Niels Pind

Preparation, characterization, and sorption properties for Ni(II) of iron oxyhydroxide–montmorillonite

Abstract The preparation, characterization, and sorption properties for Ni(II) of combined phases of iron oxyhydroxide and montmorillonite were investigated. Two different preparation procedures were explored. In the first method, Fe(III) was contacted with montmorillonite at pH 2.5, and ferrihydrite was formed on the montmorillonite surface by slowly raising pH to 8.0 (Fe–mont). In the second method, O2 was bubbled through a solution (pH 7.0) containing Fe(II) and montmorillonite. This caused Fe(III) to precipitate as lepidocrocite (lep–mont). Batch adsorption experiments and the physical chemical properties of the solids, e.g. specific surface area, the point of zero charge, and the particle size distribution reflected a varying degree of interaction among the phases. In the Fe–mont system, a ferrihydrite coated montmorillonite surface was created. The result was an increase in specific surface area and sorption capacity for Ni(II) compared to the pure solids. The isoelectric point observed was typical for pure ferrihydrite. In the lep–mont system, predominantly separate phases of lepidocrocite and montmorillonite were created. The specific surface area, the isoelectric point, and the sorption capacity were significantly better predicted given the properties and weight fractions of the individual phases.

The determination of traces of cadmium, lead and thallium in fly ash by potentiometric stripping analysis

Abstract The suitability of potentiometric stripping analysis for the determination of cadmium, lead and thallium in fly ash and in waters polluted by leaching of fly ash is assessed. By an appropriate choice of medium and of electrolysis potential and by employing a rotating working electrode, it is possible to eliminate interferences from electroactive species often found in fly ash in high concentrations. The accuracy obtained in a study of a certified coal fly ash (SRM 1633a) is satisfactory.

Nutrients and heavy metals distribution in thermally treated pig manure

Ash from pig manure treated by combustion and thermal gasification was characterized and compared in terms of nutrient, i.e., potassium (K), phosphorus (P) and heavy metal, i.e., cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) contents. Total nutrient and metal concentrations were measured using energy dispersive X-ray fluorescence analysis. Acid (HNO3, H2SO4) and water-extractable concentrations were also measured both in non-classified ash and in selected ash particle size fractions using flame atomic absorption spectrometry and colorimetric spectrometry. Results indicate that ash from gasified manure contained more water-extractable K in comparison with combusted manure whereas the opposite was the case with respect to P. Heavy metals Ni, Cr and Cd were present in higher concentrations in the fine particle size fractions (< 30 µm of particle diameter), whereas K, P, Zn and Cu exhibited higher concentrations in the coarser particle size fractions (> 30 µm).

Standard-addition procedure for the determination of traces of lead in solid samples by x-ray fluorescence spectrometry

A standard-addition procedure for analysis of powdered solid samples by energy-dispersive X-ray fluorescence is described. Different amounts of the element to be determined are added to 4-6 specimens of the unknown sample. The spiked samples are prepared by mixing the powdered sample with an aqueous standard solution and drying the mixture. Homogeneously spiked samples are thus obtained with analyte and spike concentrations at the ppm level. The procedure has been investigated theoretically, and it is found suitable for the quantitative determination of lead at the ppm level. The accuracy of the technique for traces of lead has been tested on solid reference materials for the determination of lead. The quantitative results obtained compare well with those found by potentiometric stripping analysis.

Effect of electroactive substances forming water-soluble reduced species on the potentiometric stripping determination of mercury soluble metals

Abstract When localized regions with high concentrations of water-soluble reduced species are formed during the electrolysis period of potentiometric stripping analysis, the stripping signals arising from oxidation of amalgamated metallic analytes are overlapped by interfering signals. Dissolved reduced species may give rise to plateaux on the potential vs. time curve. If the re-oxidation of such reduced species is governed by transport, plateaux are developed at the equilibrium potential of the soluble redox system, while an anodic translation of plateaux is observed when the re-oxidation is kinetically controlled. These effects complicate the potentiometric stripping determination of, for example, cadmium and lead in complex samples such as decomposed, dissolved fly ash. This paper deals with the mechanisms leading to interference. It is shown that increased transport rates induced by vigorous stirring eliminate the interference problems.

