Affiliation:
1. Institute of Plant Biology, Department of Microbiology, University of Zurich, CH-8008 Zurich,1 and
2. Institute of Environmental Sciences, University of Zurich, CH-8057 Zurich,2 Switzerland
Abstract
ABSTRACT
Semicontinuous biohydrometallurgical processing of fly ash from municipal waste incineration was performed in a laboratory-scale leaching plant (LSLP) by using a mixed culture of
Thiobacillus thiooxidans
and
Thiobacillus ferrooxidans
. The LSLP consisted of three serially connected reaction vessels, reservoirs for a fly ash suspension and a bacterial stock culture, and a vacuum filter unit. The LSLP was operated with an ash concentration of 50 g liter
−1
, and the mean residence time was 6 days (2 days in each reaction vessel). The leaching efficiencies (expressed as percentages of the amounts applied) obtained for the economically most interesting metal, Zn, were up to 81%, and the leaching efficiencies for Al were up to 52%. Highly toxic Cd was completely solubilized (100%), and the leaching efficiencies for Cu, Ni, and Cr were 89, 64, and 12%, respectively. The role of
T. ferrooxidans
in metal mobilization was examined in a series of shake flask experiments. The release of copper present in the fly ash as chalcocite (Cu
2
S) or cuprite (Cu
2
O) was dependent on the metabolic activity of
T. ferrooxidans
, whereas other metals, such as Al, Cd, Cr, Ni, and Zn, were solubilized by biotically formed sulfuric acid. Chemical leaching with 5 N H
2
SO
4
resulted in significantly increased solubilization only for Zn. The LSLP developed in this study is a promising first step toward a pilot plant with a high capacity to detoxify fly ash for reuse for construction purposes and economical recovery of valuable metals.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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