F. Noli

Concentration of heavy metals and trace elements in soils, waters and vegetables and assessment of health risk in the vicinity of a lignite-fired power plant

The pollution of agricultural soils, waters and products in the regions of lignite mines and fired power plants is of great importance. The concentration of As, Βa, Co, Cr, Sr, Sc, Th, U, Zn in soils and waters in the vicinity of a lignite-fired power plant in Northern Greece was determined using Instrumental Neutron Activation Analysis. The determination frequency was every three months during a period of one year in order to evaluate the seasonal impact of the pollution to the environment. Measurements were performed in three locations around the lignite mine as well as in one reference location at a certain distance from the mine. The results, which exhibited a slight seasonal variation, were compared, where possible, with literature values from other countries. The obtained data in most of the cases did not exceed the normal levels and indicated that the investigated area was only slightly contaminated. The concentration of heavy and trace metals was also measured in three common garden crops (tomato, cucumber and parsley) grown in this area. The calculated transfer factors (TF) from soil to vegetables and health risk quotients (HQ) do not denote a health risk.

Corrosion protection of an AISI 321 stainless steel by SiC coatings

Abstract Silicon carbide coatings were produced by dynamic ion mixing (DIM) at room temperature and at 750 °C by ion beam sputtering of a SiC target and simultaneous bombardment with a 160 keV Ar+ ion beam. The chemical composition of the coatings was determined by Rutherford backscattering and by nuclear reaction analysis. The microstructural state of the coatings was investigated by high resolution transmission electron microscopy whereas their density was determined by X-ray reflectometry. It is found that, for all the deposition temperatures, the DIM treatment promotes the crystallisation of the β-SiC phase. Passivation/corrosion tests performed in 1 N H2SO4 indicate that the corrosion resistance is considerably improved by DIM regardless of the deposition temperature. It is suggested that the interface mixing along with the coating densification is responsible for the protective effect.

Investigation of cesium uptake from aqueous solutions using new titanium phosphates ion-exchangers

The uptake of cesium from aqueous solutions (pH 5) using titanium phosphates was investigated in the absence and presence of background electrolyte (0.1xa0M NaNO3) using a batch technique. The determination of cesium was performed by gamma spectroscopy using 137Cs as tracer. The obtained sorption isotherms could be satisfactorily reproduced by a Langmuir sorption equation. The maximum uptake capacity values (qmax) calculated fitting the experimental data by this equation were 167 and 118xa0mg/g for solutions of initial pH 5 in the absence and presence of background electrolyte. Kinetics data obtained at 293, 308 and 323xa0K could satisfactorily reproduced by the pseudo-second order equation. It was demonstrated that the new synthesized materials can remove considerable amounts of cesium from aqueous solutions and ion exchange is considered to be the principal mechanism for cesium removal. Toxicity characteristic leaching procedure and desorption tests provided data about the application of the sorbents in environmental remediation.

Uranium removal from aqueous solutions by raw and modified thermal power plant ash

The U(VI) removal from aqueous solutions (concentration range 125–2,000xa0mg/L, pH 3) by raw and NaOH-modified power plant ash was investigated by means of a batch method under the following experimental conditions: NaOH concentration 5xa0M, contact time 1xa0h, respectively 4xa0h, temperature 70, 90xa0°C. The amount of sorbed uranium was determined spectrophotometricaly using the Arsenazo III method. The sorbents were examined prior and after the sorption experiments by scanning electron microscopy/energy dispersive spectroscopy. Typical sorption isotherms were calculated and modeled by the Langmuir and Freundlich equations. The experimental data showed that all materials can remove considerable amounts of uranium from acidic aqueous solutions. The maximum removal efficiency (qmax) values obtained, are 126xa0mgxa0U/g for raw ash and 206xa0mgxa0U/g for NaOH-modified. Sorption kinetics measurements were performed at 298, 308 and 323xa0K and thermodynamic parameters were calculated. The kinetic data obey a pseudo-second order equation.

Investigation of uranium biosorption from aqueous solutions by Dictyopteris polypodioides brown algae

The biosorption of uranium from aqueous solutions by Dictyopteris polypodioides brown algae was investigated. The effect of pH, uranium concentration, mass of the adsorbent, temperature and contact time on the removal efficiency were studied and the results were simulated by Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. Kinetics data could be satisfactorily reproduced by the pseudo-second order equation and thermodynamic parameters were determined in order to evaluate the uranium uptake behavior. SEM/EDS and FT-IR were additionally used to characterize the algae and comprehend the sorption process which can be described as a combination of several mechanisms, including physical sorption, ion exchange and complexation.

