Weathering Of Aluminosilicate Minerals Research Articles

Enhanced trace element mobilization by Earth’s ice sheets

Trace elements sustain biological productivity, yet the significance of trace element mobilization and export in subglacial runoff from ice sheets is poorly constrained at present. Here, we present size-fractionated (0.02, 0.22, and 0.45 µm) concentrations of trace elements in subglacial waters from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Concentrations of immobile trace elements (e.g., Al, Fe, Ti) far exceed global riverine and open ocean mean values and highlight the importance of subglacial aluminosilicate mineral weathering and lack of retention of these species in sediments. Concentrations are higher from the AIS than the GrIS, highlighting the geochemical consequences of prolonged water residence times and hydrological isolation that characterize the former. The enrichment of trace elements (e.g., Co, Fe, Mn, and Zn) in subglacial meltwaters compared with seawater and typical riverine systems, together with the likely sensitivity to future ice sheet melting, suggests that their export in glacial runoff is likely to be important for biological productivity. For example, our dissolved Fe concentration (20,900 nM) and associated flux values (1.4 Gmol y-1) from AIS to the Fe-deplete Southern Ocean exceed most previous estimates by an order of magnitude. The ultimate fate of these micronutrients will depend on the reactivity of the dominant colloidal size fraction (likely controlled by nanoparticulate Al and Fe oxyhydroxide minerals) and estuarine processing. We contend that ice sheets create highly geochemically reactive particulates in subglacial environments, which play a key role in trace elemental cycles, with potentially important consequences for global carbon cycling.

The hydrogeochemistry of shallow groundwater from Lut Desert, Iran: The hottest place on Earth

This paper presents the first shallow groundwater geochemical data from the Lut Desert (Dasht-e-Lut), one of the hottest places on the planet. The waters are Na–Cl brines that have undergone extensive evaporation, but they are unlike seawater derived brines in that the K+ is low and the Ca2+ > Mg2+ and HCO3− > SO42−. In addition to evapo-concentration, the most saline samples indicate that the dissolution of previously deposited salt also acts as a major control on the geochemistry of these waters. High concentrations of gypsum in surface soils along with the water geochemistry indicate the dissolution, precipitation, and reprecipitation of evaporite salts are very important to the overall chemistry of the near surface environment. As demonstrated by the high H4SiO4 concentrations, the weathering of aluminosilicate minerals also contributes to the solutes present. Fixed nitrogen (NO3− + NO2−) concentrations suggest little to no denitrification is occurring in these waters. The processes controlling the geochemistry of the Lut waters are similar to those in other hyperarid regions of the Earth.

Ca isotopic geochemistry of an Antarctic aquatic system

AbstractThe McMurdo Dry Valleys, Antarctica, are a polar desert ecosystem. The hydrologic system of the dry valleys is linked to climate with ephemeral streams that flow from glacial melt during the austral summer. Past climate variations have strongly influenced the closed‐basin, chemically stratified lakes on the valley floor. Results of previous work point to important roles for both in‐stream processes (e.g., mineral weathering, precipitation and dissolution of salts) and in‐lake processes (e.g., mixing with paleo‐seawater and calcite precipitation) in determining the geochemistry of these lakes. These processes have a significant influence on calcium (Ca) biogeochemistry in this aquatic ecosystem, and thus variations in Ca stable isotope compositions of the waters can aid in validating the importance of these processes. We have analyzed the Ca stable isotope compositions of streams and lakes in the McMurdo Dry Valleys. The results validate the important roles of weathering of aluminosilicate minerals and/or CaCO3 in the hyporheic zone of the streams, and mixing of lake surface water with paleo‐seawater and precipitation of Ca‐salts during cryo‐concentration events to form the deep lake waters. The lakes in the McMurdo Dry Valleys evolved following different geochemical pathways, evidenced by their unique, nonsystematic Ca isotope signatures.

