Abstract
The reduction of Cr(VI) ion in 0.5 M H2SO4 deaerated solutions with different concentrations of K2CrO4 on nickel and 18Cr-10Ni stainless steel electrodes have been studied by potentiostatic polarisation technique depending on the chromate concentration in solution. The kinetic parameters -Tafel slope, charge transfer coefficient and limiting current density -were evaluated comparatively. For the solutions containing �5 mM K2CrO4 the Tafel slopes are higher on stainless steel than on nickel (around -135 mV�dec-1 for nickel and -165 mV�dec-1 for stainless steel). Moreover, by increasing the chromate concentration the Tafel slopes increase on nickel and decrease on stainless steel. The low Tafel slope values of -75 mV�dec-1 obtained on stainless steel electrode in the potential region -0.5� -0.75V vs. SCE could be due to a decrease of the charge transfer process rate because of the presence of a physical barrier. The values for the reaction rates are slightly higher for nickel than for stainless steel electrodes on all the studied potential range. The reaction product is soluble trivalent chromium, excepting the solution with 500 mM K2CrO4, when a Cr(OH)3 film may cover the electrode surface that determines the decrease of the reaction rate.
Highlights
TKe2cChrnOi4qoune depending on the chromate concentration in solution
-660 case of nickel electrode, on stainless steel electrode the curve obtained in the solution containing 0.5 mM a similar shape with the one for 0.5 M background
The cathodic Tafel plots for Ni and 18Cr-10Ni stainless steel electrodes are depicted in figures 3 and 4, respectively
Summary
TKe2cChrnOi4qoune depending on the chromate concentration in solution. The kinetic parameters -Tafel slope, charge transfer coefficient and limiting current density -were evaluated comparatively. Km2VC·rdOe4ct-h1 efoTrasftealisnlloepssesstaereel)h.iMghoerreoonvesrt,abinyleinscsrsetaeseilntghathneocnhnroicmkealte(acroonucnedn-t1r3a5tiomnVt·hdeecTa-1ffeolrsnloicpkeesl and -165 increase on nickel and decrease on stainless steel. The low Tafel slope values of -75 mV·dec-1 obtained on stainless steel electrode in the potential region -0.5÷ -0.75V vs SCE could be due to a decrease of the charge transfer process rate because of the presence of a physical barrier. The values for the reaction rates are slightly higher for nickel than for stainless steel electrodes on all the studied potential range. The reaction product is soluble trivalent chromium, excepting electrode surface that determines the the solution with 500 mM decrease of the reaction. Due to continuous increasing of industrial activities, environmental pollution is an up to date problem. The latest restrictions imposed by new environmental legislation require effective initiatives for pollution reduction, in gaseous emissions and industrial aqueous effluents and proper soil decontamination. Chromium being one of them, which are discharged in the environment, are not biodegradable and represent a threat to human health
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