Toxic Metal Removal from Polluted Soil by Acid Extraction

Sulfuric acid leaching is a promising technique to extract toxic metals from polluted soils. The objective of this study was to define the optimum sulfuric acid leaching conditions for decontamination of the fine particle fraction (< 125 mu m) of an industrial soil polluted by Cd (16.8 mg kg(-1)), Cu (3,350 mg kg(-1)), Pb (631 mg kg(-1)) and Zn (3,010 mg kg(-1)). Batch leaching tests in Erlenmeyer shake flasks showed that a soil pulp pH between 1.5 and 2.0 using a solid concentration (SC) ranging from 5 to 20 % is adequate to efficiently solubilize toxic metals. Leaching tests performed at different temperatures (20, 40, 60 and 80 A degrees C) also revealed that it is not beneficial to heat the soil suspension during the leaching treatment. The application in a 1-L stirred tank reactor of five consecutive 1-h leaching steps at 10 % SC and ambient temperature, followed by three water washings steps resulted in the following metal extraction yields: 30 % As, 90 % Cd, 43 % Co, 7 % Cr, 88 % Cu, 75 % Mn, 26 % Ni, 18 % Pb and 86 % Zn. The decontaminated soil conformed to Quebec norms for commercial and industrial use of soil.