Digital spectrometry applied to glass and ceramic sorting

Materials surface characteristics can be investigated analysing their spectral response when properly energised by a suitable source. When the source is represented by a light spectra of known characteristics the surface material response can thus be evaluated adopting a spectrophotometric approach. The analyses of the detected spectra can give useful information concerning the material characteristics and/or surface properties and status. In this perspective digital spectrophotometry can be considered as one of the basic techniques to characterise materials. The application of such a technique is usually confined in “high-tech” environments and can results quite expensive and difficult to apply in industrial “on-line” processes. In this paper recent advances in imaging spectrophotometry devices and techniques are presented with reference to the possibility to recognise different glass fragments (cullets) according to their colour and the presence of transparent polluting fragments, that is the distinction between glass from ceramic glass fragments. The work will identify the main factors influencing the selection of the proper hardware to perform the analysis and the different possible solutions in terms of installations and plant layouts. Case studies will be presented and analysed with particular reference to different classes of bulk products, glass and ceramic glass waste product to recycle, presenting different physical and surface status properties.