Clay Minerals Research Articles

Reconstructing the redox environment of the Cambrian Harkless Formation, Nevada, USA: Navigating the effects of iron-rich clay minerals on the iron speciation redox proxy

Understanding the oxygenation of ancient oceans is critical for contextualizing evolutionary events throughout Earth's history. While there are many geochemical proxies available for evaluating paleoredox state, iron speciation is one of the most robust and widely applied recorders of local bottom water redox. The proxy uses a series of sequential extractions which are operationally designed to target redox active iron in different mineral groups, including carbonates, oxides, magnetite, and sulfides. However, clay minerals that contain iron are not specifically targeted but can be important reservoirs of redox active iron. These clay minerals are abundant during many times in Earth's history, so it is critical to understand how they are extracted during iron speciation and their impact on paleoenvironmental interpretations.Here we apply the iron speciation proxy in combination with other geochemical proxies (FeT/Al, Mn enrichments) and mineralogical analyses to determine local bottom water redox conditions during deposition of the early Cambrian Harkless Formation exposed near Gold Point, Nevada, USA. The Harkless Formation contains one of the last occurrences of archaeocyathan reefs before their extinction, thus studying the underlying strata can provide information about the environmental conditions which led to reef development. Iron speciation results indicate oxic to potentially anoxic conditions in the water column. The presence of FeT/Al enrichments, Mn depletion, and the Fe-rich redox sensitive clay minerals chamosite and glauconite suggest intermittent anoxia in the water column and porewaters during some intervals of Harkless deposition. Further, by combining iron speciation extractions with petrographic and x-ray diffraction analyses, we demonstrate that glauconite and chamosite were likely formed at or below the sediment water interface and are also not consistently or fully removed by the standard sequential iron reagents, as noted by previous work.The presence of these authigenic Fe-bearing clay minerals overall results in an underestimation of the proportion of redox active iron during deposition and early sediment diagenesis that may lead to incorrect environmental characterization. We therefore advocate for caution and careful examination of the mineralogy of samples when applying the iron speciation proxy, particularly when authigenic and/or early diagenetic iron-bearing clay minerals are suspected to be present. Based upon these findings, we suggest that the Harkless Formation experienced variable local bottom water redox conditions ranging from oxic to anoxic during deposition. Changes in the relative abundances of chamosite and glauconite may also indicate an increase in oxygenation up section, suggesting that local water column oxygenation played a role in archaeocyathan reef development.

Coupled effects of iron (hydr)oxides and clay minerals on the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides

The formation of nanominerals and mineral nanoparticles (NMMNs) has drawn broad attention due to their high reactivity and omnipresence in the environment. While the heterogeneous formation of NMMNs on surfaces of various minerals has been extensively studied, little is known about how mineral heteroaggregates influence this process. Herein, we investigated how heteroaggregates of iron (hydr)oxides and clay minerals affect the heterogeneous oxidation of Mn(II) and crystallization of manganese (hydr)oxides (MnOx). Our results revealed that iron (hydr)oxides (ferrihydrite) and clay minerals (kaolinite or montmorillonite) in heteroaggregates can exert coupled effects on these processes, dictating the distribution of Mn and the morphology of MnOx. Specifically, ferrihydrite catalyzed gradual oxidative removal of Mn(II) and triggered MnOx nucleation; in contrast, kaolinite/montmorillonite rapidly adsorbed Mn(II) but hardly catalyzed its oxidation. These reactions collectively caused fast adsorption and gradual oxidation of Mn(II) on the heteroaggregates. Further, MnOx nanoparticles formed on ferrihydrite surfaces migrated to kaolinite/montmorillonite surfaces, which resulted in MnOx interacting with various component minerals of the heteroaggregates. This strongly altered the further growth pathways and the eventual morphology of MnOx. Consequently, while MnOx nanoparticles in the ferrihydrite-only system aggregated freely and formed well-extended nanowires, most of those in the ferrihydrite-kaolinite system became short nanorods due to the immobilization by kaolinite surfaces; in the ferrihydrite-montmorillonite system, considerable MnOx nanoparticles attached to montmorillonite surfaces due to strong electrostatic attraction, and further grew into blocky particles via particle attachment. These results illustrate that surface reactivities of heteroaggregated ferrihydrite and kaolinite/montmorillonite are coupled when they interact with Mn(II) or MnOx. Our work, for the first time, exemplify the cooperation between surfaces of various minerals during the heterogeneous formation of NMMNs. Findings from this study also help advance our understanding of MnOx formation on surfaces with diverse atomic structures, and also Mn cycling in the environment.

