## 2 Materials and Methods
### Fixed Samples  
Four representative mine spoil samples from the OE area and two representative samples from the AA area were selected. From each selected sample, three replicas were prepared, following the protocol explained below. The selected clayed mine spoils (18 replicas) were moistened, mixed, and sieved (1 mm) until homogeneous agglomerates (6.5% of water) were made. They were pressed (300 kg/cm\({}^{2}\), 80 \(\times\) 40 \(\times\) 5 mm) using a laboratory press (NANNETI mod. Mini-P, Faenza, Italy). The samples were fired to 995, 1050, 1100, and 1150 \({}^{\circ}\)C, keeping them for 4 h at the maximum firing temperature using a NANNETI kiln Mod. CVKN-CVKN/S, Faenza, Italy. A firing cycle similar to the one used in the local ceramic industry was simulated. A mineralogical analysis of the ceramic tile bodies (18 replicas \(\times\) 4 temperatures) was carried out by XRD following the methodology described in [7, 8, 9, 10], and by FTIR following the methodology described in [1]. In order to quantify mineral phase, ceramic pieces were ground in an agate hammer, homogeneously mixed with 10 wt% corundum, and analyzed by XRD, following the conventional RIRcor method [11]. Powder-fired samples were characterized by XRD techniques using a Siemens D5000D powder diffractometer with Cu-K\(\alpha\) radiation (\(\lambda\) = 1.5406 A), 20 in the interval between 5 to 65\({}^{\circ}\), and a scanning rate of 2\({}^{\circ}\)/min. A method for crystalline and amorphous phase quantification was used. Once the majority of pure phases in the fired samples were identified, the corresponding calibration curves were built using 676-NIST (National Institute of Standards and Technology, Gaithersburg, MD, USA) as a reference. The RIRcor values of mullite, hematite, quartz, and hercynite were taken from [4]. For the FTIR analysis, a fine powder of the different ceramic tile bodies was placed on the glass window of the ATR-FTIR instrument spectrometer (BRUKER IFS 66/S, Mannheim, Germany). This device has a medium IR source, a KBr beamsplitter, and two detectors, including a DLATGS detector (Mannheim, Germany) at room temperature for routine measurements and obtaining spectra between 7000 and 400 cm\({}^{-1}\). This method relies on the use ofthe main band of a pure mineral as a reference for the normalization of the IR spectrum of a mineral sample. In this way, the molar absorptivity coefficient in the Lambert-Beer law and the components of a mixture, in mol percentage, can be calculated. GAMS equation modeling environment and the NLP solver CONOPT (C)ARKI Consulting and Development, Bagsvaerd, Denmark) were used to correlate the experimental data in the samples considered. MCT (Mannheim, Germany) detector was cooled by high liquid nitrogen sensitivity and speed of measurement. Spectra were also compared to the RRUFF database (2237 Public Mineral Species with Samples, 3710 total Minerals Species with Samples): [[https://rruff.info/](https://rruff.info/)]([https://rruff.info/](https://rruff.info/)). This methodology allows the use of spectra libraries and linear regression algorithms for quantification purposes. A mercury penetrometer (POROSIZER 9329, Faenza, Italy) was used to determine some parameters that describe the porous texture of the studied ceramic tile bodies. Total volume of intrusion, the total pore area, the average pore radius, and apparent density of the test bodies were calculated from the intrusion curves for each of the fired tile bodies. Ceramic tile bodies were studied by back-scattering scanning electron microscopy (SEM) with energy dispersion microanalysis (EDS), using a PHILIPS XL-30 microscope (Mahwah, NJ, USA) with EDAX DX-4 microanalysis v.3.6 (0.3 mbar and 20 kV).