Simultaneous sulfide oxidation and gold dissolution by cyanide-free leaching from refractory and double refractory gold concentrates

Riina Ahtiainen,Jussi Liipo,Mari Lundström

doi:10.1016/j.mineng.2021.107042

Riina Ahtiainen, Jussi Liipo + Show 1 more

Open Access

https://doi.org/10.1016/j.mineng.2021.107042

Copy DOI

Journal: Minerals Engineering	Publication Date: Jul 7, 2021
Citations: 17	License type: cc-by

Affiliation: Aalto University, Outotec (Finland)

Abstract

Pyrite and arsenopyrite are known to be the most common gold-bearing sulfide minerals in refractory gold ores. Traditionally, these minerals have been first oxidized by roasting, acidic pressure oxidation or bio-oxidation to release gold, after which the gold is dissolved in the subsequent cyanide leaching step. The chloride (chloride-bromide) solution presents an alternative cyanide-free media, which is able not only to leach gold-bearing sulfide minerals, but also gold, in a single unit process. Therefore, the current study presents an investigation of simultaneous sulfide oxidation and gold leaching from refractory (sulfidic) and double refractory (sulfidic and preg-robbing) gold concentrates. The results show that gold extraction from the investigated refractory concentrate was linearly dependent on the sulfide oxidation: 97% sulfide oxidation resulting in 99% gold extraction, 67% sulfide oxidation resulting in 81% gold extraction, and 46% sulfide oxidation resulting in 67% gold extraction. However, with double refractory concentrate, gold extraction was as low as 18% despite 97% sulfide oxidation ([Cl-]aq,0 = 6.3 mol/L, [Br-]aq,0 = 1.0 mol/L, and [Cu2+]aq,0 = 1.6 mol/L). In order to mitigate the challenges related to gold losses due to preg-robbing, active carbon in chloride leach (CICl) as well as the addition of lead nitrate were investigated. With CICl, the gold recovery could be increased significantly (67%). Further, addition of lead nitrate to CICl was shown to improve gold recovery substantially (88%). The investigation shows that the presented cyanide-free leaching approach can address the refractory nature of gold concentrates in atmospheric pressure - the simultaneous oxidation of sulfide minerals and gold in a single unit process providing new horizons for the future of the utilization of refractory gold ores.

Highlights

Gold raw materials are becoming increasingly complex and low grade, driving the development of innovations in ore treatment
The results show that gold extraction from the investigated refractory concentrate was linearly dependent on the sulfide oxidation: 97% sulfide oxidation resulting in 99% gold extraction, 67% sulfide oxidation resulting in 81% gold extraction, and 46% sulfide oxidation resulting in 67% gold extraction
The main aim of the study was to investigate the possibility for onestep processing of refractory gold concentrates, without oxidative pretreatment, such as pressure oxidation, bio-oxidation, or roasting

Summary

Introduction

Gold raw materials are becoming increasingly complex and low grade, driving the development of innovations in ore treatment. Gold is often locked in the host mineral. Gold can be liberated from refractory ores by physical, thermal, biological, or chemical pre-treatment (La Brooy et al, 1994), after which the material is subjected to a separate gold leaching process, cyanide leaching. Roasting is the most common refractory gold ore pretreatment method. It has been in industrial use already for over 70 years (La Brooy et al, 1994; Nan et al, 2014) whereas bio-oxidation has been industrially applied for refractory raw materials since 1986 (Miller and Brown, 2005). Pyrite, and arsenopyrite dissolve and form ferric sulfate, which is transformed by hydrolysis into a solid such as hematite, basic ferric sulfate, jarosite, and ferric arsenate (Fleming, 2010)

Objectives

Methods

Results

Discussion

Conclusion