Predicting Cyanide Consumption in Gold Leaching: A Kinetic and Thermodynamic Modeling Approach

Yaser Kianinia,Glenn Hefter,Marjan Shahbazi,Mohammad Khalesi,Ahmad Khodadadi Darban,Mahmoud Abdollahy,Gamini Senanayake,Lubomir Hnedkovsky

doi:10.3390/min8030110

Yaser Kianinia, Glenn Hefter + Show 6 more

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https://doi.org/10.3390/min8030110

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Abstract

The consumption of cyanide during processing operations is a major economic cost in the extraction of gold from its ores, while the discharge of cyanide wastes may result in significant environmental pollution. Many factors influence the levels of consumption and discharge of cyanide, including ore mineralogy and lixiviant solution chemistry. This paper proposes a robust methodology to estimate leaching cyanide consumption due to oxidation and reactions with gold, chalcopyrite and pyrite minerals forming various cyanide complexes, cyanate, thiocyanate and hydroxide precipitates of copper and iron. The method involves concurrent modelling of both the oxidation and leaching kinetics of minerals and the chemical speciation of the lixiviant solutions. The model was calibrated by conducting cyanide leaching experiments on pyrite, chalcopyrite, pyrite + chalcopyrite, pyrite + chalcopyrite + gold and pyrite + chalcopyrite + gold + quartz systems and determining the total Cu, Fe, Au and CN− concentrations in solution. We show that this model can successfully estimate the formation of cyanide complexes and, hence, the consumption of cyanide.

Highlights

Gold is mainly extracted from its ores or concentrates by leaching with oxygenated cyanide solutions [1,2]
∂CM (t)/∂t = k CM (t)α CCN (t)β where, k is the reaction rate constant (mol1 − (α + β) m(α + β) − 1 ·s−1 ), CM is the concentration of mineral or gold, CCN is the concentration of free cyanide in solution and α and β are the reaction order of the model with respect to gold, mineral and cyanide concentrations
The good fit is not the only merit of the present approach. Another important outcome of the proposed methodology is that the concentration of free cyanide is predicted via calculation of all cyanide complexes formed during the leaching process

Summary

Introduction

Gold is mainly extracted from its ores or concentrates by leaching with oxygenated cyanide solutions [1,2]. The discharge of excess cyanide in wastewater, respectively constitute major economic [3,4] and environmental [5] costs in the gold industry. Wastewater streams of gold processing plants typically have to be treated to lower the concentration of cyanide and related species below regulatory limits [6]. Deschênes et al [7] showed that use of lead nitrate and oxygen (200 and 16 mg·L−1 , respectively) with high pyrite or chalcopyrite ores lowered cyanide consumption threefold and enhanced the Minerals 2018, 8, 110; doi:10.3390/min8030110 www.mdpi.com/journal/minerals

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