Showing papers in "Advanced Materials Research in 2007"

Talvivaara Black Schist Bioheapleaching Demonstration Plant

Abstract: Talvivaara complex multi-metal black schist deposit in Sotkamo, Finland, is the largest known sulfide nickel deposit in Europe with 340 million ton of classified resources. The mine can be operated for a minimum of 25 years with an annual nickel output of over 30 000 ton, which is about 2,5 % of the global production of primary nickel. Significant amounts of zinc, copper and cobalt can also be produced. In summer 2005, a 50 000 ton demonstration plant was constructed to the mine site. A representative ore sample was mined, crushed to 80 % -8 mm, agglomerated and built to a two-part heap (8 m high, 50m times 80 m). Irrigation of the heap was started in August 2005. The pilot heap was inoculated with indigenous bacteria collected from the site. The amount of bacteria in the pregnant leaching solution has been in the range of 106 – 108 cells/ml. The bacteria involved are mesophilic and thermophilic ones. The start-up of the solution flow resulted soon in elevated temperatures of over 50 0C in the pregnant leaching solution. The rise is due to the oxidation of the large quantity of pyrrhotite and pyrite in the ore. The elevated temperatures have also been maintained over the boreal winter conditions. Metal recovery was started in November 2005. At the end of the year 2006 94 % of Ni, 83 % of Zn, 3 % of Cu and 14 % of Co have been recovered. The demonstration plant is still running. The study has proven that Talvivaara black schist ore is well suited for bioheapleaching. Building of the mine will start in spring 2007, bioheapleaching in summer 2008 and the metal recovery plant in autumn 2008, if everything proceeds according to the plans.

Hemp Fibre Reinforced Poly(Lactic Acid) Composites

Abstract: The potential of hemp fibre as a reinforcing material for Poly(lactic acid) (PLA) was investigated. Good interaction between hemp fibre and PLA resulted in increases of 100% for Young’s modulus and 30% for tensile strength of composites containing 30 wt% fibre. Different predictive ‘rule of mixtures’ models (e.g. Parallel, Series and Hirsch) were assessed regarding the dependence of tensile properties on fibre loading. Limited agreement with models was observed. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) studies showed that hemp fibre increased the degree of crystallinity in PLA composites.

Effect of Particle Size on Some Properties of Rice Husk Particleboard

Abstract: The purpose of this study was to determine the effect of particle size on the mechanical properties (Modulus of Elasticity, Modulus of Rupture, and Internal Bond) and physical properties (thickness swelling and water absorption) of rice husk particleboard. The particle sizes used were 1.0mm, 1.18mm, 2mm, 2.36mm and 2.80mm. Each was mixed with a constant resin (urea formaldehyde) concentration of 20% of oven dry weight of rice husk particles. The results showed that as the particle size increased, the particleboard’s mechanical and physical properties decreased. For example, the modulus of elasticity, modulus of rupture, internal bond, thickness swelling and water absorption for 1.0mm particle size particleboard were 1590N/mm2, 11.11N/mm2, 0.28N/mm2,10.90% and 38.53% respectively, while for 2.8mm particle size they were 1958N/mm2,14.2N/mm2, 0.44N/mm2, 11.51% and 47.21% respectively. Overall results showed that particleboard made from rice husk exceed the EN standard for modulus of elasticity, modulus of rupture, internal bond. However, thickness swelling values were poor. Hence, the smaller the particle size the better the properties of the particleboard.

