Xflash 5030 silicon drift detector

were performed at X-Ray Fluorescence beamline^{35 (link),36} in 45/45° geometry at 14 keV, and therefore above the Pb-L₃ edge, in high vacuum conditions (10^–8 mbar), using a high energy multilayer. The beam spot size was of 50 × 50 µm² and the XRF data were collected using a Bruker XFlash 5030 Silicon Drift detector (SDD) mounted under 90° with respect to the primary X-ray beam. XRF spectra were processed using the open source software PyMca^{37 (link)}. The elemental quantification was obtained through a fundamental parameters fitting strategy.

Preliminary SEM analyses were performed on an Obducat CamScan 3200LV SEM using Helios software. Secondary electron imaging (SEI) and Backscattered electron imaging (BEI) images were captured, using a scan speed of S4, gun voltage of 25.00 kV and emission of 92 μA. For further SEM analyses, sample preparation was performed by rinsing a small amount of soil with distilled water (to remove any sediment coating the outside of the soil grains) and then ethanol, before oven-drying the samples for 10 min at 40°C. The cleaned soils were then transferred onto an SEM stub and sputter coated using a thin layer of platinum prior to analysis. This set of SEM analyses was performed on a Carl Zeiss Sigma VP Field Emission Gun Scanning Electron Microscope coupled to a Bruker Quantax 400 Energy Dispersive Spectrometer equipped with an Xflash 5030 Silicon Drift Detector. Analysis was carried out using an accelerating voltage of 20kV in variable pressure mode, with a mix of 40% Secondary Electron and 60% Backscattered Electron.