29 kesä PreGOLD – Bio-oxidation and autoclave pressure oxidation of gold bearing concentrates
Name: Bio-oxidation and autoclave pressure oxidation of gold bearing concentrates
Total costs (€)/Tekes support: 416 800 € / 250 000 €
Leading research organization partner: Tampere University of Technology
Contact persons: Jaakko Puhakka, Tampere University of Technology, jaakko.puhakka(at)uef.fi; Aino-Maija Lakaniemi, Tampere university of Technology, aino-maija.lakaniemi(at)tut.fi; Raisa Neitola, Geological Survey of Finland, raisa.neitola(at)gtk.fi
Research organization partners: Tampere University of Technology, Geological Survey of Finland
Company partners: Endomines Oy, Nordic Mine AB, Kemira Oyj, Outotec Finland Oyj
International partners: Chinese Academy of Sciences (China), Zijin Mining Group Co., Ltd. (China), University of Cassino and Southern Lazio (Italy)
Number of reviewed publications, incl. submitted manuscripts: 1
Number of other publications and reports: 7
Number of thesis: Doctoral 1
Need and motivation of the project:
In Finnish ores, gold is often “invisible” in the crystal lattice of sulfide minerals and thus requires pretreatment (i.e. pre-oxidation) prior to cyanide leaching. Efficient pre-oxidation processes are needed to enable improved gold recovery, increased operation capacity, decreased energy use and lower environmental impacts. PreGOLD project focused on bio-oxidation and autoclave pressure oxidation as pretreatment methods for gold ores and concentrates, because these methods are considered to have decreased energy and chemical use and lower environmental impacts compared to many other pretreatment processes.
Main set targets:
The main aims of the project were to evaluate the amenability of Finnish gold ore concentrates to bio-oxidation and autoclave pressure oxidation, and to develop unit processes for pre-oxidation and subsequent cyanide leaching of gold.
It was shown that efficient acidophilic iron and sulphur oxidising bacteria can be enriched even from environments having a pH above 5, although such a high pH is generally considered limiting for this type of microorganisms. The enriched microbial culture was also shown to actively oxidise iron and sulphur even at elevated pressure of 10 bars. Especially the treatment time of bio-oxidation was shown to be an important process parameter. Too short or too long bio-oxidation treatment seemed to lead to decreased gold yields. For example, long bio-oxidation treatment of Hosko flotation concentrate resulted in formation of fine iron sulphates to the solid bio-oxidation residue, which based on the initial findings, complicated gold recovery via cyanide leaching. Comparative experiments on bio-oxidation and autoclave oxidation of Tormua ore indicated that both processes increase gold yields. Bio-oxidation increased moderately the consumption of cyanide and lime, whereas autoclave oxidation decreased cyanide consumption but increased significantly lime consumption. Faster cyanide leaching kinetics and somewhat increased gold yields were also obtained with the tested processing aid chemicals.
Commercialization measures and/or potential
Further research and/or verification experiments are still needed before the findings of the project can lead to commercialization. However, at least three findings may have commercial and technological significance: 1) If the mechanisms of iron sulphate formation during bio-oxidation and/or the complication mechanisms of the iron sulphates on gold leaching with cyanide can be revealed, their negative effects can likely be prevented. 2) Tolerance of bio-oxidation microorganisms to high pressures indicates that bio-oxidation may be possible to operate in situ for deep ores that are hard to reach by traditional mining processes. 3) Processing aid chemicals can be used to speed up cyanide leaching and enhance gold yields at least with certain type of gold concentrates.
List of publications
Ahoranta S, Zou G, Lakaniemi A-M, Neitola R, Puhakka JA. Effect of bio-oxidation treatment time on gold recovery via cyanidation, in preparation, will be submitted in July 2016.
Ahoranta S, Zou G, Lakaniemi A-M, Puhakka J, Neitola R, Korhonen T, Mörsky P. Bio-oxidation and autoclave pressure oxidation of gold bearing concentrates (PreGOLD), poster, 9th Fennoscandian Exploration and Mining Conference, October 2013, Levi, Finland.
Puhakka J. Mining biotechnology, oral presentation, Green Mining Annual Seminar, November 2013, Helsinki, Finland.
Ahoranta S, Zou G, Lakaniemi A-M, Puhakka JA. Optimisation of bio-oxidation processes for gold recovery, oral presentation, 7th International Symposium on Biohydrometallurgy, June 2014, Falmouth, UK.
Lakaniemi A-M. Bioprocesses for resource recovery and environmental control, oral presentation, The 4th international conference: Mining Industry in the Barents Euro – Arctic Region: View to the Future, October 2014, Kirovsk, Russia.
Neitola R, Ahoranta S, Zou G, Lakaniemi A-M, Puhakka J. Bio-oxidation and autoclave pressure oxidation of gold bearing concentrates (PreGOLD), poster, Green Mining Annual Seminar, November 2014, Helsinki, Finland.
Lakaniemi A-M. Bio-oxidation and autoclave oxidation of gold bearing concentrates (PreGOLD), oral presentation, Tekes Green Mining Programme: Development of mineral processing technology seminar, August 2015, Oulu, Finland.
Ahoranta S, Zou G, Lakaniemi A-M, Neitola R, Puhakka JA. Effect of bio-oxidation treatment time on gold recovery via cyanidation, oral presentation accepted to 8th International Symposium on Biohydrometallurgy, June 2016, Falmouth, UK.
Ahoranta S. Novel bio-oxidation and arsenic control processes for gold recovery. Doctoral thesis, Tampere University of Technology, expected graduation year 2017.