Interfacial chemistry of powdered barium ferrites immersed in aqueous solutions: leaching in acidic chloride media

The kinetics of leaching and dissolution of barium mono- and hexa-ferrite in acidic chloride media are presented and discussed. The monoferrite is appreciably more reactive, and dissolves in a nearly congruent way in low pH media. In the case of barium hexaferrite, iron and barium dissolution are independent processes. Initially, fast barium leaching is observed, which is followed by a slower process controlled by diffusion through a growing iron oxide layer. Iron dissolves at nearly constant rates that are a function of pH; the apparent kinetic order on H(+) is 0.66, typical of acid dissolution mechanisms. The differing reactivities of the mono- and the hexa-ferrite relates to their crystal chemistry. (C) 2002 Kluwer Academic Publishers.