One of the great challenges for the

industry has been to find an alternative

means to process the most abundant

type of copper ore on Earth, chalcopyrite. This is

particularly important now with global demand

for copper set to increase and world copper

resources dwindling and average grades falling.

As FLSmidth Director for the Rapid Oxidative

Leach (ROL) process, Gary Roy, states: “that

makes a compelling business case for

developing more effective processes to treat

lower grade copper ores. Leaching is the most

widely used low-cost, extractive metallurgy

technique for converting metals into soluble

salts in water.

“Until now, leaching has only been applied to

oxide ores and simple sulphide ores. Nobody

has been able to identify an economically viable

process to dissolve chalcopyrite (CuFeS2). ”

In a dramatic breakthrough, FLSmidth has

cracked the code using a mechano-chemical

approach. It also won the global Top 100 R&D

award at the R&D 100s for the ROL process last

year.

Sally Rocks is Senior R&D Chemist with the

ROL process team in FLSmidth. After five years

of intensive research and laboratory work, she

and a team of chemical engineers, geologists

and minerals processing engineers has cracked

the code of primary copper sulphide leaching,

making it feasible to produce cathode copper on

site using existing equipment and bypass the

costly smelting process completely.

“We knew we were addressing a very difficult

challenge where countless other scientists have

failed and our satisfaction at finding a solution

has been immense,” Rocks states.

Leach reactions are highly complex systems

dependent upon interactions at the solid-liquid

interface. “We have succeeded by identifying a

new process that strains the atomic arrangement

of the minerals themselves, affecting the solid

below the interface,” she explains.

Chalcopyrite has presented the team with a

unique set of challenges. “It has an inbuilt

chemical defence,” she continues. “When

sulphide minerals start to leach, the resulting

elemental sulphur creates a passivating layer

consisting of a colloid film on the particle

surface that slows the chemical reactions that

leach copper.”

Chemists have struggled for years with the

challenges of this defensive passivation layer

during processing - a critical issue has always

been the high energy required which has made

leaching uneconomical.

FLSmidth notes: “Energy intensive ultra-fine

grinding, catalysts, high temperatures and high

pressures have all been trialled. And some have

succeeded. But the recovery rates have been too

low and the energy consumption too high to

create a process that could be commercially

viable.”

Rocks and her team took a mechano-chemical

approach coupled with pre-leach activation.

To activate chalcopyrite for faster copper

leach kinetics and improved copper recoveries,

the team needed to extract iron from the lattice

using copper ions. In order to initiate the process,

the research team needed to find a way to first

destabilise the structure of the chalcopyrite.

“We discovered that very small changes to

the structure of chalcopyrite could impact on

how rapidly it leaches. We designed an

'activation step', where we doped the copper-

rich chalcopyrite mineral with copper sulphate.

The copper sulphate quickly reacts with the

solid chalcopyrite to create a new solid structure

that produces strain throughout the entire

copper-bearing particle,” she explains.

That turned out to be a key process

component. The ‘doping’ was necessary to make

the chalcopyrite more reactive.

34 International Mining | NOVEMBER 2017

LEACHING & SX/EW

There have been someinteresting breakthroughsin the application of heapleaching and SX/EW, John Chadwick reports

Weatherly International’s Tschudi copper projectis an open pit copper mine located about 20 kmwest of Tsumeb, Namibia, designed to produce17,000 t/y of LME Grade A copper cathode. Theheap leach pad consists of 18 cells with anoverall pad 1,100 m by 500 m in plan. The padhas a composite clay/HDPE liner overlain by agranular drainage layer incorporating a networkof slotted drainage pipes. The solution ponds aredouble lined with HDPE incorporating a seepageinterception layer over clay bedding. The stormwater and raw water ponds have a single HDPEliner. The pad is stacked in 4 m lifts forweathered oxide ore and 6 m lifts for unalteredore to a final height of 36 m. Knight Piésoldconducted a heap leach bankable feasibilitystudy, including geotechnical investigation andlaboratory testing of both construction materialsand leached ore. This was followed by detaileddesign and construction monitoring of the leapleach pad, drainage system and collectionchannels, PLS, ILS, storm water, raffinate, SXevent, and raw water ponds

Long-term trends in processed copper ore grades.

Source:ALTA Keynote paper Process expertise: “The key to managing

hydrometallurgical project risk” by Mark Benz, President, MRB Business Services

Heaps and extracts

LEACHING &SX-EW_proof 27/10/2017 12:22 Page 1

“As chalcopyrite is a semiconductor, the

crystal lattice can react with small amounts of

copper. We used the very element we were

leaching to act as a catalyst, and then strained

the chalcopyrite crystal lattice. And in that way,

we made the entire particle more vulnerable to

chemical attack,” she adds.

The team discovered that small levels of

doping accelerated the leach kinetics of the

chalcopyrite and could significantly shorten the

required residence time within the total leach

circuit significantly.

