bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasensitive Terahertz Biosensors Based on Fano Resonance of a Graphene/Waveguide Hybrid Structure
Authors: Ruan Banxian , Guo Jun , Wu Leiming , Zhu Jiaqi , You Qi , Dai Xiaoyu , Xiang Yuanjiang
Published: August 2017

Graphene terahertz (THz) surface plasmons provide hope for developing functional devices in the THz frequency. By coupling graphene surface plasmon polaritons (SPPs) and a planar waveguide (PWG) mode, Fano resonances are demonstrated to realize an ultrasensitive terahertz biosensor. By analyzing the dispersion relation of graphene SPPs and PWG, the tunable Fano resonances in the terahertz frequency are discussed. It is found that the asymmetric lineshape of Fano resonances can be manipulated by changing the Fermi level of graphene, and the influence of the thickness of coupling layer and air layer in sandwich structure on the Fano resonances is also discussed in detail. We then apply the proposed Fano resonance to realize the ultrasensitive terahertz biosensors, it is shown that the highest sensitivities of 3260 RIU−1 are realized. Our result is two orders of a conventional surface plasmon resonance sensor. Furthermore, we find that when sensing medium is in the vicinity of water in THz, the sensitivity increases with increasing refractive index of the sensing medium.
Asymmetries in the Maintenance Performance of Spanish Industries before and after the Recession
Authors: Carnero María Carmen
Published: August 2017

Abstract: Until the last few decades, maintenance has not been considered of special importance by organisations. Thus, the number of studies that assess maintenance performance in a country is still very small, despite the relevance this area has to the level of national competitiveness. This article describes a multicriteria model integrating the fuzzy analytic hierarchy process (FAHP) with multi-attribute utility theory (MAUT) to assess the maintenance performance of large, medium and small enterprises in Spain, before and after the recession, as well as the asymmetries in the state of maintenance between different activity sectors. The weightings are converted to utility functions which allow the final utility of an alternative to be calculated via a Multi-Attribute Utility Function. From the Spanish maintenance data for different industrial sectors in 2005 and 2010, 2400 discrete probability distributions have been produced. Finally, a Monte Carlo simulation is applied for the estimation of the uncertainty. The results show that the economic crisis experienced by Spain since 2008 has negatively affected the level of maintenance applied, rather than it being considered an area that could deliver cost reductions and improvements in productivity and quality to organisations.
Teaching Enzyme Activity to the Visual Impaired and Blind Students
Authors: De Oliveira Felipe , Nascimento Agatha , Bianconi Maria
Published: August 2017

Biochemistry requires a high abstraction level, and different approaches should be used to enable the proper understanding of different subjects. In particular, students with visual impairment or blindness need special attention, not due to a lack of cognitive skills, but due to the fact that most of the teaching methods are visual. Enzyme properties are usually taught through experimental data that show how the activity changes in different conditions, which end up with the analysis of graphs. Therefore, our group developed experiments and graphical representations that enable visually impaired and blind students to understand enzyme properties. The experiments were done with pineapple bromelain, using reconstituted dry milk and gelatin as substrates. The “visualization” of the results were based on the sensation of the viscosity of the samples. The graphs were made with cold porcelain with all the labels (legends and numbers) written in Braille with a positive slate. From our experience with a blind student, both the experiments and the graphic representations were useful adaptations for teaching enzyme properties.
Relating Water Use to Tree Vitality of Populus euphratica Oliv. in the Lower Tarim River, NW China
Authors: Keyimu Maierdang , Halik Ümüt , Rouzi Aihemaitijiang
Published: August 2017

This study aimed to compare the hydraulic characteristics of different vitalities of Populus euphratica to reveal the differences in their water use strategies and water consumption to provide useful data to scale water use of riparian poplar forests in the lower reaches of the Tarim River, Northwestern China. Our results showed that the sapwood area of P. euphratica could be estimated based on its correlation with tree biometric parameters. The sapwood area of vital poplars tended to be larger than the senesced poplar despite both having the same diameter at breast height. This indicates that poplar vitality should be taken into account when estimating its sapwood area. Therefore, we established two different sapwood area estimation models for vital and senesced poplar (sapwood area = 1.452 × DBH1.553, R2 = 0.891; sapwood area = 0.915 × DBH1.618, R2 = 0.718; DBH: diameter at breast height). The sap flow process of vital and senesced poplar had certain differences and similarities; the average diurnal sap flow velocity and water consumption of vital poplar were 15.85 cm/h and 45.95 L, respectively; for the senesced poplar, it was 9.64 cm/h and 18.17 L, respectively, which were smaller than that of vital poplars. The influence of environmental factors on the sap flow velocity of two different P. euphratica was similar; the sap flow of both vital and senesced poplar had positive correlation with air temperature (R2 = 0.800 and 0.851), solar radiation (R2 = 0.732 and 0.778), vapor pressure deficit (R2 = 0.508 and 0.643) and groundwater depth (R2 = 0.301 and 0.171), while negative correlation with air humidity (R2 = −0.313 and −0.478).
Hashimoto’s Thyroiditis And Cancer: A Review
Authors: Hajj Boutros Rita , Salti Ibrahim
Published: August 2017

Background: No consensus exists on the association between Hashimoto’s thyroiditis (HT) and cancer. To resolve this controversy, this review aimed to evaluate the relationship between the two conditions.

