Stable Mineral Research Articles

Thin-section Petrography and Heavy Mineral Study of sandstones of the Barail Group of rocks occuring around Sonapur area of Jaintia Hills, Meghalaya, India

The study area represents a part of the South Shillong Shelf, Meghalaya, where sandstones belonging to the Barail Group (Eocene-Oligocene) are well exposed. Thin section petrography and heavy mineral investigations have been undertaken to assess the geological significance of the sandstones. Framework grains of the Barail sediments comprise of quartz (56.98 to 71.91%), feldspar (1.87 to 7.35%), mica (1.07 to 9.72%), lithic fragments (2.20 to 8.41%) and matrix (9.20 to 20.43%). The detrital composition of the sandstones comprises primarily of quartz grains, angular to sub-rounded, fine to medium grained and moderately sorted in nature. The sandstones are classified as subarkose, feldspathic graywacke and lithic graywacke. Provenance discrimination triangular plots of QFL and QmFLt reflect that the detritus were mostly derived from cratonic interior sources. The Diamond diagram indicates that the Barail sandstones were derived from middle and upper rank metamorphic source. Heavy mineral study of these sandstones indicates the presence of zircon, tourmaline, rutile, sillimanite, kyanite, staurolite, garnet, epidote, sphene, hypersthene, hornblende, chlorite, chloritoid, andalusite, apatite and opaque minerals. The percentages of most stable heavy minerals zircon, tourmaline and rutile vary from 6.11to 21.61, 2.60 to 6.56 and 2.42 to 7.57 respectively. The ZTR maturity index varies from 15.15 to 34.37, which reflects that the sandstones are mineralogically immature. The petrographic and heavy mineral study of the sandstones suggest that the detritus was probably derived from Shillong Massif where Precambrian metamorphic rocks of pelitic and arenaceous composition with plutonic bodies were exposed around the shelf margin. As the Shillong Massif comprises of Precambrian metamorphic rocks of pelitic and semitic (arenaceous) composition with intrusive plutonic bodies.

In English

Wastewater and natural waters contain various pollutants of both natural and artificial origin. Treatment of these waters is carried out comprehensively by various methods, which significantly increases costs. Currently, the problem of a large amount of drugs entering the wastewater is very relevant. Drugs, unchanged or in the form of metabolites, enter the wastewater together with the waste products of a living organism. To solve urgent practical problems of water purification, a possibility of using natural zeolite materials as sorbents has been recently considered. Being a natural aluminosilicates of frame-type structure, these minerals have a number of unique adsorption properties that can be used in water treatment processes. Treatment with acid solutions (alkalis, salt solutions and some organic compounds) allows to improve significantly their sorption characteristics for decision of a particular problem. Zeolites, being chemically stable minerals, are capable to withstand the effects of chemically active medium without destruction of the crystal lattice. The effect of boiling acid (HC1) on natural zeolites from Georgian deposits (mordenite and clinoptilolite) and the possibility of their use for adsorption treatment of wastewater were studied in this work. Identification of modified zeolites was carried out on the basis of X-ray diffractograms and IR-spectra. It has been shown that natural clinoptilolites (mordenite and zeolite) are characterized by high thermostability and acid resistance even after acid-modification, and the resulting hydrogen forms are distinguished by high concentration of active centers; the efficiency of adsorption method for wastewater treatment from some pharmacopolutants when using acid-modified natural zeolites has been also shown. This method will solve the problem of entering the environment of drugs with lower costs

Anaerobic syntrophic system composed of phosphate solubilizing bacteria and dissimilatory iron reducing bacteria induces cadmium immobilization via secondary mineralization

Secondary mineralization is a promising method for remediating cadmium (Cd) pollution in sediments, but the poor stability of Cd-containing secondary minerals is a bottleneck that limits the development of this approach. The existence of phosphate can enhance the formation of stable secondary minerals and points a new direction for Cd immobilization. In this research, a novel syntrophic system composed of phosphate solubilizing bacteria (PSB) and dissimilatory iron reducing bacteria (DIRB) was established and the effect and mechanism of Cd immobilization in the system were also explored. The results showed that under the conditions of DIRB:PSB (V:V)= 3:1, syntrophic bacteria dosage of 5% and glucose dosage of 5 g/L, Cd incorporated in the secondary minerals could account for about 60% of the total Cd. In the pH range of 5–9, alkaline environment was conducive to the immobilization of Cd and the percentage of combined Cd was up to 58%, while the combined Cd in secondary minerals decreased from 62% to 56% with the increase of initial Cd concentration from 0.1 to 0.3 mmol/L. In addition, XRD, XPS, Mössbauer and other characterization results showed that secondary minerals, such as Cd exchange hydroxyapatite (Cd-HAP) and kryzhanovskite (Fe3(PO4)2(OH)3) were formed in this new system. The established syntrophic system of PSB and DIRB is thus a prospective bioremediation technology for Cd immobilization in sediments and can avoid the potential risk might be caused by the addition of phosphorus-containing materials.

Spatio-temporal variation of groundwater chemistry in the Upper Oti Basin of Ghana

The Oti Basin is located at northeastern part of Ghana. Two major geological formations of Voltaian sedimentary supergroup exist: Kwahu-Morago and Oti-Pendjari groups. A total of 133 groundwater samples and 7 surface water samples were collected for two major seasons, viz. dry season (February, 2020) and wet season (November, 2020), and analysed for cations and anions. This is to determine the sources of ions, including pollutants and the reactions that promote them for sustainable groundwater management. Results of major ions revealed groundwater is potable base on the WHO permissible limits. Wet season nitrate and sulphate were higher than that of dry season, suggesting anthropogenic influence. Pearson's correlation shows major contributors of total dissolved solids were Mg, Na and HCO3 with a correlation (r = 0.439, 0.874 and 0. 945) respectively. In the wet season, major contributors were TH, Mg, Na, SO4 and HCO3 with correlation (r = 0.548, 0.537, 0.856, 0.530 and 0.936) respectively. Gibbs plot suggests chemical weathering and precipitation to be the main contributors to the water chemistry. The dominant hydrochemical facies within the basin for both seasons was Na-K-HCO3 water type. The plot of Ca2+ + Mg2+ vs. HCO3- + SO42- suggests both silicate weathering and ion exchange processes are taking place within the basin. Mineral stability diagrams signify kaolinite as the most stable mineral phase in the groundwater. Chloro-alkaline indices were negative for both seasons leading to base-exchanged softened water production. Consequently, majority of ions evolved from natural geochemical processes whilst nitrate and sulphate presence might be due to anthropogenic sources.

Remediation of uranium-contaminated alkaline soil by rational application of phosphorus fertilizers: Effect and mechanism

In alkaline soil, abundant carbonates will mobilize uranium (U) and increase its ecotoxicity, which is a serious threat to crop growth. However, the knowledge of U remediation in alkaline soils remains very limited. In this study, U-contaminated alkaline soil (tillage layer) was collected from the Ili mining area of Xinjiang, the soil remediation was carried out by using phosphorus (P) fertilizers of different solubility (including KH2PO4, Ca(H2PO4)2, CaHPO4, and Ca3(PO4)2), and the pathways and mechanisms of U passivation in the alkaline soil were revealed. The results showed that water-soluble P fertilizers, KH2PO4 and Ca(H2PO4)2, were highly effective at immobilizing U, and significantly reduced the bioavailability of soil U. The exchangeable U was reduced by 70.5 ± 0.1% (KH2PO4) and 68.2 ± 1.9% (Ca(H2PO4)2), which was converted into the Fe–Mn oxide-bound and residual phases. Pot experiments showed that soil remediation by KH2PO4 significantly promoted crop growth, especially for roots, and reduced U uptake in crops by 94.5 ± 1.0%. The immobilization of U by KH2PO4 could be attributed to the release of phosphate anions, which react with the uranyl ion (UO22+) forming a stable mineral of meta-ankoleite and enhancing the binding of UO22+ to the soil Fe–Mn oxides. In addition, KH2PO4 dissolution produces acidity and P fertilizer, which can reduce soil alkalinity and improve crop growth. The findings in this work demonstrate that a rational application of P fertilizer can effectively, conveniently, and cheaply remediate U contamination and improve crop yield and safety on alkaline farmland.

Hydroxylherderite (Ca2Be2P2O8(OH)2) stability under extreme conditions (up to 750°C/100 GPa)

AbstractHydroxylherderite, Ca2Be2P2O8(OH)2, is among the most common beryllophosphates in nature and could play a substantial role in Be geochemical cycle. Hydroxylherderite P–T stability and crystal structure behavior were studied under extreme conditions (up to 750°C/100 GPa) using in situ single‐crystal and powder X‐ray diffraction and Raman spectroscopy. The mineral demonstrated high stability under high‐pressure conditions (up to ∼100 GPa) without any phase transitions. Under high‐temperature conditions, it was stable up to about 700°C, when it decomposed with the formation of fluorapatite Ca5(PO4)3F and hurlbutite CaBe2P2O8. The beryllophosphate member of the gadolinite supergroup is the most stable mineral (material) under high‐pressure conditions, compared to aluminum‐, boro‐ and beryllosilicates.

Thermodynamic stabilities of apatite phases in a wetland system: Implications for bone diagenesis

Evaluating the fate and stability of apatite minerals, the largest phosphorus (P) reservoir on Earth's surface, has direct consequences for understanding our vertebrate fossil record as well as biogeochemical cycling. Bone (bioapatite) deposited following the death of an animal represents a potential source of phosphorus in terrestrial and aquatic ecosystems for micro and macrofauna. Exposure of bone to ambient geochemical conditions also represents the first step of the fossilization process. However, the thermodynamic stability of bone in these ecosystems, which are frequently phosphorus-limited, is unknown. The goal of this study was to approach questions related to recrystallization, diagenesis, and fossilization from a thermodynamics perspective, focusing on the role of geochemistry on bioapatite (bone) preservation. By developing thermodynamic models, run using PHREEQC, the stabilities of a range of apatite and other phosphorus-bearing phases were considered under physiochemical conditions measured in a Louisiana wetland and an adjacent river. The models integrated variable temperatures (5–40 °C), concentrations of phosphorus ([PO43-] from 0.0006 to 0.0484 mmol/L), and pH (6.5–9.25) from representative waters collected over 3 years at the wetland. In all models, waters are undersaturated with respect to hydroxylapatite, except under the highest temperatures, [PO43-], and pH conditions. In contrast, fluorapatite approached stability under lower pH and temperatures, and carbonated fluorapatite exhibited a broad range of stable conditions. These results suggest that if bioapatite (bone) were deposited under these present-day conditions, solutions are predicted to be undersaturated with respect to many apatite phases, leading to mineral dissolution. However, if bioapatite undergoes substitutions forming a fluorinated and/or carbonated phase, stability may shift towards preservation. These results have implications for identifying potential biases and mechanisms driving bone preservation over geologic time in a wetland system. The modeling results demonstrate that preservation of bone is favored under subsurface (burial) rather than surface conditions, aligning with long-held views on the formation of our vertebrate fossil record.

Utilizing Soil Density Fractionation to Separate Distinct Soil Carbon Pools.

Soil organic matter (SOM) is a complicated mixture of different compounds that span the range from free, partially degraded plant components to more microbially altered compounds held in the soil aggregates to highly processed microbial by-products with strong associations with reactive soil minerals. Soil scientists have struggled to find ways to separate soil into fractions that are easily measurable and useful for soil carbon (C) modeling. Fractionating soil based on density is increasingly being used, and it is easy to perform and yields C pools based on the degree of association between the SOM and different minerals; thus, soil density fractionation can help to characterize the SOM and identify SOM stabilization mechanisms. However, the reported soil density fractionation protocols vary significantly, making the results from different studies and ecosystems hard to compare. Here, we describe a robust density fractionation procedure that separates particulate and mineral-associated organic matter and explain the benefits and drawbacks of separating soil into two, three, or more density fractions. Such fractions often differ in their chemical and mineral composition, turnover time, and degree of microbial processing, as well as the degree of mineral stabilization.

Carbonation and serpentinization of diopsidite in the Altun Mountains, NW China.

Mineral carbonation of mafic-ultramafic rocks has been highlighted as a promising way for permanent carbon capture and storage. Carbonatization involves the release of Ca, Mg and Fe from silicate minerals by dissolution and reaction in the aqueous phase to form stable carbonate minerals. Diopside is one of the most abundant mafic minerals in the lithosphere and contributes a portion of Mg and Ca to surface weathering. Here, we present detailed processes of the carbonation-coupled serpentinization of diopsidite from the Yushishan Nb-Ta deposit in the Altun Mountain, northwest China. Diopsidite is the prograde metamorphic product of siliceous dolomitic marble by full decarbonation process. Retrograde serpentinization and carbonation of diopsidite lead to the addition of CO2, H2O, light rare earth elements and fluid-mobile elements but the loss of SiO2. The diopsides are replaced by calcite and chrysotile by mineral alteration to form pseudomorphic textures. Dissolution-precipitation processes significantly affect diopside serpentinization and carbonation. The carbonation of diopside-rich rocks may be suitable for permanent CO2 storage.

A high-pressure structural transition of norsethite-type BaFe(CO3)2: Comparison with BaMg(CO3)2 and BaMn(CO3)2

Abstract Investigations on the phase stability of the norsethite-type family [BaMg(CO3)2, BaMn(CO3)2, BaFe(CO3)2] under high-pressure conditions are of great significance for understanding the structure and metal cationic (Mg2+, Fe2+, Mn2+) substitution mechanism in double divalent metal carbonates. The structural evolution and equation of state of BaFe(CO3)2 were studied at high pressure up to ~7.3 GPa by synchrotron X-ray diffraction (XRD) in diamond-anvil cell (DAC) in this study. BaFe(CO3)2 undergoes a reversible phase transition from R3m (α-phase) to C2/c (γ-phase) space groups at ~3.0 GPa. The fitted elastic parameters are V0 = 377.79(2) Å3 and K0 = 40.3(7) GPa for α-BaFe(CO3)2, V0 = 483.24(5) Å3 and K0 = 91.2(24) GPa for γ-BaFe(CO3)2 using second-order Birch-Murnaghan equation of state (BM2-EoS). Besides, the vibrational properties and structural stability of complete norsethite-type minerals were also investigated first by Raman spectroscopy combined with DAC up to 11.1 GPa. Similar structural phase transitions occur in BaMg(CO3)2, BaFe(CO3)2, BaMn(CO3)2 at 2.2–2.6, 2.6–3.7, and 3.7–4.1 GPa, respectively. The onset phase transition pressures of the norsethite-type family are much lower than that of dolomite-type Ca(Mg,Fe,Mn)(CO3)2 and calcite-type (Mg,Fe,Mn)CO3 carbonates. These results provide new insights into the divalent cation substitution effects on the stability and structural evolution of carbonates under high-pressure conditions.

The effects of washing solvents on the properties of ceramsite and heavy metal immobilization via the cosintering of municipal solid waste incineration fly ash and Cr-containing waste glass

Various washing solvents are being extensively researched to remove chlorides from municipal solid waste incineration fly ash (FA) and they have significant impacts on the recycling and reutilization of FA. The cosintering of FA and waste glass (WG) containing chromium (Cr) was explored in this study, as well as the effects of washing solutions (water [W-FA], phosphoric acid [P-FA], and sodium carbonate [Na-FA]) on the treated FA compositions, ceramsite characteristics, and heavy metals speciation. The findings demonstrated that washing process increased calcium oxide (CaO) content while reducing soluble salt level. The particle strength increased from 290.50 N to 926.78 N at 800–1050 °C, while increased from 228.68 N to 820.23 N when WG increased from 20% to 60%. Raw-FA ceramsite had a lower sintering temperature than treated FA ceramsite due to the higher particle strength and lower water absorption rate. At 1000 °C, the acid-soluble fraction of Cr of Na-FA and P-FA ceramsite was 64.72% and 9.07%, showing a promoted and inhibited effect on Cr leaching, respectively. The ecological risk index for P-FA and Na-FA ceramsite, both of which were produced at 1100 °C, were 30.61 and 46.68, respectively, indicating low environmental risk. Wollastonite was the dominating mineral phase in W-FA and Na-FA ceramsite, whereas chlorapatite and halite predominated in P-FA and Raw-FA ceramsite. Chlorine in P-FA ceramsite was combined with phosphates and calcium to generate stable minerals. Washing pretreatment reduced the environmental risk of ceramsite, and introduction of phosphorus could enhance heavy metal immobilization.

Alkaline modification on schwertmannite promoted the simultaneous immobilization of arsenite and cadmium

Arsenic (As) and cadmium (Cd) co-contamination is of most concern in the environment. Schwertmannite (Sch), a poorly crystalline Fe(III) oxyhydroxy-sulfate mineral, is extremely efficient for As immobilization owing to its unique structure, but ineffective against cationic Cd (Cd(II)) due to the acidic pH after Sch addition. In this study, an alkaline modification method was proposed to improve the treatment efficiency of schwertmannite for As(III)-Cd(II) co-contamination. Results showed that alkali soaking had no obvious effect on mineral phase, and schwertmannite was the main mineral component. Alkali-modified Sch (Sch-OH) consisted of a large number of nanoparticles superimposed on each other, with specific surface area drastically increasing from 69.7 m2/g (Sch) to 261.9 m2/g. The sulfate content in Sch-OH structure decreased by 71.5%, which contributed to the reduction of maximum adsorption capacity for As(III) (from 116.09 to 81.06 mg/g at pH 6.5). The co-existing As(III) enhanced Cd(II) adsorption onto Sch-OH by forming ternary Fe-As-Cd complexes, corresponding to an increase in adsorbed amount from 8.8 to 11.3 mg/g (in 20 mg/L Cd(II) solution). Sch-OH exhibited a higher mineral stability than Sch under flooded condition at 40°C, and its retaining ability for As(III) was stronger. In a Cd-As polluted soil, the content of KH2PO4-extractable As decreased from 6.3 to 4.8 mg/kg after 10 days-incubation with 5% Sch-OH, and the immobilization efficiency of Cd reached 49.1%. It is necessary to explore more modification methods of schwertmannite to broaden its application in metal(loid)s remediation.

K původu analcimu v mezozoických a kenozoických vulkanitech České republiky a jeho úloze v názvosloví hornin

Magmatic origin of analcime has been discussed for decades (e. g., Karlsson and Clayton 1991, 1993; Pearce 1993). Despite the fact that analcime has been re-classified as zeolite and its secondary (post-magmatic) origin is globally accepted (e. g., Roux and Hamilton 1976, Giannetti and Masi 1989, Wilkinson and Hensel 1994), it is still commonly used in classification of alkaline rocks in the Czech Republic. In these rocks, analcime can be mostly found in the pseudomorphs after leucite (Fig. 1a; see Rapprich 2003), or as a homogeneous anhedral filling in the groundmass (Fig. 1b). In the second case, the boundaries of individual analcime crystals cannot be identified due to the isotropic optical properties of analcime. Therefore, origin and growth of analcime is difficult to reconstruct. For this contribution, we have studied samples of Mesozoic and Cenozoic alkaline rocks from three localities across the Czech Republic, where partly analcimized glass in the groundmass was preserved, with an aim to better understand the origin of analcime in alkaline rocks. Mesozoic augitite from the southwestern slope of the Petřkovice Mt. near Nový Jičín (sample TG05) displays small isometric colourless, optically isotropic domains (analcime) enclosed in originally glassy groundmass (Fig. 1c–f ). This texture suggests the analcime is replacing original glass in the groundmass, enclosing also microcrysts of the stable minerals in groundmass. Very similar texture was observed also in Oligocene augitite from Mětikalov in Doupovské hory Mts. (sample DR338, Fig. 2). In this rock, the analcime domains either mantle larger phenocrysts, or are distributed within the groundmass. The growth of the analcime domains on the edges of larger phenocrysts resembles growth of spherulites, which represent products of silica-rich glass recrystallization (e. g., Breitkreuz 2013). To further investigate this possibility, additional samples were collected from Kamenický vrch near Zákupy (Fig. 3). In individual samples, number and size of analcime domains vary, which suggests, that these domains represent various stages of a continuous growth. The X-ray elemental mapping of Al and Na (Fig. 4) then shows, that the analcime domains are represented by single grains of cubic analcime. As a result, we may conclude that analcime in groundmass of Mesozoic and Cenozoic alkaline rocks originates from devitrification of original glass. These rocks hence should not be classified as “analcimites” or “analcimic …” but rather as “analcimized …” according to Le Maitre et al. (2005).

Origin and characteristics of ancient organic matter from a high‐elevation Lateglacial Alpine Nunatak (NW Italy)

AbstractIn high‐mountain areas, Pleistocene glaciations and erosion‐related processes erased most of the pre‐existing landforms and soils. However, on scattered stable surfaces, ancient soils can be locally preserved for long periods, retaining valuable palaeoenvironmental information. Such relict surfaces survived during glaciations either through coverage by non‐erosive, cold‐based, ice or as nunataks. Thus, soils preserved on such surfaces retain an excellent pedo‐signature of different specific past climatic/environmental conditions. In this study, we performed a detailed chemical characterisation of the organic material found in palaeosols, discovered inside periglacial features on a high‐elevation Lateglacial Alpine Nunatak (Stolenberg Plateau), above 3000 m a.s.l. (NW Italian Alps). The soil organic matter (OM) was separated into different pools by means of density fractionation, in order to separate the more fresh/unaltered free and occluded organic material (Light Fraction) from the stable fraction chemically bound to the mineral phase (Mineral Organic Matter—MOM). To better characterise the MOM fraction, this was further subjected to chemical fractionation, in order to separate the alkali‐extractable OM (ext‐MOM) from the fraction intimately bound to minerals. The obtained fractions were then characterised by chemical and 13C nuclear magnetic resonance (NMR), and Fourier Transform Infrared (FT‐IR) spectroscopy. The results indicated that the largest part (>90%) of organic carbon was stored in the stable MOM pool, characterised by a high degree of decomposition and consisting mainly of paraffinic substances, such as lipids and waxes (37–50%), cellulose and hemicellulose (29–37%). The OM likely originated from autochthonous, well‐adapted, ancient alpine vegetation (alpine tundra) that grew on the Plateau during warm climatic phases since the end of the Last Glacial Maximum (LGM). These results further strengthen the palaeoenvironmental reconstruction at the Stolenberg Plateau, which represents a Lateglacial Alpine Nunatak, and has acted as biological refugia (at least) since the end of the LGM.Highlights The origin and composition of ancient organic matter from a high‐elevation Alpine Nunatak were uncovered. More than 90% of organic carbon was stored in the stable mineral organic matter (MOM) pool. Based on NMR and FT‐IR spectra the MOM fraction consisted of paraffinic substances (37–50%), cellulose and hemicellulose (29–37%). The organic matter originated from ancient alpine tundra that developed on the Nunatak since the end of the Last Glacial Maximum.

Superhydrous aluminous silica phases as major water hosts in high-temperature lower mantle

Water transported by subducted oceanic plates changes mineral and rock properties at high pressures and temperatures, affecting the dynamics and evolution of the Earth's interior. Although geochemical observations imply that water should be stored in the lower mantle, the limited amounts of water incorporation in pyrolitic lower-mantle minerals suggest that water in the lower mantle may be stored in the basaltic fragments of subducted slabs. Here, we performed multianvil experiments to investigate the stability and water solubility of aluminous stishovite and CaCl2-structured silica, referred to as poststishovite, in the SiO2-Al2O3-H2O systems at 24 to 28 GPa and 1,000 to 2,000 °C, representing the pressure-temperature conditions of cold subducting slabs to hot upwelling plumes in the top lower mantle. The results indicate that both alumina and water contents in these silica minerals increase with increasing temperature under hydrous conditions due to the strong Al3+-H+ charge coupling substitution, resulting in the storage of water up to 1.1 wt %. The increase of water solubility in these hydrous aluminous silica phases at high temperatures is opposite of that of other nominally anhydrous minerals and of the stability of the hydrous minerals. This feature prevents the releasing of water from the subducting slabs and enhances the transport water into the deep lower mantle, allowing significant amounts of water storage in the high-temperature lower mantle and circulating water between the upper mantle and the lower mantle through subduction and plume upwelling. The shallower depths of midmantle seismic scatterers than expected from the pure SiO2 stishovite-poststishovite transition pressure support this scenario.

Weathering of stannite–kësterite [Cu2(Fe,Zn)SnS4] and the environmental mobility of the released elements

Abstract. The sulfidic waste dumps of the historical mining sites Giftkies and Kaňk (Czech Republic) have been exposed to a temperate climate over decades. This exposure generated low-pH conditions caused by metal sulfide decomposition. Tin sulfides of the stannite–kësterite series [Cu2(Fe,Zn)SnS4] are common Sn minerals in the ores at the investigated sites. They decompose under acidic and oxidizing conditions and form in situ secondary precipitates. Compositional analyses of primary and secondary minerals were collected by electron microprobe to track the environmental mobility of the released elements during weathering. Transmission electron microscopy revealed a diffusion-driven alteration of stannite to Sn-rich chalcopyrite and the precipitation of native copper and silver from stannite. In assemblages containing arsenopyrite, an in situ and amorphous Sn–Fe–As (SFA)-rich phase precipitated close to the Sn sulfide. The SFA precipitate contains very little sulfur, which was probably released to the aqueous phase as oxidized species, whereas small amounts of Cu and Zn were captured by the SFA. This precipitate is metastable and acts as a temporaneous sink for mobile elements (Cu, Zn) and elements derived from acid-soluble silicates and phosphates (Ca, Si, Al, and P). With advanced weathering, complex redox reactions result in the precipitation of magnetite as an oxidation product of the sulfidic material under oxidative conditions. The stable minerals goethite and cassiterite mark the end of the weathering sequence and crystallized from the amorphous SFA precipitate.

Immobilization of heavy metals in ceramsite prepared using contaminated soils: Effectiveness and potential mechanisms

Heavy metal contaminated soils pose a serious threat to the environment, and preparing ceramsite using contaminated soils was proposed as an effective method to address this threat in this study. Specifically, two typical soils (i.e., contaminated clay and sandy soil) were mixed with different ratios and calcined at temperature 1000–1200 °C to prepare ceramsite. Special attentions were paid to evaluating the immobilization of heavy metals in ceramsite and identifying the corresponding immobilization mechanisms. Using the leachability of heavy metals from ceramsite as evaluation criteria, the optimum mixing ratio of clay/sandy soil and sintering temperature were determined as 0.6:0.4 and 1200 °C. Moreover, based on the spectroscopic characterizations and thermodynamic calculation, high sintering temperature well facilitated the liquid phases formation, promoting the reactions between heavy metals and aluminosilicates and the valence state conversion of heavy metals. Accordingly, heavy metals were well immobilized in ceramsite by forming thermodynamically stable minerals, being encapsulated in solid matrix, and transforming to valence states with low mobility. The leaching conditions including pH and temperature had minimal effect on the immobilization of heavy metals in ceramsite. In summary, ceramsite prepared by contaminated soils was environmentally friendly and had good potential in engineering application as building materials.

Improved stability of design clay minerals at high temperature: A comparison study with natural ones

Clay minerals are ceramics materials that are involved in a wide range of economic uses. But, their structure and composition are modified by heating and, consequently, compromise their final applications. The actual temperatures at which changes occur vary greatly from one group to another group and even for different specimens within a given group. The aim of this research has been to evaluate the thermal behaviour of a set of design swelling micas, Na-Mica-n (Mn) and compare them with a set of natural smectites. All samples were heated in the range 200 °C to 1000 °C; afterwards, they were rehydrated thorough water suspension (0.4% wt). The results have shown that swelling micas have better property of hydration/dehydration than natural clay minerals and those with higher layer charge exhibited higher rehydration ability and dehydration temperature.

Heat Stress, Varietal Difference, and Soil Amendment Influence on Maize Grain Mineral Concentrations

Improving the mineral concentrations of maize (Zea mays L.) will aid in the reduction of malnutrition in low-resource households that consume maize-based meals regularly. The study’s objective was to compare how different soil amendments and heat-stressed environments affect grain yield and mineral concentrations in maize. The study involved heat-stressed (HS) and non-heat-stressed (NHS) environments, three maize varieties (WE3128, WE5323, and ZM1523), and three soil amendments. The essential minerals analysis of the grain revealed a significant effect of variety, soil amendment, and heat stress on the grain yield and mineral contents. Among soil amendments, mineral fertilizer amendment (MF) gave the highest grain Zinc (Zn), 37.95 ± 15.3 µg/kg, while the highest grain iron (Fe) (136.9 ± 51.3 µg/kg) and yield were obtained with a combination of mineral fertilizer/poultry-manure amendment (MPM). The treatment interactions containing MPM in both the HS and NHS environments consistently produced positive results in the three maize varieties. When compared with the non-heat-stressed environment, the heat-stressed environment reduced grain weight (GWt) by 378% while increasing grain Fe and Zn concentrations by 43.6% and 15.8%, respectively. The HS was significantly higher than the NHS by 14.6%, 34.0%, 1.5%, 11.0%, 1.9%, and 89.2% for Ca, Cl, Mg, Na, P, and S, respectively. The highest macromineral concentrations were found in WE5323. All of the NHS treatments were grouped together, with the exception of NHS-4 and NHS-7, which produced the lowest means for the number of grain and GWt in the NHS, respectively. Although the variety was inconsistent in separating the treatment interactions, there was a good level of consistency in separating the treatment interactions along the heat stress factor and soil amendment factor. The correlation results revealed that a proportional relationship between Fe and Zn and grain yield tends to decrease the grain Fe or Zn concentrations. Therefore, selecting for high grain yield only may result in lower Fe and Zn concentrations in the grain. WE5323, amended with MPM, which produced the highest grain yield and stable mineral concentrations in non-heat-stressed and heat-stressed environments, should be considered in breeding programs aiming for high grain quantity and quality.

Possible formation pathways for zeolites in closed-basin lakes on noachian Mars: Insights from geochemical modeling

Zeolites are among the most common and widespread authigenic silicate minerals found in saline-alkaline paleolacustrine environments on Earth. Analcime, a Na-zeolite, has been detected on crustal outcrops on Mars using orbital spectral image data. Identifying other zeolite species is complicated by the lack of diagnostic absorption features in spectral data and spectral similarity to some polyhydrated sulfates. Therefore, analcime is the only zeolite species so far unambiguously identified as present on Mars. The presence of certain zeolite mineral species or assemblages in a closed basin paleolake can be used to track hydrological changes in that basin. This paper discusses the application of geochemical modeling to identify zeolite phases that could have formed in closed lake basins of late Noachian Mars. The composition of the high-silica Buckskin sample from Gale crater is used as a starting material because 1) most zeolite-rich assemblages in closed hydrologic systems on Earth originate from the decomposition of high-silica volcanic glass, and 2) geochemical modeling studies are already available for the more common lower silica basalts on Mars. This study, along with previous studies involving basaltic starting materials, allow a comparison between terrestrial and Martian data and an exploration of the differences in secondary mineral precipitation with substrates of different silica contents. The EQ3/6 geochemical modeling code was adopted, and Late Noachian Mars was assumed to be warm and semi-arid, with an atmosphere with 1.3 bars of PCO2 and current Mars PO2 (14.7 μbar). The Buckskin sample was reacted with three different starting solutions including two different rainfall chemistries and an acidic H2SO4 − HCl solution, which could have formed through volcanic degassing. The mineral formation and re-dissolution patterns under different Water/Rock (W/R) ratios are also explored.The results show that near neutral and acidic solutions in closed-basin lakes filled with high-silica volcaniclastic materials could eventually produce zeolite minerals like those in saline-alkaline lakes on Earth. Analcime forms only in water-limited environments (low W/R ratio), while chabazite is present even at relatively high W/R ratio. Clinoptilolite transforms to analcime with an increase in pH, with decreased W/R ratio, and with time. Analcime was found to be the most stable zeolite mineral over the greatest range of conditions in this environment, associated with increased pH, consistent with its presence as a very common constituent of saline-alkaline lake deposits on Earth. The study shows that the mineral precipitation patterns associated with the dissolution of high-silica materials through acid weathering are comparable to the mineral precipitation patterns following the dissolution of basaltic rocks by acid weathering under 0 − 25oC conditions or hydrothermal conditions as described in previous laboratory, field, and geochemical modeling studies.