Geochemical approach to the Bou Hadjar hydrothermal system (NE Algeria)

The Bou Hadjar low-temperature hydrothermal system is located in northeast Algeria. The four main thermal springs that are the subject of the study emerge ith temperatures between 32 and 60°C from allochthonous formations. The reservoir temperature has been estimated from chemical compositions by utilizing simultaneously the silica, gas and sulfate-water oxygen isotope geothermometers, fluid-mineral equilibrium calculations, and a mixing model. According to these thermometric methods, the most probable subsurface temperature is in the range 75–106°C. The mixing model suggests a temperature of 125°C for the parent water.     

Spatial and seasonal variations and ecotoxicological significance of sediment trace metal concentrations in Kebir-Rhumel basin (Northeast of Algeria)

This study sought to assess sediment contamination by trace metals (cadmium, chromium, cobalt, copper, manganese, nickel, lead and zinc), to localize contaminated sites and to identify environmental risk for aquatic organisms in Wadis of Kebir Rhumel basin in the Northeast of Algeria. Water and surficial sediments (0-5 cm) were sampled in winter, spring, summer and autumn from 37 sites along permanent Wadis of the Kebir Rhumel basin. Sediment trace metal contents were measured by Flame Atomic Absorption Spectroscopy. Trace metals median concentrations in sediments followed a decreasing order: Mn > Zn > Pb > Cr > Cu > Ni > Co > Cd. Extreme values (dry weights) of the trace metals are as follows: 0.6-3.4 microg/g for Cd, 10-216 microg/g for Cr, 9-446 microg/g for Cu, 3-20 microg/g for Co, 105-576 microg/g for Mn, 10-46 microg/g for Ni, 11-167 microg/g for Pb, and 38-641 microg/g for Zn. According to world natural concentrations, all sediments collected were considered as contaminated by one or more elements. Comparing measured concentrations with American guidelines (Threshold Effect Level: TEL and Probable Effect Level: PEL) showed that biological effects could be occasionally observed for cadmium, chromium, lead and nickel levels but frequently observed for copper and zinc levels. Sediment quality was shown to be excellent for cobalt and manganese but medium to bad for cadmium, chromium, copper, lead, nickel and zinc regardless of sites.     

Assessment of sediment quality and pore water ecotoxicity in Kebir Rhumel basin (NE-Algeria): a combined approach

The objectives of this study are to use different approaches to assess the current pollution status in the wadis of the Kebir Rhumel basin. First, sediment trace metal contents were measured by flame atomic absorption spectroscopy. Then, sediment quality was assessed on the basis of contamination assessment indexes such as: Geoaccumulation Index (Igeo), Contamination factor (C(f)), Contamination degree (C(d)), Sediment Pollution Index (SPI) and SEQ guidelines (Consensus Sediment Quality Guidelines). In addition, several toxicity tests (Daphnia magna mobility inhibition acute test-48 h, Aliivibrio fischeri luminescence inhibition acute test - 15/30 mn and Pseudokirchneriella subcapitata growth inhibition chronic test - 72 h) were conducted to assess sediment pore water ecotoxicity. Trace metal concentrations followed the order: Mn > Zn > Pb > Cr > Cu > Ni > Co > Cd. Indexes used indicate varying degrees of sediment quality. Igeo, C(f), C(d) and SPI reveal a polymetallic contamination dominated by two or more elements in which Cd, Cu and Pb are of greatest concern. SEQ guidelines showed that biological effects on fauna would likely be observed occasionally and/or frequently for Cd, Cr, Cu, Pb and Zn contents. Test organisms exposed to sediment pore water showed that the algal P. subcapitata test was more sensitive than the D. magna and A. fischeri tests. Hence, algal growth inhibition proved to be the most sensitive response to contaminants present in sediment extracts but a significant relationship with trace metal contents was not demonstrated.     

Novel nucleophilic/basic and acidic organocatalysts for reaction between poorly reactive diisocyanate and diols

Original basic or acidic organic compounds derived from guanidine or phenyl phosphonic acid were specifically designed and tested as new catalysts for the bulk synthesis of polyurethane prepolymers from a precursor system with particularly low reactivity (secondary alcohol + aliphatic isocyanate at low temperature). Both families showed interesting catalytic activities at 60–80 °C, but must nevertheless be used in much higher amounts (1 mol%, i.e. between 0.15 and 0.50 wt%) than traditional metal-based catalysts. The efficiency of guanidine derivatives seems to be related to their nucleophilicity, whereas that of phosphonic acid derivatives depends on their acidity. However, the solubility of the considered species in the reactive medium also plays a major role. The water/alcohol selectivity of the catalysts, especially at room temperature, was then examined as an additional criterion. Guanidines are not selective and favor the reaction of isocyanate groups with water as much as that with alcohols. Phenyl phosphonic acid derivatives are more selective, and particularly pentafluorophenyl phosphonic acid displays a remarkable catalytic activity together with an acceptable selectivity and could represent an interesting and safer alternative to toxic tin and mercury derivatives for many industrial polyurethanes.     

A first-principles study of the structural,elastic, electronic,vibrational, and optical properties of BaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1?xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe_1?xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe_1?xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1?xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1?xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.