The Effect of Organic Diluent on the Extraction of Eu(III) by HEH[EHP]

ABSTRACT

Because there are fewer tools available to probe the interactions therein, the effect of the fundamental chemistry of the organic diluent on solvent extraction equilibria has been under-characterized relative to the aqueous. As a result, diluents for solvent extraction are often selected for an application not for their utility as a medium for reaction, but for other (often equally) important reasons (like low flammability). To begin to improve this imbalance in the science, twenty different diluents have been used in a study of the extraction of radiotracer ^152/154Eu³⁺ from dilute nitric acid solutions using the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]). To increase the utility of the study and to honor the memory of Professor Jan Rydberg, this investigation was conducted by a cadre of comparatively inexperienced separation scientists (who are as a result no longer inexperienced separation scientists) as a radioanalytical chemistry and solvent extraction educational exercise. Slope analysis was used to determine the apparent stoichiometry of the extracted metal complex. The results discussed in the following indicate that, while the pH dependence exhibits the expected three H⁺ exchanged per metal ion extracted, the extractant dependence suggests that the number of protonated extractant molecules in the extracted complex changes with the organic diluent. The experimentally observed “extractant dependency” ranges from 2.5 to 3.0 dimer equivalent molecules per extracted metal ion. Ironically, in the diluents exhibiting the highest apparent M:(HA)₃ stoichiometry, HEH[EHP] extracts Eu³⁺ less efficiently. Europium luminescence spectroscopy was used to probe for changes in the first coordination sphere of the complex in different diluents. A model and conceptual framework for understanding these observations is described.     

Adapting the potentially mineralizable N concept for the prediction of fertilizer N requirements

Quantification of N dynamics in the ecosystem has taken on major significance in today's society, for economic and environmental reasons. A major fraction of the available N in soils is derived from the mineralization of organic matter. For decades, scientists have attempted to quantify the rate at which soils mineralize N, but the complexity of the N cycle has made this a major task. Further, agronomists have long sought soil test methods that are practical, yet will provide accurate means of predicting the amounts and rates of release of N from soils. Such tests would allow us to make more precise fertilization decisions. This paper discusses the potentially mineralizable N concept, first promoted by Stanford and colleagues [61, 62, 64], and suggests how it may be incorporated into deterministic models, such as CERES and LEACHM, so as to provide more accurate estimates of N mineralization under field conditions. We also suggest how the potentially mineralizable N concept may be coupled to quick, routine laboratory methods of determining available soil N, such as the hot 2M KCl extracted NH₄-N method recently developed by Gianello and Bremner [35], and used together with deterministic N models, such as CERES, for predicting probable fertilizer N requirements.     

The mechanism of CO oxidation over Cu(110): Effect of CO gas energy

The effect of the temperature of gas phase CO upon the kinetics of the oxygen titration reaction: CO_g +O_a CO_2,g, has been studied. It is found that the reaction's rate is independant of CO gas temperature between 300 and 623 K. The activation energy (6.5 kcal/mole), dependence upon CO pressure (first-order), and independence upon oxygen coverage for 0.1 _o 0.4 are all independant of the CO gas phase temperature. This result rules out any Eley-Rideal type mechanism whereby CO reacts directly from the gas phase with an oxygen adatom without first being accommodated to the surface temperature in an absorbed state. The result is instead interpretable in terms of a Langmuir-Hinshelwood mechanism.Camille and Henry Dreyfus Foundation Teacher-Scholar Fellowship.     

Abrasive wear in filled elastomers

The abrasive wear of rubbers is strongly affected by the filler particles dispersed in the elastomer matrix. The fillers are incorporated usually for the purposes of mechanical reinforcement and improving the conductivity of the neat resins. It is found that the wear rates of the filled silicone rubbers increase slowly with filler concentration until a critical volume fraction,v _c, is reached, at which point they increase very rapidly with increasing filler concentration. This behaviour appeared to be universal in all the filled silicones we studied, regardless of the type of filler and silicone rubber used. However the magnitude of the critical filler fraction,v _c, can be changed significantly with the filler shape, resin cross-linking density and filler surface treatments. No reasonable relationship could be found between this wear behaviour and the mechanical properties measured in a macroscopic manner. Experimental evidence suggests that the incipient cracks that lead to wear losses may start within the thin layers of highly stressed material, the damage zones, surrounding the rigid particles. A simple model taking into account the stress concentration induced by the rigid fillers shows excellent correlation between the wear rate and the damage zones volume. With this new model, the observed wear behaviours can be explained satisfactorily.     

