Dimitris Dermatas

Utilization of fly ash for stabilization/solidification of heavy metal contaminated soils

Abstract Pozzolanic-based stabilization/solidification (S/S) is an effective, yet economic remediation technology to immobilize heavy metals in contaminated soils and sludges. In the present study, fly ash waste materials were used along with quicklime (CaO) to immobilize lead, trivalent and hexavalent chromium present in artificially contaminated clayey sand soils. The degree of heavy metal immobilization was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) as well as controlled extraction experiments. These leaching test results along with X-ray diffraction (XRD), scanning electron microscope and energy dispersive X-ray (SEM–EDX) analyses were also implemented to elucidate the mechanisms responsible for immobilization of the heavy metals under study. Finally, the reusability of the stabilized waste forms in construction applications was also investigated by performing unconfined compressive strength and swell tests. The experimental results suggest that the controlling mechanism for both lead and hexavalent chromium immobilization is surface adsorption, whereas for trivalent chromium it is hydroxide precipitation. Addition of quicklime and fly ash to the contaminated soils effectively reduced heavy metal leachability well below the nonhazardous regulatory limits. Overall, fly ash addition increases the immobilization pH region for all heavy metals tested, and significantly improves the stress-strain properties of the treated solids, thus allowing their reuse as readily available construction materials. The only potential problem associated with this quicklime–fly ash treatment is the excessive formation of the pozzolanic product ettringite in the presence of sulfates. Ettringite, when brought in contact with water, may cause significant swelling and subsequent deterioration of the stabilized matrix. Addition of minimum amounts of barium hydroxide was shown to effectively eliminate ettringite formation. Overall, due to the presence of very high levels of heavy metal contamination along with sulfates in the solid matrices under study, the results presented herein can be applied to the management of incinerator and coal fly ash, boiler slag and flue gas desulfurization wastes.

Solubility, Sorption, and Soil Respiration Effects of Tungsten and Tungsten Alloys

This laboratory study addresses issues related to the fate and transport of tungsten and tungsten oxides in the environment (soil-water). Tungsten dioxide and tungsten trioxide were dissolved in aqueous solutions whose pH had been adjusted from 4.0 to 11.0. For initial pH smaller than 10.0, dissolved tungsten concentration remained fairly constant at around 10.0 mg/L for WO2 and increased from 0.3 mg/L to 2.0 mg/L for WO3 with increasing values of initial pH. Large amounts of dissolved tungsten were found when tungsten powder or alloy pieces were exposed to aqueous solutions. The dissolution occurs along depletion in solution pH and dissolved oxygen concentration. Depending upon the alloying elements present, the final dissolved tungsten concentration varied from 70 to 475 mg/L. Reduction in pH, dissolved oxygen depletion, and high levels of dissolved tungsten may be of relevance to environmental forensics. In the presence of alloying elements such as iron, nickel, and cobalt, tungsten strongly sorbed to well-characterized model soils. Sorption of tungsten to illite and montmorillonite clays occurs with an increase in pH and appears to be nonreversible. This behavior may significantly retard tungsten mobility. The mixing of tungsten powder with soils at rates higher than 3% (w/w) resulted in acidification of the soil matrix and had a significant impact on soil microbial community as determined by soil respiration.

Phosphate treatment of firing range soils: lead fixation or phosphorus release?

Phosphate treatment of lead (Pb)-contaminated soils relies on the premise that Pb converts to the thermodynamically stable, insoluble mineral class of pyromorphites. Recent research showed that treatment performance is kinetically controlled and strongly dependent on soil pH; this study employed an acidic phosphate (P) form, monobasic calcium phosphate (MCP), to investigate treatment performance of Pb occurring in an alkaline-buffered and an acidic firing range soil. The results of leaching, X-ray powder diffraction (XRPD), and modeling analyses showed that P and Pb dissolution in the alkaline soil and transformation reactions were kinetically controlled, so that: (i) TCLP (toxicity characteristic leaching procedure) and SPLP (synthetic precipitation leaching procedure) results were poor to marginal even at high MCP dosages; (ii) brushite (Ca(HPO(4)).2H(2)O) and cerussite (PbCO(3)) persisted in XRPD patterns; and, (iii) geochemical modeling failed to predict leaching and phase assemblages. In the acidic soil, Pb-P reactions promoted further soil acidification, improved TCLP performance, and generated better agreement with the equilibrium-based model; however, SPLP and modeling results showed that Pb concentrations could not be reduced below 15 microg/L mainly due to the low soil pH. The marginal or inadequate Pb immobilization was observed in both soils despite the elevated MCP dosages, which were well in excess of the pyromorphite stoichiometric ratio (P/Pb = 0.6). Additionally, P leaching concentrations and rates were extremely high (>300 mg/L), under both SPLP and deionized (DI) water extraction conditions, and as predicted by thermodynamic equilibrium. The performance and sustainability of phosphate-based treatment therefore seem questionable.

Immobilization of mercury(II) in contaminated soil with used tire rubber

Abstract The effectiveness of used tire rubber for immobilizing Hg(II) in a contaminated soil was evaluated using batch extraction and field rainwater leaching tests. The contaminated soil was prepared using a clay-loam spiked with mercury oxide or mercury chloride to yield a Hg(II) content of 300 mg/kg. When the contaminated soil was treated with 4% of tire rubber, Hg(II) concentration in an acetic acid leachate was reduced from 3500 ppb down to 34 ppb. Hg(II) concentration in the initial rainwater leachate was reduced from 84 ppb for untreated soil to 1.2 ppb for the rubber-treated soil. After 8 months of rainwater infiltration in the field, Hg(II) concentration decreased to less than 0.2 ppb for the treated soil. The rubber-treatment inhibited the evolution of metallic Hg0 from the spiked soil samples possibly by retarding the reduction of Hg(II) to Hg0. Batch extraction and adsorption results indicated that the rubber had high adsorption capacity for Hg(II) when pH values were between 2 and 8.

Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue

The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main chromite ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of...

Investigation of Barium Treatment of Chromite Ore Processing Residue (COPR) 031

Barium addition to chromite ore processing residue (COPR) was investigated in order to address (a) the pronounced heaving phenomena that are associated with mainly the presence of ettringite and (b) hexavalent chromium leaching. Sulfate was added to representative samples of grey-black (GB) and hard-brown (HB) COPR to simulate worst-case conditions of sulfate influx and ettringite formation. Both the X-ray powder diffraction (XRPD) and the modeling results showed that ettringite is a thermodynamically favored reaction in COPR. The subsequent addition of barium lead to the formation of both barite and barium chromate, observed as solid solution between the two phases. Modeling results confirmed that barium sulfate is the more stable species that will dissolve ettringite and that barium chromate will also dissolve COPR chromate phases when sulfate is depleted. The Toxicity Characteristic Leaching Procedure (TCLP) test on GB samples showed that the optimal stoichiometry to maintain Cr and Ba TCLP concentrations below the U.S. Environmental Protection Agency regulatory limit of 5 and 100 ppm, respectively, lies between 1:1 (Ba to sulfate plus chromate ratio) and 1.5:1. The respective optimal stoichiometry for the HB COPR was found to be higher, between 2:1 and 5:1. Considering that COPR is actually a Cr-contaminated cement form, a further area of research is the identification of barium-containing wastes (i.e., heavy-metal sludges, contaminated soils, etc.) that would be suitable for combination with COPR; in this way, an environmentally sustainable yet cost-effective treatment application can be realized.

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.

Remediation of chromite ore processing residue using ferrous sulfate and calcium polysulfide

Batch tests were conducted to assess the potential use of ferrous sulfate and calcium polysulfide for the remediation of chromite ore processing residue (COPR). The remediation process entails addition of ferrous sulfate or calcium polysulfide to chemically reduce hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] in slurry form and pH adjustment to precipitate Cr(III) as chromium hydroxide. The present study investigates the effects of COPR particle size, treatment pH, and chemical dosage on the performance of the treatment. Smaller particle size resulted in increases in alkaline digestion and Toxicity Characteristic Leaching Procedure (TCLP) Cr(VI) concentrations for the untreated samples. The chemical reduction of Cr(VI) with ferrous iron and sulfides was non-stoichiometric. Four times the stoichiometric amount of ferrous iron of two times the stoichiometric amount of polysulfide were needed to meet both the New Jersey Department of Environmental Protection (NJDEP) regulatory limit of 240 mg/kg for Cr(VI) and EPA TCLP regulatory limit of 5 mg/L for chromium [C,r]. pH adjustment was necessary to prevent the formation of ettringite, a swell causing mineral, upon the introduction of sulfate to the COPR material via ferrous sulfate or calcium polysulfide. The slow hydration of some COPR minerals caused the pH of the treated COPR to creep upward during the curing period. However, when sufficient acid was added, the pH value was controlled at less than 9.27 for a curing period of 1.5 years, which prevented the formation of ettringite.

Rietveld quantification of montmorillonites in lead-contaminated soils

Abstract Differences between the observed and calculated X-ray diffraction (XRD) patterns when a Rietveld phase quantification of Pb-contaminated montmorillonite soil was attempted were found to be attributed to a misfit of the montmorillonite diffraction input data. This was due to the scattering properties of Pb combined with the ill-defined structure of montmorillonite. X-ray powder diffraction data of pure Pb-exchanged montmorillonites suggest a structural ordering of interlayer Pb. Based on structural modeling of Ca-, (Ca,Pb)- and Pb ion-exchanged montmorillonite forms, an “observed” powder file was developed, which may be used as input to Rietveld quantification of Pb-exchanged montmorillonites.

Forensic investigation of a chromium(VI) groundwater plume in Thiva, Greece

A forensic investigation was conducted with the aim of decoupling the contribution of geogenic and anthropogenic Cr(VI) sources in the wider area of Thiva. Groundwater and topsoil samples were collected from two Cr(VI) groundwater plumes of 160 μg/L and 75 μg/L. A series of evidence support the view that the origin of Cr(VI) detected in groundwater is mainly geogenic. These are: (a) the presence of Cr in topsoil of the wider area, (b) the moderate Cr(VI) groundwater concentrations, (c) the high Ni levels within the Cr(VI) plumes, (d) the predominance of Mn(IV), which is a prerequisite for Cr(III) oxidation to Cr(VI), and (e) the absence of co-contaminants. The present study also revealed that, although both Cr(VI) plumes are clearly of geogenic origin, the plume with the elevated Cr(VI) values, in the north of Thiva town, exhibits also an anthropogenic component, which can potentially be attributed to the alkaline environment associated with the old uncontrolled landfill of Thiva and the industrial cluster located in this area.