Removal of Chromium from Soils Cultivated with Maize (Zea Mays) After the Addition of Natural Minerals as Soil Amendments.

The efficiency of natural minerals, i.e. zeolite, bentonite and goethite, regarding the retention of chromium, from maize was examined. Specifically, 1.0 kg of soil, 1.0 g of soil amendment and either 50 mg L-1 Cr(III) or 1 mg L-1 Cr(VI) were added in plant pots. Then, seeds of maize were cultivated. Each treatment was repeated three times. The statistical results of the experiments were analyzed by LSD test. Cr(III) addition in soil has shown that zeolite was the only amendment that increased the dry weight. Zeolite and bentonite reduced significantly the total chromium in plants after the addition of 50 mg L-1 Cr(III). The addition of Cr(VI) in soil has shown that bentonite was the only amendment that increased the dry weight of biomass and the plants' height. All soil amendments reduced to zero the total chromium concentration measured to plants after the addition of 1 mg L-1 Cr(VI).

Spatial monitoring of arsenic and heavy metals in the Almyros area, Central Greece. Statistical approach for assessing the sources of contamination.

The purpose of this work was to provide information on As and heavy metals content in surface soils of the Almyros area, in Central Greece. A 3-year (2009-2011) research was conducted, in order to investigate the possible temporal variation of As and heavy metal levels. Each year, a number of 251 soil samples (753 totally number of samples) were collected from the area studied, using a Differential Global Positioning System (D.G.P.S.). Soil samples were analyzed for physicochemical parameters and for pseudo-total content of metals, after digestion with Aqua Regia. Thematic maps were created, with Geographic Information Systems (GIS) techniques, using geostatistical tools. The corresponding topographical diagrams covering 15,000 ha of the study area were digitized. The thematic maps and the geostatistical analysis tools were conducted with the use of ArcGIS and the extensions Geostatistical Analyst, Spatial Analyst, and 3D analyst. Factor analysis was conducted in order to assess the possible sources of the pollution. The levels of As and metals determined were lower than the maximum permitted, except for Cd, which content was, in some cases, higher than the critical limits for soils. No statistical differences were observed among the years of the study, although a trend of continuous increasing of their content was detected. Significant correlations between heavy metal fractions and soil physicochemical parameters were obtained and discussed.

Adsorption of methylene blue and methyl red dyes from aqueous solutions onto modified zeolites.

Zeolite, hematite, modified zeolite and commercial activated charcoal were examined for their ability to remove methylene blue (MB) and methyl red (MR) from their aqueous solutions. Modified zeolite and hematite were produced according to the Schwertmann and Cornell method while zeolite and commercial activated charcoal were obtained from S&B and Fluka AG companies, respectively. Adsorption experiments were conducted at three different adsorbent-to-solution ratios, namely 8, 16 and 24 g/L under environmental conditions and continuous stirring. Equilibrium isotherms of MB and MR were studied at different initial concentrations (from 5 × 10(-4) to 5 × 10(-3) g/L). MB adsorption kinetics were also studied. The maximum adsorption of MB and MR from their aqueous solutions was achieved at 24 g/L (adsorbent-to-dye solution ratio) after 1 h and was equal to 100% (MB) on modified zeolite and 99% (MR) on commercial activated charcoal, respectively. All the other materials achieved intermediate values of dye adsorption. From the applied kinetic models, the pseudo-second-order equation best described the adsorption of MB and MR. Consequently, modified zeolite showed the highest adsorption capacity for MB, while commercial activated charcoal showed the highest adsorption capacity of MR. The studied adsorbents can be used as filters to remove dyes from wastewaters.

Monitoring the variability of zinc and copper in surface soils from central Greece.

The main purpose of this investigation was the monitoring of Zn and Cu levels in soils of central Greece over three consecutive years (2005 to 2007). Soil samples were analysed for available forms (after extraction with DTPA) and for total concentrations (after digestion with Aqua Regia) of Zn and Cu. A temporal variability, from 2005 to 2007, was observed, as an increasing of 25.5% in available Zn, 25.1% in total Zn, 209% in available Cu and 19.6% in total Cu concentrations were recorded. A spatial variability was also observed and illustrated by the respective thematic maps created using geographic information systems (GIS). Significant correlations among metals concentrations and soil physicochemical parameters were obtained and discussed.

