Technical Note

Bioleaching of copper ore flotation concentrates q

Z. Sadowski a,*, E. Jazdzyk a, H. Karas b

a Department of Chemical Engineering and Heating Equipment, Wroclaw University of Technology, Wroclaw 52 370, Polandb CUPRUM, Wroclaw, Poland

Received 14 May 2002; accepted 12 October 2002

Abstract

The bioleaching of flotation concentrate is a new method for copper recovery that could form the basis of an economic and

environmentally friendly process. The main objective of this work was to evaluate a bioleaching process from the treatment of two

concentrates, (i) a copper gold bearing concentrate and (ii) an ordinary copper flotation concentrate, using mesophilic bacteria. The

special gold-bearing copper flotation concentrate was obtained from the Polkowice Mine. The second material was an ordinary

copper flotation concentrate purchased from the Lubin Mine. Bioleaching experiments were carried out in 250 ml Erlenmayer flasks

and a rotating bioreactor (biorotor). The most important operating parameters were copper dissolution (%) and surface area. A

culture of Thiobacillus ferrooxidans was used for the bioleaching tests. The bioleaching maximum was obtained at both 12% and

15% of the solid. The effect of pyrite addition on the kinetics of copper concentrate bioleaching was also investigated. It was es-

tablished that 3% of pyrite causes an increase in the bioleaching process. In the case of ordinary flotation concentrate bioleaching,

65% of the recovery was obtained at the initial stage (48 h). In the second stage, the copper recovery slowly increased and after 312 h

86% of the copper recovery was obtained. On the other hand, the surface area of copper concentrate initially increased (at 24 h it was

8.67 m2/g) and then slightly decreased in the second stage.

� 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Biotechnology; Bacteria; Bioleaching; Sulphide ores

1. Introduction

The application of the bioleaching process for copper

sulfide ores has been practiced for two decades (Poluin

and Lawrence, 1996). Today dump bioleaching of low-

grade copper ore is realized at the Quebrada Blanca

Mine (Chile) (Schnell, 1997). Futhermore, in the past ten

years increased interest has been shown in biooxidation

for gold recovery from refractory ores (Breed et al.,2000). Six plants have been commissioned for biooxi-

dation pretreatment of refractory gold-bearing ores. A

combined bioleach–biooxidation process could be used

for the recovery of both copper and gold from Polish

flotation concentrates. Sporadic research with thesematerials has been conducted in the past but has not yet

led to industrial applications. Optimum temperature,

nutrients, oxygen supply, pulp density and residence

time need to be established for the best results. During

the bioleach–biooxidation process, the copper is re-

leased into the solution and the solid is sent to a cyan-

idation process for gold recovery.

Bacterial leaching of copper sulfide flotation con-centrate is a complex process. Bioleaching of copper

flotation concentrate has been investigated by Rivera-

Santillan et al. (1999). Compared with other copper

sulfide concentrates the Polish copper flotation concen-

trate contains carbonate minerals, such as dolomite and

calcite. The microscopic observation revealed that the

gypsum precipitation occurred during a bioleaching

process. However, this precipitation may not be validbecause the gypsum aggregates were porous.

The objective of this work was to evaluate a bio-

leaching-processing route for the treatment of two flo-

tation concentrates. The second target was to investigate

the effect of pyrite addition on the process.

qPresented at Bio and Hydrometallurgy �02, Cape Town, SouthAfrica, March 2002.*Corresponding author. Tel.: +48-71-320-3863; fax: +48-71-328-

0475.

E-mail address: sadowski@iic.pwr.wroc.pl (Z. Sadowski).

0892-6875/03/$ - see front matter � 2003 Elsevier Science Ltd. All rights reserved.

PII: S0892-6875 (02 )00258-3

Minerals Engineering 16 (2003) 51–53This article is also available online at:

www.elsevier.com/locate/mineng

2. Experimental

2.1. Materials and methods

Bioleaching experiments were carried out with two

flotation concentrates. The first was a special copper

sulfide flotation concentrate, which contained gold. Itwas collected from the Polkowice Mine (Poland). Ac-

cording to the producer this concentrate contains 38

ppm of Au and 10% of Cu.

The second material was an ordinary copper flotation

concentrate purchased from the Lubin Mine (Poland).

This concentrate contains 17.43% of Cu, 18.8% of SiO2,

13.47% of MgOþ CaO, 6.38% of Al2O3 and 5.55% oftotal Fe.The bacterial culture used in the bioleaching study

was obtained from the University of Opole, Poland,

where it has been cultured continuously. The culture

consists of mainly Thiobacillus ferrooxidans.

