Migration and Transformation Behavior of Mn<sup>2+</sup> and NH<sub>4</sub><sup>+</sup>-N in Electrolytic Manganese Residue at Different Leaching pH Environments: Release Kinetic Model, Physical Phase Changes, and Formation of Manganese Oxide
Jiancheng Shu, Yaling Deng, Xiaoqing Wei, Mengjun Chen, Yong Yang, Zongyu Deng
Abstract
Mn 2+, NH 4 + -N, and heavy metals in electrolytic manganese residue (EMR) have severely polluted the environment. This study investigated the migration and transformation behaviors of Mn 2+ and NH 4 + -N in EMR at different leaching environments. The results showed that the release of Mn 2+ and NH 4 + -N was a secondary kinetic process. Physical phase analysis indicated that Mn 2+ and NH 4 + -N lost in leaching were mainly derived from (NH 4 ) 2 Mg(SO 4 ) 2 ·6H 2 O, (NH 4 ) 2 SO 4, and MnSO 4 ·H 2 O from EMR, and Mn lost from EMR during leaching was mainly exchangeable and in a soluble state, followed by a carbonate bond state. NH 4 + -N was specifically retained in EMR by electrostatic and ion exchange interactions, and a part of NH 4 + -N in EMR can be converted to NO 3 – -N on the surface of manganese oxide formed during the alkaline leaching environment. The accumulated maximum release of Mn 2+ and NH 4 + -N under an alkaline leaching environment was significantly reduced compared to an acidic environment, since Mn 2+ mainly reacted with OH – to generate Mn(OH) 2, MnOOH, and MnO 2 . In addition, releasing of heavy metal ions from EMR was a continual process. This study provides theoretical support for the harmless treatment and resource utilization of EMR.