Method for preparing soft magnetic manganese-zinc ferrite composite by removing impurities from industrial waste step by step

A method for preparing a soft magnetic manganese-zinc ferrite composite by removing impurities from industrial waste step by step, wherein recovery and preparation are performed according to the following steps:

• 1) recovery of manganese from manganese-containing waste residue
• the manganese-containing waste residue being one of manganese anode slime, electrolytic manganese residue, marine manganese nodules, and the manganese-containing waste residue produced by perillaldehyde;
• crushing the manganese-containing waste residue until the particle diameter is less than or equal to 5 mm;
• drying the crushed waste residue;
• adding a flux according to the mass of the manganese-containing waste residue, wherein the mass ratio of the flux added to the manganese-containing waste residue is (10-2):1;
• placing the manganese-containing waste residue in a muffle furnace and heating up for roasting until solid-liquid stratification appears, wherein the roasting temperature ranges from 900° C. to 1000° C. and is held for 30-45 min;
• after solid-liquid separation, reusing the liquid phase as the flux, and washing solid-phase sediments thoroughly with water to remove soluble salts remaining in the solid-phase sediment;
• adding water to the solid-phase sediments to prepare a slurry, sieving the slurry with a 120-mesh sieve and then placing the slurry in a reaction kettle with a cooling device;
• adding excess sulfuric acid according to the manganese content in the solid-phase sediments;
• in vacuum or in the presence of an inert gas, at room temperature, adding a reducing agent to reduce manganese dioxide in the manganese slurry into low-valent manganese which reacts quickly with excess sulfuric acid to convert all manganese into a manganese sulfate solution, and filtering the manganese sulfate solution to remove impurities to obtain a primary purification solution of manganese sulfate;
• adding a flocculant to remove residual Al and Si from the primary purification solution of manganese sulfate, and filtering the primary purification solution of manganese sulfate to obtain a secondary purification solution of manganese sulfate;
• adding ammonia water to adjust the pH value of the manganese sulfate solution to 5 to 7, performing separation by pressure filtration to obtain a tertiary purification solution of manganese sulfate, adding 1% to 2% ammonium sulfide to further remove remaining metal ions from the tertiary purification solution of manganese sulfate, and then filtering the tertiary purification solution of manganese sulfate to obtain a quaternary purification solution of manganese sulfate;
• 2) recovery of zinc from zinc-containing waste residue the zinc-containing waste residue being at least one of zinc slime, hot-dip galvanizing scrap, and zinc ash,
• crushing the zinc-containing waste residue until the particle diameter is less than or equal to 5 mm, drying the crushed waste residue and mixing the waste residue thoroughly with a flux;
• placing the zinc-containing waste residue in a muffle furnace and heating up to 390° C. such that the flux begins to melt and gradually penetrates into the zinc-containing waste residue, and then further heating up to 750° C. and holding the temperature for 30-45 min, removing the liquid phase portion from the melt, washing solid phase sediments with water, adding excess sulfuric acid according to the content of zinc oxide in the solid-phase sediments to obtain a zinc sulfate solution, and filtering the zinc sulfate solution to remove impurities to obtain a primary purification solution of zinc sulfate;
• adding a flocculant to remove residual Al and Si from the primary purification solution of zinc sulfate, and then filtering the primary purification solution of zinc sulfate to obtain a secondary purification solution of zinc sulfate;
• adding ammonia water to adjust the pH value of the manganese sulfate solution to 5 to 7, and performing separation by pressure filtration to obtain a tertiary purification solution of zinc sulfate;
• adding 1% to 2% ammonium sulfide to further remove metal ions from the tertiary purification solution of zinc sulfate, and then filtering the tertiary purification solution of zinc sulfate to obtain a quaternary purification solution of zinc sulfate, wherein the flux comprises, by weight, the following components:
• 30%-50% of KZrF5 and 70%-50% of Na3AlF6;
• and
• 3) Mixing the quaternary purification solution of manganese sulfate and the quaternary purification solution of zinc sulfate according to a required manganese-zinc ratio in the manganese-zinc ferrite, adding ferrous sulfate with a required Fe ratio, and coprecipitating the mixed purification solution with ammonium bicarbonate, performing washing, decomposing in a decomposing furnace the co-precipitated powder into ferric oxide, manganese tetroxide and zinc oxide, and then roasting ferric oxide, manganese tetroxide and zinc oxide to obtain the manganese-zinc ferrite composite, wherein the reducing agent is trialdehyde phloroglucinol.