# Washing Batch Test of Contaminated Sediment:
## 3 Results
### Performance of Heavy Metal Removal with Sediment Washing  
The assessment of potential treatment capacity of sediment washing, in terms of heavy metal removal, was initially performed analyzing the results of the first experimental campaign. In this case, the washing tests were carried out with laboratory batch tests on the fine sediment fraction previously sieved (<63 \(\upmu\)m), as it more contaminated. The washing tests were conducted with:  
* EDTA, a widely used agent for contaminated sediment applications, which demonstrated good extraction efficiency for many heavy metals;
* citric acid, due to its high biodegradability, being a natural product, deriving from the metabolism of most living organisms;
* acetic acid, a more degradable and less toxic compound than EDTA, but having extractive and lower-cost properties; and
* deionized water, to study metal mobility. The comparison between the different selected chelating agents (Figure 2) shows that the most performing chelating agent, in terms of removal efficiency, is the citric acid. As far as the influence of concentration, it varies according to the chelating agent and the species to be complexed. In general, comparing the performances according to the concentration of the best agent (which is somehow very economical), it can be seen, already, that, at 0.05 M, the efficiencies are more than satisfactory, also on the basis of the reduction in the use of additives. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Composite Sample**} \\ \cline{3-5}
**Parameter** & **UM** & \multicolumn{1}{c}{**Unfractionated Sediment**} & **\textless{63 \(\upmu\)m}** & **\textgreater{63 \(\upmu\)m}** \\ \hline
**TPH (C\({}_{12}\)-C\({}_{40}\))** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & 13,567.400 & 17,840.900 & 9561.002 \\
**Ni** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & 19,482.100 & 37,430.320 & 500.900 \\
**Cu** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & 170.010 & 278.100 & 180.320 \\
**Pb** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & 8525.020 & 14,343.510 & 850.010 \\
**Cr** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & 11,090.300 & 19,411.150 & 704.310 \\
**Hg** & mg kg\({}_{\mathrm{DW}}\)\({}^{-1}\) & – & – & – \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the characterization conducted during the second survey campaign. On the other hand, the parallel study on contact time showed that as time increases, from 3 h to 24 h, the metal removal efficiencies increase and, in particular, in the case of the 1 M concentration of citric acid, a significant increase in performance was found. With respect to Hg, the increase in concentrations and contact time does not seem to favor a satisfactory decontamination. The highest efficiencies (\(\sim\)37%) were obtained with 1 M citric acid and 24 h contact time. In order to complete the survey scenarios, Figure 3 shows the most significant removal efficiency values for heavy metals using EDDS (in addition to EDTA. acetic and citric acid) and pH control, based on the tests carried out on the \"composite sample\" of the second investigation campaign. Figure 2: Efficiency of removal of inorganic pollutants in the washing tests of the first survey campaign. The comparison with the data reported in the previous paragraph confirms the general observations previously discussed:  
* citric acid, in general, has guaranteed for the heavy metals tendentially greater removal efficiencies, even more in an acidic environment (pH 4) and a contact time of 5 h; high removal efficiencies were obtained for Pb (80%) at 0.5 h, pH 4, and citric acid;
* in the case of the use of EDTA, the removal efficiencies of inorganic contaminants showed higher values in the basic environment (pH 9) and at the contact time of 5 h, although lower than the removal efficiencies achieved with citric acid; and
* in the case of EDDS it is the agent that showed the clearest removal efficiencies except for the Pb (\(\sim\)78%) at pH 9 and contact time of 5 h.  
Mercury deserves a separate discussion.