Sulfidogenic biotreatment of synthetic acid mine drainage and sulfide oxidation in anaerobic baffled reactor

The treatment of synthetic acid mine drainage (AMD) water (pH 3.0-6.5) containing sulfate (3.0-3.5 g L(-1)) and various metals (Co, Cu, Fe, Mn, Ni, and Zn) was studied in an ethanol-fed sulfate-reducing 4-compartment anaerobic baffled reactor (ABR) at 32°C. The reactor was operated for 160 days at different chemical oxygen demand (COD)/sulfate ratios, hydraulic retention times (HRT), pH, and metal concentrations to study the robustness of the process. The last compartment of the reactor was aerated at different rates to study the bio-oxidation of sulfide to elemental sulfur. The highest sulfate reduction efficiency (88%) was obtained with a feed sulfate concentration of 3.5 g L(-1), COD/sulfate mass ratio of 0.737, feed pH of 3.0 and HRT of 2 days without aeration in the 4th compartment. The corresponding COD removal efficiency was about 92%. The alkalinity produced in the sulfidogenic ethanol oxidation neutralized the acidic mine water from pH 3.0-4.5 to pH 7.0-8.0. Effluent soluble and total heavy metal concentrations were substantially reduced with removal efficiencies generally higher than 99%, except for Mn (25-77%). Limited aeration in the 4th compartment of ABR promoted incomplete oxidation of sulfide to elemental sulfur rather than complete oxidation to sulfate. Depending on the aeration rate and HRT, 32-74% of produced sulfide was oxidized to elemental sulfur. This study demonstrates that by optimizing operating conditions, sulfate reduction, metal removal, alkalinity generation, and excess sulfide oxidation can be achieved in a single ABR treating AMD.     

Deconfinement leads to changes in the nanoscale plasticity of silicon

Silicon crystals have an important role in the electronics industry, and silicon nanoparticles have applications in areas such as nanoelectromechanical systems, photonics and biotechnology. However, the elastic-plastic transition observed in silicon is not fully understood; in particular, it is not known if the plasticity of silicon is determined by dislocations or by transformations between phases. Here, based on compression experiments and molecular dynamics simulations, we show that the mechanical properties of bulk silicon and silicon nanoparticles are significantly different. We find that bulk silicon exists in a state of relative constraint, with its plasticity dominated by phase transformations, whereas silicon nanoparticles are less constrained and display dislocation-driven plasticity. This transition, which we call deconfinement, can also explain the absence of phase transformations in deformed silicon nanowedges. Furthermore, the phenomenon is in agreement with effects observed in shape-memory alloy nanopillars, and provides insight into the origin of incipient plasticity.     

Arrays of indefinitely long uniform nanowires and nanotubes

Nanowires are arguably the most studied nanomaterial model to make functional devices and arrays. Although there is remarkable maturity in the chemical synthesis of complex nanowire structures, their integration and interfacing to macro systems with high yields and repeatability still require elaborate aligning, positioning and interfacing and post-synthesis techniques. Top-down fabrication methods for nanowire production, such as lithography and electrospinning, have not enjoyed comparable growth. Here we report a new thermal size-reduction process to produce well-ordered, globally oriented, indefinitely long nanowire and nanotube arrays with different materials. The new technique involves iterative co-drawing of hermetically sealed multimaterials in compatible polymer matrices similar to fibre drawing. Globally oriented, endlessly parallel, axially and radially uniform semiconducting and piezoelectric nanowire and nanotube arrays hundreds of metres long, with nanowire diameters less than 15 nm, are obtained. The resulting nanostructures are sealed inside a flexible substrate, facilitating the handling of and electrical contacting to the nanowires. Inexpensive, high-throughput, multimaterial nanowire arrays pave the way for applications including nanowire-based large-area flexible sensor platforms, phase-changememory, nanostructure-enhanced photovoltaics, semiconductor nanophotonics, dielectric metamaterials,linear and nonlinear photonics and nanowire-enabled high-performance composites.     

Change in glyceride composition of olive pomace oil during enzymatic esterification

Enzymatic esterification of free fatty acids of olive pomace oil with glycerol was investigated. The esterification reaction was carried out in the absence and presence of glycerol (glycerol to free fatty acids (FFA) molar ratio of 1/3 and 1/6). In the absence of glycerol, the FFA concentration decreased from 32 to 21% while the triglyceride concentration increased from 33 to 40% after of 8 h of reaction time. The most significant decrease in FFAs and increase in triglycerides was observed at the limiting concentration of glycerol (glycerol to FFA molar ratio of 1/3). The FFA concentration decreased to 2.5% and the triglyceride concentration increased up to 78%. The change in both FFA and triglyceride concentrations was found to be statistically significant (P < 0.05).     

Production of Si by vacuum carbothermal reduction of SiO<Subscript>2</Subscript> using concentrated solar energy

Using concentrated solar radiation as the energy source of high-temperature process heat, the carbothermal reduction of silica to silicon was examined thermodynamically and demonstrated experimentally at vacuum pressures. Reducing the system pressure favors Si(g) formation, enabling its vacuum distillation. Experimentation in a solar reactor was performed in the range 1,997–2,263 K at ∼3×10⁻³ bar with mixtures of charcoal and silica directly exposed to radiative flux intensities equivalent to 6,500 suns, yielding Si purities ranging from 66.1–79.2 wt.%. The Si purity increased with temperature. Solid characterizations showed SiC and SiO as important reaction intermediaries.     

Effect of Chemical Structure of Solid Lipid Matrix on Its Melting Behavior and Volumetric Expansion in Pressurized Carbon Dioxide

Supercritical carbon dioxide (SC-CO₂) technology offers new opportunities for green processing of lipids; however, there is little information of the melting behavior and volumetric expansion of solid lipids in pressurized CO₂. In this study, melting behavior and volumetric expansion of two different solid lipid classes and the effect of the structural differences within the same lipid class on the melting behavior in pressurized CO₂ were investigated. The melting point of the solid lipids decreased linearly with increasing pressures up to a certain level; then, it stayed constant. The highest melting point depression was observed for soybean oil monoacylglycerol (SO-MAG) at 51.5 °C/110 bar, whereas the lowest was for fully hydrogenated soybean oil (FHSO) containing 30% SO-MAG at 55.0 °C/79 bar. Melting point depression depended on lipid class. SO-MAG exhibited a higher melting point depression than FHSO (triacylglycerol form), and its blends with SO-MAG. There was no difference in melting point depression between glyceryl 1,2-distearate and glyceryl 1,3-distearate up to 200 bar (P > 0.05). A positive correlation between the melting point depression and volumetric expansion of solid lipids was observed. The highest volumetric expansion was for SO-MAG in the linear region of the melting point depression curve, achieving 14.4% expansion compared to 9.3% for FHSO (P < 0.05). The highest dT/dP value (0.17 °C bar⁻¹) was obtained for SO-MAG, whereas the FHSO (0.09 °C bar⁻¹) had the lowest one. Findings of this study will help optimize solid lipid-involving SC-CO₂ processes for better protection of heat-sensitive compounds while improving energy efficiency.