“Other technologies have relied on fine

grinding to increase the surface area of the

particles. While fine grinding is effective, it also

requires a lot of energy. We needed to come up

with a low-energy process,” she explains.

To ensure continued leaching, despite the

passivation layer, the team developed a

mechano-chemical leach reactor, a Stirred Media

Reactor (SMRt). This is 30 times milder than a

regular stirred media mill, and 100 times milder

than that of regular grinding. The primary leach

vessels are linked to this satellite reactor, and

the leaching materials circulate between the

two.

The SMRt gently scrubs the surface of the

particles causing abrasion of passivating films

and exposing reactive mineral surfaces. The

abrasion of the particle surfaces is balanced to

match the leach rate of the particles, so that the

soft sulphur layer is removed with minimal energy.

The reactor also harnesses free radicals. At

the freshly fractured mineral’s surface, a number

of transitory, high-energy surface states are

produced; including the likelihood of surface

bound free radicals producing reactive oxygen

species. With half-lives of seconds to minutes,

the benefits to be gained from the generation of

these highly-reactive surface species are lost if

the processes of grinding and chemical leaching

are performed separately, Rocks explains.

“People have really underestimated the

reactivity of fresh mineral surfaces,” she says.

Thanks to the low grinding rates of the SMRt

the team could combine mechanical and

chemical energy and take advantage of the free

radicals. The unstable species on the mineral

surface quickly react with the ferric lixiviant and

result in faster copper leach kinetics, reducing

overall energy consumption.

In December 2016, the ROL process team

succeeded in leaching chalcopyrite in an

integrated pilot plant, combining leach and SX-

EW. Roy is excited: “We produced 99.9% pure

copper cathode on a continuous basis, with full

recycle process streams. Next step is to work

with customers on a large scale demonstration

plant”. ROL performance summary:

n Leaches chalcopyrite in less than six hours

n Leaches arsenic containing minerals in 15-30

hours

n Process low grade concentrates between 7

and 20% Cu

n Integrates with existing SX-EW technologies

– FLSmidth can retrofit existing leach

infrastructure by adding SMRt reactors

n Operates at atmospheric pressures and 80-90°C

- reduces CAPEX as no pressure vessels required

n Is amenable to a feed particle size P90 of 40-

60 µm - so no up-front fine grinding required

n No catalyst required - reduces OPEX and no

catalyst recovery, regeneration or recycling

unit operations required

n Can easily be scaled from 5,000 t/y cathode

up to 100,000 t/y cathode

n Is autogenously heated and net

consumption of acid is neutral

n Recovery of other metals like zinc or lead

that may be penalised by smelter can turn to

revenue. Further ability to extract gold and

silver

n Treat arsenic bearing concentrates on site,

reducing smelter penalties and avoid risk of

future regulations on transport of high

arsenic levels

n Concentrates with high arsenic bearing

minerals like enargite or arsenopyrite, have

higher Cu grades, and also higher amount of

gold or silver than clean concentrates. This

higher value can be unlocked if the ore can

be processed without smelters. This also

expands ‘usable reserves’.

LEACHING & SX/EW

LEACHING &SX-EW_proof 27/10/2017 10:53 Page 2

HPGR breakthrough During the recent Vancouver Gold Conference,

Holger Plath, Vice President of thyssenkrupp

USA, provided an update on the successful use of

HPGR in gold leaching. Although HPGR

technology has been recognised since the late

1980s as a potential powerful tool for heap

leaching, operational applications did not

proceed until recently. Today, four gold

operations have implemented HPGRs. All of

those process operations confirm the early

assessments, ie using HPGR within the crushing

stages shows significant benefits for improving

the overall hydrometallurgical parameters.

The largest and most interesting such gold

heap leach HPGR project is at Golden Queen in

California. It has installed a tkIS Polycom HPGR

unit and operates under the following

parameters:

Historically, concerns were voiced in the

industry regarding the generation of excessive

amounts of fines when using HPGR as a tertiary

crusher. These were not substantiated. These

concerns have been addressed via a combination

of efforts including better ore characterisation,

optimal HPGR operation, agglomeration, heap

construction, leach practices and avoidance of

heap compaction. Although HPGR’s major benefit

to hydrometallurgy is its micro-fracturing of the

rock matrix, it does generate some finer product

sizes which are inherently beneficial for gold heap

leaching. Extensive testing between 1996 and

2016 has documented that HPGR technology,

when used under best-practice operating

conditions, including the adequate pressure

settings, will not introduce excessive amounts of

finer material.

The operational data confirm that the HPGR’s

performance contributes to substantially better

gold extractions (several percent) which are in

line with the bench- and pilot testing. In order to

assist in future gold leach operations in North

America for converting to or using HPGR,

thyssenkrupp has installed a Pilotwal HPGR unit

at the Kappes, Cassiday & Associates test

facilities in Reno, Nevada. This unit can handle

samples as small as 100 kg for trade-off and

feasibility studies but it can also process up to 20

t/h for larger scale testing and semi-commercial

purposes.