Comparative Study of Biogas Production from Five Substrates

Abstract: In this work, a comparative study of biogas production from poultry droppings, cattle dung, kitchen waste, fruit waste and vegetable waste was done under the same operating conditions. 3kg of each waste was mixed with 9kg of water and loaded into the 5 constructed digesters. Biogas production was measured using water displacement method for a period of 40 days and at an average temperature of 30.5oC. Results indicated that poultry droppings produced 0.0332dm3/day, cow dung produced 0.0238dm3/day, Kitchen waste produced 0.0080dm3/day, vegetable waste produced 0.0066dm3/day and fruit waste with 0.0022dm3/day. It is concluded that poultry droppings produced more biogas because it contains more nutrients and nitrogen compared with plant and other animal waste

Hydrogen Storage Properties of Mg-Al Alloy Prepared by Super Lamination Technique

Abstract: Microstructures and hydrogen storage properties of Mg-Al super laminate composite alloys were investigated. The laminated sample was made by alternately stacking Mg films and Al films. The laminate was subjected to repetition of stacking and cold-rolling under an ambient condition (super lamination technique), combined with final heat treatment under an argon gas atmosphere. The number of films and thickness was nearly 15000 layers and about 50μm, respectivery. Their microstructures and hydrogen storage properties were studied by scanning electron microscopy, X-ray diffractometry and volumetric method by use of a Sieverts-type apparatus. In heat treatment process at 673K, Mg17Al12 intermetallic compound was formed by interdiffusion. This compound absorbed and desorbed hydrogen reversibly through the disproportionation and recombination react at 673K.

Monitoring of Microbial Community Inhabiting a Low-Grade Copper Sulphide Ore by Quantitative Real-Time PCR Analysis of 16S rRNA Genes

Abstract: Microbial heap bioleaching is being used as an industrial process to recover copper from low grade ores. It is known that a consortium of different microorganisms participates in this process. Therefore identification and quantification of communities inhabiting heap bioleaching operations is a key step for understanding the dynamics and role of these microorganisms in the process. A quantitative real-time PCR approach was used to investigate the microbial dynamics in this process. To study the microbial population inhabiting a low-grade copper sulphide ore bioleaching industrial heap process at Escondida Mine in Chile, 16S rRNA genetic libraries were constructed using bacterial and archaeal universal primers. Phylogenetic analyses of sequences retrieved from genetic libraries showed that the community is mainly composed by microoganisms related to Acidithiobacillus ferrooxidans (2 strains), Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, Leptospirillum ferriphilum and the archaea Ferroplasma. Specific primers for real-time PCR determination were designed and tested to amplify each of the sequences obtained by cloning. Standard curves for real time PCR were performed using plasmid DNA from selected clones. This methodology is actually being used to monitor relevant microorganisms inhabiting this low-grade copper sulphide ore bioleaching industrial heap.

Control of degradation of biocompatible magnesium in a pseudo-physiological environment by a ceramic like anodized coating

Abstract: Magnesium alloys are potential biodegradable implant materials. However, magnesium alloys normally corrode rapidly in the in-vivo fluid, resulting in subcutaneous gas bubbles and alkalisation of the in-vivo solution. The paper presents a new approach to control the degradation rate of magnesium in a simulated body fluid (SBF) through employing a recently developed anodising technique. It was found that the ceramic like anodised coating formed on the surface of magnesium can effectively slow down the biodegradation process and hence result in slow hydrogen evolution and solution alkalisation processes. The results imply that an anodised magnesium alloy may be successfully used as a biodegradable implant material.

I-V Characteristics for Bifacial Silicon Solar Cell under a Magnetic Field

Abstract: In this work, the influence of magnetic field on I-V characteristics of bifacial silicon solar cell n+-p-p+ structure is studied under constant multispectral illumination. After resolution of continuity equation related to photogenerated minority carriers’ density in the base region of this cell, MATLAB numerical simulations of excess minority carriers’, photocurrent densities and junction photovoltage profiles, have been developed with magnetic field in the bulk of the base region. In the same way, the IV characteristics have been studied with magnetic field. It has been demonstrated that the I–V characteristics decreased. It also has shown how the I–V characteristics changed.

