Research On Lead Extraction And Glass-ceramics Synthesis From Waste Cathode Ray Tube Funnel Glass

Waste cathode-ray tubes(CRT)from televisions or computer monitors are generated at an increasing rate due to the technical innovation of replacing CRTs by advanced flat panel screen According to a white paper on E-waste Recycling Industry in China,more than 32 million units of waste televisions and 37 million units of waste computers are produced only in 2013,and 43 million tons of CRT glasses are generated in 2013.The CRT funnel glass contains high level of lead oxide(22-25 wt%)and accounts for about one third of a CRT's total weight.Currently,most of the discarded CRTs end up in landfills or incinerators,and only a small part is recycled.The CRT funnel glass may pose considerable threats to the environment and human beings if disposed improperly.In this study,a novel process has been developed for extracting lead from the hazardous waste CRT funnel glass and simultaneously producing glass-ceramics.CRT funnel glass is mixed with coal fly ash and subjected to carbon thermal reduction.The homogeneous glass melt is quenched in water to obtain parent glass.Glass-ceramics is produced from the parent glass through an appropriate heat treatment.Different factors on lead recovery rate are investigated to determine the optimum smelting conditions.X-ray diffraction(XRD)and scanning electron microscopy(SEM)are performed to investigate the changes in morphological properties of the obtained glass-ceramics.Furthermore,physical and mechanical properties of the prepared glass-ceramics are measured.The main conclusions are as followings:1.The optimum carbon loading amount,CaO/SiO2 ratio,smelting temperature and holding time for lead recovery are 1.0,0.3-0.6,1450? 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 parent glass below 0.6 wt%is successfully achieved.DTA analysis indicates that the Tg and Tc values of the parent glass both decrease with the increase of funnel glass addition.XRD analysis reveals that the main crystalline phase is gehlenite when 50-70 wt%funnel glass is added.SEM observation shows that well-crystallized crystals occur in the specimens with 50-70 wt%funnel glass additions,whereas the specimens with 40 wt%and 80 wt%glass additions exhibit a relative low crystallization degree.2.The optimum crystallization temperature for samples with 50-70 wt%funnel glass additions are 925??950? and 925?.In that case,the apparent density of FG50-70 samples is up to 2.51-2.69 g/cm3,water absorption is 0.65-1.42 wt%,hardness is 533-642 kg/mm2,acid resistance is 2.37-3.28 wt%,and alkali resistance is 0.01-0.04 wt%.3.The optimum crystallization time for samples with 50-70 wt%funnel glass additions are 4 h?3 h and 3 h.Under these conditions,the main the apparent density is 2.55-2.71 g/cm3,water absorption is 0.61-1.12 wt%,hardness is 582-658 kg/mm2,acid resistance is 2.14-2.83 wt%,and mass loss for alkali resistance is negligible.The FG70 specimens show more desirable physical and mechanical properties and chemical resistance when compared with the FG50 and FG60 specimens.