more than a century of progress - min-eng.com machine (formally bateman bqr) (inset) here at messina...

Flotation has been at the heart of the

mineral processing industry for over 100

years, addressing the ‘sulphide’ problem of

the early 1900s, and continues to provide one of

the most important tools in mineral separation

today. The realisation of the effect of a minerals

hydrophobicity on flotation all those years ago

has allowed us to treat oxides, sulphides and

carbonates, coals and industrial minerals

economically, and will continue to do so in the

future.

There have been a number of important

changes in the industry over the years as flotation

technology and equipment have advanced.

Xstrata Technology considers “the most noticeable

has been the increase in sizes of the flotation

machines, from the multiple small square cells

that were initially used, to the 300 m³ round cells

used today that are the norm in large scale plants.

“Other changes have been more subtle, but

equally as important. One of these has been the

design of the flotation circuit to make the most

of the liberation and surface chemistry effects of

the minerals. In a lot of these situations it is not

a matter of ‘bigger is better’, that will make the

process work, but being smarter in the

application of flotation technology.”

Xstrata Technology is one company that

believes the smarter use of flotation machines

can deliver big improvements in plant

performance. Through its use of the naturally

aspirated Jameson Cell, Xstrata Technology has

been making inroads into the processing of

more complex ores. Having a small footprint,

and using the high intensity mixing environment

of slurry and naturally induced air in a simple

downcomer, the Jameson Cell provides an ideal

environment for the separation of hydrophobic

particles and gangue, it says. The small

footprint of the cells also makes them ideal to

retrofit into a circuit especially where space is

tight.

While the cell has been included in some

flotation applications as the only flotation

technology such as coal and SX-EW, the main

applications in base metals have seen the cell

operating in conjunction with conventional cells.

The combination of the two technologies

enables the Jameson Cell to target the quicker

floating material, while the conventional cells

target the slower floating material. “Such a

combination provides a superior overall grade

recovery response for the whole circuit, than

just one technology type on its own,” Xstrata

Technology says. Below are some of the duties

for which the Jameson Cell can be used.

Jameson Cells in a scalping operation target

fast floating liberated minerals, and produce a

final grade concentrate from them. The wash

water added to the Jameson Cell assists in

obtaining the required concentrate grade due to

washing out the entrained gangue. Scalping can

be done at the head of the cleaner (also known

as pre cleaning), or at the head of the rougher

(also known as pre roughing), and minimises

the downstream flotation capacity using

conventional cells needed to recover the slower

floating minerals.

Sometimes deleterious elements found in the

orebody are naturally highly hydrophobic, and

need to be removed at the start of flotation,

otherwise they will report with the valuable

minerals to the concentrate and effect

concentrate grade. Mineral species such as talc,

carbon and carbon associated minerals, such as

carbonaceous pyrite, can all be difficult to

depress in a flotation circuit. On the other hand,

floating them off in a prefloat circuit before the

rougher is an easier way to handle them.

Jameson Cells acting as a prefloat cell at the

head of a rougher circuit, or treating the

hydrophobic gangue as a prefloat rougher

cleaner, is an ideal way to produce a ‘throw

away’ product before flotation of the valuable

minerals, minimising reagent use and circulating

loads.

Jameson Cells can be used in cleaning circuits

to produce consistent final grade concentrates.

The ability of the cell to keep a constant pulp

level, even with up stream disturbances or loss

of feed, enables a constant grade to be

obtained.

Xstrata Technology concludes: “Importantly in

a lot of these circuits, it is not the selection of

one type of technology that produces the

FLOTATION

24 International Mining | NOVEMBER 2011

More than a century of progressJohn Chadwick examines new technologies and applications from some of the keyplayers in mineral flotation, a technique that is so important to the global industry

Stawell gold mine in co-operation with OutotecServices completed a flotation circuit upgradeon time and on budget last year that, instead ofthe projected 3.5% improvement, resulted in anincrease of 4.5% since the project wascompleted. Payback was also impressive,occurring within less than four months.

FLOTATION

required grade and recovery, but the selection of

several technologies to get the best results. The

interaction of slow floating and fast floating

minerals, entrainment, hydrophobic gangue and

a myriad of other variables make it rare for just

one type of technology to prevail, but the

combination of different flotation machines can

achieve the required outcome more efficiently,

as well as make the circuit robust enough to

handle variations in feed quality.”

The Jameson Cell has benefitted from over 20

years of continuous development. Early this

year, the 300th cell was sold into Capcoal’s Lake

Lindsay coal operation in the Bowen Basin of

Australia. Around this time there were a number

of coal projects taking in new Jameson Cells,

including expansion projects for Wesfarmers’

Curragh and Gloucester Coal’s Stratford

operations (both in Australia), Riversdales’

Benga project in Mozambique and Energy

Resources’ Ukhaa Khudag coking coal project in

Mongolia.

Le Huynh, Jameson Cell Manager, said the

interest for coal preparation plants has

remained strong, where operators needed

dependable and reliable technology to treat fine

coal, an important source of revenue. During

2010, the Jameson Cell business also found

success in other applications, including

recovering organic from a copper raffinate

stream at Xstrata-Anglo American’s Collahuasi

copper SX-EW plant in Chile.

Le said the consistent generation of very fine

bubbles and the high intensity mixing in the

Jameson Cell, was ideal for recovering very low

concentrations of organic from raffinate

streams, typically less than several hundred

ppm. High throughput in a small footprint,

simple operation and extremely low

maintenance due to no moving parts in the cell

are distinct advantages in this application.

The cell is designed with features specific to

suit such hydrometallurgy applications including

specialist materials, a flat-bottomed flotation

tank with integrated pump box and tailings

recycle system, and large downcomers. The

Collahuasi cell was the first of its type in Chile,

though there are many other large cells installed

in SX-EW plants in Mexico, USA and Australia to

treat both raffinate and electrolyte streams.

Dominic Fragomeni, Manager Process

Mineralogy, Xstrata Process Support (XPS),

notes that accurate, rapid development of a

milling and flotation flowsheet for a new

orebody is key to successful mine development.

Time-honoured conventional practice has

typically favoured the extraction of a bulk

sample of up to several hundred tonnes for

conventional pilot plant campaigns which could

operate at several hundred kilograms per hour.

