Mid Sweden University

With the rapid expansion of the waste incineration business both in Europe and globally, there is a growing need for the elemental analysis for fly ash from municipal solid waste incineration. In this work, samples of washed and unwashed ash from municipal solid waste incineration in Sundsvall are evaluated. Qualitative analysis and semi-quantitative analysis are used to compare two elemental analysis methods, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) measurement. Both methods are used to retrieve the difference in elemental composition between washed and unwashed fly ash. SEM-EDS accurately detects light elements from well-prepared samples in a vacuum environment, while, for online measurements, XRF is a potential method that analyses hazardous metal content in the fly ash. 

In most cases, direct X-ray fluorescence (XRF) analysis of solutions entails technical difficulties due to a high X-ray scattering background resulting in a spectrum with a poor signal-to-noise ratio (SNR). Key factors that determine the sensitivity of the method are the energy resolution of the detector and the amount of scattered radiation in the energy range of interest. Limiting the width of the primary spectrum by the use of secondary targets, or filters, can greatly improve the sensitivity for specific portions of the spectrum. This paper demonstrates a potential method for SNR optimization in direct XRF analysis of chromium (Cr) contamination. The suggested method requires minimal sample preparation and achieves higher sensitivity compared to existing direct XRF analysis. Two states of samples, fly ash and leachate from municipal solid waste incineration, were investigated. The effects of filter material, its absorption edge and filter thickness were analyzed using the combination of Monte Carlo N-Particle (MCNP) code and energy-dispersive XRF spectrometry. The applied filter removes primary photons with energies interfering with fluorescence photons from the element of interest, thus results in lower background scattering in the spectrum. The SNR of Cr peak increases with filter thickness and reaches a saturation value when further increased thickness only increases the measurement time. Measurements and simulations show that a Cu filter with a thickness between 100 μm and 140 μm is optimal for detecting Cr by taking into account both the SNR and the exposure time. With direct XRF analysis for solutions, the limit of quantitation (LOQ) of the achieved system was 0.32 mg/L for Cr, which is well below the allowed standard limitation for landfills in Sweden. This work shows that XRF can gain enough sensitivity for direct monitoring to certify that the Cr content in leachate is below environmental limits.

Due to the availability of X-ray imaging detectors, full-field X-ray fluorescence (FF-XRF) imaging technique has become achievable, which provides an alternative to scanning X-ray fluorescence imaging with a micro-focus X-ray beamline. In this paper, we present a setup based on straight capillary optics and an energy-dispersive hybrid pixel detector, which can perform simultaneous mapping of several chemical elements. The photon transmission efficiency and spatial resolution are compared between two X-ray collimation setups: one using pinhole optics and one using straight polycapillary optics. There is a tradeoff between the spatial resolution and transmission efficiency when considering X-ray optics. When optimizing the spatial resolution, using straight capillary optics achieved a higher intensity gain when comparing with the pinhole setup. Characterization of the polycapillary imaging setup is performed through analyzing various samples in order to investigate the spatial frequency response and the energy sensitivity. This developed setup is capable of FF-XRF imaging in characteristic energies below 20 keV, while for higher energies the spatial resolution is affected by photon transmission through the collimator. This work shows the potential of the FF-XRF instrument in the monitoring of toxic metal distributions in environmental mapping measurements.

As there are increasing demands to replace plastics especially as packaging material with renewable, easy to recycle and compostable materials as those produced by paper industry, there is an increasing demand also to improve the fundamental scientific understanding of pulp and paper manufacturing systems. High yield pulping (HYP) processes, such as CTMP, are increasingly interesting for packaging material as well as manufacturing of hygiene paper. The yield from wood chips to final fiber is about 90%-98% and due to that, the lignin (28% of coniferous wood) plays a key role when designing properties of packing materials. A key unit operation when producing CTMP is the pre-treatment of wood chips before defibration. In order to separate the wood to individual fibers with a minimum amount of electricity it is necessary to soften the lignin. The lignin is softened by means of a combination of sulphonation at high pH and elevated temperatures in the preheater and in the refiner, where the fiber separation occurs. As the size of wood chips is normally about 20 mm in length, 3-4 mm in thickness at the same time the fiber size is 20-40 μm in width with 1.5-5 mm in length, it is challenging to create a process technology that gives an even distribution across the wood chips of the sodium sulphite (Na2SO3) containing liquid used for impregnation. In order to improve the impregnation technology, it is valuable to measure the sulphonation degree on a detailed level. Our XRF imaging system using a collimated X-Ray source and an energy-dispersive X-Ray spectroscopy can make an image of sulphur (S) and sodium (Na) across wood chips or in individual fibers.