Ophthalmic glass lens waste as an alternative soluble silica source for alkali-activation reactions

Abstract

This research study was aimed at assessing the potential use of glass powder (GW), from the production of optical lenses, as a substitute of commercial sodium silicate (SS), to produce fly ash-based alkaline cements. The dissolution of the GW and the subsequent activation were achieved either with a cleaning solution (CS) from the aluminium casting industry, and a commercial sodium hydroxide solution (SH) so as to. Firstly, GW dissolution with CS and SH was evaluated at different time and temperatures, i.e.,16 h, 3, 7 and 28 days at 20 °C and 16 h at 20, 40, 60 and 80 °C, to find the best dissolution rate, which an optimum point was observed when CS was the dissolving agent. Then, several pastes were synthesized and cured for 7 days at 50 °C to assess their mechanical behaviour and alkaline-activated gel formation by compressive strength test. Furthermore, reaction products were characterized by X-ray diffraction (XRD) and electron microscopy (SEM/EDX). The observations reveal that although SH solution acted well to dissolve GW, so that the compressive strength was close to that of SS, CS also showed reasonable potential to be used as a dissolving agent for GW, rendering a cheap and environmentally friendly alternative activator. Microstructural analysis also illustrated the rise in the crystallinity of the reaction products obtained from industrial by-products, i.e., GW and CS.