04-05_Leachingetc_Program
HIGHLIGHTS 2004-2005
TECHNOLOGY TRANSFER
Expert service continued to be provided to industry for identifying and characterising phase separation and/or organic degradation problems in solvent extraction plants. Several projects on organic degradation in solvent
extraction systems were completed for local clients.
The first phase of the AMIRA P706 “Improving Solvent Extraction Technology” project was successfully completed.
The AMIRA P705 “Improved Anode & Cathode Processes
in the Electrowinning of Base Metals” project continued to assist industry partners.
There was increasing interest from industry in novel
solvent extraction process options involving synergistic reagents.
Industry support expanded for research on the kinetics and mechanisms of the leaching of chalcopyrite (a major copper sulfide mineral).
Collaborative work with industry was undertaken on
several aspects of the recovery of nickel and cobalt from laterite ores and the leaching of titanium minerals. Professional development courses in hydrometallurgy
were delivered to industry personnel in several locations around the world.
ADVANCING THE SCIENCE
Research into the electrochemistry of fine mineral
sulfide particles yielded important new insights into the mechanisms of the oxidation and reduction of these materials, which were presented at an international conference.
Further advances were achieved in the fundamental understanding of the mechanisms of the dissolution of chalcopyrite.
Additions were made to the growing database on
synergistic reagents for the selective extraction of base metals.
Improved understanding of the role of various metal ions on the corrosion of lead anodes in base metal electrowinning was gained.
Computational fluid dynamics models for solvent
extraction equipment were developed and validated using sophisticated laser technologies.
The Leaching, Separation & Reduction Program undertook research on:
finding environmentally acceptable methods for leaching mineral sulfides sulfur chemistry in the oxidation and leaching of sulfide minerals
increasing the efficiency of solvent extraction processes and equipment
developing novel solvent extraction processes for base metals
applying ion exchange resins to the separation and recovery of metals minimising energy consumption and increasing the yield and quality of base metals produced by electrowinning.EXPERTISE:
leaching, in particular the application of electrochemistry to the study of leaching processes metal ion separation and concentration using solvent extraction and ion exchange electrowinning of metals, including nickel, copper and zinc.
Leaching, Separation and Reduction Program
In related work, a major investigation into the fundamental aspects of the leaching of titanium minerals was started during the last year in collaboration with a major industrial sponsor. The results have shown that satisfactory dissolution can be achieved under milder conditions than previously obtained by a suitable choice of conditions which were identified in an electrochemical study of the minerals under typical leaching conditions.
SEPARATION PROCESSES
The Leaching Program’s fundamental research in the area
of separation processes focused largely on solvent extraction (SX) during the past year with two main themes. In the first of these, work continued in the search for, and development of, synergistic SX (SSX) systems aimed at recovering metals from leach solutions more efficiently. This research has continued to add to the database of pH isotherms for previously known and novel SX systems. The work has
also led to a greater understanding of synergistic solvent extraction systems that can often result in unexpected trends based on the accepted roles of extractants and synergists with different metals, and has resulted in several novel extraction systems that have been provisionally patented.
It has been particularly rewarding that a variety of opportunities have arisen to test these new SSX systems for application in the industry. Thus, two novel SSX systems have been tested with pilot and plant solutions and excellent results have been achieved.
Potential applications of SSX systems to operations
has highlighted the need for parallel studies devoted to the analysis, monitoring and degradation of organic reagents used in solvent extraction. Methods have been developed to identify and monitor degradation products from extractants, primarily using gas chromatography and mass spectrometry, complemented by carbon nuclear magnetic resonance, infrared spectroscopy and microanalysis for more detailed analysis.
Other studies involved measurements of aqueous entrainment in organic streams and organic entrainment
in aqueous streams. These measurements were applied to
a number of SX systems to assess the impact of organic degradation products on performance. This enhanced capability is available to serve industry and was used in the study of selected SX systems as part of the AMIRA P706 “Improving Solvent Extraction Technology” project.
The AMIRA P706 project involved a close collaboration between the Parker Centre and CSIRO Minerals’ CFD (computational fluid dynamics) Group. A large part of
the research program was focused on the optimisation of current equipment such as mixer settlers and new equipment such pulsed columns, through developing a fundamental understanding of the parameters that control their performance.
