Green Synthesis of Resin Supported Nanoiron and Evaluation of Efficiency for the Remediation of Cr(VI) Contaminated Groundwater by Batch Tests.

In this study the fixation of nano zero valent iron (nZVI) on a polymeric matrix applying an environmentally friendly technique and the performance of this material for the treatment of Cr(VI) contaminated groundwater were evaluated. The investigated method could be applied in a pump & treat groundwater remediation system. A macroreticular cationic resin was selected as porous host material. It was found that green tea polyphenols were able to penetrate within the macroporous resin matrix and obtain the reduction of Fe(III) to the elemental state. The effectiveness of this composite material in removing Cr(VI) contaminated waters was evaluated by conducting batch tests. It was found that the reduction of Cr(VI) follows a kinetics law of first order with respect to the concentration of Cr(VI) and to the amount of nZVI per liter of solution. The kinetic constant varied between 5·10-3 and 0.5·10-3 per min and per mM of nZVI in the pH range 3.5-7.5.

Hexavalent chromium reduction by gallic acid.

Cr(VI) is widely used in industry and often large quantities have been accidently or due to lack of precautions released at the environment. The presence of high concentrations of Cr(VI) in waste streams causes concern due to its toxicity and solubility. However the Cr(III) is a useful micronutrient in human diet. The reduction of Cr(VI) to Cr(III) is a promising technology for a clean environment. Polyphenols are commonly found in plants and they are considered as strong natural antioxidants. In this study the reduction of hexavalent to trivalent chromium using gallic acid (GA), a polyhydroxyphenolic compound, was evaluated. The effect of pH, temperature, and Cr(VI) concentration on the kinetics of Cr(VI) reduction by GA were examined by conducting batch tests. It was found that reduction of Cr(VI) by GA is a rapid reaction under mild acidic conditions. Reduction was found to follow a 2nd order kinetics with respect to Cr(VI) concentration in the pH range 3-5. The results of the present study indicated that the treatment of contaminated waters with initial concentration of Cr(VI) 100 µΜ by gallic acid, below the environmental limit of 0.96 µM, required 20 min at pH 3 and 40 min at pH 4. At higher pH a different reduction mechanism seems to prevail and the required time for Cr(VI) reduction was approximately 10 h at pH 5 and 42 h at pH 6. The increase of temperature25 °C to 35 °C, at pH 6, was slightly accelerated the reaction.

Assessment of chromium biostabilization in contaminated soils using standard leaching and sequential extraction techniques.

The iron reducing microorganism Desulfuromonas palmitatis was evaluated as potential biostabilization agent for the remediation of chromate contaminated soils. D. palmitatis were used for the treatment of soil samples artificially contaminated with Cr(VI) at two levels, i.e. 200 and 500 mg kg(-1). The efficiency of the treatment was evaluated by applying several standard extraction techniques on the soil samples before and after treatment, such as the EN12457 standard leaching test, the US EPA 3060A alkaline digestion method and the BCR sequential extraction procedure. The water soluble chromium as evaluated with the EN leaching test, was found to decrease after the biostabilization treatment from 13 to less than 0.5 mg kg(-1) and from 120 to 5.6 mg kg(-1) for the soil samples contaminated with 200 and 500 mg Cr(VI) per kg soil respectively. The BCR sequential extraction scheme, although not providing accurate estimates about the initial chromium speciation in contaminated soils, proved to be a useful tool for monitoring the relative changes in element partitioning, as a consequence of the stabilization treatment. After bioreduction, the percentage of chromium retained in the two least soluble BCR fractions, i.e. the "oxidizable" and "residual" fractions, increased from 54 and 73% to more than 96% in both soils.

Development of silica protective layer on pyrite surface: a column study.

An appealing technique to prevent and/or minimize pyrite oxidation and subsequent acid generation in mine waste sites is the formation of a protective coating on the surface of sulfide grains. To investigate the conditions for the formation of an efficient coating on pyritic tailings, column tests were performed. These tests involved the treatment with a coating solution, which was continuously recycled through the packed bed of tailings. The coating solution was consisted of SiO4-4 oxyanions, an oxidant (H2O2), and adjusted to pH 6. The effect of the volume of coating solution per mass of material (L/S ratio), Si concentration and treatment duration on coating formation was studied. Based on the results, a protective coating can be developed on the pyrite particles following treatment with a solution of 0.1 mM Si concentration, which resulted in the reduction of sulfate release by 84% compared to non-treated pyrite samples.

