Changes In Mineral Composition Research Articles

Study on the Applicability of Deterioration Detection Techniques for Sandstone Heritage in Multi Environment using MLP-Attention Model

Abstract. Stone cultural heritage, encompassing a broad spectrum of artifacts such as stone artworks, buildings, tools, and utensils, represents one of the most significant categories of cultural heritage. However, the conservation of these cultural heritage faces challenges from the process of deterioration. This degradation not only compromises the structural integrity of the heritage but also results in the loss of invaluable historical information. Thus, there emerges a critical demand for effective methods to detect and assess the condition of stone cultural heritage, enabling timely and precise conservation interventions. Here we obtained sandstone samples under different deteriorative environments through laboratory-simulated deterioration experiments and employed a variety of detection technologies to capture a series of changes in the deterioration detection parameters during the sandstone deterioration process. Subsequently, a deep learning model was established to correlate the detection parameters with the degree of stone deterioration. A SHAP analysis was then conducted to determine the contribution of various parameters to the degree of stone weathering under different experimental environments, providing recommendations for selecting appropriate detection technologies and indicators adapted to different deterioration environments. To further analyze the deterioration processes of the stone samples, XRD analysis was conducted to observe changes in mineral composition throughout the deterioration process. SEM images were utilized to examine the changes in micro-morphology and the internal pore structure associated with deterioration. This study provides a basis for the scientific design of deterioration detection schemes by selecting the most suitable testing technology for optimal deterioration assessment under specific environmental conditions.

Aging damage characteristics of acid‐etched sandstone samples

AbstractTo investigate the erosive damage effect of the acidic solution on sandstone, experiments were conducted to examine the macro‐ and micro‐characteristics of sandstone samples under different acid etching times. Microscopic morphology changes, pore structure characteristics, mineral composition changes, and mechanical response characteristics were obtained before and after acid etching. Finally, a comprehensive evaluation index for acid etching damage was proposed. The results show that: (1) Acidic solution will erode the sandstone skeleton and cause the sandstone to collapse. The etched surface appears “flocculent” and yellow sediment is produced. (2) The pores in sandstone samples are mainly micro‐ and mesopores, and the total porosity increases exponentially with the duration of acid etching. The volume fraction of micropores can reach up to 81.5%. (3) The acid etching process of sandstone samples includes physical diffusion and chemical dissolution, which can be divided into four stages and three regions from the outside to the inside. After acid etching, the uniaxial compression failure mode of the sample changes from shear to mixed shear‐tensile failure. (4) The comprehensive evaluation index based on three failure modes generated during the loading process shows good consistency with the overall changes of characteristics parameters such as elastic modulus, peak stress, and peak strain. The research findings of this paper can provide theoretical support for the assessment of rock mass stability and disaster prevention in acidic environments.

Short-term interactions between Longmaxi shale and carbon dioxide-based fracturing fluids

The shale is a dense quarried rock material containing abundant shale oil/gas. Extracting shale gas usually requires fracturing the rock formation to speed up gas desorption and migration. Supercritical carbon dioxide fracturing, as an environmentally friendly and waterless fracturing technique of reservoir stimulation, gains increasing recognition in commercial exploitation of shale oil and gas. However, there is insufficient understanding on the interaction between carbon dioxide-based fracturing fluids and shale, as well as its influence on the mechanical parameters of shale, which are pivotal for determining injection parameters and forming the fracture network. This study focuses on the injection of carbon dioxide-based fracturing fluids to enhance shale gas extraction and carbon dioxide sequestration. Simulation tests of injection were conducted to investigate the influence of different fracturing fluids (deionized water, gaseous/supercritical carbon dioxide, gaseous/supercritical carbon dioxide mixed with brine) injected into shale reservoirs on the microstructure and mechanical properties of shale after short-term physicochemical interaction. This article adopts research methods such as uniaxial compression and uniaxial tensile mechanical experiments based on acoustic emission monitoring and various physical characterizations such as scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectrometer, etc. Results show that following treatment with different carbon dioxide-based fluids, the uniaxial tensile/compressive strength, elastic modulus, fractal dimension of pore structure, and the brittleness index of shale exhibit varying degrees of decrease compared to those of dry untreated shale samples. After interacting with different carbon dioxide-based fracturing fluids, the mechanical parameters and brittleness index of shale decrease more significantly than that of the others as the addition of brine. This study shows that the water in carbon dioxide-based fracturing fluids is a controlling factor affecting the elastic modulus of shale. Additionally, the ductility of the shale increases and the acoustic emission emitting lag due to the coupling effects of brine and carbon dioxide. The change law of the elemental and mineral composition of the shale is consistent with the mechanical strength; and the change of element content and mineral composition is the most significant. Compared to gaseous carbon dioxide, the supercritical carbon dioxide has a greater impact on mineral composition of the shale. The change of mechanical strength and microstructure evolution mechanism caused by the short-term interactions between the shale and fracturing fluids provide theoretical references and implications for the determination of injection parameters and permeability transformation of the Longmaxi shale reservoirs.

