Weathering Of Glass Research Articles

Aluminoborosilicate waste glass dissolution under alkaline conditions at 40°C: implications for a chemical affinity-based rate equation

Environmental context. The production of nuclear materials has generated a very large amount of highly radioactive wastes that need to be disposed of in a manner that will keep them from posing a danger for millions of years until the radioactivity decays. The process being considered for this daunting task is to contain the wastes in glass. Although studies with ancient and natural glass suggest the weathering of glass is slow, experiments are being conducted to determine the impact of this material on the natural environment and attempt to predict its long-term behaviour. The present paper briefly discusses three models that are being considered for implementing this process and the one that appears to hold the most promise. Abstract. Single-pass flow-through experiments were conducted with aluminoborosilicate waste glasses to evaluate how changes in solution composition affect the dissolution rate (r) at 40°C and pH (23°C) = 9.0. The three prototypic low-activity waste (LAW) glasses, LAWE-1A, -95A and -290A, used in these experiments span a wide range covering the expected processing composition of candidate immobilised low-activity waste (ILAW) glasses. Results suggest incongruent release of Al, B, Na, and Si at low flow-rate (q) to sample surface area (S), in units of (m s–1), (log10(q/S) < –8.9) whereas congruent release is observed at high q/S (log10(q/S) > –7.9). Dissolution rates increase from log10(q/S) ≈ –9.3 to –8.0 and then become constant at log10(q/S) > –7.9. Forward (maximum) dissolution rates, based on B release, are the same irrespective of glass composition, evident by the dissolution rates being within the experimental error of one another (r1A = 0.0301 ± 0.0153 g m–2 day–1, r95A = 0.0248 ± 0.0125 g m–2 day–1, and r290A = 0.0389 ± 0.0197 g m–2 day–1). The results also illustrate that as the activity of SiO2(aq) increases, the rate of glass dissolution decreases to a residual rate. The pseudo-equilibrium constant, Kg, (log10(Kg) = –3.7) predicted with these results is slightly lower than the K for chalcedony (log10(K) = –3.48) at 40°C. Finally, these results support the use of a chemical affinity-based rate law to describe glass dissolution as a function of solution composition.

Clay minerals, oxyhydroxide formation, element leaching and humus development in volcanic soils

A weathering sequence with soils developing on volcanic, trachy-basaltic parent materials with ages ranging from 100–115,000 years in the Etna region served as the basis to analyse and calculate the accumulation and stabilisation mechanisms of soil organic matter (SOM), the transformation of pedogenic Fe and Al, the formation and transformation of clay minerals, the weathering indices and, by means of mass-balance calculations, net losses of the main elements. Although the soils were influenced by ash depositions during their development and the soil on the oldest lava flow developed to a great extent under a different climate, leaching of elements and mineral formation and transformation could still be measured. Leaching of major base cations coupled with a corresponding passive enrichment of Al or Fe was a main weathering mechanism and was especially pronounced in the early stages of soil formation due to mineral or glass weathering. With time, the weathering indexes (such as the (K + Ca)/Ti ratio) tend to an asymptotic value: chemical and mineralogical changes between 15,000 and 115,000 years in the A and B horizons were small. In contrast to this, the accumulation of newly formed ITM (imogolite type materials) and ferrihydrite showed a rather linear behaviour with time. Weathering consisted of the dissolution of primary minerals such as plagioclase, pyroxenes or olivine, the breakdown of volcanic glass and the formation of secondary minerals such as ITM and ferrihydrite. The main mineral transformations were volcanic glass ➔ imogolite ➔ kaolinite (clay fraction). In the most weathered horizons a very small amount of 2:1 clay minerals could be found that were probably liberated from the inner part of volcanic glass debris. The rate of formation and transformation of 2:1 clay minerals in the investigated soils was very low; no major changes could be observed even after 115,000 years of soil evolution. This can be explained by the addition of ash and the too low precipitation rates. In general, soil erosion played a subordinate role, except possibly for the oldest soils (115,000 years). The youngest soils with an age < 2000 years had the highest accumulation rate of organic C (about 3.0 g C/m 2/year). After about 15,000 years, the accumulation rate of organic C in the soils tended to zero. Soil organic carbon reached an asymptotic value with abundances close to 20 kg/m 2 after about 20,000 years. In general, the preservation and stabilisation of SOM were due to poorly crystalline Al- and Fe-phases (pyrophosphate-extractable), kaolinite and the clay content. These parameters correlated well with the organic C. Imogolite-type material did not contribute significantly to the stabilisation of soil organic matter.