Significant achievements of the P706 project included the development of a two-phase CFD model for the prediction of droplet size and drop size distribution in pulsed columns that includes drop break-up and coalescence. Measurements in a pilot column were made to validate the model. In the case of mixer settlers, a better understanding of the effect of picket fences and flow patterns in settlers was obtained. A comparison of mixer settlers and pulsed columns for copper extraction indicated that both achieve about the same copper extraction with similar entrainment although the pulsed column has a much smaller footprint but consumes more energy.
The application of ion exchange resins for separating, purifying and concentrating metal ions from leach solutions and pulps continued at a considerably reduced level. A PhD degree that involved a project on a resin-in-pulp process for recovering nickel and cobalt from laterite leach pulp was awarded during the past year. ELECTROWINNING PROCESSES
The electrowinning stage is often the most capital-intensive part of a base metal hydrometallurgical operation and can involve the highest component of the operating costs. It is also the most crucial stage in relation to the quality of the final metal product. Research into metal reduction in the last year has focused primarily on the AMIRA P705 project that is aimed at improved anode and cathode processes in the electrowinning of base metals.
During the past year, several aspects of the anode and cathode processes involved in the electrowinning of zinc and copper were investigated. In particular, factors that contribute to the long-term corrosion of a number of lead based alloys used as anodes were investigated as part of
an on-going accumulation of comparative data on anode performance. This applied research was complemented by more fundamental studies of the mechanisms of the anodic reactions involved in corrosion. As part of this project, a PhD student at the University of Queensland made significant progress in an investigation of the mechanism of the action of cobalt ions in reducing the corrosion rate of lead alloy electrodes and lead contamination of cathodes in copper electrowinning.
In the case of cathodic processes, recent work has focused on developing an understanding of the major factors that contribute to the quality of copper cathodes produced under typical electrowinning conditions. A completed experimental design in laboratory cells under controlled conditions has confirmed a number of industry observations, and is being used as part of a MSc thesis. In the case of zinc, methods to alleviate the detrimental effect of fluoride ions on the ability to strip zinc from aluminium blanks were investigated. This work should lead to further testwork in sponsor operations.
The Electrochemistry of Sulfide Mineral Particles
RESEARCH TEAM Mike Nicol (Project Leader)
Hajime Miki
Lilian Velásquez
(Murdoch University) INDUSTRY COLLABORATION
BHP Billiton
PROJECT DURATION
2002-2005OBJECTIVES
Sulfide minerals are a
major resource for base and
precious metals. Traditional
pyrometallurgical processing
of many of these ores is
no longer environmentally
acceptable nor economically
viable with the increasingly
important proportion of low-
grade and “dirty” concentrates.
Hydrometallurgical alternatives
are increasingly being
considered but are currently
often not viable unless carried
out under extreme conditions.
This project will lead to a
better understanding of the
mechanisms by which sulfide
minerals are dissolved in
conventional, pressure and
biological leaching processes.
This will, in turn, lead to new,
improved methods and reagents
which will enable more efficient
and selective leaching processes
to be developed, optimised and
controlled.
In particular, this project
aims to:
use modern electrochemical
techniques to study
the kinetics (rates) and
the mechanisms of the
dissolution of selected
sulfide minerals under the
conditions of atmospheric,
pressure and biological
leaching processes
apply the fundamental
knowledge gained from
these studies to optimise
existing processes for sulfide
minerals and develop novel
processes
assess the potential of an
electrochemical technique
for mineralogical analysis
of mixed sulfide ores and
concentrates.
ACTIVITIES
Postdoctoral fellow Dr
Hajime Miki continued to exploit
the novel technique which he
has developed for studying
the electrochemistry of fine
mineral particles. Relatively
simple techniques have been
developed which enable the
electrochemistry of sulfide
minerals to be studied with
particles varying in size from
above 100μm to less than 1μm.
Both oxidative and reductive
processes were studied with
this electrochemical technique
using the sulfide minerals pyrite,
arsenopyrite and chalcopyrite.
These studies showed that it is
possible to completely oxidise
or reduce these minerals during
a single voltammetric sweep.
The resulting voltammogram
produces peaks which are
characteristic of each mineral
and can be used to qualitatively
identify the minerals.
In the case of chalcopyrite, it
has been demonstrated that the
charge involved in the anodic
oxidation can be quantitatively
related to the amount of
copper dissolved. Quantitative
information can be obtained
using peak fitting techniques.
Interesting differences in
the behaviour of the minerals in
sulfuric and hydrochloric acids
was observed, particularly in the
case of pyrite for which a second
major peak is obtained. This
second peak has been attributed
to the oxidation of elemental
sulfur in the presence of chloride
ions.