A receptor model for urban aerosols based on oblique factor analysis

Abstract A procedure is outlined for the construction of receptor models of urban aerosols, based on factor analysis. The advantage of the procedure is that the covariation of source impacts is included in the construction of the models. The results are compared with results obtained by other receptor-modelling procedures. It was found that procedures based on correlating sources were physically sound as well as in mutual agreement. Procedures based on non-correlating sources were found to generate physically obscure models.

A versatile spectrometer for secondary x-ray fluorescence excitation

Abstract Inexpensive research equipment for secondary x-ray fluorescence excitation is described. The primary beam from a high-powered x-ray tube is collimated onto the targets, six of which may be easily and safely interchanged. A collimator system ensures that the detector receives radiation from well defined areas of the sample. The geometry minimizes radiation from Compton scattering, the twice-scattered continuum radiation from the x-ray tube, and the characteristic lines from the secondary target. The unit is designed for use with standard x-ray tubes and generators, and is part of an energy-dispersive spectrometer used for multielement analysis. The performance of the system with a variety of samples is described.

Procedure for background estimation in energy-dispersive X-ray fluorescence spectra

Abstract A method for semi-automatic background estimation in energy-dispersive x-ray fluorescence spectra is outlined. Two cubic splines were investigated and the spline called the Butland interpolant was chosen for further investigation. Prior to the calculation of the spline, peak regions are set up, and suitable knots are defined outside the peak regions. To set up the peak regions, an automatic peak-search routine and a calibration equation are used. For a given peak, the latter relates the full width at half maximum (FWHM) to the peak centre. In turn, the size of the peak regions are defined by the FWHM multiplied by a constant given by the user. The method was tested on several types of spectra. It was found that the optimal size of the peak region decreased with increasing peak density. Reproducibility tests showed that the standard deviation of the summation of counts within a peak region and after background subtraction was less than would be expected from the counting statistics.

Measurement of peak areas in energy-dispersive x-ray fluorescence spectrometry

Abstract An algorithm is outlined for the measurement of peak areas in spectra obtained by energy-dispersive x-ray fluorescence techniques. Each fluorescence line is assumed to be a pure Gaussian function. Initially, a calibration equation relating the full width at half maximum (FWHM) to the centre of the peak is set up. Then, in an unknown spectrum, the Gauss function parameters are found by a stepwise procedure making a non-linear minimization procedure redundant. First, the background is estimated and subtracted; then the peak centres are found, and the FWHM is given by the calibration equation, which relates FWHM to the position of the peak centre. Finally, the amplitudes are estimated from a set of linear equations. The reliability of the proposed algorithm was proved for a variety of samples. The method was compared with a non-linear x2 minimization routine. Quantitative analysis of two standard reference alloys was accurate. Below 20 keV, a suitable FWHM calibration is obtained from a set of Kα lines. Above 20 keV, a set of Kβ1,3 lines is recommended.

Software package for quantitative analysis of solid materials by energy-dispersive x-ray fluorescence spectrometry without absolute calibration

Abstract A software package for quantifying elements in solids from energy-dispersive x-ray fluorescence data is described. The algorithm is based on the fundamental parameter approach and facilitates the simultaneous determination of several elements at widely varying concentrations. The software comprises three programs. One program, for spectrometer control and data acquisition, resides in a dedicated microcomputer. The two other programs, for spectra deconvulution and data evaluation, reside in a larger central computer. On-line communication between the computers is feasible, and the system facilitates the implementation of new improved programs. The performance of the system was tested on standard reference materials, and satisfactory accuracy was obtained for up to 21 elements.