Pure Mineral Research Articles

Spectral Variability of Rocks and Soils on the Jezero Crater Floor: A Summary of Multispectral Observations From Perseverance's Mastcam‐Z Instrument

AbstractNASA's Mars‐2020 Perseverance rover spent its first year in Jezero crater studying the mafic lava flows of the Máaz formation and the ultramafic cumulates of the Séítah formation, both of which have undergone minor alteration and are variably covered by coatings, dust, and/or soil deposits. Documenting the rock and soil characteristics across the crater floor is critical for establishing the geologic context of Perseverance's cached samples—which will eventually be returned to Earth—and for interpreting the deposition and modification of the Máaz and Séítah formations. Mastcam‐Z, a pair of multispectral, stereoscopic zoom‐lens cameras, provides broadband red/green/blue and narrowband visible to near‐infrared images (VNIR, 440–1,020 nm). From multispectral observations from sols 0 to 380, we compiled a database of ∼2,400 representative Mastcam‐Z spectra. We analyzed principal components, spectral parameters, and laboratory spectra of pure minerals and natural rock surfaces to interpret the spectral diversity of rocks and soils. We define eight spectral classes of rocks: Dusty, Hematite‐like, Coated, Low‐Ca Pyroxene‐like, Olivine‐like, Weathered Olivine‐like, Fe‐rich Pyroxene‐like, and Dark Oxide‐like. The variability of soil spectra in the Jezero crater floor is controlled primarily by the amount of dust and indicates a largely consistent soil mineralogy across the traverse, with the exception of the area disturbed by the landing event. In comparison to rock spectra from the Curiosity rover's Mastcam instrument in Gale crater, rocks on the Jezero crater floor are generally less spectrally diverse, but the Olivine‐like rocks within the Séítah formation represent a new spectral rock class in Mars surface exploration.

Experimental and simulation study on the estimation of surface relaxivity of clay minerals

Nuclear Magnetic Resonance (NMR) is an important tool for the evaluation of pore structure and petrophysical properties of reservoir rocks. Pore Surface relaxivity (ρ2), which controls the relaxation decay due to the interaction between the spins and the pore surface, is an important parameter that impacts the interpretation of NMR for petrophysical properties. Sandstone rocks have complex minerology and consist of different clay minerals. Earlier efforts have reported the surface relaxivity of different rock types such as sandstone or carbonate, but less attention was given to the estimation of individual clay minerals surface relaxivity. The surface complexity and variable mineralogy (especially paramagnetic and ferromagnetic minerals) of clays can both impact the surface relaxivity and relaxation times in clays and porous media containing clays. This study, using for the first time both simulation and experimental approaches, aims to systematically investigate the surface relaxivity of clays characterized by variable mineralogy and iron content. A glass beads sample (iron free) and 5 different pure clay minerals samples (ranked by increasing iron content: Kaolinite, Smectite, Illite, Chlorite, and Nontronite) were prepared with similar average grain sizes (500 μm). The determination of surface relaxivity requires prior measurement of pore surface-to-volume ratio (S/V) using an independent method in addition to obtaining T2 relaxation time. Two methods, among the most widely used, were used here for S/V determination including BET N2 gas adsorption and 3D micro CT imaging. The 3D images were also used to conduct NMR simulations to reproduce the experimental data. The estimated surface relaxivity values from both methods were compared and correlated to the iron content of the different clays. The surface relaxivity values obtained based on BET-derived S/V showed reasonable values (29–343 μm/s) that have a strong positive relationship with iron content of the clays. The documented equation relating surface relaxivity and iron content can be potentially utilized to predict surface relaxivity based on the compositional analysis of clays. On the other hand, digital images did not capture the surface complexity of clays thus significantly underestimated S/V which consequently resulted in overestimated surface relaxivity (898–11000 μm/s) that were physically non-feasible. Supporting the same argument, the simulated T2 relaxation distribution showed significant mismatch with the experimental data for the clay samples while an excellent match was observed for the glass beads sample. This can be attributed to the smooth surface of the glass beads, unlike the complex clays. The reported surface relaxivity values (based on BET-derived S/V) for the individual clay minerals can be used to perform NMR simulation and interpretation studies conducted on sandstone or shale formations. Careful attention should be given when performing NMR simulation on micro-CT digital images of samples containing clay due to the inadequacy of such images in capturing the complex surface and microporous nature of clays. The outcomes from this study can improve the interpretation of NMR T2 data and the determination of NMR-derived pore size distribution and petrophysical properties. The reported surface relaxivity values for clay can also inform the NMR simulation.

