Limestone Samples Research Articles

UJI PARAMETER KIMIA BATU GAMPING SEBAGAI BAHAN BAKU SEMEN PADA LOKASI PENAMBANGAN CV THIAK KELURAHAN ARDIPURA KOTA JAYAPURA

Limestone mining owned by CV Thiak, which is located in the Ardipura II Jayapura city, has been operating for a long time. However, the utilization of limestone is only used as a mixed material in construction such as offices, schools, brdges and others. One sample of the use og limestone is a raw material for making cement. This study aims to determine the chemical content of limestone belonging to CV Thiak so that it can also be used as a raw material for making cement. The research stage is at the beginning with initial of reaserch location and mapping to determine the coordinates of the sampling location. Samples were taken at two different locations. Next, the stage of taking limestone as a sample for testing. The next stage is the description of the limestone to determine of type of limestone. The stage of sending limestone samples to the Mineral Engineering Laboratory in Bandung city to determine the chemical content contained in the sample. The last stage is the analysis of chemical parameters as data from laboratory test using the X-Ray Fluoresence method. Some of the chemical parameters analyzed were CaCO3, CaO, MgO, Al2O3, Fe2O3 and SiO2. From the results of the analysis, it is known that the two limestone sample belonging to CV Thiak have very high CaCO3 content. The CaCO3 at the first point has a level of 98,78 %. Meanwhile, the sample at the second point has a CaCO3 content of 98,38 %. For levels of CaO, the first point is 55,35 % and the second point is 55,13 %. By looking at the value of the content of CaCO3 and CaO, the quality of CV Thiak’s limestone is very good and meets the standars as cement raw materials, according to Portland cement standards

Correlation of P-wave velocity with mechanical and physical properties of limestone with statistical analysis

This study aims to investigate the correlation between the P-wave velocity (Vp) and the mechanical and the physical properties of the limestone; Vp tests were conducted on over 320 limestone samples. Moreover, the effects of the mineralogical, textural, and chemical composition of limestone were also studied through thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF). The relationships between the Vp and the uniaxial compressive strength (UCS), point load index (PLI(Is(50)), 2nd cycle of slake durability index (Id2), natural unit weight (γn), specific gravity (Gs(c)), water absorption by weight (WA), and porosity (n) were estimated using representative empirical equations. The empirical equations were validated by Student’s t test that has indicated the existence of strong relationships between the mechanical and physical properties of the intact limestone with Vp; the calculated t-values were higher than the t-critical value. Furthermore, the results of previously available studies were compared with the results of this study in terms of the generated equations for Vp values and the slope of a 1:1 line, which was used to appraise the predicted and measured values. This study demonstrates that the UCS, PLI(Is(50)), Id2, γn, Gs(c), WA, and n values of an intact limestone can be predicted by using Vp, which is fast, easy, economical and nondestructive test.

Effects of calcination variables on quicklime yield of Nkalagu limestone

Calcination of Nkalagu limestone for the production of agricultural quicklime is presented. It entails improving the quality of limestone through calcination process. Appropriate scientific instruments/techniques (x-ray diffractometer and scanning electron microscopy) were used for the characterization of the uncalcined and calcined limestone samples. Effects of calcination variables on the quicklime yield were examined. Central composite design of design expert software was used to optimize the calcination process. Analyses of the results revealed that calcite was the major limestone’s mineralogical composition. Quadratic model adequately described the relationship between quicklime yield and calcination factors of temperature, particle size and time. Quadratic model adequately described the relationship between quicklime yield and calcination factors of temperature, particle size and time. The optimum yield of 74.00% was obtained at optima operating conditions; temperature of 937.41 0C, particle size of 85.99µm and time of 3.7 hrs. Characteristics of the quicklime showed that the calcination improved the quality of the sample in terms of mineralogical properties. It is recommended that the generated model should be used to develop chemical plant/equipment for limestone calcination process.

Does bacterial weathering play a significant role in rock weathering?