The Effect of Alloying Elements on the c/a Ratio of Magnesium Binary Alloys

Abstract: In order to clarify the effect of alloying elements on the axial ratio of magnesium binary solid solutions, the solid solutions of Mg-Al, Mg-Zn, and Mg-Li with various concentrations were casted and homogenized. Synchrotron X-ray diffraction patterns were then obtained from annealed powder samples and analyzed using the Rietveld method. The effects of solutes concentration on lattice parameters were explained on the basis of atomic size difference and valence electron effect, which changes electron overlap of magnesium. It has been found in this study that Al and Li raise and reduce the c/a ratio, respectively, while Zn has no effect on the c/a ratio.

Development of Combined Manufacturing Technologies for High-Strength Structure Components

Abstract: Novel manufacturing technologies for high-strength structural components of aluminium allow a local modification of material properties to respond to operational demands. Machining and finishing processes for changing material properties like deep rolling or rubbing are to be combined to a single process step. The intention is the controlled adjustment of the component’s properties by the modification of its subsurface. For that purpose the essential understanding of the interaction mechanisms of the basic processes turning, deep rolling and rubbing is necessary. Influences of the tool geometry as well as of the process parameters on the material properties are investigated. The results will be extended by parameter studies within numerical simulations. Thereafter, combinations of the basic processes in process sequences are analyzed to their ability to modify the subsurface properties. In consideration of these results, a prototypic combined turn-rolling tool is developed

Novel Steel Corrosion Protection by Microbial Extracellular Polymeric Substances (EPS) – Biofilm-Induced Corrosion Inhibition

Abstract: Microbially influenced corrosion (MIC) of steel has gained increasing attention in recent years because the damage caused by this process is a significant cost factor for industry. Consequently, inhibition of corrosion and especially the development of corrosion protective films is an important present-day research topic. In this connection, application of microbially produced EPS for mitigating steel corrosion is an innovative idea. However, observations of ”protective” biofilms on metallic surfaces have been previously reported. Their inhibiting effect is generally thought to be caused by oxygen depletion or the formation of passivating layers. In contrast to many conventional corrosion protective methods, EPS or EPS-derived agents would be a cheap and environmentally friendly solution. Extensive research activities are still required, before biofilms or cell-free EPS can be used for corrosion protection on larger scale. In this study, we are developing a novel EPS-based corrosion protection method for unalloyed and corrosion resistant steel in aqueous media, which is based upon the application of microbial metabolic products. EPS of various sulfatereducing bacteria and other microorganisms are investigated for their inhibiting effect. The extent of such inhibition is evaluated in a model test system, in which different steels are subjected to corrosive conditions under sulfate-reducing conditions. To elucidate the protective mechanisms, comparative analyses of the chemical composition of the applied EPS are performed.

Solar Tracker Technologies: Market Trends and Field Applications

Abstract: Solar energy is increasingly becoming a significant component in the energy profiles of several tropical nations. This paper discusses trends in solar tracking technologies: analyzing the cost of acquisition, domains of application, maintenance costs and efficiency improvements. The paper concludes that hydraulic-based tracking systems are suitable for low capacity installations with low pay loads while polar axis tracking systems offer a performance nearly equal to that of two-axis tracking systems, at the cost of single axis trackers.

Nanoindentation Characterization of Mechanical Properties of Ferrite and Austenite in Duplex Stainless Steel

Abstract: The mechanical properties of as-cast and hot-forging duplex stainless steel samples with the same compositions were characterized by nanoindentation. The effect of surface treating method and working state of the sample on the nanoindentation results of ferrite and austenite were discussed. The results show that the Young’s modulus and hardness of ferrite and austenite may be affected by the treating method of sample surface. The difference of Young’s modulus average of ferrite or austenite between as-cast and hot-forging duplex stainless steel samples is not great, but the hardness average of ferrite or austenite in hot-forging sample is obviously higher than those of as-cast sample. The difference of hardness between ferrite and austenite in the same sample is not great, but the young’s modulus of ferrite is higher than that of austenite.