Other positive aspects of HPGR use in leaching

increasingly confirm the value of this technology

not only as a high(er) throughput, power- and

steel-wear saving comminution system but also

as a metallurgical tool. These include, Plath

reports, but are not limited to the following:

n Higher availability than any conventional

crusher

n Studded tyre wear protection achieved

extended lifetime of the rolls from 3,000 to

>10,000 h

n Possible rapid adjustments of pressure and

roll speed to match the geo-metallurgical

variance of the ore

n Possible recycling of edge material of the

HPGR discharge material for a finer product

n Indications that HPGR use will result in both

lower retained and saturated moisture in the

heap (depending on the ore/rock type)

n Even with variable rock types and alteration,

HPGRs can generate discharge products

which (a) exhibit good agglomeration and (b)

show favourable PSDs for geo-technical heap

stability

n Faster leach kinetics

n Substantial increases of gold extractions with

up to 20% higher than achieved via

conventional crushing

n Recent publications suggest that HPGR may

even offer a good potential for heap leaching

Witwatersrand gold ores.

Re-thinking the standard approach of leaching

gold ores with new HPGR flowsheet and process

concepts may actually achieve metallurgical

results thus far believed to be out of reach. The

concept of de-sliming prior to leaching, has

become of considerable significance (again) with

the use of HPGR. Finally, larger HPGR units could

become a cutting-edge optimisation for bio-

leaching of low-grade refractory ores using a

combination of finer blasting and a primary

crusher followed by in-pit HPGR.

Best practiceA panel discussion was held immediately

following the Cyanide Alleviation/Alternatives

Forum during the Gold-PM Sessions at ALTA 2017

in Perth in May. The discussion centred mainly on

cyanide recovery/recycle and on-site cyanide

manufacture as key issues in satisfying the

concerns of regulators and the public and

allowing its use to continue.

Ralph Hackle, Rio Tinto (Australia), pointed out

that there was a panic about cyanide and a push

towards alternatives to cyanide in the late 1990s,

which perhaps is happening again. “It appears to

be similar to the sentiment around coal mining

and renewable energy. The fact is that cyanide is

technically and economically superior to any other

lixiviant. We’ve made some incremental

improvements with alternative lixiviants, but

cyanide is still ‘king’, and is used for most of the

world’s gold production. If cyanide is banned, gold

production will decline and the price will go up.”

He agreed with Malcolm Paterson, PT Green

Gold Engineering (Indonesia) (see August 2017

issue p45) that the best approach is to make

cyanide acceptable. Paterson believes that on-

site production of cyanide is an important issue

in changing the public perception about cyanide.

Xianwen Dai, CSIRO Mineral Resources

(Australia) reported that the Chinese government

has become tougher in approving plants using

cyanide, and Chinese companies have become

interested in thiosulphate. A cyanide sales tax

has been introduced and cyanide is not allowed

near population centres and environmental

protection zones. The trend is towards the

Chinese government becoming increasingly strict

on the use of cyanide.

Panayiotis Papacharalmbous, PT Kisangani

Boomi (Indonesia), commented that in Indonesia

it is not just an environmental issue, but also

about conservation of minerals. So, unless

operators can show that they are getting good

recoveries, it will be difficult to get a permit. The

trend is towards looking beyond processes such

as heap leaching with 70% recovery to better

processes with 95% or higher if possible. Some

of these alternative processes still have quite a

way to catch up with cyanide.

ALTA’s Alan Turner asked whether we are

heading for an increasing number of

governments banning cyanide, and increasing

community and media opposition. If so, is the

industry taking it seriously enough in developing

alternatives, or is the mining industry burying its

head in the sand?

Cyanide alternativesChairing the discussion, Stephen La Brooy,

Ausenco (Australia) opened the panel and the

floor for questions regarding cyanide

alternatives. He noted that the main sessions

included papers on chloride, bromide,

thiosulphate, thiourea, and that several of the

world’s experts on the application of

thiosulphate were present.

John O’Callaghan, Newcrest, (Australia), asked

whether there are alternatives being worked on

which were not covered during the main

LEACHING & SX/EW

n HPGR model POLYCOM® 17/12-5

n Operating mode Continuous, open circuit (option for edge recycle)

n Feed material heap-leachable gold ore

n Throughput 750 t/h (fresh feed, dry base) (Nominal)

n Design throughput 900 t/h (with edge recycle)

n Feed moisture 3%

n Feed size F100 <45 mm

n Product size P80 <6 mm

n Agglomeration drum with cement addition

36 International Mining | NOVEMBER 2017

LEACHING &SX-EW_proof 24/10/2017 11:11 Page 3

sessions. He reported that he has looked at

chloride extensively, and believes that for a high

chloride process, recycle of the chloride and

maintaining the water balance is hard work.

Whereas it is okay for anode slimes, for ores and

concentrates it is more difficult, though not

impossible, and needs a good business case. He

said that the industry must come up with

something, as the currently feasible alternative

to cyanide is leaving the gold in the ground,

which is a difficult decision if the deposit is high

grade. A higher cost process with lower efficiency

compared with cyanide may be preferable under

those conditions.

