Rezvan Torkaman

Chemometric assisted ultrasound leaching-solid phase extraction followed by dispersive-solidification liquid-liquid microextraction for determination of organophosphorus pesticides in soil samples.

Ultrasound leaching-solid phase extraction (USL-SPE) followed by dispersive-solidification liquid-liquid microextraction (DSLLME) was developed for preconcentration and determination of organophosphorus pesticides (OPPs) in soil samples prior gas chromatography-mass spectrometry analysis. At first, OPPs were ultrasonically leached from soil samples by using methanol. After centrifugation, the separated methanol was diluted to 50 mL with double-distillated water and passed through the C18 SPE cartridge. OPPs were eluted with 1 mL acetonitrile. Thus, 1 mL acetonitrile extract (disperser solvent) and 10 µL 1-undecanol (extraction solvent) were added to 5 mL double-distilled water and a DSLLME technique was applied. The variables of interest in the USL-SPE-DSLLME method were optimized with the aid of chemometric approaches. First, in screening experiments, fractional factorial design (FFD) was used for selecting the variables which significantly affected the extraction procedure. Afterwards, the significant variables were optimized using response surface methodology (RSM) based on central composite design (CCD). Under the optimum conditions, the enrichment factors were 6890-8830. The linear range was 0.025-625 ng g(-1) and limits of detection (LODs) were between 0.012 and 0.2 ng g(-1). The relative standard deviations (RSDs) were in the range of 4.06-8.9% (n=6). The relative recoveries of OPPs from different soil samples were 85-98%.

Computational simulation of CO2 removal from gas mixtures by chemical absorbents in porous membranes

In this study chemical absorption of CO2 from a N2/CO2 gas mixture in tetramethylammonium glycinate ([N1111][Gly]) solution using hollow-fiber membrane contactors by employing the CFD (computational fluid dynamics) method was investigated. A two dimensional mathematical model was developed to describe diffusion in axial and radial directions of the HFMC (hollow-fiber membrane contactor). Also, the model gives an account of convection in the tube and the shell sides with chemical reaction between CO2 and the absorbent. Results of simulation showed good agreement with experimental data which reveals the validity of the model. CO2 absorption from the gas mixture increases as the flow rate and the concentration of the absorbent goes up. On the other hand, increase of gas flow rate decreases removal of CO2. The proposed model can predict CO2 capture from gas mixtures in HFMCs.

A new model for prediction of drop size distribution in a liquid–liquid extraction column

In this study, a new model for prediction of drop size distribution is proposed in the asymmetric rotating disc pilot plant column (ARDC) by the maximum entropy density approximation technique. The liquid extraction systems including toluene–water, n-butyl acetate–water and n-butanol–water were used with this column. An image analysis technique was applied to determine the drop size distribution as a function of operating parameters and physical properties. By applying abrupt changes of the operating parameters, the drop behaviors in the column were investigated. The results show that the agitation speed has a main effect on the drop size distribution in the column. However, the effects of phase flow rates are not significant. The empirical correlations are proposed to describe Lagrange multipliers in the maximum entropy function in terms of operating variables and physical properties of the systems. Except for these findings, an empirical correlation is proposed for estimation of the Sauter mean drop diameter in terms of operating variables, column geometry and physical properties. The proposed correlations are evaluated based on the goodness of fit statistics, namely, χ2, R2 and RMSE. The fitting results by the maximum entropy principle method seem to be fairly accurate and reasonable on the basis of the experimental data. These completed sets of data could be used for modeling approaches in the liquid–liquid extraction columns.

Ultra-preconcentration and determination of organophosphorus pesticides in soil samples by a combination of ultrasound assisted leaching-solid phase extraction and low-density solvent based dispersive liquid–liquid microextraction

An ultra-preconcentration technique composed of ultrasound assisted leaching-solid phase extraction (USAL-SPE) and low-density solvent based dispersive liquid–liquid microextraction (LDS-DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) was developed for preconcentration and determination of organophosphorus pesticides (OPPs) in soil samples. Parameters that affect the efficiency of the procedure were investigated by a fractional factorial design (FFD). Afterwards, variables showing significant effects on the analytical responses were considered using response surface methodology (RSM) based on a central composite design (CCD). Under optimum conditions, the enrichment factors were 7215–9842, the linear range was 0.012–625 ng g−1 and limits of detection (LODs) were between 0.002 and 0.125 ng g−1. The relative standard deviations (RSDs) were in the range of 5.4–8.3% (n = 6), and the relative recoveries of OPPs from different soil samples were 84–98%. The proposed methodology constitutes a suitable approach for the analysis of OPPs in complex soil samples and requires minimum organic solvents consumption, sample manipulation and increased sample throughput.

Investigations on the complete removal of iron(III) interference on the uranium(VI) extraction from sulfate leach liquor using Alamine 336 in kerosene

Abstract Uranyl sulfate obtained by uranium ore leaching of an industrial sample deposit of Gachin site was used for uranium separation by the solvent extraction technique. The presence of other elements in the sulfate leach liquors has a negative impact on the uranium extraction process using Alamine 336; therefore, the operating costs are increased. In this study, the separation of uranium(VI) and iron(III) by Alamine 336 and kerosene have been examined as an extractant and a diluent, respectively. For this purpose, the effects of operating parameters on the extraction process such as Alamine 336 concentration, modifier concentration, contact time, initial aqueous pH, sulfate ion concentration, temperature, and stripping agents were investigated. Also, the complete removal of iron(III) interference from the sulfate leach liquor before the extraction step has been studied with reducing agents. The equilibrium constants and stoichiometric coefficients for uranium and iron extraction with Alamine 336 in the sulfate leach liquors were calculated. Likewise, the values of the thermodynamic parameters such as Gibbs energy, enthalpy and entropy were determined to prove the exothermic and spontaneous reactions. The mentioned procedure is proposed for the uranium separation from the impurities in the sulfate ores using tertiary amine for production of purified uranium.

CFD simulation of water transport through porous membrane evaporators

AbstractMembrane evaporation (ME) presents interesting working conditions including low operating temperature and also low energy consumption. These advantages make the process attractive for concentration of aqueous solutions containing heat-sensitive components. Performance of ME process carried out in a flat-sheet membrane contactor was studied theoretically in this work. A three-dimensional mathematical model was developed to predict the performance of ME process. The concentration, momentum, and energy equations were solved for description of process. Finite element method was utilized for solution of governing equations and simulation of process. By obtaining the concentration distribution, the flux of water evaporation was determined and compared with the experimental data reported in literature. It was also indicated that the developed three-dimensional model is appropriate for the prediction of the performance of membrane evaporators. The simulation results revealed that enhancement of velocity o...