Novel technique for the preparation and analysis of powder-based polished sections by automated optical Mineralogy: Part 1 – Comparative study of representativity

Reflected optical microscopy is an affordable technique that can be used for automated quantitative mineralogical analysis. Polished sections are a common format used to analyze representative powdered mineral samples. The epoxy resin used to make polished sections for quantitative automated mineralogy is known to cause preferential sedimentation (or segregation) of the particles through the polished section. This phenomenon results in biased polished sections. Carbon-based resin preparation is now widely used to overcome this problem. This study presents a new resin for polished section preparation, acrylic resin, which can provide ready-to-analyze polished sections in less than three hours (instead of more than 10 h for other resins).This work investigated the effect of other polished section resin preparation protocols and compared them, including rheological measurements and automated optical microscopy analyses. The aim was to compare the polished section preparation techniques aiming at determining the technique which allows a reliable mineral abundance while not introducing a bias due to segregation in the polished sections. To do so, standard mineral powders were prepared using different pure opaque minerals at a calibrated size fraction of 20–75 μm. The results suggest that the rheological behavior of the fast-hardening acrylic resin allowed an accurate modal composition to be obtained while avoiding any preferential sedimentation of the particles compared to the other studied resins.

The role of suspended extracellular polymeric substance (EPS) on equilibrium flocculation of clay minerals in high salinity water

Biophysical cohesive mud, consisting of clay minerals and extracellular polymeric substance (EPS), plays significant role in determining sediments, nutrients and pollutants transport in estuarine and coastal systems. Series of laboratory jar experiments have been conducted aiming at filling the gap of knowledge regarding how biological cohesive EPS affects equilibrium flocculation of EPS-mineral mixtures. Four types of common clay (chlorite, kaolinite, illite and montmorillonite) were chosen due to their abundance in estuarine mud and distinct crystal chemistry and structures. Turbulent shear throughout all the experimental runs were constantly provided at a mean shear parameter of G ≈ 15 s−1 being equivalent to high tidal influenced estuarine turbulent environment. The results reveal that adding EPS increases the equilibrium floc size evidently. The pure mineral flocs show unimodal equilibrium floc size distribution (eFSD) with single peak located at microfloc range (<200 μm) while the EPS-mineral flocs show bimodal eFSD with a secondary peak located in macroflocs range (>200 μm) mostly. Moreover, EPS largely reduces the effective density in EPS-mineral flocs by 1∼2 magnitude. Most importantly, the terminal settling velocity of flocs shows size-dominated in uniform mineral floc cases but density-dominated in EPS-mineral mixture floc cases especially in macroflocs. To model a full floc size or settling velocity distributions in natural environments, furtherly quantification of EPS functions within the large-sized non-fractal mixture floc individually becomes a necessity.

Performance analysis of vapor compression refrigeration system using varying concentrations of copper oxide (CuO)/mineral oil (MO) based nanosuspension

The nanofluid is being utilized for more than a decade to improve the theocentric properties of various thermal systems. In the presented work, the copper oxide (CuO) nanoparticle suspension is utilized to improve the performance of the vapor compression refrigeration system. Mineral oil is utilized as the base fluid for the synthesis of CuO-based nanosuspension. The nanosuspension is synthesized with a concentration of 0.02 wt%, 0.04 wt% and 0.06 wt%. For the refrigeration system, R600a refrigerant is used. The experimental analysis is carried out in two phases. In the first phase of the experimental analysis, the CuO-based nanosuspension is synthesized and the thermophysical properties such as thermal conductivity, specific heat, and density are evaluated. In the second phase, the synthesized nanosuspension has been incorporated into the refrigeration system. The performance parameters such as COP, power consumption, and pull-down time are investigated using R600a/MO/CuO-based nanosuspension. From the first phase of the experimentation, it is concluded the CuO nanoparticle significantly enhances the thermophysical properties of the pure mineral. A significant gain in thermal conductivity and density is noted along with a reduction in the specific heat of the pure mineral oil. Similarly, from the second phase of the experimentation, it observed that the higher average gain in the COP by 30.2%, reduction of power consumption by 12.53%, and reduction in pull down time is noted by using 0.06 wt% of CuO-MO-based nanosuspension.