Methods: Using Pub-Med database, we searched studies relevant to the topic focusing on the association between HT and Papillary Thyroid Cancer (PTC), as well as the association between HT and Primary Thyroid Lymphoma (PTL).

Findings: Both HT and PTC are common worldwide, and the two conditions may be closely related. However, the relationship remains controversial. Some studies found that PTC coexisted with HT 2.8-fold more frequently, with variable prevalence ranging from 0.5 to 30%. In contrast to surgical and pathological series that suggested a positive correlation between the two diseases and even a cause-and-effect relationship, the other studies evaluating fine-needle aspirate specimens did not find a statistically significant correlation. On the other hand, the relationship between PTL and HT appears well established.

Conclusion: The existing data provide inconsistent evidence favoring a causal relationship between HT and PTC. Prospective studies are needed to further elucidate the relationship. However patients with HT are at risk for PTL. Therefore careful observation and follow-up of HT patients is recommended.
2010 August 1–2 Sympathetic Eruptions. II. Magnetic Topology of the MHD Background Field
Authors: Titov Viacheslav S. , Mikić Zoran , Török Tibor , Linker Jon A. , Panasenco Olga
Published: August 2017

Using a potential field source-surface (PFSS) model, we recently analyzed the global topology of the background coronal magnetic field for a sequence of coronal mass ejections (CMEs) that occurred on 2010 August 1–2. Here we repeat this analysis for the background field reproduced by a magnetohydrodynamic (MHD) model that incorporates plasma thermodynamics. As for the PFSS model, we find that all three CME source regions contain a coronal hole (CH) that is separated from neighboring CHs by topologically very similar pseudo-streamer structures. However, the two models yield very different results for the size, shape, and flux of the CHs. We find that the helmet-streamer cusp line, which corresponds to a source-surface null line in the PFSS model, is structurally unstable and does not form in the MHD model. Our analysis indicates that, generally, in MHD configurations, this line instead consists of a multiple-null separator passing along the edge of disconnected-flux regions. Some of these regions are transient and may be the origin of the so-called streamer blobs. We show that the core topological structure of such blobs is a three-dimensional “plasmoid” consisting of two conjoined flux ropes of opposite handedness, which connect at a spiral null point of the magnetic field. Our analysis reveals that such plasmoids also appear in pseudo-streamers on much smaller scales. These new insights into the coronal magnetic topology provide some intriguing implications for solar energetic particle events and for the properties of the slow solar wind.
Capilla, en Texas
Authors: Fehr Arthur , Granger Charles
Published: August 2017

Magníficamente emplazada, junto al río y en la cúspide de una pequeña colina, se levanta esta capilla como representación viva y patente del ideal religioso y nexo de unión en el desarrollo de una comunidad naciente. Desde lo alto se divisa un panorama espléndido, con el agua a sus pies y la extensión verde y sedante de las colinas y prados téjanos.
Effect of Ultrasonic Treatment on Morphology and Mechanical Properties of Bioplastic from Cassava Starch with Nanoclay Reinforcement
Authors: Eko Wahyuningtiyas Nanang , Suryanto Heru
Published: August 2017

The research is to investigate influence of sonication treatment on the morphologi and mechanical properties of bioplastic filler nanoclay with different nanoclay concentration. The bioplastic was prepared using blending method among bioplastic, glycerol, and nanoclay with assistance of sonication treatment of 30 mins. Structural characterization of bioplastic was examined using scanning electron microscopy (SEM), mechanical properties using durumeter Shore A, tensile strength and the physical properties using density. SEM evidence on a bioplastic basis. Hardness of bioplastic with addition of nanoclay 5.0% (b/b) and sonication treatment produce bioplastic with maximum hardness properties increased to 76.24 Shore A, tensile strength of 13.5 and Young’s modulus of 47, as well as the added density of 1.238 g/cm3. Nanoclay 7.5% (b/b) upwards will experience decreased hardness and experience agglomerate and debonding.
Analysis of Surface Texture of High Aspect Ratio Blind Micro Holes on Titanium Alloy (Ti-6Al-4V) in Micro Electrical Discharge Drilling
Authors: Barman Swapan , Puri Asit Baran , Nagahanumaiah
Published: August 2017

Efficiency of any machining process depends on the effectiveness of final outcomes. Surface integrity plays an important role in functional performance of a part or component. Traditionally, surface roughness is considered to be the principal parameter to assess the surface integrity of a machined surface. In this paper, the influences of machining parameters like gap voltage, capacitance and depth of hole on the surface finish parameters like Ra and Sa of micro holes have been studied in micro electrical discharge drilling. The high aspect ratio blind micro holes were drilled on titanium alloy (Ti-6Al-4V) with cylindrical tungsten tool electrodes. The experimentation was carried out adopting a full factorial design (33). The simultaneous effects of machining parameters on responses were analysed using response surface methodology. Multiple linear regression models were developed for responses to obtain the correlation between machining parameters and machining outputs. Multi-objective optimization has been performed with the aid of the desirability function approach.
Effect of Honing Parameters on Generated Surface Quality of Cylinder Liner within Automotive Engine Production
Authors: Vrabel' Marek , Maňková Ildikó , Durakbasa Numan M.
Published: August 2017

