*2.1. Materials and Carbonation Test*

The material used for the development of this methodology proposal was a brick type widely used in construction, which was specifically a clinker brick (MPC2) from Malpesa S.L. (Bailén, South of Spain) fired at 1050 ◦C.

The samples were subjected to a crushing process for granulometric conditioning. Fractions of less than 4 mm were selected to obtain size ratios consistent with the diameter of the reactor, obtaining homogeneous distribution so that there was a predominance of coarser fractions corresponding to conventional waste shredding.

Carbonation tests were carried out in a 0.3 L volume hermetic reactor (Parr Instruments Co., Moline, IL, USA). The fixed conditions were 10 bars of CO2, 4:1 solid–water ratio, and room temperature. The variable conditions were reaction time (between 24 and 720 h) and particle size (<4, 2–4, and 1–2 mm). These particle-size fractions were selected because they were the most representative results of the crushing treatment. Additionally, a test was carried at low pressure (1 bar), room temperature, and a 4:1 solid–water ratio in a 5 L volume hermetic reactor of continuous flow to maintain pressure at 1 bar during the 720 h of reaction time.

Post-treatment, the samples were dried at 100 ◦C for 24 h, powdered, and sieved at 50 μm for subsequent analysis.

#### *2.2. Instrumental Techniques: Methodology*

Major multielemental chemical composition (in oxides) was performed with an automated Panalytical Axios model wavelength-dispersive X-ray fluorescence spectrometer (WDXRF). The samples were prepared for analysis as glass discs to reduce the "matrix effect."

The mineralogical composition of the untreated and treated samples was determined by X-ray diffraction (XRD) using a Bruker D8 Advance diffractometer (Bruker AXS, Berlin, Germany) with standard monochromatic Cu–Kα radiation at 40 kV and 30 mA with a Ni filter and Linxeye 1D detector. Routine scanning was performed with a 0.015◦ 2θ step size, and at 0.1 s per step from 3◦ to 70◦. Rietveld refinement was also realized to determine the quantitative composition of the untreated bricks. In this case, scanning was performed with a 0.010◦ 2θ step size at 0.5 s per step in the range of 3◦–120◦ and adding zincite (15 wt %) as an internal standard. Rietveld refinement for the present phase quantification was done with Bruker's commercial Topas v5 software (Bruker AXS, Berlin, Germany).

In addition, previous carbonation analysis was carried out by X-ray diffraction using a Bruker D8 Advance powder diffractometer (Bruker AXS, Berlin, Germany) equipped with an Anton Paar XRK 900 reactor chamber (Anton Parr GmbH, Graz, Austria) and high-sensitivity detector Bruker Vantec 1 (Bruker AXS, Berlin, Germany). This chamber was designed for X-ray diffraction experiments of up to 900 ◦C and 10 bar for solid state–gas reactions. Standard monochromatic Cu–Kα radiation operating at 40 kV and 40 mA was employed. Scanning was performed with a 0.022◦ 2θ step size at 0.2 s per step from 3◦ to 70◦. Samples were in a CO2-rich environment for 24 h in this reactor chamber.

Macro- and micro-observations were obtained by stereomicroscope using a Greenough Leica S8 APO (Leica Microsystems GmbH, Wetzlar, Germany) equipped with a DC300 camera (Leica Microsystems GmbH, Wetzlar, Germany) and by scanning electronic microscopy (SEM) using a JEOL 6460 LV microscope (JEOL Ltd., Akishima, Japan) equipped with energy-dispersive spectrometers (Oxford Instruments INCA, Oxford, UK).

The carbonate content of the carbonated samples was determined by two analytical methods: differential thermal and thermogravimetric analysis (DTA-TG) and an elemental analyzer. DTA-TG were performed on a TG Netzsch STA 409 PC. Samples (around 150 mg) were heated in an aluminum oxide crucible under a nitrogen atmosphere at 10 ◦C min−<sup>1</sup> from room temperature to 1200 ◦C. Weight loss was measured by thermogravimetric analysis in the temperature range of 450–900 ◦C relative to the total carbonated decomposition. Elemental carbon content was measured using an elemental analyzer, Leco Truspec CHNS Micro (St. Joseph, MI, USA), which calculated the carbonated ratio by assuming that the whole carbon content was calcite.

Soluble Si, Ca, and Mg ions of the original and treated samples were also determined. Analysis was performed with simultaneous inductively coupled plasma optical emission spectrometry (IPC-OES) analysis using a Horiba Jobin Yvon ULTIMA 2 model instrument (Horiba Scientific, Palaiseau, France). The samples were prepared by mixing the solid-powder samples with water and stirring for 24 h, isolating the liquid phase by centrifugation, and filtering using a Nylon 0.22 μm syringe filter (MilliporeSigma, Burlington, MA, USA).

Specific surface area (BET) and microporosity were measured with a Micromeritics Gemini 2360 instrument (Micromeritics Instrument Corp, Norcross, GA, USA) using the absorption of N2 at liquid nitrogen temperature. Before measuring, all samples were degassed using a Flow Prep 060 Micromeritics degasser (Micromeritics Instrument Corp, Norcross, GA, USA) with dry nitrogen gas at 80 ◦C for 12 h. Nanoporosity was measured with an ASAP 2420 instrument (Micromeritics Instrument Corp, Norcross, GA, USA) using CO2 absorption at room temperature. Samples were degassed at 150 ◦C for 1.5 h and finally outgassed to 10−<sup>3</sup> Torr. Macro- and mesoporosity were studied using mercury porosimeter Quantachrome Instruments Pore Master 60-GT (Quantachrome Instruments, Boynton Beach, FL, USA).
