Convert iron tailings waste into a novel Mg-Fe-Al hybrid magnetic coagulant for enhanced pretreatment of swine wastewater

Swine wastewater is a type of highly turbid wastewater with extremly high concentration of COD, NH 4 + , and total phosphorus. To address the drawbacks of commercial coagulants in the pretreatment of swine wastewater, such as loose flocs, slow settling rates, and the inability to remove NH 4 + , a novel Mg-Fe-Al hybrid magnetic coagulant (Mg/Fe/Al-MC) is prepared by using the high-pressure acid leaching (HPAL) technology based on iron tailings waste. Compared to atmospheric acid leaching (AAL), HPAL significantly increased the iron leaching rate from 22 % to 61 %. The specific surface area was increased from 5.1 to 9.2 m 2 /g. The study revealed the synergistic crystallization-coagulation-adsorption mechanism for the purification of swine wastewater. When the dosage of Mg/Fe/Al-MC was 2.5 g/L and pH was 9.0, the removal efficiency of NH 4 + reached 60 % by forming magnesium ammonium phosphate (MAP). Zeta potential results indicated that the coagulation mechanism of Mg/Fe/Al-MC is primarily based on electrostatic neutralization. After maturing Mg/Fe/Al-MC for 60 h, the content of essential polymeric Fe-Al hydroxide complexes [Fe(III)+Al(III)](b) reached 22.7 %. The insoluble porous particles exhibited a significant adsorption capacity, suggesting its important role in pollutant removal. Under the action of an external magnetic field, the settling velocity of Mg/Fe/Al-MC was significantly faster than that of polyaluminum chloride (PAC), with a much higher clear water yield of 75.5 %. This study provides new pathway for the enhanced pretreatment of swine wastewater.