Tanase Dobre

Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl(2)) and sodium carbonate (Na(2)CO(3)) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.

Composite films of poly(vinyl alcohol)–chitosan–bacterial cellulose for drug controlled release

Mono and multilayer composite films of poly(vinyl alcohol)-chitosan-bacterial cellulose (PVA/chitosan/BC) have been prepared to achieve controlled release of ibuprofen sodium salt (IbuNa) as model drug. The composite films have been characterized by Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Surface morphology was investigated by scanning electron microscopy (SEM). Equilibrium swelling was measured in water at two different pH values and in vitro release of IbuNa in pH 1.2 and pH 7.4 media was studied. The release experiments revealed that drug release is pH sensitive. The release kinetics of IbuNa could be described by the Fickian model of diffusion with a good agreement. The IbuNa release rate was decreasing for all the films as the BC concentration was increased in the films composition, the decrease being higher for the multilayer films.

Reactive extraction of phenols using sulfuric acid salts of trioctylamine

An experimental study of phenol and o-cresol reactive extraction using sulfuric acid salts of trioctylamine, via emulsion liquid membrane is presented. The effects of carrier concentration and of the volume ratio of phases were investigated. Two models, one proposed by Chaudhury and Pyle (1992) and the second proposed by Yan (1993) were tested. The model predictions are in good agreement with the experimental data.

Influence of sodium dodecyl sulfate and cetyl trimethylammonium bromide upon calcium carbonate precipitation on bacterial cellulose

Calcium carbonate was deposed on bacterial cellulose (BC) never-dried membranes in the presence of different concentrations of sodium dodecyl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB) by a precipitation reaction between aqueous solutions of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) containing, or not, surfactant in their composition. Different shapes of crystals were obtained from rhombohedral ones to flowerlike, depending on surfactant type and concentration. From the two surfactants tested, SDS has a greater influence on calcium carbonate morphology than CTAB. The only polymorph obtained in all studied cases was calcite. The composite films BC-calcite were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The obtained BC-calcium carbonate composites could be used in paper manufacturing.

Potassium sorbate release from poly(vinyl alcohol)-bacterial cellulose films ‡

Active packaging materials are the subject of research because their performance exceeds that of traditional packaging. From this class, antimicrobial materials extend the shelf-life of products and reduce the risk of contamination by pathogens. In this paper, new composite materials with antimicrobial properties are obtained by using polyvinyl alcohol and bacterial cellulose powder. Potassium (2E,4E)-hexa-2,4-dienoate was used as the antimicrobial agent. The films thus obtained were characterised using Fourier-transform infrared spectroscopy and scanning electron microscopy. Mass transfer phenomena concerning the release of potassium (2E,4E)-hexa-2,4-dienoate were investigated. The results indicated that the new biocomposite films could be used as antimicrobial packaging materials.

Uranium (VI) adsorption equilibrium on purolite resin SGA 600 U/3472

AbstractThis paper characterizes uranium (VI) sorption from synthetic solutions using a fixed bed Purolite resin SGA 600 U/3472 system. The effect of the sulphate anion presence in the liquid phase on sorbtion dynamics and equilibrium is analysed. In the industrial processing of solutions obtained from leaching of uranium ore (alkaline/acid), in a continuous system, there are several compounds which strongly compete with uranium for ion exchange sites and consequently these substances depress the uranium adsorption. The influence of vanadate, molybdate, chloride, and nitrate is known, therefore, in this paper, the adsorption equilibrium isotherms for uranium (VI) are obtained for different sulphate ion concentrations in solution. The adsorption capacity variation of the Purolite resin SGA 600U/3472 with the number of adsorption/desorption cycles is also studied. The experimental results reveal the negative impact of high sulphate ion content in solution on the adsorption capacity of the resin Purolite SG 600 U / 3472 with uranium (VI) and therefore it is considered one of the compounds which strongly affect the uranium adsorption.

Catalytic Effects at Pyrolysis of Wheat Grains Impregnated with Nickel Salts

Pyrolysis was performed on wheat grains untreated or impregnated with nickel nitrate solutions, into a fixed bed column, in the presence of a carbon dioxide stream. This produced a char with or without nickel, pyrolytic oil and a gaseous fraction. The distribution of these fractions was dependent on variations in heat flux, carbon dioxide superficial velocity and nickel nitrate solution concentration. The paper focused on establishing the qualitative and quantitative influence of these experimental variables on pyrolysis dynamics. In order to obtain a process characterization, a factorial experiment was used, wherein the pyrolysed material mass, collected oil mass, operating time, material bed temperature, volatiles temperature and column wall temperature were the evaluated process responses. A model reproducing pyrolysis curves was proposed considering the process dynamics as a result of competition between the appearance and extension of local pyrolysis points.

Use of bacterial cellulose-glycerol-poly(vinyl alcohol) composites in drug release

Bacterial cellulose (BC) is a biomaterial suited for various biomedical applications, due to its unique nanostructure, that confers remarkable physical and chemical properties, such as: excellent elasticity, biocompatibility, high purity, high tensile strength and high elastic modulus. The article describes the mechanism and amoxicillin release profiles from bacterial cellulose-glycerol-poly(vinyl alcohol) composites, in the aim to use such systems in controlled drug delivery field. Obtained data from these composites were slightly smaller than BC-Glycerol, probably due to the fact that PVA layers provide an additional barrier for drug release. The presented data are of interest for the biomaterials community.

Modelling of water consumption in a spent fuel storage facility

In current practice, spent fuel is most commonly stored in a special basin of distilled or demineralised water for a required time period to reduce the amount of heat generated by radioactive decay to a level that can permit reprocessing. The processes taking place inside the spent fuel induce complex processes in the storage basin. The loss of water from the storage basin by means of simultaneous heat and mass transfer between water and the surrounding air is the case analysed in this paper by modelling. The developed model can be easily coupled with others, particularly models providing a consistent explanation of known situations (oxygen delivery from the basin, discharging of gases generated by processes from the fuel, increasing of the water activity, etc.). In this paper, some concrete references are related to the spent fuel storage facility at Magurele, Romania.

Differential liquid–solid extraction of sulphur from volcanic-type ore

Sulphur recovery from low grade ore has been achieved by solvent extraction method, in a differential, continuous extractor. The mathematical models, describing the differential extraction, have been adapted by attributing numerical values to its parameters. Additional measurements for equilibrium characteristics are needed. Simulations have been performed to study the influence of temperature, liquid/solid ratio and conveyer speed on the extraction efficiency. The results, represented in graphs, illustrating the correlation between the extraction efficiency and the working parameters are in good agreement with the experimental data.