bluuebunny/crossref_metadata_2025 huggingface dataset:
Brush-Deburring Evaluation of Austenitic Stainless Steel
Authors: Kodácsy János , Líska János
Published: August 2017

Users impose increased requirements for companies, which produce equipments used in energy industry, because none of them can afford to loss of production at using of these equipments. The same situation is at gas turbines. Engineers carefully pay attention for every detail – the components go through a strict quality control. The burr formation, as an accompanying phenomenon strongly influences the quality of production. The deburring process effects also the economic characteristics. This article describes the possibility of deburring of a component which is used for gas turbines, The article shows results from carried out studies and described the possibility of by describing of results from brushing process.
FEA-Based Comparative Investigation on High Speed Machining of Aluminum Alloys AA6061-T6 and AA7075-T651
Authors: Jomaa Walid , Songmene Victor , Bocher Philippe , Gakwaya Augustin
Published: August 2017

Independent research studies have shown notable dissimilarity in the machining behaviour of aluminum alloys AA6061−T6 and AA7075−T651 commonly used in automotive and aeronautical applications. The present work attempts to investigate this dissimilarity based on experimental and numerical data with a focus on chip formation and generated residual stresses under similar high−speed machining (HSM) conditions. The numerical data were calculated by a finite element modeling (FEM) developed using DeformTM 2D software. The results showed that both studied alloys exhibit different chip formation mechanisms and residual stress states at the machined surfaces. On one hand, the AA6061−T6 alloy generates continuous chips and tensile residual stresses whereas the AA7075−T651 alloy produces segmented chips and compressive residual stresses. FEM results showed that the AA6061−T6 alloy generates lower cutting temperature at the tool−chip interface along with higher equivalent total strains at the machined surface as compared to the AA7075−T651 alloy. Based on the experimental and numerical results, it was pointed out that the differences in terms of thermal conductivity and initial yield stress are the main reasons explaining the dissimilarity observed.
Specific Cutting Force in Turning of Sintered Nickel Alloy
Authors: Struzikiewicz Grzegorz , Rumian Ksenia
Published: August 2017

This paper presents the results of the experiments which aimed to determine the value of the specific cutting force (SCF) during longitudinal turning of sintered alloy Inconel PWA. The analysis of the influence of cutting speed on the value of SCF was carried out. Taguchi L9 (2)3 orthogonal array has been applied for experimental design. S/N ratio and ANOVA analyses were performed to identify significant parameters influencing specific cutting force. The analysis presents the method that reduces the cutting power during turning of sintered nickel alloy.
On Systematic CAD/CAM Modeling of Blow Molds for Plastic Bottles
Authors: Krimpenis Agathoklis A. , Tsakanikas John G.
Published: August 2017

A systematic and detailed approach in design and manufacturing of blow molds for bottles made of PET and PP plastic material with CAD/CAM software tools is presented, as many production errors and product deficiencies stem from inaccurate and imprecise tooling. Apart from high mold accuracy, proper planning also includes the minimization of mold machining costs, which mainly derives from CNC machining time and cutting tool wear. Blow mold design and manufacturing revolves around two major axes: (a) mold material and (b) machining parameter values. The former is critical in terms of production rates and mold life-cycle and the latter has a great impact on mold manufacturing cost, as well as on quality of the produced plastic bottles. Proper choice of machining parameters has a significant impact on thermal conductivity, durability, hardness, stiffness and roughness of the mold. The proposed methodology was implemented on three different test cases (beverage plastic bottles molds) and it was concluded that even the same machining parameter values offer the same mold quality.
A Generic Multi-Axis Post-Processor Engine for Optimal CNC Data Creation and Intelligent Surface Machining
Authors: Fountas Nikolaos A. , Stergiou Constantinos I. , Vaxevanidis Nikolaos M. , Benhadj-Djilali Redha
Published: August 2017

This paper focuses on the development of a multi-axis post-processor engine with a curvature-based feed adaptation module, capable of extracting generic CNC data for high precision machining. The motivation of this work stems from the drawback of standard and commercial post-processors to modify their internal source codes so as to be implemented to newly-developed functions which integrate modern CNC units. The multi-axis post-processor proposed in this work operates as a stand-alone function of an artificial intelligent module that optimizes machining parameters for standard swept cut multi-axis surface tool-paths. The post-processor developed receives APT source files previously been optimized by means of a genetic algorithm that handles cutting tool selection; radial cut engagement; maximum discretization step; lead and tilt angles. The algorithm optimizes the aforementioned machining parameters towards the minimization of the number of cutter locations found in a specific APT source file as well as the surface machining error as a combined effect of chordal deviation and scallop height. The final APT output is then properly handled by the post-processor engine so as to extract the final ISO code for a double-pivoted head 5-axis CNC machine and compute optimal values for feed rate in each NC block considering the interpolation error and curvature analysis given the surface properties. To simulate and verify our proposals, the MAZAK Vortex 1000 gantry-type 5-axis CNC machine tool equipped with a Fanuc 15i CNC unit has been selected as the manufacturing resource corresponding to the final CNC output that the proposed post-processor computes. A benchmark sculptured part is created and used for the virtual material removal simulation in CATIA® V5 R18. For that part, both the proposed post-processor engine and a commercially available post-processor were employed to extract G-code data whilst it was shown that identical outputs were obtained.
Optimization of In-Plant Production Supply with Black Hole Algorithm
Authors: Veres Péter , Bányai Tamás , Illés Béla
Published: August 2017