Incorporation of zero valent iron nanoparticles in the matrix of cationic resin beads for the remediation of Cr(VI) contaminated waters.

The objective of present study was to obtain the fixation of nano zero valent iron (nZVI) particles on a permeable matrix and evaluate the performance of this composite material for the removal of Cr(VI) from contaminated waters. The experiments were carried out using the cationic resin Dowex 50WX2 as porous support of the iron nanoparticles. The work was carried out in two phases. The first phase involved the fixation of nZVI on the resin matrix. The resin granules were initially mixed with a FeCl3 solution to obtain the adsorption of Fe(III). Then the Fe(III) loaded resin (RFe) was treated with polyphenol solutions to obtain the reduction of Fe(III) to the elemental state. Two polyphenol solutions were tested as reductants, i.e. green tea extract and gallic acid. Green tea was found to be inefficient, probably due to the relatively big size of the contained polyphenol molecules, but gallic acid molecules were able to reach adsorbed Fe(III) and reduce the cations to the elemental state. The second phase was focused on the investigation of Cr(VI) reduction kinetics using the nanoiron loaded resins (R-nFe). It was found that the reduction follows a kinetic law of first order with respect to Cr(VI) and to the embedded nanoiron. Compared to other similar products, this composite material was found to have comparable performance regarding reaction rates and higher degree of iron utilization. Namely the rate constant for the reduction of Cr(VI), in the presence of 1 mM nZVI, was equivalent to 1.4 h of half-life time at pH 3.2 and increased to 24 h at pH 8.5. The degree of iron utilization was as high as 0.8 mol of reduced Cr(VI) per mole of iron. It was also found that this composite material can be easily regenerated and reused for Cr(VI) reduction without significant loss of efficiency.

Bona-fide method for the determination of short range order and transport properties in a ferro-aluminosilicate slag.

The thermodynamics, structural and transport properties (density, melting point, heat capacity, thermal expansion coefficient, viscosity and electrical conductivity) of a ferro-aluminosilicate slag have been studied in the solid and liquid state (1273-2273 K) using molecular dynamics. The simulations were based on a Buckingham-type potential, which was extended here, to account for the presence of Cr and Cu. The potential was optimized by fitting pair distribution function partials to values determined by Reverse Monte Carlo modelling of X-ray and neutron diffraction experiments. The resulting short range order features and ring statistics were in tight agreement with experimental data and created consensus for the accurate prediction of transport properties. Accordingly, calculations yielded rational values both for the average heat capacity, equal to 1668.58 J/(kg·K), and for the viscosity, in the range of 4.09-87.64 cP. The potential was consistent in predicting accurate values for mass density (i.e. 2961.50 kg/m(3) vs. an experimental value of 2940 kg/m(3)) and for electrical conductivity (5.3-233 S/m within a temperature range of 1273.15-2273.15 K).

Investigation of potential soil contamination with Cr and Ni in four metal finishing facilities at Asopos industrial area.

The objective of this work was to investigate whether previous disposal practices in four metal finishing facilities, located at Asopos river basin (East-Central Greece), have caused any potential serious contamination of soils. The study focused mainly on Cr and Ni, which are the primary elements of concern in the area. To estimate the natural geochemical levels of Cr and Ni, thirty soil samples were collected from locations that were not suspected of any contamination. In this group of samples, Cr concentration varied between 60 and 418 mg/kg, and Ni concentrations varied from 91 to 1200 mg/kg. The second group of samples consisted of more than 100 drill cores and surface soil samples, potentially affected by the disposal of effluents and/or the drainage of runoff water from the industrial facilities. According to the findings of the study, the disposal of treated effluents in absorption type sinks resulted occasionally in the contamination of a thin layer of soil just at the bottom of the sinks, but there was no indication of downward migration, since Cr and Ni concentrations in the lower soil layers were similar to those of the reference soils.

Origin and concentration profile of chromium in a Greek aquifer.

