From: Amara Graps (Amara.Graps@mpi-hd.mpg.de)
Date: Wed May 23 2001 - 03:19:15 MDT
>From Scientific Computing Newsline #40 , May 2001
http://scnewsline.campublishers.com
Bugs that eat computers
Researchers in the Institute for Environmental Science at the
University of Zurich may have discovered the ultimate computer
bug. Not this time a fault in software but real microbes that can
digest redundant circuit boards, gather up the heavy metals -
such as copper - which have gone into their manufacture and allow
these metals to be recycled for further use.
The conventional method of dealing with electronic waste is to
grind or incinerate the material, once any components that can be
reused have been removed. This process produces a fine-grained
dust. Now Dr Helmut Brandl and his colleagues at Zurich have
found an inexpensive way of recovering metals from the dust for
reuse.
Relatively common bacteria, such as Thiobacilli ferroxidans and
Thiobacilli thiooxidans, are already utilized in mining for the
extraction of metals such as copper. Both types of bacteria
acquire their metabolic energy through the oxidation of reduced
sulphur compounds.
Dr Brandl believes that heterotrophic bacteria and yeasts could
be utilized to leach lead, copper and tin from printed circuit
boards. A sulfolobus-like organism mobilises gallium from
compound semiconductors. Fungi (such as penicillin) and bacteria
are capable of growing on electronic waste. The formation of
inorganic acids (e.g. sulphuric acid) through bacteria and the
formation of organic acids such as citric acid and gluconic acid
through fungi, cause dissolution of metals. In addition,
dissolution of metals can be achieved with oxidation processes
e.g. iron oxidation with thiobacilli. Fungi, because of the
organic metabolic products (chelating agent), are able to
maintain the metals in a dissolved state in a certain range, more
or less independently of the pH value. Penicillium simplicissimum
is able to efficiently mobilize many metals (Ni, Pb, Sn, Zn) in a
single stage procedure.
This procedure allows metals to be separated completely from the
electronic waste. It is very simple then to recover the metals
from the various leaching liquids. In a first step, the biomass
is removed by filtering. Then, the pH content of the filtrate is
increased by the addition of caustic soda, which facilitates a
metal fractionation (sequential precipitation). Aluminium and
copper in particular can be recovered as hydroxide in this way.
www.unizh.ch/uwinst/indexe.html
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Amara Graps | Max-Planck-Institut fuer Kernphysik
Interplanetary Dust Group | Saupfercheckweg 1
+49-6221-516-543 | 69117 Heidelberg, GERMANY
Amara.Graps@mpi-hd.mpg.de * http://galileo.mpi-hd.mpg.de/~graps
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"Never fight an inanimate object." - P. J. O'Rourke
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