| dc.description.abstract | Ostlänken (The Eastern link) is going to be a new main railway in Sweden, between Södertälje and
Linköping. The railroad will go through areas where there could be high sulphide concentration in the
rocks, and during the construction, large amounts of rock is going to be excavated. Since sulphides
reacts with water and oxygen, and causes acidification and leaching of metals, exposed sulphides in
the excavated rocks can be very harmful to the local ecosystems. Trafikverket (The Swedish Transport
Administration) has been working with SGU (Geological Survey of Sweden) to map the area and take
samples of rocks with potentially high sulphur concentrations. However, current methods for
analysing the samples are time consuming. The aim of this project is therefore to evaluate a new,
quicker, method using an pXRF (Portable X-Ray Fluorescence).
A pXRF sends out X-rays that excites electrons in the rock that then emits a characteristic X-ray which
the instrument detects. The instrument has been used for detecting other elements, however
measuring sulphur is challenging since it is a lightweight element with low characteristic energy. This
means that the X-ray can’t penetrate very deep, and the sample size of the pXRF becomes quite
small. The new method using a pXRF for sulphur concentration therefore needs to take this into
consideration.
Furthermore, the pXRF requires a calibration specific to each rock type to work. Therefore SGU
samples sent to the laboratory for testing were also used for calibration of the instrument. During
the calibration, different beam times of the pXRF was also tested in the laboratory figure out what
would be optimal to gain most accurate results. Finally, during field work, the sites that SGU had
sampled were revisited and measured using the pXRF to be able to compare the pXRF measurements
with the results from the original laboratory work. Some additional measurements were made
nearby the original sample sites to see how the results were affected by measuring on weathered
rock surfaces.
The results showed that the averages of the field measurements were close to the results of the
powdered samples that had been analysed in a laboratory. This means that for the sites that were
investigated in this paper the method is working. Each measurement series consisted of 30 pXRF
measurements and results show large differences within the measurement series’ due to the
heterogenous distribution of sulphides. Therefore, it is important to make many measurements. The
method could be a useful tool for initial screening in an area that could have high sulphur
concentrations to be able to focus other more time-consuming methods to areas that are of interest. | en_US |
