The Determination of Contaminant Release from the PBO-Fe2O3-SiO2-Na2O Vitrification System, Using Industrial Solid Waste or Artificial Mixtures

In the current study, the leachability of lead from the PbO-Fe₂O₃-SiO₂-Na₂O vitrification system was examined by the application of DIN 38414 S4 and TCLP (Toxicity Characteristic Leaching Procedure) standard leaching tests. Various compositions, containing industrial or artificially created solid waste, were examined. Among the main conclusions from the results obtained was that the initial lead content, expressed as PbO and varied between 4–24% w/w, does not influence directly the release of lead from the vitrified samples. The other oxides, as well as other factors e.g. crystal formation on the glass surface, proved to be more important. Similar data were obtained regarding the content of iron oxide (the initial content of Fe₂O₃ varied from 30–54% w/w), although in this case the sodium concentrations measured in the leachates were generally found to increase with increasing initial iron oxide content and with the respective formation of crystals. The stoichiometry of lead and sodium, as measured in the leachates, was not constant for all the examined cases, showing that the mechanism of release depends upon the initial compositions and the presence of crystals on the glass surface. Improved results, regarding leachability and homogeneity without the presence of crystallites on the glass surface, were obtained when the initial ratio SiO₂/Na₂O (% w/w) was 2.33. By maintaining this ratio and when the examined waste was gradually added in the initial composition, the results obtained, concerning sodium concentration and pH values, can be described mathematically, by introducing an appropriate constant factor.