Where sample extraction is limited, much

reliance has been placed on locked cycle tests

alone to produce design basis criteria. These

approaches can be lengthy, expensive, carry

scale up risk, and have seen a wide range of

successes and failures at commissioning and

during life of a mine.

XPS has miniaturised the pilot plant process.

At the same time, it has improved the

representativeness of results from the pilot

plant campaign by using exploration drill core to

formulate the pilot plant sample. This Flotation

Mini Pilot Plant (MPP) was developed in

collaboration with Eriez subsidiary Canadian

Processing Technologies (CPT) and operates in

fully continuous mode either around the clock or

can be made to demonstrate unit operations on

a shift basis. The feed samples are in the range

of 0.5-5 t and can consist of exploration ½ NQ

drill core which improves the sample

representativeness. The MPP operates in the

range of 7-20 kg/h, an order of magnitude lower

in sample mass and typically at a lower cost

when compared to conventional pilot plants.

XPS has developed and validated a

representative sampling strategy, an appropriate

quality control model for metallurgical results

and has accurately demonstrated operations

results using Raglan and Strathcona ores and

flowsheets. These validation campaigns, in

‘scale down’ mode from the full scale plants,

have produced actual mill recoveries to within

0.5% at the same concentrate grade with

internal material balance consistent with the

plant.

When designing a plant to recover copper,

Scott Kay, Process Engineer with METS suggests

(in METS Gazette, issue 32, October 2011) it

would be prudent “to perform some

mineralogical analysis test work such as

QEMSCAN (Quantitative Evaluation of Mineral

by Scanning electron microscopy) to provide

some knowledge on the proportion of sulphide

and oxide minerals present, the grain sizes of

each mineral and a suggested grind size before

jumping into the bulk of the beneficiation test

work.

“Ideally, the characteristics of the copper

bearing minerals should suggest an appropriate

grinding circuit P80 of between 100 and 200 μm

(0.1 and 0.2 mm), which can be controlled by

cyclones, or in some cases fi ne screens.

“Flotation reagent selection is paramount and

test work is necessary to ensure the optimum

reagent suite is utilised. If the ore contains a low

amount of iron sulphides, xanthate collectors

are often suitable to float copper sulphide


Jameson Cell in a cleanerscalping duty at Phu Kham,Laos, producing final gradecopper concentrate prior toconventional cleaning circuit(flowsheet presented in Mayat Austmine 2011, Brisbane)

minerals. If native gold is present,

dithiophosphates can be used which are less

selective to iron sulphides. Increasing and

controlling the pH within the flotation vessel

to between 10 and 12 causes the process to

become more selective, away from iron sulphide

gangue minerals such as pyrite to produce a

cleaner copper mineral concentrate. Depending

on the ore mineralogy, activators and

depressants may be required to achieve the

optimum reagent suite.

“Recovery of copper oxide minerals can be

achieved with flotation by sulphidising the ore.

In essence, this creates a thin layer of copper

sulphide (chalcocite) on the oxide grains which

can then be activated and collected in the froth.

When employed, this occurs after the sulphide

flotation stage, however, this is not commonly

used as other beneficiation processes, such as

leaching and SX-EW are often more cost

effective for copper oxide minerals.

“A common flotation circuit usually includes a

rougher/scavenger and a cleaner stage. As most

copper orebodies exhibit an in-situ grade of less

than 1% Cu, the mass pull to the rougher froth is

often low. This means that the throughput of the

cleaner stage is significantly less than the

throughput of the rougher stage which imparts a

relatively low capital and operating cost to the

flotation circuit.

“To counteract the possible absence of a

scavenger stage, a slightly higher mass pull to

the rougher froth is targeted (although still low

overall) to increase overall copper recovery. The

rougher froth can then be reground to increase

the liberation of the copper sulphides from the

iron sulphides before being fed to the cleaner

flotation vessels. This results in a significant

upgrade in copper in the cleaner froth whilst still

achieving a high copper recovery. The final

flotation concentrate usually contains between

25 and 40% Cu.”


The Delkor BQRflotation machine(formally Bateman BQR)(inset) here at Messina MowanaCopper mine in Botswana. 15 x 50BQR and 16 x 200BQR flotation cells for Copper roughing,cleaning & re-cleaning. Oxide / Sulphide

FLOTATION

Alain Kabemba, Flotation Process Specialist

at Delkor notes the major trend to treating

lower-grade and more finely disseminated ores

and lately the re-treatment of tailings. He also

points to the broad applicability of size to below

10 μm.

Real systems do not fulfil ideal conditions,

mainly because of feed variation or

disturbances. “Before considering disturbances

to flotation specifically,” Kabemba says “it is

important to emphasise the interlock between

grinding and flotation, not only with respect to

particle size effects, but equally to flotation feed

rate variations. The grinding circuit is usually

designed to produce the optimum size

distribution established in testing and given in

the design criteria. When the product size alters

from this optimum, control requires either

changing feed tonnage to the circuit or changing

product volume, with either causing changes in

flotation feed rates.

“While grindability changes due to the

variation in ore properties are disturbances to

the grinding circuit, they generate feed rate

changes as disturbances to the flotation circuit.

The variations in ore properties which affect

flotation from those assumed in the design

criteria must therefore necessarily include

grindability changes.

“This reflects important differences in

flotation machine characteristics between the

two processes. Grinding circuits are built and

designed with fixed total mill volumes and

energy input, so the grinding intensity is not a

controllable variable, instead grinding retention

time is changed by variation of feed rates. In

contrast, the flotation circuit is provided both

with adjustable froth and pulp volume for

variation of flotation intensity by aeration rate or

hydrodynamic adjustment. Reagent levels and

dosages provide a further means for intensity

control.”

One recent trend has been towards larger,

metallurgical efficient and more cost effective

machines. These depart from the simpler

tank/mechanism combination towards design

which segregates and directs flow and towards

providing an external air supply for types which

had been self aerating and towards the

application of hydrodynamic principles to cell

design, like the Delkor BQR range of flotation

machines, initially the Bateman BQR Float Cells.

Bateman has steadily developed the BQR

flotation cells which have been in application for

the past 30 years, and with its acquisition of

Delkor in 2008, decided to rebrand the

equipment into the Delkor equipment range.

Kabemba explains that BQR cell capacities

range from 0.5 to 150 m3 currently installed, and

can be used in any application as roughers,

scavengers and in cleaning and re-cleaning

circuits.

