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J. Thiiming et al.
was maintained over the solution, during the experiments, so as to avoid the
oxygen getting into the cell.
The influence of hypochlorite concentration in the current efficiency for
mercury deposition was calculated evaluating cyclic voltammograms. For this
purpose, the charge of the cathodic branch was measured at varying hypochlorite
concentrations.
4.2
Results
4.2.1
Voltammetric Studies
The limiting current density measured at a potential of -0.90 V(SCE) is
illustrated in the Levich plot (Fig. 4) for mercury concentration of 5 x 10- 4 molli.
From the slope of the Levich plot and using the literature value for the kinematic
viscosity of 8 x 10- 7 m 2 S-I (Washburn 1929), the calculated diffusion coefficient
is 4.3 x 10- 9 m 2 S-I. This result is in close agreement with the reported value in
the literature (Matlosz and Newman 1986).
Cyclic voltammograms of solutions containing 0.4 mmolll dissolved mercury,
1 molll chloride and 0-15 mmolll HOCI indicate that there is no influence of
HOCI on mercury deposition but on the current efficiency, which decreases
exponentially as the HOCI concentration increases (Fig. 5).
CiJ
E
o
:.;:c
E
0.7
0.6
0.5
0.4
7
9
11
13
-{f
Fig. 4. Limiting current density against square root of the electrode angular velocity.
(Hg2+) = 5 X 10- 4 mol dm- 3 , (NaCI) = 0.83 molll