Pavel Janoš

Removal of basic (Methylene Blue) and acid (Egacid Orange) dyes from waters by sorption on chemically treated wood shavings.

Spruce wood shavings from Picea abies were used for an adsorptive removal of both basic as well as acid dyes from waters. The sorption properties of the sorbents were modified with HCl, Na(2)CO(3) and Na(2)HPO(4). The treatment of the wood sorbents with alkaline carbonate solution as well as with phosphate solution increased the sorption ability for the basic dye (Methylene Blue), whereas the treatment with mineral acid decreased the sorption ability for Methylene Blue to some extent. The opposite is true for the sorption of the acid dye--Egacid Orange. The maximum sorption capacities estimated from the Langmuir-Freundlich isotherms ranged from 0.060 to 0.165 mmol g(-1) for Methylene Blue, and from 0.045 to 0.513 mmol g(-1) for Egacid Orange. The basic dye sorption decreased at low pH values in accordance with a presupposed ion-exchange mechanism of the sorption. The sorption of acid dye, on the other hand, decreased with increasing pH. The presence of inorganic salts as well as surfactants exhibited only minor effects on the dye sorption.

Humic acids from coals of the North-Bohemian coal field I. Preparation and characterisation

Abstract Humic acids were prepared from young North-Bohemian brown coals using alkaline extraction, sedimentation/filtration and acidic precipitation; membrane separations were applied to refine some preparatives. Samples were characterised by chemical analyses, molecular mass distribution, E4/E6 coefficient, IR spectra, 13C-NMR spectra and EPR spectra. The properties of the coal-derived humic acids were compared with the properties of humic acids prepared from chernozem and peat and with the properties of a commercially available humic acid from Fluka.

Humic acids from coals of the North-Bohemian coal field: II☆. Metal-binding capacity under static conditions

Abstract The interactions of metal cations (Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn) with solid humic acids (HAs) were investigated in a batch arrangement. The sorption of metals on the surface of HAs depends strongly on the pH — sorption decreases with decreasing pH. The metal-binding capacities estimated from the metal–humate binding model range from ca. 0.4 mmol/g (Fe, Ni, Zn) to 1.7 mmol/g (Pb). Of the examined metal cations, Pb 2+ binds most strongly to solid HAs. The order of the metal–humate binding strength is consistent with series found in the literature and is based on the stability constants of metal–humate complexes. In comparison with coal-derived HAs, soil HAs from chernozem (and also low molecular weight HAs) exhibited markedly higher metal-binding capacities, whereas the capacity of oxyhumolite (the raw material for HA production) was lower.

Cerium dioxide as a new reactive sorbent for fast degradation of parathion methyl and some other organophosphates

Abstract Cerium dioxide was used for the first time as reactive sorbent for the degradation of the organophosphate pesticides parathion methyl, chlorpyrifos, dichlofenthion, fenchlorphos, and prothiofos, as well as of some chemical warfare agents-nerve gases soman and O -ethyl S -[2-(diisopropylamino) ethyl] methylphosphonothioate (VX). CeO 2 specimens were prepared by calcination of basic cerous carbonate obtained by precipitation from an aqueous solution. The CeO 2 samples containing certain amounts (1 wt.%-5 wt.%) of the neighboring lanthanides (La, Pr, Nd) were prepared in a similar way from pure lanthanide salts. It was shown that ceria accelerated markedly the decomposition of parathion methyl causing the cleavage of the P-O-aryl bond in the pesticide molecule. A similar reaction mechanism was proposed for the degradation of other organophosphate pesticides and nerve agents. The degradation times (reaction half-times) were in an order of minutes in the presence of CeO 2 , compared to hours or days under common environmental conditions. The reaction in suitable organic solvents allowed conversions of about 90% for parathion methyl loading of 20 mg pesticide/g CeO 2 within 2 h with a reactant half-life in the order of 0.1 min. The key parameter governing the degradation efficiency of CeO 2 was the temperature during calcination. At optimum calcination temperature (about 773.15 K), the produced ceria retained a sufficiently high surface area, and attained an optimum degree of crystallinity (related to a number of crystal defects, and thus potential reactive sites). The presence of other lanthanides somewhat decreased the reaction rate, but this effect was not detrimental and permitted the possible use of chemically impure ceria as a reactive sorbent. A fast organophosphate degradation was demonstrated not only in non-polar solvents (such as heptane), but also in polar aprotic solvents (acetonitrile, acetone) that are miscible with water. This opens new possibilities for designing more versatile decontamination strategies. The cleavage of phosphate ester bonds is of a great importance not only for the degradation of dangerous chemicals (chemical weapons, pesticides), but also for interactions of ceria (especially the nano-sized one) in biologically relevant systems.

