A Kinetic Study on Enhanced Cementation of Gold Ions by Galvanic Interactions between Aluminum (Al) as an Electron Donor and Activated Carbon (AC) as an Electron Mediator in Ammonium Thiosulfate System

Sanghee Jeon,Naoki Hiroyoshi,Mayumi Ito,Akuru Kuze,Sharrydon Bright,Ilhwan Park

doi:10.3390/min12010091

Sanghee Jeon, Naoki Hiroyoshi + Show 4 more

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https://doi.org/10.3390/min12010091

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Journal: Minerals	Publication Date: Jan 13, 2022
Citations: 6	License type: CC BY 4.0

Affiliation: Hokkaido University, University of Zimbabwe

Abstract

The enhanced cementation technique by galvanic interaction of aluminum (Al; electron donor) and activated carbon (AC; electron mediator) to recover gold (Au) ions from the ammonium thiosulfate solution is a promising technique to eliminate the challenges of poor recovery in the system. This study presents the kinetics of Au ion cementation in an ammonium thiosulfate lixiviant as functions of initial Au concentration, size/amount of Al and AC, temperature, and shaking speed. The recovery results basically followed first order kinetics and showed that the cementation rate increased with a higher initial concentration of Au, smaller electron donor size, greater both electron donor and mediator quantity, decrease in temperature, and higher shaking speed in the system, while size of electron mediator did not significantly affect Au recovery.

Highlights

Climate change is an urgent global issue affecting industries and communities alike.To reduce greenhouse gas emissions for achieving a climate-neutral world, countries worldwide aim to fulfill a Paris Agreement aligned to a target of transitioning to low/zerocarbon energy sources by promoting next-generation vehicles and developing mobility business by the mid-century [1,2]
The present study investigated the kinetics of enhanced Au ions cementation by galvanic interaction between Al and activated carbon (AC) in ammonium thiosulfate lixiviant with batch-type experiments as functions of initial Au concentration, size of Al and AC particles, their mixing ratio, and temperature as well as shaking speed, and a morphology study on the cemented Au was carried out
Al likely acted as the primary electron donor and the attached AC served as an electron mediator from Al to Au-thiosulfate complex (Au(S2O3)23−), a configuration that promoted both galvanic interactions and Au recovery, cementation [15]

Summary

Introduction

Climate change is an urgent global issue affecting industries and communities alike.To reduce greenhouse gas emissions for achieving a climate-neutral world, countries worldwide aim to fulfill a Paris Agreement aligned to a target of transitioning to low/zerocarbon energy sources by promoting next-generation vehicles and developing mobility business by the mid-century [1,2]. In Au-hydrometallurgy, copper (Cu)-catalyzed ammonium thiosulfate leaching has gained increasing attention as an alternative to the conventional cyanide solvent due to its non-toxicity, low corrosiveness, and high selectivity for Au [3,4,5]. The adsorption of Au ions onto activated carbon (AC) has been the mainstay of Au-hydrometallurgy for several decades in cyanide-based lixiviants due to its high efficiency, relatively low cost, and high purity of the products [10]; its application is not preferred in the ammonium thiosulfate system. Zero-valent copper, zinc (ZVZn), aluminum (Al), and iron (ZVI) are reasonable choices in cyanide-based lixiviants [10,12,13,14] but their application to thiosulfate solution is difficult because of the dissolution of the cementing agents (i.e., Cu and Zn) or the formation of the oxide/sulfide layers on the cementing agents (i.e., Al and Fe). The abundant sulfur and Cu ions in the solution restrict the application of solvent extraction and electrowinning as well due to the contamination of the products and the increased energy requirements [10]

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