## 3 Results
### Acid Corrosion Resistance of Brick Materials  
Phenomena of degrading/melting of crystalline forms (illite, zeolites and sand) were observed in the present work at elevated temperatures. Owing to the combined use of XRD, TGA/DSC, and ESEM/EDS, a detailed thermal analysis evidenced the presence of a novel material in which both analcine-leucite solid solutions and multite were heterogeneously distributed and enclosed inside a silica-rich matrix.  
Therefore, we attempted to demonstrate the benefits of using alkali-brick as an adsorbent, and after calcination, as a chemically stable matrix for the immobilization of zeolitic extra-framework cations. To this end, it was necessary to know whether the chemical stability of heated alkali-brick was sufficient to consider it as a toxic-element immobilizer. We therefore decided to examine the corrosion resistance of the brick material by performing hydrochloride acid attack. A series of leaching tests were conducted under highly aggressive conditions by submerging 1 day calcined alkali-brick samples in an HCl solution (1 mol\(\cdot\)L\({}^{-1}\)). Chemical analyses of recovered solutions were then carried out by ICP-OES or ICP-MS to gain insights into the degradation state of the attacked material.  
Before that, alkali-brick pellets were initially suspended in M\({}^{+/++}\) solution (M\({}^{+/++}\): Cs\({}^{+}\), Rb\({}^{+}\), Co\({}^{2+}\), or Sr\({}^{2+}\)) to allow interfacial Na\({}^{+}\)/M\({}^{+/++}\) exchanges to occur. The recovered pellets (i.e., M\({}^{+/++}\)-doped alkali-brick) were then dried at different temperatures for 1 day: 90 \({}^{\circ}\)C; 600 \({}^{\circ}\)C, 800 \({}^{\circ}\)C, 1000 \({}^{\circ}\)C, and 1150 \({}^{\circ}\)C. For each heated-brick sample, a leaching test was conducted in 1 mol\(\cdot\)L\({}^{-1}\)-HCl solution for 1 day. As expected, because of the degradation of the zeolitic support under highly acidic conditions [52], silicon and aluminum (constituting zeolitic frameworks), sodium, and adsorbed elements (present in the extra frameworks) were found to be easily released from the samples treated at 90 \({}^{\circ}\)C (Figure 7).  
This attack was further improved by the hierarchical porous characteristics of the alkali-activated brick (having micro-pores, meso-pores, and macro-pores [57]), enhancing the diffusion of aggressive ions from the immersion solution into brick aggregates. At  
Figure 7: Release of elements during acid attack of alkali-brick aggregates immersed in hydrochloride acid (1 mol\(\cdot\)L\({}^{-1}\)) for 1 day.  
temperatures of 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the effects of the acid attack diminished noticeably due to changes in the porous properties of heated brick (depletion of BET surface area and the BJH adsorption/desorption cumulative volume of pores; see Table 2).  
At temperatures \(\geq\) 1000 \({}^{\circ}\)C, a significant decline in leaching was observed. The weak cationic leaching in the brick samples which were previously treated at elevated temperatures could be explained by the fact that illicit and zeolitic specimens were significantly degraded/transformed into novel crystalline minerals (especially into analcine-leucite and mullite) and incorporated inside a silica-rich matrix with a smooth surfaces and glassy morphology (as shown in Figures 4 and 5). Furthermore, the loss of micro-porosity on the brick surfaces (Table 2) contributed to improving the acid-corrosion resistance of the material.