bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical Modeling and Experimental Investigations of Isothermal Solidification during Transient Liquid Phase Bonding of Nickel Superalloys
Authors: Arafin Muhammad A. , Medraj Mamoun , Turner Daniel P. , Bocher Philippe
Published: March 2009

Mathematical model, based on Fick’s second law of diffusion, was used to predict the time
required to complete isothermal solidification and to determine the effect of process variables during
the transient liquid phase bonding of Inconel 625 and 718 superalloys with nickel based brazing filler
alloy BNi-2. Experimental investigations were carried out in the range of 1325 – 1394K to verify the
model and the predicted times were in excellent agreement with the experimentally determined values.
The obtained activation energies for diffusion of boron were very close to the ones reported for other
nickel base polycrystalline superalloys; however, it was observed that the time required for complete
isothermal solidification are significantly less than that of other nickel based superalloys with
different nickel based brazing filler alloys. Because of this advantage, these combinations of base and
filler alloys are expected to replace other currently used ones. Further, significant reduction of holding
time was observed with increasing brazing temperature and with decreasing joint gap. The
composition of the joints at the end of holding period, when the holding time was not sufficient to
complete isothermal soldification, has been determined in order to predict the amount of brittle
eutectic phases in the final joint microstructures.
Lining of Cast Iron Cylinder with Copper Alloy
Authors: Shen Yan Bai , Yamazaki Toshinari , Jin Cheng Ji , Kikuta Toshio , Nakatani Noriyuki
Published: March 2009

One method for lining the inner surface of a steel cylinder with copper alloy is to pour
molten copper alloy into a heated cylinder, which has been previously filled with borax anhydride.
This process replaces the molten borax anhydride with molten copper alloy. After the cylinder is
cooled, the embedded copper alloy is drilled along its center axis so that a prescribed thickness of
the copper alloy may remain. However, when the cylinder is made of cast iron including high
concentration of carbon, the copper alloy does not bond to the inner surface of the cylinder. To solve
this problem, we investigated to utilize the decarburization phenomenon. Two methods were
investigated. In one method, the cast iron cylinder filled with FeO powder is heated at a high
temperature so that the carbon precipitates in the cast iron may get out through reaction with O2
formed by decomposition of FeO. In the other method, the cast iron cylinder is only heated in air. A
decarburized layer is formed beneath an oxide layer. In both methods, the lining of cast iron with
copper alloy was attained.
Modeling and Experiment of Deformation Texture Development for Pure Al by CPFEM with EBSD Data
Authors: Pi Hua Chun , Han Jing Tao , Zhang Chuan Guo , Tieu A. Kiet , Jiang Zheng Yi
Published: March 2009

Two polycrystal models are implemented into the finite element code to model texture
development for pure Al under uniaxial tensile deformation and cold rolling deformation with
EBSD data. Both models predictions in tensile deformation are reasonable agreement with the
experimental data. Texture development under cold rolling predicted by the finite element model is
more approximate to the measurement than Taylor-type model. Some other ideal orientations are
failed to be predicted.
Tin Oxide One-Dimensional Nanomaterials Grown on Silver-Coated Substrates
Authors: Kim Hyoun Woo , Lee Jong Woo , Shim S.H.
Published: March 2009

We demonstrated the production of tin oxide (SnO2) one-dimensional (1D) nanostructures
on silver (Ag)-coated substrates by the thermal evaporation of Sn powders. Scanning electron
microscopy revealed that the product consisted of 1D nanomaterials with average diameters or widths
in the range of 50-1300 nm. X-ray diffraction and high resolution electron microscopy coincidentally
indicated that the nanostructures were mainly single-crystalline rutile structure of SnO2. The PL
measurement with the Gaussian fitting showed visible light emission bands centered at 579 nm and
624 nm.
Recrystallization during Beta Working of IMI834
Authors: Vo Phuong , Jahazi Mohammad , Yue Stephen
Published: March 2009

The microstructure evolution of near-alpha IMI834 titanium alloy during hot working in
the beta phase temperature regime has been investigated with regard to the effects of deformation and
heat treatments. Typical cogging conditions were simulated through compression testing at
temperatures of 1025°C-1100°C, strain rates of 0.01s-1-1s-1, and post- deformation heat treatments up
to 4h. An analysis of flow behaviour and as-deformed microstructures revealed mechanisms of
dynamic recovery and recrystallization in operation during deformation. However, complete grain
refinement was not achieved through dynamic recrystallization and subsequent heat treatment was
required for microstructure homogenization through metadynamic recrystallization and grain growth.
The mechanisms of dynamic and metadynamic recrystallization are considered through quantitative
measures of beta grain size and available literature models.
The Effect of Small Amounts of Yttrium Addition on Static and under Superplastic Deformation Grain Growth in Newly Developed α+β Type, Ti-4.5Al-6Nb-2Mo-2Fe Alloy
Authors: Poorganji Behrang , Hotta S. , Murakami Taichi , Narushima Takayuki , Iguchi Yasutaka , Ouchi Chiaki
Published: March 2009

