Lead generation and separation mechanisms from lead silicate glass by reduction-melting

Abstract

Reduction-melting is a method to separate lead from waste cathode ray tube (CRT) lead glass. To study the mechanism of lead separation, melting tests using model lead silicate glass rather than actual CRT glass were carried out. Crushed model lead glass mixed with activated carbon (reducing agent) and Na₂CO₃ (flux) was heated and quenched at target temperatures to stop the reaction. Tomographic images of the quenched samples were observed by X-ray computed tomography. Further, the samples were evaluated by X-ray diffractometer, X-ray fluorescence spectrometer, and mass change determinations. From these results, it was found that reduction of lead glass and separation of lead occur with the following mechanisms. Elemental Pb (lead) was generated from below 973 K before the sample had melted completely. At 1273 K and above, whole of the sample had become a melt, and the Pb separated and settled out of the glass. Gas released during the melting process agitate the melt and promote the Pb settling.