Trace and rare earth element content of white clay soils of the Three River Plain, Heilongjiang Province, P.R. China

Abstract

Three representative pedons of white clay soils in the Three River Plain, Heilongjiang Province, P.R. China were sampled to establish background levels of trace elements and rare earth elements (REE) and to evaluate pedogenic redistribution of these elements. Trace elements and REE in soil samples and clay separates were measured by instrumental neutron activation analysis. New information was obtained for the background levels and pedogenic behavior of 20 trace elements and 10 REE. Cl, Br, I and Hg were enriched in the Ah horizon. Elements having an adsorption affinity for Mn and Fe oxyhydroxides (As, Co and Mn) were concentrated in the E horizon. Elements associated with clay minerals (Cr, Rb, V and Zn) were elevated in soil samples from the illuvial horizon, while elements present in resistant minerals (Sr, Ti, Hf and Zr) had relatively uniform profile distributions. Possible chemical causes of the trace element redistribution and partitioning are also discussed in the paper. REE were enriched in clay fractions compared to whole soil. Ce positive anomalies seen in normalized curves of REE for the E horizon were attributed to precipitation and accumulation of the element in pedogenic Fe-Mn nodules. The Gd break, even-odd and tetrad effects were present in normalized curves, which indicates fractionation of REE during weathering. The high ratio of light REE (sum La) to heavy REE (sum Lu) for the soil can be attributed to a warm, humid geochemical weathering environment in the past.