Microwave Assisted Comminution of Rare Earth Ore Brendan Gribbons; Prof. Kristian Waters; Adam Jordens
McGill University – Department of Mining and Materials Engineering
Experimental Procedure
Motivation
Introduction
Conclusions and Acknowledgements
Microwave Heating
• A rare earth mineral is a mineral containing one or more rare earth elements (the fifteen lanthanides, along with scandium and yttrium).
• Rare earth minerals are very important in a number of commercial applications. • China produces 95% of the world’s rare earth minerals and has restricted exports of these
minerals.1
• Reserves of rare earth minerals are abundant, however it is difficult to find reserves with sufficient concentrations for mining to be profitable. 2
• The comminution process is extremely inefficient and expensive, accounting for 3% of the world’s energy consumption.3
• Microwaving ore prior to the comminution process has been shown to reduce energy consumption and could make extraction of less concentrated deposits more economically viable.2
Untreated Ore Microwaveable Crucibles 3000W Microwave Dry Screen
• Microwaves are radio waves that heat materials through dielectric heating.
• Valuable minerals are typically dielectrics and gangue minerals are typically transparent to microwaves2
• When exposed to microwaves, the dipoles within a dielectric material will rotate with the alternating field.2
• Resulting internal friction will cause differential heating in the ore, causing rock failure through micro-fracture formation.2
• As different minerals respond at different rates to temperature changes (rate of expansion or contraction), differential stresses are created at the grain boundaries.2
• Quenching of ore causes thermal shock, further weakening the mineral lattice.2
Results
• Representative 500g samples were microwaved at both 800W and 3000W. 800W: 2:00 min, 3:00 min, 4:00 min. 3000W: 30s, 60s, 90s
• Samples were quenched and wet ground for 78 minutes in a ball mill • A size analysis of the sample was done to determine the 80% passing
size. • Repeated 5 times at each power level and time interval. • Theoretical bond work index calculated and compared to bond work
index of feed. • No reduction in the bond work index was observed
Theoretical Bond Work Index2
• P and F refers to the product and feed 80% passing sizes). R: Untreated, T: treated
Avalon’s Thor Lake Ore Mineralogy Primary rare earth-bearing minerals : Zircon and Bastäsite
Thermally Assisted Liberation
Ball Mill Wet Screen 1. Willie D. Jones. (2010) “The Rare-Earth-Metal Bottleneck” http://spectrum.ieee.org/consumer-electronics/gadgets/the-rareearthmetal-bottleneck 2. Vorster, W. (2001) “The Effect of Microwave Radiation on Mineral Processing”, PhD Thesis The University of Birmingham (UK). 3. S.W. Kingman. (2004) “Recent Developments in Microwave Assisted Comminution”.
65
75
85
95
10 100 1000
Size (micron)
Size Analysis - Rare Earth - 3000W
Feed
30s
60s
90s
Cu
mu
lati
ve P
assi
ng
(%)
65
75
85
95
10 100 1000
Size (micron)
Size Analysis - Rare Earth - 800W
Feed
2:00
3:00
4:00
Cu
mu
lati
ve P
assi
ng
(%)
94
96
98
100
102
104
106
Feed 30s 60s 90s
Theoretical Bond Work Index - 3000W
Exposure Time (seconds)
Theo
reti
cal P
erce
nta
ge o
f B
on
d W
ork
Ind
ex o
f Fe
ed (
%)
94
96
98
100
102
104
106
Feed 2:00 3:00 4:00
Theoretical Bond Work Index - 800W
Exposure Time (minutes)
Theo
reti
cal P
erce
nta
ge o
f B
on
d W
ork
Ind
ex o
f Fe
ed (
%)
• Microwave treatment of the Avalon Thor Lake Ore had no positive effect on the bond work index and therefore treatment on an industrial scale would not improve efficiency
Thank you to • The McGill Summer Undergraduate Research in Engineering Program • McGill Mineral Processing Group of the Department of Mining and Materials Engineering • Pejman Nekoovaght for his assistance with the microwave