He further commented that we need to keep

looking at alternative technologies, including

revisiting old technologies. We mustn’t get

bogged down into the way a lixiviant has been

used in the past, and think outside the box. We

need to encourage academics and researchers to

keep working on alternatives as one day it may

be beyond our control and we may be forced to

do something different.

La Brooy agreed and put forward the example

of all the work done on copper catalysed

ammonium thiosulphate, yet the first plant uses

calcium thiosulphate.

Petrus van Staden, Mintek (South Africa),

proposed that there are two ‘holy grails’ the

industry is searching for – a cyanide free gold

process and an in-situ process which avoids

mining. He asked whether we could select a

subset of the cyanide free processes as

contenders for in-situ application. For in-situ

application, a reagent needs to be stable

underground and controllable from the surface.

Xianwen reported that CSIRO is doing work on

in-situ leaching, and has done column leach test

work for a gold mine in Australia using a

particular product. The results are promising and

CSIRO is waiting for the company to decide to go

to the next stage. He considers that thiosulphate

could be one of the options for in-situ

applications.

Van Staden commented that on one hand, we

need something stable and controllable, and on

the other hand if it escapes into the environment

it must biodegrade so that it is not a lasting legacy.

Elsayed Oraby, Gold Technology Group, Curtin

University, (Australia) said that glycine covers

most of these points and has a wide range of

metal stability for gold and copper (pH 7-12). It is

non-toxic and environmentally benign, and is a

good candidate for in-situ leaching (see Gold

without tears, IM, August 2017, pp34-49)

Paul Breuer, CSIRO (Australia), floor, said that,

as pointed out by La Brooy in his keynote

presentation, for in-situ the issues are very

similar to above ground processing for all the

alternative lixiviants. The amount of reagent

recovery, recycle and re-use that is achievable is

probably going to be the biggest driver. It’s the

complete process, not just having a reagent that

can leach gold.

Karel Osten, Amec Foster Wheeler (Australia),

reported that many years ago he worked on in-

situ leaching trials with thiourea. It worked pretty

well, but the main problem was the loss of

solution and reagent. Apart from anything else,

for successful in-situ leaching you have to find

the right orebody with the appropriate

permeability. Many gold orebodies don’t fit this

criterion.

Paterson said that in-situ is a niche process for

gold, applicable to a very small percentage of

orebodies. Normal mining/leaching applies to a

much higher percentage of orebodies and

therefore deserves more focus. Also, above

ground mining is much easier to control.

Breuer responded that CSIRO is looking at in-

situ as a game changer, even for hard orebodies.

Some of the technologies being looked at for

increasing permeability include hydraulic

fracturing, cryogenic cracking, chemical means of

creating microfractures, and electro kinetics.

Van Staden reported that from the point of

view of the South African gold industry, in-situ is

viewed as a possible long-term solution as mines

become deeper, to reduce underground fatalities.

Taylor said that a lot of developers of new

processes are technology companies, often very

underfunded, and have a tendency to collapse

with time.

Therefore,

wouldn’t it be a

good thing to

have some sort of

industry funding

so that the

technologies will

still be available if

a cyanide ban

does come?

Oraby reported

that the Curtin

work on glycine

has received good

support and

encouragement

from the big gold

producers.

Turner said that

Mark Benz’

nickel-cobalt-

copper keynote

paper is well

worth reading as

it talks about the

value of process

technology in

mining companies

and how it should

be treated as an investment and not something

the accountants cut off when the going gets

tough. Benz emphasised the need for mining

companies to keep a strong internal technical

department, to liaise with universities and

engineering companies, and collaborate around

the industry. He pointed out that many successful

technologies have been developed in this

manner, but when innovations become isolated in

technology companies, they tend not to get off

the ground.

La Brooy added that it’s only when the mining

companies become involved in the development

process that there is someone with the drive to

actually do it. It’s only when there is someone

who actually needs the solution that the process

is commercialised. Barrick put in 15-20 years’

work before thiosulphate leaching at Goldstrike

was commercialised.

He also observed that the gold industry used

to be open, but now companies tend to have IP

control departments and safeguards. Conversely,

the aluminium industry has gone the other way;

they used to be secretive but now are more open.

Maybe the cyanide challenge will bring the gold

industry together to lower the cyanide profile.

Summary of key points from the panel

discussion:

n The application of a totally closed system

with cyanide recycle designed and operated

under chemical industry standards, together

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38 International Mining | NOVEMBER 2017

with on-site cyanide production, may make

the use of cyanide acceptable, at least in

some jurisdictions

n It is imperative to continue to work on

developing alternative leaching systems in

case a widespread cyanide ban should

eventuate

n Alternatives to cyanide could play an

important role if research work on improving

ore permeability makes it feasible to apply in-

situ leaching to gold ores

The use of oxygenated sulphuric acid leaching

with added sodium chloride was pioneered in the

copper matte leach plant at Port Pirie in South

Australia (now owned and operated by Nyrstar) in

the 1980s. This plant produces 4,500 t/y of EW

copper cathode. Some earlier attempts were

made to adapt the process to the leaching of

chalcopyrite and mixed copper sulphide

concentrates. Leaching of chalcopyrite was

successfully achieved, but the process has never

been extended beyond the Port Pirie site, due to

a variety of commercial reasons.

