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pH-Dependent Release of Cadmium, Copper, and Lead from Natural and Sludge-Amended Soils

Sukreeyapongse, Orathai, Holm, Peter E., Strobel, Bjarne W., Panichsakpatana, Supamard, Magid, Jakob, Hansen, Hans Christian Bruun
Journal of environmental quality 2002 v.31 no.6 pp. 1901-1909
Hapludalfs, Kandiustults, cadmium, copper, desorption, heavy metals, leaching, lead, pH, protons, soil properties
The pH-dependent release of cadmium, copper, and lead from soil materials was studied by use of a stirred flow cell to quantify their release and release rates, and to evaluate the method as a test for the bonding strength and potential mobility of heavy metals in soils. Soil materials from sludge-amended and nonamended A horizons from a Thai coarse-textured Kandiustult and a Danish loamy Hapludalf were characterized and tested. For each soil sample, release experiments with steady state pH values in the range 2.9 to 7.1 and duration of 7 d were performed. The effluent was continuously collected and analyzed. Release rates and total releases were higher for the Hapludalf than the Kandiustult and higher for the sludge-amended soils than the nonamended soils. With two exceptions the relative release rates (release rate/total content of metal in soil) plotted vs. steady state pH followed the same curves for each metal, indicating similar bonding strengths. These curves could be described by a rate expression of the form: relative release rate = [H], with specific (empirical constant) and (rate constant) parameters for each metal demonstrating that metal release in these systems can be explained by proton-induced desorption and dissolution reactions. With decreasing pH, pronounced increases in release rates were observed in the sequence cadmium > lead > copper, which express the order of metal lability in the soils. The flow cell system is useful for comparison of metal releases as a function of soil properties, and can be used as a test to rank soils with respect to heavy metal leaching.