“The main objectives of the BQR design were

to achieve the following core hydrodynamic

functions:

■ Provide good contact between solid particles

and air bubbles

■ Maintain a stable froth/pulp interface

■ Adequately suspend the solid particles in the

slurry

■ Provide sufficient froth removal capacity

■ Provide adequate retention time to allow the

desired recovery of valuable constituent.

“This led to the following benefits

■ Highest possible effective volume and

reduced the froth travel distance

■ Improved metallurgical performances in

terms of grade recovery and reduced capital

and operating costs based on reduced

fabrication material and ease of maintenance

Kabemba says “there are not many

differences in terms of design between BQR

Flotation cells; however, from the BQR1000

upwards, the flotation cells have internal

launders to maintain the design objectives and

benefits highlighted.

“Operating variables, such as impeller speed,

air rate, pulp and froth depths have to be

adjustable over a sufficient range to provide

optimum results with a given ore, grind and

chemical treatment, but adjustment should not

extend beyond the hydrodynamic regime in

which good flotation is possible.”

FLOTATION

NOVEMBER 2011 | International Mining 29

Proven PerformanceLarox Flowsys is now Flowrox

FLOWROX VALVES AND PUMPS for abrasive, corrosive and other demanding shut-off, control, pumping and dosing applications.

EXPERTISE WITH INSIGHT• Over 30 years of experience• More than 100 000 installed products worldwide

PARTICIPATING PARTNER• Long-term partnerships with the customers• Close cooperation between experts in all disciplines

FACILITATING PERFORMANCE• The lowest total costs of ownership • Improved efficiency and extended service intervals

Flowrox OyMarssitie 1P.O. Box 338FI-53101 LappeenrantaFinland

Tel. +358 201 113 311Fax +358 201 113 [email protected]

Meet us at

Flotation ’11

Conference

The largest current BQR flotation machine is

shown in the table below. In the near future the

BQR2000 (200 m3) and BQR3000 (300 m3) will

be available to the market.

Kabemba also explained that “circular cells

reduce the amount of dead volume when

compared to square cells. This enables a much

higher effective pulp volume, hence increasing

the effective energy input into the flotation cell.

In addition ‘tank type’ cells offer enhanced froth

removal due to the uniform shape of the circular

launders.”

He concluded that “fully automated flotation

cells are becoming more and more common with

the aid of smart control and advances in

software in the marketplace.”

Better fine particlerecoveryFLSmidth’s flotation team

notes that fundamental

flotation models suggest

that a relationship exists

between fine particle

recovery and turbulent

dissipation energy1.

Conversely, increased

turbulence in the rotor-

stator region is theoretically related to higher

detachment rates of the coarser size range2.

Conceptually, the suggested modes of recovery

for the extreme size distribution regions appear

to be diametrically opposed.

Industrial applications have previously

confirmed that imparting greater power to

flotation slurries yields significant

improvements in fine particle recovery.

However, recovery of the coarser size class

favours an opposing approach, The FLSmidth

team believe. An improvement in the kinetics of

the fine and coarse size classes, provided there

is no adverse metallurgical influence on the

intermediate size ranges, is obviously beneficial

to the overall recovery response. Managing the

local energy dissipation, and hence the power

imparted to the slurry, offers the benefit of

targeting the particle size ranges exhibiting

slower kinetics.

New concept, Hybrid Energy Flotation™

(HEF™), using phenomena described above was

recently introduced by FLSmidth. In principle it

decouples regimes where fine and coarse

particles are preferentially floated. HEF includes

three sections:

1. Standard flotation machines (energy, rpm,

rotor size) at the beginning of the row, where

Designations BQR 1500

Nameplate Volume (m^3) 150

Diameter (m) 6.1

Height (m) 5.98

Total surface Area (m^2) 29.22

Effective surface Area (m^2) 15.28

Total volume (m^3) 174.7

Volume in internal launders 4.08

Volume lost in stator tube 1.06

Crowder diameter at surface 2.5

Volume lost in Crowder 2.05

Effective volume - no air 167.5

Effective Volume – aerated 150.8

Copper andmolybdenite recovery of-20 μm fraction in HEFcleaner duty

FLOTATION


If you need MORE growth or want to generate LEAN efficiencies, contact SGS. Daily, the SGS global team delivers technical expertise, effective services and sustainable solutions that can enhance your project.

SGS IS THE WORLD’S LEADING INSPECTION, VERIFICATION, TESTING AND CERTIFICATION COMPANY

www.sgs.com/[email protected]

FOCUSED + BEST PRACTICES

TESTING + EXPERIENCE

TROUBLESHOOTING + EFFICIENCY

PRODUCTIVITY + SUSTAINABILITY

TECHNOLOGIES + KNOW HOW

EXPERTISE + TECHNICAL DEPTHTRANSPARENCY + RISK MITIGATION

MARKET INSIGHT + COST REDUCTIONSDEVELOPMENT + STREAMLINED PROCESSES

CONFIDENCE + EFFICIENT LOGISTICSSPEED-TO-MARKET + GLOBAL NETWORK

COMPETITIVE ADVANTAGE + PRODUCTIVITY

MORE + LEANGROWTH EFFICIENCIES

World Class Solutions for the Global Minerals Industry

JKTech is the world leader in resource characterisation and mining process improvement

JKTech’s innovative expertise offers tailored solutions across the entire life of mine:

Maximise Profitability | Increase Throughput | Increase Recovery

Reduce Costs | Improve Sustainability | Manage Risk

Comminution, Flotation, Mining, Geometallurgy, Sustainability, Risk Management and Process Statistics

flotation is froth phase limited and

operational and set-up parameters have small

influence on the recovery

2. Higher power flotation machines (high rpm,

standard rotor size) at the end of the row to

increase recovery of fine particles

3. Lower power flotation machines (low rpm,

larger rotor) at the end of the row (mixed with

higher energy cells) to increase recovery of

coarse particles.

This concept was successfully implemented

at the Mineral Park concentrator in Arizona and

will be expanded at various mines in the nearest

future.

This subject will be expanded upon at the 5th

International Flotation Conference (Flotation '11)

in Cape Town, South Africa. The fundamental

parameters that influence fine and coarse

particle recovery will be reviewed. The potential

dual recovery benefit is then presented in terms

of its practical implementation in a scavenging

application. HEF is proposed as the preferred

methodology of recovering these ‘slow-floating’

size ranges; a method that opposes the

traditional approach of residence time

compensation.

