# Assessment of Characteristics of Acid Mine Drainage Treated with Fly Ash
## 3 Results and Discussion
### AMD Quality Analysis and Neutralization Potential  
In the present research, AMD analysis revealed low pH, high TDS concentrations, electrical conductivity and various elemental ions (Table 3). Considerable neutralization of AMD was achieved with the addition of fly ash, as shown in Table 4. Fly ash showed a pH of 12, and as such the pH of AMD was elevated from 2.5 to 6.0 within 35 days (Figure 5). There was a decreasing trend in all chemical species of the leachate. The pH remained relatively constant after 35 days of the experiment. These results may be attributed to the fly ash Ca-bearing minerals [23]. It has also been postulated that CaO reacts with the other silicos and aluminous materials of the fly ash and forms cementitious complexes that stabilize AMD's leaching elements [25]. Comparison of the four samples showed that the highest CaO content was found in the Anpara TPP fly ash. However, silicates and aluminum and ferrous oxides also contribute to acid buffering at low pH [23].  
Electrical conductivity and TDS of the treated AMD were reduced. All of the leachates showed an initial decrease in the sulfate concentrations. This was due to the formation of CaSO\({}_{4}\) upon reaction with the fly ash. Al concentration decreased from 33.7 mg L\({}^{-1}\) to 21.0 mg L\({}^{-1}\). It was believed that the aluminum reacted with the silica in the ash and formed more mullite. In general, the heavy-metal concentrations decreased. B, Ba, Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr and Zn concentrations were all low and decreased to undetectable  
Figure 4: SEM images (2 μm) of fly ashes from Anpara, Shaktinagar, Renusagar and Vindhyachal TPPs.  
levels. In brief, after the described laboratory experiment, the physicochemical parameters of the AMD from the abandoned mine were under the permissible limits for release in water catchments.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter \({}^{*}\)**} & \multirow{2}{*}{**Unit**} & \multicolumn{4}{c}{**Thermal Power Plant**} \\ \cline{3-5}  & & **Anpara** & **Renusagar** & **Shaktinagar** & **Vindhyachal** \\ \cline{3-5}  & & & \multicolumn{4}{c}{**Concentration**} \\ \hline pH & – & 6.0 & 6.0 & 6.0 & 6.0 \\ EC & \(\mu\)S/m & 765.0 & 780.0 & 735.0 & 752.0 \\ TDS & ppm & 682.0 & 675.0 & 695.0 &  
The amount of fly ash required to reach acceptable limits is approximately 4-5 times higher than the lime requirement; therefore, high amounts of fly ash can be disposed of. It should be noted that fly ash may contain metals of toxicological concern, such as Cd, Cr, Co, Ni and Pb [35]; these metals may leach into the environment during the AMD neutralization process, creating additional problems. If high amounts of fly ash are used, more metals are released into the environment [23]. So, only 30% of the produced fly ash was used in this experiment. Nevertheless, these elements' leaching can be limited by maintaining near-neutral pH conditions and adding materials that can absorb and adsorb them. It is known that the mine waste material itself can achieve the latter [22]; furthermore, low AMD pH is counterbalanced by high fly ash pH, and vice versa [34], so near-neutral conditions can be achieved. The remaining materials (treated AMD) may be processed further (for example, with zeolite), and the solid residue may be used as a mine backfill material for a true zero-waste environmental management scheme [24].