Biomedical subjects

Lionel J J Catalan

Publications and source records attributed to Lionel J J Catalan.

7 recordsLinked to original sources

PubMed2006

Comparison of various detection limit estimates for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection.

This paper addresses the variations that presently exist regarding the definition, determination, and reporting of detection limits for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection (GC-PFPD). Gas standards containing hydrogen sulphide (H(2)S), carbonyl sulphide (COS), sulphur dioxide (SO(2)), methyl mercaptan (CH(3)SH), dimethyl sulphide (DMS), carbon disulphide (CS(2)), and dimethyl disulphide (DMDS) in concentrations varying from 0.36ppb (v/v) up to 1.5ppm (v/v) in nitrogen were prepared with permeation tubes and introduced in the gas chromatograph using a 0.25-ml gas sampling loop. After measuring the PFPD response versus concentration, the method detection limit (MDL), the Hubaux-Vos detection limit (x(D)), the absolute instrument sensitivity (AIS), and the sulphur detectivity (D(s)) were determined for each sulphur compound. The results show that the MDL determined by the US Environmental Protection Agency procedure consistently underestimates the minimum concentrations of volatile sulphur compounds that can be practically distinguished from the background noise with the PFPD. The Hubaux-Vos detection limits and the AIS values are several times higher than the MDL, and provide more conservative estimates of the lowest concentrations that can be reliably detected. Sulphur detectivities are well correlated with AIS values but only poorly correlated with MDL values. The AIS is recommended as a reliable and cost-effective measure of detection limit for volatile sulphur compounds by GC-PFPD, since the AIS is easier and faster to determine than the MDL and the Hubaux-Vos detection limit. In addition, this study confirmed that the PFPD response is nearly quadratic with respect to concentration for all volatile sulphur compounds.

Chromatography, Gas↗

PubMed2004

Compositional changes in cement-stabilized waste during leach tests--comparison of SEM/EDX data with predictions from geochemical speciation modeling.

Cement-based stabilization/solidification (s/s) is a widely used treatment process for hazardous wastes containing toxic metals. The treated waste consists of a complex mixture of several solid phases produced by cement hydration reactions. Understanding and predicting the effects of leaching on these individual phases is essential for assessing the long-term immobilization of metal contaminants in s/s waste exposed to rain and groundwater. In this paper, particles of crushed Portland cement doped with copper, lead, and zinc nitrates were leached with nitric acid solutions maintained at constant pH in the range pH 4-7. Changes in solid composition at the microscopic scale were measured by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDX). The geochemical equilibrium model SOLTEQ-B, which accounts for the incongruent solubility behavior of calcium silicate hydrate, was used to simulate the compositional changes in the hydration gel for increasing extents of leaching. Measured concentrations of calcium, silicon, and sulfur were successfully predicted at all extents of leaching. Aluminum, lead, and zinc concentrations were also in good agreement with model predictions, except in the remineralization zones that form when metals solubilized in the outer regions of the s/s waste particles diffuse toward the interior and reprecipitate at higher pH. Copper was less accurately modeled at high extents of leaching. Accounting for the incorporation of contaminant metals into the cement hydration gel (in opposition to assuming the presence of individual metal hydroxides) is crucial for successfully predicting contaminant metal concentrations in the hydration gel at low and intermediate extents of leaching.

Journal Article↗

PubMed2004

Effect of remineralization on heavy-metal leaching from cement-stabilized/solidified waste.

Crushed samples of stabilized/solidified (s/s) waste were leached at constant leachate pH in the pH range 4-7 with nitric acid solutions to evaluate the influence of remineralization on metal release. The s/s waste consisted of synthetic heavy-metal sludge containing 0.1 mol L(-1) copper nitrate, 0.1 mol L(-1) zinc nitrate, and 0.1 mol L(-1) lead nitrate mixed with ordinary Portland cement. Unleached and leached particles were characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry. Two consecutive leaching fronts advancing from the surface of the particles toward the center were identified: the first front was associated with the dissolution of portlandite and partial reaction of the calcium silicate hydrate gel, while the second front was associated with the dissolution of calcium-aluminum hydroxy sulfates such as ettringite and monosulfate. At pH 4 and 5, a remineralization zone rich in heavy metals formed immediately behind the second leaching front. The shell extending from the remineralization zone to the surface of the particles was depleted in calcium, sulfate, and heavy metals. As a result of remineralization, heavy-metal releases to the leachate were reduced by factors ranging between 3.2 and 6.2 at pH 4 and between 74 and 193 at pH 5. At pH 6 and 7, remineralization of Pb and Zn occurred further behind the second leaching front and closer to the surface of the particles. The amount of heavy-metal release depended on both the leachate pH and the remineralization factor.