Capillary electrophoretic estimation of sulfate stability constants of metal ions and determination of alkali and alkaline earth metals in waters

We studied the influence of sulfate concentration on the effective mobilities of mono-, di- and tervalent ions and developed a method for the determination of sulfate stability constants. Relative migration times of several cations were determined. Capillary electrophoresis with indirect detection using 4 mmol/l copper(II) sulfate, 18-crown-6 and formic acid in background electrolyte was then applied to the determination of the metal ions in mineral and tap waters samples. The results were compared with those of ion chromatography. The CE detection limits were estimated [signal/noise ratio (S/N)=3] in the range from 0.59 (for Li) to 12.9 mg/l (for Ba).

Role of chemical equilibria in the capillary electrophoresis of inorganic substances

Abstract Electrophoretic behaviour of low-molecular-mass substances and their separation can be effectively manipulated employing selective interactions between the separated ions and components of working solutions. Proper selection of operational electrolytes can considerably enhance the selectivity of electrophoretic separations without expensive modifications of instrumentation. Complex-forming acid–base and ion association equilibria are most important for influencing the effective mobilities of inorganic cations and anions. These can be used for optimization of separations. On the other hand, capillary electrophoretic methods can be used for investigations of chemical equilibria and measurements of physicochemical characteristics, such as stability, dissociation/protonation, ion association, etc., constants. Formation of complexes of the separated ions with suitable ligands contained in the working solutions is especially useful in the case of the capillary electrophoretic determination of metals (transition and heavy metals, rare earth elements). As can be seen from a number of published operational systems, similar complexing agents are used in various electrophoretic modes, namely in capillary zone electrophoresis (CZE) and in capillary isotachophoresis (ITP). Hence the previously described systems for ITP separations can serve as an inspiration in the course of the development of new CZE methods.

Humic acids from coal of the North-Bohemia coal field: III☆. Metal-binding properties of humic acids — measurements in a column arrangement

Abstract The ion exchange properties of humic acids prepared from oxidized young coals of the North-Bohemia coal field, the so-called oxyhumolites, were measured. A flow arrangement was used, i.e. separation of metals in columns packed with activated humic acids. Solutions containing only one metal (Pb 2+ , Cd 2+ , Cu 2+ , Zn 2+ , Ni 2+ , Ca 2+ , Mg 2+ Co 2+ , Mn 2+ ) and solutions containing two and more metals were tested. The penetrating capacities were measured for a number of metal ions under conditions emulating industrial applications of humate-based sorbents. Penetrating capacities are related to the total capacities estimated from measurements in a static system and a metal-binding model published previously, although they are, as expected, slightly lower.

Assessment of heavy metals leachability from metallo-organic sorbent-iron humate-with the aid of sequential extraction test

The sequential extraction test, known as a BCR procedure, was used to assess a leachability of heavy metals (Zn, Cd, Pb, Cu) from the metallo-organic sorbent-iron humate-loaded with these metals. The sequential test allowed to discriminate between various fractions of heavy metals, namely the acid-extractable fraction, the fraction bound to Fe oxides, and the fraction bound to organic matter. It was proven that the heavy metals are bound mainly to Fe oxides and organic matter, and thus they may be relatively hardly liberated into the environment. The BCR sequential extraction test exhibited a very good repeatability, when it was applied to the loaded sorbent-relative standard deviations were typically lower than 10%.

An ion-exchange separation of metal cations on a C-18 column coated with dodecylsulphate.

The retention mechanism was studied for the cations of the alkaline earth metals and Zn(2+) Ni(2+), Co(2+), Cd(2+) and Bi(3+) on a C(18) column permanently coated with sodium dodecylsulphate, with aqueous mobile phases containing cupric chloride or sulphate, or cerous nitrate. The dependencies of the logarithm or the capacity ratio on the logarithm of the eluent concentration were linear, demonstrating that ion-exchange was the predominating separation mode; the slopes of these dependencies were in good agreement with the values predicted from the ion-exchange theory. Indirect UV photometric detection yielded limits of detection (LOD) of 21, 44, 120 and 275 ng in the volume injected, 20 mul, for Mg(2+), Ca(2+), Sr(2+) and Ba(2+), respectively, with the 10(-2)M copper(II) chloride mobile phase; the respective LOD values decreased to 0.8, 1.6, 3.0 and 6.7 ng with the 5 x 10(-4)M cerium(III) nitrate eluent. The method was found to be primarily suitable for determination of the alkaline earths and was applied to analyses of surface and mineral waters.

Extraction-spectrometric determination of lead in high-purity aluminium salts

Trace amounts of lead were determined in high purity aluminium salts (especially in ammonium aluminium sulfate) using inductively coupled plasma-optical emission spectrometry (ICP-OES) after extractive pre-concentration and matrix separation. Metals were extracted from the aluminium matrix in the form of chelates with ammonium pyrolidine dithoocarbamate into methyl isobutyketone. The organic extract was digested with nitric acid and hydrogen peroxide. The limit of detection for the determination of lead in crystalline ammonium aluminium sulfate was ca. 0.044 mug g(-1). The relative expanded uncertainty of the lead determination was ca. 23% at the level of 0.2 mug g(-1) and ca. 16% at the level of 1.0 mug g(-1). The main uncertainty contribution was associated with repeatability of the whole analytical procedure.