Investigation of the interaction of Greek dolomitic marble with metal aqueous solutions using rutherford backscattering and X-ray photoelectron spectroscopy

The interaction of Greek dolomitic marble (from Thassos island, northern Greece) with Co2+, Cd2+, Pb2+ and Cr 3+ containing aqueous solutions was studied by characterizing the surface of the solid experimental samples, using a combination of spectroscopic, microscopic, and diffraction techniques (RBS, XPS, SEM-EDS, FT-IR, powder-XRD). The obtained results indicated a considerable Cd2+ and Co 2+ sorption on the dissolved surface of the carbonate substrate, whereas, under the same experimental conditions, the Pb2+ and Cr 3+ interaction is more intense leading to extended overgrowth of crystalline Pb2+ carbonates and massive surface precipitation of amorphous Cr3+ hydroxide/oxyhydroxide. © 2007 Akadémiai Kiadó

Spectroscopic characterization of Greek dolomitic marble surface interacted with uranium and thorium in aqueous solutions

The surface of a typical Greek (Thassian) dolomitic marble was studied after interaction with U- and Th-containing aqueous solutions (1000 mg/L, free-drift experiments for 1 week at atmospheric PCO2), using 12C-RBS and Laser μ-Raman spectroscopy. Powder-XRD and SEM-EDS were also applied to investigate the phases deposited on the surface of the interacted samples. The obtained results indicated a considerable removal of U from the aqueous medium mainly due to massive surface precipitation of amorphous UO2-hydroxide phases forming a relatively thick (μm-sized) coating on the carbonate substrate. The interaction of Th with dolomitic marble surface is also intense leading to a formation of an amorphous Th-hydroxide layer of similar thickness but of significantly lower elemental atomic proportion. © 2008 Elsevier B.V. All rights reserved

Use of combination of accelerator-based ion-beam analysis techniques to the investigation of the corrosion behavior of CoCrMo alloy

Nuclear Reaction Analysis - NRA in combination with d-RBS (Ed: 1.35 MeV) was applied in order to investigate the corrosion behavior of CoCrMo alloy. The corrosion resistance of the alloy was compared to that of modified CoCrMo samples by several techniques as plasma nitriding and oxidizing at moderate temperature (∼400 °C). Electrochemical techniques in simulated body fluid 0.9% NaCl (37 °C) were applied in order to accelerate the corrosion process. The nitrogen depth distribution before and after the corrosion was determined using the 14N(d,α)12C and the 14N(d,p)15N nuclear reactions whereas the oxygen by the 16O(d,p)17O. The surface morphology and microstructure was investigated using microscopy techniques. It was found that surface treatments produce thick nitrided layers (5-6 μm) consisting of a supersaturated nitrogen solution (nitrogen concentration is ∼30 at.%) in the matrix (expanded phase γN) and a thin oxygen solution (0.3 μm). The samples subjected to plasma nitridation and oxidation exhibited the lowest deterioration and better resistance to corrosion compared to the single nitrided or single oxidized and the untreated material. This could be attributed to the modified surface region with the high nitrogen content and the presence of oxygen

Chromium (VI) uptake by polyhexamethylene-guanidine-modified natural zeolitic materials

The Cr(VI) uptake from aqueous solutions by polyhexamethylene-guanidine-modified natural zeolitic materials from Metaxades, Greece (PHMG-MTX) and Tedzami, Georgia (PHMG-TZ) was investigated using batch techniques. Spectrophotometry using 1,5-diphenylcarbazide for colour development was used for Cr determination. The Cr(VI)-solution concentration varied between 5 and 50 mg/L and the initial pH was adjusted to 3.0, 4.0 and 5.0. Additional experiments were conducted in the presence of competing anions (background electrolyte I = 0.1 M established by 0.1 M NaNO3 and 0.033 M Na2SO4) on solutions with unadjusted pH. For comparison, the Cr(VI) adsorption by Tedzami tuffs modified by octadecylpolyhexamethylene-guanidine-chloride (ODPHMG-TZ) was also investigated. All investigated materials adsorbed considerable amounts of Cr(VI)-oxyanions. It was shown that the Cr(VI)-uptake strongly depended on pH and the presence of competing anions. The Cr(VI)-oxyanion uptake by PHMG-TZ was slightly higher than that observed for ODPHMG-TZ, whereas the sorption capacity of PHMG-MTX was of the same order of magnitude as Metaxades tuffs modified by hexadecyl-trimethylammonium-bromide. The experimental data obtained for pHinit = 3.0 were selected for modeling the adsorption behavior of the materials using six isotherm equations (Freundlich (F), Langmuir (L), Langmuir-Freundlich (L-F), Dubinin-Radushkevich (D-R), Redlich-Peterson (R-P), Toth (T)). The obtained modeling results indicated that, although the three-parameter models, taking into account the surface heterogeneity, provided the closest approach to the measurement data, the parameters estimates could be highly biased. On the other hand, the two-parameter Langmuir isotherm was sufficient to describe the process equilibrium in terms of smallest number of adjustable parameters and approximation of the sorption capacity. © 2007 Elsevier Inc. All rights reserved