Location Of Trace Elements Research Articles

Location of Trace Elements in Unpolluted Soils by a Combined Method

A sequential extraction procedure was combined with physical fractionation and mineralogy to determine the distribution of trace elements (TE) among the different phases of a poorly weathered sample. It was first fractionated into five particle‐size fractions. Two of these were selected for sequential extractions on the basis of their contrasting mineralogical compositions. A five‐step sequential extraction scheme was employed. The studied sample is mostly composed of hornblende, quartz, and feldspars. Early weathering has already occurred, resulting in the formation of smectite and oxides. Sequential extractions show that the studied elements are mostly associated with the residual phases. Hornblende was the main TE bearer of the primary minerals, whereas TEs released through weathering precipitated in both smectite and oxides. Oxides were found to scavenge copper (Cu) and cobalt (Co) more efficiently than smectite. Copper and nickel (Ni) were more concentrated in smectite than in hornblende.

Location of trace elements in soil profiles: total contents of particle-size separates

Total contents of 21 trace elements were determined in particle size separates from the horizons of four profiles, two freely drained and two very poorly drained, of Scottish soils on drifts of basic igneous and granitic origin. Trace elements, including Co, Cu, Li, Mn, Ni, V, Zn and also Fe contained in the more easily weathered ferromagnesian minerals, tend to accumulate in the clay and silt. Elements such as Ti and Zr and also La and Y contained in resistant minerals accumulate in the silt or fine sand. Ti and Zr are mobilised to some extent, however, as these elements are present in the clay separates and in some cases show enrichment therein.The alkali metals Li and Rb accumulate in the silt and clay particularly in the granitic soils, while the alkaline earth metals Ba and Sr occur in greatest concentrations in the sands due to their being held largely in resistant feldspar minerals. On release these elements are not strongly adsorbed by the clay.Very poor pedological drainage leads to increased weathering and release of such elements as Co, Cu, Ni, V and Zn from the coarse or fine sands with correspondingly greater enrichment of the associated silt and clay. Weathering and enrichment of the fine fractions takes place largely in situ, there being little evidence of downward translocation due to leaching.

Location of trace elements in soil profiles: total and extractable contents of individual horizons

ABSTRACTTotal contents of 29 trace and major elements and extractable contents of 20 elements were determined in the horizons of 4 profiles, 2 freely drained and 2 very poorly drained, of Scottish soils on drifts of basic igneous or granitic origin. The probable behaviour of other elements is suggested in the light of the results obtained. It is shown that in the course of pedological weathering, many elements are mobilised and become extractable by relatively weak reagents such as ammonium acetate (when readily exchangeable), dilute acetic acid (when less readily exchangeable or acid-soluble) or EDTA (when chelated or exchangeable). The forms in which different elements occur in the different horizons are assessed. In the surface horizons rich in organic matter many elements, such as Co, Ni, Fe, V, Cu, Cd, Sn and Pb, appear to occur mainly in chelated form; fewer, particularly Mn, are only in exchangeable form with plant uptake being largely responsible. Lower in the profiles the most common forms are acetic acid-soluble or, in gleyed horizons, exchangeable. In these horizons the degree of mobilisation is greater than in the corresponding freely drained horizons, the effect being most apparent for elements in readily weathered minerals.