Photocatalytic oxidation of methylene blue dye under visible light by Ni doped Ag2S nanoparticles

Ag₂S nanoparticles were prepared using a hydrothermal method, and Ni was doped via a photo-assisted deposition method. The samples produced were characterized using different tools. Furthermore, the catalytic performance of the Ag₂S and Ni/Ag₂S samples was examined in the degradation of methylene blue dye under visible light. The UV–vis spectral analysis detected a red shift after loading of Ni. The maximum degradation efficiency achieved was 100% with 3 wt% Ni/Ag₂S as the photocatalyst after a 40-min reaction time. The catalyst could be reused without any loss in activity for the first five cycles.     

Modelling uncertainty in social–natural interactions

Socio-ecological systems can be represented as a complex network of causal interactions. Modelling such systems requires methodologies that are able to take uncertainty into account. Due to their probabilistic nature, Bayesian networks are a powerful tool for representing complex systems where interactions between variables are subject to uncertainty. In this paper, we study the interactions between social and natural subsystems (land use and water flow components) using hybrid Bayesian networks based on the Mixture of Truncated Exponentials model. This study aims to provide a new methodology to model systemic change in a socio-ecological context. Two endogenous changes – agricultural intensification and the maintenance of traditional cropland – are proposed. Intensification of the agricultural practices leads to a rise in the rate of immigration to the area, as well as to greater water losses through evaporation. By contrast, maintenance of traditional cropland hardly changes the social structure, while increasing evapotranspiration rates and improving the control over runoff water. These results indicate that hybrid Bayesian networks are an excellent tool for modelling social–natural interactions.     

Numerical simulations of comminution slurries over complex topographies: Putting together CFD and pipeline integrity

The use of computational fluid dynamics gives new and interesting insights for risk analysis of cross-country ore hydraulic transport operations. In particular, they offer the possibility to predict, with reasonable accuracy, the progression and final condition of spills driven by pipeline leaks at selected locations, at a relatively modest computational cost. In this work, a depth-averaged, two-dimensional numerical model is used to simulate an ore concentrate pipeline rupture and subsequent spill, reproduced as a constant flow condition at the leak point. Although the model is well suited to solve the governing flow equations on arbitrary topographies by means of digital elevation models, two specific locations featuring relatively mild and steep slopes, are analysed with regard to their implications on the potential requirements for emergency team response. Results, obtained using different slurry rheologies, are compared with those obtained using a simpler, common flow resistance model derived for water flowing over rough surfaces.     

Developing real time operating rules for trading discharge permits in rivers: Application of Bayesian Networks

Transferable discharge permit (TDP) programs show potential cost-effective methods of pollution control in river systems. Nevertheless, there remain uncertainties that, if not adequately addressed, might impair their success. Trading Ratio System (TRS) suggested by Hung and Shaw [2005. A trading-ratio system for trading water pollution discharge permits. Journal of Environmental Economics and Management 49, 83–102] is a cost-effective tool for water quality management in river systems, which provides the optimum trading pattern among dischargers. TRS has been designed for a single conservative water quality variable and the existing uncertainties are not incorporated. In this study, TRS is extended to be applicable to Biochemical Oxygen Demand (BOD) and Dissolved Oxygen (DO) management in river systems and uncertainties in input variables of river water quality simulation model are also considered. In the proposed methodology, low water quality is also quantified as a fuzzy event and fuzzy risk of violating the water quality standards is estimated at each checkpoint along the river. The Extended Trading Ratio System (ETRS) is used in a Monte Carlo Analysis to provide the required data for training and validating a Bayesian Network (BN). The trained BN can be used for real time river water quality management and provides the probability density functions of treatment levels and trading discharge permit policies. The methodology is successfully applied to the Zarjub River in the northern part of Iran to show its usefulness as a cost-effective and risk-informed decision-making tool in real time river water quality management.     