Relationships among pH, aluminum solubility and aluminum complexation with organic matter in acid forest soils of the Northeastern United States

We investigated the interactions among pH, Al solubility and Al–soil organic matter (SOM) complexation to test the hypothesis that competition between Al and H ions for cation binding sites on soil organic matter (SOM) determines soil pH and Al solubility in acidic forest soils in the northeastern U.S. Samples from five soil horizons in 39 forested watersheds across the northeastern U.S. were used with two Al complexation models to test the hypothesis. Our results indicated that Al solubility increases with soil depth when pH is less than 4.5 and the ratio of the fractions of organically bound Al and H(NAl/NH) or the ratio of organically bound Al to total organic carbon (Alorg/C) remains roughly constant within each horizon. Both the NAl/NH and the Alorg/C ratios are effective measures of the ratio of sites bound to Al and H in Al–SOM complexation models. The log-linear relationship pAlKCl-p(Alorg/C)=0.75×pHKCl-1.56 (r=0.86,P<.0001) can be used to describe Al–pH relationships in Oie, Oa, Bh and Bs1 horizon samples from across the region. The competition between H+ and Al3+ for binding to SOM affects soil pH and Al solubility to a greater degree in Oa and Bs1 horizons than in Oie and E horizons. Our data are consistent with the conceptual model that portrays the Al–pH relationship in acid forest soils as a balance between organic acidity and alkalinity produced through the weathering of aluminosilicate minerals.

ESCALATING APPLICATIONS OF HALLOYSITE NANOTUBES

ABSTRACT In nanotechnology different nano materials are used like carbon nanotubes, nanofluids, nanoparticles, nanoemulsions, nanocapsules, etc. Due to their toxic effects the results of these nano materials are not considered safe for humans and for the environment as well. Halloysite nanotubules (HNTs) having low cost are naturally occurring environmental friendly nanotubules. These are distinctive and handy materials formed by face weathering of aluminosilicate minerals having definite ratio of aluminum, silicon, hydrogen, and oxygen. HNTs have high mechanical strength and modulus. Due to these properties it is ideal for various applications; remediation of ecological contaminants, these are acting as a career for the delivery of drugs and various macro molecules, storage of H 2 gas, for catalytic conversions and for the processing of hydrocarbons. These are also used in anticancer therapy, sustained delivery for certain agents, as a template or nanoreactor for biocatalyst, in personal care, cosmetics and as environment caring. They are also used in the fabrication of high quality white-ware ceramics, nanotemplates and nano scale reaction bottles. Due to easy dispersability in polymer matrix, abundant availability and biocompatibility, HNTs are also used in different epoxy (EP) composites. In this review, we have tried to recap the different aspects of halloysites nanotubes for their use in different research fields.

Silica cycling in the ultra-oligotrophic eastern Mediterranean Sea

Abstract. Although silica is a key plant nutrient, there have been few studies aimed at understanding the Si cycle in the eastern Mediterranean Sea (EMS). Here we use a combination of new measurements and literature values to explain the silicic acid distribution across the basin and to calculate a silica budget to identify the key controlling processes. The surface water concentration of ∼1 μM, which is unchanging seasonally across the basin, was due to the inflow of western Mediterranean Sea (WMS) water at the Straits of Sicily. It does not change seasonally because there is only a sparse population of diatoms due to the low nutrient (N and P) supply to the photic zone in the EMS. The concentration of silicic acid in the deep water of the western Ionian Sea (6.3 μM) close to the S Adriatic are an of formation was due to the preformed silicic acid (3 μM) plus biogenic silica (BSi) from the dissolution of diatoms from the winter phytoplankton bloom (3.2 μM). The increase of 4.4 μM across the deep water of the EMS was due to silicic acid formed from in situ diagenetic weathering of aluminosilicate minerals fluxing out of the sediment. The major inputs to the EMS are silicic acid and BSi inflowing from the western Mediterranean (121 × 109 mol Si yr−1 silicic acid and 16 × 109 mol Si yr−1 BSi), silicic acid fluxing from the sediment (54 × 109 mol Si yr−1) and riverine (27 × 109 mol Si yr−1) and subterranean groundwater (9.7 × 109 mol Si yr−1) inputs, with only a minor direct input from dissolution of dust in the water column (1 × 109 mol Si yr−1). This budget shows the importance of rapidly dissolving BSi and in situ weathering of aluminosilicate minerals as sources of silica to balance the net export of silicic acid at the Straits of Sicily. Future measurements to improve the accuracy of this preliminary budget have been identified.