SURFACE CHARACTERISATION AND CORROSION BEHAVIOUR OF SIC-COATED AISI 321 STAINLESS STEEL

Abstract The influence of SiC-coatings on the corrosion properties of AISI 321 austenitic stainless steel (Fe/Cr18/Ni8/Ti) in 1N H 2 SO 4 was studied. SiC-coatings of various thicknesses (100–800 nm) were prepared at room temperature (RT) or at temperatures up to 750°C by ion beam sputtering of a SiC-target. The growing films could be continuously bombarded with a 160 keV Ar + ion beam and the role of this Dynamic Ion Mixing (DIM) on both the structure and corrosion resistance was investigated. The chemical composition of the coatings was determined by Rutherford Backscattering (RBS) using 1.8 MeV α-particles and by Nuclear Reaction Analysis (NRA). Transmission Electron Microscopy (TEM) observations were also performed for the determination of the microstructural state of the samples. The characterisation shows, that for all the deposition temperatures the DIM-treatment promotes the crystallisation of the β-SiC phase. It was also found, that the corrosion resistance of the stainless steel is considerably improved when the coatings are deposited by DIM regardless of the deposition temperature. The possible mechanisms are discussed and it is suggested that the interface mixing along with the coating densification effect are responsible for the improvement of the corrosion resistance.

Toxic element concentrations in airborne particulate matter in the area of Thessaloniki, Greece

Abstract In order to evaluate the environmental pollution of Thessaloniki, As, Co, Cr, Cs, Fe, Sb and Zn have been determined by means of instrumental neutron activation analysis (INAA) in air particulate samples obtained at two sampling points located in the urban and the rural area of the city. The elements determined were characterized with respect to their origin. The contribution of polluted road-side dust to the elemental concentration in the atmosphere was found to be more significant for As, Co, Cr and Zn, whereas Br and Sb seem to originate from emission sources other than wind-blown road-side dust.

Uranium removal from aqueous solutions using a raw and HDTMA-modified phillipsite-bearing tuff

The interaction of uranium aqueous solutions (pH 3 and 4) with a phillipsitic tuff was investigated in absence and presence of 0.1xa0M NaNO3. The uranium determination was performed using the arsenazo-III method. Its removal was mainly due to its interaction with the surface of the tuff constituents. HDTMA-modified tuff was used to remove carbonato uranyl-complexes from solutions of pH 8, 9 and 10. Uptake- and kinetics data for 25, 35, 45 and 55xa0°C modeling was performed for both raw- and modified tuff. Explanation of the uranium uptake behavior of the tuff was attempted on the basis of thermodynamic calculations.

New materials synthesized from ash under moderate conditions for removal of toxic and radioactive metals

Power plant ash was used to synthesize new materials by hydrothermal treatment and ultrasonic activation in an alkaline medium (5xa0M NaOH) under moderate experimental conditions. The obtained materials were characterized by a variety of techniques (SEM/EDS, INAA, XRD, FTIR, BET). Preliminary investigation of the Ba, Cd, Cr, Cs, Eu and U removal efficiency was performed by batch experiments using radiotracers and spectroscopic techniques as well as desorption studies. The results indicated that the new materials are very efficient in removing the above mentioned metals from aqueous solutions and can be considered as potential low-cost sorbents in environmental technology.

The effect of Zr-implantation on the thermal oxidation and aqueous corrosion of AISI 321 stainless steel

Abstract The effect of Zr-implantation (energy: 40 keV, dose: 1 × 10 17 ions/cm 2 ) on the oxidation of AISI 321 austenitic stainless steel (Fe/Cr18/Ni8/Ti) has been studied at temperatures of 450, 550 and 650°C, in air. The duration of the oxidation was varied between one and six days. The oxygen distribution on the oxidized samples has been determined using the 16 O(d, p) 17 O nuclear reaction whereas the zirconium depth profile by means of Rutherford backscattering spectroscopy (RBS) using α-particles as projectiles. X-ray photoelectron spectroscopy (XPS) was used as support to these measurements. The morphology and the surface microstructure of the specimens were investigated by scanning electron and scanning transmission electron microscopy (SEM and STEM). The evaluation of the data has indicated that the implantation of Zr-ions leads to a chromium depletion in the near-surface layers and enhances the oxidation of the implanted samples compared to the initial material. Electrochemical experiments of the Zr-implanted steel performed in 1N sulphuric acid solution (H 2 SO 4 1N) showed an increase of the corrosion resistance.