Responses of the refractory and free-milling gold ores to chloride leaching as an eco-friendly alternative to the cyanidation method

Mohammad Shafiei; Mohammad Raouf Hosseini; Ebrahim Azimi; Sebastien Farnaud

doi:10.1016/j.inoche.2025.115104

Responses of the refractory and free-milling gold ores to chloride leaching as an eco-friendly alternative to the cyanidation method

Isfahan University of Technology

Research output: Contribution to journal › Article › peer-review

1 Citation (Scopus)

Abstract

Gold cyanidation has been of interest as a dissolution method for over a centry due to its high efficiency and selectivity to gold, and good stability. However, it has basic drawbacks such as long process time, high reagent costs, lower yields in refractory ores, cyanide regeneration complexity, and high toxicity of cyanide compounds. The present study investigates the potential of chloride leaching as as a faster and more sustainable alternative to dissolving gold from the refractory (RO) and free-milling (FO) ores with a focus on the novel application of sodium hypochlorite as an oxidant. The selected RO sample consisted of pyrite and quartz as the main mineral phases, with the gold encapsulated in pyrite. For FO, hematite and goethite were the main gold-bearing minerals. According to the diagnostic leaching tests, 95 % and 68 % of Au from the FO and RO, respectively, were dissolved after 48 h cyanidation. Cupric chloride, ferric chloride, hydrogen peroxide, and sodium hypochlorite were examined as oxidants but only the latter increased the oxidation-reduction potential (ORP) of the RO and FO pulps to over 800 and 1000 mV, respectively. Optimal leaching conditions, i.e. 1 M HCl, 5 M Cl⁻, and 2 % NaOCl at 80 °C, recovered 94 % (FO) and 58 % (RO) gold within 3 h. This demonstrates an eightfold increase in reaction rate compared to cyanidation, with similar efficiency. The results highlight the potential of hypochlorite-assisted chloride leaching as a viable, greener alternative for rapid gold extraction, particularly from free-milling ores, with promising application to certain refractory ores.

Original language	English
Article number	115104
Number of pages	9
Journal	Inorganic Chemistry Communications
Volume	180
Issue number	Part 2
Early online date	16 Jul 2025
DOIs	https://doi.org/10.1016/j.inoche.2025.115104
Publication status	Published - Oct 2025

Bibliographical note

© 2025 Elsevier B.V
Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.

This document is the author’s post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.

Funding

The research work was financially supported by the Iran Minerals Production and Supply Company (IMPASCO) and the Mouteh gold complex under contract number: 1400/25113.

Keywords

Chloride leaching
Cyanidation
Gold
Hypoclorite
Optimization
Refractory ore

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Inorganic Chemistry
Materials Chemistry

Access to Document

10.1016/j.inoche.2025.115104

Hosseini2025AAMAccepted author manuscript, 2.95 MBLicence: CC BY-NC-ND

Cite this

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abstract = "Gold cyanidation has been of interest as a dissolution method for over a centry due to its high efficiency and selectivity to gold, and good stability. However, it has basic drawbacks such as long process time, high reagent costs, lower yields in refractory ores, cyanide regeneration complexity, and high toxicity of cyanide compounds. The present study investigates the potential of chloride leaching as as a faster and more sustainable alternative to dissolving gold from the refractory (RO) and free-milling (FO) ores with a focus on the novel application of sodium hypochlorite as an oxidant. The selected RO sample consisted of pyrite and quartz as the main mineral phases, with the gold encapsulated in pyrite. For FO, hematite and goethite were the main gold-bearing minerals. According to the diagnostic leaching tests, 95 \% and 68 \% of Au from the FO and RO, respectively, were dissolved after 48 h cyanidation. Cupric chloride, ferric chloride, hydrogen peroxide, and sodium hypochlorite were examined as oxidants but only the latter increased the oxidation-reduction potential (ORP) of the RO and FO pulps to over 800 and 1000 mV, respectively. Optimal leaching conditions, i.e. 1 M HCl, 5 M Cl−, and 2 \% NaOCl at 80 °C, recovered 94 \% (FO) and 58 \% (RO) gold within 3 h. This demonstrates an eightfold increase in reaction rate compared to cyanidation, with similar efficiency. The results highlight the potential of hypochlorite-assisted chloride leaching as a viable, greener alternative for rapid gold extraction, particularly from free-milling ores, with promising application to certain refractory ores.",

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AU - Farnaud, Sebastien

N1 - © 2025 Elsevier B.V Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. This document is the author’s post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.