The ALTA 2017 paper Acid Chloride-Sulphate

Leaching of Magnetite Hosted Chalcopyrite

Concentrates from the Viscaria Copper Project In

Sweden by Nigel Ricketts of Altrius Engineering

Services and Ray Robinson of Avalon Minerals

outlines the successful leaching trials using this

leaching system to leach magnetite hosted

chalcopyrite mineralisation from Viscaria. “The

mineralisation contains both talc and magnetite,

with very little pyrite. The chalcopyrite was able

to be leached to up to 96% recovery within eight

hours from a variety of flotation concentrates.

The rapid dissolution of magnetite means that

the flotation should be taken to a cleaner

concentrate before leaching in order to minimise

the acid consumption. It was also found to be

possible to precipitate the iron dissolved from

both the magnetite and chalcopyrite during the

leach as a jarosite, potentially eliminating the

need for a dedicated iron removal step in the

flowsheet.”

The leaching regime followed on from the

findings of the Port Pirie researchers and

consisted of the following variables:

n Acid addition as 98% sulphuric acid – 80-90

g/litre

n Copper sulphate – added to 5 g/litre to

minimise H2S formation on start-up

n Sodium chloride – added to 30 g/litre

chloride

n Pulp density – usually 10% solids by weight

n Oxygen addition – 0.25 litre/min

n Temperature - 95°C aim

n Agitation – 1,000 rpm on the Rushton impeller

Jack Bender, Mining Solutions, BASF Corp,

reported on large-scale column testing

performed in An Effective New Leaching Aid

Successfully Tested with Oxide and Mixed

Sulphide Copper Ores. Some 90 kg of an

agglomerated ore was leached for 60-120 days in

batches of 16 columns, at which point roughly

75% of the total copper was leached for oxide

ores and 60% of the sulphide ores. The leaching

aid candidate achieved a 5-20% increase in

copper recovery over columns without leaching

aids with an overall standard deviation of less

than 1% for the data between columns.

In addition to the column testing, the leaching

aids were subjected to bacteriological

compatibility testing to ensure no adverse effect

to the existing microorganisms in the ore. Results

of the testing showed little overall negative effect

on the micro-organisms. Surface-active surfactant

type leaching aids tend to have a negative effect

on SX and can have a negative effect on the EW

system. Leaching aid SX compatibility was

accomplished by batch and continuous processes.

The testing included extraction/stripping kinetics,

selectivity, phase disengagement, loading and

organic solubility testing.

It was determined that the concentration of

chloride/nitrate can influence the efficiency of

the leaching aid, with a slightly negative effect at

very high concentrations. In addition to the

column testing, the leaching aids were subjected

to chemical compatibility testing to ensure that

there are no negative effects on downstream

processes. Based on the results of the current

column testing, BASF is moving forward with

customer trials.

HeapSim Modelling of High Temperature Heap

Bioleaching Data by van Staden et al looked back

at high-temperature heap bioleaching

undertaken in 2006 and 2007 in three pilot heaps

at the Sarcheshmeh copper mine in Iran, each

consisting of approximately 20,000 t of a low-

grade hypogene/supergene ore mixture. The

design and operation incorporated measures for

preserving the chemical reaction heat to

maximise internal heap temperature. In so doing,

the leach kinetics would presumably be

enhanced, in particular that of the more

refractory minerals such as chalcopyrite.

Some of the raw data obtained has been

published, but this paper represents a more

comprehensive study and the first attempt at

fitting the data to a mathematical model. The

HeapSim model was chosen for the task since it

deals rigourously with simultaneous heat and

mass transfer in a heap and provides variable

kinetic parameters for both chemical and

bacterial reactions.

The paper gives an overview of the design,

operation, monitoring and control of the pilot

plant, which included some unique and novel

features. Particular challenges associated with

the mass balancing and data interpretation, and

how they were addressed, are discussed. The

model parameters required for obtaining a

convincing correlation between the plant and

model data provide deeper insight into the

relative impacts of aeration and irrigation rate,

acid addition, mineral and gangue reaction rate

constants, irrigation temperature and mass

transfer phenomena on the externally observed

performance. The sensitivity of the model results

to variations in these parameters around the

optimal fit identifies the rate-limiting factors of

the process. From this information conclusions

and recommendations follow for future attempts

at high-temperature heap bioleaching and its

modelling.

