The Role of Magnesium Hydroxide on Thiosulfate Stability and Gold Recovery in Ammonium Thiosulfate Leaching Systems
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Authors
Chae, Sujin
Date
2025-05-06
Type
thesis
Language
eng
Keyword
Ammonium thiosulfate , Gold leaching , Column leaching , Heap leaching , Magnesium hydroxide
Alternative Title
Abstract
Ammonium thiosulfate has been recognized as a viable cyanide alternative for gold leaching due to its lower environmental impact. However, challenges such as thiosulfate decomposition, by-product formation, and surface passivation limit its efficiency. To address these challenges, Mg(OH)2 was added to the system to stabilize pH and reduce thiosulfate decomposition. This study assessed the impact of Mg(OH)2 on enhancing gold leaching efficiency using electrochemical tests, bench-scale leaching, column leaching, and gold recovery via ion-exchange resin experiments.
Electrochemical tests demonstrated that Mg(OH)2 enhances gold oxidation by stabilizing pH and suppressing by-product formation. However, this effect is only noticeable at pH levels around 9.0, due to the low solubility of Mg(OH)2 at a higher pH level. Open circuit potential and linear sweep voltammetry tests showed improved gold oxidation kinetics with 0.01 M of Mg(OH)2 addition in 0.1 M of thiosulfate solution. Chronoamperometry tests for 3 hours revealed a gradual increase in gold and magnesium concentrations over time, indicating sustained pH compensation due to the controlled dissolution of Mg(OH)2.
Bench-scale leaching tests highlighted the benefits of Mg(OH)2 under varying operational parameters in a 24-hour test. Gold recovery reached 75% at pH 9.0 adjusted with NH4OH, compared to 68% at pH 9.5 adjusted with Ca(OH)2. Continuous dissolution of Mg(OH)2 maintained pH stability, but gold recovery was further enhanced when Mg(OH)2 increased from 0.01 to 0.05 M. Column leaching tests demonstrated Mg(OH)2 stabilization in a more extended period of up to 14 days for larger-scale applications such as heap leaching. The gradual dissolution of Mg(OH)2 stabilized pH at around 9.5 for up to 8 days, improving gold recovery from 46.6% to 55.1% as Mg(OH)2 concentration increased from 0 to 0.02 gMg(OH)2/gore. pH stabilization also stabilized thiosulfate concentrations while reducing by-product levels, though copper precipitation was observed due to elevated pH.
Resin recovery tests examined the effects of pH stabilization by Mg(OH)2 during leaching on subsequent gold adsorption performance. Solutions prepared with Mg(OH)2 demonstrated reduced tetrathionate and trithionate concentrations, minimizing competitive adsorption and improving gold recovery selectivity.
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Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.