Extraction of copper and zinc from naturally contaminated copper mine soils: Chemical fractionation analysis and risk assessment

The leaching behaviour of Cu and Zn from contaminated soils at a copper mine was investigated using four extractants: citric acid (CA), oxalic acid (OA), ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA). Six soil samples were characterized for the distribution of four chemical fractions of Cu or Zn (acid-soluble, reducible, oxidizable and residual). For the extraction of Cu, EDTA is more effective than other extractants when the concentration is less than 0.02 mol/L. The leaching efficiency for Cu was at least 15% higher for EDTA than for the other extractants at the same concentrations. Similar leaching behaviour was observed in the extraction of Zn. After extraction by CA, OA, EDTA or NTA, the acid-soluble fractions and the reducible fractions of Cu were the main fractions extracted. The potential environmental risks related to speciation were evaluated, and after extraction these risks were reduced.