Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation

The cost of lime/limestone for neutralisation is the second largest operating cost in bioleaching. Therefore, these studies have been conducted with the aim to investigate the possibilities for use of by-products such as mesalime and electric arc furnace (EAF) dust for neutralisation during biooxidation of a refractory gold concentrate. Experiments were carried out using a retention time of 57 h in a one-stage reactor and the influence of two industrial by-products on the biooxidation performance was evaluated. The neutralising capacity of EAF dust was lower, while the mesalime was similar to the Ca(OH)₂ reference. The arsenopyrite oxidation in experiments ranged from 85% to 90%, whereas the pyrite oxidation was 63–74%. In subsequent cyanidation, final gold recoveries of 90% were achieved in bioresidues from mesalime and Ca(OH)₂, while the EAF dust bioresidue had a recovery of 85%. A comparatively high elemental sulphur content in EAF dust probably encapsulates part of the gold, which explains the lower recovery for the EAF dust bioresidue despite a longer residence time. Cyanide consumption was relatively high and ranged from 8.1 to 9.2 kg/ton feed after 24 h of cyanidation. Overall, the by-products tested here have proved to be feasible options as neutralising agents in bioleaching operations.     

Ion-beam doping during molecular beam epitaxy

Compositional modifications on the atomic scale, made possible through molecular beam epitaxy, have opened up a new range of semiconductor devices. Some recent work has investigated the addition of ion dopants during molecular beam epitaxy, with the goal of improving electrical and optical properties.     

Au schottky barrier diodes on β-SiC thin films deposited on silicon substrates by reactive magnetron sputtering technique

β-SiC thin films have been grown on (100) silicon substrates using reactive magnetron sputtering of a silicon target in an Ar/CH₄ mixed plasma. For the first time it has been possible to make gold Schottky diodes on β-SiC grown by reactive magnetron sputtering. Current-voltage measurements showed an ideality factor of 1.27 and a leakage current density of 4 μA/cm². Capacitance-voltage measurements gave a barrier height of 1.04 eV. The static dielectric constant for β-SiC was determined to be 9.     

Thermal stability and crystallization of amorphous Si1−xBx, Si1−xPx and Si1−xSbx alloy thin films

The thermal stability and crystallization of the amorphous Si_1−xP_x, Si_1−xB_x and Si_1−xSb_x alloy systems have been studied by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). It was found that the amorphous Si-P and Si-B alloys have a high thermal stability and crystallize at temperatures as high as 1150°C, whereas amorphous Si-Sb alloys are unstable and crystallize already at 350°C. The thermal stability is explained by strong Si-P and Si-B bonds, whilst the instability is explained by the weakening of Si-Si bonds by the presence of Sb atoms (< 17 at.% Sb) and by weak Si-Sb and Sb-Sb bonds (> 17 at.% Sb). The thermal stability and instability of the amorphous alloys were correctly predicted from calculated Gibbs free energy diagrams (GFED). The calculated GFED were also used together with the observed crystallization temperatures to successfully predict the first crystalline phase to form in the Si-P and Si-B systems. The first crystalline phases that formed were Si (< 40 at.% B and < 30 at.% P), a newly reported phosphide, Si₁₂P₅ (30 at.% P), and SiP (> 30 at.% P).     

1260 nm InGaAs vertical-cavity lasers

The fabrication and performance of highly strained double-quantum well InGaAs/GaAs vertical-cavity lasers with record-long emission wavelength of 1260 nm at room temperature is reported. Depending on device diameter, the minimum threshold current is in the low mA-regime while the maximum output power exceeds 1 mW. The devices work continuous-wave over a wide temperature range of at least 10-120°C     

N1s Electron Binding Energies of CN_x Thin Films Grown by Magnetron Sputtering at Different Temperature

Carbon nitride thin films deposited using dc unbalanced magnetron sputtering system have been analyzed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT1R) and Raman spectroscopy. The XPS data show that N1s binding states depend on substrate temperature Ts, in which the peak at 400.0 eV increases with Ts, whereas the peak at 398.3 eV decreases with Ts slightly On the basis of XPS, FT1R and Raman spectra, the assignment of N1s electron binding energies was made. The peak at 400.0 eV is attributed to N atoms bonded to sp2 coordinated C atoms. The peak at 398.3 eV is attributed to N atoms bonded to sp3 coordinated C atoms as well as N C bonds.     

Effects of substrate temperature and substrate material on the structure of reactively sputtered TiN films

Stoichiometric TiN films were reactively magnetron sputtered in an Ar-N₂ atmosphere. The films were deposited at various substrate temperatures in the range 200–650°C onto two types of substrate material, high speed steel and stainless steel. The microstructure of the films obtained was investigated by the use of a transmission electron microscope and the morphology was studied in a scanning electron microscope. Measurements of the hardness were also performed. The analysis of the microstructure shows that the growth of the film is markedly influenced by the substrate material. In particular, the high speed steel substrates were found to have a considerable influence on the microstructure. The vanadium carbide particles in these steels, which have a good lattice match to TiN, stimulate a localized epitaxial growth to occur on these carbide particles. This results in a microstructure consisting of large grains surrounded by small grains. The shape of the large grains is influenced by the temperature. In the development of these large grains cracks and/or voids occur in and around the grains at substrate temperatures above 400°C and the hardness drops by about 20%. No large grains were found on films deposited onto stainless steel and their hardness increases slightly with temperature. High hardness for films deposited onto the high speed steel substrate at temperatures above 400°C can also be obtained if a substrate bias is used. Ion bombardment during film growth suppresses the formation of the large grains with voided or cracked boundaries because of a continuous renucleation process. The formation of the different microstructures is discussed in terms of surface energy minimization and thermally activated processes as surface and grain boundary migration.     

A note on class effects in Aptitude?×?Treatment interactions.

Results pertaining to methodological aspects of an Aptitude?×?Treatment interaction study previously conducted by the author (1977) with 271 5th graders are presented. One treatment group in the study was given imagery instructions, the other had no imagery instructions. Among the aptitude variables were 2 versions of a paired-associates learning task. Within-class analyses and analyses in which class effects were allowed to have influence were conducted. In the latter analyses there were several significant Aptitude?×?Treatment interactions with subscores derived from the paired-associates tasks, but this was not the case in the within-class analyses. The interactions found are interpreted as being consequences of class effects with respect to errors of measurement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)