Cradle to grave
n an effort to improve leach kinetics
and recoveries of primary copper
concentrates, FLSmidth has developed
the rapid oxidative leach (ROL) process
which, the company says, is capable of
attaining over 97% copper dissolution
in less than six hours under atmospheric
conditions.
This advance is particularly significant as
the life cycle of many copper ore bodies sees
the mineralogy transitioning from oxides
to secondary and primary sulphides, which
have decreasing ore grades and are more
difficult to process. These operations need
cost-efficient leach processes to maintain
their copper production, and also to take
advantage of new ore bodies, especially
those containing arsenic-rich minerals
like enargite.
In the FLSmidth ROL process, a
simple way has been found to leach copper
sulphide concentrates, with chalcopyrite as
the predominant copper-bearing mineral, at
85–95°C and under atmospheric pressure.
At a pilot plant facility at FLSmidth’s
technology centre in Salt Lake City, US,
ROL needs six hours to
leach copper
I
The FLSmidth ROL process technology is faster,
simpler, and improves the sustainability of
existing mines.
over 250 batch leach tests have been
completed in 10-litre and 100-litre reactors,
using copper concentrates from over 30
different sources.
The efficiency of the FLSmidth ROL
process is based on a mechano-chemical
approach that takes advantage of transitory
surface defect structures generated during
particle fracture. A patented activation
process is employed that chemically alters
the mineral lattice structure, promoting
rapid dissolution of the metals into solution.
Most of FLSmidth’s test work to date has
been on primary chalcopyrite concentrates,
although there has been some focus on
enargite and arsenopyrite concentrates.
YK chills at
Impala
T
wo York YK centrifugal chillers have
been installed at Impala Platinum’s
(Implats’) No. 16 Shaft close to
Rustenburg in the North West Province. The
chillers supplied by Johnson Controls is for the
planned second-phase expansion of cooling
capacity for No. 16 Shaft as it heads toward a
depth of 1 650m.
The surface air cooling plant for the No.
16 Shaft was designed and established in
2008 by mine ventilation and refrigeration
specialists Bluhm Burton Engineering (BBE)
Consulting, who were appointed by Implats to
provide a turnkey solution that included the
design, construction, and commissioning of
the overall refrigeration plant and air-cooling
[44] MINING MIRROR FEBRUARY 2019
system. According to Richard Gundersen of
BBE, the cooling plant is designed to facilitate
six chillers in total as production builds up
and demand for cooling increases. The first
two chillers, also York machines, were installed
almost 10 years ago; Implats is now entering the
second phase of the cooling expansion.
Russell Hattingh of Johnson Controls says
that the two 7 MWR York YK chillers are
newer models of the two York machines initially
installed. “They deliver improved performance
and offer a wider operating envelope, while still
meeting the Impala standard,” he says.
The initial cooling solution — including the
first two refrigeration machines, the initial two
condenser cooling towers, the complete spray
chamber shells, and spray piping for the first
phase of bulk air cooling — was constructed in
2008. For the second phase, two new machines
have been installed and two new cooling towers
have been constructed. The new chillers will add
about 14 MWR of cooling.
Gundersen says: “We need air cooled to
approximately 13°C on the surface so that
The FLSmidth ROL pilot plant installed in Utah, US.
Johnson Controls has supplied the second round
of York chillers at Implats’ No. 16 Shaft.
the working areas, at a depth of 1 650m, are
below the legal working limit. The virgin rock
temperatures are 55°C at these depths, so
cooling is vital for production. Water is chilled
by the refrigeration machines and sprayed into
the horizontal spray chambers. Axial flow fans
force ambient air through the spray chambers
and into the barrel of the main (downcast)
shaft to reach the underground workings.
With the added cooling capacity, Implats
will meet the environmental needs of the
workforce.”
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