## 3 Results
### Influence of Particle Grain Size and Crushing Conditions on the Leaching Behaviour of RAs  
Table 5 shows the results obtained from the leaching tests carried out on the selected 12 RAs, according to the limits imposed by the M.D 186/2006. As previously mentioned, in order to evaluate the influence of the particle size and the volumetric reduction by crushing on the release of contaminants, the leaching tests were performed according to the UNI EN 12457-2 (d\({}_{\rm max}\)\(\leq\) 4 mm) and UNI EN 12457-4 (d\({}_{\rm max}\)\(\leq\) 10 mm) standards and in conditions of only sieving or crushing of the material. In particular, the pollutant concentrations that exceed the regulatory limits for recovery are marked in grey and bold. Figure 8: COD release in CDWs and RAs (**left**) and EWC code responsible for the highest release (**right**). Figure 7: Mercury release in CDWs and RAs (**left**) and EWC code responsible for the highest release (**right**). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & \multicolumn{6}{c}{\(\mathbf{d\leq 4\ mm}\)} & \multicolumn{6}{c}{\(\mathbf{d\leq 10\ mm}\)} & \multicolumn{6}{c}{\(\mathbf{Limit\ Values}\)} \\ \cline{3-10}
**Parameter** & **Unit** & \multicolumn{2}{c}{**Only Sieved**} & \multicolumn{2}{c}{**Crushed**} & \multicolumn{2}{c}{**Only Sieved**} & \multicolumn{2}{c}{**Crushed**} & \multicolumn{2}{c}{**Limit Values**} \\ \cline{3-10}  & & **MRA \({}^{1}\)** & **RCA** & **MRA \({}^{1}\)** & **RCA** & **MRA \({}^{1}\)** & **RCA** & **MRA \({}^{1}\)** & **RCA** \\ \hline pH & - & 10.4-109 & 11.4 & 107–11.1 & 11.3 & 106–11 & 11.5 & 107–11 & 11.4 & 5.5–12 \\ Nitrates & (mg/L) & 14–27 & 3 & 14-24 & 3 & 13–23 & 3 & 13–21 & 2 & 50 \\ Fluorides & (mg/L) & 0.3-0.5 & 0.3 & 0.3-0.6 & 0.3 & 0.3-0.5 & 0.3 & 0.3-0.5 & 0.3 & 1.5 \\ Solupdates & (mg/L) & 85–94 & 39 & 78–95 & 53 & 71–99 & 32 & 71–98 & 36 & 250 \\ Chlorides & (mg/L) & 5–8 & 1 & 5–8 & 1 & 4–7 & 1 & 5–7 & 1 & 100 \\ Cyanide & (mg/L) & 5 & 5 & 5 & 5 & 5 & 5 & 5 & 5 & 50 \\ barium & (mg/L) & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 1 \\ Copper & (mg/L) & 0.02-0.04 & 0.01 & 0.01-0.03 & 0.01 & 0.02-0.03 & 0.01 & 0.02-0.03 & 0.01 & 0.05 \\ Zinc & (mg/L) & 0.05 & 0.05 & 0.05 & 0.1 & 0.05 & 0.05 & 0.05 & 0.05 & 3 \\ Beryllium & (mg/L) & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 10 \\ Cobalt & (mg/L) & 5 & 5 & 5 & 5 & 5 & 5 & 5 & 5 & 250 \\ Nickel & (mg/L) & 2–4 & 2 & 2–4 & 2 & 2–4 & 2 & 2–4 & 2 & 10 \\ Vanadium & (mg/L) & 2–36 & 16 & 27–29 & 22 & 27–33 & 13 & 29–32 & 15 & 250 \\ Arsenic & (mg/L) & 1–3 & 1 & 1–3 & 1 & 1–3 & 1 & 1–3 & 1 & 50 \\ Caadmium & (mg/L) & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 5 \\ Tot. chromium & (mg/L) & 15–35 & 48 & 17–43 & **67** & 15–30 & 46 & 16–30 & 44 & 50 \\ Lead & (mg/L) & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 50 \\ Selenium & (mg/L) & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 10 \\ Mercury & (mg/L) & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 0.1 & 1 \\ COD & (mg/L) & **17–31** & 12 & **16-36** & 8 & **14-33** & 12 & **21-35** & 9 & 30 \\ \hline \end{tabular} Data marked in bold are values that exceed the regulatory limits imposed by MD. 186/2006. \({}^{1}\) The pollutant concentrations are indicated as a range of values detected in the MRAs produced by the two treatment plants.  
\end{table} 
Table 5: Leaching behaviour of MRAs and RCAs tested according to the EN 12457-2 (d\(\leq\) 4 mm) and EN 12457-4 (d \(\leq\) 10 mm) methods, under conditions of only sieving and crushing. Generally, the pollutant concentrations comply with the regulatory limits imposed by the M.D. 186/2006, except for total chromium and COD. In particular, total chromium was identified as critical for a crushed RCA, while COD for all the tested MRAs. Figure 9 shows the pH values recorded in plants A and B in relation to the type of RA (RCA or MRA), particle sizes, and test conditions (i.e., material only sieved or crushed). As shown, the pH is always alkaline (pH > 10) for both MRAs and RCAs and below the regulatory limit of 12.