Characterization and availability of cyanide in solid mine tailings from gold extraction plants

The aim of this study was to investigate the availability and fate of cyanide in gold mill solid tailings. For this purpose, aged (6-9 years) and recently discharged (3 months) tailings were sampled at various depths from two gold mining sites in Quebec (Canada). A physicochemical characterization of the tailings along with a bacterial enumeration was performed and batch-leaching tests with water and caustic solution were conducted to assess the soluble cyanide fraction. Following the standard acid reflux/distillation method, the total cyanide concentration (CN(T)) in fresh tailings was higher (average of 19.5 +/- 2.0 compared to 3.2 +/- 0.7 mg/kg) and the pH more alkaline (10.6 +/- 0.1 compared to 7.6 +/- 0.2) compared to aged ones. In aged tailings, the enumeration of total heterotrophic (10(4)-10(6) cfu/g) and cyanide-resistant bacteria (10(2)-10(5) cfu/g) showed a significant indigenous microflora, but no growth on agar plates was detected in fresh tailings, suggesting an evolution and a gradual acclimatization of bacterial populations with weathering. Elevated concentrations of CN(T), weak acid dissociable cyanide (CN(WAD)), cyanate (CNO-), and thiocyanate (SCN-) were measured in the supernatant solution of the fresh tailings samples collected in-situ, highlighting their reactivity, whereas these species were not detectable in aged tailings. Accordingly, when batch-leaching tests were performed with fresh samples, 68-72% of the total cyanide was released into aqueous solution with more than 20% being CN(WAD). Again, CN(T) and CN(WAD) were not detectable during leaching of aged tailings. In fresh tailings, approximately 50% of the cyanides were quantifiable with the standard acid reflux/distillation method (readily soluble cyanides, and weak to moderately strong complexes), whereas in aged tailings only 15 to 33% of the actual total cyanide content was measured by the standard method. These results stress the necessity of performing a preliminary alkaline extraction prior to total cyanide determination. In summary, this study revealed a difference in physicochemical properties, cyanide concentration and speciation, viable bacterial populations and cyanide leaching behavior between aged and fresh solid mine tailings. The findings indicate that the more reactive cyanide species initially associated with the solid tailings have naturally degraded within the mine tailings impoundment area, resulting primarily from volatilization (decrease in pH), leaching, and bacterial degradation.     

Realization of high transparent conductive vanadium-doped zinc oxide thin films onto flexible PEN substrates by RF-magnetron sputtering using nanopowders targets

RF-magnetron sputtering has been carried out at room temperature to deposit vanadium-doped zinc oxide (VZO) nanostructured thin films onto flexible PEN substrates. The sputtering targets of compacted VZO nanopowder have been prepared using a rapid and inexpensive Sol-Gel synthesis followed by a supercritical drying process. Structural and morphological study of VZO particles in the targets has been carried out via X-ray diffraction and Transmission Electron Microscopy (TEM). The nanostructured thin films have been characterized to analyze the structural, morphological, electrical and optical properties as a function of vanadium content from 0 to 4 at.%. Structural characterization of VZO thin films revealed that the deposited thin films have been grown preferentially along (002) and exhibit the hexagonal wurtzite structure. The cross-sectional and microstructural analysis performed by Scanning Electron Microscopy (SEM) confirms the columnar growth of nanostructures. The deposited thin films exhibit transparent behavior with transmission >70% in the visible region. It has been observed that nanostructured thin films with vanadium content of 2% have demonstrated the lowest resistivity (6.71 × 10^?4 Ω cm) with Hall mobility of 10.62 cm² V^?1 s^?1. The deposited vanadium doped nanostructured thin films would have potential applications in electronic and optoelectronic devices.     

Synergetic association of grafted PLA and functionalized graphene on the properties of the designed nanocomposites

The synergetic association of poly(lactic acid) grafted with maleic anhydride (MA-g-PLA) containing 0.44 wt% of maleic anhydride and epoxy-functionalized graphene (GFe) on the properties of the designed nanocomposites was studied. Rheological, mechanical and barrier properties of PLA nanocomposites were studied using different content of epoxy-functionalized graphene and MA-g-PLA compatibilizer. The PLA/MA-g-PLA/GFe nanocomposites prepared by melt blending, containing 5 wt% of MA-g-PLA, yield a maximum in storage modulus G′ and a rheological plateau at low frequencies, with a content of epoxy-functionalized graphene comprised between 4 and 7 wt%. This phenomenon was ascribed to a pseudo-solid behavior resulting from the high degree of epoxy-functionalized graphene exfoliation due to strong interfacial interactions with PLA and epoxy-functionalized graphene. The better mechanical and barrier performances were obtained with PLA/GFe containing 10 wt% of epoxy-functionalized graphene and 5 wt% of MA-g-PLA compatibilizer. The variation of the percentage of compatibilizer showed that 5 wt% of maleated PLA was sufficient to improve the thermal, rheological, mechanical and barrier properties of the PLA nanocomposite containing 7 wt% of epoxy-functionalized graphene.     

A Mutasynthesis Approach with a Penicillium chrysogenum ΔroqA Strain Yields New Roquefortine D Analogues

Penicillium chrysogenum, which lacks the roqA gene, processes synthetic, exogenously added histidyltryptophanyldiketopiperazine (HTD) to yield a set of roquefortine‐based secondary metabolites also produced by the wild‐type strain. Feeding a number of synthetic HTD analogues to the ΔroqA strain gives rise to the biosynthesis of a number of new roquefortine D derivatives, depending on the nature of the synthetic HTD added. Besides delivering semisynthetic roquefortine analogues, the mutasynthesis studies presented here also shed light on the substrate preferences and molecular mechanisms employed by the roquefortine C/D biosynthesis gene cluster, knowledge that may be tapped for the future development of more complex semisynthetic roquefortine‐based secondary metabolites.     

Optimization of the dynamic wavefront control of a pulsed kilojoule/nanosecond-petawatt laser facility

The wavefront aberrations in a large-scale, flash-lamp-pumped, high-energy, high-power glass laser system can degrade considerably the quality of the final focal spot, and limit severely the repetition rate. The various aberrations induced on the Laboratoire pour l'Utilisation des Lasers Intenses (LULI), laser facility (LULI2000) throughout the amplification are identified and analyzed in detail. Based on these analyses, an optimized procedure for dynamic wavefront control is then designed and implemented. The lower-order Zernike aberrations can be effectively reduced by combining an adaptive-optics setup, comprising a bimorph deformable mirror and a four-wave lateral shearing interferometer, with a precise alignment system. This enables the laser chain to produce a reproducible focal spot close to the diffraction limit (Strehl ratio approximately 0.7). This allows also to increase the repetition rate, initially limited by the recovery time of the laser amplifiers, by a factor of 2 (one shot per hour). The proposed procedure provides an attractive alternative for dynamic correction of the wavefront aberrations of a laser facility as complex as the LULI2000.     

Electrochemically deposited poly(3,4-propylenedioxythiophene) for dye-sensitized solar cell

Journal of Applied Electrochemistry - In this work, poly(3,4-propylenedioxythiophene) (PProDOT)-based counter electrode (CE) was elaborated. The PProDOT polymer was electropolymerized by using...