Evaluation of solid residues quality after enhanced Cu leaching of polluted soils

Excavation followed by landfilling is one of the most common methods for treating soils contaminated with metals. Removing the metals through soil washing not only allows valuable substances to be recovered, but also results in cleaner soil residues. In this project a method for leaching and recovering Cu from polluted soils using acidic wastewater is further developed and evaluated, with special attention to the leaching process. In addition, the qualities of the soil residues are assessed in order to investigate how the proposed remediation method affects the soil properties. Soil samples highly polluted with copper (Cu) were collected from two sites in Sweden. After acidic leaching and water washing, the Cu content of the soil samples was reduced five times or more. The original soils could not even be deposited in landfills for hazardous waste; however after treatment of the soils according to the proposed method, the Cu leaching decreased six-fold and the solid residue was safe enough to be deposited in landfills for non-hazardous waste. The soil function “soil as filter and buffer for heavy metals” was evaluated using the TUSEC (technique for soil evaluation and categorization for natural and anthropogenic soils) manual. Originally the soils were of “low” i.e. class 4 or “very low capacity of binding and buffering heavy metals” i.e. class 5, while after the remediation process, both soils were categorized as Class 5. To summarize, the proposed method clearly shows potential not only for remediation of Cu polluted soils but also indicate a potential for recovery and reuse of Cu from the leachates generated. Even though the previously highly polluted soils could not be directly put back at the original sites, the solid residues could be deposited in landfills for non-hazardous waste, which is an improvement, considering the original soils could not even be deposited in a landfill for hazardous waste.