Eriez® Flotation Group introduced the

StackCell® flotation concept in 2009. This

innovative technology recovers fine particles

more efficiently than mechanical flotation cells.

“We’ve taken the inherent

advantages of mechanical flotation

and adapted them to a new

design that is significantly

smaller and requires less

energy,” explained Eriez Vice

President Mike Mankosa. “We

focused on reducing the

retention time and energy

consumption by implementing a

completely different approach

to the flotation process. This new

approach provides all the

performance advantages of column

flotation while greatly reducing capital,

installation and operation costs.”

At the core of the StackCell technology is a

proprietary feed aeration system that

concentrates the energy used to generate

bubbles and provides bubble/particle

contacting in a relatively small volume. An

impeller in the aeration chamber located in the

centre of the cell shears the air into extremely

fine bubbles in the presence of feed slurry,

thereby promoting bubble/particle contact.

Unlike conventional, mechanically agitated

flotation cells, the energy imparted to the slurry

is used solely to generate bubbles rather than to

maintain particles in suspension. This leads to

reduced mixing in the cell and shorter residence

time requirements.

The StackCell sparging system operates with

low pressure, energy efficient blowers that

decrease power consumption by 50% compared

to air compressors or multi-stage blowers used

in other flotation devices.

The low-profile StackCell design features an

adjustable water system for froth washing and

also takes advantage of a cell-to-cell

configuration to minimise short-circuiting and

improve recovery rates. Space requirements for

StackCell offers column-likeperformance in a substantially

smaller footprint thanconventional cells.

These compact,stackable units

provideconsiderable

savings for newinstallations and

are ideal forexpanding

capacity in anexisting plant


FLOTATION

the StackCell design are approximately half of

equivalent column circuits, with corresponding

reductions in weight leading to reductions in

installation costs. Units can be shipped fully

assembled and lifted into place without the

need for field fabrication.

This technology can provide recoveries and

product qualities comparable to column

flotation systems while using a low profile

design. Not intended to replace the need for

column flotation, it does provide an alternative

method to column-like performance where

space and/or capital is limited. The small size

and low weight of the new StackCell makes

possible lower cost upgrades where a single cell

or series of cells may be placed into a currently

overloaded flotation circuit with minimal retrofit

costs.

Steve Flatman, General Manager of Maelgwyn

Mineral Services (MMS) also comments on the

“trend of moving towards a finer grind to

improve mineral liberation. Unfortunately

conventional tank flotation cells are relatively

inefficient in recovering these metal fines below

30 μm and very inefficient at the ultra fine grind

sizes below 15 μm. The incorporation of regrind

mills on rougher concentrates has further

exacerbated this problem. To date the

conventional flotation tank cell manufacturers

have attempted to counter this fall off in

recovery of fine particles by inputting increasing

amounts of energy (bigger agitation motors)

into the system to improve bubble particle

contact. Unfortunately this tends to compromise

coarse particle recovery.”

He says the solution is MMS’s “Imhoflot

pneumatic flotation technology and specifically

the Imhoflot G-Cell. Recent pilot plant test work

at a nickel operation with a three stage Imhoflot

G-Cell pilot plant enabled an additional 30%

nickel to be recovered from the conventional

flotation tank cell final plant tails. The recovery

was predominantly associated with the minus-11

μm fraction indicating that this improved

recovery was not just related to additional

residence time. The above results are in line

with an earlier pilot plant trial using G-Cells on a

zinc operation where an additional 10-20% zinc

was recovered from cleaner tailings this time

being associated with minus 7 μm material.

“It is postulated that the above

improvements are related to the order of

magnitude increase in terms of air rate

(m³/min/m³ pulp)for the G-Cells due to their

principle of operation where forced bubble

particle contact takes place in the aeration

chamber rather than the cell itself with the cell

merely acting as a froth separation chamber.

Typically in percentage terms the G-Cell air rates

are five to ten times that of conventional

flotation although the overall or total air usage

is approximately half.

“When this additional targeted energy input

is combined with the centrifugal action of the G-

Cell and small bubbles benefits are obtained in

both the flotation rate (kinetics) and overall

recovery. The improved kinetics results in a

much lower residence time than conventional

flotation facilitating a double benefit of both

reduced footprint and improved recovery.”

A technical paper will be presented at the

MEI Flotation 11 Conference in South Africa

providing more detail on the specific case

studies.

Metso notes a main drawback of column

cells being low recovery performance, typically

resulting in bigger circulating loads. Its CISA

sparger is derived from the patented Microcel™

technology and enhances metallurgical

performance by allowing flexibility on the grade-

recovery curve. Metso Cisa says the main

advantages of its column technology include:

■ Improved recovery and optimised grade

■ Increased throughput

■ Enhanced bubble particle contact

■ No plugging

■ On-line replacement and reduced wear and

maintenance

■ Unique sparger Technology.

At the bottom of the column, the sparger

system raises mineral recovery by increased

carrying capacity due to finer bubble sizes. This

maximises the bubble surface area flux which is

a standard parameter in evaluating flotation

device performance. It also provides maximum

particle-bubble contacts within the static mixers

and effective reagent activation from the

mechanical operation of the pump.

It is well known that coarse particles behave

poorly in a conventional flotation cell and were

previously regarded as ‘non-floatable’. However,

recent laboratory work demonstrates that

Fluidised Bed Froth (FBF) flotation extends the

upper size limit of flotation recovery by a factor

of 2-3 resulting in significant concentrator

performance benefits. AMIRA’s P1047 project,

Improved Coarse Particle Recovery by FBF

Flotation, is expected to commence in 2012, and

will be structured in two phases.

Some of the benefits for FBF technology are:

■ Early rejection of gangue with minimum

mineral loss

Potential for significant increase in

concentrator throughput or significant

improvement in capital efficiency

■ Reduced energy consumption

Independent modelling predicts that if particles

of 1 mm can be floated, comminution energy

consumption will be lowered by at least 20%.

■ Better management of water requirement

FBF cells can take product straight from the

milling circuit without dilution, and the feed to

the FBF cell could be up to 80% w/w solids,

which could lead to significant savings in

process water demand.

■ Improve recovery of metallic and other dense

minerals.

