Influence of Ferric and Ferrous Iron on Chemical and Bacterial Leaching of Copper Flotation Concentrates

Ali Ahmadi

doi:10.4236/ijnm.2012.13006

Abstract

The effects of ferrous and ferric iron as well as redox potential on copper and iron extraction from the copper flotation concentrate of Sarcheshmeh, Kerman, Iran, were evaluated using shake flask leaching examinations. Experiments were carried out in the presence and absence of a mixed culture of moderately thermophile microorganisms at 50?C. Chemical leaching experiments were performed in the absence and presence of 0.15 M iron (ferric added medium, ferrous added medium and a mixture medium regulated at 420 mV, Pt. vs. Ag/AgCl). In addition, bioleaching experiments were carried out in the presence and absence of 0.1 M iron (ferric and ferrous added mediua) at pulp density 10% (w/v), inoculated bacteria 20% (v/v), initial pH 1.6, nutrient medium Norris and yeast extract addition 0.02% (w/w). Abiotic leaching tests showed that the addition of iron at low solution redox potentials significantly increased the rate and extent of copper dissolution but when ferric iron was added, despite a higher initial rate of copper dissolution, leaching process stopped. Addition of both ferrous and ferric iron to the bioleaching medium levelled off the copper extraction and had an inhibitory effect which decreased the final redox potential. The monitoring of ferrous iron, ferric iron and copper extraction in leach solutions gave helpful results to understand the behaviour of iron cations during chemical and bacterial leaching processes.

Highlights

During the last recent decades, copper leaching has been extensively studied as an alternative route to treat chalcopyrite concentrates.The driving force in the leaching of metallic sulfides such as chalcopyrite, chalcocite and covellite is determined by the difference in the rest potential of the minerals present, and the redox potential of the leaching solution which mainly depends on the ferric to ferrous iron ratio as described by the Nernst equation (Equation (1)) [1]
Variation of redox potential shows that in the ferrous medium, ferric ions were produced during leaching of the concentrate, while in the ferric medium, ferrous ions were entered into the solution
The decrease of redox potential in the ferric medium was mainly attributed as a result of reducing ferric iron to ferrous iron on the surface of the minerals

Summary

Introduction

During the last recent decades, copper leaching has been extensively studied as an alternative route to treat chalcopyrite concentrates.The driving force in the leaching of metallic sulfides such as chalcopyrite, chalcocite and covellite is determined by the difference in the rest potential of the minerals present, and the redox potential of the leaching solution which mainly depends on the ferric to ferrous iron ratio as described by the Nernst equation (Equation (1)) [1]. In bioleaching of copper concentrates, redox potential is one of the most important environmental parameters which affect biological and chemical subsystems. It increases by the activity of iron-oxidizing microorganisms. This increase is beneficial for the dissolution of most of the metallic sulfides such as chalcocite, covellite and pyrite, but, in the case of chalcopyrite, the leaching behavior is more complicated in which its dissolution rate is maximal at low redox potentials [2,3,4,5,6,7,8,9,10,11]

Methods

Results

Conclusion