Leaching Behavior of Metallic Elements from Mine Soils Amended with AMD Sludge, Steel Slag, and Limestone Depending on Hydrodynamic Conditions.

Metals and metalloids (hereafter referred to as “metallic elements”) are leached from mine-impacted soils (hereafter referred to as “mine soil”), and are moved downward by seepage, leading to contamination of surrounding soils and watersheds near the mine sites. Immobilization of metallic elements by amendments is one of the environmentally friendly and cost-effective remediation methods for metal contaminated soil. Hydrodynamic conditions, such as flow interruption and repeated drying-wetting cycle, have an impact on leaching and transport of metallic elements in soil water system.

The objectives of this study was to characterize the leaching behavior of metallic elements from mine soil amended with three amendments (acid mine drainage sludge (AMD), steel slag (SS), and limestone (LS)) under various hydrodynamic conditions.

To do this, 1) mine soils were collected from the across abandoned mine site located in Korea. Three amendments were used in this study; AMD sludge (AMD), steel slag (SS), and limestone (LS). Amendments were applied to soils at 5% w/w ratio, and incubated for 1 month at room temperature. 2) Batch sequential desorption experiments were conducted to examine the maximum capacity of leaching of metallic elements from amended mine soils. 3) 1-D transport experiments were carried out with flow interruption for 48h in saturated soils.

Amendments increased the pH value and attenuated aqueous concentration of metallic elements in leachate, but amendment effects on pH rise and immobilization wore off during the ongoing consecutive leaching procedure. Rewetting after drying in batch leaching tests and resumption of flow after interruption in 1-D leaching tests leaded to the rise in concentration of metallic elements.  

The long-term stability of amendments in field with cyclic dry-wet conditions is the important factor for efficient remediation procedure. This study showed that AMD, SS, and LS had sufficient ability to immobilize metallic elements, but repeated leaching diminished its stability especially under dry-wet cycles.