Leaching behaviour and the solution consumption of uranium-vanadium ore in alkali carbonate–bicarbonate column leaching

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Although heap leaching using sulfuric acid was introduced to the uranium industry in the 1950s, sodium carbonate–bicarbonate (alkaline) heap leaching of low-grade Ca-carbonate-rich uranium ores has recently gained popularity. This study presents the results of two column tests on a calcrete-type uranium–vanadium (carnotite) ore using a mixture of sodium carbonate and bicarbonate (Na2CO3/NaHCO3) as the leach solution. This data was kindly supplied by Toro Energy Ltd. The experimental data comprised physical–chemical leach information and two different irrigation rates (10 and 20 L/h·m2). The experimental data indicated that the carnotite ore with high calcium carbonate (CaCO3) can be leached effectively using the alkaline leach solution. The increase in the irrigation rate increased the uranium and vanadium extraction and decreased their concentration in the effluent. The column leach data was therefore fitted to a simplified first-order kinetic model using two approaches, a general form and a second based on the reagent consumption per unit mass of the initial valuable species (U and V). As reagent consumption is a key economic factor in the heap leaching process, having a kinetic leaching model incorporating reagent consumption would provide useful techno-economic information. In this regards a new leaching index of (β) is also introduced. Both approaches of the first order kinetic model provide a good agreement with the column testing data

Dense circumnuclear molecular gas in starburst galaxies

We present results from a study of the dense circumnuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas.We characterize the dense gas traced by HCN, HCO and HNC and examine its kinematics in the circumnuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1-0) and HCO (1-0) in seven of the nine galaxies and HNC (1-0) in four. Approximately 7 arcsec resolution maps of the circumnuclear molecular gas are presented. The velocity-integrated intensity ratios, HCO (1-0)/HCN (1-0) and HNC (1-0)/HCN (1-0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps, we identify photon-dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region.We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray-dominated region chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made. © 2016 The Authors.This project was supported by the Brother Vincent Cotter Award for Physics (UNSW). LVM has been supported by Grant AYA2011-30491-C02-01 co-financed by MICINN and FEDER funds, and the Junta de Andalucia (Spain) grants P08-FQM-4205 and TIC-114. WAB acknowledges the support as a Visiting Professor of the Chinese Academy of Sciences (KJZD-EW-T01). The research leading to these results has received funding from the European Community's Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No 229517.Peer Reviewe

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution