Bioleaching of Gold Ore

Topics: Bacteria, 16S ribosomal RNA, Ribosomal RNA Pages: 25 (6507 words) Published: October 29, 2010
Insights intothe dynamics of bacterial communities during
chalcopyrite bioleaching
Zhiguo He1,2, Fengling Gao1,2, Jiancun Zhao1,2, Yuehua Hu1,2 & Guanzhou Qiu1,2 1School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, China; and 2Key Laboratory of Biometallurgy, Ministry of Education, Changsha, Hunan, China

Correspondence: Zhiguo He, School of
Minerals Processing and Bioengineering,
Central South University, Changsha, Hunan
410083, China. Tel./fax: 186 731 88879815;
Received 19 December 2009; revised 14 April
2010; accepted 17 June 2010.
Final version published online 3 August 2010.
Editor: Alfons Stams
DGGE; RFLP; bioleaching; acid mine drainage;
The microbial ecology of the bioleaching of chalcopyrite ores is poorly understood and little effort has been made to handle the microbiological components of these processes. In this study, the composition and structure of microbial communities in acid mineral bioleaching systems have been studied using a PCR-based cloning approach. Denaturing gradient gel electrophoresis (DGGE) analysis of PCRamplified 16S rRNA gene fragments from bacteria was used to evaluate the changes in the bacterial community in the process of chalcopyrite bioleaching in a shaken flask system. The results revealed that the bacterial community was disturbed after the addition of chalcopyrite. Phylogenetic analyses of 16S rRNA gene fragments revealed that the retrieved sequences clustered together with the genera Acidithiobacillus, Leptospirillum, and Acidovorax. Multidimensional scaling analysis of DGGE banding patterns revealed that the process of chalcopyrite bioleaching in 46 days was divided into four stages. In the first stage, Leptospirillum were dominant. In the second stage, Leptospirillum and Acidithiobacillus groups were mainly detected. In the third and fourth stages, the bacterial community was relatively stable and was dominated by Leptospirillum and Acidithiobacillus. These results extend our knowledge on the microbial dynamics in chalcopyrite bioleaching, a key issue required to improve commercial applications.

The abundance of the copper-bearing chalcopyrite (CuFeS2)
has motivated considerable attempts toward the development
of low-cost technologies such as bioleaching in order to
extract usable copper. Many researchers have investigated the possibility of using thermophilic instead of mesophilic microorganisms to improve the bioleaching rate of chalcopyrite.
Although the use of thermophiles in leaching sulfide minerals considerably improves reaction kinetics and avoids excessive chalcopyrite passivation, which hinders continuous bioleaching (Sandstr¨om & Petersson, 1997; Gomez et al., 1999a, b),

this application is difficult and expensive, especially when dealing with low-grade chalcopyrite. On the other hand,
mesophiles or moderately thermophilic microorganisms
can tolerate higher pulp density than thermophilic microorganisms (Ehrlich, 2001). Therefore, new ways to improve
bioleaching of chalcopyrite with mesophiles should be investigated. However, the paucity of information in the public
domain on the ability of mesophilic microorganisms to grow
on and leach Cu from chalcopyrite ore has limited its
implementation on a commercial scale (Plumb et al., 2008).
Detailed descriptions of changes during bioleaching in the
bacterial community structure and accompanying chalcopyrite
leaching kinetics have not been published. During bioleaching, the microbial community is still treated as a ‘black
box’, because many environmental bacteria cannot yet be
purely cultured using conventional laboratory techniques.
The leaching of chalcopyrite can be represented by the
following reactions (Vilc ´aez et al., 2008):
Ferric ion consumption (reaction 1):
CuFeS2 þ 4Fe3þ ! Cu2þ þ 5Fe2þ þ 2S0
Acid consumption...
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