Method for preparing manganese ferrite by circularly leaching pyrolusite from acidic wastewater of steel mill

The invention discloses a method for preparing manganese ferrite by circularly leaching pyrolusite from acidic wastewater of a steel mill. The method comprises the following steps: adding the pyrolusite into the acidic wastewater of the steel mill for reduction leaching; when the molar ratio of Fe < 2 + > in the acid wastewater of the steel mill to Mn < 4 + > in the pyrolusite is less than 2.4, extracting 0-40% by volume of a leaching solution to carry out waste iron scrap reduction, and returning the reduced solution to circularly leach the pyrolusite; after the pyrolusite is subjected to reduction leaching, the pH value of 60-100% by volume of a leaching solution is adjusted, impurities are removed, the molar ratio of Mn < 2 + > to Fe < 3 + > in the solution is adjusted through Mn < 2 + > salt and Fe < 3 + > salt, the pH value of the solution is adjusted through NaOH, and then manganese ferrite is prepared through an ultrasonic liquid-phase coprecipitation method. According to the method, the acid wastewate