REPROCESSING AND TAILINGS REDUCTION
It is the junior and mid-tier miners – not the Tier
1 outfits – able to more easily incorporate the new
technologies CDE and others offer to carry out
such processing, according to McCormick.
“Contrary to the assumption, I think the
transition to dry stacked/filtered tailings is more
accessible to junior and mid-tier miners who have
increased flexibility to incorporate new
technologies into their plant design,” she said.
“For Tier 1 miners, the scale of dewatering existing
and historical dams presents significant
commercial risk due to the expense involved.”
The company has a few case studies to back
this opinion up.
Zero-waste initiative
In working with junior miners from prefeasibility
through to development stage, CDE offers cost-
effective modular equipment design to achieve
minimal tailings and minimise environmental
footprint, while also opening new revenue streams
for customers, McCormick explained.
One of the company’s differentiators is its focus
on “life-cycle economics”, with CDE working to
identify markets for by-products of mining as part
of its zero-waste initiative.
This initiative sees the company look at the
entire supply chain in which its customers operate.
In South Africa, for example, CDE has a
customer purchasing historic mine waste dump
material that it processes through one of its plants
to produce a fine sand gold-bearing concentrate
that is sold back to the mine for reprocessing.
Simultaneously, the plant produces one sand
and two aggregate materials which are sold to the
construction industry, while the land where the
dumps were once situated is repurposed for
development.
In Latin America, the company is also working
on projects such as AuVert Mining’s asset in
Colombia. Here, AuVert’s technology is being
combined with CDE’s experience in dewatering
and tailings management to extract the remaining
precious metals existing in the ground, while
removing up to 93% of residual mercury which has
to date prevented this land from being used by the
local population.
CDE’s plant designs might also factor in
supplying ‘by-products’ to other industries.
“At CDE we try to identify alternative markets
for the by-products, such as creating sand and
aggregates suitable for construction, as well as
land rehabilitation and paste and backfill,”
McCormick said. “For us, it is important that we
strive towards a zero-waste goal.”
The company’s largest reprocessing project to
date has come in Australia and involved “a first-of-
kind opportunity” to design a turnkey solution for
the upgrading of legacy iron ore waste to a high-
value product, she said.
At a combined throughput of 950 t/h, the
12 International Mining | MAY 2020
SIMEC installation is the company’s largest
processing facility for low-grade beneficiation.
The project will see almost 18 Mt of low grade,
extremely abrasive hematite iron ore turned into a
saleable product for SIMEC in South Australia.
The two plants on site remove silica and
alumina from the feed material, gravity separating
low-grade from high-grade ore in the process.
Silica levels, which range from 14% to 20% in the
barren ore, have reduced to 6.4% after processing;
while alumina levels, which range from 5.9% to
8.8%, have reduced to 2.8% after processing.
The iron ore wash plant also removes clays from
the feed material, with the combined effect
moving the iron content from between 43.4-52.7%
Fe in the feed to 63-64% Fe at a yield of 50%,
according to McCormick.
The plant consists of an initial washing and
screening stage using CDE’s M-Series™ modular
range equipment followed by scrubbing of the
coarser fraction by RotoMax™ log washers. Dry
screening using CDE’s patented Infinity Screen™
range follows prior to gravity beneficiation in the
coarse and fine jigs, and dewatering and
conveying to stockpiles via more than 20 CDE
conveyors across the two processing plants.
The finer fraction is further washed and
separated prior to being de-slimed in cyclones at
200 mesh and gravity beneficiated through a
series of spiral banks. Three of CDE’s A1500
AquaCycle™ thickeners are deployed across the
two plants to form a concentrated tailings sludge
and recycle process water, the company noted.
McCormick said these projects have sparked
the interest of many similar providers on a global
basis who are increasingly recognising the value
retained in legacy waste.
A fitting solution
While all in the industry would agree that
providing an effective and sustainable tailings
management and dewatering solution is easier on
greenfield sites, there are few opportunities such
as this on the market.
As a result, CDE has designed its EvoWash™
and AquaCycle™ combination to slot into a wet
processing circuit for tailings dewatering, while its
Plate Press filtration system, which has been in
demand as of late, is able to be incorporated into
the mix and achieve higher levels of water
recovery and dry stacking.
Adam Holland, Head of Mining at CDE, walked
IM through the offering.
“The EvoWash is a compact, modular washing
system which integrates a high-frequency
dewatering screen, sump and hydrocyclones to
provide unrivalled control of silt cut points and
eliminate the loss of quality coarser articles to the
fines dewatering circuit,” he said.
The system effectively deslimes and dewaters
the tailings, while simultaneously creating
valuable materials for the construction market and
incorporates patented Infinity Screen technology
for optimal dewatering results, Holland added.
The CDE AquaCycle water management system
provides the required high rate thickening to
recover up to 90% of the process water for re-
circulation around the washing plant while
thickening a tailings sludge.
“The AquaCycle M offers a fully modular skid
mounted option for customers who want to avoid
civils work,” Holland added.
CDE’s Plate Press filtration system is designed
and built to deliver maximum plant efficiency,
eliminating the need for tailings dams, or settling
ponds and significantly reducing waste handling,
according to Holland. “The market-leading
automated cloth wash system delivers maximum
dewatering performance, recycling up to 95%
process water,” he said.
The company is also working on an “Ultra-fines
solution” to provide a modular tailings dewatering
and beneficiation unit that will accept a dredge or
dry feed to recover and upgrade the target
mineral, while retaining the by-products for use in
other applications, according to Holland.
“The vision is that of a compact footprint
system that can be easily relocated as each area
of a tailings deposit is reprocessed,” he said,
adding that a combination of this solution with the
Plate Press filtration platform, using both
membrane squeezing and cake blowing, could
achieve moisture contents as low as 8-9%.
Such a solution appears to be aimed at the
junior and mid-tier market McCormick previously
spoke of, allowing for progressive rehabilitation/
reprocessing at lower throughputs and cost.
Holland said the company is working with
strategic partners, customers and academic
institutions to progress the Ultra-fines solution
during 2020.
Conceptual thinking
Speaking of reducing the moisture content of
tailings, the Metso VPX filter made a big splash
when it was unveiled to the mining world last year.
Not only did the filter provide the pressure,
throughput capacity and electromechanical
operation miners had been calling for, it also
helped form Metso’s tailings management concept.
This concept, which envisages filtered tailings
as the most promising and sustainable way
forward, addresses not only the demand for
dewatering fresh tailings, but also the ability for
miners to reprocess existing dams, turning ‘waste
into value’. On the latter, the company has
conducted studies that showed processing one
unit of tailings could be up to three times more
cost-effective than processing virgin material.
The tailings management concept is hitting
home in South America where Metso recently set
up its pilot VPX unit, according to Rodrigo