Anestis Filippidis

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.

Environmentally important elements in fly ashes and their leachates of the power stations of Greece

The relative mass of major and trace elements that potentially can be released from the fly ashes generated in the main Greek power plants (Megalopolis A, Amynteon, Agios Dimitrios, Ptolemais, and Kardia) when they are landfilled and exposed to water have been determined. These fly ashes were subject to a one-stage leaching procedure using the Synthetic Groundwater Leaching Procedure (SGLP) test to simulate this situation. The elements Si, Al, Fe, Ti, Ca, Mg, Na, K, S, Ag, As, B, Ba, Be, Bi, Br, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Ga, Gd, Ge, Hf, Ho, I, La, Li, Lu, Mn, Mo, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Th, Tl, Tm, U, V, W, Y, Yb, Zn, and Zr have been studied. Results show that the elements with the highest potential hazard for the environment are S, Ca, Br, I, Mo, and Sr. The elements with a moderate mobility are K, Na, Ti, B, Ba, Cd, Cr, Cs, Li, Rb, Sb, Se, Sn, W, and Zn. Si, Al, Fe, Mg, Ag, As, Be, Bi, Ce, Co, Cu, Dy, Er, Eu, Ga, Gd, Ge, Hf, Ho, La, Lu, Mn, Nb, Nd, Ni, Pb, Pr, Sc, Sm, Ta, Tb, Th, Tl, Tm, U, V, Y, Yb, and Zr have a low mobility and, consequently, a low potential hazard for the environment.

Mineralogical and chemical investigation of fly ash from the Main and Northern lignite fields in Ptolemais, Greece

Lignite fly ash from the Main and Northern lignite fields of Ptolemais, Greece, is mainly composed of anhydrite, lime, calcite, gehlenite and quartz. Also present, in minor and trace amounts, are portlandite, hatrurite, akermanite, ettringite, plagioclase, alkali feldspar, mica, gypsum, bassanite, brownmillerite, tobermorite and unburnt lignite. Calcite, quartz, feldspars and mica were initially contained in the mined lignite. Anhydrite, lime, portlandite, gehlenite, akermanite, hatrurite and brownmillerite were formed due to the ashing process at different temperatures (> ~400 °C), while gypsum, bassanite, ettringite and tobermorite were formed due to the subsequent soaking of the fly ash, at temperatures around 42–200 °C. The chemical composition of the fly ash corresponds approximately to that of coal combustion slags, lignite fly ash of Gardanne-Provence, France, and Portland clinker. The chemical and mineralogical composition of the fly ash reveal properties of concern to the construction industry and even to health and the environment.

Morphology and trace element contents of the fly ash from main and Northern lignite fields, Ptolemais, Greece

Abstract Morphological and elemental characteristics of fly ash from lignites in Ptolemais coalfield, Northern Greece, were studied using scanning electron microscopy and inductively coupled plasma. Morphologically, fly ash consists of irregularly shaped, oval and spherical particles. Plerospheres, cenospheres and μm spherical particles are also present. The fly ash is enriched in W, Ni and Cr, as compared to Clarkes earth. However, it is enriched only in W compared to the 1000 °C lignite ash from the same lignite basin. The trace elements investigated are grouped into three categories: 1. (1) with organic affinity (W); 2. (2) with inorganic affinity (Mo, Pb, U, Cu, Ni, V, Cr), and 3. (3) with intermediate affinity (Sc, Co, Zn, Rb, Sr, Y, Zr, Ba, La, Yb).

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.

Leachability of Major and Trace Elements of Fly Ash from Ptolemais Power Station, Northern Greece

Major (Si, Al, Fe, Ti, Ca, Mg, Na, K, and S) and trace (Ag, As, B, Ba, Be, Bi, Br, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Ga, Gd, Ge, Hf, Ho I, La, Li, Lu, Mn, Mo, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Th, Tl, Tm, U V, W, Y, Yb Zn, and Zr) elements were determined in experimental leachates of fly ash from the Ptolemais coal-fired power plant (Northern Greece). This plant has a total capacity of 620 MW and consumes lignite from the Ptolemais basin. Experimental leaching was carried out using one stage and column leaching procedures. These leaching experiments allowed for the characterization of the relative mass leached and the element behavior in function of time. Relative mass leached is generally low. Only Sr and Mo are lost during the first five pore volumes of the leaching. The foremost transformations are relatively fast, implying mainly Ca and S reactions and an important lowering of pH values. The results can be used in the disposal assessment of this combustion byproduct to model more accurately the behavior of major and trace elements released during fly ash landfilling.