Construction Materials↗

PubMed2004

A two-front leach model for cement-stabilized heavy metal waste.

Quantitative scanning electron microscope (SEM) studies of cement-stabilized waste specimens exposed to a leaching solution at constant pH in the range 4-7 have shown that the acid neutralization capacity (ANC) of the waste matrix is consumed at two consecutive leaching fronts. The first front is associated with the dissolution of portlandite (Ca(OH)2) and the partial reaction of calcium silicate hydrate (CSH) gel. The second front marks the dissolution of Ca-Al hydroxy sulfate minerals. The advancement of the first front is limited by the diffusion of OH- ions from the first front toward the leaching solution. The advancement of the second front, however, is controlled by the diffusion of H+ ions from the leaching solution toward the second front. Leaching of copper, zinc, and lead only occurs between the second front and the specimen surface. The leaching behavior of metals is modeled by considering that metals are leached from the waste matrix as a result of the advancement of the second front. The proposed model takes into account the leachable metal fraction in the waste matrix and the effect of metal remineralization on metal mobility.

Construction Materials↗

PubMed2002

Study of the physical and chemical mechanisms influencing the long-term environmental stability of natrojarosite waste treated by stabilization/solidification.

Natrojarosite is a residue of zinc refining generated in large quantities by zinc producers in many parts of the world. Stabilization/solidification (s/s) is currently used to immobilize heavy metals prior to storage of the solidified material as a heap. Our study aimed at assessing the long-term environmental stability of treated natrojarosite waste in the field situation. Flow-through leaching tests were carried out on monolithic samples in a modified triaxial cell and on crushed samples in packed columns. Tests with monolithic samples simulated natural infiltration through treated material containing few cracks and fractures, whereas, packed column tests were more representative of weathered material. The microstructure of leached and unleached materials was characterized by scanning electron microscopy and X-ray energy dispersive spectrometry (SEM-EDX). The results of flow-through leaching tests combined with microscopic characterization and geochemical equilibrium calculations provided valuable insights on the physical and chemical mechanisms influencing the long-term leaching behavior. This information was used to develop a mathematical model for alkalinity depletion in the treated waste. When infiltration of acid rain through the material was considered, the model predicted that the leachate would remain at high pH for many thousands of years in the field.

Acid Rain↗

PubMed2002

Reactivity of oxidized sulfidic mine tailings during lime treatment.

Lime amendment is a common method for neutralizing the accumulated acidity and sequestering metals in oxidized mine tailings. This study assessed the reactivity of sulfide oxidation products during lime treatment of tailings samples from the Kam Kotia mine site in Timmins, Ontario. The contributions of several alkalinity consumption mechanisms to the lime requirements were compared. Methods involved lime treatment tests, multiple water extractions, sequential extractions, analytical scanning electron microscopy, and X-ray diffractometry. The majority of the alkalinity consumption was due to the reaction of water-insoluble Fe-oxyhydroxysulfate minerals (including K-jarosite, Na-jarosite, H-jarosite, and schwertmannite) with lime to form Fe-oxyhydroxides (including goethite) and gypsum. The cation exchange capacity of the oxidized tailings contributed a minor proportion to the alkalinity consumption. Measurements of water-soluble acidity underestimated lime requirements by more than 50% on average.

Calcium Compounds↗

PubMedDate not supplied

Use of alkaline extraction to quantify sulfate concentration in oxidized mine tailings.

An alkaline extraction method has been developed for the determination of total sulfate in mine tailings containing secondary sulfate minerals formed by the oxidation of primary sulfides. Oxidized tailings were extracted with a 0.3 M NaOH solution at a liquid/solid ratio of 30 at room temperature for 16 h. The sulfate concentration in the extracts was determined by ion chromatography (IC). The coefficient of variation for sulfate determinations ranged from 1.9 to 3.2% for five tailings samples collected at two tailings impoundments. Mineralogical analysis of the tailings by scanning electron microscopy/X-ray energy dispersive spectrometry (SEM/EDS) demonstrated that the extraction of sulfate was complete, with the exception of extremely insoluble barite. The proposed method is simple, yields an accurate yet rapid measurement of sulfate, and involves a safer laboratory operation than conventional methods that make use of strong HCl acid solutions. Moreover, this method allows the specific measurement of sulfate in the extract, whereas conventional methods are generally limited to the measurement of total S by inductively coupled plasma atomic emission spectrometry (ICP-AES) due to the interference of chloride with sulfate in IC.

Chromatography↗