AUGUST 2009 International Mining 23

WORLD COPPER

Copper recovery

The metallurgical heart of the majority of

copper oxide processes is the heap

leaching operation. Mineral Engineering

Technical Services (METS) in Perth notes the

success of this unit operation “is so important

that operators need to understand the

ramifications of their decisions or non-decisions

and how they could affect the downstream

processing.

“Heap leaching is an operation that can be

described as a scientific art whereby principles

of science can be used to guide experienced

personnel in attaining their goals.” Success or

failure is dependent upon a number of factors:

■ The type of ore to be treated

■ The extent of test work needed to

characterise the process

■ The interpretation of the test work results

■ Ore preparation prior to stacking

■ Agglomeration requirements

Although many of these can be, and are,

scientifically interpolated and used, their

understanding alone does not guarantee success.

Some of the issues that can make or break

an operation could relate to:

■ Compliance with the “smaller” requirements

of environmental authorities

■ Adequate and timely drainage of solution

from the base of a leaching lift

■ The degree of saturation in the pads

■ Heap porosity. Coarser or finer ore, which is

better?

■ Higher or lower irrigation rates. Which

would produce a better result?

■ Laying out irrigation pipe work for ease of

operation and maintenance

■ The addition of water, raffinate during

agglomeration where needed.

METS says “these sorts of issues are

generally personnel dependent and they have

the capacity to inflict unknowing harm on the

operations if they are not addressed adequately

and in a timely manner.

“Finally, regardless of the scientific principles

used for ore preparation, stacking and heap

leaching, the success of this part of the project

depends heavily on the personnel involved.”

METS has extensive experience in this area

having undertaken many projects including

various operations in gold, copper and nickel,

as well as technical audits and Due Diligence. A

full paper entitled Trips and Traps for Copper

Heap Leaching written by Damian Connelly and

Jeff West can be found on www.mets.net.au.

Improving flotationFlotation was covered in detail last month, but

its efficient use is so critical in copper recovery it

is always worth checking that the circuits are

operating at their optimum, to maximise

recovery. Dr Robert Coleman, Flotation

Manager at Outotec in Australia notes that

With input from many suppliers, John Chadwick looks atthe basics of heap leaching, Esperanza’s planned use of seawater for flotation and other flotation advances, tankhousemanagement and advances in extracting byproducts

Above: for on-off leach pads Tenova TAKRAF

developed a new generation of mobile conveyor

bridge with a reduced number of segments and

crawlers, and simplified maintenance and control. An

on-off leach pad consists of a Mobile Stacking

Conveyor Bridge (MSCB) receiving the heap from the

incoming leach pad feed conveyor via tripper car. The

stacker itself with another tripper car travels

permanently on the MSCB and dumps the material

onto the pad. As soon as the stacker reaches the end

of the bridge the MSCB segment travels

simultaneously a short distance for the next stacking

slice. After sufficient leaching time a bucketwheel style

reclaimer, connected to the Mobile Reclaiming

Conveyor Bridge (MRCB) excavates the material, which

will be transferred further via MRCB to the leach pad

load out conveyor in the centre of the leach pad.

Finally the leached material will be conveyed to a

spreader on a waste dump. Tenova TAKRAFs Heap

Leach Equipment works at several locations in Chile

with capacities between 5,000 m3/h and 7,400 m3/h

24 International Mining AUGUST 2009

metallurgy is one area that “immediately brings

rewards to the bottom line. In today’s

challenging environment improving the

metallurgical performance of a flotation cell

can mean the difference between operating at

a profit or at a loss.

“The heart of the mechanical flotation cell is

the rotor-stator mechanism. The mechanism

mixes the slurry, disperses the air and generates

the kinetic turbulent energy required to

accelerate the particles and attach them to the

bubbles. Outotec’s new rotor-stator

mechanism, FloatForce®, ensures optimised

mixing in the flotation cell – ensuring benefits

such as enhanced flotation cell hydrodynamics,

large air dispersion range with efficient mixing

and improved wear life.

“In FloatForce, the rotor design ensures the

air is introduced to the impeller’s peripheral

area and thus the core of the rotor is used only

for slurry pumping without diluting it with air.