A Study of the Operating Parameters of a Sulphate-Reducing Fixed-Bed Reactor for the Treatment of Metal-Bearing Wastewater

Abstract: An upflow fixed-bed sulphate-reducing reactor has been set up and monitored for the treatment of metal-bearing wastewater. Zinc has been chosen as the target metal to be sequestered from influent water stream at initial concentrations ranging from 50 to 400 mg/l and initial pH values ranging from 3 to 5. Main operating parameters of the reactor, such as the composition and content of electron donor, electron acceptor, sulphate and metal removal capacity, have been monitored during ten months of continuous operation. The results obtained have shown that the reactor has a considerable capacity of completely reducing sulphates for initial concentrations up to 7,200 mg/l, completely removing soluble zinc for initial concentrations up to 400 mg/l and completely removing Total Organic Carbon (TOC), for initial concentrations up to 1,500 mg/l.

Remediation of Acid Mine Drainage by Means of Biological and Chemical Methods

Abstract: The formation and treatment of acid mine drainage is the biggest environmental problems relating to mining and processing activities in the worldwide. Various methods are used for the sulphates and heavy metals removal from acid mine drainage in the world, but any of them is universal. Main aim of the paper is the interpretation of chemical and biological-chemical methods for the metals and sulphates removal from acid mine drainage sample. The chemical method is based on the sulphates precipitation by the sodium aluminate in combination with the calcium hydrate. The biological-chemical method is based on the application of sulphate-reducing bacteria (SRB). A sample of acid mine drainage from the abandoned and flooded deposit of Smolnik located in Slovak republic was used in this study.

Natural Fibre-Reinforced Thermoplastics Processed by Rotational Moulding

Abstract: Rotational moulding or rotomoulding is a manufacturing process best suited for producing one-piece, hollow plastic products. The raw materials can be in powder or liquid form with linear polyethylene of varying densities being dominant worldwide. Due to the modest material properties of polyethylene, reinforcement in various forms have been incorporated within the rotomoulded components to improve the performance of these products. With the abundance and eco-friendliness of natural fibre resources, this study has focused on the use of sisal and woodfibres along with linear medium density polyethylene (LMDPE) powder to produce rotomoulded composite components. Tensile and impact properties of the rotomoulded natural fibre-reinforced composites have been determined as a function of fibre content.

Biorecovery of Gold from Jewellery Wastes by Escherichia Coli and Biomanufacture of Active Au-Nanomaterial

Abstract: Microbial reduction of Au(III) from HAuCl4 was demonstrated. Escherichia coli and Desulfovibrio desulfuricans reduced 1 mM Au(III) in 60 and 120 min at pH 6.9 and 2.3 respectively. TEM and elemental analysis showed the formation of Au(0) nanoparticles and their pH-dependent cellular localisation. The concept was applied to the recovery of gold from jewellery waste leachates using E. coli. Bio-Au(0) nanoparticles were tested for catalytic activity in the oxidation of glycerol, achieving 30% conversion to glyceric acid. A simple bioprocess for conversion of waste to new material is suggested.

A Ductile UFG Al Alloy via Cryomilling and Quasi-Isostatic Forging

Abstract: Mechanical milling of Al alloy powder in liquid nitrogen leads to a large reduction in the scale of the microstructure and results in material with high thermal stability and strength. However, it is important to consolidate the powder and achieve bulk material with sufficient toughness and ductility for structural applications. In this investigation, hot isostatic pressing, followed by quasiisostatic forging and hot rolling, were performed to fabricate Al 5083 plate with a predominantly ultra-fine grained microstructure. Plate produced in this way possessed enhanced tensile strength and ductility, exceeding that of conventionally processed material.

