No abstract

By a simple washing of vaterite with ultrapure water, it transforms rapidly into cubic calcite. When the solid is washed with Cu 2+ solutions, the transformation depends on the concentrations of the copper solutions applied in the process. For concentrations of 10 -4 mol dm -3 , a certain delay in the transformation process is detected, and the obtained cubic calcite seems to be in the form of Cu x Ca 1-x CO 3 . For concentrations of 10 -3 mol dm -3 , the vaterite structure remains stable with time, and this stability seems to be correlated with the saturation of the surface by Cu 2+ in place of Ca 2+ . For concentrations of 10 -2 mol dm -3 , a mixture of vaterite, aragonite, cubic calcite, and malachite is obtained during the transformation process.

Abstract. The techniques of diffusional equilibrium in thin films (DET) and diffusional gradients in thin films (DGT) were used to obtain high resolution pore water profiles of total dissolved and labile trace (mobilizable) metals in the sediments of the Rupel River, Belgium. DGT measures labile metal species in situ by immobilizing them on a resin gel after diffusion through a diffusive gel whereas for DET an equilibrium is established between the DET gel and the pore water. Concentrations of Pb and Zn obtained by DGT were in good agreement with the results obtained by centrifugation, and thus were well buffered by rapid equilibrium with the solid phase, whereas Fe, Mn and Cd were very tightly bound to the sediment phase and large differences were observed between the labile and the total metal concentrations. Cu, Zn, Co and Ni show intermediated behavior.Good correlations were found between the profiles of As and Fe and Mn and Co for DET as well as DGT showing a close link between the geochemical behavior of these elements. Cu, Zn, Pb and Cd are also influenced by the reductive mobilization of Fe and Mn oxides but are also closely linked to the bacterial degradation of organic matter in the surface sediments as to the precipitation of metal sulfides in the deeper layers.