In this study, we propose a process to prepare Mn-Zn ferrite powder, using oxides of manganese and zinc extracted from used dry batteries, and ferrous chloride solution from waste steel pickling liquor. The hydrothermal process was used to convert the starting raw materials into Mn-Zn ferrite powder. This powder revealed the formation of cubic ferrite with a saturation magnetization (M-s) of 58.8 emu/g and an intrinsic coercive force (H-c) of 3.8 Oe. The average lattice thermal expansion coefficient alpha(a) (200 degrees-500 degrees C) of this Mn-Zn ferrite powder was 14.14 x 10(-6) K-1. The toroidal specimen sintered at 1300 degrees C in a controlled oxygen atmosphere presented a flat profile of initial permeability (mu(i)) of 2150-2200, in the frequency range 0.1-20 kHz, which allows its use in magnetic applications. This useful technology, combined with environment and materials engineering, can promote the recycling of dry batteries and contribute to the preservation of the earth. Moreover, this technology can also decrease the cost of disposal of the used dried batteries and waste steel pickling liquor.