Valorization of waste glass from discarded fluorescent lamps as additional active material in the synthesis of alkali-activated materials

Currently, the hazardous potential of spent fluorescent lamps due to their mercury content, which usually exceeds the limit allowed by standards, it is well known. When these are taken out from use, mercury is distributed between all the components of the lamp; in particular, it can be found in the phosphorescent powder called “phosphor” which is attached as a thin layer on the walls of the lamps. Although many efforts have been made to develop technologies for recovery of mercury, in many cases their effectiveness is very hard to be proved from both technical and economic points of view. Therefore, this
work is focused on evaluating the feasibility of valorising this type of waste glass as an active precursor for the synthesis of fly ash-based alkali-activated materials. In this respect, the potential of synthesized alkali-activated materials to immobilize mercury from waste glass added to the synthesis mixture was experimentally proved through compliance leaching tests.
Important microstructural changes that appear with the increasing addition of waste glass to the synthesis mixture were highlighted by SEM and N2-BET analysis. Sharp increase in the SiO2/Al2O3 molar ratio of the synthesis mixture with the increasing addition of waste glass leads to an increase in the unreacted glassy fraction that acts as defect sites in the structure of the alkali-activated material, having a negative effect on its mechanical properties. However, the compressive strength tests showed that an addition of waste glass up to 5% of the total mass of the synthesis mixture has a beneficial effect on the
compressive strength of alkali-activated materials.