2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P36 bIOLEAChING OF ANTIMONy MINERALS
by bACTERIA ACiDiTHiObACillus
ferrOOxiDANs AND DesulfOvibriO
DesulfuriCANs
ALEnA LUPTáKOVá a , EVA MAČInGOVá a , STEFAnO
UBALDInI b and JAnA JEnČáROVá a
Institute of Geotechnics of Slovak Academy of Sciences, Watsonova
45, 043 53 Kosice, Slovak Republic,
luptakal@saske.sk
Introduction
In several gold ores, gold is trapped in the matrix in of
metallic sulphides (FeS 2 , Sb 2 S 3 etc.). In such cases recovery
of gold from refractory ores requires a pre-treatment to liberate
the gold particles from the host mineral. For the pre-treatment
of gold ores exist several hydro- and biohydrometallurgical
processes 1 . The fundamental of biohydrometallurgical
processing for sulphide minerals is the application of microorganisms,
which on the basis of their metabolic processes
can increase or decrease mobility of metals 2,3,4 .
In the area of biohydrometallurgical processing of goldbearing
antimony sulphide minerals and concentrates the
iron- and sulphur-oxidising bacteria have the very important
function as well as on the ground the new knowledge also
the sulphate-reducing bacteria 5,6,7 . Using involved bacteria
to catalyse the breakdown of sulphides that host the gold
is an important biological method for the pre-treatment of
refractory gold ores. Following this biological treatment
a combination of chemical and physical methods are used for
leaching (e.g. the cyanide process) and concentration (e.g.
the electrowinning) of gold. Although these methods are well
accepted by industry, they harbour limitations in the processing
of low-grade refractory ores, and regulatory agency/public
acceptance of cyanide use. The objectives of this work
were to evaluate the use of iron- and sulphur-oxidising bacteria
Acidithiobacillus ferrooxidans (At. ferrooxidans) and
sulphate-reducing bacteria Desulfovibrio desulfuricans (Dsv.
desulfuricans) in the biohydrometallurgical processing of
gold-bearing antimony sulphide minerals. Experiments were
conducted at laboratory scale on a refractory gold-bearing
stibnite coming from Santa Rosa de Capacirca Mine, Bolivia.
Involved bacteria were used separately at different conditions
for the pre-treatment of the aforementioned sample in order
to increase the subsequent gold recovery during cyanidation
processes. The At. ferrooxidans application is based on the
their ability to oxidize and dissolve pyrite and stibnite, thus
releasing the entrapped gold particles. The using of the bacteria
Dsv. desulfuricans is based on their ability of the bacterially
H 2 S production for the alkaline leaching of stibnite.
Experimental
M i c r o o r g a n i s m s
In the experiment were used bacteria At. ferrooxidans
isolated from the acid mine water 8 (deposit Smolník, Slovakia)
and Dsv. desulfuricans isolated from the potable mineral
s409
water 9 (Gajdovka spring, Kosice, Slovakia). The isolation
was performed by the modified dilution method 10 .
S a m p l e s o f O r e
The sample of gold-bearing antimony sulfide minerals
used was obtained from Bolivia 6 (Santa Rosa de Capacirca
Mine). Mineralogical characterisation by X-ray Diffraction
(XRD) showed the presence of quartz (SiO 2 ), stibnite (Sb 2 S 3 )
and pyrite (FeS 2 ). Their chemical composition includes
21.93 % Si, 4.94 % Sb, 4.28 % Fe and 3.77 % (S). Quantitative
chemical analysis was performed by Inductively Coupled
Plasma Spectrometry (ICP).
B i o l e a c h i n g T e s t b y B a c t e r i a
Bacteria At. ferrooxidans and Dsv. desulfuricans were
used separately. The experimental tests were conducted in a
fed batch reactor at 30 °C under aerobic and dynamic conditions
(with At. ferrooxidans) and anaerobic and static conditions
(with Dsv. desulfuricans). The weight of the sample
of gold-bearing antimony sulfide minerals was of 10 g. The
total volume of feed solution consisted of 100 ml selective
nutrient medium 1 9K(A) for At.f. with pH 2.5; and DSM-63
medium 10 for Dsv. desulfuricans with pH 7.5. The abiotic
control was carried out without the bacteria application at
the same conditions. Dissolved metals in liquid phase during
the experiments were determined using an atomic absorption
spectrophotometer. After 120 days the solid phases were
recovered by filtration and were saved for the consequently
test of cyanidation.
Results
The results of the bioleaching i.e. the pre-treatment of
gold-bearing antimony sulphide minerals are demonstrated
by Figs. 1.–4.
Fig. 1. Dissolution of Fe by bacteria Acidithiobacillus ferrooxidans
from the sample of gold-bearing antimony sulfide minerals.
c – concentration of Fe, t – time of bioleaching,
– Acidithiobacillus ferrooxidans, – abiotic control
Fig. 1. presents the dissolution of the Fe by bacteria
At. ferrooxidans and in the cases from the start until the end
of experiments the concentration of Fe in liquid phase increase.
From beginning, probably due to interaction between