Dating of groundwater using uranium isotopes disequilibrium in Siwa Oasis, Western Desert, Egypt

Data on the recent migratory history of radionuclides as well as geochemical circumstances can be obtained from the disequilibrium of the uranium series, which is often brought on by groundwater flow and host rock. Groundwater from the Siwa Oasis is a vital source of water for many uses, and it is distributed widely throughout the Western Desert. Groundwater in Siwa Oasis was dated using measurements of uranium in the water. In water samples that exhibited disequilibrium behavior, the activity concentrations of radionuclides from the 238U, 235U and 232Th series were measured. Therefore we conclude that the measured waters are rich in the 234U and 230Th. The secular equilibrium between 234U and 230Th indicates that colloidal transport could be the mechanism for the mobility of 230Th in groundwater. Higher 230Th levels in the samples show that the aquifer is deep and may have a large amount of thorium-bearing minerals. The lake and groundwater estimated ages showed that the time of uranium migration happened between 60 and 130 ka ago. This aquifer is rich in mineral deposits, as evidenced by the extraordinarily high content of radionuclides. The 230Th/232Th activity ratio of the samples, indicating pure carbonate minerals, ranged from 12.58 to 20.86.

The effects of saline water on the recovery of lead and zinc sulfide during froth flotation

In this study, we investigated the effects of water salinity on the flotation performance of pure lead and zinc sulfide mineral samples as well as a Pb/Zn complex sulfide ore by means of micro-flotation and batch flotation experiments. Our results showed higher PbS and ZnS recoveries in more concentrated NaCl salt solutions. The results for the experiments using seawater demonstrated that in the presence of additional ions, such as Ca2+ and Mg2+, the recovery of PbS and ZnS was significantly reduced.As part of this investigation, we developed and implemented a surface complexation model for ZnS based on the presence of two differently charged surface sites. Zeta potential measurements of ZnS particles were used to optimise the parameters of our model. It was found that the surface potentials calculated using this model were in good agreement with the experimental zeta potentials, validating the model for predicting the zeta potential behaviour of ZnS particles over a broad range of pH and NaCl concentrations.Additionally, total interaction free energies were determined as a function of separation distance, representing particle–particle and particle-bubble interactions of our study in different NaCl concentrations. The theoretical analyses showed that asymmetric Pb/Zn particle–particle interactions were repulsive at lower NaCl concentrations, before becoming purely attractive at higher NaCl concentrations. For the case of the symmetric particle–particle interactions, attraction controlled all interactions, regardless of NaCl concentration. The calculated PbS-bubble interactions were repulsive in lower NaCl concentrations but became increasingly attractive in higher NaCl concentrations. Strong repulsions controlled all ZnS-bubble interactions, and these interactions remained repulsive with increasing NaCl concentration. The theoretical projections presented in this study were in good agreement with the measured saline water flotation phenomena.

Recent Research on Different Parts and Extracts of Opuntia dillenii and Its Bioactive Components, Functional Properties, and Applications

Opuntia dillenii (O. dillenii) is a plant belonging to the Cactaceae family that is abundant in tropical and subtropical regions worldwide. O. dillenii is consumed as a local delicacy and has no other current use. To understand the nutritional value of O. dillenii in human health and its application in the food, cosmetic, and drug industries, this review summarizes information on the chemical compounds (pure α-pyrone compounds, flavonoids, phenolic acids, polysaccharides, minerals, fatty acids, and betalains) and biological properties (anti-diabetic, anti-hyperglycemic, antihyperlipidemic, anti-atherosclerotic, anti-inflammatory, analgesic, antimicrobial, antifungal, antiviral, anti-spermatogenic, anticancer, antilarval, anti-angiogenic, and antioxidant) of extracts from each part of the plant (fruit juice, fruit peel, cladode, and seeds) (aqueous, ethanolic, and methanolic), and seed oil. In addition, data related to the recent applications of O. dillenii in various industries (e.g., edible coatings, food supplements, cosmetics, nanoparticles, and wastewater treatment) are provided.

