Abstract: In this paper, a central composite design was applied to optimize the bioleaching of iron
from a kaolin sample containing 2.2% iron impurity by Aspergillus niger isolated from pistachio
shell. The strains were inoculated into 500 ml flasks containing 100 ml media consisted of (g/l):
sucrose 120; NH4NO3 0.45; KH2PO4 0.1; MgSO4.7H2O 0.3; FeSO4.7H2O 10-4; ZnSO4.7H2O 25×10-
5. The effects of initial pH, sugar and spore concentrations on iron removal extent were investigated.
The two-level factorial design points were pH 2 and 5, sugar conc. 70 g/l and 130 g/l, spore conc.
9×107 and 35×107 spores/l. Also, the increase of dissolved iron, oxalic acid concentration, changes
in pH value, and sugar concentration were registered. Consequently, after 10 days, the iron
concentration of the best condition reached to 179.3 ppm that means 38.8% of the total iron content
is removed. Furthermore, the data analysis showed that all the factors are significant, and the iron
removal extent increases by increasing the initial pH to 4.4, sucrose content to 93.8 g/l, and spore
concentration to 305.5 spores/μl, but further increase in each factor value has negative effect on the
Abstract: Bioleaching of pre-treated spent refinery catalyst was performed using sulfur and iron
oxidizing bacteria separately. Both the mixed cultures were grown at various concentration of either
ferrous sulfate or elemental sulfur. Bioleaching process was conducted by varying the reaction time,
effect of substrates and effect of catalyst amount. Under the most favourable transport conditions
examined, (5g/L spent catalysts, 10g/L ferrous sulfate, reaction time 7 days) the mixed iron
oxidizing bacteria were able to recover Ni, V, and Mo of 90, 80 and 54 % respectively. Higher
catalyst and ferrous sulfate concentration showed decline result in recovery of Mo and V. Ni
showed consistent results throughout the series of experiments (88 to 90% recovery).
The mixed sulfur oxidizing bacteria were observed to be more effective than the iron oxidizing
bacteria. The sulfur oxidizing cells were able to recover Ni, V and Mo of 88, 94 and 46 %
respectively (spent catalysts 50g/L, elemental sulfur of 2% (w/v), reaction time 7 days). The
oxidation of elemental sulfur to sulfate could play a vital role for extraction of the metals.
Abstract: Bioleaching is technology applicable to iron extraction from low-grade non-metallic raw
materials. Bioleaching of quartz sands and feldspars involves the action of heterotrophic bacteria.
Impurities include fine – grained limonite, goethite, hematite or mica were removed by the
reductive dissolution of Fe3+ in linked with the silicate mineral destruction. Heterotrophic bacteria
produced organic acids that are able to solubilize Fe oxide and silicates but require organic carbon
as a source of energy. Molasses is a relatively inexpensive carbon source used for various industrial
fermentations and contains also other nutrients that accounted for the enhancement of iron
dissolution in this study. The admixture of pigments in molasses coloured the samples, but the
discoloration could be removed by the addition of NaClO following the bioleaching step. The
feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw
materials. The Fe content in the quartz sands and feldspar samples by the biological leaching
decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the
decrease of Fe content in 74% was achieved. However, the application of magnetic separation of
quartz sands after bioleaching resulted in total iron removal of 93 % and in such combined way
prepared product contained 0.024 % of Fe2O3.
Achieved results on iron removal point to the fact that combination of leaching and magnetic
separation enables to obtain product usable in glass and ceramic industry.
Abstract: Iron oxidizing bacteria Acidithiobacillus ferrooxidans, iron reducing bacteria
Acidiphilium spp. and their mixture were applied for leaching of iron impurities from quartz sand.
The bacterial leaching was carried out in order to decrease the amount of colouring iron oxides and
to improve the technological properties of the raw material. Mineralogical analysis confirmed the
presence of siderite, iron-bearing muscovite and various amorphous and crystalline forms of iron
oxides occurring both free and coating siderite and quartz particles. Mössbauer spectroscopy
revealed various oxidation and magnetic states of iron ions, with the prevalence of reduced ionic
species. Highest extraction of iron was achieved with pure culture of iron-reducing bacteria with
ferrous iron as dominant species in the leaching liquor. Surprisingly, iron oxidizing bacteria caused
passivation of the surface of iron-bearing minerals, resulting in the depression of iron leaching in
comparison with abiotic control. Ferric iron was major species in the leaching solution containing
the mixed culture of iron-oxidizing and iron-reducing bacteria. The mixture was far less efficient in
iron extraction than pure culture of iron-reducing bacteria.
