OPHIC
ALMOST
CERTAIN
High Risk
15
High Risk
10
Extreme
Risk
6
Extreme Risk
3
Extreme
Risk
1
LIKELY Moderate Risk
19
High Risk
14
High Risk
9
Extreme Risk
5
Extreme
Risk
2
POSSIBLE Low Risk
22
Moderate
Risk
18
High Risk
13
Extreme Risk
8
Extreme
Risk
4
UNLIKELY Low Risk
24
Low Risk
21
Moderate
Risk
17
High Risk
12
Extreme
Risk
7
RARE Low Risk
25
Low Risk
23
Moderate
Risk
20
High Risk
16
High Risk
11
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Zircon Leach Final Product Brightness
• Premium product - excellent
market acceptance
• High brightness
• U+Th<500 ppm
• Other contaminants - TiO2
low
Leached (1) RMB Tiwest Iluka
Leached (2) DMS Mozambique Sierra Leone
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More Zircon Samples
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Conclusions
• Specific proprietary technical information has been intentionally withheld because
of confidentiality
• A number of process routes are available as listed in the public domain literature
• Mineralogical differences result in different efficiencies of removal of U+Th
• Project development will take several years from benchscale to production plant
• No commercial plants have been built at this point in time - this could change in
the next couple of years
• Lack of transparency between producers because competitive market is an issue
in terms of who is doing what - very secretive industry, industrial minerals,
marketing is the key
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Conclusions
• Growing market in China for ceramics – urbanisation and higher
standard of living
• METS Engineering has developed a unique processing procedure that
has superior to all other options
• Premium products are more desirable
− Ceramic glazes brightness is highly desirable
− Competitive marketing
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References
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Additional References
1. Yusoff M.S.2002 . Uranium & thorium Leaching of Malaysian Zircon at
Various Heat Treatment Temperatures.
2. Eyal Y. and Olander d.R. 1990. Leaching of uranium & Thorium from
Monazite: Initial leaching, Geomechanica Acta. 54: 1867-1877.
3. Ashraf M. Kinetics of Alkaline Pressure Leaching of Mechanically
Modified zircon Concentrate. 2006.
4. Sto, K. Sigra Jr. Basei, M.A.S., Nutman, A P. and Sprosser, W. Leaching
techniques and Partial Digestion using Microwave Oven: Treatment
procedures for U-Pb Dating of Metamitic and Overgrown Zircon. South
American symposium on Isotope Geology
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Acknowledgements
• Thanks to Informa Mineral Sands 2017 for the opportunity
• Thanks to Mineral Sands companies for permission to publish
• Thanks also to all colleagues, laboratory staff and other consultants for
their help and contribution
• Thanks to vendors for the photos
• Thanks to METS Engineering for permission to publish