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Ghana Post Digital Address: GA-018-1233

Upgrade of Gold Recovery from Refractory Carbonaceous Gold Ores using Phanerochaete chrysosporium – Prof Grace Ofori-Sarpong

Speaker – Professor Aaron Lawson


Prof Grace Ofori-Sarpong is a Professor of Minerals Engineering, and currently the Dean of School of Postgraduate Studies at the University of Mines and Technology (UMaT), Tarkwa, Ghana. Her previous positions held in UMaT include Acting Pro Vice Chancellor, Dean of Faculty of Mineral Resources Technology, Vice Dean of Planning and Quality Assurance Unit, Head of Petroleum Engineering Department, Head of Environmental and Safety Engineering Department, and Coordinator of University Examinations. Grace serves as a member on several national boards including the Governing Boards of the Minerals Income Investment Fund, Ghana Chamber of Mines Tertiary Education Fund, and the Governing Council of University of Mines and Technology. In addition, she serves/has served on the Governing Board of Academic City College, and numerous national and international committees including the Ministerial Committee of Enquiry on Health and Safety in the Mining Industry, the Publication Committee of Ghana Academy of Arts and Sciences, the Committee of Independent Reviewers for International PhD Scholarship, and as Associate Editor of Journal of Sustainable Metallurgy. She has also served as organiser, keynote speaker, resource person and moderator for several conferences, workshops and seminars both locally and internationally.

Grace is actively involved in research and consultancy in the areas of precious minerals beneficiation, aqueous processing, mine waste treatment, acid mine drainage issues, and myco-hydrometallurgy, among others, and she has about 80 technical publications to her credit. With about 20 years’ experience in lecturing and research in minerals-related issues and community service, Grace has made a lot of strides including receiving an international award in 2017 from OWSD-Elsevier Foundation for her contribution in science and her positive role in inspiring and mentoring females to reduce the gender gap in STEM. Grace is the Founder and President of Ladies in Mining and Allied Professions in Ghana (LiMAP-Gh), a Fellow of the Ghana Academy of Arts and Sciences (GAAS), and West African Institute of Mining, Metallurgy and Petroleum (WAIMM). She is also a member of the Society for Mining, Metallurgy and Exploration Engineers (SME), International Association of Engineers, Society of Petroleum Engineers (SPE) and Women in Mining, Ghana. Grace holds PhD in Energy and Mineral Engineering from Pennsylvania State University, University Park, USA, MSc in Environmental Resources Management and BSc in Metallurgical Engineering, both from the Kwame Nkrumah University of Science and Technology, KNUST, Kumasi, Ghana.

Synopsis of Lecture

Gold ores consist of those that are easy to treat (free-milling) and others difficult to treat (refractory). Cyanide dissolution of gold from refractory carbonaceous ores has attendant serious challenges as the contained natural Carbonaceous Matter (CM) preg-robs dissolved gold leading to a decrease in overall gold recovery, a phenomenon termed preg-robbing. The CM behaves similarly to activated carbon, and thus has a strong affinity for the dissolved gold ions (Au(CN)2).

To control preg-robbing, Carbonaceous Gold Ores (CGO) require pretreatment to deactivate the CM prior to cyanidation, and the conventional processes employed include the use of blanking agents and roasting. With microbial processes becoming more acceptable as environmentally-friendly processes, the fungus, Phanerochaete chrysosporium was employed to assess its ability to deactivate CM, and decrease preg-robbing, with the ultimate aim of increasing overall gold recovery. Anthracite (a mature form of coal) was used as surrogate for the CM, and after surface biotransformation with P. chrysosporium, the ability of anthracite to adsorb gold decreased by over 90%. Scanning electron microscopy and Raman spectroscopy of anthracite revealed detraction in the structured nature of the CM required for gold adsorption, while pore structure measurement indicated drastic reduction in surface area and micropore volume, and enlargement in average pore diameter, all of which reduces gold adsorption on CM.

To ascertain the ability of P. chrysosporium to enhance overall gold recovery, surrogate CGO was prepared by adding 3% anthracite to Free-milling Gold Ore (FGO), containing mainly quartz, feldspar and sericite, with 3.5 g/t gold, 0.13% sulphide sulphur and 0.06% organic carbon. The FGO and the surrogate CGO gave cyanidation gold recoveries of 95.5% and 54.8% respectively. After fungal treatment of the CGO, gold recovery increased to 82.5% recovery. The results demonstrate a potentially effective alternative pretreatment process that utilises the fungus, P. chrysosporium, in reducing preg-robbing in gold extraction, and the varied conditions used affirm that the fungus can degrade CM in several growth media, and in a wide range of time, pulp density, temperature and pH.

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