In a continuous FBF Cell, dense mineral

particles will tend to sink to the bottom and

accumulate in the cell, thus they can be

recovered in a concentrated form by emptying

the cell periodically. This could be a significant

benefit where the concentration of the heavy

metallic material is too low to warrant a

separate treatment plant to recover them.

Upgraded servicesIn Australia, Northgate Minerals’ Stawell gold

mine recently completed a project through

which it aimed to increase recoveries by 3.5% by

upgrading the flotation plant. This upgrade was

implemented after Stawell changed its

production profile to process lower grade ore at

higher throughput rates.

Instead of the projected 3.5% improvement,

Imhoflot stage G1.2 pilot plant

FLOTATION


the upgrade from Outotec Services has resulted

in an increase of 4.5% since the project was

completed on time and on budget last year,

despite the wettest seasonal weather in recorded

history. Payback was also impressive, occurring

within less than four months. “The projected

payback was 5.5 months, so it was a pleasant

surprise when it happened so soon” explains

Jodie Hendy, senior metallurgist at Stawell.

The project has also achieved payback in less

than four months and has delivered further

ongoing benefits, including easier operation and

reduced maintenance costs, says Outotec

Services, which worked in close partnership

with Stawell Gold to ensure the site remained

fully operational during the upgrade.

The mine, which has produced more than 2

Moz in its 26-year history, previously employed

a flotation circuit consisting of a bank of eight

mechanical trough cells in the rougher circuit,

followed by two banks of 2 x OK3 Outotec cells

as cleaners. The feed rate to the cells was

between 90-105 t/h, at 50-55% solids. The

overall flotation circuit was not performing at

optimal rate due to entrainment problems in the

rougher cells when feed density increased from

45% to 55% solids, typically at 105 t/h.

In anticipation of future production levels and

as part of Stawell’s focus on operational

excellence, it was decided to upgrade the

flotation circuit. Following a site audit from

Outotec Services, a 2 x TankCell® -20 configuration

equipped with larger TankCell -30 mechanisms

was proposed to help optimise flotation. The

larger mechanisms would allow operation at

very high percent solids (50% and over).

The TankCell design also allows a much

deeper froth depth and better concentrate grade

through optimised launder lip length and

surface area. These cells known for great

performance, ease of operation and reduced

power and air consumption. Outotec Services

was commissioned to handle the complete

turnkey solution of the new rougher circuit,

including design, supply, installation and

commissioning.

The schedule was demanding but achievable,

in just 30 weeks. It was decided to adopt the

partnering approach between Stawell and

Outotec Services, because this collaborative

method ensured open communication, with all

parties having greater ownership of the project

and its aims. This close teamwork resulted in

meticulous planning and site remaining fully

operational at all times. Pipework and electrical

easement ducts, for example, were rerouted

early in the project. Tie-in points for new cells

and rerouting of pipework were also planned

upfront in the project and all disruptive work

was completed during shutdowns.

The project overcame a number of challenges,

including an extremely limited footprint, which

was adjacent to a gabion wall, close to the run-

of-mine pad and also close to a reagents shed,

which could not be moved. Additionally, existing

process requirements at Stawell required specific

elevations for the new TankCells. Structural

stability was the main issue when designing the

tank support structure due to the height of the

tanks and the limited footprint. Sufficient

stiffness was required such that the operation

frequencies of the TankCells would not interfere

with the natural frequency of the tank support

structure. Through FE modelling of the structure,

section sizes and bracing orientations were

optimised to produce the required stiffness.

Despite the challenges, the turnkey

installation of the new rougher circuit, along

with blowers for the complete flotation circuit,

was completed within deadlines. Because all

tie-in points had been already carefully planned

upfront, commissioning was a seamless exercise.

Designed to cope with projected increases in

production and considerably more operator

friendly than its predecessor, the new TankCell -

20 cells have quickly proved their worth at site.

The air demand for the old rougher cells, for

example, was estimated at over 3,000 Am3/h,

whereas the estimated air demand on the

Outotec TankCells is a maximum of 992 Am3/h.

The Outotec FloatForce® rotor-stator

mechanism, with its unique design, delivers

enhanced flotation cell hydrodynamics and

improved wear life and maintenance.

“Maintenance on the Outotec TankCells has

also been minimal since the upgrade, Hendy

commented. “Basically we check the cells

during shutdowns but there has been no

maintenance required in the nine months since

commissioning. “The TankCells have really

delivered on their reputation. Basically, they do

exactly what they are supposed to do.”

Smarter reagent useTurning to flotation reagents, Frank Cappuccitti,

President of Flottec explains that Flottec and

Cidra are “working very hard jointly on

developing instruments that will measure

hydrodynamics in the flotation cell and circuit in

a bid for better flotation control. This would be a

great step forward in using a combination of

reagents and sensors to optimise flotation

systems. It brings together the knowledge we

have developed in both how reagents effect

hydrodynamics and measuring the

hydrodynamics to maintain optimum conditions.

He explains that back in the 1990s, when he

worked at a well-known mining chemicals

supplier, “we spent most of our research on

trying to find the best collectors. The thinking

was that we could try to develop collectors with

absolute specificity. In other words, we could

develop a collector that would float only specific

minerals and provide clients with an almost

perfect flotation separation. This was our

approach to flotation optimisation.

Unfortunately, we discovered that there was no

such thing as absolute specificity. In fact, we

had trouble measuring any improvements in the

circuits because they were multi-variant and

highly complex. Every change made was always

a trade off between grade, recovery and cost.

Changing one thing in the circuit seemed to

improve something but always got a negative

response in some other variable. It was also

very hard to measure the performance of the

flotation circuit because the only real

parameters you could measure on line were

concentrate grades and tails of the circuits,

which were always after the fact. There was little

ability and understanding about what real time

FLOTATION


Fluidised Bed Flotation concept cell

measurements we could take other than air

rates, cell levels and flow rates. So even if we

got an improvement or a response to a change,

we never knew if that was a response to a

change or a natural variation in the system.

Every test needed long term statistical trials to

get some confidence in any real change.

“So, I wrote a paper in the 1990s that

basically said that until we could measure the

real time variables in a flotation system and

learned to really understand and control the

system, we were limited in our ability to work on

continuous improvement in reagent

optimisation. We needed new sensors that could

measure the performance of the flotation circuit

so we could learn to control it. Once we got

this, then we could actually measure

improvements and use this to develop reagents.

“Fortunately, with the advent of strong

computing power and software, we have moved

forward tremendously in the last decade in

understanding the flotation circuit. Froth

cameras that tried to measure froth grade and

velocity were one of the first new sensors

developed to assist in optimising circuits.

Through the work of universities such as McGill

and organisations like JKtech, new sensors have

been developed that could actually measure

reliably and in real time the hydrodynamic

parameters in the flotation cell. Flotation cell

hydrodynamics (gas dispersion parameters) is

critical to the performance of the cell. When we

talk about these parameters, we are talking

about measuring what is happening in a

flotation cell. Flotation is really about making

bubbles and using the surface area of the

bubble to do the work of transporting

hydrophobic minerals to the froth. In flotation

cells, we add air, create bubbles of a certain size

and speed that provide the surface area to do

the flotation. The more bubbles and the smaller

the bubble, the more surface area we have to do

the work. This surface area we create is known

as the surface bubble flux (Sb) and controls the

kinetics of flotation. Now that we have

instruments that can measure the air into a cell

(known as Jg), measure the size of the bubble

diameter (Db) and the gas hold up (Eg), we can

figure out how the relationship between these

parameters and how they affect the Sb and

flotation circuit performance. We can also now

do research on how reagents can be used to

control these parameters as well.

“Research of the last few years has shown

that frothers actually play a much more

important role in flotation hydrodynamics than

once thought. Frothers perform two major

functions. They create and maintain small

bubbles in the pulp to transport the minerals

and they create the froth on top of the cell to

hold the minerals until they can be recovered.

The froth is created because frothers allow a

film of water to form on the bubbles which

makes them stable enough not to break when

they reach the surface of the cell. Fortunately,

the water drains over a short period of time and

the froth will eventually break down. Froth

breakdown is essential for cleaning and

transporting the concentrates. Small bubbles

are essential in making flotation efficient. For

the same volume of air in a cell, smaller bubbles

give much higher surface area, which in turn

gives much higher kinetics.

“We now know that as you increase the

concentration of frothers to the cell, the bubble

size gets smaller, and the film of water on the

bubble gets bigger. But bubble size does not

keep getting smaller forever. The frother will

reduce the bubble down to a certain size, which

is about the same for all frothers in the same set

of conditions. The concentration of frother

where the bubble is at a minimum is known as

the critical coalescence concentration or CCC.

Each frother has a different CCC. Each frother

also has a different ability to add water to the

bubble and hence provides different froth

stability. This also changes with concentration.

We have learned in the last few years that each

frother has a hydrodynamic curve which relates

the bubble size with the froth stability. Strong

frothers give very high froth stability at the CCC,

while weak frothers give very low stability of the

froth at the CCC.

“This new understanding of how frothers

affect flotation cell hydrodynamics has lead to

new methodologies to optimise flotation

circuits. Flottec has worked on an optimisation

system where a frother is added to a circuit at

the CCC (which guarantees maximum kinetics or

maximum Sb) and the performance is measured.

Then frothers of different strength are added

(always at the CCC) until the right strength for

maximum performance is determined. Adding

the frother at the CCC is the critical optimisation

difference. By doing this you are always

guaranteed to have maximum kinetics. If the

frother used is too strong, the dosage will have

to be cut back below the CCC or the froth will be

too persistent. This lowers flotation kinetics. If

the frother is too weak, too much has to be

added to get the froth strength and this

increases cost and likely reduces recovery.

Flottec has been conducting research with

McGill University to develop the hydrodynamic

curves and CCC for all families of frothers in

order to implement the new methodology of

frother optimisation in plants.

“The next step in this research is to be able to

use new sensor technology to measure and

control the flotation system by controlling the

hydrodynamics in the cell. With our current

knowledge of how air rate, cell levels, and

frother addition affect bubble size, water

recovery and gas hold up, we can use these

control variables to maintain the optimum

hydrodynamics in the cell resulting in the

optimum flotation circuit performance. Flottec is

working with companies like Cidra to develop

new sensors that can provide real time

information on cell hydrodynamics (gas

dispersion parameters) and on froth stability

properties in order for us to optimise the

reagents and operating strategies used in a

plant. This will bring flotation performance to

the next level.”

Clariant Mining Solutions business is

investing considerably in mining chemicals. It

has opened a new laboratory at its US

headquarters in Houston, Texas, dedicated to

the development and optimisation of chemical

solutions for North American customers. The

laboratory is part of a planned multi-million

dollar investment into Clariant’s global Mining

Solutions business, which includes establishing

several new Mining Solutions laboratories

around the world. This network is intended to

enable the business to better support customer

needs and address regional challenges. The new

laboratories will complement existing facilities

in Europe and Latin America.

FLOTATION


Flottec frothers – hydrodynamic profiles - foamheight versus gas holdup, 5 litres/min

“Mining is a strategic focus area for Clariant,”

said Christopher Oversby, Global Head of

Clariant’s Oil & Mining Services business unit.

“This investment further demonstrates Clariant’s

ongoing commitment to providing innovative

technologies and solutions for our mining

customers around the world.”

The Houston laboratory will process ore

samples from customers in the USA and Canada.

These samples were previously handled in

Clariant’s mining laboratories located in South

America and at the company’s global research

facility in Frankfurt, Germany. “We are very

excited about the new mining laboratory and the

opportunity it provides us for offering our North

American mineral processing customers even

more localised services and attention,” said

Paul Gould, Global Head of Marketing and

Application Development for Clariant Mining

Solutions. “The Houston lab will allow Clariant

technicians to more efficiently develop

optimised reagent solutions for our US and

Canadian customers.”

Additionally, Clariant is in the process of

developing a new Clariant Innovation Center in

Frankfurt at a cost of €50 million. Employing

nearly 500 people and covering 30,000 m2, the

facility will focus on customers using an integrated

multidisciplinary approach to problem solving.

Clariant says “an open innovation approach on

joint ventures with external partners will ensure

the acceleration of the ‘idea-to-market’ process.

Mining research and development will also be

part of this facility.”

Axis House has been developing reagent

technologies for the past 10 years, at its

flotation laboratory in Cape Town, South Africa

and more recently at it metallurgical labs in

Sydney and Melbourne. These were acquired

when Axis House bought the oxide flotation

reagent technology from Ausmelt Chemicals. A

practical application technology strategy was

followed with Axis House providing a

complimentary suite selection and optimisation

service to its clients, who were then mainly

interested in the Axis developed technology of

combining fatty acids, hydroxamates and

sulphidisation suites to effectively and

economically float oxide minerals.

