Microbial community dynamics during a demonstration-scale bioheap leaching operation

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

Microbial community dynamics during a demonstration-scale bioheap leaching operation

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

A conceptual flowsheet for heap leaching of platinum group metals (PGMs) from a low-grade ore concentrate

This research proposes a new conceptual process to economically extract platinum group metals (PGMs), and as a secondary aim, base metals (BMs) from a low-grade concentrate originating from typical PGM concentrator plants. Slurry made from the concentrate was coated onto granite pebbles and packed into a column, in which it was bioleached with a mixed culture of thermophiles and mesophiles at 65 °C. After 30 days the extractions achieved were 52% copper, 95% nickel and 85% cobalt. The residual concentrate material was subsequently subjected to a cyanide leach also in a packed column operating at a room temperature of 23 °C. After 21 days 20.3% Pt, 87% Pd and 46% Rh were extracted. Using these results and projected extractions over longer operating times, a conceptual flowsheet was proposed for a possible process route to recover PGM values circumventing the problematic smelter route for this material