New α+β type titanium alloy with Ti-4.5Al-6Nb-2Mo-2Fe was developed
on the basis of using biocompatible elements and eliminating the cytotoxic ones such
as Vanadium, while achieving the desirable mechanical properties such as appropriate
strength, cold workability and low superplastic forming (SPF) temperature. The
present study was conducted to investigate the effect of yttrium addition of less than
0.05% into this alloy on static and under superplastic deformation grain growth
behavior. The new alloy bar manufactured by α+β processing and annealed at 1073K
yielded extremely fine two-phase microstructure with α grain size around 2μm.
Specimens were heated at temperatures of 1048, 1073 and 1098K and kept for times
between 3.6 to 172.8KS. Yttrium forms in-situ Y2O3 particles, and the presence of
these particles yield finer two phase microstructure due to their retardation effect on β
phase grain growth. Grain growth behavior during hot deformation was investigated
by hot compression test in use of a hot working simulator of THERMEC-Master Z.
Strain rate was varied from 2×10-2 to 2×10-4S-1 and strain was 0.69. Grain size of
both α and β phases increased with a reduction of strain rate, and Y2O3 particle was
also effective to retard grain growth under hot deformation. It was confirmed from
comparison of grain growth during isothermal heating with and without hot
deformation that grain growth was much accelerated by deformation. All of these
results were discussed based on grain growth mechanism or model for two-phase
microstructures as well as superplastic deformation mechanism.
The Microstructure and Creep Behavior of a Boron-Modified Ti-15Al-33Nb (at%) Alloy
Authors: Cowen C.J. , Boehlert Carl J.
Published: March 2009

The affect of boron (B) on the microstructure and creep behavior of a Ti-15Al-33Nb (at%)
alloy was investigated. In addition to the normal constituent phases present in the monolithic alloy,
the B-modified alloy contained borides enriched in titanium and niobium. These borides were
present in the form of needles/laths up to 50 μm long and 10 μm wide which took up 5-9% of the
volume. Constant load, tensile-creep experiments were performed in the stress range of 150-340
MPa and the temperature range of 650-710°C, in both air and vacuum environments. An addition
of 0.5 at% B did not improve the creep resistance of the monolithic alloy, while the addition of 5
at% B significantly improved the creep resistance.
Soldering Properties of Sn-Zn-X Micro Solder Powders Fabricated by Melts Dispersion Technique
Authors: Youn Jeong Il , Ha Won , Kim Young Jig
Published: March 2009

Melts dispersion technique is a new process to produce solder powders in oil surroundings
by the formation of molten metal’s droplets. The entire viscosity of the fluid after uniform mixture of
melts and oil mainly affected the shape and size of the solder powder. The size of solder powder was
increased and the irregular shape was altered into the spherical shape with increasing the fluid
viscosity. The effect of alloying elements, such as Mg, Al and Ti, on Sn-Zn solder for the oxidation
resistance was investigated using the solder paste mixed solder powder fabricated by melts dispersion
technique at optimum conditions and RMA type flux. The oxygen concentration was reduced by the
addition of alloying elements, especially, by Ti adding.
Effects of Processing on the Yield and Physico-Chemical Properties of Cassava Products
Authors: Ikujenlola A.V. , Opawale Benjamin O.
Published: March 2009

Freshly harvested cassava(Manihot esculenta) roots were processed into selected products( gari, ‘pupuru’,
‘Lafun’, chips and starch) using unit operations such as peeling, washing, cutting, grating, dewatering(fermentation),
smoking, granulated roasting(garifying), milling, packaging). The effects of processing on the yield and phsicochemical
properties of the products were investigated. The results showed that peeling accounted for about 22% loss,
grating and dewatering operations resulted in over 25% loss. Peeling, dewatering and various drying operations resulted
in the detoxification of the products, also moisture contents and pH of the products were reduced. The final yields stood
at 22.60%, 31.80%, 40.50%,50.60% and 57.20% for starch, gari, ‘pupuru’, ‘lafun’ and chips respectively. The protein
contents of the products ranged between 1.60% and 2.80%. The moisture contents ranged between 8.50% and 10.60%
for all the products. The processing operations affected the yield and the physico- chemical properties of the cassava
products. Cassava processors should take precautionary measures to reduce wastage thereby increasing the yield and
returns for their labour.
Stability of Gas Injection Using Lateral Wells in Layered Oil Reservoirs
Authors: Adewole E. Steve , Rai B.M.
Published: March 2009

The stability of gas injection in a layered reservoir drilled with lateral wells, is studied
using a generalized pressure distribution-dependent mobility ratio expression. Stable injection
guarantees clean oil production. The mobility ratio compared layers’ fluid velocities across a
common permeable interface. Studies were based on injected gas compressibilities and viscosities
only. Results show that injection stability is affected by (1) injected gas properties, and (2) injection
layer; i.e., whether gas cycling (bottom layer injection) or gas injection (top layer injection). Gas
cycling tends to exhibit more instability than gas injection operation.
The Virtual Well Engineer – A Real – Time Surveillance Tool for Managed Pressure Drilling Operations
Authors: Oyeneyin Babs Mufutau , Burge Phil , Hogg Lisa , Anderson Chris
Published: March 2009

Well engineers face ever increasing technical challenge of drilling in complex
environments and the use of Managed Pressure Drilling(MPD) techniques to control annular
pressure for improved drilling performance in the oil industry has growing interest[1-4].
Understanding hole cleaning and controlling annular pressure in this complex environment is
becoming increasingly important for a range of applications. The Virtual Well Engineer[VWE] has
been identified as the engineering tool to address these issues in order to deliver a successful MPD
operation. The VWE is the product name for a suite of well planning , monitoring and simulation
packages with focus on Managed Pressure Drilling includng underbalanced drilling that allows the
well engineering team to interact with virtual reality. Recent works initiated by the Well
Engineering Group at The Robert Gordon University have extended the knowledge of multiphase
flow in a drilling annulus through the tracking of the transient multiphase flow pattern prevailing
and effects on hole cleaning , the pressure profiles and identification of hot spots in concentric and
eccentric annular sections . The mechanistic models developed at RGU form the core algorithms
for the VWE. This paper presents the architecture and functional capabilities of the VWE –
HydraulicsDTS™ , which is used in simulating well operations.
I-V Characteristics for Bifacial Silicon Solar Cell under a Magnetic Field
Authors: Madougou Saïdou , Made F. , Boukary M.S. , Sissoko G.
Published: March 2009

