Heap bio-oxidation and gold recovery at newmont mining: First-year results

Newmont Mining Corporation began commercial gold production using whole-ore bio-oxidation from Carlin Trend ores in 2000. Commercialization of the bio-oxidation process culminates a 12-year R&D project designed to recover gold from low-grade siliceous sulfidic refractory ores and low-grade sulfidic carbonaceous refractory. This paper outlines Newmont’s biomilling process and reviews data from the first year of commercial operation.     

Aminoacyl-tRNA Synthetases as Valuable Targets for Antimicrobial Drug Discovery

Aminoacyl-tRNA synthetases (aaRSs) catalyze the esterification of tRNA with a cognate amino acid and are essential enzymes in all three kingdoms of life. Due to their important role in the translation of the genetic code, aaRSs have been recognized as suitable targets for the development of small molecule anti-infectives. In this review, following a concise discussion of aaRS catalytic and proof-reading activities, the various inhibitory mechanisms of reported natural and synthetic aaRS inhibitors are discussed. Using the expanding repository of ligand-bound X-ray crystal structures, we classified these compounds based on their binding sites, focusing on their ability to compete with the association of one, or more of the canonical aaRS substrates. In parallel, we examined the determinants of species-selectivity and discuss potential resistance mechanisms of some of the inhibitor classes. Combined, this structural perspective highlights the opportunities for further exploration of the aaRS enzyme family as antimicrobial targets.     

Fine grinding of thermoplastics by high speed friction grinding assisted by guar gum

High speed friction grinding has been used to grind plant and food substances in water but never been explored for grinding of thermoplastics like polylactic acid (PLA), low and high density polyethylene and polypropylene. Such grinding was investigated in this work and was made possible by using 0.5% guar gum solution instead of just water because increasing the viscosity of water reduced their settling and the speed of passing through the grinder. Tensile, flexural, and impact strengths of the plastics were studied and higher grinding efficiency of PLA could be explained by its low elongation-at-break compared to low density polyethylene, high density polyethylene, and polypropylene. The microplastics (2000–45 μm) were studied for mass and particle size distributions and by scanning electron microscopy, ¹³C CP/MAS NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. In addition, viscosity of guar gum and contact angles was measured. This new technology can produce finely ground microplastics (710–45 μm) for a variety of applications.     

Essentiality of fatty acids

All fatty acids have important functions, but the term “essential” is applied only to those polyunsaturated fatty acids (PUFA) that are necessary for good health and cannot be completely synthesized in the body. The need for arachidonic acid, which is utilized for eicosanoid synthesis and is a constituent of membrane phospholipids involved in signal transduction, is the main reason why the n-6 class of PUFA are essential. Physiological data indicate that n-3 PUFA also are essential. Although eicosapentaenoic acid also is a substrate for eicosanoid synthesis, docosahexaenoic acid (DHA) is more likely to be the essential n-3 constituent because it is necessary for optimal visual acuity and neural development. DHA is present in large amounts in the ethanolamine and serine phospholipids, suggesting that its function involves membrane structure. Because the metabolism of n-6 PUFA is geared primarily to produce arachidonic acid, only small amounts of 22-carbon n-6 PUFA are ordinarily formed. Thus, the essentiality of n-3 PUFA may be due to their ability to supply enough 22-carbon PUFA for optimal membrane function rather than to a unique biochemical property of DHA.     

Model-based multivariable control of the drying of a thin sheet of fibres in a continuous infrared dryer

We developed an Internal Model Control (IMC) algorithm for drying a thin textile fabric, continuously passing through an electric infrared dryer, based on a reduced linear model of the drying dynamics. This model relates the controlled variables, the humidity and temperature of the web at the dryer outlet, to the manipulated variables, the electrical power supplied to the sources and the web speed through the dryer, and also to changes in the initial humidity of the web at the dryer inlet. The control algorithm was first tested by simulation using the model in regulation mode, and in set-point tracking mode, to vary the manipulated variables so as to maintain the controlled variables at their respective set-points when the inlet web temperature and humidity were changed. The performance under simulated operational conditions was compared to that of a conventional feedback proportional-integral (PI) controller coupled with a feedforward control. The IMC controller was then tested directly in regulation mode using a pilot scale infrared dryer, acting simultaneously on the manipulated variables, the emitter power and the web speed, to control the fabric temperature and humidity at the dryer outlet. The experimental results were compared with those from the above feedback-feedforward controller, on the pilot scale dryer. The results have indicated that the closed-loop stability of the process is assured simply by choosing a stable IMC controller. Also, such a controller does not require the design of specific compensators for the strong interactions between variables of the drying process.     