Use of an iron-overexchanged clinoptilolite for the removal of Cu2+ ions from heavily contaminated drinking water samples.

Clinoptilolite, a natural zeolite, was used for the synthesis of a high surface area clinoptilolite-iron oxide system, in order to be used for the removal of Cu2+ ions from drinking water samples. The solid system was obtained by adding natural clinoptilolite in an iron nitrate solution under strongly basic conditions. The Clin-Fe system has specific surface area equal to 151 m2 g(-1) and is fully iron exchanged (Fe/Al=1.23). Batch adsorption experiments were carried out to determine the effectiveness of the Clin and the Clin-Fe system in removal of copper from drinking water. Adsorption experiments were conducted by mixing 1.00 g of each of the substrates with certain volume of water samples contaminated with 10 different Cu concentrations (from 3.15x10(-5) to 315x10(-2) M or from 2.00 to 2000 ppm Cu). For our experimental conditions, the maximum adsorbed Cu amount on Clin was 13.6 mg g(-1) whereas on the Clin-Fe system was 37.5 mg g(-1). The main factors that contribute to different adsorption capacities of the two solids are due to new surface species and negative charge of the Clin-Fe system. In addition, the release of counterbalanced ions (i.e. Ca2+, Mg2+, Na+ and K+) was examined, as well as the dissolution of framework Si and Al. It was found that for the most of the samples the Clin-Fe system releases lower concentrations of Ca, Mg and Na and higher concentrations of K than Clin, while the dissolution of Si/Al was limited. Changes in the composition of water samples, as well as in their pH and conductivities values were reported and explained.

Preparation, characterization and sorption properties for phosphates of hematite, bentonite and bentonite-hematite systems.

Hematite was prepared using Fe(NO3)3*9H2O. Bentonite was first saturated with sodium and then was transformed to the hydrogen form. The bentonite-hematite (b-h) system was prepared by the mixing of hematite and bentonite at pH 6.0, and a hematite-coated bentonite surface was created. The physical and chemical properties of the above solids were studied from the information given by X-ray, IR and NMR spectra and by measurement of specific surface and point of zero charge. The results of the above study show that the bentonite-hematite system is not a physical mixture of hematite and bentonite. Hematite moved into bentonite's interlayer space, coating these planes throughout. Consequently, Al-substitution and structural H2O/OH displacement of hematite took place. The system has a specific surface, less than bentonite and greater than hematite, while its p.z.c. is higher than bentonite and lower than hematite. Adsorption experiments of phosphates at different concentrations and pH were carried out and the constant capacitance model was used to describe phosphate adsorption by hematite, bentonite and the bentonite-hematite system. The model is characterized by a ligand exchange mechanism based on the assumption that the charge is attributed both on adsorbate and adsorbent, and is proven to successfully describe the adsorption of phosphate on these materials along with the effect of varying pH values. Ma-Za 1 and Ma-Za 2 (two computer programs) were used for this purpose. The model successfully gave a description (both quantitative and qualitative) of the adsorption of phosphate anions across the pH range (3.8-9.0). Furthermore, it can be successfully applied in systems as the bentonite-hematite system by utilizing the surface protonation-dissociation constant of hematite. The model, when applied in such systems, procreates the exact shape of the adsorption isotherms for the entire pH range of 3.8-9.0. The constant capacitance model was able to describe phosphorous adsorption on hematite and the bentonite-hematite system. The accurate fit of the model to phosphorous adsorption on hematite and the bentonite-hematite system suggests that inner sphere surface complexation is the appropriate adsorption mechanism for these materials.

Copper adsorption and Si, Al, Ca, Mg, and Na release from clinoptilolite.

