Effect of fluidized-bed carrier material on biologicalferric sulphate generation

Minerals Engineering 20(2007)

Effect of fluidized-bed carrier material on biologicalferric sulphate generation

Effect of fluidized-bed carrier material on biologicalferric sulphate generation

782–792

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Effect of fluidized-bed carrier material on biologicalferric sulphate generation

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E?ectof ?uidized-bedcarrier material on biological ferric

sulphate generation

T. van der Meer

b

a,b, *

, P.H.-M. Kinnunen a , A.H. Kaksonen b , J.A. Puhakka

a

b

Outokumpu Technology, Research Center, Pori, Finland

Institute of Environmental Engineering and Biotechnology, Tampere University of Technology, Tampere, Finland

Received 4October 2006; accepted 8February 2007

Available online 3April 2007

Abstract

High biomass hold-up and high iron oxidation rates of a biological ferric sulphate generating ?uidized-bedreactor (FBR)requires a carrier material with high speci?csurface area, high porosity and inertness. In this work, the e?ectof activated carbon (AC),diatoma-ceous earth (Celite)and Al 2O 3(Compalox)carrier materials on the ferric sulphate generation in FBRs were studied. Compalox dissolved during the experiments and formed an un?uidizableaggregate, and was therefore rejected. The slow dissolution of Celite resulted in a light, ?ne-grained,layer on top of the ?uidizedbed that had to be changed into fresh Celite. AC resisted well the friction caused by ?u-idization. The iron oxidation in the continuous-?owFBRs became limited by oxygen supply already at loading rates of 2.5kg Fe 2+m À3h À1. Iron oxidation rates of 27.6and 25.7kg m À3h À1were obtained in batch FBR experiments with AC and Celite, respectively.

Biomass accumulation of 6.2·1010, 2.4·1010and 8.0·109cells per g of carrier was detected on Celite, AC and Compalox, respec-tively. The bacterial community structures on the carrier materials were revealed by Polymerase Chain Reaction and Denaturating Gra-dient Gel Electrophoresis (PCR-DGGE)followed by partial sequencing of the 16S rRNA gene. Two bacterial strains, Leptospirillum ferriphilum and a strain similar to a strain uno?ciallynamed ‘‘Ferrimicrobium acidiphilum ’’,were detected. Examination of the carrier material surfaces with scanning electron microscopy (SEM)coupled with energy dispersive spectroscopy (EDS)revealed that all carrier materials were covered with jarosite precipitates and that the bacteria were mainly retained on the jarosite covered areas. In conclusion, AC was the most promising carrier material for a large-scale biological ferric sulphate generating FBR based on its availability, dura-bility and the achieved high iron oxidation rates. Ó2007Published by Elsevier Ltd.

Keywords:Iron oxidation; Fluidized-bed; Leptospirillum ferriphilum ; Biomass carrier

1. Introduction

Microbial iron oxidation has been exploited in bioleach-ing, treatment of acid mine drainage (Sandstro ¨mand Mattsson, 2001), and removal of H 2S from gases (Park et al., 2005). The optimum pH area for acidophilic iron oxi-dizing bacteria is generally between 1.5and 2.0(Rawlings,

Corresponding author. Address:Institute of Environmental Engineer-ing and Biotechnology, Tampere University of Technology, Tampere, Finland. Tel.:+358408297310; fax:+35826265310.

E-mail address:tuomas.van.der.meer@http://www.mianfeiwendang.com(T.van der Meer).

0892-6875/$-see front matter Ó2007Published by Elsevier Ltd. doi:10.1016/j.mineng.2007.02.002

*

2002). The low pH is also important in respect to ferric iron solubility, as ferric iron has extremely low solubility at pH >2.5(Grishin et al., 1988). In bioleaching, sulphide minerals are chemically oxidized by ferric iron (Fe3+) and the resulting ferrous iron (Fe2+) is regenerated to ferric iron by micro-organisms. (Forreviews, see Rohwerder et al., 2003; Sand et al., 2001). The biological regeneration of fer-ric iron can take place within the sulphide mineral leaching unit (e.g.heap, tank) (Boon and Heijnen, 1998; Komnitsas and Pooley, 1991), or in a separate reactor from which the (re)generatedferric lixiviant may be pumped to the leach-ing unit (Carranza et al., 1997). The use of an iron oxida-tion unit allows the separation of the biological and

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