Stabilization of hazardous lead glass sludge using reactive magnesia via the fabrication of lightweight building bricks

The role of low-quality calcined clay in enhancing the performance of cement mortar exposed to normal and aggressive media

This study focuses on the role of low-quality calcined Fanja (FNJ) clay in enhancing the behavior of cured cement mortar (CM) and its resistivity to chloride and sulfuric acid attack. Ordinary Portland cement was replaced with different quantities (10%, 25%, 35%, and 50% by weight) of FNJ, which was calcined at different temperatures (620 °C, 760 °C, and 900 °C). After 28 days of curing, all the hardened mortars were immersed in 5% sulfuric acid for up to 12 weeks. Additionally, a rapid chloride permeability test was conducted on the 91-day cured CM and CM-FNJ samples to evaluate the affinity of calcined FNJs to retard the chloride diffusion into CM. The results showed that all samples containing FNJ900 showed better physical and mechanical properties than the control sample, while CM with NFJ760 recorded nearly similar performance as CM-NFJ900. In contrast, the CM-FNJ620 mixtures showed lower properties than those of other mixtures. In addition to the pozzolanic reactivity of the calcined clay, the presence of hematite in the calcined clay strongly contributed to increasing the mechanical properties of the hardened mortar through forming calcium ferrosilicate hydrate binding phase, as confirmed by X-ray diffraction. Moreover, the existence of hematite increased the resistivity of CM against sulfuric acid attack as it acts as a buffer for an acidic medium. Compared with CM-FNJ900, the CM-FNJ760 is recommended for use as it exhibited a higher strength activity index and comparable resistance to accelerated chloride diffusion and sulfuric acid accompanied by lower energy demand and lower CO2 emission, achieving the concept of 'sustainability'.

Role of silicate-rich and silicate-less industrial solid wastes in the physicomechanical properties and durability of low quality metakaolin-blended cement

Although calcined clay-blended cement offers higher performance and durability compared to neat Portland cement (PC), its extensive use of natural clay leads to the depletion of natural non-renewable resources. To address this concern, this study focuses on the utilization of supplementary cementitious materials-based waste products as a substitute for PC. The blended cement was optimized with a low replacement level of 10 wt.% calcined Fanja clay (FNJ) as a low-grade metakaolin (MK) and 90 wt.% PC. Various types of industrial solid wastes (ISWs) were incorporated into the PC-FNJ blend in place of PC. The ISWs utilized included silicate-rich wastes, such as silica fume (SF) and glass waste (GW) powder, as well as silicate-less waste, such as marble dust (MD). The results revealed that incorporating 10 wt.% SF into the PC-FNJ mixture resulted in a considerable decrease in the flow rate while improving its early mechanical strength. GW, as another silicate waste, also enhanced early mechanical properties but not as much as SF. However, the composite of PC-FNJ-GW exhibited higher workability than the neat PC, PC-FNJ, and PC-FNJ-SF. The mixtures of PC-FNJ-MD demonstrated the same trend. Embedding SF into PC-FNJ-GW and PC-FNJ-MD substantially decreased both their flowability and mechanical properties. Nonetheless, all composites containing ISWs showed higher flexural strength, higher resistivity to chloride diffusivity, and higher or comparable acid and salt resistivity.

Valorizing hazardous lead glass sludge and alumina flakes filling waste for the synthesis of geopolymer building bricks

Geopolymer bricks from lead glass sludge (LGS) and alumina flakes filling (AFF) waste were synthesized in the present work. AFF waste was chemically treated to prepare sodium aluminate (NaAlO₂) powder. Silicate source (untreated LGS and thermally treated one at 600 °C (LGS600)) and sodium oxide (Na₂O) concentration (as NaAlO₂) were the compositional parameters, which affected the physical and mechanical properties (compressive strength, water absorption, and bulk density) of the prepared bricks. High organic matter content inside LGS caused a retardation effect on the geopolymerization process, resulting in the formation of hardened bricks with modest 90-day compressive strengths (2.13 to 4.4 MPa). Using LGS600 enhanced the mechanical properties of the fabricated bricks, achieving a maximum 90-day compressive strength of 22.35 MPa at 3 wt.% Na₂O. Sodium aluminosilicate hydrate was the main activation product inside all samples, as confirmed by X-ray diffraction and thermal analyses. Acetic acid leaching test also proved that all LGS600-NaAlO₂ mixtures represented Pb concentrations in leachates lower than the permissible level of characteristic leaching procedures, indicating the mitigation of environmental problems caused by these wastes.

Reuse of lead glass sludge in the fabrication of thermally insulating foamed glass with outstanding properties and high Pb-stabilization

This study represents the sustainable/safe consumption of lead glass sludge (LGS) in the fabrication of thermally insulating foamed glass via sintering (750-950º C) and chlorination processes. The impact of selected additives including calcium chloride (CaCl₂) and sodium hydroxide (NaOH) on the foaming efficiency and Pb-stabilization has been deeply investigated. LGS is mainly lead silicate material with considerable content of calcium carbonate, which acts as foaming agent during sintering process. The newly developed foamed-materials exhibited thermal conductivity of 0.054-0.136 W/m.K, density of 0.23-1.10 g/cm³, porosity of 63.3-92.6%, and compressive strength of 0.10-2.69 MPa. X-ray diffraction proved that the immobilization mechanism was attributed to the transformation of free Pb within LGS into insoluble ganomalite Pb₉Ca₅MnSi₉O₃₃ phase. Adding NaOH enhanced the foaming process accompanied by a significant reduction in Pb-leaching. Incorporating CaCl₂ has resulted in a retardation in Pb-leaching, which associated with Pb-stabilization and Pb-vaporization. In an attempt to reduce CO₂-emission, the potential use of alkali-rich-wastewater (AW) as eco-friendly alkali source in lieu of NaOH was studied. Regardless of the variation in Pb-concentrations in leachates, all samples recorded Pb-concentrations lower than the safe limit (≤ 5 mg/l), achieving Pb-immobilization of 95.98-99.87%. The significantly reduced thermal conductivity and enhanced Pb-immobilization efficiency along with the reasonable compressive strength summarize the major innovation presented in this study.