Advanced Materials Research Vols. 71-73

Abstract: Two novel experimental approaches have been developed to investigate the attachment of microorganisms to sulphide minerals as a function of the mineral and microbial phase in a joint project with BHP Billiton, conceptualised in 2005 and initiated in 2006. In the first approach, selective attachment of pure cultures to minerals was studied in the “particle coated column reactor” using A. ferrooxidans and L. ferriphilum. The saturated reactor containing glass beads coated with fine mineral concentrates provided a quantifiable surface area of mineral concentrate and maintained good fluid flow. Results are reported for chalcopyrite and pyrite concentrates, a low grade chalcopyrite ore and quartzite. The latter, representing typical gangue material, is used as a control. A. ferrooxidans displayed greater attachment to pyrite, and selective attachment to sulfide minerals over quartz. Similar attachment behaviour trends resulted for Leptospirillum spp. In the second approach, a novel technique was developed to investigate microbial ecology of microbe-mineral attachment, site and mineral specific associations of microorganisms and spatial organisation of microbial communities present. Qualitative assessment and visualisation of microorganisms associated with the mineral surface and subsequent biofilm development was shown in the biofilm reactor, using microscopy techniques and fluorochromes. FISH analyses of A. ferrooxidans and L. ferriphilum on massive chalcopyrite sections are presented. The consequence of the observed attachment on heap bioleach performance is discussed.

Abstract: The aim of the present investigation is to obtain tapping mode images of Acidithiobacillus ferrooxidans and interfacial forces between Acidithiobacillus ferrooxidans cells and silicon nitride tip of AFM. The effect of exposure of cells to toxic metal ions like arsenic on the morphology of the cells was investigated by the section analysis of the AFM images obtained. Effect of glutaraldehyde fixation on force curves is also analyzed.

Abstract: This study reports the effect of sulfuric acid concentration on chalcopyrite chemical leaching in very simple H2SO4 solution systems ranging from 23g/L to 30g/L, with 2.5% chalcopyrite concentrate at 30°C. Copper extraction from chalcopyrite increases with an increase in sulfuric acid concentration, e.g. 86%, 90% and 92% after 96 days at 23g/L, 25/L and 27g/L H2SO4 solution respectively. Sulfur element formed on the surface of chalcopyrite was very porous as the result of an electron probe microanalyzer (EPMA). Copper extraction, however, leveled out at 35% after 20 days when the sulfuric acid concentration was higher than 28g/L on 25g/L of chalcopyrite concentrate. Sulfur element was detected by X-ray analysis as only a leaching reaction product. The passivation may be caused by thick elemental surface formed on the surface of chalcopyrite.

Abstract: In a series of studies, various aspects of thermophilic bioleaching of chalcopyrite minerals and concentrates have been analyzed. Although the main objective was the elucidation of the catalytic effect of thermophiles in leaching chalcopyrite, various other new findings contributed to a better understanding of interactions among chemical, physicochemical and biological factors, which influence the bioleaching of chalcopyrite with thermophiles. Additionally, in order to bridge laboratory results and field applications, novel mathematical models as well as an alternative method to efficiently leach chalcopyrite without thermophiles are the contributions of this research.

Abstract: The focus of this paper is on the treatment of low-grade chalcopyrite-pyrite containing concentrates. The bioleaching of chalcopyrite is a major challenge due to slow copper leach kinetics and poor copper extractions. Bioleaching tests were carried out in bench-scale piloting facilities, comprising fully controlled multi-stage continuously operated reactor systems using moderate thermophile and thermophile consortia under both uncontrolled and controlled redox potential conditions. Bioleaching operating conditions and control strategies have been identified, which have the potential to significantly increase the rate of Cu leaching and to reduce process costs by allowing control of the amount of pyrite oxidised.

Abstract: In tank bioleaching, decreasing particle size of milled concentrates has been shown to improve leaching performance owing to increased mineral surface area and mechanical activation effects of fine mineral particles. However, evidence suggests a critical lower limit of particle size distribution exists below which the performance of the thermophilic iron and sulfur oxidizer Sulfolobus metallicus is compromised and complete culture death may result. This paper proposes an explanation for these observations at fine fractions through identifying a relationship between mineral composition of six sulfide concentrates, their extent of milling and the generation of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) and hydroxyl radicals (•OH) in slurries. The effect of oxidative stress induced in the absence of minerals on growth and bioleaching performance of S. metallicus is studied.

Abstract: The microbial microenvironment in heaps is strongly influenced by ore mineralogy. While laboratory studies on microbial activity under controlled conditions provide a good understanding how bioleaching organisms might assist in metal extraction, examination of the ore, its mineralogy and leaching chemistry offer additional valuable insights. Some examples are discussed and illustrated with data for a copper-nickel sulfide ore.

Abstract: A dump located in the proximity of the Vlaikov Vrah mine, Bulgaria, and containing about 120 000 tons of run-of-mine mining wastes (low-grade ores and rock mass), since 1968 was subjected initially to spontaneous natural bioleaching based on the rains as irrigating leach solutions, then from 1972 to 2003 to commercial-scale bioleaching by means of irrigation with acidified leach solutions, and since 2004- again to spontaneous natural bioleaching. The monitoring of these processes during this 40-year period revealed considerable changes in the composition, geotechnical and acid-base properties of the dump material, as well as in the diversity, number and activity of its microflora.The data obtained during this study were used to stimulate the bioleaching process in the huge commercial-scale copper dump leaching operation at Vlaikov Vrah mine in which about forty million tons of such mining wastes were treated.

Abstract: For the purpose of investigations of the different situations when the cells of Acidianus manzaensis can or can not attach the surface of the chalcopyrite. Three experiments were carried out in the modified shake flasks, and in one of the experiments the cells could not attach the surface of the chalcopyrite, but could participate in the solution chemistry of the process. The redox potential, pH, cell density, copper, ion and thiosulfate concentration in the solution were monitored in the experiments, and the morphological feature and chemical composition of the leached residues were analyzed by SEM and XRD. The most leach effiency of Cu and Fe was reached in the experiment that the Acidianus manzaensis could attach the surface of the chalcopyrite. However, the unattached Acidianus manzaensis could also leach the chalcopyrite, but it was less actively than attached cells. There was no precipitation of jarosite in the leached residues of the three experiments, but there was sulfur in the leached residues when the cells could not attach the chalcopyrite. So the surface passivating layer of sulfur can be removed only when the Acidianus manzaensis can attach the surface of the chalcopyrite. From these results it become apparent that the leach of the chalcopyrite is the cooperative action of the attached and unattached Acidianus manzaensis.

Abstract: The effect of different microbial consortia on the leaching of chalcopyrite was studied at different temperatures and solution compositions with Boliden’s Aitik ore in column reactors simulating heap bioleaching. The columns were equipped with sampling chambers and chalcopyrite mineral electrodes in order to investigate the passivation of chalcopyrite. The sampling chambers were filled with agglomerated ore and pieces of chalcopyrite-rich ore. In addition to chemical analysis of the leaching solution and solids the progress of leaching of chalcopyrite was studied by continuous potential measurements with chalcopyrite electrodes. The occurrence and composition of potentially passivating layers on the surfaces of the electrodes and the samples taken from sample chambers were examined by optical and scanning electron microscopy.