## 4 Results and Discussion
### Estimation of biogeochemical Mineral Neoprecipitation  
Two precipitate generation phenomena were recorded in the experiments after whey addition. The first (bright coloured) precipitate appeared a few hours after cultivation. The second (dark coloured) precipitate originated after the reduction of sulphate ions for 1-6 months. Scanning electron microscopy (SEM) solid-phase analysis revealed two dominant phases differing in both morphology and particle composition. The first phase (Figure 6A) is represented by heterogeneous particles with abundant sharp faces; the appearance of this phase in the first hours after mixing the solutions suggests that the disequilibrium of the solution arising from mixing is the source of its formation. The phase contains high concentrations of phosphorus and calcium without uranium. The second phase is a sintered aggregate containing a large number of spherical and elongated particles of 1-5 \(\upmu\)m (Figure 6B). This phase contains considerably more S, Fe, Na, and K, with high concentrations of uranium of up to 5.36 wt. % (Table 8). According to the chemical composition, we may assume that sulphides were added to the first (apatite-like) phase over time, as evidenced by the sharp drop in the concentration of sulphate in the solution (Figure 3). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Phase**} & \multicolumn{10}{c}{**Element, wt. \%**} \\ \cline{3-14}  & & **Si** & **Al** & **Fe** & **Mg** & **Ca** & **Na** & **K** & **Ni** & **U** & **P** & **S** & **Cl** & **O** \\ \hline
1 & A & 0.38 & 0.33 & 0.29 & 1.87 & 25.8 & 0.98 & 0.15 & n.d. & n.d. & 15.19 & 0.31 & 0.19 & 54.51 \\
2 & A & 0.42 & 0.38 & 0.37 & 2.09 & 24.53 & 0.81 & 0.1 & n.d. & n.d. & 14.95 & 0.19 & 0.16 & 56 \\
3 & A & 0.35 & 0.3 & 0.25 & 1.75 & 22.65 & 1.05 & 0.12 & n.d. & n.d. & 16.52 & 0.22 & 0.19 & 56.6 \\
4 & A & 0.54 & 0.44 & 0.44 & 1.6 & 20.99 & 0.99 & 0.11 & 0.1 & n.d. & 14.7 & 0.2 & 0.21 & 59.68 \\
5 & A & 0.36 & 0.31 & 0.22 & 1.99 & 23.23 & 0.87 & 0.19 & 0.15 & n.d. & 13.9 & 0.29 & 0.25 & 58.24 \\
6 & B & 0.74 & n.d. & 0.47 & 2.19 & 20.79 & 6.07 & 0.4 & n.d. & 2.2 & 11.15 & 1.8 & 1.53 & 52.67 \\
7 & B & 0.92 & n.d. & 0.78 & 2.19 & 18 & 6.76 & 0.88 & n.d. & 5.36 & 10.41 & 2.4 & 1.77 & 50.51 \\
8 & B & 0.96 & n.d. & 0.64 & 2.29 & 19.43 & 6.56 & 0.64 & 0.34 & 5.23 & 11.12 & 2.2 & 1.65 & 48.95 \\
9 & B & 0.83 & n.d. & 0.62 & 2.19 & 19.39 & 6.415 & 0.64 & n.d. & 3.78 & 10.78 & 2.1 & 1.65 & 51.59 \\
10 & B & 0.88 & n.d. & 0.73 & 2.13 & 19.05 & 7.06 & 0.62 & 0.41 & 4.12 & 13.08 & 2.41 & 1.57 & 47.94 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Elemental composition of the precipitate phases after whey addition. Figure 6: First (bright) phase (**A**) and second (dark) phase (**B**) of the precipitate (see Table 8 for the composition). Based on the data obtained, it can be concluded that nitrate reduction can be successfully activated by the addition of organics to groundwater aquifers in situ. A decrease in nitrate concentration reduces the migration activity of uranium since the associated decrease in Eh leads to uranium reduction and immobilization. The risk-free prediction of uranium behaviour and risk assessment of uranium remobilization remain important tasks. There are a group of factors that determine the behaviour of uranium in biochemical processes and have different influences on its (im)mobilization. These factors include the following:  
* Microbial catabolic reduction of uranium, leading to the formation of an amorphous uranium phase (\"biogenic uraninite\"), which has a much higher solubility than other forms of uranium (uraninite logK\({}_{\text{s}}\) -4.84; UO\({}_{\text{2(am)}}\) logK\({}_{\text{s}}\) 0.11) and is very important for the design of more effective posttreatment reduction strategies. * Uranium sorption on rocks that can be covered by biofilms of different compositions and intensities.