In this work, the influence of magnetic field on I-V characteristics of bifacial silicon solar
cell n+-p-p+ structure is studied under constant multispectral illumination. After resolution of continuity
equation related to photogenerated minority carriers’ density in the base region of this cell, MATLAB
numerical simulations of excess minority carriers’, photocurrent densities and junction photovoltage
profiles, have been developed with magnetic field in the bulk of the base region. In the same way, the IV
characteristics have been studied with magnetic field. It has been demonstrated that the I–V
characteristics decreased. It also has shown how the I–V characteristics changed.
Solar Tracker Technologies: Market Trends and Field Applications
Authors: Agee John T. , Obok Opok Andrew , de Lazzer Marie
Published: March 2009

Solar energy is increasingly becoming a significant component in the energy profiles of
several tropical nations. This paper discusses trends in solar tracking technologies: analyzing the
cost of acquisition, domains of application, maintenance costs and efficiency improvements. The
paper concludes that hydraulic-based tracking systems are suitable for low capacity installations
with low pay loads while polar axis tracking systems offer a performance nearly equal to that of
two-axis tracking systems, at the cost of single axis trackers.
Internal Combustion Engines: A Computerized Design Approach
Authors: Akpobi John A. , Oboh P.
Published: March 2009

This paper describes computer-aided-design software which accurately and efficiently
designs internal combustion engine (I.C.) parts with the aid of Microsoft Visual Basic Object -
oriented programming language. In addition to numerically outputting solutions (design
parameters), the software also provides graphical solutions which facilitates easy visualization of
trends in the variation of the solutions with important parameters. We then illustrate its accuracy
and efficiency with some benchmark examples.
An Environmental Assessment of the Life Cycle of the Plastic Carrier Bag in Zimbabwe
Authors: Mbohwa C. , Manjera G.
Published: March 2009

Plastic carrier bags have gained popularity with Zimbabwean shoppers since they
provide convenient carriage of groceries and related goods. However most of these have a short
useful life and are often disposed into landfills or littered. This research was aimed at assessing the
interaction between the High Density Polyethylene (HDPE) plastic carrier bag life cycle and the
environment, hence identifying specific life cycle stages that pose significant threats to the
environment. The study was conducted in accordance with the ISO 14040 based Life Cycle
Assessment (LCA) methodology. The life cycle stages assessed include the extraction of HDPE,
transportation of HDPE pellets, production of the bags, transportation of the finished goods to
retailers and disposal scenarios. Improvement strategies were then identified to optimise the
environmental performance of the plastic carrier bags.
Investigation of Harmonics in Power Generating Systems
Authors: Emagbetere J.O. , Kuale P.A.
Published: March 2009

This paper investigates harmonics in power systems especially harmonics produced by
synchronous generators as well as those by distributed generation systems, particularly these days
when private generating systems are on the increase in Nigeria. For the work done so far, we found
that some generators have near square waves, and these are characterized by their odd harmonics.
An investigation of the harmonic emf waves conducted shows that these generators produces
harmonic alternating mmf’s and fluxes. All harmonic fluxes produce emfs which are undesirable.
The effect of these harmonics results in additional losses, vibration and noise, interferences, and
very often stall motors. However the useful torque of a machine is usually produced by the
fundamental flux wave which is a pure sine wave. The work is on-going. The waveforms are being
analyzed so as to determine the full spectrum of the harmonics present in each case and
subsequently investigate their effects in telecommunication systems including the present day GSM.
Cobalt and Nickel Recoveries from Laterite Tailings by Organic and Inorganic Bioacids
Authors: Coto Orquidea , Galizia Federico , González Ernesto , Hernández Ianeya , Marrero Jeannette , Donati Edgardo R.
Published: March 2009

Cuban serpentines are known as one of the richest deposits of Ni and Co in the world. These ores are usually treated by pyrometallurgy or by hydrometallurgy. These processes generate huge volumes of mining residues, which still contains high amounts of Ni (0.25 %) and Co (0.09 %). Since metals are partially oxidized, the chances to use sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) which are able to generate sulfuric acid to leach the residues from Caron process have been evaluated. Thus, in this work, inorganic and organic acids produced in cultures with A. niger or A. thiooxidans respectively were used to study the extraction of Co and Ni from laterite tailings. The results were compared with those obtained in leaching experiments with direct inoculation of those microorganisms. 7 and 16 % of Ni and Co were leached after 3 days using A. niger and sucrose as carbon source. In stage batch one using A. thiooxidans and elemental sulfur as energy source higher percentages of metal solubilization were reached after 15 days. In stage batch two experiments were carried out using inorganic and/or organic bioacids. Metal recoveries in stage batch two using sulfuric bioacid were higher (79 % Ni and 58 % Co) than those obtained with citric bioacid (2.4 % Ni, and 38% Co). However metal recoveries using chemical leaching with citric acid were much higher (80.4 % Ni and 50 % Co using 0.5 M citric acid). Since the mineralogy composition of raw material is a parameter very important to select the leaching agent of oxide ore, the leaching of residue nickel-ferrous of the Caron process with bio-sulfuric acid produced in A. thiooxidans cultures could be an attractive alternative in the development of a sustainable technology in Cuban mining-metallurgy industry.
Microbial Populations in a 110 Ton-Scale Column for the Recovery of Metals from Black Schist Ores
Authors: Hallberg Kevin B. , Johnson D. Barrie , Langwaldt Jörg , Joulian Catherine
Published: March 2009

