The retention behaviour and separation of some water-soluble organophosphorus insecticides on polyester-based polyurethane foams.
This paper reports the concentration of some dissolved organic phosphorus insecticides in water by open-cell polyurethane foam. The results of preliminary screening tests on the retention of the tested insecticides (Diazinon, Malathion and Chloropyrifos) by polyester foams indicated that a very high percent removal of the insecticides was obtained. The retention rate was fast and reaches equilibrium in a few minutes. The various parameters affecting the preconcentration of the tested insecticides by unloaded foam, e.g. pH, extraction media, shaking time, salt effect, flow rate, temperature and sample volumes have been optimized via the static mode of separation. The unloaded foams were employed in columns for the retention and recovery of the tested species. The sorption efficiency and the recovery of the tested compounds by the unloaded foam column were found to be up to 95.5%. The equivalent to a theoretical plate by the unloaded foam was found in the range 1.12 - 1.32 +/- 0.2 mm. The sorption mechanism of the tested species by the foam is discussed. The separation of some of the tested species in a mixture was achieved. The foam membrane offers unique advantages over conventional bulk-type granular sorbents and solvent extraction in offering high flow rates, rapid, versatile, effective separation and preconcentration of different species from aqueous samples. The foam provides the advantages of being, insoluble, easily separable and non-polluting, as well as inexpensive.
Detection and semiquantitative determination of bismuth(III) in water on immobilized and plasticized polyurethane foams with some chromogenic reagents.
Polyurethane foams immobilizing 1,2-di-(2-fluorophenyl)-3-mercaptoformazan (F(2)H(2)Dz) and dithizone (H(2)Dz) have been used for the detection of bismuth(III) in water via batch, dynamic and pulsated column modes of extraction. The detection limits of bismuth(III) with the F(2)H(2)Dz- and H(2)Dz-immobilized foams were found to be 0.01 and 0.02 mug ml(-1) respectively. Lower concentrations (</=1 ppb) of bismuth(III) were also detected by employing dynamic and pulsated columns packed with plasticized tri-n-butylphosphate and F(2)H(2)Dz-immobilized reagent foams. The electronic spectra and partition coefficients of the reagents H(2)Dz and F(2)H(2)Dz and their bismuth(III) chelates in chloroform and in polyurethane foams have been determined. Bismuth (V) was also detected by the proposed procedure after prior reduction to bismuth(III) with sulphur dioxide at pH < 1. The effect of diverse ions on the detection of 1 mug of bismuth(III) was critically investigated using F(2)H(2)Dz-immobilized foam.
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).