Soil utilization analysis of synergistic pyrolysis products of flue gas desulfurization gypsum and biomass

Flue gas desulfurization gypsum (FGDG) is one of the typical bulk solid wastes. With its vast production and considerable storage capacity, it accumulates in substantial quantities, occupies an extensive amount of land, and poses a severe pollutant threat to the ecological environment. To achieve large-scale consumption of FGDG, this study puts forward a method for the soil utilization and ecological reconstruction involving the co-pyrolysis of FGDG and biomass. The main emphasis is placed on exploring the alterations in leaching toxicity and plant-available elements under diverse conditions of temperature, biomass addition, and pyrolysis time. The co-pyrolysis parameters were optimized, and the changes in mineral composition of FGDG and biomass under different pyrolysis circumstances were investigated using XRD and SEM characterization methods. The experimental outcomes demonstrated that the optimal pyrolysis conditions were a temperature of 700 °C, a biomass content of 60 %, and a pyrolysis time of 5 h. The toxic and harmful substances within FGDG were solidified and stabilized, achieving a harmless treatment of FGDG. Simultaneously, the usable elements for plants were released. Through the analysis of mineral composition and microstructure, it was discovered that the pyrolysis products contain a considerable amount of CaSO4 and C, and the microstructure mainly consists of porous aggregates. The reason for the reduced leaching efficiency of toxic and harmful substances might be attributed to the formation of stable minerals such as heavy metals through crystallization and vitrification mineralization after the removal of crystal water from FGDG. Under the reduction effect of C, the available elements for plants are liberated. This study furnishes a theoretical basis for the industrial application of FGDG and biomass for large-scale soil utilization treatment.

Investigations of the impact of geothermal water reinjection on water-rock interaction through laboratory experiments and numerical simulations

In the quest for sustainable geothermal energy production, the adoption of geothermal reinjection technology has become a crucial element in the development of geothermal resources. However, the processes of injection and extraction can lead to interactions between water and rock within the geothermal reservoir, resulting in pore blockage. This study focuses on the Kaifeng Zhenyu Garden geothermal field as a case study to examine the water-rock interactions that occur during geothermal reinjection, as well as the subsequent changes in mineral composition and porosity within the reservoir. The findings reveal that the primary minerals undergoing dissolution are dolomite and feldspar, with the precipitation of calcite and clay minerals following suit. Additionally, results from field simulations corroborate that dolomite and feldspar are the main minerals dissolving, accompanied by the precipitation of calcite and illite. Notably, significant changes in mineral dissolution and precipitation near the geothermal well have led to a slight reduction in the reservoir's porosity. This investigation provides valuable insights into the water-rock interactions involved in geothermal reinjection processes across various geothermal fields.

