Selective leaching of elements associated with Mn – Fe oxides in forest soil, and comparison of two sequential extraction methods

Abstract.

For selective dissolution of Mn oxides as components of soil (easily reducible oxides) 0.05 mol L^–1 and 0.1 mol L^–1 NH₂OH·HCl acidified to pH 2 and for dissolution of Fe oxides (crystalline form of the oxides) 0.25 mol L^–1 NH₂OH·HCl in 25% acetic acid, 0.2 mol L^–1 oxalate buffer and 0.1 mol L^–1 ascorbic acid in oxalate buffer were tested. Dissolved elements were determined by ICP–MS and ICP–OES. The studies indicate that the use of 0.05 mol L^–1 NH₂OH·HCl in nitric acid solution (pH 2) and 0.1 mol L^–1 ascorbic acid in 0.2 mol L^–1 oxalate buffer led to selective leaching of trace metals bound by Mn and Fe oxide phases in soil. Comparison of different extraction schemes indicates that the trace elements investigated are mainly bound to minerals consisting of crystalline Fe oxides and insoluble minerals (under the extraction conditions used). The studies also indicate that Mn oxides and organic matter retain a major mobile fraction of the elements investigated in the soil.