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The adsorption of the aurocyanide ion onto carbon: An investigation using scanning tunneling spectroscopy

Clark, M.L. (2000) The adsorption of the aurocyanide ion onto carbon: An investigation using scanning tunneling spectroscopy. PhD thesis, Murdoch University.

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Abstract

The carbon-in-pulp process uses activated carbon to win gold from gold-bearing solutions. This process is very effective in winning the gold, and has been used commercially for many decades. Despite numerous studies into the adsorption mechanism, no consensus has yet been reached as to how the gold is adsorbed onto the carbon.

Scanning tunneling spectroscopy is a technique that makes use of the electronic information contained in a scanning tunneling microscope image, to gain information about the material being studied on an atom-by-atom basis. Although STS has had considerable use in UHV studies, very little use has been made of the technique in air or under liquid. Yet STS has the potential to be a valuable tool for in situ studies where other surface analysis techniques cannot be used.

In this work, STS has been used to study the adsorption of gold onto carbon in situ. The principle method of STS used was I/V spectroscopy. In this method, the bias voltage of the tip is ramped over a specified range and the tunneling current is recorded and plotted out on a graph. The type of material on the surface beneath the tip determines the shape of the graph.

A number of different materials were successfully examined in air and under liquid by this method. This established a baseline of which materials could be distinguished in situ.

The technique was applied to material adsorbed onto HOPG from a solution of potassium aurocyanide and calcium chloride. The spectra were then compared to the spectrum of elemental gold and the spectrum of AuCN. The composition of the adsorbed material was then identified. This identification made possible some conclusions concerning the various proposed methods of aurocyanide adsorption.

Some investigations into aurocyanide adsorption onto activated carbon were also conducted using I/V spectroscopy, with less clear results. Reasons for this are discussed.

Item Type: Thesis (PhD)
Murdoch Affiliation: Division of Science and Engineering
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Thurgate, Stephen
URI: http://researchrepository.murdoch.edu.au/id/eprint/52706
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