In the first year of this project, we have successfully developed an analytical protocol for tracing slag materials from three steel plants (i.e., LC, LD and CS) using the Sr-Nd-Pb isotope ratios. This year, we further evaluate the reliability of the combined Sr-Nd-Pb isotope approach in slags as a reliable tracer for discriminating sources of slags, and to better constrain where the Sr-Nd-Pb isotopic signals in slags come from. To do so, we collected slag samples twice from the three plants (June and October, 2018), which were used to investigate if there is any temporal varitions of Sr-Nd-Pb isotope signatures from the studied plants. Several fluxes (including lime, ferro-silicon, ferromanganese, ferromanganese-silicon, megnisium oxide and fluorite) were also sampled for identifying possible sources of Sr-Nd-Pb in slag samples. The results show that reductive or oxidative slags from the three plants can be discriminated by Sr-Nd-Pb isotope ratios. However, Isotope ratios of slags are significantly different between the samples collected in 2013 and 2018, probably due to changes in sources of fluxes through time. The measured isotope data of the fluxes indicate that Sr and Nd isotope ratios are mainly controlled by lime and ferro-silicon, and Pb isope ratios are most likely related to ferro-silicon or ferromanganese. Our results demonstrate that sources of slags can be discriminated by the combined Sr-Nd-Pb isotope ratios, and has great potential as a probe for tracing sources of slags if the databases for plants and associated fluxes can be established.

Sr-Nd-Pb isotope ratios, environmental forensics, wastes