Early on the focus was on developing

reagents to float complex ores which contained

multiple minerals with varying flotation kinetics

Often the limiting factor was not only the

sluggish flotation kinetics of the minerals but

the process plant’s own equipment limitations,

like flotation and conditioning times. Developing

a reagent that floated a certain mineral was

simply not enough. The solution was to develop

suites of reagents which could function

synergistically. By altering the types of

collectors and the dosages, the company could

optimise both the use of the processing

equipment and the collecting power. It says

“this approach has successfully been applied to

various types of base metal oxide ores.”

It is now taking this innovative approach into

the field of rare earth element (REE) flotation.

This fits into the Axis House business plan as

the chemistries are quite similar to what is in

existence at Axis already. Of course some

tweaks will have to be made to the reagents as

well as the laboratories – this process has

already started, with the first batch of REE test

material having arrived at Cape Town, and new

reagent samples at the ready. There are a large

number of REE projects coming online in the

next few years. Most of these orebodies have

not been previously treated at industrial level

and so will face difficulties when scaling up.

REO (Rare Earth Oxides) are often difficult to

float and the development of multiple collector

systems for these ore types would help increase

the viability of these projects.

Jerry Sullivan, Global Marketing Manager-

Mineral Processing, Cytec Industries Inc,

discussed collectors, which contain mineral-

selective functional groups. “They have a

hydrophobic hydrocarbon tail. Changing the

molecule’s functional group changes the

preference for what mineral it will adsorb on to.

Changing the length of the hydrocarbon chain

changes the hydrophobicity of the molecule.

This is related to the strength of the collector.

“Within the collector molecule, there are

donor atoms whose goal is to form bonds with

acceptor atoms within the ore. Nitrogen,

oxygen, and sulphur are the most important

donor atoms in all reagent chemistry. Sulphur

is the most important donor in sulphide

collectors. Nitrogen and oxygen are additional

donor atoms. Phosphorous and carbon are

central atoms carrying the donors. They only

have indirect participation in interactions.” He

noted the general characteristics of sulphide

collectors to be:

■ Ionic collectors are stronger and less

selective

■ Neutral, ‘oily’ collectors are weaker, more

selective

■ Higher homologues (more carbons) are

stronger than lower homologues (fewer

carbons)

■ Cytec’s NCPs are very selective collectors

■ Selectivities of collectors have been

extensively studied, and are well established

in terms of:

■ Mineralogical preferences

■ pH effects.

“There is a strong case for formulated

products (or blends),” he continued “That is

because mineralogy is complex. Plant

performance is also inherently variable.

Mineralogy changes routinely. In addition,

different minerals have different affinities for

reagents. Various minerals will compete for a

given reagent. Modifiers used will also influence

reagent partitioning. Particle size distribution

will also affect recoveries (recovery losses in

coarse and fine size range). A single collector

will not be sufficiently robust. Indeed, most

plants use two or more collectors. The goal is to

pick reagents that will get to the right minerals.

Utilising a collector blend can balance cost and

performance.

“Cytec has multiple collectors and collector

blends that are continuously being developed to

tailor to the customer’s application.” A few of

the collector families that have recently been

introduced to the market include the new XR

Series Xanthate Replacement Collectors,

developed to meet the desire to replace

xanthates. “This new series of collectors are

cost competitive with xanthates and are strong

collectors but with high selectivity. In addition,

they are safer and vastly improves handling and

level of toxic exposure of the personnel to

product, stock safety management and

simplifies plant operations.

The XD 5002 blends were developed to

operate in a broad pH range 8-12 and be highly

selective in Cu/Mo, Cu/Au sulphide ores,

enhance Mo recovery in Cu/Mo bulk float and

enhance Au recovery in Cu/Au ores. The

MAXGOLD™ blends were introduced to float

primary Au ores; auriferous pyrite, arsenopyrite,

and tellurides and are also capable of enhancing

recovery in Cu/Au ores.

Monitoring and controlIt is now possible to use measurement devices

based on impedance tomography to create real-

time 3D images. The technology opens up

entirely new possibilities in controlling flotation

processes. “With Flotation Watch the operator

can see what takes place underneath the

surface. Flotation Watch measures several

parameters at the same time, on-line. The

sensor can measure the stiffness of the froth,

the thickness of the froth, analyse the interface

area between the froth and the slurry and it can

analyse the slurry too depending on the

customer needs,” says Jukka Hakola, Numcore’s

Vice President of Sales and Marketing.

With Numcore measurement devices, the size

and quantity of air bubbles and the solid matter

content of the froth bed can be monitored by

means of electric conductivity distribution.

“With Flotation Watch the stiffness of the

flotation froth can be measured and this helps

to keep the recovery in higher level. The signals

for the production failures, such as hardening

and collapse of the froth bed, can be seen

beforehand and avoided. This way we can help

FLOTATION


to minimise the losses in the flotation process,”

says Hakola.

Real-time characteristics are a key in this

technology; in other words, the system

continuously provides the operator with factual

data on what is happening in the flotation cells,

for example the location of minerals and the

bottom surface of the froth bed. “Because it has

not been possible to look inside tanks,

controlling a mineral concentration process has

largely been based on experience-derived

knowhow. Now that operators can ‘look’ inside

the process, it is possible for them to maintain

an optimal mix all the time,” says Hakola.

Numcore has, in close co-operation with a few

key customers, developed measurement

technology to better serve everyday work. “We

have now delivered several Flotation Watch

sensors to flotation cells in several markets and

for different metals such as copper, zinc and

gold. One of the main benefits is that

contamination of the probe is taken into account

in mathematical formula and the measurement

probe does not need to be cleaned. Our sensor

has been in a zinc rougher flotation cell for nine

months and is giving accurate results to the

operator. We can now offer automated control

for flotation process with Flotation Watch and

see that this can bring new benefits for our

customers,” he promises.

Numcore’s measurement technology is

currently in test use at Inmet’s Pyhäsalmi

copper-zinc mine (IM, April 2010,

pp10-18), among others.

