Soil Remediation: Metal Leaching from Contaminated Soil through the Modified BCR Sequential Extraction Procedure

Sequential extraction is a useful method of identifying how toxic trace metals bind to soil particles and the strength of these bonds. This is very essential knowledge to reach an efficient soil washing when dealing with remediation of metal-contaminated soil. Sequential extraction uses a succession of extractions on a soil same sample, with extraction liquids expected to promote decreasing mobility of metal fractions from the soil. The sequence selected in this study is a three-step scheme which mainly follows the modified BCR method, but with improvements in the second step. A less toxic and more environmental friendly chemical, ascorbic acid has been used instead of NH2OHHCl. Four different soil samples from the contaminated sites, Köpmannebro and Österbybruk, were investigated. All metal contaminants were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), but only analysis results of Cr, Cu and Pb were evaluated about their possibilities to leach and potential for recover. The results show that except for the clay soil, the highest percentage of Cr, Cu and Pb were generally in the residual fraction. The metal contaminants are stable and immobile to leach and contaminate the surrounding ecosystem. Stronger acids will be required to improve the efficiency of the soil washing. Copper is the metal easiest to be extracted from all the soil samples, as the total extractable content can be up to 70% in clay soil. It is more interesting and valuable to recover Cu from the site Köpmannebro, according to the higher occurrence of extractable and soluble Cu compounds found in the clay sample from this site. The potential for Cu recovery is higher from the grinded bark then from the remaining ash after bark incineration. The new improved BCR scheme used in this study can be a good alternative for applying the sequential extraction method. The results and findings in this study can also serve as a good guideline for remediation activities on-site at other saw mill and forest industry contaminated sites in Sweden.