Flotation circuit optimisation using

modelling and simulation software

Authors: Authors: Authors: Authors: Rob Rob Rob Rob Coleman & Coleman & Coleman & Coleman & PerttiPerttiPerttiPertti LambergLambergLambergLamberg

How is your flotation plant running? Is it achieving target throughput,recovery and grade? If not, why not? Could it be due to feed orevariability, grinding and liberation issues or reagent type and dosage?Or could it be insufficient residence time since you are now operatingat 50% more throughput than originally designed?

When was the mineralogy of the feed last measured? Or ametallurgical survey to determine accurate flows around the circuitconducted? How about the gas dispersion in each flotation cell – arebubbles of the correct distribution for given particle sizes beingcreated?

It is nearly impossible to optimise your flotation circuit performancewithout knowing the answers to these questions.

Over the past decade there has been a significant advance in flotationcircuit optimisation through performance benchmarking usingmetallurgical modelling and steady-state computer simulation. Thisbenchmarking includes traditional measures, such as grade and

1

Pulp level control in flotation circuits

Issue 26 – August 2010

Outotec Australia’s Outotec Australia’s Outotec Australia’s Outotec Australia’s quarterly equarterly equarterly equarterly e----newsletternewsletternewsletternewsletter

Contents

Flotation circuit optimisation: 1

Protecting your mill: 5

Angas Mine: 9

Ou

tpu

t benchmarking includes traditional measures, such as grade andrecovery, as well as new flotation measures, such as ore floatability,bubble surface area flux and froth recovery.

Such circuit optimisation is a powerful tool in achieving the bestpossible flotation performance. Outotec’s HSC Chemistry software,which incorporates a new simulation module, can assist with thisoptimisation.

Firstly,Firstly,Firstly,Firstly, howhowhowhow dodododo youyouyouyou benchmarkbenchmarkbenchmarkbenchmark youryouryouryour flotationflotationflotationflotation circuit?circuit?circuit?circuit?

There are several ways to do this, including:

� MineralogicalMineralogicalMineralogicalMineralogical assessmentassessmentassessmentassessment ofofofof flotationflotationflotationflotation streamsstreamsstreamsstreams: determine theore mineralogy, degree of liberation, mineral associations andlocking at different particle sizes.

� MetallurgicalMetallurgicalMetallurgicalMetallurgical assessmentassessmentassessmentassessment ofofofof performanceperformanceperformanceperformance: perform plantsurveys to determine grades and recoveries of streams aroundthe circuit (requires mass balancing of experimental data). Frothcarry rates, concentrate lip loadings and flotation cell residencetimes can also be determined.

� ComparisonComparisonComparisonComparison ofofofof plantplantplantplant totototo laboratorylaboratorylaboratorylaboratory performanceperformanceperformanceperformance: determinethe maximum attainable recovery from the ore and compare thisto current plant recovery.

� GasGasGasGas dispersiondispersiondispersiondispersion inininin eacheacheacheach flotationflotationflotationflotation cellcellcellcell: determine the bubblesize distribution, air hold-up, superficial gas velocity and bubblesurface area flux.

� FrothFrothFrothFroth phasephasephasephase performanceperformanceperformanceperformance: determine the recovery across thefroth phase, froth stability and froth transport distances.

Editor:Laura WhiteLaura WhiteLaura WhiteLaura White

laura.white@outotec.comlaura.white@outotec.comlaura.white@outotec.comlaura.white@outotec.com

www.outotec.comwww.outotec.comwww.outotec.comwww.outotec.com

Ou

tpu

t

ModellingModellingModellingModelling andandandand simulatingsimulatingsimulatingsimulating flotationflotationflotationflotation performanceperformanceperformanceperformance

The results from these studies can then be used to calibrate a floatability component model of thecircuit. The flotation model developed by the AMIRA P9 Project, of which Outotec is a sponsor, isregarded by industry as the most suitable flotation model to use for circuit optimisation. Thismodel incorporates ore floatability with flotation cell pulp and froth parameters, residence time,entrainment and water recovery to the concentrate.

