Aggregation and Magnetic Separation of Polyethylene Microparticles from Aqueous Solutions

The determination of the amount and composition of artificial polymer microparticles in ponds requires the preparation of representative water samples. A new method has been proposed in this work for magnetic separation of polyethylene microparticles (PEMPs, 10–200 μm), with the method implying their aggregation with magnetic nanoparticles. Composite magnetic nanoparticles containing magnetite cores and silica shells functionalized with amino groups (Fe₃O₄@SiO₂–NH₂, d_hydr = 200 nm) have been synthesized and characterized. Due to electrostatic interactions, these nanoparticles can form aggregates with polyethylene particles and be separated from water under the action of a gradient magnetic field. The effects of added salts (NaCl, Na₂SO₄, NaH₂PO₄, and CaCl₂) and a surfactant, sodium dodecyl sulfate (SDS), on the separation conditions of PEMPs from water have been studied. It has been shown that the addition of the magnetic particles in concentration c = 0.01 g/L to aqueous suspensions containing NaCl and NaH₂PO₄ (c = 10 mM), and SDS (c = 3 mM) provides an efficiency of magnetic separation of PEMPs equal to, at least, 98% after preliminary exposure for 30 min and magnetic sedimentation for 15 min. As the concentration of NaCl and NaH₂PO₄ is increased to 100 mM or in the presence of Na₂SO₄, the efficiency of PEMP magnetic separation decreases. In the presence of CaCl₂ and SDS, the efficiency of the magnetic sedimentation is no less than 98% at the studied concentrations of the salts. At least 80% of PEMPs are separated by magnetic filtration from model solutions simulating river and sea water within 5 min.