Therefore the mixing capacity is maintained

even when the air feed rate is high. Since the

slurry flow through the impeller remains high, it

is possible to disperse large amounts of air

evenly into fine bubbles without any drop-off in

mixing and, as a consequence, there is no

sanding at the cell bottom.

“The new design of the FloatForce stator

provides a free inlet with a focus on a critical

flow path and a small and well-defined wear

area. Changes to the way the stator blades are

installed has also improved the time required

for maintenance. Straightforward maintenance

means less time and less cost.”

Also, Outotec’s reversible FlowBooster has

shown a range of benefits for large flotation

cells, including:

■ 10% improvement in primary mixing flow

■ 7% improvement in secondary mixing flow

■ Easy installation and maintenance, simply

bolts to lower impeller shaft

■ Potential to further optimise reagent

additions to large flotation cells

■ Improves flotation efficiency in cells above

150 m3 or those with a high SG gangue.

Recent test work has shown that when the

FloatForce and FlowBooster are installed

together, it is possible to slow down the motor

speed and reduce the power draw from the

mechanism, without affecting the metallurgical

performance. This not only leads to energy

savings but an improvement in metallurgical

performance may also be achieved by an

increase in coarse particle recovery.

A team of Metso Minerals’ flotation

specialists report1 that “the recent combination

of Computational Fluid Dynamics (CFD) and

Discrete Element Modeling (DEM) can provide

considerable insight into the performance of

flotation cells. One area of interest from a

fundamental equipment design perspective has

been the influence of flotation cell size and the

inflow rate on the metallurgical performance of

the cell. One of the specific design objectives

when increasing the size of flotation cells, or

increasing the feed flow to the flotation cell, is

to ensure that the feed stream flowing into the

cell does not have an opportunity to bypass the

mechanism.”

Their initial modelling efforts aimed at

quantifying the inter-relationship of cell size,

inflow rates, and feed and discharge box

placement, on the retention time distribution

of solids in the flotation cell, and the fraction

of particles that bypass the mechanism on a

size by size basis.

The paper referenced here is the first report

on a series of CFD investigations on the Metso

Minerals RCS flotation machine carried out by

the Metso Minerals Process Technology Group.

The full paper can be accessed on www.im-

mining.com, on the lower left hand side of our

home page.

The group’s conclusions were that “the flow

of particles through flotation cells is a highly

non-linear system. Intuitive assumptions on

the impact of changes in the operating

conditions, or the design of the cell, can be

misleading. The apparent differences in

possible conclusions that might be derived

from any single method of analysis highlights

the complexity of these systems. The

combined use of CFD and DEM modelling of

flotation cells can therefore provide valuable

insights on how changes in the operating

variables, or changes in the design of the cell,

may affect the transport of material through

the cell.

“At this time, no specific links are being

presumed between parameters such as the

residence time distributions and the bypass of

the mechanism, and the performance of the

cell. Those links will form part of an ongoing

study.

“CFD modelling provides very useful

knowledge on the flow of the slurry through a

flotation cell, but it can be difficult to quantify

differences in a meaningful way. DEM

modelling allows one to query almost any

aspect of the path of particles through the cell,

including time spent and location in the

flotation cell, and passes through the

mechanism. When those parameters are

correlated to cell performance, the combined

tools will provide a powerful method of

determining cell operating and design

parameters.”

Saline process waterIn 2008, Aker Solutions was awarded the

EPCM contract to develop the Esperanza

copper/gold project in the Atacama desert, the

driest desert in the world, 180 km northeast of

the city of Antofagasta and 100 km from

Calama, at an elevation of 2,100 m above sea

WORLD COPPER

In 2008, Aker Solutions was awarded the EPCM

contract to develop the Esperanza copper/gold project

in the Atacama desert, the driest desert in the world

level. The facility will use only raw untreated sea water in its production

process.

The Esperanza project is owned by Minera Esperanza, a partnership

between Antofagasta Minerals (70%) and Marubeni Corp (30%). It is a

sulphide deposit which will produce copper concentrate containing gold

and silver byproduct credits through a conventional milling and flotation

process. It becomes Antofagasta’s fourth operation in Chile, joining El

Tesoro, Michilla and Los Pelambres. Having conducted the feasibility studies,

Aker Solutions’ EPCM scope includes the design of the facilities for the

production of copper concentrates and construction management of the

development of the operation from ore extraction to mine infrastructure

and port facilities.

