Automatic sorting of aluminium alloys by fast LIBS identification

The recycling process of aluminium requires only 5 % of the energy needed for the production of primary aluminium and saves natural resources. However, producing high-quality secondary aluminium out of recycled material is only possible if the scrap is available in pre-sorted fractions of cast and wrought alloys. To date, conventional analysing and sorting techniques do not permit an economic alloy specific separation of light metals. A new, laser-based identification and sorting procedure is developed and implemented in a LIBS demonstrator in order to obtain high material throughput with at the same time high degree of purity of the sorted fractions. Calibration measurements with a total set of 36 certified reference samples were carried out for static and moving samples at a velocity of 3 m/s and the general feasibility of LIBS measurements at moving samples was verified. For the comparability to other experimental set-ups limits of detection for the major alloying elements Si, Fe, Cu, Mn, Mg, Cr, Ni and Ti are determined in aluminium for the static case. The performance of internal standardisation and additive interelement corrections to improve calibration and evaluation functions is shown. The combination of these methods reduces the residue standard deviations by a factor greater than 4.