Once the model is calibrated, it can be set-up in a flotation circuit simulator, such as Outotec’sHSC Sim 7.0. The simulator is then able to predict the performance of the flotation circuit undervarious hypothetical changes to the operation of the circuit. This can include changes to feedproperties (such as throughput, mineral content and grind size), flotation cell operating properties(such as air rate and froth depth) and circuit configuration (for example recirculating the cleanerscavenger tails to the scavengers, or the addition of more flotation cells to increase residencetime).

This provides an extremely powerful tool to assist with optimising flotation performance. Thelatest version of HSC Chemistry software, 7.0, includes further optimisations of existing tools suchas a steady state process simulator and flowsheet capabilities, along with further additions.

So,So,So,So, whatwhatwhatwhat cancancancan HSCHSCHSCHSC SimSimSimSim do?do?do?do?

StageStageStageStage 1111 –––– flowsheetflowsheetflowsheetflowsheet designdesigndesigndesignThe first stage of any flotation optimisation process is drawing the flowsheet, which is donegraphically by the user. HSC also includes “check for error” tools to ensure various streams are

Output Australia | August 2010 | Page 2

graphically by the user. HSC also includes “check for error” tools to ensure various streams areproperly connected to the units and the process has input and output streams. If your process islarge, the flowsheet can be split into several pages, ie comminution on one page, flotation on thenext etc, followed by a summary page.

StageStageStageStage 2222 &&&& 3333 –––– massmassmassmass balancingbalancingbalancingbalancing andandandand calibrationcalibrationcalibrationcalibrationThe next stage is mass balancing the experimental data for the development of the model. HSCSim has a new experimental mode, which can collate, organise and visualise survey or laboratorydata. A “Mass Balancing and Data Reconciliation” module is included and has the followingfeatures (Figure 1):

� Individual sampling error for each stream and general or individual error model for eachmeasurement

� 1D (unsized), 1.5D (sized but no assays) and 2D (size-by-size assays) mass balancing

� Various regression options such as least-squares regression

� Versatile visualisation tools such as parity charts and stream tables and mass balancereports

Once the experimental data has been mass balanced, the model parameters can be determined.Calibration comes next and includes elements such as global mineralogy and feed streams(grades and flowrates). The simulator element of optimisation is then ready to run.

StageStageStageStage 4444 ---- simulationsimulationsimulationsimulationMost of the more advanced software nowadays includes a mineralogical database. HSC Chemistry7.0, has over 4,500 different species and more than 13,000 different minerals. In simulation youcan select the best matching mineral or add your own minerals into the database. It is possible toset-up HSC so that each person at a site uses and shares the very same database on the localnetwork. HSC even has a versatile tool for automatically converting elemental assays to mineralgrades.

As mineral processes do not treat minerals, but particles of different sizes and differentcompositions, it is important the software is designed on that basis. With HSC, you select 5 differentminerals in 5 size fractions, with 3 different behaviour types for each mineral, and HSC will create 75particles (mineral x size x types). Particles have global properties like size, specific gravity andcomposition and each unit uses these particle properties to determine what to do with each particle.

A structure based on particles allows you to load your liberation data from an MLA (MineralLiberation Analyser) into the simulator and simulate the process with true (measured) particles. Inthe highest level, i.e. with true particles, you can have very detailed information on your processlosses and impurities. At particle level you can simulate scenarios like:

� How will the change in grind influence the metallurgical performance of the plant?

� How will change in liberation influence the metallurgical performance of the plant?

� How will the concentrate quality change if we target to reject/accept some of the minerals?

Output Australia | August 2010 | Page 3

Figure 1 - Mass balance of unsized (1D) or size-by-size (2D), using HSC Sim 7.0

CaseCaseCaseCase studystudystudystudy

HSC Sim was used to design the flowsheet of the Esperanza copper-gold deposit in Chile. Oneparticular task of the software was to understand what benefits, if any, would result from theinclusion of a SkimAir flash flotation cell in the process cyclone underflows. Using client laboratorytestwork, the resulting elemental data was converted to minerals, and their pilot testwork data wasmass balanced, with models built using both laboratory flotation tests. The simulation wasestablished on a “mineral-by-size by floatability type” level. Several different scenarios weresimulated, including: circuit with and without SkimAir; number and type of rougher cells; flashcleaning; varying head grades and ore types and differing feed rates.