Volcanic soil formation in Calabria (southern Italy): The Cecita Lake geosol in the late Quaternary geomorphological evolution of the Sila uplands

This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS 14C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals.

Accelerated weathering of high-level and plutonium-bearing lanthanide borosilicate waste glasses under hydraulically unsaturated conditions

The US Department of Energy (DOE) has proposed that a can-in-canister waste package design be used for disposal of excess weapons-grade Pu at the proposed mined geologic repository at Yucca Mountain, Nevada. This configuration consists of a high-level waste (HLW) canister fitted with a rack that holds mini-canisters containing a Pu-bearing lanthanide borosilicate (LaBS) waste glass and/or titanate-based ceramic (∼15% of the total canister volume). The remaining volume of the HLW canister is then filled with HLW glass (∼85% of the total canister volume). A 6-a pressurized unsaturated flow (PUF) test was conducted to investigate waste form–waste form interactions that may occur when water penetrates the canisters and contacts the waste forms. The PUF column volumetric water content was observed to increase steadily during the test because of water accumulation associated with alteration phases formed on the surfaces of the glasses. Periodic excursions in effluent pH, electrical conductivity, and solution chemistry were monitored and correlated with the formation of a clay phase(s) during the test. Geochemical modeling, with the EQ3NR code, of select effluent solution samples suggests the dominant secondary reaction product for the surrogate HLW glass, SRL-202, is a smectite di-octahedral clay phase(s), possibly nontronite [Na 0.33 Fe 2(AlSi) 4O 10(OH) 2 · n(H 2O)] or beidellite [Na 0.33Al 2.33Si 3.67O 10(OH) 2]. This clay phase was identified in scanning electron microscope (SEM) images as discrete spherical particles growing out of a hydrated gel layer on reacted SRL-202 glass. Alpha energy analysis (AEA) of aliquots of select effluent samples that were filtered through a 1.8 nm filter suggest that approximately 80% of the total measurable Pu was in the form of a filterable particulate, in comparison to unfiltered aliquots of the same sample. These results suggest the filterable particles are >1.8 nm but smaller than the 0.2 μm average diameter openings of the Ti porous plate situated at the base of the column. In this advection-dominated system, Pu appeared to be migrating principally as or in association with colloids after being released from the LaBS glass. Analyses of reacted LaBS glass particles with SEM with energy dispersive X-ray spectroscopy suggest that Pu may have segregated into a discrete disk-like phase, possibly PuO 2. Alteration products that contain the neutron absorber Gd have not been positively identified. Separation of the Pu and the neutron absorber Gd during glass dissolution and transport could be a criticality issue for the proposed repository. However, the translation and interpretation of these long-term PUF test results to actual disposed waste packages requires further analysis.

Micromorphology of soils derived from volcanic ash in Europe: a review and synthesis

SummaryAn analysis of the available literature on European volcanic ash soils has been made. Most has been published in Congress proceedings and Journals of national societies, less than half in English. More than half of the papers deal with soils on the Canary Islands. Many papers focus only on one aspect, and complete descriptions are found only in recent publications. Often the use of vague micromorphological terminology and the absence of analytical data make interpretation and comparisons difficult or impossible. Nonetheless, some general features do emerge. In the least‐weathered soils, the micromass forms first coatings around the coarse constituents, later granules, finally giving rise to a loose granular microstructure in the topsoil, and a compacted granular one in the Bw horizons of typic andic materials. The b‐fabric of the micromass is undifferentiated. With increasing weathering, clay coatings appear, the microstructure becomes more blocky and the b‐fabric becomes speckled or even striated. In Vertisols and Aridisols, micromorphological characteristics are not much different from those in the comparable non‐volcanic soils, except generally for the tendency to granular (intrapedal) microstructures. In Icelandic soils, microstratification, lenticular microstructure and preservation of plant residues as a result of cryic conditions and permanent volcanic and aeolian activity are observed. Weathering of volcanic glass in well‐drained conditions yields allophane alteromorphs similar to palagonite, which are easily subject to fragmentation by pedoturbation. The possible influence of surface transport and burial on the formation of Bw‐horizons in andic materials is discussed.