Logistic process is a basic factor in the success of manufacturing plants’ operation and has a direct impact on its efficiency, flexibility and reliability. Today’s successful operation of manufacturing processes views logistics as a high priority to ensure maximum utilization of resources. The material supply of manufacturing processes in the automotive industry is usually based on supermarkets and milk runs. This paper proposes an integrated supply model of manufacturing processes, which includes facility location and assignment. After a careful literature review, this paper introduces a mathematical model to formulate the problem of supermarkets and milk run based supply of machines. The model seeks the optimal location of buffers as well as the optimal assignment of buffers and machines so as to minimize the material handling costs while taking into account order limits of machines and capacities of resources. Next, we demonstrate an enhanced black hole algorithm dealing with multi-objective supply chain model to find the optimal structure of the system. Numerical results demonstrate how the proposed model supports the efficiency, flexibility and reliability of the manufacturing process.
Electrochemical Process Engineering in Biohydrometallurgical Metal Recovery from Mineral Sulfides
Authors: Tanne Christoph , Schippers Axel
Published: August 2017

Primary copper sulfides are recalcitrant to bioleaching, probably due to semi-conductivity or passivation effects which result in slow dissolution kinetics. The mineral dissolution strongly depends on redox reactions and, consequently, electrochemical techniques are recommendable for analyzing and processing of redox-active minerals. For this reason we installed a three electrode system into a conventional bioreactor. Electrolytic bioleaching was applied to a copper concentrate from black shale ore. First results verified the operational capability of ferric iron reduction during electrochemical leaching and that bioleaching is not hindered by the physical presence of the electrochemical setup. Although the working electrode was able to reduce ferric iron and to regenerate it as electron supply for ferrous iron oxidizing microorganisms, the electron input into the bioleaching process has to be further increased to keep up with fast biocatalytical iron oxidation.
Comparative Bioleaching and Mineralogical Characterization of Black Shale-Hosted Ores and Corresponding Flotation Concentrates
Authors: Kamradt Andreas , Schaefer Juliane , Schippers Axel , Hedrich Sabrina
Published: August 2017

In this study, two black shale copper ores from different Mid-European Kupferschiefer-type deposits and their flotation concentrates were used for bioleaching tests. All samples were subjected to stirred tank bioleaching using an acidophilic, moderately thermophilic microbial consortium. The distribution of sulfides and gangue minerals in the ores, copper concentrates and residues of both, bioleaching and sterile chemical control tests were investigated using EDX-based particle analysis. The black shale ores and the extracted copper concentrates varied in their mineralogical composition with respect to the distribution of sulfides and gangue. While the copper-bearing sulfides in the Sangerhausen black shale and concentrate were dominated by bornite and chalcopyrite, the Rudna black shale and its flotation concentrate were rich in chalcocite and bornite. Differences in the portion of gangue minerals were detected in particular for carbonates that represented the dominant mineral group in the Rudna black shale and its copper concentrate. Distinct Cu dissolution kinetics and recovery rates of Co and other associated metals were observed for the various materials processed by bioleaching. Copper sulfides were completely dissolved also in both black shale ores. However, the sulfide distribution in the bioleaching residues of the Sangerhausen concentrate revealed that a significant portion of chalcopyrite was not leached. Even higher recovery rates for copper and other metals were determined for the bioleaching tests on the Rudna concentrate, in which copper sulfides were nearly completely dissolved. Alteration of copper sulfides and the formation of calcium sulfate were in particular observed in the sterile control residue of the Rudna concentrate, due to excessively use of sulfuric acid for pH stabilization. Lead sulfate precipitates increasingly occurred in the bioleaching residues, but represented also a common secondary phase in the sterile leaching residues.
Pilot-Scale Bioleaching of Metals from Pyritic Ashes
Authors: Vuorenmaa Elina A. , Mäkinen Jarno , Korhonen Tero , Neitola Raisa , Kaksonen Anna H.
Published: August 2017

Solid waste from sulfuric acid production may contain relatively high levels of metals such as Fe, Zn, Co, Cu and As that are harmful if inappropriately disposed of in the environment, but may be a valuable resource if metals can be recovered. The objective of this research was to investigate the pilot-scale acid bioleaching of metals from pyritic ashes, originating from the roasting of pyrite ores for sulfuric acid production and consisting mainly of hematite. Bioleaching was carried out at 25 °C in pilot-scale continuously stirred tank reactors (CSTR), with 50 L working volume in mineral salts medium supplemented with trace elements, 1 % (w/v) elemental sulfur and with pyritic ash pulp densities 10 % and 20 %. The reactors were inoculated with a mixed culture of iron- and sulfur-oxidising acidophiles containing Acidithiobacillus (At.) ferrooxidans, At. thiooxidans/albertensis, At. caldus, Leptospirillum ferrooxidans, Sulfobacillus (Sb.) thermosulfidooxidans, Sb. thermotolerans and some members of Alicyclobacillus genus. Metal leaching yields from pyritic ashes in the CSTR after 32 days were 54.6-56.7 % Cu, 41.7-43.2 % Zn, 1.7-1.8 % Co, 3.0-5.4 % As and 0.3-0.5 % Fe. Solution pH decreased during the experiment from 2.9 to 1.9-2.2. Elemental analysis using X-ray fluorescence showed that the contents of metals, except for As, in the leach residue were below the higher guideline values given in the Government decree on the assessment of the soil contamination and remediation needs by the Ministry of the Environment, Finland. Bioleaching facilitated the extraction of metals from pyritic ashes and the mitigation of environmental risks related to the residue disposal for other metals except for As.
Bioleaching Experiments on a Low-Grade Complex Zinc Ore from Inner Mongolia
Authors: Li Jia Feng , Tong Lin Lin , Chen Qiao , Jin Zhe Nan , Yang Hong Ying
Published: August 2017

