Dr David Ralph

Room: PhSc/2.011

Research

Interactions between micro-organisms and minerals
Micro-organisms interact with a huge variety of minerals in many different ways. The growth of cells which cause decay in teeth, the corrosion of metal structures in marine environments and the formation of acid mine drainage are all examples of a destructive and undesired interaction between microbial cells and minerals. The bio-oxidation of sulphide minerals in hydrometallurgical processes is an example of how microbial metabolism is used commercially.

With such a broad scope for study, opportunities exist for students with microbiology and environmental skills to complement their studies with a chemical and industrial focus. Our research group is concentrating on the parts played by microbes in hydrometallurgy but even this relatively narrow field (of bio-hydrometallurgy) has shown a huge variety of active cell types and many interesting facets for further study.
The range of the groups activities in industrial microbiology fall within three general areas, each with its own special types of biota and each having a special economic and social importance.

Projects

1. Mine Tailings Treatment

The advantage that biocatalysts such as lithotrophic cells possess is the ability to make more of itself. The use of this advantage in large scale, low cost technology is a bit of a puzzle, partly from an engineering point of view eg. how best does one bring a 5 hectare (by 10 m deep) strata of tailings into contact with 1 x 1018 bacterial cells? And also because we don't really know what they do when they get there.

2. SX colonies

You'd be forgiven for imagining that the oil - water interface in a solvent extraction (SX) process would be too inhospitable to support life. It's usually very warm, acidic and rather concentrated but yeast cells survive readily. Once established at the interface, the circuit can misbehave terribly producing large amounts of interfacial goop or crud and costing a lot. Whenever we see an SX circuit crud sample it seems to show spheroid cells and filamentous biomass. Could there be a connection?

3. Bio-oxidation of sulphides

Large heaps of mineral sulphides can be colonised by lithotrophic (rock eating) cells which catalyse the dissolution of desired metal values. How they actually perform this marvellous feat is still a mystery and understanding how it works is a challenge. If the leaching rate can be improved and predicted many different processing options become possible.

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