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A bioleaching study was conducted with six nickel sulphide ores from different geographical locations across Canada. Mineralogical and chemical examination revealed considerable variability between the samples, particularly in the silicate phases. The ores contain 0.3–1% nickel, primarily in pentlandite and secondarily in pyrrhotite. Copper is present primarily in chalcopyrite, and cobalt in pentlandite. The ores were subjected to the same crushing and grinding procedure, and bioleached under the same conditions for 3 weeks with a mixed culture of iron- and sulphur-oxidizing bacteria. Stirred-tank experiments with finely ground ore (−147 μm) at 30 °C were conducted to assess the effect of pH (2–5) and the impact of the bacteria. Nickel extraction from pentlandite and pyrrhotite during bioleaching at pH 2 and 3 was generally good (49–86% after 3 weeks), and cobalt extraction tracked nickel extraction over most conditions. All six ores showed a similar response to a change in pH; an increase in pH from 2 to 3 resulted in approximately the same nickel and cobalt extraction (within statistical error), and a statistically significant reduction in sulphuric acid consumption, dissolved iron, and magnesium extraction.

The focus of this study is to characterize the bacterial community structure present during stirred-tank bioleaching of a low-grade nickel sulphide ore at different temperatures (5 to 45 °C) and pH levels (3 and 5). This is a continuation of previous work, which was designed to assess the technical feasibility of applying elevated-pH bioleaching to this same ore from Manitoba, Canada. A combination of classical microbiological and molecular biological techniques has been used to identify and enumerate the members of the bacterial consortia over the course of the five-week experiments. DGGE analysis revealed the presence of at least 16 distinct 16S rRNA gene sequences, 14 of which are closely related to existing GenBank sequences. Two sequences were detected that are not closely related to existing GenBank sequences and may possibly be from novel species. Thirteen sequences are related to gene sequences of genera that have previously been detected in bioleaching environments (Acidithiobacillus, Leptospirillum, Sulfobacillus, Acidiphilium, Ferrimicrobium, and Acidimicrobium). Members from the genus Acidithiobacillus were dominant at all temperatures except 45 °C, at which Sulfobacillus spp. were dominant. Many of the acidithiobacilli are most closely related to strains of Acidithiobacillus ferrooxidans, and different strains were dominant under different experimental conditions, indicating considerable phenotypic heterogeneity within the species., Cet article porte essentiellement sur la caractérisation de la structure des communautés bactériennes présentes au cours de la biolixiviation en réacteurs agités d’un minerai de sulfure de nickel à faible teneur à différentes températures (de 5 à 45 °C) et à différents pH (3 et 5). Il s’agit de la suite de travaux antérieurs, dont le but était d’évaluer la faisabilité technique quant à l’utilisation de la biolixiviation à un pH élevé pour ce même minerai provenant du Manitoba (Canada). Une combinaison de techniques classiques microbiologiques et de biologie moléculaire a été utilisée pour identifier et recenser les membres des communautés bactériennes au cours des expériences menées pendant cinq semaines. Une analyse par électrophorèse en gel de gradient dénaturant (DGGE) a révélé la présence d’au moins 16 séquences distinctes de gènes d’ARNr 16S, dont 14 d’entre elles sont étroitement liées à des séquences existantes dans GenBank. Deux séquences détectées diffèrent grandement des séquences existantes dans GenBank et pourraient correspondre à de nouvelles espèces. Treize séquences sont liées à des séquences de gènes appartenant à des genres détectés antérieurement dans des milieux de biolixiviation (Acidithiobacillus, Leptospirillum, Sulfobacillus, Acidiphilium, Ferrimicrobium et Acidimicrobium). Les membres du genre Acidithiobacillus sont dominants à toutes les températures, sauf à 45 °C, température à laquelle ceux du genre Sulfobacillus spp. sont dominants. Bon nombre des acidithiobacilles sont les plus apparentés aux souches Acidithiobacillus ferrooxidans, et des souches différentes étaient dominantes sous différentes conditions expérimentales, ce qui indique une hétérogénéité phénotypique considérable au sein de l’espèce.

