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The development of resin sorbents selective for gold in ammoniacal thiosulfate leach liquors

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Grosse, AC (2006) The development of resin sorbents selective for gold in ammoniacal thiosulfate leach liquors. PhD thesis, University of Tasmania.

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Abstract

A set of 48 novel ion-exchange (1EX) resins bearing a range of amine and
quaternary ammonium moieties were prepared on a polystyrene-divinylbenzene
substrate. These were tested in Bottle-Roll (B/R) tests using a simulated ammoniacal
thiosulfate leach solution. The relative gold sorption capacities of these resins were
compared and assessed in terms of common structural features, with a view to
developing a gold-selective resin for use with thiosulfate leachates. Elution of the
gold-loaded resins was also examined, and a shortlist of promising structural
features was derived from the combined results.
A common reaction scheme was employed for most preparations, via
treatment of the exhaustively chloromethylated resin substrate with excess amine in
dimethylformamide. The subsequent functionalised resins were characterised using
infra-red spectroscopy, solid state 13C-NMR spectroscopy, ion-exchange testing and
elemental analysis. The weak-base resins prepared in this manner were then
exhaustively allcylated with either benzyl chloride or iodomethane, to provide a
range of structurally related moieties. These included alkylated derivatives of
ethanolamine, diethanolamine, piperidine, morpholine, piperazine, imidazole, and
tetramethy1-1,2-diaminoethane.
The resin moieties were examined by computational techniques to determine
approximate pKavalues, and by 13C-NMR spectroscopy. Minimum-energy structural
conformations were obtained using molecular modelling (MM+ parameters). The
gold and copper thiosulfate complexes, along with the thiosulfate, trithionate and
tetrathionate anions were modelled using ab-initio density functional theory (DFT).
The performance of the resins was compared in B/R tests using an artificial
leach liquor (pH —10.2) containing gold (20 ppm), copper (200 ppm), ammonia (1.3 M) and thiosulfate (0.1 M). Gold sorption by the resin was followed by periodic
sampling of the liquor and AAS analysis, over a 24 hour period. Relative gold
affinity for each resin was assessed using the ratio of maximum gold sorption to LEX
capacity (ie. [Au]R/Cm), with values ranging up to 16.2 mmol Au per mol of EEX
sites (resin BIM1; N'-benzylimidazole).
Comparison between the various methyl and benzyl- derivatives showed that
gold loading was relatively insensitive to the steric bulk of the functional group.
However, gold affinity was apparently enhanced by 2-hydroxyethyl and imidazolium
moieties. A set of promising moieties (piperidineethanol, quinuclidine, TMEDA,
and methyl derivatives of diethanolamine, imidazole, morpholine and piperazine)
had similar [Au]R/Cm values to the commercial IEX resins Dowex-1, IRA-410 and
Amberlite A26 (-10 mmol/mol). These resins were examined in controlled B/R tests
spiked with 10 ppm trithionate, with the trithionate and tetrathionate concentrations
followed by ion chromatography (IC). The novel resins loaded more slowly and were
more perturbed by the presence of an initial 10 ppm trithionate, while the
commercial resins were more rapidly fouled by trithionate.
The quinuclidine resin was subjected to four cycles of B/R gold loading and
elution. The resin retained 89% of the initial gold sorption capacity, and 99% of the
adsorbed gold was eluted with a modified nitrate eluent.

Item Type: Thesis (PhD)
Keywords: Ion exchange resins, Gold compounds
Copyright Holders: The Author
Copyright Information:

Copyright 2006 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:

No access or viewing until 7 September 2007. Thesis (PhD)--University of Tasmania, 2006. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:11
Last Modified: 15 Mar 2017 01:36
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