## 3 Results  
### By-Products Characterization  
The ASEC treatment of the three samples resulted in the complete removal of the dissolved elements from the liquid samples yielding pure water and crystallized solids with a moisture content of <1% (Figure 2). The whole volume of liquid sample treated was collected at the output of the ASEC system as clean/transparent water for each one of the samples. On the other hand, solids were also collected as dried conglomerates (Figure 2). The solid samples were weighted as 27.3 g/L of dried solids for the Rio Tinto river sample, 30.21 g/L for the Tharsis sample, and 68.73 g/L of dried solids for the dredged material sample. There was a recovery of almost 100% of the injected volume of each sample (50 L) as transparent water, as shown in Figure 2. The depurated obtained water showed properties similar to pure water: pH-6.5-7, EC < 56 \(\mu\)S/cm, TDS< 0.03 mg/L, and the complete removal of the dissolved elements (Table 1). In the case of the mining residues (I\({}_{\text{RioTinto}}\), I\({}_{\text{Thrasis}}\)), there was a sharp rise in pH, from 3.70 and 3.15 to pH values of typical pure water 6.69 and 6.79, respectively. The electrical conductivity (EC) decreased in magnitude from mS to \(\mu\)S, from 2.5 mS/cm for I\({}_{\text{RioTinto}}\) and 12 mS/cm for I\({}_{\text{Thrasis}}\) to values of EC below 55 \(\mu\)S/cm. The high concentrations of acidity, sulphate, metals and metalloids (such as Fe, Al, Cu, Zn, As, Co, Cd, Ni), and REE in these mining samples are the resultant product of the intense sulphide oxidation processes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & & \multicolumn{2}{c}{**Input**} & \multicolumn{3}{c}{**Output**} \\ \hline  & & **I\({}_{\text{RioTinto}}\)** & **I\({}_{\text{Thrasis}}\)** & **I\({}_{\text{Dedged}}\)** & **O\({}_{\text{RioTinto}}\)** & **O\({}_{\text{Thrasis}}\)** & **O\({}_{\text{Dedged}}\)** \\ \hline Ph & & 3.70 & 3.15 & 7.27 & 6.69 & 6.79 & 7.82 \\ EC & \(\mu\)S/cm & 2450 & 12,140 & 52,300 & 55.5 & 35.8 & 40.4 \\ TDS & mg/L & 1516 & 7530 & 32,400 & 0.034 & 0.022 & 0.025 \\ T & \({}^{\circ}\)C & 10.1 & 15.0 & 11.9 & 9.1 & 14.2 & 10.3 \\ Li & ppb & 177.1 & 1356 & 166.9 & n.d. & n.d. & n.d. \\ B & ppb & 255.1 & 92.9 & 5367 & n.d. & n.d. & n.d. \\ Na & ppm & 41.65 & 67.44 & 12.90 & n.d. & n.d. \\ Mg & ppm & 88.14 & 1.29 & 1609 & n.d. & n.d. & n.d. \\ Al & ppb & 85,070 & 806,164 & 59.6 & n.d. & n.d. & n.d. \\ \hline \end{tabular}
\end{table} 
Table 1: Physicochemical properties of samples (Rio Tinto River, Thrasis mine, and dredged material) before (Input: I) and after (Output: O) treatment with ASEC technology. Figure 2: Collected samples (**top left**) and the treated fluid (**top right**) from the Rio Tinto river, Thrasis mine and the dredged material. Below are the results in crystallized solids after the treatment with ASEC technology. In the case of the dredged material sample (I\({}_{\text{Dredged}}\)), the pH was not as low (7.27), but the O sample showed a slightly increased pH of 7.82. Instead, the strong EC of 52.3 mS/cm and the TDS of 32,400 mg/L decreased sharply to 40.4 \(\upmu\)S/cm and 0.025 mg/L in the treated water, but also removal of all studied elements was observed in the O\({}_{\text{Dredged}}\). The mineralogy of the collected solid samples from Rio Tinto, Tharsis and Huelva was analyzed using XRD (Figure 3). The elemental composition of the solid by-product from the Rio Tinto river mining sample after treatment of the water with ASEC technology was 41% S and 35% Fe. These elements appear as hydrated sulphates of Zn, Cu and Al [46] thoughout XRD (Figure 4). A similar composition was observed for solids collected after the treatment of the Tharsis sample, where the major composition was iron sulphates, and other oxyhydrosulphates, such as Mn, Ca, Zn or Al, but some iron oxides were also detected (Figure 4). The AMD solid particle sample examination showed that trace elements are included within a matrix of large trace element-rich Fe sulphate particles and Fe-Mn oxides [46] (Figure 4).