Long-term effectiveness of heavy metal(loid) stabilization: Development of an assessing method

In-situ stabilization technology offers a cost-effective solution for the remediation of heavy metal(loid) (HM) contaminated soils. However, the lack of a reliable method to assess the long-term effectiveness of HM stabilization significantly impedes the practical application of this technology. To address this gap, we have devised an innovative method that integrates acid rain leaching with dry-wet alternation to evaluate the long-term effectiveness of HM stabilization. We initiate the acid rain leaching process by adding 200 mL of a H₂SO₄ and HNO₃ solution, with a pH of 3.20, to 20 g of tested soil and stirring at 30 ± 2 rpm for 2 hours. After decanting the supernatant, we dried the soil in a water bath at 60°C. Then repeat this leaching and drying cycle until HM in the leachate either exceed the preset thresholds or become stable. The time-dependent effectiveness of the stabilization is calculated based on the annual average rainfall, and the number of cycles. By using multiple types of soils contaminated with various HM, we demonstrated that this method is versatile and not limited by the types of soil or HM, and exhibits excellent multi-laboratory precision. The method exhibited excellent multi-laboratory precision, with over 82% of samples having a relative standard deviation (RSD) of less than 30%. This method is of significance for not only mitigating the risk of re-contamination from HM reactivation post-remediation, but also broadening the disposal options for remediated soils beyond landfill, thereby fostering environmentally sustainable practices.