Figure 2 shows the simulation results with and without the inclusion of the SkimAir. The simulationsshowed that the SkimAir circuit produces 7.6% higher overall recovery for gold and 2.2% for copper.SkimAir technology was selected following these results and Esperanza will be commissioned in2010.

Output Australia | August 2010 | Page 4

SummarySummarySummarySummary

The use of software tools forthe simulation of the flotationcircuit are a major advance inflotation modelling andoptimisation. Steady-statesimulators can be used fortasks including circuitdiagnosis, process bottle-neckidentification, ascertaining theeffect of various parameterson metallurgical performanceand sizing process unitsproperly.

Some of the more advancedsimulation tools, such asOutotec’s HSC Sim, enablesyou to simulate mineralprocesses in different levels,from comminution circuitswith sizes and no composition,through to flotation processeswith minerals by size byfloatability components, to full

SkimAir Rougher

Grinding

Cleaner

Scavenger

Cyclone

Ore

Cyclone UF

SK Tail

SK Conc

Cyclone OF

Rougher Tail

Rougher Conc

Cleaner Conc

Cleaner Tail

Scavenger Conc

Scavenger Tail

Final Tail

Final Conc

CUF+SKTail Flash Cleaning

Flash Cleaner Conc

Flash Cleaner Tail

100

788

502

0

0

100.0

17.7

402

82.3

79.9

2.46

20.1

79.9

402

0

0

Au Rec%

0

Esperanza Flotation Circuit ModelingOutotec Research, Pertti LambergFebruary 2008

167

86.884.3

Porphyry Conventional

Final concentrate

Cu Grade % 30.1

Cu Recovery % 94.7

Au grade g/t 13.9

Au Recovery % 79.9

HSC Chemistry 6.1

SkimAir Rougher

Cyclone

Cyclone UF

Cyclone OF

Final Tail

163

40.6

Au Rec%Esperanza Flotation Circuit ModelingOutotec Research, Pertti LambergFebruary 2008

Porpyry FlashHSC Chemistry 6.1

If you would like more information, click here to contact

rob.coleman@outotec.com

_______________________________________________________________________________________________

Dr Rob Coleman is currently Technology Leader – Flotation for Outotec Pty Ltd in Australia. He has aChemical Engineering degree and a Doctorate in Minerals Processing. Rob has over 15 yearsexperience in the operation, modelling and optimisation of flotation circuits.

Dr Pertti Lamberg is Senior Technology Adviser at Outotec Research based in Pori, Finland. Pertti hasa Doctorate in Geology, and has over 10 years of experience in modelling and simulating of mineralsprocesses. He is one of the developers of the HSC Chemistry software.

floatability components, to fullprocesses with true particleswith measured liberation(MLA) data. Additionally,experimental data can becollected, elemental assaysconverted to mineral grades,circuits mass balanced anddata reconciled in mineral-by-size level. Powerfully, differentscenarios can be run with theprocess simulation, savinghundreds of man hours (andpotential human inaccuracies)in the process.

Grinding

Cleaner

Scavenger

OreSK Tail

SK Conc

Rougher Tail

Rougher Conc

Cleaner Conc

Cleaner Tail

Scavenger Conc

Scavenger Tail

Final Tail

Final Conc

CUF+SKTail Flash Cleaning

Flash Cleaner Conc

Flash Cleaner Tail

100

320

204

104

12.7

0

27.9

27.7

0.24

12.9

87.1

104

0

0

59.4

55.0

27.327.1

Final concentrate

Cu Grade % 17.9

Cu Recovery % 96.9

Au grade g/t 8.8

Au Recovery % 87.1

Figures 2. Gold recovery (distribution) in the Esperanza flotation circuitwithout SkimAir (above) and where cyclone underflow is directed to theSkimAir flotation machine (below).

Output Australia | August 2010 | Page 5

Protecting your mill – by mindset or by accident?

Author: Author: Author: Author: Daniel BraithwaiteDaniel BraithwaiteDaniel BraithwaiteDaniel Braithwaite

Without question, one of the most critical components in a plant’s throughput is the grinding mill. Ittherefore makes sound economic sense to protect the mill from unnecessary, preventable andcostly damage. This is even more important in current times as mills are under even greaterpressure, with lower grade orebodies and higher resulting throughputs. The chart below shows justhow much mill sizes have increased in the last ten to fifteen years.

