3Mn3O4 + 8H3PO4 → Mn3(PO4)2 + 6MnPO4 + 12H2O
Manganese(II,III) oxide react with phosphoric acid to produce manganese(II) orthophosphate, orthomanganese(III) phosphate and water. Phosphoric acid - diluted solution. The reaction takes place in a boiling solution.