A RAPID METHOD FOR THE CHEMICAL ANALYSIS OF CHARCOAL IRON FURNACE SLAGS

Up until the mid-1800s, charcoal blast furnaces were used to produce cast iron in the United States. Glassy slag was produced as a waste product during the reduction of local iron ores and the separation of chemical impurities using a limestone flux material. Detailed slag analysis provides a chemical fingerprint that is useful to archaeologists in determining furnace temperatures and the relative efficiency at which a blast furnace operated, and to determine regional sources of iron ore and flux material used during furnace operation. Laser induced breakdown spectroscopy (LIBS) was used for the analysis of iron furnace slags collected from historic sites in Pennsylvania. LIBS is a versatile in situ method that requires minimal sample preparation, and can provide rapid results. Plasma was generated by application of 1064nm wavelength Nd:YAG laser beam to the surface of pellets created from powdered slags by adding starch as a binder. Concentrations of Al, Ca, Fe, K, Mg, Mn, and Si were determined by identifying their characteristic spectral signatures. Univariate and multivariate analyses were performed for the quantification of these elements and the latter better described the chemical characteristics of the slags. The limit of detection for Al, Ca, Fe, K, Mg, Mn, and Si were 0.10, 0.22, 0.02, 0.01, 0.01, 0.005, and 0.18 %, respectively. The preliminary LIBS estimates were found to be in good agreement with analysis performed by inductively coupled plasma optical emission spectrometry (ICP-OES).