Heap bioleaching of a complex sulfide ore: Part II. Effect of temperature on base metal extraction and bacterial compositions

The effect of low to moderate temperatures (7 to 50 degrees C) on the bioleaching of a low-grade, multi-metal black schist ore from Finland in which pentlandite was the main valuable mineral, was studied using columns at set temperatures. The iron and sulfur-oxidizing microbial culture used were enriched from the ore deposit water samples. At 7 degrees C and 21 degrees C, the leach liquor redox potential stabilized to 500-600 mV, whereas at 35 degrees C and at 50 degrees C it varied between 300 and 500 mV. Microbial iron oxidation started after a lag phase of 20 days at 7 degrees C and after 60 days of operation, total iron and Fe-tot/Fe2+-ratio were higher in the 7 degrees C column leach liquor than at other temperatures. At 50 degrees C, all dissolved iron remained in ferrous form and did not indicate microbial activity. Highest bioleaching recoveries of Ni (26%), Zn (18%) and Co (6%) were obtained after 140 days at 21 degrees C. At 50 degrees C, bioleaching decreased due to the lack of ferric ion. The microbial composition, as measured by Polymerase Chain Reaction (PCR)-Denaturing Gradient Gel Electrophoresis (DGGE)-sequencing approach, was affected by temperature. Acidithiobacillus ferrooxidans was the most common species in the leach liquor at 7 degrees C; while at 35 degrees C Leptospirillum ferrooxidans dominated and at 50 degrees C, Sulfobacillus thermotolerans was the most common organism. Total liquid-phase cell counts were higher at 7 degrees C than at other temperatures. Thus the boreal ore deposit enrichment culture was composed of microorganisms capable of being active over a wide temperature range. (C) 2009 Elsevier B.V. All rights reserved.