Bacterial weathering plays a significant role in rock weathering, yet only a limited number of studies were conducted on this topic. The recent rapid developments in geomicrobiology are expected to increase the pace of research in this area. The extent and duration of the biological weathering processes on mineral and rock samples and minerals preferred by bacteria are still not fully understood due to the wide variety of both bacterial species and rock types. Biological weathering of rock types found in Turkey has also not been studied before. Here, we investigated the effects of two species of bacteria actively contributing to rock weathering on three rock types commonly used as building stone materials in Turkey. Granite, andesite, and limestone samples could interact with Bacillus species (B. subtilis and B. pumilus) in closed system reactors. Samples obtained from these reactors were analysed via scanning electron microscopy (SEM) monitoring to identify morphological features and chemical composition changes. Chemical elements consumed most by bacteria were identified. Changes in the colour index were determined via RGB measurements. The effects of experimental conditions on bacterial growth were monitored via daily optical density measurements. The effects of bacteria on the physical properties of rock samples were also evaluated. B. subtilis and B. pumilus were found to be more aggressive on limestone/andesite and granite, respectively.

Synchrotron 4D X-Ray Imaging Reveals Strain Localization at the Onset of System-Size Failure in Porous Reservoir Rocks

Understanding the mechanisms of strain localization leading to brittle failure in reservoir rocks can shed light on geomechanical processes such as porosity and permeability evolution during rock deformation, induced seismicity, fracturing, and subsidence in geological reservoirs. We perform triaxial compression tests on three types of porous reservoir rocks to reveal the local deformation mechanisms that control system-size failure. We deformed cylindrical samples of Adamswiller sandstone (23% porosity), Bentheim sandstone (23% porosity), and Anstrude limestone (20% porosity), using an X-ray transparent triaxial deformation apparatus. This apparatus enables the acquisition of three-dimensional synchrotron X-ray images, under in situ stress conditions. Analysis of the tomograms provide 3D distributions of the microfractures and dilatant pores from which we calculated the evolving macroporosity. Digital volume correlation analysis reveals the dominant strain localization mechanisms by providing the incremental strain components of pairs of tomograms. In the three rock types, damage localized as a single shear band or by the formation of conjugate bands at failure. The porosity evolution closely matches the evolution of the incremental strain components of dilation, contraction, and shear. With increasing confinement, the dominant strain in the sandstones shifts from dilative strain (Bentheim sandstone) to contractive strain (Adamswiller sandstone). Our study also links the formation of compactive shear bands with porosity variations in Anstrude limestone, which is characterized by a complex pore geometry. Scanning electron microscopy images indicate that the microscale mechanisms guiding strain localization are pore collapse and grain crushing in sandstones, and pore collapse, pore-emanated fractures and cataclasis in limestones. Our dynamic X-ray microtomography data brings unique insights on the correlation between the evolutions of rock microstructure, porosity evolution, and macroscopic strain during the approach to brittle failure in reservoir rocks.

Geochemistry of upper Palaeozoic ‘thin-layer’ limestones in the southern North China Craton: implications for closure of the northeastern Palaeotethys Ocean

AbstractDuring the late Palaeozoic Era, a series of related marine strata dominated by multi-layer limestones were deposited in the southern North China Craton. In order to gain new insights into the systematic geochemistry of the carbonate succession of the representative formation (Taiyuan Formation), we examined 59 limestone samples collected from the Huaibei Coal Basin (HCB), with a view towards quantitatively determining the major and trace elements and stable isotope compositions. The data obtained can provide essential evidence for reconstruction of the depositional palaeo-environment and tectonic setting of the Taiyuan Formation. Both X-ray diffraction analyses and palaeoredox proxies (e.g. V/Cr, V/(V + Ni) and authigenic U) indicated that the limestone layers were deposited in an oxic–dysoxic zone, with calcite as the main component. Moreover, palaeomagnetic evidence provided support for the conclusion that these limestones were laid down within an epicontinental sea depositional environment under a warm or hot palaeoclimate during the transition between late Carboniferous and early Permian time. Additionally, evidence obtained from our analyses of trace and rare earth elements revealed that the tectonic setting of the Taiyuan Formation (L1–L5) in the HCB transited from an open ocean to a passive continental margin, thereby indicating that this transformation stemmed from the subduction closure of the northeastern Palaeotethys Ocean. The findings of this study would be of interest to those working on the upper Palaeozoic marine strata in the southern North China Craton.

