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Wakeman K.D.,Tampere University of Technology | Erving L.,Tampere University of Technology | Riekkola-Vanhanen M.L.,Talvivaara Mining Company Plc. | Puhakka J.A.,Tampere University of Technology
Water Research

Silage was used as source of carbon and electrons for enrichment of silage-degrading and sulfate reducing bacteria (SRB) from boreal, acidic, metals-containing peat-bog samples and to support their use in batch and semi-batch systems in treatment of synthetic waste water. Sulfidogenic silage utilization resulted in a rapid decrease in lactate concentrations; concentrations of acetate, butyrate and propionate increased concomitantly. Synthetic waste water consisting of Mn, Mg and Fe (II) ions inhibited sulfate reduction at concentrations of 6 g/l, 8 g/l and 1 g/l respectively. During treatment, Mn and Mg ions remained in solution while Fe ions partially precipitated. Up to 87 mg sulfate was reduced per gram of silage. Sulfate reduction rates of 34, 22 and 6 mg/l/day were obtained at temperatures of 30, 20 and 9 °C respectively. In semi-batch reactors operated at low pH, the iron precipitation capacity was controlled by sulfate reduction rates and by partial loss of hydrogen sulfide to the gas phase. Passive reactor systems should, therefore, be operated at neutral pH. Metals tolerant, silage-fermenting (predominantly species belonging to genus Clostridium) and sulfate reducing bacteria (including a species similar to the psychrotolerant Desulfovibrio arcticus) were obtained from the peat bog samples. This work demonstrates that silage supports sulfate reduction and can be used as a low cost carbon and electron source for SRB in treatment of metals-containing waste water. © 2010 Elsevier Ltd. Source

Saari P.,Talvivaara Sotkamo Mine Ltd. | Riekkola-Vanhanen M.,Talvivaara Mining Company Plc.
Journal of the Southern African Institute of Mining and Metallurgy

The Talvivaara deposits are located in Eastern Finland, within the Kainuu Schist Belt. These polymetallic sulphide deposits are of relatively low grade, but bioheapleaching enables economically profitable nickel extraction from the ore. Zinc, cobalt, and copper are also produced. Talvivaara's production process begins with large-scale open-pit mining and four crushing stages, followed by stacking of the ore in bioleaching heaps. The ore is first leached for 13-14 months on the primary leach pad, after which the leached ore is reclaimed, conveyed, and re-stacked on the secondary heap pad. After secondary leaching, the barren ore will remain on the secondary heaps permanently. In the metals recovery process, the metals are precipitated from the pregnant leaching solution. Construction of the process was begun in spring of 2007 and first metal sulphides were produced at the plant in October 2008. The development of the bioheapleaching process was begun in a 17 000 t on-site pilot heap operated during 2005-2008 and has continued in the industrial heap. At industrial scale, the development measures have focused on improving the permeability and aeration of the heap. Challenges with crushing and aerations systems at the beginning of industrial-scale leaching delayed the increase in metal recovery, but after the first two operational years the leaching results have improved significantly and the process is performing as targeted. © The Southern African Institute of Mining and Metallurgy, 2012. Source

Riekkola-Vanhanen M.,Talvivaara Mining Company Plc.
Minerals Engineering

The latest commercial application of bioleaching, and the first in Europe, is the Talvivaara Sotkamo Mine in North-Eastern Finland. The ore is low grade black schist, and contains pentlandite, pyrrhotite, chalcopyrite, sphalerite and pyrite as the main sulphide minerals. The ore and the possible utilization of the deposits have been extensively studied for over 20 years. Bioheapleaching technology was chosen for the extraction of nickel from the ore based on its favourable capital and operational costs and the good performance data obtained in a large on-site pilot trial. Mining was started in Sotkamo in April 2008 and building of the industrial scale bioheap in August 2008. The first shipment of nickel sulphide product was delivered to the customer in February 2009. The mining method at Talvivaara is open pit mining, after which the ore is crushed and screened, agglomerated and finally stacked on the primary heap pad. Air is supplied to the stacked ore with low pressure fans through aeration piping inside the heap. The heap is irrigated from the top with acidic leaching solution, and the solution is collected from the bottom of the heap. A 10% side flow is taken for metals recovery and the rest of the solution is recycled back to the irrigation of the heap. After approximately 13-14 months of bioleaching on the primary pad, anticipated recoveries are about 70% for nickel and 60% for zinc. The leached ore is then reclaimed and re-stacked onto the secondary heap pad. In secondary leaching the rest of nickel and zinc and part of cobalt and copper will be leached. The anticipated total recoveries after both primary and secondary leaching are 85% for nickel, 80% for zinc, and 50% for both copper and cobalt. In the metals recovery process, the metals are precipitated from the pregnant leaching solution using gaseous hydrogen sulphide. The resulting products are intermediates which are transported for further processing in refineries operated by the company's customers. © 2013 Elsevier Ltd. All rights reserved. Source

