Kinetics of Nickel, Iron, and their Alloys Dissolution in Nitric Acid

A rotating disk method is used to investigate the dissolution rate of metallic iron, nickel, and their alloys in nitric acid media. Discs 2 cm in diameter made of nickel grade N1 and Armco iron, as well as two samples with an Ni:Fe ratio of 15:85 and 50:50 are used. The effect of temperature, initial nitric acid concentration, disk rotation rate, and process duration on specimen dissolution rate are investigated. The rate is determined by the amount of dissolved metal per unit of time from a disk unit surface. Regression analysis is used to describe the effect of nitric acid concentration on specimen dissolution rate. It is found that the dissolution rate of iron metal is up to 20–60 times faster than nickel metal dissolution rate. The effect of HNO₃ temperature and initial concentration when dissolving Ni and Fe alloys in nitric acid is investigated. With an increase in temperature from 303 to 353 K ([HNO₃] = 0.2 M, Ni:Fe = 50:50) the amount of dissolved Fe and Ni increases by a factor of 8–9. Dissolution of Ni:Fe alloy (15:85) under the same conditions results in an increase in dissolved iron by a factor of four. An increase in nickel concentration in solution occurs within 30 minutes, after which the concentration does not change. In experiments with Ni:Fe alloy = 50:50 the amount of dissolved Fe is 1.8–2.3 times greater than the amount of dissolved Ni depending on the initial acidity.