One of the key parameter in evaluation of cylindrical surface quality of the engine liners is surface roughness. A large number of process factors affecting a final surface topography, which has direct impact on fuel consumption and CO2 emission. A suitable choice of honing conditions can results not only to better surface quality, but it can contributes to reducing of environmental impacts in automobile transport. Twelve different engine cylinder liners were machined in various combinations of cutting parameters. Experimental testing was realised on real production machine tool, where process factors were cutting speed, machining allowance and stone pressure of honing tool. All factors have 4 levels and parameters of surface roughness CR, CF, CL were selected as a variables and suitable indicators for surface quality assessment. The results show that influence of the tool stone pressure on honed surface is more significant than effect of cutting speed. Effect of machining allowance is negligible as well.
Machining Efficiency Increase when Nickel Based Alloy Machining
Authors: Matras Andrzej , Zębala Wojciech
Published: August 2017

Paper presents some investigations, concerning simulation of the nickel based alloy machining. The aim of the research was an optimization of the cutting data for the purpose to increase the machining efficiency and stabilization of the tangential component of the total cutting force at the assumed level. A dedicated physical material model was built and then included to the simulation strategy. Authors demonstrated the influence of the feed rate optimization on the tangential component of the total cutting force value changes and the chip area and in this way the improvement of the cutting process.
Comparison of Theoretical and Real Surface Roughness in Case of Ball-End Milling
Authors: Mikó Balázs , Tóth Balázs , Varga Bálint
Published: August 2017

In case of free form surface milling the quality of the manufacturing is described by the accuracy of the shape and the surface roughness. The 3D surface finishing milling by ball-end milling cutter is one of the most often used machining technologies. In case of ball-end milling the surface roughness can be described theoretically based on the tool diameter and the density of the tool path, but the experience shows than other parameters have effect on the surface roughness. In the article the effect of the different cutting parameters, like feed (fz), depth of cut (ap) and width of cut (ae), is presented in case of plane surface, and the surface roughness is compared with the theoretical roughness, and an estimation method is presented.
Deformation and FEM Analysis of the Chip Root in Face Milling Process
Authors: Pokorný Peter , Zaujec Rudolf , Šimna Vladimír , Vopát Tomáš
Published: August 2017

This paper was focused on analysis of deformation process in the chip root after milling of material C45. The aim of research was to evaluate the degree of deformation by using the method of oriented test lines. Experimental value of degree of deformation was compared to achieve in computer simulation of milling process in Deform software. The results from the chip root indicates of little differences between simulations and experimental obtained value of degree of deformation.
Computer Aided Concept Building
Authors: Takács Ágnes
Published: August 2017

The paper presents the results of a research that defined the weaknesses of design methodology. The end of the research project that suggests solutions for the determined weaknesses is a software that is suitable for efficient application in a very early phase of the design process, in conceptual design. It can be beneficial for mechanical engineers in the world today when we have got everything except for time and money.
An Ontology Based Semantic Machine Tool Selection for Multi Scale Wire EDM Processes
Authors: Sadigh Bahram Lotfi , Oliaei Samad Nadimi Bavil , Dadvandipour Samad
Published: August 2017

Manufacturing high-tech complex products which contain multi-scale complex features without outsourcing considering company's capabilities is quite difficult. Outsourcing some processes to other independent companies is a crucial step toward fabricating a product. To find the most suitable partner company several critical parameters should be considered including company machine-park, skilled personnel, infrastructure, etc. Having comprehensive information about necessary machine tool(s) to outsourcing related manufacturing process is essential. Focusing on Wire Electro Discharge Machining (WEDM) process, the objective of this paper is to introduce a platform to store and analyze information and data about part(s) and machine tools and show out coming results as a list of capable machine tools to produce the desired parts with multi-scale features.
Indirect Impacts of Drastic Scrap Rate Reduction on Costs of Production Process in Precision Machining
Authors: Molnar Viktor
Published: August 2017

The Lean Six Sigma (LSS) conception and other solutions in modern manufacturing and management systems have rapidly spread in precision machining in the last decades. Cost components related to quality control of precision parts are analyzed in the paper on the basis of the cutting edge LSS approach. An optimization framework intended to increase the efficiency of production process planning is introduced. The model helps in calculating economic profit, which differs from accounting profit with the extent of opportunity costs. It is found that drastic reduction of the scrap rate, though increasing customer satisfaction, is not always a proper solution due to the extent of quality cost. The applicability of the elaborated framework was tested and some promising results gained during managerial interviews are also summarized in the paper.
The Effect of Machining Toolpath on Surface Roughness and Dimensional Accuracy for High-Speed Micro Milling
Authors: Dadgari Amin , Huo De Hong , Swailes David
Published: August 2017

