Permeability evolution during progressive development of deformation bands in porous sandstones

[1] Triaxial deformation experiments were carried out on large (0.1 m) diameter cores of a porous sandstone in order to investigate the evolution of bulk sample permeability as a function of axial strain and effective confining pressure. The log permeability of each sample evolved via three stages: (1) a linear decrease prior to sample failure associated with poroelastic compaction, (2) a transient increase associated with dynamic stress drop, and (3) a systematic quasi-static decrease associated with progressive formation of new deformation bands with increasing inelastic axial strain. A quantitative model for permeability evolution with increasing inelastic axial strain is used to analyze the permeability data in the postfailure stage. The model explicitly accounts for the observed fault zone geometry, allowing the permeability of individual deformation bands to be estimated from measured bulk parameters. In a test of the model for Clashach sandstone, the parameters vary systematically with confining pressure and define a simple constitutive rule for bulk permeability of the sample as a function of inelastic axial strain and effective confining pressure. The parameters may thus be useful in predicting fault permeability and sealing potential as a function of burial depth and faul

Reducing the Competition: A Dual-Purpose Ionic Liquid for the Extraction of Gallium from Iron Chloride Solutions

The separation of gallium from iron by solvent extraction from chloride media is challenging because the anionic chloridometalates, FeCl4− and GaCl4−, display similar chemical properties. However, we report here that the selective separation of gallium from iron in HCl solution can be achieved using the dual-purpose ionic liquid methyltrioctylammonium iodide in a solvent extraction process. In this case, the reduction of Fe3+ to Fe2+ by the iodide counterion was found to inhibit Fe transport, facilitating quantitative Ga extraction by the ionic liquid with minimal Fe extraction from 2 M HCl

Understanding the recovery of rare-earth elements by ammonium salts

While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2− are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery

BENEFIT OF COMPLEMENTARY METHODS FOR CHARACTERIZING SANDSTONE CORES

ABSTRACT: This Paper is based on detailed mineralogical, structural, petrophysical and geochemical studies of sandstone core samples, using routine methods. These include Magnetic Resonance Imaging (MRI), Nuclear Magnetic Resonance (NMR), X-ray Computer Tomography (CT) Scanning, particle size analysis, point counting based on petrographic thin sections, Environmental Scanning Microscopy (ESEM), X-Ray Diffraction (XRD), and X-Ray Fluorescence (XRF). In this study we demonstrate the feasibility of combing these complementary methods of measurements in the characterization of sandstone cores. Four types of sandstones (Slick Rock Aeolian, Fife, Locharbriggs and Berea sandstones) that differ in grain size, porosity and mineralogy have been characterized. The results of the different methods used were found to be consistent with each other, but the combination of a variety of methods has allowed a more complete characterization of the rock samples than each method used on its own. This study has shown that rock heterogeneity at the sub-cm scale may have a significant effect on reservoir petrophysical characterization

Influence of Maternal Season on Field Establishment of Sorghum Varieties Grown in Zimbabwe

Maternal season defined, as the prevailing environmental conditions during crop growth has been known to influence not only grain yield but also seed quality. A laboratory and field experiment were conducted in October 2014, to determine the influence of total rainfall and mean monthly temperature on germination, vigor and emergence of sorghum seeds which were harvested from three different seasons and were kept under controlled conditions. The laboratory experiment was a 3 x 3 factorial experiment laid in completely randomized block design (CRD) replicated three times. The first factor was variety (Macia, SDSL 89473 and Sima), the second factor was growing season (2004/5, 2006/7, 2007/8). A field experiment was carried out to investigate the emergence of seed materials used in the laboratory experiment. The experiment was a 3 x 3 x 3 factorial treatment structure laid out in a Randomized Complete Block Design (RCBD) with the third factor being sowing depth at 5.0, 7.5 and 10.0 cm. Seedling emergence was observed at 10 days after sowing. In the laboratory experiment it was observed that there was no significant difference (P>0.05) on the effects of season and variety on germination of seeds. However, there was significant difference (P<0.001) on seed vigor due to variety under laboratory conditions. For the field experiment, there was significant interaction (P<0.001) on seedling emergence due to season, sowing depth and variety. The highest emergence for all varieties was observed at a sowing depth of 5cm. It can be concluded that maternal season, which is the season in which the seed was grown, has great influence on the vigor of seed produced under dry-land agriculture. There is need to repeat the experiment using more seed lots harvested at many different seasons in order to determine the exact optimum amount of rainfall and temperatures during the maternal season that will promote optimal germination and emergence of dry-land sorghum varieties

