###### Abstract
It is worth noting that BMO is one of the most active minerals in terrestrial and aqueous environments, with excellent sorption capacity, large specific surface area and strong oxidizing properties [19]. BMO is capable of immobilizing toxic metals or nutrients from rivers in solid hydroxyl precipitates [20]. As the streams around the mine area have been flowing through the Mn-containing wastewater for a long time, the microorganisms in the sediment have strong sorption and oxidation ability for manganese, and the presence of Mn-oxidizing bacteria (MOB) also contributes to the formation of BMO in the sediment. The continuous production of fresh Mn-oxide provides a large number of new sorption sites for the continuous uptake of manganese. Moreover, the accumulation of proteins in the extracellular polymers (EPS) of microorganisms by the addition of manganese is also an important factor in the extracellular sorption of manganese [21]. Most of the manganese oxides present in soils, sediments and aquatic environments are generally considered to be the result of biological oxidation, and their metabolic processes demonstrate the combined effect of biooxidation and biosorption in manganese purification processes [22]. In the aqueous environment, manganese is often present in the free state (Mn(II)) or insoluble oxidized state (Mn(III) and Mn(IV)) [23]. After being accumulated in the sediment through the sorption process, manganese is utilized as an essential nutrient for the biosystem or oxidized by manganese-oxidizing microorganisms into biological manganese oxide (BMO) [24]. Subsequently, the dissolved Mn(II) was oxidized to Mn(IV) under aerobic conditions, and precipitated to manganese oxides and hydroxides, completing the initial fixation of manganese. Some of the buried manganese oxides and hydroxides in the sediments are reduced to Mn(II) and combined with carbonate in the pore water to form manganese carbonate mineralized deposits in the organic-rich sediment [8]. Since manganese is a transition metal with an alternating redox state, the change of oxygen condition in the sediment easily leads to the reductive dissolution of Mn-oxides [25]. The sorption of Mn(II) by natural sediments is not fully reversible, and the manganese cycle is enhanced with increasing amounts of deposition. Benthic fauna and other physical disturbances allow Mn-containing particles in anoxic subsurface sediments to move to the oxygenated sediment-water interface, triggering the desorption and oxidation of manganese. Manganese oxide buried below the redox boundary is reduced and dissolved to Mn(II), and Mn(II) diffused upward above the redox boundary is oxidized to insoluble Mn(IV). Subsequently, the generated Mn(II) is adsorbed onto the adjacent manganese oxide or hydroxyl surface. As the manganese reduction process continues, the available sorption sites gradually decrease until saturation is reached. The unadsorbed Mn(II) is then released into the pore water, leading to secondary contamination of the overlying water. The sorption of heavy metal ions by sediments is the key to preventing and controlling the migration of pollutants and plays an important role in the geochemical cycling of heavy metals. To better understand the sorption behaviour of manganese ions in natural systems, we need to further investigate the process and mechanism of manganese sorption/desorption equilibrium for the treatment and effective recovery of manganese metal. Current studies on sediment sorption of heavy metals have focused on the analysis of the sorption effects of silt, clay, aqueous Fe-Mn oxides and organic matter in them [24]. However, there are fewer studies on the effects of microbial and Fe-Mn oxide transformation processes on heavy metal sorption.