Paleostress Analysis from Calcite Twins at the Longshan Dome (Central Hunan, South China): Mesozoic Mega-Fold Superimposition in the Reworked Continent

It is generally accepted that during the Mesozoic NE−NNE-trending folds overprinted E−W-trending folds to form the Longshan dome in the central South China continent, although the interference map does not tell the relative ages of the fold sets. In an effort to deepen our understanding of the process of reworking the continent, paleostress analysis using calcite twins was carried out in this study to verify or falsify this model. Ten limestone samples were collected from Upper-Paleozoic limestones on the flanks of the dome and were measured using the universal stage for calcite e-twins. E-twins in the samples are divisible into two kinds, thick (≥1 μm) and thin (<1 μm), indicative of relatively higher and lower deformation temperatures, respectively. Stress estimates obtained using the improved version of Shan et al.’s (2019) method were grouped into two layer-parallel shortening (LPS) subsets and three non-LPS subsets. These subsets comprise four tectonic regimes: NWW−SEE compression (LPS1 and non-LPS1), NNE−SSW compression (LPS2 and non-LPS2), NW−SE extension (non-LPS3a) and NNE−SSW extension (non-LPS3b). They were further arranged in a temperature-decreasing order to establish a complex deformation sequence of the study area. In the sequence NE−NNE-trending folds have an older age than E−W-trending folds, something different from the model. The approximately N−S regional compression responsible for the former folds should have a profound effect on the intensely deformed continent, something ignored in earlier work.

Elastic Properties of Pannonian Basin Limestone under Different Saturation Conditions

Understanding elastic properties of reservoir rocks is essential for seismic modeling under different saturation conditions as well as lithology discrimination. Experiments on elastic properties of limestones are significantly less published compared to siliciclastic sedimentary rocks. The current study presents the results of laboratory measurements on Pannonian Basin limestone cores. The research was carried out for the first time for a hydrocarbon reservoir in the Bjelovar Depression, located in the southern part of the Pannonian Basin. Ultrasonic velocity measurements and determination of dynamic elastic properties were performed on limestone plugs, in dry and saturated condition under different confining pressure steps. Based on the results obtained in laboratory conditions, an empirical relationship between shear wave velocity (Vs) and compressional wave velocity (Vp) has been defined. The saturated samples show an effect of shear modulus weakening, while three samples have a shear modulus strengthening effect. Two models were used in the interpretation of the measured data, the Kuster and Toksöz and the Xu-Payne model. The results show that the Xu-Payne model describes the data well and the dominant pore type system in the limestone samples can been identified. The interpretation revealed an interparticle pore system with a fraction of microcracks from 20% to 35%. The results have helped to understand the elastic properties of limestones from the southern part of the Pannonian Basin, which are necessary for any process of reservoir characterization, such as porosity distribution and permeability variation.

Limestone Microfacies Punung Formation at Bangbang River, Sumbermanjing Wetan, Malang, East Java

Malang and Wonosari areas are located in Southern Mountains of Java, and their rock variations are comparable. Study focuses on limestone found at Sumbermanjing Wetan, Malang, that has been identified as part of Wonosari Formation. This place is closer to Punung area as viewed from the type location. Limestone microfacies approach is used to determine whether the limestone belongs to Wonosari or Punung formations. Methods used to identify standard microfacies types and facies zone are measured stratigraphy, petrographic analysis, and microfossil analysis. Measured stratigraphy was conducted along Bangbang River, and seven limestone samples were collected for analysis. Findings showed three standard microfacies types: SMF-5 characterized by packstone or rudstone with a mudstone matrix, SMF-8 characterized by wackstone or floatstone with complete fossils, and SMF-18 characterized by grainstone or packstone with abundant foraminifera or algae. Limestone belongs to facies zone (FZ) 7 - 8, which is characterized by presence of packestone, wackestone, clay sized limestone, and benthic algae foraminifers. Limestone ages range from Middle to Upper Miocene (N12 - N16), were formed in an inner Neritic. Limestone is equivalent to Wonosari and Punung Formations, based on standard microfacies type, facies zone, and age range. When lignite intercalation are present, the limestone is equivalent to the Punung Formation.

