# The Experimental Study of Innovative Methods Regarding the Removal of Sm(III)
## 3 Results and Discussion
### Extraction Results  
In this paper, the possibility of using sodium dodecyl sulfate for the removal of Sm3+ by extraction with isocotyl alcohol is studied (Figure 5). The 0.001 M standard test solutions of Sm3+ nitrates were used.  
The extraction was conducted for 30 min. Aqueous and organic phases were separated in separate funnels of 0.25 or 0.5 L in capacity. Phase separation occurred over 3 to 5 days. The aqueous phase was analyzed by a photometric method for REE cations content. The form of salts extracted to the organic phase was determined by the IR spectroscopy method [35].  
Sodium dodecyl sulphate (NaDS) is insoluble in non-polar solvents and, moreover, it is practically insoluble in alcohols. In this study, sodium dodecyl sulphate was added to the aqueous phase and isooctyl alcohol (C\({}_{8}\)H\({}_{18}\)O, 2-ethyl-1-hexanol) was used as an extractant.  
During the experiment, it was discovered that NaDS goes to into the organic phase in the form of Ln(C\({}_{12}\)H\({}_{25}\)OSO\({}_{3}\))\({}_{3}\) solutes. Solubility can be explained by the polar group orientation towards the cation and solvate screening from the outer side by non-polar radicals. Apparently, alcohol molecules interact with REE cations as well, which confirms the stretching frequency \(\mathbf{v}_{\text{o-H}}\) shift and the lack of lanthanide dodecyl sulphate dissolution in non-polar solvents [35].  
Figure 5: Scheme of the extraction process in the NaDS—Sm(NO3)3—2-octanol system.  
Certain experiments showed that rare earth elements are poorly extracted by alcohol in the absence of NaDS. When extracting holmium (III) cations at pH = 6.0, K\({}_{\text{distr}}\) was 4.46, whereas in the presence of sodium dodecyl sulphate, it was 360. Thus, isocotyl alcohol is an extractant, while NaDS acts as a carrier agent. Thus, the proposed extraction technique in the system, namely sodium dodecyl sulphate--lanthanide salt aqueous solution--isooctyl alcohol, significantly increases K\({}_{\text{distr}}\) in the studied solutions.  
Figure 6 shows the results of the experimental study of samarium (III) extraction. The initial concentration of REE was 0.001 M and the sodium dodecyl sulphate concentration corresponded to the chemical reaction (1) stoichiometry and was 0.003 M. The organic phase volume (V\({}_{\text{org}}\)) was 5 mL and aqueous phase volume (V\({}_{\text{aq}}\)) was 200 mL, i.e., the ratio V\({}_{\text{org}}\):V\({}_{\text{aq}}\) = 1:40.  
During the extraction, the dependence of K\({}_{\text{distr}}\) from pH was weak and Sm\({}^{3+}\) has the maximum K\({}_{\text{distr}}\) at pH = 5.0. The distribution coefficient is significantly higher than when extracting by carboxylic acids. Removal from acidic mediums is possible.  
Table 5 shows the results of the Sm\({}^{3+}\) extraction with different initial concentrations at pH = 4.0.  
According to the extractant efficiency series, as shown in Table 6, one can come to the conclusion that sodium dodecyl sulphate has the most negative Gibbs energy of solvation \(\Delta_{\text{S}}\)G\({}^{2}\)298 and correspondingly the maximum K\({}_{\text{distr}}\). In addition, it was discovered that when saturating isooctyl alcohol with sodium dodecyl sulphate, the spectrum remained unchanged, which demonstrates NaDS insolubility in alcohol [35].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{\(\Delta_{\text{S}}\)G\({}^{2}\)298,} & & & & \\
**kj/mol** & **TBP** & **TABAN** & **HNaft** & **Hol** & **NaDS** \\ \hline Ce & \(-4.1\pm 0.2\) & \(-7.9\pm 0.5\) & \(-27.6\pm 0.4\) & \(-33.1\pm 0.4\) & - \\ Sm & - & - & \(-22.2\pm 0.5\) & \(-35.8\pm 0.5\) & \(-70.0\pm 0.5\) \\ \hline \hline \end{tabular} Abbreviations: TBP, tributyl phosphate; TABAN, trialkylbenzyl ammonium nitrate; HNaft, napthemic acid; and Hol, oleic acid.  
\end{table}
Table 6: Gibbs energy of solvation when extracting Ce and Sm by different extractants [34].  
Figure 6: Samarium (III) cations’ distribution coefficients as a function of solution pH.