The effect of SO₃-Ph-BTBP on stainless steel corrosion in nitric acid

SO₃-Ph-BTBP is a hydrophilic tetra-N-dentate ligand proposed for An(III)/Ln(III) separation by solvent extraction, and a candidate for use in future advanced reprocessing schemes such as GANEX and SANEX. We present the first study of the effect of SO₃-Ph-BTBP on the corrosion behavior of stainless steels. Specifically, studies have been performed using steels and conditions equivalent to those found in relevant nuclear reprocessing flow sheets. SO₃-Ph-BTBP has been shown to have little effect on either steel passivation or reductive dissolution. However, if driven cathodically into a region of hydrogen evolution at the electrode surface or conversely anodically into a region of transpassive dissolution, observed currents are reduced in the presence of SO₃-Ph-BTBP, suggesting corrosion inhibition of the steel potentially through weak absorption of a SO₃-Ph-BTBP layer at the metal-solution interface. The lack of any observed corrosion acceleration via complexation of Fe³⁺ is surprising and has been suggested to be due to the slow extraction kinetics of SO₃-Ph-BTBP as a result of a requirement for a trans- to cis-conformational change before binding.