Selective separation of Cs-contaminated clay from soil using polyethylenimine-coated magnetic nanoparticles

We evaluated the feasibility of using magnetic nanoparticles (MNPs) coated with polyethylenimine (PEI), a cationic polymer, to remediate radioactive contaminated soil by separating Cs-contaminated clay from the soil. The influences of the solution pH, PEI-to-MNPs mass ratio, and the PEI-MNPs dose on the magnetic separation performance were systematically examined. The highest SE% of illite from solution through electrostatic attraction was approximately 100% at a mass ratio of 0.04 g-PEI-MNPs/g-clay. The PEI coating clearly enhanced the adhesion between MNPs and clay minerals by increasing the quantity of functional amine groups available for adsorbing negatively charged clay minerals. In separation experiments using a soil mixture, the PEI-coated MNPs selectively separated clay- and silt-sized fine particles smaller than 0.038 mm even in the presence of a large amount of sand when used at a low dose (mass ratio of 0.05 g-PEI-MNPs/g-clay) and without pH control. We also used the PEI-MNPs to separate ¹³⁷Cs-contaminated illite from soil under an external magnetic field. After magnetic separation, the highest removal efficiency achieved for ¹³⁷Cs removal from the treated soil was 81.7% at a low nanoparticle dosage, which resulted in satisfying the reduction of radioactivity and waste volume. The results clearly demonstrate that the selective separation of Cs-contaminated clay using PEI-coated MNPs is a promising technique for remediating radioactive soil.