The work is based on a simple premise that an

appropriate ratio of mass flows of irrigation

solution (downward) and of air (upward) would

preserve chemical reaction heat in the heaps

thereby achieving the maximum possible average

temperature practically achievable. That would

LEACHING & SX/EW

The acid chloride-sulphate leach systemdeveloped by Pasminco at Port Pirie (now ownedand redeveloped by Nyrstar) is an oftenoverlooked leaching system, despite the coppermatte leach plant being in operation since 1984,producing in excess of 4,000 t/y of high qualitycathode copper. It is one of the few atmosphericleaching technologies capable of leachingchalcopyrite to high recoveries. The newlydiscovered ability to co-precipitate iron whilstleaching chalcopyrite should provide renewedinterest in this technology

LEACHING &SX-EW_proof 24/10/2017 11:11 Page 5

accelerate the kinetics of leaching of refractory

minerals (such as chalcopyrite but also of the

principal contributor of heat, iron and acid

namely pyrite) which would render heap

bioleaching a viable alternative for copper

extraction from low-grade whole chalcopyrite ore.

The authors conclude that “at least for the

case study presented here it seems that the

desired preservation of heat has not occurred to

the same extent as predicted. This possibility

needs to be accounted for in any future designs

of high-temperature heap bioleaching processes.

“Furthermore, temperature is not the only

parameter governing effective kinetics of

extraction, and is not throughout the entire

process the most important. In this case study

the limited availability of acid has governed the

rate of extraction during the earlier part of the

process. Furthermore, the modelling results

suggest that diffusional mass transfer limitations

became the limiting factor of the process by the

time that 40 to 50% copper extraction had occurred.

“Ore heaps exhibit limited permeability to air

flow, which can be expected to be further

reduced the more saturated it becomes in

solution. Apart from limiting the benefit that

could therefore be had from heat transfer from

the solution to the gaseous phase to preserve

heat within the heap, the case of column 1

illustrated that the availability of oxygen could

also become rate-limiting.

“Therefore, the design of heaps intended for

high-temperature heap bioleaching need to

incorporate means to ensure adequate supplies

of acid and oxygen and to prevent, delay or

mitigate insofar as possible diffusional mass

transfer limitations, throughout the full duration

of the process.

“To date the technology has not been

commercially adopted with the lack of flat ground

at Darehzare rendering it expensive, and the

enhancement of the resource by continued

exploration having shifted the economically

optimal process from heap leaching to

concentrate production.

“However interest in it remains and it is

currently being considered for low-grade primary

sulphide ore leaching at Sarcheshmeh.”

Chelating resinsIn his ALTA presentation Selective Chelating Ion

Exchange Resins in Base Metal Recovery and

Refining, Stefan Neufeind (LANXESS) commented

that “the commercial introduction of chelating

ion exchange (IX) resins in the middle of last

century represented a groundbreaking milestone

for the application of solid based adsorbers in

the treatment of aqueous streams. Hitherto, the

properties of ‘classical’ anion and cation exchange

resins had been limited to the separation of

negatively and positively charged ions or the

preferred adsorption of multivalent cations/anions.

Henceforth, the ‘new’ chelating resins bearing

iminodiacetic acid (IDA) functional groups allowed

to distinguish between two or more types of

transition metals with the same ionic charge and to

selectively capture only one species.”

His paper gives a comprehensive overview on

the use of IDA, aminomethylphosphonic acid

(AMPA), bispicolylamine (BiPA), thiourea and other

chelating resins at different stages of metal

winning, ie: (i) Primary extraction/separation of

base metals from leachates to yield concentrates;

(ii) Removal of trace impurities from concentrates

prior to EW and precipitation steps; (iii) Elimination

of heavy metals from mine waste waters to reduce

the ecological footprint of a mine (iv) Recovery of

trace amounts of metals from residual ores in order

to manage the legacy of mining activities.

For example, LANXESS’s Lewatit® MonoPlus TP

207 is a weakly acidic, macroporous cation

exchange resin with chelating iminodiaceticacid

groups designed for the selective extraction of

heavy metal cations from weakly acidic to weakly

basic solutions. Divalent cations are removed

from neutralised waters in the following order

(decreasing affinity):

Copper > vanadium (VO2+) > uranium (UO22+ >

lead > nickel > zinc > cadmium > cobalt> iron (II)

> beryllium > manganese >> calcium >

magnesium > strontium > barium >>> sodium.

The monodisperse, uniform sized beads of

MonoPlus TP 207 are mechanically and

osmotically more stable than ion exchange resin

beads with heterodisperse bead size distribution.

Additionally they offer superior kinetic behaviour

which leads to faster uptake of cations and a

better utilisation of capacity.

Among other applications Lewatit MonoPlus TP

207 is used for the removal nickel, cobalt and

copper from various hydrometallurgical streams.

Lewatit® MDS TP 220 is especially suitable for

the use in the purification of cobalt electrolytes

(cobalt/nickel separation), separation of

nickel/copper from ferric solutions, the recovery

of copper from strongly acidic solutions (pH <2)

and the adsorption of heavy metals (eg copper)

from solutions containing strong chelating agents

like EDTA.

