The solvent extraction behaviour of chromium with Bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex [R] 272)

The bulk of the world's known nickel reserves are contained in laterite ores but sulphidic ores remain the main source of the Western world's nickel production. With the continuing increase in nickel consumption and the depletion of sulphidic ores, the traditional source of nickel, the extraction of nickel from lateritic ores has been the subject of research interest worldwide. Advances in pressure acid leaching (PAL) technology have resulted in significant commercial attempts to extract nickel from these ores. Leaching the ore with sulphuric acid at elevated temperatures and pressures allows almost complete dissolution of the nickel and cobalt, a valuable byproduct of these ores, but yields highly contaminated pregnant leach solutions. Separating and purifying the nickel and cobalt from these solutions remains a hindrance to full commercial production. Several purifying techniques have been commercialised but all suffer from continuing technical problems. Among them, however, the direct solvent extraction (DSX) technique offers several advantages. Direct solvent extraction involves the separation of the nickel and cobalt directly from the partially neutralised pregnant liquor stream (PLS) by solvent extraction with Cyanex(R) 272 as the extractant. However certain contaminants adversely affect the solvent extraction process. Among them is chromium and little is known about the solvent extraction behaviour of this metal. The present work investigated the solvent extraction of chromium with Cyanex(R) 272. It was found that the solvent extraction behaviour of chromium(III) and chromium(VI), both of which could be found in PAL-generated PLS, are distinctly different.For chromium(III), solvent extraction tests showed that (a) it is extracted in the pH range 4-7; (b) the extraction is partly influenced by diffusion; (c) the apparent equilibration time is significantly longer than most transition metals; (d) increases in temperature from 22 to 40 C resulted in increases in the extraction; (e) the pH0.5 increases in the order nitrate < chloride < sulphate in the presence of these anions; (f) the presence of acetate depresses extraction of chromium(III) when the solution is allowed to stand before extraction; (g) in the PLS, chromium(III) precipitated at lower pH than that predicted by the solubility product principle; and (h) the pH0.5 decreases as the Cyanex(R) 272 concentration increases. Chromium(III) is initially extracted by solvation of its inner sphere complex, which then undergoes further reaction in the organic phase leading to the formation of a much more stable species that is difficult to strip. A reaction scheme together with a description of both the initially extracted and resulting stable species is proposed. Extraction of chromium(VI), on the other hand, (a) occurs at pH less than 2 by solvation of chromic acid; (b) is independent of the aqueous phase composition; (c) does not occur in the pH range (3-6) used in the separation of nickel and cobalt. The latter is irrespective of temperature up to 40 C, the use of industrial PLS as the aqueous phase or the presence of an anti-oxidant in the organic phase. The stripping of chromium(III) from a loaded organic phase can be achieved using 1-4 mol L-1 mineral acids provided the stable organic species have not formed making industrial scale stripping of chromium(III) from Cyanex(R) 272 difficult. The exact composition of the aqueous phase during extraction affects the stripping efficiency

A Timelapse Camera Dataset and Markov Model of Dust Devil Activity at Eldorado Playa, Nevada, USA

We report a May-June 2015 survey of dust devil activity on a Nevada desert playa using an inexpensive digital timelapse camera. We discuss techniques for exploiting the large volume of data (∼32,700 images, made publicly-available) generated in these observations, similar to imaging from Mars landers and rovers, noting the diurnal image filesize variations as a useful quick-look metric of weather conditions. We present results from a semi-automated image classification: this classification is available to other workers, for example for benchmarking automated procedures. The acquisition of images at 1/min for some 36 days permits study of the diurnal variation of dust devil activity (e.g. 85% of the dust devil images [i.e. those images manually classified as showing dust devils] occur between 12:00 and 17:00; during the period of peak activity 13:00–15:00 about 7% of images contain well-defined dust devils of several meters diameter or larger). The data also permit the dependence of dust devil characteristics on ambient conditions. We construct a simple two-state Markov model for the occurrence and persistence of dust devils (a few per cent chance that new dust devil activity appears in the next image; and a ∼45% chance that activity stops) which may help inform strategies for acquiring and interpreting field observations

