Lead extraction and glass-ceramics synthesis from waste cathode ray tube funnel glass through cooperative smelting process with coal fly ash

Abstract

In this study, a novel process was developed for extracting lead from the hazardous waste cathode ray tube (CRT) funnel glass and simultaneously producing glass-ceramics. CRT funnel glass was mixed with coal fly ash and subjected to carbon thermal reduction with the addition of CaO. The homogeneous glass melt and reduced metallic lead were quenched in water. Glass-ceramics were produced from the parent glass through an appropriate heat treatment. The optimum carbon loading amount (calculated as the molar ratio of C/PbO), CaO/SiO2 ratio, smelting temperature and holding time for lead recovery were 1.0, 0.3–0.6, 1450 °C and 2 h, respectively. Under these conditions, more than 95% of lead can be extracted from the funnel glass and a low lead content of the resultant parent glass below 0.6 wt% was successfully achieved. CaO behaved as a network modifier to reduce the viscosity of the glass and also acted as a substitution to release lead oxide from the silicate network structure, resulting in a high lead separation efficiency. X-ray diffraction (XRD) analysis revealed that the main crystalline phase was gehlenite when 50–70 wt% funnel glass was added. Scanning electron microscopy (SEM) observation showed that well-crystallized crystals occurred in the specimens with 50–70 wt% funnel glass additions, whereas the specimens with 40 wt% and 80 wt% glass additions exhibited a relative low crystallization degree. Furthermore, property measurements, chemical resistance tests and leaching characteristics of heavy metals confirmed the possibility of engineering and construction applications of the superior glass-ceramic products. Overall results indicate that the process proposed in this paper is an effective and promising approach for reutilization of obsolete CRT funnel glass.