Assessment of Dissolution of Silicate Rock Reference Materials with Ammonium Bifluoride and Nitric Acid in a Microwave Oven

The complete dissolution of representative test portions of powdered rock samples for the determination of the mass fractions of trace elements by ICP‐MS relies either on aggressive and time‐consuming acid digestions or fusion/sintering with appropriate fluxes. Here, we evaluate a microwave oven dissolution method that employs a solution of NH₄HF₂ and HNO₃. The entire procedure occurs in a closed vessel system and takes up to 4 h. In hundreds of digestions, the precipitation of fluorides was never observed. Replicate decomposition of 100 mg of twenty‐one international reference materials (RMs) of igneous rocks, and also one of a shale presented mostly satisfactory recoveries of forty‐one trace elements. Important exceptions were Zr and Hf in G‐2 and GSP‐2 (mean recoveries of ca. 70%), although for four other felsic rock RMs, the digestion was complete. For ultramafic rock RMs, we present Cr results that indicate quantitative dissolution of Cr‐bearing phases. We discuss the findings and conclude that advances in sample preparation of geological materials for instrumental analysis would benefit from a better understanding of how specific characteristics, such as composition and crystallinity of certain minerals, may affect their reactivity.     

Diffraction of P, S and Rayleigh waves by three-dimensional topographies

The diffraction of P, S and Rayleigh waves by 3-D topographies in an elastic half-space is studied using a simplified indirect boundary element method (IBEM). This technique is based on the integral representation of the diffracted elastic fields in terms of single-layer boundary sources. It can be seen as a numerical realization of Huygens principle because diffracted waves are constructed at the boundaries from where they are radiated by means of boundary sources. A Fredholm integral equation of the second kind for such sources is obtained from the stress-free boundary conditions. A simplified discretization scheme for the numerical and analytical integration of the exact Green's functions, which employs circles of various sizes to cover most of the boundary surface, is used.
The incidence of elastic waves on 3-D topographical profiles is studied. We analyse the displacement amplitudes in the frequency, space and time domains. The results show that the vertical walls of a cylindrical cavity are strong diffractors producing emission of energy in all directions. In the case of a mountain and incident P, SV and SH waves the results show a great variability of the surface ground motion. These spatial variations are due to the interference between locally generated diffracted waves. A polarization analysis of the surface displacement at different locations shows that the diffracted waves are mostly surface and creeping waves.     

Interactions of cadmium(II) and protons with dead biomass of marine algae Fucus sp.

Samples of dead biomass from the marine brown algae Fucus ceranoides, Fucus vesiculosus and Fucus serratus were studied for their ability to remove cadmium from aqueous solutions. The metal sorption process is rapid, with 90% of the metal uptake completed within the first 25 min of contact. The kinetic data was described successfully by a pseudo second order chemical sorption process with rate constants of ca. 0.6 g mmol^− 1 min^− 1. At pH 4.5, the raw biomass of the three species exhibited equilibrium uptake capacities for Cd as high as 0.8 mmol g^− 1 (90 mg g^− 1), on a dry weight basis, without chemical pretreatment. These sorption capacities are much higher than those reported for activated carbon and chitin. The sorption of Cd was found to increase as pH increases, reaching a plateau at pH 5.Batch sorption experiments and continuous potentiometric titrations of acid-treated biomass samples in 0.05 M NaNO₃ were used to derive thermodynamic binding parameters according to the NICCA model. The total amount of acid sites was 2.4–2.9 mmol g^− 1, with median values of the affinity distribution for protons and cadmium ions, log K˜_H and log K˜_Cd, of 3.7 and 2.69, respectively (conditional values). The apparent heterogeneity of the sorbent was successfully taken into account by the empirical NICCA isotherm, which described very well the competition between protons and metal ions, in contrast with a simpler discrete competitive Langmuir model.The experimental results demonstrate that these seaweeds constitute a promising, efficient, cheap and biodegradable sorbent biomaterial for cadmium removal from wastewaters. This use would represent an example of exploitation of a renewable marine resource in water treatment technologies for the prevention of heavy metal pollution in the environment.     

