Mineralogical characterization of South African Mine tailings with aim of evaluating their potential

295 Pages·2017·5.78 MB·English

Mineralogical characterization of South African mine
tailings with aim of evaluating their potential for the
purposes of Mineral Carbonation

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Maxwell Amponsah-Dacostao
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A thesis submitted for the degree of Master of Science in the
Department of Geological Sciences,
University of Cape Town, South Africa.

2017
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The copyright of this thesis vests in the author. No
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quotation from it or information derived from it is to be

published without full acknowledgeement of the source.
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The thesis is to be used for private study or non-
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commercial research purposes only.

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Published by the Universit y of Cape Town (UCT) in terms
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of the non-exclusive license granted to UCT by the author.
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DECLARATION
I know the meaning of plagiarism and declare that all the work contained in this thesis,
save for that which is properly acknowledged, is my own.
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Signature removed
Maxwell Amponsah-Dacosta
13 January 2017
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ABSTRACT
South Africa is an energy intensive economy which primarily relies on the burning of
fossil fuel such as coal. The South African coal energy sector accounts for
approximately 420 million metric tonnes of carbon dioxide emitted per annum. With
present alarming concerns with regards to the ever-increasing atmospheric carbon
dioxide concentrations resulting in global warming and climate change, several
mitigation strategies have to be implemented. A majority of Carbon Capture and
Storage (CCS) technologies require monitoring from potential leakages, making the
process expensive. However, a benign technology exists to permanently store away
anthropogenic CO with products obtained instantaneously. This CCS technology is
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known as Mineral Carbonation. The fundamental procedure is a reaction between
(magnesium - calcium - iron) silicates and CO to form carbonates. The products of
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from the reaction require no monitoring and the fear of leakage of CO is eliminated.
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Moreover, the carbonates from this technology are useful in the road, agriculture and
building industries. The CO storage capacity in mineral carbonation exceeds other
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CCS techniques.
The South African mineral industry annually produce immense tonnages of ultramafic
mine tailings. Due to the generally fine nature of the tailings, no further cost would be
incurred in grinding the material. The platinum group metal (PGM), nickel and copper
companies are examples of industries that produce massive tonnages of which could
serve as potential feedstock for the purposes of mineral carbonation. Recent studies
have shown that, the potential feedstock could sequester close of 70% of the annual
CO produced at Secunda, South Africa.
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A mineralogical investigation into the mineral carbonation potential of mine tailings
was conducted using samples from seven mining companies. Four of the mining
operations considered (Impala, Rustenburg, Amandelbult and Mogalakwena) are
PGM operations mining the Merensky, Upper Group 2 (UG-2) and Platreef. Nkomati
was another operation selected for the study, with samples collected from the Main
Mineralised Zone (MMZ) and Chromititic Peridotite Mineralized Zone (PCMZ). Tailings
material from the dormant O’okiep operation was the seventh, chosen for the study.
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To determine the suitability of these tailings for mineral carbonation, the particle size,
surface area and mineral for each individual operation was accounted using Malvern,
BET analysis, XRF, QXRD and QEMSCAN respectively.
The overall fine-grained nature of the mine tailings was manifested in the particle size
distribution results were sizes ranged from d(0.5) = 33.67 (Nkomati) to d(0.5) = 231.45
(Impala). The range in surface area was 1.45 m2/g (Amandelbult) to 5.89 m2/g
(Nkomati).
A theoretical carbonation capacity ranking scheme was developed where the seven
mining companies selected for this study were graded based on their suitability for
mineral carbonation. Three distinct factors made up the classification criteria of the
ranking scheme. The first was the carbonation capacity. This was determined by the
mineralogy, the R value and the tonnage of mine waste produced annually. The
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second major factor was the reactivity (ignoring kinetics) of the tailings. In this case,
the particle size distribution and surface area of the respective mine tailings were
considered. Thirdly, the distance from the CO (Secunda) source was taken into
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account as the cost of transporting CO to the mineral carbonation facility should be
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weighed up. In using these principles, Nkomati was unquestionably ranked first while
O’okiep was rated last priority among the seven operations.
The motive behind was to improve upon the theoretical carbonation capacity ranking
scheme and in turn examining a variety of South African mine tailings for the purposes
of detailed mineral carbonation studies in South Africa.

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CONFERENCE PRESENTATIONS
Oral Presentation: Mineralogical characterization of mine tailings for Mineral
Carbonation.1-5 December 2014. 2nd National Global Change Conference. Port
Elizabeth, South Africa.
Oral Presentation: Mineralogical characterization of South African mine tailings for the
purposes of Mineral Carbonation. 1-5 September 2014. 21st General Meeting of the
International Mineralogical Association (IMA), Johannesburg, South Africa.
Poster Presentation: South African mine tailings for the Mineral Carbonation, an
interdisciplinary response to mine closure.18-22 August 2014. 12th International Mine
Water Association Congress (IMWA 2014), Xuzhou, China.
Poster Presentation: Mineralogical characterization of South African mine tailings for
Mineral Carbonation.17 April 2014. Postgraduate Research Expo. University of Cape
Town, South Africa.
Oral Presentation: Mineralogical characterization of mine tailings for the purposes of
Mineral Carbonation. 07 November 2013. Minerals to Metals (MtM) Research Day,
Cape Town, South Africa.

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ACKNOWLEDGEMENTS
Successful completion of this research project could not have been made possible
without the cooperation of many individuals. I wish to express my profound gratitude
to the Almighty God for His care and strength He gave me in order to complete this
research project. A big thank you goes to my supervisor Prof David Louis Reid for his
guidance and relentless motivation that he offered me during the research work as
well as the compilation and preparation of this report.
A special word of appreciation goes to the management and staff of Anglo Platinum,
Impala Platinum and Nkomati Mine for the innumerable assistance in sampling of their
respective tailings. The department of Chemical Engineering and Geological Sciences
at the University of Cape Town provided laboratory assistance in sampling preparation
and mineralogical data acquisition. I greatly acknowledge the contributions of each
and every staff member of these department. The Julian Baring Scholarship
Organisation was my financial backbone and I appreciate their immerse support
throughout this project.
I owe a depth of gratitude to my parents, Dr Francis Amponsah-Dacosta and Mrs
Cynthia Amponsah-Dacosta. I also wish to express my heartfelt appreciation to my
siblings, Edina and David, for the encouragement and moral support during the
challenging moments of the project. Finally, a big thank you goes to Ms Euraeffie
Oppon for her endless support and motivation, making the impossible seem possible
during the toughest moments of this project.

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