Study on the radon exhalation rate of phyllite under thermal effects

As a result of human underground mining activities, phyllite has been extensively reused to make raw ceramic materials and concrete aggregates. Building materials are a significant source of indoor radon, and radon gas emitted from phyllite poses radiation risks to humans. High temperatures can alter the structural properties of rocks, impacting radon exhalation. Thus, this study examined phyllite's radon exhalation rate after heat treatment ranging from 25 °C to 1000 °C. The effects of changes in pore structure and mineral composition on phyllite's radon exhalation were analyzed in detail using nuclear magnetic resonance (NMR), polarizing optical microscopy (POM), three-dimensional microscopy (3DM), and scanning electron microscopy (SEM). Results indicate that the radon exhalation rate initially increases and then decreases with rising temperature. This rate correlates positively with both total porosity and micropore porosity. Processes such as free water evaporation, pyrite oxidation, quartz phase transformation, and chlorite dehydroxylation within phyllite contribute to pore development and the movement of free radon within pore spaces. The highest total porosity and radon exhalation rate occur at 700 °C, measuring 8.6 % and 6.14 Bq/m2·h, respectively—4.30 times and 1.18 times higher than at 25 °C. Additionally, mineral decomposition and melting reduce pore connectivity and effective porosity, hindering radon migration. These findings offer guidance for assessing radon radiation risks and indoor radon potential in phyllite-based building materials.

Assessment of surface microhardness of enamel surface treated with Nano- HAP serum before and after bleaching

Background: Although bleaching is typically considered a safe procedure, various investigations have found minor negative effects and changes in mineral composition. The aim was to Evaluate and compare the efficacy of using Nanohydroxyapatite serum on surface microhardness of enamel surface before and after bleaching with chemically cured Boost bleaching. Material and methods: ten sound human permanent upper and lower premolar teeth were used and their roots were removed 2 mm apically to the cementoenamel junction, the crowns were sectioned mesiodistally into two halves buccal and lingual/palatal, the buccal surface was further subdivided into two halves. The samples were embeded in an acrylic resin, resulting in 30 specimens divided into 3 groups: Control group: using Boost bleaching and stored in artificial saliva for 14 days, prevention group: nanohydroxyaptite (n-HAP) serum applied 2-3 min once daily for 10 days followed by bleaching then stored for 14 days in artificial saliva and treatment group: in which bleaching used before nanohydroxyapatite serum and stored in artificial saliva for 14 days. The samples were subjected to a Vickers microhardness test measured at 4 times: base line, after nanohydroxyapatitem, after one day of bleaching and after storage in artificial saliva for 14 days in all groups. The data were analyzed statistically using repeated analysis of variance (ANOVA) test followed by Tukey's test. Results: there was a significant increase in microhardness in the prevention group (p<0.05) while there was no significant difference in microhardness readings in control and treatment groups (p> 0.05). Conclusion: n-HAP may enhance the microhardness of a bleached enamel surface when used as a preventive & treatment measure. Suggested that a higher increase in enamel microhardness occurs when n-HAP is used for 2-3 min once daily for 10 days before bleaching and maintaining this increase even after storage for 14 days in artificial saliva.

Mineral Composition and Distribution of Silt and Oxides in Shatt Al-Arab Deposits, Basra, Iraq

Understanding the mineral composition and distribution of river deposits is crucial for environmental management, resource utilization, and geological studies. This study aims to investigate the mineral composition and distribution of silt and oxides in the deposits of the Shatt al-Arab River, specifically in the Faw area of Basra Governorate. Samples were collected from depths of 0-30, 30-60, and 60-90 cm. The silt fraction (2-53 micrometers) was isolated, and mineral analysis was conducted using XRD and a point-counting device. Morphological characteristics were determined using a polarized light microscope. XRD analysis revealed the presence of minerals such as quartz, calcite, dolomite, smectite, kaolinite, chlorite, illite, hematite, magnetite, and albite at varying depths. Polarized light microscopy identified additional minerals within light and heavy fractions. The study found a dominance of monocrystalline quartz and opaque minerals, with magnetite being more prevalent than hematite across all depths and a high correlation coefficient with depth (0.96). Depth-specific variations in mineral composition suggest the need for further research in different locations and at greater depths. These findings provide insights into sedimentary processes and potential resource utilization in the region, making this study significant for regional geological and environmental research. Future research should focus on the temporal changes in mineral composition and their impact on sediment dynamics to enhance the understanding of regional geological history and resource management.