The electrochemical
technique offers the possibility
of providing mineralogical
information for individual
particles based on an
electrochemical voltammetric
fingerprint.
BHP Billiton has continued
to support a major on-going
project on chalcopyrite leaching
in chloride and mixed chloride/
sulfate solutions as part of a
longer term collaboration into
the fundamentals of the leaching
of chalcopyrite and other copper
sulfide minerals.
A major part of this
research is being undertaken
as a PhD project by Ms Lilian
Velásquez. The most recent
work has confirmed that there
are two parallel reactions which
contribute to the dissolution
of chalcopyrite. The relative
rates of each reaction depend
on a number of factors, the
most important of which is the
electrochemical potential of the
mineral surface. Minimisation
of the well-known “passivation”
of the dissolution reaction can
be controlled by minimising
the reaction that causes the
passivation.
FUTURE WORK
The CRC-funded project has
now completed its three-year
work program. Potential future
work includes:
further evaluation of the
novel electrochemical
technique as a potential
mineralogical tool by
investigating the response
of a variety of sulfide
concentrates
continuing research into the
relative roles of oxidative
and non-oxidative processes
in the leaching of selected
sulfide minerals
further development of
controlled potential leaching
to a practical application in
the treatment of chalcopyrite
ores and concentrates.
OUTCOMES
Improved understanding of
the roles of oxidative and
non-oxidative processes in
the leaching of chalcopyrite.
Novel technique for studying
fine mineral particles further
refined.
Presentations and
publication of aspects of the
dissolution of chalcopyrite.
Major collaborative project
with industry on the leaching
of copper sulfide minerals.
Improving Solvent
Extraction (SX) Technology
RESEARCH TEAM
Chu Yong Cheng (Project Leader)Keith Barnard Peter Miovski
Nicki Turner Mark Urbani
RESEARCH COLLABORATION
CSIRO Minerals
CSIRO Minerals’ CFD Group
INDUSTRY COLLABORATION
Anglo American Platinum Baja Mining Corp
Bateman Solvent Extraction BHP Billiton
Cognis Australia Kvaerner E&C Minara Resources Phelps Dodge
Queensland Nickel Sinclair Knight Merz WMC Resources
PROJECT DURATION
2002-2005
OBJECTIVES
The minerals industry needs new solvent extraction (SX) techniques to improve
metal separation and to reduce organic losses in SX circuits due to degradation and entrainment (organic droplets trapped in aqueous solution or vice versa). Therefore, this project aims to assist the industry by:
searching for synergistic SX
systems to improve metal selectivity and applying new synergistic systems to recover metals from leach solutions more efficiently
better understanding
degradation of organics and entrainment and developing remediation methods for degraded organics and entrainment.
ACTIVITIES
SYNERGISTIC SOLVENT EXTRACTION (SSX)
Synergistic SX uses a
combination of extractant and synergist which work together to improve metal selectivity. The systematic study of a number of synergistic systems in this project has resulted in three main outputs:
(i) a database of pH extraction
isotherms for previously known and novel SX systems (ii) greater understanding of
synergistic SX, particularly unexpected data on the different roles of extractants and synergists with different metals (iii)new processes relevant to
industry (which have been provisionally patented), including but not limited to
the recovery of nickel and cobalt in the nickel industry.It has been particularly rewarding that opportunities have arisen to test the systems for application in the industry. Two novel SSX systems have been tested with plant solutions at batch and pilot scale, with excellent results achieved. Additional SSX systems have been tested for different applications.
PHASE SEPARATION
AND ORGANIC REAGENT DEGRADATION
Potential applications of the synergistic SX systems to operations has highlighted the need for parallel studies in organic monitoring and degradation.
Methods have been developed to identify and
monitor degradation products from reagents.
Other studies involved measurements of aqueous
entrainment in organic streams and organic entrainment in aqueous streams. These measurements were applied to a number of SX systems to assess the impact of organic degradation products on performance.
The enhanced capability in this area is available to serve industry and, indeed, was
applied to the study of selected SX systems as part of the AMIRA P706 project.
