Heavy metal leaching of contaminated soils from a metallurgical plant

Laboratory tests were carried out to determine the primary parameters affecting the efficiency of the process of leaching heavy metals from natural soil collected inside a metallurgical plant in Italy. The soil samples tested consisted primarily of medium density, fine silica sand that had been contaminated with lead and zinc metallurgical wastes by percolating rainwater. Samples were obtained 12m below ground level in an area where the surface consists of artificial strata composed of soil mixed with metallurgical solid waste. The soil layer tested hosts a low-permeability aquifer (at depths generally greater than 10m below ground level) that is also contaminated by heavy metals. Batch leaching experiments were conducted using acid solutions (acetic, nitric, hydrochloric and sulphuric) as extracting agents. During leaching tests, concentrations of Zn, Pb, Cd, Cu, Mn and Al were monitored. The results indicate that the best leaching solution varies for all analytes and soil samples examined. Statistical analysis was used to identify correlations between efficiency and leaching rate.