Mathematical optimization of multilinear and artificial neural network regressions for mineral composition of different tea types infusions

The objective of this study was to investigate the change in mineral composition depending on tea variety, tea concentration, and steeping time. Four different tea varieties, black Ceylon (BC), black Turkish (BT), green Ceylon (GC), and green Turkish (GT), were used to produce teas at concentrations of 1, 2, and 3%, respectively. These teas were produced using 7 different steeping times: 2, 5, 10, 20, 30, 45, and 60 min. It was also aimed to optimize the regression equations utilizing these factors to identify parameters conducive to maximizing Zn, K, Cu, Mg, Ca, Na, and Fe levels; minimizing Al content, and maintaining Mn level at 5.3 mg/L. The optimal conditions for achieving a Mn content of 5.3 mg/L in black Turkish tea entailed steeping at a concentration of 1.94% for 11.4 min. Variations in K and Mg levels across teas were inconsistent with those observed for other minerals, whereas variations in Al, Cu, Fe, Mn, Na, and Zn levels exhibited a close relationship. Overall, mineral levels in tea can be predicted through regression analysis, and by mathematically optimizing the resultant equations, the requisite conditions for tea production can be determined to achieve maximum, minimum, or target mineral values.

Impact of dissolution and precipitation on pore structure in CO2 sequestration within tight sandstone reservoirs

Complex physical and chemical reactions during CO2 sequestration alter the microscopic pore structure of geological formations, impacting sequestration stability. To investigate CO2 sequestration dynamics, comprehensive physical simulation experiments were conducted under varied pressures, coupled with assessments of changes in mineral composition, ion concentrations, pore morphology, permeability, and sequestration capacity before and after experimentation. Simultaneously, a method using NMR T2 spectra changes to measure pore volume shift and estimate CO2 sequestration is introduced. It quantifies CO2 needed for mineralization of soluble minerals. However, when CO2 dissolves in crude oil, the precipitation of asphaltene compounds impairs both seepage and storage capacities. Notably, the impact of dissolution and precipitation is closely associated with storage pressure, with a particularly pronounced influence on smaller pores. As pressure levels rise, the magnitude of pore alterations progressively increases. At a pressure threshold of 25 MPa, the rate of change in small pores due to dissolution reaches a maximum of 39.14%, while precipitation results in a change rate of −58.05% for small pores. The observed formation of dissolution pores and micro-cracks during dissolution, coupled with asphaltene precipitation, provides crucial insights for establishing CO2 sequestration parameters and optimizing strategies in low permeability reservoirs.

The combination of arginine and fluoride-containing bioactive glass acted synergistically in inhibiting enamel demineralization in permanent teeth

ObjectivesTo evaluate the in-vitro efficacy of inhibiting enamel demineralization using arginine in combination with fluoride-containing bioactive glass (FBG). MethodsIn this study, the healthy enamel blocks were first demineralized in acetic acid for 24 h, then soaked in anti-demineralization treatment solutions containing either arginine or FBG or both for 96 h.The specimens treated in acetic acid were applied as the control group. The pH, calcium and phosphorus ion concentrations of the solutions were measured before and after treatment. Changes in enamel mineral weight, microhardness, and composition were also analyzed. ResultsThe present of arginine facilitated fluorine release from treatment solutions with the presence of FBG. Both arginine and FBG significantly increased the pH of treatment solutions and prevented the further mineral weight loss compared to the control group. All anti-demineralization treatment groups showed significant increases in microhardness, but there was no statistical difference among the treatment groups. The SEM analysis showed enamel restoration in the arginine and FBG groups upon treatment, while the combined groups showing a superior anti-demineralization efficacy. 19F NMR showed the formation of fluorapatite in samples treated with solutions containing FBG. ConclusionsBoth arginine and FBG could inhibit enamel demineralization to some extent, and their combination demonstrated an enhanced anti-demineralization efficacy. The low-concentration combination group exhibited anti-demineralization effects comparable to those of high-concentration ones. Clinical SignificanceThis study introduces a new approach for caries prevention by combining the application of arginine and FBG. The release of fluorine promoted by the presented arginine along with calcium and phosphorus ions from FBG facilitated FAP formation. Additionally, the increment of pH resulting from arginine and FBG degradation further prevents enamel demineralization.

