P. Misaelides

Thorium and uranium uptake by natural zeolitic materials

Abstract The thorium and uranium uptake from their aqueous solutions by unpretreated and NaCl-pretreated zeolite-bearing volcanoclastic rock samples from Metaxades (Thrace, Greece) has been studied using a batch-type method. The concentration of the solutions varied between 50 and 20 000 mg/l. The NaCl pretreatment of the materials improved the thorium but not the uranium uptake. The absolute thorium uptake by the pretreated material, determined using neutron activation and X-ray fluorescence techniques, reached 12.41 mg/g, whereas the uranium uptake by the raw material was 8.70 mg/g. The uptake distribution coefficients ( K d ) indicated that the relative thorium and uranium uptake is higher for initial concentrations below 250 mg/l. The zeolitic materials showed exceptional resistance to the initial low pH of the solutions used. The pH in was significantly increased due to the simultaneous hydrogen-ion uptake. The thorium and uranium uptake is a rather complicated phenomenon related to the aqueous chemistry of the elements, the nature of the constituent minerals and the properties of the zeoliferous rock specimens. The various metal species are bound through different uptake processes such as ion-exchange, adsorption and surface precipitation. Microporous minerals (zeolites, phyllosilicates) are mainly responsible for the considerable uptake ability of the rock samples studied.

Natural microporous materials in environmental technology.

Clay Minerals.- Structure and Chemical Characteristics of Modified Clays.- Pillared Clays: Chemistry and Prospects.- Hg2+ Trapping by Thiol - Functionalised Mesoporous Silica Molecular Sieves.- The Use of Clays as Sorbents and Catalysts.- Contaminant Plume Management Utilising In Situ Organoclay Sorbent Zones.- Atomistic Computer Modelling of Chiral Pillared Clays.- Natural Microporous Materials of Central Slovakia.- Sorption and Leaching Properties of the Composites and Complexes of Natural Microporous Materials.- Experimental Study on the Formation of Heavy Metal Sulphides Using Layer Silicates: Environmental Aspects.- Diffusion of Radionuclides in Clay-Based Ceramics.- Natural Zeolites.- Zeoponic Substrates for Space Applications: Advances in the Use of Natural Zeolites for Plant Growth.- Natural Zeolites and Nuclear-Waste Management: The Case of Yucca Mountain, Nevada, USA.- Interaction of Actinides with Natural Microporous Materials.- Environmental Applications of Natural Zeolitic Materials Based on their Ion Exchange Properties.- Zeolitised Materials of the Mediterranean Area as Adsorbents for Environmental Protection.- Distribution of Industrial Minerals in Sardinia (Italy): Clinoptilolite Bearing Rocks of the Logudoro Region.- Application of Microporous Materials for the Recovery of Nutrients From Wastewaters.- Transition Metal Complexes Supported on Natural Zeolitic Materials: An Overview.- Heterogeneous Catalysis at Supercritical Conditions Using Microporous Materials. Environmental Advantages.- Properties of NaOH-Treated Slovak Zeolitic Tuff and its Sorption Ability Towards Some Cations.- Zeolites in Aquacultural Primary Production.- Sorption of Cadmium(II) and Nickel(II) on a Natural Zeolite Rich in Clinoptilolite.- Environmental Applications of Modified Natural Zeolites.- Romanian Volcanic Tuffs Exploitation in Environmental Protection.- Sorption of Heavy Metals and Radionuclides on Zeolites and Clays.- A Preliminary Study of Mercury Uptake by a Greek Zeoliferous Rock.- Natural Sorbents as Barriers against Migration of Radionuclides from Radioactive Waste Repositories.- Preparation of a Modified Adsorbent Based on Clinoptilolite and its Application for the Removal of Iron and Manganese Ions from Artesian Water.- Natural Microporous Oxides.- Metal Detachments from (Hydr)Oxide Mineral Surfaces. A Molecular View.- Using Magnetites to Remediate Heavy Metal Wastewaters from Acid-Mine Drainage.- Wastewater Treatment Technology Based on Iron Oxides.- Goethite Mineral as a Sorbent for Heavy Metal Ions.- Reversed-Phase Column Extraction Studies using a Standardised and Silanised Anatolian Perlite.- Characterisation of Natural Microporous Manganese Oxides: The Case of Todorokite.- Modelling Sorption of Metals From Aqueous Solution onto Mineral Particles: The Case of-Arsenic Ions and Goethite Ore.- Preparation of Granular Forms of Powdered Materials for their Application in Column Packed Beds.- The Molecular Layering Method as a Basis of Chemical Nanotechnology.- Other Natural Microporous Materials.- Natural Chitin Containing Materials for Colour Removal from Textile Wastewaters.- List of Participants.

The chemical behavior of natural zeolites in aqueous environments: Interactions between low-silica zeolites and 1 M NaCl solutions of different initial pH-values

A natural zeolitic material composed of microscale intergrowths of the low-silica zeolites natrolite and thomsonite (NAT/THO) was found to be more reactive in distilled water compared to the high-silica zeolites heulandite and stilbite. Relevant experiments using 1 M NaCl solutions of different initial pH-values revealed a pH increase in the acidic region and an analogous decrease in the basic region, indicating that the NAT/THO material shows a tendency to neutralize the solutions behaving either as a proton acceptor or as a proton donor. This amphoteric character is related to the H+ uptake, as well as to the OH− attack to surface reactions sites of the crystals. However, phase transformations to analcime in the base-treated low-silica zeolites were also noted. The interaction of the hydrogen ions with the aluminosilicate framework of the zeolites caused in a small extent, degradation-dissolution phenomena, resulting in surface-eroded crystals.

