GOLD EXTRACTION
many factors including slurry temperature,
solution and slurry chemistry, slurry viscosity,
agitator type, dimensions and power, oxygen
bubble residence time, oxygen purity, tank
geometry and oxygen injection technique.
Oxygen generation represents an important
operating cost for the Albion Process. Pivotal to
the process operating economically at
atmospheric pressure is the capability to
efficiently transfer oxygen while using as much
oxygen injected to the process as possible. To
respond to this Glencore Technology developed
the HyperSparge™ supersonic gas injector.
The paper Oxygen mass transfer in the Albion
Process: from the laboratory to the plant by
Glencore Technology’s Paul Voigt, Daniel Mallah
and Mike Hourn, (Proceedings of EMC 2017)
compares the HyperSparge against other
sparging techniques to quantify the benefits of
oxygen injection via a supersonic gas jet on scale
up of the oxygen mass transfer system. It then
examines plant survey data from the GPM project
to demonstrate the very high oxygen utilisation
that can be achieved with a correctly designed
oxygen mass transfer system.
Its specific purpose is to float coarse particles
containing only small amounts of exposed
hydrophobic minerals. Over the last decade, this
technology has been successfully applied to
industrial minerals with several full-scale units
installed to recover particles up to and exceeding
3,000 μm in diameter.
More recently, sulphide-based test work has
shown that this novel device is also capable of
recovering metalliferous values at a grind size
that is much coarser than currently used in
industrial concentrators, according to J D Miller et
al in the IMPC paper Significance of Exposed
Grain Surface Area in Coarse Particle Flotation of
Low-Grade Gold Ore with the HydroFloat™
Technology, Quebec City, September 2016. Mike
Mankosa, Eriez Executive Vice President of Global
Technology, was a co-author.
“In the current study, high resolution X-ray
microtomography (HRXMT) was used to
experimentally compare the degree of exposed
grain surface area necessary to recover coarse
particles using the HydroFloat technology to that
attainable using a traditional mechanical
flotation cell. The data indicate that exposed
GPM gold Albion Process plant design criteria
Parameter
Throughput
S 2- concentration
S 2- oxidation
Oxygen Utilisation
Required k L a
CIL Gold recovery
Units
t/h Design
13.1 Actual
14.5
%
%
%
m.s -1
% 17.6
76
80
0.12
90 10.0 - 20.0
70 - 82
90
0.14
95
The authors conclude that: “Oxygen injection
using convergent-divergent nozzles generate
superior thrust and oxygen mass transfer
compared to other gas injection techniques.
Power delivered to the system is more efficient
through gas injection rather than mechanical
agitation. The HyperSparge is a development of
the convergent-divergent nozzle and offers
additional advantages over other sparging
technologies contributing to a safer work
environment, maximising process run-time and
optimising energy input through the agitator. GT
successfully scaled up the oxygen mass transfer
system from the laboratory to the industrial scale
at the GPM Albion Process plant which achieves
greater than design performance in terms of
oxygen mass transfer and oxygen utilisation.”
And optimising flotation
Conventional flotation machines are typically
limited to a particle top size of 150-200 μm due
to inherent constraints created by the pulp and
froth phases. To overcome these limitations, a
novel fluidised-bed flotation system has been
developed by Eriez – the HydroFloat™ Separator.
40 International Mining | AUGUST 2017
grain surface area is a critical factor for coarse
particle flotation. For the gold-bearing sulphide
ore examined in this study, the HRXMT data
suggest that near complete recoveries of coarse
(850×500 nanometre) multiphase particles
containing as little as 1% exposed grain surface
area were realistically attainable using
HydroFloat. As such, this new technology may
offer a unique opportunity for increasing
concentrator capacity by increasing the primary
grind size needed for rougher/scavenger
separations.”
The HydroFloat Separator is an aerated
fluidised-bed (or teeter-bed) separator. The
synergistic effect of combining flotation with
gravity concentration results in an outcome that
cannot be achieved by either approach alone,
says Eriez.
“Air bubbles are dispersed by the fluidisation
system, percolate through the hindered-setting
zone and attach to the hydrophobic component
altering its density and rendering it sufficiently
buoyant to float and be recovered. The use of the
dense phase, fluidised bed eliminates axial
mixing, increases coarse particle residence time
How the Eriez HydroFloat technology works
and improves the flotation rate through enhanced
bubble-particle interactions.” As a result, the rate
of recovery is high for both fully-liberated and
semi-liberated particles.
“HydroFloat separators improve coarse particle
recovery through:
n Increased bubble/particle collision rates
n Increased bubble/particle sliding time
n Increased residence time
n Decreased mixing
n Decreased turbulence and detachment
n Decreased buoyancy restrictions.
As we know, froth flotation selectively
separates hydrophobic materials from
hydrophilic materials. Air bubbles can only stick
to the desired mineral particles if they can
displace water from the mineral surface, and can
only continue to support the mineral particles at
the surface if they can form a stable froth
achieved by using flotation reagents.”
“As the characteristics of froth can vary from
day to day, a thorough understanding of froth
transfer applications is critical when designing
and selecting froth pumps. Insufficient froth
volume factor (FVF) knowledge can often
contribute to incorrect froth pump selections and
hopper designs,” states Warren Taylor, Product
Specialist at Weir Minerals.
Pumping mineral froths using standard slurry
pumps often leads to problems for operators,
especially when treating mixed ores.
Furthermore, froths can easily vary from brittle
froth – generally large bubbles that are easily
broken down, to very tenacious froth – generally
fine, tightly bound air bubbles that remain in a
froth state for many hours.
In high FVF conditions such as medium to
tenacious froths, air separation from the liquid
contributes to air-binding within the eye of the
impeller. This may create the expectation of
cavitation, but rather than the collapse of vapour
pockets, the entrained air bubbles rapidly expand
in areas of low pressure w ithin the pump impeller