Effect of organic residues and liming materials on metal extraction from a mining-contaminated soil

Incubation tests were used to assess the effectiveness of three different organic residues and three different liming materials, alone or in combination, in the remediation of a mine contaminated soil. The organic residues tested were sewage sludge from a municipal wastewater treatment plant (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC), applied at 100 and 200 Mg ha-1. The liming materials tested were agriculture limestone (6.4 Mg ha-1), calcium oxide (3.7 Mg ha-1), and sugar beet sludge (12.2 Mg ha-1) from the sugar manufacturing process. The soil and mixtures of soil and amendments were adjusted to 70% of the maximum water holding capacity and incubated for 28 days in a controlled-temperature room at 20°C ± 1°C. At the end of the incubation, samples were analyzed for pH, electrical conductivity, organic matter content, CaCl2-extractable, and' NH4Ac/HAc+ EDTA-extractable metal fractions (Cu, Zn, and Pb). Correlations among the variables and/or similarities among the treatments were identified by principal component analysis and hierarchical cluster analysis. The amendments tested decreased the CaCl2-extractable Cu and Zn fractions, considered as mobile metal fractions, to below analytical detectable limits, providing organic matter to the soil with levels between 1% and 2% at the end of the experiment, significantly different relatively to the original soil. pH and electrical conductivity reached high values when using 200 Mg ha-1 SS or 200 Mg ha-1 MSWC, with any of the liming materials tested, making these application rates excessive for this particular situation. Furthermore, the treatments using MSWC increased the NH4Ac/HAc+ EDTA-extractable Cu, Pb, and Zn fractions, considered as mobilizable metal fractions, as did the 200 Mg ha -1SS for Pb and Zn. Considering the overall results, the compost made from garden waste decreased metal solubility in the soil and increased soil pH and organic matter content, without the addition of large amounts of soluble salts, and without increasing the mobilizable metal content. Of the organic materials tested, this was the only one that can be considered adequate for remediation of the contaminated soil under study, at the application rates tested. Copyright © 2008 Taylor and Francis Group, LLC.