Biodepression of Copper-Activated Pyrite with Acidithiobacillus ferrooxidans in Flotation with Fresh and Seawater

Francisca San Martín,Ignacio Valles,Claudio Aguilar,Tomás Vargas,Willy Kracht

doi:10.3390/min11101039

Francisca San Martín, Ignacio Valles + Show 3 more

Open Access

https://doi.org/10.3390/min11101039

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Abstract

Acidithiobacillus ferrooxidans has been shown to be a good depressant of pyrite in freshwater and seawater flotation. However, the effect of these bacteria over copper-activated pyrite has not been studied. At the industrial scale, the activation of pyrite with copper is a common process that occurs because Cu2+ ions, released from other minerals, react with pyrite. This is a problem because Cu2+ ions facilitate the reaction of pyrite with the xanthate collectors, becoming hydrophobic and reaching the froth. In this study, microflotation experiments in a Hallimond tube were conducted to evaluate the depressant effect of A. ferrooxidans over non-activated and Cu-activated pyrite in freshwater and seawater flotation. The experiments were carried out at pH 4, 6, 8, 10 and 12 and pyrite was mixed with CuSO4 at 2.5×10−5 and 5×10−5 M in order to activate its surface. Considering the results obtained in the microflotation tests, it is possible to conclude that Acidithiobacillus ferrooxidans is able to depress non-activated and Cu-activated pyrite at the entire pH range studied (4–12) in freshwater. On the other hand, the use of bacteria in flotation with seawater proved to be effective to depress non-activated and Cu-activated pyrite at pH 8 and 10 with better results achieved at pH 10. At this pH, the non-activated pyrite recovery dropped from 96% to 15%, and the recovery of Cu-activated pyrite dropped from 95% to 32% when the activation was carried out at 2.5×10−5 M, and from 87% to 50% when the activation was conducted at 5×10−5 M of CuSO4. The XPS analysis showed that chalcopyrite and copper (II) hydroxide were formed on the pyrite surface when it is contacted with CuSO4.

Highlights

The activation of pyrite with copper represents a problem when processing copper sulfide minerals by flotation
The copper ions released from sulfide minerals present in the pulp are adsorbed on the pyrite surface, allowing it to react with the collector
The microflotation experiments in freshwater showed that A. ferrooxidans is able to depress non-activated and Cu-activated pyrite at the entire pH range studied (4–12), with better results achieved at pH 4, 6 and 12

Summary

Introduction

The activation of pyrite with copper represents a problem when processing copper sulfide minerals by flotation. The copper ions released from sulfide minerals present in the pulp are adsorbed on the pyrite surface, allowing it to react with the collector. Pyrite reacts naturally with xanthate collectors at low pH with the formation of dixanthogen and ironxanthate over its surface [1,2,3]. At high pH, the absorption of xanthate is not as significant as at low pH, so pyrite recovery is lower making possible its separation from copper sulfide minerals which are able to float at high pH values [2]. When Cu2+ ions are present in the pulp, pyrite recovery increases considerably even at high pH. Leppinen [2] studied the activation of pyrite with copper between pH 4 and 12, and determined that the highest activation of pyrite occurs between pH 7 and 9, where recoveries of Cu-activated pyrite are significantly higher than non-activated pyrite

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