A surface complexation model for cadmium and lead adsorption onto diatom surface

This work is devoted to the physico-chemical study of cadmium and lead interaction with diatom–water interfaces for two marine planktonic (Thalassiosira weissflogii = TW, Skeletonema costatum = SC) and two freshwater periphytic species (Achnanthidium minutissimum = AMIN, Navicula minima = NMIN) by combining adsorption measurements with surface complexation modeling. Reversible adsorption experiments were performed at 20 °C after 3 h of exposure as a function of pH, metal concentration in solution, and ionic strength. While the shape of pH-dependent adsorption edge is similar among all four diatom species, the constant-pH adsorption isotherm and maximal binding capacities differ. These observations allowed us to construct a surface complexation model for cadmium and lead binding by diatom surfaces that postulates the constant capacitance of the electric double layer and considers Cd and Pb complexation with mainly carboxylic and, partially, silanol groups. Parameters of this model are in agreement with previous acid–base titration results and allow quantitative reproduction of all adsorption experiments.     

Can stable isotopes be used to monitor landfill leachate impact on surface waters?

Bacterially mediated methanogenesis in municipal solid waste landfills has been shown to cause an enrichment of carbon stable isotope ratios of dissolved inorganic carbon and hydrogen stable isotope ratios of water in landfill leachate. In the present study, we investigate the universality of this enrichment in leachate obtained from four diverse landfill sites in New Zealand. At each site, surface water samples upstream and downstream of landfills were analysed to examine the applicability of stable isotope ratios as a tool for monitoring leachate contamination in landfill-associated streams. The design of leachate collection systems, operational history, and landfill location appeared to strongly influence leachate isotopic values and the effectiveness of isotope ratios as an environmental monitoring tool for surface water.     

Geochemical evolution of the Capim River kaolin, Northern Brazil

The Capim River kaolin, located in the eastern Brazilian Amazon, constitutes one of the most important kaolin deposits in the world. Known for its high whiteness, its noble application is in the paper industry. Studies were carried out on samples from the six facies of the deposit (sand kaolin, soft kaolin, lower transition facies, ferruginous crust, upper transition facies and flint kaolin) in order to trace its geochemical evolution. The kaolin developed at the expense of Cretaceous sandy–clayey sediments of the Ipixuna Formation. Intense lateritic processes characterized by ferruginization and deferruginization mechanisms led to the distinction of the different facies.     

Holocene record of productivity in the NW Iberian continental shelf

A multiproxy approach (textural characteristics, heavy metal concentrations and benthic foraminifera data) was adopted to study the OMEX core KSGX 40, collected at the Galicia Mud Deposit (NW Iberian outer continental shelf) and recording the last ca. 4.8 ka cal BP. Geochemical profiles of Fe, Mn, Zn, Co, Cr, Cu, Ni, Pb, Al and Ca show significant temporal variations. Benthic foraminifera productivity proxy suggests that the recorded muddy events were contemporaneous of a higher C_org flux to the marine benthic environment. The higher flux of organic matter, following a long-term intensification of the upwelling and coinciding with a finer sedimentation, led to depressed levels of oxygen beneath the water-sediments interface and to early diagenetic processes of several redox-sensitive elements.     

Platinum and palladium mobility in supergene environment: The residual origin of the Pirogues River mineralization, New Caledonia

Eluvial concentration of platinum-group minerals (PGM) has developed in the south of New Caledonia, from the weathering of a mafic and ultramafic cumulate. The platinum/palladium (Pt/Pd) ratio evolution from the bottom to the top of the weathering profile indicates a chemical mobilization of Pd in supergene environment. The examination by scanning electron microscopy of the residual PGM collected in the weathering profile and their chemical characterization by electronic microprobe show a preservation of the structure and chemical signature (in the core of the grains) of the fresh PGM. This clearly demonstrates that the PGM studied here are residual and are affected by dissolution process.     