The arsenic problemAn increasing proportion of the known remaining

copper deposits of the world contain high levels

of arsenic. Many new projects under

prefeasibility study have the combination of high

quality copper and high arsenic. In Chile, where

more than 20% of the global copper deposits are

based, half the mines are contending with increased

arsenic in the orebodies, and that proportion is

projected to increase in the coming years.

Most smelters reject concentrates containing

arsenic. Others impose significant treatment cost

penalties for concentrates containing more than

0.1% As. This currently impacts more than 20% of

the world’s copper concentrate output, FLSmidth

reports. “Since 2014, the volume of copper

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concentrate with high levels of arsenic has

exceeded treatment capacity in smelters. Today,

only one smelter in the world is willing to treat

large volumes of concentrates containing more

than 1% As.”

A high level of arsenic often correlates with a

high gold grades, providing an additional source

of revenue, but copper producers receive only

partial credit from the smelter. For other metals

such as zinc, lead, and manganese, they pay

penalties to the smelters.

The ROL process covered at the beginning of

this article can leach copper from arsenic-laden

concentrates. By producing copper on-site,

miners maintain control of and avoid having to

transport arsenic-bearing residues. The ROL

process furthermore enables recovery of pay

metals on site and avoids the economic penalties

imposed by smelters.

Another emergent technology, the Toowong

Process, is now being commercialised after

successful piloting. Toowong is a unique

technology for the removal of As, Sb and other

deleterious elements from base metal

concentrates. The process selectively leaches the

deleterious elements, leaving the metals of value in

the concentrate as a premium clean product. The

process uses alkaline leaching chemistry

developed and patented by Core Resources in

2008-2012, and was demonstrated in a $4.5 million

integrated continuous leaching pilot plant in 2012.

The pilot plant treated 1.5 t from three global

resources: Bulgaria, Philippines, and Chile:

n >90% As removal

n Final concentrate >0.1% As, down from 1.1%

n Arsenic product generated

n Low reagent consumption

n Process demonstrated at continuous steady

state.

n Chemically separates arsenic at the mine site

n Captures arsenic in an environmentally stable

form

n Returns arsenic to its original native location

n Creates premium clean copper concentrate

for shipment to smelter

n No downstream copper metal recovery required

n Environmentally superior technology

n Enabling technology for stranded

projects

n Significant cost savings for current

mines.

The value that the Toowong Process

presents for mining operations lies not

simply in a treatment process for the

removal of arsenic, but in its potential to

enable a re-optimisation of the mining

schedule without the constraint of

planning around deleterious elements.

Recent work by Core, with its

engineering partner, Mineral

Technologies, and Whittle Consulting,

has focused on developing capital and operating

costs for the Toowong Process, along with

quantifying its potential overall impact on the

NPV of an arsenic-constrained project. The ALTA

Metallurgical paper, The Economics of Removing

Arsenic from Copper Concentrates using the

Toowong Process by Peter Rohner et al presents

these results, as applied to an operation

producing 40,000 t/y of copper concentrate.

Leach clarificationEffective clarification of silver and gold cyanide

leach solutions, a key factor in the Merrill-Crowe

process, is critical. Many silver and gold

operations rely on Veolia’s leaf filtration systems.

Veolia's Whittier™ filtration technologies help

ensure a higher quality filtrate

for better recovery in a reduced

footprint. The Filtra-Matic™

pre-coat pressure leaf filter and

Auto-Jet™ self-cleaning

pressure filter are both ideal for

leach clarification applications.

Key benefits Include:

n For tough filtration projects involving large

flow rates

n Particle removal down to 1µm

n Durable leaves designed to provide maximum

strength

n Filter leaves designed for uniform flow

distribution and cake formation

n Auto Jet has improved cleaning with rotating

leaves during spray sluicing

n Quick opening door on Auto-Jet design

n Hydraulic retracting shell or head on Filtra-

Matic

Thanks to a superior, patented sluicing design,

Auto-Jet maintains its fully rated capacity even

when heavy, sticky or unusually tenacious cake is

encountered, Veolia says. “Its efficient sluicing

system ensures thorough cleaning of every

square inch of filter surface area every time.”

Filtra-Matic is especially useful where a dry

cake discharge is desired. Designed for operating

efficiency and easy maintenance, this filter is

offered in two basic models: the Filtra-Matic RT

with its unique retracting tank, and the Filtra-

Matic RB featuring a retracting bundle design.

Watch your oxygenAs OreMax points out, oxygen is an essential

element in the leaching process. Efficient heap

leach operations require that oxygen plus the

lixiviant be present to dissolve the mineral

deposits into the leach solution. In general, the

higher the oxygen level, the greater the mineral

recovery. Applying too much leach solution

saturates the crushed ore and drives out the

oxygen. Maximum leaching efficiency is achieved

when the leach solution moves through the ore

by means of capillary action.

