Removal of phosphate from wastewater by using open gradient superconducting magnetic separation as pretreatment for high gradient superconducting magnetic separation

The removal of phosphate from wastewater using a combination of open gradient superconducting magnetic separation (OGMS) and high gradient superconducting magnetic separation (HGMS) was investigated. The magnetic seeding material used was Fe3O4, and a novel composite inorganic coagulant was added to combine the phosphate with the magnetic seed. The important parameters that influenced the removal efficiency of phosphate in OGMS or HGMS, slow mixing time, magnetic seeding dosage, coagulant dosage, hydraulic retention time, magnetic field strength and flow rate, were systematically investigated. The performance of the OGMS–HGMS process was evaluated by treating synthetic phosphate wastewater. The results showed that all of the investigated parameters except for slow mixing time had a significant effect on phosphate removal. The phosphate concentration was reduced from 0.50 to 0.01 mg/L under the following optimal reaction conditions: coagulant dosage, 50 mg/L; Fe3O4, 100 mg/L; magnet working current, 160 A; hydraulic retention time in OGMS, 0.5 min; and flow rate in HGMS, 2 L/min. Overall, the use of OGMS as a pretreatment for HGMS was shown to be a good method of increasing phosphate removal efficiency while simultaneously increasing the flow rate of HGMS.