Black schist ores in Finland are often enriched with sulfide minerals, containing a variety
of base metals such as nickel, copper, zinc and cobalt. As these ores are low grade with respect to
the metals contained and the sulfide minerals cannot be effectively concentrated from the schists,
they are currently being studied with regard to their suitability for bioleaching [1]. As part of this
investigation, a large-scale column measuring 3 x 3 x 9 m was built and filled with 110 tons of the
crushed black schist ore. A solution was circulated in the column for 95 weeks; this solution was
adjusted to 1.8 prior to entry in the column and averaged 2.7 when leaving the column. During this
time, approximately 22% of Mn, 10% of Ni and 5% of Zn were leached from the ore. Iron was also
leached, but precipitated in the column. Any soluble iron in the effluent was mainly Fe (II). During
this same time period, total cell counts averaged 3.6 x 107 cells/ml of effluent. On three different
occasions over nearly a one-year period, culturable cells were enumerated on a variety of solid
media [2] and represented only about 1% of the total cell counts. Of the culturable cells, ironoxidizing
acidophiles (namely Acidithiobacillus ferrooxidans) far outnumbered any other
acidophile by at least a factor of ten. Changes in populations were also monitored by molecular
means (T-RFLP and SSCP) on five different occasions during the same year; again, populations in
early samples were dominated by Acidithiobacillus ferrooxidans (at least two strains/sub-species).
As the temperature of the column was increased from ~20 to 35°C by heating both the recirculated
liquor and the air used for column aeration, the relative abundance of At. ferrooxidans-like bacteria
decreased while the abundance of unidentified bacteria increased. Some of these bacteria have also
been detected in lab-scale column experiments using the same ore [3]. Total cell counts varied little
as the temperature increased, nor was there any change in the rate of metal leaching. It was apparent
that even though the leaching of metals from black schist ores was not greatly influenced by
increases of temperature in the column, active microbial populations were present and were
influenced by temperature.
Application of Sulfate Reduction for the Biological Conversion of Anglesite to Galena
Authors: Wolthoorn Anke , Kuitert Simon , Dijkman Henk , Huisman Jacco L.
Published: March 2009

In a bench scale trial biological sulfate reduction was applied to convert anglesite
(PbSO4) to galena (PbS). Anglesite is a main constituent of waste fractions such as the residue from
an indirect leaching process or in lead paste from spent car batteries. The goal of this study was to
develop a technology to decrease the lead (Pb) emissions by converting PbSO4 from a waste
fraction into PbS, which can be recovered from the waste fraction using a flotation process or an
electrochemical process. The conversion of anglesite to galena is based on the biological sulfate
reduction process and a metal precipitation process. First sulfate is biologically reduced to sulfide.
Secondly, the Pb2+ from the PbSO4 reacts chemically with the sulfide resulting from the first
reaction.
A bench-scale reactor was started up using sulfate- and sulfur-containing influent. The reactor
was seeded with biocatalyst from several full-scale reactors. Anglesite-containing residue was
added batch-wise when the formation of sulfide started. The residue contained mainly PbSO4
(51.7%), sulfate (SO4
2-, 19.9%) and elemental sulfur (S0, 15.1%). Galena precipitates in the
bioreactor due to the near-neutral pH at which sulfate reduction is carried out. During the
experiment a surplus of sulfide relative to Pb was maintained to prevent the formation of PbCO3
and the accompanying pH decrease that would unavoidable result in the inhibition of the
biocatalyst. Both sulfate and sulfur present in the residue were biologically reduced. The formation
of PbS was confirmed by the increased Pb:O ratio of the sludge (1:0.03) relative to the Pb:O ratio of
the residue (1:0.3). A potential large-scale application is proposed.
New Xochiquetzalli Method for Sulfide Ion Determination in Aqueous Media. Application to Tailings Analysis.
Authors: Juárez-García L. , Rivera-Santillán R.E.
Published: March 2009

Mining activities have deleterious impacts on the environment, such as the formation of
acid mine drainage (AMD), which occurs by the action of acidophilic bacteria in tailing deposits,
generating diverse types of pollution. Hence it is important to examine the potential of mining waste
material to produce acid solutions. Currently, the determination of the net potential of neutralization
considers the criteria of the Enviromental Protection Agency of the United States. It was concluded
from experiments carried out with diverse samples from Mexico that the tailing samples studied
have a high capacity of autoneutralization; although the drainage waters from the tailings and the
aqueous extracts from tailing samples react acidic. It is obvious that this method of determination of
the neutralization potential and the criteria accepted at the moment do not reflect the reality of the
problem. The sulfide analysis in aqueous solution consists of an indirect titration of the excess
iodine in two phases (water/ CCl4) with a thiosulfate solution using starch as indicator. Since the
iodine is insoluble in water, the equivalent point can be uncertain because part of the iodine can be
retained by the starch. Thus, the XOCHIQUETZALLI method for the sulfide ion titration, has been
developed. It covers the chemical aspects of the titration procedure, such as the suitable reagents
and the maximum permissible concentrations, based on the law of Lambert and Beer. This titration
procedure was successfully applied to determine dissolved sulfides extracted from tailing samples.
Biosorption as Main Uranium Accumulation Mechanism in Wetlands
Authors: Schöner Angelika , Büchel Georg , Sauter Martin
Published: March 2009

