Application of Laser-Induced Plasma Spectroscopy to Sorting Aluminum Alloy Scrap

The applicability of laser-induced plasma spectroscopy (LIPS) for sorting of aluminum alloy scrap was studied. The combination of a pulsed Nd:YAG laser with an objective lens having a long focal length of 600 mm was used to generate plasmas, and the emitted light was analyzed spectroscopically by a compact fiber-optic spectrometer having a CCD array detector. The emission characteristics of laser-induced plasmas, in terms of the laser pulse energy and sample height, were investigated to determine the optimum conditions for quantitative analysis. The experimental results showed that the line-to-background ratio was maximized at a laser pulse energy of around 30 mJ. Also, the variations in the spectral line intensity due to changes in the sample height could be compensated by the method of an internal standard, which normalizes the line intensity of the analyte element to the line intensity of the matrix element. Based on the results, standard aluminum alloy samples were analyzed and calibration curves were constructed for elements of silicon, copper, zinc, magnesium and manganese. Aluminum alloy scrap pieces, consisting of cast and wrought alloys, were sorted successfully by the obtained calibration curves.