From dangerous wastes to green construction materials, as thermally stable-radiation blocker, in presence of meso-porous magnesia and alumina

The nominal objective behind this study is to recycle iron-rich slag (GGBFS) and lead-rich glass waste (LRGW) as industrial solid wastes in the presence of meso-porous magnesia or alumina to produce sustainable, eco-friendly, and high-performance binding materials. Four NaOH-activated composites (AACs) pastes have been prepared: Pure alkali-activated slag (AAS), AAS-20%LRGW, AAS-20%LRGW-3% meso-porous MgO, and AAS-20%LRGW-3% meso-porous Al2O3. After the hardening process, the compressive strength was measured at 1, 7 and 28-days of normal curing (high humidity at 25 degrees C). Thermal stability test for all AACs, after 28-days, was conducted at 250, 500 and 750 degrees C. Two different radio-active isotopes (Cs-137 and Co-60) were used, as gamma radiation sources, to investigate the attenuation performance of all prepared AACs. The results confirmed that, among the four composites, AAS-20%LRGW-3% meso-porous MgO composite pastes possessed the highest compressive strength (29.3 MPa), highest thermal stability (25 MPa, 18.2 MPa and 10 MPa at 250 degrees C, 500 degrees C and 750 degrees C, respectively). Moreover, this composite has the highest gamma radiation shielding performance, whatever the intensity of the gamma-ray or firing temperature. At cesium isotope, it was found that the mu values were 0.199 +/- 0.003, 0.197 +/- 0.003, 0.194 +/- 0.005 and 0.188 +/- 0.005 cm-1 at 25, 250, 500 and 750 degrees C, respectively. This efficiency is attributed to the role of meso-porous MgO; it has a high surface area (8891 cm2/g), high adsorption capacity (2.042 cm3/g), and low average pore diameter (37.17 nm); these textural characteristics helped much in the generation of additional hydrates/binding phases such as calcium-silicate-hydrates (CSHs), calcium-aluminate-hydrates (CAHs), calcium-aluminosilicate hydrates (CASHs as gehlenite or hydrogarnet), hydrotalcite, magnesium silicate hydrates (MSHs) as well as sodium-alumino-silicate-hydrates (NASHs) and lead silicates (Pb3SiO5). All these phases were detected via XRD, TGA/DTG as well as SEM/EDX techniques. Moreover, the inclusion of meso-porous MgO enhanced the immobilization of hazardous lead according to the obtained data from the toxicity characteristics leaching procedure (TCLP). Hence, we recommend using AAS-20%LRGW-3%MgO composite as gamma-radiation blocker in medical fields and concrete landfills containing dangerous radioactive wastes.