Papers by Ioannis Pashalidis
Processes, Dec 2, 2019
The Cu(II) adsorption from aqueous solutions by magnetic biochar obtained from pine needles has b... more The Cu(II) adsorption from aqueous solutions by magnetic biochar obtained from pine needles has been studied by means of batch-type experiments. The biochar fibers have been magnetized prior (pncm: carbonized-magnetized pine needles) and after oxidation (pncom: carbonized-oxidized-magnetized pine needles) and have been used as adsorbents to study the presence of carboxylic moieties on the magnetization and following adsorption process. The effect of pH (2-10), initial metal concentration (10 −5-9•10 −3 mol•L −1) and contact time (0-60 min) has been studied by varying the respective parameter, and the adsorbents have been characterized by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurements prior and after Cu(II)-adsorption. FTIR measurements were performed to investigate the formation of surface species and XRD measurements to record possible solid phase formation and characterize formed solids, including the evaluation of their average crystal size. The data obtained from the batch-type studies show that the oxidized magnetic biochar (pncom) presents significantly higher adsorption capacity (1.0 mmol g −1) compared to pncm (0.4 mmol g −1), which is ascribed to the synergistic effect of the carboxylic moieties present on the pncom surface, and the adsorption process follows the pseudo-second order kinetics. On the other hand, the FTIR spectra prove the formation of inner-sphere complexes and XRD diffractograms indicate Cu(II) solid phase formation at pH 6 and increased metal ion concentrations.
arXiv (Cornell University), Apr 28, 2003
The alpha-radiometric determination of uranium after its pre-concentration from natural water sam... more The alpha-radiometric determination of uranium after its pre-concentration from natural water samples using the cation-exchange resin Chelex-100, its selective extraction by tributylphosphate and electrodeposition on stainless steel discs is reported. The validity of the separation procedure and the chemical recoveries were checked by addition of uranium standard solution as well as by tracing with U 232. The average uranium yield was determined to be (97 ± 2) % for the cation-exchange, (95 ± 2) % for the liquidliquid extraction, and more than 99% for the electrodeposition. Employing highresolution α-spectroscopy, the measured activity of the U 238 and U 234 radioisotopes was found to be of similar magnitude; i.e. ∼7 mBq L −1 and ∼35 mBq L −1 for ground-and seawater samples, respectively. The energy resolution (FWHM) of the α−peaks was 22 keV, while the Minimum Detectable Activity (MDA) was estimated to be 1 mBq L −1
Journal of Molecular Liquids, Apr 1, 2020
Journal of Radioanalytical and Nuclear Chemistry, 2004
The alpha-radiometric determination of uranium after its pre-concentration from natural water sam... more The alpha-radiometric determination of uranium after its pre-concentration from natural water samples using the cation-exchange resin Chelex-100, its selective extraction by tributylphosphate and electrodeposition on stainless steel discs is reported. The validity of the separation procedure and the chemical recoveries were checked by addition of uranium standard solution as well as by tracing with U 232. The average uranium yield was determined to be (97 ± 2) % for the cation-exchange, (95 ± 2) % for the liquidliquid extraction, and more than 99% for the electrodeposition. Employing highresolution α-spectroscopy, the measured activity of the U 238 and U 234 radioisotopes was found to be of similar magnitude; i.e. ∼7 mBq L −1 and ∼35 mBq L −1 for ground-and seawater samples, respectively. The energy resolution (FWHM) of the α−peaks was 22 keV, while the Minimum Detectable Activity (MDA) was estimated to be 1 mBq L −1
Journal of Radioanalytical and Nuclear Chemistry, Apr 29, 2019
Desalination and Water Treatment, Apr 6, 2016
Journal of Radioanalytical and Nuclear Chemistry, Jun 16, 2018
The present study deals with the preparation of oxidized biochar fibres derived from Luffa cylind... more The present study deals with the preparation of oxidized biochar fibres derived from Luffa cylindrica sponges and the subsequent adsorption of Th(IV). The adsorption experiments were performed by batch-type experiments and include the effect of various physiochemical parameters, as well as characterization of the solid phases by means of spectroscopic (FTIR) and XRD measurements. The experimental data are best described by the pseudo-second order kinetic model (R 2 = 0.998) and the adsorbent was found to have a relatively high adsorption capacity (q max = 70 mg g-1) even at pH 3, attributed to the formation of inner-sphere complexes.
Environmental Research, May 1, 2023
Journal of Molecular Liquids, Dec 1, 2022
Journal of Radioanalytical and Nuclear Chemistry, Jan 22, 2009
ABSTRACT
Journal of Environmental Radioactivity, Oct 1, 2009
Phosphogypsum is a waste by-product of the phosphate fertilizer industry, which is usually dispos... more Phosphogypsum is a waste by-product of the phosphate fertilizer industry, which is usually disposed in the environment because of its restricted use in industrial applications. Physico-chemical conditions existing in stack fluids and leachates are of major importance and determine solubility and redox stability of phosphogypsum, as well as radionuclide release from stacks to terrestrial environments. The aim of this study is to assess the effect of key parameters (e.g. ionic strength, temperature, pH) on the solubility of phosphogypsum. Phosphogypsum sampling and in-situ measurements were carried out at a coastal stack in Cyprus, solubility experiments were performed in simulated laboratory systems and thermodynamic calculations by means of MINTEQA2, an equilibrium speciation model. Generally, increasing ionic strength and temperature leads to increased phosphogypsum solubility, with the former being much more effective. The increased solubility of phosphogypsum in saline solutions is attributed solely to ionic strength effects on the activity of ionic species in solution and no solid phase transformations could be observed. The effect of pH on phosphogypsum solubility seems to be insignificant at least in a pH range between 4 and 8. Regarding uranium levels, there is a strong correlation between salinity and uranium concentration and linear correlation between phosphogypsum solubility and uranium levels in stack solutions, indicating the incorporation of uranium into the gypsum lattice and the formation of a solid solution.
