Evaluation of the Potential Stabilization of Lead-contaminated Soil using Coal Gasification Slag and Flue Gas Desulfurization Gypsum

In this study, the feasibility of recycling coal gasification slag and flue gas desulfurization gypsum as a stabilizer for lead-contaminated soil is evaluated. The study is divided into three stages. First, the heavy metal content and leachability of the coal gasification slag and flue gas desulfurization gypsum were assessed to confirm their environmental safety as a recycling material. Second, the stabilization of lead-contaminated soil was evaluated via dissolution testing by mixing either slag or gypsum with artificially contaminated soil at levels of 1%, 4%, 7%, and 10%. Finally, XRD and SEM-EDS analysis was conducted to identify the stabilization mechanisms using the soil and stabilizer mixture cured for 28 days. It was found that the slag and gypsum had no heavy metal content or elution, meaning they were suitable for recycling in accordance with Korean waste recycling criteria. When the slag and gypsum were mixed independently with the contaminated soil, it was found that an application ratio of 7% had the highest stabilization efficiency, thus this was selected as the optimal mixing ratio. XRD analysis of soil samples stabilized for 28 days with the addition of 7% slag and gypsum, peaks for ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O), calcite (CaCO₃), and portlandite (Ca(OH)₂) were observed. Through SEM-EDS analysis, acicular ettringite with a structure suitable for adsorbing or solid solution of heavy metals was identified. Therefore, in this study, the potential of coal gasification slag and flue gas desulfurization gypsum as stabilizers in lead-contaminated soil was confirmed, representing an economical and environmentally friendly means of recycling by-products from power plants.