*2.3. Mineralogical Analysis*

Dried FA samples were mixed with 20 wt.% corundum (internal standard) and milled for 6 min using an XRD-McCrown Mill Retsch GmbH, Haan, Germany). The powder was then filled in a glass capillary (0.3 mm diameter, Hilgenberg Glass no. 10). The measurement was done at the Swiss-Norwegian Beamline (SNBL) (at the European Synchrotron Radiation Facility (ESRF) in Grenoble using a Pilatus 2M (Dectris, Baden, Switzerland) detector measuring from 0.0051 to 34.3751 [◦2θ] with a step size of 0.01 [ ◦2θ] and a scan step time of 1 s by radiating the capillary using a focused beam (diameter 100 μ) with a wavelength of 0.69264 Å and 17.9 keV. Phase identification and quantification was done using TOPAS Academics V6 (Coelho Software, Brisbane, Australia) and HighScorePlus 4.6 (Malvern Panalytical, Malvern, UK) using the Rietveld method.

### *2.4. Acid Neutralizing Capacity*

FA (2 g) was added into 20 mL Mili-Q water (L/S ratio of 10). The suspension was then titrated in 40 steps using a 785 DPM Titrino device (Metrohm, Herisau, Switzerland) by adding every 10 min 1 mL 1M HCl under constant stirring. This procedure was determined in a previous study to best describe the behavior of FA for acid leaching conditions [14].