Assessment of Molybdenum and Antimony speciation in excavated rocks and soils from the Parisian basin using mineralogical and chemical analyses coupled to geochemical modelling

In the Parisian basin area, soils excavated from public works sites often reveal naturally occurring trace elements contaminations, especially in Molybdenum (Mo) and Antimony (Sb). More specifically, the relatively strong solubility of Mo and Sb in these excavated soils prevents them from being re-used or disposed of in inert waste type landfills according to the French regulation, which is based on leaching rather than total content. Furthermore, the observed total contents are in general relatively low making it difficult to determine correctly the speciation of the trace elements. Yet, this is a key information to estimate the potential environmental risks associated to Mo and/or Sb leaching.Various direct and indirect methods of mineralogical and chemical characterizations were used in this study and coupled to geochemical modelling in the objective to determine the speciation and potential mobility of Mo and Sb in 4 samples of excavated rocks and soils from the Parisian basin. Three of them were raw materials, each one excavated in a single (but different) geological formation during classic earthworks. The fourth was a tunnel muck (a slurry) dug at the border between two geological formations and having undergone various treatments (e.g. liming) during the process of excavation. Studied samples all showed low total content of Mo and Sb. Mobility was particularly concerning for Mo in the carbonated sample (CS) and the tunnel muck (TM). Mo was found systematically carried by strontium sulfates (celestite, SrSO4) in marly limestones samples. pH dependence leaching tests coupled to geochemical modelling confirmed celestite as a major sink of Mo, while also pointing out its influence on Sb speciation. In the calcareous sample, Mo and Sb mobility was mainly controlled by complexation onto iron oxides surfaces with high pH dependency. Furthermore, in this sample, correlations between Trace Elements (TE) and Sr concentrations were assumed to occur through incorporation in carbonates rather than through associations with celestite. Associations with iron sulfides were suggested to be responsible for a small fraction of total leachable Mo and only under basic conditions. Finally, geochemical modelling was used to describe accurately Mo and Sb speciations in the tunnel muck pointing out a more complex partitioning influenced by the treatment undergone during the excavation process. Results presented here suggested that Mo and Sb speciations show great similarities and vary significantly depending on the excavated material. It is also inferred that pH changes of materials especially expected for the alkaline tunnel muck could further increase TE mobility.

Investigation on surface strength of acid fracture from scratch test

Acid fracture surface strength plays an important role in acid fracture conductivity. Previous experimental studies have proven mechanical deterioration of carbonate after acid etching. However, such conclusion drawn from cylindrical samples could not be applied into conductivity evaluation as such samples represent the rock mechanical properties of the carbonate mass rather than the fracture surface. As another representative of fracture surface strength, embedment strength has not met an agreement on the evolution pattern during acid etching. So the absence of fracture surface strength measurement data during acid etching causes a challenge to conductivity evaluation and acid fracturing optimization. In an effort to overcome this challenge, scratch test was adopted for the measurement of the fracture surface strength before and after acid etching, as scratch test could acquire the uniaxial compressive strength of asperities on the fracture surface. In an aim to study the influence of mineral composition, acid contact time and acid injection rate, acid etching experiments under different etching conditions were carried out. The scratch test results uncovered the strong heterogeneity on the limestone samples, and strength of limestone fracture surface would experience both rising and declining trend during acid etching process. Dolomite in limestone samples was responsible for the strength increase while Calcite contributed to the decrease of strength according to the X-ray diffraction experimental results. What is more, the rising Dolomite strength and the decreasing Calcite strength affected the average strength of acidized fracture inherently. As acid contact time increased, the firstly strengthened then weakened Dolomite strength and constantly decreasing Calcite strength gave rise to an average surface strength change tendency that rises in the beginning and later declines. The change tendency of surface strength clearly indicated an optimal acid contact time in acid fracturing operation. Calcite strength showed the decreasing trend and Dolomite exhibited both the rising and decreasing trend as injection rate increased, resulting in an indefinite evolution trend of average strength of acid fracture surface.

