On the Mechanism of Anodic Chlorate Formation in Dilute NaCl Solutions

Abstract

The rates of anodic chlorate formation were measured under a variety of well‐defined hydrodynamic conditions. In dilute normalNaCl solutions false(<0.1Mfalse) these rates are up to 60 times larger than those calculated for mass transport control as hitherto postulated. The rates of chlorate formation were calculated using a model which involves the coupling of mass transfer with a chemical reaction (chlorine hydrolysis) proceeding in the diffusion layer. The agreement between the calculated and the experimental values is satisfactory. The model used describes adequately the mechanism of anodic chlorate formation in the range of conditions investigated. In dilute normalNaCl solutions the rate of chlorate formation is governed by the kinetics of the chlorine hydrolysis. At higher chloride concentrations equilibrium may limit the hydrolysis and the mechanism of the process then changes accordingly.

Anodic chlorate formation on platinized titanium

“…The experimental apparatus used has been described before [8]. It consisted of an electrochemical flow channel cell through which the electrolyte was recirculated continuously.…”

“…). Concentrations of hypochlorite and chlorate were determined periodically using a potentiometric titration method which has been described elsewhere [8]. During electrolysis of dilute NaC1 solutions, chloride concentration was determined simultaneously and adjusted if necessary by adding HC1 to the cell electrolyte and neutralizing with NaOH.…”

“…The rate of anodic chlorate formation (Equation 2) has been studied previously by the authors on graphite electrodes [8,9] under conditions where reaction (1) was negligible. It was found that observed rates in dilute NaC1 solution (<0.1…”

Electrooxidation as a Pretreatment Process Before Cyanidation

“…Only the PdO coated anode showed slightly lower values than the others. Ibl and Landolt have also studied the anodic chlorate formation in dilute NaCI solutions in a diaphragm type cell using graphite electrodes (10). The diaphragm was porous polyethylene and the solution temperature was 70.5°C.…”

“…The diaphragm was porous polyethylene and the solution temperature was 70.5°C. Hypochlorite and chlorate concentrations were measured as a function of time and the results are illustrated in Figure 3 (10). In the each run, the change of hypochlorite concentration with time was followed until a steady state with a constant hypochlorite concentration was reached.…”