Aker Solutions notes that “from the outset of the project, Esperanza

has sought to be a model mining project, considering all HSE aspects,

from design to commissioning. Reducing the environmental footprint of

the operations is of key importance. Using sustainable design technology

in this project means the facility will use only sea water in its production

process, instead of valuable ‘desert water’ from the limited resources in

the area.”

On this project Aker Solutions is also pioneering a new,

environmentally-friendly, state-of-the-art technology for thickened tailings.

The technology used in these thickened tailings avoids heavy metals

infiltration to underground desert waters, dramatically reduces desert

water consumption and cuts dust emissions into the atmosphere. “All

this, will ensure a high level of stability for the tailings, both during the

lifecycle structures and decommissioning,” Aker Solutions reports.

An Environmental Impact Assessment, approved in 2008, allowed the

construction works in the first half of that year. Pre-stripping and other

early works began in early February 2008. Production is scheduled to

begin by the end of 2010. Esperanza’s 104.2 Mt of oxide reserves grading

0.37% Cu will be treated at El Tosoro. Its sulphide reserves total 1,204.4

Mt at 0.45% Cu, 0.012% Mo and 0.147 g/t Au.

In its first ten years of operations, Esperanza is expected to produce an

annual average of approximately 700,000 t of concentrate containing

191,000 t of payable copper, 215,000 oz of gold and 1.1 Moz of silver.

Molybdenum production is expected to begin from 2015, with some

2,100 t/y produced over the following five years. Antofagasta’s $1billion

Los Pelambres expansion and this $2.2 billion Esperanza project are

expected to increase annual group copper production by 60% to nearly

700,000 t from 2011.

Four pump stations, at an estimated cost of $300 million, will be

required to transport the sea water the 145 km from the coast up to the

deposit through steel pipes that will follow the same route as the

concentrate pipeline that will transport the copper concentrate in pulp

from down to Michilla’s port installations on the coast.

26 International Mining AUGUST 2009

WORLD COPPER

Outotec’s FloatForce ensures optimised mixing in the flotation cell providing

enhanced flotation cell hydrodynamics, large air dispersion range with efficient

mixing and improved wear life

The highest consumption of water by the concentrator plant is

estimated at more than 600 litres/s for milling (a 12.2 m SAG mill and

two 8.2 m ball mills) and flotation. Only 10% of the sea water will be

desalinated, for human consumption and concentrate washing.

Antofagasta is well experienced at using sea water in its operations, it

has the knowledge of the type of additives to use, the rubber coatings and

the special paint required for the flotation cells, to reduce the corrosive

effects of the sea water to the minimum. Also, Aguas de Antofagasta

(Chile) is a sister company, selling some 43 million m3/y of water.

Antofagasta conducted a series of flotation studies at SGS Minerals

Services. Outotec used the data from these studies on optimised flotation

research for the project, simulating the flotation circuit to find the optimal

flowsheet for the highest Au and Cu recoveries for the required Cu

concentrate grade. Simulations included both high-grade porphyry and

andesite ores. For both ore types conventional flotation and a circuit with

Flash flotation were simulated. In addition cleaning of the Flash

concentrate and the effect of flotation residence time in the rougher bank

(flotation volume) on recovery were studied by modelling and simulation.

(http://downloads.gecamin.cl/

cierre_eventos/procemin2008/rsmns/00129_00636_rs.pdf)

The simulation verified that Flash flotation technology would provide

higher recovery for gold and also indicated that there is potential to achieve

higher copper recoveries. The difference compared to conventional flotation

is 5% for gold and 2% for copper. The results of the pilot test were in

accordance with the simulations.

In the flotation circuit using Flash flotation the simulation shows that a

separate final grade product can be produced by cleaning the SkimAir

concentrate. Simulation indicates that in the flotation circuit with SkimAir

there is potential for 40-50% flotation volume decrease in the rougher

bank to achieve the same gold recovery, with corresponding copper grade,

as in the conventional circuit. Esperanza’s aim is to use flotation

technologies that will minimise energy consumption, maximise the recovery

of copper, gold and molybdenum, and reduce water consumption. It will

use 26 large Flash cells (300 m3) for better gold recovery.