Iron redox shuttling and uptake by silicate minerals on the Namibian mud belt

Anoxic marine sediments represent an important source of bioavailable iron (Fe) to the ocean. The highest sedimentary Fe fluxes are observed in open-marine oxygen minimum zones where anoxic bottom waters are in contact with ferruginous surface sediments. Here, sedimentary Fe release, transport and re-deposition (i.e., Fe shuttling) may generate a lateral pattern of sedimentary Fe enrichment and depletion, which can be used to trace redox-related Fe mobility in the paleo-record. However, depending on the balance between terrigenous and authigenic (i.e., shuttle-related) Fe flux, the stability of bottom water redox conditions as well as post-depositional processes of mineral alteration, the sedimentary fingerprint of an Fe redox shuttle may be obscured and difficult to identify.We investigated sedimentary Fe cycling along two transects across the Namibian mud belt with variable terrigenous sedimentation (23°S < 25°S) and during two seasons with opposing bottom water redox conditions (oxic in austral winter versus anoxic to sulfidic in austral summer). On both transects, substantial benthic Fe fluxes up to −50 µmol m−2 d−1 were inferred based on pore water profiles. The magnitude of these fluxes is comparable to those reported for other open-marine oxygen minimum zones. On the transect at 23°S, Fe source areas with ferruginous surface sediments were clearly separated from Fe sink areas with highly sulfidic surface sediments. Therefore, Fe redox shuttling was reflected by a lateral pattern of reactive Fe depletion and enrichment relative to the terrigenous background sedimentation. By contrast, on the transect at 25°S, benthic Fe fluxes were temporally and spatially more variable and surface sediments were ferruginous or only weakly sulfidic. Therefore, sedimentary Fe depletion and enrichment was less pronounced at 25°S. In the Fe sink area at 23°S, hydrogen sulfide was present at the sediment surface during both sampling campaigns and solid phase data suggest that Fe sulfide minerals represented the main burial phase of reactive Fe. By contrast, at 25°S excess Fe was associated with potassium (K) rather than reduced sulfur. While a differing sediment provenance cannot be ruled out entirely, combined evidence from pore water silica profiles, K to Fe stoichiometric relationships and electron microprobe images suggest that laterally derived excess Fe was incorporated into pre-existing and/or authigenic clay minerals during early diagenesis. Iron uptake by clay minerals may be supported by frequent redox oscillations and sediment mixing preventing preservation of Fe sulfide minerals and promoting Fe and K fixation in clay minerals. The burial fluxes of excess Fe associated with sulfide minerals at 23°S and silicate minerals at 25°S were similar. Our findings thus underscore that neoformation or alteration of silicate minerals can be important processes within the low-temperature marine Fe cycle.

