PROCESS DESIGN
continuous froth phase minimises drop back that
can occur at the pulp/froth interface.
The device consists of a circular tank subdivided
into an upper freeboard compartment, a middle
separation chamber and a lower dewatering cone.
Similar to a typical hindered-bed separator, feed
solids are introduced just above the middle
separation chamber and are permitted to settle
against an upward rising current of water or other
fluidising medium. The upward flow creates a
fluidised “teeter bed” of suspended particles with
high interstitial liquid velocities that resist the
pene tration of slow settling particles. Gas is then
introduced and dispersed along with frother into the
fluidisation network through an externally located
high-shear sparging system. As the air bubbles rise
through the teeter bed, they become attached to
hydrophobic particles, thereby reducing their effective
density and simultaneously increasing their buoyancy.
The particles may be naturally hydrophobic or made
hydrophobic through the addition of flotation
collectors. The lighter bubble-particle aggregates rise
to the top of the denser teeter bed where they
accumulate due to their lower density.
Particles having minimal exposure of
hydrophobic surface with bubble attachment are
very effectively prevented from being lost to
tailings by the action of the teeter bed. The
accumulated aggregates lift off the teeter-bed
interface and are carried upward through the
freeboard compartment due to increased
buoyancy created by the initial and, potentially,
subsequent bubble attachment. The bubble-
particle aggregates are then rapidly carried by
the rising flow of fluidisation water upward
through the freeboard compartment where they
overflow into a collection launder. Due to the
constant overflow of fluidisation water, only a
thin froth layer forms at the top of the flotation
pulp. Hydrophilic particles that do not attach to
the air bubbles (rock) continue to move down
through the teeter bed, settle into the dewatering
cone, and are discharged through the underflow
nozzle. The flow through the underflow nozzle is
automatically controlled based on readings from
an electronic level indicator.
More than 40 full-scale HydroFloat units have
been successfully installed within the industrial
minerals market. Due to that success, test work
continues to be carried out for metalliferous ores.
The results from multiple on-going, site-based test
campaigns and laboratory-based investigations
indicate that the particle size range for successful
flotation can be increased dramatically using this
technology – even with a minimal exposure of
hydrophobic grain surfaces. Data continue to show
that fluidised-bed flotation can increase coarse
particle recovery and improve process economics
by capturing particles that would require
significantly more grinding or otherwise be lost
when using traditional flotation methods.
Most recently, potential applications of this
innovative technology in the sulphide minerals
industry have been considered. This was
demonstrated through multiple test programs on
both copper and gold which clearly show a high
degree of recovery can be obtained for particles
up to 0.850 mm. These data also indicate that
significant savings can be realised through the
rejection of well-liberated siliceous gangue that
would otherwise consume capacity in the
grinding circuit.
A demonstration pilot plant was commissioned
to treat tailings from a copper concentrator. The
coarse values recovered using this innovative
technology were captured from a stream just
prior to discharge into an impoundment. These
values, some with minimal exposed sulphide
surface expression, were predominantly coarse,
low-grade sulphides that had not been recovered
using the conventional cell technology installed
in the main concentrator. Data show that
substantial gains can be achieved using this
novel approach to recover values previously
discarded to a typical sulphide tailings stream.
The data generated from these laboratory and
pilot testing efforts have been used to model and
simulate innovative flotation circuits which have
been designed to take advantage of the benefits
afforded by fluidised-bed flotation technology.
Process economics can be vastly improved by
capturing particles that would either require
significantly more grinding or be lost when using
traditional flotation methods. In fact, one study
indicated that the capacity of a primary grinding
circuit can be increased by 20-25% for a
hypothetical concentrator treating a typical
porphyry copper ore.
As this technology progresses, it provides
process engineers with another tool for circuit
optimisation where the engineered solution
includes less grinding, increased capacity, higher
recovery and, most importantly, reduced costs. It
is becoming increasingly more important to
demonstrate payback as the traditional approach
of simply adding additional capacity is not as
clear cut when determining payback with respect
to complete utilisation of the resource.
FLSmidth launches Reflux Classifier
plant
FLSmidth has officially launched its modular
Reflux™ Classifier plant for fines gravity
separation applications. The integrated
engineered modular solution is based on its well-
proven RC™ technology, which improves the
performance of gravity separation circuits, when
compared to spirals and hydrosizers.
The RC™ comprises the lamella settler,
autogenous dense-medium separation, and
fluidised bed separator. “The RC™ technology is
based on dense-media separation and is
combined with a lamella plate design, which is
unique to the RC™ and, therefore, allows for the
recovery of the valuable material in the
processing plant,” FLSmidth Country Head and
Minerals sub-Saharan Africa VP Deon de Kock
stated to Mining Weekly at the launch of the 100
t/h modular plant at the FLSmidth Supercenter in
Delmas, Gauteng, recently.
The key plant component are tanks, FLSmidth
Krebs pumps, cyclones, Krebs Tech-Taylor valves,
Technegate valves, the FLSmidth Ludowici
vibrating screen, the Reflux™ Classifier, and
dewatering equipment, as well as the Meshcape ®
Screen Media that comprises the polyurethane
screen panels. The plant is also fitted with a
lightning protection system for optimum safety.
The RC™ plant is also automated, using
advanced instrumentation and control, and
includes the FLSmidth automation control system
control centre. The FLSmidth equipment
technologies also interface optimally with the
RC™, which ensures that the feed material is
correctly prepared prior to its reporting to the
RC™ so that it operates to specification.
The modular solution is targeted at various
applications, including chromite, ch romite from
UG2 platinum-group metal circuit applications,
iron ore, metallurgical and thermal coal, mineral
sands, spodumene, cassiterite and other heavy
mineral applications.
The company says that in terms of recovery
efficiency, this plant will allow for some UG2
chrome recovery operations to more than double
their current output, as it can, for example,
produce between 10,000 t and 13,000 t of chrome
concentrate. It can achieve anything from 15% to
22% of additional yield on this spiral tail that
currently goes to waste.
Additionally, the modular RC™ plant can be
integrated into a brownfield plant and retrofitted
to replace less efficient technology. Users can
leverage the flexibility of the plant’s modularity,
as each section is contained within the
dimensions of a 20 ft shipping container. The
combination of these sections or containers
allows for the plant to be configured according to
various and specific process requirements.
The configuration is easily adjustable to
accommodate the changing process or ore
conditions within given parameters, and this
offers enhanced flexibility. The dimensions of the
unit and modularity of the plant allow for easy
relocations where needed, while rapid on-site
installation is possible, as the frames of each
modular section are easily assembled and locked
together.
To provide customers easy access to the
solution and enhance productivity partnerships
with the mining industry, FLSmidth will offer the
plant on a build, own, operate and maintain model
or a build, own, operate and transfer model. IM
JANUARY 2018 | International Mining 73