Corneliu Cojocaru

Removal of cobalt ions from aqueous solutions by polymer assisted ultrafiltration using experimental design approach. part 1: optimization of complexation conditions.

The polymer assisted ultrafiltration process combines the selectivity of the chelating agent with the filtration ability of the membrane acting in synergy. Such hybrid process (complexation-ultrafiltration) is influenced by several factors and therefore the application of experimental design for process optimization using a reduced number of experiments is of great importance. The present work deals with the investigation and optimization of cobalt ions removal from aqueous solutions by polymer enhanced ultrafiltration using experimental design and response surface methodological approach. Polyethyleneimine has been used as chelating agent for cobalt complexation and the ultrafiltration experiments were carried out in dead-end operating mode using a flat-sheet membrane made from regenerated cellulose. The aim of this part of experiments was to find optimal conditions for cobalt complexation, i.e. the influence of initial concentration of cobalt in feed solution, polymer/metal ratio and pH of feed solution, on the rejection efficiency and binding capacity of the polymer. In this respect, the central compositional design has been used for planning the experiments and for construction of second-order response surface models applicable for predictions. The analysis of variance has been employed for statistical validation of regression models. The optimum conditions for maximum rejection efficiency of 96.65% has been figured out experimentally by gradient method and was found to be as follows: [Co(2+)](0)=65 mg/L, polymer/metal ratio=5.88 and pH 6.84.

Removal of cobalt ions from aqueous solutions by polymer assisted ultrafiltration using experimental design approach: Part 2: Optimization of hydrodynamic conditions for a crossflow ultrafiltration module with rotating part

Application of shear-enhanced crossflow ultrafiltration for separation of cobalt ions from synthetic wastewaters by prior complexation with polyethyleneimine has been investigated via experimental design approach. The hydrodynamic conditions in the module with tubular metallic membrane have been planned according to full factorial design in order to figure out the main and interaction effects of process factors upon permeate flux and cumulative flux decline. It has been noticed that the turbulent flow induced by rotation of inner cylinder in the module conducts to growth of permeate flux, normalized flux and membrane permeability as well as to decreasing of permeate flux decline. In addition, the rotation has led to self-cleaning effect as a result of the reduction of estimated polymer layer thickness on the membrane surface. The optimal hydrodynamic conditions in the module have been figured out by response surface methodology and overlap contour plot, being as follows: DeltaP=70 kPa, Q(R)=108 L/h and W=2800 rpm. In such conditions the maximal permeate flux and the minimal flux decline has been observed.

Modeling and multi-response optimization of pervaporation of organic aqueous solutions using desirability function approach.

The factorial design of experiments and desirability function approach has been applied for multi-response optimization in pervaporation separation process. Two organic aqueous solutions were considered as model mixtures, water/acetonitrile and water/ethanol mixtures. Two responses have been employed in multi-response optimization of pervaporation, total permeate flux and organic selectivity. The effects of three experimental factors (feed temperature, initial concentration of organic compound in feed solution, and downstream pressure) on the pervaporation responses have been investigated. The experiments were performed according to a 2(3) full factorial experimental design. The factorial models have been obtained from experimental design and validated statistically by analysis of variance (ANOVA). The spatial representations of the response functions were drawn together with the corresponding contour line plots. Factorial models have been used to develop the overall desirability function. In addition, the overlap contour plots were presented to identify the desirability zone and to determine the optimum point. The optimal operating conditions were found to be, in the case of water/acetonitrile mixture, a feed temperature of 55 degrees C, an initial concentration of 6.58% and a downstream pressure of 13.99 kPa, while for water/ethanol mixture a feed temperature of 55 degrees C, an initial concentration of 4.53% and a downstream pressure of 9.57 kPa. Under such optimum conditions it was observed experimentally an improvement of both the total permeate flux and selectivity.