Biorecovery of Platinum Group Metals from Secondary Sources

Abstract: Since 1998 demand for the platinum group metals (PGM) has exceeded supply resulting in large price increases. Undersupply, combined with rising costs prompts environmentally friendly recycling technologies. Leachates containing PGM were produced from secondary waste sources using microwave leaching technology with the aim of recovering precious metals using bacterial biomass. Previous studies showed that metallised biomass exhibits catalytic activity; hence metal is not only recovered but can be converted into a valuable product. Cells of Escherichia coli MC4100 that had been pre-metallised with Pt were more effective at reducing PGM from the leachates. The solid recovered from the leachate onto the bacteria was characterised using X-ray Powder Diffraction (XRD) and Energy Dispersive X-ray Microanalysis (EDX). Metallised biomass was tested for catalytic activity (reduction of Cr(VI) to Cr(III)) to compare the ‘quality’ of polymetallic bacterial-based catalysts versus counterparts made from single and mixed metal model solutions.

Bioleaching of a Rich-In-Carbonates Copper Ore at Alkaline pH

Abstract: A rich-in- carbonates copper ore was subjected to bioleaching under alkaline pH conditions by means of different microorganisms or their metabolites. The ore contained 1.40% copper, 1.94% sulphur, 3.25% iron and 20.3% carbonates, and had a pH of 8.6 and a highly positive net neutralization potential (325 kg CaCO3/t). Copper was present mainly as different sulphide minerals (bornite, covellite, chalcopyrite). The leaching was carried out by means of the shake-flask technique at 32 oC using finely ground (minus 100 μm) ore. The following microorganisms were used to leach the sample: ammonifying bacteria (related to the genera Bacillus, Acinetocater and Vibrio); heterotrophic bacteria (Acetobacter and Pseudomonas) and fungi (Asperillus niger and Penicillium chrysogenum) producing citric acid; heterotrophic bacteria (Micrococcus, Alcaligenes and Bacillus) producing amino acids (mainly alanine); basophilic chemolithotrophic bacteria (Thiobacillus thioparus, Hallothiobacillus neapolitanus, Starkeya novella; ”silicate bacteria” (Bacillus circulans) producing organic acids and exopolysaccharides; bacteria possessing urease enzymatic activity (Corynebacterium). The best results were achieved by means of a mixed culture of urease-possessing bacteria, which under certain conditions was able to solubilize 64.4% of the copper within 30 days of leaching.

Effects of Processing on the Yield and Physico-Chemical Properties of Cassava Products

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

Deformation Behaviour of Composites Reinforced with Four Different Linen Flax Yarn Structures

Abstract: Four types of yarns were made from flax sliver (Linum usitatissimum) as reinforcements in composites: (1) twist-less, (2) two-fold, (3) high-twist singles and (4) medium-twist singles yarns. Flexural, compressive and tensile properties of the epoxy composites were compared.

Biological Removal of Ions: Principles and Applications

Abstract: Microbial cell – soluble species interactions can be part of technologies for the treatment of metal/metalloid and radionuclide bearing water streams in order to sequester the targeted species. Interactions of microbial cells and soluble targeted species include passive and active processes of metabolically inactive or active biomass, and result in the reduction of their mobility and toxicity. Different parts of the cell may sequester targeted species via processes such as complexation, chelation, coordination, ion exchange, precipitation and reduction. Collectively, these mechanisms have been referred to as sorption and the overall phenomenon as biosorption. The term biosorption is generally used to describe the passive interaction of microbial biomass with targeted species. The technologies based on these processes, lead to the set up of units, mainly in the form of packed bed reactors similar to the configuration of ion exchange resins reactors, placed at the end of a treatment process as a polishing stage. In order to maintain durability of the sorbent, the microbial cells harvested from different sources, are formulated into particles by way of immobilization – pelletization. In the early years of Biosorption, a significant effort was devoted to study the reusability of the sorbent by repeated sorption – desorption cycles, in order to reduce the operating cost of the technology. The availability of the biosorbent material, the reversibility of the desorption process, the presence of competing co-ions and organic molecules, posed significant scepticism and finally serious doubt about the industrial applicability of biosorption as a stand alone technology. However the mechanisms are active and present in biological reactors, and can contribute to overall species sequestering. Biological reactors based on active microbial biomass as alternative to passive sorption, exploit the self regenerating features of living biomass along with the traits of microbial metabolism. Active cells produce metabolites (i.e. EPS, simple inorganic moieties etc.) interacting chemically with the targeted species. The active biomass offers the additional attractive feature of forming biofilms on the surface of carrier materials allowing a natural way of cell immobilization. Different biofilm reactor configurations e.g. static or moving bed filters, fluidized bed reactors, rotating biological contactors support the development of biofilms. Conditions such as temperature, pH, presence of toxic compounds etc. should be considered in the applicability of the technology. Important metabolically mediated immobilization processes for metal/metalloid and radionuclide species are bioprecipitation and bioreduction. Bioprecipitation processes include the transformation of soluble species to insoluble hydroxides, carbonates, phosphates, sulfides or metal – organic complexes as a result of the microbial metabolism. In the case of biological reduction, the cells may use the species as terminal electron acceptors in anoxic environments to produce energy or reduce the toxicity of the cells microenvironment. Such processes form the basis for treatment technologies which are recently developed and applied both in pilot and full scale.