Modelling Spectral Unmixing of Geological Mixtures: An Experimental Study Using Rock Samples

Spectral unmixing of geological mixtures, such as rocks, is a challenging inversion problem because of nonlinear interactions of light with the intimately mixed minerals at a microscopic scale. The fine-scale mixing of minerals in rocks limits the sensor’s ability to identify pure mineral endmembers and spectrally resolve these constituents within a given spatial resolution. In this study, we attempt to model the spectral unmixing of two rocks, namely, serpentinite and granite, by acquiring their hyperspectral images in a controlled environment, having uniform illumination, using a laboratory-based imaging spectroradiometer. The endmember spectra of each rock were identified by comparing a limited set of pure hyperspectral image pixels with the constituent minerals of the rocks based on their diagnostic spectral features. A series of spectral unmixing paradigms for explaining geological mixtures, including those ranging from simple physics-based light interaction models (linear, bilinear, and polynomial models) to classification-based models (support vector machines (SVMs) and half Siamese network (HSN)), were tested to estimate the fractional abundances of the endmembers at each pixel position of the image. The analysis of the results of the spectral unmixing algorithms using the ground truth abundance maps and actual mineralogical composition of the rock samples (estimated using X-ray diffraction (XRD) analysis) indicate a better performance of the pure pixel-guided HSN model in comparison to the linear, bilinear, polynomial, and SVM-based unmixing approaches. The HSN-based approach yielded reduced errors of abundance estimation, image reconstruction, and mineralogical composition for serpentinite and granite. With its ability to train using limited pure pixels, the half-Siamese network model has a scope for spectrally unmixing rock samples of varying mineralogical composition and grain sizes. Hence, HSN-based approaches effectively address the modelling of nonlinear mixing in geological mixtures.

Dynamic stability of mineral-associated organic matter: enhanced stability and turnover through organic fertilization in a temperate agricultural topsoil

Soil organic matter (SOM) plays a vital role for soil quality, sustainable food production and climate change mitigation. It is common knowledge that SOM consists of different pools with varying qualities, quantities, and turnover times. However, it is still poorly understood how mineral and organic fertilization affects the formation and stabilization of mineral-associated organic matter (MAOM) and how long it can remain there. Here, we report on the long-term effects of different farming systems on the stability and turnover of the fine silt and clay-sized MAOM fraction (<6.3 μm) of a Haplic Luvisol (0–20 cm) in the DOK long-term trial (Switzerland). We compared three farming systems with contrasting fertilization (CONMIN = pure mineral, CONFYM = mineral + organic, BIODYN = pure organic) with an unfertilized control (NOFERT) between 1982 and 2017. We performed specific surface area (SSA) measurements on fractionated MAOM samples (<6.3 μm) from 1982 to 2017, before and after removal of OM, measured the 14C activity of all samples during the entire period and estimated the mean residence time (MRT) with a model taking into account ‘bomb 14C’ and radioactive decay. We found constant MAOM-C contents under organic fertilization. Results of SSA analysis indicate best conditions for MAOM-C stabilization under organic fertilization and different sorption mechanisms in MAOM between farming systems with and without organic fertilization. The modelled MRTs were significantly higher in NOFERT (238 ± 40 yrs) and CONMIN (195 ± 27 yrs), compared to CONFYM (138 ± 18 yrs) and BIODYN (140 ± 19 yrs), implying a high C turnover (i.e. more active MAOM) at high C contents under organic fertilization. Our findings show that MAOM is not the dead OM but corroborates the concept of ‘dynamic stability’. Continuous OM inputs from organic fertilizers and their rapid and constant turnover are needed to stabilize the “stable” MAOM-C fraction.