Minera Esperanza’s Leonardo Parraguez and Luis Bernal reported on a

Chemical study for the selectivity and metal recovery in sea water

flotation (www.procemin.cl/resumenes_09/88. pdf).

The Esperanza mine has some zones of high pyrite content – over 3%

and a pyrite/copper ratio of over five - that makes it difficult in a sea

water environment to achieve a copper grade in the concentrate of over

28%. This is due to the buffer effect of sea water that constrains lime

addition, the main pyrite depressant used in flotation. However the high

pyrite ore is a small part of the total resources and an optimisation plan is

under development to improve the concentrate quality from these ores.

Excessive use of lime as a depressant mitigates the recovery of

molybdenum in the cleaning stage and the gold as well. They bring

together two problems in parallel, to improve the cleanliness of the

concentrate and to achieve acceptable recoveries of these metals.

The main conclusions of the studies conducted are:

■ The nature electrochemistry of sea water results in leaching of the

copper's small quantities activating the pyrite that adhere to its

surface

■ The process water recovered presents more favourable behaviour for

moly recovery than the fresh sea water. There is some kind of cleaning

of sea water achieved due to the action of the lime

■ For minerals with high pyrite content it is necessary to use another

depressant that strengthens the depression of the lime

■ Flotation of sulphides with sea water forces metallurgists to study the

physical- chemical behaviour in interactions with the aqueous media.

WORLD COPPER UnlockingMineral Wealth

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AUGUST 2009 International Mining 27

Tankhouse managementAlso in Australia, the 6th Annual PACE Zenith

Awards were held in Sydney in June and MIPAC

took first prize for its CellView® wireless

tankhouse management solution in the metals

products category. MIPAC was also selected as

a finalist in the mining, aggregates and cement

category for its Advanced Control Strategies work

with Xstrata Zinc Concentrator in Mount Isa.

CellView provides wireless condition

monitoring for tankhouse management and

was developed in response to a need for tools

that enable a more efficient, safe and profitable

refinery operation. CellView is a critical

foundation for effective tankhouse

management and enables customers to achieve

optimum production, quality, safety and

environmental standards. It combines the latest

advances in wireless technology with an

extremely robust design to increase the

efficiency and profitability of electro-refining

and winning operations.

MIPAC says CellView “significantly improves

copper and other electrolytic process operations.”

It was developed in Xstrata’s Townsville refinery

and has been trialled in Europe.

“CellView allows operators to produce more

cathode at a higher, more consistent quality

without having to increase inputs.” explains

Tony Mathison, Product Manager, MIPAC. The

first order was received, through Xstrata

Technology, for a major new copper plant

project with Kazzinc in Kazakhstan. CellView is

also being trialled with one of Europe’s largest

copper producers and processers.

CellView provides continuous, real time

monitoring of cell performance and enables

increased production through early detection of

process problems. MIPAC also reports that it

“reduces maintenance and implementation

costs, particularly compared to hard-wired

systems [and] is at least 25% smaller than

alternatives and therefore uses much less of the

precious real estate in a tankhouse.”

MIPAC’s Copper Concentration Monitor is a

rugged online process solution that automates

the control of the copper stripping process,

removing the need for manual chemical

analysis during electro refining. Designed in

cooperation with Copper Refineries Pty it

continuously monitors copper concentration in

electrolyte enabling:

■ Constant levels within the tanks, reducing

the chance of unsafe hydrogen gas

production

■ Minimal human intervention and integration

with the wider plant control systems

increasing efficiency, reducing operations

costs and improving the quality of

production.

Byproduct recoveryThere is increasing industry interest in

technologies to treat sulphur-rich residues from

hydrometallurgical processes – with the aim of

not only improving sustainable storage but also

capturing sulphur, precious metals and other

byproducts. Such residues result from

hydrometallurgical processes commonly used in

the production of copper, zinc and nickel.

