Experimental study on removal of microplastics from aqueous solution by magnetic force effect on the magnetic sepiolite

Abstract

Microplastics of small sizes and large specific surface areas are very difficult to degrade in the ocean. They spontaneously adsorb marine harmful substances and carry them permanently. Hence, aquatic environments and human health face great threats. Therefore, it is necessary to seek an efficient microplastic removal method. In this study, magnetic separation technology was used to remove microplastics. A magnetic sepiolite was prepared using the co-precipitation method to serve as a magnetic medium carrier. This magnetic sepiolite was separated in a magnetic field generated using a permanent magnet. By doing this, the polyethylene (PE) coating on it was removed simultaneously. The magnetic sepiolite in the removed mixtures was then recycled after being cleaned in a magnetic tube. Research indicates that the specific magnetic susceptibility of the magnetic sepiolite is 55.8 × 10-2 cm3/g. When the mass ratio of magnetic sepiolite to PE was 4:1 and the magnetic field intensity was 285.23 kA/m, the removal effect of PE appeared after 6 s, and it was enhanced 12 s later. At 600 s, the turbidity value was 2.6 NTU and the removal efficiency of PE was 98.4%. A scanning electron microscopy (SEM) analysis showed that a great number of fiber filaments appeared on the surface of the PE in the removed mixtures. Magnetic sepiolite was found in the PE particles using X-ray diffraction (XRD)/Fourier transform infrared spectroscopy (FTIR) and particle analysis, and this demonstrated that the magnetic sepiolite was loaded (wrapped or embedded or adsorption) on the surface of the PE so successfully, that the mixtures could be separated from the aqueous solution in a suitable magnetic field as strong magnetic materials. The removal efficiency of PE still exceeded 90% after five times using the recycled magnetic sepiolite from the magnetic tube. In this study, the PE removal technology in an aqueous solution was examined from the perspective of the design of magnetic functional materials and magnetic separation. This technology has an economic benefit as an environmental protection technology.