## 3 Results
### Modeling Adsorption from Uranium in Solution
#### 3.2.3 Transport Modeling in URP Columns  
Table 7 shows the U concentrations of the URP**6** sediments. WURP**6** samples show increasing U concentrations for longer times of the experiment, suggesting possible displacement of uranophane U along the column (see Appendix B, Table B6, from samples 2 to 6). Cation concentrations are shown in Appendix B.1, Table B2. The concentrations of the solid samples URP6 CSC and URP6 FSC are much higher than those of the original sediments (see Section 3.1). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**UN12**} \\ \hline
**Sample Type** & **ID Sample** & \({}^{234}\)**U Bq kg\({}^{-1}\)** & \({}^{238}\)**U Bq kg\({}^{-1}\)** & **RQ (\%)** & \({}^{238}\)**U mg kg\({}^{-1}\)** \\ \hline \multirow{6}{*}{Solid} & UN12 CSC & \(1104\pm 21\) & \(2269\pm 40\) & 90 & 184 \\ \cline{2-6}  & UN12 FSC & \(803\pm 17\) & \(1532\pm 30\) & 85 & 124 \\ \cline{1-1} \cline{2-6}  & UN12 CS & \(1151\pm 21\) & \(2222\pm 37\) & 74 & 180 \\ \cline{1-1} \cline{2-6}  & UN12 PS & \(811\pm 16\) & \(1810\pm 32\) & 98 & 147 \\ \cline{1-1} \cline{2-6}  & UN12C\({}_{1}\) & \(1816\pm 25\) & \(3736\pm 48\) & 80 & 303 \\ \cline{1-1} \cline{2-6}  & UN12C\({}_{2}\) & \(1148\pm 22\) & \(2149\pm 39\) & 92 & 174 \\ \hline \multirow{3}{*}{Superantant} & \multicolumn{3}{c}{\({}^{234}\)U Bq L\({}^{-1}\)} & \({}^{238}\)U Bq L\({}^{-1}\) & RQ (\%) & \({}^{238}\)U mg L\({}^{-1}\) \\ \cline{2-6}  & WUN12 CSC & \(4.5\pm 0.1\) & \(8.9\pm 0.2\) & 58 & 0.72 \\ \cline{1-1} \cline{2-6}  & WUN12 FSC & \(2.68\pm 0.04\) & \(5.5\pm 0.1\) & X & 0.45 \\ \hline \hline \end{tabular}  
* The uncertainty of the supernatant solution experiments is approximately 15%, see Appendix A.1.  
\end{table} 
Table 6: U activity concentration in solid samples and the supernatant solutions * of the UN12 column. U concentrations in URP12 sediments are presented in Table 8. The effluents from the WURP12 column showed U concentrations below the detection limit. Cation concentrations are shown in Appendix B.1, Table B2. The concentration values of U in WURP6 and the U in solid samples of URP6 can be explained by the entrainment of uranium in the form of uranophane ore particles or dissolved, entrained along the column. However, uranium concentrations in the water of the URP12 experiment are not detected, and the values in the sediments are much lower than those of URP6. In the URP12 experiment, organic matter was formed at the top (see Appendix B.3, Figure B7). U in (UO2)\({}^{2+}\) could be reduced and precipitated [64]. U concentrations in URP12 sediments were attributed to U being transported in particulate form (see below). The CS and FSC materials acted as a filter and trapped the uranophane particles that managed to pass through the fine sand. Samples WURP6 CSC, WURP6 FSC, WURP12 CSC, and WURP12 FSC have U concentrations between 0.03 and 0.1 mg L\({}^{-1}\). Because the differences in U concentration between the solutions of the WURP6 and WURP12 fractions are insignificant, it is difficult to elucidate whether a desorption process occurred. However, if the presence of URP12 organic matter is considered, the U concentrations in WURP12 CSC and WURP12 FSC can be attributed to uranophane particles transported to the CSC and FSC segments. To elucidate whether U transport occurs in particulate or dissolved form, the sediments of the CS, FS, C\({}_{1}\), and C\({}_{2}\) fractions were observed by SEM-EDS (see Appendix B.3, Figures B5 and B6). The obtained spectra did not reveal the presence of uranium, indicating that its concentration is below the detection limit.