Optimization of Co2+ ions removal from water solutions via polymer enhanced ultrafiltration with application of PVA and sulfonated PVA as complexing agents

The paper presents the results of the studies of UF-complexation process applied for the removal of Co(2+) ions from water solutions. As binding agents for cobalt ions, the PVA polymer (M(w)=10,000) and its sulfonated form, synthesized in the laboratory, have been used. The method of experimental design and response surface methodology have been employed to find out the optimal conditions for the complexation process and to evaluate the interaction between the input variables, i.e., initial cobalt concentration, pH and amount of the polymer used, expressed as a polymer/Co(2+) ratio r. The data collected by the designed experiments showed that sulfonation of polymer has improved significantly the binding ability of PVA. The optimal conditions of cobalt ions complexation established by response surface model for non-sulfonated PVA polymer have been found to be as follows: the initial concentration of Co(2+)=5.70 mg L(-1), the ratio between polymer and metal ions, r=8.58 and pH=5.93. The removal efficiency of Co(2+) in these conditions was 31.81%. For sulfonated PVA polymer, the optimal conditions determined are as follows: initial concentration of [Co(2+)](0)=10 mg L(-1), r=1.2 and pH=6.5. For these conditions, a removal efficiency of 99.98% has been determined. The experiments showed that Co(2+) removal ability of sulfonated PVA was much higher than its non-sulfonated precursor. Although the polymer concentrations used in the tests with sulfonated PVA were approximately ten times lower than the non-sulfonated one, the removal efficiency of cobalt ions was significantly higher.

Experimental design and optimization of leaching process for recovery of valuable chemical elements (U, La, V, Mo, Yb and Th) from low-grade uranium ore

The paper deals with experimental design and optimization of leaching process of uranium and associated metals from low-grade, Polish ores. The chemical elements of interest for extraction from the ore were U, La, V, Mo, Yb and Th. Sulphuric acid has been used as leaching reagent. Based on the design of experiments the second-order regression models have been constructed to approximate the leaching efficiency of elements. The graphical illustrations using 3-D surface plots have been employed in order to identify the main, quadratic and interaction effects of the factors. The multi-objective optimization method based on desirability approach has been applied in this study. The optimum condition have been determined as P=5 bar, T=120 °C and t=90 min. Under these optimal conditions, the overall extraction performance is 81.43% (for U), 64.24% (for La), 98.38% (for V), 43.69% (for Yb) and 76.89% (for Mo) and 97.00% (for Th).

Nanosized spinel ferrites synthesized by sol-gel autocombustion for optimized removal of azo dye from aqueous solution

Nanosized spinel ferrites MFe2O4 (M = Ni, Co, and Zn) have been prepared by sol-gel autocombustion method using citric acid as a fuel agent. The materials are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The spinel ferrites have been applied for Congo-Red (CR) dye adsorption using batch technique. Different kinetic and equilibrium models have been fitted by nonlinear regression to analyze the adsorption data. In accordance with Langmuir isotherm, the maximum adsorption capacity at 293 K is 14.06mg/g for CoFe2O4 and 17.13 mg/g for NiFe2O4. The values of mean free energy determined from Dubinin-Radushkevich isotherm are higher than 8 (kJ mol-1), indicating a chemisorption mechanism. Based on the calculated thermodynamic parameters (free energy, enthalpy, and entropy) the adsorption of CR onto ferrites is a spontaneous and endothermic process. Response surface methodology has been applied to construct the multiple regression models for prediction of the adsorption capacity and removal efficiency. The model-based optimization has been performed using genetic algorithms and desirability function approach. The single-objective optimization has yielded a maximum value of color removal efficiency of 98.995%, using NiFe2O4 adsorbent. The multiobjective optimization has resulted in the improvement of both removal efficiency and adsorption capacity.