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.

Mineralogical components of some thermally decomposed lignite and lignite ash from the Ptolemais basin, Greece

Abstract Two samples of Pliocene lignites from the Ptolemais basin of Greece, one from the upper and one from the lower lignite seams, were heated and dried in air at 50°C intervals from 50 to 1200°C. The two lignite samples initially contained the same minerals, namely calcite, dolomite, quartz, kaolinite, illite, pyrite and gypsum, but in different proportions. The lignite sample from the upper lignite seam is rich in Fe 2 O 3 , CaO and SO 3 , while that from the lower lignite seam is rich in SiO 2 and Al 2 O 3 . Hematite, periclase, melilites, calcium ferrite and brownmillerite are constituents of the 1200°C lignite ash from both samples. The heating conditions and the chemistry of the samples lowered the formation temperatures of brownmillerite, which appeared in both samples at 950°C. In the Fe 2 O 3 , CaO- and SO 3 -rich sample, magnesioferrite is present from 850 to 1100°C and hematite appears at 300°C. In the SiO 2 - and Al 2 O 3 -rich sample, magnesioferrite was not detected at any temperature and hematite appeared at 600°C. Anhydrite, which normally decomposes in air at 1638°C, is the main constituent at 1150°C, on heating the lignite sample that was rich in Fe 2 O 3 , CaO and SO 3 . Anhydrite diminishes at 1200°C. In the SiO 2 - and Al 2 O 3 -rich lignite sample, anhydrite is main constituent at 1100°C, but diminishes considerably at 1150°C and decomposes at 1200°C.

Factors affecting the distribution of potentially toxic elements in surface soils around an industrialized area of northwestern Greece

In order to investigate the factors influencing the distribution of 32 potentially toxic elements in the Ptolemais–Kozani basin, northwestern Greece, 38 soil samples were collected and analyzed. Concentrations of Al, Ca, Fe, K, Mg, Mn, Na, P, Ti, Ba, Co, Cr, Cu, La, Li, Ni, Pb, Sc, Sr, V, Y, and Zn were determined by ICP-AES and concentrations of As, Bi, Cd, Cs, Mo, Rb, Sb, Th, Tl, and U by ICP-MS. Bivariate analysis, principal component analysis, and geostatistical analysis were employed to investigate the factors influencing the distribution of the elements determined in the study area. The results indicate that the distribution of the majority of elements determined, especially for Cr, Ni, and associated elements, is greatly influenced by the geology and geomorphology of the study area. Principal component analysis has yielded four factors that explain over 77% of the total variance in the data. These factors are as follows: lithophilic elements that are associated with Al silicates minerals of K (factor I: 29.4%), ultramafic rocks (factor II: 20.5%), elements that are coprecipitated with Fe and Mn oxides (factor III: 18.0%), and anthropogenic activities (factor IV: 9.3%). The anthropogenic activities that influence the distribution of several potentially toxic elements (i.e., Cd, Cu, Pb, Zn) are agricultural practices and the deposition of fly ash in the vicinity of the local power stations.

Environmental Effects of Lignite and Intermediate Steriles Coexcavation in the Southern Lignite Field Mine of Ptolemais, Northern Greece

The majority of the thin intercalated sterile layers, which are coexcavated with lignite in the Southern Field mine of Ptolemais, Northern Greece, are petrologically characterized as marly limestones. They consist of 90-95% calcite, 5-7% micas + clays, and < 4% feldspars. The coexcavation of lignite with marly limestones and/or carbonaceous marls increases a) the content of the carbonate minerals (already contained in lignite), b) the ash content, and c) the total and free CaO content of the lignite-ash and decreases the calorific value of the mined lignite. The increase of total CaO deteriorates the power plant operation due to fouling effects, while the increase of the CaO (free) content of the lignite ash results in an increase of the solid particle emissions from the electrostatic precipitators of Agios Dimitrios Power Plant. The temperature increase, which follows the hydration of CaO (free) , results in the evaporation of the ash water and the long-term damage of the ash transportation equipment as well. The concentration of CaO (free) in the lignite ash is estimated through a coefficient, which is obtained from the ratio of the CO 2 content (db) and the ash content (db) of the mined lignite. The improvement of lignite quality, reducing the CaCO 3 content, results in a better power plant operation in terms of economy and environmental protection.