Manganese ferrite nanoparticles were prepared by microwave-sonication assisted hydrothermal route and produced from wastes of Li-ion batteries and pyrite ash. The leaching solution of waste pyrite ash was used as the Fe source while the Mn-bearing solution recovered from the Li-ion battery recycling process was used as the Mn source. X-ray diffractometry showed that manganese ferrite can be obtained as single crystalline phase. Scanning electron microscope images showed that double-pyramid or octahedral particles were formed with an average size of 24.3 nm. These MnFe2O4 nanoparticles demonstrated good sorption capacity toward As (101 +/- 0.5 mg/g at pH 3).