This study is a continuation of previous work designed to assess the effect of elevated-pH bioleaching on a low-grade ultramafic nickel sulphide ore from Manitoba, Canada. The ore contains 21% magnesium and 0.3% nickel. Nickel is the only significant metal value, and is present primarily as pentlandite. A substantial fraction of the magnesium is present as lizardite, making processing of the ore difficult with conventional pyro- and biohydrometallurgical techniques. This work has two objectives: to maximize nickel extraction, and to minimize magnesium mobilization. Five-week stirred-tank bioleaching experiments were conducted with finely ground ore (− 147 µm) at three pH levels (3, 4 and 5) and five temperatures (5, 15, 22.5, 30, and 45 °C). The initial rate of nickel extraction from pentlandite was observed to be inversely correlated to acidity at all temperatures, while the final extraction of nickel after 5 weeks was determined to be moderately correlated to acidity at high temperatures and negatively correlated to acidity at low temperatures. The advantage of elevated-pH bioleaching was most evident at 5 °C, in which the final extraction of nickel at pH 5 was approximately 250% greater than at pH 3. Electron probe X-ray microanalysis of the post-leach residues revealed that the un-reacted lizardite was enriched with nickel during experiments conducted at pH 5, and that the extent of enrichment was a strong function of temperature. The undesirable extraction of magnesium exhibited a strong negative pH–temperature interaction and the consumption of sulphuric acid directly tracked the extraction of magnesium over all experimental conditions. Bioleaching at elevated pH substantially increased the ratio of nickel to magnesium in the leachate, and resulted in a substantial reduction in sulphuric acid consumption.

The purpose of the present work is to investigate the technical feasibility of using elevated-pH bioleaching on a low-grade ultramafic nickel sulphide ore from Manitoba, Canada, which is not currently exploitable with conventional technologies. The ore contains 21% magnesium (~ 35% MgO) and 0.3% nickel. Nickel is the only significant metal value, and is present primarily as pentlandite. A substantial fraction of the magnesium is present as lizardite, making processing difficult with conventional pyro- and biohydrometallurgical techniques. This work has two equally important objectives: to minimize magnesium mobilization and to maintain an acceptable level of nickel extraction. Five-week stirred-tank bioleaching experiments were conducted with finely ground ore (− 147 µm) at 30 °C to study the effect of pH (2 to 6) on nickel and magnesium extraction. The rate of nickel extraction from pentlandite was found to be relatively insensitive to acidity at low pH and positively correlated to acidity at high pH. During the first three weeks of bioleaching, nickel was extracted at similar rates for experiments conducted at pH ≤ 5, with over 70% of the nickel extracted in that timeframe. The leaching of magnesium showed a greater dependency on pH, gradually decreasing from 70 to 10% at pH 2 and 5 respectively, after five weeks. Bioleaching at elevated pH substantially increased the ratio of nickel to magnesium in the leachate, and resulted in substantially less sulphuric acid consumption.

Although nitrification/denitrification processes have been used to remove ammonia and nitrate from municipal and industrial processes, there are few reported results on the removal of these ions from mine effluents. Ammonia and nitrate are present in the effluent due to the widespread use of ammonium-nitrate-fuel oil (ANFO) as a blasting agent, and the use of other nitrogen-containing reagents in the mill. Unlike other process effluents, there is very little nutrient content in mine effluents. The objective of this work was to develop a microbial process for the removal of ammonia from simulated mine effluents. Biologically, this is accomplished in two steps. In the first step, ammonia is oxidized to nitrate, and in the second step, nitrate is reduced to dinitrogen gas. Ammonia oxidation (nitrification) was tested using both continuously stirred tank reactors and trickling filters. The stirred tank reactor was chosen for the combined system because it produced final effluents with lower ammonia concentrations. For nitrate reduction (denitrification), a packed bed reactor operated in the upflow mode was tested with methanol being used as a carbon and energy source. The nitrate profiles within the denitrification reactor showed an exponential decay, a characteristic of plug flow conditions. A simulation model was developed for the denitrification reactor which described performance as a function of feed nitrate (NO3) and methanol concentrations (MeOH) and retention time (RT): Productivity (mg NO3/l per hour)=0.722(NO3)+(MeOH)[1.416−0.024 (MeOH)+0.0011(NO3)−0.776(RT)]. The methanol to nitrate ratio required for denitrification was 0.86:1. When the two processes were set up in series, it was successful in removing ∼90% of the nitrogen.