As sorption onto Fe-based nanoparticles and recovery from soils by means of wet high intensity magnetic separation

Abstract

In this work, we studied the soil washing of an As-polluted soil utilizing Wet High Intensity Magnetic Separation (WHIMS) after pre-treatment with nanoparticles. First, Fe-Ni nanoparticles of high saturation magnetization and appropriate size were synthesized. Soil samples were then pre-treated with a dose of nanoparticles before undergoing magnetic separation at different field intensities. Two nanoparticles doses were used and, in addition, control trials with un-pre-treated soil were also performed. Nickel concentration, and magnetic properties served to evaluate the underlying physical behavior of the nanoparticles subjected to magnetic separation. Additionally, leaching tests and As speciation was performed to evaluate As immobilization due to sorption onto the nanoparticles. For the interpretation of the chemical separation results we propose a novel efficiency index, considering both As concentration and weight recoveries. Results show that separation efficiency after nanoparticles pre-treatment yielded better results for lower separation voltages than no pre-treatment, indicating that nanoparticles reported to the magnetic fraction with the As adsorbed onto them. In contrast, at higher separation voltages, more paramagnetic materials reported to the magnetic fraction, thus hindering As separation. Besides, As immobilization was also observed in the nanoparticles pre-treated samples. Accordingly, we obtained a combined soil treatment approach, involving both, the reduction of the volume of polluted soil (physical soil washing) and its stabilization.