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Chromatographic and electromigrative determination of sulfur-oxygen anions in gold thiosulfate leach solutions

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O'Reilly, John William 2003 , 'Chromatographic and electromigrative determination of sulfur-oxygen anions in gold thiosulfate leach solutions', PhD thesis, University of Tasmania.

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Abstract

This work presents a series of investigations into the use of chromatographic and
electromigrative techniques for the analysis of gold thiosulfate leach solutions.
The focus of the project was determination of the gold thiosulfate complex
(Au(S203)23-), thiosulfate (S2O32-) , the polythionates (SxO62-, x = 3 to 5) and
sulfate (So42-) in these liquors.
The fundamental behaviour of the gold thiosulfate complex was studied in an ion
interaction chromatographic system. Partial dissociation or decomposition of the
gold complex occurred on-column in standards, although this was minimised
through adding thiosulfate to the eluent. Addition of the matrix ions, thiosulfate,
trithionate, tetrathionate or the leach matrix to gold thiosulfate samples further
complicated the chromatography, with the gold peak area dependent on the
concentrations of these species in solution. Broadening of the gold peak occurred
in solutions containing high concentrations of thiosulfate or the leach matrix that
was in part attributed to a self-elution effect. Other mechanisms were also thought
to affect the chromatography, such as the type of stationary phase. These
problems prevented the successful determination of gold thiosulfate in the leach
matrix.
Ion-interaction chromatography was successfully applied to the determination of
trithionate, tetrathionate, and pentathionate in undiluted leach liquors. A total
analysis time of 18 min was required for the developed method using a Dionex
NS 1-5 µ column with guard and an eluent comprising an acetonitrile step gradient
at injection from 15% to 28% v/v, 3 mM tetrabutylammonium hydroxide and
2.5 mM sodium carbonate. Detection limits for polythionates using a 10 µL injection
volume ranged between 5-23 µM for conductivity and 4-68 µM for UV
detection based on a signal to noise ratio of 2.
The electromigrative methods, capillary electrophoresis, isotachophoresis and
mixed mode isotachophoresis/capillary electrophoresis were also investigated for
their applicability to the determination of sulfur-oxygen species in thiosulfate
leach liquors. Using capillary electrophoresis a method was developed that
allowed the separation of thiosulfate, polythionates and the gold thiosulfate
complex. The method separated the five species in under 3 min with a total
analysis time of 8 min, using an electrolyte containing 25 mM bis-tris adjusted to
pH 6.0 with sulfuric acid and an applied voltage of-30 kV. Quantification of the
gold thiosulfate complex was not possible by this technique due to inconsistent
peak areas and peak splitting effects induced by the presence of other sulfur
oxygen species in the sample. Detection limits of the method ranged between 0.5
2 µM. The teclmique was applied successfully to a thiosulfate leach liquor diluted
1:100.
Using isotachophoresis, simultaneous determination of thiosulfate and sulfate, in
less than 30 minutes, was possible for a synthetic thiosulfate leach liquor
requiring a dilution factor of only 2:5. Detection limits of the developed method
were 1.3 mM for sulfate and 2.1 mM for thiosulfate. The method also showed
promise for the simultaneous determination of thiosulfate, sulfate, trithionate and
tetrathionate in these leach solutions. The concept of single capillary
isotachophoresis/capillary electrophoresis for these sulfur ions was also
demonstrated, however problems with reproducible quantitation prevented· the
development of a working method.

Item Type: Thesis - PhD
Authors/Creators:O'Reilly, John William
Keywords: Thiosulphates, Anions, Chromatographic analysis, Electrodiffusion, Chemistry, Analytic
Copyright Holders: The Author
Copyright Information:

Copyright 2003 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

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