Predominant Mineral Phase Research Articles

Optimization of Crystal Structures in Polylithionite Concentrate: A Molecular Dynamics Approach to Lithium Extraction Efficiency.

Molecular dynamics (MD) techniques offer significant potential for optimizing mineral extraction processes by simulating economically or physically restrictive conditions at the laboratory level. Lithium, a crucial metal in the electromobility era, exemplifies the need for ongoing re-evaluation of extraction techniques. This research aims to simulate the crystal structures of mineral species present in a polylithionite mineral concentrate [KLi2Al(Si4O10)(F,OH)2] using crystallographic data obtained from X-ray diffraction analysis. This study focuses on optimizing these structures, validating them through density comparisons, and determining the interaction parameter between the identified phases and lithium oxide (Li2O). The X-ray diffraction analysis revealed five predominant mineral phases: quartz (SiO2), calcite [Ca(CO3)], pyrite (FeS2), cassiterite (SiO2), and a compound Pb6O2(BO3)2SO4. Structural data, including lattice parameters, space groups, and atomic coordinates, were used to construct the crystal structures with Materials Studio 8.0, employing the Crystal Builder module. Optimization was performed using the Forcite module with the Smart optimization algorithm and the Universal force field. The interaction parameter (χ) indicated an affinity between lithium oxide and pyrite, as well as between calcite and quartz.

Microstructural characteristics of aluminosilicate minerals in cement clinker prepared from coal gangue, carbide slag, and desulfurization gypsum

Utilizing solid waste to prepare cement clinker with low-calcium minerals is crucial for the low-carbon evolution of cementitious materials. In this study, a belite-ye’elimite-ternesite cement clinker was prepared using coal gangue, carbide slag, and desulfurization gypsum instead of non-renewable resources. The evolution law of the silica-alumina mineral phase in cement clinker under different calcining temperatures was tested and analysed. The results show that the predominant mineral phases in cement clinker consist of belite, ye’elimite, and ternesite at 1200 °C to 1250 °C. The composition of cement clinker transforms into belite and ye’elimite as the calcination temperature increases to 1300–1400 °C. At 1400 ℃, the content of belite in cement clinker reaches a remarkable 85 %. The results of XPS and NMR spectra showed that the chemical binding energy and chemical shift of Al in the cement clinker changed after calcination, representing the transformation of the aluminate in kaolinite, with [AlO6], to ye’elimite, with [AlO4]. The peak fitting results of 29Si NMR spectra semi-quantitatively describe the transition process of the silicate mineral phase from kaolinite to ternesite and then to belite. Morphologically, the increase in calcination temperature leads to a significant enlargement of the grain size of belite in cement clinker. This study can provide a basis for research on the phase regulation of cement clinker composed mainly of low-calcium minerals.

Suitability evaluation of selected sand geological formations for synthesis high purity crystalline silica, Iraq

This study aims determination if the sand collected from Injana and Dibdibba Formations are suitable for use as low-cost raw materials in the manufacture of high-purity crystalline silica. Sand is distributed in vast quantities within the two Formations, which occupy large portions of Iraq’s southern desert. Quartz is the predominant mineral phase, followed by calcite, feldspar, and dolomite respectively, based on mineral analysis data. SiO2 is the main oxide in sand with an average of (82.76%), (90.24%) and the rest of oxides are CaO (6.28%), (1.64%), Al2O3 (4.02%),(3.19%), Fe2O3(2.73%), (0.86%), K2O+ Na2O (2.05%), (2.51%), SO3(0.05%), (0.47%), MnO (0.01%), (0.03%) P2O2 (0.23%),(0.03%), and MgO (1.75%), (1.01%) in Injana and Dibdibba Formations respectively, which are considered as impurities impact the manufacturing properties of sand. The coprecipitation method, which produces high purity crystalline silica at a low cost, involves three steps: the first involves soaking raw sand powder in 2M HCl for 24 hours; The second involves mix purified sand with NaOH while stirring and heating it to 95C° to produce Na2SiO3; and the third involves adding 3M HCl to sodium silicate solution to produce Si(OH)4 and drying it to produce high purity of silica. The prepared silica got mineral analysis and chemical analysis. The synthesized silica was in the crystalline phase, according to the results of the mineral characterization. In synthetic silica of Injana and Dibdibba sand, The amount of SiO2 increased according to chemical analysis, reaching 96.62%, and 97.69% respectively, while all other oxides (impurities) were lowered to their lowest levels. FE-SEM revealed the existence of spherical, well-agglomerated synthetic silica particles within the size 28.6 nm and 24.76 nm in synthetic silica particles of Injana sand and Dibdibba sand respectively.

