HEAP LEACHING AND SX
The Olympic Dam process flowsheet includes
grinding, flotation, leaching, solvent extraction,
smelting and refining, with the concentrator
processing run-of-mine ore via bulk sulphide
flotation to produce a copper concentrate and
flotation tailings
recovered from the flotation tailings by leaching
in sulphuric acid, using sodium chlorate as an
oxidant. The uranium is recovered and
concentrated from the leach liquor using solvent
extraction, after which a uranium ore concentrate
is formed by precipitation and calcination.
The uranium, specifically, can be categorised
into three main minerals – uraninite, coffinite and
brannerite – with all three coming with different
compositions and textures, according to John
Lawson of ANSTO Minerals.
“Also, these minerals are found within diverse
ore types with varying gangue mineralogy, each
with different degrees of uranium mineral
liberation,” he wrote in the abstract for his paper,
The development of a geometallurgical uranium
leaching model as a predictive tool for leach
optimisation, presented at the ALTA 2019
conference in Perth, Australia, in May.
“This diversity means that the optimum leaching
conditions can be significantly different for ores
from different parts of the deposit,” he said.
BHP currently has a batch leach system in
place which samples the stopes scheduled for
upcoming production, allowing the leaching
process to be optimised in terms of acid
addition, oxidant addition and temperature.
This process might be accurate, but it is slow
and costly, according to Lawson.
This has led both ANSTO and the Olympic Dam
processing team to look for an alternative.
The resultant model, Lawson said, predicts the
leach response to changes in pH, oxidation-
reduction potential and temperature and, thus,
provides the required information in a “fast and
inexpensive manner”.
Lawson explained: “The model does not rely
on the measurement of uranium mineral contents
by quantitative SEM (structural equation
modelling), but defines four forms of uranium
each with different leaching behaviour.”
These are not specific to any uranium mineral;
the characteristics are derived from nearly two
thousand data points from previous laboratory
leach programs with the
proportions of these forms of
uranium in a new ore
determined from the ore’s
measured response during a
specially designed standard
leach.
He said: “This approach
provides a solution to the
problem which arises when a
particular uranium mineral
exhibits different leaching rates depending on its
degree of alteration and liberation.”
So far, validation trials have shown the
predictions are sufficiently accurate for the
model to be trialled as part of the production
planning system at Olympic Dam, with Lawson
adding: “If the model continues to provide good
outcomes, it will become the sole method for the
optimisation of leach conditions within the
geometallurgy production planning system.”
It is copper recovery and production that
Bureau Veritas has recently been helping
Olympic Dam out with.
Earlier this year, the two companies said they
had successfully completed heap leach research
and development trials, in South Australia,
confirming the viability of the technology to
extract copper from a range of Olympic Dam ores
at the mine.
The program began in 2012 and was
conducted at a purpose-built, small-scale heap
leach facility at Wingfield run by Bureau Veritas,
under direction from BHP and with support from
the South Australia Government.
BHP’s General Manager of Olympic Dam’s
Surface Processing, Chris Barnesby, said the
companies “safely and successfully” produced 19 t
of good quality copper, most of which went back
into the smelter and off to customers.
Despite the success of the project, he said the
deployment of such technology was a “matter for
future consideration”, explaining there were
many factors involved in deciding to roll out the
technology on a commercial scale.
But, as BHP said, the research and
development program had the potential to benefit
the mining industry more broadly in South
Australia, “as heap leaching has the potential to
deliver lower capital and operating costs,
increased scalability, reduced potable water use
and the ability to process lower-grade ores”.
Clint Bowker, Bureau Veritas Manager of Major
Projects, said the heap leach facility will remain
on care and maintenance mode for the future but
would be available as a resource to the mining
community for further research.
Reagent trials
In this same feature last year, we reported on the
development of BASF’s leaching aids for heap
and dump leaching systems and, since then, Jack
Bender, Global Hydrometallurgy Technology
Manager, has been at the ALTA 2019 conference
reporting on field trials of LixTRA™ at mine sites
treating copper secondary sulphide and oxide ores.
In his paper, Field results from leaching aid
trials using BASF’s LixTRA reagent, Bender said
results from these tests had exceeded
expectations with most ores having 20-35% more
copper leached at a given time.
The two studies Bender homed in on during
the conference involved, in the first case, the
customer performing 1 m column, 6 m column
and mini heap leach (1,000 t) trials. The second
case study saw the customer perform 4 m
column trials.
In the first case study – taking place in Asia
Pacific – a series of eight 1 m column tests
containing some 100 kg of ore were conducted.
The columns were operated for 176 days, but,
during the run, the feed to the columns was
altered resulting in the columns no longer being
comparable.
Two 6 m columns were run at the same time as
this, with one used as a control and one dosed
with 25 ppm LixTRA leaching aid.
Leaching of these columns was performed
over around 170 days and, in that time, the
leaching maintained around a 50% increase in
copper leached over the control column. Residue
analysis indicated much higher leaching rates of
the larger particles for the LixTRA treated ore
compared with the control, Bender noted.
On a larger 1,000 t mini leach trial, the LixTRA
results were equally impressive.
Containing 400 m³ of raffinate, heaps one and
two were composed of fresh ore where heap one
had no leaching aid and heap two had LixTRA at
30 ppm concentration. The latter had a
substantial increase in copper leached with
around 33% more than the control at any one
time over the testing period.
It was a similar result with the second
customer – also in Asia Pacific – where the
leaching aid treated columns leached 35% more
copper than the control columns.
These trials clearly show LixTRA could have a
place in future leaching operations, but BASF
says it will have to work with clients to examine
where the optimal reagent addition point is
within each company’s processing operation.
“While it might seem obvious that addition
into the raffinate lines is the best option for
controlling the concentration of the reagents to
the heaps, it is often not possible,” Bender said.
The more raffinate lines in place from the
raffinate pond, the higher the number of
pumping stations and the more complicated the
addition of the reagent is, he explained.
Bender, coming to his conclusion, had this to
say about the LixTRA trials: “Large-scale testing
NOVEMBER 2019 | International Mining 41