This paper investigates different machining toolpath strategies on machining efficiency and accuracy in the micro milling of linear and circular micro geometric features. Although micro milling includes many characteristics of the conventional machining process, detrimental size effect in downscaling of the process can lead to excessive tool wear and machining instability, which would, in turn, affects the geometrical accuracy and surface roughness. Most of the research in micro milling reported in literature focused on optimising specific machining parameters, such as feed rate and depth of cut, to achieve lower cutting force, better surface roughness, and higher material removal rate. However, there was little attention given to the suitability and effect of machining tool path strategies. In this research, a tool path optimisation method with respect to surface roughness and dimensional accuracy is proposed and tested experimentally. Various toolpath strategies, including lace(0°), lace(45°), lace(90°), concentric and waveform in producing linear and circular micro geometric features were compared and analysed. Experimental results show that the most common used strategies lace(0°) and concentric reported in the literature have provided the least satisfactory machining performance, while waveform toolpath provides the best balance of machining performance for both linear and circular geometries. Hence, at process planning stage it is critical to assign a suitable machining toolpath strategy to geometries accordingly. The paper concludes that an optimal choice of machining strategies in process planning is as important as balancing machining parameters to achieve desired machining performance.
Influence Analysis of Micro-Milling Vibrational Phenomena on Workpiece Topomorphy
Authors: Stergianni Evlampia , Sagris Dimitrios , Tsiafis Christos , David Constantine , Tsiafis Ioannis
Published: August 2017

In metal machining processes, it is necessary to study the vibration phenomena which take place in cutting area between the cutting tool and the workpiece in order to ascertain the factors that affect them. Subject of this paper is the analysis of the influence of vibration phenomena during micro-milling on chip formation mechanisms and thereby on the workpiece topomorphy. In particular, the cutting parameters, such as the cutting speed, the feed rate and the axial cutting depth, which affect the workpiece topomorphy are experimentally studied. Based on cutting force measurements correlated with the workpiece topomorphy under various cutting process parameters useful results are extracted. In this way, the impact of vibration phenomena, taking place in micro-milling due to the cutting process, on the workpiece topomorphy can be evaluated.
Integration of Process Mechanics and Materials Mechanics for Precision Machining
Authors: Liang Steven Y. , Pan Zhi Peng
Published: August 2017

On process mechanics, the mechanical and thermal stresses and their distributions within the material as imposed by machining is essential, and on materials mechanics, the crystal plasticity and microstructural dynamics of recrystallization, texture evolution, phase field variation, as well as constitutive of flow stress and other properties play pivotal roles. Furthermore, mechanical, thermal, and even chemical stresses imposed by machining effect the evolution of part microstructure and bulk properties, but on the other hand the materials microstructure can also change the flow stress characteristics and heat generation mechanics of machining. This process-materials interaction of bilateral nature is not clearly understood in the current literature. This paper outlines an iterative blending scheme to factor in both the process mechanics and materials mechanics in one analysis platform to facilitate the predictive modeling and planning of precision machining. The integration of the two mechanics domains combines macroscopic analysis of contact plasticity and moving heat source with the microscopic analysis of constitutive and homogenization modeling, to achieve a holistic descript of precision machining thus supporting process design and optimization. Steels, and titanium alloys are discussed as example material families in machining.
In-Plane Longitudinal Cutting in Single-Crystal Silicon Wafer Surface Micromachining
Authors: de los Reyes Ronald Allan S.
Published: August 2017

The current concept of grinding or abrasive machining involves the formation and removal of segmented strips of material termed chips from the surface of the solid. A novel cutting mechanism is hereby presented in this research study that suggests that the generation of chips from the surface does not occur but only a shearing process that splits material creating added surface features and textures in the silicon surface. This arises from the unique set of factors of abrasive grit size, thrust force, polishing speed, and polishing time that lead to phase transformations in the surface layers of the silicon wafers. Statistical analysis of the factor effects yielded results that show the surface roughness values, Ra and Rz, increasing without any appreciable change in the thickness of the silicon wafers. This can be attributed to the proposed cutting mechanism indicating that only in-plane surface shearing occurred due to the change of the silicon crystal structure from exhibiting brittle behavior to that of ductile mode of deformation. Moreover, experimental quantities of the specific energy for surface machining of silicon was calculated with an overall mean of 50.5 GPa. This is about 33% less than the currently accepted value and can be considered further evidence that polymorphic transitions to a softer material occurred rendering the surface layers more susceptible to longitudinal cutting deformation and fracture. A model based on the inverted spherical cap or spherical bottom geometry for the individual abrasive particle is also proposed, verified by a finite element method analysis simulation, that can mathematically describe this particular micromachining process.
Screening of Important Variables of Organic Acids Degradation by Phanerochaete chrysosporium Using Plackett-Burman Design in Refractory Arsenic-Bearing and Carbonaceous Gold Ores
Authors: Liu Qian , Yang Hong Ying , Tong Lin Lin , Peng Jing
Published: August 2017

In this study, the important variables of organic acids degradation with Phanerochaete chrysosporium were selected in refractory arsenic-bearing and carbonaceous gold ores. The eight variables of fungal degradation of carbonaceous matter were confirmed by the previous single factor experiments, which were guaiacol concentration, dextrin concentration, tween-80 concentration, oxalic acid concentration, hydrogen peroxide concentration, pulp density, fungal concentration and action time. The most important factors influencing organic acids degradation (p < 0.05), as identified by a two-level Plackett-Burman design with above-mentioned eight variables, were pulp density, oxalic acid concentration and action time. The pulp density could influence the effective contact area between organic acids and fungi, the shear stress and the mass transfer efficiency of degradation system. Oxalic acid could affect the fungal growth and the enzymes activity by adjusting pH value of degradation system. Organic acids could not be fully degraded when the fungal action time was the very short or excessively long. A long action time could lead to the lack of nutrients and the accumulation of toxic and harmful substances.
Microbial Community Analysis inside a Biooxidation Heap for Gold Recovery in Equador
Authors: Aspiazu Carlos L. , Aguirre Paulina , Hedrich Sabrina , Schippers Axel
Published: August 2017