The hydro-geochemistry of groundwater resources in an area with prevailing saline groundwater, lower Shire Valley, Malawi

The area considered in this study lies within the western section of the East African Rift System (EARS) and saline groundwater occurs in some parts of the valley plain. Hydrochemical groundwater types were classified into three groups (G1–G3), indicating different stages of groundwater chemical evolution. An overall incongruent weathering of aluminosilicate minerals causes the groundwater solution to generally be in equilibrium with montmorillonite. Ca–(Mg)–HCO3 groundwater (G1), with relatively low TDS (average TDS=548mg/L), are mainly found in areas with Karoo basalt and Precambrian basement complex rocks. This water type is mainly governed by aluminosilicate weathering. Towards the middle of the valley, Na- and mixed cation-HCO3 groundwater (G2; average TDS=1061mg/L) predominates. This water type results from a combination of aluminosilicate mineral weathering, cation exchange and precipitation of clays and carbonates. The increase in ionic strength of G2 samples, in comparison with G1 samples, is attributed to mixing with high TDS groundwater in G3. Brackish and saline groundwaters (G3; average TDS=3457mg/L) are dominated by sodium, chloride and sulphate ions, which is attributable to dissolution of Cl− and SO42- evaporative salts. These are found in clusters and in aquifers with low recharge capacity (low transmissivity) and are attributable to intrusion of mineralised groundwater probably through fault zones from mainly sedimentary Karoo and Cretaceous Lupata formations. Evaporation plays a role in brackish/saline groundwaters found in areas with shallow water table along the Shire River.

Water–Rock Interactions: An Investigation of the Relationships Between Mineralogy and Groundwater Composition and Flow in a Subtropical Basalt Aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO2 (atmospheric + soil) + pyroxene + feldspars + olivine yields H4SiO4, HCO3−, Mg2+, Na+, Ca2+ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement.

Hydro-geochemical processes in an area with saline groundwater in lower Shire River valley, Malawi: An integrated application of hierarchical cluster and principal component analyses

Abstract Our ability to adapt to changes in groundwater quality, arising from a changing climate and/or local pressures, is dependent on comprehension of the governing controls of spatial variation in groundwater chemistry. This paper presents results of an assessment of dominant hydro-geochemical processes controlling groundwater chemical composition, using an integrated application of hierarchical cluster analysis (HCA) and principal component analysis (PCA) of a major ion dataset of groundwater from lower Shire River valley, Malawi. The area is in the southernmost part of the western section of the East African Rift System (EARS) and has localised occurrence of saline groundwater. HCA classified samples into three main clusters (C1–C3) according to their dominant chemical composition: C1 (dominant composition: Na–Cl; median TDS: 3436 mg L −1 ), C2 (dominant composition: Na–HCO 3 ; median TDS: 966 mg L −1 ) and C3 (dominant composition: alkali earths–HCO 3 ; median TDS: 528 mg L −1 ). These clusters were in turn described by the principal components PC1, PC3 and PC2, respectively, resulting from the PCA. The results of the PCA and geochemical interpretation suggest that the spatial variation of groundwater quality in the area is influenced by the following processes: C3 samples result mainly from H 2 CO 3 weathering of aluminosilicate minerals by percolating water supersaturated with CO 2 . In addition to aluminosilicate weathering, C2 samples are influenced by the processes of cation exchange of Ca 2+ and Mg 2+ in the water for Na + on clay minerals, and carbonate precipitation. The increase in ionic strength of C2 samples is attributed to mixing with high TDS groundwater in proximity with C2 samples. The saline/brackish C1 groundwater results from the processes of evaporation (for samples with high water table close to the Shire marshes) and dissolution of Cl − and SO 4 -evaporative salts followed by mineralised seep from sedimentary Karoo and Cretaceous Lupata sandstones.

A review of soil quality indicators and five key issues after 12 yr soil quality monitoring in the Waikato region

AbstractAn ongoing programme of soil quality assessment in the Waikato region of New Zealand is providing baseline data and allowing identification of the impacts of land use and associated key soil quality issues. In this paper, we review the strengths and weaknesses of key soil quality indicators and provide summary statistics for chemical, physical and biochemical parameters in both background and production soils of the Waikato Region. Statistical comparison of production to background soils, time related trends, relative surface enrichments, and correlations enable us to infer likely and potential impacts of human activity on the region’s soil resource. Five key issues that cause loss of soil resource have been identified. These are soil compaction, loss of soil organic matter, excessively high fertility levels, erosion risk, and accumulation of contaminants. In addition, evidence exists for accelerated attack or weathering of aluminosilicate minerals in farmed soils [dealumination, Australian Journal Soil Research (2009) vol. 47, 828–838], a process previously only recognized in soils adjacent to aluminium smelters.

Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products

High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as ‘geopolymerisation’. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution–reorientation–solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.

Weathering control over geomorphology of supermature Proterozoic Delhi quartzites of India

AbstractQuartz and quartzite are thought to be resistant as a mineral and a rock respectively; however, we have shown that the presence of small amounts of pyrite in the quartzites makes them vulnerable to weathering. We observe that weathering of Proterozoic quartzite in the semi‐arid conditions around Delhi proceeded from fractures towards the inside and produced weathering rinds. The chemical index of alteration (CIA), which is actually a measure of weathering of aluminosilicate minerals, increases from the core outwards, through the rinds. Although aluminosilicate minerals occur only as minor phases (&lt;2 per cent), their weathering indicates a movement of the weathering front from the periphery towards the core. We have suggested a coupled mechanism in which the dissolution of pyrites by moving water produced a sulphate‐bearing acidic solution and ferrous iron, which reacted with aluminosilicate minerals and quartz, respectively. This initially makes the Delhi quartzite porous and subsequently friable. The total disintegration of grain to grain contacts imparted friability to this quartzite to produce silica sand. Subsequent physical erosion of loose sand, produced during rind development in the outermost zones, has given rise to features like tors, spheroids, gullies, cavities and small‐scale caves on these quartzites. Thus, the terrain has acquired ruggedness in semi‐arid conditions. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Mineralogical Characterisation of Sediments at the Drigg Low Level Radioactive Waste Disposal Site and the Influence on Groundwater Chemistry

ABSTRACTPetrographic microscopy, scanning and transmission electron microscopy, X-ray diffractometry, surface area and cation exchange analyses have been undertaken on a suite of ‘bulk’ and size separated sediment fractions from the Drigg site. The data indicate a complex phyllosilicate assemblage consisting of illitic and vermiculite material derived from the complex weathering history of the siliceous, micaceous, feldspathic and chloritic parent clasts. Coarse grains range from clean fresh looking ‘polished’ clasts to heavily coated with iron oxides and oxyhydroxides. The surfaces of most igneous clasts (granites and volcanics) are usually highly altered to micaceous (‘illitic’), chloritic and vermiculitic clays. Carbonates, such as calcite, dolomite and siderite, are present, particularly in the more shallow formations. The properties of the sediments have a clear impact on the evolution of groundwater chemistry. Redox conditions are consistent with equilibrium between iron oxyhdroxides and siderite, both present in Drigg sediments. Drigg groundwater samples are close to equilibrium with calcite, which not only controls the concentration of dissolved calcium and bicarbonate ions, but also the groundwater pH. Concentrations of potassium and magnesium are controlled by ion exchange reactions, while both mineralogical and groundwater evidence show that some weathering of aluminosilicate minerals is occurring, although equilibrium is not reached.

Environmental geochemistry of Damodar River basin, east coast of India

Water and bed sediment samples collected from the Damodar River and its tributaries were analysed to study elemental chemistry and suspended load characteristics of the river basin. Na and Ca are the dominant cations and HCO3 is the dominant anion. The water chemistry of the Damodar River basin strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area. High concentrations of SO4 and PO4 at some sites indicate the mining and anthropogenic impact on water quality. The high concentration of dissolved silica, relatively high (Na+K)/TZ+ ratio (0.2–0.4) and low equivalent ratio of (Ca+Mg)/(Na+K) indicate that dissolved ions contribute significantly to the weathering of aluminosilicate minerals of crystalline rocks. The seasonal data show a minimum ionic concentration in the monsoon season, reflecting the influence of atmospheric precipitation on total dissolved solids contents. The suspended sediments show a positive correlation with discharge and both discharge and suspended load reach their maximum value during the monsoon season. Kaolinite is the mineral that is possibly in equilibrium with the water. This implies that the chemistry of the Damodar River water favours kaolinite formation. The concentration of heavy metals in the finer size fraction (<37 μ m) is significantly higher than the bulk composition. The geoaccumulation index values calculated for Fe, Mn, Zn, Ni and Cr are well below zero, suggesting that there is no pollution from these metals in Damodar River sediments.

