5 Metallic Technetium, Corrosion, Technetium Alloys …
127
are rapidly oxidized by HNO 2 to Tc(IV) and Tc(V). The latter are reduced back
to Tc(III) at the electrode surface. Tc(IV) and Tc(V) undergo a hydrolysis process,
which leads to the formation of poorly soluble hydroxocomplexes. The current efficiency of the Tc electrodeposition on a graphite electrode (S/V = 2500 m
−1 ) in 1 M
HNO 3 is low and for 2 h of the electrolysis it is equal to 9.05, 23.5 and 35.0% for −
0.5, 0.8 and −1.2 V, respectively.
Hoshi et al. (2007) investigated the electroreduction of the pertechnetates in 0.1–
9 M HNO 3 with addition of 0.1 M N 2 H 4 . The electroreduction was carried out at −
0.3 V (vs. Ag, AgCl) using a glassy carbon fiber electrode in a flow-type electrolysis cell. The solution remaining after completing the process was analyzed using
UV–Vis, which detected Tc(SCN)
2−
6 complex. These authors identified Tc(IV) as
the product of the pertechnetates electrochemical reduction. The more recent experiments performed in 6 M HNO 3 have shown that the reduction of the pertechnetates
in solutions containing Pu and Np ionic forms leads to formation of Tc(IV) (Hoshi
et al. 2007).
The electrochemical characterization of Tc–U–hydrazine systems in the basic
environment was of interest to Peretrukhin et al. (1998). The authors applied polarographic measurements with a hanging mercury drop electrode. They observed a
3-electron irreversible reduction of Tc(VII) to Tc(IV). The half-wave potential of
this redox couple was found to be equal to −0.69 V (vs. Ag, AgCl). A one-electron
reduction of U(VI) to U(V) was observed at −0.87 V. An analysis of the difference
in the potentials of reactions of both elements (E = about 0.18 V) led these authors
to the conclusion that Tc should interact with U(VI) and this process may partially
proceed with participation of unstable U(V) intermediates. Very complex chemical
processes were observed in 0.5–4 M NaOH solutions containing pertechnetates (1
× 10
−5
÷ 2 × 10
−4 mol dm
−3 ), N 2 H 5 NO 3 (0.01–0.3 M) and sodium uranate. At
room temperature, N 2 H 5 NO 3 completely reduced pertechnetates in such solutions
within 5–10 min. An interaction of hydrazine with of 2 × 10
−4 M Tc(VII) and 2
× 10
−4 M U(VI) in 0.5 and 2 M NaOH led to formation of Tc(IV) hydrous oxide,
which changes the solution color to brown-reddish. The complete reduction of the
pertechnetates was confirmed by electrochemical measurements. A decrease in the
concentration of U(VI) in the solution was attributed to its sorption and/or polymerization at the surface of TcO 2 ·xH 2 O as well as its partial reduction by hydrazine in
the presence of Tc(IV) to U 3 O 8 ·nH 2 O and UO 2 ·nH 2 O.
The electrochemical studies on the pertechnetates reduction in an alkaline environment with high ionic strength solutions (up to 2 M NaOH and 5 M NaNO 3 ) have
been reported by Chatterjee et al. (2018). The authors noted unexpected stability
of Tc(VI or V?) forms. Also Chotkowski (2018) examined the mechanism of the
pertechnetates reduction in NaOH solutions with concentration of up to 10 M NaOH.
The results of both works are discussed in detail in Chap. 3.
The catalytic properties of technetium in the solutions containing hydrazine and
selected actinides were also discussed by other authors (e.g. Koltunov et al. 1986;
Kemp et al. 1993; German et al. 2011; Marchenko et al. 2008; Zhou et al. 2014). These
works analyzed reduced technetium species generated under various experimental
127
are rapidly oxidized by HNO 2 to Tc(IV) and Tc(V). The latter are reduced back
to Tc(III) at the electrode surface. Tc(IV) and Tc(V) undergo a hydrolysis process,
which leads to the formation of poorly soluble hydroxocomplexes. The current efficiency of the Tc electrodeposition on a graphite electrode (S/V = 2500 m
−1 ) in 1 M
HNO 3 is low and for 2 h of the electrolysis it is equal to 9.05, 23.5 and 35.0% for −
0.5, 0.8 and −1.2 V, respectively.
Hoshi et al. (2007) investigated the electroreduction of the pertechnetates in 0.1–
9 M HNO 3 with addition of 0.1 M N 2 H 4 . The electroreduction was carried out at −
0.3 V (vs. Ag, AgCl) using a glassy carbon fiber electrode in a flow-type electrolysis cell. The solution remaining after completing the process was analyzed using
UV–Vis, which detected Tc(SCN)
2−
6 complex. These authors identified Tc(IV) as
the product of the pertechnetates electrochemical reduction. The more recent experiments performed in 6 M HNO 3 have shown that the reduction of the pertechnetates
in solutions containing Pu and Np ionic forms leads to formation of Tc(IV) (Hoshi
et al. 2007).
The electrochemical characterization of Tc–U–hydrazine systems in the basic
environment was of interest to Peretrukhin et al. (1998). The authors applied polarographic measurements with a hanging mercury drop electrode. They observed a
3-electron irreversible reduction of Tc(VII) to Tc(IV). The half-wave potential of
this redox couple was found to be equal to −0.69 V (vs. Ag, AgCl). A one-electron
reduction of U(VI) to U(V) was observed at −0.87 V. An analysis of the difference
in the potentials of reactions of both elements (E = about 0.18 V) led these authors
to the conclusion that Tc should interact with U(VI) and this process may partially
proceed with participation of unstable U(V) intermediates. Very complex chemical
processes were observed in 0.5–4 M NaOH solutions containing pertechnetates (1
× 10
−5
÷ 2 × 10
−4 mol dm
−3 ), N 2 H 5 NO 3 (0.01–0.3 M) and sodium uranate. At
room temperature, N 2 H 5 NO 3 completely reduced pertechnetates in such solutions
within 5–10 min. An interaction of hydrazine with of 2 × 10
−4 M Tc(VII) and 2
× 10
−4 M U(VI) in 0.5 and 2 M NaOH led to formation of Tc(IV) hydrous oxide,
which changes the solution color to brown-reddish. The complete reduction of the
pertechnetates was confirmed by electrochemical measurements. A decrease in the
concentration of U(VI) in the solution was attributed to its sorption and/or polymerization at the surface of TcO 2 ·xH 2 O as well as its partial reduction by hydrazine in
the presence of Tc(IV) to U 3 O 8 ·nH 2 O and UO 2 ·nH 2 O.
The electrochemical studies on the pertechnetates reduction in an alkaline environment with high ionic strength solutions (up to 2 M NaOH and 5 M NaNO 3 ) have
been reported by Chatterjee et al. (2018). The authors noted unexpected stability
of Tc(VI or V?) forms. Also Chotkowski (2018) examined the mechanism of the
pertechnetates reduction in NaOH solutions with concentration of up to 10 M NaOH.
The results of both works are discussed in detail in Chap. 3.
The catalytic properties of technetium in the solutions containing hydrazine and
selected actinides were also discussed by other authors (e.g. Koltunov et al. 1986;
Kemp et al. 1993; German et al. 2011; Marchenko et al. 2008; Zhou et al. 2014). These
works analyzed reduced technetium species generated under various experimental