Figure 1: Average mill size sold (in power) per year

The saying “the bigger they are – the harder they fall” has never been truer than for grinding mills.Nowadays, larger mills require more sophisticated bearings and lubrication systems as they aresubjected to higher loads and stresses. Larger mills also have higher throughputs, meaning thatthe opportunity cost in lost production with an unscheduled shutdown can run into hundreds ofthousands of dollars. The question then is; how do you best protect a mill from preventabledamage?

ModernModernModernModern controlcontrolcontrolcontrol systemssystemssystemssystems

A modern mill should be supplied not only with an up-to-date control system, but also a controlphilosophy which protects the mill. As a part of this control system, critical mill areas should havetransducers to sense, in real time, the condition of each given part. This is then fed back to thecontrol system which, as part of the control philosophy, will digest the information and makedecisions based upon pre-set interlocks. In general, there are three types of interlocks;

1.1.1.1. PermissivePermissivePermissivePermissive interlocksinterlocksinterlocksinterlocks::::

Conditions that must be met before a mill isallowed to start (e.g. bearing lubricationpumps must be running to allow the mill tostart)

2.2.2.2. AlarmAlarmAlarmAlarm interlocksinterlocksinterlocksinterlocks::::

Conditions that will cause the mill to raisean alarm, but not prevent the mill fromoperating (e.g. bearing temperature loweror higher than normal will trigger an alarm)

3.3.3.3. TripTripTripTrip interlocksinterlocksinterlocksinterlocks::::

Conditions that will cause the mill to ceaseoperation (e.g. dangerous bearingtemperature will stop the mill fromoperating) Damage to a bronze radial bearing when interlocks

were bypassed

Output Australia | August 2010 | Page 6

It is important to understand that the set points for these interlocks are selected to prevent the millfrom operating under conditions that have the potential to cause significant damage. It can betempting for an untrained or inexperienced operator to change these set points or bypass theinterlocks to keep a mill operational, however this mindset fails to consider the potential damagethis may cause. Instead, a short investigation to find out why an interlock is tripping and fixing it maysave an extended shutdown in the future and thousands of dollars in repair in the process.

For example, an interlock could trip if the oil cooling heat exchanger or its upstream strainerbecomes filled with dust. This would, in hot climates, reduce the efficiency of the heat exchange,causing the hydrostatic bearing lubrication oil to increase in temperature. This would first trip analarm interlock, warning that the temperature is higher than usual and close to being dangerouslyhigh. If this alarm was ignored, and the temperature kept rising, a trip interlock would activate andstop the mill to protect the bearings from damage. Damage could occur due to the fact that, as oilincreases, the viscosity lowers, reducing the oil film thickness at the bearing. Should the tripinterlock be bypassed in this condition, the mill would be running with an oil temperature that mayallow the bearing’s oil film thickness to reduce to the point where there is journal-to-bearingcontact, thereby damaging the bearings and mill journal. Repairing such damage would mean ashutdown of up to one week (or more depending on spares availability). Had the mill been inspectedat the first alarm, the simple process of cleaning dust from the heat exchanger or its upstreamcooling water strainer would have solved the problem.

StandStandStandStand alonealonealonealone millmillmillmill controlcontrolcontrolcontrol systemssystemssystemssystems

In stand-alone mill control panels, interlocks cannot be bypassed so easily. They usually havepassword protected PLC programs, and require specific knowledge or highly skilled personnel tobypass or change the interlocks. Where the mill control and interlocks are part of the centralisedmine control system, bypassing an interlock may be as easy as a few clicks on a mouse. So, in thesesituations it may be worth upgrading to a stand-alone control system, or putting the necessaryprotection in place to prevent unwanted interlock bypass. When purchasing a new mill orrefurbishing an older mill, it is important to take into consideration the additional protection a stand-alone mill control system will provide. It is also worth considering that electrical technology movesat lightning pace when compared to mechanical technology (especially mills), and reputable millmanufacturers are constantly reviewing and updating the best practices of mill operation andcontrol.

