Interaction of metallic materials with simulated kraft digester white liquor - Towards the electrochemical detection of sulphide

The electrochemical behaviour of a range of metals (Pt, Pd, Ir, and Fe) as electrode materials in simulated kraft digester white liquor (a concentrated sodium hydroxide solution with or without the addition of sodium sulphide at 170 degrees C) has been compared by registering quasi-steady state current vs. potential curves. chronoamperometric responses at constant potential and impedance spectra. The results in the vicinity of the zero-current potential point to a two-step reaction with an adsorbed intermediate, possibly elemental sulphur, being rate limiting on the noble metals. At more positive potentials, a new process is detected on all the materials. According to relevant thermodynamic calculations, this process most probably corresponds to the oxidation of sulphide to polysulphide. Current densities measured on Pt and Fe in a wide potential range is linearly dependent on sulphide concentration. The associated chronoamperometric response is fast enough so that Pt can be regarded as a promising material for the electrochemical detection of sulphide in kraft digesters. (C) 2011 Elsevier B.V. All rights reserved.