Petrography and Geochemistry of the Baska Piwaza Ore Mineralization, Halgurd Mountain, Iraqi Kurdistan Region: Insights on the Genesis

This paper is the first attempt to study the mineralogical and geochemical features of mineralization hosted within the volcanic rocks of the Baska Piwaza section, at Halgurd Mountain, which is the highest mountain in Kurdistan and the whole of Iraq. The host lithologies in the studied section represent mostly volcanic rocks (basalts to andesites), and secondary sedimentary lithologies, such as radiolarian chert. There are two main stages of oxide and sulfide mineralization that can be recognized under three-time epochs which are early, middle and late stages that caused the formation of oxide and sulfides ore minerals. The most dominant oxide mineral is hematite, with minor contribution of magnetite, goethite, and rutile. In terms of sulfides, pyrite is the predominant mineral phase with secondary contribution of chalcopyrite. The petrographic study and XRD data of the host volcanic rocks reveal that the most abundant minerals are plagioclase, K-feldspar, pyroxene, and amphibole, while the secondary minerals are quartz, calcite, clinochlore, sericite, prehnite, pumpellyite, and muscovite. Additionally, the radiolarian chert is comprised by quartz, hematite, calcite, ankerite, clay minerals, and apatite which is characterized by low silica content and high iron oxide. Low concentration of TiO2 ,and Fe2O3 are suggesting the quartz vein occurred with the volcanic rocks are formed due to low hydrothermal fluid. Field observation, petrographical and geochemical data indicate that the rocks of the Baska Piwaza section are influenced by hydrothermal alteration, due to the high value of Loss On Ignition (LOI) and the high ratio of alkalis (Na2O+K2O). Moreover, evidences of chloritization and sericitization of the mafic minerals, and feldspar minerals respectively support the hydrothermal impact.

Characterization of pulp calcifications and changes in their composition after treatments with citric acid and ethylenediaminetetraacetic acid solutions.

The ectopic calcifications of non-mineralized tissues can occur in several forms throughout life, such as pulpal calcification. The presence of pulp stones is a challenge in endodontic treatment because they partially or fully obliterate the pulp chamber hindering access to root canals and their subsequent shaping. This study aimed to determine their crystallographic properties and evaluate the capacity of citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) to promote the demineralization of pulp calcifications. The samples were obtained from patients with indications of endodontic treatment, and the radiographic examination was suggestive of pulp stone in at least one permanent tooth. The samples were isolated and analyzed by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX). The Fourier Transform by high resolution-transmission electron microscopy, Raman microscopy, and X-ray diffraction (XRD) were used to identify the mineral phase and crystallographic characteristics. To evaluate the effect of CA and EDTA on the crystallinity of calcifications, they were submerged into these two individual solutions and the changes were assessed in situ by Raman spectroscopy. The SEM images obtained from calcifications demonstrated irregular morphologies. EDX of sample surfaces shows a high presence of oxygen, carbon, calcium, and phosphorous, however, other elements such as sodium, magnesium, nitrogen, chlorine, potassium, sulfur, and zinc were identified in less quantity. According to Raman, XRD, and high-resolution transmission electron microscopy, the predominant mineral phase identified in the pulpal calcification was a poor crystallinity apatite. According to in situ analyses, the effect of CA and EDTA was observed on the signals of PO4 3- and CH2 groups corresponding to inorganic and organic components. The changes with CA were evident at 7min while the effect of EDTA was observed until 15 min of treatment. All results indicate that pulp stones have a heterogeneous composition principally composed of apatite with low crystallinity. The solubility of these pathological minerals is adequate using solutions such as EDTA or CA; however, the effectivity depends on the mineralization grade of calcifications, time, and concentration of exposition to this chemical.