Quality of technological limestone quality as an important aspect of the efficiency of sugar beet factories

The authors studied 252 samples of limestone mined in 2014-2020 on the territory of 5 fields located in 2 regions of the Central Federal District of the Russian Federation. Limestone quality was assessed by the content of calcium carbonate and associated impurities. According to the results of the assessment, a number of deposits were formed in decreasing limestone quality. The highest quality was noted at the East-Bernikovskoe deposit (Tula region), containing on average 95.3% of calcium carbonate. Through the example of 10 beet sugar factories located in 5 regions of the Central Federal District, the influence of the quality of limestone on its consumption in sugar production was assessed. The authors studied the data on the consumption of limestone of the considered deposits at sugar beet factories, which was used in the period from 2014 to 2020. According to the results, a number of deposits were determined to increase the consumption of limestone in the production of sugar, which coincided with a number in terms of decreasing quality. A lower consumption of limestone was noted at beet sugar factories that used limestone from the East-Bernikovskoe (in average 3.81% during the studied period). Therefore, the choice of limestone of a certain deposit for the use in sugar production is a factor in enhancement of operating efficiency of beet sugar factories.

Physical and chemically changes in limestone intruded by trachytic dyke: implications for cement raw material

Limestone samples intruded by trachyte dike from the Tonasa Formation in Bantimurung, Indonesia have been investigated for their suitability for cement manufacturing. The objective of this study is to analyze the physical and chemical characteristics of the limestone surround an intrusion with the petrographic and XRF methods. Field observation shows a gradation of color (reddish to grey) away from intrusion contacts. Petrographic analysis shows metasomatic indication by the presence of garnet and wollastonite within the limestone at 0 - 20 meters from the intrusion contact. The geochemical analysis shows a decreasing degree trend of CaO2, and Fe2O3, however SiO2, Al2O3, and MgO increase towards the intrusion contact. According to the petrographic and geochemical characteristics indicate the limestone fulfills requirements as raw material for cement, even though the ideal composition for the cement industry is the limestone which is located between 20 - 70 meters from the intrusion contact.

Designing Raw Mix for Manufacturing Portland Cement using Euphrates Formation Marl Instead of Clays

Portland Cement is manufactured by adding 3% gypsum to clinker which is produced by grinding, pulverizing, mixing, and then burning a raw mix of silica, and calcium carbonate. Limestone is the main source of carbonates, while clay collected from arable land is the main source of silica. The marl in the Euphrates Formation was studied as an alternative to arable lands. Nine boreholes drilled and penetrated the marl layer in selected locations at the Kufa cement quarry. Forty-one samples of marl from boreholes and four samples of limestone from the closed area were collected. The chemical content of the major oxides and the hardness of the marl layer was very encouraging as a raw material for Portland Cement as they are SiO2 (17.60), CaO (37.89), MgO (1.94), Fe2O3 (2.47), Al2O3 (4.21), K2O (0.731), SO3 (0.35), and Na2O (0.062). The marl was used in designing a raw material mix suitable for rotary kiln feed and produced a clinker conforming to the approved specifications. The designing a raw mix consisting of 80.30% of marl with 19.70% of limestone. The investment of the marl layer can be used as an ideal alternative to the arable clay giving fit quality to the international specifications, reducing production costs during quarry operations, reducing the energy consumption and equipment wearing.

Roughness of fracture surfaces in numerical models and laboratory experiments

Abstract. We investigate the influence of stress conditions during fracture formation on the geometry and roughness of fracture surfaces. Rough fracture surfaces have been generated in numerical simulations of triaxial deformation experiments using the discrete element method and in a small number of laboratory experiments on limestone and sandstone samples. Digital surface models of the rock samples fractured in the laboratory experiments were produced using high-resolution photogrammetry. The roughness of the surfaces was analyzed in terms of absolute roughness measures such as an estimated joint roughness coefficient (JRC) and in terms of its scaling properties. The results show that all analyzed surfaces are self-affine but with different Hurst exponents between the numerical models and the real rock samples. Results from numerical simulations using a wide range of stress conditions to generate the fracture surfaces show a weak decrease of the Hurst exponents with increasing confining stress and a larger absolute roughness for transversely isotropic stress conditions compared to true triaxial conditions. Other than that, our results suggest that stress conditions have little influence on the surface roughness of newly formed fractures.