AMIRA P706 “IMPROVING SOLVENT EXTRACTION TECHNOLOGY” PROJECT
The industry-sponsored AMIRA P706 project focused on optimising the use of current SX equipment such as mixer-
settlers and new equipment such as pulsed columns, through developing a fundamental
understanding of the parameters that control their performance. Significant achievements of the AMIRA P706 project are:(i) A two-phase Computational
Fluid Dynamics (CFD) model for pulsed columns has been developed, which includes drop break-up and coalescence. Measurements have been made to validate the model. The two-phase model was used to predict droplet size and drop size distribution in pulsed columns.(ii) Single and two-phase CFD
mixer and settler models have been developed, and used to obtain a better understanding of the effect of picket fences and flow patterns in settlers.A comparison of a mixer-settler and a pulsed column for copper extraction indicated that both achieve about the same copper extraction with similar entrainment; the pulsed column has a much smaller footprint but consumes more energy.
FUTURE WORK
The CRC-funded project has now completed its three-year work program. Potential future work includes:
developing new synergistic
SX systems and applying to mineral industries
understanding fundamentals
of synergistic SX systems by identifying organic species in solutions.
OUTCOMES
Provisionally patented new
synergistic SX processes tested.
CFD models developed for
SX equipment (mixer-settlers and pulsed columns) and validated using sophisticated laser technologies.
The set-up for PIV (particle image velocimetry) measurements of the fluid flow in a pulsed column using laser equipment. These velocity measurements were used to validate the pulsed column CFD model.
AMIRA Project P705: Improved Anode and Cathode Processes in Base Metal Electrowinning
RESEARCH TEAM Mike Nicol (Project Leader)
Nursen Guresin
Justin McGinnity
Nigel Tuffrey
Anthony Blackett
RESEARCH STUDENTS
Helen Fletcher
Thu Nguyen RESEARCH COLLABORATION
Murdoch University University of Queensland INDUSTRY COLLABORATION Bateman Engineering
BHP Billiton
Birla Nifty
Consolidated Alloys
Hatch Associates
MERIWA
Phelps Dodge
RSR Technologies
Teck Cominco
PROJECT DURATION
2003-2006OBJECTIVES
Leaching and solution
purification, followed by
electrowinning to recover
the metal from solution, is a
common and growing route
to the production of base
metals such as copper, zinc,
nickel and cobalt. Typically, the
electrowinning stage is the most
capital-intensive part of this
process and involves the highest
component of the operating
costs. It is also the most crucial
stage in relation to the quality of
the final product.
This project comprises two
concurrent modules: New and
Improved Anode Technology
and Enhanced Product Quality.
In particular, the project
aims to:
identify and demonstrate
options for improving the life
of current anode materials,
reducing their operating
potential and minimising
impurities from these
materials
identify, evaluate and
recommend alternative
anode materials with
improved corrosion
resistance and reduced
operating potentials
identify and demonstrate
options for improving
cathode product quality –
particularly for zinc, copper,
nickel and cobalt cathodes
– and thereby increasing
plant throughput.
ACTIVITIES
This project commenced
in January 2003. Significant
progress has been made since
that time on activities in both
modules.
During the past year,
several aspects of the anode
and cathode processes involved
in the electrowinning of zinc
and copper were investigated.
In particular, factors that
contribute to the long-term
corrosion of a number of lead-
based alloys used as anodes
were investigated as part of
an on-going accumulation of
comparative data on anode
performance.
This applied research
has been complemented by
more fundamental studies
of the mechanisms of the
anodic reactions involved
in corrosion. As part of this
project, a PhD student at the
University of Queensland has
made significant progress on
investigating the mechanism
of the action of cobalt ions in
reducing the corrosion rate of
lead alloy electrodes and lead
contamination of cathodes in
copper electrowinning.
In the case of cathodic
processes, recent work has
focused on developing an
understanding of the major
factors that contribute to the
quality of copper cathodes
produced under typical
electrowinning conditions.
Utilisation of an experimental
design of laboratory cells
under controlled conditions has
confirmed a number of industry
observations, and is being
used as part of a MSc thesis.
In the case of zinc, methods to
alleviate the detrimental effect
of fluoride ions on the ability
to strip zinc from aluminium
blanks have been investigated.
These investigations should lead
to further testwork in sponsor
operations.
In order to promote the
benefits of the P705 project
and to assist with the transfer
of the technology to the
industrial sponsors, further
visits were made in the past
year to operations in North
and South America. During
these visits, courses on copper
electrowinning were delivered
to plant personnel in both
Arizona (USA) and Santiago
(Chile) while a general course
on electrowinning was presented
in Brazil.
