Novel two-step process for remediation of Cs-contaminated soil assisted by magnetic composites

Abstract

In this study, a new approach to remediate Cs+-contaminated soil using magnetic composites to improve both the efficiency of separation of clay particles and Cs+ desorption is proposed. An ultrasonic dispersion and magnetic separation process were first performed to selectively remove clay particles from soil. In the soil dispersion solution, polyethylenimine-grafted Fe3O4 nanoparticles were selectively bonded with clay particles through electrostatic attraction, enabling the clay particles to be easily separated from the solution under an external magnetic field. In a Cs+ desorption process, Cs+ removal increased with increasing HNO3 concentration and temperature; the addition of K+ to the acid solution further enhanced Cs+ desorption by replacing Cs+ on the accessible sites of the sand. The addition of a magnetic adsorbent (Fe3O4@SiO2@KTiFC, where KTiFC is potassium titanium(IV) hexacyanoferrate) to the acid treatment substantially improved Cs+ desorption (95.2%) by preventing re-adsorption of Cs+ onto the sand. Based on these results, we evaluated the applicability of the proposed process to the decontamination of radioactive soil. The clay separation process substantially reduced the radioactivity level of the soil from 1630 to 222 Bq/kg by concentrating most of the 137Cs into the magnetic fraction. After treatment of the residual sand using the optimized Cs+ desorption method, the final radioactivity of the treated soil (73.5 wt% of initial soil) was 53 Bq/kg, which is less than the clearance level (100 Bq/kg). Therefore, the proposed method is potentially an effective and practical approach for the decontamination of radioactive soil.