Predicting the Uniaxial Compressive Strength of a Limestone Exposed to High Temperatures by Point Load and Leeb Rebound Hardness Testing

The effect of exposure to high temperature on rock strength is a topic of interest in many engineering fields. In general, rock strength is known to decrease as temperature increases. The most common test used to evaluate the rock strength is the uniaxial compressive strength test (UCS). It can only be carried out in laboratory and presents some limitations in terms of the number, type and preparation of the samples. Such constrains are more evident in case of rocks from historical monuments affected by a fire, where the availability of samples is limited. There are alternatives for an indirect determination of UCS, such as the point load test (PLT), or non-destructive tests such as the Schmidt’s hammer, that can also be performed in situ. The aims of this research are: (i) measuring the effect of high temperatures and cooling methods on the strength and hardness of a limestone named Pedra de Borriol widely used in several historic buildings on the E of Spain, and (ii) studying the possibility of indirectly obtaining UCS by means of PLT and Leeb hardness tests (LHT), using Equotip type D. Limestone samples were heated to 105 (standard conditions), 200, 300, 400, 500, 600, 700, 800 and 900 ºC and cooled slowly (in air) and quickly (immersed in water). After that, UCS, PLT and LHT tests were performed to evaluate the changes as temperature increases. Results show decreases over 90% in UCS, of between 50 and 70% in PLT index and smaller than 60% in LHT index. Insignificant differences between cooling methods were observed, although slowly cooled samples provide slightly higher values than quickly cooled ones. The results indicate that LHT can be used to indirectly estimate UCS, providing an acceptable prediction. Research on correlating strength parameters in rocks after thermally treated is still scarce. This research novelty provides correlations to predict UCS in historic buildings if affected by a fire, from PLT and non-destructive methods such as LHT whose determination is quicker and easier.

Late diagenetic evolution of Ordovician limestones in the Baltoscandian basin revealed through trace-element mapping and in situ U–Pb dating of calcite

Carbonate rocks are important paleo-environmental records, with bulk chemical and isotopic compositions commonly used to deduce temperatures, redox conditions, etc. Diagenetic (re)crystallization of clasts and cements is common, may perturb the chemical and isotopic systems typically interpreted to reflect conditions at the timing of deposition, may occur essentially synchronous with or long after deposition, and is difficult to date. Advances in in situ carbonate trace-element mapping and U–Pb dating by LA-ICP-MS provide opportunities to determine the absolute timing of diagenesis which can then be related to the age of deposition of carbonate rocks. We applied these techniques to two samples of well-preserved Ordovician bioclastic limestones from the Viki drill core, western Estonia (Baltoscandian basin) with precisely constrained depositional ages (ca. 459 and 444 Ma) and comprehensively detailed post-depositional histories which indicate that they were never deeply buried nor significantly heated following deposition. Previously published K–Ar data for K-bentonites from the Viki core and elsewhere in the Baltoscandian basin do, however, indicate diagenesis long before the timing of maximum burial. Optical petrography and backscatter-electron (“BSE”) imaging reveal low-porosity “BSE-bright” calcite spar cement in pore spaces between “BSE-dark” micro-porous carbonate bioclasts. Trace-element mapping of several areas (several mm2 each) in each thin section by LA-quadrupole-ICP-MS reveals variably elevated Mn/Sr, U concentration, and 238U/206Pb in the calcite spar cement. These maps were subsequently used to guide the placement of laser spots for U–Pb dating by LA-multicollector-ICP-MS. Primary bioclastic carbonate in both samples has low U/Pbc (with 238U/206Pb < ~6.5) and, thus, yields imprecise Concordia-intercept dates, which nonetheless overlap with the depositional ages. Calcite spar cement has higher U/Pbc (with 238U/206Pb up to ~15.7) and yields intercept dates of ca. 414–412 Ma in each sample. Individual common-Pb-corrected dates—particularly those for domains with the highest U/Pbc—are as young as ca. 376 Ma. The timing of diagenetic calcite (re)crystallization and cementation identified here is tens of Myr later than deposition and overlaps with the previously published K–Ar dates, and also with the timing of continent collision during the Caledonian orogeny in Scandinavia. The calcite U–Pb and K-bentonite K–Ar chronometers yield consistent records of what may have been tectonic-driven diagenesis far inboard (>600 km) from the orogenic front. Furthermore, this work demonstrates that apparently pristine carbonates may have experienced recrystallization (or at least chemical-isotopic perturbation) in open systems long after deposition and should be carefully scrutinized before using bulk-sample paleoenvironmental proxies.

