Amount and Composition of NOx Generated by Metal (Cu, Ni, and Fe) Dissolution Reaction with Nitric Acid

In metal dissolution processes, the amount and composition of NOx generated by a reaction using nitric acid vary with complex factors. To treat harmful NOx generated by metal dissolution with nitric acid, the amount and composition of generated NOx was estimated by a kinetic profile of the metal dissolution reaction in nitric acid. To construct a kinetic profile of metal dissolution in nitric acid, we selected copper (Cu), nickel (Ni), and iron (Fe) since they are metals often used in metal dissolution processes. The effects of concentration of nitric acid and reaction temperature on the molar amount and molar composition of NOx (= NO + NO2) generated by metal dissolution in nitric acid were studied. In the case of Cu or Fe dissolution reactions, when the concentration of nitric acid was between 8 and 11 mol [Formula: see text] dm[Formula: see text] at 80[Formula: see text]C, the molar ratio of NO2 to total NOx generated (NO2/NOx) was almost 0.9. The molar ratio of NO2/NOx also showed dependence on concentration of nitric acid from 3 to 8 mol · dm−3. In the case of Ni dissolution reaction, the generated amount of NOx was quite low. Activation energies were obtained at various concentrations of nitric acid by kinetic analysis of metal dissolution. Molar ratios of NOx generated to metal dissolved (NOx/Cu or NOx/Fe) were obtained at various concentrations of nitric acid. When the concentration of nitric acid was high, the molar ratios of NOx/Cu and NOx/Fe were high. The molar ratio of NOx/Fe was higher than that of NOx/Cu.