Papers by Keyword: Metals

Abstract: The processing conditions of the of electronic wastes are largely dependent on environmental standards and requirements. Modern technologies for processing electronic waste should meet the increased demand for metals as well as the requirements. Electronic wastes can be classified as hazardous materials, as household and industrial electrical devices, which contain components such as batteries, capacitors, cathode ray tubes, etc. Electronic waste can consist of a large number of components of various sizes, shapes and chemical composition. Some of them contain hazardous metals, including mercury, lead, cadmium. The presence of precious metals in electronic waste such as gold, silver, platinum, palladium, as well as non-ferrous metals (copper, nickel, zinc, tin, etc.) make it attractive for processing. In industry, both hydrometallurgical and pyrometallurgical methods are used to extract valuable metals from electronic waste. Applied technologies may have both advantages and disadvantages.

Abstract: In magnetically ordered metals the magnitude of the local atomic moment become temperature dependent. To deal with this problem on the ab-initio level one need to employ a specific methodology for calculation of the electronic structure that takes into the account the magnetic disorder effects. In addition one needs to setup a special statistical models allowing simultaneously for ab-initio mapping and for the variation of the local spin magnitude. To this end here we discuss and employ methodology that is based on the Disordered Local Moment (DLM) formalism, spin-constraint Local Spin Density Approximation (LSDA) and Lichtenstein theorem for calculation of the inter-site exchange interactions. An extended classical Heisenberg Hamiltonian used for mapping allows for the variation of the lattice site spin magnitude. We consider here three representative canonical transition metals ferromagnets hcp Gd, bcc Fe and fcc Ni with quite a different character of the magnetic moment localization and illustrate the relative importance of the longitudinal spin fluctuations and the magnetic disorder induced electronic structure reconstruction. We use recently introduced linear measure [1] for integration over the longitudinal spin component in the classical configurational spin space.

Abstract: The validation of classical potentials for describing multicomponent materials in complex geometries and their high temperature structural modifications (disordering and melting) requires to verify both a faithful description of the individual phases and a convincing scheme for the mixed interactions, like it is the case of the embedded atom scheme. The present paper addresses the former task for an embedded atom potential for copper, namely the widely adopted parametrization by Zhou, through application to bulk, surface and nanocluster systems. It is found that the melting point is underestimated by 200 degrees with respect to experiment, but structural and temperature-dependent properties are otherwise faithfully reproduced.

Abstract: Using microorganisms to mediate crystallisation of metals and minerals in open-culture bioreactors has potential to recover recyclable materials from dilute aqueous streams, but also to prevent their emission to the environment. Although this potential is already exploited in practice to some extent, biological crystallization for metal recovery is still largely a black box technology with limited understanding of the role of the microorganisms in the crystallization, and the differences with chemical crystallisation. Using biocrystallisation of scorodite (FeAsO₄.2H₂O) and sphalerite (ZnS) as examples we propose that the role of microorganisms strongly depends on established saturation state of the solution. For scorodite, microorganisms are used to exert control over the crystallization as their ferrous iron-oxidizing activity keeps the solution slightly oversaturated. Also, the oversaturation level is kept homogeneous because of continuous biological formation of the reactant ferrous iron throughout the solution. In continuous bioreactor experiments on which we reported previously, scorodite crystal sizes still increased after 72 days of bioreactor operation indicating that indeed crystal growth was favored over nucleation. On the other hand, in our experiments with zinc sulfide, crystallization proceeded in highly oversaturated solutions in a continuous sulfate reducing bioreactor fed with a zinc sulfate solution and H₂/CO₂ as electron donor and carbon source. The high oversaturation likely resulted in dominant primary nucleation in the bulk solution, with little or no control over crystal growth, even though agglomeration may still have occurred. This was exemplified by particle sizes which decreased in the bioreactor experiment and remained stable after already about 2 weeks of operation.

Abstract: 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.

Abstract: In the present study we explore the idea of biotechnologically produced metallophore mixtures as selective chelating compounds for economically valuable metals from various sources. A complex soil matrix with natural levels of metal mineralization was employed as a potential source of metals. We focused on gallium-chelating metallophore preparations of two soil bacteria (Gordonia rubripertincta CWB2 and Paracoccus denitrificans PD1222) which were compared to the commercially available desferrioxamine B (DFOB). As a reference, the binding of iron was analyzed. The herein described successful mobilization of metals such as gallium from soil provides first hints towards alternative strategies, such as phytomining, sensor development, or solvent extraction based on metallophores. The metallophore mixture produced by the strains showed best results at pH 8 and allowed to mobilize gallium about three times better as the pure commercially available DFOB.

Abstract: Sulfate is a pollutant present in the mining waste water and acid mine drainage. High levels of sulfate can generate important environmental problems. One of the alternatives proposed for the treatment of water with high levels of sulfate is the use of sulfate-reducing microorganisms. This work describes the synergistic combination of a treatment system for the removal of metals by biosorption with the strain Bacillus sp. NRRL-B-30881 to reduce the inhibiting concentration of metals in waters, followed by a new process of sulfate removal that uses a halotolerant sulfate-reducing microbial consortium. The results show that the sulfate reducing consortium can be cultured and is able to reduce the sulfate concentration using cheaper complex organic substrates like spirulina, cellulose and industrial starch. The sulfate reducing consortium was cultured on a bioreactor with Celite R-635, as support material. Using this bioreactor it was possible to reduce the sulfate concentration in the culture medium in batch or semi-continuous operation. An acid mine drainage was pretreated by lime and treated by biosortion in order to increase the pH and reduce the heavy metals concentration. Subsequently the remaining sulfate was removed by the developed process. This integrated biological process represents a more economical alternative for the removal of metal by biosortion and the removal of sulfate using a sulfate reducing consortium.

Abstract: The crystallization kinetics of melt-spun Cu_64.5Zr_35.5 amorphous alloy ribbons was investigated using differential scanning calorimetry (DSC) at different heating rates. Besides, the Kissinger and isoconversional approaches were used to obtain the crystallization kinetic parameters. As shown in the results, the activation energies for glass transition and crystallization process at the onset, peak and end crystallization temperatures were obtained by means of Kissinger equation to be 577.65 ± 34, 539.86 ± 54, 518.25 ± 20 and 224.84 ± 2 kJ/mol, respectively. The nucleation activation energy E_nucleation is greater than grain growth activation energy E_growth, indicating that the nucleation process is harder than grain growth. The local activation energy E_α decreases in the whole crystallization process, which suggests that crystallization process is increasingly easy.

Abstract: Sterling alloy is widely used in the jewelry industry. Its anti-tarnish property is one of its most important characteristics. In this study, the effect of tin on the corrosion resistance, and tarnish resistance properties of sterling silver alloy were investigated quantized. The difference between anti-corrosion and anti-tarnish properties was investigated in this paper. The tarnish and corrosion resistance of sterling silver improved as tin content increased. However, there was a point at which increasing tin content further led to poor anti-tarnish properties, even though the alloy retained considerable anti-corrosive properties.

Abstract: In this work our goal is to better understand the origin of the cyclic accumulation of the inelastic strain (often called ratcheting) observed in 304L SS subjected to uniaxial cyclic stress control at room temperature. Recent works performed in the frame of small strain assumption attribute this phenomenon essentially to creep [1]. However, outside this frame, it seems that creep is not the only contributor in this phenomenon [2]. New experiments are performed here in order to investigate the role played by creep, cyclic softening, fatigue damage and ratcheting in this observation.