A novel approach to sorbent-based remediation of soil impacted by organic micropollutants and heavy metals using granular biochar amendment and magnetic separation

Soil remediation by sorbent amendment is a popular method to immobilize contaminants but it is limited by the fact that the sorbent cannot be retrieved from the soil, posing as a threat to its quality, due to the gradual leaching of the sorbed contaminants. To address this challenge, this work proposes the use of granular-sized, magnetically retrievable sorbents for soil remediation. Specifically, granular biochar, that offers favorable sorption sites for both organic and inorganic contaminants, was used to treat contaminated soil samples. It is demonstrated that sorbent size plays a crucial role in its separation from the soil matrix by magnetic field. Granular magnetic biochar (gMBC) of 1-2 mm was found to be the most suitable sorbent size because it does not assimilate into the soil matrix and can be quantitatively retrieved both from wet and dry soil by means of magnetism, yielding a sorbent-free matrix. In this manner, the soil is relieved from both the hazardous contaminants and the contaminant-laden sorbent. Using gMBC, the remediation of contaminated soil from both organic micropollutants and heavy metals was optimized accomplishing remediation efficiencies from 40% to 90% for organic compounds and 30-65% for heavy metals through sorption and chemical transformation of the contaminants. The results of the study show that granular magnetic sorbents can be an effective and practical solution to the remediation of soils by facilitating their retrieval directly from the solid matrix which is not possible with micro/nanoparticle sorbents.