On-line iron-ore slurry monitoring for real-time process control of pellet making processes using laser-induced breakdown spectroscopy: graphitic vs. total carbon detection

Chemical composition of iron-ore pellets has a significant impact on their quality and commercial value. Laser-induced breakdown spectroscopy (LIBS) technique has been extensively tested on line, at industrial pelletizing plants. It proved successful at measuring Si, Ca, Mg, Al and graphitic C contents of different iron-ore slurries prior to filtration and pelletizing. For this specific application, the sensitivity of the technique compares with the one obtained from dedicated chemical laboratories. But the real advantage of LIBS technique is that the results are delivered continuously and in real time compared to periodic sampling and standard analytical delays of more than 1 h. Consequently, LIBS gives a more representative reading of the state of the process - particularly when rapid perturbations occur - and allows process optimization and quality improvement. In this work, special attention was given to the fact that the detection system, with specific settings, gives direct measurement for either graphitic carbon (coke breeze) or total carbon (coke breeze, flux and natural carbonate). Graphitic carbon content is a key parameter for both the pellet production cost and its final commercial value. LIBS is a sensitive technique that can detect small variations. But matrix effects affect the spectral lines and it is sometimes difficult to establish universal calibration curve. This problem is partially overcome by the use of a multivariable calibration that corrects for matrix effects and evaluates a confidence level based on expertise for each measurement. Current research is aimed at the development of commercial equipment for continuous industrial use. (C) 2001 Elsevier Science B.V. All rights reserved.