Nymphodora Papassiopi

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.

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.

Removal of contaminant metals from fine grained soils, using agglomeration, chloride solutions and pile leaching techniques

A leaching process based on the use of a HCl-CaCl2 solution, with total chloride concentration 4M, was investigated for the removal of contaminant metals from fine acidic soils. The possibility to apply this treatment on piles constructed on-site was also examined as a low cost treatment option. The soil sample used in the study was fine in texture, i.e. clay loam, acidic (pH 5.6), and contaminated mainly with Pb, up to 16000mg Pb/kg dry soil, due to past mining activities. The experimental work comprised all the treatment stages, including agglomeration of fine soil particles to increase the permeability of soil, leaching of the agglomerated soil in a laboratory column, removal of metals from the leachate, regeneration and recycling of the leaching solution and final washing of the treated soil. The initial agglomeration treatment resulted in the formation of coarse aggregates and the percolation of leaching solution through the soil column was maintained at high levels, i.e.75ml/cm(2) per day, during the whole treatment. A low amount of HCl acid was required for the removal contaminants from this particular soil, i.e. 0.44mol HCl/kg soil, due to the absence of acid consuming minerals. The extractions achieved were 94% for Pb, 78% for Zn and more than 70% for Cd. The co-dissolution of soil matrix was very limited, with a total weight loss about 3.5%. The final pH of the soil after washing was found to be 5.15, i.e. slightly lower compared to the initial pH of the soil. The results of this study indicate that chloride leaching, in combination with agglomeration and pile leaching techniques, can be a cost effective option for the removal of metal contaminants from fine acidic soils.

Environmental characterisation of the sulphidic tailings in Lavrion

Abstract Intensive mining and metallurgical activities in Lavrion over a time span of over 2700 years resulted in the formation of huge spoils of mining, milling and metallurgical wastes and tailings, most of them characterised as toxic and hazardous. Toxic elements are released by a number of mechanisms and migrate to the surrounding area, contributing to the widespread soil contamination. Three main types of spoils exist: sulphidic flotation tailings, oxidic-carbonaceous-silicate beneficiation tailings and metallurgical slags. This paper deals with the sulphidic flotation tailings. For the estimation of the risk that these tailings pose to the environment and for the conceptual development of a remediation strategy, complete characterisation was done according to the following methodology: Drillholes were placed within the spoils and undisturbed core samples were taken and characterised chemically and mineralogically, their net neutralisation potential (NNP) was determined using static tests and their toxicity using the EPA TCLP test, speciation of the toxic metals was determined in some cases using the sequential extraction technique and the bioavailable fraction determined by EDTA extraction. Some geotechnical characteristics of the spoils, as density and permeability were determined in-situ. Piezometers were installed within the boreholes and the pore water quality and level was monitored. The above information is being critically assessed and employed for the selection and design of the optimum rehabilitation scheme.

On the kinetics of magnesia hydration in magnesium acetate solutions

High-quality magnesium hydroxide powders can be produced by hydrating slow-reacting magnesia in dilute magnesium acetate solutions. The kinetics of this process are very crucial for process design and control, and for the production of a powder with desirable particle morphology. In this work, industrial heavily-burned magnesia powders were hydrated in 0.01-0.1 mol/dm 3 magnesium acetate solutions at temperatures ranging between 333 and 363 K. Examination of the magnesium hydroxide produced and the analysis of the kinetic data suggest that the hydration of heavily burned magnesia in magnesium acetate solutions is a dissolution-precipitation process controlled by the dissolution of magnesia particles. The activation energy was estimated to be 60 kJ/mol, while the reaction order with respect to acetate concentration was found to be about one.

Carbonate-rich mining tailings in Lavrion: risk assessment and proposed rehabilitation schemes☆

Abstract In Lavrion, Greece, the mining and metallurgical activities that were particularly intensive during the last century resulted in the generation of huge amounts of wastes, including acid-generating sulfidic tailings, carbonaceous tailings and slags. Their improper management in the past resulted in the migration of heavy metals to the surroundings, contributing to widespread soil contamination. As a result, the local population is exposed to multiple hazardous pollution sources. The present study aims to combine the available geochemical characterisation techniques and risk assessment tools in order to identify the specific risks associated with the carbonate wastes and determine the remedial measures required accordingly. The risk assessment study of the carbonate tailings resulted in the identification of three high-risk exposure routes for humans: direct contact, ingestion and inhalation of contaminated material. Plant uptake and secondary contamination of soils are rated as high-risk exposure routes only for ‘Savoura’ tailings. Quantification of the human health risks indicated that direct ingestion of contaminated particles is the most important exposure route for the intake of contaminants by humans. The intake of Pb, As and Cd by adults and children living in the vicinity of carbonaceous tailings was found to exceed the maximum tolerable risk. Based on the risk assessment results, several remediation options were examined, aimed at either removing the source or breaking the significant source–pathway–target relationships.