Cation exchange reactions controlling desorption of 90Sr 2+ from coarse-grained contaminated sediments at the Hanford site, Washington

Nuclear waste that bore 90Sr 2+ was accidentally leaked into the vadose zone at the Hanford site, and was immobilized at relatively shallow depths in sediments containing little apparent clay or silt-sized components. Sr 2+, 90Sr 2+, Mg 2+, and Ca 2+ was desorbed and total inorganic carbon concentration was monitored during the equilibration of this sediment with varying concentrations of Na +, Ca 2+. A cation exchange model previously developed for similar sediments was applied to these results as a predictor of final solution compositions. The model included binary exchange reactions for the four operant cations and an equilibrium dissolution/precipitation reaction for calcite. The model successfully predicted the desorption data. The contaminated sediment was also examined using digital autoradiography, a sensitive tool for imaging the distribution of radioactivity. The exchanger phase containing 90Sr was found to consist of smectite formed from weathering of mesostasis glass in basaltic lithic fragments. These clasts are a significant component of Hanford formation sands. The relatively small but significant cation exchange capacity of these sediments was thus a consequence of reaction with physically sequestered clays in sediment that contained essentially no fine-grained material. The nature of this exchange component explained the relatively slow (scale of days) evolution of desorption solutions. The experimental and model results indicated that there is little risk of migration of 90Sr 2+ to the water table.

Raman identification of ancient stained glasses and their degree of deterioration

AbstractThe aim of this investigation was to establish a Raman procedure for on‐site identification of stained‐glass windows and their deterioration level. This study of a representative series of stained‐glass pieces dating from the thirteenth to seventeenth, nineteenth and twenty‐first centuries made it possible to classify the glasses into four types: Type 1 (rare, Ca‐rich Na silicate), Type 2 (rare, Na‐rich, Ca silicate), Type 3 (more frequent, KCa silicate) and a variant of Type 3, referred to as 3bis. Ion exchange of the alkali cations was made in boiling sulfuric acid and related to structural and compositional changes, which were analyzed with IR and Raman spectroscopy, optical microscopy and EDS. Measurements of the film thickness showed a great discrepancy between the ion‐exchange rates of KCa (Type 3: 60 µm/h) and NaCa (Type 2: 15 µm/h) silicates with that of Type 1 Ca‐silicate (0.05 µm/h). IR and Raman spectra provided proof that the nanostructure of the glass was modified, chiefly by the downward (Raman) and upward (IR) shift of the position of the main SiO stretching peak and a decrease in the intensity of the Boson peak, as well as the Raman 580 cm−1 SiO bending peak. The decrease in intensity of the narrow ∼950 cm−1 Raman peak, assigned to (earth)alkali nano crystallites in the glassy network, is correlated with the K/Na ion loss and glass weathering. Consequently Type 3bis samples are in fact glasses, in which the surface is depleted of K/Na ions. Optical micrographs support the macroscopic compositional and structural heterogeneity of the ancient glasses. This work demonstrates the potential of Raman scattering for in situ measurements of the degree of weathering of ancient stained glasses. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Condensation on ancient stained glass windows and efficiency of protective glazing systems: two French case studies, Sainte-Chapelle (Paris) and Saint-Urbain Basilica (Troyes)