Application of Particle and Laser Beams in Materials Technology

Preface. I: Fundamentals. II: Surface Analysis Techniques. III: Laser Beams in Materials Technology. IV: Accelerator-Based Techniques in Materials Technology. V: Materials Modification. VI: Synchrotron Radiation. Index.

Trace element contents in composited samples of three lignite seams from the central part of the Drama lignite deposit, Macedonia, Greece

Abstract Drill core samples of three lignite seams from the central part of the Drama lignite deposit and their corresponding 1000°C ash samples were analyzed for their trace element contents by Instrumental Neutron Activation (INAA) and Inductively Coupled Plasma (ICP) analyses. Compared to crustal abundances, the lignite samples are enriched in As, Br, Mo and Sb, while Ba, Co, Cr, Cs, Eu, Hf, La, Lu, Rb, Sc, Sm, Tb, Yb, Zn, Zr and Au are depleted. While Br is negatively correlated with the ash content of the lignite samples, Ce, Co, Cr, La, Sc, Sm and Yb are positively correlated. Elements from the sorrounding rocks and mineralizations of the Drama Basin have influenced the inorganic constituents of the lignite.

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.

Uranium sorption from aqueous solutions on sodium-form of HEU-type zeolite crystals

The uranium sorption from aqueous solutions (concentration range 50–20.000 mg/l) by the sodium-form (Na-form) of HEU-type zeolite crystals (particle-size <20 μm) has been investigated by means of a batch-type method. The INAA, RI-XRF, powder-XRF, SEM-EDS and FT-IR techniques were used for the study of the experimental products. The absolute uranium uptake by the material reached the value of 11.68 mg/g in the case of initial concentraton 20,000 mg/l. On the other hand theKd-values indicated that the relative uranium uptake, and consequently the percentage of removal, is higher for concentrations below 100 mg/l. The uranium uptake by the zeolite is attributed to different sorption processes such as ion-exchange, adsorption and surface precipitation, taking place both to the interior and the surface of the crystals and strongly depending on the pH of the solutions. The investigated zeolitic material was sufficiently resistant at the low initial pH of the solutions with dealumination phaenomena only observed in the case of the most acidic solution used.

Caesium selectivity and fixation by vermiculite in the presence of various competing cations

Caesium selectivity coefficients (k(G)) that were determined with respect to Na-, Mg-, Ca-, Sr- and Ba-ions, for Kent and Libby vermiculites,ranged from 4.8 to 11 (litres/mol) [Formula: see text], much higher than those with respect to K- and NH(4)-ions (0.01 to 0.06), indicating the high affinity of vermiculite for the weakly hydrated cations. Higher K(G) values were also found for low and extremely low Cs concentrations. Vermiculite samples were very effective in removing (137)Cs from solutions containing traces of (137)Cs (4 ng litre(-1)) and extremely higher quantities of K-, NH(4)-, Na-, Mg- and Ca-ions (500 mg litre(-1)). 0.5N chloride solutions of H, NH(4), K, Na, Mg and Ca were unable to remove Cs from Cs-saturated v vermiculite samples which had undergone heating at 110 degrees C. Significant quantities (50-65%) of fixed Cs were removed from these samples only after treatment with strong acids. The high preference and fixing ability of vermiculite for Cs suggests the use of this mineral as a radioactive Cs decontaminating agent.

Heavy metal uptake by zeoliferous rocks from Metaxades, Thrace, Greece : an exploratory study

The uptake of mercury, cadmium and silver from aqueous solutions by unpretreated and NaCl-pretreated clinoptilolite-bearing volcaniclastic rocks from Metaxades (Thrace, Greece) has been studied using a batch method with radioactive tracers (197Hg,115Cd and110mAg). The concentration of the solutions used varied between approximately 1000 and 17000 ppm. An improvement of the uptake ability was observed in the case of NaCl-pretreated material for all the investigated metals and especially for mercury at the upper part of the concentration range studied. The heavy metal uptake is attributed to different mechanisms taking place both at the rock grains and their individual mineral components.

Investigation of chemical processes at mineral surfaces using accelerator-based and surface analytical techniques: heavy metal sorption on zeolite crystals

Abstract Natural HEU-type zeolite crystals were exposed to copper, mercury, lead and uranium aqueous solutions. The reacted zeolite samples obtained were examined using SEM-EDS and further investigated by means of 12 C-RBS and XPS. The 12 C-RBS study proved an inhomogeneous depth distribution of sorbed metals on the mineral surface and particularly an intense metal accumulation in the near-surface layers of the material, which can be attributed to an anomalous diffusion of metal cations into the micropores due to ion-exchange reactions. This phenomenon strongly depends on the size of the zeolite crystals, the treatment time and the type of the exchangeable cations. In addition in the case of mercury and uranium, metal-rich “layers” supported on the surface could also be identified. The XPS results showed that these “layers” consist of metal oxides and hydroxides adsorbed and precipitated during the interaction of the zeolite with the heavy metal-containing aqueous solutions. The surface morphology and microtopography seem to play an important role to the chemical processes taking place at the zeolite surface.