Developments in the characterisation of waste materials for environmental impact assessment purposes

The characterisation of waste is entering a new phase with the latest developments of characterisation leaching tests and associated modelling capabilities. The currently applied too simple testing approaches lead to poor choices in waste management. With the increased insight in release controlling processes chemical speciation aspects can be addressed even in the most complex and heterogeneous waste materials. From a composition perspective materials may be highly variable, but often materials are far more consistent in their leaching behaviour. This aspect should be exploited more extensively as it holds the key to treat waste materials in such a way that long term solutions are achieved rather than reaching temporary gains.     

Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering

Understanding the evolution of geochemical and geomorphic systems requires measurements of long-term rates of physical erosion and chemical weathering. Erosion and weathering rates have traditionally been estimated from measurements of sediment and solute fluxes in streams. However, modern sediment and solute fluxes are often decoupled from long-term rates of erosion and weathering, due to storage or re-mobilization of sediment and solutes upstream from the sampling point. Recently, cosmogenic nuclides such as ¹⁰Be and ²⁶Al have become important new tools for measuring long-term rates of physical erosion and chemical weathering. Cosmogenic nuclides can be used to infer the total denudation flux (the sum of the rates of physical erosion and chemical weathering) in actively eroding terrain. Here we review recent work showing how this total denudation flux can be partitioned into its physical and chemical components, using the enrichment of insoluble tracers (such as Zr) in regolith relative to parent rock. By combining cosmogenic nuclide measurements with the bulk elemental composition of rock and soil, geochemists can measure rates of physical erosion and chemical weathering over 1000- to 10,000-year time scales.     

Airborne gamma-ray spectrometry to quantify chemical erosion processes

Airborne gamma-ray spectrometry data (uranium, potassium and thorium contents) reveal geochemical heterogeneities within the monolithological Hyrôme watershed (ca. 150 km²) in the Armorican massif (western France). Our observations and computations provide important constraints on the spatial distribution and the associated magnitudes of chemical erosion processes at the scale of a small watershed. Two distinct, partially preserved, weathering profiles exhibit a strong correlation between regolith evolution and airborne-derived K/Th ratios, suggesting that the variability is linked to supergene processes. Using both airborne data and laboratory measurements on rock samples, the total net export of potassium has been estimated at 422 ± 50 kg/m² and the chemical weathering rate of potassium at 17 ± 2 kg/km²/a.     

Micro-spectroscopic investigations of highly heterogeneous waste repository materials

Assuring safe disposal and long-term storage of radioactive and toxic wastes corresponds to a primary environmental task of present societies. To improve any technical limitation, a mechanistic understanding of the processes governing the binding of heavy metals and radionuclides is required. In this study, the significance of synchrotron-based X-ray microprobes for elucidating the spatial distribution and the speciation of radionuclides in highly heterogeneous waste repository materials will be outlined. A case study on the uptake process of Co in cementitious engineered barrier materials exposed to microbial degradation will be presented.     

Neoproterozoic alkaline magmatism at Sivamalai, southern India

The Sivamalai alkaline complex lies at the southern margin of the Cauvery Shear System that separates the Archaean and Proterozoic domains of the Southern Granulite Terrain in India. U–Pb TIMS dating of zircon from a pegmatitic syenite sample in the complex yields a concordant age of 590.2 ± 1.3 (2σ) Ma which is interpreted to date the intrusion of the alkaline rocks. A lower concordia intercept at 168 ± 210 Ma defined by two grains with high common lead may indicate post-magmatic disturbances due to recrystallisation which is also evident in the CL images of the zircons. EPMA dating of monazite from a post-kinematic pegmatite which intrudes the crystalline basement hosting the alkaline rocks yields an age of 478 ± 29 (2σ) Ma and provides a lower bracket for the main phase of tectonism in this part of the Southern Granulite Terrain. The Pan-African high-grade metamorphism and ductile deformation has thus most likely affected the alkaline rocks. This is supported by the presence of a metamorphic foliation and extensive recrystallisation textures seen in the rocks. The major and trace element concentrations measured on selected samples reveals the presence of both enriched and depleted rock types. The enriched group includes ferrosyenite and nepheline syenite while the depleted group has only nepheline syenites. The trace element depletion of some nepheline syenites is interpreted to be a result of fractional crystallization involving the removal of accessory phases like zircon, titanite, apatite and allanite.