## 3 Results
### Statistical Evaluation of Leaching Behaviour of CDWs and RAs
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{**Unit**} & \multicolumn{3}{c}{**CDWs**} & \multicolumn{3}{c}{**RAs**} & \multirow{2}{*}{**Limit Values**} \\ \cline{3-3} \cline{5-8}  & & **Min** & **Max** & **Mean** & **Min** & **Max** & **Mean** & **M.D. 186/2006** \\ \hline pH & - & 6.58 & 12 & 8.30 & 6.90 & 12 & 8.85 & 5.5–12 \\ Nitrates & (mg/L) & 0.10 & **95.20** & 4.68 & 0.10 & 49.50 & 9.47 & 50 \\ Fluorides & (mg/L) & 0.05 & **6.16** & 0.54 & 0.01 & 1.21 & 0.23 & 1.5 \\ Sulphates & (mg/L) & 0.80 & **457** & 30.77 & 5 & 219.20 & 34.38 & 250 \\ Chlorides & (mg/L) & 0.08 & **102.80** & 10.60 & 1 & 51.40 & 11.06 & 100 \\ Cyanide & (\(\mu\)g/L) & 0.10 & 30 & 6.77 & 0.05 & 50 & 13.72 & 50 \\ Barium & (mg/L) & 0.01 & 1 & 0.12 & 0.01 & 0.50 & 0.08 & 1 \\ Copper & (mg/L) & 0 & 0.02 & 0.01 & 0.0002 & 1 & 0.02 & 0.05 \\ Zinc & (mg/L) & 0.001 & 0.42 & 0.07 & 0.005 & 1.64 & 0.14 & 3 \\ Berillium & (\(\mu\)g/L) & 0.20 & 10 & 1.48 & 0.10 & 5 & 1.96 & 10 \\ Cobalt & (\(\mu\)g/L) & 0.10 & 41.30 & 7.68 & 0.51 & 30 & 5.42 & 250 \\ Nickel & (\(\mu\)g/L) & 0.01 & **190** & 9.72 & 0.10 & 10 & 3.64 & 10 \\ Vanadium & (\(\mu\)g/L) & 0.10 & 118 & 14.91 & 0.30 & 64.40 & 13.84 & 250 \\ Arsenic & (\(\mu\)g/L) & 0.01 & 35 & 5.87 & 0.10 & 22.50 & 5.04 & 50 \\ Cadmium & (\(\mu\)g/L) & 0.05 & **10** & 1.53 & 0.10 & 5 & 2.00 & 5 \\ Total chromium & (\(\mu\)g/L) & 0.01 & **1361** & 38.65 & 1 & **183** & 18.70 & 50 \\ Lead & (\(\mu\)g/L) & 0.02 & 28 & 4.64 & 0.10 & **79** & 5.55 & 50 \\ Selenium & (\(\mu\)g/L) & 0.10 & 10 & 3.10 & 0.10 & 10 & 3.53 & 10 \\ Mercury & (\(\mu\)g/L) & 0.01 & **50** & **2.11** & 0.10 & **1.62** & 0.60 & 1 \\ Asbestos & (mg/L) & 0 & 30 & 3.82 & 0.01 & 30 & 2.45 & 30 \\ COD & (mg/L) & 4 & **443** & **30.35** & 5 & **43.40** & 17.93 & 30 \\ \hline \hline \end{tabular} Data marked in bold are values that exceed the regulatory limits imposed by M.D. 186/2006.  
\end{table} 
Table 4: Leaching properties of CDWs and RAs (contaminant releases reported in the average and minimum–maximum range). As previously stated, total chromium is one of the most conflictive elements for CDW recovery and RA use. As shown in Figure 6, the greatest criticality was found in RAs as part of the samples analysed (i.e., upper whisker) show total chromium concentrations higher than the regulatory limit of 50 \(\upmu\)g/L. From the analysis developed, the main source of chromium are cementitious materials (EWC 170101), in which 50% of the total concentrations are close to the regulatory limit. This is mainly due to the presence of Portland cement [41] and the mortar adhered to the original natural aggregate [21]. The results are generally aligned well with the existing literature. In fact, as confirmed by several authors [45, 46, 57, 58, 59], total chromium is one of the parameters most released by cement when subjected to leaching test. This is mainly due to the raw materials and fuels used during its production [57]. Several studies have also demonstrated that total Cr is one the most leachable and unstable metal even in crushed granular concrete samples [44, 60]. According to [PERSON] et al. [18], [PERSON] et al. [20], and [PERSON] et al. [8], also mixed CDWs (EWC 170904) containing ceramic fractions, bricks, tiles, and more can be a source of total chromium. Figure 7 shows the mercury concentrations in both CDWs and RAs. The results showed mercury releases close to the regulatory limit of 1 \(\upmu\)g/L in both CDWs and RAs. In particular, the greatest criticality was identified in RAs, in which 25% of all concentrations exceed the limit for recovery. These results confirm the considerations presented by the authors [PERSON] et al. [61] and [PERSON] et al. [62]. In particular, based on both compliance and availability test, the authors [PERSON] et al. [61] found mercury concentrations higher than those reported by other studies [36, 42] and above the permissible limits prescribed for inert waste landfills.