When dealing with a low-grade complex Zinc ore from Inner Mongolia, problems of low leaching rate, high energy consumption, low economic benefits and pollution were encountered. To treat this low-grade zinc ore economically and effectively, bioleaching was used. This approach produces reliable data for an environmentally friendly and efficient processing of the zinc ore. The results indicate that Zinc occurs in the ore mainly as sphalerite, the latter also containing Indium. The experimental results demonstrated an excellent leaching performance: A leaching rate of nearly 100% is achieved at a temperature of 45°C, a pulp concentration of 10%, an initial pH of 1.8, and an aeration rate of 0.8m3/h. In the initial stage the leaching rate is higher than at the end. It starts with 85% of zinc leaching rate in three days. The Indium in the sphalerite is leached almost completely. This makes a further comprehensive use of such resources possible.
Recovery of Copper from Pyritic Copper Ores Using a Biosurfactant-Producing Mixotrophic Bacterium as Bioflotation Reagent
Authors: Sanwani Edy , Mirahati Riria Zendy , Chaerun Siti Khodijah
Published: August 2017

In an attempt to investigate the use of bacteria and their metabolites as bioflotation reagents for environmentally friendly mineral processing, laboratory cell flotation tests were carried out using copper sulfide ores bearing a high content of pyrite, which were mixed with a biosurfactant-producing mixotrophic bacterium as bioflotation reagents. The interaction of bacterial cells and their metabolic products with the sulfide ores resulted in the alteration of the surface chemistry of both ores and bacterial cells as evidenced by FTIR and SEM-EDS observations as well as surface tension and contact angle measurements. The change in the surface properties of the sulfide ores in turn enabled the bacterium to function as flotation bioregeants in the flotation of copper sulfide ores as a function of bacterial cell concentration, conditioning time, flotation time and pH. Overall, the bacterium and its metabolites as bioreagents yielded flotation recoveries which might be attributed to the multi-function of the bacterium as depressant, collector and frother. Thus, the bacteria tested in this study could potentially be used as flotation bioreagents, providing an alternative to conventional flotation reagents.
Insights into Heap Bioleaching at the Agglomerate-Scale
Authors: Cox Alison , Bryan Christopher G.
Published: August 2017

Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.
Nickel Bioleaching at Elevated pH: Research and Application
Authors: Sun Jian Zhi , Chen Bo Wei , Wen Jian Kang , Wu Biao
Published: August 2017

Biohydrometallurgy has broad application prospect in the treatment of low-grade nickel sulfide ore. However, quite a number of nickel sulfide deposits are associated with basic gangue minerals such as contain olivine, serpentine. The high basic gangue minerals will lead to a higher acid consumption and make it difficult to bioleach at pH below 2.5. It is crucial to improve processes and adapt bacteria with this kind of ore. This paper reviews the experimental researches and industrial applications for bioleaching of the high acid consumption nickel sulfide ores. It is suggested that bioleaching at elevated pH will have similar leaching rate compared with pH below 2.5, meanwhile the cost will be decreased remarkably due to a lower acid consumption and less dissolved impurity ions.
Bioleaching of Low-Grade Chalcopyrite Ore by the Thermophilic Archaean Acidianus brierleyi
Authors: Saitoh Norizoh , Nomura Toshiyuki , Konishi Yasuhiro
Published: August 2017

The thermophilic archaean, Acidianus brierleyi, was examined for its feasibility to bioleach copper from a low-grade chalcopyrite ore (1.15 % copper, 20.4 % iron and 2.63 wt% sulfur) at 65°C and pH 1.8-2.5. The chalcopyrite leaching was markedly accelerated in the presence of A. brierleyi, and an extremely high 80% leaching of copper in the low-grade ore (25-38 μm particles) was achieved in 14 days in a batch stirred reactor. By comparison, the leaching of iron was very slow and only a slight 5 % iron was leached in 14 days in the presence or absence of A. brierleyi. In other words, A. brierleyi selectively leached chalcopyrite while magnetite leaching by A. brierleyi was negligible. Moreover, bioleaching of the low-grade ore (53-75 μm particles) yielded 55% copper recovery after 20 days of operation in a column reactor. The good results for the copper bioleaching in the column reactor are very similar to those in the stirred reactor. These results lead to the conclusion that the thermophile bioleaching with A. brierleyi is attractive as an economical and environmentally friendly process for good copper extraction from low-grade chalcopyrite ore.
Characterization and Localized Insight into Leaching of Sulfide Minerals
Authors: Chen Miao , Yang Yi , Vepsalainen Mikko
Published: August 2017