In this paper the origin and concentration of chromium (Cr) in an ophiolitic aquifer in Vergina, northern Greece were investigated. The study area has only agricultural activity so that industrial Cr contamination was precluded. Soil sampling included topsoil and drillcore samples collected down to 98 m depth. Groundwater samples were collected from three existing wells and a spring at the area and from different depths of the soil boring using the discrete sampling method. Mineralogical analysis of soils confirmed the presence of ultramafic minerals, including chrysotile and chromite. Soil elemental analysis showed significant concentration of total chromium (Crtot; max 12,000 mg/kg) and hexavalent chromium (Cr(VI); max 7.5mg/kg). Significant Crtot (91 µg/L) and Cr(VI) (64 µg/L) concentrations exceeding the drinking water limit of 50 µg/L were also detected in groundwater. In both the discrete soil and groundwater samples a decreasing trend of Cr(VI) concentration was observed with increasing depth, while Crtot increased. The increasing trend in Crtot is attributed to the increasing contribution of unweathered ultramafic minerals with depth, while the decreasing Cr(VI) may be related to the increasing soil pH that does not favor Cr(III) oxidation by Mn-oxides.

Evaluation of monobasic calcium phosphate for the immobilization of heavy metals in contaminated soils from Lavrion.

The objective of this work was to evaluate the efficiency of monobasic calcium phosphate for the stabilization of heavy metals in contaminated soils. The treatment was applied on a soil sample from the Lavrion mining area, Greece, heavily contaminated with Pb, Zn, Cd and As and characterized as toxic in respect to Pb according to the US EPA toxicity characteristics leaching procedure (TCLP). The efficiency of stabilization was evaluated based on two criteria: (a) the reduction of metals mobility below the TCLP regulatory limits; (b) the reduction of phytoaccumulation. Phytoaccumulation was evaluated both indirectly by applying leaching tests using EDTA, DTPA and NaHCO(3) solutions and directly by carrying out pot experiments with Phaseolus vulgaris as plant indicator. This treatment was found to immobilize Pb and Cd, whereas As and Zn were slightly mobilized. No effect on phytoaccumulation was observed. Moreover, the treatment had a negative effect on plants growth, which was combined with a strong deficiency of Ca in the tissue of leaves.

Potential use of lignite fly ash for the control of acid generation from sulphidic wastes.

In the present paper, the potential use of lignite fly ash in the control of acid generation from sulphidic tailings disposed of at Lavrion, Greece was studied. Long-term laboratory column kinetic tests were performed on tailings containing 27% S, which were homogeneously mixed with various amounts of fly ash, ranging from 10 to 63% w/w. The drainage quality of the columns was monitored over a test period of 600 days. Chemical and mineralogical characterisation of column solid residues was performed after a 270-day test period. The hydraulic conductivity of the mixtures was also measured to evaluate the potential of fly ash to form a low permeability layer. Based on the results, the addition of fly ash to sulphidic tailings, even at the lower amount, increased the pH of the drainage at values of 8.6-10.0 and decreased the dissolved concentrations of contaminants, mainly Zn and Mn, to values that meet the European regulatory limits for potable water. Higher fly ash addition to tailings, at amounts of 31 and 63% w/w also reduced the water permeability of material from 1.2 x 10(-5) cm/sec to 3 x 10(-7) and 2.5 x 10(-8) m/s, respectively.

Stabilization of Pb and As in soils by applying combined treatment with phosphates and ferrous iron.

The chemical immobilization of Pb and As in contaminated soil from Lavrion, Greece, using monocalcium phosphate and ferrous sulfate as stabilizing agents was investigated. Monocalcium phosphate was added to contaminated soil at PO(4) to Pb molar ratios equal to 0, 0.5, 1, 1.5 and 2.5, whereas ferrous sulfate was added at Fe to As molar ratios equal to 0, 2.5, 5, 10 and 20. Phosphates addition to contaminated soil decreased Pb leachability, but resulted in significant mobilization of As. Simultaneous immobilization of Pb and As was obtained only when soil was treated with mixtures of phosphates and ferrous sulfate. Arsenic uptake by plants was also seen to increase when soil was treated only with phosphates, but co-addition of ferrous sulfate was efficient in maintaining As phytoaccumulation at low levels. The addition of at least 1.5M/M phosphates and 10M/M iron sulfate to soil reduced the dissolved levels of Pb and As in the water extracts to values in compliance with the EU drinking water standards. However, both additives contributed in the acidification of soil, decreasing pH from 7.8 to values as low as 5.6 and induced the mobilization of pH sensitive elements, such as Zn and Cd.