Magnetic polymeric ferric magnesium chloride: Fe species distribution, characterization and coagulation removal of microplastics in water

Abstract

A novel composite coagulant, magnetic polymerized ferric magnesium chloride (MPFMC), was prepared based on traditional inorganic coagulants of polymeric ferric chloride (PFC). It was used to remove polystyrene (PS), a major component of microplastics that is easily suspended in water. The distribution of Fe species under different preparation conditions was investigated, and the physical and chemical properties of MPFMC were characterized using FTIR, XRD, SEM, and VSM. The effects of dosage, pH and temperature on the removal of PS by MPFMC and the floc structures were also investigated. PS removal was maximized when n(Fe) : n(Mg) = 4 : 1, n(OH)/n(Fe + Mg) = 0.4 and M_Fe3O4 : M_Fe = 2 : 1. The content of Fe(b), the most critical component of the iron salt coagulant, increased compared with that of PFC after the introduction of appropriate amounts of magnesium salt and Fe₃O₄. In addition, MPFMC has a wide adaptability to pH and temperature. When the dosage of MPFMC was 0.12 mmol L⁻¹ (pH of 4.5–9.5, temperature of 19–34 °C, rapid stirring at 300 rpm for 2 min, slow stirring at 100 rpm for 10 min, and external magnetic field settling for 10 min), the coagulation performance was excellent, and the removal of PS was greater than 85%. The fractal dimension peak value of the flocs formed reached 1.87, and the floc structure was dense. In conclusion, the modification of introducing magnetic particles and magnesium salt into PFC has proven to be an effective strategy for improving the removal efficiency of microplastics by iron salt coagulants.