In a mine owned by the company Orenas S.A. (Equador), a biooxidation process for gold recovery has been developed. Refractory gold ore was crushed, milled and 500 ton of flotation concentrate was agglomerated by coating a support rock. This was piled up on a liner and the biooxidation process in the heap of 35x25x6 m3 was run for approximately 150 days. The oxidized material was subsequently removed for further processing. An outcrop allowed for depth dependent sampling of altogether 36 samples at three sites over the complete depth of 6 m. The fine fraction was removed from the host rock and sent to the laboratory for analysis of the microbial community. The pH ranged between 2.2 and 2.9. Total cell counts determined via counting under a fluorescence microscope after SYBR Green staining indicated a high microbial colonialization of the heap in all depths between 106 to 109 cells per g concentrate, however the highest cell numbers were mainly found in the upper 50 cm. Most-probable-number determination of living, acidophilic iron (II)-oxidizers for one site also revealed a decrease of cell numbers with depth (between 104 to 108 cells per g concentrate). Further molecular analyses of the community composition based on extracted DNA and 16S rRNA gene analyses by TRFLP and qPCR revealed a complex archaeal and bacterial community within the heap. It can be stated that an active community of acidophiles runs the biooxidation process in all sampled parts of the heap.
A Comparison of Bioleaching Behavior of Two Pure Chalcopyrite Minerals through Investigating Chalcopyrite Crystallographic Properties
Authors: Zhang Yan Sheng , Zhang Jia Ming , Zhang Bo , Chang Ke Xin , Wang Jun , Xie Jian Ping , Qin Wen Qing , Qiu Guan Zhou
Published: August 2017

Chemical element analysis and X-ray diffraction (XRD) analysis showed that the two chalcopyrite minerals were of high purity. A mixed culture of moderately thermophiles was used for chalcopyrite bioleaching at 45°C and the copper recovery of chalcopyrite (a) and chalcopyrite (b) was 66.1% and 21.4%, respectively, after 19 days of leaching. Bioleaching behavior of the two different chalcopyrite samples was studied through comparing the lattice parameter and grain size of chalcopyrite. It was shown that lattice parameter and grain size are not the key factors affecting the leaching of chalcopyrite. The corrosion current density of chalcopyrite (a) calculated through Tafel curves was 1.149 μA/cm2, while that of chalcopyrite (b) was only 0.5696 μA/cm2. The higher corrosion current density suggested that chalcopyrite (a) can be more easily dissolved than chalcopyrite (b).
Research on Bio-Leaching of Nickel-Bearing Tailings in Jilin, China
Authors: Wang Xin , Yang Hong Ying , Tong Lin Lin , Jin Zhe Nan , Zhao Su Xing
Published: August 2017

Gradually bio-metallurgy technology is becoming an irreplaceable new technology. The nickel-bearing tailings in Jilin, China contains Ni 0.13 %, Cu 0.03%, Co 0.01%, S 15.20%, Fe 6.30%. A comparative study of the HQ0211 bacteria, indigenous bacteria (after the domestication named ZXJE511 bacteria) and acid pool leaching revealed that the local species ore leaching was preferably the best way. At pH 2.0, room temperature (about 23°C), pulp density 20%,the Ni, Co and Cu leaching rates were 70.08%, 40% and 57.67 % , respectively ,after 38 days of bioleaching, proving the superiority of the bacterial leaching of Ni, Co, Cu from tailings. Biological leaching tailings solved the problem of the conventional methods which could not be addressed by acid leaching. This technology is environmentally friendly and can make maximum use of the resources, thereby avoiding the waste of the resources.
Comparative Variants of Microbial Pretreatment and Subsequent Chemical Leaching of a Gold-Bearing Sulphide Concentrate
Authors: Spasova Irena , Nicolova Marina , Georgiev Plamen , Groudev Stoyan
Published: August 2017

A sulphide concentrate containing 31.4% total sulphur (in which 30.7% was sulphidic), 31.8% iron, 8.0% arsenic, 18.5 g/t gold and 32.9 g/t silver finely disseminated in pyrite and arsenopyrite as the most essential components was subjected to microbial pretreatment to expose the precious metals from the sulphide matrix. Three different types of microbial cultures were tested for their ability to oxidize the sulphides and to expose the precious metals for the subsequent chemical leaching: mesophilic chemolithotrophic bacteria with a temperature optimum for their growth and activity at about 32 – 37°C, moderate thermophilic bacteria with the relevant optimum at 53 – 59°C, and hyperthermophilic archaea at 75 – 84°C. The microbial pretreatment of the concentrate was carried out in reactors with mechanical stirring and enhanced aeration by air enriched in CO2. It was found that sulphide oxidation of about 40 – 45 % was sufficient for achieving gold extraction higher than 90% during the subsequent leaching of the pretreated concentrate by different gold-solubilizing reagent (cyanide, thiourea, thiosulphate). The highest rate of sulphide oxidation was achieved by a mixed culture of hyperthermophilic archaea at 82°C but at relatively low pulp densities (within 7 – 9%). At higher pulp densities (within 10 – 25%) the highest rates were achieved by means of moderate thermophilic bacteria at 57 – 59°C.
Biological Production of Copper Sulfide Concentrate from Flotation Tailings and Low Grade Ore
Authors: Zepeda Víctor J. , Nancucheo Ivan , Guillen Milton , Becerra Enrique , Escuti Camila , Cautivo Dina , González Daniella , Colipai C. , Demergasso Cecilia , Galleguillos Pedro A.
Published: August 2017