Nurmi P.,Tampere University of Technology | Ozkaya B.,Tampere University of Technology | Sasaki K.,Kyushu University | Kaksonen A.H.,Tampere University of Technology | And 4 more authors.

Effluents from bioleaching processes cause severe problems if dispersed in the environment since they typically have very low pH values and high sulfate and ferric iron concentrations. Dissolved iron may also interfere with the metal recovery. In the bioleaching circuit, partial removal of dissolved iron and sulfate is needed to alleviate process disturbances. In this study, an integrated, bench-scale process comprising a fluidized-bed reactor (FBR) and a gravity settler was developed for controlled biological oxidation of ferrous iron and precipitative removal of ferric iron and sulfate for use in waste management of heap bioleaching processes. The FBR for iron oxidation by an enrichment culture dominated by Leptospirillum ferriphilum was operated at 37 ± 2 °C. The FBR recycle liquor was partially neutralized with 10 M KOH or 50 g/L CaCO3 slurry to promote ferric iron and sulfate precipitation. With 6 ± 1.5 g Fe2+/L in the feed and KOH-adjusted pH 3.5, the oxidation rate of Fe2+ was 3.7 g/L h and 99% precipitation of ferric iron was achieved in the process. Adjustment with CaCO3 to pH 3.2 slightly decreased the oxidation rate to 3.3 g/L h and 98% of ferric iron precipitated. With 15 g Fe2+/L in the feed, the oxidation rate was 7.0 g Fe2+/L h coupled with 96% precipitation of ferric iron. A solid solution of jarosite was the main product of ferric iron precipitation with KOH adjustment and with minor amounts of goethite at the higher pH range. Adjustment of the pH with CaCO3 precipitated ferric iron also as a solid solution of jarosite, and sulfate precipitated also in the form of gypsum (CaSO4·2H2O) especially at the higher pH values. © 2009 Elsevier B.V. All rights reserved. Source

Halinen A.-K.,Tampere University of Technology | Beecroft N.J.,Tampere University of Technology | Beecroft N.J.,University of Surrey | Maatta K.,Tampere University of Technology | And 6 more authors.

In the present work the microbial community of a low grade nickel ore demonstration-scale bioheap was examined under varying weather (outside air temperature between + 30 and - 39 °C) and operational conditions over a period of three years in Talvivaara, Finland. After the start-up of heap irrigation, oxidation of pyrrhotite and pyrite increased the heap temperature up to 90 °C. Leach liquor temperatures varied between 60 and 15 °C over the operation period, affecting the progress of sulfide ore oxidation. The microbial communities were profiled by polymerase chain reaction (PCR) - denaturing gradient gel electrophoresis (DGGE) followed by partial sequencing of 16S rRNA gene. Large temperature gradients prevailed resulting in the simultaneous presence of active mesophilic and thermophilic iron- and/or sulfur-oxidisers in the heap. As mineral oxidation progressed microbial diversity decreased and Acidithiobacillus ferrooxidans became increasingly dominant. The number of bacteria in the leach liquors was in the range of 10 5-10 7 cells mL - 1. After one year of bioheap operation several ore samples were drilled from the heap and A. ferrooxidans, Acidithiobacillus caldus, an uncultured bacterium clone H70 related organism, Ferrimicrobium acidiphilum and a bacterium related to Sulfobacillus thermosulfidooxidans were found. Cell counts from the ore samples varied between 10 5 and 10 7 cells g - 1 ore sample. The archaeal species present in leach liquors were novel and related to uncultivated species. During the secondary leaching phase the leaching community remained steady. A. ferrooxidans dominated, and an uncultured bacterium clone H70-related organism and Leptospirillum ferrooxidans were present. © 2012 Elsevier B.V. All rights reserved. Source

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