Thermodynamic studies on HF-HNO3-H2O solutions containing iron, chromium and nickel

Abstract

The solubility of pure metals of iron, chromium and nickel and alloys of AISI 316 and 416 stainless steels in HF- HNO3-H2O solutions was studied under different acid concentrations. The chemical analysis of the equilibrium solutions and solid was carried out using atomic absorption spectrophotometer (AA), X-ray diffraction and scanning electron microscope (SEM) methods. All experiments were done at 298 K and one atmosphere. The results showed that the solubilities of iron, chromium and nickel increased with increase in concentration of hydrofluoric and nitric acids. The stable solid phases formed in the solution with stainless steels solution were mainly FeFy 3H20. The theoretical solubility of iron, chromium and nickel have been calculated at 4 molality of HNO3 with an assumption of an ideal solution. An excellent agreement between the experimental data and the theoretical data is observed.