Response surface methodology for the modelling of 85Sr adsorption on zeolite 3A and pumice

The adsorption of 85Sr from aqueous solutions on to zeolite 3A and three types of pumice materials (i.e. Kayseri, Isparta and Nevsehir) was investigated in this study. Experiments with radioactive 85Sr were performed to test the sorption ability of the sorbents to remove this radioisotope from liquid radioactive wastes. The influence of sorbent dosage and initial activity of feed solution on the decontamination factor were analysed and optimized by means of response surface methodology. The parameters of the experiments, namely temperature, pH, time, stirring efficiency, were selected in preliminary tests. The experimental results showed that the most efficient pumice sorbent for 85Sr is Isparta, for which a maximal decontamination factor of 76.92 was obtained by using the sorbent dosage of 0.5% w/v. However, the commercial zeolite 3A was 2.71-fold more efficient than Isparta pumice for decontamination of strontium radioactive solutions. Isparta pumice is a low-cost natural sorbent, and its ability to effectively bind strontium radioisotope from water solutions suggests that this material has further applications for radioactive waste treatment.

Multi-Objective Optimization of Indigo Carmine Removal by an Electrocoagulation/GAC Coupling Process in a Batch Reactor

A coupling process between Electrocoagulation (EC) and GAC was employed to separate dyes from aqueous solutions. The removal of an indigoid dye, namely C.I. Acid Blue 74, was tested. A novel approach for optimizing EC-based techniques is presented. In addition to maximizing removal efficiency, minimizing consumptions of energy and electrode materials were also targeted by means of multi-objective optimization in order to reduce the specific costs. A very good cost-efficiency feature of EC/GAC coupling process operated under optimal conditions to treat wastewater from dyestuff has been revealed. The independent variables considered were the current density, influent pH, contact time, granular activated carbon dose, and initial dye concentration. Simple maximization of color removal efficiency and multi-objective optimization were compared. Two different constraints were considered for each type of optimization. The determined costs outline the cheapness feature of the EC/GAC system as a potential dye wastewater treatment technology.

Flexible cyclic siloxane core enhances the transfection efficiency of polyethylenimine-based non-viral gene vectors

Transfection of nucleic acid molecules, large enough to interfere with the genetic mechanisms of active cells, can be performed by means of small carriers, able to collectively collaborate in generating cargocomplexes that could be involved in passive mechanisms of cellular uptake. The present work describes the synthesis, characterization, and evaluation of transfection efficacy of a conjugate molecule, which comprises a cyclic siloxane ring (2,4,6,8-tetramethylcyclotetrasiloxane, cD4 H) as the core, and, on average, 3.76 molecules of 2 kDa polyethyleneimine (PEI) as cationic branches, with an average molecular mass of 7.3 kDa. As demonstrated by in silico molecular modeling and dynamic simulation, the conjugate molecule (cD4 H-AGE-PEI) tends to adopt an asymmetric structure, specific for amphipathic molecules (confirmed by a log P value of -1.902 ± 0.06), that favors a rapid interaction with nucleic acids. The conjugate and the polyplexes with the pEYFP plasmid were proved to be non-cytotoxic, and capable of ensuring transfection yields better than 30%, on HEK 293T cell culture, superior to the value obtained using the SuperFect® reagent. We presume that the increased transfection efficacy originates in the ability of the conjugate to locally tightly encompass pDNA molecules by electrostatic interaction mediated by the short PEI branches, and consequently to expose the siloxane hydrophobic moiety, which decreases the interaction energy with the lipid layers.

Application of Low-Cost Sorbent for Oil Spill Sorption Using Response Surface Methodological Approach

The paper deals with oil spill clean-up using peat as low-cost sorbent material. Light fuel oil of regional production has been used in all experiments as the representative petroleum product. The design of experiments and response surface methodological approach has been used for the investigation of sorption process. A regression equation (response surface model) has been proposed for the prediction of removal efficiency as a function of design variables (factors), i.e., sorbent dosage, drainage time and initial thickness of oil slick on water. A very good agreement between the experimental data and response surface model has been found. The linkage between the removal efficiency and factors has been illustrated via response surface plots and contour lines maps. Based on the regression equation the maximal removal efficiency has been found by optimization.