## 2 Background
### Characterization of the Spent Refractory Materials  
The assessment of chemical toxicity of raw wastes, as well as of spent refractory materials, was conducted according to the standard leaching protocol EN 12457.04, which provides information on the mobility behavior of refractory materials of a particle size below 4 mm and applying a liquid to solid ratio of 10 L/Kg dry matter [17]. The characterization of the spent refractory materials is based on the Council Decision 2003/33/EC, regarding the acceptance of spent refractories at landfills [15]. The compliance of the testing results of the examined spent refractories with the Council Decision 2003/33/EC is a prerequisite in order for a spent refractory material to be accepted for dumping in a specific landfill [8]. Values of pH and concentration of arsenic (As), barium (Ba), cadmium (Cd), chromium total (Crtotal), copper (Cu), mercury (Hg), molybdenum (Mo), nickel (Ni), lead (Pb), antimony (Sb), selenium (Se), zinc (Zn), fluoride (F), chloride (Cl), and sulfate (SO4\({}^{2-}\)) determined in the leachates of the spent refractory materials are compared against values given by Council Decision 2003/33/EC. According to this comparison, the spent refractory materials are classified as inert, non-hazardous, and hazardous (Table 1).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Leaching Limit Values (L/S = 10 L/Kg)**} \\ \hline
**Component** & **Inert** & **Non-Hazardous** & **Hazardous (L\({}_{\text{z}}\))** \\ \hline pH & minimum 6 & & mg/Kg \\ As & 0.5 & 2 & 25 \\ Ba & 20 & 100 & 300 \\ Cd & 0.04 & 1 & 5 \\ Crtotal & 0.5 & 10 & 70 \\ Cu & 2 & 50 & 100 \\ Hg & 0.01 & 0.2 & 2 \\ Mo & 0.5 & 10 & 30 \\ Ni & 0.4 & 10 & 40 \\ Pb & 0.5 & 10 & 50 \\ Sb & 0.06 & 0.7 & 5 \\ Se & 0.1 & 0.5 & 7 \\ Zn & 4 & 50 & 200 \\ F & 10 & 150 & 500 \\ Cl\({}^{-}\) & 800 & 15,000 & 25,000 \\ SO4\({}^{2-}\) & 1000 & 20,000 & 50,000 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Leaching limit values established by Council Decision 2003/33/EC [15].  
For the implementation of the proposed methodological approach, specific laboratory work and sample treatments have to be implemented.  
The leachability of potentially hazardous substances from waste and spent refractory materials depends on the grain size distribution, solid-to-liquid ratio, mineral composition of the virgin material, content of amorphous components, and structure [9]. The As, Ba, Cd, Cr, Sb, Se, Hg, Mo, Ni, and Pb content of the leachates was obtained applying inductively plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The Cu and Zn concentration of the leachate was determined using atomic absorption spectroscopy (AAS). Fluoride, Cl\({}^{-}\), and SO\({}_{4}\)\({}^{2-}\) concentrations in leachates were measured applying titrating and gravimetric methods, respectively. X-ray diffraction (XRD) was applied for mineralogical characterization of spent refractory materials. As a complementary technique with XRD analysis, scanning electron microscopic (SEM) analysis was applied. In general, the mineralogical and chemical composition results are discussed to explain further the findings of the leachability tests and mobility of inorganic substances.