To improve the efficiency of sustainable recovery of valuable resources (such as copper, gold, uranium), advanced technologies of electrochemistry, surface chemistry and materials characterization, such as Synchrotron X ray-absorption spectroscopy (XAS), X-Ray photoelectron spectroscopy (XPS), and in situ X-ray Diffraction (XRD) have been employed to investigate the interactions between microbes and sulfide minerals in situ to gain a detailed understanding of the chemical reaction mechanisms operating in bioleaching. It has been demonstrated that alternating current Scanning Electrochemical Microscopy (ac-SECM) allows for straightforward characterization of sulfide mineral samples in aqueous solution. With the technology localized electrochemical properties of the mineral surface including the surface current mapping can be achieved. Robust chemical sensors have been developed for real time, in-situ monitoring of key leaching process parameters.
Bioleaching of Chalcopyrite with Two Different Metallogenic Types: A Mineralogical Perspective
Authors: Deng Sha , Gu Guo Hua , Ji Jing , Xu Bao Ke
Published: August 2017

The bioleaching behaviors of chalcopyrite with two different metallogenic types by iron- and sulfur-oxidizing Sulfobacillus thermosulfidooxidans were investigated. It was found that the skarn-type chalcopyrite (STC) exhibited much faster leaching rate and the copper extraction was 33.34% after 21 days of biooxidation, while that of the porphyry-type chalcopyrite (PTC) was only 23.53%. The reasons were explained from the perspective of mineralogy. The analysis of XRD indicated that STC had slightly larger cell parameters than PTC. More stepped and bulgy structures were observed on the STC surface, as displayed in SEM images. The XPS spectra showed that copper on the surfaces of the two types of chalcopyrite mainly existed in the form of Cu(I), and STC had much higher copper content and lower Cu 2p3/2 binding energy than PTC. These differences in mineralogy resulted in the more excellent bioleaching kinetics of STC. This study is pretty useful in understanding the relation between the bioleaching behaviors of chalcopyrite and the mineralogical properties.
Microbial Community Composition of Mine Wastes in Cornwall and West Devon (UK)
Authors: Sbaffi Tomasa , Buckling Angus , Bryan Christopher G.
Published: August 2017

Mine wastes and control soils from twelve sites around Cornwall and West Devon (UK) were analysed for microbial community structure, pH and readily extractible metals (an indication of mobility). About 70% of total diversity observed was constituted by six phyla (Acidobacteria, Chloroflexi, Planctomycetes, Proteobacteria, Verrucomicrobia, and candidate division AD3). Microbial community structure revealed patterns of distribution that mostly differed between waste samples and controls. Cluster analysis of the geochemical data (pH and readily extractible metals) indicated the presence of four groups; two groups of controls and two of samples defined by similar features. pH appeared to correlate with the portion of shared community.
Process and Cost Improved Agitator Solutions for Bioleach Reactors
Authors: Jung Jochen , Keller Wolfgang
Published: August 2017

As mineralogy has become more complex in the long history of hydrometallurgical processing, the process routes and equipment used had to adapt to the changing conditions [1]. Hydrometallurgical bioleaching processes have been developed for different key metals such as gold, nickel and copper amongst others, to overcome the limitations of leaching sulphidic ores.
The core of such a hydrometallurgical bioleaching plant is a cascade of stirred atmospheric tank reactors. Large volumes of air that are blown into these tanks must be dispersed by the agitator in order to provide the necessary oxygen mass transfer rates. At the same time the agitator system must be able to properly suspend all solids, homogenize the vessel contents and remove the exothermic reaction heat by inner tube bundles to achieve optimal reaction conditions.
Besides the ‘economies of scale’ and advances in process results, cost optimization of such systems is fundamental. Therefore EKATO has developed the Combijet+ technology which has significantly reduced power requirements, compared to conventional agitators. Another advantage of the Combijet+ technology is that the gas is injected directly into the highest shear zones, at the impeller blades. As a result the oxygen mass transfer is improved and also substantial cost savings for compressor power are possible.
The technical paper will present EKATO’s Combijet technologies which support the next step towards a new generation of biohydrometallurgical processing plants. It will also give examples of large scale commercial applications where this technology is successfully in operation.
16S rRNA and Multilocus Phylogenetic Analysis of the Iron Oxidizing Acidophiles of the Acidiferrobacteraceae Family
Authors: Issotta Francisco , Covarrubias Paulo C. , Moya-Beltrán Ana , Bellenberg Sören , Thyssen Christian , Sand Wolfgang , Nuñez Harold , Mena Cristóbal , Holmes David S. , Quatrini Raquel , Vera Véliz Mario
Published: August 2017