Effect of Freeze-thaw Cycles on Microstructure and Mechanical Properties of Limestone

In studying the effect of freeze-thaw cycles on the microstructure and mechanical properties of limestone, scanning electron microscope, low-field nuclear magnetic resonance, and uniaxial compression tests are carried out on the limestone samples dried and subject to 5, 10, 15, and 20 freeze-thaw cycles. Through analysis and discussion, it was found that the number of freeze-thaw cycles has a significant effect on the microstructure of the limestone samples. Compared to the dry samples, the number of microcracks of the limestone samples subjected to freeze-thaw cycles is increased. Moreover, the crack width is positively correlated to the number of freeze-thaw cycles. With an increase in freeze-thaw cycles, the signal intensity of the T2 spectrum is considerably increased, and the connectivity of the micropores and fissures is increased. In addition, the peak compressive strength and elastic modulus showed a significant negative correlation with the number of freeze-thaw cycles. Again, compared to the dry samples, the peak compressive strength of the samples subject to 5, 10, 15, and 20 freeze-thaw cycles decreased by 14.7%, 22.0%, 28.7%, and 37.5%, respectively. The elastic modulus also decreased by 8.0%, 11.4%, 11.7%, and 21.5%, respectively. Therefore, these findings provide basic parameters for the stability evaluation of rock slopes in Northwest Guizhou.

Thermodynamic Analysis of the Temperature Effect on Calcite Surface Reactions in Aqueous Environments

Reactive transport models for subsurface applications, particularly those for modified salinity waterflooding (MSW) in carbonates, have to be equipped with thermodynamic models that can reliably predict/describe adsorption phenomena at variable temperature conditions. To advance the understanding of the calcite reactivity at high temperatures, combining experimental and modeling studies is required. Therefore, we used a surface complexation model (SCM) to describe the reactivity at the calcite–water interface and obtained the enthalpies of the surface reactions by fitting the SCM either to high-temperature electrokinetic data obtained through streaming potential measurements on limestone samples or to the effluent concentration from single-phase flooding experiments. We assumed that the equilibrium constants of the surface reactions follow a temperature dependence according to van’t Hoff equation. Our calculations suggest that calcite protonation is more exothermic compared to other minerals (e.g., silica, hematite) and that the adsorption of Ca2+, Mg2+, and SO42– are all endothermic, with SO42– having the highest reaction enthalpy. We further show that the inferred enthalpies were in agreement with enthalpy changes from published microcalorimetry experiments. Despite the consistency with microcalorimetry data, the obtained enthalpies are not undisputable, and additional data are necessary to unequivocally constrain the temperature effect on the calcite surface reactivity.

Petrography, geochemistry and industrial quality of the Etono limestone in Ugep Southwest, Southeastern Nigeria

Petrographic and geochemical analyses were carried out on limestones occurring in Etono, Southwest Ugep, Southeastern Nigeria to determine their chemical composition, industrial uses and classification. Samples of limestone in the area were subjected to petrographic study and analyzed geochemically using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and X-Ray Fluorescence (XRF) techniques. The petrographic analysis reveals that the Etono limestone contains high percentage of carbonate materials with scanty organic remains and patches of iron. The bulk- rock composition of the limestone shows that the average SiO2 = 9.02%, Al2O3 = 1.95%, Fe2O3 = 2.08%, MgO = 0.39%, K2O = 0.47%, Na2O = 0.00%, CaO = 47.92%, SO2 = 0.24% and LOl = 37.37%. The limestone is classified based on their moderately high CaO, SiO2 and LOl and very low MgO. The mean CaO (47.92%) of Etono Limestone is high relative to the mean CaO of Agoi Ibami Limestone (43.83%) but low relative to the Mfamosing Limestone (55.30%) and the mean SiO2 values of 9.02% is high relative to Mfamosing Limestone (0.38%) but low relative to Agoi Ibami Limestone (13.93%). Results of the geochemical investigation reveal a shallow marine environment of deposition (EOD) for Etono Limestone. The higher values of CaO and LOl and lower values of SiO2 of the limestone suggest that it can be used for cement production, building stone, filler and agricultural purposes.