FUTURE WORK
Analyse the results from
the experimental design
on the effects of metal
ions in solution on the
corrosion of anodes and
the quality of the cathodes
produced during copper
electrowinning.
Refine methods to alleviate
the detrimental effect of
fluoride ions on the ability
to strip zinc from aluminium
blanks.
Establish the mechanism
of the action of cobalt
ions in reducing anode
corrosion during copper
electrowinning (as a PhD
project).
Prepare comprehensive
reports summarising the
results of the overall P705
project.
Prepare a proposal for the
next phase of the P705
project.
OUTCOMES
Effects of anode
composition, pretreatment
and periodic open-circuit on
corrosion rates established.
Increased understanding of
the role of some metal ions
on the corrosion of lead
anodes.
Methods developed for
alleviation of the detrimental
effects of fluoride ions in
zinc electrowinning.
Continued technology
transfer to sponsor
operations, including on-site
courses.
PhD Project:
Effect of Cobalt on the Corrosion of Lead Anodes
STUDENT
Thu Nguyen
SUPERVISORS
Dr Nursen Guresin Prof Mike Nicol
COLLABORATION
Murdoch University
University of Queensland
INDUSTRY COLLABORATION
Bateman Engineering
BHP Billiton Birla Nifty
Consolidated Alloys Hatch Associates MERIWA
Phelps Dodge RSR Technologies Teck Cominco
PROJECT DURATION
2004-2007
OBJECTIVES
The positive effect of cobalt on the corrosion of lead anodes used in copper electrowinning was first reported in the early 1930’s. It has since been confirmed in several studies and actual plant operations that the addition of a small amount of cobalt to the electrowinning electrolyte solution significantly reduces the corrosion rate of lead anodes and the potential for oxygen evolution at the anode. However, the exact
mechanism by which cobalt acts on the corrosion process is not yet fully understood.
This project aims to study the mechanism of the effect of cobalt on the corrosion of lead alloy anodes in the electrowinning of copper from copper sulfate-sulfuric acid electrolyte solutions.
ACTIVITIES
Electrochemical studies of the effect of the cobalt
concentration and other factors (eg temperature, current density, acid concentration and electrode rotation speed) on the corrosion rate of lead anodes and on the potential for oxygen evolution have been completed. The effect of cobalt on the oxygen evolution process on platinum and lead dioxide anodes was also examined. Cobalt had no effect on the oxygen overpotential on a platinum anode. The
presence of cobalt reduced the oxygen overpotential on an electrodeposited lead dioxide film on a carbon substrate.
The effect of cobalt in this case was, however, slightly less pronounced than the effect on a lead-calcium-tin alloy anode. The difference may be ascribed to the composition of the
anodic films formed on the two electrodes.
The change in corrosion rate with electrode potential is expected to cause a change in the nature of the corrosion layer formed on the lead-calcium-tin anode surface. In the absence of cobalt, the corrosion film was thick, porous and discontinuous. The film developed in the
presence of cobalt was thin and compact.
In sulfuric acid solutions
(with or without cobalt), the fresh lead-calcium-tin anode surface is initially covered with a layer of lead sulfate which later is transformed into lead dioxide.Characterisation of the corrosion film that develops on the lead-calcium-tin
anode surface in the absence and presence of cobalt was undertaken using X-ray
photoelectron spectrometry. When cobalt was added to the electrolyte, less lead dioxide was formed on the anode surface, with the anodic film being predominantly composed of lead sulfate. It is possible that the lead sulfate formed in the presence of cobalt has a different structure than that formed in the absence of cobalt and is more difficult to oxidise.
FUTURE WORK
Continue studies on
the composition of the anodic films under various experimental conditions. Investigate the appearance
and the structure of the lead sulfate layer formed on the anode surface under different conditions with and without the addition of cobalt.
Determine the catalytic
effect of lead dioxide on the oxidation of cobalt(II) to cobalt(III).
OUTCOMES
Studies on the composition
of the anodic corrosion film provided some insight into its formation in sulfuric acid solutions. The results confirmed that the presence of cobalt promotes the formation of lead sulfate while retarding the
formation of lead dioxide. The lead sulfate crystal
formed in electrolyte solution containing cobalt may have a different structure than that produced in the absence of cobalt and be more difficult to oxidise.
Scanning electron microscopy images of the anodic corrosion film formed on lead-calcium-tin anodes:(a) in the absence of cobalt (b) in the presence of cobalt.
(a)(b)