Properties of saline soil stabilized with fly ash and modified aeolian sand

Against the backdrop of saline soil solidification and the resource utilization of solid waste and aeolian sand in cold and arid regions, this study employs locally accessible fly ash and aeolian sand to solidify saline soil. By combining unconfined compressive strength tests, X-ray diffraction analysis, scanning electron microscopy, orthogonal experiments, and single-factor analysis, the strength characteristics, mineral composition, and interfacial structure changes of saline soil solidified with different freeze-thaw cycles and varying amounts of fly ash, aeolian sand, and alkali activators were investigated. The effects of each factor were analyzed to determine the optimal mixture ratio and to explore the solidification mechanism.The results indicate that the unconfined compressive strength of saline soil is most significantly enhanced when solidified with a combination of fly ash, aeolian sand, and alkali activators. The optimal mixture ratio was found to be 24 % fly ash, 7 % aeolian sand, and 4.5 mol/L alkali activator. With the incorporation of these solidifying materials, the failure mode of saline soil transitions from plastic to brittle, and the stress-strain curve exhibited a strain-softening behavior. The combined solidification method demonstrated the most pronounced effect in mitigating freeze-thaw damage, with the unconfined compressive strength of the solidified soil reaching 7.01 MPa after seven freeze-thaw cycles, compared to 0.03 MPa for the untreated soil, an increase by a factor of 234.This significant enhancement is attributed to the formation of substantial gel substances, which mitigate the strength loss caused by freeze-thaw cycles. The gel locking mechanism between particles in the solidified soil far exceeds the detrimental effects of freeze-thaw cycles, effectively inhibiting freeze-thaw deterioration. Additionally, the reaction pathways involving AFt and AFm phases reduce the content of SO42- and Cl- in the solidified soil, effectively suppressing salt expansion and significantly improving the soil's strength.

Study on the failure mechanism of high-temperature granite under two cooling modes

In the geothermal development of hot dry rock (HDR), both the drilling of the wellbore and the heat exchange of the heat reservoir involve the effects of different cold and hot conditions on the high-temperature rock mass. The testing machine for rock mechanics was used to conduct a uniaxial compression test and carry out micro testing on the treated samples; furthermore, with the help of scanning electron microscopy the fracture mechanism of granite subjected to different temperatures and cooling methods was studied. The results show: (1) With the gradual increase in temperature, the compressive strength of granite under the two cooling methods gradually decreases. (2) The failure modes of the samples under the two cooling methods are mainly shear failure of the "Y" type. The degree of damage of the sample under water cooling is significantly greater than that under natural cooling. Electron micrographs could confirm these results. (3) It can be obtained by testing the mineral composition and element changes of granite at different temperatures. When the temperature reaches 600℃, its change is more pronounced. The results of this study can provide a theoretical reference for the failure of the wellbore and the degree of fracture of the thermal reservoir rock mass during geothermal development.

Lithofacies, changes in mineral composition and reservoir properties of the Maykopian sediments in the Yevlakh-Aghjabedi Depression

