Spatial diversity of Cr distribution in soil and groundwater sites in relation with land use management in a Mediterranean region: The case of C. Evia and Assopos-Thiva Basins, Greece.

The present study compiles new and literature data in a GIS platform aiming to (a) evaluate the extent and magnitude of Cr contamination in a Mediterranean region (Assopos-Thiva and Central Evia (Euboea) Basins, Greece); (b) combine spatial distribution of Cr in soil and groundwater with land use maps; (c) determine geochemical constraints on contamination by Cr; and (d) provide information that will be useful for better management of land use in a Mediterranean type ecosystem in order to prevent further degradation of natural resources. The spatial diversity of Cr distribution in soils and groundwater throughout the C. Evia and Assopos-Thiva Basins is considered. It is attributed to both natural Cr sources (Cr-bearing peridotites, affecting primarily soil) and human (industrial) activities (the dominant source of groundwater contamination). A combination of the spatial distribution of metals in soil and land use maps was used to define the specific areas of agricultural land use with elevated heavy metal contents. Furthermore, the combination of the spatial distribution of Cr in groundwater and land use maps allows for definition of specific areas of industrial land use with elevated Cr concentrations (Inofita, south Assopos-Thiva Basin). Despite the good correlation (r = 0.75) between Cr(VI) and the strong oxidant NO3- in C. Evia, the lower standard potential (E0) values for NO3- compared to those for Cr2O72- (the latter is a stronger oxidant than the former) suggest that NO3- is not an oxidant of Cr. This detailed assessment and presentation of the available analytical data for soil and groundwater in Assopos-Thiva and C. Evia Basins on a land use map provides information for land management decision makers.

Comparative uptake study of toxic elements from aqueous media by the different particle-size-fractions of fly ash.

The purpose of the study described in this paper was to determine the removal of Cr (total), Cr (VI), Cu, Ni, Pb, Zn and Cd from wastewater using different particle-size-fractions of highly calcareous and highly siliceous fly ashes (FAs). Three different Hellenic FAs (two calcareous and one siliceous) were tested for their capability of precipitating heavy metals from aqueous solutions. Each FA sample was separated into six different size-fractions with a grain diameter range of: [(0-25) (25-40) (40-90) (90-150) (150-400) and (>400)] µm. The different FA grain-fractions were evaluated in terms of their chemical composition, pH, Loss on Ignition (LOI) and CaO(f) (%). Batch adsorption experiments were then carried out, indicating that the various grain-fractions of the highly siliceous FA were more efficient in precipitating Cr (VI) but less capable of retaining Cd, Cu, Ni, Pb and Zn. On the other hand, the high-Ca fly ashes were proven to be more efficient in uptaking Cd, Cu, Ni, Pb and Zn, but less in hexavalent chromium. This particular tendency was also confirmed in the case of the different particle-size-fractions of same fly ashes. It was actually verified that FAs can be more effective in the field of industrial wastewater-remediation when separated into their size-fractions.

Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials.

Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, were utilized as raw materials for the synthesis of zeolitic products. The two FAs underwent a hydrothermal activation with 1M NaOH solution. Two different FA/NaOH solution/ratios (50, 100g/L) were applied for each sample and several zeolitic materials were formed. The experimental products were characterized by means of X-ray diffraction (XRD) and energy dispersive X-ray coupled-scanning electron microscope (EDX/SEM), while X-ray fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro- and macroporosity. Afterwards the hybrid materials were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids. Main parameters for the precipitation of the heavy metals, as it was concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.