The efficiency of natural wetlands for entrapment and concentration of aqueous uranium (U) was investigated in former uranium mining regions in the eastern part of Germany. Hydrogeochemical analyses of sediments, plants, surface and pore waters from selected small-sized wetlands show that U is predominantly accumulated in an environment where sulfate reduction is insignificant. From soil sequential extraction it is known that the bulk of U is retained in moderately labile forms, predominantly as organically bound or acid soluble phases (“specifically adsorbed”). Uranium could be identified by SEM/EDX, indicating that biosorption of U as cation or complex is important. However, the highest U concentrations prevail in Al-rich, inorganic agglomerates of colloidal phases. These agglomerates are as well very often non-specifically adsorbed to organic matter (plant debris, microorganisms) in the soils, promoting indirect biosorption of U.
Bioremediation In Situ of an Alkaline Soil Polluted with Heavy Metals
Authors: Groudeva V.I. , Doycheva A. , Krumova K. , Groudev Stoyan N.
Published: March 2009

An experimental plot consisting of alkaline soil heavily polluted with heavy metals
(copper, zinc, cadmium) was treated in situ by stimulating the activity of the indigenous soil
microflora, which contained different metal-solubilizing microorganisms. This was achieved by
adding to the soil solid biodegradable organic substrates (cow manure, plant compost, straw),
zeolite saturated with ammonium phosphate and aqueous solution containing acetate, lactate and
magnesium chloride. An efficient removal of the above-mentioned heavy metals was achieved via
the drainage water and their residual contents in the soil decreased to below the relevant permissible
levels within 18 months of treatment. The metals were solubilized mainly as complexes with the
organic acids added by the irrigating water solutions or secreted by the indigenous heterotrophic
microorganisms. The effluents containing dissolved metals were efficiently treated by means of a
wetland constructed near to the experimental plot.
Bioremediation of Dredged Sediments Polluted by Heavy Metals
Authors: Beolchini F. , Ubaldini S. , Passariello B. , Gül N. , Türe D. , Vegliò Francesco , Danovaro R. , Dell'Anno A.
Published: March 2009

The present work deals with a bioremediation study of a heavy-metal polluted harbour
sediment, obtained from the Italian Adriatic Coast. Bioleaching of the sediment sample was
performed with a mixed culture of acidophilic, chemi-autotrophic Fe/S oxidising bacteria. The
effect of an anaerobic biostimulation pre-treatment on the extent of Cd, Cu, Zn, Ni, Pb, Hg, As, Cr
extraction by bioleaching was evaluated. The biostimulation pre-treatment was intended to
stimulate autochthonous sulfate reducing strains, to enhance the sulfide fraction in the sediment, to
favour subsequent activity of reduced-sulfur-oxidizing bacteria in the subsequent bioaugmentation
(bioleaching). The effect of the duration of anaerobic pre-treatment (21 and 30 days) in the presence
and absence of 1% glucose was tested. The results obtained showed that the activity of the reducedsulfur-
oxidising strains was significantly enhanced after an anaerobic pre-treatment of the
sediments and showed real promise for the application of bioleaching for metal polluted sediments.
Recent Advances in Electron Transfer Between Biofilms and Metals
Authors: Bergel Alain
Published: March 2009

Microbial biofilms produce electrochemical interactions with metal surfaces by following
a wide variety of different electron exchange pathways. Reviewing the mechanisms identified in the
biocorrosion of steels leads us to distinguish direct and indirect mechanisms for biofilm-catalysed
cathodic reactions. Indirect mechanisms are due to the production of metal oxides or hydrogen
peroxide (aerobic corrosion) or metal sulphides (anaerobic corrosion), which further react with the
metal surface. Direct mechanisms involve adsorbed biocompounds, generally enzymes or their
active sites, which catalyse the cathodic reduction of oxygen for aerobic biocorrosion or the
proton/water reduction in anaerobic processes. Recent studies dealing with the role of hydrogenases
in anaerobic corrosion have shed light on the important role of phosphate species via so-called
cathodic deprotonation. Advances in the development of microbial fuel cells have also resulted in
new concepts, mainly for oxidation processes. Some microbial cells have been shown to be able to
produce their own electron mediators. Others can transfer electrons directly to electrodes through
membrane-bound electron shuttles or achieve long-range transfer through conductive pili.
Is the Quorum Sensing Type AI-1 System of Acidithiobacillus ferrooxidans Involved in its Attachment to Mineral Surfaces?
Authors: Ruíz Lina María , Gonzalez Alex , Frezza Marine , Soulère Laurent , Queneau Yves , Doutheau Alain , Rohwerder Thore , Sand Wolfgang , Jerez Carlos A. , Guiliani Nicolas
Published: March 2009