Bacterial flora of processed broiler chicken skin after successive washings in mixtures of potassium hydroxide and lauric acid

Changes in the size of populations of different groups of bacteria composing the normal flora of processed broiler skin were examined after each of five consecutive washings in mixtures of potassium hydroxide (KOH) and lauric acid (LA). Portions of skin from commercially processed broiler carcasses were washed in distilled water (control) or in mixtures of 0.25% KOH-0.5% LA or 0.5% KOH-1% LA by using a stomacher laboratory blender to agitate the skin in the solutions. After each wash, skin was transferred to fresh solutions, and washing was repeated to provide samples washed one to five times in each solution. Bacteria in rinsates of the washed skin were enumerated on plate count (PC) agar, Staphylococcus (STA) agar, Levine eosin methylene blue (EMB) agar, lactic acid bacteria (LAB) agar, and Perfringens (PER) agar with TSC supplement. Selected isolates recovered on each medium were identified. Overall, no significant differences were observed in numbers of bacteria recovered on PC, STA, or EMB agars from skin after repeated washing in water, but there were significant reductions in the number of bacteria recovered on LAB and PER agars. Repeated washing of skin in 0.25% KOH-0.5% LA or 0.5% KOH-1% LA generally produced significant reductions in the number of bacteria recovered on all media. Furthermore, no bacteria were recovered on PER agar from skin washed five times in 0.25% KOH-0.5% LA. Likewise, no bacteria were recovered on EMB or LAB agars from skin washed three or more times in 0.5% KOH-1% LA or on PER agar from skin washed four or five times in this solution. Staphylococcus spp. were identified as the skin isolates with the highest degree of resistance to the bactericidal activity of KOH-LA. Findings indicate that although bacteria may be continually shed from poultry skin after repeated washings, bactericidal surfactants can be used to remove and kill several types of bacteria found on the surface of the skin of processed broilers.     

Determination of added fat in meat paste using microwave and millimetre wave techniques

By evaluating the sensitivity of measurement parameters such as dielectric constant and microwave loss to fat content, several microwave and millimetre methods were compared to identify optimal frequency measurement bands. The results showed that the optimum frequency range lay between 8 and 20GHz where these parameters vary linearly, by up to a factor of 8, as fat is increased to 50% volume. A narrowband waveguide sensor cell was designed and constructed for this optimum range. The imaginary part (ε') of the complex permittivity demonstrated a better measurements resolution for determining fat content than the real part (ε'). The waveguide method has excellent repeatability as indicated by low relative standard deviation (RSD<4.88%). Temperature and sample density had minimal impact on the accuracy, repeatability and robustness of the final measurement system. A method of mixtures model for complex permittivity was shown to be a useful predictor of fat content.     

NATURAL CONVECTION IN A VERTICAL,ASYMMETRICALLY HEATED,PERMEABLE WALLED CHANNEL

Developing natural convection in an asymmetrically heated, open-ended vertical channel was studied both experimentally and numerically. A tightly stretched, perforated, plastic radiation shield was suspended parallel to an electrically heated aluminum plate to form a vertical channel. In order to model the heat transfer and fluid flow in the vertical channel, the unsteady, two-dimensional Navier-Stokes equations were solved using a primitive variable, finite-difference formulation. Flow through the perforated boundary was modeled using a modified form of Darcy's law. Radiative exchange between the boundaries and between the boundaries and the environment was included. The predicted mass flow was within 3% of that measured experimentally. Both the average plate temperature and the bulk exit channel air temperature were within 1·2°C of the measured values. However, the predicted average temperature of the radiation shield was 8°C higher than that measured.     

Exact solutions for vibration and buckling of an SS-C-SS-C rectangular plate loaded by linearly varying in-plane stresses

Exact solutions are presented for the free vibration and buckling of rectangular plates having two opposite edges (x=0 and a) simply supported and the other two (y=0 and b) clamped, with the simply supported edges subjected to a linearly varying normal stress σ_x=−N₀[1−α(y/b)]/h, where h is the plate thickness. By assuming the transverse displacement (w) to vary as sin(mπx/a), the governing partial differential equation of motion is reduced to an ordinary differential equation in y with variable coefficients, for which an exact solution is obtained as a power series (the method of Frobenius). Applying the clamped boundary conditions at y=0 and b yields the frequency determinant. Buckling loads arise as the frequencies approach zero. A careful study of the convergence of the power series is made. Buckling loads are determined for loading parameters α=0,0.5,1,1.5,2, for which α=2 is a pure in-plane bending moment. Comparisons are made with published buckling loads for α=0,1,2 obtained by the method of integration of the differential equation (α=0) or the method of energy (α=1,2). Novel results are presented for the free vibration frequencies of rectangular plates with aspect ratios a/b=0.5,1,2 subjected to three types of loadings (α=0,1,2), with load intensities N₀/N_cr=0,0.5,0.8,0.95,1, where N_cr is the critical buckling load of the plate. Contour plots of buckling and free vibration mode shapes are also shown.