The family Acidiferrobacteraceae (order Acidiferrobacterales) currently contains three genera of chemolithoautotrophs: Sulfuricaulis (2016), Sulfurifustis (2015) and Acidiferrobacter (2011). While the two former are neutrophilic sulfur oxidizers isolated from lake sediments in Japan, the latter is an extremely acidophilic, moderately osmophilic, thermotolerant iron/sulfur oxidizer known to occur in macroscopic streamers in Rio Tinto, Spain and in acid waters worldwide. The type strains of both Sulfuricaulis limnicola (HA5T) and Sulfurifustis variabilis (skN76T) have been sequenced, and the draft genome of the ZJ isolate of Acidiferrobacter thiooxydans (MDCF01) has recently been deposited in public databases. Despite this fact, little evidence on the genomic diversity and evolution of this group has been presented so far. Using comparative genomic analyses and phylogenetic reconstruction strategies, we explored the evolutionary information contained in the available genome sequences to shed light on the taxonomic status of a novel isolate of the genus Acidiferrobacter (SP-III/3; DSM 27195).
Inhibition Kinetics of Iron Oxidation by Leptospirillum ferriphilum to Residual Thiocyanate Present in Bioremediated Cyanidation Tailings Wastewater
Authors: Edward Catherine J. , Kotsiopoulos Athanasios , Harrison Susan T.L.
Published: August 2017

Inhibition of iron oxidation by Leptospirillum ferriphilum in the presence of thiocyanate (SCN-) was studied in small-scale batch experiments. The L. ferriphilum culture was challenged with SCN- over a range of 0 mg/l to 10 mg/l. The data showed that L. ferriphilum was able to utilise ferrous iron at low-level concentrations of SCN- (0.25 mg/l to 1.75 mg/l), however exhibited a reduction in oxidation rate relative to the control (0 mg/l). Moreover, introduction of SCN- at low-level concentrations resulted in a lag in iron oxidation activity, specifically at concentrations of 1 mg/l, 1.25 mg/l and 1.75 mg/l. No iron oxidation was observed at SCN- concentrations above 1.75 mg/l, indicating complete inhibition. As L. ferriphilum is the dominant iron oxidising bacteria within biooxidation tanks, evidence of sustained iron oxidation activity at low-level SCN- concentrations affirms the potential of recycling bioremediated cyanidation wastewater within biooxidation circuits in bioprocesses for gold recovery from sulfidic minerals as residual SCN- concentrations in remediated effluent are reportedly lower than 0.25 mg/l. The inhibition kinetics of this system need to be explored further in order to develop a deeper understanding of the system such that it may be applied to inform process operation.
Fungal Mineralization Processes in Rio Tinto
Authors: Oggerin Monike , Rodríguez Nuria , Amils Ricardo
Published: August 2017

Eukaryotic diversity in Río Tinto turns out to be unexpectedly high when compared to the prokaryotic one. Unlike the prokaryotic community, little is known about the role of the most abundant eukaryotes, mainly algae and fungi, in this ecosystem. Previous studies using acidophilic fungi isolated from the Tinto basin have shown their ability to specifically sequester toxic metals. We have also been able to demonstrate their direct implication in the geochemical cycles through biomineralization processes. Although the role that fungi may play in the Tinto basin is still poorly understood, is becoming clear that they participate very actively in the geological conformation of the environment, generating minerals of possible economical interest.
Linking Microbial Community Dynamics in BIOX® Leaching Tanks to Process Conditions: Integrating Lab and Commercial Experience
Authors: Smart Mariette , Huddy Robert J. , Edward Catherine J. , Fourie Charl , Shumba Trust , Iron Jonathan , Harrison Susan T.L.
Published: August 2017

In the commercial BIOX® process, an acidophilic mixed bacterial and archaeal community dominated by iron and sulphur oxidising microorganisms is used to facilitate the recovery of precious metals from refractory gold-bearing sulphidic mineral concentrates. Characterisation of the microbial communities associated with commercial BIOX® reactors from four continents revealed a significant shift in the microbial community structure compared to that of the seed culture, maintained at SGS (South Africa). This has motivated more detailed study of the microbial community dynamics in the process. Microbial speciation of a subset of the BIOX® reactors at Fairview mines (Barberton, South Africa) and two laboratory maintained reactors housed at Centre for Bioprocess Engineering Research, University of Cape Town, has been performed tri-annually for three years by quantitative real-time polymerase chain reaction. The laboratory BIOX® culture maintained on Fairview concentrate was dominated by the desired iron oxidiser, Leptospirillum ferriphilum, and sulphur oxidiser, Acidithiobacillus caldus, when operated under standard BIOX® conditions. Shifts in the microbial community as a result of altered operating conditions were transient and did not result in a loss of the microbial diversity of the BIOX® culture. The community structure of the Fairview mines BIOX® reactor tanks showed archaeal dominance of these communities by organisms such as the iron oxidiser Ferroplasma acidiphilum and a Thermoplasma sp. for the period monitored. Shifts in the microbial community were observed across the monitoring period and mapped to changes in performance of the commercial process plant. Understanding the effect of changes in the plant operating conditions on the BIOX® community structure may assist in providing conditions that support the desired microbial consortium for optimal biooxidation to maximize gold recovery.
Biochemical Aspects of Energy Metabolism in Sulfobacillus thermotolerans
Authors: Panyushkina Anna , Melamud Vitaliy , Tsaplina Iraida
Published: August 2017

