The Research On Chemical Extraction Technologies Of Heavy Metal Contaminated Soils

There are about 474 metal mines in Hunan Province. Most of the tailings have been left without any management in these mines. It has become the main source of heavy metal contamination in the mining areas, which including soil substrates contaminated, soil texture destroyed, short of nutrient, ecological landscape destroyed, water pollution and biological diversity decrease. Work should do to restore the ecology on mined areas. Basing on the research ago, choosing soil samples from two sites including Chejiang copper mine and Yongzhou copper mine, we investigated the application of soil washing technology in tailing soils.In the first study, EDTA, HNO3 and CaCl₂ were used as extractants to remove Pb, Zn and Cu from tailing soils. The redistributions of Pb, Zn and Cu were determined using the sequential extraction procedure of the optimized European Community Burean of Reference (BCR) before and after extraction. The results indicated that EDTA and HNO3 were both effective extracting agents and CaCl₂ may be used in soil extraction because it was less harmful to the soil environment. The extractability of the extractants for Pb and Zn was in the order: EDTA > HNO3 > CaCl₂, while for Cu it was in the order: HNO3 > EDTA > CaCl₂. After EDTA extraction, the proportion of Pb, Zn and Cu in the four fractions varied largely, which was related to the strong extraction and complexation ability. Implying that EDTA was able to extract certain amounts of metal from the silicate matrix. The percentage of Pb, Zn and Cu in reducible fraction, oxidizable fraction and residual fraction changed little compared to acid-extractable fraction before and after extraction with HNO3 and CaCl₂, which showed that HNO3 and CaCl₂ could mostly extract the metal in acid-extractable fraction. The results also suggested that the lability of metal in soil, the kinetics of metal desorption/dissolution and the kinds of extractants were the factors controlling the effects of metal extraction.In the second study, EDTA was used as extractant to leach Pb, Zn, Cu and Cd from tailing soils in soil columns. The redistributions of Pb, Zn, Cu and Cd were determined using the sequential extraction procedure of the optimized European Community Burean of Reference (BCR) before and after extraction. The results indicated that EDTA was a effective extracting agent because of its strong chelating ability for different heavy metals. Percentage extractabilities of metal followed the sequence of Cd > Zn > Cu > Pb. The four fractions of...