Yevlakh-Aghjabadi depression is a well explored oil province located in the Middle Kura basin between Greater and Lesser Caucasus.The study investigates the lithofacial, mineralogical, and collector properties of the Maykopian sedimentary series within the Yevlakh-Aghjabadi depression, focusing on the Oligocene to Early Miocene epoch. Maykop deposits are widely distributed in the foothill regions of the Lesser Caucasus, both at the surface as natural outcrops and in the geological structure of deeper formations. In this article, in addition to core samples, the results of fieldworks have also been widely discussed. The conducted research indicates favorable paleogeographic conditions for oil and gas presence in these depressions. The sedimentary sequence, up to 2200 meters thick, is divided into Lower and Upper Maykopian subgroups, showing fluctuating thickness distribution. The primary source of clastic materials for the Maykopian suit is the Lesser Caucasus Mountain range. The lithological composition consists of clay, sandstones, and conglomerates, influenced by paleogeographic changes and paleochannels. Collector properties vary, with Lower Maykopian sediments exhibiting better characteristics, especially in the south-western part of the basin. The mineralogical composition dominated by fine-grained feldspars, impacts reservoir quality. Maykopian suits in the oil and gas regions of Ganja and Muradkhanli, which encompass the southernwestern and northern-eastern flanks of the Yevlakh-Aghjabedibasin, as well as conducting extensive research on reservoir properties, will enable the proper direction of future exploration activities. For this purpose, the overall condition of the Maykopian suits and the distribution of lithofacies have been analyzed, and the characteristics of hydrocarbon reservoirs have been determined. Keywords: lithology; lithofacies; Maykopian; sandy and clayey sediments; argillaceous sandstones; porosity; permeability.

Microstructural alterations of coal induced by interaction with sequestered supercritical carbon dioxide

A total of four samples with different coal ranks were exposed to supercritical CO2 (SC–CO2) fluids for one week at 313.15 K and 12 MPa. FTIR and X-ray diffraction were combined to explore the changes in functional groups, mineral compositions and aromatic microcrystallite structures of coal samples before and after SC-CO2 interaction. The results indicate that a great number of aliphatic hydrocarbons in coal are extracted and the content is reduced by 47.83–83.08 %, whereas the oxygen-containing groups are slightly changed within 8 %. The content of carbonate minerals is decreased by 29.05–46.11 % after SC-CO2 saturation, while quartz content is enhanced. The changes in coal crystalline structures are attributed to the mineral dissolution and hydrocarbon extraction during SC-CO2 saturation. Numerous voids are generated among aromatic layers after mineral dissolution, which directly enlarges the layer spacing of aromatic sheets. The extraction of aliphatic hydrocarbons can not only further increase layer spacing, but also loosen the coal macromolecular structure. Consequently, the directional alignment of aromatic microcrystallites is reduced within coal, leading to the decline of stacking height and aromatic layers. These findings are of significance for assessing both the recovery of CO2-enhanced coalbed methane and the trapping of CO2 in coal reservoirs.

Intrinsic mechanisms of shale hydration-induced structural changes

The interaction between a water-based working fluid and shale causes a change in shale structure, resulting in wellbore instability and greatly increasing drilling costs. On the basis of the black rock samples of the Longmaxi Formation, the structural change characteristics and internal mechanisms of shale hydration are investigated using scanning electron microscopy, fixed-point observation experiments, X-ray diffraction experiments, ion analysis, and energy spectroscopy analysis. In this study, the changes in the microscopic elements during the propagation of macroscopic cracks to hydration were studied and the ion exchange of brine and mineral hydration was analyzed. The results indicate that the interaction between water and shale leads to shale fracture along the bedding plane, the expansion of primary fractures, the generation of new fractures, and the occurrence of a high number of dissolution phenomena. The ion exchange cation precipitation of shale and the fluid is dominated by Ca2+, and the anion precipitated is mainly SO42−. Through the energy spectrum analysis of the whole-rock mineral composition changes and shale structural changes, it is believed that shale dissolution is mainly from carbonatite minerals, such as calcite. While the oxidation of pyrite in the aqueous environment provides a large amount of SO42− and H+ and fracture propagation mainly occurs in areas where non quartz inorganic minerals are distributed on the bedding plane. The intrinsic mechanism of shale hydration structural changes is revealed through the structural changes, mineral composition changes, and chemical reactions present during the water–shale interaction, which is significant for ensuring the wellbore stability of drilling.