Bacteria of the genus Sulfobacillus are successfully used in biotechnologies of treatment of sulfide ore materials. However, energy processes are still poorly understood in sulfobacilli. Several enzymes encoded in the genomes of sulfobacilli are putatively involved in the initial phase of Fe2+ oxidation. Cytochromes c, sulfocyanins, and rusticyanin-like proteins were revealed in genomes of these bacteria. Thus, a membrane bound cytochrome c can be reduced directly by Fe2+, and electrons can be further transferred to sulfocyanin, rusticyanin or some other components of the transport chain. HPLC identification of prosthetic groups of cytochromes predicts the possible presence of heme c in the cells of thermotolerant sulfobacillus. Determination of metal content in the cells shows that sulfobacillus harbours higher levels of copper ions under specific conditions. This can be explained by higher expression of copper-containing proteins, including cupredoxins.
The Effect of Initial Solution pH on Surface Properties of Ferric Ion Precipitates Formed during Biooxidation of Ferrous Ion by Leptospirillum ferriphilum
Authors: Mabusela Bongo , Ojumu Tunde Victor
Published: August 2017

While bioleaching is a proven technology for the efficient recovery of base metals from sulphide minerals, its sustenance is dependent on the continuous availability of ferric ion, Fe3+, in soluble form, in bioleach liquor. However, the solubility of ferric ion is low at higher pH thus resulting in the formation of various types of ferric ion precipitates, which decreases leaching efficiency by trapping the leached metals in solution through an adsorption. The effect of initial solution pH on the surface properties of ferric ion precipitates was investigated with a view to establish a relationship between operational pH and surface charge on precipitate and to relate this to the precipitates metal adsorption properties. Ferric ion precipitates recovered from a typical biooxidation process were characterized by XRD, SEM, PSD and zeta potential. Potassium-hydronium jarosite were the main phases identified by X-ray diffraction (XRD) analyses. The SEM results revealed that the precipitates had smooth surfaces with development of sharp edges on the precipitates formed at high pH. The precipitates formed at higher pH had less positive charge and scavenged more copper ions due to the high electrostatic attraction forces. The results from this study revealed that surface charge on a precipitate can give an indication of its metal adsorption capacity and that in order to prevent metal loss and improve extraction efficiency, solution conditions should be maintained such that the resulting precipitates have high positive surface charge to promote high electrostatic repulsion forces.
Construction of a Cell Surface Engineered Yeast Aims to Selectively Recover Molybdenum, a Rare Metal
Authors: Chien Mei Fang , Ikeda Naoya , Kubota Kengo , Inoue Chihiro
Published: August 2017

The depletion of rare metals is an issue of major concern since rare metals are limited in the abundance but essential for high technology industry. However, the present rare metal recovery technical by chemical methods has high environmental impact, poor selectivity, and is too expensive to be practical. To resolve these problems, this study aimed to create a rare metal recover system using yeast, and molybdenum was selected as the first target. A molybdenum binding protein, ModE, which was derived from Escherichia coli was selected. A fusion gene was generated by linking partial modE with a secretion signal and a domain of α-agglutinin to display the ModE on the surface of yeast cells. The expression of fusion protein on the cell surface was detected by immunofluorescence labeling. As for the recovery experiment, the engineered yeast cells were incubated in 10 mM of sodium molybdate solution for 2 h, and the recovery of molybdenum ion was measured by ICP-AES. The results of fluorescence micrographs showed that the designed fusion protein was successfully expressed on yeast cell surface. According to the results of ICP-AES, the cell surface engineered yeast adsorbed molybdenum and the cells after 72~84 h incubation gave the best adsorption. Besides, the results suggested that the optimization of each functional domain in the fusion protein was important. The selectivity and the lower limit of recoverable concentration are under investigation, while this study provides a preliminary result of bio-extraction technology using cell surface engineered yeast.
EPS Characterization of a Cell Wall-Lacking Archaeon Ferroplasma acidiphilum
Authors: Zhang Rui Yong , Blanchard Veronique , Vera Véliz Mario , Sand Wolfgang
Published: August 2017

We studied the surface properties of F. acidiphilum DSM 28986 by attenuated total reflection-Fourier transformed infra-red (ATR-FTIR) spectroscopy and microbial adhesion to hydrocarbon (MATH) techniques. In addition, extracellular polymeric substances (EPS) were extracted and characterized by conventional colorimetric analysis and fluorescence lectin-binding analysis (FLBA). Results showed that: 1) cells selectively adhered to mineral surfaces and showed maximum attachment to pyrite of approx. 50% within 30 min; 2) EPS synthesis by F. acidiphilum DSM 28986 was influenced by growth substrates; and 3) tightly-bound EPS (capsular EPS) were composed of carbohydrates and proteins. In contrast, loosely-bound EPS (colloidal EPS) were mainly characterized as carbohydrates. Monosaccharides like glucose, fucose, arabinose, galactose, mannose, and sialic acid were detected in the EPS of F. acidiphilum DSM 28986. This study provides first insight into surface characterization of the cell wall-lacking archaeon F. acidiphilum and facilitates the understanding of interactions of this organism with other acidophiles and metal sulfides.
Phage Display - A Promising Tool for the Recovery of Valuable Metals from Primary and Secondary Resources
Authors: Matys Sabine , Lederer Franziska L. , Schönberger Nora , Braun Robert , Lehmann Falk , Flemming Katrin , Bachmann Stefanie , Curtis Susan , MacGillivray Ross T.A. , Pollmann Katrin
Published: August 2017