Journal of Environmental Radioactivity, Feb 1, 2008
The effect of the matrix composition (main constituents) on the concentration and chemical behavi... more The effect of the matrix composition (main constituents) on the concentration and chemical behavior of uranium in phosphogypsum stack solutions and leachates has been investigated. Solid and aqueous samples were taken from three different sub-areas of a phosphogypsum stack at a coastal area in Vasilikos (Cyprus). The sub-areas are characterized whether by their acidity (e.g. "aged" and "non-aged" phosphogypsum) or by their salt content, originating from pulping water during wet stacking or (after deposition) from the adjacent sea. Measurements in stack solutions and leachates showed that phosphogypsum characteristics affect both, the concentration and the chemical behavior of uranium in solution. Uranium concentration in solutions of increased salinity is up to three orders of magnitude higher than in solutions of low salinity and this is attributed to the effect of ionic strength on the solubility of phosphogypsum. Modelling showed that uranium in stack solutions is predominantly present in the form of uranium(VI) phosphate complexes (e.g. UO(2)(H(2)PO(4))(2), UO(2)HPO(4)), whereas in leachates uranium(VI) fluoro complexes (e.g. UO(2)F(2), UO(2)F(3)(-)) are predominant in solution. The latter indicates that elution of uranium from phosphogypsum takes places most probably in the form of fluoro complexes. Both, effective elution by saline water and direct migration of uranium to the sea, where it forms very stable uranium(VI) carbonato complexes, indicate that the adjacent sea will be the final receptor of uranium released from Vasilikos phosphogypsum.
Applied Radiation and Isotopes, Oct 1, 2016
Carbohydrate Polymers, Sep 1, 2019
Increased uranium adsorption by PVP/Chitosan blended nanofibers Formation of inner-sphere com... more Increased uranium adsorption by PVP/Chitosan blended nanofibers Formation of inner-sphere complexes indicated by FTIR Endothermic, entropy-driven adsorption process pH-depended adsorption efficiency ABSTRACT PVP/chitosan blended nanofibers have been prepared and investigated as adsorbent material for the removal of hexavalent uranium (U(VI)) from aqueous solutions. The nanofibers have been characterized prior and after U(VI) adsorption by SEM and FTIR measurements, and the effect of various parameters such as metal-ion concentration temperature and contact time on the adsorption efficiency has been investigated by batch-type experiments. The material presents increased sorption capacity (qmax= (167 ±25) g kg-1 at pH 6.0) and increased chemical affinity for U(VI), which is attributed to the fibrous structure of the material and the presence of polar groups (e.g. carbonyl groups) on the blended nanofibers. FTIR spectroscopic measurements indicate the formation of inner sphere complexes between U(VI) and the surface moieties, and thermodynamic and kinetic data reveal a relatively fast (k1= 0.01 min-1), entropy-driven process (ΔH o = 56.3 kJ mol-1 and ΔS o = 293.7 J K-1 mol-1). Recycling experiments have shown that the material can be used up to four times with less than 10% efficiency loss.
Journal of Radioanalytical and Nuclear Chemistry, Nov 21, 2022
Journal of Molecular Liquids, Apr 1, 2022
Radiochimica Acta, Jun 1, 1993
Solubility products of Pu0 2 C0 3 (s) and U0 2 C0 3 (s) are determined in0.1 M NaC10 4 at 22± 1 °... more Solubility products of Pu0 2 C0 3 (s) and U0 2 C0 3 (s) are determined in0.1 M NaC10 4 at 22± 1 °C under 100%, 1 % and0.03% C0 2. The carbonate precipitates of Pu(VI) and U(VI), prepared under 100% C0 2 at neutral pH, are characterized by powder diffraction measurement, IR spectroscopy and UV spectroscopy. The solubility experiment is carried out in different CO3" concentrations and pH. The speciation of Pu0 2 + and UO2 + in equilibrium solutions is made by UV spectroscopy and the total concentrations of Pu(VI) and U(VI) are determined by liquid scintillation spectrometry and ICP-AES, respectively. The concentration correlation of [M0 2 + ] vs. [C0 3~] gives a slope of negative unity, while [M0 2 + ] vs. pH shows a slope of-2 irrespective of C0 2 partial pressure. The fact concludes that the present experiment comprises solid-liquid phase equilibrium reactions with only M0 2 C0 3 (s). The solubility products converted to zero ionic strength are found to be logÄ^p =-14.84+0.10 for Pu0 2 C0 3 (s) and logÄj"=-14.22+0.14 for U0 2 C0 3 (s).
Journal of Radioanalytical and Nuclear Chemistry, Nov 1, 2022
Journal of Radioanalytical and Nuclear Chemistry, Nov 2, 2022
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Papers by Ioannis Pashalidis