Effect of high temperature on the mixed mode I-II fracture characteristics of hot-dry rock

To investigate the variation law of rock fracture characteristics with temperature in hot-dry reservoirs, the pure mode I, pure mode II and mixed mode I-II loading experiments were carried out on sandstone and granite at room temperature and after high-temperature (100 °C, 300 °C, 500 °C and 700 °C) treatment by using the central cracked Brazilian disk (CCBD) specimen. The changes of parameters such as failure load, fracture toughness and fracture envelope with temperature were discussed, and the changes of rock mineral composition and fracture surface morphology were analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. The results showed that the influence of temperature on the fracture characteristics of sandstone and granite presents different evolution laws.With the increase of temperature, the failure modes of sandstone and granite all change from brittle failure to ductile failure, but the critical temperature of the transition is different. Granite shows obvious ductile failure characteristics at 500 °C, while sandstone shows slight ductile failure characteristics at 500 °C.The failure load and fracture toughness of sandstone increase first and then decrease with the increase of temperature, which indicates that within a certain range, the temperature has a toughening effect on sandstone, and can improve its failure resistance. However, the failure load and fracture toughness of granite always decrease with the increase of temperature, which indicates that the temperature only has a deteriorating effect on granite. In the range of 100 °C to 500 °C, the temperature enhances (sandstone) or weakens (granite) the mode I fracture toughness of rocks more than it enhances or weakens the mode II fracture toughness. However, when the temperature is 700 °C, the temperature weakens the mode II fracture toughness more than the mode I fracture toughness. The area enclosed by the fracture envelope of sandstone first increases and then decreases with the increase of temperature, while the area enclosed by the fracture envelope of granite decreases with the increase of temperature. As the temperature increases, the tortuosity of the crack paths in sandstone and granite increases, the cross-section morphology becomes rougher, and the internal fissures and fragmentation increase.

Prediction of the mineral components spatial distribution in tailings ferruginous quartzite enrichments

In Ukraine, a significant mass of potential man-made deposits is represented by waste from ferruginous quartzite enrichment. The mineral mass of such deposits is mixture of iron-containing minerals (magnetite, ilmenite) and quartz. The M.S. Poliakov Institute of Geotechnical Mechanics has developed a new methodology for the mineral components spatial distribution predicting in tailings of ferruginous quartzite enrichment. It includes the fractional and mineralogical composition of the samples study by optical method, and spatial useful components distribution of prognostication in waste and predictive plans construction for the useful components spatial placement. A previously unknown pattern of changes in mineral composition of wastes from mining ore production was revealed which caused by the turbulent transportation mode and waste deposition on the tailing (potential man-made deposit) area. This regularity arises from the fact that with decrease in the size of the mineral components particles with size of 0-200 microns, the share of the magnetic mineral magnetite increases linearly and, accordingly, the share of the non-magnetic mineral quartz decreases. The obtained new properties of man-made deposits from the waste (tailings) can be used in creation of resource-saving technology for the iron ore man-made raw materials processing and to determine their suitability for mining.

Experimental Study on Salt-Bearing Sandstone Samples Under the Change of Temperature and Humidity Cycle

ABSTRACT Salt crystallization is a common type of disease in grottoes. Due to the change in temperature and humidity, the soluble salt originally existing in sandstone will have a negative impact on the protection of rock relics. In this study, sandstone samples containing Na2SO4 solution and distilled water were used to study the difference in sample damage under the condition of temperature and humidity cycle changes. It was found that the damage degree of samples containing soluble salts was much higher than that of salt-free samples, especially under the influence of freeze-thaw cycles. With the increase of freeze-thaw cycles, the internal friction angle and wave velocity of sandstone decrease linearly, while the surface hardness, tensile strength, and cohesion decrease exponentially. In addition, the damage caused by freeze-thaw cycles and dry-wet cycles develops from the inside to the outside of the rock sample, which is manifested by the increase in the number of macropores and the emergence of new pores. The different combinations of several effects lead to different changes in pore structure and mineral composition of the samples under the four conditions. The research results are helpful in providing a scientific basis for the disease control of stone cultural relics.

Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II)

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of 57Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using 57Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in 57Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.