Photocatalytical transformation of fluorotelomer- and perfluorosulfonamide-based PFAS on mineral surfaces and soils in aqueous suspensions

Per- and polyfluorinated substances (PFAS) are widely used industrial and household chemicals and occur on various contaminated field sites. To better understand their behavior on soils, spike experiments were performed with 6:2 diPAP (6:2 polyfluoroalkyl phosphate diester) on pure mineral phases (titanium dioxide, goethite and silicon dioxide) in aqueous suspensions under artificial sunlight. Further experiments were performed with uncontaminated soil and four precursor PFAS. Titanium dioxide (referenced as 100 %) showed the highest reactiveness to transform 6:2 diPAP to its primary metabolite 6:2 fluorotelomer carboxylic acid, followed by goethite with the addition of oxalate (4.7 %), silicon dioxide (1.7 %) and soil (0.0024 %). Experiments with four precursors [6:2 diPAP, 6:2 fluorotelomer mercapto alkyl phosphate (FTMAP), N-ethyl perfluorooctane sulfonamide ethanol–based phosphate diester (diSAmPAP), N-ethyl perfluorooctane sulfonamidoacetic acid (EtFOSAA)] on natural soils showed a transformation of all four precursors by simulated sunlight. The production of the primary intermediate from 6:2 FTMAP (6:2 FTSA, rate constant k = 2.7∗10−3h−1) was approximately 13-times faster than from 6:2 diPAP (6:2 FTCA, rate constant k = 1.9∗10−4h−1). EtFOSAA was completely decomposed within 48 h whereas only ~7 % diSAmPAP was transformed in the same time. The primary photochemical transformation product of diSAmPAP and EtFOSAA was PFOA, PFOS was not detected. The production rate constant of PFOA varied significantly between EtFOSAA (k = 0.01h−1) and diSAmPAP (k = 1.3∗10−3h−1). Photochemically produced PFOA consisted of branched and linear isomers and can therefore be used in source tracking. Experiments with different soils suggest that the oxidation of EtFOSAA to PFOA is expected to primarily be driven by hydroxyl radicals, whereas for the oxidation of EtFOSAA to further intermediates, another mechanism instead or in addition to the oxidation by hydroxyl radicals is responsible.

Study on Grinding Behavior Characteristics under Low-Speed Grinding Condition

In order to explore the crushing mechanism of minerals, this paper attempts to eliminate the throwing effect of media and study the grinding characteristics of minerals only under the action of abrasion force. In this paper, the method of removing the throwing state of media is to adjust the mill to a lower rotational speed, so that the grinding media are all in a cascading state. Three single-component pure minerals, quartz, pyrrhotite, and pyrite, commonly found in complex ores, were selected as research objects to study the grinding behavior characteristics of the three minerals only under the force of abrasion. The effects of mineral species, feed-particle sizes, grinding time, and other factors on the particle-size distribution and product-generation rate of grinding products are studied. The results show that from the particle-size distribution of grinding products, the yield of coarse particles is the highest, while the yield and t10 value of other fine particles are very low. The feed-particle size and the hardness of the mineral sample affect the grinding behavior. The product particle size is mainly 0.71 times the feed-particle size, and the other fine particle sizes generated are less than 0.5 times the feed-particle size.

Spectroscopic characterisation of feedstock for copper smelters by machine-learning

ABSTRACT A flame-emission spectrometer was built to determine the elemental composition of powdered minerals that are important in copper smelting processes. The feedstock, consisting of milled concentrate, was fed into an oxyacetylene flame without sample preparation. The elemental composition (Cu, Fe, S, Si, and Zn) was determined by applying an artificial neural network (ANN) to a set of emission spectra obtained from Cu and Fe pure elemental powders, five pure mineral powders of known composition and 30 binary mixtures of these mineral samples. The ANN model was able to accurately predict the Cu and Fe content of these mineral powders within better than 2% of the value obtained from ICP-OES. The analysis was repeated on 12 industrial samples with well-known compositions. Spectra from these samples were analyzed both in isolation of the reference minerals and together with the reference minerals, giving similar results.

