Simultaneous removal of manganese and ammonium nitrogen from mine water using sodium hexametaphosphate modified natural zeolite loaded by 3D MnOx

Abstract

Manganese and ammonia nitrogen pollution are widespread in the water of northern Chinese mines, exacerbating regional water scarcity and potential ecological issues. This study aimed to remova dissolved manganese(II) and ammonia nitrogen from mine water using a natural zeolite (NZ) modified with sodium hexametaphosphate impregnation (SHMP-NZ) and loaded with 3D manganese(III)/(IV) oxide nanosheets (SHMP-NZ/MnOx). The influence of factors such as pH value, dissolved oxygen, and coexisting ions on adsorption was investigated. The capacity of NZ to removing ammonium was determined by SHMP impregnation, while the capability to remove manganese was determined by 3D manganese(III)/(IV) oxide nanosheets. Compared to NZ, SHMP-NZ/MnOx exhibited an increased efficiency of 39.93% and 41.54% in the simultaneously removing low-concentration manganese(II) and ammonia nitrogen, respectively. Adsorption processes of manganese and ammonia nitrogen onto NZ and SHMP-NZ/MnOx followed the Elovich and pseudo second order kinetic models, respectively. Both materials exhibited stages of external diffusion, internal diffusion, and reaction equilibrium during adsorption. The maximum adsorption capacities of SHMP-NZ/MnOx for manganese(II) and ammonia nitrogen were 10.12 mg/g and 26.24 mg/g, representing improvements of 72.7% and 113.2%, respectively, compared to NZ. The primary mechanism for ammonia nitrogen removal by SHMP-NZ/MnOx was based on ion exchange, while manganese(II) removal was mediated by Mn3+/Mn4+ species. A regeneration study over five cycles indicated that SHMP-NZ/MnOx possessed promising reusability potential.