Enhanced selective separation of fine particles from Cs-contaminated soil using magnetic nanoparticles

Abstract

In the case of the contaminated soil from the nuclear sites, higher concentrations are found in smaller particles by analyzing the distributions of radioactivity for the various soil particle sizes. Therefore, the methods to separate the highly contaminated smallest particles from the remaining materials are essential to any soil decontamination strategy. The aim of the study was to investigate the magnetic separation of Cs-contaminated clay from soil by using naked Fe3O4 nanoparticles under low pH condition. For the magnetic separation of clay from the solution, the synthesized magnetic nanoparticles (MNPs) were mixed with clay at various MNPs/clay mass ratios in the pH-adjusted solution, and then the MNPs–clay complexes were separated from the solution by using a permanent magnet. The effects of combining the magnetic and sieving methods were also evaluated. The magnetic separations of clay from soil were carried out in an open Plexiglas chamber. When sieve separation was combined with magnetic separation, the 200-mesh sieve was inserted into the chamber in the vertical direction. After magnetic separation, the particle size distribution of each soil fraction was analyzed. In addition, waste volume reduction and the Cs removal from contaminated soil by using magnetic-sieving separation were assessed. The efficiency of the recovery of clay minerals from the solution increases significantly with the increases in the MNP dosage and is more than 90% under acidic conditions when the mass ratio of MNPs to clay is near 0.1. Increases in electrostatic attraction and dispersion at low pH are beneficial for the magnetic separation of the clay mineral. In separation experiments on soil mixtures, MNPs were found to separate silt- and clay-sized fine particles selectively; the separation efficiency improves when a sieve is used to exclude physically large particles. In addition, we used the magnetic-sieving separation method to separate Cs-contaminated fine soil under acidic conditions: a decontamination efficiency of the treated soil of 58.5% was achieved by removing the highly contaminated fine soil fraction. The use of magnetic separation under acidic conditions was found to be highly effective for soil decontamination through the selective removal of fine clay particles without additional treatment. Therefore, the proposed magnetic-sieving separation using MNPs may be a viable option for removing fine particles from contaminated soil in the remediation of radioactive soil.