| This research was directed at the recycling of radioactively contaminated stainless steel by Electroslag Remelting. Factors influencing ingot quality and elemental partitioning between stainless steel and slag were studied. Stainless steel (304L) electrodes measuring 2.5 inches in diameter were coated with blends of rare earth element oxides to simulate surface contaminated scrap metal. These electrodes were melted into a 3.75 inch diameter round mold using thirteen different slags representing a factor space on the ternary CaF{dollar}sb2{dollar}/CaO/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} phase diagram. Samples of each ingot, slag cap, and slag skin were analyzed for the presence of the surrogate elements. During each melt, changes in current, voltage, power, and impedance were electronically recorded. Thermochemical modeling was used to predict the partitioning of elements between the metal and the slag and to provide insight into the chemical mechanisms by which certain elements are captured by a slag. Analysis of the remelted steel showed that, for each slag tested, the level of surrogate elements was less than the detection limit of 1 ppm, except when the choice of slag caused oxide entrapment on the ingot surfaces. Slag chemistry was shown to influence the final chemistry of the ingot produced, as well as its surface quality. Most of the slags tested did not cause the steel to deviate from the chemistry for 304L, and, in fact, resulted in a decrease in the levels of elements such as sulfur and silicon. In particular, slag chemistry was shown to influence the partitioning of surrogates between the slag skin and the slag cap. This partitioning may be explained by studying the mechanisms by which slag skins are formed and the prevalent surrogate bearing species present in slags of different chemistries. Ideally, radionuclides would be partitioned to the slag cap, which could easily be disposed of at the end of the melt. |