Damage to an inching drive when the mill was started with the inch drive engaged. The safety systems had been compromised

Output Australia | August 2010 | Page 7

ControlControl systemsystem upgradesupgrades

Damage to the axial bearing when a mill was started with a frozen charge. Locked charge interlocks on modern mills can prevent this

ControlControlControlControl systemsystemsystemsystem upgradesupgradesupgradesupgrades

With this in mind, mill control philosophies and systems may be subject to upgrades over only a shortelapsed period of time, so it is always worth speaking regularly to the manufacturers and discussing ifyour control system can be upgraded to meet current best-practices.

Firmware upgrades are very important, as they are generally released by the PLC manufactures toupdate the functionality of a CPU, or to prevent a re-occurrence of a recently discovered fault. Theneed for a firmware upgrade should be reviewed every six months and will require the services ofskilled PLC programmer. If the status of the firmware onsite is known, this review may be able to beperformed offsite.

TipsTipsTipsTips onononon maintenancemaintenancemaintenancemaintenance ofofofof controlcontrolcontrolcontrol systemssystemssystemssystems

Site maintenance personnel also need to be aware that the control systems protecting the mill requireregular maintenance, which includes the following checks:

1. Ensure that the control system is installed in a protected area, away from the presence ofextreme heat, moisture and dust

2. Ensure the panel exhaust fans are operating correctly, and filters cleaned regularly

3. Ensure the panel doors are sealing sufficiently to prevent the ingress of dust and water

4. Ensure that any PLC forces and bridges are recorded and action put in place to remove assoon as possible. Note that bridges and forces should only ever be used in circumstanceswith no other alternatives

5. Review the system set points regularly to ensure they are correct

6. Ensure the PLC firmware is regularly reviewed and updates downloaded to the PLC

Output Australia | August 2010 | Page 8

ConclusionConclusionConclusionConclusion

A broken down mill will generally mean an idle plant, or at the very least a highly compromisedplant. An up-to-date control system, operated correctly, will assist in preventing break downs. Thisis only effective, however, when combined with a sense of ownership of the mill (across all levels ofmine management and operations).

In such a scenario, there is a commitment to monitor, investigate and repair faults as (or before)they occur, rather than blindly bypassing the control system. With such an approach, when weprotect our mills by mindset rather than by accident, responsible care of the mill is probable, ratherthan accidental, and an increased overall mill availability will be the result

Mill control system guidelinesMill control system guidelinesMill control system guidelinesMill control system guidelines

NeverNeverNeverNever AlwaysAlwaysAlwaysAlways

Ignore alarm interlocksInvestigate what has changed to cause the alarm interlock to activate

Bypass trip interlocksInvestigate what has changed to cause the trip interlock to activate

Bypass permissive interlocks to get a mill operating Investigate what has changed to cause the permissive interlock to activate

Change alarm or trip interlock settings Consult with mill suppliers before making changes

.

____________________________________________________________________________________________

If you would like more information, click here to contact

daniel.braithwaite@outotec.com

Daniel Braithwaite is a Mechanical Engineer working with Outotec's Grinding Engineering departmentin Perth. Daniel has a Mechanical Engineering degree from UWA and technician level engineeringqualifications obtained overseas. For the past four years he has worked in the equipment selectionand design for mining applications in Australia. Prior to that, Daniel spent five years in themanufacturing industry in the UK.

Omit maintenance of the control system from schedules

Ensure the control system is properly maintained

Assume that if everything is running well, that it will continue to do so

Monitor trends and have your mill inspected on a regular basis (for discussion on this see the article ‘Planning for Mill Maintenance’ Output August 2009)

Author: Author: Author: Author: John John John John DurieDurieDurieDurie

A case study: Filters and Angas Mine

Output Australia | August 2010 | Page 9

Angas Zinc Mine, South Australia

The Angas Zinc Mine,located in South Australia,is 100% owned andoperated by TerraminAustralia Ltd. The mineexceeded all productionstart-up expectations byusing the latesttechnology in OutotecLarox CC filters (formerlyLarox Ceramec capillaryaction disc filters), whichis drying higher thanexpected grades of zincand lead concentrate.Following commissioningin July 2008, site wasbrought into fullproduction six monthsearly, in January 2009.