Flotation tailings are hazardous due to physical and chemical instability and are currently considered one of the main pollution concerns of mining industry. Most of these tailings are fine-grained residues with low copper content (0.1-0.8%) and include toxic compounds, such as heavy metals, arsenic, and flotation reagents, among others. Another hazard is the generation of acid mine drainage (AMD) due to biological oxidation of tailings. On the other hand, low-grade ore is challenging the mining industry to commercially produce copper.The main objective of this work was to assess the use of flotation tailings and low-grade ore to produce a biologically-produced copper sulfide, as a product for further pyrometallurgical or fine chemistry processing. Low-grade ore and flotation tailings were first agglomerated at different proportions and leaching tests were performed in 1m columns, using either industrial or synthetic raffinate solution. Then, the PLS solution obtained from the column tests was subjected to selective precipitation of copper by using biogenic hydrogen sulfide (H2S) generated by a mixed culture of neutrophilic sulfate reducing bacteria (SRB), enriched from sediments of Caracarani river (located at 4,600 m over sea level in northern Chile).Over 91% of the copper soluble present in the PLS was recovered as copper sulfide in 28 days, while ferrous iron, other metals and arsenic remained in solution. Analysis performed by XRD confirmed the presence of copper in the precipitate (58% as covellite). This work demonstrates the possibility to apply bioleaching and bio-precipitation technologies to treat tailings and low-grade copper ore to produce a high quality copper sulfide.
Pyrite Oxidation by Moderately Thermophilic Microorganisms
Authors: Bulaev Aleksander , Labyrich Maria
Published: August 2017

The goal of the present work was to compare the rates of pyrite oxidation by different microorganisms, representatives of the groups predominating in biohydrometallurgical processes. The experiments were conducted in flasks with 100 mL of the medium containing mineral salts, 0.02% of yeast extract, and 2 g of pyrite at 45°C on rotation shaker (200 rpm) for 30 days. Strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans VKMV 1269T, and Acidiplasma sp. MBA-1 were used in the study. Different combinations of the strains were used in the experiments (pure cultures of S. thermosulfidooxidans VKMV 1269T, Aсidiplasma sp. MBA-1, A. caldus MBC-1, as well as mixed cultures S. thermosulfidooxidans VKMV 1269T + A. caldus MBC-1, Aсidiplasma sp. MBA-1 + A. caldus MBC-1, S. thermosulfidooxidans VKMV 1269T + Aсidiplasma sp. MBA-1). Iron concentrations in the medium were the highest in the variants “S. thermosulfidooxidans VKMV 1269T + A. caldus MBC-1”, “Aсidiplasma sp. MBA-1 + A. caldus MBC-1”, and “Sb. thermosulfidooxidans VKMV 1269T + Aсidiplasma sp. MBA-1” and achieved 3.8, 3.5, and 3.3 g/L, respectively. Iron concentration in sterile control as well as in the experiments with pure cultures of Aсidiplasma sp. MBA-1 and A. caldus MBC-1 were very low. It demonstrated that in these variants pyrite was almost not oxidized. In the experiment with the pure culture of S. thermosulfidooxidans VKMV 1269T, the rate of oxidation was high during 10 d of the experiment but then the oxidation activity drastically decreased. The ferric iron concentration achieved a maximum of 1.8 g/L and then decreased, whereas the ferrous iron concentration began to increase. Revealed differences in pyrite oxidation rates can be explained by differences in the physiological properties between the microorganisms. Results of the present work suggest that different groups of microorganisms have different impact in pyrite biooxidation.
Investigating the Microbial Metabolic Activity on Mineral Surfaces of Pyrite-Rich Waste Rocks in an Unsaturated Heap-Simulating Column System
Authors: Makaula Didi , Huddy Robert J. , Fagan-Endres Marijke A. , Harrison Susan T.L.
Published: August 2017

Microbial association with and colonisation of mineral surfaces plays a key role in enhancing the extraction of metals from ores during heap bioleaching processes. On the other hand, if uncontrolled, the same association can also lead to the generation of acid rock drainage (ARD) effluents from mine waste. This study aims to measure microbial metabolic activity of a mixed mesophilic culture on the surfaces of pyrite-bearing waste rocks of different grades over time. The waste rocks are milled, size fractionated and coated onto glass beads, to provide a defined surface area. The metabolic activity on the mineral surface is measured with isothermal microcalorimetry (IMC) complemented with scanning electron microscopy (SEM) and analysis of solution chemistry to measure leach agents and metal release into the pregnant leach solution (PLS). The waste rock samples showed a similar degree of leaching when the solution chemistry was analysed, despite having different sulphide content. However, when metabolic activity of the micro-organisms on the mineral surface was measured, greater activity was seen with higher sulphide content. This data informs an ongoing study to establish a flow-through configuration of the biokinetic test for ARD prediction accounting for both leach solution and microbial-mineral interaction as well as differing kinetics of acid-neutralising and generating reactions to enable the refinement of the current batch method.
Reductive Dissolution of a Lateritic Ore Containing Rare Earth Elements (REE) Using Acidithiobacillus Species
Authors: Nancucheo Ivan , Johnson D. Barrie , Lopes Manoel , Oliveira Guilherme
Published: August 2017