Influence of the key factors on the performance of steel slag-desulphurisation gypsum-based hydration-carbonation materials

This study focuses on the influence of liquid-solid ratio, carbonation time and curing method on the carbonation reaction, and then mainly discusses the carbonation effects of four curing methods and reaction mechanisms to improve the carbonation efficiency of steel slag (SS)-desulphurisation gypsum (DG) and the strength of carbonated products. The results showed that the compressive strength of the SS–DG samples could be increased to 57.56 MPa by optimising the liquid–solid ratio to 1:5, carbonation time to 12 h, and curing method to 1dW (hydration for 1 d) + 2 dC (carbonation for 2 d). Furthermore, the compressive strength of samples cured for 1dW+2dC could increase by 33.40% compared to that cured for 2dC. The predominant mineral phases that react with CO2 in steel slag were dicalcium and tricalcium silicates, according to microanalysis (including XRD, TG–DTA, SEM-EDS and FTIR). Approximately 8% ettringite and 5% Ca(OH)2 could be generated during the hydration process and they would be then further carbonated to afford CaCO3. In the curing process, the method of hydration followed by carbonation considerably promoted the carbonation efficiency and formation of CaCO3 by approximately 5% compared with the method of direct carbonation. The overall time of hydration and carbonation was the same while the sequencing was different; the reactants CaCO3 obtained from the curing method of 1 dW + 2 dC was increased by 2% compared with the curing method of 1dC + 1dW + 1dC, which further indicated that the curing method of hydration and then carbonation could better improve the carbonation reaction efficiency.

Karst bauxite formation during Miocene Climatic Optimum (central Dalmatia, Croatia): mineralogical, compositional and geochronological perspectives

The Miocene Climatic Optimum (MCO) represents a global warm period (approximately 17–14.7 Ma) interrupting a long-term period of Cenozoic cooling. To elucidate if bauxitization took place in southeastern European mid-latitude areas during the MCO, we studied a section of undated massive karst bauxite (Crveni Klanac, CK) in central Dalmatia, Croatia, hosted in Upper Cretaceous limestones and overlain by Miocene Sinj Basin lacustrine deposits. Integrated mineralogical, morphological and geochemical analyses indicate the predominant mineral phases of the homogenous bauxite matrix are authigenic, subhedral to euhedral kaolinite and gibbsite. The in-situ mineralization was a consequence of pedogenic processes, indicating the CK bauxites formed autochthonously. In situ U–Pb zircon ages of the lower, middle and upper parts of the CK bauxite are very similar, dominated by Miocene and Oligocene ages, indicating that they all share similar protolith(s). Subsequent high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) analyses indicate a maximum depositional age (MDA) for the pre-bauxitic material of 16.9576 ± 0.021 Ma (2σ uncertainty, incorporating decay constant uncertainty). This MDA, a maximum age of autochthonous bauxitization, coincides with the onset of the MCO. Based on currently available geochronological constraints, the maximum timeframe for CK bauxitization was less than ~ 700 ka, which matches the records of the MCO in paleo-mid-latitude Europe. The potential imprint of pre-17 Ma bauxitization and contribution of older (i.e., Upper Paleogene) bauxite deposits resedimented to the CK profile, as well as degree of potential parautochthonous origin of the CK bauxites, is yet to be investigated. More than simply aligning with regional and local reconstructions of continental climatic conditions during the onset and the early stages of the MCO, the high degree of autochthony of the CK bauxites provide a precise climatic constraint. For in-situ bauxitization to occur in the southeastern parts of mid-latitude continental Europe, paleoclimatic and paleoenvironmental conditions must have had mean annual temperature greater than 17–22 °C and mean annual precipitation of more than 1100–1200 mm.

Hydrogeochemical contrasts in the shallow aquifer systems of the Lower Katari Basin and Southern Poopó Basin, Bolivian Altiplano

Drinking water sources in the southeastern part of Lake Titicaca (Lower Katari Basin: LKB) and the southern part of Lake Poopó (Southern Poopó Basin: SPB) have high concentrations of arsenic (As), >10 μg/L compared to the WHO and NB-512 guideline value. These regions belong to the Bolivian Altiplano and are characterized by a semiarid climate, slow hydrological flow, with geological formations of volcanic origin, in addition to brines and other mineral deposits. The present study is focused on comparing the geochemical processes of As in relation to the sources and mobilization in groundwater (GW) in LKB and SPB. Groundwater (GW), surface water (SW) and sediment samples were collected from both basins. The As (LKB: 0.8–288 μg/L and SPB: 2.6–207 μg/L), boron (B) (LKB: 96–2473 μg/L and SPB: 507–4359 μg/L), manganese (Mn) (LKB: 0.6–7259 μg/L) and salinity (LKB: 125–11740 μS/cm) were found to be higher than the WHO guideline values, which is a serious concern about the GW quality for human consumption. The dissolution and exchange of bases are the processes that govern the mineralization of GW. Load of solids and liquids of anthropogenic origin in surface water (LKB) represents an environmental problem for communities on river banks. The spatial distribution of As was attributed to the geology of both the basins and the heterogeneously distributed evaporites in the sediments. The highest As concentrations are found in alluvial sediments of the northern region of LKB and “PACK belt” (an approximately 25 km long belt stretching along the southern shores of the Lake Poopó, between the villages of Pampa Aullagas and Condo K) in SPB. Sequential extraction of sediment and mineral saturation indices indicate that iron (Fe) and aluminum (Al) oxides as well as hydroxides are the most predominant mineral phases as potential sorbents of As.

Firing behaviour of Tertiary, Cretaceous and Permo-Triassic clays from Castellon ceramic cluster (Spain)

This study is focused on the knowledge of clays historically used in manufacturing of ceramic pavement and coatings from the province of Castellon (NE, Spain) with a large ceramic industry. This research began in the early 1980s in the research group led by Professor T. Sanfeliu and continues today. This review paper and the last advances in knowledge have been written in honor of Professor E. Galán, one of the pioneers in the study of ceramic clays and kaolin in Spain. The objective of this paper is to extract conclusions about mineralogy, porosity and bending strength in ceramic test bodies manufactured using Tertiary-age, Cretaceous and Permo–Triassic local clays. Tertiary clays show a high CaO content and their predominant mineral phases are calcite and quartz. Cretaceous clays show a scarce CaO content. These Cretaceous raw materials are clays with high quartz and illite percentages. Permo–Triassic clays present a difference in the K2O and Fe2O3 content. The mineralogical composition is mainly formed by quartz, clay minerals and hematites. Ceramic test bodies were molded by extrusion and undergoing a firing process. Characterization of the fired clays was accomplished by TOM and XRD. Granular texture and porphyry structure, quartz phenocrysts and opaque hematite crystals were observed. Illitic clays rich in carbonates form plagioclases, wollastonite and gehlenite from 950 °C. In samples with low content in calcite and dolomite, the predominant mineral phases are quartz and hematite from 1000 °C onwards. A mercury porosimeter was used for determining the porous texture of ceramic matrix. A progressive reduction in open porosity and an increase of bending strength are observed with increasing temperature. The essays for bending strength were carried out by an INSTRON. A decline in porosity was observed when temperature rise associated with an increase in bending strength. Establishing relations between bending strength and the seven parameters studied link to the porous behaviour of the ceramic tests it was not possible because empirical equations do not fit experimental results.

Effect of BaO on mechanical and hydration characteristic of C8A6P as predominant mineral in phosphoaluminate cement

Phosphoaluminate cement clinker (PAC) was one type of cementitious material due to its high durability and mechanical performance. As the predominant mineral phase in PAC, the high-temperature formation and property of calcium phosphoaluminate mineral (C8A6P) were related closely with hydration and mechanical characteristic for PAC. Thus, the influence of BaO on the performance of C8A6P mineral phase was investigated carefully in this paper. It was found that BaO of 17.5–20% content could endow C8A6P mineral with predominant mechanical performance. This was due to the fact that C8A6P mineral was activated by BaO. Excessive BaO would lead to the formation of new unexpected phase BaO·Al2O3. The limited solid solubility of BaO in C8A6P mineral was 20%. The addition of BaO changed the ratio of hydration products of C2(A,P)H8 and C(A,P)H10 for C8A6P mineral.

Iron-mediated deep-time preservation of osteocytes in a Middle Triassic reptile bone

ABSTRACT Fossil bone cells (osteocytes) are known mainly from the shape-casting vacuities they leave behind after cell decay; however, they may occasionally be preserved as three-dimensionally fossilized soft parts. Here we present brownish to rust-coloured microbodies, extracted from a Middle Triassic (ca. 245 Ma) bone of the reptile Nothosaurus, which are morphologically consistent with bone cells of present-day vertebrates. In situ imaging shows that these structures, which are reminiscent of bone cells, are harboured in lacunae framed by the bone matrix. Chemical characterization using energy-dispersive X-ray, Raman, and X-ray photoelectron spectroscopy revealed the presence of various phases of iron oxide mineralization. The predominant mineral phases are hematite and goethite; magnetite and maghemite appear to occur sporadically. It is not clear how these nanograined mineral phases were formed. Most likely mineralization proceeded very early and was triggered by local microenvironmental conditions favouring the precipitation of iron phases. The absence of a distinct signal indicating organic molecules suggests that the original bone cells underwent autolysis or other degradative processes before or during mineralization.

Mineralogical characterization of the thrusted manganese ore above the Blackridge Thrust Fault, Kalahari Manganese Field: The footprint of the Mukulu Enrichment

AbstractThe thrusted manganese ore above the Blackridge Thrust Fault is a predominantly unstudied ore‐type and as such, there is an urgent need to petrographically characterize it. A total of 80 samples were collected from the thrusted lower manganese ore bed of six boreholes on Mukulu in the north of the Kalahari Manganese Field. Each sample underwent a range of optical and electron petrographic analyses in order to effectively characterize three dominant stages of alteration, namely Stages 1, 2 and 3. Similar to the hydrothermally‐altered Wessels‐type manganese ore, braunite II is the predominant mineral phase present during Stage 1 alteration, and alters to bixbyite with increasing proximity to normal faults at the onset of Stage 2 alteration. The final stage of alteration is exhibited by the development of hausmannite and jacobsite adjacent to the ferruginised zone at the normal fault plane. Apatite precipitation, in abundances previously undocumented in the Kalahari Manganese Field, is a hallmark feature of the newly identified Mukulu Enrichment. This supergene‐related enrichment process contributed to the significant abundance of arsenic‐bearing apatite in the ore, whilst residually enriching the ore‐hosted Fe and Mn oxides.

Variability in composition and physical properties of the sedimentary basement of Mt Etna, Italy

The sub-volcanic basement at Mt Etna (Italy) comprises thick sedimentary sequences. An understanding of the physical, mechanical, and microstructural properties of these sequences, and an appreciation of their variability, is important for an accurate assessment of the structural stability of Mt Etna. Here, we present a combined field and laboratory study in which we explore the extent of variability of the materials comprising the sedimentary basement of Mt Etna. To this end, we sampled twelve different lithological units that span the sediments of the Apenninic-Maghrebian Chain (from both the Sicilide and Ionides sequences) and the Hyblean Plateau. X-ray diffraction analysis of the blocks collected show that calcite and quartz are the predominant mineral phases. Textural analysis highlights the wide variability in rock microstructures, with features such as the presence/absence of fractures or veins, pore size and shape, and grain size and shape varying tremendously between the samples. One consequence of this microstructural, textural, and mineralogical variability is that the rock units are characterised by very different values of porosity, P-wave velocity, uniaxial compressive strength, and static Young’s modulus. For example, strength and Young’s modulus vary by a factor of twenty and an order of magnitude, respectively. Our study affirms the vast heterogeneity of the sub-volcanic sedimentary basement of Mt Etna and, on this basis, we urge caution when selecting potentially oversimplified input parameters for models of flank stability.

Silicon and oxygen isotopic composition of igneous rocks from the eastern Manus Basin

This paper reports silicon and oxygen isotopes of 20 kinds of igneous rocks and their major elements from the eastern Manus Basin. Combining silicon and oxygen isotopic data from other studies, we suppose that both delta Si-30 and delta O-18 values increase with the increasing of SiO2 content. It means that the fractionation of silicon and oxygen isotopes are affected by the silica content. The positive correlation between CaO/Al2O3 ratios and MgO and that between Si/Al and SiO2 content indicate that clinopyroxene is the predominant mineral phase in our samples. We suppose that the fractionation of silicon and oxygen isotopes are influenced by mineral fractional crystallization. Probably, it is due to their different silicon and oxygen bridges. In this study, the delta S-30(imean value) = -0.17aEuro degrees +/- 0.17aEuro degrees and delta O-18(mean value) = +6.07aEuro degrees +/- 0.57aEuro degrees are higher than normal delta Si-30 and delta O-18 values of mantle, and we propose that these igneous rocks in the eastern Manus Basin are affected by hydrothermal alteration.

Arsenic Scavenging by Aluminum-Substituted Ferrihydrites in a Circumneutral pH River Impacted by Acid Mine Drainage.

Ferrihydrite (Fh) is a nanocrystalline ferric oxyhydroxide involved in the retention of pollutants in natural systems and in water-treatment processes. The status and properties of major chemical impurities in natural Fh is however still scarcely documented. Here we investigated the structure of aluminum-rich Fh, and their role in arsenic scavenging in river-bed sediments from a circumneutral river (pH 6-7) impacted by an arsenic-rich acid mine drainage (AMD). Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge shows that Fh is the predominant mineral phase forming after neutralization of the AMD, in association with minor amount of schwertmannite transported from the AMD. TEM-EDXS elemental mapping and SEM-EDXS analyses combined with EXAFS analysis indicates that Al(3+) substitutes for Fe(3+) ions into the Fh structure in the natural sediment samples, with local aluminum concentration within the 25-30 ± 10 mol %Al range. Synthetic aluminous Fh prepared in the present study are found to be less Al-substituted (14-20 ± 5 mol %Al). Finally, EXAFS analysis at the arsenic K-edge indicates that As(V) form similar inner-sphere surface complexes on the natural and synthetic Al-substituted Fh studied. Our results provide direct evidence for the scavenging of arsenic by natural Al-Fh, which emphasize the possible implication of such material for scavenging pollutants in natural or engineered systems.

Geochemical Effects of Storing CO2 in the Basal Aquifer that Underlies the Prairie Region in Canada

In the area underlain by the Basal Aquifer in the Prairie region of Canada, there are 20 large CO2 sources (coal-fired power plants, oil sands and heavy oil production and upgraders, refineries, chemical and petrochemical plants, fertilizer plants and cement plants) that emit more than 1 Mt CO2/year each, for a total of 83 Mt CO2/year,which represents 12% of canada ‘s anual greenhouse gas emissions. If post-combustion capture technologies are used, 75 Gt CO2/year can be captured from these sources, with a composition (% mass) estimated to be 99.95% CO2, 0.02% N2/Ar/O2, and 0.03% H2O. The Basal Aquifer comprises Middle Cambrian sandstones that overlie the crystalline Precambrian basement in the Alberta basin and the Canadian part of the Williston basin. Shales constitute the primary caprock of the Basal Aquifer. Pressures in the aquifer generally follow a gradient of 10.8kPa/m. Temperatures in the aquifer vary between >150°C in the deepest part of the Alberta Basin to less than 10°C in outcrop areas. Water salinity ranges from > 300,000mg/L in central Alberta to < 10,000mg/L in the southwest and in the east. The formation water in the aquifer region suitable for CO2 storage is NaCl dominated. Generally, at in-situ conditions, these waters are saturated with CaSO4 (anhydrite), with some at NaCl (halite) saturation. The mineralogy of the aquifer rocks and caprock were determined using a suite of laboratory analyses and normative calculations on core samples. The dominant mineral in the Basal Aquifer formation in regions suitable for CO2 storage is quartz, which is generally present in the 65% to 95% range, while potassium feldspar is the next most common silicate. Pyrite is present in trace amounts in many of the samples. Calcite and illite, when present, are primarily pore- filling minerals. Calcium sulphate (anhydrite) is present in many of the samples, and, when present, is a pore-filling phase. In regard to the caprock, quartz is still a predominant mineral phase, comprising of at least one third of the rock for all samples. Potassium feldspar, illite and kaolinite are the next most common minerals. The ability of the rocks of the Basal Aquifer to react with CO2 is limited, with potassium feldspar and complex clays providing the bulk the reactive capacity via the formation of kaolinite, or potentially a coupled reaction forming alunite and calcite in anhydrite-bearing zones. The effect of these reactions on CO2 storage capacity, aquifer porosity and permeability is limited, allowing decoupling of flow from geochemical processes. Caprock reactivity towards CO2 is much greater due to its more complex mineralogy, however they will not propagate far into the caprock due to its low permeability, thus allowing decoupling of flow and geochemical processes.

Distribution and mineralogy of carbonate sediments on Antarctic shelves

We analyzed 214 new core-top samples for their CaCO3 content from shelves all around Antarctica in order to understand their distribution and contribution to the marine carbon cycle. The distribution of sedimentary CaCO3 on the Antarctic shelves is connected to environmental parameters where we considered water depth, width of the shelf, sea-ice coverage and primary production. While CaCO3 contents of surface sediments are usually low, high (>15%) CaCO3 contents occur at shallow water depths (150–200m) on the narrow shelves of the eastern Weddell Sea and at a depth range of 600–900m on the broader and deeper shelves of the Amundsen, Bellingshausen and western Weddell Seas. Regions with high primary production, such as the Ross Sea and the western Antarctic Peninsula region, have generally low CaCO3 contents in the surface sediments.The predominant mineral phase of CaCO3 on the Antarctic shelves is low-magnesium calcite. With respect to ocean acidification, our findings suggest that dissolution of carbonates in Antarctic shelf sediments may be an important negative feedback only after the onset of calcite undersaturation on the Antarctic shelves.Macrozoobenthic CaCO3 standing stocks do not increase the CaCO3 budget significantly as they are two orders of magnitude lower than the budget of the sediments.This first circumpolar compilation of Antarctic shelf carbonate data does not claim to be complete. Future studies are encouraged and needed to fill data gaps especially in the under-sampled southwest Pacific and Indian Ocean sectors of the Southern Ocean.

Origin of Clay Minerals in Soils on Pyroclastic Deposits in the Island of Lipari (Italy)

AbstractThe island of Lipari (Italy) is characterized by calc-alkaline to potassic volcanism and a Mediterranean-type climate. The mineralogical and chemical features of two different soil profiles with ages of 92,000 and 10,000–40,000 y, respectively, have been investigated. There were no Andisols, but Vitric and Vertic Cambisols have developed at both sites. Although the morphology of the soils was similar, remarkable differences in the clay mineralogy between the two sites were observed. The site with the Vitric Cambisol was associated with the weathering sequence: glass → halloysite → kaolinite or interstratified kaolinite-2:1 clay minerals. Both sites had smectite in the clay fraction and, to a large extent, this smectite had a low charge and could be characterized as a dioctahedral montmorillonite. At the site with a Vertic Cambisol, smectite was the predominant mineral phase in the clay fraction. The smectites (predominantly montmorillonite) found in this soil were probably not of pedogenetic origin and are, therefore, inherited from the parent material. Their formation is due to hydrothermal alteration of glass particles during or immediately after the emplacement of the pyroclastic flow. The octahedral character of the smectites did not change from the C to the A horizon indicating that they are resistant to weathering processes. A high-charge expandable mineral was detected in small concentrations in the Vertic Cambisol and had a dioctahedral structure. In this case also, no signs of significant weathering or transformation could be detected in the soil profile. In contrast to many other investigations, no active smectite formation within the soil profiles could be measured. The subtropical and rather dry climate in Lipari might, therefore, favor the persistence of dioctahedral low-charge montmorillonites that are associated with a small amount of a high-charge expandable mineral in the soil.

Long-term behaviour of the Wyoming bentonite MX-80 in high saline solutions

The mineralogical and chemical changes of bentonites were studied under the boundary conditions of a repository in salt formations by means of a literature review, a natural analogue study, and laboratory experiments. In the natural analogue study the expandability of clays from deep boreholes in the East Slovakian Basin was found to be dependent not only on depth and temperature but also on the salinity of the pore waters. In laboratory experiments the fraction <2 μm of the MX-80 bentonite was reacted with two high saline solutions, a NaCl- and a MgCl 2-rich brine at 25, 90 and 150 °C, at three different pH levels, 1, 6.5, and 13. In all experiments, montmorillonite remained at all temperatures and all pH the predominant mineral phase over 580 days, with full ethylene–glycol expandability to 17 Å. However, significant changes could be detected by looking at parameters like morphology, crystallinity, particle height, particle surface, interlayer charge, and chemistry of octahedral layers. The experimental results of this study suggest that under repository conditions a certain percentage the MX-80 montmorillonites will be transformed in kaolinites and pyrophyllites rather than in illites. The investigated reactions not only caused mineralogical changes but also considerable changes of the water uptake capacity. The MX-80 montmorillonites in salt solutions lost about half of their water uptake capacity compared with pure water. The reduction was found to be dependent on the reaction time and temperature. Smectites in salt solutions with cement lost their water uptake capacity almost completely.

Long-term behaviour of the Wyoming bentonite MX-80 in high saline solutions

The mineralogical and chemical changes of bentonites were studied under the boundary conditions of a repository in salt formations by means of a literature review, a natural analogue study, and laboratory experiments. In the natural analogue study the expandability of clays from deep boreholes in the East Slovakian Basin was found to be dependent not only on depth and temperature but also on the salinity of the pore waters. In laboratory experiments the fraction <2 μm of the MX-80 bentonite was reacted with two high saline solutions, a NaCl- and a MgCl2-rich brine at 25, 90 and 150 °C, at three different pH levels, 1, 6.5, and 13. In all experiments, montmorillonite remained at all temperatures and all pH the predominant mineral phase over 580 days, with full ethylene–glycol expandability to 17 Å. However, significant changes could be detected by looking at parameters like morphology, crystallinity, particle height, particle surface, interlayer charge, and chemistry of octahedral layers. The experimental results of this study suggest that under repository conditions a certain percentage the MX-80 montmorillonites will be transformed in kaolinites and pyrophyllites rather than in illites. The investigated reactions not only caused mineralogical changes but also considerable changes of the water uptake capacity. The MX-80 montmorillonites in salt solutions lost about half of their water uptake capacity compared with pure water. The reduction was found to be dependent on the reaction time and temperature. Smectites in salt solutions with cement lost their water uptake capacity almost completely.