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