Ideally, solution percolates through the ore by

means of capillary action leaving pockets of

oxygen in the pores between particles. Applying

too much solution hinders the leaching reaction.

When solution has completely filled into the

pores, the ore is said to be ‘saturated’. Bacteria,

which are crucial to the copper leaching process,

die from oxygen deprivation.

OreMax offers six suggestions to prevent leach

pad saturation.

Use a tensiometer: Measure the moisture

content of your leach pad at all times. This will

give you the feedback you need to properly

manage your solution application. It is

recommended to use a tensiometer to measure

each cell. This measures water potential or

tension. Water potential is

commonly measured in units of bars

(and centibars in the English system

of measurement) or kilopascals (in

metric units).

Control your pressure: One of the

major causes of over application of

leach solution is not controlling the

operating pressures of drip lines. A

15% variance in pressure from the

recommended operating pressure

will cause a 15% over or under

application of solution. OreMax

recommends using individual

regulators to monitor pressure of

40 International Mining | NOVEMBER 2017

LEACHING & SX/EW

OreMax says “the Max Emitter is the most plugresistant emitter available on the market today.Plugging results in reduced extraction andcauses the system hydraulics to change therebynegatively changing the solution applicationrates. The patented emitter design enableslower flow rates without the dripper plugging.Using the Max-Emitter will usually increaseextraction and bring mine performance muchcloser to original performance specifications”

LEACHING &SX-EW_proof 24/10/2017 11:11 Page 7

each line which gives the best control of pressure. Alternatively, use a larger

pressure valve for an entire zone.

Use Emitters that are Plug Resistant: If emitters plug production is lost

because the application rate of solution in that area will change. Furthermore if a

high number of emitters are plugged it increases the system pressure and causes

the remaining emitters to over apply solution.

Space out emitters: Over saturation is associated with close spacing of

emitters. By spreading out the wetting patterns it allows forincreased

capillary movement of solution and reduces saturation. Wetting diameter is

usually 76 cm in diameter or more, except in extremely sandy soils (like

beach sand). It is always surprising how far the solution spreads

underground and there are virtually no dry spots between emitters below

the surface. Typical spacing would be 2 litre at 46 cm, 4 litre at 60 cm and 8

litre at 80 cm, depending on desired application rate. Also, significant cost

savings result from spreading out the emitters and reducing emitter line

purchase proportionately.

Dry out saturated pad: If pads do become over saturated it is wise to let

them dry out. Allow time for gravity to drain the excess solution from the

pad. When the draining stops, the pad will remain at field capacity but air

with oxygen will have filled the pore spaces. Finally, reapply the solution at

the proper rate.

Break up soil sealing: Oversaturated ore with a high silt/clay content

probably means the ‘soil’ has been sealed. Once this happens solution can

no longer penetrate and consequently leach solution application is very

uneven. It is recommended to use a ripper to break up the sealing close to

the surface.

Process monitoringBASF’s Mining Solutions team services over 90 customer locations across

Australia, with sales and technical personnel travelling great distances to

monitor its customers’ inventory levels, track product use rates and review

plant performance.

While this service component of chemical supply remains critical, the

requirement for the staff to be physically present for this type of assessment

limits the number of times it is possible to inspect customers’ operations,

especially sites which are very remote. BASF also recognises the safety benefits

of reducing staff driving/travel time and the value of being able to respond to

customer issues faster. Understanding this reality, the Mining Solutions team

considered how to offer an improved service model to customers.

Working with engineering business partner DELCAD, BASF’s Mining

Solutions team has begun to implement telemetry operating systems as a

technical engineering solution to this challenge. Telemetry operating

systems enable remote monitoring of real-time data that is accessible from

anywhere, at any time.

So how does it work? Telemetry unit hardware is installed at the

customer site, permanently or temporarily, being adaptable to BASF

supplied equipment such as powder and liquid product storage tanks,

dosing pump skids and Alcotech® units. So this service is applicable to both

heap leach/SX and flotation (the other major processing article this month).

The hardware uses the existing equipment power supply and links to

digital or analogue instrument signals that feed measured data to a web-

based monitoring facility (Eagle.IO). The Eagle.IO web interface is

compatible with both PCs and mobile devices facilitating ease of access for

management. The web-based dashboard can be configured to show as little

or as much information as the inputs and telemetry units provide plus

additional options of site location (map and satellite views), photos of the

site equipment, historic charting, alarm history, individual level signals or

operational status (in real time). IM

For further information on the ALTA papers discussed go to

www.altamet.com.au

LEACHING & SX/EW

23rd AnnualMetallurgical Event

90 papers25 countries

Call for Papers

Forums and Panels

Hydromet Processing of Copper, Nickel and Cobalt

Sulphides

Lithium Processing

Refractory and Complex Gold Ores

www.altamet.com.au

Nickel-Cobalt-Copper Uranium-REE-Li

and Gold-PMConference & Exhibitionand ISR Symposium

19-26 May, Perth, Australia

LEACHING &SX-EW_proof 24/10/2017 11:11 Page 8