Biofilm development plays a pivotal role in the bioleaching process. The attachment of the acidophilic chemolithotrophic Acidithiobacillus ferrooxidans to mineral surfaces is mediated by extracellular polymeric substances (EPS) involved in biofilm development. Previous work suggests that EPS composition of A. ferrooxidans is adapted to the energy source and, accordingly, the bacterium must be able to sense the surface to which attachment occurs with the consequent triggering of the expression of different EPS-genes. Quorum sensing (QS) is recognized as one of the main regulators of biofilm formation. A. ferrooxidans possesses a functional QS type AI-1 system and the analysis of culture supernatants revealed us that this bacterium is able to synthesize nine different homoserine lactones (AHLs) whose acyl-chain lengths oscillate between 8 and 16 carbons and include an alcohol or a ketone function at the C3 position. The transcription levels of the afeI gene encoding for the AHL synthase are higher in cells grown in sulfur and thiosulfate media than in iron-grown cells, suggesting that biofilm formation in A. ferrooxidans would be regulated by the QS type AI-1 system. In the present study, the effect of several synthetic AHLs and analogues on the attachment of A. ferrooxidans to pyrite was analyzed. Preliminary results suggest that some of these molecules are changing the bacterial attachment to pyrite.
Bioflotation of a Black Shale Copper Ore
Authors: Spasova Irena , Nicolova Marina , Groudev Stoyan N.
Published: March 2009

A sample of black shale fraction of copper ore from the Lubin deposit, Poland, was
subjected to pretreatment by different microorganisms to improve the copper recovery during the
subsequent flotation. Chemolithotrophic bacteria grown on So and S2O3
2- were used to depress
pyrite before flotation by means of ethyl xantate as collector. Sulphate-reducing bacteria were used
to perform a prior sulphidization of the black shales before flotation by means of the same collector.
Two-stage flotation experiments were carried out in which initially the gangue minerals of the ore
were depressed by means of “silicate” bacteria and then, during the flotation of the non-floated
product from the first stage, the pyrite was depressed by means of pretreatment with So- grown
chemolithotrophs. In all these cases the microbial pretreatment had positive effect on the copper
recovery.
Inhibition of Microbiologically Influenced Corrosion of Mild Steel and Stainless Steel 316 by an Organic Inhibitor
Authors: Sheng Xiao Xia , Ting Yen Peng , Pehkonen Simo Olavi
Published: March 2009

Microbiologically influenced corrosion (MIC) is a serious problem that continues to plague many industrial systems. In this study, a method to prevent MIC by the use of an azole-type organic compound on the metal substrates was studied. Inhibition of MIC of mild steel and stainless steel 316 by 2-Methylbenzimidazole (MBI) in seawater with sulphate-reducing bacteria (SRB) was investigated using electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). MBI was shown to be an effective inhibitor in controlling MIC by two strains of sulphate-reducing bacteria: Desulfovibrio desulfuricans, and a local marine isolate. EIS analysis shows an increase in charge transfer resistance for both mild steel and stainless steel 316 after the addition of MBI in the aqueous solution. AFM analyses show a decrease in the surface roughness and pit depth after the addition of MBI. Of the two bacterial strains, it is found that MBI is more effective in the inhibition of corrosion by D. desulfuricans. At a concentration of 1mM, MBI shows a higher MIC inhibition effect on stainless steel 316 (corrosion inhibition 99.5%) than on the mild steel (corrosion inhibition 59.4%). These results indicate that MBI shows potential application in the inhibition of MIC of metal substrates.
Application Potential of Biohydrometallurgy in the Iranian Mining Industry
Authors: Ranjbar M. , Schaffie M. , Pazouki Mohammad , Ghazi R. , Akbary A. , Zanddevakili S. , Seied Baghery S.A. , Manafi Z.
Published: March 2009

Several studies and different successful commercial applications had demonstrated that bioleaching can be an innovative approach that is capable to provide mining industry opportunities for essential growth in the medium term[2-18]. To identify the commercial application potential of bioleaching in Iranian copper industry, a research program was initiated. The objective of the main part of this program was to evaluate bacterial leaching processes for copper recovery from (i) high grade ores and flotation concentrates and (ii) low grade ores and flotation tailings. The latest results of these studies indicates the general operability of the bioleaching in both cases. At optimum conditions, the copper extraction from low grade materials was more than 80% and that from high grade ores and flotation concentrates about 95%, which should be high enough to justify the process economically.
Influence of Growth Substrate and Attachment Substratum on EPS and Biofilm Formation by Acidithiobacillus ferrooxidans
Authors: Harneit Kerstin , Sand Wolfgang
Published: March 2009

Extracellular polymeric substances (EPS) of Acidithiobacillus ferrooxidans and other
leaching microorganisms mediate the attachment of cells to pyrite and other minerals. They also
play a pivotal role in indirect leaching of base and precious metals via the contact mechanism. The
aim of this study is to get more insight on the influence of the growth substrates iron(II) ions, pyrite,
chalcopyrite and elemental sulfur on EPS formation, attachment and biofilm formation. The
synthesis of EPS by cells of A. ferrooxidans strain A2 is strongely influenced by the growth
substrate or attachment substratum of the cells. Cells grown with soluble iron(II) ions generally
generate less EPS than cells grown with solid pyrite, chalcopyrite or elemental sulfur. Planktonic
cells grown in the presence of solid substrate produce two to four times more EPS than iron(II) ion
grown cells. With sessile cells, this factor is further increased to 50 to 240 depending on the specific
substrate. The EPS of all the differently grown planktonic and sessile cells of A. ferrooxidans strain
A2 contained neutral sugars, fatty acids, uronic acids, proteins and metal ions. The composition of
these compounds varied with the growth substrate and type (planktonic or sessile). The attachment
behavior of cells of A. ferrooxidans strain A2 also differed with the substrate of the pre-culture.
Cells grown on iron(II) ions, pyrite or chalcopyrite attached rapidly to pyrite and chalcopyrite,
while attachment to elemental sulfur was poor. On the contrary, sulfur grown cells attached well to
elemental sulfur but weakly to pyrite and chalcopyrite. Attachment of EPS-free cells to all
substrates was also diminished. Cells of A. ferrooxidans strain A2 cover mineral surfaces with a
dense biofilm after a few days of cultivation, as visualized by fluorescence microscopy and AFM.
Large amounts of EPS are formed, which eventually cover the cells and the mineral surface. Even
after a few weeks of cultivation the biofilm remained monolayered on all substrates.
Biomining in the Post-Genomic Age: Advances and Perspectives
Authors: Jerez Carlos A.
Published: March 2009

