E. Börje Lindström

Bacterial Oxidation of Refractory Sulfide Ores for Gold Recovery

AbstractThe microbiological leaching of refractory sulfide ores (pyrite, arsenopyrite) for recovery of gold is reviewed in this article. The underlying physiological, biochemical, and genetic fundamentals of the bacteria involved (Thiobacillus and Sulfolobus spp.) are complex and have yet to be elucidated in depth. The chemistry of acid and biological leaching of pyrite and arsenopyrite minerals is also complex, and many of the individual reactions are not known in detail. Bacterial leaching is discussed in relation to chemical speciation at acid pH values. Attempts to develop models for a better understanding of bioleaching processes are summarized. The importance of pH, redox potential, temperature, sulfur balance, and toxic metals is evaluated for optimizing conditions for bacterial activity. Gold is finely disseminated in refractory sulfide ores, thereby decreasing Au recoveries upon conventional cyanidation for gold dissolution. In the bioleaching process, bacteria remove the sulfide minerals by oxid...

Seasonal changes in the distribution and exchange of inorganic nitrogen between sediment and water in the Northern Baltic (Gulf of Bothnia)

Seasonal changes in the distribution and exchange of inorganic nitrogen between sediment and water in the Northern Baltic (Gulf of Bothnia)

Sulfate Reduction Potential in Sediments in the Norilsk Mining Area, Northern Siberia

Abstract The purpose of this study was to characterize the distribution and activity of sulfate-reducing bacteria in tailings and sediments impacted by effluents from mining and smelting operations in the Norilsk area in northern Siberia. The Norilsk mining complex involves three smelter operations, a hydrometallurgical plant, and extensive tailings areas located in the permafrost zone. Sulfate reduction rates measured with a 35SO4 2− tracer technique under various in-situ conditions ranged from 0.05 to 30 nmol S cm−3 day−1. Acetate and glucose addition greatly stimulated sulfate reduction, whereas lactate had less effect. The most pronounced stimulation of sulfate reduction (6.5-fold) was observed with phosphate amendment. Most-probable-number (MPN) counts of sulfate-reducing bacteria in media with glucose, ethanol, lactate, and acetate as electron donors were generally highest at around 107 cells ml−1. The actual MPN counts varied with the sample, electron donor, and incubation conditions (pH 7.2 vs. pH 3.5; 28°C vs. 4°C). Enrichment cultures of sulfate-reducing bacteria were established from a sample that showed the highest rate of sulfate reduction. After multiple serial transfers, the dominant sulfate-reducers were identified by fluorescence in situ hybridization using genus and group-specific 16S rRNA-targeted oligonucleotide probes. Desulfobulbus spp. prevailed in ethanol and lactate enrichments and the Desulfosarcina-Desulfococcus group dominated in acetate and benzoate enrichments. Psychrophilic Desulfotalea-Desulfofustis and moderately psychrophilic Desulforhopalus spp. were identified in enrichments incubated at 4°C, but they were also found in mesophilic enrichments.

A sequential two-step process using moderately and extremely thermophilic cultures for biooxidation of refractory gold concentrates

In many cases, the use of extreme thermophiles, like the archeon Sulfolobus metallicus, in a continuous bioleaching process of gold concentrates is limited by the arsenic content in the feed. In this work, a sequential two-step bioleaching process for gold-containing refractory pyrite/arsenopyrite concentrates has been investigated for the possibility of lowering the toxicity of arsenic with respect to the extremely thermophilic culture. In the first stage, a moderately thermophilic culture was used followed by the extremely thermophilic S. metallicus in the second stage. It was found that the S. metallicus culture survives higher arsenic concentrations than expected when the concentrate was pre-oxidized at a lower temperature. Thus, with this sequential two-step bioleaching process, it is possible to reduce the toxicity of the released arsenic. Therefore, the use of higher pulp densities of arsenic-containing minerals is enabled. When the leached mineral residues were subjected to cyanidation, cyanide consumption and thiocyanate formation were significantly lower after the second stage. In addition, a somewhat higher gold and silver grade was found in the residue from the concentrate ultimately oxidized by S. metallicus.

Thermophilic bioleaching of arsenopyrite using Sulfolobus and a semi-continuous laboratory procedure

SummaryA laboratory equipment for pumping slurries is described. The pumping is performed semi-continuously by using a plastic syringe, a set of different valves, and a programmable electronic unit. The reproducibility of the pumping is demonstrated. Bioleaching of a gold-containing arsenopyrite slurry was done withSulfolobus at 70°C using the semi-continuous procedure and with a retention time of 100 h for the mineral. Arsenic was completely released at a rate of 109 mg l−1 h−1. The gold recovery is related to the amount of iron and arsenic dissolved and is shown to have a correlation factor of approximately one relative to the release of arsenic.

Optimization of pyrite bioleaching using Sulfolobus acidocaldarius

Optimization of batch pyrite bioleaching with Sulfolobus acidocaldarius was performed using statistical modelling and experimental design. First a screening design was made followed by response surface modelling. The dominating factors identified were pH, pulp density and particle size. The highest batch leaching rate after optimization was 270 mg iron·l−1·h−1 for 6% (w/v) pulp density, pH = 1.5 and particle size <20 μm. This represents a 3.5-fold increase from the leaching rate of 80 mg iron·l−1·h−1 obtained under our standard laboratory conditions.