Introduction
Recycling of waste dry batteries (WDBs) is attracting great attention because of their toxic impact on environments and the associated potential of re-useable valuable metals. More than
8000 tons of WDBs are being generated annually in Taiwan according to the Taiwan Recycling Fund Management Board. Nevertheless, in 2011 only 3300 tons of WDBs in Taiwan were recycled, meaning that the uncollected or untreated WDBs could amount to 5700 tons.The hazardous heavy metals that can potentially leach from WDBs, such as Hg, Cd, Mn, Zn, Pb, and Ni, will result in a harmful impact on human beings and living creatures [1]. Two major recycling technologies, namely pyrometallurgy and hydrometallurgy, for treating WDBs have been developed in recent years [2–9]. For example, de Oliveira et al. [10] reported that Hg could be eliminated from WDBs by a pyrometallurgical method, while Zn could be recycled by distillation after the decontamination of Hg. Although pyrometallurgy has some advantages, the problems of large-scale and secondary pollution from this process still need to be resolved. Based on hydrometallurgy combined with other integrated methods like electrolysis, each substance in WDBs could be recycled [11–13]. The hydrometallurgy method is more popular in the market, but the solvents used and the time consumed are major issues [2,14]. Mn-Zn ferrites are very important ferromagnetic materials used comprehensively in many magnetic applications, such as recording heads and transformers [13]. Numerous products (e.g. power transformers, cores for inductors, noise filters, and magnetic amplifiers) are made of Mn-Zn ferrites [14–16]. With the unique characteristics of low core losses and high permeability, Mn-Zn ferrites have become a very useful material in electronic applications.