Sustainable utilization of sodium silicate-based lead glass sludge as an alkali-activator for alkali-activated slag: Performance, characterization, and Pb-stabilization

Despite commercial sodium silicate (CSS) is widely used as an alkaline activator for alkali-activated materials (AAMs), its manufacture consumes a significant amount of energy and results in the emission of a considerable amount of CO2. These drawbacks have led to the search for more environmentally friendly alternatives. Therefore, this study aims to produce synthetic sodium silicate (SNS) from lead glass sludge (LGS) for the first time, to be used as an alkali-activator for blast-furnace slag (BFS). SNS was prepared through the thermochemical treatment of LGS in the presence of NaOH at different temperatures (200, 400, and 600 degrees C, namely SNS200, SNS400, and SNS600, respectively) for 1 h. Regardless of the treatment temperature, different contents of SNSs were mixed with BFS to achieve Na2O concentrations of 2, 4, 6, and 8 wt%. BFS activated with 4% CSS was used for comparison purposes. The results demonstrated that the thermochemical process of LGS not only induced the formation of sodium silicate but also transformed the soluble Pb-heavy metal into an insoluble form. The BFSSNS dry blends can readily interact with water to yield hardened materials with physical and mechanical properties dependent on the SNS processing conditions and SNS content. The specimens activated with 4 wt% SNS400 exhibited higher compressive strength, lower drying shrinkage, and shorter setting time compared to those activated by 4% CSS.