SOLUTION CHEMISTRY OF HNO3/HF PICKLE MIXTURES

Fundamental aspects of nitric and hydrofluoric mixed-acid pickle solution chemistry are discussed. Results from a computer model designed to predict the behavior of the pickle acid mixture are compared with measured parameters. There is a continuous increase in the complexed fluoride-to-iron ratio as the solution HF/Fe ratio and the F (total)/Fe ratio increases. Dissolved chromium only marginally reduces the HF concentration. The complexation reactions result in the generation of nitric acid with the consumption of hydrofluoric acid, leading to higher than expected nitric acid concentration values. Although further refinements to the computer model are needed, the model gives new insight to the behavior of pickle solutions, such as the distribution of various fluoride species at different F/Fe ratios. © 1990 The Minerals, Metals & Material Society.