Organic matter accumulation during the Holocene in the Guadalquivir marshlands (SW Spain)

The distribution of biomarker compounds and magnetic susceptibility observed in the sediment from a 20 m core drilled in the marshlands of the estuarine region of the Guadalquivir River (southwest coast of Spain) has allowed us to reconstruct the palaeoenvironmental evolution of this area during the Holocene. Several organic compounds (n‐alkanes, n‐ketones, n‐alkanols, n‐alkanoic acids and organic sulphur), as well as different biomarker ratios, have been used to show changing environmental conditions through time. These geochemical proxies suggest good preservation of the organic matter, although some diagenesis has occurred to particular organic compounds, especially the n‐alkanoic acids. Our data indicate a major allochthonous supply of terrestrial plants, with less influence from aquatic plants or algae through the core. There are markedly different palaeoenvironmental conditions between the uppermost 5 m (last 6 ka cal. B.P.) and the rest of the core. From 5 m (ca 6 ka cal. B.P.) to 19 m (ca 8 ka cal. B.P.) depth the palaeoenvironmental conditions were almost constant. Based on organic sulphur content and n‐alkane content logs, anoxic conditions prevailed from 8 to 6 ka cal. B.P., while oxic conditions with enhanced convection of water (prevalence of fluvial input), and consequently a greater organic matter supply, predominated in the upper 5 m of the core. Similarly, little variation in the magnetic susceptibility profile below 5 m indicates stable environmental conditions, while in the upper 5 m conditions shifted to one with elevated water input and clastic sediment supply. This is linked to palaeofloral alterations in the Guadiamar/Guadalquivir drainage basins and/or anthropogenic effects. We propose that from ca 8 to 6 ka cal. B.P. a stable landscape physiognomy in the surroundings of the estuarine area of the Guadalquivir River, with a predominance of pines and grassland. However, over the last 6 ka cal. B.P. a variation in the terrestrial plant biomarker compounds suggests an alternation of relatively dry and humid phases and/or the impact of human populations on altering the vegetation community have occurred. Copyright © 2007 John Wiley & Sons, Ltd.     

Megafan formation driven by explosive volcanism and active tectonic processes in a humid tropical environment

Quaternary volcanism in the Central Cordillera of Costa Rica has created an orographic barrier that concentrates rainfall on its northern side. This humid climate produces weathered bedrock prone to landsliding. Ash fall from explosive eruptions kills the vegetation cover and intensifies erosion processes. These eruptions, hydrothermal activity and associated earthquakes destabilize the slopes of river valleys, and even the volcanic edifices, producing landslides and large debris avalanches. All these processes mobilize an extra sediment input that is deposited in the piedmont lowlands forming the Santa Clara megafan. The megafans described in the literature mainly grow according to climatic fluctuations; however, sedimentation in the Santa Clara megafan is also controlled by endogenic processes with longer recurrence periods. Analysis of this megafan provides new insight into the origin and evolution of these landforms. In volcanic regions, active volcanism should be considered when investigating the formation of some megafans.     

Effect of adjoining structures on seismic response of tunnels

In this paper the seismic behaviour of buried concrete tunnels is studied using the finite element method. The numerical tool employed is the well-known soil–structure interaction computer program FLUSH and thus analyses are carried out in the frequency domain. The seismic environment is supposed to consist of vertically propagating shear and compression waves that reproduce artificial accelerograms of a broad frequency content at selected control points. The effect of near or adjacent massive structures, such as those of nuclear power plants, is evaluated showing their influence on tunnel response. The results calculated for acceleration levels, internal structural loads, response spectra, etc., are analysed and compared either with those obtained from soil free-field response or with others computed using an alternative simplified methodology, providing useful information for preliminary design purposes.     

Seismic earth thrust against massive building walls

The problem of earth thrust for a massive building in a seismic environment is analysed. Intertial and kinematic soil-structure interactions are considered by modelling the soil and the structure together. The problem is solved in the frequency domain by using the computer code FLUSH. Results show that the horizontal component of the seismic earth thrust is much greater than that obtained when applying the Mononobe-Okabe theory. This study establishes a set of conclusicns and recommendations for both design and practical purposes, and proposes future lines of investigation.