Assessing the surface composition of soil particles from some Podzolic soils by X-ray photoelectron spectroscopy

We have applied X-ray photoelectron spectroscopy (XPS) to assess the surface composition of soil particles in the AB, Bf, and Bhf horizons of some Podzolic soils from British Columbia, Canada. Since the analysis is restricted to a 'depth' of < 10 nm from the particle surface, this technique is uniquely suited to this purpose. For the soils used here, the elements detected in decreasing order of abundance are oxygen (46-54%), carbon (13-38%), silicon (3.2-20%), aluminium (4.8-14%), iron (1.0-4.4%), and nitrogen (0.4-2.9%). Small amounts of sodium and magnesium are also measured. In comparison with the corresponding values for the bulk soils, the surface of soil particles is enriched in C, N, and Al. As C and N may be assigned to organic matter (OM), this finding is strongly indicative of the presence of Al-organic complexes as a coating over soil particle surfaces. Unlike Al, Fe is relatively depleted at the surface of soil particles probably because Fe tends to precipitate as an oxyhydroxide phase in the pH range (4.1-5.3) of the soils sampled. Silicon is also depleted at soil particle surfaces but the extent of depletion is smaller for the AB than for the underlying Bf horizons. (C) 1998 Elsevier Science B.V. All rights reserved.