28 research outputs found
Early diagenesis and isotopic composition of lead in Lake Laisan, northern Sweden
Water column (dissolved/suspended phase, sediment traps) and sediment data (pore-water, solid-phase sediment) were combined with stable Pb and Pb-210 isotope data to trace the early diagenetic behaviour and geochemical cycling of Pb in Lake Laisan, a lake which has received large quantities of anthropogenic Pb since the early 1940s. Early diagenetic remobilisation of Pb is indicated by a subsurface pore-water Pb maximum (120 mug 1(-1)) in the oxic surface layer of the sediment, where the solid-phase Pb concentration is 3400-4600 mug g(-1). The remobilisation of Pb appears to be caused by a pH-controlled desorption of Pb from solid-phase sediment, which is consistent with a model describing surface complexation of Pb(II) on hydrous goethite surfaces. The diffusive Pb flux from the subsurface pore-water maximum towards the sediment surface (36 mug cm(-2) year(-1)) exceeds the depositional Pb flux (8.6 mug cm(-2) year(-1)) by approximately a factor of four, indicating that Pb is highly mobile in the sediment. Stable Pb isotope data and a mass balance calculation suggest that Pb diffusing upwards is, to a large extent, trapped in the surface sediment. Lead that may diffuse into the slightly alkaline lake water appears to be efficiently sorbed to suspended particulate matter, resulting in low dissolved Pb concentrations in the water column (0.040-0.046 mug 1(-1)). Sorption of Pb to suspended particulate matter is consistent with the elevated suspended particulate Pb concentrations in the hypolimnion (3800-4000 mug g(-1)), and the fact that the stable Pb isotopic compositions of suspended matter and pore-water are similar
Remediation of a marine shore tailings deposit and the importance of water-rock interaction on element cycling in the coastal aquifer
We present the study of the geochemical processes associated with the
first successful remediation of a marine shore tailings deposit in a
coastal desert environment (Bahia de Ite, in the Atacama Desert of
Peru). The remediation approach implemented a wetland on top of the
oxidized tailings. The site is characterized by a high hydrauliz
gradient produced by agricultural irrigation on upstream gravel terraces
that pushed river water (similar to 500 mg/L SO(4)) toward the sea and
through the tailings deposit. The geochemical and isotopic
(delta(2)H(water) and delta(18)O(water), delta(34)S(sulfate) ,
delta(18)O(sulfate)) approach applied here revealed that evaporite
horizons (anhydrite and halite) in the gravel terraces are the source of
increased concentrations of SO(4), Cl, and Na up to similar to 1500 mg/L
in the springs at the base of the gravel terraces. Deeper groundwater
interacting with underlying marine sequences increased the
concentrations of SO(4), Cl, and Na up to 6000 mg/L and increased the
alkalinity up to 923 mg/L CaCO(3) eq. in the coastal aquifer. These
waters infiltrated into the tailings deposit at the shelf-tailings
interface. Nonremediated tailings had a low-pH oxidation zone (pH 1-4)
with significant accumulations of efflorescent salts (10-20 cm thick) at
the surface because of upward capillary transport of metal cations in
the arid climate. Remediated tailings were characterized by neutral pH
and reducing conditions (pH similar to 7, Eh similar to 100 mV). As a
result, most bivalent metals such as Cu, Zn, and Ni had very low
concentrations (around 0.01 mg/L or below detection limit) because of
reduction and sorption processes. In contrast, these reducing conditions
increased the mobility of iron from two sources in this system: (1) The
originally Fe(III)-rich oxidation zone, where Fe(II) was reduced during
the remediation process and formed an Fe(II) plume, and (2) reductive
dissolution of Fe(III) oxides present in the original shelf lithology
formed an Fe-Mn plume at 10-m depth. These two Fe-rich plumes were
pushed toward the shoreline where more oxidizing and higher pH
conditions triggered the precipitation of Fe(HI)hydroxide coatings on
silicates. These coatings acted as a filter for the arsenic, which
naturally infiltrated with the river water (similar to 500 mu g/L As
natural background) into the tailings deposit