Typically they contain elemental sulphur,

gypsum (from lime neutralisation), iron oxides,

acid insoluble concentrate components, minor

base metals and precious metals.

These residues currently require long-term

storage. Because residue with a high elemental

sulphur content is flammable, sub-aqueous

storage in a low dissolved-oxygen environment

has been one option, but a number of

environmental bodies have questioned the long

term desirability of this, arguing that the

material is not inert.

Vale has expressed interest to AMIRA in a

research program to explore improved

treatment processes which would address both

these sustainability issues and recovery of

byproducts. Because of the widespread use of

these hydrometallurgical processes, there would

appear to be benefits in other companies

joining the project.

Canadian and other North American

researchers would play a key role, with

28 International Mining AUGUST 2009

Preliminary flowsheet for Starfield Resources’ Primary

Leach Process. The company continues to do value

engineering as it develops the pilot plant, therefore

this flowsheet could change slightly. For example, at

this juncture, the company is relatively sure that one

stage of leaching will be sufficient

WORLD COPPER

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Memorial University, Newfoundland, keen to be involved. Further

information is available from Terry Braden, Regional Manager of AMIRA

North America. (Terry.Braden@amira.com.au)

Starfield Resources reports that it has already developed such a

technology. It has funded development of an innovative

hydrometallurgical process to recover metals from its Ferguson Lake

massive sulphide ore. This, Starfield describes as “the largest base and

precious metals project in Nunavut. The project’s massive sulphide

resource is estimated at 44 Mt with the potential to dramatically increase

in size. With one-third of the resource in the Indicated category, the

project is approaching the advanced development stage. A scoping study

was filed on SEDAR in May 2008, and an update to this study was

completed in December 2008 by Scott Wilson RPA. Both of the foregoing

studies indicated the project to be economically attractive.

“The hydrometallurgical process is unique in that it recovers most of

the metals (nickel, copper and cobalt) and turns typical problem elements

(sulphur and iron) into marketable byproducts. The process also has

another unique byproduct – energy. In fact, sufficient energy is produced

to power the production plant and the mine, with some excess power

remaining for potential sale to local communities,” says André Douchane,

President & CEO of Starfield Resources.

The process captures the sulphur and iron in an environmentally

acceptable form, and transforms it into byproducts instead of pollutants.

Iron is converted into hematite, which is non-toxic and potentially

marketable. Sulphur is converted into sulphuric acid.

As shown in the flowsheet, the Primary Leach process outputs

hydrogen sulphide gas. This H2S gas is reacted with oxygen, resulting in

the release of extreme heat (1,600°C) and sulphuric acid (H2SO4). The

extreme heat is captured to produce super-heated high pressure steam

sufficient to power steam-driven electrical generation.

“The ability to produce our own energy is a tremendous saving to both

our costs and the environment. With an expected ore feed of 6,000 t/d,

the Primary Leach Process generates 65 t/h of H2S. Burning the H2S

provides 1,000,000 megajoules/h of energy. To produce the same amount

of energy using fuel oil would require 24,000 litres/h. At $0.90/litre of

fuel oil, that’s a cost saving of $21,600/h! And that doesn’t include the

costs of shipping vast amounts of diesel fuel to the production plant or

mine. Not using 24,000 litres/h of fuel oil, prevents 60 t/h of CO2 being

emitted into the atmosphere,” states Dr. Bryn Harris (an expert in

hydrometallurgy and Starfield’s consultant on the process).

Versatile smelterAs part of a program to further optimise plant operations at the Horne

smelter in northwest Quebec, Canada, both in terms of copper

production and overall plant performance aspects, a number of new plant

models were recently developed and implemented. This involved the

development and initial applications of a new tool developed using the

ARENA software to model the plant logistics and scheduling – Discrete

Event Simulation. The present model also uses data available from earlier

heat and mass balance models and focuses on plant logistics and

scheduling aspects of the smelting, converting, fie refining and casting

operations at the smelter.

This plant is the largest custom feed smelter in North America.

Operating as a fully custom smelter since 1976 when the famed Horne

copper-gold mine closed after more than 50 years of operation, the plant

now treats a wide range of shipped copper concentrates and copper-

containing recyclable materials imported from many parts of the world.