Synthesis, characterization and stability of Cr(III) and Fe(III) hydroxides.

Chromium is a common contaminant of soils and aquifers and constitutes a major environmental problem. In nature, chromium usually exists in the form of two oxidation states, trivalent, Cr(III), which is relatively innocuous for biota and for the aquatic environment, and hexavalent, Cr(VI) which is toxic, carcinogenic and very soluble. Accordingly, the majority of wastewater and groundwater treatment technologies, include a stage where Cr(VI) is reduced to Cr(III), in order to remove chromium from the aqueous phase and bind the element in the form of environmentally stable solid compounds. In the absence of iron the final product is typically of the form Cr(OH)3·xH2O whereas in the presence of iron the precipitate is a mixed Fe(1-x)Crx(OH)3 phase. In this study, we report on the synthesis, characterisation and stability of mixed (Fex,Cr1-x)(OH)3 hydroxides as compared to the stability of Cr(OH)3. We established that the plain Cr(III) hydroxide, abiding to the approximate molecular formula Cr(OH)3·3H2O, was crystalline, highly soluble, i.e. unstable, with a tendency to transform into the stable amorphous hydroxide Cr(OH)3(am) phase. Mixed Fe0.75Cr0.25(OH)3 hydroxides were found to be of the ferrihydrite structure, Fe(OH)3, and we correlated their solubility to that of a solid solution formed by plain ferrihydrite and the amorphous Cr(III) hydroxide. Both our experimental results and thermodynamic calculations indicated that mixed Fe(III)-Cr(III) hydroxides are more effective enhancers of groundwater quality, in comparison to the plain amorphous or crystalline Cr(III) hydroxides, the latter found to have a solubility typically higher than 50μg/l (maximum EU permitted Cr level in drinking water), while the amorphous Cr(OH)3(am) phase was within the drinking water threshold in the range 5.7

Investigating the Use of Iron Reducing Bacteria for the Removal of Arsenic from Contaminated Soils

Clean-up techniques, which were developed for removing cationic heavy metals from contaminated soils, are inappropriate for the metalloid As, which is a common and highly toxic pollutant. Because arsenic is mainly found associated with the hydrous ferric oxides of the soil, a possible mechanism for the mobilisation of this element is the reductive dissolution of Fe(III) oxyhydroxides. In this paper we investigate the possibility to mobilise arsenic, using the Fe(III)-reducing bacterium Desulfuromonas Palmitatis. The initial experiments were carried out using a crystalline ferric arsenate as model compound, i.e. scorodite (FeAsO4.2H2O). D. palmitatis was found able to reduce the trivalent iron of scorodite at a percentage of 80% within 16 days, but arsenic remained in the pentavalent state, and reprecipitated with Fe(II) in the form of low solubility ferrous arsenates. To avoid the precipitation of ferrous arsenates the subsequent experiments with soil were conducted by combining the reducing ability of D. palmitatis with the chelating strength of EDTA (ethylenediamine tetracetic acid), which can form strong aqueous complexes with Fe(II). Approximately 60% of Fe and 75% of As were recovered in the aqueous solution in the presence of EDTA, while in the simple biological treatment no Fe was dissolved and only a 3% of As was mobilised.

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.

Reduction of nitrate by copper-coated ZVI nanoparticles

abstract Nano zero-valent iron has been shown to be effective for the removal of nitrates from natural wastes and wastewaters. This work studies the application of surface-modified nano zero-valent iron as bimetallic Fe/Cu particles to remove high concentration of nitrates. Dispersed nano-Fe/Cu particles were synthesized by chemical reduction and examined by X-ray diffraction, scanning electron microscopy, and BET surface area analysis. Batch experiments were conducted to investigate the effectiveness of bimetallic particles on the reduction and removal of nitrates. The parameters investigated included the copper content (0.5, 5, 10, and 20% w/w) in zero-valent iron nanoparticles and the initial concentration of nitrates (100, 200, 300, and 500 mg/L). During the experiments, the aqueous solution was analyzed to determine the evolution of as well as , NH3, and which were produced as intermediate and final products. Based on the results obtained, it was concluded that the optimum coating rate was 5% w/w cop...