1764
Mechanism of Ultrasound-Intensified Leaching and
Its Enhancement on the Cyanidation Process of
Gold Refractory Tailings
Livison Madumira, Jean Jacques Kalombo Mbayo, Sehliselo Ndlovu
School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment,
University of the Witwatersrand, Johannesburg, South Africa
DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand,
Johannesburg South Africa
ABSTRACT: Cyanidation leaching is a critical step in gold processing, and conventional techniques typically
involve lengthy reaction times when employed for processing refractory gold ores due to poor recoveries. To
overcome these limitations, ultrasound-assisted leaching has emerged as a promising alternative method due
to its effectiveness, efficiency, and relatively reduced environmental impact. Propagation of ultrasound waves
through a liquid medium leads to the formation and collapse of tiny bubbles in the liquid, generating localized
high temperatures and pressures. This phenomenon known as acoustic cavitation is responsible for the unique
effects of ultrasound in gold leaching. The work presented herein looks to explore the mechanism of ultrasound
leaching in gold processing of a refractory gold tailings sample from a plant in South Africa. Results from the
investigation have shown that the use of ultrasound-assisted leaching contributes to increased gold recoveries,
reduced leaching time and enhanced particle size reduction. Furthermore, ultrasound-assisted leaching was
observed to modify the physicochemical properties of the leaching system by altering solution pH, temperature,
and redox potential, thereby influencing the kinetics and thermodynamics of gold dissolution. The results of the
study also showed the generation of hydroxyl radicals which were postulated to initiate the oxidation of pyrite
and subsequently opening up the gold occluded in the sulphide matrix, increasing the gold yield in solution.
Keywords: gold leach tailings, ultrasound leaching, acoustic cavitation
INTRODUCTION
Gold tailings refractoriness is caused by several reasons
which include encapsulation of gold by minerals such as
pyrite and iron oxides, chemical interferences, formation
of passivation layer during leaching, the existence of preg-
robbing elements in form of carbonaceous materials and
silicates and lastly leach robbing elements such as copper.
Gold tailings are predominantly made of quartz (SiO2) and
iron oxide (Fe2O3) and a small percentage of phyllosilicates,
pyrite as well as other sulphides, (Marsden and House,
2006). Witwatersrand tailings are the waste materials left
over from the recovery of gold from the Witwatersrand
Basin in South Africa. The Witwatersrand Basin is one
of the largest gold deposits in the world, and it has been
a major source of gold production since the late 1800s.
The extraction of gold from the ore in the Witwatersrand
Mechanism of Ultrasound-Intensified Leaching and
Its Enhancement on the Cyanidation Process of
Gold Refractory Tailings
Livison Madumira, Jean Jacques Kalombo Mbayo, Sehliselo Ndlovu
School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment,
University of the Witwatersrand, Johannesburg, South Africa
DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand,
Johannesburg South Africa
ABSTRACT: Cyanidation leaching is a critical step in gold processing, and conventional techniques typically
involve lengthy reaction times when employed for processing refractory gold ores due to poor recoveries. To
overcome these limitations, ultrasound-assisted leaching has emerged as a promising alternative method due
to its effectiveness, efficiency, and relatively reduced environmental impact. Propagation of ultrasound waves
through a liquid medium leads to the formation and collapse of tiny bubbles in the liquid, generating localized
high temperatures and pressures. This phenomenon known as acoustic cavitation is responsible for the unique
effects of ultrasound in gold leaching. The work presented herein looks to explore the mechanism of ultrasound
leaching in gold processing of a refractory gold tailings sample from a plant in South Africa. Results from the
investigation have shown that the use of ultrasound-assisted leaching contributes to increased gold recoveries,
reduced leaching time and enhanced particle size reduction. Furthermore, ultrasound-assisted leaching was
observed to modify the physicochemical properties of the leaching system by altering solution pH, temperature,
and redox potential, thereby influencing the kinetics and thermodynamics of gold dissolution. The results of the
study also showed the generation of hydroxyl radicals which were postulated to initiate the oxidation of pyrite
and subsequently opening up the gold occluded in the sulphide matrix, increasing the gold yield in solution.
Keywords: gold leach tailings, ultrasound leaching, acoustic cavitation
INTRODUCTION
Gold tailings refractoriness is caused by several reasons
which include encapsulation of gold by minerals such as
pyrite and iron oxides, chemical interferences, formation
of passivation layer during leaching, the existence of preg-
robbing elements in form of carbonaceous materials and
silicates and lastly leach robbing elements such as copper.
Gold tailings are predominantly made of quartz (SiO2) and
iron oxide (Fe2O3) and a small percentage of phyllosilicates,
pyrite as well as other sulphides, (Marsden and House,
2006). Witwatersrand tailings are the waste materials left
over from the recovery of gold from the Witwatersrand
Basin in South Africa. The Witwatersrand Basin is one
of the largest gold deposits in the world, and it has been
a major source of gold production since the late 1800s.
The extraction of gold from the ore in the Witwatersrand