Doctoral Thesis
Comparative study of gold and silver leaching in chloride systems, using gold and silver nanoparticles and application to ores and concentrates
Doctor of Philosophy (PhD), Murdoch University
2023
Abstract
One of the most studied alternatives to cyanide, for gold leaching, are chloride solutions, due to their fast kinetics and wide applicability. Gold and silver nanoparticles exhibit characteristic absorption peaks in the visible region of the electromagnetic spectrum. Whilst their chemical properties are the same as in the bulk metal, their large surface area to volume ratio leads to faster dissolution. These properties make them convenient materials for the study of leaching reactions.
Of the several methods investigated, gold and silver nanoparticles, produced by reduction with trisodium citrate and stabilization with Polyvinyl alcohol were most suitable. The dissolution of gold and silver, in NaCl and NH4Cl solutions with HOCl, FeCl3 and CuCl2 oxidants, with and without additives, were studied using UV–visible spectroscopy, potentiometry and dissolved oxygen measurements.
Gold dissolution was favored by high chloride, HOCl, FeCl3 and low CuCl2 concentrations, at low pH. Silver dissolution was favored by high chloride, CuCl2 and FeCl3 concentrations, but was independent of pH and HOCl concentration. Silver leached faster than gold, and gold-silver alloy nanoparticles, which were true alloys, leached faster with higher silver content. Without additives, the best leaching performance was with the HOCl/NaCl system at pH 4. Addition of thiourea (TU) and oxygen to the FeCl3/NaCl system produced significant improvement to the leaching of gold nanoparticles, producing 88.4% recovery, without precipitation. The kinetics of dissolution was best fitted by the Avrami model.
The measured spectra and equilibrium gold and platinum potentials showed that the HOCl and FeCl3 oxidants produced Au(III) but CuCl2 produced Au(I) during leaching. For ore materials, the maximum gold recovery, of 54.6%, was produced by the FeCl3/NaCl/TU system on a roasted calcine. The presence of gangue minerals likely caused low gold and silver recoveries; therefore, this research could be applied more effectively in the leaching of electronic scrap.
Details
- Title
- Comparative study of gold and silver leaching in chloride systems, using gold and silver nanoparticles and application to ores and concentrates
- Authors/Creators
- Chris M Burtt
- Contributors
- Gamini Senanayake (Supervisor) - Murdoch University, Centre for Water, Energy and Waste
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Identifiers
- 991005687462507891
- Murdoch Affiliation
- Murdoch University
- Resource Type
- Doctoral Thesis
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