SOLVENT EXTRACTION OF URANIUM(VI) AND THORIUM(IV) WITH A TETRA-CARBOXYLATED CALIX[4]ARENE AND EFFECT OF ALKALI IONS (Na+, K+)

ABSTRACT

The solvent extraction of uranium(VI) and thorium(IV) with a tetra-carboxylated calix[4]arene (LH₄) in chloroform has been studied in the presence or absence of alkali ions (M⁺=Na⁺, K⁺). When studied alone, UO₂ ²⁺ and Th⁴⁺ were extracted into chloroform as 2:2 and 1:1 metal:ligand complexes, respectively. The efficiency of extraction increases in the presence of alkali ions, due to the formation of heteronuclear complexes. For uranium(VI), the extracted species are found to be both 2:2:2 and 1:1:1 (uoi₂ ²⁺:M⁺:LH₄,) mixed complexes. For Th(IV) in the presence of Na⁺, the formation of a mixed complex in 1:1:1 (Th(IV):Na⁺:LH₄,) proportions has been evidenced. However, the exact nature of this species could not be determined. In practical grounds, LH. may be useful as a selective extracting agent for Th(IV) with respect to U(VI) since separation factor Th(IV)/U(VI) close to 1000 have been measured in competitive extraction, in the presence or absence of alkali ions.     

LCA of poplar bioenergy system compared with Brassica carinata energy crop and natural gas in regional scenario

The poplar bioenergy system has been analysed applying life cycle assessment (LCA) to compare its environmental performance to: Ethiopian mustard bioenergy system and natural gas. The life cycle impact assessment (LCIA) shows that the use of fertilizers is the highest impact in four of the 10 environmental categories, representing between 39% and 67% of the impact in them. The diesel used in transport vehicles and agricultural tractors also has a significant impact in another five of the 10 analysed categories 40–85%. The poplar bioenergy system contributes to global warming with 1.90–1.98 g CO₂ eq MJ^?1 biomass produced. The production and transport as far as the thermoelectric plant of the poplar biomass consumes 0.02 MJ of primary energy per 1 MJ of biomass stored. In comparison with Ethiopian mustard and natural gas, it reduces primary energy consumption by 83% and 89% and the greenhouse gas emission by 84% and 89%, respectively. The results of the analysis support that the poplar bioenergy system is viable from an energy balance and environmental perspective for producing energy in southern Europe, as long as it is cultivated in areas where water is available. This latter point and the better environmental performance of both crops in comparison to natural gas allows us to affirm that the combination of several crops adapted to the local agro-climatic conditions of the territory will be the most suitable strategy in Mediterranean areas that wish to reach the global energy production targets in terms of biomass established by the European Union (EU).     

Feasibility assessment of Brassica carinata bioenergy systems in Southern Europe

A detailed reliability assessment was made of electricity generation systems in Spain that are based on Brassica carinata cultivation. The assessment considers the following chain of energy generation: biomass cultivation and harvesting, transportation and electricity generation in biomass power plants (10, 25 and 50 MW). Flue gas desulphurisation systems have been included for larger plants following the criteria of the Spanish legislative framework. Six scenarios were analysed in accordance with the following aspects: two crop distributions around the power plant and three power plant sizes. The results show that the cost of biomass delivered at the power plants ranges from 107.81 to 112.54 € Mg⁻¹ dry basis.Sensibility analysis shows that variation in biomass production in the field demonstrates that biomass cost delivered at the plant is notably affected and consequently so is the system's feasibility.Furthermore, the increase of the price of CO₂ emission credits, also considered in sensibility analysis, can help to improve the reliability of systems because of the increase of gross profit for each scenario.This study clears up the Economic uncertainty of B. carinata biomass energy systems based on the single use of this renewable energy resource. Higher crop productivities are needed to ensure an economic reliability of the analysed systems. On the other hand biomass mix can solve SO₂ emission cleaning cost for large power plants, improving the reliability of B. carinata application as fuel.     

Environmental Assessment of Sewer Construction in Small to Medium Sized Cities Using Life Cycle Assessment

In a world with an increasing urban population, analysing the construction impacts of sanitation infrastructures through Life Cycle Assessment (LCA) is necessary for defining the best environmental management strategies. In this study, the environmental impacts of one linear meter of sewer constructive solution were analysed for different pipe materials and diameters used in Southern Europe; a unit of different sewer appurtenances (pump, manhole and inspection chamber) was also considered. The impacts of the pipe materials were compared considering different lifespan periods and high-density polyethylene (HDPE) turned out to be the worst option, being polyvinyl chloride (PVC) and concrete the most favourable ones. Few data are available on the material and energy flows in the installation stage; therefore, a comparative analysis of trenches with sand and concrete bedding was conducted. The results show that the installation stage represents up to 80 % of the total life-cycle impact of the constructive solutions. Concrete pipes with half-concrete/half-sand bedding are the best option and produce 20–30 % of the impact of HDPE pipes with concrete bedding. Hence, designers should focus not only on the pipe but also on the trench model. A methodology was presented to enable the impact aggregation of the different sewer elements, and Betanzos (Spain) was selected to conduct a pilot study in small cities. In the future, studies will need to incorporate the use and maintenance stage, as it is not standard and varies according to the physical features of the cities. Finally, this study provides basic concepts for developing eco-efficiency indicators.     

Bridging at the Nanometric Scale in 2.5D Cf–SiC Composites

This short paper presents the matrix microcrack bridging at a nanometric scale which was evidenced during creep tests of 2.5D C_f–SiC composites. It also shows the importance of the investigations of mechanical behavior of composite materials at all the different scales: from the macroscopic down to the nanoscopic one.     

Pediatric radiography. The nurses' role]

After a brief review of advanced radiographic diagnostic techniques, how to utilize them in the most cost-effective manner and minimize their risks, the authors examine the role of the nurse in using exploratory radiography in children. Patient opposition, immobilization and protection are some of the possible problems that one might encounter when working in this setting.     

Novel calixarene derivatives as inhibitors of mild C-38 steel corrosion in 1 M HCl

Calixarenes CA1–CA4 containing one to four 4-imidazolylethylamidocarbonyl groups were synthesized and tested as inhibitors for the corrosion of mild steel in 1 M HCl at 308 K. The study was made using Tafel polarisation and weight-loss methods. In contrast to CA1, calixarenes CA2–CA4 were good inhibitors, reaching inhibition efficiencies (E%) of 94 to 100% at 10⁻⁴ M. The values of the inhibition efficiency calculated by the two techniques were in acceptable agreement. E% increased with the number of 4-imidazolylethylamidocarbonyl groups attached to the calixarene. Polarisation curves showed that CA2–CA4 act as mixed-type inhibitors. Their adsorption on the steel surface followed a Langmuir isotherm. Thermodynamic parameters of adsorption were also deduced.