The multidisciplinary EC VIDRIO project has the purpose of providing a better understanding of the effect of the environment on glass surfaces and paint (grisaille) and to evaluate the efficiency of the protective glazing system, in order to find sustainable solutions to protect ancient stained glass windows from the main causes of glass weathering, in particular the condensation phenomenon. Hence, a new device, named “dew point sensor”, was built and patented to protect the stained glass windows by detecting the condensation on the glass surface. The research was focused on laboratory tests and experimental campaigns: two important French monuments, Sainte-Chapelle in Paris and Saint-Urbain Basilica in Troyes, were monitored, while the study in Cologne Cathedral (Germany) is still in progress. Three different systems were used to detect the phenomenon of condensation in order to evaluate and compare their accuracy and reliability: the indirect measurement through mathematic calculations using air temperature and relative humidity, and two direct measurements by means of the dew point and the leaf wetness sensors. The laboratory tests and research in the field made evident the errors associated with the measurements of the condensation process, and the accuracy and reliability of the new device. The efficiency of the protective glazing system, as regards to the weathering of the stained glass windows, has been confirmed. In fact, the presence of a protective glazing reduces the danger of condensation on the internal side of the ancient window and also the total time of the high relative humidity values of the air in contact with the protected window.

Mineral weathering in trachydacitic-derived soils and saprolites involving formation of embryonic halloysite and gibbsite at Mt. Amiata, Central Italy

Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, central Italy, and is composed largely of trachydacitic rocks. The soils of Mt. Amiata show a dark, carbon-rich A horizon that overlies a slightly structured Bw horizon or, directly, a very thick saprolite, which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material. Mineral weathering in two of these soils, one under beech and the other under chestnut, was studied in detail. The mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar (principally K-feldspar), biotite and pyroxene. The main weathering products are an embryonic form of halloysite and gibbsite, while allophane is usually absent or occurs in minor amounts. SEM evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where Si is preferentially depleted in relation to Al. In the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner. However, the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile.

Localized Weathering: Implications for Theoretical and Applied Studies

In situ quantification of localized weathering processes on basalt flows in New Mexico and Hawaii demonstrates that small-area factors can be more important than other more readily observable factors. Further, it demonstrates that the factorial concept of the Pope Boundary-Layer weathering model is partially solvable, that organic weathering can accentuate glass weathering (with implications for climate models and storage of nuclear waste), and that silica coatings are not a simple solution for the preservation of stone monuments. Enhancement of glass weathering by lichens on the McCartys flow, El Malpais National Monument, New Mexico, remains restricted to a half-millimeter directly underneath the lichen-covered surface. In contrast, although the inorganic rock coating of silica glaze reduces weathering directly underneath the coating by up to nine times rates found in uncoated locales, silica glaze can almost double variability in weathering along its margins.

玄武岩ガラスの風化プロセスにおける希土類元素, ウラン, トリウムの地球化学的挙動に関する研究

黒ボク土, ローム層の化学分析を行うことで, 玄武岩ガラスの風化作用, 土壌化作用に伴う希土類元素 (REE) (Am, Cmの化学的類似元素), ウラン, トリウムの長期的挙動について調べた. 黒ボク土中では, 玄武岩ガラスは変質し, 粘土鉱物, 水酸化鉄へと変化していく. これらに伴うアルカリ元素, アルカリ土類元素の溶脱率は大きい. REEは玄武岩ガラスより溶脱するが, その移動度は小さい. ウラン, トリウムも若干溶脱するが, その溶脱率は小さい. 黒ボク土の下部のローム層では, REEの溶脱率は小さく, むしろ蓄積される場合もある. 黒ボク土の堆積速度と, 溶脱率より, REEと U, Thの玄武岩ガラスからの最大溶脱率が3000年間でそれぞれ約 50%, 30%, 30%と推定された. しかし, 溶脱した REE, ウラン, トリウムは, 下部のローム層中で溶脱されにくいので, より長期間の黒ボク土やローム層からのこれらの元素の溶脱率は小さいといえる.

