Cornelia Păcurariu

Kinetic and thermodynamic studies on methylene blue biosorption using corn-husk

A low-cost waste biomass derived from corn plant (husk) was tested as an alternative to other expensive treatment options, for the removal of methylene blue (MB), from aqueous solutions. The effects of different experimental parameters, such as biosorbent dosage, dye concentration, contact time, and temperature, on the adsorption process were investigated. An optimum value of discoloration was observed at pH 6.0 and 2 g L−1 biomass dosage. The amount of dye removed per adsorbent unit decreased with increasing adsorbent dosage, temperature, and increased with increasing contact time, and concentration. Experimental data were modeled using first-order, pseudo-second-order, Elovich, and intraparticle diffusion kinetics models. The adsorption kinetics of MB could be described by the pseudo-second order reaction model. The experimental data were fitted to: Langmuir, Freundlich, Temkin, Redlich–Peterson, Toth, and Sips isotherm models and the best fitting was obtained with the Sips model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) obtained revealed that MB adsorption is a spontaneous, exothermic and physical process. The obtained results indicated that corn husk as a low-cost biomaterial is an attractive candidate for the removal of basic dye MB from aqueous solutions.

Combustion synthesis of some iron oxides used as adsorbents for phenol and p-chlorophenol removal from wastewater

The effect of the fuel nature and of the reaction atmosphere (in air/in the absence of air) on the synthesis of iron oxides by the combustion method was investigated. Working in air, using urea with ammonium chloride as fuel, the final product of reaction is α-Fe2O3. Working in the absence of air, using oxalic, tartaric, respectively, citric acid as fuel, the single phase resulted in combustion reaction was Fe3O4. From the synthesized iron oxides investigated as potential sorbents for the removal of phenol and p-chlorophenol (PCP) from wastewater, only the sorbents obtained using tartaric acid as fuel (S3) and those obtained using citric acid as fuel (S2) show adsorption capacity for the two pollutants. The sorbent S3 shows better adsorption capacity for both phenol and for PCP compared with sorbent S2.

Kinetic study of the crystallization processes of some glass ceramics based on basalt, via thermal analysis

The paper presents the kinetic study of the crystallization processes which take place at the obtaining of some glass ceramics, starting from two basalt glasses with different oxide composition. The activation energies have been calculated using Kissingers equation and verified with the Ozawas equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20°C min-1. By X-ray diffraction it was established that the crystalline phase formed in the crystallization process represent a pyroxenic solid solution, Ca(Mg,Fe)SiO3.

Magnetic nanopowder as effective adsorbent for the removal of Congo Red from aqueous solution

A magnetic iron oxide nanopowder (MnP), prepared by a simple and efficient combustion synthesis technique, was tested for the removal of the anionic dye Congo Red (CR) from aqueous solution. The influence of solution pH, adsorbent dose, temperature, contact time and initial dye concentration on the adsorption of CR onto MnP were investigated. It was shown that the CR adsorption was pH dependent and the adsorption mechanism was governed by electrostatic forces. The adsorption kinetic was best described by the pseudo-second-order model and the equilibrium data were well fitted to the Langmuir isotherm, yielding maximum adsorption capacity of 54.46 mg g(-1). The undeniable advantages of the MnP adsorbent such as inexpensive preparation method, good adsorption capacity and easy separation using an external magnetic field, recommend it as a promising candidate for the removal of anionic dyes from polluted water.

Adsorption of phenol and p-chlorophenol from aqueous solutions by magnetic nanopowder.

A new magnetic iron oxide nanopowder (MNM) was prepared, characterized and tested as adsorbent for the removal of phenol and p-chlorophenol (PCP) from aqueous solution. The iron oxide was obtained by a new combustion method which allows the direct obtaining of magnetic nanopowder covered with some organic residues resulting from fuel combustion. The magnetic powder was characterized in terms of phase composition, structure, texture, magnetic properties and carbon content. The adsorption kinetics was examined by the pseudo-first-order and pseudo-second-order models and the equilibrium data were fitted with Langmuir and Freundlich isotherms. The results confirmed the good adsorption capacity of the new magnetic nanopowder for the removal of phenol and PCP from aqueous solutions and its great potential for practical applications.

Basalt Based Glass Ceramics. Kinetic Studies of the Crystallization Processes

There have been obtained pyroxene glass-ceramic products starting from basalt-based glasses with nucleation agents addition (TiO2, CaF2, ZrO2). The activation energy of the crystallization processes has been determined based on thermal analysis (DTA). The physicomechanical properties of the obtained glass ceramic products have been correlated with their composition, obtaining conditions and texture. Introduction Glass ceramics based on basalt (easy accessible natural rock) develop a high mechanical and abrasion resistance as well as a good chemical stability [1,2].The studies in the literature [1-3], as well as a series of our own [4-7], show that reaching the physico-mechanical and chemical high performances for glass-ceramics assumes to choose an optimum chemical composition for the basalt glass, using the proper nucleation agents and adequate thermal treatments to make possible the crystallization processes. The main crystalline phase in basalt-based glass ceramics is the pyroxene solid solution: (Ca,Mg,Fe)SiO3 [1,5-7]. Some kinetic studies of the crystallization processes in the basalt-based glass ceramics, in which different nucleation agents (TiO2, CaF2, ZrO2) have been used represented the object of some previous papers [8,9]. The purpose of the present paper is to establish a correlation between the composition of the basalt glass, the proportion and the nature of the nucleation agents, the activation energy of the crystallization processes and the physico-mechanical properties of the obtained glass-ceramics. Experimental First, there have been elaborated the basalt based glasses using as main raw material the Şanoviţa basalt (Timiş) having the chemical composition presented in table 1 (sample SB). Table 1. Oxide composition (% weight) of the studied mixtures. Sample symbol SiO2 Al2O3 Fe2O3 CaO MgO Na2O+ K2O TiO2 Molar ratio: SiO2/MeO SB 52.21 12.33 9.55 14.29 10.29 1.18 0.15 1.378 BD 46.39 10.98 8.45 21.00 11.42 1.65 0.11 1.009 BVM 50.82 12.05 9.28 15.48 11.08 1.14 0.15 1.266 In order to realize a molar ratio SiO2/MeO (Me=Ca, Mg, Fe) close to 1 (specific for the pyroxene solid solution) glasses BD and BVM have been elaborated; their composition has been obtained by MgCO3 and CaCO3 addition to the natural basalt (SB). Based on our experience and on the literature data [1-7] concerning the obtainment of pyroxene glass ceramic products, there have been also elaborated basalt glasses having in their composition different nucleating agents: 3%CaF2 (sample Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1879-1882 doi:10.4028/www.scientific.net/KEM.264-268.1879

Removal of Colored Organic Pollutants from Wastewaters by Magnetite/Carbon Nanocomposites: Single and Binary Systems

This work develops a methodology for selective removal of industrial dyes from wastewaters using adsorption technology based on magnetic adsorbents. The magnetic nanoparticles embedded within a matrix of activated carbon were tested as adsorbents for removal of industrial dyes from aqueous solutions. The effects of four independent variables, solution pH, initial concentration of pollutant, adsorbent dose, contact time, and their interactions on the adsorption capacity of the nanocomposite were investigated in order to optimize the process. The removal efficiency of pollutants depends on solution pH and increases with increasing the carbon content, with initial concentration of the pollutants, the temperature, and the dose of magnetite/carbon nanocomposites. Pseudo-second-order kinetic model was fitted to the kinetic data, and adsorption isotherm analysis and thermodynamics were used to elucidate the adsorption mechanism. The maximum adsorption capacities were 223.82 mg g−1 for Nylosan Blue, 114.68 mg g−1 for Chromazurol S, and 286.91 mg g−1 for Basic Red 2. The regeneration and reuse of the sorbent were evaluated in seven adsorption/desorption cycles. The optimum conditions obtained for individual adsorption were selected as starting conditions for simultaneous adsorption of dyes. In binary systems, in normal conditions, selectivity decreases in the order: Red Basic 2 > Nylosan Blue > Chromazurol S.