Migration and Transformation Behavior of Mn²⁺ and NH₄ ⁺-N in Electrolytic Manganese Residue at Different Leaching pH Environments: Release Kinetic Model, Physical Phase Changes, and Formation of Manganese Oxide

Mn2+, NH4 (+)-N, and heavymetalsin electrolytic manganese residue (EMR) have severely polluted theenvironment. This study investigated the migration and transformationbehaviors of Mn2+ and NH4 (+)-N in EMRat different leaching environments. The results showed that the releaseof Mn2+ and NH4 (+)-N was a secondarykinetic process. Physical phase analysis indicated that Mn2+ and NH4 (+)-N lost in leaching were mainly derivedfrom (NH4)(2)Mg(SO4)(2)center dot 6H(2)O, (NH4)(2)SO4, and MnSO4 center dot H2O from EMR, and Mn lost from EMR duringleaching was mainly exchangeable and in a soluble state, followedby a carbonate bond state. NH4 (+)-N was specificallyretained in EMR by electrostatic and ion exchange interactions, anda part of NH4 (+)-N in EMR can be converted toNO(3) (-)-N on the surface of manganese oxideformed during the alkaline leaching environment. The accumulated maximumrelease of Mn2+ and NH4 (+)-N underan alkaline leaching environment was significantly reduced comparedto an acidic environment, since Mn2+ mainly reacted withOH(-) to generate Mn(OH)(2), MnOOH, and MnO2. In addition, releasing of heavy metal ions from EMR wasa continual process. This study provides theoretical support for theharmless treatment and resource utilization of EMR. Migration and transformation behaviorsof Mn2+ and NH4 (+)-N in electrolyticmanganese residueat different leaching environments were investigated.