Preparation of CaAl2O4: Eu2+ Long Persistent Blue Phosphor

Abstract: CaAl2O4:Eu2+ with high brightness and long persistent luminescence were prepared by solid state reaction method. The phosphor compositions with varying Eu2+ were investigated by powder X-ray diffractometer (XRD), SEM, TEM, photoluminescence excitation and emission spectra. Broad band UV excited luminescence of the CaAl2O4:Eu2+ was observed in the blue region (λmax = 440 nm) due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. The particle size also plays a role deciding the luminescence characteristics of these phosphors. The decay time of the persistence indicated that the persistent luminescence phosphor has bright phosphorescence and maintains a long duration.

A Novel Process for Lowering the Cost of Titanium

Abstract: Titanium and titanium alloys are the materials of choice for many industrial applications because of their attractive combination of low density, good mechanical properties, and high corrosion resistance, and titanium is the fourth most abundant metal in the earth crust (0.86 % by weight) behind aluminum, iron, and magnesium. However, titanium and titanium alloys are not widely. The reason for this is the high cost of titanium and titanium alloys! The cost gap for titanium and titanium alloys widens when they are used for fabricating components and structures. Consequently, much effort has been expended to reduce the cost of titanium and titanium alloys. In conjunction with the University of Waikato, Titanox Development Limited-New Zealand has been successful in creating a modified novel process to produce TiAl based alloy powders with different particle sizes and compositions at low cost. The process offers several benefits to the titanium industry the most significant one of which is that it displays the potential to significantly reduce the commercial production costs of Ti-Al based alloys. This paper describes the Titanox Development Limited technology in brief, and shows how it can economically produce titanium alloy powders for different industrial applications and making titanium alloys affordable. The process has been disclosed in a PCT (Patent Corporation Treaty) application which was approved in 2004 [1], and the related patent applications either have been approved or are being filed in different countries.

Characterisation of Factors in the Bacterial Leaching of Nickel Laterites Using Statistical Design of Experiments

Abstract: Identifying influential factors in the bacterial leaching of nickel laterites using a mixed culture of chemolithotrophic micro-organisms was explored using the approach of statistical design of experiments. In a series of experiments, pH, particle size, pulp density, type of substrate and inoculum size were statistically combined using a quarter fractional factorial designs 2 5−2 III and tested for their influence on nickel recovery using chemolithotrophic microorganisms. The results indicated that inoculum size was not statistically significant while the rest of the factors were statistically significant. Under the ranges studied the interaction between the variables was found to be weak. The results also showed that recovery was maximized at low pH and low pulp density. In the range studied, particles of less than 38μm had a negative influence on nickel recovery. Sulphur substrate also showed better effects than pyrite.

