## 3 Results
### By-Products Characterization
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & & **Input** & & & **Output** & \\ \hline  & & **I\({}_{\text{RioTinto}}\)** & **I\({}_{\text{Tharsis}}\)** & **I\({}_{\text{Dredged}}\)** & **O\({}_{\text{RioTinto}}\)** & **O\({}_{\text{Tharsis}}\)** & **O\({}_{\text{Dredged}}\)** \\ \hline K & ppm & 6.0 & 4.6 & 500 & n.d. & n.d. & n.d. \\ Ca & ppm & 4.3 & 20.2 & 50.8 & n.d. & n.d. & n.d. \\ Cr & ppb & 912 & 298 & n.d. & n.d. & n.d. & n.d. \\ Mn & ppm & 8.4 & 134 & 1.07 & n.d. & n.d. & n.d. \\ Fe & ppm & 162 & 2844 & 12.6 & n.d. & n.d. & n.d. \\ Co & ppb & 547 & 9348 & 4.5 & n.d. & n.d. & n.d. \\ Ni & ppb & 93.0 & 4076 & 1.4 & n.d. & n.d. & n.d. \\ Cu & ppb & 116,239 & 186,798 & 16,340 & n.d. & n.d & n.d \\ Zn & ppb & 18,173 & 367,775 & 1108 & n.d. & n.d & n.d. \\ As & ppb & 2593 & 5821 & 470.7 & n.d. & n.d. & n.d. \\ Se & ppb & 2403 & 1511 & 1481 & n.d. & n.d. & n.d. \\ Ag & ppb & 12.7 & 11.9 & 11.8 & n.d. & n.d. & n.d. \\ Cd & ppb & 90.3 & 967.0 & n.d. & n.d. & n.d. \\ Ba & ppb & 46.5 & 347.9 & 104.6 & n.d. & n.d. & n.d. \\ Pb & ppb & 199.0 & 80.1 & n.d. & n.d. & n.d. & n.d. \\ Sr & ppb & 179.3 & 224.5 & 10,127 & n.d. & n.d. & n.d. \\ La & ppb & 27.3 & 270.4 & 2.8 & n.d. & n.d. & n.d. \\ Ce & ppb & 66.5 & 795.0 & n.d. & n.d. & n.d. & n.d. \\ Pr & ppb & 14.9 & 112.1 & n.d. & n.d. & n.d. & n.d. \\ Nd & ppb & 44.6 & 495.3 & n.d. & n.d. & n.d. & n.d. \\ Sm & ppb & 19.2 & 149.3 & n.d. & n.d. & n.d. & n.d. \\ Eu & ppb & 9.9 & 39.4 & n.d. & n.d. & n.d. & n.d. \\ Gd & ppb & 19.7 & 173.3 & n.d. & n.d. & n.d. & n.d. \\ Tb & ppb & 8.4 & 30.5 & n.d. & n.d. & n.d. & n.d. \\ Dy & ppb & 17.1 & 137.2 & n.d. & n.d. & n.d. & n.d. \\ Ho & ppb & 7.2 & 29.6 & n.d. & n.d. & n.d. & n.d. \\ Er & ppb & 11.7 & 69.6 & n.d. & n.d. & n.d. & n.d. \\ Tm & ppb & 6.3 & 12.9 & n.d. & n.d. & n.d. & n.d. \\ Yb & ppb & 10.1 & 56.8 & n.d. & n.d. & n.d. & n.d. \\ Th & ppb & 24.5 & 732.3 & 100.8 & n.d. & n.d. & n.d. \\ U & ppb & 62.4 & 320.9 & 9.7 & n.d. & n.d. & n.d. \\ Y & ppb & 86.5 & 1801 & n.d. & n.d. & n.d. & n.d. \\ Mo & ppb & n.d. & 51.3 & n.d. & n.d. & n.d. & n.d. \\ Au & ppb & n.d. & 0.9 & 0.48 & n.d. & n.d. & n.d. \\ \hline \end{tabular} n.d.: not detected.  
\end{table} 
Table 1: _Cont._Meanwhile, the dredged material mineralogy is dominated by iron-bearing silicates, where some toxic elements (Cu, Zn, Ni, etc.) (Figures 3 and 4) are preserved by weathering and soil forming processes as less reactive and mobile [47]. Some elements found in elevated concentrations, such as Cu, Cd, Zn or As, are mainly associated with discharges of the Odiel-Rio Tinto watershed due to mining activity [47]. But the binding of these elements also depends on the pH of elements (Table 1), e.g., for low pH, iron and S are associated with As and Pb. In contrast, the estuarine mixing processes promote the precipitation of Fe and Al oxyhydroxysulfates (pH \(<\) 6), so contaminants (Cu, Cd, Zn) are associated with S [48]. The main mineral formations found were anhydrous sulphate of Zn, and other sulphates of Cu, Al, and Fe in the Rio Tinto solid sample. In the Tharsis sample, Fe-sulphides prevailed, along with anhydrous sulphate of Fe, oxyhydroxide of manganese (manganite), sulphate of Zn, and Cu sulphides, among others (Figure 4). SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\) and CaO are the main chemical compositions of dredged material determined by various authors [11]. In the case of sediments from the Ria of Huelva, apart from the industrial activities (acid mining), there are further salt-induced physical mixing processes and muddy deposits, bioturbation, and urban wastes from the vicinity of Huelva. Contamination input also stems from harbouring activities, the presence of phosphoglysum deposits (from the fertilizer industry), and phosphate carbonates rich in Fe storage [49]  
Figure 3: Elemental composition (in %) of the crystallized solid samples from Rio Tinto (**a**), Tharsis (**b**) and dredged material (**c**) after ASEC deportation.