Jay R. Black

Complexation of metal ions in brines: application of electronic spectroscopy in the study of the Cu(II)-LiCl-H2O system between 25 and 90°c

Abstract The concentration and transport of metals in hydrothermal solutions depend on how metals ions combine with ligands to form complexes, and experimental methods are necessary to identify the important complexes. UV-Vis-NIR spectrophotometry was used to study the formation of Cu(II)-chloride complexes in LiCl brines up to very high chlorinities (18 m LiCl), at temperatures between 25°C and 90°C. The number of Cu(II)-chloride complexes necessary to account for the variation in spectra with varying chloride molality at each temperature was estimated using principal component analysis. The molar absorptivity coefficients and concentrations of each complex were then determined using a “model-free” analysis, which does not require any assumption about the chemistry of the system, other than the number of absorbing species present. Subsequently, the results from the “model-free” analysis were integrated with independent experimental evidence to develop a thermodynamic speciation model, where the logarithms of the equilibrium constants for Cu(II)-chloride formation reactions were fitted to the data using a non-linear least-squares approach. Maps of the residual function were used to estimate uncertainties in the fitted equilibrium constants. The results of this study are similar to published properties of distorted octahedral [CuCl(OH 2 ) 5 ] + and [CuCl 2 (OH 2 ) 4 ] 0 at all temperatures, but diverge for [CuCl 3 (OH 2 ) 3 ] − and distorted tetrahedral [CuCl 4 ] 2− . Moreover, the data suggest the presence of [CuCl 5 ] 3− , probably with D 3h point group, at very high salt concentration. This study demonstrates that it is possible to determine apparent thermodynamic equilibrium constants for the formation of complexes of trace amount of metals in highly concentrated brines, such as those associated with many ore deposits. The results are dependent on the choice of activity coefficients for charged and neutral aqueous complexes, but this influence is relatively small compared with the experimental uncertainty. This study shows that Cu 2+ chloro-complexes, predominantly [CuCl 2 (OH 2 ) 4 ] 0 and [CuCl 4 ] 2− , will play a dominant role in nature where free oxygen is available (near-surface), and where chloride activities are very high (evaporitic basins; hypersaline soils).

Electrochemical Isotope Effect and Lithium Isotope Separation

A large electrochemical isotopic effect is observed upon the electrodeposition of lithium from solutions of propylene carbonate producing isotopically light metal deposits. The magnitude of fractionation is controlled by the applied overpotential and is largest close to equilibrium. Calculated partition function ratios for tetrahedrally coordinated lithium complexes and metallic lithium predict an equilibrium fractionation close to that measured experimentally.

Letting the ‘cat’ out of the bag: pouch young development of the extinct Tasmanian tiger revealed by X-ray computed tomography

The Tasmanian tiger or thylacine (Thylacinus cynocephalus) was an iconic Australian marsupial predator that was hunted to extinction in the early 1900s. Despite sharing striking similarities with canids, they failed to evolve many of the specialized anatomical features that characterize carnivorous placental mammals. These evolutionary limitations are thought to arise from functional constraints associated with the marsupial mode of reproduction, in which otherwise highly altricial young use their well-developed forelimbs to climb to the pouch and mouth to suckle. Here we present the first three-dimensional digital developmental series of the thylacine throughout its pouch life using X-ray computed tomography on all known ethanol-preserved specimens. Based on detailed skeletal measurements, we refine the species growth curve to improve age estimates for the individuals. Comparison of allometric growth trends in the appendicular skeleton (fore- and hindlimbs) with that of other placental and marsupial mammals revealed that despite their unique adult morphologies, thylacines retained a generalized early marsupial ontogeny. Our approach also revealed mislabelled specimens that possessed large epipubic bones (vestigial in thylacine) and differing vertebral numbers. All of our generated CT models are publicly available, preserving their developmental morphology and providing a novel digital resource for future studies of this unique marsupial.