Copper adsorption onto clinoptilolite (natural zeolite), Al/Si dissolution, and Mg, Ca, and Na release from the substrate were the subjects of the investigation described here. Experimental variables were Cu and electrolyte concentrations and solution pH. Copper adsorption was found to increase with increased pH and with decreased electrolyte concentration. Large amounts of K were also adsorbed from electrolyte. Since solution pH was assumed as a variable, the effects of [H(+)] differentiation on Cu adsorption and on Al/Si dissolution were also examined. Al dissolution was affected mainly by electrolyte concentration, whereas Si dissolution was affected mainly by adsorbed Cu amount. It was assumed that the release of Mg, Ca, and Na occurs through ion-exchange reactions with solution K(+), because their release is affected more by electrolyte concentration than by adsorbed Cu. From the study of FTIR spectra for various samples used in the present investigation, we observed that the removal of framework Si/Al shifts the band which was attributed to O-T-O stretching vibration toward higher frequency. Significant changes were observed for the bands assigned to Si-OH-Al bridges and to monomeric and polymeric hydrogen bonds at the region between 3650 and 3200 cm(-1). It is proposed that the Cu species caused the destruction of H-bonded structures, whereas K adsorbed species were located at exchangeable sites after an ion-exchange process between K and Ca, Mg, and Na from the zeolite's surface. An expansion of the zeolite framework was detected from XRD patterns under acid conditions.

Levels of heavy metals pollution in different types of soil of central Greece.

This investigation was performed in order to clarify the degree of heavy metals pollution in forest, agricultural and industrial surface soil samples in relation to pre-anthropogenic soils of Almyros region, in Central Greece. In 2004 and 2005 soil samples were collected and analysed for available (DTPA method) and total (Aqua Regia method) Cd, Cr, Cu, Pb, Zn and Ni concentrations. For each metal the enrichment factor with respect to the levels in pre-anthropogenic soils was calculated. All the types of soils appeared to be less polluted than in other investigations. In agricultural and industrial soils the available Cd concentration was higher than the other metals studied. The enrichment factor of Cu in relation to total concentration has the maximum value of the metals studied.

Influence of some soil parameters on heavy metals accumulation by vegetables grown in agricultural soils of different soil orders.

The main purpose of this research was to determine the levels of heavy metals in tomato, potato and lettuce, grown in agricultural soils of different soil orders (Alfisols, Endisols and Vertisols), located at Central Greece. Soil samples were analysed for available forms (after extraction with DTPA) and for total concentrations (after digestion with Aqua Regia) of metals. Zn, Cu, Cr and Ni were the common metals detected in the vegetables studied. Pb and Cd concentrations were low and in some cases not detectable. Significant correlations among metals concentrations and soil physicochemical parameters were obtained and discussed. The pH value and the percentage of clay content were found to determine the solubility of metals in the soil and their availability for uptake by plants.

Phosphate Adsorption on Hematite, Kaolinite, and Kaolinite-Hematite (k-h) Systems As Described by a Constant Capacitance Model

The constant capacitance model was used to describe phosphate adsorption on hematite, kaolinite, and a kaolinite-hematite system (k-h). The model assumes a ligand exchange mechanism and considers the charge on both adsorbate and adsorbent. The model is shown to provide a quantitative description of phosphate adsorption on these, including the effect of varying pH values. The computer program Ma-Za 2, a program that fits equilibrium constants to experimental data using an optimization technique, was used to obtain optimal values for the anion surface complexation constants on hematite, kaolinite, and a kaolinite-hematite system, while the PC program Ma-Za 1 in Q-Basic language was used for the application of the constant capacitance model. The model represented adsorption of phosphate anions well over the entire pH range studied (3.8-9.0). The main advantage of the model is its ability to represent changes in anion adsorption occurring with changes in pH. Extension of the model to describe phosphate adsorption in a mixed system, such as the kaolinite-hematite system, using the surface protonation-dissociation constant of hematite was qualitatively successful. In mixed system the model reproduced the shape of the adsorption isotherms well over the pH range 3.8-9.0. However, phosphate adsorption was overestimated. The hematite and the kaolinite-hematite system were synthesized and identified by X-ray, NMR, and FT-IR spectroscopy.