Acid leaching behavior of zinc ferrite in an agitated vessel

Leaching behaviors of synthetic zinc ferrite particles in acid solutions (HNO3, HCl and H2SO4) were studied by the use of an agitated vessel. The rate-controlling step was found to be the chemical reaction at the surface of the particle. The apparent activation energy was about 66 kJ/mol for HNO3, 92 kJ/mol for HCl, and 68 kJ/mol for H2SO4, respectively. Only in some cases of leaching with HNO3 solution, did the leaching rate appear to decrease with time. In that case, a nonstoichiometric dissolution with a preferred dissolution of zinc was observed. This phenomenon is more pronounced at high temperatures and high agitation speeds. Scanning Electron Microscope observations showed that the particles agglomerated. Furthermore, the number of particles in the solution decreased during the experiments. The results of several analyses; XRD, FT-IR spectrum, EDS and EPMA, showed that there were precipitates composed of iron and nitrate between agglomerated particles. These precipitates appear to cause the non stoichiometric dissolution and the particle agglomeration which decreases the reaction area of the particles.