Interfacial Adsorption Mechanism of Diethyldithiocarbamate in High-Sulfur Residue Flotation

Diethyldithiocarbamate (DDTC) is employed in the sulfide ore flotation process due to its excellent collection performance. Herein, we investigated the interfacial adsorption behavior of DDTC on the four main mineral phases of high-sulfur residue: sulfur, pyrite, sphalerite, and lead sulfate. The adsorption behavior of DDTC and H2O, namely, the adsorption structure and the energy and electron localization function cross section, were explored using density function theory calculation. The results were helpful in constructing a coadsorption model of DDTC and H2O, which was validated by pure mineral flotation and characterization of Fourier transform infrared spectra. The coadsorption model indicated that the adsorption of DDTC on sulfur, sphalerite, and lead sulfate was weak with physical bonding, while its adsorption on pyrite was strong with chemical bonding. Practical bench-scale high-sulfur residue flotation was performed, and the result was different from that obtained from pure mineral flotation. Our developed model predictions and mineral fugacity pattern analysis were synergistically used to explain this difference. Overall, this work proposes for the first time a coadsorption model of DDTC and H2O and provides important insights into interfacial adsorption in high-sulfur residue flotation.

Selective Flocculation/Magnetic Separation of Ultrafine Iron Ore Particles with Corn Starch and Polyacrylamides: A Comparative Study

ABSTRACT This paper presents the results of a selective flocculation/magnetic separation study performed with a sample of iron ore slime from the desliming stage of the industrial flotation circuit of a mine in the southern region in the Quadrilátero Ferrífero-Brazil that was discarded in a tailings dam. Zeta potential measurements of pure minerals previously identified in the sample (goethite = 52.4%, hematite = 26.2%, quartz = 12.3%, kaolinite = 8.2%, and others = 0. 9%) were evaluated to assess the influence of the reagents used (sodium hexametaphosphate – SHMP (dispersant)) and flocculants (corn starch, nonionic polyacrylamide – P2500 and cationic polyacrylamide – P806)) on their surface properties and consequently on the stability of suspensions of the slime and of the pure minerals individually, aiming to establish conditions for selective separation between Fe-bearing minerals (goethite and hematite) and gangue minerals (quartz and kaolinite) in the subsequent magnetic separation step. At pH 10 and a 25 mg/L dosage of SHMP, a higher Fe recovery was verified with starch (2000 g/t) in relation to nonionic and cationic polyacrylamides, and similar Fe contents in all dosages tested of the flocculants.

A laboratory study of the phase ratio imagery method

As a new planetary remote sensing tool, the phase ratio imagery calculates the ratio of images taken at different phase angles and may suppress surface albedo variations and enhance surface texture features. This technique has been used in the study of surface structure of airless bodies such as the Moon and Mercury. To understand the effectiveness of the method, we carried out laboratory phase ratio measurements on eight planetary analog materials including four pure minerals olivine, orthopyroxene, labradorite, ilmenite and four mixtures, the lunar regolith simulant JSC-1A, the lunar highland simulant, the Martian soil simulant, and the CI asteroid simulant, all in two size distributions, 0–45 μm and 90–105 μm. For each sample, the phase ratio A(α1)/A(α2) is obtained by measuring the reflectance at two phase angles α1 and α2 with α1<α2 at two radiation wavelengths, 633 nm and 905 nm. The results show that: (1) The particle size distributions can be differentiated by measuring the phase ratio A(α1)/A(α2), and in order to increase the discriminative power of the particle size distribution, the value of (α1-α2) should be as large as possible. (2) For pure minerals, larger grains have smaller phase ratio values, because larger grains of pure minerals are more forward scattering, leading to larger A(α2) and thus smaller phase ratio. For mixtures with simulated agglutinates that hold minerals together as composite particles, larger grains have higher phase ratios because they are less forward scattering due to multiple internal reflections and hence more absorptions. Since real planetary regoliths are likely dominated by composite particles with agglutinates, it is expected that larger grains would have larger phase ratio values.

