Optimization for removal of ruthenium from nitric acid solution by volatilizing with electrochemical oxidation

Figures & data

Figure 1. Schematic diagram of oxidation cell.

Figure 2. Schematic diagram of oxidation cell and condensate recovery for evaporation test.

Table 1. Experimental conditions of electrochemical oxidation.

	Temperature (°C)	Ce concentration (mg/L)	Reflux/Evaportion	Diaphragm
A	95	0	Reflux	O
B	50	0	Reflux	O
C	95	3.0×10^3	Reflux	O
D^*	95	0	Evaporation	O
E	95	0	Reflux	X
Note: *The same volume of nitric acid(0.01 M) was added as evaporated one, so as to keep electrolyte as the same volume and acidity.

Table 2. Relative oxidation/reduction potential for ruthenium species (vs. SHE).

Table 3. Oxidation/reduction potentials(V) for Ru valency.

Ag/AgCl		SHE		Reaction
E pa	E pc	E pa	E pc
1.5	1.32	1.70	1.52	Ru(8) ↠ Ru(4),(3.75)
				Ru(7) ↠ Ru(4),(3.75),(3.5)
0.98	0.91	1.18	1.11	Ru(4) ↠ Ru(3.75)
Note: Numbers in brackets indicate ‘atomic valence’.

Figure 3. Cyclic voltammogram at 25°C.

Figure 4. Cyclic voltammogram at 25, 50, 70 and 95°C.

Figure 5. Decreasing ratio of Ru concentration, [Ru] _t /[Ru]₀, with time.

Table 4. Raction rate constant k ₁ for each electrochemical oxidation condition.

Condition	Rate constant (h^−1)	Corelation coefficient(r ^2)
A	0.19	0.990
B	0.045	0.993
C	0.18	0.998
D	0.14	0.966
E	0.12	0.925

Figure 6. Relation of amount of removed Ru and quantity of electricity.

Figure 7. Ru ionic species in electrolyte with and without diaphragm.