P. Vassileva

Investigation on natural and pretreated Bulgarian clinoptilolite for ammonium ions removal from aqueous solutions.

The possibilities for ammonium ions removal from aqueous solutions by natural and NaCl pretreated Bulgarian clinoptilolite from Beli plast deposit were studied. Experiments were carried out using batch method. The adsorption of NH4(+) was investigated as a function of the solution pH, dosage of adsorbent, initial ammonium concentration and temperature. The results clearly showed that the treatment with NaCl improved both the adsorption capacity and the removal efficiency of natural clinoptilolite. The equilibrium experimental data for adsorbed NH4(+) ions on clinoptilolite samples were correlated better by the Langmuir isotherm model. The maximum adsorption capacities for ammonium ions shown by natural and pretreated clinoptilolites (CL_Na and CL_Na(t)) were 7.85, 12.29 and 18.40 mg/g, respectively. The results indicated a significant potential of the natural and conditioned clinoptilolites as adsorbents for ammonium removal.

REMOVAL OF METAL IONS FROM AQUEOUS SOLUTIONS USING PYROLYZED RICE HUSKS: ADSORPTION KINETICS AND EQUILIBRIA

Four carbon/silica-containing materials obtained by pyrolysis of rice husks were characterized and their adsorption properties towards some metal ions were evaluated. GC/MS analysis and FT-IR spectroscopy were applied for identification of functional groups finely dispersed on the surface. Their amounts were gravimetrically determined after extraction with acetone. The specific surface area and porosity of the materials were characterized by the Brunauer-Emmett-Teller (BET) method and by mercury porosimetry, respectively. The adsorption properties of the carbonized rice husks towards Fe(III), Pb(II), Cr(III), and Cu(II) ions in single- and multicomponent aqueous solutions also containing Ni(II), Co(II), Mn(II), and Cd(II) were studied in a batch system. The effects of contact time, acidity of initial solutions, and metal ion concentrations were followed. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to analyze kinetic data. Equilibrium experimental data were fitted to linear Langmuir and Freundlich models. The maximum adsorption capacities for single- and multicomponent adsorption were calculated and compared with literature data. A correlation between the adsorption properties of pyrolyzed rice husks and their textural and surface parameters was established. Possibilities for desorption of the investigated ions were estimated.

Adsorption of Some Transition Metal Ions [Cu(II), Fe(III), Cr(III) and Au(III)] onto Lignite-based Activated Carbons Modified by Oxidation

The main purpose of the present work was to study the adsorption of some transition metal ions from aqueous solution via a novel porous material obtained from Bulgarian lignite (Chukurovo deposit) and its oxidized modifications. The adsorption of Cu(II), Fe(III), Cr(III) and Au(III) ions was investigated using batch methods to study solutions with different concentrations and acidities. It was found that the adsorption process was affected significantly by the pH value of the aqueous solution. Treatment of the equilibrium data using the linear Langmuir, Freundlich and Dubinin-Radushkevich models allowed the maximum adsorption capacities to be calculated. The uptake of Au(III) ions was almost 100% for the three adsorbents investigated, being greater than 300 mg/ℓ and independent of the pH over the pH range studied. The initial activated carbon proved to be the most suitable for the selective adsorption of Au(III) ions from aqueous solutions in the presence of other transition metal ions, while its oxidized modification Ch-P exhibited an enhanced adsorption efficiency towards transition metals.

Synthesis, characterization and adsorption properties of nanostructured hybrid materials modified by boron and zirconium

AbstractThe adsorption properties of two new nanostructured hybrid materials containing B2O3 and ZrO2 were studied. The new organic-inorganic materials were synthesized via a sol-gel method. As a modifying agent, a quantity of 10 wt.% Zr(OPr)4 or B(OCH3)3 was added. The structure of the hybrid materials was investigated by means of (Fourier transform infrared spectroscopy (FTIR), x-ray diffractometry (XRD), scanning electron microscopy (SEM), (atomic force microscopy (AFM) and nuclear magnetic resonance spectroscopy (NMR). Based on the obtained data, the most probable cross-linking mechanism for the derived gels was proposed. The characterization of texture parameters of both materials was carried out with the use of low-temperature adsorption of nitrogen. Adsorption of Cu(II), Fe(III), Cr(III), Cd(II) and Pb(II) ions on both materials was investigated using multi-component solutions with different concentrations and acidity by means of the batch method. Kinetics of adsorption was also investigated. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. The adsorption was significantly affected by the pH value. Equilibrium data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models and maximum adsorption capacities were calculated.