Abstract: The sphalerite-pyrite oxidation by Acidithiobacillus ferrooxidans was studied to analyze
how the formation of the elemental sulfur layers occurs around sphalerite grains. Two possible
mechanisms of formation have been raised. One mechanism corresponds to the formation of sulfur
pseudomorphs where, both, iron and zinc have been leached of the sphalerite, whereas compound
sulfur is oxidized, in situ, to elemental sulfur, leaving an unreacted core of sphalerite that remains in
the center. Another mechanism consists in the dissolution of iron, zinc and sulfur presents. When
the attack by Fe3+ as by H+ broken the S-metal bonds, sulfur is then oxidized to a series of sulfur
intermediate compounds. These compounds in solution then are oxidized to elemental sulfur, which
precipitates on sphalerite grains.
Abstract: An experimental campaign was conducted for monitoring the formation of hydrocarbon
gaseous compounds during bioleaching of copper sulphide ores with mesophilic microorganisms.
Three different mineral samples were used: a pyrite concentrate, a chalcopyrite concentrate and a
copper sulphide ore rock from El Teniente mine containing 1 % copper. Mineral samples were
bioleached in 250 ml shake flasks containing 100 ml of basal medium inoculated either with a pure
strain of Acidithiobacillus ferrooxidans or a natural bacteria consortium obtained from the acid
leaching of El Teniente ore in columns. Each sealed system shake flask was fed with a flow of
synthetic air and the exit stream was passed through a column containing an adsorbent material and
next through a water trap as to avoid back air contamination from the environment. Compounds
present in the adsorbent material after 90 days of bioleaching were analysed using a gas
chromatography mass spectrometry technique with a procedure that detects 162 different
hydrocarbon gaseous compounds (SGH). Results showed that the bacterial communities in copper
sulphide bioleaching results in the formation of some hydrocarbon gaseous compounds, mainly
various types of methyl benzene and branched alkanes. The formation of these organic compounds is
likely to be related to the presence of heterothrofic microorganisms present in the natural populations.
Abstract: Bioleaching of the copper flue dust emanating from smelters at Sarcheshmeh Copper
Complex has been studied. At the present, the dust is sent back to the smelter, which reduces its
efficiency. In this study, a continuous system including a feed tank and two-stage aerated stirred
tank bioreactors was established. Mixed mesophile bacteria with different amounts of the dust
containing 35% of copper mainly in the form of sulfide minerals were used. The effects of pulp
densities, residence times and temperatures on the final copper recovery and redox potential were
experienced. Despite the copper concentrates bioleaching, the process of dust bio-treating was net
acid consuming. Lower pulp densities resulted in a stable redox potential in both reactors. However,
increasing the pulp density to 7%, was created an unstable redox potential in the first bioreactor
especially at lower temperatures. Final copper recoveries were calculated for pulp densities of 2%,
4% and 7%, were 91.8%, 90.3% and 87.6% with residence times of 2.7, 4 and 6 days respectively.
The promising results indicated that bioleaching is a feasible process that can be applied to copper
Abstract: In this study, the viscosities and conductivities of bioleaching solution were determined by
Ubbelohde viscometer and conductivity meter, respectively. The mean ionic activity coefficients,
relative partial molar free energies of copper bioleaching solution at above experimental temperatures
ranging from 298 K to 313 K have been calculated. Simultaneously, these characters of copper
bioleaching solution were compared with and without mesophilic bacteria. The experimental data
showed that the viscosities and thermodynamic properties for bioleaching solution would be crucial
to minimize the third phase formation so as to increase extraction efficiency.
Abstract: Based on the bioleaching mechanism and electrochemical studies of covellite, the
dissolution rate of covellite mineral is accelerated through increasing the redox potential (Eh) of the
leach. In the present work, some methods were adopted to enhance the bioleaching of covellite
concentrate (collected from Zijinshan copper mine, Fujian province, China) by adding different
oxidants such as pure pyrite, ferric ions and H2O2. The goal of this study was to provide appropriate
operating parameters for the industry application and increase the efficiency of the bioleaching of
copper mine. The results showed that the optimal way to increase the redox potential (Eh) level was
the addition of pure pyrite. This method could effectively raise the Eh of bioleaching process while
the effect of environmental change was negligible. It could quicken the leaching process and
enhance the final copper recovery through the addition of pyrite by 1:1 or 1:2 ratio of covellite
concentrate to pyrite.
Abstract: In heap bioleaching the dissolution of gangue minerals from igneous ore materials can
lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach
solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the
target minerals. The kinetics of the oxidation process have been well studied for Leptospirillum and
Acidithiobacillus species in tank systems. Although not directly comparable, kinetic parameters
derived for tank systems do apply also for heap bioleach conditions. In the present study the effect
of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g/L and
combined concentrations 0 to 16 g/L each has been investigated in continuous culture using
Leptospirillum ferriphilum. Increasing the concentrations of the salts increasingly depresses the rate
of ferrous iron oxidation and also shifts the viable range more and more into the low potential
region. Al significantly reduces the amount of carbon maintained in the reactor (assumed to be
commensurate with biomass), whereas Mg actually enhances it at low concentrations. In both cases,
however, the rate is always depressed. The results indicate that heap cultures are likely to perform
sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.