Systems Microbiology is a new way to approach research in microbiology. The idea is to treat the microorganism or community as a whole, integrating fundamental biological knowledge with OMICS research (genomics, proteomics, transcriptomics, metabolomics) and bioinformatics to obtain a global picture of how a microbial cell operates in the community. The oxidative reactions resulting in the extraction of dissolved metal values from ores is the outcome of a consortium of different microorganisms. Therefore, this bioleaching community is particularly amenable for the application of Systems Microbiology. As more genomic sequences of different biomining microorganisms become available, it will be possible to define the molecular adaptations of bacteria to their environment, the interactions between the members of the community and to predict favorable or negative changes to efficiently control metal solubilization. Some key phenomena to understand the process of biomining are biochemistry of iron and sulfur compound oxidation, bacteria-mineral interactions (chemotaxis, cell-cell communication, adhesion, biofilm formation) and several adaptive responses allowing the microorganisms to survive in a bioleaching environment. These variables should be considered in an integrative way from now on. Together with recently developed molecular methods to monitor the behavior and evolution of microbial participants during bioleaching operations, Systems Microbiology will offer a comprehensive view of the bioleaching community. The power of the OMICS approaches will be briefly reviewed. It is expected they will provide not only exciting new findings but also will allow predictions on how to keep the microbial consortium healthy and therefore efficient during the entire process of bioleaching.
Related Arsenic Resistance Transposons Occur in Leptospirilli Isolated from Different Continents
Authors: Kloppers Arista , Deane Shelly M. , Rawlings Douglas E.
Published: March 2009

Acidithiobacillus caldus and Leptospirillum ferriphilum dominate the microbial
consortium used in continuous-flow, stirred tank processes used to treat gold-bearing arsenopyrite
concentrates in South Africa. These microorganisms were adapted to high concentrations of arsenic
over several years and both types of microorganisms were found to contain two sets of arsenic
resistance genes. One set was present on all isolates of a species irrespective of whether they were
highly arsenic resistant or not, while a second, transposon-located set was present in only those
strains that had been adapted to high concentrations of arsenic.
We isolated a Leptospirillum ferrooxidans from the microbial consortium present in
arsenopyrite treatment tanks from Tamboraque (near Lima, Peru) that had not been inoculated with
an arsenic-adapted consortium from South Africa. This allowed us to determine whether these
microorganisms had acquired similar arsenic resistance mechanisms as contained on the
transposons in the highly arsenic resistant South African cultures. Several isolates of both
Leptospirillum ferriphilum and L. ferrooxidans from Europe as well as a "Leptospirillum
ferrodiazotrophum" were also screened to detect whether they contained similar arsenic resistance
transposons even though they had not been selected for enhanced arsenic resistance.
Transposons containing arsenic resistance genes that were identical or closely related to those
from South Africa were found in both L. ferrooxidans and L. ferriphilum isolates from South
America and Europe. The widespread occurrence of arsenic resistance transposons suggests that it
should be possible to select for highly arsenic resistant biomining microorganisms from many
different sources and therefore, unnecessary to acquire pre-adapted arsenic resistant consortia.
Differential Genetic Expression in Heap Bioleaching of Low-Grade Copper Sulphide Ore at Escondida Mine, Chile
Authors: Galleguillos Pedro A. , Zepeda V. , Galleguillos F. , Castillo Danny , Guiliani Nicolas , Remonsellez Francisco , Ortiz E. , Demergasso Cecilia
Published: March 2009

During the last decades, microbial bioleaching of metallic sulphide ores has become a very important process in the mining industry. The study of biodiversity in those systems has revealed the occurrence of several acidophilic organisms, forming a dynamic community including Bacteria and Archaea. Despite the importance of the heap bioleaching process, the metabolic behaviour of a microbial community in bioleaching systems remains unknown. The role played by members of the community inhabiting a bioheap environment has been estimated by the phenotypic characteristics of pure cultures, such as iron oxidation, sulphur oxidation, resistance to high ion concentration and metal tolerance, among others. The global genomic expression of the community inhabiting an industrial bioheap of low-grade copper sulphide ore at Escondida mine in Chile was investigated by random arbitrary primed polymerase chain reaction (RAP-PCR). Three random primers were used and twenty differentially expressed bands were cloned and sequenced. Several sequences were related to 16S rRNA of members of the microbial community; two sequences were related to the α subunit of pyruvate dehydrogenase from Acidithiobacillus ferrooxidans. The expression levels of the pyruvate dehydrogenase gene in samples from an industrial bioleaching operation at different stages were checked by quantitative real-time PCR.
Involvement of Iron Oxidation Enzyme System in Sulfur Oxidation of Acidithiobacillus ferrooxidans ATCC 23270
Authors: Taha Taher M. , Kanao Tadayoshi , Takeuchi Fumiaki , Sugio Tsuyoshi
Published: March 2009

