Abstract: Manganese sulfate was prepared by reaction between pyrolusite and sulfur oxide from the pyrolysis of magnesium sulfate.Mn₃O₄ can be prepared by pyrolysing the precursor MnCO₃.The precursor was synthesized by solid-state ball milling reaction between NH₄HCO₃ and MnSO₄·H₂O at room temperature.Effects of materials mix ratio，milling time，and ball-feed mass ratio on the conversion of manganese sulfate were investigated respectively.The products were analyzed by XRD.Results showed that the conversion rate of MnSO₄·H₂O could reach 99.8% under the conditions of mix ratio 3.5∶1（amount-of-substance ratio of NH₄HCO₃ to MnSO₄·H₂O），milling time 40 min，and ball-feed mass ratio 5∶1.The Mn₃O₄，whose purity was 99.9%，can be prepared by pyrolysing manganese carbonate at 1 000 ℃ for 1 h.The process has the advantages of simple in operation，high product purity，and low cost，and it can provide a new route for the preparation Mn₃O₄ from MnSO₄·H₂O.

Key words: manganese sulfate, manganese carbonate, trimanganese tetroxide, solid-state ball milling reaction