The development of effective and ecofriendly processes for the recovery of critical elements poses a challenge for scientists all over the world. A novel approach is the generation of highly specific peptides that bind with high affinity to individual elements of interest. The peptides are selected by phage surface display (PSD) technology. In this study, PSD technology has been applied in two different approaches. The focus of the first approach was the identification of peptides that bind specifically to special particles of interest that are part of electronic scrap aiming towards the development of new recycling processes. In the second approach, metal ion binding peptides were isolated via PSD to use them for the targeted removal and enrichment of these elements from complex leaching solutions or from industrial waters. To address the economic production of peptides, the development of a new expression system is also part of this study.
Investigation of Fluoride Tolerance in Acidithiobacillus ferrooxidans
Authors: Tao Jie Meng , Ma Li Yuan , Qin Chong , Yin Hua Qun , Liang Yi Li , Qiu Guan Zhou , Liu Xue Duan
Published: August 2017

Anionic ion species occur in gangue minerals and impact the bioleaching efficiency even at low concentrations. Recently, the detrimental influence of fluoride ions on bioleaching microorganisms has caused great attention in research. However, the tolerance mechanisms of bioleaching microorganisms for fluoride are still unclear. In order to reveal fluoride tolerance, culture experiments with different concentrations of fluoride and ferrous iron-grown Acidithiobacillus ferrooxidans were carried out. The results showed that oxidation-reduction potential, oxidation capacity of iron and cell density were all negatively correlated to the fluoride concentration. The growth of A. ferrooxidans showed a longer delayed time and a slower growth rate when fluoride concentration increased. The fluoride tolerance for A. ferrooxidans could be attributed to the generated ferric ions from ferrous oxidation. Ferric ions reacted with HF to decrease the concentration of F- and finally reduced the toxicity of fluoride on A. ferrooxidans.
Identification of Sulfur Activation Relevant Protein Genes of Extremely Thermophilic Acidianus manzaensis
Authors: Liu Hong Chang , Xia Jin Lan , Nie Zhen Yuan , Ma Ya Long , Yang Yun , Liu Li Zhu , Pan Xuan , Yuan Peng
Published: August 2017

The sulfur activation by extracellular proteins is considered as the crucial stage during biooxidation of elemental sulfur (S0). In order to study genes encoding sulfur-activation related extracellular proteins of extremely thermophilic Acidianus manzaensis, the extracellular proteins with higher abundance for the strain grown on S0 allotropes than that on Fe2+ were first screened by two-dimensional gel electrophoresis, and then identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Nine genes amplified with PCR were satisfactory according to their agarose gel electrophoresis. The differential expression of these nine genes when the strain grown on S0 allotropes and Fe2+ were analyzed with real-time quantitative PCR (RT-qPCR). Results showed that seven of them were higher expressed when the strain grown on S0 allotropes than on Fe2+, indicating they may be related with sulfur activation by A. manzaensis.
Resistance of Moderately Thermophilic Acidophilic Microorganisms to Ferric Iron Ions
Authors: Bulaev Aleksander
Published: August 2017

Resistance of microorganisms predominating in biohydrometallurgical processes including bacteria of the genus Sulfobaсillus and archaea of the genus Acidiplasma to ferric iron ions was studied. Capabilities of the strains for growth and ferrous iron oxidation in the media containing high concentrations of ferric iron ions (of 250 to 1000 mM) were evaluated. Ferric iron ions significantly inhibited oxidative activity and growth of the studied microorganisms. It was revealed that bacteria of the genus Sulfobacillus were not able to oxidize ferrous iron actively when ferric iron concentration exceeded 500 mM, whereas archaea of the genus Acidiplasma completely oxidized ferrous iron in the medium containing 1000 mM of Fe3+. Growth of the microorganisms was inhibited by relatively low concentrations of ferric iron. Microorganisms did not grow in the medium containing more than 750 mM of Fe3+ and cells of all studied strains lysed in presence of high concentrations of ferric iron. It was shown, that archaea of the genus Acidiplasma of the family Ferroplasmaceae were more resistant to high concentrations of ferric iron than bacteria of the genus Sulfobacillus. The results obtained are important for understanding of the regularities of the formation of microbial communities performing technological processes.
Microbial Population of Industrial Biooxidation Reactors
Authors: Bulaev Aleksander , Belyi Aleksandr , Panyushkina Anna , Solopova Natalia , Pivovarova Tatyana
Published: August 2017