The Effect of Aluminium and Magnesium Sulphate on the Rate of Ferrous Iron Oxidation by Leptospirillum ferriphilum in Continuous Culture

Abstract: In heap bioleaching the dissolution of gangue minerals from igneous ore materials can lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the target minerals. The kinetics of the oxidation process have been well studied for Leptospirillum and Acidithiobacillus species in tank systems. Although not directly comparable, kinetic parameters derived for tank systems do apply also for heap bioleach conditions. In the present study the effect of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g/L and combined concentrations 0 to 16 g/L each has been investigated in continuous culture using Leptospirillum ferriphilum. Increasing the concentrations of the salts increasingly depresses the rate of ferrous iron oxidation and also shifts the viable range more and more into the low potential region. Al significantly reduces the amount of carbon maintained in the reactor (assumed to be commensurate with biomass), whereas Mg actually enhances it at low concentrations. In both cases, however, the rate is always depressed. The results indicate that heap cultures are likely to perform sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.

Selective Coagulation in Chalcopyrite/Pyrite Mineral System Using Acidithiobacillus Group Bacteria

Abstract: Acidithiobacillus ferrooxidans cells grown in ferrous ions were used to study the surface modification of pyrite and chalcopyrite, with focus on coagulation of very fine particles (-5 m). The zeta-potential studies of the minerals, before and after bacterial treatment, showed that the cells have a distinct influence on the surface charge of pyrite and chalcopyrite. The maximum coagulation of particles determined by Turbiscan as a function of pH correlated well with the zetapotential results. Using diffuse reflectance FT-IR spectroscopic studies, the adhesion of cells showed a varied influence on these minerals. The results demonstrate that Acidithiobacillus ferrooxidans interact with pyrite and chalcopyrite differently, allowing selective coagulation of one mineral from the other under different pH conditions.

Lead and Gold Removal Using Sugar-Beet Pectin Gels with and without Immobilized Fucus Vesiculosus

Abstract: Sugar-beet pectin gels are a novel material with applications in heavy and precious metal removal and biomass immobilization which are similar to those of alginate. This paper presents the experimental results of the kinetics of Pb(II) and Au(III) batch removal with these gels, with and without immobilized biomass of the brown algae Fucus vesiculosus. The evolution of the metal concentration, solution pH and Ca2+ liberation was determined. The biomass was characterized before and after the metal removal using SEM-EDX, FESEM, FETEM, XRD and FTIR techniques. The Pb(II) removal followed a typical biosorption kinetics with a final equilibrium metal concentration. The immobilized algae had different biosorptive behaviour than both the original sugar-beet pectin gels and the free biomass. There was no Au(III) removal with the pectin gels without algae. In the case of the immobilized biomass, the Au(III) recovery occurred in two stages, where the biosorption was followed by the reduction of the Au(III) to Au(0) due to the presence of the own algae. The Au(0) precipitated preferably on the surface of the algal biomass and in the form of colloidal gold in the solution and entrapped within the pectin gel matrix.

Hydrogen Separation Characteristics of SiC Nanoporous Membrane at High Temperature

Abstract: Ceramic membranes having less than 1nm size pores have great potential for gas separation at high temperature due to their good thermal stability. Moreover, nanoporous silicon carbide membrane has potential application under hydrothermal condition at high temperature since it is highly stable at high temperature. In this research, nanoporous SiC membrane has been developed on porous alumina support using preceramic polymer. Pore size of the SiC membrane was controlled using polystylene(PS) as the pore forming agent. The SiC membrane having controlled pore size was characterized with SEM, EDS, FT-IR, XRD and pore size measurement. The hydrogen permeability and selectivity toward nitrogen gas of the developed membrane were 0.3 x 10-6 mole/m2.s.pa and 4.1, respectively. The nanoporous hydrogen selective SiC membrane shows promising application in membrane reactor for steam reforming reacti on of natural gas, water gas shift reactions and hydrogen separation from coal gasification such as Integrated Gasification Combined Cycle (IGCC).