# The Experimental Study of Innovative Methods Regarding the Removal of Sm(III)
## 3 Results and Discussion
### Results of the Ion Flotation Method
Conductometric titration was carried out as follows: 10 mL aliquots of Sm(NO)\({}_{3}\) solution with the concentration of 0.001 mol\(\cdot\)kg\({}^{-1}\), acidified by nitric acid down to pH = 3 (approximately), were titrated with 0.002 N solution of NaOH. After the addition of each portion of 1-2 mL alkali solution, the solution was agitated until the establishment of the constant value of specific electrical conductivity, measured by the \"Anion 4100\" conductometer. At the same time, the pH value was measured by the \"Anion 7010\" ion meter. After the results, the titration curve was plotted as shown in Figure 4.  
By analyzing these relationships, we see that at pH = 5.3, there was a break in the curve of the specific electrical conductivity as a function of the added alkali with a transition to an almost horizontal part, which shows the added hydroxyl anions' fixation into poorly dissociated compounds. As the formation of hydroxides was not observed (optical density of solutions did not change), this part was responsible for the formation of hydroxo-complexes. By the quantity of milliequivalents of alkali used here, one can determine that the process flows until the formation of Sm(OH)\({}^{2+}\) monohydroxo-complexes. The specified pH value was taken as the pH of the complex formation onset of pH\({}_{\text{compl}}\). Upon the completion of the complex formation, a near-linear growth of electrical conductivity with the addition of alkali was observed. At pH = 6.49, the growth of electrical conductivity stops. This part of the titration curve corresponds to the hydroxide sedimentation. The latter was observed visually and confirmed by an increase in the optical density of solutions. The quantity of milliequivalents of alkali used here meets the following reaction: Sm(OH)\({}^{2+}\) + OH\({}^{-}\) = Sm(OH)\({}_{3}\). The pH value corresponding to the horizontal part of the titration curve was taken as the pH of hydrate formation pH\({}_{\text{hydr}}\). Furthermore, on the titration curve, the near-linear growth of the specific electrical conductivity was observed because of the excess alkali. The obtained calculated values are shown in Table 2.  
Figure 4: Specific electrical conductivity of the Sm(NO)\({}_{3}\) solution and pH as a function of the NaOH solution volume in the course of conductometric titration. The obtained Gibbs energy value of the Sm(OH)\({}_{3}\) formation agrees well with the database [32], in which the value of \(-1281.56\)\(\pm\)\(3.77\) kJ/mol is specified (Table 2). The Gibbs energy value of samarium hydroxo-complex differs greatly from literature data, namely from \(-848.10\)\(\pm\)\(3.35\)[32] and \(-859.95\)[33]. We calculated the values of Sm(OH)\({}^{2+}\) hydroxo-complex instability constants according to data from [32; 34] and calculated the values \(8.4\)\(\times\)\(10^{-6}\) and \(3.47\)\(\times\)\(10^{-7}\), corresponding to the pH of the complex formation onset by Formula (2), equal to \(8.0\) and \(6.7\). These values, however, were higher than the pH values of the hydrate formation that we determined and calculated based on \(\Delta\)/\(G^{0}\)\({}_{298}\) Sm(OH)\({}_{3}\) from the reference book [34]. This is contradictory as the formation of hydroxo-complexes should carry at a pH below the pH of the hydrate formation and precede the hydroxide precipitation.