# Determination of Arsenic Species Distribution
## 4 Results of Geochemical and Geophysical Studies
### Arsenic Species  
As a result of the sequential extraction procedure, the arsenic content was estimated in the fractions of the leaching solutions to determine the percentage of different arsenic species. The content of element species (C) in the solid was calculated using the formula:  
\[\mathrm{C(mg/kg)=C(mg/L)*V(L)/m(kg)} \tag{1}\]  
where V is the volume of solution in liters (L), and m is the sample weight (kg). Table 4 shows the results of the analysis of the content of arsenic in various fractions, both in solutions of stepwise leaching and in terms of solid tailings. The distribution of arsenic species by fraction in the solid, shown in Table 4, was evaluated according to the results:  
1. In total, 9.3% of the total arsenic is represented by water-soluble forms, specifically--3.7% of As\({}^{\mathrm{V}}\) and 5.6 % of As\({}^{\mathrm{III}}\) (for example, in Mg, Ca, ammonia, arsenate, and arsenate according to its solubility product);
2. in total, 30% is represented by bound/co-precipitated with magnesium, i.e., potentially water-soluble forms, 18% of As\({}^{\mathrm{V}}\) and 12% of As\({}^{\mathrm{III}}\) (corresponding to Mg and Ca arsenates and arsenates remaining in the precipitate according to their solubility product);
3. in total, 17% is represented by adsorbed on the surface of carbonates (calcite and dolomite) 9.8% of As\({}^{\mathrm{V}}\) and 7% of As\({}^{\mathrm{III}}\);
4. in total, 17% is associated with oxides/hydroxides of iron/manganese, of which 9.3% is As\({}^{\mathrm{III}}\), 7.5% is As\({}^{\mathrm{V}}\);
5. in total, 19% is associated with easily oxidized minerals (residual arsenides and isomorphic admixture in sulfides) and organic material;
6. and in total, only 7.7% is accounted for by non-oxidized arsenic minerals (for example, As-crystallohydrates, As\({}^{\mathrm{III}}\) oxides). Thus, the percentage of the most mobile forms of arsenic is 56% of the total arsenic in tailings materials, represented by water-soluble forms (fraction F1), potentially water-soluble (fraction F2), and adsorbed on the surface of carbonates (fraction F3), of which 23% is As\({}^{\mathrm{III}}\) and 33% is As\({}^{\mathrm{V}}\) (Table 5). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Fraction** & **F1** & **F2** & **F3** & **F4** & **F5** & **F6** & \begin{tabular}{c} **Total** \\ **Content** \\ \end{tabular} \\ \hline \multirow{3}{*}{Solutions} & As\({}^{\mathrm{III}}\) & 3.1 \(\pm\) 0.5 & 13 \(\pm\) 1 & 7.6 \(\pm\) 0.3 & 10 \(\pm\) 1 & - & - & - \\  & As\({}^{\mathrm{V}}\) & 5.0 \(\pm\) 0.9 & 20 \(\pm\) 5 & 10 \(\pm\) 1 & 8 \(\pm\) 3 & - & - & - \\  & As\({}^{\mathrm{total}}\) & 8.1 \(\pm\) 0.8 & 33 \(\pm\) 5 & 18 \(\pm\) 1 & 18 \(\pm\) 3 & 33 \(\pm\) 0.5 & 12 \(\pm\) 1 & - \\ \hline \multirow{3}{*}{Solid} & As\({}^{\mathrm{III}}\) & 160 \(\pm\) 25 & 530 \(\pm\) 60 & 300 \(\pm\) 20 & 400 \(\pm\) 40 & - & - & \
\begin{tabular}{c} 1400 \(\pm\) 140 \\ (For F1-F4) \\ \end{tabular} \\ \cline{2-8}  & As\({}^{\mathrm{V}}\) & 240 \(\pm\) 50 & 770 \(\pm\) 160 & 420 \(\pm\) 45 & 320 \(\pm\) 130 & - & - &
\begin{tabular}{c} 1750 \(\pm\) 220 \\ (For F1-F4) \\ \end{tabular} \\ \cline{2-8}  & As\({}^{\mathrm{total}}\) & 400 \(\pm\) 40 & 1300 \(\pm\) 150 & 720 \(\pm\) 40 & 720 \(\pm\) 120 & 810 \(\pm\) 20 & 330 \(\pm\) 20 & 4300 \(\pm\) 600 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Arsenic content in solutions (mg/L) and solid tailings (mg/kg). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fraction** & **F1** & **F2** & **F3** & **F4** & **F5** & **F6** & **Share** \\ \hline As\({}^{\mathrm{III}}\) & 3.7 & 12 & 7.0 & 9.3 & - & - & 32 (For F1-F4) \\ As\({}^{\mathrm{V}}\) & 5.6 & 18 & 9.8 & 7.5 & - & - & 41 (For F1-F4) \\ As\({}^{\mathrm{total}}\) & 9.3 & 30 & 17 & 17 & 19 & 7.7 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Distribution of arsenic species in leach fraction solutions. %.