Microbial population performing biooxidation of flotation concentrate of gold bearing sulfide ore containing pyrite, arsenopyrite, and pyrrhotite was studied using cultural and molecular biological (metagenomics sequencing of V3-V4 fragments of 16S rRNA gene) approaches. The biooxidation of the concentrate was conducted at temperatures from 38 to 42°C. Strains of Acidithiobacillus thiooxidans, Acidiphilium multivorum, Leptospirillum ferriphilum, Sulfobacillus thermotolerans, Ferroplasma acidarmanus, and Ferroplasma acidiphilum were isolated from the samples of the pulp from biooxidation reactors. It was shown that optimum temperatures of isolated strains were from 38 to 40°C. Metagenomic analysis demonstrated predominance of the genera Acidiferrobacter, Acidithiobacillus, Acidiphilum, Leptospirillum, and Ferroplasma. According to results of molecular biological analysis, share of the genus Acidithiobacillus was of 0 to 25%, share of the genus Acidiferrobacter was of 7 to 56%, share of the genus Acidiphilum was of 0.03 to 36%, share of the genus Leptospirillum was of 0.7 to 7%, whereas share of the archaea of the genus Ferroplasma was of 33 to 94%. Thus, it was shown that representatives of the genus Ferroplasma can play significant role in bioleach process. Representatives of the genus Acidiferrobacter were previously detected in acid mine drainages, acid soils as well as in bioleach heaps and reactors, whereas data on predominance of the genus in tank bioleach processes have not been presented in the literature. In the present study, strains of the genus Acidiferrobacter were not isolated despite application of the nutrient media recommended for Acidiferrobacter and their properties were not studied. Nevertheless, results of the present study suggest that representatives of the genus Acidiferrobacter have a great impact on industrial bioleach processes.
Molecular Response of the Acidophilic Iron Oxidizer “Ferrovum” sp. JA12 to the Exposure to Elevated Concentrations of Ferrous Iron
Authors: Ullrich Sophie R. , Poehlein Anja , Levicán Gloria J. , Schlömann Michael , Mühling Martin
Published: August 2017

The response to elevated ferrous iron concentrations was investigated in the acidophilic iron oxidizer “Ferrovum” sp. JA12 at transcriptome level. Detoxification of reactive oxygen species appears to be the most important strategy to cope with oxidative stress. The proposed iron oxidation model in “Ferrovum” spp. was supported by the transcriptome data of “Ferrovum” sp. JA12. Several gene candidates of the iron oxidation model are organized in a gene cluster conserved in iron oxidizing betaproteobacteria and zetaproteobacteria possibly indicating a common origin of iron oxidation.
The Surface Chemistry Characterization of Pyrite, Sphalerite and Molybdenite after Bioleaching
Authors: Ghassa Sina , Abdollahi Hadi , Gharabaghi Mahdi , Chehreh Chelgani Saeed , Jafari Mohammad
Published: August 2017

The mineral surface chemistry characterization is essential to describe the dissolution kinetics in leaching and bioleaching. Five different methods, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, have been applied to study the surface chemistry changes during pyrite, sphalerite and molybdenite bioleaching. The surface characterizations have been done for samples before and after biological and chemical leaching. The SEM images illustrated that the minerals surfaces were smooth before processing, while they covered with an ash layer after biological treatment. Although EDS analysis and Raman spectrum demonstrated the potassium jarosite formation on the pyrite surface during bioleaching, the formation of jarosite layer did not occur on the sphalerite surfaces during bioleaching. On the other hand, a sulfur layer formation on the sphalerite surface was confirmed by mentioned characterization methods. Finally, according to the XRD and EDS spectrum the molybdenite surface had been covered both with sulfur and jarosite.
Siderophore Purification via Immobilized Metal Affinity Chromatography
Authors: Heine Thomas , Mehnert Marika , Schwabe Rïngo , Tischler Dirk
Published: August 2017

Siderophores are low-molecular weight compounds that are produced by organisms to assimilate vital Fe3+ out of iron-deficient environments. They are of interest for several (bio-) technological applications because of their high selectivity for several metal ions. Unfortunately, the concentration in supernatants is often low and thus it is challenging to purify or even enrich these compounds. We applied different types of siderophores onto an immobilized metal-resin that was loaded with either Ni2+, Co2+ or Fe3+. Elution was done with ethanol to reduce salt load and facilitate downstream processing. Thus, it is possible to enrich as well as desalt a sample within one-step from culture supernatant, which allows faster characterization and application of siderophores.
Comparative Analysis of Functional Gene Diversity of Acid Mine Drainage and its Sediment by Geochip Technology
Authors: Tan Ling , Yun Hui , Xu Xia Yi , He Jia , Wu Hai Yan , Qiu Guan Zhou , Liu Xin Xing , Xie Jian Ping
Published: August 2017

The diversity of microbial community is well studied in past decades, however, the functional gene diversity in AMD and sediment are still unclear. In this study, four samples, which included two mine drainages and two sediments were taken from two typical copper mines in the southeast of China. Community DNA from the AMD and corresponding sediments were were extracted, purified, amplified, labeled and hybridized with GeoChip 2.0. The results showed that total 28, 126, 1131, 1875 functional genes were detected in DX_110, YP_NK, DX_110N, YP_NKN, respectively, which including carbon and nitrogen fixation, carbon degradation, methane metabolism, ammonification, nitrification, denitrification, nitrogen reduction, sulfur reduction and metal resistance genes. Sediment nearby the mine drainage may play an important role in microbial geochemical processes, since more functional genes and higher diversity were detected in sediment than in AMD.