Growth of A. ferrooxidans ATCC 23270 cells in sulfur medium with 0.005% ferric sulfate for 3, 4, 5, 6, 7 and 10 days gave the maximum growth yield of 45, 58, 76, 86, 90 and 95 mg protein per liter medium, respectively. Iron oxidase activities of 1-, 2- and 3- day-cultured cells on sulfur with 0.005% ferric sulfate (3.4, 3.5 and 0.8 μmol Fe2+ oxidized/mg protein/min) were approximately 68, 70 and 16% of iron-grown ATCC 23270 cells (5.0 μmol/mg protein/min). In contrast iron oxidase activities of 1-, 2- and 3-day cultured cells on sulfur without iron (4.9, 3.8 and 2.7 μmol Fe2+ oxidized/mg protein/min) were approximately 98, 76 and 54% of the iron oxidase activity observed in iron-grown ATCC 23270 cell. SFORase activities of 3 day-cultured cell on sulfur with and without ferric sulfate (0.62 and 0.31 μmol Fe2+ produced/mg protein/min) were approximately 20 and 10 fold higher than that of iron-grown cell (0.03 μmol Fe2+ produced/mg protein/min). Both iron oxidase and SFORase activities increased at early-log phase and decreased at late-lag phase during growth of the strain on sulfur with or without Fe3+. The plasma membranes which had iron oxidase activity were prepared not only from iron-grown cells but also sulfur-grown cells. Iron oxidase activities of the plasma membranes prepared from sulfur- and iron-grown cells were 3.6 and 4.5 nmol Fe2+ oxidized per mg protein per min. These results suggest that iron oxidation enzyme system has a role in part in the energy generation of this bacterium from sulfur.
Chalcopyrite and Bornite Differentially Affect Protein Synthesis in Planktonic Cells of Acidithiobacillus ferrooxidans
Authors: Felício Ana P. , de Oliveira Eliandre , Odean Maria A. , Garcia Jr. Oswaldo , Bertolini Maria C. , Ferraz Lúcio F.C. , Reis Fernanda C. , Ottoboni Laura M.M. , Novo Maria T.M.
Published: March 2009

Acidithiobacillus ferrooxidans is used in bioleaching industrial operations to recover metal ions from mineral sulfides. Chalcopyrite and bornite are copper sulfides that have the same elemental composition, but differ in their susceptibility to the bioleaching process. Our objective was to identify differentially expressed proteins in A. ferrooxidans LR cells exposed to chalcopyrite or bornite, as a sole energy source, for 24 hours. Compared to the control (without minerals), proteins were induced or repressed in planktonic cells after contact with chalcopyrite or bornite by 24 hours. These results demonstrated that the time of exposure to the copper minerals was enough to trigger distinct responses in the A. ferrooxidans metabolism.
Reduction of Soluble and Solid Ferric Iron by Acidiphilium SJH
Authors: Vašková Alexandra , Kupka Daniel
Published: March 2009

Facultative Fe(III)-reducing bacterium Acidiphilium SJH was incubated in media with ferric iron under various conditions with respect to oxygen availability for the growing cells. The bacteria oxidized organic substratum to carbon dioxide using oxygen and ferric iron as terminal electron acceptors. Ferric iron reduction was observed in all incubation modes. The distribution of reducing equivalents from the oxidation of organic carbon for the reduction of both O2 and Fe(III) was evaluated from CO2 production rate and O2 consumption rate. In fully aerobic conditions approximately 10 % of CO2 produced was coupled with reduction of Fe(III) as terminal electron acceptor. Under aerobic conditions, the ratio of CO2 produced to O2 consumed remained unaffected in a broad concentration range of dissolved oxygen. In the course of oxygen limitation (microaerobic conditions) the molar CO2 to O2 ratio increased from approx. 1 to 2 and even much more with respect to oxygen transfer rate during incubation. On the other hand no bacterial growth and extremely slow iron reduction was observed in obligatory anaerobic conditions in a reactor purged with either pure or CO2-enriched nitrogen.
Bacterial Activity at Low Temperature in Cultures Derived from a Low-Grade Copper Sulphide Bioleaching Heap at the Escondida Mine, Chile
Authors: Zepeda V. , Galleguillos F. , Castillo Danny , Lastra Manuel , Demergasso Cecilia
Published: March 2009

The majority of mining companies in the north of Chile that use biohydrometallurgical processes to leach low-grade copper sulphide ore are located in the high Andes. This makes the study of the effect of low temperature on bacterial activity important for the design and optimization of the bioleaching process. In this study bacterial activity of iron and sulphur oxidizing microorganisms was analyzed in the laboratory at various temperatures. Flask tests were carried out at a range of temperatures to determine the bacterial activity in pregnant leaching solution (PLS) from a pilot plant at the Escondida Mine. Ratkowsky curves were constructed by monitoring the concentration of ferrous iron and acid production during the tests. Also leaching tests were carried out at ~10 and ~20°C on a 1 m column using a copper ore sample. In an industrial solution in flask tests, iron oxidizing activity was observed until the temperature was reduced to 20°C. In the same culture, after an adaptation process, iron oxidizing activity was observed down to 5°C. In the column tests, 41.2% of copper was recovered after 91 days of leaching at 10 °C and 57.2 % at ~20°C. Predominant 16S rRNA gene sequences were related to Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferriphilum.