It is only in the past decade or so that industrial exploitation of
biological resources and techniques has become regarded as a
distinct discipline. Commonly referred to as Biotechnology, it
embraces biochemistry, microbiology and the engineering
sciences and is mainly aimed at the biological conversion of
suitable raw materials into desired end products. The catalytic
agents are more often than not bacteria although other
micro-organisms such as fungi are used. The range of micro-organisms used is wide and the choice
depends upon the desired end product, which in turn depends
upon the metabolic attributes, genetically engineered or
otherwise, of the cells. The metabolic diversity of
micro-organisms has been applied to processes such as antibiotic
production, food processing, brewing and chemical production,
and of course extraction of metals from ores. Metabolic diversity is, to a certain extent, based on nutrition,
which, in its simplest form, can be divided into energy source,
carbon requirements and nature of the electron donor producing
reducing power to the cells. The source of energy may be light,
in which case the organisms are phototrophic (eg green plants,
algae). The carbon requirements and reducing power may come
from organic sources. These organisms are then called
heterotrophic (eg man and most bacteria, including the well
known Escherichia colt). However, there is a group of bacteria
whose energy metabolism depends upon chemical redox
reactions, use inorganic carbon (CO2) and obtain their reducing
power from reduced chemicals such as metal sulphides. These
are known as chemolithotrophs. They play an important role in
mineral recycling in nature and are also ideal for extraction of
metals from ores. This is because they are extremeophiles being
acidophilic (grow at very low pH) and sometimes also
thermophilic (grow at very high temperatures). These bacteria operate in such hostile environments that
competition, or contamination, by other organisms does not
occur. Extraction of metals from ores by chemolithotrophic bacteria is
commonly referred to as biohydrometallurgy. Other related areas
are bioadsorption of metals from dilute solution,- microbial
treatment of metal contaminated wastes and removal of toxic
chemicals produced or used during mineral processing. This paper basically reviews the work that Gencor has
undertaken in the field of biohydrometallurgy and the
advancements it has made in commercialising the technology, but
also touches on certain long-term areas of research that are
currently under investigation.