Bulgarian natural diatomites: modification and characterization

Natural Bulgarian diatomite modified by oxidation with sulfuric acid and H2O2 or by coating with manganese oxide was characterized considering its chemical composition, surface area, pore volume, and structure. Modified diatomites displayed larger surface area and pore volumes in comparison with untreated natural diatomite, which favored their sorption behavior. Sorption properties of diatomites towards Fe3+, Pb2+, Cu2+, Cd2+, Mn2+, Ni2+, Co2+, Cr3+, Pd2+, Ca2+, and Mg2+ were investigated and their sorption capacities were determined. Sorption properties of manganese oxide-modified diatomite were superior to those of diatomite modified by oxidation. Owing to its high sorption capacity towards Co2+, Ni2+, Pb2+, Cr3+, Fe2+, Cu2+, and Cd2+, the manganese oxide-modified diatomite is a promising low-cost sorbent for selective removal of milligram amounts of these toxic metal ions from contaminated water.

Sorption of Co(II), Ni(II), Ag(I) and Au(III) on pyrazolone-containing inorganic sorbents

The sorption capacity of 3-methyl-1-phenyl-pyrazolone-5 (HMPP)- modified inorganic sorbents has been investigated. The new sorbents are suitable for simultaneous concentration of the 3d elements being investigated over a wide pH range. Choosing appropriate pH values for the corresponding elements, it is possible to achieve their separate extraction.

Adsorption properties of a nanostructured hybrid material containing aluminium towards some metal ions

AbstractIn the present work the adsorption of some transition metal ions from aqueous solutions on a silica-based nanostructured hybrid material modified by aluminium was investigated. The novel organic-inorganic material was synthesized via a sol-gel method through hydrolysis and co-condensation reactions. Its structure was characterized by means of SEM, XRD and FTIR. Based on the data obtained the most probable cross-linking mechanism for the derived xerogel was proposed. The characterization of its texture parameters was carried out by low-temperature adsorption of nitrogen. The adsorption properties of this material with respect to Cu(II), Cr(III) and Pb(II) ions from single-component aqueous solutions and multi-component aqueous solutions containing also Cd(II) and Fe(III) were evaluated. The effect of contact time, acidity of initial solutions and metal ion concentrations was investigated using the batch method. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. In all cases the adsorption was significantly affected by the pH value. Equilibrium modelling data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models. Best fit was observed for Langmuir model, which showed determination coefficients greater than 0.992 for all ions studied. The maximum adsorption capacities for single- and multi-component adsorption were calculated.

Total reflection X-ray fluorescence analysis of fly ash from Bulgarian coal-fired power plants

The contents of Cl, Ca, K, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ba and Pb in raw coal fly ash from five Bulgarian power plants were determined by total reflection X-ray fluorescence (TXRF), using gallium as the internal standard. The samples were analysed as in slurry form in Triton™ X-114. The experimental parameters, such as grain size, concentrations of fly ash slurry and excitation time were optimised. For validation of the method, the certified reference material BCR-176R fly ash was used. The precision of the results obtained is characterised by a relative standard deviation of approximately 10%. The resulting data confirm the suitability of TXRF for the simultaneous determination of major, minor and trace elements in coal fly ash samples. Further advantages provided by TXRF are easy sample preparation (no sample dissolution) and the small sample amount required for analysis.

Phosphazenes on diatomaceous earths in water adsorption

Hexachlorocyclotriphosphazene (T) and poly-bis-(trifluoroethoxy)phosphazene (A) deposited separately on wide-pore kieselguhr supports result in composite adsorbents of an increased adsorption capacity for water vapour per unit surface area. Deposition alters the adsorption behaviour of T and A themselves due to high dispersion and conformation changes of polymer chains within the pores in comparison with the initial solid state.

Water vapour adsorption on phosphazenes

We report the adsorption isotherms of water vapour at 22°C on six representatives of the phosphazene family: hexachlorocyclotriphosphazene (I), bis-(dimethylamino)-tetrachlorocyclotriphosphazene (II), bis-(dimethylamino)-bis-(trifluoroethoxy)-dichlorocyclotriphosphazene (III), octabutylaminocyclotetraphosphazene (IV), phospham (V) and poly-bis-(trifluoroethoxy)phosphazene (VI). The phosphazenes chosen differ in how their N-P backbone is built up (cyclic I-IV, cyclomatrix V and linear VI), in their degree of polymerization (trimers I-III, tetramer IV and polymers V and VI) as well as in the type of substituents at the phosphorous atoms