Experimental Study Of Cu And Zn Isotope Fractionation At Low Temperature

The geochemical cycling of metals in hydrosphere and soil environments involves adsorption and leaching, two important processes of low-temperature supergene environment. Understanding the mechanisms of isotope fractionation during these processes is pivotal for applying Cu-Zn isotopes as a tracer for geochemical recycling.The contents and achievements obtained in the present doctoral dissertation can be summarized as follows:(1) long-term external reproducibility better than ±0.05‰ for ?65Cu, ±0.05‰ for ?56Fe and ±0.06‰ for ?66Zn was routinely obtained. The improved precision of stable Cu isotopic analysis demonstrates that igneous rocks are not homogeneous in Cu isotopic composition.(2) The adsorption experiments show that light Cu isotopes are preferentially adsorbed onto the kaolinite surface, leaving the residual solutions enriched in heavy isotopes. the Δ65Cuadsorbed-solution value is strongly affected by the initial Cu concentration, contact time and the ionic strength, which is critical for interpreting Cu isotopic variations in sediments from estuarine settings, where salinity varies substantially. The Δ65Cuadsorbed-solution value is insensitive to p H and temperature. This is important for interpreting Cu isotopic compositions of the oceans in oxic depositional settings, regardless of variable temperatures in geological time. XRD and Rayleigh modeling show that such isotope fractionation of copper may have been caused by the preferential adsorption of isotopically different Cu species(Cu(H2O)62+) in aqueous solutions.(3) At different experimental conditions, Zn isotopic compositions do not change during adsorbed onto the kaolinite surface. This may be due to zinc only has one specie(Zn(H2O)62+) in aqueous solutions.(4) The oxidative weathering of basalts and chalcopyrite produce a substantial fractionation of Cu isotope(?65Cuaq-solid) between the leached solutions(Cuaq) and the initial powders(Cusolid). At high p H, Cu initially released into solutions were isotopically heavier, and these results can explain why the natural water has the heavier Cu isotopes than the natural soils. At low p H, as the percentage of leached Cu increases, the ?65Cuaq values decrease first and then increase, these results can explain the water has the light Cu isotope composition in the acid region. XRD and isotopic analysis show that the mechanism responsible for the Cu isotope frationation of the basalts during leaching is due to the basalts have the different phase, which has different leaching rates. But the mechanism of the Cu isotope frationation of chalcopyrite during leaching is due to the relative diffuse rates of 65 Cu and 63 Cu.(5) Cu-Zn isotope can appear the opposite trend during the weathering, but it will be changed if there are other factocs.Based on the establishment of high precision Cu-Fe-Zn analysis method, we carried out for the first time a series of experiments to investigate the isotope fractionation of Cu during adsorption and leaching for a wide range of conditions. Our study represents one important step for future studies to use Cu isotopes to trace the source of metal contaminants in natural soils.