The copper concentrates include both conventional and complex types,

while the recyclable materials cover a wide range of different products

such as spent processing slag, catalysts and metallic alloys, as well as

AUGUST 2009 International Mining 29

30 International Mining AUGUST 2009

recycled electronic components containing

appreciable quantities of copper metal and/or

precious metals. The plant feed materials,

totaling some 780,000 to 850,000 t/y, are

typically smelted in the Noranda Process

Reactor, while some feed materials may also be

handled in the Noranda Converter (NCV). Each

of these units operates in a continuous manner.

In the Noranda reactor, a 73% Cu matte

containing some 3-4% Fe is produced along

with reactor slag. The reactor matte is tapped

and conveniently transferred within the same

building to the adjacent NCV unit for

continuous conversion to blister copper, while

the reactor slag is also tapped and after

cooling, is treated for copper recovery by

milling and flotation. The NCV blister copper in

turn is periodically tapped and transferred by

ladle car to a separate building (converter aisle)

where a number of batch operations are

carried out.

Firstly, the pyro-refining vessels (or PRV)

undertake desulphurisation and impurity control.

Secondly, the copper is transferred to the anode

furnaces for de-oxidation using natural gas

injection prior to anode casting. The cast anodes

are then shipped to Xstrata Copper’s Montréal

East refinery where high grade cathode copper is

produced by electrorefining, along with recovery

of precious metals.

The objective of the modelling work was to

provide a tool for evaluating different operating

scenarios. The model was used to examine the

impact of a number of plant parameters. For

example, a feed high in copper content may

potentially pose a processing constraint

downstream of the NCV, while treating higher

quantities of lower grade feed and recyclables

may potentially pose a smelting bottleneck in

order to maintain a given copper throughput

rate. Particular attention was given in the

model development to the cycles between the

PRVs, the anode furnaces, the anode

casting operation and the crane logic.

As regards anode casting, it was

confirmed that increasing the actual

anode casting rate alone could

potentially be counterproductive since a

given amount of wheel maintenance

and preparation time is required

between extended casts of several

anode furnace charges. Hence, it was

found beneficial to slow down the

casting rate to ‘catch’ the next charge

of anode-ready copper that is ready for

casting rather than continue at full

casting rate. This approach has been

practiced for several years at the Horne

smelter, but the value of the model

now is that the productivity gain of this

practice can now be quantified or,

alternatively, the gain of other potential

strategies intended to improve the plant

productivity can also be quantified.

In another simulation scenario and for a given

feed mix, the feed rate to the Noranda Reactor

was gradually increased and the processing

capability of the downstream units was

observed, in particular regarding a potential

bottleneck situation to occur in different sections

of the converter aisle and casting wheel.

The model was developed and put into

service in early 2008 and already has proven

valuable in evaluating potential operating

scenarios. The work also shows that the

modelling activities carried out by Xstrata Process

Support in collaboration with the Horne are

quite capable of handling this type of complex

plant and indicating the potential productivity

gains with alternative operating strategies. IM

References1. Lichter, Jens; Potapov, Alexander and Peaker, Richard,

The use of computational fluid dynamics and discrete

element modelling to understand the effect of cell size

and inflow rate on flotation bank retention time

distribution and mechanism performance, Proceedings

39th AGM of Can. Min. Proc., CIM, pp473-496.

2. Coursol P. et al, Optimisation of the Xstrata Copper-

Horne smelter operation using discrete event

simulation, CIM Magazine, Vol 4, No. 2 (2009)

A schematic illustration of the main units at the Horne

smelter considered in the logistic model, taken from

the main screen of the ARENA model. The diagram

includes the Noranda Process Reactor and the NCV

shown in the upper part of the diagram, with the PRV

units and anode furnaces shown along the middle-

lower part of the diagram; the two converter cranes

which can traverse the length of the converter aisle

are shown in the lower part of the diagram. A

number of data boxes presenting numerical data

related to matte, metal and slag parameters are also

shown. These include for example, the actual quantity

and melt levels in the Noranda reactor and the NCV.

The display also includes data pertaining to plant

conditions when throughput may be lowered on

account of local ambient air conditions in town (The

SCI label in the upper part of the figure)

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