AMIRKABIR
Year:2004 | Volume:15 | Issue:58-C|Papers Count:5

An equation has been suggested which correlate the NMR and refractometry results to evaluate the stability constant of electron donor acceptor complexes. Using this equation the stability constant of complexation between carbon tetrachloride and toluene in cyclohexane has been studied by refractometry and NMR spectroscopy.    

In this work, the activation energy in the viscosity equation derived on the basis of Eyring's absolute irate theory is expressed in terms of a simple two-parameter linear function of temperature. The viscosity data of 111 pure components are used to evaluate the parameters of activation energy and, then they are correlated in terms of each component characteristics, such as reduced boiling point and acentric factor. The results of viscosity calculations are compared with those of the other models and are how a higher accuracy of the results obtained by the viscosity equation used in this work.    

There are great interests in searching for natural compound, preferably from plant sources, exhibiting antioxidant activity in order to decrease/eliminate use of the synthetic antioxidants. Hulls from two most prominent varieties of Iran's Pistachio have been examined for the presence of components showing antioxidant activity. The polyphenolics yields of the different solvent extracts (ethanol, methanol, and aqueous solutions of these two) were measured using the Folin method. The methanol extract of Damghan hulls had higher amount of total phenolics as compared to that of the ethanolic extract. Although, recovery of the total phenolics from ethanolic and methanolic extract of hulls of Kerman pistachio, showed to be comparable. The highest yield of phenolics from Damghan variety using aqueous solution of ethanol (50:50(H2O)) was 28.8mg per g of the dried pistachio hulls. While the yield of the ethanolic (75:25(H2O)) extract from Kerman's pistachio hulls was 19.8 mg per g dried pistachio hulls. The extraction was carried out in the form of four successive steps, and the extracts were pooled to obtain an estimation of the total extractable phenolics. Thiocyanate assay was used to assess the degree of the antioxidative activities of the extracts. The aqueous ethanolic (75:25 EtOH-H2O) extract for both of the pistachio varieties   showed to have highest degree of inhibition of linoleic peroxidation at the levels of 93 and 99% respectively, very comparable with that of the synthetic type of antioxidant BHA. Hplc analysis   revealed presence of gallic acid in the above-mentioned extracts. Percentage (%) of gallic acid in the recovered phenolics from the extracts was 79 and 82 for Damghan and Kerman varieties, respectively.      

The thermodynamic properties of OH-bonding solutions have been investigated by NMR is spectroscopy for two binary systems of alcohols (Methanol and Ethanol) in CCl4 at temperatures 308, 328, 318 and 338 K. A modified model based on the two previous models Athermal Association model (AA) and Association with Variable Equilibrium Constant model (AVEC) have been used for, fitting the experimental data. The activity coefficients and the excess thermodynamic properties (GE, HE) of associated alcohols were calculated by the proposed modified model and the results were compared with data of vapor pressure measurement. This comparison indicated that the proposed model is capable of treating the NMR data to obtain the thermodynamic properties of the associated solutions.    

In this research the effect of population ratio in three- membered mixed cultures consisting of 5 different strains on the bioleaching of sulfidic copper ores was evaluated. Three strains were Leptospirillum ferrooxidans DSM2705, Thiobacillus thiooxidans DSM622 and Thiobacillus ferrooxidans DSM11477, Thiobacillus ferrooxidans DSM9465 and Thiobacillus ferrooxidans DSM1927. Each group contains L.f, T.t and one of the T.f strains in 9 different population ratios. Also the role of ferrous ion concentration in related microbial medium on bioleaching rate was investigated. It was found that type of microorganism, population ratio and ferrous ion concentration influence the bioleaching rate. For a low grade copper ore the highest copper recovery was obtained by using a mixed culture of L.f, T.t, and T.f DSM9465 with the population ratio of 3:5:1 in a medium containing 20 g/L ferrous sulfate. In other experiments, the best results for bioleaching of a chalcopyrite ore was obtained with the same mixed culture and a mixed culture containing L.f, T.t and T.f DSM11477 with population ratio of 3:5:1, in medium containing 20 g/L ferrous sulfate. The best result for bioleaching of low grade copper ore was 26% during 17 days while for chalcopyrite ore was 26% during 27 days, which show an increase of 12% and 46%  respectively.