Lateritic deposits containing rare earth elements (REE) are important resources in Brazil, where monazite is the main REE-bearing mineral and is frequently associated with iron hydroxy-oxides and quartz. In order to recover valuable metals such as REE and uranium, experiments were carried out under reductive mineral dissolution using Acidithiobacillus species. In terms of phosphate, aerobic reductive dissolution at pH 0.9 using A. thiooxidans extracted about 35% of that present in the ore which is and indicator of the dissolution of monazite. Although only ~9% of the cerium and 5% of the lanthanum were extracted, ~72% of the uranium was solubilized, indicating that it was more susceptible to extraction by reductive dissolution than the other two REE.
Effect of Temperature Ramping on Stirred Tank Bioleaching of a Copper Concentrate
Authors: Hedrich Sabrina , Joulian Catherine , Graupner Torsten , Schippers Axel , Guézennec Anne Gwénaëlle
Published: August 2017

Kupferschiefer-type ore represents an important source for base metals and several studies concerning the bioleaching of black shale ores and Cu concentrates have been carried out with focus on various microbial communities and processing parameters. However, the incomplete dissolution of chalcopyrite remains a key issue for copper ore bioleaching improvement and requires further investigations in order to ensure an optimal control of the process for upscaling. Our study clearly showed that bioleaching tests are characterized by two separate phases with a distinct optimal temperature. A distinct effect of the temperature on the copper recovery and the advantage of temperature ramp in order to enhance copper bioleaching and chalcopyrite dissolution were demonstrated.
Mineralogical Dynamics of Primary Copper Sulfides Mediated by Acidophilic Biofilm Formation
Authors: Bobadilla-Fazzini Roberto A.
Published: August 2017

Bioleaching of copper sulfides is catalyzed by iron-and sulfur-oxidizing acidophilic microorganisms attached to the mineral surface forming a biofilm. However, the link between copper sulfides bioleaching and biofilm formation is not yet fully understood. Understanding the factors that are limiting the bioleaching kinetics for different copper sulfide minerals through exhaustive mineralogical analysis of the mineral surface with concomitant biofilm formation during the leaching process will deliver new process conditions with enhanced kinetics and higher copper recovery. In this work we have developed and standardized a reproducible flow cell method able to mimic heap/dump bioleaching laminar flow conditions to study the mineralogical dynamics by advanced mineralogical analysis including QEMSCAN and SEM-EDS coupled to biofilm formation analysis. Based on this method, the bioleaching mineralogical dynamics of primary copper sulfides (enargite (Cu3AsS4), chalcopyrite (CuFeS2) and bornite (Cu5FeS4)) have been determined in the presence of biofilm formation. Supported by the observed mineralogical dynamics, different mechanisms of dissolution for bioleaching were observed as well as selective biofilm formation over the mineral surface, showing enhanced conditions for copper recovery.
Genetic Basis of Metal Resistance in Acidiphilium sp. DSM 27270 (Yenapatur)
Authors: Issotta Francisco , Bobadilla-Fazzini Roberto A. , Moya-Beltrán Ana , Covarrubias Paulo C. , Quatrini Raquel , Martinez Patricio
Published: August 2017

Acidiphilium sp. DSM 27270 (Yenapatur) forms part of a microbial consortium isolated from copper mines in Chile, that is currently used in state of the art industrial-scale biotechnology. Its taxonomic assignment is still tentative and is metal resistance and homeostatic responses poorly characterized. Here we report the genomic taxonomy evaluation of the Yenapatur strain and the preliminary characterization of its metal resistance and homeostatic responses. The genome of Yenapatur was re-assembled, annotated and compared to other sequenced strains of the genus. Genomic signatures were derived to better define the taxonomy of the strain. The minimum inhibitory concentrations of diverse cations and anions (Cu (II), Fe (II), Mg (II), Mn (II), Zn (II), Al (III), As (III), Fe (III), chloride and nitrate) were determined. Known resistance determinants were profiled in the genome of Yenapatur and publically available sequenced Acidiphilium strains. Results are presented and discussed under the light of the operational conditions in which Yenapatur thrives.
Microorganisms Oxidize Iron (II) Ions in the Presence of High Concentrations of Sodium Chloride - Potentially Useful for Bioleaching
Authors: Huynh Dieu , Kaschabek Stefan , Sand Wolfgang , Schlömann Michael
Published: August 2017

Acidophilic leaching microorganisms have been reported to be in general intolerant to high salinity, namely high concentrations of chloride. At present this restriction hampers the use of sea water for bioleaching technology. Enrichment cultures obtained in this study from a former ore deposit near the Spanish coast oxidize ferrous iron in the presence of up to 50 gL-1 NaCl at pH 2.5 and 37°C. The presence of at least 5 gL-1 NaCl was shown to be an obligate requirement for iron oxidation. The major microbial groups comprise Alicyclobacillus and Arthrobacter. The findings may be of biotechnological relevance.
Enzymatic Pre-Treatment of Carbonaceous Matter in Preg-Robbing Gold Ores: Effect of Ferrous Ion Additives
Authors: Konadu Kojo T. , Sasaki Keiko , Osseo-Asare Kwadwo , Kaneta Takashi
Published: August 2017