Direct evidence of basic aluminium sulphate minerals in an S‐impacted Andosol

SummaryThe formation of basic aluminium sulphate (BAS) minerals [(K,Na)nAlx(OH)y(SO4)z] has often been invoked to explain sulphate retention in soils. These minerals have not yet, however, been directly observed in the soil. We extracted the clay fractions of Andosols intercepting large inputs of volcanogenic sulphur dioxide and acids (HCl, HF), simply by dispersing clays with Na+‐resins in deionized water without any other chemical treatment. Clay fractions concentrate 39–63% of total sulphur content of soil. Transmission electron microscopy coupled with energy‐dispersive analysis revealed the presence of BAS particles, appearing as nodules and spheres. These particles have an equivalent diameter smaller than 0.2 µm. They have an Al:S ratio close to 2.2 and 3.8 and are possibly amorphous aluminite or basaluminite, respectively. They seem to have been formed in microenvironments enriched in sulphate, but also in fluoride anions. Their formation seems to have been enhanced by the combination of large inputs of acids and SO2 and an effective Al supply from weathering of volcanic glass.

Glasses on the seabed: surface study of chemical corrosion in sunken Roman glasses

The current work aims to describe surface weathering of ancient glasses in marine environment. All data are collected using different techniques: optical microscopy, RGA, surface techniques (XPS, SEM and SIMS). Three types of glass weathering have been observed: white glass, glossy glass and glass showing growth rings. A compact structure characterizes white glasses, while a porous structure with flaked layers is typical of glossy glasses. White glasses show different abundance of characteristic elements or molecules (Mg(II), Sb(V), Ti(IV) and micro-crystalline silica). Glossy glasses, instead, are characterized by peeling layers of nearly pure silica glass, with small differences in composition owing to ionic mobility phenomena. Data suggest a time relation between white and glossy glasses. Visible growth rings characterize the third class of glass. They are made of titanium and antimony compounds centers surrounded by many rings with the same composition. Their temporal evolution has been explained according to the theory of ‘Liesegang rings’. Hypotheses on antimony and titanium origins are reported.

Genesis of Tephra‐derived Soils from the Roccamonfina Volcano, South Central Italy

The properties of seven pedons, formed in three different tephra deposits inside the main caldera of the Roccamonfina volcano, were examined to better understand the genesis of these soils. Three of these soils derived from trachytic ash deposits are deep and porous and have andic properties, imogolite, and high allophane content. In these ash‐derived soils, neogenesis of crystalline clays is limited but include halloysite and hydroxy‐interlayered vermiculite. Hydrated halloysite is present only in the deepest horizons of two of these pedons. By contrast, the deep and clayey soil formed from alkali basaltic scoria and the shallow and slowly permeable soils derived from consolidated trachyandesitic tuffs have weak andic properties. In these soils, allophane content is negligible and pedogenesis induces the neogenesis of crystalline clays dominated by halloysite. Unlike the ash‐derived soils, hydrated halloysite is present through most of the pedons. Climate, topography, and vegetation do not appear to be limiting factors for allophane formation in the area. The hydraulic properties of the parent material, possibly together with the time of pedogenesis, apparently affect the different pedogenetic trends of these soils. Allophanic soils developed in younger, porous, permeable ash deposits where rapid glass weathering is favored and Al and Si are readily available for allophane formation. By contrast, non‐allophanic soils developed in older, less porous, and less permeable scoria and consolidated tuffs where pedogenesis induces the neogenesis of crystalline clays and hydrated halloysite is probably formed by in situ weathering of volcanic glass. Allophanic and non‐allophanic soils are then coexisting in similar landscapes under similar climatic conditions.

Origin and diagenesis of blue-green clays and volcanic glass in the Pleistocene of the Côte d'Ivoire–Ghana Marginal Ridge (ODP Leg 159, Site 959)