Thermal stability of polyaniline

Thermal stability data for neutral (emeraldine base) and doped polyaniline with various counter anions are reported. The emeraldine base is a highly heat-stable polymer, with thermal stability up to 420 °C. The thermal stability of doped polyaniline is dependent on the counter anion. The methane sulfonic acid doped polyaniline is stable up to 250 °C. The decomposition of the doped polyaniline is seen as a two-step process. The first step is the loss of the dopant and the second step corresponds to the decomposition of the backbone.     

Multidisciplinary approach to defining public e-procurement and evaluating its impact on procurement efficiency

Utilising the methodology of content analysis, this study uses a multidisciplinary approach to define public e-procurement. Various aspects of e-procurement have been discussed from information systems, supply chain management, electronic commerce/electronic government, and public procurement to come up with an integrated definition of public e-procurement. Following this, e-procurement assimilation has been defined and its impact on procurement efficiency has been evaluated. Following the confirmatory factor analysis in structural equation modelling, dimensional level analysis in ANOVA has been undertaken for the three forms of e-procurement technologies namely e-tendering, e-catalogue management systems, and e-marketplace. The results show the positive and significant impact of the assimilation process on procurement efficiency.     

Ontogenetic changes in pharyngeal morphology correlate with a diet shift from arthropods to dreissenid mussels in round gobies (Neogobius melanostomus)

The potential of predators to regulate populations of dreissenid mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) has been addressed since early in the dreissenid invasion of North America. Round gobies (Neogobius melanostomus) larger than approximately 60 mm have been shown to prey extensively on dreissenids, whereas smaller round gobies feed mainly on aquatic insects and crustaceans. We propose that ontogenetic changes in pharyngeal morphology may contribute to this diet shift in round gobies. Pharyngeals of 69 round gobies ranging from 31 to 164 mm total length were investigated using light microscopy and scanning electron microscopy. Areas of lower pharyngeals and pharyngobranchial 2 increased allometrically with fish length. Pharyngeals of round gobies smaller than 50 mm contained narrow (< 0.1 mm diameter) papilliform teeth that are consistent with eating soft-bodied prey. By the time round gobies reached approximately 80 mm in length, pharyngeals contained larger diameter (0.3-0.5 mm) molariform teeth typical of those found in molluscivorous fish. Pharyngeal teeth of the largest round gobies also showed considerable wear. Although changes in pharyngeal morphology may contribute to the previously described diet shift in round gobies as they age, genetic and environmental factors both likely influence pharyngeal remodeling and therefore merit further investigation.     

Explicit formulae for completions of linear time varying singular systems of differential equations

Completions of linear time varying singular systems of the formE(t)x(t)+F(t)x(t)=f(t) are explicitly computed using recent results on rational matrix functions. The algorithm and the theory behind it are carefully described. Computational issues are discussed.Research supported in part by the U.S. Army Research Office under DAAL03-89-D-0003, and the National Science Foundation under ECS-9012909.     

Impulse strengths in rapid granular shear flows

Summary This paper describes measurements of the impulses that particles experience while undergoing rapid shear. These were performed with an eye towards understanding the processes that lead to particle attrition and fracture. The measurements were taken from a discrete particle computer simulation of a simple shear flow of spheres. Special attention is paid to the strongest impulses as these will do the most damage. The results indicate that the largest impulses arise, not from the mean shear flow, but from the random particle velocities that are characterized by the so-called granular temperature. Measurements of the largest impulses are presented as functions of particle properties and solid concentration. Histograms of the impulse strengths illustrate the effect of concentration and particle surface friction. Finally, geometric distributions are presented that illustrate the shear induced anisotropy in the impulse strengths.