According to Seppo Lähteenmäki,

Processing Mill Manager, the

system has provided accurate

information on the condition of

the froth bed, and the technology

has functioned reliably. “We have

tested the device for a few

months, and it has provided clear

benefits for those operators who

have received operator training for

it and actively monitored the data

provided by the system. The

device appears to be so useful, in

fact, that we are seriously

considering buying it after the test

period,” he says.

Mettler Toledo notes that pH greatly

determines the efficiency of the flotation, which

minerals will float, or even if there will be any

flotation at all. The critical pH value for efficient

flotation depends on the mineral and the

collector. Below this value the mineral will float,

above it, it will not (or, in some cases, vice versa).

In a recent white paper www.mt.com/pro-ph-

flotation, the company says “in order to

overcome difficulties with the hostile

environment in flotation cells, sensor

manufacturers are very creative in their choice of

sensor design. It is possible to find pH

electrodes with a ceramic, plastic, rubber or

even a wood reference diaphragm. Still, their

performance can be severely limited as the

colloidal particles and sulphides interfere

almost instantly with the reference system. The

sensor’s maintenance requirement is therefore

high, requiring very frequent cleaning and

calibration, and usually sensor life is short.”

Mettler Toledo has acknowledged this issue

and to combat it has designed the InPro 4260i

pH electrode with Xerolyt® Extra solid polymer

electrolyte. The InPro 4260i does not have a

diaphragm and instead features an open

Need a better way to free your froth?

Worldwide Slurry Pumping Solutions

Install the HVF (High Volume Froth Pump.) Our pump removes air from the impeller eye while running, which allows continuous operation and improved efficiency. This pump won’t stop you up.

Designed for air-entrained slurries, the HVF pump can be used in phosphate, hard rock mining and oil sands applications.

HVF Pump

Got a froth problem we can solve? GIW offers expert slurry pumping solutions around the globe. Minerals are everywhere. So is GIW.

GIW Industries, Inc.

Relation between collector and critical pH value

FLOTATION


junction, which is an opening that allows direct

contact between the process medium and the

electrolyte. Contrary to the miniscule capillaries

of any other type of diaphragm in conventional

pH electrodes, the diameter of the open junction

is extremely large and much less susceptible to

clogging or fouling. Another significant

difference is in the choice of polymer electrolyte.

Xerolyt® Extra was designed specifically for

service in tough environments to provide a strong

and lasting barrier against sulphide poisoning.

The company’s Intelligent Sensor

Management (ISM) is a platform based on

sensors with embedded digital technology for

better pH management. The integrated system

consists of a digital sensor and

ISM-compatible transmitter. The

key to the technology is a

microprocessor which is contained

within the sensor head and is

powered by and read through the

transmitter. Critical sensor

information such as identification,

calibration data, time in operation

and process environment exposure

are all recorded and used to

continuously monitor the health of

the sensor.

By constantly keeping track of process pH

value, temperature and operating hours, ISM

calculates when sensor calibration, cleaning or

replacement will be needed. Any need for

maintenance is recognised at an early stage.

In recent years, researchers at Imperial

College have been focusing on measuring air

recovery in industrial flotation cells and have

found that a peak in metallurgical performance

(improvements in both grade and recovery)

corresponds well with a peak in air recovery.

Major platinum and copper operations have

already observed the benefits of using this

methodology as developed by the researchers.

JKTech is now licensed by Imperial Innovations

to commercially provide this methodology and

associated benefits to the global minerals industry.

The PAR technique comprises two stages –

evaluation and implementation. The evaluation

stage involves determining the effect of the

technology at a mine site, typically determining

the peak air recovery for a bank (or banks) of

flotation cells and evaluating the resultant

metallurgical performance. The implementation

stage involves setting the air rates to those that

maximise the air and/or metal recovery, and

support and training of site personnel including

operating manuals. The implementation stage

requires an end-user license to be obtained by

the sites through Imperial Innovations.

Pumping frothGIW Industries has launched its new High

Volume Froth (HVF) pump. Unlike any other

pump on the market, GIW says, the HVF pump

can pump froth without airlocks. It provides

continuous operation without shutdown or

operator intervention. The new hydraulic design

actually removes air from the impeller eye while

the pump is running, so you can keep your

process moving and improve efficiency.

The GIW HVF can be retrofit into many

existing froth applications. The pump's de-

aeration system includes a patent-pending

vented impeller and airlock venting. This helps

to eliminate sump overflow due to pump airlock;

reduce downtime; and allow water use to be

restricted to the bare minimum. Fewer pumps

are required for less capital expense, requiring

less water and power usage.

The HVF pump has been fully tested on froth

and viscous liquids. The pump exceeded

expectations at a large phosphate company in

Finland. The company's existing pumps were not

able to provide the required flow and were

airlocking at only one-third of process design

capacity. After installing an HVF pump, the

company achieved a flow of 415 m3/h.

Traditional slurry pumps are prone to airlock

when working with slurries that incorporate

froth. A pump works by pulling in a liquid at a

certain pressure and adding mechanical force to

expel the liquid at a higher pressure. The air in

the froth does not want to move to a higher-

pressure zone, and it is prone to build up at the

lower-pressure pump entrance. The

accumulation of air can eventually block the

pump entrance completely, leading to airlock,

which requires pump shutdown or operator

intervention to avoid sump overflow.

How is GIW’s HVF pump different? The main

innovation is in the impeller design. Typically, air

bubbles gather at the centre of the impeller as

the heavier fluids are spun to the outer edges.

The HVF pump's de-aeration system includes

the vented impeller and airlock venting. In the

HVF pump, small holes in the centre of the

impeller allow air bubbles to pass through to a

separate port. The port vents air up and out of

the pump to normal atmospheric pressure.

Any liquid that passes through the port is

returned to the process tank. Air is no longer

building up at the impeller eye or pump

entrance, so airlock is avoided. IM

References1. Schubert, H. "On the optimization of hydrodynamics

in fine particle flotation." Minerals Engineering 21,

2008: 930-936.

2. Jameson, G. J. "New directions in flotation machine

design." Minerals Engineering 23, 2010: 835-841.

Designed for air-entrained slurries, the pumpcan be used in phosphate mining, hard rockmining and oil sands. The pump offersimproved efficiency and is environmentallyfriendly and cost-effective, GIW reports


FLOTATION

more than a century of progress - min-eng.com machine (formally bateman bqr) (inset) here at messina...

Documents