Acidic dissolution of zinc ferrite

The dissolution of synthetic and industrial zinc ferrite was studied in HNO₃, HClO₄ and H₂SO₄ solutions, at temperatures ranging from 75°C to 95°C and in the presence of an excess of Fe²⁺, Fe³⁺ or Zn²⁺ ions. The rate constant describing this dissolution process was obtained by using a surface-reaction controlled, shrinking core model, which yielded good results. The dissolution rate zinc ferrite depends on the square root of the hydrogen ion activity in H₂SO₄ and HClO₄ solutions. The apparent activation energy for the dissolution equals 74±2 kJ/mol in H₂SO₄, 47±22 kJ/mol in HClO₄ and 37±16 kJ/mol in HNO₃. The order of the rate constant was 0.6 in the Fe²⁺ and -0.5 in the Fe³⁺ concentration. The rate constant for the dissolution of industrial zinc ferrite was 20-50% lower than for synthetic zinc ferrite. The presence of 85 g/l Zn²⁺ in the leach solution retarded the dissolution rate of zinc ferrite. A dissolution mechanism is proposed which qualitatively explains the results obtained.