The Ocean Drilling Program (ODP) Site 959 was drilled in the northern border of the Côte d'Ivoire–Ghana Ridge at a water depth of 2100 m. Pleistocene total thickness does not exceed 20 m. Winnowing processes resulted in a low accumulation rate and notable stratigraphic hiatuses. During the Late Pleistocene, bottom circulation was very active and controlled laminae deposition (contourites) which increased the concentration of glauconitic infillings of foraminifera, and of volcanic glass and blue-green grains more rarely, with one or several subordinate ferromagnesian silicates. Volcanic glass generally was X-ray amorphous and schematically classified as basic to intermediate (44–60% SiO 2 ). Opal-A or opal-CT suggested the beginning of the palagonitisation process, and previous smectitic deposits may have been eroded mechanically. The blue-green grains presented two main types of mineralogic composition: (1) neoformed K, Fe-smectite associated with zeolite (like phillipsite) and unequal amounts of quartz and anorthite; (2) feldspathic grains dominated by albite but including quartz, volcanic glass and smectites as accessory components. They were more or less associated with the volcanic glass. On the basis of their chemical composition, the genetic relationship between the blue-green grains and the volcanic glass seemed to be obvious although some heterogeneous grains seemed to be primary ignimbrite and not the result of glass weathering. The most reasonable origin of these pyroclastic ejecta would be explosive events from the Cameroon Volcanic Ridge, especially from the Sao Thome and Principe Islands and Mount Cameroon area. This is supported both by grain geochemistry and the time of volcanic activity, i.e. Pleistocene. After westward wind transport (some 1200 km) and ash fall-out, the subsequent winnowing by bottom currents controlled the concentration of the volcanic grains previously disseminated inside the hemipelagic sediment. Palagonitisation, and especially phillipsite formation, may result from a relatively rapid reaction during burial diagenesis (<1 m.y.), in deep-sea deposits at relatively low sedimentation rate. However, it cannot be excluded that the weathering had begun widely on the Cameroon Ridge before the explosive event.

Weathering of glass in moist and polluted air

During the present century, stained glass windows in European cathedrals have shown a rapid deterioration due to weathering. It is widely believed that this rapid deterioration is a result of airborne pollutants not present for most of the 6–8 centuries since these cathedrals were built. To explore this idea, we have exposed soda-lime glass samples to ambients in which temperature, relative humidity (RH), and pollutant (SO 2 and NO 2) concentration were systematically varied. After exposure, the surfaces of these glass samples were analyzed using nuclear reaction analysis (NRA) (to measure hydrogen profiles) and Rutherford backscattering. Glasses subject to cracking during hydration, such as the glass used in many historic stained glass windows, are also discussed.

Geochemistry and significance of basaltic rocks dredged from the South Tasman Rise and adjacent seamounts

Basalts dredged from two seamounts separated by some 200 km and built on ca 50–35 Ma oceanic crust west of Tasmania have slightly LREE‐depleted N‐MORB affinities and were probably generated in a spreading ridge or near‐ridge setting. They are compositionally very similar to 60 Ma basalts drilled at DSDP Site 282, midway between these seamounts. Taken together, these basalts provide a useful dataset for the compositional features of MORB erupted early in the rifting history of Tasmania separating from Antarctica. Well‐preserved intraplate alkaline basalts with HIMU geochemical affinities have been sampled from Cascade Seamount, which forms the peak of the East Tasman Plateau. Far more altered alkaline intraplate basalts dredged at several other locations within the South Tasman Rise south of Tasmania, and on seamounts built on oceanic crust and thinned continental crust south of the East Tasman Plateau, also show typically HIMU affinities for immobile trace‐element ratios (e.g. low Zr/Nb values, 3–5), but have undergone strong rare‐earth element mobility associated with sea‐floor weathering and replacement of glass by chemisorbed biogenic phosphate. Dolerites with some strong affinities to the Jurassic dolerites of Tasmania were dredged in the central section of the South Tasman Rise.

Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography

Surface samples, mostly from abyssal sediments of the South Atlantic, from parts of the equatorial Atlantic, and of the Antarctic Ocean, were investigated for clay content and clay mineral composition. Maps of relative clay mineral content were compiled, which improve previous maps by showing more details, especially at high latitudes. Large-scale relations regarding the origin and transport paths of detrital clay are revealed. High smectite concentrations are observed in abyssal regions, primarily derived from southernmost South America and from minor sources in Southwest Africa. Near submarine volcanoes of the Antarctic Ocean (South Sandwich, Bouvet Island) smectite contents exhibit distinct maxima, which is ascribed to the weathering of altered basalts and volcanic glasses. The illite distribution can be subdivided into five major zones including two maxima revealing both South African and Antarctic sources. A particularly high amount of Mg- and Fe-rich illites are observed close to East Antarctica. They are derived from biotite-bearing crystalline rocks and transported to the west by the East Antarctic Coastal Current. Chiorite and well-crystallized dioctaedral illite are typical minerals enriched within the Subantarctic and Polarfrontal-Zone but of minor importance off East Antarctica. Kaolinite dominates the clay mineral assemblage at low latitudes, where the continental source rocks (West Africa, Brazil) are mainly affected by intensive chemical weathering. Surprisingly, a slight increase of kaolinite is observed in the Enderby Basin and near the Filchner-Ronne Ice shelf. The investigated area can be subdivided into ten, large-scale clay facies zones with characteristic possible source regions and transport paths. Clay mineral assemblages of the largest part of the South Atlantic, especially of the western basins are dominated by chlorite and illite derived from the Antarctic Peninsula and southernmost South America and supported by advection within the Circumantarctic Deep Water flow. In contrast, the East Antarctic provinces are relatively small. Assemblages of the eastern basins north of 30°S are strongly influenced by African sources, controlled by weathering regimes on land and by a complex interaction of wind, river and deep ocean transport. The strong gradient in clay mineral composition at the Brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins.

Geochemical evolution of basaltic rocks subjected to weathering: Fate of the major elements, rare earth elements, and thorium

Eleven Icelandic hyaloclastites altered in freshwater have been studied. The weathering of basaltic glass, which is their primary constituent, leads to precipitation of clayey and possibly zeolitic phases. The dissolution reaction progress (mass of dissolved glass per liter of solution) governs the chemistry of the secondary phases, which control the residence time of the solution through their influence on rock permeability. They contribute to the regulation of reaction advancement. The reaction progress, ξ, can be calculated according to: ξ = [Sr w·(I w−I sp)·(I G + 9.375)] [Sr G·(I SP−I G)·(I W + 9.375)] , where I w , I G and I SP are the isotopic strontium ratios of initial water, of pristine glass, and secondary products, respectively, and Sr W and Sr G the strontium contents of initial water and glass. The amount of dissolved glass per liter of solution is estimated to be in the order of 0.01–0.1 g for samples 90000–100000 years old. A global agreement is found between this result and estimations that can be made on the basis of thermodynamic modelling. Expressing the geochemical budget as a function of the reaction progress allows a look at the evolving aspect of the rock/water interaction: 1. (1) According to the budget calculated for the major elements, the rock undergoes a global loss of matter which decreases with increasing reaction progress (from −45 to about 0% losses). For the most evolved samples, the transformation of the pristine basaltic glass to the alteration products is a nearly conservative process. 2. (2) There is increasing evidence that rare earth elements, particularly LREEs, can be mobilized during alteration processes. Our study corroborates this view as we demonstrate that REEs can be significantly mobilized during basaltic glass weathering. Nevertheless, no fractionation among the suite of REEs was observed. We show that Th and REE behaviours are similar. Mass balance calculations account for Th and REE losses up to 40%. These losses are not related to the reaction progress but could be due to a colloidal or particulate transport. The REE contents of the secondary clayey phases is showed to be linked to their degree of crystallinity. The need to take into account the latter parameter to modelize the long-term behaviour of the elements adsorbed onto clay minerals is outlined.

Waste Glass Weathering

ABSTRACTThe weathering of glass is reviewed by examining processes that affect the reaction of commercial, historical, natural, and nuclear waste glass under conditions of contact with humid air and slowly dripping water, which may lead to immersion in nearly static solution. Radionuclide release data from weathered glass under conditions that may exist in an unsaturated environment are presented and compared to release under standard leaching conditions. While the comparison between the release under weathering and leaching conditions is not exact, due to variability of reaction in humid air, evidence is presented of radionuclide release under a variety of conditions. These results suggest that both the amount and form of radionuclide release can be affected by the weathering of glass.