Electro-magnetic transport behavior of La0.7Ca0.3MnO3/SnO2 composites

The composites of (1 ? x)La_0.7Ca_0.3MnO₃ (LCMO) + xSnO₂ (x = 0.01, 0.05, 0.10, 0.30, 0.50, 0.60, 0.65 and 0.70) were synthesized by conventional solid-state reaction method. The results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicate that SnO₂ and LCMO coexist in the composites and SnO₂ mainly segregates at the grain boundaries of LCMO, which are in accordance with the results of the magnetic measurements. The detailed electrical characterizations for all the samples showed that a new metal–insulator (M–I) transition temperature (T_P2) appeared at a lower temperature compared with the intrinsic metal–insulator (M–I) transition temperature (T_P1) when x < 0.50 (T_P1 > T_P2). When x > 0.50, T_P1 disappeared, leaving only T_P2. The resistivity percolation threshold of the composites occurred at x = 0.60. Corresponding to the two M–I transition peaks, the curves of magnetoresistance against temperature also showed two peaks for all composites. These phenomena can be explained by the segregation of a new phase related to SnO₂ at the grain boundaries or surfaces of the LCMO grains.     

Effect of surface modification on the performance of negative electrodes in Ni/MH batteries

The performance of a Nickel/Metal Hydride (Ni/MH) battery closely depends on the characteristics of the negative MH electrode. Exchange current density, high-rate dischargeability, discharge potential and apparent activation energy of a MH electrode are very important properties, among which the high-rate dischargeability and discharge potential of a MH electrode determine the specific energy and specific power of electric vehicles (EVs) when Ni/MH batteries are applied to EVs. Significant improvements in exchange current density, high-rate dischargeability and discharge potential of a MH electrode have been observed for a $\text{9.0}\text{wt}$% copper coated LaNi_4.7Al_0.3 MH electrode. The high-rate dischargeabilities were determined to be 88.4% for the LaNi_4.7Al_0.3 electrode and 99.4% for Cu-coated LaNi_4.7Al_0.3 electrode. The discharge potential for the Cu-coated LaNi_4.7Al_0.3 electrode is lower (i.e. more negative) than that for the LaNi_4.7Al_0.3 electrode, especially at a large discharge current density (i.e. $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$). The discharge potentials of the Cu-coated LaNi_4.7Al_0.3 electrode are almost the same value (i.e. $\text{−0.930}\text{V}$ vs. Hg/Hgo) at both 20 and $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$ discharge current densities. There is no significant difference between the two apparent activation energies for the electrode reactions for the electrodes with and without the microencapsulation of the MH powders at the same hydrogen concentration.     

Simulation of water–rock interaction in the Yellowstone geothermal system using TOUGHREACT

The Yellowstone geothermal system provides an ideal opportunity to test the ability of reactive transport models to simulate the chemical and hydrological effects of water–rock interaction. Previous studies of the Yellowstone geothermal system have characterized water–rock interaction through analysis of rocks and fluids obtained from both surface and downhole samples. Fluid chemistry, rock mineralogy, permeability, porosity, and thermal data obtained from the Y-8 borehole in Upper Geyser Basin were used to constrain a series of reactive transport simulations of the Yellowstone geothermal system using TOUGHREACT. Three distinct stratigraphic units were encountered in the 153.4 m deep Y-8 drill core: volcaniclastic sandstone, perlitic rhyolitic lava, and nonwelded pumiceous tuff. The main alteration phases identified in the Y-8 core samples include clay minerals, zeolites, silica polymorphs, adularia, and calcite. Temperatures observed in the Y-8 borehole increase with depth from sub-boiling conditions at the surface to a maximum of 169.8 °C at a depth of 104.1 m, with near-isothermal conditions persisting down to the well bottom. 1-D models of the Y-8 core hole were constructed to simulate the observed alteration mineral assemblage given the initial rock mineralogy and observed fluid chemistry and temperatures. Preliminary simulations involving the perlitic rhyolitic lava unit are consistent with the observed alteration of rhyolitic glass to form celadonite.     

Cyanide recovery in hydrometallurgical plants: use of synthetic solutions constituted by metallic cyanide complexes

Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the pH of the solution by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at recognizing the chemical relations between the cyanide and metals during distillation. The regeneration of cyanide from gold processing proved to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved.