Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)

Xiaoliang Liu,Xi Zhang,Tao Jiang,Yinghe He,Yongbin Yang,Bin Xu,Xin Min,Qian Li

doi:10.3390/met7070278

Xiaoliang Liu, Xi Zhang + Show 6 more

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https://doi.org/10.3390/met7070278

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Journal: Metals	Publication Date: Jul 19, 2017
Citations: 26	License type: CC BY 4.0

Affiliation: Central South University, James Cook University

Abstract

The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This detrimental effect became more severe with increasing pyrite content. Further, the presence of pyrite also substantially slowed the gold leaching kinetics and reduced the overall gold dissolution. The reduction in gold dissolution was found to be caused primarily by the surface passivation of the gold. The negative effects of pyrite, however, can be alleviated by the addition of AAPP. Comparison of zeta potentials of pyrite with and without AAPP suggests that AAPP had adsorbed on the surface of the pyrite and weakened the catalytic effect of pyrite on the thiosulfate decomposition by blocking the contact between the pyrite and thiosulfate anions. AAPP also competed with thiosulfate anions to complex with the cupric ion at the axial coordinate sites, and thus abated the oxidation of thiosulfate by cupric ions. Moreover, the indiscriminate adsorption of AAPP on the surfaces of gold and passivation species prevented the passivation of the gold surface by surface charge and electrostatic repulsion. Therefore, AAPP effectively stabilized the thiosulfate in the solution and facilitated the gold leaching in the presence of pyrite.

Highlights

Ammoniacal thiosulfate has been studied over the last three decades as a nontoxic and highly-efficient alternative lixiviant to cyanide for leaching gold from gold ores with copper(II) acting as a catalyst [1,2]
During gold leaching in copper ammoniacal thiosulfate solutions, pyrite could significantly accelerate the decomposition of thiosulfate and inhibit the leaching of gold
It was found that the mixed slurry potential was not the leading factor for both promoted thiosulfate decomposition and restricted gold leaching kinetics

Summary

Introduction

Ammoniacal thiosulfate has been studied over the last three decades as a nontoxic and highly-efficient alternative lixiviant to cyanide for leaching gold from gold ores with copper(II) acting as a catalyst [1,2]. The aerated thiosulfate leaching of gold is very slow in the absence of copper(II), but in the presence of copper(II) the rate of gold dissolution in ammoniacal thiosulfate solutions can be increased by 18–20 fold [1]. The thiosulfate degradation leads to higher reagent cost, and results in the generation of copper sulfide and sulfur layers which can passivate gold and hinder the leaching rate [19,20,21,22]. The successful application of the thiosulfate leaching technology is obviously restricted by the high thiosulfate consumption and the gold surface passivation

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Conclusion