Guilin Han

Enrichment and Release of Rare Earth Elements during Weathering of Sedimentary Rocks in Wujiang Catchments, Southwest China

Abstract Thirteen weathering profiles of sedimentary rocks such as limestone, dolomitic limestone, dolomite, sillicalite, black shale and purple sandrock from Wujiang catchments were selected for study on enrichment and release behavior of rare earth elements (REE) during weathering, and its impact on plant growth and riverine REE distribution in the catchments with methods of hierachical cluster analysis and mass balance calculation in order to set a basis for riverine material source research and agricultural production. The results show that the enrichment degree of REE in calcareous soils from the Wujiang catchments is much higher than that of limestone, yellow soil, upper continental crust (UCC), China soil (CS) and world soil (WS). The ability of enrichment and release of REE is partly controlled by distribution of REE in bedrocks, contents and adsorption ability of organic matters, clay minerals and Fe-oxides/hydroxides in weathering profiles. The REE released from weathering of carbonate rocks and clastic rocks can be absorbed and utilized by local plants. The results also reveal that release of REE and Fe mainly from weathering of carbonate rocks and partly from clastic rocks exerts an important control on riverine REE distribution.

Mobilisation and transport of arsenic and antimony in the adjacent environment of Yata gold mine, Guizhou province, China

Arsenic and antimony distribution in water, sediment, soil and plants in the Yata gold mine and surrounding area, southwestern China, was investigated, so as to elucidate the mobilisation, transport, and distribution of As and Sb in mine environments. While oxidation of sulfide minerals mobilises both As and Sb, gold extraction by cyanidation is found to mobilise a large amount of Sb. Strontium concentration in water is proposed as an indicator for the oxidation of sulfide minerals in mine environments rich in carbonate. The partitioning of As, Sb, Fe, Cu, Zn and Sr between suspended particulate matter (SPM) and water shows a particle concentration effect. The partition coefficient (K(d)) decreases in the order Fe > Zn > Cu > As = Sb > Sr, consistent with the low affinity of As and Sb to SPM and the significant presence of As and Sb in soluble phase of water. During the transport of metalloids in water downstream of the mine area, As is released from the particulate or sediment to water as a result of the slight increase of pH, whereas Sb is not. The accumulation of As and Sb in soil and prevalent plants is minor with exceptions of rice root and Equisetumarvensel. The As and Sb concentration in the plants appears to be independent of the total As and Sb concentration in soil.

Hydrogeochemistry of Wujiang River water in Guizhou Province, China

The chemical composition of Wujiang River water represents that of river water from the typical carbonate areas. Its hydrogeochemical characteristics are different from those of global major rivers. The Wujiang River and its tributaries have high total dissolved solid concentrations, with Ca2+ and HCO3− being dominant, Mg2+ and SO42− coming next. Both Na+ + K+ and Cl− + Si account for 5%–10% of the total cations and anions, respectively. These general features show the chemical composition of river water is largely controlled by carbonate weathering, with the impact of silicate and evaporate weathering being of less importance. Production activity, mining practice and industrial pollution also have some influence on the chemical composition of river water.

Strontium isotopic geochemistry of the Changjiang estuarine waters: Implications for water-sediment interaction

The Sr concentrations and87Sr/86Sr ratios have been measured for the Changjiang estuarine waters with a main purpose to understand physical and chemical processes at the estuary. The result shows that the Changjiang River water has higher Sr concentration (150 ng/g) and lower87Sr/86Sr ratio (0.7105) when compared with the average values (0.7119 for87Sr/86Sr and 78ppb for Sr, respectively) of large world rivers. In the mixing process, no simple mixing of two end-members has been found according to the variations of Sr concentration and isotope ratios. There is an abrupt rise of Sr isotope ratios at the salinity about 1mg/g during river-sea water mixing at the estuary. This abrupt rise of Sr isotope ratios is mostly ascribed to the strong water-sediment interaction, because there exists the same rise of suspended particulate materials due to energetic resuspension of bottom sediments.