In its first year of life, the low-cost mine, with a resource of 2.4 million tonnes and situated only 60 kilometresfrom Adelaide, has produced nearly 23,000 tonnes of high-grade lead and zinc concentrate by the end of itssecond quarter.

The mine’s remarkable start-up performance far exceeded expectations and is due in part to an advancedfiltering and drying system. Angas’s installation of two Outotec Larox CC filters (formerly Larox Cerameccapillary action disc filters) for its zinc and lead concentrators, is fed by two Larox Flowsys peristaltic pumps.

Angas Zinc Mine, South Australia

Outotec Larox CC30 & CC15 filters

Output Australia | August 2010 | Page 10

HoseHoseHoseHose compressionscompressionscompressionscompressions reducedreducedreducedreduced bybybyby 50505050%%%%

The feed pumps employ a single, bearing-mounted eccentric roller design that compresses each hoseonce during a 360o operating cycle. This feature reduces the hose compressions required by 50%, whencompared to traditional peristaltic pumps that use two sliding shoes.

FiltersFiltersFiltersFilters inininin actionactionactionaction

Outotec Larox CC144 filter – 144m2 filtration area

The two Outotec Larox CC filters in situ use capillary action within ceramic disks to dewater the lead andzinc concentrates. The extracted filtrates are very high in clarity while the dried filter cakes meetrequired transport moisture limits (TMLs) for their ore grades.

After slurry thickening, the pumps feed the relatively coarse lead (P80, 50µm) and zinc (P80, 71µm)concentrates into their respective filtering system. Here, concentrates coat the ceramic disk segmentsduring immersion in slurry baths, dewatering starts immediately via capillary action. Extracted filtratepasses through the microporous structure in each disk before being transferred away by a small 2.2 kWvacuum pump. The dried filter cake that remains is continuously scraped off as the disks rotate.

QuickQuickQuickQuick upgradeupgradeupgradeupgrade

When lead grades rose higher than expected soon after installation, the filters were quickly upgraded,providing Angas with a 30% increase in filtration capacity, allowing the handling of higher leadconcentrates when the ore grade is high. As a result of this upgrade, the lead filter can capably handlehigher lead head grade ore and increase production while still producing filter cake under the requiredTML.

The Outotec Larox CC filter has undergone extensive development to establish itself as a top performerin the global mineral, metallurgical and mining market. This filter, with new ultrasonic positioningbetween the disks, is currently being utilised by Angas at rates of 75% to 90% over a 24-hour period,depending on the ore grade being received.

FilterFilterFilterFilter benefitsbenefitsbenefitsbenefits

The many benefits of using the Outotec Larox CC filters and Larox Flowsys Peristaltic include a plug-and-play design, no downtime is required for maintaining filter disks, only once-a-month maintenancechecks are needed for filter ultrasonics and seals, and routine filter backwashing is automatic and takesonly half an hour per shift. Also feed pump hose leaks can be easily detected, revolution counters canrecord pump hose life (thereby reducing unscheduled stoppages) and processing noise levels can bekept to a minimum.

Output Australia | August 2010 | Page 11

Angas’s general manager John Burgess reports he is “pleasantly surprised” at the ongoing performanceof his dewatering system. “It’s a good mine that is professionally set out and producing on its investmentbecause things are done right”. So much so in fact, that the Algerian government is interested in whatTerramin are doing at the Angas mine for Terramin’s development of its large Tala Hamza zinc deposit inAlgeria.

Outotec service engineer performing

If you would like more information, click here to contact

john.durie@outotec.com

John Durie is Regional Director Sales for Outotec Filters Australia Pty Ltd. John has over 30 yearsexperience in mining equipment supply. With experience in drilling, milling, crushing, screening andfiltration, John is also a founding Board member of the Filtration & Separation Association ofAustralasia.

_______________________________________________________________________________________________

Outotec service engineer performing final installation inspection

OUTPUT AUSTRALIA EDITOR

Laura White – Marketing Manager, Minerals ProcessingTel: +61 2 9984 2500Email: laura.white@outotec.com