Effect of Sequence in Extraction of Trace Metals from Soils

Abstract

AbstractWhile many workers have utilized various reagents for sequential extraction of soil trace metals, few studies have examined the order of extraction for key steps in the sequential procedure. In this study, several sequences involving both adsorbed and structural (occluded) metal extractants were evaluated to determine the most appropriate sequential methodology for extracting different forms of Cu, Fe, and Mn. For “specifically adsorbed” metals, Pb(NO3)2 and CH3COOH were used. The results showed that the former reagent extracted less Cu, Mn, and Fe and was probably more specific in replacing metals covalently bound to adsorption sites. Lead nitrate was therefore placed before CH3COOH extraction in the sequence. Chao's NH2OH·HCl reagent and K4P2O7, used for Mn oxide and organic metal removal, respectively, were found to solubilize significantly different amounts of Cu and Mn depending on sequence, with K4P2O7 extracting more metal when used first. As NH2OH·HCl has little effect on organic metals, it should be used before K4P2O7. Noncrystalline and crystalline Fe compounds are solubilized next, using a variety of reagents, and residual (silicate lattice) metals are dissolved in the final step. A nine‐step sequential method is proposed to characterize trace metals in agricultural, polluted, and waste‐amended soils.