Laser-induced breakdown spectroscopy analysis of the free surface of liquid secondary copper slag

The present study focuses on the in-situ analysis of slags from secondary copper production by means of laser induced breakdown spectroscopy (LIBS) in order to improve the process efficiency and the end product quality. Synthetic slag samples, simulating secondary copper production slags, were melted in a laboratory induction furnace and were analyzed using LIBS. SiO2 and FeO were the major components and Al2O3, ZnO and CuO were introduced in the synthetic slag as minor components with concentrations below 10 wt%. The solidified samples were analyzed by means of X-ray wavelength dispersive spectroscopy in an electron probe micro analyzer (WDSEPMA) and the obtained elemental composition was used as reference for the construction of calibration curves for the elements of interest, i.e. Si, Fe, Al, Zn and Cu. The quality of these calibration models was evaluated by the coefficient of correlation (R-2). The accuracy was estimated by means of the prediction error percentage obtained from cross-validation of the calibration curves as well as by external validation using samples originating from industry. The last samples were melted under the same conditions as those of the laboratory prepared samples, and LIBS spectra were collected from the free surface of their melts. Furthermore, the solidified industrial samples were analyzed by WDS-EPMA and the determined concentrations were compared with the ones obtained using LIBS. Results were obtained for SiO2, FeO, ZnO and CuO with the accuracies better than 13.5%, which are considered as satisfactory. The quantification of Al2O3 was significantly influenced by self-absorption. The limits of detection (LOD) of the elements with respect to their oxides, i.e. SiO2, FeO, Al2O3, ZnO and CuO, were estimated as 1.5 wt%, 1.0 wt%, 0.097 wt%, 0.15 wt% and 0.012 wt%, respectively, which are appropriate for the targeted application.