Lithium-ferrate-based cathodes for molten carbonate fuel cells

Argonne National Laboratory is developing advanced cathodes for pressurized operation of the molten carbonate fuel cell (MCFC) at approximately 650 degrees Centigrade. These cathodes are based on lithium ferrate (LiFeO[sub 2]) which is attractive because of its very low solubility in the molten (Li,K)[sub 2]CO[sub 3] electrolyte. Because of its high resistivity, LiFeO[sub 2] cannot be used as a direct substitute for NiO. Cation substitution is, therefore, necessary to decrease resistivity. The effect of cation substitution on the resistivity and deformation of LiFeO[sub 2] was determined. The substitutes were chosen because their respective oxides as well as LiFeO[sub 2] crystallize with the rock-salt structure

Questioning policy, youth participation and lifestyle sports

Young people have been identified as a key target group for whom participation in sport and physical activity could have important benefits to health and wellbeing and consequently have been the focus of several government policies to increase participation in the UK. Lifestyle sports represent one such strategy for encouraging and sustaining new engagements in sport and physical activity in youth groups, however, there is at present a lack of understanding of the use of these activities within policy contexts. This paper presents findings from a government initiative which sought to increase participation in sport for young people through provision of facilities for mountain biking in a forest in south-east England. Findings from qualitative research with 40 young people who participated in mountain biking at the case study location highlight the importance of non-traditional sports as a means to experience the natural environments through forms of consumption which are healthy, active and appeal to their identities. In addition, however, the paper raises questions over the accessibility of schemes for some individuals and social groups, and the ability to incorporate sports which are inherently participant-led into state-managed schemes. Lifestyle sports such as mountain biking involve distinct forms of participation which present a challenge for policy-makers who seek to create and maintain sustainable communities of youth participants

An Investigation Demonstrating the Feasibility of Microwave Sintering of Base-Metal-Electrode Multilayer Capacitors

Abstract. A microwave sintering technique has been developed for base-metal electrode (BME) multilayer ceramic capacitors (MLCCs). Commercial green chips of size 0603 MLC with nickel electrodes were sintered in a microwave field. With a specially designed susceptor/insulation package to optimize coupling and uniformity of heating, a number of sintering experiments were conducted in the temperature range of 1200 to 1250 • C in a multimode microwave cavity operating at 2.45 GHz under a partially reducing atmosphere. Microstructure of the microwave processed MLCCs was investigated with both SEM and TEM techniques. The dielectric properties of the microwave sintered MLCCs were measured and compared with those sintered using conventional process at 1320 • C and lower pO 2 &apos;s ≈ 10 −9 atms. The results demonstrate that nickel electrodes remain metallic after microwave sintering even though the pO 2 &apos;s were relatively high and would thermodynamically favor NiO. The microwave sintered samples showed a dense, fine and uniform microstructure. The properties of the microwavesintered samples were comparable to the conventionally sintered samples. The microwave processing was found to have enhanced sintering kinetics of the BME MLCCs, lowering sintering temperature by about 100 • C and also the processing time by about 90%

Superconducting wires

The requirement of high critical current density has prompted extensive research on ceramic processing of high-T/sub c/ superconductors. An overview of wire fabrication techniques and the limitations they impose on component design will be presented. The effects of processing on microstructure and critical current density will also be discussed. Particle alignment has been observed in extruded samples which is attributed to high shear stresses during plastic forming. Composites of superconductor and silver in several configurations have been made with little deleterious effect on the superconducting properties. 35 refs., 2 figs., 1 tab

Strength and flexibility of bulk high-{Tc} superconductors

Strength, fracture toughness, and elastic modulus data have been gathered for bulk high-temperature superconductors, commercial 99.9% Ag, and a 1.2 at.% Mg/Ag alloy. These data have been used to calculate fracture strains for bulk conductors. The calculations indicate that the superconducting cores of clad tapes should begin to fracture at strains below 0.2%. In addition, residual strains in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes have been measured by neutron diffraction. An explanation is offered for why many tapes appear to be able to tolerate large strains before exhibiting a reduction in current transport