Ecological co-benefits from sea cucumber farming: Holothuria scabra increases growth rate of seagrass

Sea cucumber aquaculture is increasing in extent and importance throughout the Indo-Pacific region, supplying a luxury seafood market in Asia. In this context, the grow-out of hatchery-bred juveniles in community-farmed pens is proving to be a viable model, providing increased income security and alternative livelihood options to resource-limited communities. Here, we report a study of the impacts of such sea cucumber farming on the growth of seagrass (a favourable habitat for the animals) at a village-scale aquaculture site in southwest Madagascar. Using experiments, we found that the presence of the hatchery-bred sea cucumber Holothuria scabra (sandfish), at stocking densities of 300 g m-2 (similar to the density used in the farmed pens, but relatively high for natural populations), resulted in a large (~30%), statistically significant increase in the leaf extension rate of the locally dominant seagrass species Thalassia hemprichii. However, the other dominant seagrass species, Cymodocea serrulata, did not significantly change its leaf extension rate in the presence of H. scabra. Since seagrass is a globally important coastal habitat, supporting high biodiversity, carbon sequestration, shoreline stability and nursery grounds for commercial and small-scale fisheries, the positive effect of H. scabra farming on the growth rate of at least one dominant seagrass species implies potential important ecological co-benefits. These co-benefits of H. scabra farming are likely to be relevant across the tropical Indo-Pacific coastlines, where this species is cultured

Shape-Selective Supramolecular Capsules for Actinide Precipitation and Separation

Improving actinide separations is key to reducing barriers to medical and industrial actinide isotope production and to addressing the challenges associated with the reprocessing of spent nuclear fuel. Here, we report the first example of a supramolecular anion recognition process that can achieve this goal. We have designed a preorganized triamidoarene receptor that induces quantitative precipitation of the early actinides Th(IV), Np(IV), and Pu(IV) from industrially relevant conditions through the formation of self-assembled hydrogen-bonded capsules. Selectivity over the later An(III) elements is shown through modulation of the nitric acid concentration, and no precipitation of actinyl or transition-metal ions occurs. The Np, Pu, and Am precipitates were characterized structurally by single-crystal X-ray diffraction and reveal shape specificity of the internal hydrogen-bonding array for the encapsulated hexanitratometalates. This work complements ion-exchange resins for 5f-element separations and illustrates the significant potential of supramolecular separation methods that target anionic actinide species

A Simple Supramolecular Approach to Recycling Rare Earth Elements

The rapid increase in demand for rare-earth elements reflects their crucial roles in climate critical technologies. However, the lack of simple solutions for the separation of these metals from waste materials and ores represents a significant barrier to sustainable and environmentally benign rare-earth production. We report the application of a supramolecular approach to this challenge, using a triamido-arene receptor to selectively precipitate f-elements through their encapsulation as hexanitratometalates. Single-step, near quantitative recovery of Nd/Pr directly from magnet scrap was observed without the need for pH adjustment or pretreatment of the acidic leach solution. The rare-earth nitrate was rapidly stripped from the host−guest precipitate with water and the receptor recycled for further use. Near quantitative and highly selective uptake of La−Nd and Th from lateritic rare-earth ores was also achieved with no uptake of any non-f-element. These results show that targeting f-element metalates in separations chemistry can deliver exceptional and unique selectivity that may have significant consequences in the sustainable production of the rare-earth elements