Mineral effects on methane hydrate formation and distribution in sand sediments

Methane hydrate is a promising energy resource widely occurring in the world, but the formation and distribution of methane hydrate in marine sediments with complex minerals remains unclear. Due to the small pore space and fine-grained size of clay minerals, the contact relationship between methane hydrate and clay mineral surface under excess water has not been characterized fully, which is required to investigate the mineral effect on methane hydrate formation. In this study, cryo-SEM was applied to observe the distribution of methane hydrate synthesized in pure quartz sands and the quartz sands mixed with montmorillonite or illite separately. According to the results of the research, methane hydrate dispersedly forms in the pore space away from and on the surface of quartz under a local excess water condition. In addition, methane hydrate occurs away from montmorillonite in pores with excess water and contacts the edge of montmorillonite under a local excess-gas condition. Moreover, methane hydrate was only observed to form away from illite aggregates in the pore with residual water. Montmorillonite and illite influence the preferable distribution of methane hydrate to occur away from mineral surface in excess water condition. In the sediments composed of different minerals, methane hydrate forms stochastically in the pore space and grows up individually. As a result, the findings of this study significantly expand the understanding of the formation and distribution of methane hydrate in marine sediments and the prediction of physical properties of hydrate-bearing sediments, and provide insights into natural gas hydrate exploration and production.

Exploring acid mine drainage treatment through adsorption: a bibliometric analysis.

Discharge of acidic wastewater from mining activities (acid mine drainage (AMD)) is a major global environmental and public health issue. Although several approaches, including chemical precipitation and membrane technology, have been developed to treat AMD, adsorption has emerged as the most promising technology due to its cost-effectiveness and efficacy. Despite the wide adoption of adsorption in treating AMD, the evolution of research in this area remains poorly understood. To address this gap, a bibliometric analysis of the most recent literature involving the application of adsorption in AMD remediation was conducted by merging datasets of articles from Scopus (1127) and the Web of Science Core Collection (1422), over the past decade (2013-2022). This analysis revealed a yearly increase of 11% in research publications, primarily contributed by China, the United States, and South Africa. Keyword analysis revealed that natural schwertmannites and their transformations, activated carbon, zeolites, and clay minerals, are the most extensively employed adsorbents for the removal of common metals (arsenic, chromium, iron, manganese, among others). The findings underscore the need for future focuses on recovering rare earth elements, using nanoparticles and modified materials, pursuing low-cost, sustainable solutions, integrating hybrid technologies, pilot-scale studies, exploring circular economic applications of AMD sludges, and inter-continental collaborations. These insights hold significant future implications, serving as a valuable reference to stakeholders in the mining industry.

Effect of TiO2 nanoparticles on the assembly of a copolymer-clay dispersion

Nanocomposites based on copolymer and clay minerals are attracting increasing attention as they are appropriate for extensive applications. In this work, we present results from an experimental study on the effects of TiO2 nanoparticles on a pluronic-F127/laponite water solution in the sol state. Differential Scanning Calorimetry (DSC), Dynamic Light Scattering (DLS) and Fourier Transform Infrared Attenuated Total Reflection Spectroscopy (FTIR-ATR) were used to characterize the systems. By DSC and DLS measurements the occurrence of micellization was first investigated. The temperature induced self-assembly was then studied by DLS identifying three relaxations associated to differently sized diffusing structures. The correlation between dynamics and bonding structure was thoroughly investigated by analyzing some specific infrared vibrational bands. In particular, the study of the characteristic absorption band of the ether groups in the dry state allowed to evaluate the amorphous/crystalline component evidencing the presence of more extended conformations in presence of the higher TiO2. Finally, the analysis of the bending mode for the residual water provided valuable insight about structural OH groups enabling a distinction between different types of water molecules associated to the copolymer/nanoparticle systems.

Hydrothermal overprinting of the Li-rich strata deposited in the Mesoproterozoic Wumishan Formation, Hebei Province, North China

Lithium (Li), as a strategic critical metal, plays a pivotal role in the emerging energy landscape, particularly in the context of Li-ion batteries driving the new energy economy. Recently, Li-rich strata (with Li2O > 0.3 wt%) have been discovered in the Mesoproterozoic Wumishan Formation in Hebei Province, North China, suggesting a prospective Li reservoir. This study investigates these Li-rich strata using geochemical and in-situ micro-analytical techniques to explore the occurrence of Li and the formation mechanism of Li-host minerals, aiming for a comprehensive understanding of the supernormal enrichment of Li. The Li-rich samples are predominantly composed of dolomite and quartz, followed by clay minerals such as illite, interstratified illite–smectite (I/S), and chlorite, with minor amounts of K-feldspar, albite, biotite, calcite, baryte, fluorite and fluorapatite. In-situ analysis and 7Li NMR spectroscopy reveal that Li predominantly occupies the octahedral sites within the structures of authigenic illite and I/S, while its absence in clastic illite, clastic chlorite, unaltered K-feldspar, and dolomite. The presence of veined minerals (e.g., fluorite, baryte, and calcite) and a strong positive correlation between Li and F imply that post-depositional hydrothermal fluids have significantly contributed to the formation of Li-host minerals. The paragenesis of these minerals suggests that Li-bearing illite has formed through the hydrothermal alteration of K-feldspar. These Li-bearing illites subsequently transformed into Li-bearing I/S, consisting of illite-rich I/S and smectite-rich I/S, under continuous hydrothermal alteration. Lithium could have been leached from the surrounding carbonate rock and tuff through water–rock interaction and subsequently enriched by post-depositional hydrothermal fluids in specific regions, leading to mineralization. These findings provide valuable insights for targeting exploration of this promising Li resource.

Differential mineral diagenetic evolution of lacustrine shale: Implications for CO2 storage

Understanding the differential diagenetic evolution of different lithofacies is essential for assessing the spatial development of shale reservoirs. These insights are crucial in predicting sealing integrity and storage capacity for sequestered CO2. In this study, we examined seven wells from the Cretaceous Qingshankou Formation in the Songliao Basin, China, with vitrinite reflectance (Ro) values ranging from 0.60 % to 1.62 %. Thin section-based petrographic observations, coupled with QEMSCAN analysis, were used to classify the different lithofacies. X-ray diffraction (XRD) analysis of clay minerals, field emission scanning electron microscope (FE-SEM), and energy-dispersive spectrum (EDS) analyses were employed to analyze the mineral textures, pore types, and diagenetic pathways. The results showed that early diagenetic mineral phases include calcite cement (1st phase), framboidal and microcrystalline pyrite, ferroan and non-ferroan dolomite. Intermediate diagenetic mineral phases were marked by illitization of smectite, chlorite formed by chloritization of smectite and alteration of K-feldspar, and the formation of authigenic albite and quartz, calcite cement (2nd phase) and ankerite. Given the higher potential reaction rate of CO2-fluid‑carbonate systems, we propose that the lithofacies dominated by carbonate minerals are not effective for CO2 storage, even in short-term. In contrast, lithofacies rich in feldspar and clay minerals are likely to be more effective for long-term CO2 storage.

The evolution of amino acids under asteroidal aqueous alteration

Carbonaceous chondrites contain amino acids, with variable abundances and isotope compositions between and within carbonaceous chondrites. The parent body processes, and the presence of clay minerals may explain those differences. Here, we experimentally investigate the evolution of 6 amino acids (glycine, β-alanine, α-alanine, 2-aminoisobutyric acid, γ-aminobutyric acid, and isovaline) exposed to hydrothermal conditions in the presence or absence of silicates. We determined the chemical nature and isotopic composition of the organic compounds of the soluble and solid fractions of the residues using X-ray diffraction, spectroscopy, and mass-spectrometry methods. Glycine and α-alanine exhibit a rather high stability, which is consistent with the measured abundances of α-alanine and glycine in chondrites having experienced various degrees of aqueous alteration. In the meantime, the evolution of β-alanine under hydrothermal conditions leads to the formation of a new compound, which likely results from the decarboxylation and deamination of β-alanine followed by recombination. More than 95 % of γ-ABA was transformed into 2-pyrrolidione though self-cyclization during the aqueous alteration. The solid residues of the experiments conducted in the presence of clay minerals contain organic material, with abundances varying depending on the amino acid used for the experiments (TOC isovaline > 2-aminoisobutyric acid > γ-aminobutyric acid > glycine > α-alanine > β-alanine). Clay minerals thus preferentially trap branched amino acids over chained amino acids, likely within their interlayer spaces as suggested by XRD data. The δ13C values of amino acids have not changed significantly during the experiments, even with the presence of silicates. Thus, the δ13C values of amino acids reported in CR and CM chondrites likely relate to synthetic conditions or the origin of their precursors (i.e. inherited from the pre-accretion processes).

Use of Nondestructive Impedance Spectroscopy for the Assessment of Clay–Lime Reaction Kinetics: Influence of Clay Mineralogy, Lime Content, and Curing Conditions

Use of Nondestructive Impedance Spectroscopy for the Assessment of Clay–Lime Reaction Kinetics: Influence of Clay Mineralogy, Lime Content, and Curing Conditions

Mechanism of tetracycline sorption on carbon-bentonite

Antibiotics increased industrial production is the reason of their occurrence in wastewater, soils, groundwater, and drinking water. In this regard, treating the environment for pharmaceuticals is one of the urgent environmental challenges. Synthesis of adsorbents using different types of raw materials by the methods of mechanochemical activation makes it possible to significantly increase their sorption capacity due to the accumulation of various kinds of defects in the crystal structure of the adsorbent. We obtained the bentonite-carbon composite using roller-ring vibratory mill with coal-bentonite ratio of 30 : 70 and 50 : 50. However, the nature of the interaction between carbon and bentonite correlates with changes of surface area and porosity. The porous structure parameters of the samples show the mechanochemical activation of the mixture involves their components interactions. The authors studied the structural and chemical changes during the modification of bentonite with activated carbon by analysing the vibrational spectra of carbon, initial, and modified aluminosilicate samples. According to infrared spectroscopy of adsorbents, absorption bands characteristic of Si-O-C bond vibrations occurred. The paper investigates the sorption capacity of mechanochemically modified natural clay mineral Dash-Salakhli bentonite towards tetracycline hydrochloride. Research investigates the kinetics of the process and rapid sorption of tetracycline. The paper provides possible mechanisms of chemisorption due to donor-acceptor interaction and ion-exchange processes.

Molecular insights into the binding mechanism of strontium and cesium on phyllosilicates with different expandability

The environmental fate of strontium (Sr) and cesium (Cs), as the critical radioactive fission products, have raised significant concerns regarding radioactive waste disposal and environmental protection. The current study investigated the distinction in the binding configurations of Sr2+ and Cs+ on various 2:1 phyllosilicate (illite, vermiculite, and montmorillonite) by combining batch adsorption, sequential extraction, and spectroscopic analyses. The results show that strontium adsorption is strongly influenced by pH as well as ionic strength, while there is no significant variability in strontium adsorption by different types of clay minerals. EXAFS analysis confirms the outer complexation of strontium on the planar sites of the clay minerals, i.e., Sr2+ is surrounded by ~8.0 O atoms, RSr-O ≈ 2.6 Å, and that process is mainly realized by ion exchange. In contrast, Cs+ adsorption was markedly influenced by the variety of clay minerals but less by pH and ionic strength, the presence of humic acid (HA) inhibited Cs+ adsorption. The inner-sphere complexation formed mainly at the frayed edge sites on illite, and interlayer sites on vermiculite and montmorillonite, was the dominant mechanism for Cs+ adsorption. In addition, the collapse of the interlayer space of vermiculite induced by Cs+ adsorption on the interlayer sites was responsible for the more stable and irreversible immobilization. The findings in present work highlighted the significance of prevailed mineral in governing environmental migration risk of radionuclides, the revealed adsorption mechanism and binding configuration of Sr2+ and Cs+ on typical phyllosilicates would be referable in constructing a reliable migration model of Sr2+ and Cs+ in natural media.

Evolution of [formula omitted]-spacing in clay with PEG bulk volume fraction and molecular weight: Theoretical and experimental study

In the pursuit of ensuring the sustainability of the construction sector and fortifying its resilience against climate change, scientists have dedicated significant efforts to explore new classes of innovative, affordable, and technologically advanced materials that exhibit high efficiency, thereby securing the future for generations to come. In this context, we have opted to produce clay-polymer ecosystems through the direct insertion process. The PEG2000/clay and PEG6000/clay composites underwent analysis using X-ray diffraction (XRD) techniques, revealing the evolution of dhklconcerning the PEG bulk volume fraction. The results indicate the presence of two adsorption cycles, each comprising three stages (dilute, two-dimensional semi-dilute, and plateau). Each cycle delineates the incorporation of a polymer layer into the interlayer spaces of clay minerals. To elucidate this adsorption process, we have proposed a model depicting PEG chain conformation in confined spaces, represented as both monolayer and bilayer configurations. The influence of PEG molecular weight is distinctly evident in the dhklevolution across various clay categories. Ultimately, the application of scaling theory to model the experimental results proves to be robust, offering a precise description of the three discussed regimes.

Identification of Clay mineral deposits in the South-Eastern region of Uttar Pradesh, India, using Remote Sensing

Identification of Clay mineral deposits in the South-Eastern region of Uttar Pradesh, India, using Remote Sensing

Solar-driven calcination of clays for sustainable zeolite production: CO2 capture performance at ambient conditions

This study presents the environmentally sustainable synthesis of zeolites from solar-calcined kaolin and halloysite, emphasizing their application in CO2 capture due to their distinctive porous structures and chemical attributes. Expanding upon prior research that utilized solar energy for kaolin calcination, we now explore halloysite as an alternative clay mineral for zeolite production and CO2 capture. Employing a solar simulator, halloysite was calcined at temperatures ranging from 700 to 1000 °C, resulting in the synthesis of zeolites 4A and 13X via hydrothermal methods. The synthesized zeolites were characterized using X-ray diffraction (XRD), low angle XRD (LA-XRD), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM), and Brunauer–Emmett–Teller (BET) surface area measurements. Notably, the presence of Al-Si spinel, which crystallizes at elevated solar calcination temperatures, persisted within the zeolite 13X matrix, inducing a secondary mesoporous phase. The observed hysteresis in 13X samples, rather than confirming the mesoporous character of zeolite 13X, indicates a tandem effect of mesoporous Al-Si spinel with microporous zeolite 13X, exemplifying systems known as micro/mesoporous zeolitic composites (MZCs). The correlation obtained between the interplanar distances calculated from LA-XRD and pore size distributions acquired from the BJH desorption branches highlights LA-XRD as an alternative analysis method for assessing mesoporosity. While the microporosity of Al-Si spinel possessing 13X samples positively correlates with CO2 capture performance, mesoporosity appears to have minimal impact. Among the zeolites synthesized using solar energy, zeolite 4A (LTA) demonstrates superior CO2 capture capability, achieving an adsorption capacity of 2.15 mmol/g at 25 °C and 1 bar. This study highlights the potential of solar energy in producing eco-friendly zeolites from kaolin and halloysite for improved CO2 capture, advancing sustainable environmental solutions.

Transfer of rare earth elements from clay-sized fraction to phosphate in East South Pacific Ocean: Implication for REY-rich sediment related to hydrothermal influence

Pelagic sediment enriched in critical metals (e.g. rare earth elements and yttrium, REY) has attracted much attention in recent years. Extensive research has focused on identifying the specific host mineral of REY in bulk pelagic sediment, however, research on clay-sized fraction of REY-rich sediment has not been fully understood yet. In this study, we aimed to investigate the host phase and migration mechanism of REY in clay-sized fractions from two cores, GC23 and GC17, located on the western and eastern sides of the East Pacific Rise (EPR), respectively. To the best of our knowledge, this is the first comprehensive investigation of the clay-sized fraction of REY-rich sediment associated with hydrothermal activity. Results show that GC23 contains negligible clay minerals but well-crystallized Fe oxyhydroxides, while GC17 is rich in smectite and poor-crystallized Fe oxyhydroxides. REY are predominantly hosted in poorly crystallized Fe-Mn oxyhydroxides, with some phosphorus selectively scavenged by Fe oxyhydroxides from seawater. In addition, fluorapatite nanocrystals were first observed within the matrix of Fe oxyhydroxides using transmission electron microscopy (TEM), indicating the formation of fluorapatite. The post-Archean average shale (PAAS)-normalized REY patterns show similar seawater-like patterns in both the clay-sized and silt-sized fraction. The clay-sized fractions primarily derived from hydrothermal plumes plays an important role in scavenging REY from ambient seawater. This study represents a significant step towards understanding the formation of REY-rich sediment related to hydrothermal activity. A two-stage mineralization process is proposed for the formation of REY-rich sediment near the EPR fields. Firstly, REY are initially scavenged by hydrothermal Fe-Mn oxyhydroxide particles from seawater during their lateral dispersion with hydrothermal plumes under low sedimentation rate until they are buried by newly formed precipitates. With the process of early diagenesis, poor crystallized Fe oxyhydroxides will be experienced recrystallization. Subsequently, REY would be released into porewater with the process of recrystallization due to their tendency to remain in a poorly crystallized phase. Ultimately, they are captured by biogenic apatite and/or fluorapatite. The case study indicates that REY-rich sediments may primarily formed within the dispersion area of hydrothermal plumes. Simultaneously, the necessity of slow sedimentation rates, greater water depth, and deep currents all accountable for the formation of REY-rich layers.

Microplastic accumulation and transport in agricultural soils with long-term sewage sludge amendments

Land application of sewage sludge brings microplastic contamination to soil. However, studies regarding the occurrence and mobility of sludge-borne microplastics in soil are insufficient. In the present study, based on an experimental field, the effects of sludge application amount on the accumulation and migration of microplastics in 0–20 (upper) and 20–40cm (lower) soil layers were evaluated. After 16 years of continuous sludge application (36 t/ha per year), the microplastic content and migration ratio in upper soil reached 6,811 particles/kg and 148%, which was about 5 and 20 times, respectively, higher than that of the control soil without sludge. The microplastics in upper and lower soil layers, were mainly 0.2–0.5mm in size, mostly fibrous in shape, primarily transparent in color, and predominantly rayon in composition. Microplastic surfaces may persistently adsorb clay minerals and iron/titanium oxides from soil, posing potential environmental risks. Sludge application had a significant positive correlation with soil microplastic abundance, resulting in a good fit of predictive model constructed for microplastic accumulation in sludge-amended soils. These findings help to improve the knowledge on environmental behavior of microplastics in sludge-amended soil, and can provide a scientific basis for the regulation of microplastic pollution during sludge land application.

КЕРАМИКАЛЫҚ ЖОЛ ТӨСЕНІШТЕРДІ ӨНДІРУДЕГІ КЕРАМИКАЛЫҚ МАССА КОМПОЗИЦИЯСЫН ЖЕТІЛДІРУ

The article presents the results of a study of the chemical and mineralogical composition of the raw material components in the ceramic mass and provides techniques for the technology of laying ceramic material by vibropressing using talc rock in the mass and methods for determining the composition of clay raw materials. Formulations for the production of ceramic road surfaces, taking into account the factors of preference for mixtures to improve the properties of the finished product as a molding, drying and ceramic material, have been studied in two different components. It was found that the introduction of talc into the ceramic composition has an effect on the formation of high-temperature augite and amphibole phases and the intensification of the formation of minerals in clay, on the formation of high-temperature phases - sanidine, ackermanite elements. This process leads to an increase in the physical and mechanical properties of the resulting samples.The main patterns of formation of the structure and phase of ceramic compositions by firing in the temperature range 1000оC-1100оC were studied by isothermal control.In this pattern, sintering processes with solid and solid liquid-phase syntheses were carried out to ensure the phase - mineral composition, the study clarified the production of high-strength and frost-resistant ceramic pavement. In order to be used in the improvement of the city territory (sidewalks, alleys, park areas, playgrounds, etc.), the possibility of obtaining ceramic road surfaces that meet environmental and operational requirements has been proven. It has been established that one of the priority properties of ceramic road surfaces is a significant abundance of their porosity (25-30%), which allows you to quickly absorb moisture from precipitation (rain, sleet, etc.) and filter water through the body into the ground.Such properties of ceramic paving stones prevent the accumulation of moisture on the surface of the roadway and create comfortable conditions during pedestrian movement, reducing the likelihood of ice formation on the surface of the paving stones in the cold season.

Mineralogical Impact on the Compaction of Residual Gabbro Soils in the Construction of Platinum Tailings Storage Facilities

AbstractOver the past decade, there have been 45 tailings storage facility (TSF) disasters worldwide resulting in fatalities, serious environmental damage, and the destruction of entire ecosystems. These failures often stem from substandard design or operational practices. Many TSFs are constructed in regions associated with intrusive mafic rocks such as gabbro, norite, pyroxenite, and anorthosite, which are commonly found alongside platinum group metals in areas like the Bushveld Igneous Complex in South Africa and the Great Dyke in Zimbabwe. The stability of these structures can be significantly influenced by the residual soils present at the construction sites. Residual soils, both cohesive and non-cohesive, contain varying quantities of different minerals, which can impact the compaction characteristics and, consequently, the stability of the TSF foundations. Cohesive soils rich in clay minerals, such as kaolinite and smectite, exhibit properties that can hinder effective soil compaction. The expansive nature of smectite due to its ability to absorb large amounts of water and host free exchangeable cations counteracts the compaction process, reducing soil stability. Soil compaction is a complex process influenced by several factors, including compaction effort, method, water content, particle size distribution, and mineralogy. This study aimed to analyse these factors using a series of laboratory tests, including foundation indicators, MOD AASHTO compaction testing, and X-ray diffraction analysis, on residual soils from two TSF construction sites. The findings revealed that soils with high clay content tend to retain more water and have a higher optimum water content, adversely affecting their compaction properties. This study highlights the critical need to consider the mineralogical composition and weathering effects of residual soils in the design and construction of TSFs. By improving our understanding of these factors, we can enhance the stability of TSF foundations, reducing the likelihood of future failures. The insights gained from this research highlight the importance of thorough geotechnical assessments in the successful design and maintenance of TSFs.

Enhanced sequestration of ciprofloxacin from aqueous solution using composite montmorillonite-kaolin clay adsorbent

Clay minerals are low-cost and environmentally benign natural adsorbents with huge potential for removing micropollutants from aqueous solutions owing to their intrinsic surface properties. In this study, montmorillonite and kaolin clay minerals were activated using NaNO3 and HNO3 to develop activated montmorillonite- kaolin clay composites (AMKCC) material for the sequestration of ciprofloxacin (CIP) from aqueous solution. The developed AMKCC was characterized using X-ray fluorescence (XRF), Brunauer-emmett-teller (BET), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The BET analysis reveals an improved BET surface area, pore volume and pore diameter of 139.13 m2/g, 0.17 cm3/g and 2.18 nm, respectively. At optimum conditions, pH (3.56), initial concentration (16.74 mg/L), time (77.9 mins) and adsorbent dosage (0.4 g), the percentage of ciprofloxacin removed from aqueous solution was 97 %. The adsorption of ciprofloxacin (CIP) using AMKCC was spontaneous, feasible, endothermic, and followed Freundlich isotherm with pseudo-second-order kinetics. The maximum monolayer adsorption capacity of AMKCC is 344.82 mg/g. The desorption studies revealed HCl as the best eluent for AMKCC regeneration. Therefore, AMKCC has considerable potential for the adsorption of pharmaceuticals from aqueous solution.