Effect of fluidized-bed carrier material on biological ferric sulphate generation

T. van der Meer, P. H.M. Kinnunen, A. H. Kaksonen, J. A. Puhakka

Research output: Contribution to journalArticleScientificpeer-review

13 Citations (Scopus)


High biomass hold-up and high iron oxidation rates of a biological ferric sulphate generating fluidized-bed reactor (FBR) requires a carrier material with high specific surface area, high porosity and inertness. In this work, the effect of activated carbon (AC), diatomaceous earth (Celite) and Al2O3 (Compalox) carrier materials on the ferric sulphate generation in FBRs were studied. Compalox dissolved during the experiments and formed an unfluidizable aggregate, and was therefore rejected. The slow dissolution of Celite resulted in a light, fine-grained, layer on top of the fluidized bed that had to be changed into fresh Celite. AC resisted well the friction caused by fluidization. The iron oxidation in the continuous-flow FBRs became limited by oxygen supply already at loading rates of 2.5 kg Fe2+ m-3 h-1. Iron oxidation rates of 27.6 and 25.7 kg m-3 h-1 were obtained in batch FBR experiments with AC and Celite, respectively. Biomass accumulation of 6.2 × 1010, 2.4 × 1010 and 8.0 × 109 cells per g of carrier was detected on Celite, AC and Compalox, respectively. The bacterial community structures on the carrier materials were revealed by Polymerase Chain Reaction and Denaturating Gradient 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 unofficially named "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, durability and the achieved high iron oxidation rates.

Original languageEnglish
Pages (from-to)782-792
Number of pages11
JournalMinerals Engineering
Issue number8
Publication statusPublished - 1 Jul 2007
MoE publication typeNot Eligible


  • Biomass carrier
  • Fluidized-bed
  • Iron oxidation
  • Leptospirillum ferriphilum


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