The use of soil-flushing to remediate metal contamination in a smelting slag dumping area: Column and pilot-scale experiments

The conditions for the remediation of metal contaminated soils by using the soil-flushing technique are evaluated. A pilot-scale test and a column experiment were carried out in order to evaluate the efficiency of flushing to remove metals from an old mining area that had been heavily contaminated by uncontrolled dumping of base-metal smelting slags. A pilot-scale site (0.9 ha) in the contaminated area was flushed in situ. The volume of water injected and pumped reached approximately 1.2 and 2.3 pore volumes, respectively.The results of the pilot-scale study showed the removal of Al (43.1–81.1%), Co (24.5–82.4%), Cu (0–55%), Fe (0–84.7%), Mn (66.2–85.8%), Mo (0–51.7%), Ni (0–46.4%) and Zn (0–83.4%), although considerable differences between control wells were observed. In addition, other metals such as As, Se, Sb, Cd and Pb were mobilized or removed in negligible amounts from the groundwater.Geochemical modelling of groundwater showed that ferrihydrite was undersaturated in nearly all of the samples, which may explain the mobilization of As, Sb and Se. Also, jarosite, jarosite-Na and melanterite were undersaturated in most of the sampling wells, which suggests that As may be mobilized when these materials dissolve. Soil-flushing could be used as an effective remediation technique in areas contaminated by mining and metallurgical activities when the porous media is permeable and the possible kinetic processes related to the contaminants are negligible.

Research highlights
► In situ soil-flushing is an innovative remediation technology that may remove the contaminants and reduces the need of excavation, handling or transportation of hazardous substances.
► Thus, the main theme contributes to the knowledge of metal removal from mine waste by flushing, showing the possible application of this technology to remediation of metal-contaminated areas.
► Also, the study showed the possible treatment of low-permeability or heterogeneous soils, that frequently are difficult to treat.