Hydrogeochemistry and environmental isotope investigations of the North Diamaré Plain, northern Cameroon

This paper discusses the results of environmental isotopes and major chemical data for thirteen selected groundwater samples representative of the North Diamaré Plain in the extreme north of Cameroon. The 18O and 2H concentrations for all the investigated groundwaters vary from −0.27 to −4.3696% and from −7.1 to −26.696%, respectively. In the conventional d 2Hd 18O diagram, the distribution of data points indicates that most of the analysed groundwaters have been affected by evaporation. Chemically, the groundwaters are of mixed CaNa bicarbonate type, and display high concentrations of dissolved silica (84–116 mg l −1). As inferred from the saturation index calculations and selected mineral stability diagrams, the groundwater chemistry may be adequately explained by both the weathering of alumino-silicate minerals and cation exchange between the groundwaters and clay minerals.

Hydrochemistry and rock weathering in a sub-tropical Lesser Himalayan river basin in Kumaun, India

Major ion chemistry of the water of the Gaula catchment — a medium-sized Lesser Himalayan basin in Kumaun, was measured in 1983 and 1984. The results show the influence of rock weathering on the concentration of major constituents in the ground water and surface water. The catchment lithology contributes a large part of the major constituents in the waters; Ca and Mg account for 40–73% of the cations and HCO 3 accounts for 48–98% of anions, and the equivalent ratio of Ca + Mg to Na + K is about nine. Cl + SO 4 accounts for 12–16% in the anion balance and does not represent a contribution from soil salt. The low Mg:Ca ratio (0.1–0.4) and high bicarbonate suggest the possibility of carbonate precipitation between the upper and the lower reaches. The excess Na over Cl, low Mg:Ca ratio and relatively high abundance of silica in the upper reaches indicate weathering of aluminosilicate minerals of crystalline rocks (granite, mica schist and quartz porphyry), and particularly of Na- and K-feldspar and quartz. Intense weathering of pyrite and or gypsum associated with the carbonate rocks is reflected by the substantially higher abundance of SO 4, low silica and the low Na:Cl ratio. In comparison with the Indian peninsular rivers, the low concentrations of the major constituents in the water of this Lesser Himalayan catchment indicate rapid infiltration and quick outflow of the rainwater and thus a short residence time for water, during which interaction with the rocks could occur, because of the steep slopes.

Soil‐Saprolite Profiles Derived from Mafic Rocks in the North Carolina Piedmont: II. Association of Free Iron Oxides with Soils and Clays

AbstractThe association of free Fe oxides with soils and clays from two Enon sandy loam (Ultic Hapludalfs, fine, mixed, thermic) soil‐saprolite profiles was studied. Goethite was the dominant Fe oxide identified. Lepidocrocite was detected in trace amounts in some samples. FeCBD/clay ratios were highest in the epipedons of these soils suggesting the concentrating of Fe oxides as a result of aluminosilicate mineral weathering. External (BET‐N2) surface area measurements of non‐deferrated and deferrated clays were analyzed in conjunction with electron micrographs of selected clay fractions to determine the association of free Fe oxides with aluminosilicate clays as a function of depth in the profile. Free Fe oxides were found to exist mainly as small, discrete clusters in the A and B horizons of both profiles and specific of the clay surface decreased as a result of treatment for Fe removal. However, external surface areas increased for the saprolite (Cr) horizon clays after deferration. One subfraction identified as having an increase in surface area after deferration was fine clay from the Cr2 horizon, Enon (metagabbro) profile. Chemical data and electron micrographs suggest that either partial dissolution of small, poorly crystalline aluminosilicate clays or removal of some Fe or non‐Fe oxide aggregating agent results in breakdown of the fine clays into smaller particles of higher net specific surface.