HOF Citations 2016 Comminution - Jo Pease and Bill Johnson | Page 2

COMMINUTION

in several parts of the circuit in a staged regrind and
flotation approach to achieve the high recovery
increase. After that I was CEO of Xstrata Technology
which further developed and commercialised the
technology to the industry. This included scale up to
3 MW (and design of an 8 MW mill), development of
a low cost ceramic media and integral media
addition and recovery system, and the application of
the technology – and the staged regrind and
flotation approach – in copper, nickel, platinum, iron
ore, gold, lead zinc and coal industries; and the
application of ultrafine grinding to leaching
flowsheets as well as flotation (including the Albion
process, replacing roasting at Kalgoorlie
Consolidated Gold Mines, and the Phelps Dodge
Morenci chalcopyrite leach). The rapid development
and commercialisation led to significant metallurgical
improvements in multiple commodities and
countries, and was enabling technology for many.
Once external adoption commenced, our team
achieved rapid global adoption of over 100 MW
installed power in a few years. The IsaMill, and
derivative high-speed inert stirred mills, are now a
standard industry tool, and an essential one to deal
with reducing grain size and increased impurities in
mineral deposits.”
Bill Johnson
Dr Bill Johnson led the development of the IsaMill,
and the application of ultrafine grinding and flotation
to the minerals industry. Bill was head of Minerals
Processing Research at Mount Isa Mines in the
1980s and 1990s, when he was tasked with finding
a treatment solution for the extremely fine grained
McArthur River lead-zinc-silver deposit in the
Northern Territory of Australia. This large high grade
deposit was discovered in the 1950s, but had defied
economic processing due to mineral grain size that
was below 5 microns – finer than the size many
people regard as unfloatable “slimes”. Instead, Bill
knew that fine particles with fresh surfaces were
easy to float, but that the barrier was technology to
economically grind to this size.
Tumbling ball mills with large steel balls cannot
practically grind to below 10 microns; even the
relatively new (in the 1990s). Tower mills were not
practical – their energy efficiency drops rapidly
below 20 microns. Further the large amount of steel
media (inefficiently) consumed contaminated the
surface of fine particles with iron hydroxides, making
it very difficult to get flotation selectivity and
recovery. Bill knew that if there was an answer to
economic ultrafine grinding, it would not be found in
the minerals industry. Instead, he looked in manufacturing, where he found small scale batch mills
grinding specialist (high value) products like printer
ink, paint pigments, pharmaceuticals and cocoa for
chocolate. These mills used very fine, expensive
media stirred at high speed in a small batch mill. Bill
then set him team about solving several problems to
apply this to the minerals industry:
• The mills needed to be scaled up 1 or 2 orders of
magnitude larger than the manufacturing mills

• They had to operate on large tonnages of low

value product treated continuously, not in small batches

• To operate continuously, they needed a way to
discharge fine product while still retaining the fine
(1-2 mm) media
• The media needed to be inert (not steel) to give
minerals a clean surface needed for selective fines
flotation
• The media also needed to be low cost –
manufacturing applications (with high value product)
used specialist glass media that cost over
$20,000/tonne in 1990. Bill knew the minerals
industry needed a cheaper alternative.
By working with the German manufacturer Netzsch,
Bill and his team developed the IsaMill, with the
following features:
• It used grains of smelter slag as a source of free
grinding media, stirred at high speed (up to 20 m/s).
• It retained media in the mill with a centripetal
separator at the mill discharge, which retained
coarse particles of media and ore, while passing
water and fines. An added benefit was that this
provided both grinding and classification in the
one device.
• The inert grinding environment provided fresh
clean particle surfaces that responded well to
flotation. At McArthur River, about 96% of the
particles were below 2.5 microns, and were
recovered at high grade and high recovery in
conventional flotation cells.
• The IsaMill technology was far more energy
efficient than tumbling or tower mills to grind below
20 microns, and had further significant benefits from
the improved surface chemistry and flotation.
• The mills were first installed at the Mount Isa lead
zinc concentrator, where they increased lead
performance by over 5%, and zinc performance by
over 15%.
• Once developed, the IsaMills enabled the
development of the McArthur River deposit (and
several others since).
• The IsaMills spawned a range of similar
technologies for ultrafine grinding, including the
SMD, VTX, Deswik and HIG mills.

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