Bioleaching experiments were carried out in 250 ml

Erlenmeyer flasks that were placed in a water-condi-

tioned shaker. The temperature and rotation rate were

maintained constantly at 28 �C. Bacterial activity wasmonitored by the protein concentration and Lowry

method (Lowry et al., 1951). The progress of bioleach-

ing was monitored through measurements of [Fe2þ],

[Fe3þ], [Cu2þ], pH, and redox potential. The concen-

tration of ferric ions in the solution was determined by

the titration method. Ferrous ions were oxidized to

ferric ions and measured in the same way (Marczenko,

1979). Copper was determined by the cupferron method(Lipiec and Szmal, 1978). Dissolved oxygen measure-

ments in the suspension were made using an oxygen

electrode connected to an oxygen meter. In order to

determine the mineral solubilisation, the specific surface

area was measured. The specific surface area of the

samples was determined according to the BET method,

by means of a FlowSorb II apparatus. Part of the ex-

periments were performed using an original bioreactor(biorotor) (Rossi, 1999). Rotation speed of the barrel

was set at 1.00 rad s�1. During the bioleaching experi-

ments, samples of suspension were taken periodically

and, after a phase separation, were analysed for copper,

iron and surface area.

3. Results and discussion

3.1. Bioleaching of gold–copper concentrate

The bioleaching experiments in shaken flasks were

carried out using various solid concentrations. The

range of solid concentration was between 12% and 25%.

The results of the leaching of gold–copper concentrate

are shown in Fig. 1. As can be seen the best results wereobtained at 12% and 15% of solid. The surface area of

gold-bearing flotation concentrate increased from 2.92to 7.33 m2/g and 7.37 m2/g after 168 h (7 days) biooxi-

dation.

The effect of the ferrous iron concentration on the

bioleaching kinetics was investigated. Three different

media containing different quantities of iron(II) (0, 2

and 9 g/l) were used. The copper dissolution in these

tests reached 31.4%, 53.5% and 55.82% for 0, 2, and 9 K,

respectively. These results indicate that media rich inferrous iron can leach copper better than the inoculum

free of ferrous iron.

The effect of pyrite addition on the rate of bioleach-

ing of copper concentrate was investigated. The bio-

leaching data indicate that 3% pyrite addition resulted

in the best efficiency of copper leaching. In the presence

of 3% pyrite the surface area increased from 2.92 to

7.886 m2/g.

3.2. Bioleaching of copper flotation concentrate

A biooxidation experiment has also been performed

using the biorotor. The results of the bioleaching of

copper flotation concentrate in the biorotor are shown

in Fig. 2. Two stages of biooxidation can be identified:

(i) dramatic increase of Cu2þ concentration during thefirst 48 h, (ii) weak increase of the copper recovery.

Fig. 2 shows Fe2þ, Fe3þ, protein and copper con-

centration during the bacterial leaching of copper flo-

tation concentrate. During the first 48 h of bioleaching,

up to 60% copper was dissolved. After that time, copper

dissolution considerably increased, reaching 86% in 312

h (13 days). The evolution of the Fe2þ and Fe3þ con-

centrations in the solution indicates a bacterial activity.The maximum microbial cell concentration and activity

were observed at 144 h (6 days).

The presence of different sulfides dissolved during the

bioleaching can affect the copper mineral leaching. The

consequence of pyrite addition was to increase the Fe3þ

ion concentration, the [Fe3þ/Fe2þ] ratio and the redox

Fig. 1. Effect of the percent solids concentration on the leaching of

gold–copper flotation concentrate (K––control; B––bioleaching).

52 Z. Sadowski et al. / Minerals Engineering 16 (2003) 51–53

potential of the solution. The changes in the surface

areas clearly demonstrate the important role played by

pyrite addition in the microbiological leaching of flota-

tion concentrate by T. ferrooxidans (Fig. 3).

As can be seen in Table 1, the bacterial leaching of

copper flotation concentrate with different ratios of py-

rite is promoted by a small amount of pyrite (3%). The

high concentration of pyrite seemed to have an inhibi-

tive affect.

4. Conclusion

These results have demonstrated that the bioleaching

of Polish copper ore flotation concentrates can be rea-

lised in a special bioreactor (biorotor). Copper recovery

was satisfactory (86% after 13 days treatment). The highcopper extraction was achieved in the presence of iron

ions (2 K medium) or pyrite (3%). The changes in the

surface area of the leached solid phase may be effective

as an indicator of the bioleaching process.

Acknowledgements

The authors thank Dr. T. Farbiszewska for providing

T. ferrooxidans and Dr. S. Simons for his review of the

manuscript.

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Fig. 2. Variation of Fe2þ, Fe3þ, protein concentration and percent

recovery of copper in bioleaching of copper flotation concentrate.

Fig. 3. Changes in the surface area of copper flotation concentrate

during bioleaching in the biorotor.

Table 1

Surface areas of copper concentrate after the bacterial leaching in the

presence of pyrite

Pyrite quantity Surface area (m2/g)

Initial sample 2.92

Without pyrite 7.173

3% 9.329

5% 9.002

10% 8.947

20% 7.05

Z. Sadowski et al. / Minerals Engineering 16 (2003) 51–53 53