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N2 - Gold cyanidation has been of interest as a dissolution method for over a centry due to its high efficiency and selectivity to gold, and good stability. However, it has basic drawbacks such as long process time, high reagent costs, lower yields in refractory ores, cyanide regeneration complexity, and high toxicity of cyanide compounds. The present study investigates the potential of chloride leaching as as a faster and more sustainable alternative to dissolving gold from the refractory (RO) and free-milling (FO) ores with a focus on the novel application of sodium hypochlorite as an oxidant. The selected RO sample consisted of pyrite and quartz as the main mineral phases, with the gold encapsulated in pyrite. For FO, hematite and goethite were the main gold-bearing minerals. According to the diagnostic leaching tests, 95 % and 68 % of Au from the FO and RO, respectively, were dissolved after 48 h cyanidation. Cupric chloride, ferric chloride, hydrogen peroxide, and sodium hypochlorite were examined as oxidants but only the latter increased the oxidation-reduction potential (ORP) of the RO and FO pulps to over 800 and 1000 mV, respectively. Optimal leaching conditions, i.e. 1 M HCl, 5 M Cl−, and 2 % NaOCl at 80 °C, recovered 94 % (FO) and 58 % (RO) gold within 3 h. This demonstrates an eightfold increase in reaction rate compared to cyanidation, with similar efficiency. The results highlight the potential of hypochlorite-assisted chloride leaching as a viable, greener alternative for rapid gold extraction, particularly from free-milling ores, with promising application to certain refractory ores.

AB - Gold cyanidation has been of interest as a dissolution method for over a centry due to its high efficiency and selectivity to gold, and good stability. However, it has basic drawbacks such as long process time, high reagent costs, lower yields in refractory ores, cyanide regeneration complexity, and high toxicity of cyanide compounds. The present study investigates the potential of chloride leaching as as a faster and more sustainable alternative to dissolving gold from the refractory (RO) and free-milling (FO) ores with a focus on the novel application of sodium hypochlorite as an oxidant. The selected RO sample consisted of pyrite and quartz as the main mineral phases, with the gold encapsulated in pyrite. For FO, hematite and goethite were the main gold-bearing minerals. According to the diagnostic leaching tests, 95 % and 68 % of Au from the FO and RO, respectively, were dissolved after 48 h cyanidation. Cupric chloride, ferric chloride, hydrogen peroxide, and sodium hypochlorite were examined as oxidants but only the latter increased the oxidation-reduction potential (ORP) of the RO and FO pulps to over 800 and 1000 mV, respectively. Optimal leaching conditions, i.e. 1 M HCl, 5 M Cl−, and 2 % NaOCl at 80 °C, recovered 94 % (FO) and 58 % (RO) gold within 3 h. This demonstrates an eightfold increase in reaction rate compared to cyanidation, with similar efficiency. The results highlight the potential of hypochlorite-assisted chloride leaching as a viable, greener alternative for rapid gold extraction, particularly from free-milling ores, with promising application to certain refractory ores.

KW - Chloride leaching

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KW - Hypoclorite

KW - Optimization

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M3 - Article

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SN - 1387-7003

VL - 180

JO - Inorganic Chemistry Communications

JF - Inorganic Chemistry Communications

IS - Part 2

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ER -

Responses of the refractory and free-milling gold ores to chloride leaching as an eco-friendly alternative to the cyanidation method

Abstract

Bibliographical note

Funding

Keywords

ASJC Scopus subject areas

Access to Document

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