Determination of free hydrofluoric and nitric acids in pickling bath liquors using a fluoride-selective electrode and alkalimetric titration

Abstract

A method is proposed for the determination of free hydrofluoric and nitric acids in pickling bath liquors by combining direct potentiometry with a fluoride-selective electrode and an alkalimetric titration. The correct choice of bridging solution for the reference electrode eliminates the influence of varying nitric acid concentrations on the determination of fluoride. The results of the methods have been compared with results obtained using the LECO AT-50 acid analyser and the correlations obtained were good. The determinations do not require expensive equipment and can be completed within 10–15 min.

The method outlined has been in use at the Outokumpu Oy Stainless Steel Division since 1978. The events of under-and over-pickling and total acid consumption have decreased in this time.