The bio-treatment of double refractory gold ores (DRGO) to reduce preg-robbing needs to account for the heterogeneity of the ore so as to acquire a much more complete picture of the system. To this end, the effects of ferrous ion additives on the degradation of powdered activated carbon (PAC) by cell-free spent medium (CFSM) was studied. Au(CN)2- adsorption and Raman spectrometric results suggest that the ferrous salt could have possibly reacted with some biogenic hydrogen peroxide to aid in the degradation of PAC. The bio-treatment produced mixed solid residues containing some partially degraded aromatic compounds which were soluble in alkaline solutions. Ultimately, biodegradation of PAC using CFSM in the presence of 50 µM FeSO4.7H2O for 7 days followed by washing with 3 mM NaOH reduced Au(CN)2- uptake by 80%.
Revisiting the Chrome Azurol S Assay for Various Metal Ions
Authors: Mehnert Marika , Retamal-Morales Gerardo , Schwabe Rïngo , Vater Sabine , Heine Thomas , Levicán Gloria J. , Schlömann Michael , Tischler Dirk
Published: August 2017

Siderophores play an important role in the solubilisation and mobilization of iron (III) and various metal ions. To have a useful method to test siderophores in culture supernatants for their metal binding affinity, we redesigned and optimized the liquid CAS-assay for selected metal ions. CAS-assay solutions were calibrated with desferrioxamine B in different concentrations to calculate DFOB-equivalents to get a semi-quantitative evaluation. With these assay solutions, we were able to test siderophores in culture supernatants for their ability to chelate with Fe, Al, Ga, Cu, V and As.
Diversity of Thermophilic Iron-Pyrite-Oxidizing Enrichments from Solfataric Hot Springs in the Chilean Altiplano
Authors: Barahona Sergio , Cortés Johanna , Hengst Martha , Dorador Cristina , Remonsellez Francisco
Published: August 2017

Relatively little is known about the microbial communities present in natural environments that meet physico-chemical conditions for the development of potential leaching microorganisms such as thermal ecosystems from the Chilean Altiplano. Thermophilic leaching enrichments were obtained and identified from a high altitude solfataric pound in Lirima hot springs in the Chilean Altiplano. This ecosystem is characterized by hot underground freshwaters, enriched in sulfur compounds showing pH from neutral to acidic. Microbial diversity has been scarcely explored here, and preliminary results demonstrate that hydrothermal pounds are represented by thermophilic anaerobic and acidophilic taxa. Thermophilic leaching cultures in shake flasks were obtained using ferrous iron and pyrite as energy source. The presence of Bacteria and Archaea in oxidizing enrichments was determined by PCR amplification of 16S rRNA genes. A preliminary analysis of microbial diversity using massive sequencing revealed that Bacteria were more abundant than Archaea in both enrichments. Specifically for the iron-oxidizing culture, the majority of the sequences clustered within the Proteobacteria phylum (79%). Among Proteobacteria, the proportion of Betaproteobacteria (42.2%) and Gammaproteobacteria (21.27%) was much higher than that of Alphaproteobacteria (15.5%). Within the Betaproteobacteria class, the most frequent genus was Leptothrix-like. Similar results were obtained for the pyrite oxidizing culture. Interestingly, this study shows the presence of microorganisms close to the Leptothrix genus under low pH conditions (1.7-2.8) and their capacity to grow at high temperatures with ferrous iron or pyrite as sole energy source
Leaching of Pyrite by Acidithiobacillus ferrooxidans Monitored by Electrochemical Methods
Authors: Saavedra Albert , Cortón Eduardo
Published: August 2017

The aim of this work was to use electrochemical methods, capable to follow the corrosion of minerals, in order to monitor the progressive attack of the bacteria on the mineral. The assay was performed in a three electrode cell, with pyrite as the working electrode. The tests were performed in the absence and presence of iron; when present it was in low concentration. In order to compare the bacterial attack with other conditions, the study was conducted in three systems: live bacteria in culture media, dead bacteria in culture media, and sterile culture media, used as a control. The initial bacterial concentration was 106 bact.mL-1. To follow the process, current and corrosion potential were calculated. Live bacteria system showed a continuous increase of current with respect to the incubation time, being up to 4-times higher in the condition with iron (the corrosion current is related to the increase of the mineral area, produced by the bacterial attack, which was corroborated identifying by SEM the bacterial fingerprint on the mineral). Dead bacteria and sterile culture medium showed no current increase with respect to time. In addition, voltammetric studies shown that in live bacteria system the surface area increased when the biofilm was present. Whereas, in the dead bacteria system only the presence of some organic compounds interacting with the mineral was detected. The controls (sterile culture medium) showed the presence of iron hydroxides complexes and elemental sulfur, product of chemical leaching and the initial phase of a passivation process.
With this study we demonstrated that the leaching process can be monitored by electrochemical methods, where the process of bacterial-mineral interaction could be followed, and also simultaneously identifying the initial processes of passivation. Our work can be useful for the development of a device for the in situ monitoring of biomining processes.