Preparation of a coagulant of polysilicate aluminum ferric from foundry dust and its coagulation performance in treatment of swine wastewater

Polysilicate aluminum ferric (FD-PSAF) was prepared from foundry dust under polymerization temperature of 50 degrees C, polymerization time of 2 h and pH 2, to produce its amorphous Si-Al-Fe polymer. Removal efficiency of chemical oxygen demand (COD), color, turbidity and phosphate from swine wastewater reached 50.4%, 95.7%, 97.1% and 99.7% after addition of 10 mL/L of the prepared FD-PSAF, which were higher than those obtained when using polysilicate aluminum ferric (PSAF), polyaluminum chloride (PAC) and polymerized ferrous sulfate (PFS). The percentage content of Fe-b for PFS, PSAF and the prepared FD-PSAF was 7%, 11% and 24%, respectively. The mean particle size in the swine wastewater increased from 39 nm to 84 nm, 1003 nm, 1198 nm and 2138 nm respectively after the addition of PSAF, PAC, PFS and prepared FD-PSAF into the swine wastewater. The prepared FD-PSAF with the higher coagulation performance could be related to its higher percentage content of Fe-b and greater particle aggregation ability. The removal efficiency of color, turbidity and phosphate from swine wastewater by FD-PSAF did not obviously change with storage time from 1 d to 32 d, indicating that FD-PSAF had good stability performance. The FD-PSAF is an efficient coagulant that could be used to treat swine wastewater.