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This invention discloses a method for preparing 4N ammonium permanganate from low-concentration rhenium-containing waste acid, which is divided into a crude refining stage and a refining stage. The crude refining stage includes a rhenium precipitation process, a leaching process, a hydrolysis process, an acidification process, an extraction process, a back-extraction process, and a crystallization process. The refining stage includes a crude ammonium permanganate dissolution process, an ion exchange process, an extraction process, a back-extraction process, a crystallization process, and a nitration-recrystallization process, ultimately obtaining ammonium permanganate with a purity of 99.99%. In the crude refining stage, this invention first prepares 4N ammonium permanganate from low-concentration rhenium-containing waste acid. Rhenium is efficiently and selectively enriched in concentrated waste acid to obtain a 1% grade rhenium precipitate. Then, a weak oxidation leaching process is used to remove impurities from the precipitate, followed by calcium hydroxide hydrolysis, acidification, high-efficiency extraction, back-extraction, and crystallization to obtain a crude ammonium perrhenate product with a grade of ≥99%. In the refining stage, the crude ammonium perrhenate is dissolved a second time, and a resin ion exchange, extraction, back-extraction, and crystallization process is used to obtain a refined ammonium perrhenate with a grade of ≥99.9%. Finally, a nitration-recrystallization process is used to remove impurities from the refined ammonium perrhenate to achieve a 4N grade quality.