## 2 Materials and Methods  
The residues collected by SIDENOR were characterised by an EVO 50 Zeiss W filament SEM, equipped with an Inca Oxford energy-dispersive X-ray spectroscopy (EDS) probe. Fine samples were analysed in as-received condition using carbon adhesive on aluminium stubs to handle the material. Coarse samples were moulded in a bicomponent cold araldite-based resin, grinded by abrasive papers and polished by 1 \(\upmu\)m diamond paste on metallurgical velvet. General chemical composition measurement by EDS was performed on an area of 5 mm\({}^{2}\). Heat treatments for measurement of moisture, loss of ignition (LOI) and carbonate content were performed according to the following standards:  
* EN 14346:2006: Characterisation of waste--Calculation of dry matter by determination of dry residue or water content
* EN 15169:2007: Characterisation of waste--Determination of loss on ignition in waste, sludge and sediments* EN 459-25:2010: Building lime--Test methods For each temperature test, absolute mass variation was expressed as \[\text{mass loss}[\%]=\frac{m_{i}-m_{f}}{m_{i}-m_{c}}\] where \(m_{i}\) is the initial mass of the sample, \(m_{f}\) is the mass of the sample after heat treatment and \(m_{c}\) is the mass of the empty crucible. Water content measurement was performed at 105 \({}^{\circ}\)C, dwelling the samples overnight in the furnace; LOI was measured at 550 \({}^{\circ}\)C, dwelling the samples for 2 h; and carbonates concentration was measured at 1050 \({}^{\circ}\)C, dwelling the samples for 2 h. Dry mass and water content were expressed as indicated in the EN 14346 standard as \[m_{DR}=\frac{m_{c}-m_{a}}{m_{b}-m_{a}}\cdot 100\] \[m_{W}=100-m_{DR}\] where \(m_{DR}\) is the dry residue of the sample, \(m_{c}\) is the mass of the crucible containing the dried sample, \(m_{b}\) is the mass of the crucible containing the undried sample, \(m_{a}\) is the mass of the empty crucible and \(m_{W}\) is the water content of the sample. LOI, associated with the hydroxide within the samples, was expressed as indicated in the EN 15169 standard as \[m_{LOI}=\left(\frac{m_{b}-m_{c}}{m_{d}-m_{a}}\cdot 100-(100-m_{DR})\right) \frac{100}{m_{DR}}\] where \(m_{LOI}\) is the loss of ignition of the sample. Carbonate content was expressed as indicated in the EN 459-2 standard as \[m_{C}=\left(\left(\frac{m_{11}-m_{12}}{m_{11}}\cdot 100\right)-\left(\frac{m_{b}- m_{c}}{m_{d}-m_{a}}\cdot 100\right)\right)\frac{100}{100-\left(\frac{m_{b}-m_{c}}{m _{d}-m_{a}}\cdot 100\right)}\] where \(m_{11}\) is the mass of the sample before ignition at 1050 \({}^{\circ}\)C; \(m_{12}\) is the mass of the sample after ignition at 1050 \({}^{\circ}\)C; and \(m_{a}\), \(m_{b}\), \(m_{c}\) and \(m_{d}\) are the masses referring to the LOI determination. Thermal gravimetric-differential scanning calorimetry (TG-DSC) simultaneous thermal analysis was performed on 25 mg of sample in a Labsys Setaram machine, with a heating ramp of 30 \({}^{\circ}\)C/min from room temperature to 1200 \({}^{\circ}\)C under Ar atmosphere and using Al\({}_{2}\)O\({}_{3}\) pans of 100 \(\mu\)L. The identification of the transformation highlighted by TG-DSC analysis was performed according to the \"Handbook of thermogravimetric system of minerals and its use in geological practice\" [12]. XRD on as-received fines (grinding sludge (GS), oxy-cutting fines and combustion chamber dusts) was carried out by means of a Rigaku Smartlab SE diffractometer in 0-0 Bragg-Brentano configuration and employing Cu K\(\alpha\) radiation (\(\lambda\) = 1.54 A). Two grams of dried material (105 \({}^{\circ}\)C overnight), manually homogenised in an agate mortar, were scanned from 5\({}^{\circ}\) to 80\({}^{\circ}\) 20 at 0.5\({}^{\circ}\)/min with a step size of 0.02\({}^{\circ}\), with a fixed divergence slit size 0.5\({}^{\circ}\) and a 120 rpm rotating sample stage. The diffracted beam was collected by means of a 1D D/teX Ultra 250 detector with an XRF suppressor filter.