Geochemical Study On Mobility Of Heavy Metals In Bank Sediments Distributed In Xiangtan Section Of The Xiangjiang River

In this study, the river-bank sediments distributed in the Xiangtan City that the Xiangjiang River pass through were vertical-profile sampled at the Zhubugang and Xiashesi areas, and geochemically investigated using technqiues including XRF(X-ray fluorescence) and ICP-MS(inductively coupled plasma mass spectrometry). The concentrations of major elements and trace elements including the heavy metals in the sediments were analyzed. The results through PCA analysis 、 Pearson correlation analysis and step regression analysis showed that river-bank sediment in Xiangtan City of Xiangjiang River has the following charactrizaton:(1) The major elements of SiO2, K2 O, TiO2 is relatively stable, while Na2 O, MnO, LOI content of component variation significantly(Cv>0.2).The results show that the sediments are characterized by depletion of alkali elements including Na2 O, CaO and MgO; and by significant enrichment of Fe2O3 and MnO, meanwhile Al2O3, MgO, P2O5 and LOI et al have significant grain-sized effect; Major elements trace of sediment source rocks: Xiangtan river-bank sediments of Xiangjiang River source is the upstream granite.(2) The average content and variation of rare earth element: La, Ce, Pr, Nd, Sm et al is significantly increased from XS to ZB; the light rare earth element is relatively enriched and heavy element is relatively depeletion, the rare earth element distribution plot tends to granite plot compared with upper continent,Yangtze River and suspended solids in Xiangjiang River, which may indicate that granite is the sediments source of Xiangtan river-bank sediment; the Ceanom is above-0.10 which may say that reducing environment is the study area sediment deposition environment; there are no large differences insediment deposition rate between XS and ZB, but ZB sediment may be nearly to sediment source. All of the high field strength elements vertical variation characterization is not significant.(3) Enrichment index results indicate that: bank sediment is concentrated and enriched with element Zn, Pb, Mn, Ni, Th, U, V, Ba, Sc, Cr et al are not very enriched. These metal enrichment may cause heavy metal contamination to the sediments.Evaluation by using the geo-accumulation index(Igeo) shows that bank sediments of Xiangtan city were potentially contaminated by heavy metals Zn, Pb, Cu; Ba, Sc, V, Cr, Co, Ni, Th, U were not harmful to the sediment. The element content of Fe2O3, LOI, ∑REE et al and Eu/Eu*ratio can be used as a geographic indictor to heavy metal contamination and those special elements may indicate the heavy metal contamination.(4) The PCA analysis and Pearson correlation analysis are used to get information on the possible host mineral phases for heavy metals in the sediments, and the results show that metals Th, U may mostly hosted in detrital minerals(e.g., quartz, and feldspar), and heavy metals Ba, Sc, V,Cr, Co, Mn, Cu, Pb and Zn in Fe-Mn(hydro)-oxides(e.g., hematite, and pyrolusite). These hosted in detrital minerals are mostly immobile, and mainly of natural source, and these heavy metals Mn, V, Co, Cr, Cu, Pb,and Zn are the mobile elements in the sediments, which may be mobilized to migrate due to change of oxidation and reduction condition.That may cause the river-bank sediments to be a possible source of heavy metal contamination.