X-ray Fluorescence Spectrometry for Environmental Applications

Abstract: Heavy metal contamination in environmental applications is particularly important because of its potential impact on associated ecosystems and human health. At present, monitoring of heavy metals is usually done by taking and preparing samples for off-line laboratory measurements. X-ray fluorescence (XRF) analysis is a powerful and widely used tool for determining the elemental composition and concentration of chemical species in materials. This project is a feasibility study for the possibility of on-line XRF systems for continuousand direct analysis of industrial processes and environmental emissions.The feasibility of such measurements depends on the accuracy with which the concentration can be measured within a given response time. Therefore, this project is focused on investigating possible background suppression of the XRF spectrum. First, an XRF setup has been built, and its capability has been compared to a commercial scanning electron microscope with energy dispersive spectroscopy (SEM-EDS). The qualitative analysis and semi-quantitative analysis of heavy metal contamination in fly ash was performed and compared. Due to minimal sample preparation, the developed XRF system is suitable for in-situ measurements. A series of experiments was performed to optimize the signal-to-noise ratio of the spectra achieved from chromium contaminated liquid samples. The most significant factor turned out to be the primary X-ray source filter. Numerical simulation models have been developed in the Monte Carlo N-particle radiation transport code (MCNP), to calculate the X-ray fluorescence intensities and the detection limit for chromium in liquid samples. The experimental results agree with the results predicted by the simulation model, hence the model is used for optimization of the XRF system. Further, XRF mapping of chemical element distributions on a microscopic level has been obtained by using both X-ray scanning microscopy and full-field projection microscopy. The resultingdata from these microscopy measurements can guide further comprehensive environmental and industrial monitoring missions by providing additional spatial distribution information.In conclusion, the first research contribution presented in this thesis is the demonstration of the possibility to perform in-situ XRF measurements of chromium contamination in leachate with a limit of detection below the legal environmental limits. The second is the demonstration of XRF mapping on amicroscopy level, where a polycapillary X-ray optics setup achieves a similar intensity as a geometrically corresponding pinhole optics setup.