Study on Impact Crushing Characteristics of Minerals Based on Drop Weight Tests

The degree of difficulty in crushing an ore depends on the composition of the ore itself. Due to different types and compositions of ores, the crushing mechanism of ores during the crushing process is also different. In order to quantitatively analyze the impact crushing characteristics of mineral components in ores, this paper takes pure mineral quartz, pyrrhotite, and pyrite as the research objects and uses the universal drop weight impact crushing test equipment and standard test methods developed by the JK Mineral Research Center of the University of Queensland, Australia, to conduct JK drop weight tests on these three pure mineral samples. The results show that the particle size distribution of impact crushing products is wide, covering all particle sizes from “0” to close to the feed particle size, and the yield distribution of each product particle size is relatively uniform. There are critical values and “energy barrier” effects for the impact-specific crushing energy. The impact-specific crushing energy has a significant impact on the particle size composition and crushing effect of the crushing product, and there is an interactive effect between the impact-specific crushing energy and the feed particle size and mineral type. The impact crushing resistance of the sample can be characterized by using Mohs hardness, impact crushing characteristic parameters, impact crushing resistance level, and the yield limit value t10 of the characteristic crushing particle size. The overall characterization results have good consistency.

Hydrogen physisorption in earth-minerals: Insights for hydrogen subsurface storage

Physisorption can contribute to hydrogen subsurface storage. However, hydrogen physisorption at the surface of geological samples is mostly unknown. We are unaware of previous studies that investigate H2 Physisorption in wide range of pure inorganic and organic earth minerals. Knowledge about H2 Physisorption is required to evaluate the suitability of underground H2 storage. We thus evaluated H2 physisorption on common earth minerals, including illite, kaolinite, quartz, calcite, and kerogen via lab experiments and Grand Canonical Monte Carlo (GCMC) simulations at temperature ranging between 273 and 373 K and pressure ranging between 5 MPa to 40 MPa. The simulation results, including densities and H2 adsorption uptakes, are in agreement with experimental results. The quantity of adsorbed hydrogen ranked as: illite > kerogen > kaolinite > quartz > calcite; and Gibbs energy change, enthalpy change, and isosteric heat energy indicated that H2 adsorption spontaneity increases as illite > kerogen > kaolinite > calcite > quartz. We conclude that H2 adsorption is high on the high-surface-area materials (clays or kerogen), and that H2 adsorption on earth minerals could improve the effectiveness of subsurface H2 storage.

Biophysical flocculation reduces variability of cohesive sediment settling velocity

Biophysical cohesion, introduced predominantly by Extracellular Polymeric Substances (EPS) during mineral flocculation in subaqueous environments, plays important role in morphodynamics, biogeochemical cycles and ecosystem processes. However, the mechanism of how EPS functioning with cohesive particles and affects settling behaviors remain poorly understood. We measure initial flocculation rate, floc size and settling velocity of mineral and artificial EPS (Xanthan gum) mixtures. Combining results from these and previous studies demonstrate coherent intensification of EPS-related flocculation compare with those of pure mineral and oil-mineral mixtures. Importantly, the presence of EPS fundamentally changes floc structure and reduces variability of settling velocity. Measured data shows that ratios of microfloc and macrofloc settling velocity for pure mineral flocs is 3.9 but greatly reduced to a lowest value of 1.6 due to biological EPS addition. The low variability of settling velocity due to EPS participation explains the seemingly inconsistent results previously observed between field and laboratory studies.

Behavior of cement-stabilized marine clay and pure clay minerals exposed to high salinity grout

Soil-cement columns created by the injection of grout into the soil are common in practice for stabilizing soft soil in coastal areas. The behavior of clay-cement under marine conditions, especially considering the effect of both the clay mineral type and water salinity, has been less considered. The current study investigated the effects of high salinity grout on the mechanical and the physical behavior of cement-stabilized marine clay at a range of cement contents and water-to-cement ratios. The performance of the cement-stabilized marine clay was compared with those of kaolinite as an inactive clay and bentonite as an active clay. The results showed that, when saline water was used in the soil–cement mixtures containing kaolinite or marine clay, there was no decrease in strength and the cement content had no effect on the results. For active bentonite at 5% and 10% cement contents, the curing time had a negative effect on the strength; over time, the strength of the mixtures decreased. In practice, there should be no concern about the use of saline water to create grout at cement contents greater that 15%. However, if the clayey soil contains active minerals, a cement content of less than 15% is not recommended.