Fluoride effect on the electrochemical behaviour of the Fe(III)/Fe(II) system in H3PO4+H2O+HF

Electrochemical behaviour of iron ions on a gold electrode in H3PO4 and in H3PO4-HF solutions was studied to access the influence of fluoride ion on t he electrochemical properties. Voltammetric and potentiometric studies show ed that the Fe(III)/Fe(II) system in H3PO4-HF is generally reversible. This reversibility decreases when HF is added. The diffusion coefficient of iron ions was determined in different media wi th and without HF at 20, 40 and 60 degrees C. Comparisons between complexed species in phosphoric solutions with or without HF have been made. UV-spec tra in different media show that there is no evidence of a new iron-fluorid e complex, but a Fe-O-P-F bond is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.