3.1.2. Effect of initial hexavalent chromium concentration
In order to evaluate the effect of initial hexavalent chromium
concentration at constant current on residual concentration
of solution containing Hexavalent Chromium ions, the solutions
with different initial hexavalent chromium concentrations
in the range of 40–200 mg/l were treated by EC using
iron electrodes in the current of 1 A. As shown in Fig. 4 the
initial hexavalent chromium concentration increased from 40
to 200 mg/l as the residual concentration increased linearly
from 0 to 107 mg/l respectively. This behavior is due to the
lack of flocs for adsorption of excess hexavalent chromium
at high concentrations and also due to the lower rates of iron
corrosion and increasing iron surface passivation at higher
chromate concentrations [34]. The reason for decreasing the
removal efficiency of hexavalent chromium with an increase
in its initial concentration is deducible from Faraday’s law.
According to Faraday’s law, when current density is constant,