Review of trace toxic elements (Pb, Cd, Hg, As, Sb, Bi, Se, Te) and their deportment in gold processing. Part 1: Mineralogy, aqueous chemistry and toxicity

A literature review on the deportment of trace toxic elements (Pb, Cd, Hg, As, Sb, Bi, Se, and Te) in gold processing by cyanidation is presented which compiles the current knowledge in this area and highlights the gaps. This review, together with further research on the gaps in the thermodynamics and kinetics of these systems, aims to support the development of computer models to predict the chemical speciation and deportment of these elements through the various stages of the gold cyanidation process. The first part of this review is a collation of the relevant information on trace element mineralogy, aqueous chemistry and toxicity, together with a comparison of two available software packages (JESS and OLI) for thermodynamic modelling. Chemical speciation modelling can assist in understanding the chemistry of the trace toxic elements in gold cyanidation solutions which remains largely unexplored. Many significant differences exist between the predicted speciation of these trace elements for different types of modelling software due to differences in the thermodynamic data used, the paucity of data that exists under appropriate non-ideal conditions, and the methods used by the software packages to estimate thermodynamic parameters under these conditions. The toxicity and environmental guidelines of the chosen trace element species that exist in aqueous solutions are discussed to better understand the health and environmental risks associated with the presence of these elements in gold ores

Investigation of complexation and solubility equilibria in the copper(I)/cyanide system at 25°C

The complexation of copper(I) by cyanide ions (CN−) in aqueous solution has been studied by glass electrode potentiometry at 25 °C and ionic strengths (I) of 1, 3 and 5 M in NaCl media. Overall formation constants, βn, for the equilibria: Cu+(aq) + nCN−(aq) ⇌ Cu(CN)n(n − 1)−(aq) with n = 2, 3 and 4, were quantified, along with the ionization constant (Kw) of water and the acid dissociation constant (Ka) of HCN(aq). The solubility constants *Ksn for the equilibria: CuCN(s) + (n − 1)HCN0(aq) ⇌ Cu(CN)n(n − 1)−(aq) + (n − 1)H+(aq) were also determined from a re-analysis of published solubility data for CuCN(s) in acidic cyanide solutions at I = 1 M(NaCl) and 25 °C. Because of the instability of uncomplexed Cu+(aq) and parameter correlations in the data, neither β1 nor the solubility product Ks0 (CuCN(s) ⇌ Cu+(aq) + CN−(aq)) could be reliably determined from the present data although estimates are presented

Tropical Warm Pool International Cloud Experiment TWP-ICE Cloud and rain characteristics in the Australian Monsoon

The impact of oceanic convection on its environment and the relationship between the characteristics of the convection and the resulting cirrus characteristics is still not understood. An intense airborne measurement campaign combined with an extensive network of ground-based observations is being planned for the region near Darwin, Northern Australia, during January-February, 2006, to address these questions. The Tropical Warm Pool International Cloud Experiment (TWP-ICE) will be the first field program in the tropics that attempts to describe the evolution of tropical convection, including the large scale heat, moisture, and momentum budgets, while at the same time obtaining detailed observations of cloud properties and the impact of the clouds on the environment. The emphasis will be on cirrus for the cloud properties component of the experiment. Cirrus clouds are ubiquitous in the tropics and have a large impact on their environment but the properties of these clouds are poorly understood. A crucial product from this experiment will be a dataset suitable to provide the forcing and testing required by cloud-resolving models and parameterizations in global climate models. This dataset will provide the necessary link between cloud properties and the models that are attempting to simulate them

Switching model with two habitats and a predator involving group defence

Switching model with one predator and two prey species is considered. The prey species have the ability of group defence. Therefore, the predator will be attracted towards that habitat where prey are less in number. The stability analysis is carried out for two equilibrium values. The theoretical results are compared with the numerical results for a set of values. The Hopf bifuracation analysis is done to support the stability results

Randomly generated polytopes for testing mathematical programming algorithms

Randomly generated polytopes are used frequently to test and compare algorithms for a variety of mathematical programming problems. These polytopes are constructed by generating linear inequality constraints with coefficients drawn independently from a distribution such as the uniform or the normal. It is noted that this class of 'random' polytopes has a special property: the angles between the hyperplanes, though dependent on the specific distribution used, tend to be equal when the dimension of the space increases. Obviously this structure of 'random' polytopes may bias test results

Electronic and structural properties of superconducting MgB2_2, CaSi2_2 and related compounds

We report a detailed study of the electronic and structural properties of the 39K superconductor \mgbtwo and of several related systems of the same family, namely \mgalbtwo, \bebtwo, \casitwo and \cabesi. Our calculations, which include zone-center phonon frequencies and transport properties, are performed within the local density approximation to the density functional theory, using the full-potential linearized augmented plane wave (FLAPW) and the norm-conserving pseudopotential methods. Our results indicate essentially three-dimensional properties for these compounds; however, strongly two-dimensional $\sigma$-bonding bands contribute significantly at the Fermi level. Similarities and differences between \mgbtwo and \bebtwo (whose superconducting properties have not been yet investigated) are analyzed in detail. Our calculations for \mgalbtwo show that metal substitution cannot be fully described in a rigid band model. \casitwo is studied as a function of pressure, and Be substitution in the Si planes leads to a stable compound similar in many aspects to diborides.Comment: Revised version, Phys.Rev.B in pres

Enhanced quantum entanglement in the non-Markovian dynamics of biomolecular excitons

We show that quantum coherence of biomolecular excitons is maintained over exceedingly long times due to the constructive role of their non-Markovian protein-solvent environment. Using a numerically exact approach, we demonstrate that a slow quantum bath helps to sustain quantum entanglement of two pairs of Forster coupled excitons, in contrast to a Markovian environment. We consider the crossover from a fast to a slow bath and from weak to strong dissipation and show that a slow bath can generate robust entanglement. This persists to surprisingly high temperatures, even higher than the excitonic gap and is absent for a Markovian bath.Comment: online-published version, minor modification

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV

We report the results of a study of color coherence effects in ppbar collisions based on data collected by the D0 detector during the 1994-1995 run of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8 TeV. Initial-to-final state color interference effects are studied by examining particle distribution patterns in events with a W boson and at least one jet. The data are compared to Monte Carlo simulations with different color coherence implementations and to an analytic modified-leading-logarithm perturbative calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters