Manganese ore tailings packed electrochemical precipitation wall: A novel approach of phosphorus removal and mechanistic insights.

Phosphorus (P) is vital crucial for aquatic ecosystems, but excessive P can cause harm to the environment. Hence it is necessary to remove P from wastewater. Manganese ore tailings (MnT) are rich in metal elements such as Ca, Mg, Fe and Mn which can be used to remove P by precipitation. This study proposes a novel method for continuously removing P from wastewater by MnT packed electrochemical precipitation wall (EPW). The optimum conditions for removing P by MnT packed EPW are 8.0 of the initial pH, current density of 2.4 mA/cm2, P concentration of 0.5 mM, and feed rate of 18 mL/min. Under this condition, the removal P efficiency is 88.41 % which is 39 percentage points higher than that of without electric field. The concentrations of Fe, Ca and Mg in the effluent are within acceptable limits for surface water, but the concentration of Mn exceeds the standard and requires additional treatment. Mechanism analysis indicates that H+ formed at the anode releases Mg2+, Fe3+, Mn2+ and Ca2+, and the OH- generated at the cathode forms a local alkaline environment to promote the precipitation of phosphate. Density functional theory (DFT) reveals the interactions between PO43- and metal ions, and the preferred precipitation order of phosphates by MnT packed EPW for removing P (Ca3(PO4)2>Mn3(PO4)2>Mg3(PO4)2>FePO4). This study not only achieved harmless disposal of MnT, but also provided a solution for the continuous P removal, realizing the dual benefit of efficient disposal of waste and wastewater.