10:45 AM - 12:15 PM
[AGE27-P09] Insolubilizing Lead and Arsenic-contaminated Soils subjected to Freeze-thaw Cycles
Keywords:soil contamination, heavy metals, soil freezing and thawing, insolubilization
Heavy metal contamination is often not only caused by a single heavy metal but by multiple heavy metals. Insolubilization treatment is used as a countermeasure against heavy metal contamination. It involves adding an insolubilizing reagent into the soil to change the heavy metals into a chemically stable state and prevent their diffusion and elution in the soil. To insolubilize multiple heavy metals, insolubilization is carried out by mixing the insolubilizing reagents targeted for each heavy metal into the soil. However, when multiple insolubilizing reagents are included, the stability of the reaction may be affected and reduced. In cold regions where temperatures drop below zero during winter, subsoil water experience multiple freezing and thawing. This repeated freezing and thawing of soil may reduce reaction rates during insolubilization and affect minerals' chemical stability and physical degradation. Hence, the objective of this study is to investigate how these freeze-thaw cycles of soils affect the insolubilization of heavy metals.
We have simulated heavy metal-contaminated soils: lead contamination, arsenic contamination, and lead-arsenic contamination. They were treated with insolubilization and then subjected to freeze-thaw cycles. A water extraction test was carried out, and pH, soil total carbon content, and cation and anion exchange capacity of soils were determined for evaluation.
Effect of freeze-thaw cycles on the insolubilization of lead and arsenic in Pb contamination and As contamination were insignificant. Regarding PbAs contamination in soils subjected to freeze-thaw cycles, even though the concentration of Pb and As decreased initially, they increased after 20 days in silica sand. Whereas for field soil, the initial reaction of reagents was delayed, but after 40 days, concentrations of Pb and As were similar regardless of freeze-thaw cycles or not. This shows that for silica sand, prolonged freeze-thaw cycles reduced the stability of insolubilized heavy metals. The delay in field soil could be due to the initial decomposition of soil organic matter, but that did not stop the insolubilizing reagents from reacting with the heavy metal ions. Until clearer correlations between freeze-thaw cycles and the efficacy of insolubilization are made, it is necessary to continue verifying the effectiveness of insolubilization under various environmental conditions.
We have simulated heavy metal-contaminated soils: lead contamination, arsenic contamination, and lead-arsenic contamination. They were treated with insolubilization and then subjected to freeze-thaw cycles. A water extraction test was carried out, and pH, soil total carbon content, and cation and anion exchange capacity of soils were determined for evaluation.
Effect of freeze-thaw cycles on the insolubilization of lead and arsenic in Pb contamination and As contamination were insignificant. Regarding PbAs contamination in soils subjected to freeze-thaw cycles, even though the concentration of Pb and As decreased initially, they increased after 20 days in silica sand. Whereas for field soil, the initial reaction of reagents was delayed, but after 40 days, concentrations of Pb and As were similar regardless of freeze-thaw cycles or not. This shows that for silica sand, prolonged freeze-thaw cycles reduced the stability of insolubilized heavy metals. The delay in field soil could be due to the initial decomposition of soil organic matter, but that did not stop the insolubilizing reagents from reacting with the heavy metal ions. Until clearer correlations between freeze-thaw cycles and the efficacy of insolubilization are made, it is necessary to continue verifying the effectiveness of insolubilization under various environmental conditions.